Page 1
Page 2
Page 3
The Project Gutenberg eBook of The Cambridge natural history, Vol.
02 (of 10)
This eBook is for the use of anyone anywhere in the United States and most
other parts of the world at no cost and with almost no restrictions whatsoever.
You may copy it, give it away or re-use it under the terms of the Project
Gutenberg License included with this eBook or online at www.gutenberg.org.
If you are not located in the United States, you will have to check the laws of
the country where you are located before using this eBook.
Title: The Cambridge natural history, Vol. 02 (of 10)
Editor: S. F. Harmer
Author: Frank E. Beddard
W. B. Benham
F. W. Gamble
Marcus Hartog
Lilian Sheldon
Editor: Sir A. E. Shipley
Release date: October 16, 2023 [eBook #71891]
Language: English
Original publication: New York: MacMillan and Co., 1901
Other information and formats: www.gutenberg.org/ebooks/71891
Credits: Keith Edkins, Peter Becker and the Online Distributed Proofreading
Team at https://www.pgdp.net (This file was produced from images
generously made available by The Internet Archive)
*** START OF THE PROJECT GUTENBERG EBOOK THE CAMBRIDGE
NATURAL HISTORY, VOL. 02 (OF 10) ***
02 (of 10)
This eBook is for the use of anyone anywhere in the United States and most
other parts of the world at no cost and with almost no restrictions whatsoever.
You may copy it, give it away or re-use it under the terms of the Project
Gutenberg License included with this eBook or online at www.gutenberg.org.
If you are not located in the United States, you will have to check the laws of
the country where you are located before using this eBook.
Title: The Cambridge natural history, Vol. 02 (of 10)
Editor: S. F. Harmer
Author: Frank E. Beddard
W. B. Benham
F. W. Gamble
Marcus Hartog
Lilian Sheldon
Editor: Sir A. E. Shipley
Release date: October 16, 2023 [eBook #71891]
Language: English
Original publication: New York: MacMillan and Co., 1901
Other information and formats: www.gutenberg.org/ebooks/71891
Credits: Keith Edkins, Peter Becker and the Online Distributed Proofreading
Team at https://www.pgdp.net (This file was produced from images
generously made available by The Internet Archive)
*** START OF THE PROJECT GUTENBERG EBOOK THE CAMBRIDGE
NATURAL HISTORY, VOL. 02 (OF 10) ***
Page 4
THE
CAMBRIDGE NATURAL HISTORY
EDITED BY
S. F. HARMER, M.A., Fellow of King's College, Cambridge; Superintendent of
the University Museum of Zoology
AND
A. E. SHIPLEY, M.A., Fellow of Christ's College, Cambridge; University Lecturer
on the Morphology of Invertebrates
VOLUME II
FLATWORMS AND MESOZOA
By F. W. Gamble, M.Sc. (Vict.), Owens College
NEMERTINES
By Miss L. Sheldon, Newnham College, Cambridge
THREAD-WORMS AND SAGITTA
By A. E. Shipley, M.A., Fellow of Christ's College, Cambridge
ROTIFERS
CAMBRIDGE NATURAL HISTORY
EDITED BY
S. F. HARMER, M.A., Fellow of King's College, Cambridge; Superintendent of
the University Museum of Zoology
AND
A. E. SHIPLEY, M.A., Fellow of Christ's College, Cambridge; University Lecturer
on the Morphology of Invertebrates
VOLUME II
FLATWORMS AND MESOZOA
By F. W. Gamble, M.Sc. (Vict.), Owens College
NEMERTINES
By Miss L. Sheldon, Newnham College, Cambridge
THREAD-WORMS AND SAGITTA
By A. E. Shipley, M.A., Fellow of Christ's College, Cambridge
ROTIFERS
Page 5
By Marcus Hartog, M.A., Trinity College, Cambridge (D.Sc. Lond.), Professor of Natural History in
the Queen's College, Cork
POLYCHAET WORMS
By W. Blaxland Benham, D.Sc. (Lond.), Hon. M.A. (Oxon.), Aldrichian Demonstrator of Comparative
Anatomy in the University of Oxford
EARTHWORMS AND LEECHES
By F. E. Beddard, M.A. (Oxon.), F.R.S., Prosector to the Zoological Society, London
GEPHYREA AND PHORONIS
By A. E. Shipley, M.A., Fellow of Christ's College, Cambridge
POLYZOA
By S. F. Harmer, M.A., Fellow of King's College, Cambridge
London
MACMILLAN AND CO., Limited
NEW YORK: THE MACMILLAN COMPANY
1901
All rights reserved
'Nous allons faire des vers ensemble'
André de Chénier
First Edition 1896. Reprinted 1901
the Queen's College, Cork
POLYCHAET WORMS
By W. Blaxland Benham, D.Sc. (Lond.), Hon. M.A. (Oxon.), Aldrichian Demonstrator of Comparative
Anatomy in the University of Oxford
EARTHWORMS AND LEECHES
By F. E. Beddard, M.A. (Oxon.), F.R.S., Prosector to the Zoological Society, London
GEPHYREA AND PHORONIS
By A. E. Shipley, M.A., Fellow of Christ's College, Cambridge
POLYZOA
By S. F. Harmer, M.A., Fellow of King's College, Cambridge
London
MACMILLAN AND CO., Limited
NEW YORK: THE MACMILLAN COMPANY
1901
All rights reserved
'Nous allons faire des vers ensemble'
André de Chénier
First Edition 1896. Reprinted 1901
Page 6
CONTENTS
PAGE
Scheme of the Classification adopted in this Book ix
PLATYHELMINTHES AND MESOZOA
CHAPTER I
TURBELLARIA
Introduction—description of the Polyclad Leptoplana tremellaris—
Appearance—Habits—Structure: Polycladida—Classification—
Habits—Anatomy—Development: Tricladida—Occurrence—
Structure—Classification: Rhabdocoelida—Occurrence—Habits
—Reproduction—Classification 3
CHAPTER II
TREMATODA
Characters of Trematodes—Habits and Structure of Trematoda
Ectoparasitica (Monogenea)—Life-Histories of Polystomum
integerrimum, Diplozoon paradoxum, and Gyrodactylus elegans—
Trematoda Endoparasitica (Digenea)—Occurrence and Habits of
Digenea—Life-History of Distomum macrostomum—Distomum
hepaticum and its Effects—Bilharzia haematobia—Bisexual
Trematodes—Table of Hosts—Classification 51
CHAPTER III
CESTODA
Introduction—Nature of Cestodes—Occurrence of Cestodes—The
Tape-Worms of Man and Domestic Animals—Table of Life-
Histories of Principal Cestodes of Man and Domestic Animals—
Structure and Development of Cestodes—Table for the
Discrimination of the More Usual Cestodes of Man and Domestic
Animals—Classification 74
CHAPTER IV
MESOZOA
Dicyemidae—Structure—Reproduction—Occurrence: Orthonectidae—
Occurrence—Structure: Trichoplax: Salinella 92
PAGE
Scheme of the Classification adopted in this Book ix
PLATYHELMINTHES AND MESOZOA
CHAPTER I
TURBELLARIA
Introduction—description of the Polyclad Leptoplana tremellaris—
Appearance—Habits—Structure: Polycladida—Classification—
Habits—Anatomy—Development: Tricladida—Occurrence—
Structure—Classification: Rhabdocoelida—Occurrence—Habits
—Reproduction—Classification 3
CHAPTER II
TREMATODA
Characters of Trematodes—Habits and Structure of Trematoda
Ectoparasitica (Monogenea)—Life-Histories of Polystomum
integerrimum, Diplozoon paradoxum, and Gyrodactylus elegans—
Trematoda Endoparasitica (Digenea)—Occurrence and Habits of
Digenea—Life-History of Distomum macrostomum—Distomum
hepaticum and its Effects—Bilharzia haematobia—Bisexual
Trematodes—Table of Hosts—Classification 51
CHAPTER III
CESTODA
Introduction—Nature of Cestodes—Occurrence of Cestodes—The
Tape-Worms of Man and Domestic Animals—Table of Life-
Histories of Principal Cestodes of Man and Domestic Animals—
Structure and Development of Cestodes—Table for the
Discrimination of the More Usual Cestodes of Man and Domestic
Animals—Classification 74
CHAPTER IV
MESOZOA
Dicyemidae—Structure—Reproduction—Occurrence: Orthonectidae—
Occurrence—Structure: Trichoplax: Salinella 92
Page 7
NEMERTINEA
CHAPTER V
NEMERTINEA
Introductory—External Characters—Anatomy—Classification—
Development—Habits—Regeneration—Breeding—Geographical
Distribution—Land, Fresh-Water, and Parasitic Forms—Affinities 99
NEMATHELMINTHES AND CHAETOGNATHA
CHAPTER VI
NEMATHELMINTHES
Introduction—Nematoda—Anatomy—Embryology—Classification—
Ascaridae—Strongylidae—Trichotrachelidae—Filariidae—
Mermithidae—Anguillulidae—Enoplidae—Parasitism:
Nematomorpha—Anatomy—Classification—Life-History:
Acanthocephala—Anatomy—Embryology—Classification 123
CHAPTER VII
CHAETOGNATHA
Structure—Reproduction—Habits—Food—Classification—Table of
Identification [see also p. 534] 186
ROTIFERA, GASTROTRICHA, AND
KINORHYNCHA
CHAPTER VIII
ROTIFERA, GASTROTRICHA, AND KINORHYNCHA
Rotifera—History—External Features—Movements—Anatomy—
Reproduction—Embryology—Classification—Distribution—
Affinities: Gastrotricha: Kinorhyncha 197
ARCHIANNELIDA, POLYCHAETA, AND
MYZOSTOMARIA
CHAPTER IX
The Chaetopodous Worms—The Archiannelida—Anatomy of Nereis, as
Typical of the Polychaeta 241
CHAPTER V
NEMERTINEA
Introductory—External Characters—Anatomy—Classification—
Development—Habits—Regeneration—Breeding—Geographical
Distribution—Land, Fresh-Water, and Parasitic Forms—Affinities 99
NEMATHELMINTHES AND CHAETOGNATHA
CHAPTER VI
NEMATHELMINTHES
Introduction—Nematoda—Anatomy—Embryology—Classification—
Ascaridae—Strongylidae—Trichotrachelidae—Filariidae—
Mermithidae—Anguillulidae—Enoplidae—Parasitism:
Nematomorpha—Anatomy—Classification—Life-History:
Acanthocephala—Anatomy—Embryology—Classification 123
CHAPTER VII
CHAETOGNATHA
Structure—Reproduction—Habits—Food—Classification—Table of
Identification [see also p. 534] 186
ROTIFERA, GASTROTRICHA, AND
KINORHYNCHA
CHAPTER VIII
ROTIFERA, GASTROTRICHA, AND KINORHYNCHA
Rotifera—History—External Features—Movements—Anatomy—
Reproduction—Embryology—Classification—Distribution—
Affinities: Gastrotricha: Kinorhyncha 197
ARCHIANNELIDA, POLYCHAETA, AND
MYZOSTOMARIA
CHAPTER IX
The Chaetopodous Worms—The Archiannelida—Anatomy of Nereis, as
Typical of the Polychaeta 241
Page 8
CHAPTER X
Classification of the Polychaeta—Shape—Head—Parapodia—Chaetae
—Gills—Internal Organs—Jaws—Sense Organs—Reproduction
—Larval Forms—Budding—Fission—Branching—Regeneration 257
CHAPTER XI
Natural History of Polychaetes—General Habits—Character of Tube
and its Formation—Colouring—Protective and Mimetic Devices—
Phosphorescence—Food—Uses—Associated Worms—Worms as
Hosts—Distribution—Fossil Remains 284
CHAPTER XII
Characters of the Sub-Orders of Polychaetes—Characters of the
Families—Description of British Genera and Species: the
Myzostomaria 303
OLIGOCHAETA (EARTHWORMS, ETC.), AND
HIRUDINEA (LEECHES)
CHAPTER XIII
OLIGOCHAETA (EARTHWORMS AND THEIR ALLIES)
Introduction—Anatomy—Reproduction—Bionomics—Distribution—
Classification—Microdrili and Megadrili 347
CHAPTER XIV
HIRUDINEA (LEECHES)
Introduction—Anatomy—Reproduction—Classification—
Rhynchobdellae and Gnathobdellae 392
GEPHYREA AND PHORONIS
CHAPTER XV
GEPHYREA
Introduction—Anatomy—Development—Sipunculoidea—Priapuloidea
—Echiuroidea—Epithetosomatoidea—Affinities of the Group 411
CHAPTER XVI
PHORONIS
History—Habits—Structure—Reproduction—Larva—Metamorphosis
—List of Species and Localities—Systematic Position 450
Classification of the Polychaeta—Shape—Head—Parapodia—Chaetae
—Gills—Internal Organs—Jaws—Sense Organs—Reproduction
—Larval Forms—Budding—Fission—Branching—Regeneration 257
CHAPTER XI
Natural History of Polychaetes—General Habits—Character of Tube
and its Formation—Colouring—Protective and Mimetic Devices—
Phosphorescence—Food—Uses—Associated Worms—Worms as
Hosts—Distribution—Fossil Remains 284
CHAPTER XII
Characters of the Sub-Orders of Polychaetes—Characters of the
Families—Description of British Genera and Species: the
Myzostomaria 303
OLIGOCHAETA (EARTHWORMS, ETC.), AND
HIRUDINEA (LEECHES)
CHAPTER XIII
OLIGOCHAETA (EARTHWORMS AND THEIR ALLIES)
Introduction—Anatomy—Reproduction—Bionomics—Distribution—
Classification—Microdrili and Megadrili 347
CHAPTER XIV
HIRUDINEA (LEECHES)
Introduction—Anatomy—Reproduction—Classification—
Rhynchobdellae and Gnathobdellae 392
GEPHYREA AND PHORONIS
CHAPTER XV
GEPHYREA
Introduction—Anatomy—Development—Sipunculoidea—Priapuloidea
—Echiuroidea—Epithetosomatoidea—Affinities of the Group 411
CHAPTER XVI
PHORONIS
History—Habits—Structure—Reproduction—Larva—Metamorphosis
—List of Species and Localities—Systematic Position 450
Page 9
POLYZOA
CHAPTER XVII
POLYZOA
Introduction—General Characters and Terminology—Brown Bodies—
History—Outlines of Classification—Marine Polyzoa—
Occurrence—Forms of Colony and of Zooecia—Ovicells—
Avicularia—Vibracula—Entoprocta 465
CHAPTER XVIII
POLYZOA—continued
Fresh-water Polyzoa—Phylactolaemata—Occurrence—Structure of
Cristatella—Division of Colony—Movements of Colony—
Retraction And Protrusion of Polypides in Polyzoa—Statoblasts
—Table for Determination of Genera of Fresh-water Polyzoa—
Reproductive Processes of Polyzoa—Development—Affinities—
Metamorphosis—Budding 492
CHAPTER XIX
POLYZOA—continued
Classification—Geographical Distribution—Palaeontology—Methods
for the Examination of Specific Characters—Terminology—Key
for the Determination of the Genera of British Marine Polyzoa 515
Addendum to Chaetognatha 534
Index 535
CHAPTER XVII
POLYZOA
Introduction—General Characters and Terminology—Brown Bodies—
History—Outlines of Classification—Marine Polyzoa—
Occurrence—Forms of Colony and of Zooecia—Ovicells—
Avicularia—Vibracula—Entoprocta 465
CHAPTER XVIII
POLYZOA—continued
Fresh-water Polyzoa—Phylactolaemata—Occurrence—Structure of
Cristatella—Division of Colony—Movements of Colony—
Retraction And Protrusion of Polypides in Polyzoa—Statoblasts
—Table for Determination of Genera of Fresh-water Polyzoa—
Reproductive Processes of Polyzoa—Development—Affinities—
Metamorphosis—Budding 492
CHAPTER XIX
POLYZOA—continued
Classification—Geographical Distribution—Palaeontology—Methods
for the Examination of Specific Characters—Terminology—Key
for the Determination of the Genera of British Marine Polyzoa 515
Addendum to Chaetognatha 534
Index 535
Page 10
SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK
PLATYHELMINTHES (p. 3)
Family.
TURBELLARIA Planoceridae
(p. 3) (p. 19).
Leptoplanidae
Acotylea
(p. 19).
(p. 16)
Cestoplanidae
(p. 19).
Enantiidae (p. 19).
Polycladida
Anonymidae
(p. 7)
(p. 19)
Pseudoceridae
(p. 19).
Cotylea
Euryleptidae
(p. 19).
Prosthiostomatidae
(p. 19).
Paludicola
Planariidae (p. 42).
(p. 30)
Procerodidae
(p. 42).
Maricola
= Gundidae.
(pp. 30, 32)
Tricladida Bdellouridae
(p. 30) (p. 42).
Bipaliidae (p. 42).
Geoplanidae
Terricola
(p. 42).
(pp. 30, 33)
Rhynchodemidae
(p. 42).
Rhabdocoelida Proporidae (p. 49).
(p. 42) Acoela (p. 42) Aphanostomatidae
(p. 49).
Rhabdocoela Macrostomatidae
(p. 43) (p. 49).
Microstomatidae
(p. 49).
PLATYHELMINTHES (p. 3)
Family.
TURBELLARIA Planoceridae
(p. 3) (p. 19).
Leptoplanidae
Acotylea
(p. 19).
(p. 16)
Cestoplanidae
(p. 19).
Enantiidae (p. 19).
Polycladida
Anonymidae
(p. 7)
(p. 19)
Pseudoceridae
(p. 19).
Cotylea
Euryleptidae
(p. 19).
Prosthiostomatidae
(p. 19).
Paludicola
Planariidae (p. 42).
(p. 30)
Procerodidae
(p. 42).
Maricola
= Gundidae.
(pp. 30, 32)
Tricladida Bdellouridae
(p. 30) (p. 42).
Bipaliidae (p. 42).
Geoplanidae
Terricola
(p. 42).
(pp. 30, 33)
Rhynchodemidae
(p. 42).
Rhabdocoelida Proporidae (p. 49).
(p. 42) Acoela (p. 42) Aphanostomatidae
(p. 49).
Rhabdocoela Macrostomatidae
(p. 43) (p. 49).
Microstomatidae
(p. 49).
Page 11
Prorhynchidae
(p. 49).
Mesostomatidae
(p. 49).
Proboscidae
(p. 49).
Vorticidae (p. 50).
Solenopharyngidae
(p. 50).
Plagiostomatidae
(p. 50).
Alloeocoela
Bothrioplanidae
(p. 43)
(p. 50).
Monotidae (p. 50).
Temnocephalidae
(pp. 53, 73).
Tristomatidae
(pp. 53, 73).
Monogenea (pp. 5, 52)
Polystomatidae
= Heterocotylea + Aspidocotylea
(pp. 53, 73).
(p. 73)
Gyrodactylidae
(pp. 53, 61).
Aspidobothridae
(p. 73).
TREMATODA Holostomatidae
(pp. 3, 51) (p. 73).
Amphistomatidae
(p. 73).
Distomatidae
Digenea (pp. 5, 52) (p. 73).
= Malacocotylea (p. 73) Gasterostomatidae
(p. 73).
Didymozoontidae
(p. 73).
Monostomatidae
(p. 73).
CESTODA (pp. 3, 74) Cestodariidae
= Monozoa
(p. 49).
Mesostomatidae
(p. 49).
Proboscidae
(p. 49).
Vorticidae (p. 50).
Solenopharyngidae
(p. 50).
Plagiostomatidae
(p. 50).
Alloeocoela
Bothrioplanidae
(p. 43)
(p. 50).
Monotidae (p. 50).
Temnocephalidae
(pp. 53, 73).
Tristomatidae
(pp. 53, 73).
Monogenea (pp. 5, 52)
Polystomatidae
= Heterocotylea + Aspidocotylea
(pp. 53, 73).
(p. 73)
Gyrodactylidae
(pp. 53, 61).
Aspidobothridae
(p. 73).
TREMATODA Holostomatidae
(pp. 3, 51) (p. 73).
Amphistomatidae
(p. 73).
Distomatidae
Digenea (pp. 5, 52) (p. 73).
= Malacocotylea (p. 73) Gasterostomatidae
(p. 73).
Didymozoontidae
(p. 73).
Monostomatidae
(p. 73).
CESTODA (pp. 3, 74) Cestodariidae
= Monozoa
Page 12
(p. 91).
Bothriocephalidae
(p. 91).
Tetrarhynchidae
(p. 91).
Tetraphyllidae
(p. 91).
Taeniidae (p. 91).
MESOZOA
Dicyemidae
(p. 93).
MESOZOA (pp. 3, 92)
Orthonectida
(p. 94).
NEMERTINEA (p. 99)
HOPLONEMERTEA (p. 110) = Metanemertini (p. 112).
SCHIZONEMERTEA (p. 111) = Heteronemertini (ex parte) (p. 113).
PALAEONEMERTEA (p. 111) = Protonemertini (p. 112). + Mesonemertini
(p. 112). + Heteronemertini (ex parte) (p. 113).
NEMATHELMINTHES (p. 123)
NEMATODA (pp. 123, 124) Ascaridae (p. 138).
Strongylidae
(p. 142).
Trichotrachelidae
(p. 144).
Filariidae (p. 147).
Mermithidae
(p. 150).
Anguillulidae
(p. 154).
Enoplidae
(p. 157).
Chaetosomatidae
(p. 158).
Bothriocephalidae
(p. 91).
Tetrarhynchidae
(p. 91).
Tetraphyllidae
(p. 91).
Taeniidae (p. 91).
MESOZOA
Dicyemidae
(p. 93).
MESOZOA (pp. 3, 92)
Orthonectida
(p. 94).
NEMERTINEA (p. 99)
HOPLONEMERTEA (p. 110) = Metanemertini (p. 112).
SCHIZONEMERTEA (p. 111) = Heteronemertini (ex parte) (p. 113).
PALAEONEMERTEA (p. 111) = Protonemertini (p. 112). + Mesonemertini
(p. 112). + Heteronemertini (ex parte) (p. 113).
NEMATHELMINTHES (p. 123)
NEMATODA (pp. 123, 124) Ascaridae (p. 138).
Strongylidae
(p. 142).
Trichotrachelidae
(p. 144).
Filariidae (p. 147).
Mermithidae
(p. 150).
Anguillulidae
(p. 154).
Enoplidae
(p. 157).
Chaetosomatidae
(p. 158).
Page 13
Desmoscolecidae
(p. 159).
NEMATOMORPHA (pp. 123, 164) Gordiidae (p. 164).
Echinorhynchidae
(p. 182)
Gigantorhynchidae
(p. 183).
ACANTHOCEPHALA (pp. 123, 174)
Neorhynchidae
(p. 184).
Arhynchidae
(p. 185).
CHAETOGNATHA (p. 186)
ROTIFERA (p. 197)
Flosculariidae
FLOSCULARIACEAE (p. 220) (p. 221).
Apsilidae (p. 221).
Melicertidae
(p. 221).
MELICERTACEAE (p. 221)
Trochosphaeridae
(p. 221).
Philodinidae
BDELLOIDA (p. 222)
(p. 222).
Asplanchnidae
ASPLANCHNACEAE (p. 222)
(p. 223).
Pedalionidae
SCIRTOPODA (p. 223)
(p. 223).
PLOIMA (p. 223) Illoricata (p. 223) Microcodonidae
(p. 224).
(p. 159).
NEMATOMORPHA (pp. 123, 164) Gordiidae (p. 164).
Echinorhynchidae
(p. 182)
Gigantorhynchidae
(p. 183).
ACANTHOCEPHALA (pp. 123, 174)
Neorhynchidae
(p. 184).
Arhynchidae
(p. 185).
CHAETOGNATHA (p. 186)
ROTIFERA (p. 197)
Flosculariidae
FLOSCULARIACEAE (p. 220) (p. 221).
Apsilidae (p. 221).
Melicertidae
(p. 221).
MELICERTACEAE (p. 221)
Trochosphaeridae
(p. 221).
Philodinidae
BDELLOIDA (p. 222)
(p. 222).
Asplanchnidae
ASPLANCHNACEAE (p. 222)
(p. 223).
Pedalionidae
SCIRTOPODA (p. 223)
(p. 223).
PLOIMA (p. 223) Illoricata (p. 223) Microcodonidae
(p. 224).
Page 14
Rhinopidae
(p. 224).
Hydatinidae
(p. 224).
Synchaetidae
(p. 224).
Notommatidae
(p. 224).
Drilophagidae
(p. 224).
Triarthridae
(p. 224).
Rattulidae
(p. 225).
Dinocharididae
(p. 225).
Salpinidae
(p. 225).
Euchlanididae
(p. 225).
Loricata (p. 224) Cathypnidae
(p. 225).
Coluridae (p. 225).
Pterodinidae
(p. 225).
Brachionidae
(p. 225).
Anuraeidae
(p. 225).
Seisonidae
SEISONACEAE (p. 225)
(p. 226).
GASTROTRICHA
GASTROTRICHA Euichthydina (p. 235)
(p. 231). Apodina (p. 235)
KINORHYNCHA (p. 236)
(p. 224).
Hydatinidae
(p. 224).
Synchaetidae
(p. 224).
Notommatidae
(p. 224).
Drilophagidae
(p. 224).
Triarthridae
(p. 224).
Rattulidae
(p. 225).
Dinocharididae
(p. 225).
Salpinidae
(p. 225).
Euchlanididae
(p. 225).
Loricata (p. 224) Cathypnidae
(p. 225).
Coluridae (p. 225).
Pterodinidae
(p. 225).
Brachionidae
(p. 225).
Anuraeidae
(p. 225).
Seisonidae
SEISONACEAE (p. 225)
(p. 226).
GASTROTRICHA
GASTROTRICHA Euichthydina (p. 235)
(p. 231). Apodina (p. 235)
KINORHYNCHA (p. 236)
Page 15
CHAETOPODA (p. 241)
ARCHIANNELIDA (p. 241)
POLYCHAETA Phanerocephala Syllidae (p. 306).
(pp. 241, 245) (p. 303) Hesionidae
(p. 308).
Aphroditidae
(p. 309).
Phyllodocidae
(p. 313).
Tomopteridae
(p. 315).
Nereidae (p. 315).
Nereidiformia Nephthydidae
(p. 303) (p. 317).
Amphinomidae
(p. 318).
Eunicidae (p. 318).
Glyceridae
(p. 320).
Sphaerodoridae
(p. 320).
Ariciidae (p. 321).
Typhloscolecidae
(p. 321).
Spionidae (p. 321).
Polydoridae
(p. 323).
Spioniformia Chaetopteridae
(p. 304) (p. 323).
Magelonidae (325.
Ammocharidae
(p. 325).
Terebelliformia Cirratulidae
(p. 304) (p. 325).
Terebellidae
(p. 327).
ARCHIANNELIDA (p. 241)
POLYCHAETA Phanerocephala Syllidae (p. 306).
(pp. 241, 245) (p. 303) Hesionidae
(p. 308).
Aphroditidae
(p. 309).
Phyllodocidae
(p. 313).
Tomopteridae
(p. 315).
Nereidae (p. 315).
Nereidiformia Nephthydidae
(p. 303) (p. 317).
Amphinomidae
(p. 318).
Eunicidae (p. 318).
Glyceridae
(p. 320).
Sphaerodoridae
(p. 320).
Ariciidae (p. 321).
Typhloscolecidae
(p. 321).
Spionidae (p. 321).
Polydoridae
(p. 323).
Spioniformia Chaetopteridae
(p. 304) (p. 323).
Magelonidae (325.
Ammocharidae
(p. 325).
Terebelliformia Cirratulidae
(p. 304) (p. 325).
Terebellidae
(p. 327).
Page 16
Ampharetidae
(p. 330).
Amphictenidae
(p. 330).
Capitelliformia Capitellidae
(p. 305) (p. 331).
Opheliidae
(p. 331).
Maldanidae
(p. 332).
Arenicolidae
Scoleciformia (p. 333).
(p. 305) Scalibregmidae
(p. 334).
Chlorhaemidae
(p. 334).
Sternaspidae
(p. 335).
Sabellidae
(p. 336).
Eriographidae
Sabelliformia (p. 338).
Cryptocephala (p. 305) Amphicorinidae
(p. 303) (p. 339).
Serpulidae
(p. 339).
Hermelliformia Hermellidae
(p. 306) (p. 341).
MYZOSTOMARIA (pp. 241, 341)
OLIGOCHAETA Microdrili (p. 373) Aphaneura
(pp. 241, 347) (p. 374).
Enchytraeidae
(p. 375).
Discodrilidae
(p. 376).
Phreoryctidae
(p. 376).
(p. 330).
Amphictenidae
(p. 330).
Capitelliformia Capitellidae
(p. 305) (p. 331).
Opheliidae
(p. 331).
Maldanidae
(p. 332).
Arenicolidae
Scoleciformia (p. 333).
(p. 305) Scalibregmidae
(p. 334).
Chlorhaemidae
(p. 334).
Sternaspidae
(p. 335).
Sabellidae
(p. 336).
Eriographidae
Sabelliformia (p. 338).
Cryptocephala (p. 305) Amphicorinidae
(p. 303) (p. 339).
Serpulidae
(p. 339).
Hermelliformia Hermellidae
(p. 306) (p. 341).
MYZOSTOMARIA (pp. 241, 341)
OLIGOCHAETA Microdrili (p. 373) Aphaneura
(pp. 241, 347) (p. 374).
Enchytraeidae
(p. 375).
Discodrilidae
(p. 376).
Phreoryctidae
(p. 376).
Page 17
Naidomorpha
(p. 377).
Tubificidae
(p. 378).
Lumbriculidae
(p. 379).
Moniligastridae
(p. 380).
Perichaetidae
(p. 380).
Cryptodrilidae
(p. 382).
Acanthodrilidae
(p. 384).
Megadrili (pp. 373, 374).
Eudrilidae
(p. 385).
Geoscolicidae
(p. 386).
Lumbricidae
(p. 388).
HIRUDINEA (p. 392)
Ichthyobdellidae
(p. 406).
RHYNCHOBDELLAE (p. 405)
Glossiphoniidae
(p. 406).
Gnathobdellidae
(p. 407).
GNATHOBDELLAE (p. 407)
Herpobdellidae
(p. 407).
GEPHYREA (p. 411)
SIPUNCULOIDEA (pp. 412, 420).
PRIAPULOIDEA (pp. 412, 430).
ECHIUROIDEA (pp. 412, 434).
EPITHETOSOMATOIDEA (pp. 412, 444).
(p. 377).
Tubificidae
(p. 378).
Lumbriculidae
(p. 379).
Moniligastridae
(p. 380).
Perichaetidae
(p. 380).
Cryptodrilidae
(p. 382).
Acanthodrilidae
(p. 384).
Megadrili (pp. 373, 374).
Eudrilidae
(p. 385).
Geoscolicidae
(p. 386).
Lumbricidae
(p. 388).
HIRUDINEA (p. 392)
Ichthyobdellidae
(p. 406).
RHYNCHOBDELLAE (p. 405)
Glossiphoniidae
(p. 406).
Gnathobdellidae
(p. 407).
GNATHOBDELLAE (p. 407)
Herpobdellidae
(p. 407).
GEPHYREA (p. 411)
SIPUNCULOIDEA (pp. 412, 420).
PRIAPULOIDEA (pp. 412, 430).
ECHIUROIDEA (pp. 412, 434).
EPITHETOSOMATOIDEA (pp. 412, 444).
Page 18
PHORONIS (p. 450)
POLYZOA (p. 465)
ENTOPROCTA (pp. 475, 487)
Articulata (p. 517).
Cyclostomata
Inarticulata
(p. 477)
(p. 517).
Cellularina
Cheilostomata (p. 518).
Gymnolaemata
ECTOPROCTA (p. 477) Flustrina (p. 518).
(p. 476)
(p. 475) Escharina (p. 518).
Alcyonellea
Ctenostomata (p. 518).
(p. 477) Vesicularina
(p. 518).
Phylactolaemata (pp. 476, 493)
POLYZOA (p. 465)
ENTOPROCTA (pp. 475, 487)
Articulata (p. 517).
Cyclostomata
Inarticulata
(p. 477)
(p. 517).
Cellularina
Cheilostomata (p. 518).
Gymnolaemata
ECTOPROCTA (p. 477) Flustrina (p. 518).
(p. 476)
(p. 475) Escharina (p. 518).
Alcyonellea
Ctenostomata (p. 518).
(p. 477) Vesicularina
(p. 518).
Phylactolaemata (pp. 476, 493)
Page 19
PLATYHELMINTHES AND MESOZOA
BY
F. W. GAMBLE, M.Sc. (Vict.)
Demonstrator and Assistant-Lecturer in Zoology in the Owens College, Manchester.
CHAPTER I
TURBELLARIA
INTRODUCTION: DESCRIPTION OF THE POLYCLAD LEPTOPLANA TREMELLARIS—APPEARANCE
—HABITS—STRUCTURE: POLYCLADIDA—CLASSIFICATION—HABITS—ANATOMY—
DEVELOPMENT: TRICLADIDA—OCCURRENCE—STRUCTURE—CLASSIFICATION:
RHABDOCOELIDA—OCCURRENCE—HABITS—REPRODUCTION—CLASSIFICATION.
The Platyhelminthes, or Flat Worms, form a natural assemblage of animals, the
members of which, however widely they may differ in appearance, habits, or life-
history, exhibit a fundamental similarity of organisation which justifies their
separation from other classes of worms, and their union into a distinct phylum.
Excluding the leeches (Hirudinea), and the long sea-worms (Nemertinea)—which,
though formerly included, are now treated independently—the Platyhelminthes
may be divided into three branches: (1) Turbellaria (including the Planarians), (2)
Trematoda (including the liver-flukes), and (3) Cestoda (tape-worms). The
Mesozoa will be treated as an appendix to the Platyhelminthes.
The Turbellaria were so called by Ehrenberg[1] (1831) on account of the cilia or
vibratile processes with which these aquatic animals are covered, causing by their
incessant action, tiny currents ("turbellae," disturbances) in the surrounding water.
The ciliary covering distinguishes this free-living group from the parasitic
Trematodes and Cestodes, some of which possess such an investment, but only
during their early free larval stage, for the short period when they have left the
parental host and are seeking another (Figs. 26, 27, 42).
Some Turbellaria (Rhabdocoelida) resemble Infusoria in their minute size, shape,
and movements. Nevertheless they possess an organisation of considerable
BY
F. W. GAMBLE, M.Sc. (Vict.)
Demonstrator and Assistant-Lecturer in Zoology in the Owens College, Manchester.
CHAPTER I
TURBELLARIA
INTRODUCTION: DESCRIPTION OF THE POLYCLAD LEPTOPLANA TREMELLARIS—APPEARANCE
—HABITS—STRUCTURE: POLYCLADIDA—CLASSIFICATION—HABITS—ANATOMY—
DEVELOPMENT: TRICLADIDA—OCCURRENCE—STRUCTURE—CLASSIFICATION:
RHABDOCOELIDA—OCCURRENCE—HABITS—REPRODUCTION—CLASSIFICATION.
The Platyhelminthes, or Flat Worms, form a natural assemblage of animals, the
members of which, however widely they may differ in appearance, habits, or life-
history, exhibit a fundamental similarity of organisation which justifies their
separation from other classes of worms, and their union into a distinct phylum.
Excluding the leeches (Hirudinea), and the long sea-worms (Nemertinea)—which,
though formerly included, are now treated independently—the Platyhelminthes
may be divided into three branches: (1) Turbellaria (including the Planarians), (2)
Trematoda (including the liver-flukes), and (3) Cestoda (tape-worms). The
Mesozoa will be treated as an appendix to the Platyhelminthes.
The Turbellaria were so called by Ehrenberg[1] (1831) on account of the cilia or
vibratile processes with which these aquatic animals are covered, causing by their
incessant action, tiny currents ("turbellae," disturbances) in the surrounding water.
The ciliary covering distinguishes this free-living group from the parasitic
Trematodes and Cestodes, some of which possess such an investment, but only
during their early free larval stage, for the short period when they have left the
parental host and are seeking another (Figs. 26, 27, 42).
Some Turbellaria (Rhabdocoelida) resemble Infusoria in their minute size, shape,
and movements. Nevertheless they possess an organisation of considerable
Page 20
complexity. The fresh-water Planarians (Fig. 14), abounding in ponds and streams,
vary from a quarter to half an inch in length, and are elongated and flattened. Their
body is soft, and progresses by a characteristic, even, gliding motion like a snail.
The marine Planarians or Polyclads (Fig. 8) are usually broad and leaf-like,
sometimes attaining a length of six inches, and swim or creep in a most graceful
way. Land Planarians occur in this country (Fig. 15), but far more abundantly in
tropical and sub-tropical districts, in moist places, venturing abroad at night in
pursuit of prey. They are elongated and cylindrical, in some cases measuring, when
fully extended, a foot or more in length, and are often ornamented with brilliantly
coloured, longitudinal bands.
Turbellaria are carnivorous, overpowering their prey by peculiar cutaneous
offensive weapons, and then sucking out the contents of the victim by the
"pharynx." Land Planarians feed on earthworms, molluscs, and wood-lice; fresh-
water Planarians on Oligochaet worms, water-snails, and water-beetles; marine
forms devour Polychaet worms and molluscs. Some Turbellaria seem to prefer
freshly-killed or weakly examples of animals too large to be overpowered when
fully active. Certain Rhabdocoelida are messmates of Molluscs and Echinoderms,
and a few others are truly parasitic—a mode of life adopted by all Trematodes save
Temnocephala.
The Trematodes[2] may be divided into those living on the outer surface of various
aquatic animals, usually fish (Ectoparasites); and those which penetrate more or
less deeply into the alimentary canal or the associated organs of the host
(Endoparasites). They are oval, flattened Platyhelminthes ranging from a
microscopic size to a length of three feet (Nematobothrium, Fig. 22), and are
provided with organs of adhesion by which they cling to the outer surface, or to the
interior, of the animals they inhabit. Trematodes occur parasitically in all groups of
Vertebrates, but, with the exception of the liver-flukes of the sheep (Distomum
hepaticum and D. magnum), and of Bilharzia haematobia found in man (in the
blood-vessels of the urinary bladder) over the greater part of Africa, their attacks
are not usually of a serious nature. Ectoparasitic Trematodes are Monogenetic; that
is, their larvae grow up directly into mature forms. The Endoparasitic species,
however, are usually Digenetic. Their larvae enter an Invertebrate and produce a
new generation of different larvae, and these another. The last are immature flukes.
They enter a second host, which is swallowed by the final Vertebrate host in which
they become mature.
The Cestodes or Tape-worms have undergone more profound modifications both in
structure and in mode of development. They are all endoparasitic, and, with one
vary from a quarter to half an inch in length, and are elongated and flattened. Their
body is soft, and progresses by a characteristic, even, gliding motion like a snail.
The marine Planarians or Polyclads (Fig. 8) are usually broad and leaf-like,
sometimes attaining a length of six inches, and swim or creep in a most graceful
way. Land Planarians occur in this country (Fig. 15), but far more abundantly in
tropical and sub-tropical districts, in moist places, venturing abroad at night in
pursuit of prey. They are elongated and cylindrical, in some cases measuring, when
fully extended, a foot or more in length, and are often ornamented with brilliantly
coloured, longitudinal bands.
Turbellaria are carnivorous, overpowering their prey by peculiar cutaneous
offensive weapons, and then sucking out the contents of the victim by the
"pharynx." Land Planarians feed on earthworms, molluscs, and wood-lice; fresh-
water Planarians on Oligochaet worms, water-snails, and water-beetles; marine
forms devour Polychaet worms and molluscs. Some Turbellaria seem to prefer
freshly-killed or weakly examples of animals too large to be overpowered when
fully active. Certain Rhabdocoelida are messmates of Molluscs and Echinoderms,
and a few others are truly parasitic—a mode of life adopted by all Trematodes save
Temnocephala.
The Trematodes[2] may be divided into those living on the outer surface of various
aquatic animals, usually fish (Ectoparasites); and those which penetrate more or
less deeply into the alimentary canal or the associated organs of the host
(Endoparasites). They are oval, flattened Platyhelminthes ranging from a
microscopic size to a length of three feet (Nematobothrium, Fig. 22), and are
provided with organs of adhesion by which they cling to the outer surface, or to the
interior, of the animals they inhabit. Trematodes occur parasitically in all groups of
Vertebrates, but, with the exception of the liver-flukes of the sheep (Distomum
hepaticum and D. magnum), and of Bilharzia haematobia found in man (in the
blood-vessels of the urinary bladder) over the greater part of Africa, their attacks
are not usually of a serious nature. Ectoparasitic Trematodes are Monogenetic; that
is, their larvae grow up directly into mature forms. The Endoparasitic species,
however, are usually Digenetic. Their larvae enter an Invertebrate and produce a
new generation of different larvae, and these another. The last are immature flukes.
They enter a second host, which is swallowed by the final Vertebrate host in which
they become mature.
The Cestodes or Tape-worms have undergone more profound modifications both in
structure and in mode of development. They are all endoparasitic, and, with one
Page 21
exception (Archigetes), attain maturity solely within the alimentary canal of
Vertebrates. In length they range from a few millimetres to several metres, but this
great size is attained from the need for the rapid production and accumulation of
enormous numbers of eggs. The "head" or "scolex" is attached to the mucous
membrane of the host by suckers or hooks, but there is no mouth nor any certain
trace of a digestive tract at any stage of the life-history of Cestodes. For
nourishment they absorb, through the skin, the previously-digested food (of the
host) that bathes them. In a few Cestodes the body is simple and not divided into
"proglottides" or generative segments, but in most cases it is jointed in such a way
that the last segment is the oldest, and each contains a set of reproductive organs.
The life-histories of Cestodes are most remarkable. The proglottides containing the
eggs pass out of the final host along with the faeces and enter the intermediate host
with the food. The larvae hatch, and boring their way into the blood-vessels, are
carried by the circulation to various internal organs. Here they usually become
"bladder-worms," and develop the "head" of the future sexual form. Then, if, as is
usually the case, the intermediate host is preyed upon by the final host, the larval
Cestodes enter the alimentary canal of the latter. The head of the larva alone
survives digestion, and from it the mature worm is formed.
Of these three branches of the phylum Platyhelminthes, the Turbellaria possess
features of special interest and importance. Not only do they furnish the
explanation of the structure of the two parasitic groups (which have probably
arisen from Turbellarian-like ancestors), but they occupy the lowest position in the
whole group of worms. There are reasons for thinking that this is the simplest
group of bilateral animals which adopt the habit of creeping. The Turbellaria are
most closely allied to that great extinct group from which they, the Nemertinea,
Rotifera, and even the Annelids, offer increasingly convincing evidence of having
been derived. Many questions relating to the affinities of, or the origin of organs in,
the Annelids, resolve themselves into similar questions about the Turbellaria. For
these reasons, this group is here dealt with at greater length than the others, the
interest of which is of a more special nature.
The history of our knowledge of the Cestodes dates back to ancient times, as the
presence and effects of tape-worms early attracted the attention of physicians.
Trematodes are first distinctly referred to in the sixteenth century, while Turbellaria
first figure in Trembley's memoir on Hydra (1744).[3] The whole subject of the
increase in our knowledge of parasitic Platyhelminthes is dealt with in the standard
work, The Parasites of Man, by Leuckart,[4] and a complete list of references in
zoological literature to Cestodes and Trematodes is to be found in Bronn's
Thierreich.[5] O. F. Müller[6] and Ehrenberg founded our knowledge of the
Vertebrates. In length they range from a few millimetres to several metres, but this
great size is attained from the need for the rapid production and accumulation of
enormous numbers of eggs. The "head" or "scolex" is attached to the mucous
membrane of the host by suckers or hooks, but there is no mouth nor any certain
trace of a digestive tract at any stage of the life-history of Cestodes. For
nourishment they absorb, through the skin, the previously-digested food (of the
host) that bathes them. In a few Cestodes the body is simple and not divided into
"proglottides" or generative segments, but in most cases it is jointed in such a way
that the last segment is the oldest, and each contains a set of reproductive organs.
The life-histories of Cestodes are most remarkable. The proglottides containing the
eggs pass out of the final host along with the faeces and enter the intermediate host
with the food. The larvae hatch, and boring their way into the blood-vessels, are
carried by the circulation to various internal organs. Here they usually become
"bladder-worms," and develop the "head" of the future sexual form. Then, if, as is
usually the case, the intermediate host is preyed upon by the final host, the larval
Cestodes enter the alimentary canal of the latter. The head of the larva alone
survives digestion, and from it the mature worm is formed.
Of these three branches of the phylum Platyhelminthes, the Turbellaria possess
features of special interest and importance. Not only do they furnish the
explanation of the structure of the two parasitic groups (which have probably
arisen from Turbellarian-like ancestors), but they occupy the lowest position in the
whole group of worms. There are reasons for thinking that this is the simplest
group of bilateral animals which adopt the habit of creeping. The Turbellaria are
most closely allied to that great extinct group from which they, the Nemertinea,
Rotifera, and even the Annelids, offer increasingly convincing evidence of having
been derived. Many questions relating to the affinities of, or the origin of organs in,
the Annelids, resolve themselves into similar questions about the Turbellaria. For
these reasons, this group is here dealt with at greater length than the others, the
interest of which is of a more special nature.
The history of our knowledge of the Cestodes dates back to ancient times, as the
presence and effects of tape-worms early attracted the attention of physicians.
Trematodes are first distinctly referred to in the sixteenth century, while Turbellaria
first figure in Trembley's memoir on Hydra (1744).[3] The whole subject of the
increase in our knowledge of parasitic Platyhelminthes is dealt with in the standard
work, The Parasites of Man, by Leuckart,[4] and a complete list of references in
zoological literature to Cestodes and Trematodes is to be found in Bronn's
Thierreich.[5] O. F. Müller[6] and Ehrenberg founded our knowledge of the
Page 22
Turbellaria, but for a long time the group remained in a most neglected condition.
In this country Montagu, G. Johnston, and in Ireland, William Thompson,
discovered several marine species, one of which, Planocera folium (from
Berwick), has not again been met with on British shores. Dalyell[7] conducted
classical researches on the habits of Planarians, and Faraday[8] made interesting
experiments on their power of regenerating lost parts. The credit of assigning the
correct interpretation to most of the various organs of fresh-water Planarians
belongs to von Baer[9] and Dugès,[10] while Mertens[11] effected a similar service
for the marine forms, or Polyclads. The minute Rhabdocoels were first
successfully investigated and classified by Oscar Schmidt.[12] The great work on
this group is, however, the monograph by von Graff.[13] A similarly comprehensive
and indispensable treatise by Lang, on the Polycladida,[14] contains references to
all previous publications on the group, among which the papers by Quatrefages,
Johannes Müller, Keferstein, Minot, and Hallez stand out conspicuously. Moseley's
work[15] on the Land Planarians of Ceylon is undoubtedly the most revolutionary
paper referring to this group, and the best contribution towards elucidating the
structure of the Tricladida at a time when the subject was very obscure. A
monograph on Land Planarians is being prepared by von Graff.
The Turbellaria are divided into: (1) Polycladida, marine forms with multiple
intestinal branches; (2) Tricladida, marine, fresh-water, and terrestrial Planarians
with three main intestinal branches; (3) the Rhabdocoelida, as varied in habit as the
Triclads, but possessing a straight and simple or slightly lobed, intestine. A detailed
description of an example of the Polyclads, and then a comparative account of each
division, will now be given.
Fig. 1.—Leptoplana tremellaris O. F. M. Seen from the dorsal surface. The alimentary canal
runs down the middle line and sends branches to the margin of the body. × 6.
In this country Montagu, G. Johnston, and in Ireland, William Thompson,
discovered several marine species, one of which, Planocera folium (from
Berwick), has not again been met with on British shores. Dalyell[7] conducted
classical researches on the habits of Planarians, and Faraday[8] made interesting
experiments on their power of regenerating lost parts. The credit of assigning the
correct interpretation to most of the various organs of fresh-water Planarians
belongs to von Baer[9] and Dugès,[10] while Mertens[11] effected a similar service
for the marine forms, or Polyclads. The minute Rhabdocoels were first
successfully investigated and classified by Oscar Schmidt.[12] The great work on
this group is, however, the monograph by von Graff.[13] A similarly comprehensive
and indispensable treatise by Lang, on the Polycladida,[14] contains references to
all previous publications on the group, among which the papers by Quatrefages,
Johannes Müller, Keferstein, Minot, and Hallez stand out conspicuously. Moseley's
work[15] on the Land Planarians of Ceylon is undoubtedly the most revolutionary
paper referring to this group, and the best contribution towards elucidating the
structure of the Tricladida at a time when the subject was very obscure. A
monograph on Land Planarians is being prepared by von Graff.
The Turbellaria are divided into: (1) Polycladida, marine forms with multiple
intestinal branches; (2) Tricladida, marine, fresh-water, and terrestrial Planarians
with three main intestinal branches; (3) the Rhabdocoelida, as varied in habit as the
Triclads, but possessing a straight and simple or slightly lobed, intestine. A detailed
description of an example of the Polyclads, and then a comparative account of each
division, will now be given.
Fig. 1.—Leptoplana tremellaris O. F. M. Seen from the dorsal surface. The alimentary canal
runs down the middle line and sends branches to the margin of the body. × 6.
Page 23
Turbellaria. I. Polycladida.
Description of Leptoplana tremellaris.
Appearance and Habits.—An account of the Polyclad Turbellaria may be fitly
prefaced by a description of a very common representative, Leptoplana
tremellaris, so called on account of the thin, flat body which executes when
disturbed, quivering or tremulous swimming movements.
Like all Polyclads, Leptoplana is marine. It is probably found on all European
shores, northwards to Greenland and southwards to the Red Sea, while vertically it
ranges from the littoral zone down to fifty fathoms. There is, however, an
apparently well-marked difference between the littoral specimens, which vary from
three-quarters to one inch in length, are brownish in colour and firm in consistency,
and the more delicate examples half an inch long, white with a brown tinge, which
occur in deeper water.
Fig. 2.—Leptoplana tremellaris. Three-quarters view from the ventral surface. The pharynx
(ph) is widely protruded through the month (mo) as in the act of attacking prey. br, Brain
with nerves, close to which are the four groups of eyes; mg, stomach; mgc, "marginal
groove"; pe, penis; sc, sucker; ut, uterus; vd, vasa deferentia; ♀, female genital aperture
surrounded by the shell-gland; ♂, male aperture. (Semi-diagrammatic, and × 6.)
At low water Leptoplana may be found buried in mud or on the under surface of
stones, in pools where darkness and dampness may be ensured till the return of the
tide. It is, however, by no means easy to detect and remove it from the encrusting
Polyzoa, Ascidians, or Sponges with which it is usually associated. The flat, soft,
unsegmented body is so closely appressed to the substratum that its presence is
usually only betrayed by its movement, an even gliding motion of the mobile body,
which suggested the apt name "la pellicule animée" to Dicquemare. The creeping
surface is called ventral, the upper one dorsal, and as the broader end of the body
always goes first, it is anterior as opposed to the more pointed posterior extremity.
With a lens the characters shown in Figs. 1 and 2 may be observed. The eyes are
seen as black dots near the anterior end, and are placed at the sides of a clear oval
space, the brain. Along the transparent margin of the body, the ends of the
intestinal branches may be seen. These ramify from a lobed stomach or main-gut,
Description of Leptoplana tremellaris.
Appearance and Habits.—An account of the Polyclad Turbellaria may be fitly
prefaced by a description of a very common representative, Leptoplana
tremellaris, so called on account of the thin, flat body which executes when
disturbed, quivering or tremulous swimming movements.
Like all Polyclads, Leptoplana is marine. It is probably found on all European
shores, northwards to Greenland and southwards to the Red Sea, while vertically it
ranges from the littoral zone down to fifty fathoms. There is, however, an
apparently well-marked difference between the littoral specimens, which vary from
three-quarters to one inch in length, are brownish in colour and firm in consistency,
and the more delicate examples half an inch long, white with a brown tinge, which
occur in deeper water.
Fig. 2.—Leptoplana tremellaris. Three-quarters view from the ventral surface. The pharynx
(ph) is widely protruded through the month (mo) as in the act of attacking prey. br, Brain
with nerves, close to which are the four groups of eyes; mg, stomach; mgc, "marginal
groove"; pe, penis; sc, sucker; ut, uterus; vd, vasa deferentia; ♀, female genital aperture
surrounded by the shell-gland; ♂, male aperture. (Semi-diagrammatic, and × 6.)
At low water Leptoplana may be found buried in mud or on the under surface of
stones, in pools where darkness and dampness may be ensured till the return of the
tide. It is, however, by no means easy to detect and remove it from the encrusting
Polyzoa, Ascidians, or Sponges with which it is usually associated. The flat, soft,
unsegmented body is so closely appressed to the substratum that its presence is
usually only betrayed by its movement, an even gliding motion of the mobile body,
which suggested the apt name "la pellicule animée" to Dicquemare. The creeping
surface is called ventral, the upper one dorsal, and as the broader end of the body
always goes first, it is anterior as opposed to the more pointed posterior extremity.
With a lens the characters shown in Figs. 1 and 2 may be observed. The eyes are
seen as black dots near the anterior end, and are placed at the sides of a clear oval
space, the brain. Along the transparent margin of the body, the ends of the
intestinal branches may be seen. These ramify from a lobed stomach or main-gut,
Page 24
and should the specimen be mature, the "uterus" loaded with eggs forms a dark
margin round the latter (Figs. 1 and 2, ut). The ventral surface is whitish, and
through it the "pharynx," a frilled protrusible structure, may be dimly observed.
The "mouth,"[16] through which the pharynx at the time of feeding is thrust out
(Fig. 2, mo), is almost in the centre of the ventral surface. Behind this, a white, V-
shaped mark (vd) indicates the ducts of the male reproductive organs, and still
further back is the irregular opaque mark of the "shell-gland," by which the egg-
shells are formed (Fig. 2, ♀).
Fig. 3.—Leptoplana tremellaris in the act of swimming. A, Seen from the right side during the
downward stroke (the resemblance to a skate is striking); B, from above, showing the
upward stroke and longitudinal undulations of the swimming lobes; C, side view during
the upward stroke; D, transverse sections of the body during the strokes. × 5.
Leptoplana employs two kinds of movement, creeping and swimming. Creeping is
a uniform gliding movement, caused by the cilia of the ventral surface, aided
perhaps by the longitudinal muscular layers of this surface, and is effected on the
under side of the "surface-film" of water almost as well as on a solid substratum.
Swimming is a more rapid and elegant movement, employed when alarmed or in
pursuit of prey. The expanded fore-parts of the body act as lobes, which are
flapped rapidly up over the body and then down beneath it, undulations running
rapidly down them from before backwards. The action in fact is somewhat similar
to that by which a skate swims, a resemblance pointed out long ago by Dugès[17]
(Fig. 3).
We have few direct observations on the nature of the food of Leptoplana, or the
exact mode by which it is obtained. Dalyell,[18] who observed this species very
carefully, noticed that it was nocturnal and fed upon a Nereis, becoming greatly
distended and of a green colour after the meal, but pale after a long fast.
margin round the latter (Figs. 1 and 2, ut). The ventral surface is whitish, and
through it the "pharynx," a frilled protrusible structure, may be dimly observed.
The "mouth,"[16] through which the pharynx at the time of feeding is thrust out
(Fig. 2, mo), is almost in the centre of the ventral surface. Behind this, a white, V-
shaped mark (vd) indicates the ducts of the male reproductive organs, and still
further back is the irregular opaque mark of the "shell-gland," by which the egg-
shells are formed (Fig. 2, ♀).
Fig. 3.—Leptoplana tremellaris in the act of swimming. A, Seen from the right side during the
downward stroke (the resemblance to a skate is striking); B, from above, showing the
upward stroke and longitudinal undulations of the swimming lobes; C, side view during
the upward stroke; D, transverse sections of the body during the strokes. × 5.
Leptoplana employs two kinds of movement, creeping and swimming. Creeping is
a uniform gliding movement, caused by the cilia of the ventral surface, aided
perhaps by the longitudinal muscular layers of this surface, and is effected on the
under side of the "surface-film" of water almost as well as on a solid substratum.
Swimming is a more rapid and elegant movement, employed when alarmed or in
pursuit of prey. The expanded fore-parts of the body act as lobes, which are
flapped rapidly up over the body and then down beneath it, undulations running
rapidly down them from before backwards. The action in fact is somewhat similar
to that by which a skate swims, a resemblance pointed out long ago by Dugès[17]
(Fig. 3).
We have few direct observations on the nature of the food of Leptoplana, or the
exact mode by which it is obtained. Dalyell,[18] who observed this species very
carefully, noticed that it was nocturnal and fed upon a Nereis, becoming greatly
distended and of a green colour after the meal, but pale after a long fast.
Page 25
Keferstein[19] noticed a specimen in the act of devouring a Lumbriconereis longer
than itself, and also found the radulae of Chiton and Taenioglossate Molluscs in the
intestine. That such an apparently weak and defenceless animal does overpower
large and healthy Annelids and Mollusca, has not hitherto been definitely proved.
Weak or diseased examples may be chiefly selected. The flexible Leptoplana
adheres firmly to its prey, and the rapid action of the salivary glands of its mobile
pharynx quickly softens and disintegrates the internal parts of the victim. The food
passes into the stomach (Fig. 2, mg), and is there digested. It is then transferred to
the lateral branches of the intestine, and, after all the nutritious matters have been
absorbed, the faeces are ejected with a sudden contraction of the whole body
through the pharynx into the water.
Leptoplana probably does not live more than a year. In the spring or summer,
batches of eggs are laid and fixed to algae or stones by one individual, after having
been fertilised by another. Young Leptoplana hatch out in two to three weeks, and
lead a pelagic existence till they are three or four millimetres in length. In late
summer, numbers of such immature examples may be found among sea-weeds and
Corallina in tide pools. In the succeeding spring they develop first the male and
then the female reproductive organs.
Fig. 4.—Portion of a transverse section of Leptoplana tremellaris in the hinder part of the
body. × 100. bm, Basement (skeletal) membrane; cil, cilia; d.m, diagonal muscles; d.v.m,
dorso-ventral muscles; ep, epidermis; f.p, food particles; l.g, lateral intestinal branches
cut across; l.m ext, external, and l.m int, internal longitudinal muscle layers; m.c,
glandular (mucous) cells; md, their ducts; N, longitudinal nerve; Nu, nuclei of the
intestinal epithelium; ov, ovary; ovd, oviduct; par, cells of the parenchyma; r.d, vasa
deferentia, with spermatozoa; rm, circular musculature; rh, rhabdites; sh, cells of the
shell-gland; te, testes; ve, vasa efferentia; y.c, "yellow cells." (After Lang.)
Anatomy of Leptoplana tremellaris.—Leptoplana may be divided into
corresponding halves only by a median vertical longitudinal plane. The body and
all the systems of organs are strictly bilaterally symmetrical. Excepting the cavities
of the organs themselves, the body is solid. A connective "parenchyma" (Fig. 4,
than itself, and also found the radulae of Chiton and Taenioglossate Molluscs in the
intestine. That such an apparently weak and defenceless animal does overpower
large and healthy Annelids and Mollusca, has not hitherto been definitely proved.
Weak or diseased examples may be chiefly selected. The flexible Leptoplana
adheres firmly to its prey, and the rapid action of the salivary glands of its mobile
pharynx quickly softens and disintegrates the internal parts of the victim. The food
passes into the stomach (Fig. 2, mg), and is there digested. It is then transferred to
the lateral branches of the intestine, and, after all the nutritious matters have been
absorbed, the faeces are ejected with a sudden contraction of the whole body
through the pharynx into the water.
Leptoplana probably does not live more than a year. In the spring or summer,
batches of eggs are laid and fixed to algae or stones by one individual, after having
been fertilised by another. Young Leptoplana hatch out in two to three weeks, and
lead a pelagic existence till they are three or four millimetres in length. In late
summer, numbers of such immature examples may be found among sea-weeds and
Corallina in tide pools. In the succeeding spring they develop first the male and
then the female reproductive organs.
Fig. 4.—Portion of a transverse section of Leptoplana tremellaris in the hinder part of the
body. × 100. bm, Basement (skeletal) membrane; cil, cilia; d.m, diagonal muscles; d.v.m,
dorso-ventral muscles; ep, epidermis; f.p, food particles; l.g, lateral intestinal branches
cut across; l.m ext, external, and l.m int, internal longitudinal muscle layers; m.c,
glandular (mucous) cells; md, their ducts; N, longitudinal nerve; Nu, nuclei of the
intestinal epithelium; ov, ovary; ovd, oviduct; par, cells of the parenchyma; r.d, vasa
deferentia, with spermatozoa; rm, circular musculature; rh, rhabdites; sh, cells of the
shell-gland; te, testes; ve, vasa efferentia; y.c, "yellow cells." (After Lang.)
Anatomy of Leptoplana tremellaris.—Leptoplana may be divided into
corresponding halves only by a median vertical longitudinal plane. The body and
all the systems of organs are strictly bilaterally symmetrical. Excepting the cavities
of the organs themselves, the body is solid. A connective "parenchyma" (Fig. 4,
Page 26
par) knits the various internal organs together, while it allows free play of one part
on another. These organs are enclosed in a muscular body-wall, clothed externally
by the ciliated epidermis, which is separated from the underlying musculature by a
strong membrane (Fig. 4, bm), the only skeletal element in the body.
Body-Wall.—The epidermis (Fig. 4, ep) is composed of a single layer of ciliated
cells, containing small, highly refractive, pointed rods or "rhabdites" (rh), and
gives rise to deeply-placed mucous cells (m.c), which are glandular and pour out
on the surface of the body a fluid in which the cilia vibrate. The tenacious hold on
a stone which Leptoplana exerts if suddenly disturbed, or when grasping its prey,
is probably due to the increased glutinous secretion of these glands, aided perhaps
by rhabdites, which on such occasions are shot out in great numbers. The basement
membrane is an elastic skeletal membrane composed of stellate cells embedded in
a firm matrix. It serves chiefly for the origin and insertion of the dorso-ventral
muscles (d.v.m). Under the basement membrane lies a very thin layer of transverse
muscular fibres (Fig. 4, rm), which are, however, apparently absent on the ventral
surface. Then follows a stout layer of longitudinal fibres (l.m ext), and beneath this
a diagonal layer (d.m), the fibres of which intersect along the median line in such a
way that the inner fibres of one side become the outer diagonal fibres of the other.
Lastly, within this again, on the ventral surface, is a second stout longitudinal layer
(l.m int). The sucker (sc, Figs. 2 and 5) is a modification of the body-wall at that
point. In addition to the dorso-ventral muscles, there exists a complex visceral
musculature regulating the movements of the pharynx, intestine, and copulatory
organs.
Parenchyma.—The spaces between the main organs of the body are filled by a
tissue containing various kinds of cells, salivary glands, shell-glands, and prostate
glands. Besides these, however, we find a vacuolated, nucleated, thick-walled
network, and to this the word parenchyma is properly applied. Besides its
connective function, the parenchyma confers that elasticity on the body which
Leptoplana possesses in such a high degree. Pigment cells are found in the
parenchyma in many Polyclads.
Digestive System.—The general arrangement of this system may be seen in Figs.
2, 5, and 7; and may be compared, especially when the pharynx is protruded, as in
Fig. 2, with the gastral system of a Medusa. The "mouth" (there is no anus) is
placed almost in the centre of the ventral surface. It leads (Fig. 7, B, phs) into a
chamber (the peripharyngeal space) divided into an upper and a lower division by
the insertion of a muscular collar-fold (the pharynx, ph), which may be protruded,
its free lips advancing, through the mouth (Fig. 2), and is then capable of enclosing
on another. These organs are enclosed in a muscular body-wall, clothed externally
by the ciliated epidermis, which is separated from the underlying musculature by a
strong membrane (Fig. 4, bm), the only skeletal element in the body.
Body-Wall.—The epidermis (Fig. 4, ep) is composed of a single layer of ciliated
cells, containing small, highly refractive, pointed rods or "rhabdites" (rh), and
gives rise to deeply-placed mucous cells (m.c), which are glandular and pour out
on the surface of the body a fluid in which the cilia vibrate. The tenacious hold on
a stone which Leptoplana exerts if suddenly disturbed, or when grasping its prey,
is probably due to the increased glutinous secretion of these glands, aided perhaps
by rhabdites, which on such occasions are shot out in great numbers. The basement
membrane is an elastic skeletal membrane composed of stellate cells embedded in
a firm matrix. It serves chiefly for the origin and insertion of the dorso-ventral
muscles (d.v.m). Under the basement membrane lies a very thin layer of transverse
muscular fibres (Fig. 4, rm), which are, however, apparently absent on the ventral
surface. Then follows a stout layer of longitudinal fibres (l.m ext), and beneath this
a diagonal layer (d.m), the fibres of which intersect along the median line in such a
way that the inner fibres of one side become the outer diagonal fibres of the other.
Lastly, within this again, on the ventral surface, is a second stout longitudinal layer
(l.m int). The sucker (sc, Figs. 2 and 5) is a modification of the body-wall at that
point. In addition to the dorso-ventral muscles, there exists a complex visceral
musculature regulating the movements of the pharynx, intestine, and copulatory
organs.
Parenchyma.—The spaces between the main organs of the body are filled by a
tissue containing various kinds of cells, salivary glands, shell-glands, and prostate
glands. Besides these, however, we find a vacuolated, nucleated, thick-walled
network, and to this the word parenchyma is properly applied. Besides its
connective function, the parenchyma confers that elasticity on the body which
Leptoplana possesses in such a high degree. Pigment cells are found in the
parenchyma in many Polyclads.
Digestive System.—The general arrangement of this system may be seen in Figs.
2, 5, and 7; and may be compared, especially when the pharynx is protruded, as in
Fig. 2, with the gastral system of a Medusa. The "mouth" (there is no anus) is
placed almost in the centre of the ventral surface. It leads (Fig. 7, B, phs) into a
chamber (the peripharyngeal space) divided into an upper and a lower division by
the insertion of a muscular collar-fold (the pharynx, ph), which may be protruded,
its free lips advancing, through the mouth (Fig. 2), and is then capable of enclosing
Page 27
by its mobile frilled margin, prey as large as Leptoplana itself. The upper division
of the chamber communicates by a hole in its roof[20] (the true mouth, Figs. 5 and
7, g.m) with the cavity of the main-gut or stomach (m.g), which runs almost the
length of the body in the middle line, forwards over the brain (Fig. 5, up). Seven
pairs of lateral gut-branches convey the digested food to the various organs, not
directly however, but only after the food mixed with sea-water has been repeatedly
driven by peristalsis first towards the blind end of the gut-branches and then back
towards the stomach. Respiration is probably largely effected by this means. The
epithelium of the intestine (Fig. 4, l.g) of a starving specimen is composed of
separate flagellated cells frequently containing "yellow cells."[21] After a meal,
however, the cell outlines are invisible. Gregarines, encysted Cercariae, and
Orthonectida[22] occur parasitically in the gut-branches.
An excretory system of "flame-cells" and fine vessels has hitherto been seen only
by Schultze[23] in this species, which will not, however, resist intact the
compression necessary to enable the details to be determined. They are probably
similar to those of Thysanozoon described on p. 25.
Nervous System.—The brain, which is enclosed in a tough capsule (Fig. 5, br), is
placed in front of the pharynx, but some distance behind the anterior margin of the
body. It is of an oval shape, subdivided superficially into right and left halves by a
shallow depression, and is provided in front with a pair of granular-looking
appendages, composed of ganglion-cells from which numerous sensory nerves
arise, supplying the eyes and anterior region. Posteriorly the brain gives rise to a
chiefly motor, nervous sheath (Fig. 5, nn), which invests the body just within the
musculature. This sheath is thickened along two ventral lines (Fig. 5, ln) and two
lateral lines (n.s), but is very slightly developed on the dorsal surface. Ganglion-
cells occur on the course of the nerves, and are particularly large at the point of
origin of the great motor nerves.
of the chamber communicates by a hole in its roof[20] (the true mouth, Figs. 5 and
7, g.m) with the cavity of the main-gut or stomach (m.g), which runs almost the
length of the body in the middle line, forwards over the brain (Fig. 5, up). Seven
pairs of lateral gut-branches convey the digested food to the various organs, not
directly however, but only after the food mixed with sea-water has been repeatedly
driven by peristalsis first towards the blind end of the gut-branches and then back
towards the stomach. Respiration is probably largely effected by this means. The
epithelium of the intestine (Fig. 4, l.g) of a starving specimen is composed of
separate flagellated cells frequently containing "yellow cells."[21] After a meal,
however, the cell outlines are invisible. Gregarines, encysted Cercariae, and
Orthonectida[22] occur parasitically in the gut-branches.
An excretory system of "flame-cells" and fine vessels has hitherto been seen only
by Schultze[23] in this species, which will not, however, resist intact the
compression necessary to enable the details to be determined. They are probably
similar to those of Thysanozoon described on p. 25.
Nervous System.—The brain, which is enclosed in a tough capsule (Fig. 5, br), is
placed in front of the pharynx, but some distance behind the anterior margin of the
body. It is of an oval shape, subdivided superficially into right and left halves by a
shallow depression, and is provided in front with a pair of granular-looking
appendages, composed of ganglion-cells from which numerous sensory nerves
arise, supplying the eyes and anterior region. Posteriorly the brain gives rise to a
chiefly motor, nervous sheath (Fig. 5, nn), which invests the body just within the
musculature. This sheath is thickened along two ventral lines (Fig. 5, ln) and two
lateral lines (n.s), but is very slightly developed on the dorsal surface. Ganglion-
cells occur on the course of the nerves, and are particularly large at the point of
origin of the great motor nerves.
Page 28
Fig. 5.—Diagrammatic view of the structure of Leptoplana tremellaris as a type of the
Polycladida. The body is cut across the middle to show the relative position of
organs in transverse section. In the posterior half the alimentary canal has been
bisected and removed from the left side, to exhibit the deeply placed nervous
sheath (nn) and the male reproductive organs. br, Brain; dp, "diaphragm"; e,
cerebral group of eyes; et, tentacular eye-group; gr, marginal groove; gm, true
mouth; lg, lateral gut-branch; ln, longitudinal nerve stem; m, external mouth; mg,
mg', main-gut, whole, and bisected; n, sensory nerve supplying the eyes; nn,
nervous network lying on the ventral musculature; n.s, lateral nerve; od, oviduct;
ov, ovary; pe, penis (in section); ph, pharynx; pr, prostate or "granule gland"; sc,
sucker; sg, shell-gland; te, testes; up, anterior unpaired gut-branch; ut, uterus; va,
vagina (in section); vd, vas deferens; ve, vasa efferentia; ♂, male genital pore; ♀,
female pore.
Sense Organs.—Leptoplana possesses eyes, stiff tactile, marginal cilia, and
possibly a sense organ in the "marginal groove." The eyes, which are easily
seen as collections of black dots lying at the sides of the brain, may be
divided into two paired groups: (1) cerebral eyes (Fig. 5, e), and (2) tentacle
eyes (et), which indicate the position of a pair of tentacles in allied forms
(Fig. 8, A, t and B). Each ocellus consists of a capsule placed at right angles
to the surface of the body in the parenchyma, below the dorsal muscles, and
Polycladida. The body is cut across the middle to show the relative position of
organs in transverse section. In the posterior half the alimentary canal has been
bisected and removed from the left side, to exhibit the deeply placed nervous
sheath (nn) and the male reproductive organs. br, Brain; dp, "diaphragm"; e,
cerebral group of eyes; et, tentacular eye-group; gr, marginal groove; gm, true
mouth; lg, lateral gut-branch; ln, longitudinal nerve stem; m, external mouth; mg,
mg', main-gut, whole, and bisected; n, sensory nerve supplying the eyes; nn,
nervous network lying on the ventral musculature; n.s, lateral nerve; od, oviduct;
ov, ovary; pe, penis (in section); ph, pharynx; pr, prostate or "granule gland"; sc,
sucker; sg, shell-gland; te, testes; up, anterior unpaired gut-branch; ut, uterus; va,
vagina (in section); vd, vas deferens; ve, vasa efferentia; ♂, male genital pore; ♀,
female pore.
Sense Organs.—Leptoplana possesses eyes, stiff tactile, marginal cilia, and
possibly a sense organ in the "marginal groove." The eyes, which are easily
seen as collections of black dots lying at the sides of the brain, may be
divided into two paired groups: (1) cerebral eyes (Fig. 5, e), and (2) tentacle
eyes (et), which indicate the position of a pair of tentacles in allied forms
(Fig. 8, A, t and B). Each ocellus consists of a capsule placed at right angles
to the surface of the body in the parenchyma, below the dorsal muscles, and
Page 29
with its convex face outwards. It is a single cell in which pigment granules
have accumulated. The light, however, can only reach the refractive rods,
which lie within it, obliquely at their outer ends. These rods are in
connexion with the retinal cells, and thus communicate by the optic nerve
with the brain. The cerebral eyes are really paired, and are directed some
upwards, some sideways, some downwards.
The "marginal groove" is a shallow depression of the epidermis (Fig. 5, gr)
lined by cilia, and containing the ducts of very numerous gland-cells. It runs
almost parallel to the anterior margin of the body, a short distance from it,
but we have no observations on its functions.
Fig. 6.—Diagram of an eye of Leptoplana from the tentacle group. × 600. (After Lang.)
Reproductive Organs.—Leptoplana is hermaphrodite, and, as in most
hermaphrodites, the reproductive organs are complicated. The male organs
are the first to ripen, but this does not appear to prevent an overlapping of
the periods of maturity of the male and female products, so that when the
eggs are being laid, the male organs are, apparently, still in a functional
state. The principal parts are seen in Fig. 5. The very numerous testes (te)
are placed ventrally, and are connected with fine vasa efferentia (ve), which
form a delicate network opening at various points into the two vasa
deferentia (vd). These tubes, especially when distended with spermatozoa,
may easily be seen (Fig. 2, vd) converging at the base of the penis, and
connected posteriorly by a loop that runs behind the female genital pore
(Fig. 5). The penis (pe) is pyriform and muscular, and is divided into two
chambers, a large upper one for the spermatozoa, and a smaller lower one
for the secretion of a special "prostate" gland. The apex of the penis is
eversible and not merely protrusible, being turned inside out when
evaginated. The ovaries (Fig. 5, ov) are numerous and somewhat spherical.
They are dorsally placed, but when fully developed extend deeply wherever
they can find room to do so, and they not only furnish the ova, but elaborate
have accumulated. The light, however, can only reach the refractive rods,
which lie within it, obliquely at their outer ends. These rods are in
connexion with the retinal cells, and thus communicate by the optic nerve
with the brain. The cerebral eyes are really paired, and are directed some
upwards, some sideways, some downwards.
The "marginal groove" is a shallow depression of the epidermis (Fig. 5, gr)
lined by cilia, and containing the ducts of very numerous gland-cells. It runs
almost parallel to the anterior margin of the body, a short distance from it,
but we have no observations on its functions.
Fig. 6.—Diagram of an eye of Leptoplana from the tentacle group. × 600. (After Lang.)
Reproductive Organs.—Leptoplana is hermaphrodite, and, as in most
hermaphrodites, the reproductive organs are complicated. The male organs
are the first to ripen, but this does not appear to prevent an overlapping of
the periods of maturity of the male and female products, so that when the
eggs are being laid, the male organs are, apparently, still in a functional
state. The principal parts are seen in Fig. 5. The very numerous testes (te)
are placed ventrally, and are connected with fine vasa efferentia (ve), which
form a delicate network opening at various points into the two vasa
deferentia (vd). These tubes, especially when distended with spermatozoa,
may easily be seen (Fig. 2, vd) converging at the base of the penis, and
connected posteriorly by a loop that runs behind the female genital pore
(Fig. 5). The penis (pe) is pyriform and muscular, and is divided into two
chambers, a large upper one for the spermatozoa, and a smaller lower one
for the secretion of a special "prostate" gland. The apex of the penis is
eversible and not merely protrusible, being turned inside out when
evaginated. The ovaries (Fig. 5, ov) are numerous and somewhat spherical.
They are dorsally placed, but when fully developed extend deeply wherever
they can find room to do so, and they not only furnish the ova, but elaborate
Page 30
food-yolk in the ova, as there are no special yolk-glands. The slender
oviducts (od) open at several points into the "uterus" (ut) (a misnomer, as no
development takes place within it), which encircles the pharynx, and opens
by a single duct into the vagina (va). Here the ova are probably fertilised,
and one by one invested by the shell-gland (sg) with a secretion which
hardens and forms a resistant shell. They are then laid in plate-like masses
which are attached to stones or shells. The development is a direct one, and
the young Leptoplana, which hatches in about three weeks, has the outline
of a spherical triangle, and possesses most of the organs of the adult. After
leading a floating life for a few weeks it probably attains maturity in about
nine months.
Classification, Habits, and Structure of the Polycladida.
The Polyclads were so called by Lang on account of the numerous primary
branches of their intestine. They are free-living, purely marine
Platyhelminthes, possessing multiple ovaries, distinct male and female
genital pores (Digonopora), but no yolk-glands. The eggs are small, and in
many cases give rise to a distinct larval form, known as "Müller's larva"
(Fig. 12). The Polyclads, with one exception,[24] fall into two sub-groups,
Acotylea and Cotylea:—
Character. Acotylea. Cotylea.
Sucker A sucker absent.[25] A sucker always present
(Figs. 8, D, s; 7, A, sc).
Mouth In the middle, or behind In the middle, or in front of
the middle, of the the middle, of the ventral
ventral surface. surface.
Pharynx More or less intricately Rarely folded. Usually
folded. cylindrical or trumpet-
shaped.
Tentacles A pair of dorsal A pair of marginal tentacles
tentacles usually (except in Anonymus).
present.
Development Usually direct. Larva Müller's larva present.
when present, not a Metamorphosis, however,
oviducts (od) open at several points into the "uterus" (ut) (a misnomer, as no
development takes place within it), which encircles the pharynx, and opens
by a single duct into the vagina (va). Here the ova are probably fertilised,
and one by one invested by the shell-gland (sg) with a secretion which
hardens and forms a resistant shell. They are then laid in plate-like masses
which are attached to stones or shells. The development is a direct one, and
the young Leptoplana, which hatches in about three weeks, has the outline
of a spherical triangle, and possesses most of the organs of the adult. After
leading a floating life for a few weeks it probably attains maturity in about
nine months.
Classification, Habits, and Structure of the Polycladida.
The Polyclads were so called by Lang on account of the numerous primary
branches of their intestine. They are free-living, purely marine
Platyhelminthes, possessing multiple ovaries, distinct male and female
genital pores (Digonopora), but no yolk-glands. The eggs are small, and in
many cases give rise to a distinct larval form, known as "Müller's larva"
(Fig. 12). The Polyclads, with one exception,[24] fall into two sub-groups,
Acotylea and Cotylea:—
Character. Acotylea. Cotylea.
Sucker A sucker absent.[25] A sucker always present
(Figs. 8, D, s; 7, A, sc).
Mouth In the middle, or behind In the middle, or in front of
the middle, of the the middle, of the ventral
ventral surface. surface.
Pharynx More or less intricately Rarely folded. Usually
folded. cylindrical or trumpet-
shaped.
Tentacles A pair of dorsal A pair of marginal tentacles
tentacles usually (except in Anonymus).
present.
Development Usually direct. Larva Müller's larva present.
when present, not a Metamorphosis, however,
Page 31
typical Müller's larva. extremely slight.
Fig. 8 shows that, starting with a member (A, D) of each division, in which
the mouth is almost in the middle of the ventral surface, and the brain and
sense organs somewhat remote from the anterior end, we find in the
Acotylea a series leading to an elongated form (Cestoplanidae), in which
the mouth, pharynx, and genital pores are far back near the hinder end of
the body; while in the Cotylea the series leads similarly to the elongated
Prosthiostomatidae, in which, however, the pharynx and external apertures
are in the front part of the body. This view of the morphology of the
Polyclads is due to Lang, and is based on the assumption that the more
radially-constructed forms (Fig. 8, A, D) are the primitive ones.
Fig. 7.—Diagrammatic vertical longitudinal sections: A, Of Prosthiostomum (type of
Cotylea); B, of Leptoplana; C, of Cestoplana (types of Acotylea). (After Lang.)
These figures illustrate the changes which follow the shifting of the mouth from
a central position (B) to either end of the body. br, Brain; dphm, "diaphragm";
gm, true mouth; lg, openings of lateral gut-branches; m, mouth; mg, main-gut or
stomach; mgbr, median gut-branch; ph, pharynx; ph.m, aperture in pharyngeal
fold; phs, peripharyngeal sheath; sc, sucker; ♂ , male, and ♀ , female, genital
aperture.
Fig. 8 shows that, starting with a member (A, D) of each division, in which
the mouth is almost in the middle of the ventral surface, and the brain and
sense organs somewhat remote from the anterior end, we find in the
Acotylea a series leading to an elongated form (Cestoplanidae), in which
the mouth, pharynx, and genital pores are far back near the hinder end of
the body; while in the Cotylea the series leads similarly to the elongated
Prosthiostomatidae, in which, however, the pharynx and external apertures
are in the front part of the body. This view of the morphology of the
Polyclads is due to Lang, and is based on the assumption that the more
radially-constructed forms (Fig. 8, A, D) are the primitive ones.
Fig. 7.—Diagrammatic vertical longitudinal sections: A, Of Prosthiostomum (type of
Cotylea); B, of Leptoplana; C, of Cestoplana (types of Acotylea). (After Lang.)
These figures illustrate the changes which follow the shifting of the mouth from
a central position (B) to either end of the body. br, Brain; dphm, "diaphragm";
gm, true mouth; lg, openings of lateral gut-branches; m, mouth; mg, main-gut or
stomach; mgbr, median gut-branch; ph, pharynx; ph.m, aperture in pharyngeal
fold; phs, peripharyngeal sheath; sc, sucker; ♂ , male, and ♀ , female, genital
aperture.
Page 32
Fig. 8.—Chief forms of Polycladida: A-C, Acotylea; D-F, Cotylea. A, Planocera
graffii Lang, nat. size; B, Stylochoplana maculata Stimps, × 7; C, Cestoplana
rubrocincta Lang, × 4⁄3; D, Anonymus virilis Lang, × 3, ventral surface; E,
Thysanozoon brocchii Grube, nat. size; the head is thrown back and the pharynx
(ph) is protruded. F, Prosthiostomum siphunculus Lang, × 3. Br, Brain; CG,
cerebral eye group; DM, true mouth; Ey, marginal eyes; m, mouth; MG, main-gut
or stomach; P, dorsal papillae; Ph, pharynx; s, sucker (ventral); T, tentacles; UP,
dorsal median gut-branch. ♂, male, and ♀, female, genital aperture, except in D,
where ♂ refers to the multiple penes. (After Lang and Schmidt.)
Classification of Polycladida.
ACOTYLEA.
Family. Genus. British Representatives.
Planocera (Fig. 8, A).
Planocera folium
Imogine.
Grube. Berwick-on-
Planoceridae. Conoceros.
Tweed.
With dorsal Stylochus.
Stylochoplana
tentacles. Mouth Stylochoplana (Fig. 8,
maculata Quatref.
sub-central. B).
Among brown weeds
Diplonchus.
in Laminarian zone.
Planctoplana.
graffii Lang, nat. size; B, Stylochoplana maculata Stimps, × 7; C, Cestoplana
rubrocincta Lang, × 4⁄3; D, Anonymus virilis Lang, × 3, ventral surface; E,
Thysanozoon brocchii Grube, nat. size; the head is thrown back and the pharynx
(ph) is protruded. F, Prosthiostomum siphunculus Lang, × 3. Br, Brain; CG,
cerebral eye group; DM, true mouth; Ey, marginal eyes; m, mouth; MG, main-gut
or stomach; P, dorsal papillae; Ph, pharynx; s, sucker (ventral); T, tentacles; UP,
dorsal median gut-branch. ♂, male, and ♀, female, genital aperture, except in D,
where ♂ refers to the multiple penes. (After Lang and Schmidt.)
Classification of Polycladida.
ACOTYLEA.
Family. Genus. British Representatives.
Planocera (Fig. 8, A).
Planocera folium
Imogine.
Grube. Berwick-on-
Planoceridae. Conoceros.
Tweed.
With dorsal Stylochus.
Stylochoplana
tentacles. Mouth Stylochoplana (Fig. 8,
maculata Quatref.
sub-central. B).
Among brown weeds
Diplonchus.
in Laminarian zone.
Planctoplana.
Page 33
Leptoplana
tremellaris O. F.
Discocelis.
Müll.
Leptoplanidae. Cryptocelis.
L. fallax Quatref.
Without dorsal Leptoplana.
Plymouth.
tentacles. Penis Trigonoporus.
L. droebachensis Oe.
directed backwards. ?Polypostia (see p.
Plymouth Sound.
27).
L. atomata O. F. Müll.
Doubtful species.
Cestoplana (Fig. 8,
Cestoplanidae.
C).
No tentacles. Body
In Mediterranean
elongated. Penis
and on French side
directed forwards.
of the Channel.
Enantiidae.
No sucker. No
tentacles. Main-gut Enantia.
very short. External Adriatic Sea.
apertures as in
Euryleptidae.
COTYLEA.
Anonymidae.
Anonymus (Fig. 8, D).
Mouth central. No
Naples (two
tentacles. With two
specimens).
rows of penes.
Pseudoceridae. Thysanozoon (Fig. 8,
Marginal tentacles E).
folded. Mouth in Pseudoceros.
anterior half. Yungia.
Euryleptidae. Prostheceraeus. Prostheceraeus
Tentacles usually Cycloporus. vittatus Mont. On
present and Eurylepta. west coast.
pointed, or Oligocladus. P. argus Quatref.
represented by two Stylostomum. Guernsey.
tremellaris O. F.
Discocelis.
Müll.
Leptoplanidae. Cryptocelis.
L. fallax Quatref.
Without dorsal Leptoplana.
Plymouth.
tentacles. Penis Trigonoporus.
L. droebachensis Oe.
directed backwards. ?Polypostia (see p.
Plymouth Sound.
27).
L. atomata O. F. Müll.
Doubtful species.
Cestoplana (Fig. 8,
Cestoplanidae.
C).
No tentacles. Body
In Mediterranean
elongated. Penis
and on French side
directed forwards.
of the Channel.
Enantiidae.
No sucker. No
tentacles. Main-gut Enantia.
very short. External Adriatic Sea.
apertures as in
Euryleptidae.
COTYLEA.
Anonymidae.
Anonymus (Fig. 8, D).
Mouth central. No
Naples (two
tentacles. With two
specimens).
rows of penes.
Pseudoceridae. Thysanozoon (Fig. 8,
Marginal tentacles E).
folded. Mouth in Pseudoceros.
anterior half. Yungia.
Euryleptidae. Prostheceraeus. Prostheceraeus
Tentacles usually Cycloporus. vittatus Mont. On
present and Eurylepta. west coast.
pointed, or Oligocladus. P. argus Quatref.
represented by two Stylostomum. Guernsey.
Page 34
groups of eyes. Aceros. Cycloporus papillosus
Mouth close to Lang. On Ascidians
anterior end. in 2-30 fms.
Pharynx Eurylepta cornuta
cylindrical. O.F. Müll. On
sponges and shells,
2-10 fms.
Oligocladus
sanguinolentus
Quatref.
O. auritus Clap.
Doubtful.
Stylostomum variabile
Lang.
Prosthiostomatidae.
Tentacles absent.
Body elongated.
Prosthiostomum (Fig.
Pharynx long,
8, F).
cylindrical. Penis
with accessory
muscular vesicles.
Appearance and Size of Polyclad Turbellaria.—Polyclads are almost
unique amongst animals in possessing a broad and thin, delicate body that
glides like a living pellicle over stones and weeds, moulding itself on to any
inequalities of the surface over which it is travelling, yet so fragile that a
touch of the finger will rend its tissues and often cause its speedy
dissolution. The dorsal surface in a few forms is raised into fine processes
(Planocera villosa), or into hollow papillae (Thysanozoon brocchii), and in
very rare cases may be armed with spines (Acanthozoon armatum,[26]
Enantia spinifera); in others, again, nettle-cells (nematocysts) are found
(Stylochoplana tarda, Anonymus virilis). Some Polyclads, especially the
pelagic forms, are almost transparent; in others, the colour may be an
intense orange or velvety black, and is then due to peculiar deposits in the
epidermal cells. Between these two extremes the colour is dependent upon
the blending of two sources, the pigment of the body itself and the tint of
Mouth close to Lang. On Ascidians
anterior end. in 2-30 fms.
Pharynx Eurylepta cornuta
cylindrical. O.F. Müll. On
sponges and shells,
2-10 fms.
Oligocladus
sanguinolentus
Quatref.
O. auritus Clap.
Doubtful.
Stylostomum variabile
Lang.
Prosthiostomatidae.
Tentacles absent.
Body elongated.
Prosthiostomum (Fig.
Pharynx long,
8, F).
cylindrical. Penis
with accessory
muscular vesicles.
Appearance and Size of Polyclad Turbellaria.—Polyclads are almost
unique amongst animals in possessing a broad and thin, delicate body that
glides like a living pellicle over stones and weeds, moulding itself on to any
inequalities of the surface over which it is travelling, yet so fragile that a
touch of the finger will rend its tissues and often cause its speedy
dissolution. The dorsal surface in a few forms is raised into fine processes
(Planocera villosa), or into hollow papillae (Thysanozoon brocchii), and in
very rare cases may be armed with spines (Acanthozoon armatum,[26]
Enantia spinifera); in others, again, nettle-cells (nematocysts) are found
(Stylochoplana tarda, Anonymus virilis). Some Polyclads, especially the
pelagic forms, are almost transparent; in others, the colour may be an
intense orange or velvety black, and is then due to peculiar deposits in the
epidermal cells. Between these two extremes the colour is dependent upon
the blending of two sources, the pigment of the body itself and the tint of
Page 35
the food. Thus a starved Leptoplana is almost or quite white, a specimen
fed on vascular tissue reddish. Many forms are coloured in such a way as to
make their detection exceedingly difficult, but this is probably not merely
due, as Dalyell supposed, to the substratum furnishing them with food and
thus colouring them sympathetically, but is probably a result of natural
selection.
The largest Polyclad, the bulkiest Turbellarian, is Leptoplana gigas (6
inches long and 4 in breadth), taken by Schmarda, free-swimming, off the
coast of Ceylon. The largest European form is Pseudoceros maximus, 3½
inches in length and stoutly built. A British species, Prostheceraeus vittatus,
attains a length of from 2 to 3 inches. These large forms, especially the
Pseudoceridae (pre-eminently the family of big Polyclads), are brightly
coloured, and usually possess good swimming powers, since, being broad
and flat, they are certainly not well adapted for creeping rapidly, and this is
well shown by the way these Polyclads take to swimming when in pursuit
of prey at night. The size of any individual is determined, amongst other
factors, by the period at which maturity sets in, after which probably no
increase takes place. Polyclads apparently live about twelve months, and
mature specimens of the same species vary from ½ inch to 2½ inches in
length (Thysanozoon brocchii), showing that growth is, under favourable
conditions, very rapid.
Habits of Polyclad Turbellaria.—Polyclads are exclusively marine, and
for the most part littoral, animals. Moreover, there is no evidence of their
occurrence in those inland seas where certain marine animals (including
one or two species of otherwise characteristically marine Rhabdocoelida, p.
46) have persisted under changed conditions. From half-tide mark down to
50 fathoms, some Polyclads probably occur on all coasts, but as to their
relative abundance in different seas we have very little accurate
information. The southern seas of Europe possess more individuals and
species than the northern, and probably the maximum development of the
group takes place on the coasts and coral islands of the tropics.[27] No
Polyclads have been taken below 60 fathoms; but their delicacy and
inconspicuousness render this negative evidence of little value. Six truly
pelagic forms, however, are known,[28] and these are interesting on account
fed on vascular tissue reddish. Many forms are coloured in such a way as to
make their detection exceedingly difficult, but this is probably not merely
due, as Dalyell supposed, to the substratum furnishing them with food and
thus colouring them sympathetically, but is probably a result of natural
selection.
The largest Polyclad, the bulkiest Turbellarian, is Leptoplana gigas (6
inches long and 4 in breadth), taken by Schmarda, free-swimming, off the
coast of Ceylon. The largest European form is Pseudoceros maximus, 3½
inches in length and stoutly built. A British species, Prostheceraeus vittatus,
attains a length of from 2 to 3 inches. These large forms, especially the
Pseudoceridae (pre-eminently the family of big Polyclads), are brightly
coloured, and usually possess good swimming powers, since, being broad
and flat, they are certainly not well adapted for creeping rapidly, and this is
well shown by the way these Polyclads take to swimming when in pursuit
of prey at night. The size of any individual is determined, amongst other
factors, by the period at which maturity sets in, after which probably no
increase takes place. Polyclads apparently live about twelve months, and
mature specimens of the same species vary from ½ inch to 2½ inches in
length (Thysanozoon brocchii), showing that growth is, under favourable
conditions, very rapid.
Habits of Polyclad Turbellaria.—Polyclads are exclusively marine, and
for the most part littoral, animals. Moreover, there is no evidence of their
occurrence in those inland seas where certain marine animals (including
one or two species of otherwise characteristically marine Rhabdocoelida, p.
46) have persisted under changed conditions. From half-tide mark down to
50 fathoms, some Polyclads probably occur on all coasts, but as to their
relative abundance in different seas we have very little accurate
information. The southern seas of Europe possess more individuals and
species than the northern, and probably the maximum development of the
group takes place on the coasts and coral islands of the tropics.[27] No
Polyclads have been taken below 60 fathoms; but their delicacy and
inconspicuousness render this negative evidence of little value. Six truly
pelagic forms, however, are known,[28] and these are interesting on account
Page 36
of their wide distribution (three occurring in the Atlantic, Pacific, and
Indian oceans), and also from the distinct modifications they have
undergone in relation to their pelagic existence.
Whatever may be the interpretations of the fact, Polyclads are notoriously
difficult to detect, and this fact doubtless explains the scanty references to
them by the older naturalists who collected even in tropical seas. Lang, who
worked seven years at Naples, added to the Mediterranean fauna as many
Polyclads as were previously known for all Europe, in spite of the assiduous
labours of his predecessors, Delle Chiaje and Quatrefages. Again Hallez,
collecting at Wimereux at low-water, obtained some twenty specimens of
Leptoplana tremellaris in an hour, while some other collectors working by
his side could only find two or three. Yet, even making allowance for the
difficulty of finding Polyclads, few of them appear to be abundant.
Leptoplana tremellaris is frequently associated with colonies of Botryllus,
and if separated soon perishes, whereas the free-living individuals are
distinctly hardy (Hallez). A closely allied but possibly distinct form lives
upon the surface of the Polyzoon Schizoporella, on the French side of the
Channel, and cannot long endure separation from its natural habitat, to
which it is adaptively coloured. A striking case of protective mimicry is
exhibited by Cycloporus papillosus, on the British coasts. This species,
eminently variable in colour and in the presence or absence of dorsal
papillae, is usually a quarter of an inch in length and of a firm consistency.
Fixed by its sucker to Polyclinid and other Ascidians, Cycloporus appears
part and parcel of the substratum, an interesting parallel to Lamellaria
perspicua,[29] though we are not justified in calling the Polyclad parasitic.
Indeed, though a few cases of association between Polyclads and large
Gasteropods, Holothurians, and Echinids are known,[30] there is only one
case, that of Planocera inquilina,[31] in the branchial chamber of the
Gasteropod Sycotypus canaliculatus, which would seem to bear the
interpretation of parasitism. The jet-black Pseudoceros velutinus and the
orange Yungia aurantiaca of the Mediterranean, are large conspicuous
forms with no attempt at concealment, but their taste, which is not known,
may protect them. Other habits, curiously analogous with devices employed
by Nudibranch Mollusca (compare Thysanozoon brocchii with Aeolis
Indian oceans), and also from the distinct modifications they have
undergone in relation to their pelagic existence.
Whatever may be the interpretations of the fact, Polyclads are notoriously
difficult to detect, and this fact doubtless explains the scanty references to
them by the older naturalists who collected even in tropical seas. Lang, who
worked seven years at Naples, added to the Mediterranean fauna as many
Polyclads as were previously known for all Europe, in spite of the assiduous
labours of his predecessors, Delle Chiaje and Quatrefages. Again Hallez,
collecting at Wimereux at low-water, obtained some twenty specimens of
Leptoplana tremellaris in an hour, while some other collectors working by
his side could only find two or three. Yet, even making allowance for the
difficulty of finding Polyclads, few of them appear to be abundant.
Leptoplana tremellaris is frequently associated with colonies of Botryllus,
and if separated soon perishes, whereas the free-living individuals are
distinctly hardy (Hallez). A closely allied but possibly distinct form lives
upon the surface of the Polyzoon Schizoporella, on the French side of the
Channel, and cannot long endure separation from its natural habitat, to
which it is adaptively coloured. A striking case of protective mimicry is
exhibited by Cycloporus papillosus, on the British coasts. This species,
eminently variable in colour and in the presence or absence of dorsal
papillae, is usually a quarter of an inch in length and of a firm consistency.
Fixed by its sucker to Polyclinid and other Ascidians, Cycloporus appears
part and parcel of the substratum, an interesting parallel to Lamellaria
perspicua,[29] though we are not justified in calling the Polyclad parasitic.
Indeed, though a few cases of association between Polyclads and large
Gasteropods, Holothurians, and Echinids are known,[30] there is only one
case, that of Planocera inquilina,[31] in the branchial chamber of the
Gasteropod Sycotypus canaliculatus, which would seem to bear the
interpretation of parasitism. The jet-black Pseudoceros velutinus and the
orange Yungia aurantiaca of the Mediterranean, are large conspicuous
forms with no attempt at concealment, but their taste, which is not known,
may protect them. Other habits, curiously analogous with devices employed
by Nudibranch Mollusca (compare Thysanozoon brocchii with Aeolis
Page 37
papillosa), emphasise the conclusion that the struggle for existence in the
littoral zone has adapted almost each Polyclad to its particular habitat.
As regards the vertical distribution of this group on the British coasts,
Leptoplana tremellaris has an extensive range, and appears to come from
deeper to shallower water to breed.[32] In the upper part of the Laminarian
zone, Cycloporus papillosus, and, among brown weeds, Stylochoplana
maculata are found. At and below lowest water-mark Prostheceraeus
vittatus, P. argus, and Eurylepta cornuta occur. Stylostomum variabile and
Oligocladus sanguinolentus, though occasionally found between tide-
marks, especially in the Channel Islands, are characteristic, along with
Leptoplana droebachensis and L. fallax, of dredge material from 10 to 20
fathoms.
Locomotion.—Locomotion is generally performed by Polyclads at night
when in search of food, and two methods, creeping and swimming, are
usually employed—creeping by the cilia, aided possibly, as in the case of
some Gasteropod Mollusca, by the longitudinal muscles of the ventral
surface; and swimming, by undulations of the expanded margins of the
body. In the former case the cilia work in a glandular secretion which bathes
the body, and enables them to effect their purpose equally well on different
substrata. The anterior region is generally lifted up, exploring the
surroundings by the aid of the tentacles, which are here usually present. The
rest of the body is closely appressed to the ground.
Swimming is particularly well performed by the Pseudoceridae, certain
species of Prostheceraeus, the large Planoceridae, some Stylochoplana,
Discocelis, and Leptoplana, and in the same manner as in Leptoplana
tremellaris (p. 9). In Cryptocelis, Leptoplana alcinoi, and L. pallida,
however, the whole body executes serpentine movements like an active
leech (e.g. Nephelis); a cross section of the body would thus present the
same appearance during the whole movement. Many Polyclads, notably
Anonymus (Lang), if irritated, spread out in all directions, becoming
exceeding thin and transparent.
littoral zone has adapted almost each Polyclad to its particular habitat.
As regards the vertical distribution of this group on the British coasts,
Leptoplana tremellaris has an extensive range, and appears to come from
deeper to shallower water to breed.[32] In the upper part of the Laminarian
zone, Cycloporus papillosus, and, among brown weeds, Stylochoplana
maculata are found. At and below lowest water-mark Prostheceraeus
vittatus, P. argus, and Eurylepta cornuta occur. Stylostomum variabile and
Oligocladus sanguinolentus, though occasionally found between tide-
marks, especially in the Channel Islands, are characteristic, along with
Leptoplana droebachensis and L. fallax, of dredge material from 10 to 20
fathoms.
Locomotion.—Locomotion is generally performed by Polyclads at night
when in search of food, and two methods, creeping and swimming, are
usually employed—creeping by the cilia, aided possibly, as in the case of
some Gasteropod Mollusca, by the longitudinal muscles of the ventral
surface; and swimming, by undulations of the expanded margins of the
body. In the former case the cilia work in a glandular secretion which bathes
the body, and enables them to effect their purpose equally well on different
substrata. The anterior region is generally lifted up, exploring the
surroundings by the aid of the tentacles, which are here usually present. The
rest of the body is closely appressed to the ground.
Swimming is particularly well performed by the Pseudoceridae, certain
species of Prostheceraeus, the large Planoceridae, some Stylochoplana,
Discocelis, and Leptoplana, and in the same manner as in Leptoplana
tremellaris (p. 9). In Cryptocelis, Leptoplana alcinoi, and L. pallida,
however, the whole body executes serpentine movements like an active
leech (e.g. Nephelis); a cross section of the body would thus present the
same appearance during the whole movement. Many Polyclads, notably
Anonymus (Lang), if irritated, spread out in all directions, becoming
exceeding thin and transparent.
Page 38
Fig. 9.—Discocelis lichenoides Mert. (after Mertens), creeping on the inner side of a
glass vessel by means of the lobes of the extended and exceedingly mobile
pharynx (ph). These lobes also serve to enclose Crustacea (a), and one lobe may
then be withdrawn independently of the rest, back into the body (b). The brain
(br) and shell-gland (sg) are shown by transparency.
Discocelis lichenoides, Planocera graffii, and Anonymus virilis have
peculiar modes of progression. The first, according to Mertens, will climb
up the sides of a vessel by means of the expanded lobes of the pharynx (Fig.
9, ph), a habit of considerable interest, since we know that certain
Ctenophores—Lampetia, for instance—progress when not swimming on
the expanded lobes of their "stomach."[33] Planocera and Anonymus creep
by extending parts of the anterior margin and dragging the rest of the body
behind. In consequence, the brain and dorsal tentacles may come to lie
actually behind the middle of the body, and thus no definite anterior end or
"head" advances first. Along with this curious habit it may be noticed
(Lang) that the radial symmetry of the body is well marked; but even
without accepting this author's suggestion of the concurrent development of
a "head" with locomotion in a definite direction, the facts, whether these
two forms are primitive or not, are highly interesting.
Food.—Though we are probably right in calling Polyclads a carnivorous
group, the food of very few forms has been ascertained. Those which
possess a large frilled pharynx (most Acotylea) probably enclose and digest
large, and, it may be, powerful prey, as appears to be the case in Leptoplana
tremellaris. Cryptocelis alba has been seen by Lang with the pharynx so
distended, owing to a large Drepanophorus (Nemertine) which it contained,
as to resemble a yolk-sac projecting from the under surface of an embryo.
The Cotylea such as Thysanozoon, with a bell- or trumpet-shaped pharynx,
are fond of fixing this to the side of the aquarium, but whether they thus
obtain minute organisms is not clear. Prosthiostomum shoots out its long
glass vessel by means of the lobes of the extended and exceedingly mobile
pharynx (ph). These lobes also serve to enclose Crustacea (a), and one lobe may
then be withdrawn independently of the rest, back into the body (b). The brain
(br) and shell-gland (sg) are shown by transparency.
Discocelis lichenoides, Planocera graffii, and Anonymus virilis have
peculiar modes of progression. The first, according to Mertens, will climb
up the sides of a vessel by means of the expanded lobes of the pharynx (Fig.
9, ph), a habit of considerable interest, since we know that certain
Ctenophores—Lampetia, for instance—progress when not swimming on
the expanded lobes of their "stomach."[33] Planocera and Anonymus creep
by extending parts of the anterior margin and dragging the rest of the body
behind. In consequence, the brain and dorsal tentacles may come to lie
actually behind the middle of the body, and thus no definite anterior end or
"head" advances first. Along with this curious habit it may be noticed
(Lang) that the radial symmetry of the body is well marked; but even
without accepting this author's suggestion of the concurrent development of
a "head" with locomotion in a definite direction, the facts, whether these
two forms are primitive or not, are highly interesting.
Food.—Though we are probably right in calling Polyclads a carnivorous
group, the food of very few forms has been ascertained. Those which
possess a large frilled pharynx (most Acotylea) probably enclose and digest
large, and, it may be, powerful prey, as appears to be the case in Leptoplana
tremellaris. Cryptocelis alba has been seen by Lang with the pharynx so
distended, owing to a large Drepanophorus (Nemertine) which it contained,
as to resemble a yolk-sac projecting from the under surface of an embryo.
The Cotylea such as Thysanozoon, with a bell- or trumpet-shaped pharynx,
are fond of fixing this to the side of the aquarium, but whether they thus
obtain minute organisms is not clear. Prosthiostomum shoots out its long
Page 39
pharynx with great vehemence (Fig. 8, F) and snaps up small Annelids by
its aid (Lang). Those Polyclads which, as Cycloporus and others, are
definitely associated with other organisms are not certainly known to feed
upon the latter, though "Planaria velellae" has been seen by Lesson[34]
devouring the fleshy parts of its host. The salivary glands which open on the
lips and the inner surface of the pharynx powerfully disintegrate the flesh of
the prey. Digestion takes place in the main-gut, and the circulation of the
food is accomplished by the sphinctral musculature of the intestinal
branches (conf. Leptoplana, p. 13).
Fig. 10.—Diagram of the musculature, causing peristaltic movements of the intestinal
branches of Polyclads. (After Lang.)
A distinct vent or anus is always absent. After a meal the faecal matter
collects in the main-gut, and is discharged violently by the pharynx into the
water. In a few species, however, the intestinal branches open to the exterior
(Lang). Yungia aurantiaca, a large and abundant Neapolitan form,
possesses such openings over the greater part of the dorsal surface;
Cycloporus papillosus has marginal pores; Oligocladus sanguinolentus
apparently possesses an opening at the posterior end of the main-gut; and
Thysanozoon brocchii frequently rends at this point, in consequence of the
accumulation of food.
Respiration.—The oxygen of the atmosphere dissolved in the sea-water is,
in default of a special circulatory fluid, brought to the tissues of Polyclads
in two ways. The ciliated epidermis provides a constant change of the
surrounding water, by which the superficial organs may obtain their supply;
and the peristaltic movements of the digestive system, aided by the cilia of
the endoderm cells, ensure a rough circulation of the sea-water, which
enters along with the food, to the internal organs. The papillae of
Thysanozoon brocchii, containing outgrowths of the intestinal branches, are
possibly so much additional respiratory surface, although still larger forms
(other Pseudoceridae) are devoid of such outgrowths.
its aid (Lang). Those Polyclads which, as Cycloporus and others, are
definitely associated with other organisms are not certainly known to feed
upon the latter, though "Planaria velellae" has been seen by Lesson[34]
devouring the fleshy parts of its host. The salivary glands which open on the
lips and the inner surface of the pharynx powerfully disintegrate the flesh of
the prey. Digestion takes place in the main-gut, and the circulation of the
food is accomplished by the sphinctral musculature of the intestinal
branches (conf. Leptoplana, p. 13).
Fig. 10.—Diagram of the musculature, causing peristaltic movements of the intestinal
branches of Polyclads. (After Lang.)
A distinct vent or anus is always absent. After a meal the faecal matter
collects in the main-gut, and is discharged violently by the pharynx into the
water. In a few species, however, the intestinal branches open to the exterior
(Lang). Yungia aurantiaca, a large and abundant Neapolitan form,
possesses such openings over the greater part of the dorsal surface;
Cycloporus papillosus has marginal pores; Oligocladus sanguinolentus
apparently possesses an opening at the posterior end of the main-gut; and
Thysanozoon brocchii frequently rends at this point, in consequence of the
accumulation of food.
Respiration.—The oxygen of the atmosphere dissolved in the sea-water is,
in default of a special circulatory fluid, brought to the tissues of Polyclads
in two ways. The ciliated epidermis provides a constant change of the
surrounding water, by which the superficial organs may obtain their supply;
and the peristaltic movements of the digestive system, aided by the cilia of
the endoderm cells, ensure a rough circulation of the sea-water, which
enters along with the food, to the internal organs. The papillae of
Thysanozoon brocchii, containing outgrowths of the intestinal branches, are
possibly so much additional respiratory surface, although still larger forms
(other Pseudoceridae) are devoid of such outgrowths.
Page 40
Excretion.—The excretory system of only one Polyclad (Thysanozoon
brocchii) is accurately known. Lang, by compressing light-coloured
specimens, found the three parts of the system known to occur in many
Platyhelminthes: (1) the larger longitudinal canals, and (2) the capillary
vessels, which commence with (3) the flame-cells in the parenchyma of the
body. The mode of distribution of these parts is not, however, ascertained.
The canals are delicate, sinuous, apparently intracellular tubes, coursing
close to the margin of the body and sending offsets which suspend the
canals to the dorsal surface, where possibly openings may occur. In
dilatations of these vessels bunches of cilia, and occasionally flame-cells,
are found. Usually, however, flame-cells occur at the commencement or
during the course of the capillaries, which are straight, rarely branching,
tubes of exceeding tenuity, and appear (Lang) to be outgrowths of the
flame-cells, just as the duct is an outgrowth of a gland-cell. In fact there is
little doubt that the stellate flame-cells are modified parenchymatous gland-
cells, containing a lumen filled with a fluid into which a number of cilia
project and vibrate synchronously. The cells excrete nitrogeneous waste
substances, which are then discharged into the capillaries, whence the cilia
of the main vessels drive them presumably to the exterior, though external
openings of the excretory system are not known. Traces of this system have
been observed in young Leptoplana (first by Schultze in 1854) and also in
Cestoplana.
Sensation.—A nervous sheath, with scattered ganglion cells, everywhere
underlies the musculature. It is exceedingly faintly marked on the dorsal
surface, but laterally and ventrally forms a dense network with polygonal
meshes. Thickenings of this sheath give rise to lateral nerves, and also to a
pair of stout longitudinal nerves from which the internal organs are
probably innervated. The brain, hardly distinct in pelagic Polyclads, in most
forms does not differ greatly from that of Leptoplana (p. 13).
The sense organs of Polyclads have the form of tentacles, eyes, otocysts (in
Leptoplana otophora), and stiff tactile cilia. The solid dorsal tentacles of
Planoceridae contrast strongly with the folded or pointed hollow processes
of the Cotylea. The former (Fig. 8, A, T) are muscular and very contractile,
and are placed near the brain some distance from the anterior end. The latter
are outgrowths of the front margin of the body, and are sometimes (Yungia)
brocchii) is accurately known. Lang, by compressing light-coloured
specimens, found the three parts of the system known to occur in many
Platyhelminthes: (1) the larger longitudinal canals, and (2) the capillary
vessels, which commence with (3) the flame-cells in the parenchyma of the
body. The mode of distribution of these parts is not, however, ascertained.
The canals are delicate, sinuous, apparently intracellular tubes, coursing
close to the margin of the body and sending offsets which suspend the
canals to the dorsal surface, where possibly openings may occur. In
dilatations of these vessels bunches of cilia, and occasionally flame-cells,
are found. Usually, however, flame-cells occur at the commencement or
during the course of the capillaries, which are straight, rarely branching,
tubes of exceeding tenuity, and appear (Lang) to be outgrowths of the
flame-cells, just as the duct is an outgrowth of a gland-cell. In fact there is
little doubt that the stellate flame-cells are modified parenchymatous gland-
cells, containing a lumen filled with a fluid into which a number of cilia
project and vibrate synchronously. The cells excrete nitrogeneous waste
substances, which are then discharged into the capillaries, whence the cilia
of the main vessels drive them presumably to the exterior, though external
openings of the excretory system are not known. Traces of this system have
been observed in young Leptoplana (first by Schultze in 1854) and also in
Cestoplana.
Sensation.—A nervous sheath, with scattered ganglion cells, everywhere
underlies the musculature. It is exceedingly faintly marked on the dorsal
surface, but laterally and ventrally forms a dense network with polygonal
meshes. Thickenings of this sheath give rise to lateral nerves, and also to a
pair of stout longitudinal nerves from which the internal organs are
probably innervated. The brain, hardly distinct in pelagic Polyclads, in most
forms does not differ greatly from that of Leptoplana (p. 13).
The sense organs of Polyclads have the form of tentacles, eyes, otocysts (in
Leptoplana otophora), and stiff tactile cilia. The solid dorsal tentacles of
Planoceridae contrast strongly with the folded or pointed hollow processes
of the Cotylea. The former (Fig. 8, A, T) are muscular and very contractile,
and are placed near the brain some distance from the anterior end. The latter
are outgrowths of the front margin of the body, and are sometimes (Yungia)
Page 41
provided superficially with olfactory pits and internally with eyes and
intestinal coeca.
The eyes which occur in Polyclads may be divided into (a) a pair of
cerebral groups overlying the brain; (b) those embedded in the tentacles
(tentacular group); and (c) the marginal eyes, which in Anonymus occur all
round the margin. A complex form is sometimes assumed by the cerebral
eyes of Pseudoceridae, resulting probably from incomplete fission (Fig. 11).
Leptoplana otophora was obtained by Schmarda on the south coast of
Ceylon. On each side of the brain is a capsule containing two otoliths. This
is the only known case of the occurrence of these organs in Polyclads.
Reproduction.—Although Polyclads are able to repair the result of injuries
to a very considerable extent, they are not known to multiply asexually. The
two processes are intimately associated, but, though probably all Turbellaria
can regenerate certain lost parts, asexual reproduction only occurs
sporadically.
Fig. 11.—Double eye from the cerebral group of Pseudoceros maximus. (After Lang.)
All known Polyclads are hermaphrodite. The male organs, scattered, like
the testes of Leptoplana, over the ventral surface, develop earlier than the
ovaries, though the periods of maturation overlap; hence the possibility of
self-fertilisation, though remote, is still worth consideration. The genital
apertures, through which, in the male, spermatozoa, and in the female, ova,
are emitted, are usually situated as in Leptoplana (Figs. 2 and 5, ♂ and ♀).
In Trigonoporus, a genus once found at Naples, a secondary female aperture
has been discovered leading into the female genital canal[35]; and in
Anonymus, Polypostia, and Thysanozoon (Fig. 7, E, ♂) two or more male
pores and penes have been found. Anonymus has several penes (Fig. 7, D,
♂ ) arranged radially round the body. Polypostia, a remarkable form
intestinal coeca.
The eyes which occur in Polyclads may be divided into (a) a pair of
cerebral groups overlying the brain; (b) those embedded in the tentacles
(tentacular group); and (c) the marginal eyes, which in Anonymus occur all
round the margin. A complex form is sometimes assumed by the cerebral
eyes of Pseudoceridae, resulting probably from incomplete fission (Fig. 11).
Leptoplana otophora was obtained by Schmarda on the south coast of
Ceylon. On each side of the brain is a capsule containing two otoliths. This
is the only known case of the occurrence of these organs in Polyclads.
Reproduction.—Although Polyclads are able to repair the result of injuries
to a very considerable extent, they are not known to multiply asexually. The
two processes are intimately associated, but, though probably all Turbellaria
can regenerate certain lost parts, asexual reproduction only occurs
sporadically.
Fig. 11.—Double eye from the cerebral group of Pseudoceros maximus. (After Lang.)
All known Polyclads are hermaphrodite. The male organs, scattered, like
the testes of Leptoplana, over the ventral surface, develop earlier than the
ovaries, though the periods of maturation overlap; hence the possibility of
self-fertilisation, though remote, is still worth consideration. The genital
apertures, through which, in the male, spermatozoa, and in the female, ova,
are emitted, are usually situated as in Leptoplana (Figs. 2 and 5, ♂ and ♀).
In Trigonoporus, a genus once found at Naples, a secondary female aperture
has been discovered leading into the female genital canal[35]; and in
Anonymus, Polypostia, and Thysanozoon (Fig. 7, E, ♂) two or more male
pores and penes have been found. Anonymus has several penes (Fig. 7, D,
♂ ) arranged radially round the body. Polypostia, a remarkable form
Page 42
described by Bergendal,[36] belonging to the Acotylea, possesses about
twenty such structures ranged round the female genital aperture. Lang,
whose attention was attracted by these singular facts, made the interesting
discovery that Thysanozoon uses its penes as weapons of offence rather
than as copulating organs, burying them in the skin of another Polyclad
(Yungia) that happened to cross its path, spermatozoa being of course left in
the wound. Lang further found that Prostheceraeus albocinctus and
Cryptocelis alba in this way implanted a spermatophore in the skin of
another individual of the same species, and he suggested that from this
point the spermatozoa wandered through the tissues till they met with and
fertilised the eggs. It is now known that a similar process of "hypodermic
impregnation" occurs sporadically in several groups of animals.[37]
Nevertheless, in some Polyclads it is probable, and in Stylochus
neapolitanus it is certain, that normal copulation takes place. The sperm-
masses are transferred to a coecal diverticulum of the female genital canal,
and then by a delicate mechanism, of which we know only the effects, one
spermatozoon obtains entrance into one matured ovum, which differs from
the ova of most Turbellaria in that it contains in its own protoplasm the yolk
necessary for the nutrition of the embryo. In other words, there are no
special yolk-glands. After fertilisation, the ovum in all Polyclads is coated
with a shell formed by the shell-gland, which also secretes a substance
uniting the eggs together. They are deposited on stones and shells, either in
plate-like masses or in spirals (like those of Nudibranchs). Cryptocelis alba
lays masses of an annular shape, with two ova in each shell, and buries
them in sand.
Development.[38]—The first stages in the embryology of Polyclads appear
to be very uniform. They result, in all Cotylea and in certain Planoceridae,
in the formation of a Müller's larva (Fig. 12) about a couple of weeks after
the eggs are laid. This larva (1-1.8 mm. long), which is modified in the
Planoceridae, is distinguished by the presence of a ciliated band, running
somewhat transversely round the body, and usually produced into a dorsal,
a ventral, and three pairs of lateral processes. When swimming the body is
placed as in Fig. 12, and twists round rapidly about its longitudinal axis by
means of the strong locomotor cilia placed in transverse rows upon the
processes. The cilia of each row vibrate synchronously, and recall the action
of the swimming plates of a Ctenophore. It is noteworthy that whereas
twenty such structures ranged round the female genital aperture. Lang,
whose attention was attracted by these singular facts, made the interesting
discovery that Thysanozoon uses its penes as weapons of offence rather
than as copulating organs, burying them in the skin of another Polyclad
(Yungia) that happened to cross its path, spermatozoa being of course left in
the wound. Lang further found that Prostheceraeus albocinctus and
Cryptocelis alba in this way implanted a spermatophore in the skin of
another individual of the same species, and he suggested that from this
point the spermatozoa wandered through the tissues till they met with and
fertilised the eggs. It is now known that a similar process of "hypodermic
impregnation" occurs sporadically in several groups of animals.[37]
Nevertheless, in some Polyclads it is probable, and in Stylochus
neapolitanus it is certain, that normal copulation takes place. The sperm-
masses are transferred to a coecal diverticulum of the female genital canal,
and then by a delicate mechanism, of which we know only the effects, one
spermatozoon obtains entrance into one matured ovum, which differs from
the ova of most Turbellaria in that it contains in its own protoplasm the yolk
necessary for the nutrition of the embryo. In other words, there are no
special yolk-glands. After fertilisation, the ovum in all Polyclads is coated
with a shell formed by the shell-gland, which also secretes a substance
uniting the eggs together. They are deposited on stones and shells, either in
plate-like masses or in spirals (like those of Nudibranchs). Cryptocelis alba
lays masses of an annular shape, with two ova in each shell, and buries
them in sand.
Development.[38]—The first stages in the embryology of Polyclads appear
to be very uniform. They result, in all Cotylea and in certain Planoceridae,
in the formation of a Müller's larva (Fig. 12) about a couple of weeks after
the eggs are laid. This larva (1-1.8 mm. long), which is modified in the
Planoceridae, is distinguished by the presence of a ciliated band, running
somewhat transversely round the body, and usually produced into a dorsal,
a ventral, and three pairs of lateral processes. When swimming the body is
placed as in Fig. 12, and twists round rapidly about its longitudinal axis by
means of the strong locomotor cilia placed in transverse rows upon the
processes. The cilia of each row vibrate synchronously, and recall the action
of the swimming plates of a Ctenophore. It is noteworthy that whereas
Page 43
Stylochus pilidium passes through a modified or, according to some authors,
a primitive larval stage, its near ally, S. neapolitanus, develops directly.
Most Acotylea indeed develop directly, and their free-swimming young
differ from Müller's larva merely in the absence of the ciliated band and in
the mode of swimming.
Fig. 12.—Section through Müller's larva of Thysanozoon brocchii (modified from
Lang). The right half is seen from inside. × 150. Semi-diagrammatic. br, Brain;
dl, dorsal ciliated lobe; dr, salivary gland-cells of pharynx; e, eye; ep, ciliated
epidermis containing rhabdites; mg, stomach or main-gut; mg1, unpaired gut
branch over the brain; mo, "mouth" of larva; n, n1, section of nerves; oe,
ectodermic pit forming oesophagus of larva; par, parenchyma filling the space
between the alimentary tract and the body wall; ph, pharynx lying in the cavity
of the peripharyngeal sheath, the nuclei of which are visible; sl1, sl2, sl3, lateral
ciliated lobes of the right side; vl, ventral ciliated lobe.
Fig. 13.—Diagrammatic transverse sections of a larval Polyclad at different stages, to
illustrate the development of the pharynx. (After Lang.) A, Larva of the eighth
day still within the shell. The main-gut (mg) is still solid, the epidermis is
slightly invaginated, and a pair of muscular mesodermic thickenings (ms) are
present. B, Young pelagic larva. The epidermic invagination has deepened and
developed laterally. C, The lateral pouches have formed the wall of the
peripharyngeal sheath, enclosing the mesodermic, muscular, thickening or
pharyngeal fold (ph). (Compare Fig. 12.) Towards the end of larval life, when the
ciliated processes (sl, Fig. 12) have aborted, the stage D is reached. By the
opening outwards of the pharyngeal sheath (ph.sh) the two apertures gm, or true
mouth, and m, or external mouth, are formed, which together correspond with
the oesophageal opening of the younger larva. (Compare the transverse section
in Fig. 5.)
a primitive larval stage, its near ally, S. neapolitanus, develops directly.
Most Acotylea indeed develop directly, and their free-swimming young
differ from Müller's larva merely in the absence of the ciliated band and in
the mode of swimming.
Fig. 12.—Section through Müller's larva of Thysanozoon brocchii (modified from
Lang). The right half is seen from inside. × 150. Semi-diagrammatic. br, Brain;
dl, dorsal ciliated lobe; dr, salivary gland-cells of pharynx; e, eye; ep, ciliated
epidermis containing rhabdites; mg, stomach or main-gut; mg1, unpaired gut
branch over the brain; mo, "mouth" of larva; n, n1, section of nerves; oe,
ectodermic pit forming oesophagus of larva; par, parenchyma filling the space
between the alimentary tract and the body wall; ph, pharynx lying in the cavity
of the peripharyngeal sheath, the nuclei of which are visible; sl1, sl2, sl3, lateral
ciliated lobes of the right side; vl, ventral ciliated lobe.
Fig. 13.—Diagrammatic transverse sections of a larval Polyclad at different stages, to
illustrate the development of the pharynx. (After Lang.) A, Larva of the eighth
day still within the shell. The main-gut (mg) is still solid, the epidermis is
slightly invaginated, and a pair of muscular mesodermic thickenings (ms) are
present. B, Young pelagic larva. The epidermic invagination has deepened and
developed laterally. C, The lateral pouches have formed the wall of the
peripharyngeal sheath, enclosing the mesodermic, muscular, thickening or
pharyngeal fold (ph). (Compare Fig. 12.) Towards the end of larval life, when the
ciliated processes (sl, Fig. 12) have aborted, the stage D is reached. By the
opening outwards of the pharyngeal sheath (ph.sh) the two apertures gm, or true
mouth, and m, or external mouth, are formed, which together correspond with
the oesophageal opening of the younger larva. (Compare the transverse section
in Fig. 5.)
Page 44
Polyclads possess an undoubted mesoderm, which gives rise to the muscles,
the pharyngeal fold, and the parenchyma. The ectoderm forms the
epidermis, in the cells of which the rhabdites (Fig. 12) arise, apparently as
so many condensed secretions. From the ectoderm the brain arises as two
pairs of ingrowths, which fuse together, and from these the peripheral
nervous system grows out. Three pigmented ectoderm cells give rise, by
division, to the eyes—an unpaired cell (Fig. 12, e) to the cerebral group of
eyes, and the other two to the marginal and tentacular groups. The
copulatory organs apparently arise to a large extent as ingrowths from the
ectoderm, from which the accessory glands (prostates, shell-glands) are also
formed. The endoderm forms the lining of the main-gut and its branches.
The pharynx is developed as in Fig. 13, which shows that the "mouth" of
the young larva (C) does not correspond exactly with that of the adult (D).
The salivary glands arise from ectoderm cells, which sink deeply into the
parenchyma. The reproductive organs (ovaries and testes) possibly arise by
proliferation from the gut-cells (Lang, v. Graff). The change from the larva
to the adult is gradual, the ciliary band being absorbed and the creeping
mode of life adopted.
Turbellaria. II. Tricladida.
The Triclads are most conveniently divided into three groups[39]: (i.)
Paludicola, the Planarians of ponds and streams; (ii.) the Maricola, the
Triclads of the sea; and (iii.) Terricola or Land Planarians. From the
Polyclads they differ in their mode of occurrence; in the elongated form of
their body and almost constant, mid-ventral position of the mouth; in
possessing a single external genital pore (Monogopora); and in the
production of a few, large, hard-shelled eggs provided with food-yolk.
Occurrence of the Paludicola.—The Planarians of our ponds and streams
are the most familiar and accessible Turbellaria. Their elongated, flattened
bodies, and gliding movements, render them conspicuous objects on the
under surface of stones and on the leaves of aquatic plants, where they live
gregariously. The variable Polycelis nigra (Fig. 14, H) is very abundant in
stagnant water and slowly-moving streams, whereas its ally, P. cornuta (Fig.
14, G), distinguished by a pair of tentacles, is more local. Planaria
the pharyngeal fold, and the parenchyma. The ectoderm forms the
epidermis, in the cells of which the rhabdites (Fig. 12) arise, apparently as
so many condensed secretions. From the ectoderm the brain arises as two
pairs of ingrowths, which fuse together, and from these the peripheral
nervous system grows out. Three pigmented ectoderm cells give rise, by
division, to the eyes—an unpaired cell (Fig. 12, e) to the cerebral group of
eyes, and the other two to the marginal and tentacular groups. The
copulatory organs apparently arise to a large extent as ingrowths from the
ectoderm, from which the accessory glands (prostates, shell-glands) are also
formed. The endoderm forms the lining of the main-gut and its branches.
The pharynx is developed as in Fig. 13, which shows that the "mouth" of
the young larva (C) does not correspond exactly with that of the adult (D).
The salivary glands arise from ectoderm cells, which sink deeply into the
parenchyma. The reproductive organs (ovaries and testes) possibly arise by
proliferation from the gut-cells (Lang, v. Graff). The change from the larva
to the adult is gradual, the ciliary band being absorbed and the creeping
mode of life adopted.
Turbellaria. II. Tricladida.
The Triclads are most conveniently divided into three groups[39]: (i.)
Paludicola, the Planarians of ponds and streams; (ii.) the Maricola, the
Triclads of the sea; and (iii.) Terricola or Land Planarians. From the
Polyclads they differ in their mode of occurrence; in the elongated form of
their body and almost constant, mid-ventral position of the mouth; in
possessing a single external genital pore (Monogopora); and in the
production of a few, large, hard-shelled eggs provided with food-yolk.
Occurrence of the Paludicola.—The Planarians of our ponds and streams
are the most familiar and accessible Turbellaria. Their elongated, flattened
bodies, and gliding movements, render them conspicuous objects on the
under surface of stones and on the leaves of aquatic plants, where they live
gregariously. The variable Polycelis nigra (Fig. 14, H) is very abundant in
stagnant water and slowly-moving streams, whereas its ally, P. cornuta (Fig.
14, G), distinguished by a pair of tentacles, is more local. Planaria
Page 45
(Dendrocoelum) lactea (A), P. polychroa (I), P. torva, and P. punctata are
not infrequently found together, but the last is at once the largest and rarest.
Fig. 14.—Forms of Triclads, with the distinguishing specific characters of certain
British forms. A, Planaria lactea O. F. M., × 2; B, Planaria alpina Dana, × 4
(after Kennel); C, Phagocata gracilis Leidy (after Woodworth), × 6; C', the
same with the pharynges (ph) extruded; D, Gunda ulvae Oer., × 4; E, Planaria
gonocephala Dug. (after Schmidt), × 4; F, genitalia of Gunda ulvae (after
Wendt); G, head of Polycelis cornuta Schm.; H, head of Polycelis nigra Ehr.; I,
head of Planaria polychroa Schm. K to N show the distinctive characters of the
genital ducts in K, Polycelis nigra; L, Planaria polychroa; M, Planaria alpina;
N, Planaria torva Schultze (after Iijima and v. Kennel). ga, Genital atrium; go,
common genital opening; mgr, "musculo-glandular organ"; mo, "mouth"; ovd,
oviduct; pe, penis; ph, pharynx; pyr, pyriform organs of unknown significance;
sc, sucker; sp, spermatophore lying in (ut) uterus; vd, vesicula seminalis. (All
except C and E are found in England.)
Planaria alpina (Fig. 14, B) is characteristic of cold mountain streams, but
occurs down to sea-level in England, the Isle of Man, and Ireland, and from
its abundance in spring water, probably enjoys a wide distribution
underground. In the Swiss Alps it has been found at altitudes of over 6000
feet, at lower levels in the Rhone, and also in the Lake of Geneva. This
wide distribution may perhaps be accounted for, partly, by its faculty for
asexual reproduction in summer, and also, by the production, later in the
year, of hard-shelled eggs which are laid loosely, not attached to stones or
plants.[40] But we have no really direct evidence of the means of dispersal
of this or of any of the foregoing species, although they all have a wide
distribution in Europe. Of extra-European forms the accounts that exist are
not infrequently found together, but the last is at once the largest and rarest.
Fig. 14.—Forms of Triclads, with the distinguishing specific characters of certain
British forms. A, Planaria lactea O. F. M., × 2; B, Planaria alpina Dana, × 4
(after Kennel); C, Phagocata gracilis Leidy (after Woodworth), × 6; C', the
same with the pharynges (ph) extruded; D, Gunda ulvae Oer., × 4; E, Planaria
gonocephala Dug. (after Schmidt), × 4; F, genitalia of Gunda ulvae (after
Wendt); G, head of Polycelis cornuta Schm.; H, head of Polycelis nigra Ehr.; I,
head of Planaria polychroa Schm. K to N show the distinctive characters of the
genital ducts in K, Polycelis nigra; L, Planaria polychroa; M, Planaria alpina;
N, Planaria torva Schultze (after Iijima and v. Kennel). ga, Genital atrium; go,
common genital opening; mgr, "musculo-glandular organ"; mo, "mouth"; ovd,
oviduct; pe, penis; ph, pharynx; pyr, pyriform organs of unknown significance;
sc, sucker; sp, spermatophore lying in (ut) uterus; vd, vesicula seminalis. (All
except C and E are found in England.)
Planaria alpina (Fig. 14, B) is characteristic of cold mountain streams, but
occurs down to sea-level in England, the Isle of Man, and Ireland, and from
its abundance in spring water, probably enjoys a wide distribution
underground. In the Swiss Alps it has been found at altitudes of over 6000
feet, at lower levels in the Rhone, and also in the Lake of Geneva. This
wide distribution may perhaps be accounted for, partly, by its faculty for
asexual reproduction in summer, and also, by the production, later in the
year, of hard-shelled eggs which are laid loosely, not attached to stones or
plants.[40] But we have no really direct evidence of the means of dispersal
of this or of any of the foregoing species, although they all have a wide
distribution in Europe. Of extra-European forms the accounts that exist are
Page 46
very fragmentary. The only indubitable diagnostic character of a Triclad is
the structure of its genital ducts, and this is accurately known in only a few
cases. Several species such as Dicotylus pulvinar (Fig. 16, B), at present
known only from Lake Baikal,[41] and others (Planaria mrazekii, P.
albissima) from Bohemia,[42] will doubtless be found elsewhere when they
are carefully looked for. Phagocata gracilis is a remarkable North
American form, possessing several pharynges (Fig. 14, C and C'), recalling
the independent movement of the pharyngeal lobes of Discocelis
lichenoides (Fig. 9).[43]
Occurrence of the Maricola.—Little as we accurately know of the
distribution of the fresh-water Planariae, our knowledge of the occurrence
of the marine forms is still more limited. Gunda (Procerodes) ulvae (Fig.
14, D) is the commonest European form, occurring abundantly in the upper
part of the littoral zone, on the shores of the Baltic. G. segmentata from
Messina has been carefully described by Lang,[44] but these are almost the
only species of Maricola which can be accurately determined. They differ
from the Paludicola in the position of the "uterus" behind the genital pore
and in the absence of a "musculo-glandular organ" (Fig. 14, F). A special
interest attaches to the Bdellouridae, a family containing three species, all
parasitic on Limulus from the east coast of America. These remarkable
Triclads usually have a sucker at the hinder end of the body, by which they
attach themselves firmly to the cephalo-thoracic appendages and to the gill-
plates, upon which the eggs may be found in considerable numbers. One
species, Syncoelidium pellucidum, possesses a pair of problematical organs
in the hinder part of the body, opening to the exterior ventro-laterally by a
couple of chitinous mouth-pieces, but having no connexion with the genital
ducts.[45]
Occurrence and Distribution of Land Planarians.—The terricolous
Triclads or Land Planarians are the most interesting division of the group.
Some forms, such as Bipalium kewense, attain large dimensions, being
usually 6 to 9 inches in length, and specimens fully extended have
measured 18 inches. Their bodies are frequently banded or striped with
brilliant colours. Geoplana coerulea Mos. has a blue ventral surface and is
olive green or dark Prussian blue above. G. splendens Dendy, is marked
the structure of its genital ducts, and this is accurately known in only a few
cases. Several species such as Dicotylus pulvinar (Fig. 16, B), at present
known only from Lake Baikal,[41] and others (Planaria mrazekii, P.
albissima) from Bohemia,[42] will doubtless be found elsewhere when they
are carefully looked for. Phagocata gracilis is a remarkable North
American form, possessing several pharynges (Fig. 14, C and C'), recalling
the independent movement of the pharyngeal lobes of Discocelis
lichenoides (Fig. 9).[43]
Occurrence of the Maricola.—Little as we accurately know of the
distribution of the fresh-water Planariae, our knowledge of the occurrence
of the marine forms is still more limited. Gunda (Procerodes) ulvae (Fig.
14, D) is the commonest European form, occurring abundantly in the upper
part of the littoral zone, on the shores of the Baltic. G. segmentata from
Messina has been carefully described by Lang,[44] but these are almost the
only species of Maricola which can be accurately determined. They differ
from the Paludicola in the position of the "uterus" behind the genital pore
and in the absence of a "musculo-glandular organ" (Fig. 14, F). A special
interest attaches to the Bdellouridae, a family containing three species, all
parasitic on Limulus from the east coast of America. These remarkable
Triclads usually have a sucker at the hinder end of the body, by which they
attach themselves firmly to the cephalo-thoracic appendages and to the gill-
plates, upon which the eggs may be found in considerable numbers. One
species, Syncoelidium pellucidum, possesses a pair of problematical organs
in the hinder part of the body, opening to the exterior ventro-laterally by a
couple of chitinous mouth-pieces, but having no connexion with the genital
ducts.[45]
Occurrence and Distribution of Land Planarians.—The terricolous
Triclads or Land Planarians are the most interesting division of the group.
Some forms, such as Bipalium kewense, attain large dimensions, being
usually 6 to 9 inches in length, and specimens fully extended have
measured 18 inches. Their bodies are frequently banded or striped with
brilliant colours. Geoplana coerulea Mos. has a blue ventral surface and is
olive green or dark Prussian blue above. G. splendens Dendy, is marked
Page 47
dorsally by three stripes of emerald green alternating with four dark brown
longitudinal bands. The mode of coloration, though somewhat variable, is
an important specific character. Its significance, however, is not clearly
understood. The colours may be a warning signal, as some Geoplana at
least are disagreeable to the taste of man and some birds[46]; but since Land
Planarians are largely nocturnal animals, living by day under logs, banana
leaves, and in other moist and dark situations, this explanation is clearly
insufficient. Two Geoplana have been noticed by Mr. Dendy which seem to
be protectively coloured. G. triangulata var. australis occurs abundantly in
the beech forest in the South Island of New Zealand, and its brown back
and yellow or orange ventral surface match the leaves around its haunts. G.
gelatinosa again looks like a mere slimy patch on the rotten bark where it is
found. In arid districts, during the dry season, Land Planarians burrow in
the soil and form a cyst, in which they lie coiled up, after the manner of
earthworms.[47] The glutinous investment of their delicate bodies forms a
moist medium in which the cilia covering the body (and especially the
ventral surface) may constantly and evenly vibrate, and by which they
adhere firmly to their prey. In some tropical Planarians, in addition to
possessing offensive properties, the mucus is so copious in amount and
hardens with such rapidity, that these Triclads may creep over bridges of it,
and may even be blown from one stem or branch of a plant to another,
hanging at the ends of their threads.[48]
Fig. 15.—Some Land Planarians found in Europe. A, Bipalium kewense Mos. × ⅓
(after Bergendal); B, Rhynchodemus terrestris O. F. M., × 2; C, Geodesmus
bilineatus Metsch., × 2½ (after Metschnikoff). mr, Region of mouth; gp, region
of genital pore.
longitudinal bands. The mode of coloration, though somewhat variable, is
an important specific character. Its significance, however, is not clearly
understood. The colours may be a warning signal, as some Geoplana at
least are disagreeable to the taste of man and some birds[46]; but since Land
Planarians are largely nocturnal animals, living by day under logs, banana
leaves, and in other moist and dark situations, this explanation is clearly
insufficient. Two Geoplana have been noticed by Mr. Dendy which seem to
be protectively coloured. G. triangulata var. australis occurs abundantly in
the beech forest in the South Island of New Zealand, and its brown back
and yellow or orange ventral surface match the leaves around its haunts. G.
gelatinosa again looks like a mere slimy patch on the rotten bark where it is
found. In arid districts, during the dry season, Land Planarians burrow in
the soil and form a cyst, in which they lie coiled up, after the manner of
earthworms.[47] The glutinous investment of their delicate bodies forms a
moist medium in which the cilia covering the body (and especially the
ventral surface) may constantly and evenly vibrate, and by which they
adhere firmly to their prey. In some tropical Planarians, in addition to
possessing offensive properties, the mucus is so copious in amount and
hardens with such rapidity, that these Triclads may creep over bridges of it,
and may even be blown from one stem or branch of a plant to another,
hanging at the ends of their threads.[48]
Fig. 15.—Some Land Planarians found in Europe. A, Bipalium kewense Mos. × ⅓
(after Bergendal); B, Rhynchodemus terrestris O. F. M., × 2; C, Geodesmus
bilineatus Metsch., × 2½ (after Metschnikoff). mr, Region of mouth; gp, region
of genital pore.
Page 48
In Europe there are only two or three indigenous Land Planarians, of which
Rhynchodemus terrestris O. F. M. (Fig. 15, B) is the most widely
distributed, and has been found in moist situations for the most part
wherever it has been carefully looked for. It measures about ¾ inch in
length, and is dark grey above, whitish below, and bears a pair of eyes near
the anterior extremity (Fig. 15, B). Bipalium kewense (Fig. 15, A), which
has been found in the forests of Upolu, Samoa, by Mr. J. J. Lister, has been
accidentally imported, from the (unknown) districts where it is indigenous,
with plants and soil to various parts of the world—England, Germany, the
Cape, and also to Sydney, where it appears to have established itself. In
these Bipalia living in hothouses, the genitalia never appear to attain
maturity, and apparently multiple fission and subsequent reparation of the
missing parts is the only mode of reproduction. Geodesmus bilineatus (Fig.
15, C), which has occurred at Giessen, Würzburg, and Dresden, has, in all
probability, been introduced with ferns from the West or East Indies.
Microplana humicola, described by Vejdovsky from dunghills in Bohemia,
is doubtfully indigenous.
In marked contrast with the poverty of the temperate zones in Land
Planarians, is the abundance and great variety of this group in Southern
Asia, South America, and especially in Australasia, where the rich Land
Planarian fauna has been carefully investigated by Spencer, Dendy,
Fletcher, and others, in certain parts of Victoria, New South Wales, and
New Zealand.[49] About forty species of Planarians have been discovered on
the Australian continent, thirty-five of which belong to the predominant
genus Geoplana, distinguished by the presence of numerous eyes along the
border of the simple anterior extremity. Of the remaining five, four belong
to the genus Rhynchodemus, with, lastly, the introduced Bipalium kewense.
The distribution of any one species, however, is so limited that only three
forms are common to the two former colonies; and although some of the
twenty known New Zealand Planarians (chiefly species of Geoplana), are
identical with Australian species, yet only one, or possibly two, varieties of
these species are Australian also. In addition to their prevalence in
Australasia, the Geoplanidae also occur in South America, South Africa,
Japan, and the East Indies. The Bipaliidae are characteristic of the Oriental
region, being found in China, Borneo, Bengal, and Ceylon. The
Rhynchodemidae are a cosmopolitan family, occurring in Europe, North and
Rhynchodemus terrestris O. F. M. (Fig. 15, B) is the most widely
distributed, and has been found in moist situations for the most part
wherever it has been carefully looked for. It measures about ¾ inch in
length, and is dark grey above, whitish below, and bears a pair of eyes near
the anterior extremity (Fig. 15, B). Bipalium kewense (Fig. 15, A), which
has been found in the forests of Upolu, Samoa, by Mr. J. J. Lister, has been
accidentally imported, from the (unknown) districts where it is indigenous,
with plants and soil to various parts of the world—England, Germany, the
Cape, and also to Sydney, where it appears to have established itself. In
these Bipalia living in hothouses, the genitalia never appear to attain
maturity, and apparently multiple fission and subsequent reparation of the
missing parts is the only mode of reproduction. Geodesmus bilineatus (Fig.
15, C), which has occurred at Giessen, Würzburg, and Dresden, has, in all
probability, been introduced with ferns from the West or East Indies.
Microplana humicola, described by Vejdovsky from dunghills in Bohemia,
is doubtfully indigenous.
In marked contrast with the poverty of the temperate zones in Land
Planarians, is the abundance and great variety of this group in Southern
Asia, South America, and especially in Australasia, where the rich Land
Planarian fauna has been carefully investigated by Spencer, Dendy,
Fletcher, and others, in certain parts of Victoria, New South Wales, and
New Zealand.[49] About forty species of Planarians have been discovered on
the Australian continent, thirty-five of which belong to the predominant
genus Geoplana, distinguished by the presence of numerous eyes along the
border of the simple anterior extremity. Of the remaining five, four belong
to the genus Rhynchodemus, with, lastly, the introduced Bipalium kewense.
The distribution of any one species, however, is so limited that only three
forms are common to the two former colonies; and although some of the
twenty known New Zealand Planarians (chiefly species of Geoplana), are
identical with Australian species, yet only one, or possibly two, varieties of
these species are Australian also. In addition to their prevalence in
Australasia, the Geoplanidae also occur in South America, South Africa,
Japan, and the East Indies. The Bipaliidae are characteristic of the Oriental
region, being found in China, Borneo, Bengal, and Ceylon. The
Rhynchodemidae are a cosmopolitan family, occurring in Europe, North and
Page 49
South America, the Cape of Good Hope, Ceylon, the East Indies, Australia
(particularly Lord Howe Island), and Samoa.[50]
Habits and Structure of Triclads.—The common Planaria
(Dendrocoelum) lactea, which usually progresses by ciliary action, aided, it
is said, by muscular contractions of the ventral surface, performs, if
alarmed, a series of rapid "looping" movements, by affixing a sucker (Fig.
14, A, sc), placed on the under side of the head, to the substratum, and
pulling the posterior end close to this. The sucker, discovered by Leydig, is
even better developed in P. punctata (Fig. 16, A), P. mrazekii, and P.
cavatica, and is an efficient adhering-organ which has probably been
developed from a similar but simpler structure found in a considerable
number of both fresh-water and marine Triclads (P. alpina, Fig. 16, E).
Probably the sucker of the Land Planarian Cotyloplana (D) is the same
structure, but the two suckers of Dicotylus (B) are at present unique.
Planaria dioica, found by Claparède on the coast of Normandy,[51] is
covered with minute adhesive papillae, similar to those of certain
Rhabdocoelida (e.g. Monotus, Fig. 19, D), enabling it to cling tightly to the
Zostera, and so to resist the loosening action of the waves.
Fig. 16.—Suckers of Triclads. A, Planaria punctata Pall.; a, dorsal surface of head; b,
ventral surface (freely moving) showing the sucker; c, sucker contracted (after
Hallez): B, ventral surface of head of Dicotylus pulvinar Gr., from Lake Baikal
(after Grube): C, dorsal surface of Procotylea fluviatilis Gir. (after Girard): D,
sucker of Cotyloplana whiteleggei Sp. (after Spencer): E, ventral view of head of
Planaria alpina Dana (preserved specimen); hg, adhering groove; m, thickened
musculature forming the margin of the sucker; sc, sucker; t, tentacles.
(particularly Lord Howe Island), and Samoa.[50]
Habits and Structure of Triclads.—The common Planaria
(Dendrocoelum) lactea, which usually progresses by ciliary action, aided, it
is said, by muscular contractions of the ventral surface, performs, if
alarmed, a series of rapid "looping" movements, by affixing a sucker (Fig.
14, A, sc), placed on the under side of the head, to the substratum, and
pulling the posterior end close to this. The sucker, discovered by Leydig, is
even better developed in P. punctata (Fig. 16, A), P. mrazekii, and P.
cavatica, and is an efficient adhering-organ which has probably been
developed from a similar but simpler structure found in a considerable
number of both fresh-water and marine Triclads (P. alpina, Fig. 16, E).
Probably the sucker of the Land Planarian Cotyloplana (D) is the same
structure, but the two suckers of Dicotylus (B) are at present unique.
Planaria dioica, found by Claparède on the coast of Normandy,[51] is
covered with minute adhesive papillae, similar to those of certain
Rhabdocoelida (e.g. Monotus, Fig. 19, D), enabling it to cling tightly to the
Zostera, and so to resist the loosening action of the waves.
Fig. 16.—Suckers of Triclads. A, Planaria punctata Pall.; a, dorsal surface of head; b,
ventral surface (freely moving) showing the sucker; c, sucker contracted (after
Hallez): B, ventral surface of head of Dicotylus pulvinar Gr., from Lake Baikal
(after Grube): C, dorsal surface of Procotylea fluviatilis Gir. (after Girard): D,
sucker of Cotyloplana whiteleggei Sp. (after Spencer): E, ventral view of head of
Planaria alpina Dana (preserved specimen); hg, adhering groove; m, thickened
musculature forming the margin of the sucker; sc, sucker; t, tentacles.
Page 50
The movements of Land Planarians are somewhat peculiar. The ventral
surface of Bipalium has a median groove, into which the ducts of numerous
mucus-glands open. This is bordered by two ridges clothed with long and
powerful cilia, which perform the chief part in propelling the animal, aided,
according to Lehnert,[52] by muscular waves which pass from the head,
backwards, i.e. opposite in direction to those by which a snail slides along.
This observation, however, needs confirmation. The whole body executes
sinuous movements, during which the crescentic head, lifted slightly above
the ground (Fig. 15, A), is constantly altering and regaining its normal
shape, somewhat as a Planaria lactea uses the lobes of its head. Further
examination shows that the margin of the head of Bipalium is not only
provided with eyes, but in addition, with ciliated, (probably) olfactory pits.
Such depressions, innervated directly from the cerebral ganglia, have been
found in sixteen species of Geoplana, and in one or two species of
Rhynchodemus.[53] Some Land Planarians (a species of Rhynchodemus
from Ceylon, and a Dolichoplana from the Philippines) wriggle out of a
box or the hand with great speed (Moseley).
The skin of Triclads is full of minute rods or rhabdites, which are shot out
in great numbers when the animal is irritated, and doubtless serve an
offensive purpose. The Terricola possess two kinds of these: (1) needle-like
rods; and (2) in Bipalium kewense, flagellated structures, bent into a V-form
and with a slender thread attached to one end (Shipley). In Geoplana
coerulea these bent rods furnish the blue colour of the ventral surface. The
rhabdites arise in all Triclads in cells below the basement-membrane, which
they are said to traverse in order to reach the epidermis, thus differing in
origin, and also in structure, from the rods of Polyclads.
Food.—Triclads are largely if not wholly carnivorous animals, feeding
upon Annelids, Crustacea, Insects, Insect-larvae, and Molluscs. The mouth
is usually mid-ventral or behind the middle of the body, but in the
anomalous Leimacopsis terricola Schm. from the Andes[54] and in
Dolichoplana it is near the anterior end. The pharynx (Figs. 17, 18, ph) is
cylindrical or bell-shaped, exceedingly dilatable and abundantly supplied
with glands and nervous tissue. It opens into the three main intestinal
branches, one of which runs in the median plane forwards, the others
surface of Bipalium has a median groove, into which the ducts of numerous
mucus-glands open. This is bordered by two ridges clothed with long and
powerful cilia, which perform the chief part in propelling the animal, aided,
according to Lehnert,[52] by muscular waves which pass from the head,
backwards, i.e. opposite in direction to those by which a snail slides along.
This observation, however, needs confirmation. The whole body executes
sinuous movements, during which the crescentic head, lifted slightly above
the ground (Fig. 15, A), is constantly altering and regaining its normal
shape, somewhat as a Planaria lactea uses the lobes of its head. Further
examination shows that the margin of the head of Bipalium is not only
provided with eyes, but in addition, with ciliated, (probably) olfactory pits.
Such depressions, innervated directly from the cerebral ganglia, have been
found in sixteen species of Geoplana, and in one or two species of
Rhynchodemus.[53] Some Land Planarians (a species of Rhynchodemus
from Ceylon, and a Dolichoplana from the Philippines) wriggle out of a
box or the hand with great speed (Moseley).
The skin of Triclads is full of minute rods or rhabdites, which are shot out
in great numbers when the animal is irritated, and doubtless serve an
offensive purpose. The Terricola possess two kinds of these: (1) needle-like
rods; and (2) in Bipalium kewense, flagellated structures, bent into a V-form
and with a slender thread attached to one end (Shipley). In Geoplana
coerulea these bent rods furnish the blue colour of the ventral surface. The
rhabdites arise in all Triclads in cells below the basement-membrane, which
they are said to traverse in order to reach the epidermis, thus differing in
origin, and also in structure, from the rods of Polyclads.
Food.—Triclads are largely if not wholly carnivorous animals, feeding
upon Annelids, Crustacea, Insects, Insect-larvae, and Molluscs. The mouth
is usually mid-ventral or behind the middle of the body, but in the
anomalous Leimacopsis terricola Schm. from the Andes[54] and in
Dolichoplana it is near the anterior end. The pharynx (Figs. 17, 18, ph) is
cylindrical or bell-shaped, exceedingly dilatable and abundantly supplied
with glands and nervous tissue. It opens into the three main intestinal
branches, one of which runs in the median plane forwards, the others
Page 51
backwards right and left, enclosing a space in which the genital ducts lie
(Figs. 14, A, 17). The fresh-water Planarians prey upon Oligochaeta,
Hydrophilidae (aquatic beetles), and the commoner pond-snails. Bipalium
kewense pursues earthworms, seizes the upper surface of the anterior end by
the glutinous secretion of its ventral surface, and then proceeds to envelop
part or the whole of the worm within its pharynx, which is stretched as a
thin skin over the body of its struggling prey (Lehnert). The tissues of the
latter pass into the intestine of the Planarian, and distend it greatly. After
such a meal, which lasts from one to five hours, a Bipalium may remain for
three months without seeking food. Geobia subterranea, a white eyeless
form from Brazil, pursues earthworms (Lumbricus corethrurus) in their
burrows, and has been seen by Fritz Müller sucking the blood out of a
young worm.[55] Geoplana typhlops, a Tasmanian species, is also blind, and
pursues worms, as does G. triangulata (Dendy). In Trinidad, von Kennel[56]
observed that land-snails (Subulinae) were the food of certain Land
Planarians, the name of which, however, he does not state. The pharynx was
employed to suck out the soft parts of the snail even from the upper whorls
of the shell.
Reproduction.—In Planaria lactea the numerous testes (Fig. 17, te) are
placed both above and below the alimentary canal throughout the greater
part of its course. The membrane of each gonad is continued into a minute
vas efferens, which unites with those of neighbouring testes. Two vasa
deferentia (v.d) arise thus on each side, one from the posterior, the other
from the anterior testes of the body, and open into the vesiculae seminales
(v.s), which may be seen in the living animal as tortuous whitish tubes at the
sides of the pharynx (Fig. 14, A). These open into the penis (Figs. 14, A; 17,
pe), a large pyriform organ, the apex of which, when retracted, points
forwards, projecting into the penial cavity. When this apical portion is
evaginated and turned inside out, it is of considerable length, and is able to
pass into the long slender duct of the uterus (ut) of another individual. The
penial sheath (ps) is part of the genital atrium (gs), which is developed as a
pit from the skin, and invests the end of the genital ducts, the mouth of the
pit forming the common genital pore (go), through which both male and
female genital products are emitted.
(Figs. 14, A, 17). The fresh-water Planarians prey upon Oligochaeta,
Hydrophilidae (aquatic beetles), and the commoner pond-snails. Bipalium
kewense pursues earthworms, seizes the upper surface of the anterior end by
the glutinous secretion of its ventral surface, and then proceeds to envelop
part or the whole of the worm within its pharynx, which is stretched as a
thin skin over the body of its struggling prey (Lehnert). The tissues of the
latter pass into the intestine of the Planarian, and distend it greatly. After
such a meal, which lasts from one to five hours, a Bipalium may remain for
three months without seeking food. Geobia subterranea, a white eyeless
form from Brazil, pursues earthworms (Lumbricus corethrurus) in their
burrows, and has been seen by Fritz Müller sucking the blood out of a
young worm.[55] Geoplana typhlops, a Tasmanian species, is also blind, and
pursues worms, as does G. triangulata (Dendy). In Trinidad, von Kennel[56]
observed that land-snails (Subulinae) were the food of certain Land
Planarians, the name of which, however, he does not state. The pharynx was
employed to suck out the soft parts of the snail even from the upper whorls
of the shell.
Reproduction.—In Planaria lactea the numerous testes (Fig. 17, te) are
placed both above and below the alimentary canal throughout the greater
part of its course. The membrane of each gonad is continued into a minute
vas efferens, which unites with those of neighbouring testes. Two vasa
deferentia (v.d) arise thus on each side, one from the posterior, the other
from the anterior testes of the body, and open into the vesiculae seminales
(v.s), which may be seen in the living animal as tortuous whitish tubes at the
sides of the pharynx (Fig. 14, A). These open into the penis (Figs. 14, A; 17,
pe), a large pyriform organ, the apex of which, when retracted, points
forwards, projecting into the penial cavity. When this apical portion is
evaginated and turned inside out, it is of considerable length, and is able to
pass into the long slender duct of the uterus (ut) of another individual. The
penial sheath (ps) is part of the genital atrium (gs), which is developed as a
pit from the skin, and invests the end of the genital ducts, the mouth of the
pit forming the common genital pore (go), through which both male and
female genital products are emitted.
Page 52
There are two ovaries (ov) placed far forwards, between the third and fourth
pairs of intestinal coeca. The oviducts (ovd) lie just over the lateral nerves,
and have a slightly tortuous course, at each outward bend receiving the duct
(yo) of a yolk-gland (yg), so that ova and yolk are already associated when
the oviducts open by a short unpaired tube into the genital atrium. The yolk-
glands develop rapidly,[57] and when fully formed are massive glands
occupying the spaces between the intestinal branches and the testes which
are then aborting. The so-called uterus (ut), apparently at first a
diverticulum of the genital atrium, expands behind the pharynx into a
receptacle lined by long glandular columnar cells, which, however, are not
all of the same kind. The uterine duct opens into the atrium just above the
aperture of a problematical, eversible, "musculo-glandular organ" (mgr).
Fig. 17.—Diagrammatic view of the structure of Planaria (Dendrocoelum) lactea. × 7.
The body has been cut across and a portion removed. In the posterior half the
alimentary tract of the left side is removed and the uterus, penis, and muscular
organ sliced open horizontally. The nervous system is represented by black, and
the yolk-glands by dotted lines. br, Brain; ey, eye with lens and optic nerve; go,
external genital aperture for both male and female products; gs, genital atrium;
lg, paired lateral intestinal branch; ln, longitudinal nerve; mg, unpaired anterior
intestine, the branches of which are cut off close to the main stem; mgr, eversible
pairs of intestinal coeca. The oviducts (ovd) lie just over the lateral nerves,
and have a slightly tortuous course, at each outward bend receiving the duct
(yo) of a yolk-gland (yg), so that ova and yolk are already associated when
the oviducts open by a short unpaired tube into the genital atrium. The yolk-
glands develop rapidly,[57] and when fully formed are massive glands
occupying the spaces between the intestinal branches and the testes which
are then aborting. The so-called uterus (ut), apparently at first a
diverticulum of the genital atrium, expands behind the pharynx into a
receptacle lined by long glandular columnar cells, which, however, are not
all of the same kind. The uterine duct opens into the atrium just above the
aperture of a problematical, eversible, "musculo-glandular organ" (mgr).
Fig. 17.—Diagrammatic view of the structure of Planaria (Dendrocoelum) lactea. × 7.
The body has been cut across and a portion removed. In the posterior half the
alimentary tract of the left side is removed and the uterus, penis, and muscular
organ sliced open horizontally. The nervous system is represented by black, and
the yolk-glands by dotted lines. br, Brain; ey, eye with lens and optic nerve; go,
external genital aperture for both male and female products; gs, genital atrium;
lg, paired lateral intestinal branch; ln, longitudinal nerve; mg, unpaired anterior
intestine, the branches of which are cut off close to the main stem; mgr, eversible
Page 53
"musculo-glandular organ"; nc, nerve-cells in the pharynx; nn, lateral nerve-
twigs; ns, nerve-sheath; ov, ovary; ovd, oviduct; pe, the eversible penis, the
corrugated inner white portion of which is the apex; ph, pharynx; phs,
pharyngeal sheath; pr, "prostate" or granule-gland (represented by dotted lines
opening into the penis); ps, penial sheath; te, testes; to, tactile lobe of the head;
ut, "uterus" opening into the genital atrium just above mgr; vd, vasa deferentia;
vs, vesicula seminalis; yg, yolk-glands; yo, openings of the yolk-ducts into the
oviducts.
Fertilisation appears to occur in the uterus, where ova, yolk, and
spermatozoa, or (in P. torva) spermatophores (Fig. 14, N, sp), are found.
The formation of the cocoon in Planaria lactea is probably begun in the
"uterus," but is undoubtedly completed in the genital atrium. In P.
polychroa, however, the stalked cocoon is formed wholly in the "uterus."
Thus we find two types of cocoons in different species of the genus
Planaria associated with two types of reproductive organs (Hallez):—
I. Planariae in which the two oviducts open separately into the posterior part
of the duct of the uterus. A musculo-glandular organ is absent. The cocoons
are spherical and stalked. Examples—Planaria polychroa (Fig. 14, L), P.
albissima, P. gonocephala.
II. Planariae in which the two oviducts open by means of an unpaired duct
into the genital atrium. A musculo-glandular organ present (Planaria torva
(Fig. 14, N), P. mrazekii, P. lactea, P. cavatica), or absent (P. alpina, Fig.
14, M). The cocoons are sessile.
The genitalia of the Maricola (Fig. 14, F) and Terricola do not differ very
much from those of Planaria. The uterus (greatly reduced in the Land
Planarians) lies behind the genital pore, and several ova, together with
much milky yolk, are enclosed in a capsule which is formed in the genital
atrium.
Asexual Reproduction.[58]—It has long been known that fresh-water
Planarians have not only great powers of repairing injuries, but that they use
this faculty in order to multiply by transverse fission. Planaria alpina and
Polycelis cornuta, in summer, separate off the posterior part of the body,
and this ultimately becomes an entire individual. P. albissima, and
twigs; ns, nerve-sheath; ov, ovary; ovd, oviduct; pe, the eversible penis, the
corrugated inner white portion of which is the apex; ph, pharynx; phs,
pharyngeal sheath; pr, "prostate" or granule-gland (represented by dotted lines
opening into the penis); ps, penial sheath; te, testes; to, tactile lobe of the head;
ut, "uterus" opening into the genital atrium just above mgr; vd, vasa deferentia;
vs, vesicula seminalis; yg, yolk-glands; yo, openings of the yolk-ducts into the
oviducts.
Fertilisation appears to occur in the uterus, where ova, yolk, and
spermatozoa, or (in P. torva) spermatophores (Fig. 14, N, sp), are found.
The formation of the cocoon in Planaria lactea is probably begun in the
"uterus," but is undoubtedly completed in the genital atrium. In P.
polychroa, however, the stalked cocoon is formed wholly in the "uterus."
Thus we find two types of cocoons in different species of the genus
Planaria associated with two types of reproductive organs (Hallez):—
I. Planariae in which the two oviducts open separately into the posterior part
of the duct of the uterus. A musculo-glandular organ is absent. The cocoons
are spherical and stalked. Examples—Planaria polychroa (Fig. 14, L), P.
albissima, P. gonocephala.
II. Planariae in which the two oviducts open by means of an unpaired duct
into the genital atrium. A musculo-glandular organ present (Planaria torva
(Fig. 14, N), P. mrazekii, P. lactea, P. cavatica), or absent (P. alpina, Fig.
14, M). The cocoons are sessile.
The genitalia of the Maricola (Fig. 14, F) and Terricola do not differ very
much from those of Planaria. The uterus (greatly reduced in the Land
Planarians) lies behind the genital pore, and several ova, together with
much milky yolk, are enclosed in a capsule which is formed in the genital
atrium.
Asexual Reproduction.[58]—It has long been known that fresh-water
Planarians have not only great powers of repairing injuries, but that they use
this faculty in order to multiply by transverse fission. Planaria alpina and
Polycelis cornuta, in summer, separate off the posterior part of the body,
and this ultimately becomes an entire individual. P. albissima, and
Page 54
especially P. subtentaculata, anticipate matters so far, that before fission is
complete, the new individual has a head nearly fully formed. The new
organs are largely regenerated in both parent and young, apparently by the
division and specialisation of scattered embryonic cells in the parenchyma.
The asexual reproduction of Land Planarians is not fully proved, though it
is known that they repair injuries to the body completely, and that Bipalium
kewense is often found in hothouses, divided into fragments which
regenerate all the organs of the parent, but like the latter, do not mature their
sexual organs.
Fig. 18.—Semi-diagrammatic view of the excretory system of Planaria lactea. (Partly
after Chickoff.) can, Capillary network on both dorsal and ventral surfaces; g.br,
branches of the intestine; lg, lateral branches of the digestive system; ln,
longitudinal nerve; ph, pharynx, with intermuscular capillary excretory network
arising from the point marked pht; tp, principal vessels of the excretory system,
the external opening of which is not certainly known; vs, vesicula seminalis.
Excretion.—The excretory organs of Triclads consist of flame-cells,
canaliculi, and a pair of longitudinal canals, the external openings of which,
have not been satisfactorily ascertained. The flame-cells are difficult to
detect in Planaria lactea, and the latest observer, Chickoff,[59] was unable
to see them, although to him we are indebted for figures of this system in P.
lactea (Fig. 18) and P. alpina (P. montana). In the latter, the flame-cells are
distinct, and may open directly into the two main canals or indirectly
through unbranched canaliculi. The pharynx possesses a special supply of
excretory tubules communicating with the main canals. A similar system
has been described and figured in Gunda segmentata by Lang.[60]
Classification of Tricladida.
PALUDICOLA.
Family. Genus and British Species.
complete, the new individual has a head nearly fully formed. The new
organs are largely regenerated in both parent and young, apparently by the
division and specialisation of scattered embryonic cells in the parenchyma.
The asexual reproduction of Land Planarians is not fully proved, though it
is known that they repair injuries to the body completely, and that Bipalium
kewense is often found in hothouses, divided into fragments which
regenerate all the organs of the parent, but like the latter, do not mature their
sexual organs.
Fig. 18.—Semi-diagrammatic view of the excretory system of Planaria lactea. (Partly
after Chickoff.) can, Capillary network on both dorsal and ventral surfaces; g.br,
branches of the intestine; lg, lateral branches of the digestive system; ln,
longitudinal nerve; ph, pharynx, with intermuscular capillary excretory network
arising from the point marked pht; tp, principal vessels of the excretory system,
the external opening of which is not certainly known; vs, vesicula seminalis.
Excretion.—The excretory organs of Triclads consist of flame-cells,
canaliculi, and a pair of longitudinal canals, the external openings of which,
have not been satisfactorily ascertained. The flame-cells are difficult to
detect in Planaria lactea, and the latest observer, Chickoff,[59] was unable
to see them, although to him we are indebted for figures of this system in P.
lactea (Fig. 18) and P. alpina (P. montana). In the latter, the flame-cells are
distinct, and may open directly into the two main canals or indirectly
through unbranched canaliculi. The pharynx possesses a special supply of
excretory tubules communicating with the main canals. A similar system
has been described and figured in Gunda segmentata by Lang.[60]
Classification of Tricladida.
PALUDICOLA.
Family. Genus and British Species.
Page 55
Planariidae Planaria lactea O. F. M., P. punctata Pall., P.
polychroa Schm., P. torva M. Sch., P. alpina Dana.
Polycelis nigra Ehr., P. cornuta Schm.
Anocelis.
Oligocelis, Procotyla. (Doubtful genera.)
Sorocelis.
Dicotylus.
MARICOLA.
Procerodidae Procerodes (= Gunda) ulvae Oersted, P. littoralis
(= Gundidae). van Beneden.
Cercyra.
Uteriporus.
Bdellouridae Bdelloura.
Syncoelidium.
TERRICOLA.
Bipaliidae Bipalium kewense Moseley (introduced).
Geoplanidae Geoplana.
Geodesmus.
Rhynchodemidae Rhynchodemus terrestris O. F. M.
Belonging to Dolichoplana.
undetermined Polycladus.
Families Microplana.
Leimacopsis.
Turbellaria. III. Rhabdocoelida.
The Rhabdocoelida include a very heterogeneous assemblage of usually
minute Turbellaria, distinguished collectively from the Polyclads and
Triclads by the form of the digestive tract. This is a simple or slightly lobed
sac, except in the Bothrioplanidae, which in this and many other points
closely resemble the Triclads. It is to the straight, rod-like nature of the
polychroa Schm., P. torva M. Sch., P. alpina Dana.
Polycelis nigra Ehr., P. cornuta Schm.
Anocelis.
Oligocelis, Procotyla. (Doubtful genera.)
Sorocelis.
Dicotylus.
MARICOLA.
Procerodidae Procerodes (= Gunda) ulvae Oersted, P. littoralis
(= Gundidae). van Beneden.
Cercyra.
Uteriporus.
Bdellouridae Bdelloura.
Syncoelidium.
TERRICOLA.
Bipaliidae Bipalium kewense Moseley (introduced).
Geoplanidae Geoplana.
Geodesmus.
Rhynchodemidae Rhynchodemus terrestris O. F. M.
Belonging to Dolichoplana.
undetermined Polycladus.
Families Microplana.
Leimacopsis.
Turbellaria. III. Rhabdocoelida.
The Rhabdocoelida include a very heterogeneous assemblage of usually
minute Turbellaria, distinguished collectively from the Polyclads and
Triclads by the form of the digestive tract. This is a simple or slightly lobed
sac, except in the Bothrioplanidae, which in this and many other points
closely resemble the Triclads. It is to the straight, rod-like nature of the
Page 56
alimentary canal that the name of the group refers. The size and form of the
body, and the structure of the pharynx and genitalia, vary within wide
limits.
The Rhabdocoelida are subdivided into three tribes:—
(1) Acoela, in which a sub-central mouth and pharynx are present, but lead
into the parenchyma of the body, not into an intestine with proper walls. An
excretory system has not hitherto been seen. Yolk-glands are absent. An
otolith underlies the brain. The Acoela are marine.
(2) Rhabdocoela, which possess a complete alimentary tract separated from
the body-wall (except for a few suspensory strands) by a space or body-
cavity, filled with fluid. This space is sometimes (Vortex viridis) lined by an
endothelium of flattened parenchymatous cells. There are two compact
testes, which are enclosed (as are the ovaries and yolk-glands) in a distinct
membrane. An otolith is present in some genera and species. Terrestrial,
fresh-water, marine.
(3) Alloeocoela, in which the body-cavity is greatly reduced. Except in the
Bothrioplanidae, the gonads have no distinct membrane. Testes numerous;
yolk-glands present. Marine with a few exceptions.
Occurrence and Habits of the Rhabdocoelida.—The Acoela are usually
minute, active Turbellaria abounding amongst weeds throughout the lower
half of the Littoral, and the whole of the Laminarian zone, but are most
plentiful in the pools exposed during spring-tides on our coasts, especially
on the shores of Devonshire. The species of Haplodiscus, however, and
Convoluta henseni are modified pelagic forms found in the Atlantic Ocean.
[61]
Convoluta paradoxa (Fig. 19, B) is the commonest British species. It is
from 1 to 9 mm. in length, and of a brown colour, marked above by one or
more transverse white bars. The brown colour is due to a symbiotic alga,
the nature of which has not been thoroughly investigated. In an allied
species, however (C. roscoffensis), from the coast of Brittany, the alga,
which is here green, has been carefully examined by Professor Haberlandt,
[62] and it appears from his researches that the algae form a special
body, and the structure of the pharynx and genitalia, vary within wide
limits.
The Rhabdocoelida are subdivided into three tribes:—
(1) Acoela, in which a sub-central mouth and pharynx are present, but lead
into the parenchyma of the body, not into an intestine with proper walls. An
excretory system has not hitherto been seen. Yolk-glands are absent. An
otolith underlies the brain. The Acoela are marine.
(2) Rhabdocoela, which possess a complete alimentary tract separated from
the body-wall (except for a few suspensory strands) by a space or body-
cavity, filled with fluid. This space is sometimes (Vortex viridis) lined by an
endothelium of flattened parenchymatous cells. There are two compact
testes, which are enclosed (as are the ovaries and yolk-glands) in a distinct
membrane. An otolith is present in some genera and species. Terrestrial,
fresh-water, marine.
(3) Alloeocoela, in which the body-cavity is greatly reduced. Except in the
Bothrioplanidae, the gonads have no distinct membrane. Testes numerous;
yolk-glands present. Marine with a few exceptions.
Occurrence and Habits of the Rhabdocoelida.—The Acoela are usually
minute, active Turbellaria abounding amongst weeds throughout the lower
half of the Littoral, and the whole of the Laminarian zone, but are most
plentiful in the pools exposed during spring-tides on our coasts, especially
on the shores of Devonshire. The species of Haplodiscus, however, and
Convoluta henseni are modified pelagic forms found in the Atlantic Ocean.
[61]
Convoluta paradoxa (Fig. 19, B) is the commonest British species. It is
from 1 to 9 mm. in length, and of a brown colour, marked above by one or
more transverse white bars. The brown colour is due to a symbiotic alga,
the nature of which has not been thoroughly investigated. In an allied
species, however (C. roscoffensis), from the coast of Brittany, the alga,
which is here green, has been carefully examined by Professor Haberlandt,
[62] and it appears from his researches that the algae form a special
Page 57
assimilating tissue, enabling the Convoluta to live after the fashion of a
green plant. At Roscoff, these elongated green Convoluta live gregariously
in the sandy tide-pools, fully exposed to the sun's rays, and have the
appearance of a mass of weed floating at the surface of the water. Access to
the atmosphere and to sunlight are necessary in order to enable the
assimilating tissue to form the carbohydrates, upon which this form lives
exclusively. Not only has the alga itself undergone such profound changes
(loss of membrane, inability to live independently after the death of the
host) as to disguise its true nature (a tissue-cell derived from algal
ancestors), but the Convoluta has also undergone concomitant changes, in
form, in the loss of a carnivorous habit, and in the development of marked
heliotropic movements, thus adapting itself to an holophytic or plant-like
mode of nutrition. Nevertheless the Acoela, as a group, are carnivorous,
feeding upon Diatoms, Copepoda, and small Rhabdocoela, the absence of a
digestive tract indeed being probably more apparent than real.[63]
The Rhabdocoela live under varied conditions. One form, Prorhynchus
sphyrocephalus, has been found among plants far from water in the
neighbourhood of Leyden, by De Man.[64] With this exception the group is
purely aquatic, and though a few genera and even individuals of the same
species occur both in salt and fresh water, whole sub-families and genera
are either marine or paludicolous. Among the latter, Mesostoma, Castrada,
Vortex, and Derostoma are common in brooks and ponds, especially at
certain times, often only for one month (May or June) in the year. Species
of Macrostoma, Stenostoma, and Microstoma are also abundant in similar
places. The two latter occur in chains formed by fission; but the sexual
individuals (which are of distinct sexes, contrary to the usual hermaphrodite
condition of Flat Worms) only appear at stated times and are not well
known. A large number of genera are purely marine, and one family, the
Proboscidae (distinguished by having the anterior end invaginated by
special muscles and converted into a sensory organ), is entirely so. The
most cursory examination of littoral weeds reveals species of
Macrorhynchus, Acrorhynchus, Promesostoma, Byrsophlebs, and
Proxenetes, the character of which may be gathered from von Graffs great
monograph, or from Gamble's paper on the "British Marine Turbellaria."[65]
Much, however, still remains to be done before we possess an adequate idea
of the occurrence of this group on our coasts.
green plant. At Roscoff, these elongated green Convoluta live gregariously
in the sandy tide-pools, fully exposed to the sun's rays, and have the
appearance of a mass of weed floating at the surface of the water. Access to
the atmosphere and to sunlight are necessary in order to enable the
assimilating tissue to form the carbohydrates, upon which this form lives
exclusively. Not only has the alga itself undergone such profound changes
(loss of membrane, inability to live independently after the death of the
host) as to disguise its true nature (a tissue-cell derived from algal
ancestors), but the Convoluta has also undergone concomitant changes, in
form, in the loss of a carnivorous habit, and in the development of marked
heliotropic movements, thus adapting itself to an holophytic or plant-like
mode of nutrition. Nevertheless the Acoela, as a group, are carnivorous,
feeding upon Diatoms, Copepoda, and small Rhabdocoela, the absence of a
digestive tract indeed being probably more apparent than real.[63]
The Rhabdocoela live under varied conditions. One form, Prorhynchus
sphyrocephalus, has been found among plants far from water in the
neighbourhood of Leyden, by De Man.[64] With this exception the group is
purely aquatic, and though a few genera and even individuals of the same
species occur both in salt and fresh water, whole sub-families and genera
are either marine or paludicolous. Among the latter, Mesostoma, Castrada,
Vortex, and Derostoma are common in brooks and ponds, especially at
certain times, often only for one month (May or June) in the year. Species
of Macrostoma, Stenostoma, and Microstoma are also abundant in similar
places. The two latter occur in chains formed by fission; but the sexual
individuals (which are of distinct sexes, contrary to the usual hermaphrodite
condition of Flat Worms) only appear at stated times and are not well
known. A large number of genera are purely marine, and one family, the
Proboscidae (distinguished by having the anterior end invaginated by
special muscles and converted into a sensory organ), is entirely so. The
most cursory examination of littoral weeds reveals species of
Macrorhynchus, Acrorhynchus, Promesostoma, Byrsophlebs, and
Proxenetes, the character of which may be gathered from von Graffs great
monograph, or from Gamble's paper on the "British Marine Turbellaria."[65]
Much, however, still remains to be done before we possess an adequate idea
of the occurrence of this group on our coasts.
Page 58
Fig. 19.—Forms of Rhabdocoelida. A, Mesostoma tetragonum O. F. M. (Rhabdocoela),
× 10; B, Convoluta paradoxa Oe. (Acoela), × 10; C, Vorticeros auriculatum
O. F. M., × 6; D, Monotus fuscus Oe. (Alloeocoela), × 4. ap, Adhesive papillae;
d, intestine; m, pharynx; ot, otolith; rh, rhabdites; te, testes; ut, uterus with eggs;
yg, yolk-glands; ♂, male, ♀, female genital pores. (A after Braun.)
Some Rhabdocoels are parasitic. Fecampia erythrocephala, which occurs in
the lacunar spaces and alimentary canal of young shore crabs (Carcinus
maenas), is a white cylindrical animal ¼ inch long, with a red snout. After
attaining maturity it works its way out of the crab and encysts under stones,
forming a pyriform mass in shape like a "Prince Rupert's drop." Within this
case the eggs develop, and the young probably emerge through the open
narrow end of the hard white tube, but how they reach the crab is not
known. Graffilla muricicola is found in the kidney of Murex brandaris and
M. trunculus, at Naples and Trieste; G. tethydicola in the foot of Tethys.
Anoplodium parasiticum occurs among the muscles which attach the cloaca
of Holothuria tubulosa to the body-wall; and A. schneideri occurs in the
sea-cucumber, Stichopus variegatus. These are truly parasitic forms,
constituting a special sub-family. They have no rhabdites in the skin; the
nervous system and sense-organs are only slightly developed; and the
pharynx has undergone a notable reduction in relation to the simpler mode
of obtaining nourishment. Other cases of association between certain
Rhabdocoels (closely allied to, if not identical with, certain free-living
species) and Lamellibranchs or Sea-urchins, are, however, of another kind.
Thus on the gills or in the mantle cavity of species of Mytilus, Cyprina,
Tellina, and upon the test of Clypeaster, such forms as Enterostoma mytili,
Acmostoma cyprinae, and Provortex tellinae have been found. But it is
probable that these Turbellaria here obtain merely a temporary shelter and
possibly a supply of the food of the mussel or sea-urchin.
× 10; B, Convoluta paradoxa Oe. (Acoela), × 10; C, Vorticeros auriculatum
O. F. M., × 6; D, Monotus fuscus Oe. (Alloeocoela), × 4. ap, Adhesive papillae;
d, intestine; m, pharynx; ot, otolith; rh, rhabdites; te, testes; ut, uterus with eggs;
yg, yolk-glands; ♂, male, ♀, female genital pores. (A after Braun.)
Some Rhabdocoels are parasitic. Fecampia erythrocephala, which occurs in
the lacunar spaces and alimentary canal of young shore crabs (Carcinus
maenas), is a white cylindrical animal ¼ inch long, with a red snout. After
attaining maturity it works its way out of the crab and encysts under stones,
forming a pyriform mass in shape like a "Prince Rupert's drop." Within this
case the eggs develop, and the young probably emerge through the open
narrow end of the hard white tube, but how they reach the crab is not
known. Graffilla muricicola is found in the kidney of Murex brandaris and
M. trunculus, at Naples and Trieste; G. tethydicola in the foot of Tethys.
Anoplodium parasiticum occurs among the muscles which attach the cloaca
of Holothuria tubulosa to the body-wall; and A. schneideri occurs in the
sea-cucumber, Stichopus variegatus. These are truly parasitic forms,
constituting a special sub-family. They have no rhabdites in the skin; the
nervous system and sense-organs are only slightly developed; and the
pharynx has undergone a notable reduction in relation to the simpler mode
of obtaining nourishment. Other cases of association between certain
Rhabdocoels (closely allied to, if not identical with, certain free-living
species) and Lamellibranchs or Sea-urchins, are, however, of another kind.
Thus on the gills or in the mantle cavity of species of Mytilus, Cyprina,
Tellina, and upon the test of Clypeaster, such forms as Enterostoma mytili,
Acmostoma cyprinae, and Provortex tellinae have been found. But it is
probable that these Turbellaria here obtain merely a temporary shelter and
possibly a supply of the food of the mussel or sea-urchin.
Page 59
The Alloeocoela afford a well-established case of association. Monotus
fuscus (Fig. 19, D), an abundant, active, elongated animal, lives on our
coasts in the upper part of the littoral zone among Patella, Balanus, and
sometimes Chiton. When the tide is low, the Monotus, to obtain moisture
and darkness, creeps between the mantle-folds of these animals, where it
may readily be found. Upon the return of the tide it leaves its retreat and
creeps or swims about freely. Other Alloeocoela collect in great numbers in
tufts of red-seaweeds (Florideae). By placing such tufts in vessels, the sea-
water, especially as darkness sets in, begins to swarm with Cylindrostoma
4-oculatum, species of Enterostoma and Plagiostoma; P. vittatum, with
three violet bands across the white body, being a particularly obvious form.
Vorticeros auriculatum (Fig. 19, C), another abundant species, is
remarkable for the long tentacles which can be completely withdrawn, and
in this condition it completely resembles a Plagiostoma.
The presence of a species (P. lemani) of the characteristically marine genus
Plagiostoma, in the Lake of Geneva, and in one or two other Swiss lakes, at
depths varying from 1 to 150 fathoms, is very interesting, and is perhaps the
only well-established case of the survival of a once marine Rhabdocoelid
under changed conditions. Plagiostoma lemani is by far the biggest of the
group to which it belongs, being over half an inch in length. It is usually
found in fine mud, sometimes among Chara hispida, and has the general
appearance of an inactive white slug. We are indebted to Forel and
Duplessis for the discovery of this species, and also of Otomesostoma
morgiense, a Mesostoma with an otolith, dredged in 10 to 50 fathoms in the
Lake of Geneva, the Lake of Zürich, and found recently also by Zacharias
in the Riesengebirge. The genus Bothrioplana, first found by Braun in the
water-pipes of Dorpat, has been carefully investigated by Vejdovsky,[66]
who places it in a special family, Bothrioplanidae, among the Alloeocoela.
One species has recently been found near Manchester.
A comprehensive survey of the Rhabdocoelida shows that, with the chief
exception of the Proboscidae, the more lowly organised forms, the Acoela
and Alloeocoela, are marine, whereas the fresh-water forms are in most
cases the most highly organised genera (Mesostoma, Vortex). But
Macrorhynchus helgolandicus, though minute (1.5-2 mm. long), has a more
fuscus (Fig. 19, D), an abundant, active, elongated animal, lives on our
coasts in the upper part of the littoral zone among Patella, Balanus, and
sometimes Chiton. When the tide is low, the Monotus, to obtain moisture
and darkness, creeps between the mantle-folds of these animals, where it
may readily be found. Upon the return of the tide it leaves its retreat and
creeps or swims about freely. Other Alloeocoela collect in great numbers in
tufts of red-seaweeds (Florideae). By placing such tufts in vessels, the sea-
water, especially as darkness sets in, begins to swarm with Cylindrostoma
4-oculatum, species of Enterostoma and Plagiostoma; P. vittatum, with
three violet bands across the white body, being a particularly obvious form.
Vorticeros auriculatum (Fig. 19, C), another abundant species, is
remarkable for the long tentacles which can be completely withdrawn, and
in this condition it completely resembles a Plagiostoma.
The presence of a species (P. lemani) of the characteristically marine genus
Plagiostoma, in the Lake of Geneva, and in one or two other Swiss lakes, at
depths varying from 1 to 150 fathoms, is very interesting, and is perhaps the
only well-established case of the survival of a once marine Rhabdocoelid
under changed conditions. Plagiostoma lemani is by far the biggest of the
group to which it belongs, being over half an inch in length. It is usually
found in fine mud, sometimes among Chara hispida, and has the general
appearance of an inactive white slug. We are indebted to Forel and
Duplessis for the discovery of this species, and also of Otomesostoma
morgiense, a Mesostoma with an otolith, dredged in 10 to 50 fathoms in the
Lake of Geneva, the Lake of Zürich, and found recently also by Zacharias
in the Riesengebirge. The genus Bothrioplana, first found by Braun in the
water-pipes of Dorpat, has been carefully investigated by Vejdovsky,[66]
who places it in a special family, Bothrioplanidae, among the Alloeocoela.
One species has recently been found near Manchester.
A comprehensive survey of the Rhabdocoelida shows that, with the chief
exception of the Proboscidae, the more lowly organised forms, the Acoela
and Alloeocoela, are marine, whereas the fresh-water forms are in most
cases the most highly organised genera (Mesostoma, Vortex). But
Macrorhynchus helgolandicus, though minute (1.5-2 mm. long), has a more
Page 60
complex structure[67] than any other species of the specialised marine genus
to which it belongs, and is a remarkable instance of great complexity being
associated with small size.
Reproduction.—The Rhabdocoelida present the greatest diversity in the
development of the reproductive system. The Acoela and Alloeocoela have
the simplest arrangement. Scattered testes, often without a distinct
membrane, form the spermatozoa, which in most cases wander into
parenchymatous spaces, but in Monoporus rubropunctatus and
Bothrioplana, into distinct vasa deferentia. In both groups a protrusible
penis opens independently to the exterior, and may be simply muscular or
provided with a chitinous armature. Two ovaries are present, and the
oviducts, if distinct, are continuations of the ovarian membrane. In most
forms a "bursa seminalis," which receives the spermatozoa of another
individual, is appended to the female genital canal. In many of the
Alloeocoela, however, a portion of the ovary is sterile, and its cells, forming
a yolk-gland, feed the fertile portion, the whole structure being then spoken
of as a germ-yolk-gland. In many others (Monotidae) this sterile part has
become an independent yolk-gland, which communicates by yolk-ducts
with the oviducts. The Acoela form no egg-case, the body of the parent
becoming a bag for the ova, which elaborate their own food-yolk. The
Alloeocoela lay hard-shelled eggs, which are produced in Bothrioplana and
Automolos by the activity and interaction of reproductive organs,
resembling closely those of certain Triclads.[68]
The Rhabdocoela exhibit every stage in the development of a complex
reproductive system, from the simple ovaries and testes of a Microstoma or
Macrostoma, to the intricate system of ducts and glands of a
Macrorhynchus (Proboscidae), in which there is still much to be made out.
The complications of the copulatory organs chiefly arise from the way in
which the spermatozoa are brought into contact with a nutritive prostatic
fluid, or are formed into spermatophores; and also from the penial armature,
which is often very complex, and may consist of a curved chitinoid hook or
a coiled loop (Promesostoma), of hooks (Proboscidae), or of an intricate
arrangement of plates (Proxenetes); or the penis may take on a complex
corkscrew-like form (Pseudorhynchus). The (frequently armed) female
to which it belongs, and is a remarkable instance of great complexity being
associated with small size.
Reproduction.—The Rhabdocoelida present the greatest diversity in the
development of the reproductive system. The Acoela and Alloeocoela have
the simplest arrangement. Scattered testes, often without a distinct
membrane, form the spermatozoa, which in most cases wander into
parenchymatous spaces, but in Monoporus rubropunctatus and
Bothrioplana, into distinct vasa deferentia. In both groups a protrusible
penis opens independently to the exterior, and may be simply muscular or
provided with a chitinous armature. Two ovaries are present, and the
oviducts, if distinct, are continuations of the ovarian membrane. In most
forms a "bursa seminalis," which receives the spermatozoa of another
individual, is appended to the female genital canal. In many of the
Alloeocoela, however, a portion of the ovary is sterile, and its cells, forming
a yolk-gland, feed the fertile portion, the whole structure being then spoken
of as a germ-yolk-gland. In many others (Monotidae) this sterile part has
become an independent yolk-gland, which communicates by yolk-ducts
with the oviducts. The Acoela form no egg-case, the body of the parent
becoming a bag for the ova, which elaborate their own food-yolk. The
Alloeocoela lay hard-shelled eggs, which are produced in Bothrioplana and
Automolos by the activity and interaction of reproductive organs,
resembling closely those of certain Triclads.[68]
The Rhabdocoela exhibit every stage in the development of a complex
reproductive system, from the simple ovaries and testes of a Microstoma or
Macrostoma, to the intricate system of ducts and glands of a
Macrorhynchus (Proboscidae), in which there is still much to be made out.
The complications of the copulatory organs chiefly arise from the way in
which the spermatozoa are brought into contact with a nutritive prostatic
fluid, or are formed into spermatophores; and also from the penial armature,
which is often very complex, and may consist of a curved chitinoid hook or
a coiled loop (Promesostoma), of hooks (Proboscidae), or of an intricate
arrangement of plates (Proxenetes); or the penis may take on a complex
corkscrew-like form (Pseudorhynchus). The (frequently armed) female
Page 61
genital canal usually possesses a bursa seminalis for the fertilisation of the
eggs, but a receptaculum seminis or spermatheca may serve for the
reception, the bursa, for the lodgment of the spermatozoa of another
individual. The fertilised ovum is provided with a supply of food-yolk and
with a shell, which may be formed in a special diverticulum, the "uterus."
The development of these organs strains the resources of the animal to the
utmost, and in some Proboscidae the alimentary canal is squeezed out and
disintegrates, in order to make room for them.
A few Mesostoma (M. ehrenbergii, M. productum, M. lingua) produce two
kinds of eggs—thin- and thick-shelled. The latter are laid throughout the
summer, and lie dormant through winter. The young which hatch in spring
out of these "winter" eggs develop rapidly, and when only 7 to 8 mm. long
(i.e. one-third the size of the parent) already possess functional genital
organs; the penis, however, is rudimentary, and incapable of being used for
copulation. Hence it is probable that this stunted progeny self-fertilise their
thin-shelled or "summer" eggs. After the formation of these eggs the same
parent is said (Schneider[69]) to produce thick-shelled or winter eggs, but
however that may be, the first young which hatch from the thin-shelled ova
are produced in great numbers at a time (April to May) when food is
abundant. These grow rapidly to the full size, and then having attained
maturity, cross-fertilise one another's ova, which become encased in a thick
brown shell; and it is these numerous "winter" eggs that lie dormant
throughout the autumn and winter. Many Mesostoma, and practically all
other Rhabdocoela, however, produce only thick-shelled eggs, and in all
cases it is probable that to these many species owe their wide distribution,
the exact range of which is, however, unknown, as is also the means of
dispersal.
Classification of Rhabdocoelida.
ACOELA.
Family. Genus and British species.
eggs, but a receptaculum seminis or spermatheca may serve for the
reception, the bursa, for the lodgment of the spermatozoa of another
individual. The fertilised ovum is provided with a supply of food-yolk and
with a shell, which may be formed in a special diverticulum, the "uterus."
The development of these organs strains the resources of the animal to the
utmost, and in some Proboscidae the alimentary canal is squeezed out and
disintegrates, in order to make room for them.
A few Mesostoma (M. ehrenbergii, M. productum, M. lingua) produce two
kinds of eggs—thin- and thick-shelled. The latter are laid throughout the
summer, and lie dormant through winter. The young which hatch in spring
out of these "winter" eggs develop rapidly, and when only 7 to 8 mm. long
(i.e. one-third the size of the parent) already possess functional genital
organs; the penis, however, is rudimentary, and incapable of being used for
copulation. Hence it is probable that this stunted progeny self-fertilise their
thin-shelled or "summer" eggs. After the formation of these eggs the same
parent is said (Schneider[69]) to produce thick-shelled or winter eggs, but
however that may be, the first young which hatch from the thin-shelled ova
are produced in great numbers at a time (April to May) when food is
abundant. These grow rapidly to the full size, and then having attained
maturity, cross-fertilise one another's ova, which become encased in a thick
brown shell; and it is these numerous "winter" eggs that lie dormant
throughout the autumn and winter. Many Mesostoma, and practically all
other Rhabdocoela, however, produce only thick-shelled eggs, and in all
cases it is probable that to these many species owe their wide distribution,
the exact range of which is, however, unknown, as is also the means of
dispersal.
Classification of Rhabdocoelida.
ACOELA.
Family. Genus and British species.
Page 62
Proporidae Proporus venenosus O. Sch. Plymouth.
Monoporus rubropunctatus O. Sch. Plymouth.
Haplodiscus.
Aphanostomatidae Aphanostoma diversicolor Oe. Common.
A. elegans Jen. Plymouth.
Convoluta saliens Grff. Plymouth, Millport.
C. paradoxa Oe. (Fig. 19, B). Common. C.
flavibacillum Jen. Plymouth, Port Erin,
Millport.
Amphicoerus.
Polychoerus.
RHABDOCOELA.
Macrostomatidae Mecynostoma.
Macrostoma hystrix Oe. Stagnant water.
Omalostoma.
Microstomatidae Microstoma lineare Oe. Fresh water.
M. groelandicum Lev. Plymouth, among Ulva.
Stenostoma (Catenula) lemnae Dug. Near Cork.
S. leucops O. Sch. Common in fresh water.
Alaurina claparedii Grff. Skye.
Prorhynchidae Prorhynchus stagnalis M. Sch. In Devonshire
rivers.
Promesostoma marmoratum M. Sch. Common.
P. ovoideum O. Sch., P. agile Lev. Plymouth. P.
solea O. Sch. Plymouth, Port Erin. P.
lenticulatum O. Sch. Port Erin.
Mesostomatidae Byrsophlebs graffii Jen. Plymouth, Millport.
B. intermedia Grff. Millport, Port Erin.
Proxenetes flabellifer Jen. Millport, Plymouth,
Port Erin.
P. cochlear Grff. Millport.
Otomesostoma.
Mesostoma productum Leuck., M. lingua O. Sch.,
M. ehrenbergii O. Sch., M. tetragonum O. F. M.
Monoporus rubropunctatus O. Sch. Plymouth.
Haplodiscus.
Aphanostomatidae Aphanostoma diversicolor Oe. Common.
A. elegans Jen. Plymouth.
Convoluta saliens Grff. Plymouth, Millport.
C. paradoxa Oe. (Fig. 19, B). Common. C.
flavibacillum Jen. Plymouth, Port Erin,
Millport.
Amphicoerus.
Polychoerus.
RHABDOCOELA.
Macrostomatidae Mecynostoma.
Macrostoma hystrix Oe. Stagnant water.
Omalostoma.
Microstomatidae Microstoma lineare Oe. Fresh water.
M. groelandicum Lev. Plymouth, among Ulva.
Stenostoma (Catenula) lemnae Dug. Near Cork.
S. leucops O. Sch. Common in fresh water.
Alaurina claparedii Grff. Skye.
Prorhynchidae Prorhynchus stagnalis M. Sch. In Devonshire
rivers.
Promesostoma marmoratum M. Sch. Common.
P. ovoideum O. Sch., P. agile Lev. Plymouth. P.
solea O. Sch. Plymouth, Port Erin. P.
lenticulatum O. Sch. Port Erin.
Mesostomatidae Byrsophlebs graffii Jen. Plymouth, Millport.
B. intermedia Grff. Millport, Port Erin.
Proxenetes flabellifer Jen. Millport, Plymouth,
Port Erin.
P. cochlear Grff. Millport.
Otomesostoma.
Mesostoma productum Leuck., M. lingua O. Sch.,
M. ehrenbergii O. Sch., M. tetragonum O. F. M.
Page 63
(Fig. 19, A). All at Cambridge.
M. rostratum Ehr. Widely distributed. M.
viridatum M. Sch. Manchester. M. robertsonii
Grff., M. flavidum Grff. Both at Millport.
Bothromesostoma personatum O. Sch. Preston.
Castrada.
Proboscidae Pseudorhynchus bifidus M‘Int. Millport, St.
Andrews, Port Erin.
Acrorhynchus caledonicus Clap. Generally
distributed.
Macrorhynchus naegelii Köll., M. croceus Fabr.
Plymouth, Millport.
M. helgolandicus Metsch. West coast.
Gyrator hermaphroditus Ehrbg. St. Andrews. Also
common in fresh water.
Hyporhynchus armatus Jen. Plymouth, Port Erin.
H. penicillatus O. Sch. Plymouth.
Vorticidae Schultzia. Provortex balticus M. Sch. Generally
distributed.
P. affinis Jen., P. rubrobacillus Gamb. Plymouth.
Vortex truncatus Ehrbg. Abundant in fresh water.
V. armiger O. Sch. Millport (fresh water). V.
schmidtii Grff., V. millportianus Grff. Millport.
V. viridis M. Sch. Generally distributed.
Jensenia.
Opistoma.
Derostoma unipunctatum Oe. Edinburgh.
Graffilla.
Anoplodium.
Fecampia erythrocephala Giard. Plymouth, Port
Erin.
Solenopharyngidae Solenopharynx.
ALLOEOCOELA.
Plagiostomatidae Acmostoma. Plagiostoma dioicum Metsch., P.
elongatum Gamb., P. pseudomaculatum Gamb.,
M. rostratum Ehr. Widely distributed. M.
viridatum M. Sch. Manchester. M. robertsonii
Grff., M. flavidum Grff. Both at Millport.
Bothromesostoma personatum O. Sch. Preston.
Castrada.
Proboscidae Pseudorhynchus bifidus M‘Int. Millport, St.
Andrews, Port Erin.
Acrorhynchus caledonicus Clap. Generally
distributed.
Macrorhynchus naegelii Köll., M. croceus Fabr.
Plymouth, Millport.
M. helgolandicus Metsch. West coast.
Gyrator hermaphroditus Ehrbg. St. Andrews. Also
common in fresh water.
Hyporhynchus armatus Jen. Plymouth, Port Erin.
H. penicillatus O. Sch. Plymouth.
Vorticidae Schultzia. Provortex balticus M. Sch. Generally
distributed.
P. affinis Jen., P. rubrobacillus Gamb. Plymouth.
Vortex truncatus Ehrbg. Abundant in fresh water.
V. armiger O. Sch. Millport (fresh water). V.
schmidtii Grff., V. millportianus Grff. Millport.
V. viridis M. Sch. Generally distributed.
Jensenia.
Opistoma.
Derostoma unipunctatum Oe. Edinburgh.
Graffilla.
Anoplodium.
Fecampia erythrocephala Giard. Plymouth, Port
Erin.
Solenopharyngidae Solenopharynx.
ALLOEOCOELA.
Plagiostomatidae Acmostoma. Plagiostoma dioicum Metsch., P.
elongatum Gamb., P. pseudomaculatum Gamb.,
Page 64
P. sagitta Ulj., P. caudatum Lev., P.
siphonophorum O. Sch., P. ochroleucum Grff.
All at Plymouth.
P. sulphureum Grff. Port Erin. P. vittatum F. and
Leuck. Millport, Plymouth, Port Erin. P. koreni
Jen. Plymouth, Millport. P. girardi O. Sch.
Plymouth, Port Erin, Valencia.
Vorticeros auriculatum O. F. M. (Fig. 19, C). Port
Erin, Plymouth.
V. luteum Grff. Plymouth.
Enterostoma austriacum Grff. Plymouth, Port
Erin.
E. fingalianum Clap. Skye, Plymouth. E. coecum
Grff. Millport.
Allostoma pallidum van Ben. Millport.
Cylindrostoma 4-oculatum Leuck. Skye, Millport,
Plymouth.
C. inerme Hall, C. elongatum Lev. Plymouth.
Monoophorum striatum Grff. Plymouth.
Bothrioplanidae Bothrioplana.
Bothrioplana sp.? Manchester.
Otoplana.
Monotidae Monotus lineatus O. F. M., M. fuscus Oe. (Fig. 19,
D). Both common littoral forms.
M. albus Lev. Plymouth.
Automolos unipunctatus Oe. Skye, St. Andrews,
Plymouth.
A. horridus Gamb., A. ophiocephalus O. Sch.
Plymouth.
CHAPTER II
TREMATODA
siphonophorum O. Sch., P. ochroleucum Grff.
All at Plymouth.
P. sulphureum Grff. Port Erin. P. vittatum F. and
Leuck. Millport, Plymouth, Port Erin. P. koreni
Jen. Plymouth, Millport. P. girardi O. Sch.
Plymouth, Port Erin, Valencia.
Vorticeros auriculatum O. F. M. (Fig. 19, C). Port
Erin, Plymouth.
V. luteum Grff. Plymouth.
Enterostoma austriacum Grff. Plymouth, Port
Erin.
E. fingalianum Clap. Skye, Plymouth. E. coecum
Grff. Millport.
Allostoma pallidum van Ben. Millport.
Cylindrostoma 4-oculatum Leuck. Skye, Millport,
Plymouth.
C. inerme Hall, C. elongatum Lev. Plymouth.
Monoophorum striatum Grff. Plymouth.
Bothrioplanidae Bothrioplana.
Bothrioplana sp.? Manchester.
Otoplana.
Monotidae Monotus lineatus O. F. M., M. fuscus Oe. (Fig. 19,
D). Both common littoral forms.
M. albus Lev. Plymouth.
Automolos unipunctatus Oe. Skye, St. Andrews,
Plymouth.
A. horridus Gamb., A. ophiocephalus O. Sch.
Plymouth.
CHAPTER II
TREMATODA
Page 65
CHARACTERS OF TREMATODES—HABITS AND STRUCTURE OF TREMATODA
ECTOPARASITICA (MONOGENEA)—LIFE-HISTORIES OF POLYSTOMUM INTEGERRIMUM,
DIPLOZOON PARADOXUM, AND GYRODACTYLUS ELEGANS—TREMATODA
ENDOPARASITICA (DIGENEA)—OCCURRENCE AND HABITS OF DIGENEA—LIFE-
HISTORY OF DISTOMUM MACROSTOMUM—DISTOMUM HEPATICUM AND ITS EFFECTS—
BILHARZIA HAEMATOBIA—BISEXUAL TREMATODES—TABLE OF HOSTS—
CLASSIFICATION.
From the Turbellaria we now pass on to a consideration of the second great
subdivision of the Platyhelminthes, the Trematodes or "flukes," of which
the "liver-fluke" is the best known, since it is one of the most dangerous
parasites that infest domestic animals.
It has been pointed out that the Polyclads, Triclads, and Rhabdocoels are
carnivorous, and that in each of these groups sporadic cases of parasitism
occur. In other words, when the prey is much larger than the Turbellarian,
the latter tends to become a parasite, and we can trace the development of
the parasitic habit from the gradual association of Turbellaria with
Ascidians, Crustacea, Molluscs, and Polyzoa merely for protective
purposes, through the adoption, not only of the body of the host for shelter,
but of its flesh for food; though it is only in some Rhabdocoels (Graffilla,
etc.) that there exists a degeneration corresponding to the easier mode of
nutrition and simpler life. The Trematodes,[70] however, are wholly
parasitic, either on the outer surface, the gills, or internal organs of their
host, which is almost always a Vertebrate. Some Trematodes lodge in the
mouth; others wander down the oesophagus into the stomach or intestine,
where they fix themselves to the mucous membrane. Again, others work
their way into the digestive glands by the ducts, and thus become further
and further removed from the external world, and more adapted to live in
the particular organs of that host in which they best flourish. The most
important result of the adoption of this internal habitat by endoparasitic
Trematodes is, however, seen in their life-history. If a liver-fluke were to
deposit its million or so of eggs in the bile-ducts of the sheep, and these
were to develop in situ, the host could not withstand the increased drain
upon its vital resources, and host and parasites would perish together. Hence
it is clear that the infection of a second host by Trematodes is highly
necessary, whether they be ectoparasitic, in which case the infection is
ECTOPARASITICA (MONOGENEA)—LIFE-HISTORIES OF POLYSTOMUM INTEGERRIMUM,
DIPLOZOON PARADOXUM, AND GYRODACTYLUS ELEGANS—TREMATODA
ENDOPARASITICA (DIGENEA)—OCCURRENCE AND HABITS OF DIGENEA—LIFE-
HISTORY OF DISTOMUM MACROSTOMUM—DISTOMUM HEPATICUM AND ITS EFFECTS—
BILHARZIA HAEMATOBIA—BISEXUAL TREMATODES—TABLE OF HOSTS—
CLASSIFICATION.
From the Turbellaria we now pass on to a consideration of the second great
subdivision of the Platyhelminthes, the Trematodes or "flukes," of which
the "liver-fluke" is the best known, since it is one of the most dangerous
parasites that infest domestic animals.
It has been pointed out that the Polyclads, Triclads, and Rhabdocoels are
carnivorous, and that in each of these groups sporadic cases of parasitism
occur. In other words, when the prey is much larger than the Turbellarian,
the latter tends to become a parasite, and we can trace the development of
the parasitic habit from the gradual association of Turbellaria with
Ascidians, Crustacea, Molluscs, and Polyzoa merely for protective
purposes, through the adoption, not only of the body of the host for shelter,
but of its flesh for food; though it is only in some Rhabdocoels (Graffilla,
etc.) that there exists a degeneration corresponding to the easier mode of
nutrition and simpler life. The Trematodes,[70] however, are wholly
parasitic, either on the outer surface, the gills, or internal organs of their
host, which is almost always a Vertebrate. Some Trematodes lodge in the
mouth; others wander down the oesophagus into the stomach or intestine,
where they fix themselves to the mucous membrane. Again, others work
their way into the digestive glands by the ducts, and thus become further
and further removed from the external world, and more adapted to live in
the particular organs of that host in which they best flourish. The most
important result of the adoption of this internal habitat by endoparasitic
Trematodes is, however, seen in their life-history. If a liver-fluke were to
deposit its million or so of eggs in the bile-ducts of the sheep, and these
were to develop in situ, the host could not withstand the increased drain
upon its vital resources, and host and parasites would perish together. Hence
it is clear that the infection of a second host by Trematodes is highly
necessary, whether they be ectoparasitic, in which case the infection is
Page 66
easily effected, when two hosts are in contact, by the adult worms, as well
as when they are apart, by free-swimming larvae. In endoparasitic
Trematodes it is brought about by the migration of the young to the outer
world, their entrance into a, usually, Invertebrate host and their asexual
multiplication within it, and the capture and deglutition of this
"intermediate host" by the final Vertebrate one. Within the latter the
immature parasites find out the organ in which their parents flourished, and
here they too grow and attain maturity. The chances of any one egg of an
endoparasitic Trematode producing eventually an adult are, therefore, far
less favourable than in the case of an ectoparasitic form. In other words,
while the former must lay a great number of small eggs, the latter need only
deposit a (comparatively) few large ones, and this fact has a corresponding
influence on the structure of the genitalia in the two cases. The Digenea,
which employ two hosts in a lifetime, have accordingly a different
generative mechanism from that of the Monogenea. The great need of the
latter is a powerful apparatus for adhering to the surface of the body of its
host; while the adaptations which the endoparasite requires are, in addition,
(1) protection against the solvent action of the glands of its host, (2) the
power of firm adhesion to a smooth internal surface, and (3) the ability not
only to produce a large quantity of spermatozoa and ova, but in the absence
of a fellow-parasite, to fertilise its own ova; and we find these conditions
abundantly satisfied.
Trematoda monogenea (ectoparasitica).
There are four subdivisions of the Monogenea:—
I. Temnocephalidae, with four to twelve tentacles, and one sucker
posteriorly (Fig. 20).
II. Tristomatidae, with two lateral, anteriorly-placed suckers. Oral suckers
are absent, a large posterior sucker is constant, and is often armed with
hooks (Fig. 22, C).
as when they are apart, by free-swimming larvae. In endoparasitic
Trematodes it is brought about by the migration of the young to the outer
world, their entrance into a, usually, Invertebrate host and their asexual
multiplication within it, and the capture and deglutition of this
"intermediate host" by the final Vertebrate one. Within the latter the
immature parasites find out the organ in which their parents flourished, and
here they too grow and attain maturity. The chances of any one egg of an
endoparasitic Trematode producing eventually an adult are, therefore, far
less favourable than in the case of an ectoparasitic form. In other words,
while the former must lay a great number of small eggs, the latter need only
deposit a (comparatively) few large ones, and this fact has a corresponding
influence on the structure of the genitalia in the two cases. The Digenea,
which employ two hosts in a lifetime, have accordingly a different
generative mechanism from that of the Monogenea. The great need of the
latter is a powerful apparatus for adhering to the surface of the body of its
host; while the adaptations which the endoparasite requires are, in addition,
(1) protection against the solvent action of the glands of its host, (2) the
power of firm adhesion to a smooth internal surface, and (3) the ability not
only to produce a large quantity of spermatozoa and ova, but in the absence
of a fellow-parasite, to fertilise its own ova; and we find these conditions
abundantly satisfied.
Trematoda monogenea (ectoparasitica).
There are four subdivisions of the Monogenea:—
I. Temnocephalidae, with four to twelve tentacles, and one sucker
posteriorly (Fig. 20).
II. Tristomatidae, with two lateral, anteriorly-placed suckers. Oral suckers
are absent, a large posterior sucker is constant, and is often armed with
hooks (Fig. 22, C).
Page 67
III. Polystomatidae, with, usually, two oral suckers and a posteriorly-placed
adhesive disc armed with suckers and hooks (Figs. 23 and 24).
IV. Gyrodactylidae (Fig. 29).
Habits and Structure of Ectoparasitic Trematodes.
I. Temnocephalidae.—These interesting forms, of which a good account has
lately been written by Haswell,[71] occur on the surface (rarely in the
branchial chamber) of fresh-water crayfish and crabs in Australasia, the
Malay Archipelago, Madagascar, and Chili. Others have been found on the
carapace of a fresh-water tortoise, and in the branchial chamber of the
mollusc Ampullaria from Brazil. Wood-Mason discovered others, again, in
bottles containing spirit-specimens of Indian fish. Temnocephala is rarely
more than a quarter of an inch long, and looks like a minute Cephalopod or
a broad flattened Hydra. By the ventral sucker each species adheres to its
own particular host, the tentacles being used as an anterior sucker for
"looping" movements. The food, consisting of Entomostraca, Rotifera, and
Diatoms, is first swallowed whole by the large pharynx (Fig. 20, ph), which
can be protruded through the ventrally-placed mouth, and is then received
into a simple lobed intestine (d). The skin, especially on the surface of the
tentacles, is provided here and there with patches of cilia borne by the
cellular epidermis,—the only undoubted case of external cilia occurring in
an adult Trematode. Minute rhabdites formed in special gland-cells, occur
plentifully on the tentacles, and are another distinctly Turbellarian feature.
The excretory system is peculiar (Fig. 21). Fine ducts proceed from the
various organs of the body, and open to the exterior by means of a pair of
contractile sacs placed on the dorsal surface. Each sac is a single cell, and
within it not one merely, but several "flames," or bunches of rhythmically
contractile cilia, are present. These are placed on the course of excessively
fine canals, which perforate the protoplasm of this cell. The terminal
branches of the excretory canals end in branched cells, apparently devoid of
"flames."
adhesive disc armed with suckers and hooks (Figs. 23 and 24).
IV. Gyrodactylidae (Fig. 29).
Habits and Structure of Ectoparasitic Trematodes.
I. Temnocephalidae.—These interesting forms, of which a good account has
lately been written by Haswell,[71] occur on the surface (rarely in the
branchial chamber) of fresh-water crayfish and crabs in Australasia, the
Malay Archipelago, Madagascar, and Chili. Others have been found on the
carapace of a fresh-water tortoise, and in the branchial chamber of the
mollusc Ampullaria from Brazil. Wood-Mason discovered others, again, in
bottles containing spirit-specimens of Indian fish. Temnocephala is rarely
more than a quarter of an inch long, and looks like a minute Cephalopod or
a broad flattened Hydra. By the ventral sucker each species adheres to its
own particular host, the tentacles being used as an anterior sucker for
"looping" movements. The food, consisting of Entomostraca, Rotifera, and
Diatoms, is first swallowed whole by the large pharynx (Fig. 20, ph), which
can be protruded through the ventrally-placed mouth, and is then received
into a simple lobed intestine (d). The skin, especially on the surface of the
tentacles, is provided here and there with patches of cilia borne by the
cellular epidermis,—the only undoubted case of external cilia occurring in
an adult Trematode. Minute rhabdites formed in special gland-cells, occur
plentifully on the tentacles, and are another distinctly Turbellarian feature.
The excretory system is peculiar (Fig. 21). Fine ducts proceed from the
various organs of the body, and open to the exterior by means of a pair of
contractile sacs placed on the dorsal surface. Each sac is a single cell, and
within it not one merely, but several "flames," or bunches of rhythmically
contractile cilia, are present. These are placed on the course of excessively
fine canals, which perforate the protoplasm of this cell. The terminal
branches of the excretory canals end in branched cells, apparently devoid of
"flames."
Page 68
Fig. 20.—Temnocephala novae-zealandiae Has. × 10. Ventral view to show the
digestive and reproductive systems. (After Haswell.)
Fig. 21.—The same from the dorsal surface, to show the excretory system (double line),
and the nervous system (black and shaded). (After Haswell.)
d, Intestine; dln, dorso-lateral nerve; dn, dorsal nerve; ex.o, excretory aperture on dorsal
surface; ex.s, terminal excretory sac; m, mouth; ov, ovary; ovd, oviduct; ph,
pharynx; rh, rhabdites; rh.c, cells in which the rhabdites are formed; rv, yolk
receptacle; sc, sucker; sh, shell-gland; te, testes; ut, uterus; vg, vagina; vn, ventral
nerve; vs, vesicula seminalis; yd, yolk-duct; yg, yolk-gland. ♀ , ♂ , common
genital pore.
The reproductive system is very similar to that of certain Rhabdocoels. An
armed penis and the female genital duct open into a genital atrium, and this
by a single aperture (♀, ♂, Fig. 20) to the exterior. The fertilised ovum and
yolk are enclosed in a stalked shell formed in the uterus.
The interest and importance of the Temnocephalidae lies in the fact that
they are almost as much Turbellaria as Trematodes. In habits, in the
character of the skin, the muscular, digestive, and reproductive systems,
they find their nearest allies in Rhabdocoels (Vorticidae). But in the
excretory and nervous systems, the latter composed of two dorsal, two
lateral, and two ventral trunks all connected together (Fig. 21), they are
Tristomid Trematodes. Thus they may fitly connect an account of the two
great groups.
digestive and reproductive systems. (After Haswell.)
Fig. 21.—The same from the dorsal surface, to show the excretory system (double line),
and the nervous system (black and shaded). (After Haswell.)
d, Intestine; dln, dorso-lateral nerve; dn, dorsal nerve; ex.o, excretory aperture on dorsal
surface; ex.s, terminal excretory sac; m, mouth; ov, ovary; ovd, oviduct; ph,
pharynx; rh, rhabdites; rh.c, cells in which the rhabdites are formed; rv, yolk
receptacle; sc, sucker; sh, shell-gland; te, testes; ut, uterus; vg, vagina; vn, ventral
nerve; vs, vesicula seminalis; yd, yolk-duct; yg, yolk-gland. ♀ , ♂ , common
genital pore.
The reproductive system is very similar to that of certain Rhabdocoels. An
armed penis and the female genital duct open into a genital atrium, and this
by a single aperture (♀, ♂, Fig. 20) to the exterior. The fertilised ovum and
yolk are enclosed in a stalked shell formed in the uterus.
The interest and importance of the Temnocephalidae lies in the fact that
they are almost as much Turbellaria as Trematodes. In habits, in the
character of the skin, the muscular, digestive, and reproductive systems,
they find their nearest allies in Rhabdocoels (Vorticidae). But in the
excretory and nervous systems, the latter composed of two dorsal, two
lateral, and two ventral trunks all connected together (Fig. 21), they are
Tristomid Trematodes. Thus they may fitly connect an account of the two
great groups.
Page 69
Fig. 22.—A, Nematobothrium filarina van Bened. Nat. size. Two individuals (a and b)
are found together, encysted on the branchial chamber of the Tunny. B, Udonella
caligorum Johns. A Tristomid, several of which are attached to the ovary of a
Copepod (Caligus), itself a parasite on the gills of the Hake. × 8. C, Epibdella
hippoglossi O. F. M. A Tristomid found on the body of the Halibut. Nat. size. m,
Mouth; ms, lateral suckers; ov, ovary; ps, posterior sucker; te, testes. (All after P.
J. van Beneden.)
II. Tristomatidae and III. Polystomatidae.[72]—The members of these
families are found on the body, or attached to the gills, of fresh-water and
marine fishes. The edible and inedible fish of our coasts have each their
particular ectoparasitic Trematodes; while the Minnows, Sticklebacks, and
Miller's Thumbs of streams and ponds are attacked by Diplozoon,
Gyrodactylus, and other forms. The aquatic Amphibia also harbour a
number. Polystomum integerrimum is common in the bladder of Frogs,
where it leads a practically aquatic life. Other species of Polystomum
inhabit the buccal and nasal cavities of certain Chelonia, but naturally no
terrestrial Vertebrates are infested externally by these Trematodes. The
blood and epithelia of the host are sucked, and to this end the pharynx has
frequently a chitinous armature to aid in the abrasion or inflammation of the
tissues upon which the parasite feeds. In the case of a Sturgeon attacked by
Nitzschia elongata, a Tristomid, the mouth of the host appeared to be highly
inflamed by these attacks (v. Baer).
are found together, encysted on the branchial chamber of the Tunny. B, Udonella
caligorum Johns. A Tristomid, several of which are attached to the ovary of a
Copepod (Caligus), itself a parasite on the gills of the Hake. × 8. C, Epibdella
hippoglossi O. F. M. A Tristomid found on the body of the Halibut. Nat. size. m,
Mouth; ms, lateral suckers; ov, ovary; ps, posterior sucker; te, testes. (All after P.
J. van Beneden.)
II. Tristomatidae and III. Polystomatidae.[72]—The members of these
families are found on the body, or attached to the gills, of fresh-water and
marine fishes. The edible and inedible fish of our coasts have each their
particular ectoparasitic Trematodes; while the Minnows, Sticklebacks, and
Miller's Thumbs of streams and ponds are attacked by Diplozoon,
Gyrodactylus, and other forms. The aquatic Amphibia also harbour a
number. Polystomum integerrimum is common in the bladder of Frogs,
where it leads a practically aquatic life. Other species of Polystomum
inhabit the buccal and nasal cavities of certain Chelonia, but naturally no
terrestrial Vertebrates are infested externally by these Trematodes. The
blood and epithelia of the host are sucked, and to this end the pharynx has
frequently a chitinous armature to aid in the abrasion or inflammation of the
tissues upon which the parasite feeds. In the case of a Sturgeon attacked by
Nitzschia elongata, a Tristomid, the mouth of the host appeared to be highly
inflamed by these attacks (v. Baer).
Page 70
Fig. 23.—Octobothrium merlangi Kuhn, from the gills of the whiting, × 8. int,
Intestine; ms, mouth; sc suckers with chitinoid armature; yk yolk-glands. (After
v. Nordmann.)
The suckers, in the two families under consideration, vary in number and
complexity. There is always a powerful apparatus at the hinder end of the
body securing the Trematode firmly to the slimy body or gills of its host,
and, usually in the Polystomatidae, a pair of suckers at the sides of the
mouth accessory to the pumping action of the pharynx. In Axine, and to a
less extent in Octobothrium (Fig. 23), the suckers are strengthened by a
complex hingework of chitinoid bars or hooks, which serve as insertions for
the muscles of the suckers, and thus increase their efficiency.
The mouth is invariably present just beneath the anterior end of the body. It
leads into a muscular, pumping pharynx (Fig. 24, ph), and this into a
bifurcated intestine which ends blindly. The two openings of the excretory
system lie on the dorsal surface (as in Temnocephala), and the excretory
canals branch through the substance of the body, ending usually in "flame-
cells." The nervous system is highly developed, and resembles that of
Temnocephala (Fig. 21) in detail. Upon the brain one or even two pairs of
eye-spots are present in the larvae, and may persist throughout life. Tactile
setae occur in Sphyranura, a parasite of the North American Amphibian
Necturus, but a cellular epidermis is apparently rendered impossible,
perhaps from the nature of the mucus in which the body is bathed, or to the
attempts of the host to free itself from these parasites; and hence an
investing membrane is present, which morphologically is either a modified
epithelium, or a cuticle formed by the glandular secretion of the
parenchyma.
Intestine; ms, mouth; sc suckers with chitinoid armature; yk yolk-glands. (After
v. Nordmann.)
The suckers, in the two families under consideration, vary in number and
complexity. There is always a powerful apparatus at the hinder end of the
body securing the Trematode firmly to the slimy body or gills of its host,
and, usually in the Polystomatidae, a pair of suckers at the sides of the
mouth accessory to the pumping action of the pharynx. In Axine, and to a
less extent in Octobothrium (Fig. 23), the suckers are strengthened by a
complex hingework of chitinoid bars or hooks, which serve as insertions for
the muscles of the suckers, and thus increase their efficiency.
The mouth is invariably present just beneath the anterior end of the body. It
leads into a muscular, pumping pharynx (Fig. 24, ph), and this into a
bifurcated intestine which ends blindly. The two openings of the excretory
system lie on the dorsal surface (as in Temnocephala), and the excretory
canals branch through the substance of the body, ending usually in "flame-
cells." The nervous system is highly developed, and resembles that of
Temnocephala (Fig. 21) in detail. Upon the brain one or even two pairs of
eye-spots are present in the larvae, and may persist throughout life. Tactile
setae occur in Sphyranura, a parasite of the North American Amphibian
Necturus, but a cellular epidermis is apparently rendered impossible,
perhaps from the nature of the mucus in which the body is bathed, or to the
attempts of the host to free itself from these parasites; and hence an
investing membrane is present, which morphologically is either a modified
epithelium, or a cuticle formed by the glandular secretion of the
parenchyma.
Page 71
Fig. 24.—Polystomum integerrimum Fröh., from the bladder of the Frog, and seen from
the ventral surface. The alimentary canal is black, the white dots upon it being
the yolk-glands, dvi, Ductus vitello-intestinalis (probably homologous with the
Laurer's canal or "vagina" of Digenea); eh, hooks of sucking disc; int, intestine;
m, mouth; ov, ovary; pe, penis; ph, pharynx; sc, suckers with an embryonic hook
persisting in each; te, testes; ut, uterus with eggs; vag, left vagina; vd, vas
deferens; yd, yolk-duct; yg, yolk-glands; ♂ ♀ , common genital aperture.
(Modified from Zeller.) × 8.
The reproductive organs of the Polystomatidae may be understood from
Figs. 24, 27, and 28. At the point of union of the oviduct (Fig. 28, ovd), the
vitelline ducts (yd), and the commencement of the uterus (ut), a slender duct
is given off which opens into the intestine, and is known as the "vitello-
intestinal canal" (Fig. 24, dvi; Fig. 28, gic). This duct has apparently the
same relations as the "canal of Laurer" of Digenea,[73] except only that the
latter opens to the exterior directly. In connexion with this vitello-intestinal
canal a "vagina" is present, which in Polystomum and most Monogenea is
paired (Fig. 24, vag), in Diplozoon and in one or two other forms, however,
unpaired. The vagina receives the penis of another individual during
copulation (Fig. 26), and does not appear to have an homologue in the liver-
fluke or other Digenea.
the ventral surface. The alimentary canal is black, the white dots upon it being
the yolk-glands, dvi, Ductus vitello-intestinalis (probably homologous with the
Laurer's canal or "vagina" of Digenea); eh, hooks of sucking disc; int, intestine;
m, mouth; ov, ovary; pe, penis; ph, pharynx; sc, suckers with an embryonic hook
persisting in each; te, testes; ut, uterus with eggs; vag, left vagina; vd, vas
deferens; yd, yolk-duct; yg, yolk-glands; ♂ ♀ , common genital aperture.
(Modified from Zeller.) × 8.
The reproductive organs of the Polystomatidae may be understood from
Figs. 24, 27, and 28. At the point of union of the oviduct (Fig. 28, ovd), the
vitelline ducts (yd), and the commencement of the uterus (ut), a slender duct
is given off which opens into the intestine, and is known as the "vitello-
intestinal canal" (Fig. 24, dvi; Fig. 28, gic). This duct has apparently the
same relations as the "canal of Laurer" of Digenea,[73] except only that the
latter opens to the exterior directly. In connexion with this vitello-intestinal
canal a "vagina" is present, which in Polystomum and most Monogenea is
paired (Fig. 24, vag), in Diplozoon and in one or two other forms, however,
unpaired. The vagina receives the penis of another individual during
copulation (Fig. 26), and does not appear to have an homologue in the liver-
fluke or other Digenea.
Page 72
Fig. 25.—Eggs of Monogenea. A, Eggs of Encotylabe pagelli v. Ben.-Hesse; B, eggs of
Udonella pollachii v. Ben.-Hesse (with young forms just hatching out); C, egg of
Microcotyle labracis v. Ben.-Hesse. (After van Beneden and Hesse.) × 50.
Life-Histories of the Polystomatidae.[74]—Polystomum integerrimum.
After the mutual fertilisation of two individuals, the eggs are laid in the
water by the protrusion of the body of the parent through the urinary
aperture of the Frog. About 1000 eggs are laid in the spring at the rate of
100 a day for ten days. After about six weeks, the larva (.3 mm. long)
hatches out, and swims about freely by means of bands of large ciliated
cells (Fig. 26, A); but if it does not meet with a tadpole within twenty-four
hours, it dies. Should it, however, encounter one, the larva creeps along it in
a looping fashion until it approaches the opercular spout, or opening of the
branchial chamber, on the left side; into this it darts suddenly, fixes itself,
and throws off its cilia. Here it remains eight or ten weeks, feeding,
increasing in size, and forming the suckers from behind forwards. At the
time of the tadpole's metamorphosis, the young Polystomum works its way
down the pharynx into the oesophagus and along the intestine, till it reaches
and enters the opening of the bladder. Three years afterwards it becomes
mature.
Sometimes, however, Polystomum experiences another fate. The larvae
settling down on the external gills of a young, recently-hatched tadpole, and
obtaining a richer supply of blood than in the previous case, grow far more
rapidly, so that in five weeks they are mature, although still in the branchial
chamber of the tadpole. They do not then wander into the alimentary canal,
but usually, having discharged their eggs, die at the time of the tadpole's
metamorphosis. Still more interesting, however, is the difference between
the genitalia in these and in the normal Polystomum. In contrast with the
latter, these possess (1) one testis and a rudimentary penis; and their
Udonella pollachii v. Ben.-Hesse (with young forms just hatching out); C, egg of
Microcotyle labracis v. Ben.-Hesse. (After van Beneden and Hesse.) × 50.
Life-Histories of the Polystomatidae.[74]—Polystomum integerrimum.
After the mutual fertilisation of two individuals, the eggs are laid in the
water by the protrusion of the body of the parent through the urinary
aperture of the Frog. About 1000 eggs are laid in the spring at the rate of
100 a day for ten days. After about six weeks, the larva (.3 mm. long)
hatches out, and swims about freely by means of bands of large ciliated
cells (Fig. 26, A); but if it does not meet with a tadpole within twenty-four
hours, it dies. Should it, however, encounter one, the larva creeps along it in
a looping fashion until it approaches the opercular spout, or opening of the
branchial chamber, on the left side; into this it darts suddenly, fixes itself,
and throws off its cilia. Here it remains eight or ten weeks, feeding,
increasing in size, and forming the suckers from behind forwards. At the
time of the tadpole's metamorphosis, the young Polystomum works its way
down the pharynx into the oesophagus and along the intestine, till it reaches
and enters the opening of the bladder. Three years afterwards it becomes
mature.
Sometimes, however, Polystomum experiences another fate. The larvae
settling down on the external gills of a young, recently-hatched tadpole, and
obtaining a richer supply of blood than in the previous case, grow far more
rapidly, so that in five weeks they are mature, although still in the branchial
chamber of the tadpole. They do not then wander into the alimentary canal,
but usually, having discharged their eggs, die at the time of the tadpole's
metamorphosis. Still more interesting, however, is the difference between
the genitalia in these and in the normal Polystomum. In contrast with the
latter, these possess (1) one testis and a rudimentary penis; and their
Page 73
spermatozoa differ in structure and shape from those of the normal
Polystomum. (2) The vaginae are absent, a fact connected with the absence
of a functional copulatory organ. (3) In compensation for the loss of these, a
duct connects the single testis and the point of union of oviduct and yolk-
ducts, and by this self-fertilisation occurs. (4) The uterus is absent; the
"ootype" or duct into which the shell-gland opens, communicating directly
with the exterior. In (1) and (4) these aberrant Polystomum resemble P.
ocellatum, from the Tortoise Emys europaea.
Fig. 26.—Polystomum integerrimum. A, Free-swimming larva, seen from the ventral
surface. × 80. B, Two mature individuals in mutual coition attached to the
bladder of a Frog. × 5. (After Zeller.) d, Intestine; ex.o, excretory pore, dorsal in
position, seen here by transparency; ey, eye-spots; gl, frontal glands; m, mouth;
ph, pharynx; sd, adhering disc; vag, vagina.
Fig. 27.—A, Egg of Diplozoon paradoxum v. Nord., consisting of a shell enclosing ov,
the actual ovum, surrounded by yc, the yolk-cells; B, larva just hatched (× 125);
C, two Diporpa (I and II) about to unite; D, conjugation in progress but not yet
complete. dt, Dorsal papilla; e, eye; g, intestine; m, mouth; sc, ad-oral sucker; th,
spirally-wound thread attaching the egg to the gill of the Minnow; vs, ventral
sucker; (in D) I, I, one Diporpa, ventral view; II, II, the other, dorsal view. (After
Zeller.)
Polystomum. (2) The vaginae are absent, a fact connected with the absence
of a functional copulatory organ. (3) In compensation for the loss of these, a
duct connects the single testis and the point of union of oviduct and yolk-
ducts, and by this self-fertilisation occurs. (4) The uterus is absent; the
"ootype" or duct into which the shell-gland opens, communicating directly
with the exterior. In (1) and (4) these aberrant Polystomum resemble P.
ocellatum, from the Tortoise Emys europaea.
Fig. 26.—Polystomum integerrimum. A, Free-swimming larva, seen from the ventral
surface. × 80. B, Two mature individuals in mutual coition attached to the
bladder of a Frog. × 5. (After Zeller.) d, Intestine; ex.o, excretory pore, dorsal in
position, seen here by transparency; ey, eye-spots; gl, frontal glands; m, mouth;
ph, pharynx; sd, adhering disc; vag, vagina.
Fig. 27.—A, Egg of Diplozoon paradoxum v. Nord., consisting of a shell enclosing ov,
the actual ovum, surrounded by yc, the yolk-cells; B, larva just hatched (× 125);
C, two Diporpa (I and II) about to unite; D, conjugation in progress but not yet
complete. dt, Dorsal papilla; e, eye; g, intestine; m, mouth; sc, ad-oral sucker; th,
spirally-wound thread attaching the egg to the gill of the Minnow; vs, ventral
sucker; (in D) I, I, one Diporpa, ventral view; II, II, the other, dorsal view. (After
Zeller.)
Page 74
Fig. 28.—Hinder part of the body of Diplozoon paradoxum. The fusion of the two
Diporpa, where they come into contact, is now complete. They now cross each
other like an X, and are twisted, so that Diporpa I, in front of the point of fusion,
is seen from the dorsal surface; behind, from the ventral surface; and the reverse
is the case with Diporpa II. The compound animal is seen from the opposite
surface to that shown in Fig. 27, D. The digestive and excretory organs are
omitted. (After Zeller.) I Ant. dorsal, dorsal surface of Diporpa I, facing the
anterior end; I Post. ventral, ventral surface of Diporpa I, posterior end; and
similarly for II Ant. ventral and II Post. dorsal. d, Piece of the intestine showing
opening of, gic, vitello-intestinal canal; ov, ovary; ovd, point of union of female
genital ducts; sc, suckers; te, testis; ut (in Diporpa I), "ootype" or chamber into
which shell-glands open. This is continuous with the uterus (ut) of Diporpa I;
uto, ventral opening of uterus; vag, vagina, with vd, vas deferens, permanently
inserted into it through the genital pore; yd, yolk-ducts; yg, yolk-glands.
Diplozoon paradoxum.—The life-history of Diplozoon is unique. For
whereas the larvae of most animals grow up, each into a single adult, in
Diplozoon, of the few larvae that survive the dangers of their free-
swimming existence, only those become mature which conjugate
permanently with another individual. But although there are thus only half
as many adult Diplozoon as there were conjugating larvae (or Diporpa, as
they were called when they were considered distinct forms), yet the total
number of eggs produced is probably as great as if each larva became
individually mature.
Diporpa, where they come into contact, is now complete. They now cross each
other like an X, and are twisted, so that Diporpa I, in front of the point of fusion,
is seen from the dorsal surface; behind, from the ventral surface; and the reverse
is the case with Diporpa II. The compound animal is seen from the opposite
surface to that shown in Fig. 27, D. The digestive and excretory organs are
omitted. (After Zeller.) I Ant. dorsal, dorsal surface of Diporpa I, facing the
anterior end; I Post. ventral, ventral surface of Diporpa I, posterior end; and
similarly for II Ant. ventral and II Post. dorsal. d, Piece of the intestine showing
opening of, gic, vitello-intestinal canal; ov, ovary; ovd, point of union of female
genital ducts; sc, suckers; te, testis; ut (in Diporpa I), "ootype" or chamber into
which shell-glands open. This is continuous with the uterus (ut) of Diporpa I;
uto, ventral opening of uterus; vag, vagina, with vd, vas deferens, permanently
inserted into it through the genital pore; yd, yolk-ducts; yg, yolk-glands.
Diplozoon paradoxum.—The life-history of Diplozoon is unique. For
whereas the larvae of most animals grow up, each into a single adult, in
Diplozoon, of the few larvae that survive the dangers of their free-
swimming existence, only those become mature which conjugate
permanently with another individual. But although there are thus only half
as many adult Diplozoon as there were conjugating larvae (or Diporpa, as
they were called when they were considered distinct forms), yet the total
number of eggs produced is probably as great as if each larva became
individually mature.
Page 75
Fig. 29.—Gyrodactylus elegans v. Nord., from the fins of the Stickleback. (After
v. Nordmann.) × 125. emb, Embryo.
Diplozoon paradoxum lays its eggs on the gills of the Minnow, which it
frequently infests in great numbers. The ovum divides rapidly at the
expense of the yolk-cells, and in a fortnight a larva (.2 mm. long) of the
shape and complexity shown in Fig. 27, B, hatches out, which, however,
succumbs if it does not meet with a Minnow in five or six hours. Should it
survive, a dorsal papilla, a median ventral sucker, and a second pair of
posterior suckers develop. Thus the Diporpa stage is attained. These
Diporpa may acquire a third and even a fourth pair of suckers, and continue
to live three months, but they only develop and mature their reproductive
organs, if each conjugates with another Diporpa (Fig. 27, C, D), and this
only occurs in a small percentage of instances. Each grasps the dorsal
papilla of the other by its own ventral sucker, thus undergoing a certain
amount of torsion. Where the two bodies touch, complete fusion occurs,
and, as shown in Fig. 28, the united Diporpa (or Diplozoon, as the product
is now called) decussate, each forming one limb of the X-shaped
Diplozoon, within which the two sets of complex genitalia develop (Fig.
28).
IV. Gyrodactylidae.—Gyrodactylus (Fig. 29), the structure of which is in
many ways peculiar, produces one large egg at a time. An embryo, in which
the large and smaller hooks of the adhesive disc can be seen (emb),
develops from this egg while still within the body of the parent, and may
give rise to yet another generation within itself. The details of the process
have not, however, been well ascertained.
v. Nordmann.) × 125. emb, Embryo.
Diplozoon paradoxum lays its eggs on the gills of the Minnow, which it
frequently infests in great numbers. The ovum divides rapidly at the
expense of the yolk-cells, and in a fortnight a larva (.2 mm. long) of the
shape and complexity shown in Fig. 27, B, hatches out, which, however,
succumbs if it does not meet with a Minnow in five or six hours. Should it
survive, a dorsal papilla, a median ventral sucker, and a second pair of
posterior suckers develop. Thus the Diporpa stage is attained. These
Diporpa may acquire a third and even a fourth pair of suckers, and continue
to live three months, but they only develop and mature their reproductive
organs, if each conjugates with another Diporpa (Fig. 27, C, D), and this
only occurs in a small percentage of instances. Each grasps the dorsal
papilla of the other by its own ventral sucker, thus undergoing a certain
amount of torsion. Where the two bodies touch, complete fusion occurs,
and, as shown in Fig. 28, the united Diporpa (or Diplozoon, as the product
is now called) decussate, each forming one limb of the X-shaped
Diplozoon, within which the two sets of complex genitalia develop (Fig.
28).
IV. Gyrodactylidae.—Gyrodactylus (Fig. 29), the structure of which is in
many ways peculiar, produces one large egg at a time. An embryo, in which
the large and smaller hooks of the adhesive disc can be seen (emb),
develops from this egg while still within the body of the parent, and may
give rise to yet another generation within itself. The details of the process
have not, however, been well ascertained.
Page 76
Trematoda digenea (endoparasitica).
Occurrence and Habits of Digenea.—Endoparasitic Trematodes have
been found in almost all the organs of Vertebrate hosts excepting in the
nervous, skeletal, and reproductive systems. The alimentary canal, however,
is the most usual habitat. From the buccal cavity to the large intestine, or
even to the cloaca, its different regions are the resorts of various
Trematodes. No Digenea have been found in the mouth, pharynx, or
oesophagus of Mammals; but in Birds, Reptiles, Amphibia, and especially
in Fishes, these parts are largely affected. It is a striking fact that
Trematodes should occur in the stomach of (chiefly) large predaceous
fishes, such as the Pike, Sharks, the Angler-fish, and others, considering the
powerful digestive action of the gastric juice of these carnivores. The
peculiar nature of the defence which must be employed by the parasites
against this digestive action, becomes still more marked when it is
considered that if a Trematode normally living in the stomach of one host
be transferred to that of another, it is usually speedily digested, as is shown
(p. 65) in the case of Distomum macrostomum. From these considerations
the suggestion has been made that the cutaneous secretions of these
Trematodes must act, not only as a protection against digestive or other
ferments, but that the action in each case must be a specific one (Frenzel,
Braun).
Fig. 30.—Distomum luteum v. Baer (immature), to show the arrangement of the
excretory vessels. × 50. ex.o, Excretory aperture by which the terminal
contractile duct opens—the finer vessels end in flame-cells; int, intestine; m,
mouth-sucker; ph, pharynx; vs, ventral sucker. (After la Valette.)
It is, however, in the small intestine that most Trematodes occur, as the
examination of the common Frog[75] will readily demonstrate. Both this and
the edible Frog are attacked by a dozen Distomatidae, only a few of which,
Occurrence and Habits of Digenea.—Endoparasitic Trematodes have
been found in almost all the organs of Vertebrate hosts excepting in the
nervous, skeletal, and reproductive systems. The alimentary canal, however,
is the most usual habitat. From the buccal cavity to the large intestine, or
even to the cloaca, its different regions are the resorts of various
Trematodes. No Digenea have been found in the mouth, pharynx, or
oesophagus of Mammals; but in Birds, Reptiles, Amphibia, and especially
in Fishes, these parts are largely affected. It is a striking fact that
Trematodes should occur in the stomach of (chiefly) large predaceous
fishes, such as the Pike, Sharks, the Angler-fish, and others, considering the
powerful digestive action of the gastric juice of these carnivores. The
peculiar nature of the defence which must be employed by the parasites
against this digestive action, becomes still more marked when it is
considered that if a Trematode normally living in the stomach of one host
be transferred to that of another, it is usually speedily digested, as is shown
(p. 65) in the case of Distomum macrostomum. From these considerations
the suggestion has been made that the cutaneous secretions of these
Trematodes must act, not only as a protection against digestive or other
ferments, but that the action in each case must be a specific one (Frenzel,
Braun).
Fig. 30.—Distomum luteum v. Baer (immature), to show the arrangement of the
excretory vessels. × 50. ex.o, Excretory aperture by which the terminal
contractile duct opens—the finer vessels end in flame-cells; int, intestine; m,
mouth-sucker; ph, pharynx; vs, ventral sucker. (After la Valette.)
It is, however, in the small intestine that most Trematodes occur, as the
examination of the common Frog[75] will readily demonstrate. Both this and
the edible Frog are attacked by a dozen Distomatidae, only a few of which,
Page 77
however, are common to both hosts, and a number of Holostomatidae also
pass a stage of their development within these Amphibia. Some idea of the
extent to which animals, whose habits lead to infection, may be attacked by
Trematodes (to say nothing of Cestodes and Nematodes, which often occur
also) may be gathered from the fact that in dissecting a black stork,
Nathusius found several hundred Holostomum excavatum and about a
hundred Distomum ferox in the small intestine, twenty-two D. hians in the
oesophagus, five others in the stomach, and one D. echinatum in the
intestine. Snipe, Woodcock, Sandpipers, Dunlin, Gulls, Bittern, Geese, and
Wild Ducks are, to mention a few cases, greatly infested by members of this
group.
The following Trematodes have occurred in man[76]:—
Distomum hepaticum Abild.
" lanceolatum Mehlis.
" conjunctum Cobbold.
" spathulatum Leuckart (= D. sinense Cobb., D. japonicum R.
Blanch.).
" rathouisi Poir. (probably = D. crassum Busk, D. buskii
Lank.).
" heterophyes v. Sieb.
" pulmonale Bälz (= D. ringeri Cobb., D. westermanni
Kerb.).
" oculi humani Ammon (= D. ophthalmobium Dies.).
Monostomum lentis v. Nord.
Amphistomum hominis Lewis and M‘Connell.
Bilharzia haematobia Cobb.
Life-histories of the Digenea.—The classification of Trematodes
according to their life-histories, expressed in the divisions Monogenea and
Digenea, though a very useful one, breaks down entirely in the case of
certain forms. Thus the life-history of Gyrodactylus is probably digenetic
rather than monogenetic. Aspidogaster conchicola,[77] which lives in the
pericardial cavity of the fresh-water mussel (possibly the only case of a
Trematode becoming normally mature in an Invertebrate host, since other
pass a stage of their development within these Amphibia. Some idea of the
extent to which animals, whose habits lead to infection, may be attacked by
Trematodes (to say nothing of Cestodes and Nematodes, which often occur
also) may be gathered from the fact that in dissecting a black stork,
Nathusius found several hundred Holostomum excavatum and about a
hundred Distomum ferox in the small intestine, twenty-two D. hians in the
oesophagus, five others in the stomach, and one D. echinatum in the
intestine. Snipe, Woodcock, Sandpipers, Dunlin, Gulls, Bittern, Geese, and
Wild Ducks are, to mention a few cases, greatly infested by members of this
group.
The following Trematodes have occurred in man[76]:—
Distomum hepaticum Abild.
" lanceolatum Mehlis.
" conjunctum Cobbold.
" spathulatum Leuckart (= D. sinense Cobb., D. japonicum R.
Blanch.).
" rathouisi Poir. (probably = D. crassum Busk, D. buskii
Lank.).
" heterophyes v. Sieb.
" pulmonale Bälz (= D. ringeri Cobb., D. westermanni
Kerb.).
" oculi humani Ammon (= D. ophthalmobium Dies.).
Monostomum lentis v. Nord.
Amphistomum hominis Lewis and M‘Connell.
Bilharzia haematobia Cobb.
Life-histories of the Digenea.—The classification of Trematodes
according to their life-histories, expressed in the divisions Monogenea and
Digenea, though a very useful one, breaks down entirely in the case of
certain forms. Thus the life-history of Gyrodactylus is probably digenetic
rather than monogenetic. Aspidogaster conchicola,[77] which lives in the
pericardial cavity of the fresh-water mussel (possibly the only case of a
Trematode becoming normally mature in an Invertebrate host, since other
Page 78
species of Aspidogaster live in Chelonia), produces larvae which enter
another Anodonta and develop directly into the sexual form. In other words,
Aspidogaster, though structurally a digenetic form, possesses a life-history
which is direct and simple, i.e. monogenetic.
The Holostomatidae, which live in birds of prey and aquatic birds, give rise
to eggs from which a minute larva escapes. The fate of this aquatic larva is
not directly known, but in all probability after entering a host (Fish,
Amphibian, Mollusc), it undergoes a gradual change into what has long
been known as a Tetracotyle, from the frequent presence of four (sometimes
only three) adhering organs. Fig. 31 exhibits a species which is abundant in
the lens and vitreous humour of the eye of the Perch. Its further history is
not known, but presumably the Perch is presently devoured by the final host
in which the Diplostomum attains maturity. Thus the Holostomatidae are
"metastatic" (Leuckart), their (probably) direct development requiring the
presence of two hosts.[78]
The other Digenea, the life-histories of which are known, belong to the
Distomatidae and Amphistomatidae, and we may distinguish the steps by
which the complex life-history of the liver-fluke (Distomum hepaticum) has
been brought about, by a consideration of that of Distomum macrostomum.
Fig. 31.—Diplostomum (Tetracotyle) volvens. (After v. Nordmann.) × 130. cv,
Contractile excretory vesicle; d, intestine; e, calcareous bodies in excretory
tubules; ex.o, excretory aperture; gl, glandular adhesive body; ms, oral sucker;
ph, pharynx; vs, ventral sucker.
Distomum macrostomum.—This form occurs in the intestine of several
common Passerine birds. It is remarkable not only for the large oral sucker,
but also on account of the position of the common genital pore at the
hinder, and not as usual, at the anterior, end of the body (Fig. 32, A). The
eggs pass out through this pore, and are discharged with the bird's
another Anodonta and develop directly into the sexual form. In other words,
Aspidogaster, though structurally a digenetic form, possesses a life-history
which is direct and simple, i.e. monogenetic.
The Holostomatidae, which live in birds of prey and aquatic birds, give rise
to eggs from which a minute larva escapes. The fate of this aquatic larva is
not directly known, but in all probability after entering a host (Fish,
Amphibian, Mollusc), it undergoes a gradual change into what has long
been known as a Tetracotyle, from the frequent presence of four (sometimes
only three) adhering organs. Fig. 31 exhibits a species which is abundant in
the lens and vitreous humour of the eye of the Perch. Its further history is
not known, but presumably the Perch is presently devoured by the final host
in which the Diplostomum attains maturity. Thus the Holostomatidae are
"metastatic" (Leuckart), their (probably) direct development requiring the
presence of two hosts.[78]
The other Digenea, the life-histories of which are known, belong to the
Distomatidae and Amphistomatidae, and we may distinguish the steps by
which the complex life-history of the liver-fluke (Distomum hepaticum) has
been brought about, by a consideration of that of Distomum macrostomum.
Fig. 31.—Diplostomum (Tetracotyle) volvens. (After v. Nordmann.) × 130. cv,
Contractile excretory vesicle; d, intestine; e, calcareous bodies in excretory
tubules; ex.o, excretory aperture; gl, glandular adhesive body; ms, oral sucker;
ph, pharynx; vs, ventral sucker.
Distomum macrostomum.—This form occurs in the intestine of several
common Passerine birds. It is remarkable not only for the large oral sucker,
but also on account of the position of the common genital pore at the
hinder, and not as usual, at the anterior, end of the body (Fig. 32, A). The
eggs pass out through this pore, and are discharged with the bird's
Page 79
excrement. Should a certain snail (Succinea putris) happen to rasp off the
epidermis of a leaf upon which the faeces have fallen, the eggs are
swallowed and a minute active larva is set free (Fig. 32, B). This penetrates
through the thin wall of the digestive tract of the snail, and passing into the
connective tissue, throws off its cilia and assumes the shape of Fig. 32, C.
This sporocyst, as the larva is now termed, grows rapidly in all directions
(Fig. 32, D) at the expense of the snail's tissues, until it becomes impossible
to separate parasite and host completely.
Fig. 32.—Life-history of Distomum macrostomum Rud. A, Immature Distomum (really
a tailless Cercaria) found in the swollen terminal parts of Leucochloridium (Fig.
33, B) and enclosed in two protective membranes, × 40; B, larva which hatches
out of the egg of D. macrostomum, × 125; C, the metamorphosed larva
(sporocyst) fourteen days after having entered Succinea putris, and pierced
through its intestinal wall; D, actively growing sporocyst. (After Heckert.) go,
Genital aperture; int, intestine; ms, mouth sucker; n, nervous system; ov, ovary;
ps, ventral sucker; te, testis.
Those branches which lie superficially in the cephalic region of the snail
become greatly swollen, cylindrical, and contractile. They are banded with
green and white, ornamented with red terminal spots, and pulsate rapidly.
Hence these fertile branches of the sporocyst (which in this condition was
known as Leucochloridium paradoxum, Fig. 33, B) naturally attract the
attention of insectivorous birds, which peck off the tentacles of the snail,
and with it the swollen sporocyst-branch. A sphincter muscle closes the cut
end of the fertile sac when the bird's bill nips it off. The sac contains large
numbers of young D. macrostomum (Fig. 32, A), produced by the division
of embryonic cells of the larva (Fig. 32, B), which are apparently
blastomeres of the egg reserved for this future use. It is a remarkable
circumstance that the old bird itself is immune from infection, and if it
epidermis of a leaf upon which the faeces have fallen, the eggs are
swallowed and a minute active larva is set free (Fig. 32, B). This penetrates
through the thin wall of the digestive tract of the snail, and passing into the
connective tissue, throws off its cilia and assumes the shape of Fig. 32, C.
This sporocyst, as the larva is now termed, grows rapidly in all directions
(Fig. 32, D) at the expense of the snail's tissues, until it becomes impossible
to separate parasite and host completely.
Fig. 32.—Life-history of Distomum macrostomum Rud. A, Immature Distomum (really
a tailless Cercaria) found in the swollen terminal parts of Leucochloridium (Fig.
33, B) and enclosed in two protective membranes, × 40; B, larva which hatches
out of the egg of D. macrostomum, × 125; C, the metamorphosed larva
(sporocyst) fourteen days after having entered Succinea putris, and pierced
through its intestinal wall; D, actively growing sporocyst. (After Heckert.) go,
Genital aperture; int, intestine; ms, mouth sucker; n, nervous system; ov, ovary;
ps, ventral sucker; te, testis.
Those branches which lie superficially in the cephalic region of the snail
become greatly swollen, cylindrical, and contractile. They are banded with
green and white, ornamented with red terminal spots, and pulsate rapidly.
Hence these fertile branches of the sporocyst (which in this condition was
known as Leucochloridium paradoxum, Fig. 33, B) naturally attract the
attention of insectivorous birds, which peck off the tentacles of the snail,
and with it the swollen sporocyst-branch. A sphincter muscle closes the cut
end of the fertile sac when the bird's bill nips it off. The sac contains large
numbers of young D. macrostomum (Fig. 32, A), produced by the division
of embryonic cells of the larva (Fig. 32, B), which are apparently
blastomeres of the egg reserved for this future use. It is a remarkable
circumstance that the old bird itself is immune from infection, and if it
Page 80
swallows these young Distomes, they are digested. Should, however, the
snail's tentacle and its contents be offered as food to the nestlings, their
weaker digestive powers merely set the Distomes free from the protective
membranes (Fig. 32, A), and thus the Blackcaps, Sparrows, and other birds
infested by D. macrostomum have acquired the parasite when they were
nestlings by the unintentional agency of their parents.[79] The snail
regenerates its lost tentacles only for the sporocyst to again bud off fertile
branches into them.
Fig. 33.—A, Succinea putris, infested by B, Leucochloridium paradoxum, or the fully-
formed sporocyst of Distomum macrostomum. (After Heckert.) A, Natural size;
B, × 7.
The egg of this Distome thus gives rise to a larva which enters the tissues of
one particular Mollusc. Here it becomes a branched sporocyst within which
the sexual worms are formed, apparently each from a single embryonic
blastomere ("Keimzelle"), by a process comparable with the development
of a parthenogenetic ovum, and the whole cycle has been termed
Alloiogenesis, i.e. alternation of sexual and parthenogenetic generations
(Grobben).[80] Leuckart[81] and Looss,[82] however, consider that what was
once a metamorphosis of an individual (as in the Holostomatidae) has now
become, by maturation of the Cercaria in the comparatively modern warm-
blooded bird, a metamorphosis extending over two or more generations.
Distomum (Fasciola) hepaticum.—The liver-fluke of the Sheep, which
produces the disastrous disease, liver-rot, has a distribution as wide as that
of a small water-snail, Limnaea truncatula, the connexion between the two
being, as Thomas[83] and Leuckart discovered, that this snail is the
snail's tentacle and its contents be offered as food to the nestlings, their
weaker digestive powers merely set the Distomes free from the protective
membranes (Fig. 32, A), and thus the Blackcaps, Sparrows, and other birds
infested by D. macrostomum have acquired the parasite when they were
nestlings by the unintentional agency of their parents.[79] The snail
regenerates its lost tentacles only for the sporocyst to again bud off fertile
branches into them.
Fig. 33.—A, Succinea putris, infested by B, Leucochloridium paradoxum, or the fully-
formed sporocyst of Distomum macrostomum. (After Heckert.) A, Natural size;
B, × 7.
The egg of this Distome thus gives rise to a larva which enters the tissues of
one particular Mollusc. Here it becomes a branched sporocyst within which
the sexual worms are formed, apparently each from a single embryonic
blastomere ("Keimzelle"), by a process comparable with the development
of a parthenogenetic ovum, and the whole cycle has been termed
Alloiogenesis, i.e. alternation of sexual and parthenogenetic generations
(Grobben).[80] Leuckart[81] and Looss,[82] however, consider that what was
once a metamorphosis of an individual (as in the Holostomatidae) has now
become, by maturation of the Cercaria in the comparatively modern warm-
blooded bird, a metamorphosis extending over two or more generations.
Distomum (Fasciola) hepaticum.—The liver-fluke of the Sheep, which
produces the disastrous disease, liver-rot, has a distribution as wide as that
of a small water-snail, Limnaea truncatula, the connexion between the two
being, as Thomas[83] and Leuckart discovered, that this snail is the
Page 81
intermediate host in which the earlier larval, sporocyst, and redia stages are
passed through, and a vast number of immature flukes (Cercariae) are
developed. These leave the snail and encyst upon grass, where they are
eaten by the sheep. Over the whole of Europe, Northern Asia, Abyssinia,
and North Africa, the Canaries, and the Faroes, the fluke and the snail are
known to occur, and recently the former has been found in Australia and the
Sandwich Islands, where a snail, apparently a variety of Limnaea
truncatula, is also found.[84] Over these vast areas, however, the disease
usually only occurs in certain marshy districts and at certain times of the
year. Meadows of a clayey soil, liable to be flooded (as in certain parts of
Oxfordshire), are the places where this Limnaea occurs most abundantly,
and these are consequently the most dangerous feeding-grounds for sheep.
The wet years 1816, 1817, 1830, 1853, and 1854—memorable for the
occurrence of acute liver-rot in England, Germany, and France—showed
that the weather also plays a considerable part in extending the suitable
ground for Limnaea over wide areas, which in dry years may be safe
pastures. In 1830 England lost from this cause,[85] one and a half million
sheep, representing some four millions of money, while in 1879-80 three
millions died. In 1862 Ireland lost 60 per cent of the flocks, and in 1882
vast numbers of sheep perished in Buenos Ayres from this cause. In the
United Kingdom the annual loss was formerly estimated at a million
animals, but is now probably considerably less. After infection during a wet
autumn, it is usually in the succeeding winter that the disease reaches its
height.
passed through, and a vast number of immature flukes (Cercariae) are
developed. These leave the snail and encyst upon grass, where they are
eaten by the sheep. Over the whole of Europe, Northern Asia, Abyssinia,
and North Africa, the Canaries, and the Faroes, the fluke and the snail are
known to occur, and recently the former has been found in Australia and the
Sandwich Islands, where a snail, apparently a variety of Limnaea
truncatula, is also found.[84] Over these vast areas, however, the disease
usually only occurs in certain marshy districts and at certain times of the
year. Meadows of a clayey soil, liable to be flooded (as in certain parts of
Oxfordshire), are the places where this Limnaea occurs most abundantly,
and these are consequently the most dangerous feeding-grounds for sheep.
The wet years 1816, 1817, 1830, 1853, and 1854—memorable for the
occurrence of acute liver-rot in England, Germany, and France—showed
that the weather also plays a considerable part in extending the suitable
ground for Limnaea over wide areas, which in dry years may be safe
pastures. In 1830 England lost from this cause,[85] one and a half million
sheep, representing some four millions of money, while in 1879-80 three
millions died. In 1862 Ireland lost 60 per cent of the flocks, and in 1882
vast numbers of sheep perished in Buenos Ayres from this cause. In the
United Kingdom the annual loss was formerly estimated at a million
animals, but is now probably considerably less. After infection during a wet
autumn, it is usually in the succeeding winter that the disease reaches its
height.
Page 82
The symptoms of "rot" appear about a month after infection, more acutely in
lambs than in sheep, and again, less in oxen than in sheep. At first, death may
result from cerebral apoplexy, but if the first few weeks are passed through, a
pernicious anaemia sets in, the sheep are less lively and fall at a slight touch, the
appetite diminishes, and rumination becomes irregular. The conjunctiva is of a
whitish-yellow colour, the dry, brittle wool falls off, and there is sometimes fever
and quickened respiration. In January, about three months after infection, the
wasting, or fatal, period sets in. Oedemas or swellings, usually visible before,
become larger at the dependent parts of the body, a large one in the submaxillary
region being especially well marked, and this is considered one of the most
characteristic symptoms ("watery poke"). Through this period few of the infected
sheep survive, but should they do so, the flukes begin to migrate, though some
remain much longer within the liver. Migration is effected through the bile-duct
into the duodenum and outwith the faeces, in which the altered remains of the
Distomum are sometimes scarcely recognisable. Under these circumstances (or
owing to death of the fluke in situ) the sheep recover more or less fully.
The preventive measures seem to be: (1) Destruction of the eggs and of the
manure of rotten sheep; (2) slaughter of badly fluked sheep; (3) adequate drainage
of pastures; (4) an allowance of salt and a little dry food to the sheep; and (5)
dressings of lime or salt on the ground to destroy the embryos.[86]
Distomum hepaticum, contrary to most Trematodes, enjoys a wide range of hosts.
Man himself occasionally falls a victim; thus in Dalmatia, in the Narenta Valley,
the disease is endemic but slight in its effects. The horse, deer, camel, antelopes,
goat, pig, rabbit, kangaroo, beaver, and squirrel have all been known to harbour
this fluke occasionally. In the Italian deer-parks at Mandria a large species, D.
magnum, decimated the herds some years ago; and this species, probably
imported from Italy, is now almost as dangerous a parasite on the western plains
of the United States as D. hepaticum.
Bilharzia haematobia.[87]—This formidable parasite was discovered by Bilharz in
1853 in the veins of the bladder of patients at the Cairo Hospital, and is
remarkable from its abundance on the east coast and inland countries of Africa
from Egypt to the Cape, as well as in the districts bordering Lake Nyassa and the
Zambesi river, while westwards it occurs on the Gold Coast. Mecca is a source of
infection whence Mohammedans carry the disease to distant places. In Egypt
about 30 per cent of the native population is affected by the serious disease known
lambs than in sheep, and again, less in oxen than in sheep. At first, death may
result from cerebral apoplexy, but if the first few weeks are passed through, a
pernicious anaemia sets in, the sheep are less lively and fall at a slight touch, the
appetite diminishes, and rumination becomes irregular. The conjunctiva is of a
whitish-yellow colour, the dry, brittle wool falls off, and there is sometimes fever
and quickened respiration. In January, about three months after infection, the
wasting, or fatal, period sets in. Oedemas or swellings, usually visible before,
become larger at the dependent parts of the body, a large one in the submaxillary
region being especially well marked, and this is considered one of the most
characteristic symptoms ("watery poke"). Through this period few of the infected
sheep survive, but should they do so, the flukes begin to migrate, though some
remain much longer within the liver. Migration is effected through the bile-duct
into the duodenum and outwith the faeces, in which the altered remains of the
Distomum are sometimes scarcely recognisable. Under these circumstances (or
owing to death of the fluke in situ) the sheep recover more or less fully.
The preventive measures seem to be: (1) Destruction of the eggs and of the
manure of rotten sheep; (2) slaughter of badly fluked sheep; (3) adequate drainage
of pastures; (4) an allowance of salt and a little dry food to the sheep; and (5)
dressings of lime or salt on the ground to destroy the embryos.[86]
Distomum hepaticum, contrary to most Trematodes, enjoys a wide range of hosts.
Man himself occasionally falls a victim; thus in Dalmatia, in the Narenta Valley,
the disease is endemic but slight in its effects. The horse, deer, camel, antelopes,
goat, pig, rabbit, kangaroo, beaver, and squirrel have all been known to harbour
this fluke occasionally. In the Italian deer-parks at Mandria a large species, D.
magnum, decimated the herds some years ago; and this species, probably
imported from Italy, is now almost as dangerous a parasite on the western plains
of the United States as D. hepaticum.
Bilharzia haematobia.[87]—This formidable parasite was discovered by Bilharz in
1853 in the veins of the bladder of patients at the Cairo Hospital, and is
remarkable from its abundance on the east coast and inland countries of Africa
from Egypt to the Cape, as well as in the districts bordering Lake Nyassa and the
Zambesi river, while westwards it occurs on the Gold Coast. Mecca is a source of
infection whence Mohammedans carry the disease to distant places. In Egypt
about 30 per cent of the native population is affected by the serious disease known
Page 83
as Haematuria, resulting from the attacks of Bilharzia, so that, of the many
scourges from which in Africa man suffers, this one is perhaps the most severe.
Fig. 34.—Bilharzia haematobia Cobb. × 10. The female (♀) lying in the gynaecophoric canal
of the male (♂). d, Alimentary canal; ms, oral sucker of male; vs, ventral suckers. (After
Leuckart.)
The worm is found usually in couples, which have been proved to be male and
female individuals (Fig. 34), often in considerable numbers in the veins of the
pelvic region, chiefly the veins of the bladder and of the large intestine, and it is
tolerably certain that Bilharzia enter these vessels from the portal vein. Their long
slender bodies enable them to penetrate into the finer vessels, which get partially
or entirely choked up, and the circulation accordingly impeded. But the most
serious consequences are observed in the urinary bladder. The mucous membrane
is swollen and inflamed here and there, chiefly on the dorsal surface, the
capillaries appear varicose and covered with mucus, mixed with blood-
extravasations in which Bilharzia-eggs are noticeable. The eggs also cause
numerous swollen knots in the submucous tissue. Should the disease not pass
beyond this stage (and such is usually the case, especially in South Africa), a
temporary haematuria ensues. The urine, which is only expelled with great effort,
accompanied by intense pain, is mixed with blood, mucous clots, and masses of
Bilharzia-eggs, from which some of the embryos have already hatched out. The
symptoms, however, may gradually pass away, and a more or less complete
recovery accomplished. The disease may indeed be of a far less severe character,
and may not interfere with the usual occupations of the patient; but, on the other
hand, a far more extensive thickening of the wall of the bladder sometimes
occurs; hard masses of eggs, uric acid crystals, and other deposits, may lead to the
formation of stones, degeneration of the substance of the ureter, and eventually to
that of the kidney itself. The stone, indeed, has long been known to be a prevalent
disease in Egypt, and it is now known to arise from concretions formed round
masses of Bilharzia eggs. From the portal vein, again, other Bilharzia may gain
access to the rectum, or the liver, and it has also been found in the lungs, and may
give rise to most serious complications, if indeed the patient lives.
scourges from which in Africa man suffers, this one is perhaps the most severe.
Fig. 34.—Bilharzia haematobia Cobb. × 10. The female (♀) lying in the gynaecophoric canal
of the male (♂). d, Alimentary canal; ms, oral sucker of male; vs, ventral suckers. (After
Leuckart.)
The worm is found usually in couples, which have been proved to be male and
female individuals (Fig. 34), often in considerable numbers in the veins of the
pelvic region, chiefly the veins of the bladder and of the large intestine, and it is
tolerably certain that Bilharzia enter these vessels from the portal vein. Their long
slender bodies enable them to penetrate into the finer vessels, which get partially
or entirely choked up, and the circulation accordingly impeded. But the most
serious consequences are observed in the urinary bladder. The mucous membrane
is swollen and inflamed here and there, chiefly on the dorsal surface, the
capillaries appear varicose and covered with mucus, mixed with blood-
extravasations in which Bilharzia-eggs are noticeable. The eggs also cause
numerous swollen knots in the submucous tissue. Should the disease not pass
beyond this stage (and such is usually the case, especially in South Africa), a
temporary haematuria ensues. The urine, which is only expelled with great effort,
accompanied by intense pain, is mixed with blood, mucous clots, and masses of
Bilharzia-eggs, from which some of the embryos have already hatched out. The
symptoms, however, may gradually pass away, and a more or less complete
recovery accomplished. The disease may indeed be of a far less severe character,
and may not interfere with the usual occupations of the patient; but, on the other
hand, a far more extensive thickening of the wall of the bladder sometimes
occurs; hard masses of eggs, uric acid crystals, and other deposits, may lead to the
formation of stones, degeneration of the substance of the ureter, and eventually to
that of the kidney itself. The stone, indeed, has long been known to be a prevalent
disease in Egypt, and it is now known to arise from concretions formed round
masses of Bilharzia eggs. From the portal vein, again, other Bilharzia may gain
access to the rectum, or the liver, and it has also been found in the lungs, and may
give rise to most serious complications, if indeed the patient lives.
Page 84
How infection occurs is a question to which at present no satisfactory answer can
be made. The attempt to introduce embryos of Bilharzia into the common fresh-
water animals of Alexandria has hitherto proved fruitless (Looss[88]), although
there seems little doubt that the comparative immunity of Europeans from the
disease is in some way owing to their drinking purer water than the natives.
Possibly, as Leuckart suggests, the embryo becomes a sporocyst in man himself,
somewhat as Taenia murina is known to develop in the rat without an
intermediate host.[89] The immense numbers of the parasite in one host would then
readily receive an explanation.
A Bilharzia, possibly B. haematobia, was found by Cobbold in the portal vein of
Cercopithecus fuliginosus; and B. crassa infests the cattle of Egypt, Sicily, and
certain parts of India, but does not produce haematuria.
Of the other Trematodes of man and domestic animals there is not room to speak
fully. Distomum pulmonale, which occurs in the lungs of the cat, tiger, and dog, as
well as in man, is especially common in Japan, China, Corea, and Formosa. D.
sinense and D. rathouisi have been also found in inhabitants of these countries.
Bisexual Trematodes.—Zoologically, Bilharzia is interesting from its bisexual
condition. It is not, however, the only bisexual Trematode. In cysts in the
branchial chamber of Ray's bream, Brama raii, two worms are found, which are
probably the slender male and the swollen female of the same species (Distomum
okenii). The only doubt that can arise proceeds from the tendency in all
Trematodes for the male organs to ripen before the female organs. Until we
certainly know that the swollen egg-bearing form ( ♀ ) does not arise from a
previously male form ( ♂ ), the case is open to suspicion. Since, however,
Kölliker[90] never found intermediate hermaphrodite conditions, this Distomum
may be almost certainly regarded as of distinct sexes. Didymozoon thynni
(Monostomum bipartitum), from cysts on the gills of the Tunny (Thynnus), is
another case. Two slender worms flattened posteriorly, come together, and the
body of one becomes folded to receive that of the other. They fuse completely
except for a small lateral opening through which the anterior parts of both worms
may freely protrude. The enclosing individual contains a coiled uterus filled with
eggs, and is the female, whereas the smaller individual never possesses eggs, and
is probably the male.[91] Nematobothrium (Fig. 22, A), which occurs also in the
Tunny, in the form of two immensely long individuals intricately wound about
each other in a cyst, is, however, not bisexual.
be made. The attempt to introduce embryos of Bilharzia into the common fresh-
water animals of Alexandria has hitherto proved fruitless (Looss[88]), although
there seems little doubt that the comparative immunity of Europeans from the
disease is in some way owing to their drinking purer water than the natives.
Possibly, as Leuckart suggests, the embryo becomes a sporocyst in man himself,
somewhat as Taenia murina is known to develop in the rat without an
intermediate host.[89] The immense numbers of the parasite in one host would then
readily receive an explanation.
A Bilharzia, possibly B. haematobia, was found by Cobbold in the portal vein of
Cercopithecus fuliginosus; and B. crassa infests the cattle of Egypt, Sicily, and
certain parts of India, but does not produce haematuria.
Of the other Trematodes of man and domestic animals there is not room to speak
fully. Distomum pulmonale, which occurs in the lungs of the cat, tiger, and dog, as
well as in man, is especially common in Japan, China, Corea, and Formosa. D.
sinense and D. rathouisi have been also found in inhabitants of these countries.
Bisexual Trematodes.—Zoologically, Bilharzia is interesting from its bisexual
condition. It is not, however, the only bisexual Trematode. In cysts in the
branchial chamber of Ray's bream, Brama raii, two worms are found, which are
probably the slender male and the swollen female of the same species (Distomum
okenii). The only doubt that can arise proceeds from the tendency in all
Trematodes for the male organs to ripen before the female organs. Until we
certainly know that the swollen egg-bearing form ( ♀ ) does not arise from a
previously male form ( ♂ ), the case is open to suspicion. Since, however,
Kölliker[90] never found intermediate hermaphrodite conditions, this Distomum
may be almost certainly regarded as of distinct sexes. Didymozoon thynni
(Monostomum bipartitum), from cysts on the gills of the Tunny (Thynnus), is
another case. Two slender worms flattened posteriorly, come together, and the
body of one becomes folded to receive that of the other. They fuse completely
except for a small lateral opening through which the anterior parts of both worms
may freely protrude. The enclosing individual contains a coiled uterus filled with
eggs, and is the female, whereas the smaller individual never possesses eggs, and
is probably the male.[91] Nematobothrium (Fig. 22, A), which occurs also in the
Tunny, in the form of two immensely long individuals intricately wound about
each other in a cyst, is, however, not bisexual.
Page 85
Fig. 35.—Distomum okenii Köll. Showing male and female as they occur together in the
branchial cavity of Bramaraii (Ray's bream). (From Bronn, after Kölliker.) Nat. size.
Table of Digenetic Trematodes and their Life-Histories.[92]
Host into which the Host into which the
larva enters, and in Cercariae migrate and
Species. Final host.
which Cercariae are encyst; eaten by final
eventually formed. host.
Diplodiscus Insect-larvae, Rana,
Smaller species
(Amphistomum) Rana, Bufo, Bufo, but
of Planorbis
subclavatus Triton frequently
and Cyclas
Göze omitted
Distomum advena
Duj. (D. migrans Sorex araneus Not known Limax
Duj.)
Lucullus acuspes,
D. appendiculatum Centropages
Clupea alosa Not known
Rud. hamatus
(Copepoda)
Limnaea
Ephemera, Perla,
stagnalis
D. ascidia v. Ben. Species of Bats Chironomus
Planorbis
plumosus
corneus
Frogs and Toads
Physa
D. atriventre Weinl. of Not known
heterostropha
N. America
The Dunlin
D. brachysomum
(Tringa Not known Anthura gracilis
Crepl.
alpina)
Hedgehog
D. caudatum
(Erinaceus Helix hortensis
v. Linst.
europaeus)
D. clavigerum Rud. Rana Limnaea ovata Not known
branchial cavity of Bramaraii (Ray's bream). (From Bronn, after Kölliker.) Nat. size.
Table of Digenetic Trematodes and their Life-Histories.[92]
Host into which the Host into which the
larva enters, and in Cercariae migrate and
Species. Final host.
which Cercariae are encyst; eaten by final
eventually formed. host.
Diplodiscus Insect-larvae, Rana,
Smaller species
(Amphistomum) Rana, Bufo, Bufo, but
of Planorbis
subclavatus Triton frequently
and Cyclas
Göze omitted
Distomum advena
Duj. (D. migrans Sorex araneus Not known Limax
Duj.)
Lucullus acuspes,
D. appendiculatum Centropages
Clupea alosa Not known
Rud. hamatus
(Copepoda)
Limnaea
Ephemera, Perla,
stagnalis
D. ascidia v. Ben. Species of Bats Chironomus
Planorbis
plumosus
corneus
Frogs and Toads
Physa
D. atriventre Weinl. of Not known
heterostropha
N. America
The Dunlin
D. brachysomum
(Tringa Not known Anthura gracilis
Crepl.
alpina)
Hedgehog
D. caudatum
(Erinaceus Helix hortensis
v. Linst.
europaeus)
D. clavigerum Rud. Rana Limnaea ovata Not known
Page 86
Planorbis
corneus
Limnaea sp.
Pisidium,
D. cygnoides Zed. Rana (Cercaria
Cyclas
macrocerca Fil.)
D. cylindraceum
Rana Limnaea ovata Ilybius fuliginosus
Zed.
D. dimorphum Ardea, Ciconia Different species of
Not known
Dies. (Brazil) Fishes
Species of
Cygnus, Anser, Species of Limnaea,
D. echinatum Zed.
Anas Limnaea Paludina
vivipara
L. stagnalis,
Gammarus
Limnaea
D. endolobum Duj. Rana pulex, larvae of
stagnalis
Limnophilus
rhombicus
Limnaea stagnalis,
L. ovata,
Succinea
D. globiporum pfeifferi,
Perca fluviatilis Not known
Rud. S. putris, Physa
fontinalis,
Planorbis
marginatus
D. hepaticum Sheep, Oxen, Limnaea
Omitted
Abild. Man, etc. truncatula
Lophius
D. hystrix Duj. Not known Marine Fishes
piscatorius
Warblers, Tits,
D. macrostomum
Woodpeckers, Succinea putris Omitted
Rud.
etc.
Paludina
D. militare v. Ben. Common Snipe P. vivipara
vivipara
corneus
Limnaea sp.
Pisidium,
D. cygnoides Zed. Rana (Cercaria
Cyclas
macrocerca Fil.)
D. cylindraceum
Rana Limnaea ovata Ilybius fuliginosus
Zed.
D. dimorphum Ardea, Ciconia Different species of
Not known
Dies. (Brazil) Fishes
Species of
Cygnus, Anser, Species of Limnaea,
D. echinatum Zed.
Anas Limnaea Paludina
vivipara
L. stagnalis,
Gammarus
Limnaea
D. endolobum Duj. Rana pulex, larvae of
stagnalis
Limnophilus
rhombicus
Limnaea stagnalis,
L. ovata,
Succinea
D. globiporum pfeifferi,
Perca fluviatilis Not known
Rud. S. putris, Physa
fontinalis,
Planorbis
marginatus
D. hepaticum Sheep, Oxen, Limnaea
Omitted
Abild. Man, etc. truncatula
Lophius
D. hystrix Duj. Not known Marine Fishes
piscatorius
Warblers, Tits,
D. macrostomum
Woodpeckers, Succinea putris Omitted
Rud.
etc.
Paludina
D. militare v. Ben. Common Snipe P. vivipara
vivipara
Page 87
Bithynia Cyprinus, Acerina
D. nodulosum Zed. Perca fluviatilis
tentaculata cernua
Probably omitted.
D. ovocaudatum Species of (Cercaria known
Rana esculenta
Vulp. Planorbis as C. cystophora
Wag.)
Limnaea L. stagnalis, larvae
D. retusum Duj. Rana
stagnalis of Phryganeidae
D. squamula Dies. Polecat Unknown Rana temporaria
Tropidonotus
D. signatum Duj. Unknown Rana
natrix
D. trigonocephalum Paludina
Badger, Polecat Unknown
Rud. vivipara
Ostrea edulis,
Cardium
Gasterostomum sp. Dogfish, Rays Belone vulgaris
rusticum,
C. edule
Unio, Anodonta
(Cercaria
G. fimbriatum Leuciscus
Perca, Esox known as
v. Sieb. erythrophthalmus
Bucephalus
polymorphus)
Species of Gadus
G. gracilescens Lophius (e.g.
Unknown
Rud. piscatorius G. aeglefinus),
Molva, Lophius
Monostomum Planorbis
Anas Omitted
flavum Mehl. corneus
Classification of Trematodes.—We have seen (p. 63) that it is hardly possible to
carry out fully the division of Trematodes into Monogenea and Digenea.
Nevertheless, pending further investigation on the doubtful points, this
classification may still be used. Monticelli[93] has proposed the main divisions of
a new classification, which has been also adopted by Braun, and is based on the
nature of the suckers. These divisions are indicated below in brackets.
D. nodulosum Zed. Perca fluviatilis
tentaculata cernua
Probably omitted.
D. ovocaudatum Species of (Cercaria known
Rana esculenta
Vulp. Planorbis as C. cystophora
Wag.)
Limnaea L. stagnalis, larvae
D. retusum Duj. Rana
stagnalis of Phryganeidae
D. squamula Dies. Polecat Unknown Rana temporaria
Tropidonotus
D. signatum Duj. Unknown Rana
natrix
D. trigonocephalum Paludina
Badger, Polecat Unknown
Rud. vivipara
Ostrea edulis,
Cardium
Gasterostomum sp. Dogfish, Rays Belone vulgaris
rusticum,
C. edule
Unio, Anodonta
(Cercaria
G. fimbriatum Leuciscus
Perca, Esox known as
v. Sieb. erythrophthalmus
Bucephalus
polymorphus)
Species of Gadus
G. gracilescens Lophius (e.g.
Unknown
Rud. piscatorius G. aeglefinus),
Molva, Lophius
Monostomum Planorbis
Anas Omitted
flavum Mehl. corneus
Classification of Trematodes.—We have seen (p. 63) that it is hardly possible to
carry out fully the division of Trematodes into Monogenea and Digenea.
Nevertheless, pending further investigation on the doubtful points, this
classification may still be used. Monticelli[93] has proposed the main divisions of
a new classification, which has been also adopted by Braun, and is based on the
nature of the suckers. These divisions are indicated below in brackets.
Page 88
A. Monogenea v. Ben. (Heterocotylea Mont.).
1. Fam. Temnocephalidae Hasw.
Gen. Temnocephala Hasw.
2. Fam. Tristomatidae Tschbg.
Sub-Fam. 1. Tristomatinae Mont.
Gen. Tristomum, Nitzschia, Epibdella, Trochopus,
Acanthocotyle, Phyllonella, Placunella, Encotylabe.
Sub-Fam. 2. Monocotylinae Tschbg.
Gen. Pseudocotyle, Calicotyle, Monocotyle.
Sub-Fam. 3. Udonellinae v. Ben.-Hesse.
Gen. Udonella, Echinella, Pteronella.
3. Fam. Polystomatidae Tschbg.
Sub-Fam. 4. Octocotylinae v. Ben.-Hesse.
Gen. Octobothrium, Pleurocotyle, Diplozoon, Anthocotyle,
Vallisnia, Phyllocotyle, Hexacotyle, Platycotyle,
Plectanocotyle, Diclidophora.
Sub-Fam. 5. Polystomatinae v. Ben.
Gen. Polystomum, Onchocotyle, Erpocotyle, Diplobothrium,
Sphyranura.
Sub-Fam. 6. Microcotylinae Tschbg.
Gen. Microcotyle, Gastrocotyle, Axine, Pseudaxine.
4. Fam. Gyrodactylidae v. Ben.
Sub-Fam. 7. Gyrodactylinae Par. et Per.
Gen. Gyrodactylus, Dactylogyrus, Tetraonchus, Diplectanum.
Sub-Fam. 8. Calceostominae Par. et Per.
Gen. Calceostomum, Anoplodiscus.
5. Fam. Aspidobothridae Burm. (= Aspidocotylea Mont.).
Gen. Aspidogaster, Platyaspis, Cotylogaster, Macraspis.
B. Digenea v. Ben. (Malacocotylea Mont.).
6. Fam. Holostomatidae Brandes (= Metastatica Leuckart).
Gen. Diplostomum, Polycotyle, Hemistomum, Holostomum.
7. Fam. Amphistomatidae Mont.
Gen. Amphistomum, Diplodiscus, Gastrodiscus,
Homalogaster, Gastrothylax, Aspidocotyle.
8. Fam. Distomatidae Mont.
Gen. Distomum (and sub-genera), Rhopalophorus,
Koellikeria, Bilharzia.
9. Fam. Gasterostomatidae Braun.
Gen. Gasterostomum.
1. Fam. Temnocephalidae Hasw.
Gen. Temnocephala Hasw.
2. Fam. Tristomatidae Tschbg.
Sub-Fam. 1. Tristomatinae Mont.
Gen. Tristomum, Nitzschia, Epibdella, Trochopus,
Acanthocotyle, Phyllonella, Placunella, Encotylabe.
Sub-Fam. 2. Monocotylinae Tschbg.
Gen. Pseudocotyle, Calicotyle, Monocotyle.
Sub-Fam. 3. Udonellinae v. Ben.-Hesse.
Gen. Udonella, Echinella, Pteronella.
3. Fam. Polystomatidae Tschbg.
Sub-Fam. 4. Octocotylinae v. Ben.-Hesse.
Gen. Octobothrium, Pleurocotyle, Diplozoon, Anthocotyle,
Vallisnia, Phyllocotyle, Hexacotyle, Platycotyle,
Plectanocotyle, Diclidophora.
Sub-Fam. 5. Polystomatinae v. Ben.
Gen. Polystomum, Onchocotyle, Erpocotyle, Diplobothrium,
Sphyranura.
Sub-Fam. 6. Microcotylinae Tschbg.
Gen. Microcotyle, Gastrocotyle, Axine, Pseudaxine.
4. Fam. Gyrodactylidae v. Ben.
Sub-Fam. 7. Gyrodactylinae Par. et Per.
Gen. Gyrodactylus, Dactylogyrus, Tetraonchus, Diplectanum.
Sub-Fam. 8. Calceostominae Par. et Per.
Gen. Calceostomum, Anoplodiscus.
5. Fam. Aspidobothridae Burm. (= Aspidocotylea Mont.).
Gen. Aspidogaster, Platyaspis, Cotylogaster, Macraspis.
B. Digenea v. Ben. (Malacocotylea Mont.).
6. Fam. Holostomatidae Brandes (= Metastatica Leuckart).
Gen. Diplostomum, Polycotyle, Hemistomum, Holostomum.
7. Fam. Amphistomatidae Mont.
Gen. Amphistomum, Diplodiscus, Gastrodiscus,
Homalogaster, Gastrothylax, Aspidocotyle.
8. Fam. Distomatidae Mont.
Gen. Distomum (and sub-genera), Rhopalophorus,
Koellikeria, Bilharzia.
9. Fam. Gasterostomatidae Braun.
Gen. Gasterostomum.
Page 89
10. Fam. Didymozoontidae Mont.
Gen. Didymozoon, Nematobothrium.
11. Fam. Monostomatidae Mont.
Gen. Monostomum, Notocotyle, Ogmogaster, Opisthotrema.
CHAPTER III
CESTODA
INTRODUCTION—NATURE OF CESTODES—OCCURRENCE OF CESTODES—THE TAPE-WORMS
OF MAN AND DOMESTIC ANIMALS—TABLE OF THE LIFE-HISTORIES OF THE PRINCIPAL
CESTODES OF MAN AND DOMESTIC ANIMALS—STRUCTURE AND DEVELOPMENT OF
CESTODES—TABLE FOR THE DISCRIMINATION OF THE MORE USUAL CESTODES OF MAN
AND DOMESTIC ANIMALS—CLASSIFICATION.
The Cestodes or Tape-worms are exclusively endoparasitic Platyhelminthes
living, in the adult condition, in the alimentary canal of Vertebrates, with the
exception of Archigetes (Fig. 37), which may become mature in the body-cavity
of Tubifex. In relation with this wholly parasitic existence, the Cestodes exhibit
certain characteristic modifications in structure and mode of development, such as
the formation, by the segmentation of the "neck," of a (usually) long chain of
"proglottides" or joints, which form the "body" of the Cestode; and the entire
absence of an alimentary tract, both in the larva and adult. As an adaptation to the
fixed mode of life, the anterior end (head, scolex) is modified to form an adhering
organ. Various adaptive forms of larvae are known. These live in the internal
organs of one or more intermediate hosts, and are transferred to the final host
passively during a meal. Lastly, there is the curious metamorphosis by which the
adult is formed from a portion (scolex) of the larva.[94]
Gen. Didymozoon, Nematobothrium.
11. Fam. Monostomatidae Mont.
Gen. Monostomum, Notocotyle, Ogmogaster, Opisthotrema.
CHAPTER III
CESTODA
INTRODUCTION—NATURE OF CESTODES—OCCURRENCE OF CESTODES—THE TAPE-WORMS
OF MAN AND DOMESTIC ANIMALS—TABLE OF THE LIFE-HISTORIES OF THE PRINCIPAL
CESTODES OF MAN AND DOMESTIC ANIMALS—STRUCTURE AND DEVELOPMENT OF
CESTODES—TABLE FOR THE DISCRIMINATION OF THE MORE USUAL CESTODES OF MAN
AND DOMESTIC ANIMALS—CLASSIFICATION.
The Cestodes or Tape-worms are exclusively endoparasitic Platyhelminthes
living, in the adult condition, in the alimentary canal of Vertebrates, with the
exception of Archigetes (Fig. 37), which may become mature in the body-cavity
of Tubifex. In relation with this wholly parasitic existence, the Cestodes exhibit
certain characteristic modifications in structure and mode of development, such as
the formation, by the segmentation of the "neck," of a (usually) long chain of
"proglottides" or joints, which form the "body" of the Cestode; and the entire
absence of an alimentary tract, both in the larva and adult. As an adaptation to the
fixed mode of life, the anterior end (head, scolex) is modified to form an adhering
organ. Various adaptive forms of larvae are known. These live in the internal
organs of one or more intermediate hosts, and are transferred to the final host
passively during a meal. Lastly, there is the curious metamorphosis by which the
adult is formed from a portion (scolex) of the larva.[94]
Page 90
Fig. 36.—Echinobothrium affine Dies., from the intestine of Torpedo, × 43. hd, Head; hk,
hooks; hl, lobes of the head; ov, ovary; pe, penis; ps, penis-sheath; te, testes; ut, uterus;
vag, vagina; yg, yolk-glands. (After Pintner.[95])
Taenia solium, from man (Fig. 39, B), or Echinobothrium (Fig. 36), from an
Elasmobranch fish, is fixed to the mucous lining of the intestine of its host by
means of a radially-constructed apparatus of four suckers and a circlet of hooks
(Fig. 39), which are borne by the "head" or "scolex," being that part of the worm
which is directly derived from part of the larva, and which contains the central,
commissural portion of the nervous system. Firm adhesion to the host's intestine
is necessary, in order to avoid the loosening action of the peristaltic movements of
the intestine as the food passes along. The heads of different Cestodes exhibit a
marvellous variety of suckers and hooks, from a mere muscular depression in
Schistocephalus, to the compound proboscides of Tetrarhynchus[96] which is
found in Elasmobranchs. The jointed body, often of enormous length (up to 20
yards in Bothriocephalus latus), is usually separated from the head by a slender
neck, from which the proglottides are segmented off from behind forwards, and
become more and more individualised as they recede farther away from the neck
by the intercalation of younger joints. Thus in Fig. 36 the mature, distal proglottis
has passed through all the stages represented by the other segments.
hooks; hl, lobes of the head; ov, ovary; pe, penis; ps, penis-sheath; te, testes; ut, uterus;
vag, vagina; yg, yolk-glands. (After Pintner.[95])
Taenia solium, from man (Fig. 39, B), or Echinobothrium (Fig. 36), from an
Elasmobranch fish, is fixed to the mucous lining of the intestine of its host by
means of a radially-constructed apparatus of four suckers and a circlet of hooks
(Fig. 39), which are borne by the "head" or "scolex," being that part of the worm
which is directly derived from part of the larva, and which contains the central,
commissural portion of the nervous system. Firm adhesion to the host's intestine
is necessary, in order to avoid the loosening action of the peristaltic movements of
the intestine as the food passes along. The heads of different Cestodes exhibit a
marvellous variety of suckers and hooks, from a mere muscular depression in
Schistocephalus, to the compound proboscides of Tetrarhynchus[96] which is
found in Elasmobranchs. The jointed body, often of enormous length (up to 20
yards in Bothriocephalus latus), is usually separated from the head by a slender
neck, from which the proglottides are segmented off from behind forwards, and
become more and more individualised as they recede farther away from the neck
by the intercalation of younger joints. Thus in Fig. 36 the mature, distal proglottis
has passed through all the stages represented by the other segments.
Page 91
Fig. 37.—Archigetes sieboldii (appendiculatus), from the coelom of Tubifex rivulorum. × 40.
app, Persistent larval appendage; go, genital pore; hk, persistent larval hooks; ov, ovary;
sc, sucker; te, testes; yg, yolk-glands. (After Leuckart.)
The longitudinal muscles, the nerves, and excretory vessels which supply the
proglottides are continuous throughout and with those of the head. Each joint
contains at first male genitalia comparable with those of a Trematode; then the
female organs develop, and finally self-fertilisation follows. The Cestodes feed
through their skin, probably by the aid of fine protoplasmic processes, which
penetrate the tough investing membrane and absorb the already digested food
which bathes them. When a proglottis of Calliobothrium is approaching maturity
it separates from the parent, the broken ends of muscles, nerves, and excretory
vessels speedily heal, and it is now capable of continued growth and of fairly
active movement if it remains in the intestine of the host. According to van
Beneden, it may even attain a size equal to, or exceeding, that of the whole parent
or "strobila."[97] These considerations led Leuckart, von Siebold, P. J. van
Beneden, and others, to Steenstrup's conclusion that a jointed tape-worm is really
a colony composed of two generations—the head and neck derived from the larva,
and the proglottides produced by the segmentation of the neck.[98] This view of
the colonial nature of jointed Cestodes was generally adopted from 1851 to 1880.
During the last fifteen years, however, the varied interpretations of the facts of the
ontogeny of this group have led some authors to adopt the monozootic view (that
a Cestode is one individual), others are still of the older opinion, and Hatschek
(Lehrbuch, p. 349) and Lang take up intermediate positions. Lang considers that
the formation of the joints of a tape-worm from a small fixed "scolex," is not only
largely comparable with the strobilation of a scyphistoma and the consequent
formation of a pile of medusae, as in the life-history of Aurelia, but that both
processes have arisen from the power of regenerating the necessary organs in each
of the new segments. The result in both cases is the rapid formation of a number
of joints, which gradually separate from the parent, to carry the eggs and young to
new stations. Just as some Coelenterata (Lucernaria) may be regarded as not
having advanced much beyond a scyphistoma stage, so there are unisegmental
Cestodes (e.g. Archigetes, Fig. 37) which have remained as a slightly altered but
sexual scolex, directly comparable with a Trematode, and, as all authors are
app, Persistent larval appendage; go, genital pore; hk, persistent larval hooks; ov, ovary;
sc, sucker; te, testes; yg, yolk-glands. (After Leuckart.)
The longitudinal muscles, the nerves, and excretory vessels which supply the
proglottides are continuous throughout and with those of the head. Each joint
contains at first male genitalia comparable with those of a Trematode; then the
female organs develop, and finally self-fertilisation follows. The Cestodes feed
through their skin, probably by the aid of fine protoplasmic processes, which
penetrate the tough investing membrane and absorb the already digested food
which bathes them. When a proglottis of Calliobothrium is approaching maturity
it separates from the parent, the broken ends of muscles, nerves, and excretory
vessels speedily heal, and it is now capable of continued growth and of fairly
active movement if it remains in the intestine of the host. According to van
Beneden, it may even attain a size equal to, or exceeding, that of the whole parent
or "strobila."[97] These considerations led Leuckart, von Siebold, P. J. van
Beneden, and others, to Steenstrup's conclusion that a jointed tape-worm is really
a colony composed of two generations—the head and neck derived from the larva,
and the proglottides produced by the segmentation of the neck.[98] This view of
the colonial nature of jointed Cestodes was generally adopted from 1851 to 1880.
During the last fifteen years, however, the varied interpretations of the facts of the
ontogeny of this group have led some authors to adopt the monozootic view (that
a Cestode is one individual), others are still of the older opinion, and Hatschek
(Lehrbuch, p. 349) and Lang take up intermediate positions. Lang considers that
the formation of the joints of a tape-worm from a small fixed "scolex," is not only
largely comparable with the strobilation of a scyphistoma and the consequent
formation of a pile of medusae, as in the life-history of Aurelia, but that both
processes have arisen from the power of regenerating the necessary organs in each
of the new segments. The result in both cases is the rapid formation of a number
of joints, which gradually separate from the parent, to carry the eggs and young to
new stations. Just as some Coelenterata (Lucernaria) may be regarded as not
having advanced much beyond a scyphistoma stage, so there are unisegmental
Cestodes (e.g. Archigetes, Fig. 37) which have remained as a slightly altered but
sexual scolex, directly comparable with a Trematode, and, as all authors are
Page 92
agreed, representing one generation only. Such monozootic forms are now classed
as a special family, the Cestodaria or Monozoa, of which Caryophylleus
mutabilis, from the intestine of various Cyprinoid fish, is the most abundant
representative, while Amphiptyches (Gyrocotyle) urna, from Chimaera monstrosa
of the northern hemisphere, is paralleled by A. rugosa, found in Callorhynchus
antarcticus of the southern seas.
Fig. 38.—Scolex polymorphus Rud. (larva of Calliobothrium filicolle Zschokke), from the
muscles of Apogon, a Mediterranean fish; also found in many Invertebrates (e.g. Sepia).
A, Inverted scolex, with calcareous bodies; B, everted older larva. br, Brain; exo,
terminal excretory aperture; fc, flame-cells; for.sec; secondary excretory pores; hk,
hooks of the adult Cestode; inrag, pit at the bottom of which the head is developed;
msc, anterior sucker; nl, lateral nerve; sc, suckers; tl, tp, lateral and main excretory
vessels. (After Monticelli.)
Occurrence of Cestodes.—The distribution of Cestodes and their larvae is
analogous to that of the digenetic Trematodes, although the absence of an
alimentary canal limits the habitat of the mature worms to certain sites, such as
the blood-vessels, the lymphatic and coelomic spaces, and the digestive system,
where their body may be bathed by a nutritive fluid. Almost all groups of
Vertebrates are attacked by Cestodes. Those of fishes, and particularly of
Elasmobranchs, are distinguished by certain structural and developmental
features; those of birds by others; those of mammals, by a third set of characters.
The young stages of the Cestodes of Sharks and Rays occur encysted in the body-
cavity, or in the pyloric appendages, of Teleosteans, which probably swallow them
along with those invertebrate animals upon which they prey. The larvae of the
Cestodes of carnivorous mammals or piscivorous birds, live respectively in
herbivores and fishes, but how the latter are infected we know in very few
instances. Cestode larvae are known to occur in many Invertebrates, and
as a special family, the Cestodaria or Monozoa, of which Caryophylleus
mutabilis, from the intestine of various Cyprinoid fish, is the most abundant
representative, while Amphiptyches (Gyrocotyle) urna, from Chimaera monstrosa
of the northern hemisphere, is paralleled by A. rugosa, found in Callorhynchus
antarcticus of the southern seas.
Fig. 38.—Scolex polymorphus Rud. (larva of Calliobothrium filicolle Zschokke), from the
muscles of Apogon, a Mediterranean fish; also found in many Invertebrates (e.g. Sepia).
A, Inverted scolex, with calcareous bodies; B, everted older larva. br, Brain; exo,
terminal excretory aperture; fc, flame-cells; for.sec; secondary excretory pores; hk,
hooks of the adult Cestode; inrag, pit at the bottom of which the head is developed;
msc, anterior sucker; nl, lateral nerve; sc, suckers; tl, tp, lateral and main excretory
vessels. (After Monticelli.)
Occurrence of Cestodes.—The distribution of Cestodes and their larvae is
analogous to that of the digenetic Trematodes, although the absence of an
alimentary canal limits the habitat of the mature worms to certain sites, such as
the blood-vessels, the lymphatic and coelomic spaces, and the digestive system,
where their body may be bathed by a nutritive fluid. Almost all groups of
Vertebrates are attacked by Cestodes. Those of fishes, and particularly of
Elasmobranchs, are distinguished by certain structural and developmental
features; those of birds by others; those of mammals, by a third set of characters.
The young stages of the Cestodes of Sharks and Rays occur encysted in the body-
cavity, or in the pyloric appendages, of Teleosteans, which probably swallow them
along with those invertebrate animals upon which they prey. The larvae of the
Cestodes of carnivorous mammals or piscivorous birds, live respectively in
herbivores and fishes, but how the latter are infected we know in very few
instances. Cestode larvae are known to occur in many Invertebrates, and
Page 93
occasionally are taken free swimming in the sea, presumably crossing from one
host to the next. Ctenophores, Siphonophores, Copepods, Ostracods, Decapods,
various Molluscs especially Cephalopods, Earthworms, and other Annelids, are
the intermediate hosts of these larvae (see Fig. 38), the fate of which, however,
has been determined in but few cases.
Occurrence of Cestodes in Man.[99]—Tape-worms, either in the adult or larval
stages (bladder-worms), have, from ancient times, been known to occur in man,
and in the animals that serve him as food. Until comparatively recent times,
however, the true nature of these parasites, and particularly of "hydatids" (cystic
larvae), was unrecognised. Up to the seventeenth century the larvae were regarded
as abscesses or diseased growths of the affected organs, and it was only at the
close of that century that their animal nature was even suggested. Even at the
beginning of the nineteenth century, three modes of origin of Cestodes—by
"generatio aequivoca" from the tissues of the body, or by the union of previously
distinct proglottides, or again by metamorphosis of free-living worms drunk with
water by cattle or birds (as Linnaeus suggested)—were still variously held, at a
time when Malpighi, Pallas, and Goeze had recognised the true connexion
between the cystic and segmented states of Taenia crassicollis (the cat tape-
worm), and when Goeze had seen the eggs of Taeniae, and Abildgaard[100] had
even conducted the first helminthological experiments (conversion of the larval
Schistocephalus, Fig. 40, into the adult form).
Fig. 39.—A, Taenia saginata Goeze. Nat. size. (From a specimen in the Cambridge Museum.)
The approximate lengths of the portions omitted in the drawing are given. At * (after
Leuckart) the branched uterus and the longitudinal and transverse excretory vessels are
host to the next. Ctenophores, Siphonophores, Copepods, Ostracods, Decapods,
various Molluscs especially Cephalopods, Earthworms, and other Annelids, are
the intermediate hosts of these larvae (see Fig. 38), the fate of which, however,
has been determined in but few cases.
Occurrence of Cestodes in Man.[99]—Tape-worms, either in the adult or larval
stages (bladder-worms), have, from ancient times, been known to occur in man,
and in the animals that serve him as food. Until comparatively recent times,
however, the true nature of these parasites, and particularly of "hydatids" (cystic
larvae), was unrecognised. Up to the seventeenth century the larvae were regarded
as abscesses or diseased growths of the affected organs, and it was only at the
close of that century that their animal nature was even suggested. Even at the
beginning of the nineteenth century, three modes of origin of Cestodes—by
"generatio aequivoca" from the tissues of the body, or by the union of previously
distinct proglottides, or again by metamorphosis of free-living worms drunk with
water by cattle or birds (as Linnaeus suggested)—were still variously held, at a
time when Malpighi, Pallas, and Goeze had recognised the true connexion
between the cystic and segmented states of Taenia crassicollis (the cat tape-
worm), and when Goeze had seen the eggs of Taeniae, and Abildgaard[100] had
even conducted the first helminthological experiments (conversion of the larval
Schistocephalus, Fig. 40, into the adult form).
Fig. 39.—A, Taenia saginata Goeze. Nat. size. (From a specimen in the Cambridge Museum.)
The approximate lengths of the portions omitted in the drawing are given. At * (after
Leuckart) the branched uterus and the longitudinal and transverse excretory vessels are
Page 94
shown. The genital apertures are seen as a lateral opening on each of the larger
proglottides. B, Head (scolex) of T. solium Rud. × 12. (After Leuckart.)
Generally speaking, "a tape-worm" in Western Europe will prove to be Taenia
saginata Goeze (the beef tape-worm, Fig. 39, A), exceedingly prevalent also in
the East, and indeed cosmopolitan, occurring wherever the infected flesh of the ox
is eaten in a raw or half-cooked state. Its attacks are fortunately not usually
severe. Taenia solium Rud. (the pork tape-worm) is found wherever the pig is kept
as a domestic animal, and has consequently a world-wide distribution. Its size (6-
9 feet long) and powers of adhesion would alone render T. solium a formidable
parasite. But the danger of its presence in the body of man, or in the flesh of pigs,
lies in the fact that the larva or bladder-worm (known as Cysticercus cellulosae)
can live in the most varied organs. Thus if by accident a mature proglottis be
eaten, the embryos escape, bore their way into the wall of the stomach, and
entering the portal vein, may reach in time the muscles, the brain, the eye, or even
the heart itself, and attain the cystic condition. Even more disastrous may be the
result, should some ripe joints of a mature worm work their way from the intestine
back towards the stomach. Should this happen (and though it has not been directly
proved, the possibility is to be reckoned with), the result would be the release of
vast numbers of embryos capable of inflicting fatal injury on the host. An
abnormal Cysticercus of this species is probably the Taenia (Cysticercus)
acanthotrias Weinl. (see, however, Leuckart, loc. cit. p. 711).
Taenia (Hymenolepis) nana v. Sieb.[101] is found in man in Egypt, Italy, England,
Servia, Argentine Republic, and the United States. Though small (¾-1 inch long),
its numbers usually excite digestive and nervous disorders of considerable
severity, more serious, indeed, than those caused by the commoner tape-worms.
H. diminuta Rud. (flavopunctata Weinl.), normally found in Rodents, has been
rarely recorded in man. Taenia (Dipylidium) caninum L. (= T. cucumerina Bloch
= T. elliptica Batsch), the commonest parasite of pet cats and dogs, and T.
(Davainea) madagascariensis Davaine, have occasionally been recorded from
infants and young children. But the attacks of these species are insignificant in
comparison with those of the cystic stage (Echinococcus polymorphus) of a tape-
worm (T. echinococcus v. Sieb.) which lives when mature in the dog.
Echinococcus is most frequent in Iceland, where it affects 2 to 3 per cent of the
population, and a still larger proportion of sheep; while in Copenhagen, Northern
Germany, some districts of Switzerland, and Victoria it is not uncommon, but is
frequently found during post-mortem examinations when no definite symptoms of
its presence had been previously noticed. Echinococcus[102] varies greatly in size,
proglottides. B, Head (scolex) of T. solium Rud. × 12. (After Leuckart.)
Generally speaking, "a tape-worm" in Western Europe will prove to be Taenia
saginata Goeze (the beef tape-worm, Fig. 39, A), exceedingly prevalent also in
the East, and indeed cosmopolitan, occurring wherever the infected flesh of the ox
is eaten in a raw or half-cooked state. Its attacks are fortunately not usually
severe. Taenia solium Rud. (the pork tape-worm) is found wherever the pig is kept
as a domestic animal, and has consequently a world-wide distribution. Its size (6-
9 feet long) and powers of adhesion would alone render T. solium a formidable
parasite. But the danger of its presence in the body of man, or in the flesh of pigs,
lies in the fact that the larva or bladder-worm (known as Cysticercus cellulosae)
can live in the most varied organs. Thus if by accident a mature proglottis be
eaten, the embryos escape, bore their way into the wall of the stomach, and
entering the portal vein, may reach in time the muscles, the brain, the eye, or even
the heart itself, and attain the cystic condition. Even more disastrous may be the
result, should some ripe joints of a mature worm work their way from the intestine
back towards the stomach. Should this happen (and though it has not been directly
proved, the possibility is to be reckoned with), the result would be the release of
vast numbers of embryos capable of inflicting fatal injury on the host. An
abnormal Cysticercus of this species is probably the Taenia (Cysticercus)
acanthotrias Weinl. (see, however, Leuckart, loc. cit. p. 711).
Taenia (Hymenolepis) nana v. Sieb.[101] is found in man in Egypt, Italy, England,
Servia, Argentine Republic, and the United States. Though small (¾-1 inch long),
its numbers usually excite digestive and nervous disorders of considerable
severity, more serious, indeed, than those caused by the commoner tape-worms.
H. diminuta Rud. (flavopunctata Weinl.), normally found in Rodents, has been
rarely recorded in man. Taenia (Dipylidium) caninum L. (= T. cucumerina Bloch
= T. elliptica Batsch), the commonest parasite of pet cats and dogs, and T.
(Davainea) madagascariensis Davaine, have occasionally been recorded from
infants and young children. But the attacks of these species are insignificant in
comparison with those of the cystic stage (Echinococcus polymorphus) of a tape-
worm (T. echinococcus v. Sieb.) which lives when mature in the dog.
Echinococcus is most frequent in Iceland, where it affects 2 to 3 per cent of the
population, and a still larger proportion of sheep; while in Copenhagen, Northern
Germany, some districts of Switzerland, and Victoria it is not uncommon, but is
frequently found during post-mortem examinations when no definite symptoms of
its presence had been previously noticed. Echinococcus[102] varies greatly in size,
Page 95
form, and mode of growth, but is distinguished in the formation not of one scolex
only, as in the Cysticercus, but in the production of a number of vesicles, usually
from the inner wall. Within these, large numbers of scolices may be developed.
The whole organism continues to swell by the formation of a watery liquid within
it, and if its growth be rapid the fluid tension may cause the rupture of the
enclosing connective-tissue capsule formed around the parasite, at the expense of
the host, and the protrusion of the daughter vesicles. It is the consequent injury to
the surrounding organs of the host, at this critical stage, often only reached after
the lapse of several years, that occasions serious or even fatal results.
Zoologically, Taenia echinococcus and T. coenurus are interesting, since they
exhibit an indubitable alternation of asexual generations in the larval state, with a
sexual adult stage.
Bothriocephalus latus Brems., the broad tape-worm, which attains a length of 20-
30 feet, or even more, occurs in man endemically in the eastern Baltic provinces,
certain parts of Switzerland, generally throughout Russia (especially near Kasan),
in North America, and commonly in Japan,—that is, in districts where the
population partake largely of pike or other fish in a raw or partially-cooked state.
Elsewhere it occurs sporadically, and in Munich, where it was unknown before
1880, its presence has been traced to emigrants from infected districts, who settled
on the shores of the Starenberger Lake, from which Munich was supplied with
fish. How the pike, the usual but not invariable intermediate host, becomes
infested (and its musculature is frequently riddled with the larvae) we do not
accurately know, but some Invertebrate, the prey of the pike, is probably the first
host into which the free-swimming ciliated larva (Fig. 42) finds its way. In
Greenland, B. cordatus is very common in the dog, and probably also in man,
though few cases have been recorded. B. mansoni Cobb. (= B. liguloides Leuck.)
was, till recently, known only in the larval state from China and Japan. Iijima,
however, has found older specimens in the latter country. B. cristatus Dav. is a
species founded somewhat doubtfully on two fragments found, one in a child, the
other in a man, in France.
Occurrence of Cestodes in Domestic Animals.[103]—Among domestic animals,
the dog is, undoubtedly, the most frequently attacked by Taeniae. Six species of
Taenia (T. serrata, marginata, coenurus, echinococcus, krabbei, and possibly T.
serialis), Dipylidium caninum (the commonest form), Mesocestoides lineatus, and
three or four species of Bothriocephalus have been found in the dog. The table of
life-histories (p. 83) shows that sheep, rabbits and other Rodents serve as the
intermediate hosts, in which the cystic stages of the species of Taenia are found.
Hence the prevalence of T. serrata in a given locality is connected with the
only, as in the Cysticercus, but in the production of a number of vesicles, usually
from the inner wall. Within these, large numbers of scolices may be developed.
The whole organism continues to swell by the formation of a watery liquid within
it, and if its growth be rapid the fluid tension may cause the rupture of the
enclosing connective-tissue capsule formed around the parasite, at the expense of
the host, and the protrusion of the daughter vesicles. It is the consequent injury to
the surrounding organs of the host, at this critical stage, often only reached after
the lapse of several years, that occasions serious or even fatal results.
Zoologically, Taenia echinococcus and T. coenurus are interesting, since they
exhibit an indubitable alternation of asexual generations in the larval state, with a
sexual adult stage.
Bothriocephalus latus Brems., the broad tape-worm, which attains a length of 20-
30 feet, or even more, occurs in man endemically in the eastern Baltic provinces,
certain parts of Switzerland, generally throughout Russia (especially near Kasan),
in North America, and commonly in Japan,—that is, in districts where the
population partake largely of pike or other fish in a raw or partially-cooked state.
Elsewhere it occurs sporadically, and in Munich, where it was unknown before
1880, its presence has been traced to emigrants from infected districts, who settled
on the shores of the Starenberger Lake, from which Munich was supplied with
fish. How the pike, the usual but not invariable intermediate host, becomes
infested (and its musculature is frequently riddled with the larvae) we do not
accurately know, but some Invertebrate, the prey of the pike, is probably the first
host into which the free-swimming ciliated larva (Fig. 42) finds its way. In
Greenland, B. cordatus is very common in the dog, and probably also in man,
though few cases have been recorded. B. mansoni Cobb. (= B. liguloides Leuck.)
was, till recently, known only in the larval state from China and Japan. Iijima,
however, has found older specimens in the latter country. B. cristatus Dav. is a
species founded somewhat doubtfully on two fragments found, one in a child, the
other in a man, in France.
Occurrence of Cestodes in Domestic Animals.[103]—Among domestic animals,
the dog is, undoubtedly, the most frequently attacked by Taeniae. Six species of
Taenia (T. serrata, marginata, coenurus, echinococcus, krabbei, and possibly T.
serialis), Dipylidium caninum (the commonest form), Mesocestoides lineatus, and
three or four species of Bothriocephalus have been found in the dog. The table of
life-histories (p. 83) shows that sheep, rabbits and other Rodents serve as the
intermediate hosts, in which the cystic stages of the species of Taenia are found.
Hence the prevalence of T. serrata in a given locality is connected with the
Page 96
abundance there of the rabbit and hare, in which the larva (Cysticercus pisiformis)
occurs. Bothriocephalus cordatus develops from the young stage present in the
fish which the Icelanders give to their dogs. In Iceland and certain parts of
Australia T. echinococcus infests one-third to one-half the number of dogs
examined; a fact connected with the frequency of Echinococcus in man in these
countries.
In sheep the most noteworthy and dangerous parasite is Coenurus cerebralis (or
the cystic stage of the dog-taenia, T. coenurus), which gives rise to the disease
known as "gid" or "staggers." It is found in various parts of the brain or spinal
cord, and the symptoms differ according to the position of the parasite. If this
presses upon one hemisphere the sheep describes circles and finally falls: if on the
optic lobes, the eyes are affected: if the pressure affects the cerebellum the
movements of the sheep are uncertain and incoordinated. Four or six weeks after
the appearance of the symptoms, death results from cerebral paralysis, or from
general debility, and the loss of sheep incurred by this disease (happily less
frequent in England than formerly) has been calculated by Youatt at a million for
France annually; at 35 per cent of the flocks for England in bad seasons; and
about 2 per cent for Germany. Besides sheep, which are most subject to "gid"
during their first year, various ruminants—Goat, Ox, Moufflon, Chamois, Roe,
Antelope, Reindeer, Dromedary—are attacked in the same way. A similar form,
Coenurus serialis Baill., is common in the wild rabbit in this country, and in
Australia in the hare and squirrel. It forms large swellings in the connective tissue
of various parts of the body, but usually does not affect the health of the host. It is
not known in what carnivore Taenia serialis Baill. normally occurs. Experiments
have, however, shown that it develops rapidly in dogs.
The preventive measures which are steadily diminishing the prevalence of the
Cestode parasites in man in some parts of Western Europe cannot be dealt with
here, but it may be noticed that the Jewish observance with regard to swine is the
surest preventive measure against taeniasis and trichinosis. Careful inspection of
meat and general cleanliness, are the leading measures that in these hygienic
matters secure the greatest immunity from disease.
Table of the Life-Histories of the principal Cestodes of Man and the Domestic
Animals.
Cestode. Final host. Larva. Intermediate host.
occurs. Bothriocephalus cordatus develops from the young stage present in the
fish which the Icelanders give to their dogs. In Iceland and certain parts of
Australia T. echinococcus infests one-third to one-half the number of dogs
examined; a fact connected with the frequency of Echinococcus in man in these
countries.
In sheep the most noteworthy and dangerous parasite is Coenurus cerebralis (or
the cystic stage of the dog-taenia, T. coenurus), which gives rise to the disease
known as "gid" or "staggers." It is found in various parts of the brain or spinal
cord, and the symptoms differ according to the position of the parasite. If this
presses upon one hemisphere the sheep describes circles and finally falls: if on the
optic lobes, the eyes are affected: if the pressure affects the cerebellum the
movements of the sheep are uncertain and incoordinated. Four or six weeks after
the appearance of the symptoms, death results from cerebral paralysis, or from
general debility, and the loss of sheep incurred by this disease (happily less
frequent in England than formerly) has been calculated by Youatt at a million for
France annually; at 35 per cent of the flocks for England in bad seasons; and
about 2 per cent for Germany. Besides sheep, which are most subject to "gid"
during their first year, various ruminants—Goat, Ox, Moufflon, Chamois, Roe,
Antelope, Reindeer, Dromedary—are attacked in the same way. A similar form,
Coenurus serialis Baill., is common in the wild rabbit in this country, and in
Australia in the hare and squirrel. It forms large swellings in the connective tissue
of various parts of the body, but usually does not affect the health of the host. It is
not known in what carnivore Taenia serialis Baill. normally occurs. Experiments
have, however, shown that it develops rapidly in dogs.
The preventive measures which are steadily diminishing the prevalence of the
Cestode parasites in man in some parts of Western Europe cannot be dealt with
here, but it may be noticed that the Jewish observance with regard to swine is the
surest preventive measure against taeniasis and trichinosis. Careful inspection of
meat and general cleanliness, are the leading measures that in these hygienic
matters secure the greatest immunity from disease.
Table of the Life-Histories of the principal Cestodes of Man and the Domestic
Animals.
Cestode. Final host. Larva. Intermediate host.
Page 97
Rabbit, Hare,
Taenia serrata Cysticercus
Dog Mice (liver and
Goeze pisiformis Zed.
peritoneum)
Monkeys,
Cyst. tenuicollis Ruminants,
T. marginata Batsch Dog, Wolf
Rud. Ungulates (in
peritoneum)
T. saginata Goeze
(= Ox, Giraffe (in
Man Cyst. bovis Cobb.
T. mediocanellata muscles)
Küch.)
Pig, Man,
Cyst. cellulosae
Monkeys, Bear,
Rud. (? Cyst.
T. solium Rud. Man Dog, Cat, Black
acanthotrias
Rat (in various
Weinl.)
organs)
Cat and
other Cyst. fasciolaris Rat, Mouse, Bat
T. crassicollis Rud.
Felidae, Rud. (liver)
Stoat
Brain of Sheep,
Ox, Goat,
Dog, Arctic Coenurus Dromedary,
T. coenurus Küch.
Fox cerebralis Rud. Camel,
Antelope,
Horse
Rabbit
Coenurus serialis
T. serialis Baill. ? Dog (connective
Baill.
tissue)
Man, Monkeys,
many
Echinococcus Carnivores,
Dog, Dingo, polymorphus Rodents,
T. echinococcus
Jackal, Dies.(incl. Ungulates,
v. Sieb.
Wolf E. multilocularis Ruminants, and
found in Man) Marsupials;
also in Turkey
and other birds
Moniezia expansa Sheep, Ox,
Unknown
Rud. Goat, etc.
Taenia serrata Cysticercus
Dog Mice (liver and
Goeze pisiformis Zed.
peritoneum)
Monkeys,
Cyst. tenuicollis Ruminants,
T. marginata Batsch Dog, Wolf
Rud. Ungulates (in
peritoneum)
T. saginata Goeze
(= Ox, Giraffe (in
Man Cyst. bovis Cobb.
T. mediocanellata muscles)
Küch.)
Pig, Man,
Cyst. cellulosae
Monkeys, Bear,
Rud. (? Cyst.
T. solium Rud. Man Dog, Cat, Black
acanthotrias
Rat (in various
Weinl.)
organs)
Cat and
other Cyst. fasciolaris Rat, Mouse, Bat
T. crassicollis Rud.
Felidae, Rud. (liver)
Stoat
Brain of Sheep,
Ox, Goat,
Dog, Arctic Coenurus Dromedary,
T. coenurus Küch.
Fox cerebralis Rud. Camel,
Antelope,
Horse
Rabbit
Coenurus serialis
T. serialis Baill. ? Dog (connective
Baill.
tissue)
Man, Monkeys,
many
Echinococcus Carnivores,
Dog, Dingo, polymorphus Rodents,
T. echinococcus
Jackal, Dies.(incl. Ungulates,
v. Sieb.
Wolf E. multilocularis Ruminants, and
found in Man) Marsupials;
also in Turkey
and other birds
Moniezia expansa Sheep, Ox,
Unknown
Rud. Goat, etc.
Page 98
Thysanosoma Sheep,
Unknown
fimbriata Dies. Cervidae
Stilesia
globipunctata Sheep Unknown
Riv.
Anoplocephala
Horse Unknown
perfoliata Goeze
Dipylidium caninum
L. (= Taenia Cysticercoid larva Body-cavity of
cucumerina Man, Dog, (Fig. 43), Trichodectes
Bloch = Cat Cryptocystis and Pulex of
T. elliptica trichodectis Vill. Dog
Batsch)
Cercocystis Vill.
Hymenolepis [104]
Mouse, Rat (develops Usually absent
murina Duj.
in parental host)
H. nana v. Sieb. Man Unknown
Meal-moth,
Asopia
H. diminuta Rud. (=
Man, (Pyralis)
Taenia
Mouse, Cercocystis Vill. farinalis; also
flavopunctata
Rat certain
Weinl.)
Orthoptera and
Coleoptera
The Ostracods
Candona
Duck,
rostrata and
Drepanidotaenia Goose,
Cercocystis Vill. Cypris
gracilis Zed. Wild
compressa, and
Duck
also Cyclops
viridis
Cypris
D. anatina Krabbe Duck " " incongruens,
and also Perch
Cyclops
D. setigera Fröh. Goose " "
brevicaudatus
D. infundibuliformis Common
" " House-fly
Goeze Fowl
Unknown
fimbriata Dies. Cervidae
Stilesia
globipunctata Sheep Unknown
Riv.
Anoplocephala
Horse Unknown
perfoliata Goeze
Dipylidium caninum
L. (= Taenia Cysticercoid larva Body-cavity of
cucumerina Man, Dog, (Fig. 43), Trichodectes
Bloch = Cat Cryptocystis and Pulex of
T. elliptica trichodectis Vill. Dog
Batsch)
Cercocystis Vill.
Hymenolepis [104]
Mouse, Rat (develops Usually absent
murina Duj.
in parental host)
H. nana v. Sieb. Man Unknown
Meal-moth,
Asopia
H. diminuta Rud. (=
Man, (Pyralis)
Taenia
Mouse, Cercocystis Vill. farinalis; also
flavopunctata
Rat certain
Weinl.)
Orthoptera and
Coleoptera
The Ostracods
Candona
Duck,
rostrata and
Drepanidotaenia Goose,
Cercocystis Vill. Cypris
gracilis Zed. Wild
compressa, and
Duck
also Cyclops
viridis
Cypris
D. anatina Krabbe Duck " " incongruens,
and also Perch
Cyclops
D. setigera Fröh. Goose " "
brevicaudatus
D. infundibuliformis Common
" " House-fly
Goeze Fowl
Page 99
Dicranotaenia
Duck " " Cypris ovum
coronula Duj.
Davainea ? Limax cinereus,
Fowl " "
proglottina Dav. L. agrestis
D.
madagascariensis Children Unknown
Dav.
D. friedbergeri
Pheasant Unknown ? Ants
v. Linst.
Mesocestoides
Dog Unknown
lineatus Goeze
Probably first
enters an
Plerocercoid, i.e
Invertebrate
Bothriocephalus Man, Dog, solid, elongate
host, which is
latus Brems. ? Cat larva, with no
eaten by Pike,
bladder
Perch, Trout,
etc.
Fig. 40.—A, Stickleback (Gasterosteus aculeatus) infested by an advanced larva of
Schistocephalus solidus Crepl. B, The larva. All × 1½. (From specimens in the
Cambridge University Museum.)
Structure and Development of Cestoda.[105]—Of the unsegmented Cestodes,
Caryophyllaeus mutabilis, from the intestine of carp and other Cyprinoid fishes, is
the most easily accessible form. Triaenophorus nodulosus, which is very useful
for the study of the excretory system, occurs mature in the pike. In the body-
cavity of the Stickleback (Fig. 40) a large, broad, yellow worm may sometimes be
found, the larva of Schistocephalus solidus Crepl., which occurs in the intestine of
Terns, Storks, Mergansers, and other birds. Species of Ligula are found in the
same birds. The intestine of a Lophius or Cyclopterus ("lump-fish") contains,
usually, the early and intermediate stages of various Cestodes, while the
alimentary canal of Elasmobranchs often contain many peculiar Tetrarhynchidae
and other forms. For the study of development, the Taenia anatina from the duck
Duck " " Cypris ovum
coronula Duj.
Davainea ? Limax cinereus,
Fowl " "
proglottina Dav. L. agrestis
D.
madagascariensis Children Unknown
Dav.
D. friedbergeri
Pheasant Unknown ? Ants
v. Linst.
Mesocestoides
Dog Unknown
lineatus Goeze
Probably first
enters an
Plerocercoid, i.e
Invertebrate
Bothriocephalus Man, Dog, solid, elongate
host, which is
latus Brems. ? Cat larva, with no
eaten by Pike,
bladder
Perch, Trout,
etc.
Fig. 40.—A, Stickleback (Gasterosteus aculeatus) infested by an advanced larva of
Schistocephalus solidus Crepl. B, The larva. All × 1½. (From specimens in the
Cambridge University Museum.)
Structure and Development of Cestoda.[105]—Of the unsegmented Cestodes,
Caryophyllaeus mutabilis, from the intestine of carp and other Cyprinoid fishes, is
the most easily accessible form. Triaenophorus nodulosus, which is very useful
for the study of the excretory system, occurs mature in the pike. In the body-
cavity of the Stickleback (Fig. 40) a large, broad, yellow worm may sometimes be
found, the larva of Schistocephalus solidus Crepl., which occurs in the intestine of
Terns, Storks, Mergansers, and other birds. Species of Ligula are found in the
same birds. The intestine of a Lophius or Cyclopterus ("lump-fish") contains,
usually, the early and intermediate stages of various Cestodes, while the
alimentary canal of Elasmobranchs often contain many peculiar Tetrarhynchidae
and other forms. For the study of development, the Taenia anatina from the duck
Page 100
may be used. The ripe proglottides are collected, and the eggs placed with Cypris
ovum in an aquarium, with the probability that some of the embryos will enter the
Ostracod, and the peculiar Cysticercoid may be bred.[106] Cysticercus pisiformis
and Coenurus serialis, which occur commonly in rabbits, are also suitable objects
for examination.
A Cestode such as Echinobothrium (Fig. 36) is divisible into head and
proglottides. Moniez has suggested that the head is really the morphologically
hinder end of the body, in which case the formation of proglottides would closely
resemble the mode of segmentation of an Annelid larva. The close similarity,
however, between the Cysticercoid larva (Fig. 43, F) and the Cercaria of a liver-
fluke, seems to show that the anterior end is the same in both cases, and since it
bears the central part of the nervous system, we may reasonably call it the "head."
Moreover the hinder end of a Platyhelminth usually possesses the chief excretory
pore. Another difficulty is the determination of dorsal and ventral surfaces.
Authors are agreed,—on the analogy of Trematodes, in which the testes are
usually dorsal and the ovaries ventral,—that the dorsal and ventral aspects of a
Cestode are determined by the position of these organs, although the often radially
formed "head," the lateral or superficial position of the genital apertures, and the
variability of these features, render it a matter of considerable doubt whether
"dorsal" and "ventral" are more than useful conventional terms. The suckers and
hooks are borne on a muscular cap, the "rostellum," which is only slightly
developed in the Ichthyotaeniae. The body is solid, and is divisible into an outer
muscular coat—enveloped in a (possibly epidermal) investing membrane—and an
inner parenchymatous tissue containing the chief part of the excretory, nervous,
and reproductive systems. One or two pairs of longitudinal excretory vessels are
present, usually connected by transverse ducts and opening by a single terminal
pore. Occasionally a regularly paired arrangement of lateral or secondary pores is
present (Figs. 38 and 41, for.sec). Flame-cells occur at the end of the fine tubules
(Fig. 38), and the whole system is well developed, but may undergo degenerative
changes in the older proglottides. The central nervous system varies according to
the degree of differentiation of the rostellum; and, owing to the difficulty of
staining the nerves and the contradictory statements of authors, we do not yet
possess a fully reliable account of the nervous system even of the commoner
Taeniae. Free nerve endings and other sensory terminations have been recently
stated to exist in the cuticle of Cestodes and Trematodes. If true, this would tend
to show that the parasitic mode of life of these animals demands a complex
nervous system comparable with that of the Turbellaria.
ovum in an aquarium, with the probability that some of the embryos will enter the
Ostracod, and the peculiar Cysticercoid may be bred.[106] Cysticercus pisiformis
and Coenurus serialis, which occur commonly in rabbits, are also suitable objects
for examination.
A Cestode such as Echinobothrium (Fig. 36) is divisible into head and
proglottides. Moniez has suggested that the head is really the morphologically
hinder end of the body, in which case the formation of proglottides would closely
resemble the mode of segmentation of an Annelid larva. The close similarity,
however, between the Cysticercoid larva (Fig. 43, F) and the Cercaria of a liver-
fluke, seems to show that the anterior end is the same in both cases, and since it
bears the central part of the nervous system, we may reasonably call it the "head."
Moreover the hinder end of a Platyhelminth usually possesses the chief excretory
pore. Another difficulty is the determination of dorsal and ventral surfaces.
Authors are agreed,—on the analogy of Trematodes, in which the testes are
usually dorsal and the ovaries ventral,—that the dorsal and ventral aspects of a
Cestode are determined by the position of these organs, although the often radially
formed "head," the lateral or superficial position of the genital apertures, and the
variability of these features, render it a matter of considerable doubt whether
"dorsal" and "ventral" are more than useful conventional terms. The suckers and
hooks are borne on a muscular cap, the "rostellum," which is only slightly
developed in the Ichthyotaeniae. The body is solid, and is divisible into an outer
muscular coat—enveloped in a (possibly epidermal) investing membrane—and an
inner parenchymatous tissue containing the chief part of the excretory, nervous,
and reproductive systems. One or two pairs of longitudinal excretory vessels are
present, usually connected by transverse ducts and opening by a single terminal
pore. Occasionally a regularly paired arrangement of lateral or secondary pores is
present (Figs. 38 and 41, for.sec). Flame-cells occur at the end of the fine tubules
(Fig. 38), and the whole system is well developed, but may undergo degenerative
changes in the older proglottides. The central nervous system varies according to
the degree of differentiation of the rostellum; and, owing to the difficulty of
staining the nerves and the contradictory statements of authors, we do not yet
possess a fully reliable account of the nervous system even of the commoner
Taeniae. Free nerve endings and other sensory terminations have been recently
stated to exist in the cuticle of Cestodes and Trematodes. If true, this would tend
to show that the parasitic mode of life of these animals demands a complex
nervous system comparable with that of the Turbellaria.
Page 101
Fig. 41.—Diagrammatic transverse section of Schistocephalus solidus Crepl., from the Wild-
duck, illustrative of the Cestodes with uterine aperture (uto). × 12. cs, Cirrus-sac;
for.sec, one of the paired lateral openings of the excretory vessels; ln, longitudinal
nerve; ov, ovary; ovd, oviduct; par.m, parenchymatous muscles; r.sem, receptaculum
seminis; sh.gl, shell-gland; te, testes; ut, uterus; uto, uterine pore; vag, vagina; vd, vasa
deferentia; yd, yolk-duct; yg, yolk-glands (black); ♂, male, ♀, female genital aperture.
(After Riehm.)
The reproductive organs, unlike the preceding systems, are discontinuous from
one proglottis to the next. The male and female organs and their mutual
connexions, especially in the unsegmented Cestodes, may be compared in detail
with those of Trematodes, but the difference between the arrangement of the
generative organs of various Cestodes is very great.[107] The penis (Fig. 41, cs) is
evaginated through the male pore (Fig. 41, ♂), and inserted far into the vagina (♀,
vag) of the same or another segment of the tape-worm.
Fig. 42.—A, Free-swimming, six-hooked larva of Bothriocephalus latus Brems. (the broad
tape-worm of Man), still enclosed in a ciliated (possibly cellular) double membrane or
mantle. In this condition it may continue to live in water for a week or more, but
eventually throws off its ciliated coat (as in B) and commences to creep about
vigorously by the aid of its hooks, in search of its first host, which is at present
unknown. (After Schauinsland.) × 600.
From this fact and the anatomical relations of the vagina, it is becoming
increasingly probable that the so-called uterus of Trematodes is an organ
corresponding to the vagina of Cestodes, and not to the uterus of Cestodes. The
latter opens to the exterior in Schistocephalus, Bothriocephalus, and some other
Cestodes of fishes by a special pore (Fig. 41, uto). Through this, some of the eggs
(which in these genera give rise to ciliated larvae) are enabled to escape, and need
not wait for the detachment of the proglottis, as must happen in the Taeniidae,
where the uterus is closed. This uterus, a true physiological one, is probably the
homologue of the "canal of Laurer" ("Laurer-Stieda canal," or "vagina") of
Trematoda. The fertilised ovum and yolk are brought together into the "ootype,"
where the shell-gland forms the egg-shell around them (Fig. 41, sh.gl) and the egg
duck, illustrative of the Cestodes with uterine aperture (uto). × 12. cs, Cirrus-sac;
for.sec, one of the paired lateral openings of the excretory vessels; ln, longitudinal
nerve; ov, ovary; ovd, oviduct; par.m, parenchymatous muscles; r.sem, receptaculum
seminis; sh.gl, shell-gland; te, testes; ut, uterus; uto, uterine pore; vag, vagina; vd, vasa
deferentia; yd, yolk-duct; yg, yolk-glands (black); ♂, male, ♀, female genital aperture.
(After Riehm.)
The reproductive organs, unlike the preceding systems, are discontinuous from
one proglottis to the next. The male and female organs and their mutual
connexions, especially in the unsegmented Cestodes, may be compared in detail
with those of Trematodes, but the difference between the arrangement of the
generative organs of various Cestodes is very great.[107] The penis (Fig. 41, cs) is
evaginated through the male pore (Fig. 41, ♂), and inserted far into the vagina (♀,
vag) of the same or another segment of the tape-worm.
Fig. 42.—A, Free-swimming, six-hooked larva of Bothriocephalus latus Brems. (the broad
tape-worm of Man), still enclosed in a ciliated (possibly cellular) double membrane or
mantle. In this condition it may continue to live in water for a week or more, but
eventually throws off its ciliated coat (as in B) and commences to creep about
vigorously by the aid of its hooks, in search of its first host, which is at present
unknown. (After Schauinsland.) × 600.
From this fact and the anatomical relations of the vagina, it is becoming
increasingly probable that the so-called uterus of Trematodes is an organ
corresponding to the vagina of Cestodes, and not to the uterus of Cestodes. The
latter opens to the exterior in Schistocephalus, Bothriocephalus, and some other
Cestodes of fishes by a special pore (Fig. 41, uto). Through this, some of the eggs
(which in these genera give rise to ciliated larvae) are enabled to escape, and need
not wait for the detachment of the proglottis, as must happen in the Taeniidae,
where the uterus is closed. This uterus, a true physiological one, is probably the
homologue of the "canal of Laurer" ("Laurer-Stieda canal," or "vagina") of
Trematoda. The fertilised ovum and yolk are brought together into the "ootype,"
where the shell-gland forms the egg-shell around them (Fig. 41, sh.gl) and the egg
Page 102
is then passed into the uterus. The ovum segments to form a minute six-hooked
larva, which may (Bothriidae, Fig. 42) or may not (Taeniidae) be ciliated. Thus in
Taenia serrata the proglottides are shed with the faeces of the host (dog), and they
protect the young from the desiccating influence of the surroundings. If
inadvertently eaten by a rabbit along with herbs, the proglottis and larval envelope
are digested, and by its six hooks the tiny larva bores through the gastric wall into
the portal vein, and so into the liver. Here the hooks are thrown off, and the solid
mass of cells becomes vacuolated.
Fig. 43.—Stages in the development of Dipylidium caninum L. (= Taenia elliptica Batsch, T.
cucumerina Bloch), the commonest of the Dog-Taeniae; compare Fig. 44. A, Six-
hooked larva (now often spoken of as an "Onchosphaera"); B, larva elongating;
formation of a central lacuna; C, larva further advanced; D, distinction between body
and tail is visible; E, invagination of the rostellum is commencing; F, Cysticercoid
larva with four suckers, invaginated rostellum, and excretory vessels. c, Calcareous
concretions in cells of the larva; ex.o, excretory aperture; ex.v, excretory vessels; inv,
invagination commencing; rost, rostellum; sc, suckers. (After Grassi and Rovelli;
highly magnified.)
Fig. 44.—Schematic longitudinal sections through the larvae of Dipylidium caninum L. All
these stages are passed in the body-cavity of the Dog-flea (Pulex serraticeps).
(Compare Fig. 43 for further details.) A, Six-hooked larva with developing rostellum
(shaded) and suckers (black). In this species the invagination (C, invag.) occurs after
the formation of these organs, and not, as in most Taeniae, before it. B, Invagination
commencing; the hooks are developing above the rostellum, while beneath it the
nervous system (dotted) is seen. C, The invagination has now carried the suckers
inwards. The tail has become distinct, and the whole larva at this stage is known as a
Cysticercoid. hk, Larval hooks; invag, mouth of the invagination; n, central nervous
larva, which may (Bothriidae, Fig. 42) or may not (Taeniidae) be ciliated. Thus in
Taenia serrata the proglottides are shed with the faeces of the host (dog), and they
protect the young from the desiccating influence of the surroundings. If
inadvertently eaten by a rabbit along with herbs, the proglottis and larval envelope
are digested, and by its six hooks the tiny larva bores through the gastric wall into
the portal vein, and so into the liver. Here the hooks are thrown off, and the solid
mass of cells becomes vacuolated.
Fig. 43.—Stages in the development of Dipylidium caninum L. (= Taenia elliptica Batsch, T.
cucumerina Bloch), the commonest of the Dog-Taeniae; compare Fig. 44. A, Six-
hooked larva (now often spoken of as an "Onchosphaera"); B, larva elongating;
formation of a central lacuna; C, larva further advanced; D, distinction between body
and tail is visible; E, invagination of the rostellum is commencing; F, Cysticercoid
larva with four suckers, invaginated rostellum, and excretory vessels. c, Calcareous
concretions in cells of the larva; ex.o, excretory aperture; ex.v, excretory vessels; inv,
invagination commencing; rost, rostellum; sc, suckers. (After Grassi and Rovelli;
highly magnified.)
Fig. 44.—Schematic longitudinal sections through the larvae of Dipylidium caninum L. All
these stages are passed in the body-cavity of the Dog-flea (Pulex serraticeps).
(Compare Fig. 43 for further details.) A, Six-hooked larva with developing rostellum
(shaded) and suckers (black). In this species the invagination (C, invag.) occurs after
the formation of these organs, and not, as in most Taeniae, before it. B, Invagination
commencing; the hooks are developing above the rostellum, while beneath it the
nervous system (dotted) is seen. C, The invagination has now carried the suckers
inwards. The tail has become distinct, and the whole larva at this stage is known as a
Cysticercoid. hk, Larval hooks; invag, mouth of the invagination; n, central nervous
Page 103
system; rost, rostellum and hooks; sc, suckers, of which only two can be seen in a
longitudinal section; four are really present. (After Grassi and Rovelli.)
At one pole an invagination occurs, at the bottom of which the rostellum, suckers,
and hooks are gradually formed, but inside out as compared with the head of the
Taenia serrata. At this stage the larva (Cysticercus pisiformis) has usually issued
from the liver and attached itself to the omentum. The invagination projects into
the cavity of the bladder, within which a watery fluid accumulates. Thus the
"bladder worm" is formed, the head of which is evaginated if the larva be
introduced into the digestive system of a dog. The bladder and neck of
invagination are digested, while the head, protected by these, remains, and forms
the neck, from which the proglottides are afterwards segmented off. In Taenia
(Hymenolepis) murina the whole development may take place in the parental host,
the larva living in the villi, the adults in the cavity of the same rat's intestine
(Grassi). The different forms of Cestode larvae depend largely upon the presence
and degree of development of the caudal vesicle or bladder, which in Scolex
polymorphus (Fig. 38) (the young stage of Calliobothrium filicolle Zsch.) is
practically absent. If the bladder be small, the larva is known as a Cysticercoid.
For example, the common Dipylidium caninum, which lives in the dog, has such a
larva, the development of which is explained and illustrated by Figs. 43 and 44.
The bladder becomes exceeding capacious in Coenurus and Echinococcus.
Table for the Discrimination of the more usual Cestodes of Man and
Domestic Animals.[108]
I. Scolex in most cases with hooks; uterus with a median and lateral branches;
yolk-glands simple, median; genital pore single; dorsal excretory vessel
narrower than the ventral, without a circular commissural trunk; eggs
without pyriform apparatus (processes of the ovarian membrane)
Gen. Taenia L. (s. str.)
A. Genital ducts pass on the ventral side of
the nerve and of the two longitudinal
excretory vessels T. crassicollis Rud.
B. Genital ducts pass between the dorsal and ventral longitudinal vessels.
a. Nerve present on dorsal side of genital ducts.
α. Head armed T. solium Rud.
β. Head unarmed T. saginata Goeze.
b. Nerve on ventral side of genital ducts.
Dog-Taeniae[109]
longitudinal section; four are really present. (After Grassi and Rovelli.)
At one pole an invagination occurs, at the bottom of which the rostellum, suckers,
and hooks are gradually formed, but inside out as compared with the head of the
Taenia serrata. At this stage the larva (Cysticercus pisiformis) has usually issued
from the liver and attached itself to the omentum. The invagination projects into
the cavity of the bladder, within which a watery fluid accumulates. Thus the
"bladder worm" is formed, the head of which is evaginated if the larva be
introduced into the digestive system of a dog. The bladder and neck of
invagination are digested, while the head, protected by these, remains, and forms
the neck, from which the proglottides are afterwards segmented off. In Taenia
(Hymenolepis) murina the whole development may take place in the parental host,
the larva living in the villi, the adults in the cavity of the same rat's intestine
(Grassi). The different forms of Cestode larvae depend largely upon the presence
and degree of development of the caudal vesicle or bladder, which in Scolex
polymorphus (Fig. 38) (the young stage of Calliobothrium filicolle Zsch.) is
practically absent. If the bladder be small, the larva is known as a Cysticercoid.
For example, the common Dipylidium caninum, which lives in the dog, has such a
larva, the development of which is explained and illustrated by Figs. 43 and 44.
The bladder becomes exceeding capacious in Coenurus and Echinococcus.
Table for the Discrimination of the more usual Cestodes of Man and
Domestic Animals.[108]
I. Scolex in most cases with hooks; uterus with a median and lateral branches;
yolk-glands simple, median; genital pore single; dorsal excretory vessel
narrower than the ventral, without a circular commissural trunk; eggs
without pyriform apparatus (processes of the ovarian membrane)
Gen. Taenia L. (s. str.)
A. Genital ducts pass on the ventral side of
the nerve and of the two longitudinal
excretory vessels T. crassicollis Rud.
B. Genital ducts pass between the dorsal and ventral longitudinal vessels.
a. Nerve present on dorsal side of genital ducts.
α. Head armed T. solium Rud.
β. Head unarmed T. saginata Goeze.
b. Nerve on ventral side of genital ducts.
Dog-Taeniae[109]
Page 104
Head armed; genital pore marginal and
— Single
Many proglottides; strobila several centimetres long; small hooks
with guard.
Bifid hooks, which are
— 230µ-260µ long[110]; genital
pore very distinct T. serrata Goeze.
— 136µ-157µ long; genital pore
not very salient T. serialis Ball.
Entire large hooks, which are
— 180µ-220µ long; length of
mature segments double their
width T. marginata Batsch.
— 150µ-170µ long; length of
mature segments treble their
width T. coenurus Küch.
3-4 segments; a few mm. long T. echinococcus v. Sieb.
— Double and bilateral Dipylidium caninum L.
Head unarmed; two genital pores on Mesocestoides lineatus
ventral surface Goeze.
II. Scolex without hooks; one or two transverse uteri present; one or two
genital pores and yolk-glands, the latter never median; genital ducts pass
on the dorsal side of the nerve; eggs with pyriform apparatus.
A. One transverse uterus present.
a. Uterus with bullate egg-sacs; pyriform apparatus without horns; genital
ducts between dorsal and ventral vessels
Thysanosoma Dies.
α. Head large (1.5 mm.); square lobed testes in median field; posterior
margin of segments fimbriated; genital pore double
T. fimbriata Dies.
β. Head small; no fimbriae; pore rarely
double T. giardii Riv.
b. Uterus without saccular dilatations;
segments short, thick, and slightly
imbricate Anoplocephala E. Blanch.
Horse-Taeniae.
α. Head very large
— No posterior lobes A. plicata Zed.
— Four posterior lobes A. perfoliata Goeze.
β. Head small, without posterior lobes A. mamillana Mehl.
— Single
Many proglottides; strobila several centimetres long; small hooks
with guard.
Bifid hooks, which are
— 230µ-260µ long[110]; genital
pore very distinct T. serrata Goeze.
— 136µ-157µ long; genital pore
not very salient T. serialis Ball.
Entire large hooks, which are
— 180µ-220µ long; length of
mature segments double their
width T. marginata Batsch.
— 150µ-170µ long; length of
mature segments treble their
width T. coenurus Küch.
3-4 segments; a few mm. long T. echinococcus v. Sieb.
— Double and bilateral Dipylidium caninum L.
Head unarmed; two genital pores on Mesocestoides lineatus
ventral surface Goeze.
II. Scolex without hooks; one or two transverse uteri present; one or two
genital pores and yolk-glands, the latter never median; genital ducts pass
on the dorsal side of the nerve; eggs with pyriform apparatus.
A. One transverse uterus present.
a. Uterus with bullate egg-sacs; pyriform apparatus without horns; genital
ducts between dorsal and ventral vessels
Thysanosoma Dies.
α. Head large (1.5 mm.); square lobed testes in median field; posterior
margin of segments fimbriated; genital pore double
T. fimbriata Dies.
β. Head small; no fimbriae; pore rarely
double T. giardii Riv.
b. Uterus without saccular dilatations;
segments short, thick, and slightly
imbricate Anoplocephala E. Blanch.
Horse-Taeniae.
α. Head very large
— No posterior lobes A. plicata Zed.
— Four posterior lobes A. perfoliata Goeze.
β. Head small, without posterior lobes A. mamillana Mehl.
Page 105
B. Two uteri and two genital pores present; horns of pyriform apparatus well
developed; genital ducts pass on the dorsal side of the longitudinal
vessels
Moniezia R. Bl.
a. Interproglottidal glands [111] arranged in linear series (planissima group)
M. planissima S. and H. M. benedeni Mz. M. neumani Mz.
b. Interproglottidal glands saccular (expansa group)
M. expansa Rud. M. oblongiceps S. and H. M. trigonophora S. and H.
c. Interproglottidal glands absent M. denticulata Rud. M.
(denticulata group) alba Perr.
C. Uterus single or double, without spore-like egg-sacs; eggs with a single
shell; genital pores irregularly alternate; strobila narrow; testes absent
from median part of the field
Stilesia Raill.
a. A transverse uterus in middle part of
median field; head 2 mm. diameter S. centripunctata Riv.
b. Two lateral uteri in each segment; head
less than 1 mm. in diameter S. globipunctata Riv.
III. Scolex almost invariably provided with hooks; genital pores on left border
of segment; eggs with three shells but no cornua. Segments broader than
long; posterior angles salient.
Hymenolepis Weinl.
a. Scolex with a single series of 24-30 hooks, each 14-18µ long
H. nana v. Sieb. H. murina Duj.
b. Scolex very small, unarmed H. diminuta Rud.
IV. Scolex provided with two elongated muscular pits. Body segmented; three
genital apertures in middle of ventral surface
Bothriocephalus Rud.
Body 2-20 metres in length
B. latus Brems. B. cristatus Dav. (doubtful species). B. cordatus Leuck. B.
mansoni Cobb. (= B. liguloides Leuck.)
Classification of Cestodes.—The following classification, which, so far as the
Taeniidae are concerned, follows that employed by Railliet, Blanchard, and most
recent writers, includes only a few representative genera:—
1. Fam. Cestodariidae Mont. (Monozoa Lang).
Gen. Caryophyllaeus, Archigetes, Gyrocotyle, Amphilina.
2. Fam. Bothriocephalidae.
developed; genital ducts pass on the dorsal side of the longitudinal
vessels
Moniezia R. Bl.
a. Interproglottidal glands [111] arranged in linear series (planissima group)
M. planissima S. and H. M. benedeni Mz. M. neumani Mz.
b. Interproglottidal glands saccular (expansa group)
M. expansa Rud. M. oblongiceps S. and H. M. trigonophora S. and H.
c. Interproglottidal glands absent M. denticulata Rud. M.
(denticulata group) alba Perr.
C. Uterus single or double, without spore-like egg-sacs; eggs with a single
shell; genital pores irregularly alternate; strobila narrow; testes absent
from median part of the field
Stilesia Raill.
a. A transverse uterus in middle part of
median field; head 2 mm. diameter S. centripunctata Riv.
b. Two lateral uteri in each segment; head
less than 1 mm. in diameter S. globipunctata Riv.
III. Scolex almost invariably provided with hooks; genital pores on left border
of segment; eggs with three shells but no cornua. Segments broader than
long; posterior angles salient.
Hymenolepis Weinl.
a. Scolex with a single series of 24-30 hooks, each 14-18µ long
H. nana v. Sieb. H. murina Duj.
b. Scolex very small, unarmed H. diminuta Rud.
IV. Scolex provided with two elongated muscular pits. Body segmented; three
genital apertures in middle of ventral surface
Bothriocephalus Rud.
Body 2-20 metres in length
B. latus Brems. B. cristatus Dav. (doubtful species). B. cordatus Leuck. B.
mansoni Cobb. (= B. liguloides Leuck.)
Classification of Cestodes.—The following classification, which, so far as the
Taeniidae are concerned, follows that employed by Railliet, Blanchard, and most
recent writers, includes only a few representative genera:—
1. Fam. Cestodariidae Mont. (Monozoa Lang).
Gen. Caryophyllaeus, Archigetes, Gyrocotyle, Amphilina.
2. Fam. Bothriocephalidae.
Page 106
Sub-Fam. 1. Bothriocephalinae. Gen. Bothriocephalus, Schistocephalus,
Triaenophorus (= Tricuspidaria).
Sub-Fam. 2. Ligulinae. Gen. Ligula.
Sub-Fam. 3. Solenophorinae. Gen. Solenophorus, Duthiersia.
Sub-Fam. 4. Diphyllinae. Gen. Echinobothrium.
3. Fam. Tetrarhynchidae.
Gen. Tetrarhynchus.
4. Fam. Tetraphyllidae.
Sub-Fam. 1. Phyllobothrinae. Gen. Phyllobothrium, Echeneibothrium,
etc.
Sub-Fam. 2. Phyllacanthinae. Gen. Calliobothrium, Anthobothrium, etc.
5. Fam. Taeniidae.
Sub-Fam. 1. Cystotaeninae. Gen. Taenia s. str.
Sub-Fam. 2. Anoplocephalinae. Gen. Moniezia, Thysanosoma, Stilesia,
Anoplocephala.
Sub-Fam. 3. Cystoidotaeninae. Gen. Dipylidium, Hymenolepis,
Drepanidotaenia, Dicranotaenia, Echinocotyle, Davainea.
Sub-Fam. 4. Mesocestoidinae. Gen. Mesocestoides, Dithyridium.
Sub-Fam. 5. Ichthyotaeninae. Gen. Ichthyotaenia, Corallobothrium.
CHAPTER IV
MESOZOA
DICYEMIDAE—STRUCTURE—REPRODUCTION—OCCURRENCE: ORTHONECTIDAE—
OCCURRENCE—STRUCTURE: TRICHOPLAX: SALINELLA.
The Mesozoa are an obscure group, the position of which in the animal kingdom
is still doubtful. The name Mesozoa was given to the group by its discoverer, E.
van Beneden,[112] as he concluded that they were intermediate between the
Protozoa and the higher Invertebrates. Recent authors, however, have called
attention to the resemblance existing between them and the "sporocysts" of
Trematodes, and though we still are ignorant of certain important points in their
life-histories, the Mesozoa are most conveniently (and probably rightly)
considered as an appendix to the Platyhelminthes.
Triaenophorus (= Tricuspidaria).
Sub-Fam. 2. Ligulinae. Gen. Ligula.
Sub-Fam. 3. Solenophorinae. Gen. Solenophorus, Duthiersia.
Sub-Fam. 4. Diphyllinae. Gen. Echinobothrium.
3. Fam. Tetrarhynchidae.
Gen. Tetrarhynchus.
4. Fam. Tetraphyllidae.
Sub-Fam. 1. Phyllobothrinae. Gen. Phyllobothrium, Echeneibothrium,
etc.
Sub-Fam. 2. Phyllacanthinae. Gen. Calliobothrium, Anthobothrium, etc.
5. Fam. Taeniidae.
Sub-Fam. 1. Cystotaeninae. Gen. Taenia s. str.
Sub-Fam. 2. Anoplocephalinae. Gen. Moniezia, Thysanosoma, Stilesia,
Anoplocephala.
Sub-Fam. 3. Cystoidotaeninae. Gen. Dipylidium, Hymenolepis,
Drepanidotaenia, Dicranotaenia, Echinocotyle, Davainea.
Sub-Fam. 4. Mesocestoidinae. Gen. Mesocestoides, Dithyridium.
Sub-Fam. 5. Ichthyotaeninae. Gen. Ichthyotaenia, Corallobothrium.
CHAPTER IV
MESOZOA
DICYEMIDAE—STRUCTURE—REPRODUCTION—OCCURRENCE: ORTHONECTIDAE—
OCCURRENCE—STRUCTURE: TRICHOPLAX: SALINELLA.
The Mesozoa are an obscure group, the position of which in the animal kingdom
is still doubtful. The name Mesozoa was given to the group by its discoverer, E.
van Beneden,[112] as he concluded that they were intermediate between the
Protozoa and the higher Invertebrates. Recent authors, however, have called
attention to the resemblance existing between them and the "sporocysts" of
Trematodes, and though we still are ignorant of certain important points in their
life-histories, the Mesozoa are most conveniently (and probably rightly)
considered as an appendix to the Platyhelminthes.
Page 107
Fig. 45.—A, B, C, Stages in the development of the vermiform larva in Dicyema typus van
Ben. (After Ed. van Beneden.) cal, "Calotte"; gc, germinal cell; n, nucleus of
endodermal cell.
The animals composing this group are minute and parasitic, and are composed of
a small number of cells. They may be divided into two families: the Dicyemidae,
which occur exclusively in the kidneys of certain Cephalopods (cuttle-fish); and
the Orthonectidae, which live in the brittle-star Amphiura squamata, the
Nemertine Nemertes lacteus, or the Polyclad Leptoplana tremellaris. In addition
to the undoubted Mesozoa, certain anomalous forms—Trichoplax adhaerens and
Salinella salve—may be referred to this group.
Fig. 46.—Dicyemennea eledones Wag., from the kidney of Eledone moschata. A, Full-grown
Rhombogen with infusoriform embryos (emb); B, one of the latter developing; C, fully
formed; D, calotte, composed of the upper nine cells shown in the figure. (After Ed.
van Beneden and Whitman.) emb, Infusoriform embryo; g, part of endoderm-cell where
formation of these embryos is rapidly proceeding; n.ect, nucleus of ectoderm-cell;
n.end, nucleus of endoderm-cell; p, "calotte."
Ben. (After Ed. van Beneden.) cal, "Calotte"; gc, germinal cell; n, nucleus of
endodermal cell.
The animals composing this group are minute and parasitic, and are composed of
a small number of cells. They may be divided into two families: the Dicyemidae,
which occur exclusively in the kidneys of certain Cephalopods (cuttle-fish); and
the Orthonectidae, which live in the brittle-star Amphiura squamata, the
Nemertine Nemertes lacteus, or the Polyclad Leptoplana tremellaris. In addition
to the undoubted Mesozoa, certain anomalous forms—Trichoplax adhaerens and
Salinella salve—may be referred to this group.
Fig. 46.—Dicyemennea eledones Wag., from the kidney of Eledone moschata. A, Full-grown
Rhombogen with infusoriform embryos (emb); B, one of the latter developing; C, fully
formed; D, calotte, composed of the upper nine cells shown in the figure. (After Ed.
van Beneden and Whitman.) emb, Infusoriform embryo; g, part of endoderm-cell where
formation of these embryos is rapidly proceeding; n.ect, nucleus of ectoderm-cell;
n.end, nucleus of endoderm-cell; p, "calotte."
Page 108
Dicyemidae.—If the kidney of Eledone moschata, a Cephalopod common on our
south-western shores, be opened, a number of fine, yellowish, hair-like filaments
may be seen attached at one end to its inner surface, floating in the fluid contained
in the renal cavity. These may be Dicyemennea eledones Wag., although another
form, Dicyema moschatum Whit., also occurs in the same host. D. eledones (Fig.
46) is 7 to 9 mm. long, transparent, and is composed of one large inner cell with a
simple nucleus (Fig. 46, n.end), and of an outer layer of ciliated cells, nine of
which form the "calotte" or pole by which the animal is attached. Within the
former (endodermal) cell the formation of urn-shaped "infusoriform embryos"
takes place (B and C), the fate of which is not known, but they are possibly the
males. The individual which produces these larvae is called a "Rhombogen."
Other individuals which produce a more elongated larva ("vermiform larva," Fig.
45) are called "Nematogens," and Whitman has described a third kind, which
produce first infusoriform, and then vermiform, larvae (Secondary Nematogens).
[113]
The occurrence of the known species of Dicyemids (a group which has not been
investigated on our coasts) is as follows:—
Species. Host.
Dicyema typus van Ben. Octopus vulgaris.
D. clausianum van Ben. O. macropus.
D. microcephalum Whit. O. de Filippi.
D. moschatum Whit. Eledone moschata.
D. macrocephalum van Ben. Sepiola rondeletii.
D. truncatum Whit. Rossia macrosoma, Sepia elegans, S.
officinalis.
D. schultzianum van Ben. S. biseralis, Octopus vulgaris.
Dicyemennea eledones Wag. Eledone moschata, E. aldrovandi.
D. mülleri Clap. E. cirrosa.
D. gracile Wag. Sepia officinalis.
Conocyema polymorphum van S. officinalis, Octopus vulgaris.
Ben.
Orthonectida.[114]—Two species of Orthonectids are fairly well known,
Rhopalura giardii Metschn. from Amphiura squamata, and R. intoshii Metschn.
from Nemertes lacteus. The latter appears to be very rare, the former occurring in
2 to 5 per cent of the number of hosts examined. The parasites occur in a granular
"plasmodium," the nature of which is uncertain. Metschnikoff regards it as formed
by the Orthonectids, and he considers that the cellular envelope, by which it is
south-western shores, be opened, a number of fine, yellowish, hair-like filaments
may be seen attached at one end to its inner surface, floating in the fluid contained
in the renal cavity. These may be Dicyemennea eledones Wag., although another
form, Dicyema moschatum Whit., also occurs in the same host. D. eledones (Fig.
46) is 7 to 9 mm. long, transparent, and is composed of one large inner cell with a
simple nucleus (Fig. 46, n.end), and of an outer layer of ciliated cells, nine of
which form the "calotte" or pole by which the animal is attached. Within the
former (endodermal) cell the formation of urn-shaped "infusoriform embryos"
takes place (B and C), the fate of which is not known, but they are possibly the
males. The individual which produces these larvae is called a "Rhombogen."
Other individuals which produce a more elongated larva ("vermiform larva," Fig.
45) are called "Nematogens," and Whitman has described a third kind, which
produce first infusoriform, and then vermiform, larvae (Secondary Nematogens).
[113]
The occurrence of the known species of Dicyemids (a group which has not been
investigated on our coasts) is as follows:—
Species. Host.
Dicyema typus van Ben. Octopus vulgaris.
D. clausianum van Ben. O. macropus.
D. microcephalum Whit. O. de Filippi.
D. moschatum Whit. Eledone moschata.
D. macrocephalum van Ben. Sepiola rondeletii.
D. truncatum Whit. Rossia macrosoma, Sepia elegans, S.
officinalis.
D. schultzianum van Ben. S. biseralis, Octopus vulgaris.
Dicyemennea eledones Wag. Eledone moschata, E. aldrovandi.
D. mülleri Clap. E. cirrosa.
D. gracile Wag. Sepia officinalis.
Conocyema polymorphum van S. officinalis, Octopus vulgaris.
Ben.
Orthonectida.[114]—Two species of Orthonectids are fairly well known,
Rhopalura giardii Metschn. from Amphiura squamata, and R. intoshii Metschn.
from Nemertes lacteus. The latter appears to be very rare, the former occurring in
2 to 5 per cent of the number of hosts examined. The parasites occur in a granular
"plasmodium," the nature of which is uncertain. Metschnikoff regards it as formed
by the Orthonectids, and he considers that the cellular envelope, by which it is
Page 109
sometimes enclosed, is developed from the neighbouring tissue of the host. These
granular, sometimes nucleated, plasmodial masses, which can perform active
amoeboid movements in sea-water, occur attached to the ventral part of the body-
cavity of Amphiura, and between the gut-branches and body-wall in Nemertes.
Should these hosts be infected by great numbers of the Orthonectids, their sexual
organs degenerate (as is the case with pond-snails attacked by sporocysts[115]),
and it is possible that the remains of these organs may constitute the "plasmodia"
(Braun).
Rhopalura giardii is of distinct sexes. Either males or females are found in one
Amphiura. Two kinds of females, flattened unsegmented, and cylindrical
segmented forms, are known. They consist of a ciliated ectodermal layer
enclosing an endodermal mass of eggs, between which is a fibrillar layer usually
considered to be of a muscular nature. The cylindrical female gives rise to eggs
which develop, probably exclusively, into males. The flattened female produces
eggs from which females alone arise, though the origin of the two forms of this
sex is not well ascertained. The males contain spermatozoa which fertilise the
eggs of the cylindrical female, whereas the ova of the flat form probably develop
parthenogenetically.
Fig. 47.—Rhopalura giardii Metschn. (from the brittle-star Amphiura squamata). ♂ , Full-
grown male (× 800); ♀ 1, flattened form of female (× 510); ♀ 2, cylindrical female (×
510). (After Julin.)
Trichoplax.[116]—This anomalous animal has only been found in aquaria,
originally in the marine aquarium at Graz by Schulze. It has the appearance of a
large, flattened, ciliated Amoeba (1.5-3 mm. in diameter), but is distinguished by
its structure. The upper surface is composed of a flattened epithelium. The lower
granular, sometimes nucleated, plasmodial masses, which can perform active
amoeboid movements in sea-water, occur attached to the ventral part of the body-
cavity of Amphiura, and between the gut-branches and body-wall in Nemertes.
Should these hosts be infected by great numbers of the Orthonectids, their sexual
organs degenerate (as is the case with pond-snails attacked by sporocysts[115]),
and it is possible that the remains of these organs may constitute the "plasmodia"
(Braun).
Rhopalura giardii is of distinct sexes. Either males or females are found in one
Amphiura. Two kinds of females, flattened unsegmented, and cylindrical
segmented forms, are known. They consist of a ciliated ectodermal layer
enclosing an endodermal mass of eggs, between which is a fibrillar layer usually
considered to be of a muscular nature. The cylindrical female gives rise to eggs
which develop, probably exclusively, into males. The flattened female produces
eggs from which females alone arise, though the origin of the two forms of this
sex is not well ascertained. The males contain spermatozoa which fertilise the
eggs of the cylindrical female, whereas the ova of the flat form probably develop
parthenogenetically.
Fig. 47.—Rhopalura giardii Metschn. (from the brittle-star Amphiura squamata). ♂ , Full-
grown male (× 800); ♀ 1, flattened form of female (× 510); ♀ 2, cylindrical female (×
510). (After Julin.)
Trichoplax.[116]—This anomalous animal has only been found in aquaria,
originally in the marine aquarium at Graz by Schulze. It has the appearance of a
large, flattened, ciliated Amoeba (1.5-3 mm. in diameter), but is distinguished by
its structure. The upper surface is composed of a flattened epithelium. The lower
Page 110
surface is made up of cylindrical ciliated cells, which pass imperceptibly into the
branched cells, embedded in a hyaline matrix, which compose the middle layer of
the body. No distinct organs, and beyond simple fission, no mode of reproduction,
have been observed. One species, T. adhaerens, is known, but has never been met
with in a free state.
Salinella.[117]—This is another aquarium-animal, found by Frenzel in the
Argentine, in an artificial saline solution with which he filled some aquaria. It
measures .2 mm. in length, and has a somewhat flattened, barrel-shaped
appearance. A single layer of ciliated cells bounds a central cavity opening at each
end. Fission, and conjugation followed by encystment, have been observed. One
form, S. salve, is known from salines taken from Cordova.
branched cells, embedded in a hyaline matrix, which compose the middle layer of
the body. No distinct organs, and beyond simple fission, no mode of reproduction,
have been observed. One species, T. adhaerens, is known, but has never been met
with in a free state.
Salinella.[117]—This is another aquarium-animal, found by Frenzel in the
Argentine, in an artificial saline solution with which he filled some aquaria. It
measures .2 mm. in length, and has a somewhat flattened, barrel-shaped
appearance. A single layer of ciliated cells bounds a central cavity opening at each
end. Fission, and conjugation followed by encystment, have been observed. One
form, S. salve, is known from salines taken from Cordova.
Page 111
NEMERTINEA
BY
LILIAN SHELDON
Staff Lecturer in Natural Science, Newnham College, Cambridge.
CHAPTER V
NEMERTINEA
INTRODUCTORY—EXTERNAL CHARACTERS—ANATOMY—CLASSIFICATION—
DEVELOPMENT—HABITS—REGENERATION—BREEDING—GEOGRAPHICAL DISTRIBUTION—
LAND, FRESH-WATER, AND PARASITIC FORMS—AFFINITIES
The Nemertinea form a compact group, the affinities of which have not been at
present clearly determined. Several species were mentioned and described in the
works of various naturalists during the latter half of the eighteenth century, though
their anatomy was not understood until considerably later. The first mention of
any member of the group was made by the Rev. W. Borlase in his Natural History
of Cornwall, published in 1758. He gives a short description and a rough figure of
Lineus marinus. From that time the increase in the knowledge of the group was
very gradual. New species were from time to time described, but few of the
descriptions could boast of much completeness, and many erroneous views were
held until comparatively recent years. The group was very variously classified,
but the general arrangement in early times seems to have been to unite it with the
Planarians. Valuable contributions to the history of the development were made in
1848 and the few subsequent years by Desor,[118] Gegenbaur,[119] Krohn,[120] and
Leuckart and Pagenstecher[121]; and more recently by Metschnikoff[122] and
Salensky.[123]
Nemertines for the most part closely resemble one another in all essential points,
though they differ considerably in size, colour, and external details. They vary in
length from less than an inch to thirty yards, this extreme size being attained by
Lineus marinus.
BY
LILIAN SHELDON
Staff Lecturer in Natural Science, Newnham College, Cambridge.
CHAPTER V
NEMERTINEA
INTRODUCTORY—EXTERNAL CHARACTERS—ANATOMY—CLASSIFICATION—
DEVELOPMENT—HABITS—REGENERATION—BREEDING—GEOGRAPHICAL DISTRIBUTION—
LAND, FRESH-WATER, AND PARASITIC FORMS—AFFINITIES
The Nemertinea form a compact group, the affinities of which have not been at
present clearly determined. Several species were mentioned and described in the
works of various naturalists during the latter half of the eighteenth century, though
their anatomy was not understood until considerably later. The first mention of
any member of the group was made by the Rev. W. Borlase in his Natural History
of Cornwall, published in 1758. He gives a short description and a rough figure of
Lineus marinus. From that time the increase in the knowledge of the group was
very gradual. New species were from time to time described, but few of the
descriptions could boast of much completeness, and many erroneous views were
held until comparatively recent years. The group was very variously classified,
but the general arrangement in early times seems to have been to unite it with the
Planarians. Valuable contributions to the history of the development were made in
1848 and the few subsequent years by Desor,[118] Gegenbaur,[119] Krohn,[120] and
Leuckart and Pagenstecher[121]; and more recently by Metschnikoff[122] and
Salensky.[123]
Nemertines for the most part closely resemble one another in all essential points,
though they differ considerably in size, colour, and external details. They vary in
length from less than an inch to thirty yards, this extreme size being attained by
Lineus marinus.
Page 112
Fig. 48.—Lineus marinus Mont., from the living specimen in the coiled condition. Plymouth.
× 1. a, Anterior end; b, posterior end.
Fig. 49.—L. marinus, from the same specimen as Fig. 48, in the expanded condition. a,
Anterior end; b, posterior end.
Nemertines are common on the British coasts; about forty species have been
recorded from this area. On turning over a stone on a sandy or muddy shore in a
pool left by the receding tide, there may often be seen a coiled mass, having the
appearance of a uniform slimy string twisted into a complicated knot. If it be
carefully removed, the ends can generally be made out, one bluntly rounded and
the other slightly tapering (Fig. 48, a and b). Occasionally there may be seen
attached to the blunter end a fine thread, which moves about freely. This thread
may, by an instantaneous movement, be drawn into the body, no trace of its
existence being left except at the tip of the head, where a small pore is visible; this
is the orifice through which it was withdrawn. Shortly afterwards the thread may
be again shot out, the process being instantaneous and often accomplished with
great force. This thread (Fig. 50, p) is the proboscis, a very important and
characteristic organ in Nemertines.
× 1. a, Anterior end; b, posterior end.
Fig. 49.—L. marinus, from the same specimen as Fig. 48, in the expanded condition. a,
Anterior end; b, posterior end.
Nemertines are common on the British coasts; about forty species have been
recorded from this area. On turning over a stone on a sandy or muddy shore in a
pool left by the receding tide, there may often be seen a coiled mass, having the
appearance of a uniform slimy string twisted into a complicated knot. If it be
carefully removed, the ends can generally be made out, one bluntly rounded and
the other slightly tapering (Fig. 48, a and b). Occasionally there may be seen
attached to the blunter end a fine thread, which moves about freely. This thread
may, by an instantaneous movement, be drawn into the body, no trace of its
existence being left except at the tip of the head, where a small pore is visible; this
is the orifice through which it was withdrawn. Shortly afterwards the thread may
be again shot out, the process being instantaneous and often accomplished with
great force. This thread (Fig. 50, p) is the proboscis, a very important and
characteristic organ in Nemertines.
Page 113
Most Nemertines are marine; they are mostly indifferent to climate and to the
nature of the soil on which they live.
A few forms live on land (e.g. Tetrastemma agricola,[124] Geonemertes palaensis,
[125] and G. chalicophora[126]) or in fresh water (e.g. Tetrastemma aquarum
dulcium[127] and T. lacustre[128]) in various parts of the globe. There are also
parasitic forms; the best known of which is Malacobdella.[129] A pelagic form,
Pelagonemertes,[130] has been described by Moseley.
Fig. 50.—Side view of head of Cerebratulus (Micrura) tristis Hubr., showing the everted
proboscis. Naples. × 2. Drawn from a spirit specimen. c.s, Cephalic slit; m, mouth; p,
proboscis.
External Characters.—A typical Nemertine possesses an elongated worm-like
body (Fig. 49), which is usually thrown into numerous close coils (Fig. 48). In
section it may be either round or more or less flattened, with the lateral edges in
some cases quite thin and almost fin-like. One or two broad, flattened, and leaf-
shaped forms are known, but such a condition is exceptional, and the forms in
which it occurs have probably assumed it owing to the adoption of special modes
of life.
In the ordinary forms the posterior end of the body is pointed either bluntly or
sharply. The head is somewhat broader than the rest of the body, and often
assumes a spatulate form. Eyes (Fig. 51, e) are usually present either in one or
several pairs, or in symmetrically-arranged groups on each side of the head. The
mouth (Fig. 58, m) is situated near the front end of the body on the ventral
surface, and is usually rendered conspicuous by being surrounded by thick tumid
lips. It varies in form from being slit-like to elliptical. At the anterior end of the
body a small terminal pore occurs; this is the external opening of the proboscis
(Fig. 51, p.p).
Nemertines are often very diversely and brilliantly coloured, the hues most
commonly found being white, yellow, green, deep purple, and various shades of
nature of the soil on which they live.
A few forms live on land (e.g. Tetrastemma agricola,[124] Geonemertes palaensis,
[125] and G. chalicophora[126]) or in fresh water (e.g. Tetrastemma aquarum
dulcium[127] and T. lacustre[128]) in various parts of the globe. There are also
parasitic forms; the best known of which is Malacobdella.[129] A pelagic form,
Pelagonemertes,[130] has been described by Moseley.
Fig. 50.—Side view of head of Cerebratulus (Micrura) tristis Hubr., showing the everted
proboscis. Naples. × 2. Drawn from a spirit specimen. c.s, Cephalic slit; m, mouth; p,
proboscis.
External Characters.—A typical Nemertine possesses an elongated worm-like
body (Fig. 49), which is usually thrown into numerous close coils (Fig. 48). In
section it may be either round or more or less flattened, with the lateral edges in
some cases quite thin and almost fin-like. One or two broad, flattened, and leaf-
shaped forms are known, but such a condition is exceptional, and the forms in
which it occurs have probably assumed it owing to the adoption of special modes
of life.
In the ordinary forms the posterior end of the body is pointed either bluntly or
sharply. The head is somewhat broader than the rest of the body, and often
assumes a spatulate form. Eyes (Fig. 51, e) are usually present either in one or
several pairs, or in symmetrically-arranged groups on each side of the head. The
mouth (Fig. 58, m) is situated near the front end of the body on the ventral
surface, and is usually rendered conspicuous by being surrounded by thick tumid
lips. It varies in form from being slit-like to elliptical. At the anterior end of the
body a small terminal pore occurs; this is the external opening of the proboscis
(Fig. 51, p.p).
Nemertines are often very diversely and brilliantly coloured, the hues most
commonly found being white, yellow, green, deep purple, and various shades of
Page 114
red and pink. The ventral surface is usually paler in colour than the dorsal, and the
latter is often marked by longitudinal and transverse stripes (Fig. 59) in
contrasting colours.
The whole animal is enveloped in a layer of mucus, which sometimes becomes
hardened to form a tube, and this may be still further strengthened by an
admixture of particles of sand or earth.
The body is capable to a great extent of contraction and extension, a Nemertine
many inches long being apt, when irritated or alarmed, to contract itself to the
length of not more than half an inch. Hence, unless the animal is kept and
carefully watched, a very erroneous idea may be conceived as to its size.
Anatomy.—The body-wall consists of several layers (Fig. 52), which in a typical
highly-developed Nemertine are as follows:—
1. An external epidermic layer (ep), consisting of ciliated cells, among which are
placed numerous unicellular glands. These glands probably secrete the mucus in
which the Nemertine is usually enveloped; their contents when in the body are
very highly refracting. The epidermis rests on a basement membrane (b.m).
2. The two or three muscular layers, arranged as either an external circular and an
internal longitudinal, or an inner and an outer circular separated by a longitudinal
layer, or, as in the figure (c.m and l.m), two longitudinal separated by a circular
layer.
latter is often marked by longitudinal and transverse stripes (Fig. 59) in
contrasting colours.
The whole animal is enveloped in a layer of mucus, which sometimes becomes
hardened to form a tube, and this may be still further strengthened by an
admixture of particles of sand or earth.
The body is capable to a great extent of contraction and extension, a Nemertine
many inches long being apt, when irritated or alarmed, to contract itself to the
length of not more than half an inch. Hence, unless the animal is kept and
carefully watched, a very erroneous idea may be conceived as to its size.
Anatomy.—The body-wall consists of several layers (Fig. 52), which in a typical
highly-developed Nemertine are as follows:—
1. An external epidermic layer (ep), consisting of ciliated cells, among which are
placed numerous unicellular glands. These glands probably secrete the mucus in
which the Nemertine is usually enveloped; their contents when in the body are
very highly refracting. The epidermis rests on a basement membrane (b.m).
2. The two or three muscular layers, arranged as either an external circular and an
internal longitudinal, or an inner and an outer circular separated by a longitudinal
layer, or, as in the figure (c.m and l.m), two longitudinal separated by a circular
layer.
Page 115
Fig. 51.—Amphiporus lactifloreus Johnst., drawn from the living specimen, from the dorsal
surface. Plymouth. × 2. e, Eyes; g, generative organs; n.g, nerve ganglion; p.p,
proboscis pore; p, proboscis.
3. A fairly thick connective-tissue layer often found between the epidermis and the
muscles, into which latter it gradually merges (s.t).
The Digestive System.—The mouth is placed on the ventral surface near the
anterior end of the body (Figs. 53, 58, m). It leads into a straight oesophagus (Fig.
53, oes), whence passes off the intestine (int), which is continued as a straight
non-convoluted tube to the anus (a), situated terminally at the posterior end of the
body. The intestine is thrown out throughout the greater part of its course into
paired lateral pouches.
Fig. 52.—Diagrammatic transverse section of a Nemertine (Schizonemertea) through the
middle region of the body. b.m, Basement membrane; c.m, circular muscle layer; d.b,
dorsal blood-vessel; ep, epidermis; g, generative organs; int, intestine; l.b, lateral blood-
vessel; l.m, longitudinal muscle layers; n.c, lateral nerve-cord; n.l, nerve plexus; p,
proboscis; p.s, proboscis sheath; s.t, subcutaneous layer.
surface. Plymouth. × 2. e, Eyes; g, generative organs; n.g, nerve ganglion; p.p,
proboscis pore; p, proboscis.
3. A fairly thick connective-tissue layer often found between the epidermis and the
muscles, into which latter it gradually merges (s.t).
The Digestive System.—The mouth is placed on the ventral surface near the
anterior end of the body (Figs. 53, 58, m). It leads into a straight oesophagus (Fig.
53, oes), whence passes off the intestine (int), which is continued as a straight
non-convoluted tube to the anus (a), situated terminally at the posterior end of the
body. The intestine is thrown out throughout the greater part of its course into
paired lateral pouches.
Fig. 52.—Diagrammatic transverse section of a Nemertine (Schizonemertea) through the
middle region of the body. b.m, Basement membrane; c.m, circular muscle layer; d.b,
dorsal blood-vessel; ep, epidermis; g, generative organs; int, intestine; l.b, lateral blood-
vessel; l.m, longitudinal muscle layers; n.c, lateral nerve-cord; n.l, nerve plexus; p,
proboscis; p.s, proboscis sheath; s.t, subcutaneous layer.
Page 116
The alimentary canal is lined throughout by a ciliated epithelium. The oesophagus
has, in addition to this layer, an outer thick coat of large granular cells, which
probably have a glandular function.
Proboscis.—The most characteristic organ of the Nemertines is the proboscis
(Figs. 50, 53, 54). For many years its disposition and function were
misunderstood, and it was supposed to be a portion of the digestive system. The
proboscis, which lies dorsal to the alimentary canal, opens at the extreme anterior
end of the body by a small pore (Figs. 51, 53, 58). When retracted it is sometimes
considerably folded, and lies in a long pouch or sheath. To the walls of this sheath
it is attached round its anterior end; and strong muscles unite its posterior
extremity to the sheath a short distance from the posterior end of the latter.
The proboscis seems to be exclusively a tactile and protective and defensive
organ, for which functions it is eminently fitted by the great ease and rapidity with
which it is everted or thrust out from the body. It consists of two distinct regions
(Fig. 54, g.p and m.p). In the retracted state the anterior part is a hollow tube with
very thick muscular walls made up of several layers. At the base of this part in
many of the Nemertines there is situated a sharp-pointed spine projecting forward
into the lumen, and several smaller stylets situated in a pair of vesicles close to the
base of the central spine. The position of the spines in the everted proboscis is
shown in Fig. 57. The posterior part of the proboscis is also a tube, but instead of
being muscular, its walls are glandular. This posterior glandular part is never
everted.
has, in addition to this layer, an outer thick coat of large granular cells, which
probably have a glandular function.
Proboscis.—The most characteristic organ of the Nemertines is the proboscis
(Figs. 50, 53, 54). For many years its disposition and function were
misunderstood, and it was supposed to be a portion of the digestive system. The
proboscis, which lies dorsal to the alimentary canal, opens at the extreme anterior
end of the body by a small pore (Figs. 51, 53, 58). When retracted it is sometimes
considerably folded, and lies in a long pouch or sheath. To the walls of this sheath
it is attached round its anterior end; and strong muscles unite its posterior
extremity to the sheath a short distance from the posterior end of the latter.
The proboscis seems to be exclusively a tactile and protective and defensive
organ, for which functions it is eminently fitted by the great ease and rapidity with
which it is everted or thrust out from the body. It consists of two distinct regions
(Fig. 54, g.p and m.p). In the retracted state the anterior part is a hollow tube with
very thick muscular walls made up of several layers. At the base of this part in
many of the Nemertines there is situated a sharp-pointed spine projecting forward
into the lumen, and several smaller stylets situated in a pair of vesicles close to the
base of the central spine. The position of the spines in the everted proboscis is
shown in Fig. 57. The posterior part of the proboscis is also a tube, but instead of
being muscular, its walls are glandular. This posterior glandular part is never
everted.
Page 117
Fig. 53.—Diagrammatic drawing of a Nemertine from the dorsal surface to show the position
of some of the principal organs. a, Anus; c.s, cephalic slit; g, generative organs; int,
intestine with its lateral diverticula; m, mouth; n.c, lateral nerve-cord; n.g, nerve
ganglion; oes, oesophagus; p, proboscis; p.p, proboscis pore; p.s, proboscis sheath.
The eversion is effected by a turning inside out of the anterior part of the
proboscis (Fig. 54). The process whereby the proboscis is retracted has been very
aptly compared to the effect which would be produced by the inversion of the
finger of a glove, accomplished by pulling a string attached to its tip on the inside,
the anterior muscular part being comparable to the finger and the glandular part to
the string. It is thus obvious that in the everted condition the stylet will form the
anterior tip of the proboscis, and will there be in a position for offence or defence
(Fig. 57, s).
Nervous System.[131]—The brain is composed of two ganglionic masses (Fig. 53,
n.g) lying at the anterior end of the body, one on each side of the proboscis, and
united by commissures passing round it (Fig. 55, d.c and v.c). Each ganglionic
mass is often partially divided into a dorsal and ventral lobe (n.g.d and n.g.v).
From the brain a pair of cords pass off backwards along the sides of the body
(n.c); these cords, which have no ganglionic swellings, in some forms unite with
one another above the anus. Anteriorly nerves are given off from the brain to the
eyes and front part of the head (a.n). A nerve to the proboscis is given off from the
commissure which unites the two halves of the brain dorsal to the proboscis (d.n).
of some of the principal organs. a, Anus; c.s, cephalic slit; g, generative organs; int,
intestine with its lateral diverticula; m, mouth; n.c, lateral nerve-cord; n.g, nerve
ganglion; oes, oesophagus; p, proboscis; p.p, proboscis pore; p.s, proboscis sheath.
The eversion is effected by a turning inside out of the anterior part of the
proboscis (Fig. 54). The process whereby the proboscis is retracted has been very
aptly compared to the effect which would be produced by the inversion of the
finger of a glove, accomplished by pulling a string attached to its tip on the inside,
the anterior muscular part being comparable to the finger and the glandular part to
the string. It is thus obvious that in the everted condition the stylet will form the
anterior tip of the proboscis, and will there be in a position for offence or defence
(Fig. 57, s).
Nervous System.[131]—The brain is composed of two ganglionic masses (Fig. 53,
n.g) lying at the anterior end of the body, one on each side of the proboscis, and
united by commissures passing round it (Fig. 55, d.c and v.c). Each ganglionic
mass is often partially divided into a dorsal and ventral lobe (n.g.d and n.g.v).
From the brain a pair of cords pass off backwards along the sides of the body
(n.c); these cords, which have no ganglionic swellings, in some forms unite with
one another above the anus. Anteriorly nerves are given off from the brain to the
eyes and front part of the head (a.n). A nerve to the proboscis is given off from the
commissure which unites the two halves of the brain dorsal to the proboscis (d.n).
Page 118
Fig. 54.—Diagrammatic representation of the proboscis, (A) in the retracted condition, (B) in
the everted condition. g.p, Glandular portion of the proboscis; m, muscle attaching the
proboscis to its sheath; m.p, muscular portion of the proboscis; p.p in A, proboscis pore;
p.p in B represents the position of the proboscis pore in the retracted condition of the
proboscis; p.s, proboscis sheath.
In two out of the three groups into which the Nemertines are divided, the lateral
nerve-cords are in connexion with a network or plexus of nerves lying between
the muscular layers of the body-wall (Fig. 52, n.l), and in some forms constituting
a comparatively thick layer. In these two groups there are no definite nerve
branches except the anterior ones to the head. In the third group of Nemertines the
lateral nerve-cords lie within the muscular layers of the body-wall, and in this
case paired nerve branches are given off at definite intervals throughout the whole
length of the body. These branches divide up among the organs to which they
pass, and no nerve plexus is present.
The lateral cords vary in position in different cases. Sometimes they lie laterally,
at others the cords tend to approximate to one another in the median dorsal or in
the median ventral line, though in every case they remain distinctly separated.
Sense Organs.—Sense organs are usually present in the form of eyes arranged at
the sides of the head (Fig. 51, e), sometimes as a single pair and sometimes in one
or more groups on each side. The structure of the eyes varies from a simple
pigment spot to an organ which receives a special nerve-supply from the brain,
and possesses a refracting body answering to a lens, and behind this a pigment
layer and a layer of rods. Some forms are devoid of all traces of eyes.
the everted condition. g.p, Glandular portion of the proboscis; m, muscle attaching the
proboscis to its sheath; m.p, muscular portion of the proboscis; p.p in A, proboscis pore;
p.p in B represents the position of the proboscis pore in the retracted condition of the
proboscis; p.s, proboscis sheath.
In two out of the three groups into which the Nemertines are divided, the lateral
nerve-cords are in connexion with a network or plexus of nerves lying between
the muscular layers of the body-wall (Fig. 52, n.l), and in some forms constituting
a comparatively thick layer. In these two groups there are no definite nerve
branches except the anterior ones to the head. In the third group of Nemertines the
lateral nerve-cords lie within the muscular layers of the body-wall, and in this
case paired nerve branches are given off at definite intervals throughout the whole
length of the body. These branches divide up among the organs to which they
pass, and no nerve plexus is present.
The lateral cords vary in position in different cases. Sometimes they lie laterally,
at others the cords tend to approximate to one another in the median dorsal or in
the median ventral line, though in every case they remain distinctly separated.
Sense Organs.—Sense organs are usually present in the form of eyes arranged at
the sides of the head (Fig. 51, e), sometimes as a single pair and sometimes in one
or more groups on each side. The structure of the eyes varies from a simple
pigment spot to an organ which receives a special nerve-supply from the brain,
and possesses a refracting body answering to a lens, and behind this a pigment
layer and a layer of rods. Some forms are devoid of all traces of eyes.
Page 119
Fig. 55.—Diagram to show the relations of the nervous system, circulatory system, and
proboscis sheath in the anterior end of the body in the Hoplonemertea, modified from
M‘Intosh. a.n, Nerves to anterior part of body and eyes; d.c, dorsal commissure; d.n,
median dorsal nerve; d.v, dorsal vascular trunk; l.v, lateral vascular trunk; n.c, lateral
nerve-cord; n.g.d, dorsal lobe of nerve ganglion; n.g.v, ventral lobe of nerve ganglion;
p.p, proboscis pore; p.s, proboscis sheath; v.c, ventral commissure; v.s, vascular ring or
collar.
A pair of simple auditory capsules has been found in some of the Hoplonemertea,
where they occur as small vesicles on the brain.
The whole surface of the body appears to be remarkably sensitive. In a few forms
small tufts of tactile hairs are said to be present in the region of the head, while in
others there are a few long hairs scattered sparsely among the cilia of the
epidermis.
Frontal Organ.—In many Nemertines there is present at the anterior tip of the
head a disc-shaped group of cells bearing long hairs or bristles. On this disc open
the secreting ducts of a number of gland cells lying in the head. It seems possible
that this frontal organ may function as an organ of taste.
Side Organs.—In the Carinellidae there is a pair of circular epithelial patches
lying one on each side of the body in the region of the excretory pore. The cells
composing them are richly ciliated and provided with a plentiful nerve-supply.
The function of these epithelial patches is not known, but it has been suggested
that they may be auditory organs.
Cephalic Slits and Cerebral Organs.—In most Nemertines there is a peculiar pair
of organs (Figs. 50, 53, c.s), situated in the head and in close connexion with the
brain. The function of these organs is not known. Hubrecht has suggested that
they may be respiratory, while Bürger[132] conjectures that they may be organs
which are used for discriminating the condition of the surrounding medium. In an
proboscis sheath in the anterior end of the body in the Hoplonemertea, modified from
M‘Intosh. a.n, Nerves to anterior part of body and eyes; d.c, dorsal commissure; d.n,
median dorsal nerve; d.v, dorsal vascular trunk; l.v, lateral vascular trunk; n.c, lateral
nerve-cord; n.g.d, dorsal lobe of nerve ganglion; n.g.v, ventral lobe of nerve ganglion;
p.p, proboscis pore; p.s, proboscis sheath; v.c, ventral commissure; v.s, vascular ring or
collar.
A pair of simple auditory capsules has been found in some of the Hoplonemertea,
where they occur as small vesicles on the brain.
The whole surface of the body appears to be remarkably sensitive. In a few forms
small tufts of tactile hairs are said to be present in the region of the head, while in
others there are a few long hairs scattered sparsely among the cilia of the
epidermis.
Frontal Organ.—In many Nemertines there is present at the anterior tip of the
head a disc-shaped group of cells bearing long hairs or bristles. On this disc open
the secreting ducts of a number of gland cells lying in the head. It seems possible
that this frontal organ may function as an organ of taste.
Side Organs.—In the Carinellidae there is a pair of circular epithelial patches
lying one on each side of the body in the region of the excretory pore. The cells
composing them are richly ciliated and provided with a plentiful nerve-supply.
The function of these epithelial patches is not known, but it has been suggested
that they may be auditory organs.
Cephalic Slits and Cerebral Organs.—In most Nemertines there is a peculiar pair
of organs (Figs. 50, 53, c.s), situated in the head and in close connexion with the
brain. The function of these organs is not known. Hubrecht has suggested that
they may be respiratory, while Bürger[132] conjectures that they may be organs
which are used for discriminating the condition of the surrounding medium. In an
Page 120
external examination of the head, the cephalic slits may usually be seen as a pair
of lateral furrows or pits. Their form and direction vary considerably; they may
take the form of shallow circular depressions, or they may lie longitudinally and
be slit-like in shape (Fig. 50), or the slit may lie at right angles to the long axis of
the body and be beset with short transverse furrows. In some forms these slits are
merely superficial depressions, but in others they are continued into ciliated ducts,
which pass inwards and penetrate into special lobes, consisting of glandular tissue
and ganglion cells, in close connexion with the brain. These lobes are called the
cerebral organs.
In many forms the nervous system is charged with haemoglobin, which gives to it
a bright red colour.
Circulatory or Blood-Vascular System.—The circulatory system consists of
three main longitudinal vessels, a median dorsal and a pair of lateral ones. These
are connected together posteriorly by a transverse trunk, and also throughout the
whole length of their course by branches, which are given off at regular intervals.
Anteriorly the three longitudinal vessels either all unite and form a collar (Fig. 55,
v.s) round the oesophagus, or they break up into a number of lacunar or open
spaces in free communication with one another.
The blood is usually colourless, but in some cases the corpuscles are coloured red
by haemoglobin.
Fig. 56.—Excretory system of Nemertines. A, Drepanophorus spectabilis Qtrf., part of one of
the lateral vessels encircled by branches of the excretory organ, × 585; e, main canal of
the excretory system: B, D. crassus Qtrf., a terminal branch of the excretory system, ×
585; f, ciliated flame: C, Malacobdella grossa O. F. Müll., entire animal, slightly
magnified, showing the excretory system (black) and the vascular system; e.a,
excretory aperture; d.v, dorsal vessel; l.v, lateral vessel. (From Bürger.)
Excretory System.—Max Schultze[133] found in Tetrastemma obscurum, on the
outer side of, but near to the lateral blood-vessels, a pair of canals. He observed
ciliary movements in the canals, but could not discover flame cells. Further
of lateral furrows or pits. Their form and direction vary considerably; they may
take the form of shallow circular depressions, or they may lie longitudinally and
be slit-like in shape (Fig. 50), or the slit may lie at right angles to the long axis of
the body and be beset with short transverse furrows. In some forms these slits are
merely superficial depressions, but in others they are continued into ciliated ducts,
which pass inwards and penetrate into special lobes, consisting of glandular tissue
and ganglion cells, in close connexion with the brain. These lobes are called the
cerebral organs.
In many forms the nervous system is charged with haemoglobin, which gives to it
a bright red colour.
Circulatory or Blood-Vascular System.—The circulatory system consists of
three main longitudinal vessels, a median dorsal and a pair of lateral ones. These
are connected together posteriorly by a transverse trunk, and also throughout the
whole length of their course by branches, which are given off at regular intervals.
Anteriorly the three longitudinal vessels either all unite and form a collar (Fig. 55,
v.s) round the oesophagus, or they break up into a number of lacunar or open
spaces in free communication with one another.
The blood is usually colourless, but in some cases the corpuscles are coloured red
by haemoglobin.
Fig. 56.—Excretory system of Nemertines. A, Drepanophorus spectabilis Qtrf., part of one of
the lateral vessels encircled by branches of the excretory organ, × 585; e, main canal of
the excretory system: B, D. crassus Qtrf., a terminal branch of the excretory system, ×
585; f, ciliated flame: C, Malacobdella grossa O. F. Müll., entire animal, slightly
magnified, showing the excretory system (black) and the vascular system; e.a,
excretory aperture; d.v, dorsal vessel; l.v, lateral vessel. (From Bürger.)
Excretory System.—Max Schultze[133] found in Tetrastemma obscurum, on the
outer side of, but near to the lateral blood-vessels, a pair of canals. He observed
ciliary movements in the canals, but could not discover flame cells. Further
Page 121
contributions to our knowledge of the excretory system were made by Semper,
[134] von Kennel,[135] Hubrecht,[136] and Oudemans.[137] The latter states that the
excretory system consists of a pair of canals situated laterally near the anterior end
of the body. Each canal communicates with the exterior by one or more ducts
having lateral regularly-arranged apertures. In some cases he was unable to make
out any communication with the vascular system, but in others a direct
communication, by means of open connexions with the lacunar blood spaces, is
said to occur.
Silliman[138] in Tetrastemma aquarum dulcium describes the excretory vessels as
ending in numerous capillary branches, at the blind terminations of which cilia are
present. He states that there is no important difference between the excretory
systems of Rhabdocoeles and Nemertines.
Bürger,[139] as the result of recent investigations on the excretory system in
Nemertines, finds that the minute branches end in flame-cells (Fig. 56, B) lying
on and among the blood-vessels, but having no open connexion with them.
Generative System.—The Nemertines are for the most part dioecious, only a few
certainly hermaphrodite species having been described, e.g. Tetrastemma
("Borlasia") kefersteinii Mar.[140]
The generative products in both cases are contained in sacs (Figs. 52, 53, g) which
lie in the lateral region of the body between the pouches of the alimentary canal.
The ova and spermatozoa are conveyed to the exterior by short ducts. Most
species are oviparous, though a few viviparous species are known (e.g.
Prosorhochmus claparedii).
Classification.—Nemertines were divided by M. Schultze[141] into:—
1. Enopla, in which the proboscis is armed with stylets.
2. Anopla, in which the proboscis is unarmed.
Although this classification was fairly correct as far as it went, since many other
distinctive features were correlated with the presence or absence of armature in
the proboscis, still there are several primitive forms belonging to the Anopla,
[134] von Kennel,[135] Hubrecht,[136] and Oudemans.[137] The latter states that the
excretory system consists of a pair of canals situated laterally near the anterior end
of the body. Each canal communicates with the exterior by one or more ducts
having lateral regularly-arranged apertures. In some cases he was unable to make
out any communication with the vascular system, but in others a direct
communication, by means of open connexions with the lacunar blood spaces, is
said to occur.
Silliman[138] in Tetrastemma aquarum dulcium describes the excretory vessels as
ending in numerous capillary branches, at the blind terminations of which cilia are
present. He states that there is no important difference between the excretory
systems of Rhabdocoeles and Nemertines.
Bürger,[139] as the result of recent investigations on the excretory system in
Nemertines, finds that the minute branches end in flame-cells (Fig. 56, B) lying
on and among the blood-vessels, but having no open connexion with them.
Generative System.—The Nemertines are for the most part dioecious, only a few
certainly hermaphrodite species having been described, e.g. Tetrastemma
("Borlasia") kefersteinii Mar.[140]
The generative products in both cases are contained in sacs (Figs. 52, 53, g) which
lie in the lateral region of the body between the pouches of the alimentary canal.
The ova and spermatozoa are conveyed to the exterior by short ducts. Most
species are oviparous, though a few viviparous species are known (e.g.
Prosorhochmus claparedii).
Classification.—Nemertines were divided by M. Schultze[141] into:—
1. Enopla, in which the proboscis is armed with stylets.
2. Anopla, in which the proboscis is unarmed.
Although this classification was fairly correct as far as it went, since many other
distinctive features were correlated with the presence or absence of armature in
the proboscis, still there are several primitive forms belonging to the Anopla,
Page 122
which possess characters such as render it necessary to class them together in a
separate group.
For this reason Hubrecht divided the Nemertinea into three Orders—
Hoplonemertea, Schizonemertea, Palaeonemertea; the first of these Orders
corresponding with the Enopla, and the other two with the Anopla.
Order I. Hoplonemertea.
The proboscis is armed. The epidermis rests on a thick layer of connective tissue
plentifully supplied with glands, below which is a prominent basement
membrane. The muscular layers of the body are two in number, an outer circular
and an inner longitudinal. The nerve-trunks lie within the muscular layers of the
body and give off regularly-arranged branches. There is no nerve plexus. Each of
the cephalic slits generally opens by a pore situated in the centre of a transverse
groove, which is beset along one side by a row of shorter grooves at right angles
to it. The apparatus consists of a ciliated duct surrounded by nerve tissue, and
passing into lobes of tissue which are connected with the brain by thick nerve-
cords. The mouth opens rather far forward in front of the brain. The intestinal
pouches are symmetrically arranged. Auditory organs are said to exist in some
forms, consisting of vesicles containing otoliths. The vascular trunks are
connected anteriorly by closed vessels and not by lacunar spaces.
Fig. 57.—Anterior end of the everted proboscis (Hoplonemertea). g.p, Glandular portion of
the proboscis; l.s, lateral sacs containing stylets; m.p, muscular portion of the proboscis;
s, stylet; s.b, granular basal portion of stylet.
The principal British genera and species[142] are:—
Amphiporus bioculatus M‘Int., A. dissimulans Riches, A. hastatus M‘Int., A.
lactifloreus M‘Int., A. pulcher Johnst.
Drepanophorus rubrostriatus Hubr. (= A. spectabilis Qtrf.).
separate group.
For this reason Hubrecht divided the Nemertinea into three Orders—
Hoplonemertea, Schizonemertea, Palaeonemertea; the first of these Orders
corresponding with the Enopla, and the other two with the Anopla.
Order I. Hoplonemertea.
The proboscis is armed. The epidermis rests on a thick layer of connective tissue
plentifully supplied with glands, below which is a prominent basement
membrane. The muscular layers of the body are two in number, an outer circular
and an inner longitudinal. The nerve-trunks lie within the muscular layers of the
body and give off regularly-arranged branches. There is no nerve plexus. Each of
the cephalic slits generally opens by a pore situated in the centre of a transverse
groove, which is beset along one side by a row of shorter grooves at right angles
to it. The apparatus consists of a ciliated duct surrounded by nerve tissue, and
passing into lobes of tissue which are connected with the brain by thick nerve-
cords. The mouth opens rather far forward in front of the brain. The intestinal
pouches are symmetrically arranged. Auditory organs are said to exist in some
forms, consisting of vesicles containing otoliths. The vascular trunks are
connected anteriorly by closed vessels and not by lacunar spaces.
Fig. 57.—Anterior end of the everted proboscis (Hoplonemertea). g.p, Glandular portion of
the proboscis; l.s, lateral sacs containing stylets; m.p, muscular portion of the proboscis;
s, stylet; s.b, granular basal portion of stylet.
The principal British genera and species[142] are:—
Amphiporus bioculatus M‘Int., A. dissimulans Riches, A. hastatus M‘Int., A.
lactifloreus M‘Int., A. pulcher Johnst.
Drepanophorus rubrostriatus Hubr. (= A. spectabilis Qtrf.).
Page 123
Tetrastemma ambiguum Riches, T. candidum O. F. Müll., T. dorsale Abildg.,
T. flavidum Ehrenb., T. immutabile Riches, T. melanocephalum Johnst., T.
nigrum Riches, T. robertianae M‘Int., T. vermiculatum Qtrf.
Prosorhochmus claparedii Keferstein.
Nemertes carcinophila Köll., N. gracilis Johnst., N. neesii Oerst.
Malacobdella grossa O. F. Müll.
Order II. Schizonemertea.
The proboscis is unarmed. The epidermis is separated from the layer of
connective tissue by a thin basement membrane, hence the glands in the
connective tissue are more deeply situated and have long ducts. The muscular
layers are three in number, an outer and an inner longitudinal layer between which
lies a layer of circular muscles. The lateral nerve-cords lie between the outer
longitudinal and the circular muscle layers. They are connected throughout the
body by a nerve plexus, the only definite nerve branches given off being those to
the brain, oesophagus, and proboscis. The cephalic slits are a pair of deep
longitudinal grooves at the sides of the head. From each groove a canal passes
inwards into a posterior brain-lobe. The mouth opens behind the brain, and is an
elongated slit bounded by corrugated lips. Auditory organs have not been
observed. The longitudinal vascular trunks are connected anteriorly by lacunar
spaces, and not by closed vessels.
Fig. 58.—Head end of Cerebratulus marginatus Ren., from the ventral surface. Drawn from a
spirit specimen. Naples. × 1. c.s, Cephalic slit; m, mouth; p.p, proboscis pore.
Principal British genera and species:—
T. flavidum Ehrenb., T. immutabile Riches, T. melanocephalum Johnst., T.
nigrum Riches, T. robertianae M‘Int., T. vermiculatum Qtrf.
Prosorhochmus claparedii Keferstein.
Nemertes carcinophila Köll., N. gracilis Johnst., N. neesii Oerst.
Malacobdella grossa O. F. Müll.
Order II. Schizonemertea.
The proboscis is unarmed. The epidermis is separated from the layer of
connective tissue by a thin basement membrane, hence the glands in the
connective tissue are more deeply situated and have long ducts. The muscular
layers are three in number, an outer and an inner longitudinal layer between which
lies a layer of circular muscles. The lateral nerve-cords lie between the outer
longitudinal and the circular muscle layers. They are connected throughout the
body by a nerve plexus, the only definite nerve branches given off being those to
the brain, oesophagus, and proboscis. The cephalic slits are a pair of deep
longitudinal grooves at the sides of the head. From each groove a canal passes
inwards into a posterior brain-lobe. The mouth opens behind the brain, and is an
elongated slit bounded by corrugated lips. Auditory organs have not been
observed. The longitudinal vascular trunks are connected anteriorly by lacunar
spaces, and not by closed vessels.
Fig. 58.—Head end of Cerebratulus marginatus Ren., from the ventral surface. Drawn from a
spirit specimen. Naples. × 1. c.s, Cephalic slit; m, mouth; p.p, proboscis pore.
Principal British genera and species:—
Page 124
Lineus bilineatus Ren., L. lacteus Mont., L. marinus Mont. (= L. longissimus
Gunnerus), L. gesserensis O. F. Müll. (= L. obscurus Desor and L.
sanguineus M‘Int.).
Borlasia elizabethae M‘Int.
Cerebratulus angulatus O. F. Müll., C. fuscus M‘Int., C. pantherinus Hubr.
Micrura aurantiaca Grube, M. candida Bürger, M. fasciolata Ehrenb., M.
purpurea J. Müll.
Meckelia asulcata M‘Int.
Order III. Palaeonemertea.
The proboscis is unarmed. The epidermis and connective tissue form one layer,
below which is the basement membrane. The muscular layers are three in number,
two circular separated by a longitudinal layer. The nerve-cords lie altogether
external to the muscular layers, and are connected together throughout by a
plexus. No nerve branches are given off. The brain is not divided into lobes. The
cephalic slits are only represented by a shallow depression on each side of the
head, and no canals have been observed leading from them. The intestine is
straight, and the pouches are usually absent or rudimentary. The circulatory
system is largely made up of lacunar spaces, the closed system being but little
developed.
Principal British genera and species:—
Carinella annulata Mont., C. linearis (Mont., MS.) M‘Int., C. macintoshi
Bürger (Fig. 59), C. polymorpha Ren.
Cephalothrix bioculata Oerst., C. linearis Rathke.
Valencinia lineformis M‘Int.
Gunnerus), L. gesserensis O. F. Müll. (= L. obscurus Desor and L.
sanguineus M‘Int.).
Borlasia elizabethae M‘Int.
Cerebratulus angulatus O. F. Müll., C. fuscus M‘Int., C. pantherinus Hubr.
Micrura aurantiaca Grube, M. candida Bürger, M. fasciolata Ehrenb., M.
purpurea J. Müll.
Meckelia asulcata M‘Int.
Order III. Palaeonemertea.
The proboscis is unarmed. The epidermis and connective tissue form one layer,
below which is the basement membrane. The muscular layers are three in number,
two circular separated by a longitudinal layer. The nerve-cords lie altogether
external to the muscular layers, and are connected together throughout by a
plexus. No nerve branches are given off. The brain is not divided into lobes. The
cephalic slits are only represented by a shallow depression on each side of the
head, and no canals have been observed leading from them. The intestine is
straight, and the pouches are usually absent or rudimentary. The circulatory
system is largely made up of lacunar spaces, the closed system being but little
developed.
Principal British genera and species:—
Carinella annulata Mont., C. linearis (Mont., MS.) M‘Int., C. macintoshi
Bürger (Fig. 59), C. polymorpha Ren.
Cephalothrix bioculata Oerst., C. linearis Rathke.
Valencinia lineformis M‘Int.
Page 125
Fig. 59.—Carinella macintoshi Bürger, drawn from the living specimen, slightly contracted.
Plymouth. Considerably magnified. a, Anterior end; b, posterior end.
A most important monograph by Bürger[143] on Nemertines has just been
published, but unfortunately it appeared too late to be adequately considered here.
He gives an elaborate account, illustrated by admirable figures, of the present
state of our knowledge of this group, and his work will be indispensable to future
students of the subject. The older systems of classification are criticised, and the
following scheme is adopted in their place:—
Order I. Protonemertini (= part of the Palaeonemertea, e.g. Carinella).—The
brain and lateral nerve-cords lie outside the muscle layers in the epithelium or
below the basement membrane. The body-wall consists of the following layers:
epidermis, basement membrane, circular muscles, and longitudinal muscles. The
mouth lies behind the brain. The proboscis is unarmed.
Order II. Mesonemertini (= part of the Palaeonemertea, e.g. Cephalothrix).—The
characters of this Order are similar to those of the Protonemertini except that the
brain and lateral nerve-cords lie in the muscle layers.
Order III. Metanemertini (= Hoplonemertea).—The brain and lateral nerve-cords
lie in the parenchyma of the body internal to the muscle layers. The layers of the
body-wall are similar to those of the Protonemertini. The mouth lies in front of the
brain. The proboscis is armed. At the junction of the fore- and mid-gut a
diverticulum is given off which projects forwards beneath the fore-gut and ends
blindly in front.
Order IV. Heteronemertini (= Schizonemertea, and the genera Eupolia and
Valencinia, placed provisionally by Hubrecht in the Palaeonemertea).—The body-
wall consists of the following layers: epidermis, thick cutis, and an outer and an
inner longitudinal muscle layer separated from one another by a circular muscle
layer. The brain and lateral nerve-cords lie between the outer longitudinal and the
circular muscle layers. The mouth lies behind the brain. The proboscis is
unarmed.
Plymouth. Considerably magnified. a, Anterior end; b, posterior end.
A most important monograph by Bürger[143] on Nemertines has just been
published, but unfortunately it appeared too late to be adequately considered here.
He gives an elaborate account, illustrated by admirable figures, of the present
state of our knowledge of this group, and his work will be indispensable to future
students of the subject. The older systems of classification are criticised, and the
following scheme is adopted in their place:—
Order I. Protonemertini (= part of the Palaeonemertea, e.g. Carinella).—The
brain and lateral nerve-cords lie outside the muscle layers in the epithelium or
below the basement membrane. The body-wall consists of the following layers:
epidermis, basement membrane, circular muscles, and longitudinal muscles. The
mouth lies behind the brain. The proboscis is unarmed.
Order II. Mesonemertini (= part of the Palaeonemertea, e.g. Cephalothrix).—The
characters of this Order are similar to those of the Protonemertini except that the
brain and lateral nerve-cords lie in the muscle layers.
Order III. Metanemertini (= Hoplonemertea).—The brain and lateral nerve-cords
lie in the parenchyma of the body internal to the muscle layers. The layers of the
body-wall are similar to those of the Protonemertini. The mouth lies in front of the
brain. The proboscis is armed. At the junction of the fore- and mid-gut a
diverticulum is given off which projects forwards beneath the fore-gut and ends
blindly in front.
Order IV. Heteronemertini (= Schizonemertea, and the genera Eupolia and
Valencinia, placed provisionally by Hubrecht in the Palaeonemertea).—The body-
wall consists of the following layers: epidermis, thick cutis, and an outer and an
inner longitudinal muscle layer separated from one another by a circular muscle
layer. The brain and lateral nerve-cords lie between the outer longitudinal and the
circular muscle layers. The mouth lies behind the brain. The proboscis is
unarmed.
Page 126
Development of the Nemertinea.—The development of the Palaeonemertea is at
present not known: in the Schizonemertea a larval stage occurs; while in the
Hoplonemertea the egg develops directly without undergoing any metamorphosis.
There are two forms of larva characteristic of the Schizonemertea, known
respectively as Pilidium and the Type of Desor. The Pilidium is hatched early and
leads a free-swimming existence, whereas the Type of Desor, though in many
respects resembling it, never passes through the free-swimming phase.
Fig. 60.—Diagram of a Pilidium larva. (After Salensky.) c, Tuft of cilia; m, muscle-fibres; mo,
mouth, seen through one of the lateral lobes; n, nerve-fibres; n.r, nerve-ring; n.g, nerve
ganglion; oes, oesophagus; st, stomach.
The Pilidium (Fig. 60) is a helmet-shaped larva bearing a tuft or spike dorsally,
and prolonged downwards laterally into a pair of lobes. The whole larva is
covered with cilia, there being a specially strong band round its ventral surface.
The dorsal spike is composed of a bunch of strongly developed cilia or of a long
flagellum. The alimentary canal consists of a sac constricted into oesophageal and
gastric regions (Fig. 60, oes and st). In this condition the larva swims about freely
in the water. The helmet-shaped Pilidium-skin forms no part of the future
Nemertine, the skin of which is developed as ingrowths from it; these meet one
another and unite to form a complete covering round the alimentary canal; the
larval skin is then cast off, and by a series of gradual steps the embryo develops
into the adult.
Habits.—Nemertines are often found under stones between high- and low-water
marks, lying on sandy or muddy bottoms. They are usually in the form of coiled
masses, and are generally in a state of quiescence. Hence it is probable that their
period of activity is during high-water, and that when left by the receding tide they
subside into a resting condition.
The large kinds, such as Lineus marinus, seem to be always found living alone,
but some of the smaller kinds, notably Tetrastemma dorsale and Prosorhochmus
present not known: in the Schizonemertea a larval stage occurs; while in the
Hoplonemertea the egg develops directly without undergoing any metamorphosis.
There are two forms of larva characteristic of the Schizonemertea, known
respectively as Pilidium and the Type of Desor. The Pilidium is hatched early and
leads a free-swimming existence, whereas the Type of Desor, though in many
respects resembling it, never passes through the free-swimming phase.
Fig. 60.—Diagram of a Pilidium larva. (After Salensky.) c, Tuft of cilia; m, muscle-fibres; mo,
mouth, seen through one of the lateral lobes; n, nerve-fibres; n.r, nerve-ring; n.g, nerve
ganglion; oes, oesophagus; st, stomach.
The Pilidium (Fig. 60) is a helmet-shaped larva bearing a tuft or spike dorsally,
and prolonged downwards laterally into a pair of lobes. The whole larva is
covered with cilia, there being a specially strong band round its ventral surface.
The dorsal spike is composed of a bunch of strongly developed cilia or of a long
flagellum. The alimentary canal consists of a sac constricted into oesophageal and
gastric regions (Fig. 60, oes and st). In this condition the larva swims about freely
in the water. The helmet-shaped Pilidium-skin forms no part of the future
Nemertine, the skin of which is developed as ingrowths from it; these meet one
another and unite to form a complete covering round the alimentary canal; the
larval skin is then cast off, and by a series of gradual steps the embryo develops
into the adult.
Habits.—Nemertines are often found under stones between high- and low-water
marks, lying on sandy or muddy bottoms. They are usually in the form of coiled
masses, and are generally in a state of quiescence. Hence it is probable that their
period of activity is during high-water, and that when left by the receding tide they
subside into a resting condition.
The large kinds, such as Lineus marinus, seem to be always found living alone,
but some of the smaller kinds, notably Tetrastemma dorsale and Prosorhochmus
Page 127
claparedii, have gregarious habits and live in masses, the coils of the different
individuals being inextricably mixed.
Some species, such as Micrura purpurea, Amphiporus pulcher, and Cerebratulus
angulatus, frequent empty bivalve shells, while Nemertines are often found in
empty limpet shells adhering to rocks in tidal pools. Other smaller forms resort to
no such definite protection, but live among seaweeds; some of these remain
naked, while others secrete for themselves tubes of a membranous or gelatinous
consistency. Borlasia elizabethae lives in a burrow of clay.
Nemertines are commonly dredged from a depth of six or eight fathoms. They
may sometimes be found floating on the surface of the water, and some possess
the power of swimming rapidly, propelling themselves by a lateral motion of the
tail, the sides of which are in such cases prolonged into a thin fin-like edge. This
mode of progression is usually adopted by those which frequent deep water. A
pelagic Nemertine (Pelagonemertes) was discovered by Moseley near the
southern verge of the South Australian current, being found in a trawl with deep-
sea forms from a depth of 1800 fathoms. This animal was leaf-like in shape,
bluntly pointed behind and rather square in front.
The power possessed by Nemertines of secreting mucus is very great, their course
being often traceable by the tracks which they leave behind them. Many of them
glide along with great rapidity, a mode of progression which is probably due to
the cilia covering the whole outer skin, and to the extreme contractility of the
muscles of the body-wall. In some locomotion is effected by the proboscis; this is
protruded and attaches itself by means of its spines to some foreign body, after
which the body is drawn up after it. This has been specially observed in a land
form, Tetrastemma agricola, discovered by Willemoes-Suhm in the Bermudas. On
solid bodies the movement is a kind of crawling action, the head and mouth acting
as suckers in much the same way as in many Leeches.
Most Nemertines can be very readily kept in confinement. The chief apparent
effect of such a life is a loss of colour, the animal gradually becoming pallid in
hue. Owing also to the absence of proper food they diminish very much in size,
though even when all food is kept away an animal will sometimes continue to live
as long as eighteen months.
Food.—Nemertines are carnivorous in their habits and are very voracious,
devouring any prey which comes in their way, whether it be living or dead. No
individuals being inextricably mixed.
Some species, such as Micrura purpurea, Amphiporus pulcher, and Cerebratulus
angulatus, frequent empty bivalve shells, while Nemertines are often found in
empty limpet shells adhering to rocks in tidal pools. Other smaller forms resort to
no such definite protection, but live among seaweeds; some of these remain
naked, while others secrete for themselves tubes of a membranous or gelatinous
consistency. Borlasia elizabethae lives in a burrow of clay.
Nemertines are commonly dredged from a depth of six or eight fathoms. They
may sometimes be found floating on the surface of the water, and some possess
the power of swimming rapidly, propelling themselves by a lateral motion of the
tail, the sides of which are in such cases prolonged into a thin fin-like edge. This
mode of progression is usually adopted by those which frequent deep water. A
pelagic Nemertine (Pelagonemertes) was discovered by Moseley near the
southern verge of the South Australian current, being found in a trawl with deep-
sea forms from a depth of 1800 fathoms. This animal was leaf-like in shape,
bluntly pointed behind and rather square in front.
The power possessed by Nemertines of secreting mucus is very great, their course
being often traceable by the tracks which they leave behind them. Many of them
glide along with great rapidity, a mode of progression which is probably due to
the cilia covering the whole outer skin, and to the extreme contractility of the
muscles of the body-wall. In some locomotion is effected by the proboscis; this is
protruded and attaches itself by means of its spines to some foreign body, after
which the body is drawn up after it. This has been specially observed in a land
form, Tetrastemma agricola, discovered by Willemoes-Suhm in the Bermudas. On
solid bodies the movement is a kind of crawling action, the head and mouth acting
as suckers in much the same way as in many Leeches.
Most Nemertines can be very readily kept in confinement. The chief apparent
effect of such a life is a loss of colour, the animal gradually becoming pallid in
hue. Owing also to the absence of proper food they diminish very much in size,
though even when all food is kept away an animal will sometimes continue to live
as long as eighteen months.
Food.—Nemertines are carnivorous in their habits and are very voracious,
devouring any prey which comes in their way, whether it be living or dead. No
Page 128
animal food seems to come amiss to them, and they will devour creatures of
considerable size. When in contact with its prey, the Nemertine dilates its mouth
to a large extent, and the anterior end of the oesophagus is thrust out and engulfs
the animal. Chaetopods form a favourite food material, the whole animal being
swallowed quite regardless of the hard chitinous bristles and spines with which it
is beset. The soft parts are gradually digested, the bristles and other indigestible
portions being extruded by the anus. The larger spines often pass out by
perforating passages through the wall of the intestine and through the body-wall.
The aperture thus formed appears speedily to heal after the foreign body has been
extruded.
The carnivorous habits of Nemertines even extend to cannibalism, and when kept
in confinement they frequently devour one another. For this reason it is unsafe to
keep large and small kinds together, as the small ones speedily disappear, being
used as food material by the large. If one be divided into several pieces, the pieces
are very rapidly demolished by other individuals.
Regeneration.[144]—This power is, no doubt, of great service to these animals,
since injury, or even violent local irritation, often causes complete rupture at the
point affected. It seems that the chief power of regeneration is situated in the head,
as, if a very short piece be broken off the anterior end of the body, it very rapidly
reproduces itself into a new individual. The hind end of the original body often
lives for a considerable time, but it does not in most cases appear to possess the
power of reproducing a head, and after existing for a time it dies. For a while,
however, it so far retains its vital powers that the generative products continue to
grow, and actually attain to perfection. Severe wounds also heal very quickly and
completely, and all local injuries are speedily repaired.
Owing to the force with which it is shot out, the proboscis is often completely
severed from the body, and in such a case the animal grows a new one in an
extremely short space of time. The proboscis thus broken off retains its power of
movement and contractility for a considerable time, and has been more than once
mistaken for a worm. This great vital power is probably due to the great
development of nervous tissue, the proboscis being usually richly supplied with
nerve plexuses.
One large form, Lineus sanguineus, seems to possess great recuperative powers. It
shows a marked tendency to break up into pieces, when not only the head end, but
also the other portions develop into perfect animals, each one growing a head and
considerable size. When in contact with its prey, the Nemertine dilates its mouth
to a large extent, and the anterior end of the oesophagus is thrust out and engulfs
the animal. Chaetopods form a favourite food material, the whole animal being
swallowed quite regardless of the hard chitinous bristles and spines with which it
is beset. The soft parts are gradually digested, the bristles and other indigestible
portions being extruded by the anus. The larger spines often pass out by
perforating passages through the wall of the intestine and through the body-wall.
The aperture thus formed appears speedily to heal after the foreign body has been
extruded.
The carnivorous habits of Nemertines even extend to cannibalism, and when kept
in confinement they frequently devour one another. For this reason it is unsafe to
keep large and small kinds together, as the small ones speedily disappear, being
used as food material by the large. If one be divided into several pieces, the pieces
are very rapidly demolished by other individuals.
Regeneration.[144]—This power is, no doubt, of great service to these animals,
since injury, or even violent local irritation, often causes complete rupture at the
point affected. It seems that the chief power of regeneration is situated in the head,
as, if a very short piece be broken off the anterior end of the body, it very rapidly
reproduces itself into a new individual. The hind end of the original body often
lives for a considerable time, but it does not in most cases appear to possess the
power of reproducing a head, and after existing for a time it dies. For a while,
however, it so far retains its vital powers that the generative products continue to
grow, and actually attain to perfection. Severe wounds also heal very quickly and
completely, and all local injuries are speedily repaired.
Owing to the force with which it is shot out, the proboscis is often completely
severed from the body, and in such a case the animal grows a new one in an
extremely short space of time. The proboscis thus broken off retains its power of
movement and contractility for a considerable time, and has been more than once
mistaken for a worm. This great vital power is probably due to the great
development of nervous tissue, the proboscis being usually richly supplied with
nerve plexuses.
One large form, Lineus sanguineus, seems to possess great recuperative powers. It
shows a marked tendency to break up into pieces, when not only the head end, but
also the other portions develop into perfect animals, each one growing a head and
Page 129
all the organs belonging to it. Thus in this case an animal may multiply by a
simple process of transverse fission, and form numerous complete individuals.
Breeding.—The breeding season only appears to cease in the extreme of winter.
Different genera and species seem to mature their generative products at different
times.
In the armed Nemertines the eggs are deposited separately, and are not connected
together except by such accidental mucus as the animal deposits normally; but in
the unarmed a special mucous secretion forms a thick investment for the eggs.
M‘Intosh[145] has observed the process of the deposition of the male and female
products in Nemertes gracilis. He put into a glass vessel a male and female of this
species in which the products were apparently ripe. Soon spermatozoa began to
issue in wreath-like jets from the body of the male, at first from the middle region
of the body, and afterwards anteriorly and posteriorly, until the animal was
enveloped in a dense cloud of spermatozoa. The whole process only lasted a few
minutes. When all the spermatozoa had apparently been given out, the female was
seen to protrude her head from the sand; she then passed to the side of the vessel
and deposited a group of eggs about three inches distant from the spermatozoa.
With only a few exceptions Nemertines are oviparous. Prosorhochmus claparedii,
Tetrastemma obscurum, and Monopora vivipara have been observed to contain
embryos at certain times of the year. In other forms the eggs are laid when ripe,
and development takes place subsequently to their deposition.
Geographical Distribution.—Nemertines have been found in all seas from the
arctic to the equatorial regions. Many forms are found in the British Isles both
between tide-marks and also at greater depths around our coasts. Some genera
seem to be confined to warm climates and others to cold; while others appear to
be indifferent to climate, and to subsist equally well under very various degrees of
temperature. So far as is known, the land forms are all indigenous to warm
countries.
Land Forms.—Land forms, which occur on or in moist earth under stones or
decaying vegetable matter, have been discovered and described by Semper,[146]
Willemoes-Suhm,[146] and von Graff.[146]
simple process of transverse fission, and form numerous complete individuals.
Breeding.—The breeding season only appears to cease in the extreme of winter.
Different genera and species seem to mature their generative products at different
times.
In the armed Nemertines the eggs are deposited separately, and are not connected
together except by such accidental mucus as the animal deposits normally; but in
the unarmed a special mucous secretion forms a thick investment for the eggs.
M‘Intosh[145] has observed the process of the deposition of the male and female
products in Nemertes gracilis. He put into a glass vessel a male and female of this
species in which the products were apparently ripe. Soon spermatozoa began to
issue in wreath-like jets from the body of the male, at first from the middle region
of the body, and afterwards anteriorly and posteriorly, until the animal was
enveloped in a dense cloud of spermatozoa. The whole process only lasted a few
minutes. When all the spermatozoa had apparently been given out, the female was
seen to protrude her head from the sand; she then passed to the side of the vessel
and deposited a group of eggs about three inches distant from the spermatozoa.
With only a few exceptions Nemertines are oviparous. Prosorhochmus claparedii,
Tetrastemma obscurum, and Monopora vivipara have been observed to contain
embryos at certain times of the year. In other forms the eggs are laid when ripe,
and development takes place subsequently to their deposition.
Geographical Distribution.—Nemertines have been found in all seas from the
arctic to the equatorial regions. Many forms are found in the British Isles both
between tide-marks and also at greater depths around our coasts. Some genera
seem to be confined to warm climates and others to cold; while others appear to
be indifferent to climate, and to subsist equally well under very various degrees of
temperature. So far as is known, the land forms are all indigenous to warm
countries.
Land Forms.—Land forms, which occur on or in moist earth under stones or
decaying vegetable matter, have been discovered and described by Semper,[146]
Willemoes-Suhm,[146] and von Graff.[146]
Page 130
The species found by Semper, and called by him Geonemertes palaensis, lives
under damp leaves and the roots of trees on Pelew Island in the North Pacific. It is
about 2 inches long, of a reddish-white colour, with narrow, brownish-black,
longitudinal stripes on its dorsal surface. It possesses six eyes and very small
cephalic slits and cerebral organs. The proboscis is armed, and opens by the
mouth instead of by a special pore.
The same peculiarity as to the opening of the proboscis is found in Geonemertes
chalicophora, discovered by von Graff in pots of Corypha australis in the palm-
house at Frankfurt-on-Main. He found specimens on and beneath the surface of
the earth. As it was only found in pots in which this Australian plant was growing,
von Graff thought it almost certain that it was a native of Australia. Those found
below the surface of the earth were surrounded by a transparent tube in which
particles of earth were embedded. The animal is small, only about two-fifths of an
inch in length. The colour is milk-white, with a small quantity of red pigment
anteriorly: there are four eyes, and the cephalic slits are absent.
under damp leaves and the roots of trees on Pelew Island in the North Pacific. It is
about 2 inches long, of a reddish-white colour, with narrow, brownish-black,
longitudinal stripes on its dorsal surface. It possesses six eyes and very small
cephalic slits and cerebral organs. The proboscis is armed, and opens by the
mouth instead of by a special pore.
The same peculiarity as to the opening of the proboscis is found in Geonemertes
chalicophora, discovered by von Graff in pots of Corypha australis in the palm-
house at Frankfurt-on-Main. He found specimens on and beneath the surface of
the earth. As it was only found in pots in which this Australian plant was growing,
von Graff thought it almost certain that it was a native of Australia. Those found
below the surface of the earth were surrounded by a transparent tube in which
particles of earth were embedded. The animal is small, only about two-fifths of an
inch in length. The colour is milk-white, with a small quantity of red pigment
anteriorly: there are four eyes, and the cephalic slits are absent.
Page 131
The species which was discovered by Willemoes-Suhm, and named by him
Tetrastemma agricola, lives under stones in damp earth in the Bermudas. It
differs from the other two in that the proboscis opens by a special terminal
aperture. It measures nearly an inch and a half in length, and, like G.
chalicophora, is milk-white in colour. It resembles it also in possessing four
eyes, and in the absence of cerebral organs and cephalic slits.
Fresh-water Forms.—In most cases the descriptions of fresh-water forms
are so vague and incomplete that it is difficult to determine whether or not
they are different species.
They are probably more numerous than is at present known, and are
certainly scattered widely over the face of the earth, since they have been
found in Nicaragua, at Tashkend in Turkestan, and at Philadelphia and
Monroe in the United States.
A form of which we have a full description is Tetrastemma aquarum
dulcium, found by Silliman[147] at Monroe, under stones in brooks in
company with Planarians. It is a small worm of a red or pink colour, about
half an inch in length, and it possesses usually three pairs of eyes. The
proboscis is armed, and opens by a separate aperture. The excretory system
consists of a vessel on each side of the body, each opening externally by a
pore, and internally dividing into numerous branches which end in ciliated
expansions. An individual of the same species was found by Beddard in one
of the tanks in the Botanical Gardens in Regent's Park, but as the tank is one
in which tropical plants are grown, it had almost certainly been introduced
among the roots of the plants, and cannot be considered as a British species.
A fresh-water Nemertine belonging to the genus Tetrastemma was,
however, found by Benham[148] on the roots of some water plants in the
Cherwell at Oxford. The specimen was of a bright orange colour and
measured half an inch in length.
Du Plessis[149] found another fresh-water form on the lower surface of
stones in shallow pools on the shores of the Lake of Geneva, and named it
Tetrastemma agricola, lives under stones in damp earth in the Bermudas. It
differs from the other two in that the proboscis opens by a special terminal
aperture. It measures nearly an inch and a half in length, and, like G.
chalicophora, is milk-white in colour. It resembles it also in possessing four
eyes, and in the absence of cerebral organs and cephalic slits.
Fresh-water Forms.—In most cases the descriptions of fresh-water forms
are so vague and incomplete that it is difficult to determine whether or not
they are different species.
They are probably more numerous than is at present known, and are
certainly scattered widely over the face of the earth, since they have been
found in Nicaragua, at Tashkend in Turkestan, and at Philadelphia and
Monroe in the United States.
A form of which we have a full description is Tetrastemma aquarum
dulcium, found by Silliman[147] at Monroe, under stones in brooks in
company with Planarians. It is a small worm of a red or pink colour, about
half an inch in length, and it possesses usually three pairs of eyes. The
proboscis is armed, and opens by a separate aperture. The excretory system
consists of a vessel on each side of the body, each opening externally by a
pore, and internally dividing into numerous branches which end in ciliated
expansions. An individual of the same species was found by Beddard in one
of the tanks in the Botanical Gardens in Regent's Park, but as the tank is one
in which tropical plants are grown, it had almost certainly been introduced
among the roots of the plants, and cannot be considered as a British species.
A fresh-water Nemertine belonging to the genus Tetrastemma was,
however, found by Benham[148] on the roots of some water plants in the
Cherwell at Oxford. The specimen was of a bright orange colour and
measured half an inch in length.
Du Plessis[149] found another fresh-water form on the lower surface of
stones in shallow pools on the shores of the Lake of Geneva, and named it
Page 132
Tetrastemma lacustre. It is a small animal, the largest specimens being
rather over an inch in length.
Another European genus was found in 1893 by F. E. Schulze in Berlin. It
has been fully described by T. H. Montgomery,[150] who has given it the
name of Stichostemma eilhardii.
Parasitic Forms.—The genus Malacobdella was found by von Kennel[151]
in large numbers living on Cyprina islandica, a Lamellibranch Mollusc, in
the harbour at Kiel; and it has also been described by Riches[152] as a
British form. It is attached to its host by means of a large round sucker
situated at the posterior end of the ventral surface, while the rest of the body
waves about freely in the mantle-cavity. It is perhaps hardly correct to
describe this animal as parasitic, since it does not appear to obtain its
nutriment at the expense of the host by preying on its juices. The advantage
of its position is, however, obvious, since a perpetual current of water is
kept up in the mantle-cavity of the Mollusc, and from the stream the
Nemertine is able to pick out and take for itself any food material which it
considers suitable. At the same time it is not subjected to the influence of
the winds and waves, as the shell of the mollusc acts as a barrier to prevent
the entrance of disturbing elements.
Malacobdella is short and broad, somewhat flattened dorso-ventrally. The
anterior end is bluntly rounded. The mouth opens into a wide pharynx,
which is constricted behind and then passes into the intestine; this after a
few coils opens by the anus situated dorsally immediately above the sucker.
The proboscis opens into the pharynx.
Fig. 61.—Malacobdella grossa O. F. Müll., a large female specimen. Kiel. × 1. (From
von Kennel.) A, From the dorsal surface; B, from the ventral surface.
Palaeontology.—Nemertines are unknown in a fossil state; this is probably
owing to the softness of their bodies, which would render their preservation
rather over an inch in length.
Another European genus was found in 1893 by F. E. Schulze in Berlin. It
has been fully described by T. H. Montgomery,[150] who has given it the
name of Stichostemma eilhardii.
Parasitic Forms.—The genus Malacobdella was found by von Kennel[151]
in large numbers living on Cyprina islandica, a Lamellibranch Mollusc, in
the harbour at Kiel; and it has also been described by Riches[152] as a
British form. It is attached to its host by means of a large round sucker
situated at the posterior end of the ventral surface, while the rest of the body
waves about freely in the mantle-cavity. It is perhaps hardly correct to
describe this animal as parasitic, since it does not appear to obtain its
nutriment at the expense of the host by preying on its juices. The advantage
of its position is, however, obvious, since a perpetual current of water is
kept up in the mantle-cavity of the Mollusc, and from the stream the
Nemertine is able to pick out and take for itself any food material which it
considers suitable. At the same time it is not subjected to the influence of
the winds and waves, as the shell of the mollusc acts as a barrier to prevent
the entrance of disturbing elements.
Malacobdella is short and broad, somewhat flattened dorso-ventrally. The
anterior end is bluntly rounded. The mouth opens into a wide pharynx,
which is constricted behind and then passes into the intestine; this after a
few coils opens by the anus situated dorsally immediately above the sucker.
The proboscis opens into the pharynx.
Fig. 61.—Malacobdella grossa O. F. Müll., a large female specimen. Kiel. × 1. (From
von Kennel.) A, From the dorsal surface; B, from the ventral surface.
Palaeontology.—Nemertines are unknown in a fossil state; this is probably
owing to the softness of their bodies, which would render their preservation
Page 133
extremely improbable.
Affinities.—Until recently the Nemertines were regarded as a sub-order of
the Turbellaria. They were afterwards separated from the Turbellaria and
placed as a distinct class of the phylum Platyhelminthes.
Some zoologists have considered them to be so different in many respects
from the other classes of the Platyhelminthes as to justify their being
altogether separated from that phylum, and treated as a distinct group.
If, however, the recent work of Bürger on the excretory system is to be
relied upon, the existence of flame cells would be a strong reason for
classing them among the Platyhelminthes.
Hubrecht[153] has instituted an interesting comparison between Nemertines
and Vertebrates. He compares the median dorsal nerve of Nemertines to the
spinal cord of Vertebrates; the lateral nerve-cords to the nerve of the
Vertebrate lateral line; and the lateral swellings which constitute the brain in
Nemertines to the lateral ganglia of the cephalic region in Vertebrates. This
view is strengthened by the existence of transverse nerves connecting the
lateral and dorsal nerves of Nemertines, since these may be compared with
the spinal nerves of Vertebrates. He suggests that both Nemertines and
Vertebrates may have arisen from a vermiform animal possessing a nervous
layer in the form of a plexus of nerve-fibres, the nerve tissue having
become concentrated along three lines to form a median dorsal and two
lateral nerve trunks; the former being specially developed in the Vertebrata
and the latter in the Nemertines. Hubrecht further suggests that the
notochord of Vertebrates may be a survival of the proboscis sheath of
Nemertines, while the proboscis of the latter may be represented by the
invagination to form the pituitary body in Vertebrates.
Certain authors[154] have suggested that indications exist of a relationship
between Nemertines and Balanoglossus.
The features which are supposed to indicate this are the elongated
vermiform shape showing no external signs of segmentation; the ciliated
Affinities.—Until recently the Nemertines were regarded as a sub-order of
the Turbellaria. They were afterwards separated from the Turbellaria and
placed as a distinct class of the phylum Platyhelminthes.
Some zoologists have considered them to be so different in many respects
from the other classes of the Platyhelminthes as to justify their being
altogether separated from that phylum, and treated as a distinct group.
If, however, the recent work of Bürger on the excretory system is to be
relied upon, the existence of flame cells would be a strong reason for
classing them among the Platyhelminthes.
Hubrecht[153] has instituted an interesting comparison between Nemertines
and Vertebrates. He compares the median dorsal nerve of Nemertines to the
spinal cord of Vertebrates; the lateral nerve-cords to the nerve of the
Vertebrate lateral line; and the lateral swellings which constitute the brain in
Nemertines to the lateral ganglia of the cephalic region in Vertebrates. This
view is strengthened by the existence of transverse nerves connecting the
lateral and dorsal nerves of Nemertines, since these may be compared with
the spinal nerves of Vertebrates. He suggests that both Nemertines and
Vertebrates may have arisen from a vermiform animal possessing a nervous
layer in the form of a plexus of nerve-fibres, the nerve tissue having
become concentrated along three lines to form a median dorsal and two
lateral nerve trunks; the former being specially developed in the Vertebrata
and the latter in the Nemertines. Hubrecht further suggests that the
notochord of Vertebrates may be a survival of the proboscis sheath of
Nemertines, while the proboscis of the latter may be represented by the
invagination to form the pituitary body in Vertebrates.
Certain authors[154] have suggested that indications exist of a relationship
between Nemertines and Balanoglossus.
The features which are supposed to indicate this are the elongated
vermiform shape showing no external signs of segmentation; the ciliated
Page 134
smooth skin and the possession of unicellular mucous glands; and the
protrusible proboscis, which may be comparable to the non-retractile
proboscis of Balanoglossus, a comparison which is strengthened by the fact
that in some Nemertines a sheath of nerve-fibres exists in the wall of the
proboscis corresponding to the nerve plexus in the proboscis of
Balanoglossus. In both cases an ectodermic nerve plexus exists with local
thickenings along definite lines, although these lines are not the same in the
two cases. Both possess a straight alimentary canal, ending in a terminal
anus and thrown out into paired lateral caeca, between which are the paired
metamerically-arranged generative sacs.
protrusible proboscis, which may be comparable to the non-retractile
proboscis of Balanoglossus, a comparison which is strengthened by the fact
that in some Nemertines a sheath of nerve-fibres exists in the wall of the
proboscis corresponding to the nerve plexus in the proboscis of
Balanoglossus. In both cases an ectodermic nerve plexus exists with local
thickenings along definite lines, although these lines are not the same in the
two cases. Both possess a straight alimentary canal, ending in a terminal
anus and thrown out into paired lateral caeca, between which are the paired
metamerically-arranged generative sacs.
Page 135
NEMATHELMINTHES & CHAETOGNATHA
BY
ARTHUR E. SHIPLEY, M.A.
Fellow and Tutor of Christ's College, Cambridge.
CHAPTER VI
NEMATHELMINTHES
INTRODUCTION—NEMATODA—ANATOMY—EMBRYOLOGY—CLASSIFICATION—
ASCARIDAE—STRONGYLIDAE—TRICHOTRACHELIDAE—FILARIIDAE—
MERMITHIDAE—ANGUILLULIDAE—ENOPLIDAE—PARASITISM—NEMATOMORPHA—
ANATOMY—CLASSIFICATION—LIFE-HISTORY—ACANTHOCEPHALA—ANATOMY—
EMBRYOLOGY—CLASSIFICATION.
The Nemathelminthes include three sub-Orders of very different size and
importance. These are—
i. The Nematoda.
ii. The Nematomorpha (Gordiidae).
iii. The Acanthocephala.
Although the members of these groups differ considerably from one
another, on the whole there is a closer resemblance between them than
between any one of them and any other group of animals, and there is a
certain convenience in arranging them under one head.
The following characteristics are common to all three groups of the
Nemathelminthes: they are worm-like in form, and with few exceptions are
parasitic in the bodies of other animals, either Vertebrate or Invertebrate.
Some of them spend their whole existence within the bodies of their hosts,
BY
ARTHUR E. SHIPLEY, M.A.
Fellow and Tutor of Christ's College, Cambridge.
CHAPTER VI
NEMATHELMINTHES
INTRODUCTION—NEMATODA—ANATOMY—EMBRYOLOGY—CLASSIFICATION—
ASCARIDAE—STRONGYLIDAE—TRICHOTRACHELIDAE—FILARIIDAE—
MERMITHIDAE—ANGUILLULIDAE—ENOPLIDAE—PARASITISM—NEMATOMORPHA—
ANATOMY—CLASSIFICATION—LIFE-HISTORY—ACANTHOCEPHALA—ANATOMY—
EMBRYOLOGY—CLASSIFICATION.
The Nemathelminthes include three sub-Orders of very different size and
importance. These are—
i. The Nematoda.
ii. The Nematomorpha (Gordiidae).
iii. The Acanthocephala.
Although the members of these groups differ considerably from one
another, on the whole there is a closer resemblance between them than
between any one of them and any other group of animals, and there is a
certain convenience in arranging them under one head.
The following characteristics are common to all three groups of the
Nemathelminthes: they are worm-like in form, and with few exceptions are
parasitic in the bodies of other animals, either Vertebrate or Invertebrate.
Some of them spend their whole existence within the bodies of their hosts,
Page 136
but more commonly they are only parasitic during a certain period of their
life; a few, however, lead a free life in water or in damp earth. None of the
Nemathelminthes are segmented—that is, their bodies are not divided into a
number of parts which serially repeat each other, and which resemble more
or less closely the preceding and succeeding parts. They are not provided
with any appendages or limbs, but sometimes bear a few bristles or hooks,
and in rarer cases suckers. The body, which is elongated and, as a rule,
thread-like and tapering at each end, is enclosed in a thick cuticle or
hardened secretion of the underlying cells. In no Nemathelminth is there
any closed vascular system, nor are special respiratory organs developed.
In many respects the most remarkable peculiarity of these animals is that,
with the possible exception of the excretory organs of the Acanthocephala,
there is a complete absence of cilia throughout the whole group. In this
respect they resemble the Arthropoda. The universal presence of these small
flickering processes of cells from man down to the simplest unicellular
organisms makes the absence of these structures most remarkable. In many
animals they are the sole organs of locomotion, and in almost all they
perform very important functions, both in bringing food and oxygen to the
body, and in removing waste matter from it. At present there seems to be no
adequate explanation for their absence in the two large groups mentioned
above.
Nemathelminthes are, with hardly an exception, dioecious—that is to say,
their male and female reproductive organs are in different individuals. Their
young do not differ markedly from the adults, except in the absence of
sexual organs, but the immature stages are usually termed larvae, and not
infrequently either inhabit a different host from the adult, or are free when
the adults are parasitic, or vice versâ.
Sub-Order I. Nematoda.
Anatomy.—The Nematode worms, or thread-worms, form by far the
largest and most important division of the group Nemathelminthes. The
number of species is great, and although the conditions under which they
live are of the most varied kind, there is, as a rule, little corresponding
life; a few, however, lead a free life in water or in damp earth. None of the
Nemathelminthes are segmented—that is, their bodies are not divided into a
number of parts which serially repeat each other, and which resemble more
or less closely the preceding and succeeding parts. They are not provided
with any appendages or limbs, but sometimes bear a few bristles or hooks,
and in rarer cases suckers. The body, which is elongated and, as a rule,
thread-like and tapering at each end, is enclosed in a thick cuticle or
hardened secretion of the underlying cells. In no Nemathelminth is there
any closed vascular system, nor are special respiratory organs developed.
In many respects the most remarkable peculiarity of these animals is that,
with the possible exception of the excretory organs of the Acanthocephala,
there is a complete absence of cilia throughout the whole group. In this
respect they resemble the Arthropoda. The universal presence of these small
flickering processes of cells from man down to the simplest unicellular
organisms makes the absence of these structures most remarkable. In many
animals they are the sole organs of locomotion, and in almost all they
perform very important functions, both in bringing food and oxygen to the
body, and in removing waste matter from it. At present there seems to be no
adequate explanation for their absence in the two large groups mentioned
above.
Nemathelminthes are, with hardly an exception, dioecious—that is to say,
their male and female reproductive organs are in different individuals. Their
young do not differ markedly from the adults, except in the absence of
sexual organs, but the immature stages are usually termed larvae, and not
infrequently either inhabit a different host from the adult, or are free when
the adults are parasitic, or vice versâ.
Sub-Order I. Nematoda.
Anatomy.—The Nematode worms, or thread-worms, form by far the
largest and most important division of the group Nemathelminthes. The
number of species is great, and although the conditions under which they
live are of the most varied kind, there is, as a rule, little corresponding
Page 137
difference in structure, and hence the determination of the species is
attended with no small difficulty.
With few exceptions the shape of the body is filiform (Figs. 66 and 71), the
two ends being more or less pointed, and the posterior end of the male,
which is generally a smaller animal than the female, is usually slightly
recurved. The worms are, as a rule, white, or of the colour of polished
ivory; they may be opaque or semi-transparent, but pigment spots are rarely
developed.
Minute Nematodes abound in moist soil, around the roots of plants, etc.,
and may easily be detected with the aid of a lens wriggling about amongst
the particles of sand and earth. Of the animal parasites perhaps the most
familiar is the "round worm" (Ascaris lumbricoides, Figs. 66 and 67),
which inhabits the alimentary canal of man; others are common in
domesticated animals, as A. mystax in the cat and dog, and A.
megalocephala in the horse and ox. They are also found living parasitically
in plants (Fig. 77), causing the formation of galls and other pathological
growths; Anguillula (Tylenchus) tritici causes in this way considerable
damage to corn, and others attack root-crops, cabbages, etc. The "vinegar
eel" (Anguillula aceti), which occurs so often in weak vinegar, is another
familiar example of this group.
The Skin.—The body of the worm is encased in a relatively thick,
transparent, smooth cuticle, which is turned in at the various apertures, and
lines the tubes connected with them for a greater or less distance. The
cuticle is in some cases raised to form spikes or hooks, and in certain
species, e.g. Ascaris mystax and A. transfuga, it is produced into two lateral
fins, which are supported by a thickened triradiate rod of specialised cuticle
(Fig. 62); these fins, however, do not run far down the body. As a rule the
cuticle is quite smooth, but it may be ringed, as in Filaria laticaudata and
in F. denticulata; and the rings may bear backwardly-projecting teeth.
The skin of Nematodes consists of three layers—(i.) the above-mentioned
cuticle, which is presumably secreted by (ii.) the sub-cuticle or epidermis
which underlies it; the latter surrounds in its turn (iii.) the muscular layer.
attended with no small difficulty.
With few exceptions the shape of the body is filiform (Figs. 66 and 71), the
two ends being more or less pointed, and the posterior end of the male,
which is generally a smaller animal than the female, is usually slightly
recurved. The worms are, as a rule, white, or of the colour of polished
ivory; they may be opaque or semi-transparent, but pigment spots are rarely
developed.
Minute Nematodes abound in moist soil, around the roots of plants, etc.,
and may easily be detected with the aid of a lens wriggling about amongst
the particles of sand and earth. Of the animal parasites perhaps the most
familiar is the "round worm" (Ascaris lumbricoides, Figs. 66 and 67),
which inhabits the alimentary canal of man; others are common in
domesticated animals, as A. mystax in the cat and dog, and A.
megalocephala in the horse and ox. They are also found living parasitically
in plants (Fig. 77), causing the formation of galls and other pathological
growths; Anguillula (Tylenchus) tritici causes in this way considerable
damage to corn, and others attack root-crops, cabbages, etc. The "vinegar
eel" (Anguillula aceti), which occurs so often in weak vinegar, is another
familiar example of this group.
The Skin.—The body of the worm is encased in a relatively thick,
transparent, smooth cuticle, which is turned in at the various apertures, and
lines the tubes connected with them for a greater or less distance. The
cuticle is in some cases raised to form spikes or hooks, and in certain
species, e.g. Ascaris mystax and A. transfuga, it is produced into two lateral
fins, which are supported by a thickened triradiate rod of specialised cuticle
(Fig. 62); these fins, however, do not run far down the body. As a rule the
cuticle is quite smooth, but it may be ringed, as in Filaria laticaudata and
in F. denticulata; and the rings may bear backwardly-projecting teeth.
The skin of Nematodes consists of three layers—(i.) the above-mentioned
cuticle, which is presumably secreted by (ii.) the sub-cuticle or epidermis
which underlies it; the latter surrounds in its turn (iii.) the muscular layer.
Page 138
The nature of the sub-cuticle is one of the debateable points in the
morphology of the Nematoda. No cell outlines have been detected in it,
although nuclei are scattered through it; it is in fact a syncytium, or
protoplasmic mass in which cell limits cannot be distinguished. Many of the
cells forming it have broken down into fibrils, and these form a close
meshwork, which is occasionally specialised, as, for instance, round the
nerve-cords. Along the median dorsal and ventral lines, and along the lateral
lines, this tissue is heaped up in such a way as to divide the enclosed
muscle-cells into four quadrants. These thickenings surround dorsally and
ventrally a specialised nerve-cord, and laterally the excretory canals.
According to Jammes[155] this lack of differentiation in the sub-cuticular
layer is caused by the early appearance of the cuticle, which he thinks is
necessitated, at any rate in many of the parasitic forms, by the action which
the digestive juices of the host would have on the otherwise unprotected
body-wall.
Fig. 62.—A transverse section through the body of Ascaris transfuga Rud., in the
region of the oesophagus: a, the muscular oesophagus with its triradiate lumen;
b, the cuticle; c, the sub-cuticle; d, the muscular layer; e, the lateral nerves
running in the lateral line; f, the excretory canal; g, the dorsal, and h, the ventral
nerve; i, the triradiate rod in the fin.
The nervous system, according to the same writer, is of the same nature as
this sub-cuticular tissue, only it is more differentiated, or perhaps we should
say it has retained more of the primitive cellular character of the embryonic
tissue. The fibres of the sub-cuticular tissue are closely connected with the
fibrils which compose the spongioplasm (Fig. 64, d) of the muscles,[156] and
form also the sheaths of the various nerves; in fact the passage of these
morphology of the Nematoda. No cell outlines have been detected in it,
although nuclei are scattered through it; it is in fact a syncytium, or
protoplasmic mass in which cell limits cannot be distinguished. Many of the
cells forming it have broken down into fibrils, and these form a close
meshwork, which is occasionally specialised, as, for instance, round the
nerve-cords. Along the median dorsal and ventral lines, and along the lateral
lines, this tissue is heaped up in such a way as to divide the enclosed
muscle-cells into four quadrants. These thickenings surround dorsally and
ventrally a specialised nerve-cord, and laterally the excretory canals.
According to Jammes[155] this lack of differentiation in the sub-cuticular
layer is caused by the early appearance of the cuticle, which he thinks is
necessitated, at any rate in many of the parasitic forms, by the action which
the digestive juices of the host would have on the otherwise unprotected
body-wall.
Fig. 62.—A transverse section through the body of Ascaris transfuga Rud., in the
region of the oesophagus: a, the muscular oesophagus with its triradiate lumen;
b, the cuticle; c, the sub-cuticle; d, the muscular layer; e, the lateral nerves
running in the lateral line; f, the excretory canal; g, the dorsal, and h, the ventral
nerve; i, the triradiate rod in the fin.
The nervous system, according to the same writer, is of the same nature as
this sub-cuticular tissue, only it is more differentiated, or perhaps we should
say it has retained more of the primitive cellular character of the embryonic
tissue. The fibres of the sub-cuticular tissue are closely connected with the
fibrils which compose the spongioplasm (Fig. 64, d) of the muscles,[156] and
form also the sheaths of the various nerves; in fact the passage of these
Page 139
fibrils into the nerves is so gradual that it is impossible to make any
separation between them.
The Nervous System.—The central organ of the nervous system is the
circumoesophageal ring which surrounds the pharynx, close to the anterior
end of the body, in A. megalocephala 1½ to 2 mm. behind the mouth.[157]
Ganglion cells are found in the ring, but they are not numerous, and are
chiefly aggregated round the points of origin of the nerves.
Six short nerves, three on each side of the median line, run forward from
the ring, a pair of these ending in each of the three papillae which surround
the mouth.
Behind, the nerve-ring gives off six main nerve trunks, of which the dorsal
and ventral nerves are usually the largest. These run in the median dorsal
and ventral thickenings of the sub-cuticular tissue, and are connected one
with another by numerous fine lateral branches running through the sub-
cuticle.
Fig. 63.—Diagram of the nervous system at the two ends of the body in Ascaris
megalocephala Cloq., ♂ . (After Hesse.) a, Circumoesophageal nerve-ring; b,
opening of excretory ducts; c, dorsal nerve; d, dorso-lateral nerve; e, ventro-
lateral nerve becoming the bursal nerve posteriorly; f, the ventral nerve; g,
cloacal opening; h, sub-cuticular nerves running from c to f; k, spicules.
The lateral nerves, which consist of two or four bundles, one or two lying
dorsal and one or two ventral to each excretory canal, have a double origin.
The dorsal branches arise directly from the nerve-ring, and at their point of
origin there is a considerable accumulation of ganglion cells, from which
two commissures on each side run into the ventral nerve (Fig. 63, f). The
ventral branches arise from the ventral nerve-cord immediately in front of
the excretory pore. At the posterior end the lateral nerves pass into the two
branches into which the ventral nerve divides. Just before the point where
separation between them.
The Nervous System.—The central organ of the nervous system is the
circumoesophageal ring which surrounds the pharynx, close to the anterior
end of the body, in A. megalocephala 1½ to 2 mm. behind the mouth.[157]
Ganglion cells are found in the ring, but they are not numerous, and are
chiefly aggregated round the points of origin of the nerves.
Six short nerves, three on each side of the median line, run forward from
the ring, a pair of these ending in each of the three papillae which surround
the mouth.
Behind, the nerve-ring gives off six main nerve trunks, of which the dorsal
and ventral nerves are usually the largest. These run in the median dorsal
and ventral thickenings of the sub-cuticular tissue, and are connected one
with another by numerous fine lateral branches running through the sub-
cuticle.
Fig. 63.—Diagram of the nervous system at the two ends of the body in Ascaris
megalocephala Cloq., ♂ . (After Hesse.) a, Circumoesophageal nerve-ring; b,
opening of excretory ducts; c, dorsal nerve; d, dorso-lateral nerve; e, ventro-
lateral nerve becoming the bursal nerve posteriorly; f, the ventral nerve; g,
cloacal opening; h, sub-cuticular nerves running from c to f; k, spicules.
The lateral nerves, which consist of two or four bundles, one or two lying
dorsal and one or two ventral to each excretory canal, have a double origin.
The dorsal branches arise directly from the nerve-ring, and at their point of
origin there is a considerable accumulation of ganglion cells, from which
two commissures on each side run into the ventral nerve (Fig. 63, f). The
ventral branches arise from the ventral nerve-cord immediately in front of
the excretory pore. At the posterior end the lateral nerves pass into the two
branches into which the ventral nerve divides. Just before the point where
Page 140
the ventral nerve splits it swells out into an anal ganglion situated just in
front of the anus. In the male[158] this anal ganglion gives off two lateral
nerves which pass round the cloaca and form a ring, and in this sex the
ventro-lateral nerve, which is much strengthened by fibres from the ventral
nerve, and has received, owing to the mistaken impression that it was a
special nervus recurrens, the name of the "bursal nerve," gives off
numerous branches to the sense papillae which are found in this region of
the body and on the tail. The arrangement of these parts is shown in Fig. 63.
Sense organs are but poorly developed in the Nematoda, as is usual in
animals which are, as a rule, either parasitic or live underground. Eyes,
consisting of masses of dark pigment with or without a lens, occur in the
neighbourhood of the circumoesophageal nerve-ring in some free-living
forms. Leuckart described as possible auditory organs certain giant-cells
lying near the orifice of the excretory ducts. Later research has shown these
cells to have some phagocytic action on the contents of the body-cavity.
The chief sense organs are the papillae, of which in A. megalocephala there
are two kinds, the lip papillae being distinguished from the genital papillae
by the fact that the nerve supplying them ends in a fine point and pierces the
cuticle in the former case, whilst in the latter it swells out into an "end-
organ," which is always covered by a layer of cuticle, though sometimes by
a very thin one.
Muscular System.—The muscular system is one of the most characteristic
features of the Nematoda, both as regards the histology of the muscle-cells
and the way in which the cells are arranged.
Each muscle-cell is of considerable size, and is of the shape of a somewhat
flattened spindle produced into a process near the middle. Each end of the
spindle cell is said to be continuous with the fibrils of the sub-cuticular
layer.[159] The muscle-cell consists of two portions, a contractile part which
lies next the sub-cuticle, and which usually, to some extent, wraps round the
second or medullary half. The latter consists of a fibrillar spongioplasm, in
the meshes of which lies a clear structureless hyaloplasm. The nucleus
always lies in the medullary half.
front of the anus. In the male[158] this anal ganglion gives off two lateral
nerves which pass round the cloaca and form a ring, and in this sex the
ventro-lateral nerve, which is much strengthened by fibres from the ventral
nerve, and has received, owing to the mistaken impression that it was a
special nervus recurrens, the name of the "bursal nerve," gives off
numerous branches to the sense papillae which are found in this region of
the body and on the tail. The arrangement of these parts is shown in Fig. 63.
Sense organs are but poorly developed in the Nematoda, as is usual in
animals which are, as a rule, either parasitic or live underground. Eyes,
consisting of masses of dark pigment with or without a lens, occur in the
neighbourhood of the circumoesophageal nerve-ring in some free-living
forms. Leuckart described as possible auditory organs certain giant-cells
lying near the orifice of the excretory ducts. Later research has shown these
cells to have some phagocytic action on the contents of the body-cavity.
The chief sense organs are the papillae, of which in A. megalocephala there
are two kinds, the lip papillae being distinguished from the genital papillae
by the fact that the nerve supplying them ends in a fine point and pierces the
cuticle in the former case, whilst in the latter it swells out into an "end-
organ," which is always covered by a layer of cuticle, though sometimes by
a very thin one.
Muscular System.—The muscular system is one of the most characteristic
features of the Nematoda, both as regards the histology of the muscle-cells
and the way in which the cells are arranged.
Each muscle-cell is of considerable size, and is of the shape of a somewhat
flattened spindle produced into a process near the middle. Each end of the
spindle cell is said to be continuous with the fibrils of the sub-cuticular
layer.[159] The muscle-cell consists of two portions, a contractile part which
lies next the sub-cuticle, and which usually, to some extent, wraps round the
second or medullary half. The latter consists of a fibrillar spongioplasm, in
the meshes of which lies a clear structureless hyaloplasm. The nucleus
always lies in the medullary half.
Page 141
The contractile portion consists of a number of columns, very regularly
arranged in two rows and close together, but allowing sufficient space
between adjacent columns for fibrils of the spongioplasm to penetrate; and
these become continuous with the fibrils of the sub-cuticle, which is thus
intimately connected with both nervous and muscular systems.
The medullary portion of the cell varies greatly in size; it may stretch far
into the body-cavity, which may be thereby almost occluded, or it may be
flattened out, leaving a large space around the alimentary canal. At one
point, usually about its middle, it is produced into a process, which bends
inwards towards the dorsal or ventral nerve-cord, and by means of this
process the muscle receives its nerve supply.
In most Nematodes there are numerous muscle-cells to be seen in any
transverse section, forming a layer within the sub-cuticle, and broken up
into four quadrants (Fig. 62) by the projection of the dorsal, ventral, and
lateral thickenings of the sub-cuticular tissue. In some genera, however,
such as Oxyuris, Strongylus, Pelodera, Leptodera, etc., there are but eight
muscle-cells in a row, two in each quadrant. Such genera are classed
together by Schneider,[160] and termed Meromyarii (vide p. 137).
Fig. 64.—A, transverse section through the centre of a muscle-cell; B, the same through
a nerve fibre showing the sub-cuticular fibres running into the sheath. (After
Rohde.) a, Cuticle; b, sub-cuticular fibres continuous with d; c, contractile
columns; d, network of spongioplasm; e, nucleus.
In addition to the characteristic muscles of the body-wall there are others,
such as those which move the spicules in the male, which cross the body-
arranged in two rows and close together, but allowing sufficient space
between adjacent columns for fibrils of the spongioplasm to penetrate; and
these become continuous with the fibrils of the sub-cuticle, which is thus
intimately connected with both nervous and muscular systems.
The medullary portion of the cell varies greatly in size; it may stretch far
into the body-cavity, which may be thereby almost occluded, or it may be
flattened out, leaving a large space around the alimentary canal. At one
point, usually about its middle, it is produced into a process, which bends
inwards towards the dorsal or ventral nerve-cord, and by means of this
process the muscle receives its nerve supply.
In most Nematodes there are numerous muscle-cells to be seen in any
transverse section, forming a layer within the sub-cuticle, and broken up
into four quadrants (Fig. 62) by the projection of the dorsal, ventral, and
lateral thickenings of the sub-cuticular tissue. In some genera, however,
such as Oxyuris, Strongylus, Pelodera, Leptodera, etc., there are but eight
muscle-cells in a row, two in each quadrant. Such genera are classed
together by Schneider,[160] and termed Meromyarii (vide p. 137).
Fig. 64.—A, transverse section through the centre of a muscle-cell; B, the same through
a nerve fibre showing the sub-cuticular fibres running into the sheath. (After
Rohde.) a, Cuticle; b, sub-cuticular fibres continuous with d; c, contractile
columns; d, network of spongioplasm; e, nucleus.
In addition to the characteristic muscles of the body-wall there are others,
such as those which move the spicules in the male, which cross the body-
Page 142
cavity obliquely near the anus, and such as sphincter muscles near the latter
orifice, which have not the characteristic arrangement of contractile and
medullary parts described above.
The Body-Cavity.—The skin of a Nematode, as described above, contains
most of the important organs of the body within its thickness. The chief
muscular system, the nervous system with its sense organs, and the
excretory organs are all embedded in or form part of the skin, which in its
turn encloses a cavity—the body-cavity—in which the other two systems of
organs which are found in Nematodes lie. These are the digestive system
and the reproductive system.
The body-cavity is continuous from one end of the animal to the other, and
is in no case divided up into compartments by the presence of septa or
mesenteries. It contains a coagulable fluid with numerous corpuscles; this
is, as a rule, colourless, but in Syngamus trachealis Sieb. (Fig. 70), which
lives on blood, the haemoglobin of its host tinges it red, though the colour is
said to disappear if the parasite be isolated and starved.
The morphological nature of this body-cavity affords an interesting
problem. It is not a true coelom, such as exists in the earthworm, since it is
not surrounded by mesoderm, nor do the excretory organs, with the possible
exception of one or two genera, open into it, nor do the generative cells
arise from its walls. Essentially it is a space between the mesodermic
muscle-cells which line the skin and the endodermic cells of the alimentary
canal, and although in many of its functions it resembles the coelom of
other animals, its morphological character is quite different.
There are no respiratory or circulatory organs in the Nematoda; possibly the
fluid in the body-cavity acts, to some extent, as a carrier of oxygen, but
from the inert and almost vegetative life of these animals it seems probable
that their respiratory processes are slow, and in fact Bunge[161] has shown
that Ascaris mystax, found in the intestine of the cat, will live for four or
five days in media quite free from oxygen, and that A. acus from the pike
will live and exhibit movements in the same media for from four to six
days.
orifice, which have not the characteristic arrangement of contractile and
medullary parts described above.
The Body-Cavity.—The skin of a Nematode, as described above, contains
most of the important organs of the body within its thickness. The chief
muscular system, the nervous system with its sense organs, and the
excretory organs are all embedded in or form part of the skin, which in its
turn encloses a cavity—the body-cavity—in which the other two systems of
organs which are found in Nematodes lie. These are the digestive system
and the reproductive system.
The body-cavity is continuous from one end of the animal to the other, and
is in no case divided up into compartments by the presence of septa or
mesenteries. It contains a coagulable fluid with numerous corpuscles; this
is, as a rule, colourless, but in Syngamus trachealis Sieb. (Fig. 70), which
lives on blood, the haemoglobin of its host tinges it red, though the colour is
said to disappear if the parasite be isolated and starved.
The morphological nature of this body-cavity affords an interesting
problem. It is not a true coelom, such as exists in the earthworm, since it is
not surrounded by mesoderm, nor do the excretory organs, with the possible
exception of one or two genera, open into it, nor do the generative cells
arise from its walls. Essentially it is a space between the mesodermic
muscle-cells which line the skin and the endodermic cells of the alimentary
canal, and although in many of its functions it resembles the coelom of
other animals, its morphological character is quite different.
There are no respiratory or circulatory organs in the Nematoda; possibly the
fluid in the body-cavity acts, to some extent, as a carrier of oxygen, but
from the inert and almost vegetative life of these animals it seems probable
that their respiratory processes are slow, and in fact Bunge[161] has shown
that Ascaris mystax, found in the intestine of the cat, will live for four or
five days in media quite free from oxygen, and that A. acus from the pike
will live and exhibit movements in the same media for from four to six
days.
Page 143
The Digestive System.—The mouth of the Nematoda is usually anterior
and terminal, and is surrounded by from two to six projecting lips, the most
common number being three. These lips are well provided with sense
papillae. The mouth leads into an alimentary canal, which with hardly an
exception runs straight through the body to the anus without twists or loops.
The anus is usually placed ventrally and is not terminal, but in Trichina and
Trichocephalus it is at the end of the body, and in Mermis, where the
several parts of the alimentary canal are said not to communicate, it is
absent altogether. Ichthyonema, Dracunculus, Allantonema, Atractonema,
and other Filariae are also aproctous.
The alimentary canal is divisible into three parts—(i.) the oesophagus, (ii.)
the intestine, and (iii.) the rectum. The suctorial oesophagus is a very
muscular, thick-walled tube, lined with cuticle continuous with that which
covers the body, and like it cast from time to time. Its lumen is usually
much reduced, and is almost invariably triangular or triradiate in section
(Fig. 62). In many genera the hinder end of the oesophagus is swollen into a
muscular bulb, which is armed with teeth in Heterakis, Oxyuris, Pelodera,
Leptodera, etc. Other species, such as Tylenchus, Aphelenchus, Dorylaimus,
are armed with a spear, which in Onyx,[162] a genus recently described and
allied to the last named, is borne on a special bulb. The use of the spear is to
pierce the tissue upon the juices of which the animal lives. A gland lies
embedded in the thick walls of the oesophagus, and opens into its lumen by
a fine tube. This was first described by Schneider[163] in A. megalocephala,
and more recently it has been found by Hamann[164] in a number of
Ascaridae and Strongylidae from the Adriatic, and also in Lecanocephalus.
With a few exceptions, such as Mermis, where it is blind, the oesophagus
opens posteriorly into the intestine. This is a somewhat flattened tube,
whose shape and position are often altered by the development of the
generative organs. Its wall consists of a single layer of columnar cells, with
large nuclei coated internally and externally by a layer of cuticle. The inner
layer of cuticle is usually perforated by very numerous minute pores. In
some species the intestine is degenerate, in Mermis it is a closed tube
opening neither into the oesophagus nor into the rectum; in Trichina spiralis
and in the larva of Tylenchus tritici it consists of a single row of cells
and terminal, and is surrounded by from two to six projecting lips, the most
common number being three. These lips are well provided with sense
papillae. The mouth leads into an alimentary canal, which with hardly an
exception runs straight through the body to the anus without twists or loops.
The anus is usually placed ventrally and is not terminal, but in Trichina and
Trichocephalus it is at the end of the body, and in Mermis, where the
several parts of the alimentary canal are said not to communicate, it is
absent altogether. Ichthyonema, Dracunculus, Allantonema, Atractonema,
and other Filariae are also aproctous.
The alimentary canal is divisible into three parts—(i.) the oesophagus, (ii.)
the intestine, and (iii.) the rectum. The suctorial oesophagus is a very
muscular, thick-walled tube, lined with cuticle continuous with that which
covers the body, and like it cast from time to time. Its lumen is usually
much reduced, and is almost invariably triangular or triradiate in section
(Fig. 62). In many genera the hinder end of the oesophagus is swollen into a
muscular bulb, which is armed with teeth in Heterakis, Oxyuris, Pelodera,
Leptodera, etc. Other species, such as Tylenchus, Aphelenchus, Dorylaimus,
are armed with a spear, which in Onyx,[162] a genus recently described and
allied to the last named, is borne on a special bulb. The use of the spear is to
pierce the tissue upon the juices of which the animal lives. A gland lies
embedded in the thick walls of the oesophagus, and opens into its lumen by
a fine tube. This was first described by Schneider[163] in A. megalocephala,
and more recently it has been found by Hamann[164] in a number of
Ascaridae and Strongylidae from the Adriatic, and also in Lecanocephalus.
With a few exceptions, such as Mermis, where it is blind, the oesophagus
opens posteriorly into the intestine. This is a somewhat flattened tube,
whose shape and position are often altered by the development of the
generative organs. Its wall consists of a single layer of columnar cells, with
large nuclei coated internally and externally by a layer of cuticle. The inner
layer of cuticle is usually perforated by very numerous minute pores. In
some species the intestine is degenerate, in Mermis it is a closed tube
opening neither into the oesophagus nor into the rectum; in Trichina spiralis
and in the larva of Tylenchus tritici it consists of a single row of cells
Page 144
perforated by a duct, but in the adult of the last named there are many cells
in a transverse section.
Fig. 65.—A longitudinal section through the body of Strongylus filaria Rud. (From O.
Augstein.[165]) A portion of the body, on each side of the excretory pore, is seen
in optical section. a, Mouth; b, oesophagus; c, intestine; d, excretory canal; e,
excretory pore, and the opening of the poison glands, i; f, circumoesophageal
nerve-ring; g, ventral nerve; h, dorsal nerve; i, unicellular poison glands; k,
ovary, with the ova separate; l, oviduct; m, uterus, the first egg in the uterus is
surrounded by spermatozoa; n, opening of uterus; o, inner end of ovary with the
ova undifferentiated.
In some genera, Leptodera and Pelodera, the lumen of the intestine at any
one level is bounded by two horseshoe-shaped cells, but by far the
commonest arrangement is a tube formed of fairly numerous columnar cells
crowded with granules and with large nuclei.
The rectum is usually short; its cuticular lining, like that of the oesophagus,
is cast at intervals. At its anterior end there is usually a sphincter muscle,
and its walls are divaricated by muscular strands which run from it to the
in a transverse section.
Fig. 65.—A longitudinal section through the body of Strongylus filaria Rud. (From O.
Augstein.[165]) A portion of the body, on each side of the excretory pore, is seen
in optical section. a, Mouth; b, oesophagus; c, intestine; d, excretory canal; e,
excretory pore, and the opening of the poison glands, i; f, circumoesophageal
nerve-ring; g, ventral nerve; h, dorsal nerve; i, unicellular poison glands; k,
ovary, with the ova separate; l, oviduct; m, uterus, the first egg in the uterus is
surrounded by spermatozoa; n, opening of uterus; o, inner end of ovary with the
ova undifferentiated.
In some genera, Leptodera and Pelodera, the lumen of the intestine at any
one level is bounded by two horseshoe-shaped cells, but by far the
commonest arrangement is a tube formed of fairly numerous columnar cells
crowded with granules and with large nuclei.
The rectum is usually short; its cuticular lining, like that of the oesophagus,
is cast at intervals. At its anterior end there is usually a sphincter muscle,
and its walls are divaricated by muscular strands which run from it to the
Page 145
body-wall. The anus is a transverse slit, which in the male Strongylidae is
surrounded by a funnel-shaped membrane.
The food of Nematodes seems to be almost entirely fluid, and consists, at
any rate in the parasitic forms, of the elaborated juices of their hosts. Little
is known about the nutriment of the free-living forms.
The Excretory System.—The excretory organs are peculiar, and, like many
other Nematode structures, do not fall readily into line with what is known
of similar organs in other animals. They consist of two canals embedded in
the lateral thickenings of the sub-cuticular tissue. The canals end blindly
behind, but near the anterior end of the body they bend inwards, and after
uniting, open by a common pore situated in the middle ventral line, a little
way behind the mouth. The lateral canals are in some cases continued in
front of the transverse branch, and they then end blindly in the head. The
walls of these canals consist of an internal, structureless, refractive layer
surrounded by a granular layer with nuclei. They contain a fluid, but
nothing is known of its composition.
An interesting divergence from the usual form of excretory organ has been
described by Hamann[166] in the genus Lecanocephalus. Here there is only
one canal, the right; anteriorly this bends towards the ventral surface and
opens by a small median pore close behind the nerve-ring. Posteriorly the
canal does not extend much beyond the middle of the body, where it forms
a coiled mass, and diminishing in size, opens into the body-cavity. The
same author also states that both canals in Dochmius have a similar internal
opening; these observations, if confirmed,[167] show a conformity to the
ordinary structure of excretory organs which was not supposed to exist in
the lateral canals of the Nematoda.
The Reproductive Organs.—With the exception of the genera
Angiostomum, Pelodytes, and of Rhabdonema nigrovenosum, which are
physiologically hermaphrodite and self-impregnating, the Nematodes have
separate sexes. The males are, as a rule, smaller than the females, and may
usually be distinguished by the posterior end of the body being curved
towards the ventral surface; a genital bursa, and one or more spicules are
surrounded by a funnel-shaped membrane.
The food of Nematodes seems to be almost entirely fluid, and consists, at
any rate in the parasitic forms, of the elaborated juices of their hosts. Little
is known about the nutriment of the free-living forms.
The Excretory System.—The excretory organs are peculiar, and, like many
other Nematode structures, do not fall readily into line with what is known
of similar organs in other animals. They consist of two canals embedded in
the lateral thickenings of the sub-cuticular tissue. The canals end blindly
behind, but near the anterior end of the body they bend inwards, and after
uniting, open by a common pore situated in the middle ventral line, a little
way behind the mouth. The lateral canals are in some cases continued in
front of the transverse branch, and they then end blindly in the head. The
walls of these canals consist of an internal, structureless, refractive layer
surrounded by a granular layer with nuclei. They contain a fluid, but
nothing is known of its composition.
An interesting divergence from the usual form of excretory organ has been
described by Hamann[166] in the genus Lecanocephalus. Here there is only
one canal, the right; anteriorly this bends towards the ventral surface and
opens by a small median pore close behind the nerve-ring. Posteriorly the
canal does not extend much beyond the middle of the body, where it forms
a coiled mass, and diminishing in size, opens into the body-cavity. The
same author also states that both canals in Dochmius have a similar internal
opening; these observations, if confirmed,[167] show a conformity to the
ordinary structure of excretory organs which was not supposed to exist in
the lateral canals of the Nematoda.
The Reproductive Organs.—With the exception of the genera
Angiostomum, Pelodytes, and of Rhabdonema nigrovenosum, which are
physiologically hermaphrodite and self-impregnating, the Nematodes have
separate sexes. The males are, as a rule, smaller than the females, and may
usually be distinguished by the posterior end of the body being curved
towards the ventral surface; a genital bursa, and one or more spicules are
Page 146
often found in this sex. Further, the position of the genital opening differs;
in the male the vas deferens opens on the ventral surface of the rectum close
to the anus, but the oviduct in the female opens in the ventral middle line,
usually near the middle of the body, but sometimes close behind the
excretory pore, or in some Strongylidae just in front of the anus. The tail of
the male bears very numerous papillae, which are of considerable
systematic importance.
Fig. 66.—Ascaris lumbricoides Cloq. ♂, natural size, cut open along the dorsal middle
line. a, Oesophagus; b, intestine; c, testis; d, vas deferens; h, lateral excretory
canals.
With rare exceptions, e.g. Filaria attenuata, where it is double, the male
reproductive organ consists of a single tube divisible into a testis proper, a
vas deferens, a vesicula seminalis, where the spermatozoa are stored up,
and a ductus ejaculatorius. The tube stretches through the body in a straight
line in the small free-living forms, but is thrown into loops and coils in the
larger parasitic Nematodes. Within the testis the mother-cells of the
spermatozoa are attached to a rhachis or axial cord; the mother-cells divide,
and their products ultimately form spermatozoa. The latter have a very
peculiar shape; in accordance with the universal absence of cilia in the
Nematoda the spermatozoon has no flagellum, and at first consists of a
spherical nucleated cell, on one side of which a cap or covering of some
refractive substance appears. The cap elongates and becomes conical, whilst
the protoplasmic portion of the spermatozoon throws out pseudopodia and
becomes amoeboid, but ultimately rounds itself off again. The spermatozoa
do not attain maturity until they reach the uterus of the female.
in the male the vas deferens opens on the ventral surface of the rectum close
to the anus, but the oviduct in the female opens in the ventral middle line,
usually near the middle of the body, but sometimes close behind the
excretory pore, or in some Strongylidae just in front of the anus. The tail of
the male bears very numerous papillae, which are of considerable
systematic importance.
Fig. 66.—Ascaris lumbricoides Cloq. ♂, natural size, cut open along the dorsal middle
line. a, Oesophagus; b, intestine; c, testis; d, vas deferens; h, lateral excretory
canals.
With rare exceptions, e.g. Filaria attenuata, where it is double, the male
reproductive organ consists of a single tube divisible into a testis proper, a
vas deferens, a vesicula seminalis, where the spermatozoa are stored up,
and a ductus ejaculatorius. The tube stretches through the body in a straight
line in the small free-living forms, but is thrown into loops and coils in the
larger parasitic Nematodes. Within the testis the mother-cells of the
spermatozoa are attached to a rhachis or axial cord; the mother-cells divide,
and their products ultimately form spermatozoa. The latter have a very
peculiar shape; in accordance with the universal absence of cilia in the
Nematoda the spermatozoon has no flagellum, and at first consists of a
spherical nucleated cell, on one side of which a cap or covering of some
refractive substance appears. The cap elongates and becomes conical, whilst
the protoplasmic portion of the spermatozoon throws out pseudopodia and
becomes amoeboid, but ultimately rounds itself off again. The spermatozoa
do not attain maturity until they reach the uterus of the female.
Page 147
The internal female reproductive organs are, with few exceptions (Trichina,
etc.), double, but the vagina, which is lined with cuticle continuous with
that covering the body, is always single. They are usually much coiled, and
may be divided into ovary, oviduct, and uterus. The ova arise from a
polynucleated mass of protoplasm or syncytium (Fig. 65, o) at the upper
end, and acquire distinctness as they approach the oviduct. Fertilisation
takes place in the uterus, but the segmentation may not begin until some
time after the eggs are laid; in Dochmius, however, it is well advanced at
this period, and in many genera, e.g. Pseudalius, Trichina, Dracunculus,
etc., the whole development of the larva takes place in the body of the
mother.
Fig. 67.—Ascaris lumbricoides Cloq. ♀, natural size, cut open along the median dorsal
line to show the internal organs. a, The muscular oesophagus; b, the intestine; c,
the ovary; d, the uterus; e, the vagina; f, the external opening; h, the excretory
canals; i, their opening.
Embryology.—The eggs of many of the parasitic forms require a
considerable degree of warmth to develop. Those of Ascaris lumbricoides
require a temperature of 20° C., those of Trichocephalus 22.5° C., and those
of Oxyuris vermicularis, 40° C. The latter develop in a few hours, the eggs
of Dochmius in a few days, whilst those of A. lumbricoides take weeks or
etc.), double, but the vagina, which is lined with cuticle continuous with
that covering the body, is always single. They are usually much coiled, and
may be divided into ovary, oviduct, and uterus. The ova arise from a
polynucleated mass of protoplasm or syncytium (Fig. 65, o) at the upper
end, and acquire distinctness as they approach the oviduct. Fertilisation
takes place in the uterus, but the segmentation may not begin until some
time after the eggs are laid; in Dochmius, however, it is well advanced at
this period, and in many genera, e.g. Pseudalius, Trichina, Dracunculus,
etc., the whole development of the larva takes place in the body of the
mother.
Fig. 67.—Ascaris lumbricoides Cloq. ♀, natural size, cut open along the median dorsal
line to show the internal organs. a, The muscular oesophagus; b, the intestine; c,
the ovary; d, the uterus; e, the vagina; f, the external opening; h, the excretory
canals; i, their opening.
Embryology.—The eggs of many of the parasitic forms require a
considerable degree of warmth to develop. Those of Ascaris lumbricoides
require a temperature of 20° C., those of Trichocephalus 22.5° C., and those
of Oxyuris vermicularis, 40° C. The latter develop in a few hours, the eggs
of Dochmius in a few days, whilst those of A. lumbricoides take weeks or
Page 148
even months, and the young of Trichocephalus seldom develop within a
year.[168] The ova only develop in a damp atmosphere, and they can be
arrested at almost any stage, and for considerable periods, by desiccation.
Our knowledge of the processes by which the fertilised egg-cell develops
into the larva is very imperfect. As a rule the segmentation is complete and
equal; it results in the formation of a blastula, which may take the form of a
hollow sphere of cells—A. megalocephala—or the cavity may be reduced,
and the blastula may consist of a double-layered plate, as in Cucullanus.[169]
The distinction into cells which will form the three embryonic layers, the
ectoderm, mesoderm, and endoderm, is very early evident,—in the eight-
cell stage. By the growth of one side of the blastula and the tucking in of the
other the blastula becomes converted into a gastrula, which is a two-layered
stage with a cavity opening to the exterior by a pore termed the blastopore.
In Nematodes the blastopore is elongated and slit-like; it either forms the
mouth (Cucullanus) or closes from behind forwards, the mouth ultimately
arising at the point where the blastopore finally closed (Rhabdonema
nigrovenosum). The mesodermal cells lie between the ectoderm and the
endoderm; they ultimately develop into the muscles of the body-wall, the
lateral excretory canals, and the reproductive organs; the last-named two
systems arise each[170] from a single cell. The nervous system arises from
the ectoderm, which also forms the sub-cuticle, and is turned in slightly at
the mouth and anus; the remainder of the alimentary canal develops from
the endoderm.
The post-embryonic development, which is very variable, and in many
cases very extraordinary, will be dealt with under the several families.
Classification.—The classification of the Nematodes is a matter of very
considerable difficulty; their structure is unusually monotonous, and, owing
perhaps to their largely parasitic mode of life, they show practically none of
those external features which are so useful to the systematist in other
groups. Schneider in his Monograph divides the group into three
subdivisions—(i.) the Polymyarii, in which numerous muscle cells are seen
in a transverse section; (ii.) the Meromyarii, in which only eight are seen,
two in each quadrant; and (iii.) the Holomyarii, in which the muscles are
year.[168] The ova only develop in a damp atmosphere, and they can be
arrested at almost any stage, and for considerable periods, by desiccation.
Our knowledge of the processes by which the fertilised egg-cell develops
into the larva is very imperfect. As a rule the segmentation is complete and
equal; it results in the formation of a blastula, which may take the form of a
hollow sphere of cells—A. megalocephala—or the cavity may be reduced,
and the blastula may consist of a double-layered plate, as in Cucullanus.[169]
The distinction into cells which will form the three embryonic layers, the
ectoderm, mesoderm, and endoderm, is very early evident,—in the eight-
cell stage. By the growth of one side of the blastula and the tucking in of the
other the blastula becomes converted into a gastrula, which is a two-layered
stage with a cavity opening to the exterior by a pore termed the blastopore.
In Nematodes the blastopore is elongated and slit-like; it either forms the
mouth (Cucullanus) or closes from behind forwards, the mouth ultimately
arising at the point where the blastopore finally closed (Rhabdonema
nigrovenosum). The mesodermal cells lie between the ectoderm and the
endoderm; they ultimately develop into the muscles of the body-wall, the
lateral excretory canals, and the reproductive organs; the last-named two
systems arise each[170] from a single cell. The nervous system arises from
the ectoderm, which also forms the sub-cuticle, and is turned in slightly at
the mouth and anus; the remainder of the alimentary canal develops from
the endoderm.
The post-embryonic development, which is very variable, and in many
cases very extraordinary, will be dealt with under the several families.
Classification.—The classification of the Nematodes is a matter of very
considerable difficulty; their structure is unusually monotonous, and, owing
perhaps to their largely parasitic mode of life, they show practically none of
those external features which are so useful to the systematist in other
groups. Schneider in his Monograph divides the group into three
subdivisions—(i.) the Polymyarii, in which numerous muscle cells are seen
in a transverse section; (ii.) the Meromyarii, in which only eight are seen,
two in each quadrant; and (iii.) the Holomyarii, in which the muscles are
Page 149
either not divided, or only divided by longitudinal lines. This grouping has,
however, to some extent broken down, since Bütschli[171] and others have
shown that the third subdivision is founded on insufficient observation,
whilst the first two include, in different subdivisions, Nematodes which are
closely allied in all respects except as regards their muscle cells.
The details of the life-history have been used by other writers as a basis of
classification. Linstow[172] enumerates fourteen distinct modifications of
the post-embryonic development (vide p. 159), and Örley[173] has grouped
these under three headings. The animals which fall under each group to
some extent resemble one another in structure. Örley's groups are:—
(i.) Nematozoa.—Thread-worms with free larval life, the mature forms
being parasitic in animals. Enormous numbers of eggs are produced, and
the development is indirect. The genital organs are complicated by many
convolutions.
(ii.) Rhabditiformae.—Small, as a rule microscopic, thread-worms,
usually living free, but rarely parasitic. They become sexually mature only
in decomposing organic substances, or in earth saturated with such
substances. They live gregariously and do not produce immense numbers of
ova. The metamorphosis is slight, or is complicated by sexual
metamorphosis. The oesophagus has two dilatations. The genital tubes are
simple and not coiled.
(iii.) Anguillulidae.—Small microscopic thread-worms, with a free
existence in mould or water, throughout all stages. They produce large eggs.
They are provided with a caudal sucker and bristles, sometimes with eyes
and other structures characteristic of a free life. Genital tube simple and not
coiled.
The disadvantage of such a system is, that to accurately place a specimen in
its proper class we must be acquainted with its life-history, and this is
known in but few cases.
however, to some extent broken down, since Bütschli[171] and others have
shown that the third subdivision is founded on insufficient observation,
whilst the first two include, in different subdivisions, Nematodes which are
closely allied in all respects except as regards their muscle cells.
The details of the life-history have been used by other writers as a basis of
classification. Linstow[172] enumerates fourteen distinct modifications of
the post-embryonic development (vide p. 159), and Örley[173] has grouped
these under three headings. The animals which fall under each group to
some extent resemble one another in structure. Örley's groups are:—
(i.) Nematozoa.—Thread-worms with free larval life, the mature forms
being parasitic in animals. Enormous numbers of eggs are produced, and
the development is indirect. The genital organs are complicated by many
convolutions.
(ii.) Rhabditiformae.—Small, as a rule microscopic, thread-worms,
usually living free, but rarely parasitic. They become sexually mature only
in decomposing organic substances, or in earth saturated with such
substances. They live gregariously and do not produce immense numbers of
ova. The metamorphosis is slight, or is complicated by sexual
metamorphosis. The oesophagus has two dilatations. The genital tubes are
simple and not coiled.
(iii.) Anguillulidae.—Small microscopic thread-worms, with a free
existence in mould or water, throughout all stages. They produce large eggs.
They are provided with a caudal sucker and bristles, sometimes with eyes
and other structures characteristic of a free life. Genital tube simple and not
coiled.
The disadvantage of such a system is, that to accurately place a specimen in
its proper class we must be acquainted with its life-history, and this is
known in but few cases.
Page 150
The determination of the species to which a Nematode belongs is a matter
of considerable difficulty. Amongst the more important features for
purposes of classification are the arrangement of the muscles, the character
of the tail in the male, especially when papillae are present, the number and
the size of the spicules, and the arrangement of the lips and mouth-parts
generally.
Cobb[174] has recently devised an ingenious formula in which
measurements of different parts of the body appear as percentages of the
whole length of the body. The nature of this will be understood by reference
to Fig. 68. Such a formula should, however, be used with caution, since it
rests on the assumption that the proportions of the various parts of the body
are constant in different individuals, and it is by no means certain that this is
the case.
Fig. 68.—Diagram to explain the descriptive formula used for Nematodes. (From
Cobb.) 6, 7, 8, 10, 6 are the transverse measurements, while 7, 14, 28, 50, 88 are
the corresponding longitudinal measurements. The formula in this case is
7 14 28 50 88
6 7 8 10 6
The unit of measurement is the one-hundredth part of the length of the worm. The
measurements are therefore percentages of the length.
The measurements are taken with the animal viewed in profile; the first is taken at the
base of the oesophagus, the second at the nerve-ring, the third at the cardiac
constriction, the fourth at the vulva in females and at the middle in males, the
fifth at the anus.
Taking everything into consideration, it has seemed advisable in the
following systematic account of the Nematoda to abandon the larger
groups, and to deal directly with the families. Claus distinguishes seven of
these, and the diagnoses given at the head of each are mainly taken from his
Grundzüge der Zoologie.[175]
I. Family Ascaridae.
of considerable difficulty. Amongst the more important features for
purposes of classification are the arrangement of the muscles, the character
of the tail in the male, especially when papillae are present, the number and
the size of the spicules, and the arrangement of the lips and mouth-parts
generally.
Cobb[174] has recently devised an ingenious formula in which
measurements of different parts of the body appear as percentages of the
whole length of the body. The nature of this will be understood by reference
to Fig. 68. Such a formula should, however, be used with caution, since it
rests on the assumption that the proportions of the various parts of the body
are constant in different individuals, and it is by no means certain that this is
the case.
Fig. 68.—Diagram to explain the descriptive formula used for Nematodes. (From
Cobb.) 6, 7, 8, 10, 6 are the transverse measurements, while 7, 14, 28, 50, 88 are
the corresponding longitudinal measurements. The formula in this case is
7 14 28 50 88
6 7 8 10 6
The unit of measurement is the one-hundredth part of the length of the worm. The
measurements are therefore percentages of the length.
The measurements are taken with the animal viewed in profile; the first is taken at the
base of the oesophagus, the second at the nerve-ring, the third at the cardiac
constriction, the fourth at the vulva in females and at the middle in males, the
fifth at the anus.
Taking everything into consideration, it has seemed advisable in the
following systematic account of the Nematoda to abandon the larger
groups, and to deal directly with the families. Claus distinguishes seven of
these, and the diagnoses given at the head of each are mainly taken from his
Grundzüge der Zoologie.[175]
I. Family Ascaridae.
Page 151
Body rather stout. A dorsal and two ventro-lateral lips, bearing papillae.
Buccal cavity distinct, seldom provided with chitinous armature. The
oesophagus often has two dilatations. The tail of the male is ventrally
curved, and usually there are two horny spicules. The Ascaridae are found
in the intestines of their respective hosts.
Genera: Ascaris, Heterakis, Oxyuris, Nematoxys, Oxysoma, and many
others.
Von Linstow[176] enumerates over 250 species of Ascaris, of which it will
only be possible to mention here one or two. They are all parasitic in
Vertebrata.
A. lumbricoides Linn. is one of the largest known Nematodes ♂ = 4-6 in., ♀
= 10-14 in.; Figs. 66 and 67). It is a common parasite in man, and has been
found in the ox. It is now generally recognised as the same parasite which
inhabits the pig, and which Dujardin regarded as specifically distinct, and
named A. suillae. In the latter host, however, it never attains the dimensions
it does in man. It inhabits the upper and middle parts of the small intestine,
and has been known to escape into the body-cavity and set up abscesses
there, or to make its way into the stomach, and to be voided through the
mouth. It is practically cosmopolitan in distribution, and is very common in
Japan—Baely found it in twenty-one out of twenty-three post-mortems—
and in Tonquin and tropical Africa. Heller[177] states that no one is free from
these worms in Finland, and they are common wherever there is a plentiful
water supply, as in the marshy districts of Holland and Sweden. In Iceland
alone they seem absent. When examined alive they give off an irritating
vapour which seriously affects some observers, causing catarrhal
symptoms, which in Bastian's case lasted six weeks. The usual number
found in one host is small, one to six or eight, but cases are on record where
many hundreds occurred in one person.
The details of the life-history of this form are not yet completely worked
out. The eggs leave the body of the host with the excreta, and formerly it
was thought they re-entered the alimentary canal in drinking-water, etc., and
there developed into the adult without change of host. This view has been
Buccal cavity distinct, seldom provided with chitinous armature. The
oesophagus often has two dilatations. The tail of the male is ventrally
curved, and usually there are two horny spicules. The Ascaridae are found
in the intestines of their respective hosts.
Genera: Ascaris, Heterakis, Oxyuris, Nematoxys, Oxysoma, and many
others.
Von Linstow[176] enumerates over 250 species of Ascaris, of which it will
only be possible to mention here one or two. They are all parasitic in
Vertebrata.
A. lumbricoides Linn. is one of the largest known Nematodes ♂ = 4-6 in., ♀
= 10-14 in.; Figs. 66 and 67). It is a common parasite in man, and has been
found in the ox. It is now generally recognised as the same parasite which
inhabits the pig, and which Dujardin regarded as specifically distinct, and
named A. suillae. In the latter host, however, it never attains the dimensions
it does in man. It inhabits the upper and middle parts of the small intestine,
and has been known to escape into the body-cavity and set up abscesses
there, or to make its way into the stomach, and to be voided through the
mouth. It is practically cosmopolitan in distribution, and is very common in
Japan—Baely found it in twenty-one out of twenty-three post-mortems—
and in Tonquin and tropical Africa. Heller[177] states that no one is free from
these worms in Finland, and they are common wherever there is a plentiful
water supply, as in the marshy districts of Holland and Sweden. In Iceland
alone they seem absent. When examined alive they give off an irritating
vapour which seriously affects some observers, causing catarrhal
symptoms, which in Bastian's case lasted six weeks. The usual number
found in one host is small, one to six or eight, but cases are on record where
many hundreds occurred in one person.
The details of the life-history of this form are not yet completely worked
out. The eggs leave the body of the host with the excreta, and formerly it
was thought they re-entered the alimentary canal in drinking-water, etc., and
there developed into the adult without change of host. This view has been
Page 152
combated by Leuckart, who failed to rear the Nematodes by direct feeding,
and it has been noticed that the youngest parasites found in the intestine are
already 2 to 3 mm. long. Von Linstow has recently suggested that the larval
stages may be hatched out in the body of the millipede Julus guttulatus,
whose habits might easily lead it to eat the eggs of the parasite in manured
gardens, etc., and which is itself sometimes unconsciously eaten when
hidden in fruit or vegetables. This would account for the frequent presence
of the parasite in pigs, and also for the fact that in man it is commonest in
children who are apt to eat windfalls, and in maniacs and people with
perverted tastes.
A. megalocephala, which is found in the horse, ass, zebra, ox, etc., attains
even greater dimensions than the foregoing. The male rarely exceeds 7
inches in length, but the female sometimes reaches 17 inches. They are
found in the small intestine of their hosts. Cobbold[178] succeeded in rearing
larvae which attained a high degree of organisation when the eggs were
placed amongst moist horse-dung, and it seems probable that the larvae
pass into the body of their hosts in drinking water; at any rate no
intermediate host has yet been found, and Davaine, who fed cows, and
Leuckart, who fed horses with the unhatched eggs, both failed to infect the
animals they experimented on. A. mystax, which lives in cats, dogs, and
other Carnivora, has also been found in man. It is provided with fin-like
extensions on the side of its head (cf. Fig. 62), and varies much in size in
different hosts. When first found in man it received the name of A. alata. It
becomes sexually mature in about three weeks.
One of the most remarkable cycles of development amongst the many
curious life-histories met with amongst Nematodes, is that presented by
Rhabdonema (Ascaris) nigrovenosum. The free form of this, formerly
known as a distinct species, Rhabditis nigrovenosa, lives in the excrement
of frogs, and attains sexual maturity in a very short time. The sexes pair,
and the fertilised ova give rise to embryos which hatch out within the body
of the mother, and then begin to devour her internal organs. After the
destruction of the mother, the embryos escape and live in water or slime,
and sometimes burrow into water snails, but they undergo no change until
swallowed by a frog. Then they make their way into its lungs and grow
enormously, attaining a length of almost an inch. This form, parasitic in the
and it has been noticed that the youngest parasites found in the intestine are
already 2 to 3 mm. long. Von Linstow has recently suggested that the larval
stages may be hatched out in the body of the millipede Julus guttulatus,
whose habits might easily lead it to eat the eggs of the parasite in manured
gardens, etc., and which is itself sometimes unconsciously eaten when
hidden in fruit or vegetables. This would account for the frequent presence
of the parasite in pigs, and also for the fact that in man it is commonest in
children who are apt to eat windfalls, and in maniacs and people with
perverted tastes.
A. megalocephala, which is found in the horse, ass, zebra, ox, etc., attains
even greater dimensions than the foregoing. The male rarely exceeds 7
inches in length, but the female sometimes reaches 17 inches. They are
found in the small intestine of their hosts. Cobbold[178] succeeded in rearing
larvae which attained a high degree of organisation when the eggs were
placed amongst moist horse-dung, and it seems probable that the larvae
pass into the body of their hosts in drinking water; at any rate no
intermediate host has yet been found, and Davaine, who fed cows, and
Leuckart, who fed horses with the unhatched eggs, both failed to infect the
animals they experimented on. A. mystax, which lives in cats, dogs, and
other Carnivora, has also been found in man. It is provided with fin-like
extensions on the side of its head (cf. Fig. 62), and varies much in size in
different hosts. When first found in man it received the name of A. alata. It
becomes sexually mature in about three weeks.
One of the most remarkable cycles of development amongst the many
curious life-histories met with amongst Nematodes, is that presented by
Rhabdonema (Ascaris) nigrovenosum. The free form of this, formerly
known as a distinct species, Rhabditis nigrovenosa, lives in the excrement
of frogs, and attains sexual maturity in a very short time. The sexes pair,
and the fertilised ova give rise to embryos which hatch out within the body
of the mother, and then begin to devour her internal organs. After the
destruction of the mother, the embryos escape and live in water or slime,
and sometimes burrow into water snails, but they undergo no change until
swallowed by a frog. Then they make their way into its lungs and grow
enormously, attaining a length of almost an inch. This form, parasitic in the
Page 153
frog, is a protandrous hermaphrodite, which first produces spermatozoa and
afterwards ova; the latter are fertilised by the spermatozoa, and give rise to
rhabditiform embryos, which escape by the alimentary canal and form the
free-living sexual stage mentioned above. Thus in the life-history of this
form we find an alternation of generation, a sexual free-living form
alternating with a hermaphrodite parasitic form.
Of the enormous number of other species of the genus, only a very few can
be mentioned. A. transfuga Rud. inhabits bears; A. leptoptera Rud., lions;
A. ferox H. and Ehrbg., Hyracoidea; A. depressa Rud., vultures; A.
rubicunda Schn., pythons; A. sulcata Rud., turtles; A. mucronata Schn., the
cod and pike; A. incurva Rud., the sword-fish.
Fig. 69.—A male and female Oxyuris diesingi Ham. in copula, × 60. a, Anus; b,
oesophagus; c, bulb; d, testis; e, intestine; f, ovary. (From Galeb.[179])
Oxyuris is Meromyarian (see p. 137), and is characterised by the long
capillary tail of the female. It includes another human parasite, O.
vermicularis, and it is one which it is difficult to get rid of. The female has
the characteristic tail and is about 10 mm. long. The male is smaller. They
are found in the caecum and rectum of man, and cause great irritation and
sometimes serious functional disturbance. The eggs are laid in immense
numbers but perish in water. If whilst still in the egg-shell the larvae are
afterwards ova; the latter are fertilised by the spermatozoa, and give rise to
rhabditiform embryos, which escape by the alimentary canal and form the
free-living sexual stage mentioned above. Thus in the life-history of this
form we find an alternation of generation, a sexual free-living form
alternating with a hermaphrodite parasitic form.
Of the enormous number of other species of the genus, only a very few can
be mentioned. A. transfuga Rud. inhabits bears; A. leptoptera Rud., lions;
A. ferox H. and Ehrbg., Hyracoidea; A. depressa Rud., vultures; A.
rubicunda Schn., pythons; A. sulcata Rud., turtles; A. mucronata Schn., the
cod and pike; A. incurva Rud., the sword-fish.
Fig. 69.—A male and female Oxyuris diesingi Ham. in copula, × 60. a, Anus; b,
oesophagus; c, bulb; d, testis; e, intestine; f, ovary. (From Galeb.[179])
Oxyuris is Meromyarian (see p. 137), and is characterised by the long
capillary tail of the female. It includes another human parasite, O.
vermicularis, and it is one which it is difficult to get rid of. The female has
the characteristic tail and is about 10 mm. long. The male is smaller. They
are found in the caecum and rectum of man, and cause great irritation and
sometimes serious functional disturbance. The eggs are laid in immense
numbers but perish in water. If whilst still in the egg-shell the larvae are
Page 154
swallowed on fruit or raw vegetables, etc., they are set free in the stomach
and small intestine by the action of the digestive secretions. The distribution
of this parasite is universal. Besides numerous species that inhabit the
alimentary canal of Vertebrates, such as O. ambigua Rud., found in hares
and rabbits; O. curvula Rud., in the caecum of horses; O. megatyphlon
Rud., in iguanas; several species inhabit the rectum of insects, such as O.
blattae, O. diesingi, O. blatticola, found in the cockroach; O. spirotheca,
and O. hydrophili in the water beetle Hydrophilus.[180]
The genus Nematoxys has the most complex arrangement of muscles of any
Meromyarian, and forms a transition to the Polymyarian type. The whole
body of both sexes is covered with numerous irregularly scattered papillae.
The members of this genus have hitherto been found in snakes, Amphibia,
and eels; there are but few species.
Oxysoma is another small genus with but three species, found in the
intestines of opossums, frogs, and turtles respectively.
II. Family Strongylidae.
Mouth surrounded by papillae; an armature of teeth or spines often present.
The chitinous lining of the intestine projects into the interior as ridges. No
oesophageal bulb. The male orifice at the posterior end of the body is
surrounded by a bell-shaped bursa.
Genera: Eustrongylus, Strongylus, Dochmius, Sclerostomum, Cucullanus,
Syngamus, Pseudalius, Ollulanus, and others.
The genus Eustrongylus includes two species, E. gigas Rud. and E. tubifex
Nitsch. The former attains in the female the gigantic length of 860 mm.,
with a breadth of 7 mm. and a weight of over 40 grs.[181] The male is a
quarter to a third as long as the female. This parasite inhabits the kidney
capsules of carnivorous animals, especially of those that eat fish, such as
dogs, seals, etc., and has occasionally been found in man, the horse, and the
deer. It frequently destroys the substance of the kidney. The worms are red
and small intestine by the action of the digestive secretions. The distribution
of this parasite is universal. Besides numerous species that inhabit the
alimentary canal of Vertebrates, such as O. ambigua Rud., found in hares
and rabbits; O. curvula Rud., in the caecum of horses; O. megatyphlon
Rud., in iguanas; several species inhabit the rectum of insects, such as O.
blattae, O. diesingi, O. blatticola, found in the cockroach; O. spirotheca,
and O. hydrophili in the water beetle Hydrophilus.[180]
The genus Nematoxys has the most complex arrangement of muscles of any
Meromyarian, and forms a transition to the Polymyarian type. The whole
body of both sexes is covered with numerous irregularly scattered papillae.
The members of this genus have hitherto been found in snakes, Amphibia,
and eels; there are but few species.
Oxysoma is another small genus with but three species, found in the
intestines of opossums, frogs, and turtles respectively.
II. Family Strongylidae.
Mouth surrounded by papillae; an armature of teeth or spines often present.
The chitinous lining of the intestine projects into the interior as ridges. No
oesophageal bulb. The male orifice at the posterior end of the body is
surrounded by a bell-shaped bursa.
Genera: Eustrongylus, Strongylus, Dochmius, Sclerostomum, Cucullanus,
Syngamus, Pseudalius, Ollulanus, and others.
The genus Eustrongylus includes two species, E. gigas Rud. and E. tubifex
Nitsch. The former attains in the female the gigantic length of 860 mm.,
with a breadth of 7 mm. and a weight of over 40 grs.[181] The male is a
quarter to a third as long as the female. This parasite inhabits the kidney
capsules of carnivorous animals, especially of those that eat fish, such as
dogs, seals, etc., and has occasionally been found in man, the horse, and the
deer. It frequently destroys the substance of the kidney. The worms are red
Page 155
in colour. The eggs die when exposed to desiccation for a few days, but
have been kept alive for fifteen months in water; it is believed by Schneider
and Leuckart that they are eaten by fish, and that the larvae form the Filaria
cystica found in the peritoneal membrane of the fishes Galaxias scriba and
Symbranchus laticaudatus, and that they pass into their final host, where
they become sexually mature, by the latter eating raw fish. E. tubifex is
found in aquatic birds, e.g. ducks, grebes, and divers, etc.
The genus Strongylus is easily recognised by its conspicuous genital bursa,
strengthened by variously arranged ridges which are of specific value.
There are numerous species, found in man and many other mammals, and
also in birds and reptiles. Some species inhabit the intestine, others form
aneurisms in the large blood-vessels, and cause considerable mortality
amongst horses; others live in the tracheae and lungs of cattle and sheep,
their presence often causing great loss to the farmer. No intermediate host
has been satisfactorily demonstrated; the larvae live in damp earth, and it
seems almost certain that they pass directly into their host with its food.
Dochmius (Ancylostomum) duodenalis, called by Neumann[182] Uncinaria
duodenalis, is one of the most dangerous parasites that attack man. It lives
in the duodenum and jejunum, and the fertilised eggs leave the body of its
host with the excreta, and in damp earth develop into larvae in the course of
a few days. These at first eat voraciously, but after undergoing several
moults they cease to take food and pass into the resting stage. If now they
are swallowed with drinking water, they come to rest in the small intestine
of their host, and in a few weeks become sexually mature. They cause great
harm by burrowing in the intestinal walls and destroying the capillaries.
They are found by hundreds, and even thousands, in the same host, and
produce profound anaemia, which is frequently fatal to miners, and was the
cause of a great mortality amongst the workers in the St. Gothard Tunnel
some fifteen years ago. This species is very widely spread over the face of
the globe. Dochmius trigonocephala Rud. and D. stenocephala produce
similar diseases in dogs and cats, and D. cernua Crep. is found in sheep and
goats.
have been kept alive for fifteen months in water; it is believed by Schneider
and Leuckart that they are eaten by fish, and that the larvae form the Filaria
cystica found in the peritoneal membrane of the fishes Galaxias scriba and
Symbranchus laticaudatus, and that they pass into their final host, where
they become sexually mature, by the latter eating raw fish. E. tubifex is
found in aquatic birds, e.g. ducks, grebes, and divers, etc.
The genus Strongylus is easily recognised by its conspicuous genital bursa,
strengthened by variously arranged ridges which are of specific value.
There are numerous species, found in man and many other mammals, and
also in birds and reptiles. Some species inhabit the intestine, others form
aneurisms in the large blood-vessels, and cause considerable mortality
amongst horses; others live in the tracheae and lungs of cattle and sheep,
their presence often causing great loss to the farmer. No intermediate host
has been satisfactorily demonstrated; the larvae live in damp earth, and it
seems almost certain that they pass directly into their host with its food.
Dochmius (Ancylostomum) duodenalis, called by Neumann[182] Uncinaria
duodenalis, is one of the most dangerous parasites that attack man. It lives
in the duodenum and jejunum, and the fertilised eggs leave the body of its
host with the excreta, and in damp earth develop into larvae in the course of
a few days. These at first eat voraciously, but after undergoing several
moults they cease to take food and pass into the resting stage. If now they
are swallowed with drinking water, they come to rest in the small intestine
of their host, and in a few weeks become sexually mature. They cause great
harm by burrowing in the intestinal walls and destroying the capillaries.
They are found by hundreds, and even thousands, in the same host, and
produce profound anaemia, which is frequently fatal to miners, and was the
cause of a great mortality amongst the workers in the St. Gothard Tunnel
some fifteen years ago. This species is very widely spread over the face of
the globe. Dochmius trigonocephala Rud. and D. stenocephala produce
similar diseases in dogs and cats, and D. cernua Crep. is found in sheep and
goats.
Page 156
The genus Cucullanus exists in the adult form in the intestines of fishes,
and more rarely of reptiles. C. elegans Zed., which live in fresh-water fish,
e.g. the perch, is viviparous; after birth the young pass into the water and
make their way into the alimentary canal of the small crustacean Cyclops,
and thence into its body-cavity. Here they undergo two moults,
accompanied by certain changes in structure. If this second host be
swallowed by a fish the parasites are set free, and develop generative
organs. Ollulanus tricuspis Leuck., which in the adult state is found in the
cat, chiefly in the intestine but also in the bronchi and other parts, gives rise
to larvae which are of enormous size compared with the parent; these leave
the body, and if eaten by a mouse encyst in its muscles, and if the mouse be
devoured by a cat, they complete their life-cycle by becoming sexually
mature.
The genus Syngamus infests the trachea and bronchi of birds, more rarely of
mammals. The red- or forked-worm, Syngamus trachealis Sieb., is common
in poultry and game birds, and causes the disease known as gapes, which is
especially common in young birds, and often gives rise to extensive loss.
The peculiarity of this genus is that the male is permanently attached to the
female, its genital bursa being so closely adherent to the opening of the
oviduct that two specimens cannot be separated without tearing the tissues.
The ova are not laid, but escape from the body with fully-formed embryos
in them, by the decay or rupture of their parent's body. They hatch in damp
earth or water in from one to six weeks according to the temperature. When
swallowed by a fowl they develop into adults, which reproduce eggs in less
than three weeks. No second host is needed, but the embryos remain alive
in the alimentary canal of earthworms, and these doubtless to some extent
serve to spread the disease.
and more rarely of reptiles. C. elegans Zed., which live in fresh-water fish,
e.g. the perch, is viviparous; after birth the young pass into the water and
make their way into the alimentary canal of the small crustacean Cyclops,
and thence into its body-cavity. Here they undergo two moults,
accompanied by certain changes in structure. If this second host be
swallowed by a fish the parasites are set free, and develop generative
organs. Ollulanus tricuspis Leuck., which in the adult state is found in the
cat, chiefly in the intestine but also in the bronchi and other parts, gives rise
to larvae which are of enormous size compared with the parent; these leave
the body, and if eaten by a mouse encyst in its muscles, and if the mouse be
devoured by a cat, they complete their life-cycle by becoming sexually
mature.
The genus Syngamus infests the trachea and bronchi of birds, more rarely of
mammals. The red- or forked-worm, Syngamus trachealis Sieb., is common
in poultry and game birds, and causes the disease known as gapes, which is
especially common in young birds, and often gives rise to extensive loss.
The peculiarity of this genus is that the male is permanently attached to the
female, its genital bursa being so closely adherent to the opening of the
oviduct that two specimens cannot be separated without tearing the tissues.
The ova are not laid, but escape from the body with fully-formed embryos
in them, by the decay or rupture of their parent's body. They hatch in damp
earth or water in from one to six weeks according to the temperature. When
swallowed by a fowl they develop into adults, which reproduce eggs in less
than three weeks. No second host is needed, but the embryos remain alive
in the alimentary canal of earthworms, and these doubtless to some extent
serve to spread the disease.
Page 157
Fig. 70.—Syngamus trachealis Sieb., natural size and magnified four diameters. The
small ♂ is permanently attached to the female. (From Warburton.[183])
III. Family Trichotrachelidae.
This family is characterised by the anterior end of the body being produced
into a long whip-like neck. The mouth is small and devoid of papillae. The
oesophagus is very long, and it traverses a peculiar strand of cells.
Genera: Trichocephalus, Trichina, Trichosoma, and others.
Trichocephalus dispar Rud. (hominis Gmel.) is common in man, and also
occurs in some species of monkey. It does not live freely within the
intestine, but buries its long whip-like anterior end in the mucous lining of
the caecum or colon. The eggs pass out of the body of the host. The
development of the embryo is slow, lasting many months; whilst still in the
egg-shell the embryos are swallowed, and give rise to the sexually-mature
parasite without the intervention of an intermediate host. They are by no
means uncommon. Davaine calculated that about 50 per cent of the
inhabitants of Paris were infested with them, but they give rise to little
disturbance, and only very occasionally cause serious harm. T. affinis Rud.
infests sheep; T. crenatus Rud. the pig; T. depressiusculus Rud. the dog; and
T. unguiculatus Rud. the hare and rabbit.
small ♂ is permanently attached to the female. (From Warburton.[183])
III. Family Trichotrachelidae.
This family is characterised by the anterior end of the body being produced
into a long whip-like neck. The mouth is small and devoid of papillae. The
oesophagus is very long, and it traverses a peculiar strand of cells.
Genera: Trichocephalus, Trichina, Trichosoma, and others.
Trichocephalus dispar Rud. (hominis Gmel.) is common in man, and also
occurs in some species of monkey. It does not live freely within the
intestine, but buries its long whip-like anterior end in the mucous lining of
the caecum or colon. The eggs pass out of the body of the host. The
development of the embryo is slow, lasting many months; whilst still in the
egg-shell the embryos are swallowed, and give rise to the sexually-mature
parasite without the intervention of an intermediate host. They are by no
means uncommon. Davaine calculated that about 50 per cent of the
inhabitants of Paris were infested with them, but they give rise to little
disturbance, and only very occasionally cause serious harm. T. affinis Rud.
infests sheep; T. crenatus Rud. the pig; T. depressiusculus Rud. the dog; and
T. unguiculatus Rud. the hare and rabbit.
Page 158
Fig. 71.—Trichocephalus dispar Rud., attached to part of the human colon. × 2.
The genus Trichosoma, with many species, is as a rule found in birds, but it
occurs also in mammals, as T. plica Rud. in the bladder of the fox and wolf,
T. felis cati in the bladder of the cat, T. aerophilum Duj. in the trachea of the
fox and marten. The chief interest of this genus is that, at any rate in T.
crassicauda Bel., which infests the rat, the dwarf males live two, three, or
four at a time within the uterus of the female, a condition of things which
recalls the similar arrangement found in the Gephyrean Bonellia.
Trichina spiralis is the cause of the well-known disease trichinosis, which
appears in two forms, intestinal and muscular, according to the habitat of
the parasite. The mature forms of both sexes are found in the intestine of
man and many other mammals. They have been experimentally developed
in birds, though in the latter the larval forms have never been observed. By
keeping such cold-blooded animals as the salamander at a constant
temperature, Goujon and Legros succeeded in infecting them, but the larvae
perished as soon as the artificial heat was withdrawn. Muscular trichinosis
is unknown in fishes, but the sexual form develops in their intestine.
The adult parasites of the intestine are scarcely visible to the naked eye; the
females are 3 to 4 mm. long and more numerous than the males, which
measure 1.4 to 1.6 mm. The eggs are very numerous, a single female
containing at one time 1200, and probably producing ten times as many
during her life. The embryos are hatched out within the uterus, and the
larvae leave the body of the mother through the generative pore. The minute
larvae bore through the intestinal walls of their host, and then, either
The genus Trichosoma, with many species, is as a rule found in birds, but it
occurs also in mammals, as T. plica Rud. in the bladder of the fox and wolf,
T. felis cati in the bladder of the cat, T. aerophilum Duj. in the trachea of the
fox and marten. The chief interest of this genus is that, at any rate in T.
crassicauda Bel., which infests the rat, the dwarf males live two, three, or
four at a time within the uterus of the female, a condition of things which
recalls the similar arrangement found in the Gephyrean Bonellia.
Trichina spiralis is the cause of the well-known disease trichinosis, which
appears in two forms, intestinal and muscular, according to the habitat of
the parasite. The mature forms of both sexes are found in the intestine of
man and many other mammals. They have been experimentally developed
in birds, though in the latter the larval forms have never been observed. By
keeping such cold-blooded animals as the salamander at a constant
temperature, Goujon and Legros succeeded in infecting them, but the larvae
perished as soon as the artificial heat was withdrawn. Muscular trichinosis
is unknown in fishes, but the sexual form develops in their intestine.
The adult parasites of the intestine are scarcely visible to the naked eye; the
females are 3 to 4 mm. long and more numerous than the males, which
measure 1.4 to 1.6 mm. The eggs are very numerous, a single female
containing at one time 1200, and probably producing ten times as many
during her life. The embryos are hatched out within the uterus, and the
larvae leave the body of the mother through the generative pore. The minute
larvae bore through the intestinal walls of their host, and then, either
Page 159
burrowing in the tissues or swept along in the stream of blood or lymph,
make their way all over the body, and come to rest most usually in the
muscles, but occasionally in other parts. When the larva reaches its resting-
place, it either pierces the sarcolemma and establishes itself within the
substance of the muscle-fibre, or it comes to rest between and not in the
fibres. Here its presence sets up the formation of a spindle-shaped cyst
which usually contains but one larva, though any number up to seven have
been found in one cyst. Within this the larva may remain dormant for years,
the walls of the cyst gradually undergoing a fatty or calcareous
degeneration. Almost any muscle may be affected; those most usually
infested being the muscles of the diaphragm, of the shoulder-blade, and of
the lumbar region; the larvae have also been found in the heart. The ends of
the muscles near their points of attachment are always the most thoroughly
infested.
Fig. 72.—Trichina spiralis Owen, encysted in muscle. a, Calcareous deposit. Highly
magnified. (From Leuckart.)
The number of the encapsuled larvae in one host is enormous. Leuckart
counted between 12,000 and 15,000 in a gramme of muscle, which would
give a total of thirty to forty million parasites in one host; other estimates
place the total even higher.
When trichinised meat is eaten, unless it has been thoroughly cooked, the
cysts are dissolved and the larvae are set free. Within three or four days they
become sexually mature and their ova begin to segment. The males after a
time leave the body with the excreta and perish, whilst the larvae of the new
brood make their way into the tissues of the host.
Man usually acquires trichinosis by eating uncooked or improperly-cooked
pork, and the disease is so widely spread and of such a serious nature that
most civilised countries have adopted rigorous methods for the detection of
trichinised meat. The pigs either acquire the disease by eating uncooked
make their way all over the body, and come to rest most usually in the
muscles, but occasionally in other parts. When the larva reaches its resting-
place, it either pierces the sarcolemma and establishes itself within the
substance of the muscle-fibre, or it comes to rest between and not in the
fibres. Here its presence sets up the formation of a spindle-shaped cyst
which usually contains but one larva, though any number up to seven have
been found in one cyst. Within this the larva may remain dormant for years,
the walls of the cyst gradually undergoing a fatty or calcareous
degeneration. Almost any muscle may be affected; those most usually
infested being the muscles of the diaphragm, of the shoulder-blade, and of
the lumbar region; the larvae have also been found in the heart. The ends of
the muscles near their points of attachment are always the most thoroughly
infested.
Fig. 72.—Trichina spiralis Owen, encysted in muscle. a, Calcareous deposit. Highly
magnified. (From Leuckart.)
The number of the encapsuled larvae in one host is enormous. Leuckart
counted between 12,000 and 15,000 in a gramme of muscle, which would
give a total of thirty to forty million parasites in one host; other estimates
place the total even higher.
When trichinised meat is eaten, unless it has been thoroughly cooked, the
cysts are dissolved and the larvae are set free. Within three or four days they
become sexually mature and their ova begin to segment. The males after a
time leave the body with the excreta and perish, whilst the larvae of the new
brood make their way into the tissues of the host.
Man usually acquires trichinosis by eating uncooked or improperly-cooked
pork, and the disease is so widely spread and of such a serious nature that
most civilised countries have adopted rigorous methods for the detection of
trichinised meat. The pigs either acquire the disease by eating uncooked
Page 160
swine's flesh, which is frequently given them in the form of offal, or by
devouring rats, which are very susceptible to the disease.
IV. Family Filariidae.
Mouth with two lips, or without lips. Six oral papillae often present, and
sometimes a horny oral capsule. Four pre-anal pairs of papillae, and
sometimes an unpaired one as well. Two unequal spicula or a single one.
Genera: Filaria, Ichthyonema, Hystrichis, Spiroptera, Dispharagus, and
others.
The genus Filaria is a very large one. Like Ascaris, it is confined to
Vertebrates, but usually lives in the tissues of the body and not in the
intestines. F. (Dracunculus) medinensis Gmel., the guinea-worm, is well
known as a human parasite in hot countries; it also occurs in the horse and
dog. The female has an average length of 50 to 80 cm., but gigantic forms
with a length of 4 metres have been described. The alimentary canal is
degenerate. In adult females the body is completely occupied by a uterus
crowded with eggs and embryos, which can only escape by the rupture of
the mother's body, as the genital ducts have disappeared. Its original home
is tropical Asia and Africa, but it has been introduced into South America
with the negroes.
The female lives coiled up in the subcutaneous tissues, usually in those of
the legs. Its presence gives rise to painful tumours. When these break the
female protrudes, and may be withdrawn from the body by very carefully
rolling it round a stick or pencil. This must be done very slowly, a few
inches a day, as the rupture of the body sets free the contained embryos, and
may result in the death of the host. The embryos normally bore their way
into the body of the fresh-water Cyclops, and are re-introduced into their
Vertebrate hosts with the drinking-water. It is usually stated that the female
alone is known, and that it is uncertain whether it is hermaphrodite or
whether both sexes are present in the Cyclops. Recently Dr. Charles[184] has
described a specimen found in the mesentery of a human subject, from an
devouring rats, which are very susceptible to the disease.
IV. Family Filariidae.
Mouth with two lips, or without lips. Six oral papillae often present, and
sometimes a horny oral capsule. Four pre-anal pairs of papillae, and
sometimes an unpaired one as well. Two unequal spicula or a single one.
Genera: Filaria, Ichthyonema, Hystrichis, Spiroptera, Dispharagus, and
others.
The genus Filaria is a very large one. Like Ascaris, it is confined to
Vertebrates, but usually lives in the tissues of the body and not in the
intestines. F. (Dracunculus) medinensis Gmel., the guinea-worm, is well
known as a human parasite in hot countries; it also occurs in the horse and
dog. The female has an average length of 50 to 80 cm., but gigantic forms
with a length of 4 metres have been described. The alimentary canal is
degenerate. In adult females the body is completely occupied by a uterus
crowded with eggs and embryos, which can only escape by the rupture of
the mother's body, as the genital ducts have disappeared. Its original home
is tropical Asia and Africa, but it has been introduced into South America
with the negroes.
The female lives coiled up in the subcutaneous tissues, usually in those of
the legs. Its presence gives rise to painful tumours. When these break the
female protrudes, and may be withdrawn from the body by very carefully
rolling it round a stick or pencil. This must be done very slowly, a few
inches a day, as the rupture of the body sets free the contained embryos, and
may result in the death of the host. The embryos normally bore their way
into the body of the fresh-water Cyclops, and are re-introduced into their
Vertebrate hosts with the drinking-water. It is usually stated that the female
alone is known, and that it is uncertain whether it is hermaphrodite or
whether both sexes are present in the Cyclops. Recently Dr. Charles[184] has
described a specimen found in the mesentery of a human subject, from an
Page 161
orifice in the middle of whose body he was able to draw a much smaller
specimen, and he thinks this may be the long-sought-for male.
Fig. 73.—A, View of the heart of a dog infested with Filaria immitis[185] Leidy; the
right ventricle and base of the pulmonary artery have been opened. a, Aorta; b,
pulmonary artery; c, vena cava; d, right ventricle; e, appendix of left auricle; f,
appendix of right auricle. B, A female F. immitis removed from the heart to show
its length. Natural size.
Filaria immitis Leidy, the cruel worm, is common in dogs in China and the
East generally. It is not unknown in America and Europe. It occurs in such
large clusters in the right ventricle that it is difficult to see how the
circulation can proceed. The intermediate host is unknown, but from the
prevalence of the disease in marshy country it is probably some aquatic
animal. The larvae are said by Manson to disappear from the peripheral
circulation of the dog during the day, but not to such a marked extent as do
the F. sanguinis hominis Lew., var. nocturna Man. They were found by
Galeb and Pourquier in the foetus of an infested bitch, a fact which
establishes the transmission of such parasites through the placenta.
Filaria sanguinis hominis nocturna.—The female of this parasite has been
described as living in the lymphatic glands of man. The embryos escape
from it into the lymph, and thus reach the blood. According to Manson the
intermediate host is the mosquito, in whose stomach the embryos undergo
their larval changes. When the mosquito dies the larvae escape into the
water, and then make their way into the alimentary canal of man, where
they are believed to pair, and whence the female makes its way to the
lymphatics. The presence of this Filaria causes great functional
disturbance. One of the most remarkable features of it is that the larvae,
which are very numerous in the blood during the night, disappear during the
specimen, and he thinks this may be the long-sought-for male.
Fig. 73.—A, View of the heart of a dog infested with Filaria immitis[185] Leidy; the
right ventricle and base of the pulmonary artery have been opened. a, Aorta; b,
pulmonary artery; c, vena cava; d, right ventricle; e, appendix of left auricle; f,
appendix of right auricle. B, A female F. immitis removed from the heart to show
its length. Natural size.
Filaria immitis Leidy, the cruel worm, is common in dogs in China and the
East generally. It is not unknown in America and Europe. It occurs in such
large clusters in the right ventricle that it is difficult to see how the
circulation can proceed. The intermediate host is unknown, but from the
prevalence of the disease in marshy country it is probably some aquatic
animal. The larvae are said by Manson to disappear from the peripheral
circulation of the dog during the day, but not to such a marked extent as do
the F. sanguinis hominis Lew., var. nocturna Man. They were found by
Galeb and Pourquier in the foetus of an infested bitch, a fact which
establishes the transmission of such parasites through the placenta.
Filaria sanguinis hominis nocturna.—The female of this parasite has been
described as living in the lymphatic glands of man. The embryos escape
from it into the lymph, and thus reach the blood. According to Manson the
intermediate host is the mosquito, in whose stomach the embryos undergo
their larval changes. When the mosquito dies the larvae escape into the
water, and then make their way into the alimentary canal of man, where
they are believed to pair, and whence the female makes its way to the
lymphatics. The presence of this Filaria causes great functional
disturbance. One of the most remarkable features of it is that the larvae,
which are very numerous in the blood during the night, disappear during the
Page 162
day, and are not to be found. Recently Manson[186] has described two new
varieties: F. san. hom. diurna, in which the conditions of things are
reversed, the larvae being found by day and not by night; and F. san. hom.
perstans, in which the larvae occur both by day and by night. The larvae are
long-lived, and were found by Manson in the blood of a negro who had not
been in Africa, where it is endemic, for six years. The same observer is
inclined to associate the presence of F. san. hom. perstans with the fatal
disease known as "sleeping sickness." He also suggests that the mature form
of the variety diurna is the F. loa, which is not uncommon in the eyes of
negroes, and that its intermediate host may be one of the blood-sucking flies
so common on the west coast of Africa.
The genus Ichthyonema is confined to fishes. The male is very minute and
the female partly degenerate. It has no anus and no external opening to its
generative organs. The uterus fills up almost the whole of the body-cavity. I.
sanguineum Rud. is found encapsuled in the peritoneum of many fish.
Hystrichis and Dispharagus are confined to birds, where they occur in the
oesophagus and stomach. Spiroptera reticulata Crep. occurs in horses,
twisted in a spiral round tendons and muscles, forming tumours which
require to be opened.
V. Family Mermithidae.
Nematodes without anus and with six mouth papillae. Two spicules in the
males and three rows of numerous papillae.
Genera: Mermis, Bradynema, Atractonema, Allantonema, Sphaerularia,
and others.
As a rule the Nematoda show but little trace of their parasitic mode of life,
but in this family there is considerable degeneration, and in extreme cases
the body of the female is reduced to a simple sac crowded with eggs. They
are exclusively parasitic in insects. In some respects their structure shows a
varieties: F. san. hom. diurna, in which the conditions of things are
reversed, the larvae being found by day and not by night; and F. san. hom.
perstans, in which the larvae occur both by day and by night. The larvae are
long-lived, and were found by Manson in the blood of a negro who had not
been in Africa, where it is endemic, for six years. The same observer is
inclined to associate the presence of F. san. hom. perstans with the fatal
disease known as "sleeping sickness." He also suggests that the mature form
of the variety diurna is the F. loa, which is not uncommon in the eyes of
negroes, and that its intermediate host may be one of the blood-sucking flies
so common on the west coast of Africa.
The genus Ichthyonema is confined to fishes. The male is very minute and
the female partly degenerate. It has no anus and no external opening to its
generative organs. The uterus fills up almost the whole of the body-cavity. I.
sanguineum Rud. is found encapsuled in the peritoneum of many fish.
Hystrichis and Dispharagus are confined to birds, where they occur in the
oesophagus and stomach. Spiroptera reticulata Crep. occurs in horses,
twisted in a spiral round tendons and muscles, forming tumours which
require to be opened.
V. Family Mermithidae.
Nematodes without anus and with six mouth papillae. Two spicules in the
males and three rows of numerous papillae.
Genera: Mermis, Bradynema, Atractonema, Allantonema, Sphaerularia,
and others.
As a rule the Nematoda show but little trace of their parasitic mode of life,
but in this family there is considerable degeneration, and in extreme cases
the body of the female is reduced to a simple sac crowded with eggs. They
are exclusively parasitic in insects. In some respects their structure shows a
Page 163
transition towards Nectonema and the Gordiidae; especially is this the case
in the structure of their ventral nerve-cord.
The sexual form of Mermis nigrescens Duj.[187] lives in damp earth, and
after storms and in the early morning is sometimes found in such numbers
crawling up the stalks of plants, as to give rise to the popular idea that there
has been a shower of worms. The male is unknown; the female lays her
eggs in the ground, and there they hatch out. It is not known exactly how
the larvae make their way into the grasshoppers in whose body-cavity they
live, but in an allied species, M. albicans v. Sieb., the larvae have been
observed boring their way into small caterpillars through their skin, and it
seems probable that the larvae of M. nigrescens burrow in a similar way
into young Orthoptera.
Bradynema rigidum Leuck.[188] is found in the adult stage living freely in
the body-cavity of a small beetle Aphodius fimetarius, one of the
Scarabeidae, from two to three to as many as thirty being found in one host,
which does not seem much injured by their presence. The parasite is
without mouth, anus, or excretory pore. The eggs hatch out in the uterus of
the mother, and the larvae are male and female; they make their way into
the body-cavity of the host, and here they pass an unusually long time, five
months, soaking in osmotically the nutriment contained in the blood of the
insect. Eventually they burrow through the walls of the intestine, and
leaving the body of their host through the anus, find their way to the earth.
Here, according to zur Strassen, the females die without playing any part in
the perpetuation of the species. The males, on the other hand, having
developed spermatozoa whilst in the larval stage (paedogenesis), afterwards
form ova, and are in fact protandrous hermaphrodites, and become the
mature parasites of the beetle, though how they enter the body of the host is
unknown.
in the structure of their ventral nerve-cord.
The sexual form of Mermis nigrescens Duj.[187] lives in damp earth, and
after storms and in the early morning is sometimes found in such numbers
crawling up the stalks of plants, as to give rise to the popular idea that there
has been a shower of worms. The male is unknown; the female lays her
eggs in the ground, and there they hatch out. It is not known exactly how
the larvae make their way into the grasshoppers in whose body-cavity they
live, but in an allied species, M. albicans v. Sieb., the larvae have been
observed boring their way into small caterpillars through their skin, and it
seems probable that the larvae of M. nigrescens burrow in a similar way
into young Orthoptera.
Bradynema rigidum Leuck.[188] is found in the adult stage living freely in
the body-cavity of a small beetle Aphodius fimetarius, one of the
Scarabeidae, from two to three to as many as thirty being found in one host,
which does not seem much injured by their presence. The parasite is
without mouth, anus, or excretory pore. The eggs hatch out in the uterus of
the mother, and the larvae are male and female; they make their way into
the body-cavity of the host, and here they pass an unusually long time, five
months, soaking in osmotically the nutriment contained in the blood of the
insect. Eventually they burrow through the walls of the intestine, and
leaving the body of their host through the anus, find their way to the earth.
Here, according to zur Strassen, the females die without playing any part in
the perpetuation of the species. The males, on the other hand, having
developed spermatozoa whilst in the larval stage (paedogenesis), afterwards
form ova, and are in fact protandrous hermaphrodites, and become the
mature parasites of the beetle, though how they enter the body of the host is
unknown.
Page 164
Fig. 74.—Allantonema mirabile Leuck. (From Leuckart.) A, Male Rhabditis stage,
sexually mature, × 100; B, the mature female parasitic form, × 17, showing at the
upper end part of the capsule richly supplied with the tracheae of the host, a
beetle; C, female Rhabditis stage, sexually mature, × 100; D, the larva developed
from the Rhabditis form, × 102.
The phenomenon presented by the hermaphroditism of Bradynema is, as far
as we know, at present unique, as, though some other Nematodes are
hermaphrodite, in their case the hermaphrodite form alternates with a
bisexual generation. It is further interesting as showing a means by which
hermaphroditism may arise, by the suppression of the females and the
assumption of their functions by the male. In the case of Rhabdonema
nigrovenosum, no females appear in the alternate generation.
Fig. 75.—Atractonema gibbosum Leuck. (From Leuckart.) 1, Female with commencing
prolapsus of the uterus and neighbouring parts, × 130; 2, a further stage, the
female being now sexually mature, × 15; 3, a still older stage, with commencing
degeneration of the body of the female, × 15.
sexually mature, × 100; B, the mature female parasitic form, × 17, showing at the
upper end part of the capsule richly supplied with the tracheae of the host, a
beetle; C, female Rhabditis stage, sexually mature, × 100; D, the larva developed
from the Rhabditis form, × 102.
The phenomenon presented by the hermaphroditism of Bradynema is, as far
as we know, at present unique, as, though some other Nematodes are
hermaphrodite, in their case the hermaphrodite form alternates with a
bisexual generation. It is further interesting as showing a means by which
hermaphroditism may arise, by the suppression of the females and the
assumption of their functions by the male. In the case of Rhabdonema
nigrovenosum, no females appear in the alternate generation.
Fig. 75.—Atractonema gibbosum Leuck. (From Leuckart.) 1, Female with commencing
prolapsus of the uterus and neighbouring parts, × 130; 2, a further stage, the
female being now sexually mature, × 15; 3, a still older stage, with commencing
degeneration of the body of the female, × 15.
Page 165
A similar protandry exists in the parasitic forms of Allantonema,[189] of
which there are several species—A. mirabile in Hylobius pini, A. sylvaticum
in Geotrupes sylvatica, A. diplogaster in Tomicus typographicus; but in
their case the male and female forms which leave their host pair in the
damp earth and give rise to larvae which make their way into the body of
the beetle-grubs. Here they undergo very extensive retrogressive change.
The body of the female, which becomes the shape of a thick sausage, is
encapsuled and surrounded by a curious hypertrophied network of tracheae
(Fig. 74). As is usually the case with the degenerate parasitic forms, there
are practically no organs but the ovary, and this is embedded in a fatty
parenchyma which fills all the space within the skin.
Fig. 76.—Four stages in the life-history of Sphaerularia bombi Dufour, ♀ . (From
Leuckart.) A, Beginning of the protrusion of the uterus (b), × 66; B, later stage, ×
66; C, later stage, × 12; D, the protrusion is complete, × 6. In each case a
represents the Nematode, and b its protruded uterus.
Atractonema gibbosum, which lives in the body-cavity of the larva of
Cecidomyia pini, has a similar life-history, but the parasitic form has a
structural peculiarity which merits attention (Fig. 75). At the time of sexual
maturity a swelling, which is caused by the prolapsus of the uterus and
vagina, appears at the posterior end of the body; this swelling increases
until it equals the rest of the body of the Nematode in size. Even this is far
surpassed by a similar protuberance in Sphaerularia bombi, where the
evaginated sac grows with such extreme rapidity that in a few weeks its
length increases from .25 mm. to 15 mm. and its volume 60,000-fold, the
increase being due, according to Leuckart, to the increase in size of the
individual cells and not to their multiplication. The Nematode which has
produced this enormous growth gets relatively smaller and smaller, and
which there are several species—A. mirabile in Hylobius pini, A. sylvaticum
in Geotrupes sylvatica, A. diplogaster in Tomicus typographicus; but in
their case the male and female forms which leave their host pair in the
damp earth and give rise to larvae which make their way into the body of
the beetle-grubs. Here they undergo very extensive retrogressive change.
The body of the female, which becomes the shape of a thick sausage, is
encapsuled and surrounded by a curious hypertrophied network of tracheae
(Fig. 74). As is usually the case with the degenerate parasitic forms, there
are practically no organs but the ovary, and this is embedded in a fatty
parenchyma which fills all the space within the skin.
Fig. 76.—Four stages in the life-history of Sphaerularia bombi Dufour, ♀ . (From
Leuckart.) A, Beginning of the protrusion of the uterus (b), × 66; B, later stage, ×
66; C, later stage, × 12; D, the protrusion is complete, × 6. In each case a
represents the Nematode, and b its protruded uterus.
Atractonema gibbosum, which lives in the body-cavity of the larva of
Cecidomyia pini, has a similar life-history, but the parasitic form has a
structural peculiarity which merits attention (Fig. 75). At the time of sexual
maturity a swelling, which is caused by the prolapsus of the uterus and
vagina, appears at the posterior end of the body; this swelling increases
until it equals the rest of the body of the Nematode in size. Even this is far
surpassed by a similar protuberance in Sphaerularia bombi, where the
evaginated sac grows with such extreme rapidity that in a few weeks its
length increases from .25 mm. to 15 mm. and its volume 60,000-fold, the
increase being due, according to Leuckart, to the increase in size of the
individual cells and not to their multiplication. The Nematode which has
produced this enormous growth gets relatively smaller and smaller, and
Page 166
ultimately drops off (Fig. 76). The sexual larvae which arise from the eggs
in this sac leave the body of the bee in which this species is parasitic by the
anus, and may live in damp earth, moss, etc., for months without taking
nourishment, until the autumn, when they become sexually mature and,
according to Leuckart, pair. The fertilised female is believed to bore her
way into the humble-bee whilst the latter is seeking her underground winter
quarters; this accounts for the fact that only queen bees are infected. The
parasite is widely distributed both in Europe and North America; it is found
in many species of Bombus, but most frequently in B. lapidarius and B.
terrestris. The presence of the Sphaerularia affects the reproductive organs
of the host, and reduces their fertility, so that an infected queen bee never
succeeds in forming a colony.
VI. Family Anguillulidae.
For the most part free living and of small size. The oesophagus has usually
a double swelling or two oesophageal bulbs. The male has two equal
spicula.
Genera: Diplogaster, Mononchus, Rhabditis, Tylenchus, Anguillula, and
many others.
Many species of this family live in humus or decaying matter; others live
on, or are parasitic in, plants; some, such as Anguillula aceti, which is found
in vinegar and in paste, live in organic fluids.
The part played by the presence of these Nematodes in the soil is not
thoroughly understood; sometimes they occur in great numbers, and even
when not directly parasitic in plants, probably do them much damage.
Cobb[190] has recently described from Australia and Fiji over eighty species,
one-half of them new, which occur mostly in the earth, and many of them
among plant roots. They frequently crawl up on to plants, especially on to
seedlings. An instance of this is given as follows: "The edible part of three
bunches of nice-looking celery bought of a Chinaman in Sydney was cut off
as far up as it was tender, nearly to the first leaflets. It was washed by hand
in this sac leave the body of the bee in which this species is parasitic by the
anus, and may live in damp earth, moss, etc., for months without taking
nourishment, until the autumn, when they become sexually mature and,
according to Leuckart, pair. The fertilised female is believed to bore her
way into the humble-bee whilst the latter is seeking her underground winter
quarters; this accounts for the fact that only queen bees are infected. The
parasite is widely distributed both in Europe and North America; it is found
in many species of Bombus, but most frequently in B. lapidarius and B.
terrestris. The presence of the Sphaerularia affects the reproductive organs
of the host, and reduces their fertility, so that an infected queen bee never
succeeds in forming a colony.
VI. Family Anguillulidae.
For the most part free living and of small size. The oesophagus has usually
a double swelling or two oesophageal bulbs. The male has two equal
spicula.
Genera: Diplogaster, Mononchus, Rhabditis, Tylenchus, Anguillula, and
many others.
Many species of this family live in humus or decaying matter; others live
on, or are parasitic in, plants; some, such as Anguillula aceti, which is found
in vinegar and in paste, live in organic fluids.
The part played by the presence of these Nematodes in the soil is not
thoroughly understood; sometimes they occur in great numbers, and even
when not directly parasitic in plants, probably do them much damage.
Cobb[190] has recently described from Australia and Fiji over eighty species,
one-half of them new, which occur mostly in the earth, and many of them
among plant roots. They frequently crawl up on to plants, especially on to
seedlings. An instance of this is given as follows: "The edible part of three
bunches of nice-looking celery bought of a Chinaman in Sydney was cut off
as far up as it was tender, nearly to the first leaflets. It was washed by hand
Page 167
in a tin dish in tank water, free from Nematodes. The washings gave about
200 to 300 Nematodes, belonging to five different genera."
It is very probable that many of the free-living forms which have received
distinct specific names may ultimately turn out to be but stages in the life-
history of some of the parasitic species. Von Linstow[191] has pointed out
that the free form of A. diplogaster, if found alone, would be placed in the
genus Diplogaster; similarly the bisexual form of Ascaris nigrovenosa is
known as Rhabditis nigrovenosa.
Those Nematodes which live parasitically in plants, e.g. many of the genera
Tylenchus and Aphelenchus and Heterodera, as well as those which only
pierce the epidermis of the roots (the remaining species of the above-named
genera), are provided with a spine which works to and fro through the
mouth and assists the animal to bore into the tissues of the plant. Tylenchus
devastatrix lives and reproduces in leaves and stems (never in the roots,
except in the case of hops[192]) of many cultivated plants, such as rye, oats,
onions, etc. "Clover sickness" is probably caused by this Nematode. The
plants become infected by the thread-worms in the soil during the spring;
their presence causes swellings and often kills the plant, in which case the
worms return to the soil or remain in the straw.
Tylenchus tritici Need. is the cause of "ear-cockles" in corn. These take the
form of brown or purple galls, which replace the grains of corn, and which
contain hundreds of minute Nematodes. In these galls they are motionless,
and are capable of surviving in dryness for at least twenty years; but when
moistened,—for instance, by the gall falling on damp earth,—they resume
their vitality and make their way to the young wheat plants, and then,
wriggling up the leaves and stems, find their way to the ear. Here they pair,
and producing a gall-like growth in the flower, lay numerous eggs, from
which arise the Nematodes of the ear-cockle.
200 to 300 Nematodes, belonging to five different genera."
It is very probable that many of the free-living forms which have received
distinct specific names may ultimately turn out to be but stages in the life-
history of some of the parasitic species. Von Linstow[191] has pointed out
that the free form of A. diplogaster, if found alone, would be placed in the
genus Diplogaster; similarly the bisexual form of Ascaris nigrovenosa is
known as Rhabditis nigrovenosa.
Those Nematodes which live parasitically in plants, e.g. many of the genera
Tylenchus and Aphelenchus and Heterodera, as well as those which only
pierce the epidermis of the roots (the remaining species of the above-named
genera), are provided with a spine which works to and fro through the
mouth and assists the animal to bore into the tissues of the plant. Tylenchus
devastatrix lives and reproduces in leaves and stems (never in the roots,
except in the case of hops[192]) of many cultivated plants, such as rye, oats,
onions, etc. "Clover sickness" is probably caused by this Nematode. The
plants become infected by the thread-worms in the soil during the spring;
their presence causes swellings and often kills the plant, in which case the
worms return to the soil or remain in the straw.
Tylenchus tritici Need. is the cause of "ear-cockles" in corn. These take the
form of brown or purple galls, which replace the grains of corn, and which
contain hundreds of minute Nematodes. In these galls they are motionless,
and are capable of surviving in dryness for at least twenty years; but when
moistened,—for instance, by the gall falling on damp earth,—they resume
their vitality and make their way to the young wheat plants, and then,
wriggling up the leaves and stems, find their way to the ear. Here they pair,
and producing a gall-like growth in the flower, lay numerous eggs, from
which arise the Nematodes of the ear-cockle.
Page 168
Fig. 77.—A, a, Female Heterodera schachtii Schmidt, breaking through the epidermis
of a root; the head is still embedded in the parenchyma of the root: B, a, larvae
boring their way into a root; b, larva of the immobile kind surrounded by the old
skin, living as an ectoparasite on the outside of the root. (From Strubell.)
Heterodera schachtii[193] Schmidt, is the cause of the "beet sickness," and
forms galls or swellings on the roots of many plants, in England especially
on the roots of tomatoes and cucumbers. The free larvae live in the earth
and make their way into the smaller rootlets; here the female larvae shed
their skin, lose their characteristic Nematode form, and become citron-
shaped (Fig. 78, D). The male larvae undergo a change, and after a period
of rest cast their skin and, leaving the rootlet, seek out the females. The
female does not undergo this second ecdysis, but its generative organs grow
and mature in what is practically a larval stage. The embryos develop
within the body of the mother, and, escaping through the uterus, ultimately
cause her death. They then make their way into the earth. The cycle of the
development takes but four or five weeks, so that, as in the case of
Tylenchus devastatrix, there are several broods in a year; T. tritici, on the
other hand, has but one.
Fig. 78.—A, Male Heterodera schachtii strongly magnified; a, head lappets; b, mouth
cavity; c, spine; d, muscle of spine; e, gland; f, oesophagus; g, bulb; h, nerve-
ring; i, excretory pore; j, intestine; k, testis; l, intestine; m, muscles moving
spicule; n, spicule: B, first motile larva: C, second immovable parasitic larva
casting its skin: D, a female with one half of the body-wall taken away to show
of a root; the head is still embedded in the parenchyma of the root: B, a, larvae
boring their way into a root; b, larva of the immobile kind surrounded by the old
skin, living as an ectoparasite on the outside of the root. (From Strubell.)
Heterodera schachtii[193] Schmidt, is the cause of the "beet sickness," and
forms galls or swellings on the roots of many plants, in England especially
on the roots of tomatoes and cucumbers. The free larvae live in the earth
and make their way into the smaller rootlets; here the female larvae shed
their skin, lose their characteristic Nematode form, and become citron-
shaped (Fig. 78, D). The male larvae undergo a change, and after a period
of rest cast their skin and, leaving the rootlet, seek out the females. The
female does not undergo this second ecdysis, but its generative organs grow
and mature in what is practically a larval stage. The embryos develop
within the body of the mother, and, escaping through the uterus, ultimately
cause her death. They then make their way into the earth. The cycle of the
development takes but four or five weeks, so that, as in the case of
Tylenchus devastatrix, there are several broods in a year; T. tritici, on the
other hand, has but one.
Fig. 78.—A, Male Heterodera schachtii strongly magnified; a, head lappets; b, mouth
cavity; c, spine; d, muscle of spine; e, gland; f, oesophagus; g, bulb; h, nerve-
ring; i, excretory pore; j, intestine; k, testis; l, intestine; m, muscles moving
spicule; n, spicule: B, first motile larva: C, second immovable parasitic larva
casting its skin: D, a female with one half of the body-wall taken away to show
Page 169
the coiling generative organs; a, boring apparatus; b, oesophageal bulb; c,
excretory pore; d, alimentary canal; e, anus; f, ovary: E, a male shortly before
casting its larval skin.
Vuillemin and Legrain[194] point out that while Heterodera is injurious to
cultivated plants growing in damp soil, its presence is advantageous to
those that grow in deserts. It is very common in the Sahara, and attacks
many plants which are immune from it elsewhere. It causes the rootlets to
swell out, and the bladder-like extensions thus formed act as reservoirs for
water.
Many other species attack plants; Tylenchus millefolii Löw forms galls on
Achillea, T. dipsaci Kühn. on the teazle. They all seem to have great powers
of resisting desiccation. The former species, when dried and placed in a
herbarium in May, gave rise to active worms when moistened the following
October; and the corn eel-worm is said to survive twenty-seven years in a
state of suspended animation. On the other hand, although these Nematodes
like moisture, they cannot withstand submersion in water for any time.
They can resist a considerable degree of cold, and a species, Aphelenchus
nivalis Auriv.,[195] has been described from Spitzbergen, where it lives in
the snow amongst a small red alga, Sphaerella nivalis.
VII. Family Enoplidae.
Small, as a rule free-living, usually marine Nematodes, without a second
oesophageal bulb. Eyes and mouth-armature often present. Fine hairs and
bristles sometimes surround the mouth.
Genera: Enoplus, Dorylaimus, Enchelidium, and others.
The genus Enoplus is exclusively marine, living amongst Algae and
Hydroids in shallow water and moving actively about, but never coiling
into spirals. De Man[196] describes Enoplus brevis Bast. as being attacked
by a plant parasite, probably a Bacterium, of a greenish colour, which
infested the muscles and gave them a peculiar colour.
excretory pore; d, alimentary canal; e, anus; f, ovary: E, a male shortly before
casting its larval skin.
Vuillemin and Legrain[194] point out that while Heterodera is injurious to
cultivated plants growing in damp soil, its presence is advantageous to
those that grow in deserts. It is very common in the Sahara, and attacks
many plants which are immune from it elsewhere. It causes the rootlets to
swell out, and the bladder-like extensions thus formed act as reservoirs for
water.
Many other species attack plants; Tylenchus millefolii Löw forms galls on
Achillea, T. dipsaci Kühn. on the teazle. They all seem to have great powers
of resisting desiccation. The former species, when dried and placed in a
herbarium in May, gave rise to active worms when moistened the following
October; and the corn eel-worm is said to survive twenty-seven years in a
state of suspended animation. On the other hand, although these Nematodes
like moisture, they cannot withstand submersion in water for any time.
They can resist a considerable degree of cold, and a species, Aphelenchus
nivalis Auriv.,[195] has been described from Spitzbergen, where it lives in
the snow amongst a small red alga, Sphaerella nivalis.
VII. Family Enoplidae.
Small, as a rule free-living, usually marine Nematodes, without a second
oesophageal bulb. Eyes and mouth-armature often present. Fine hairs and
bristles sometimes surround the mouth.
Genera: Enoplus, Dorylaimus, Enchelidium, and others.
The genus Enoplus is exclusively marine, living amongst Algae and
Hydroids in shallow water and moving actively about, but never coiling
into spirals. De Man[196] describes Enoplus brevis Bast. as being attacked
by a plant parasite, probably a Bacterium, of a greenish colour, which
infested the muscles and gave them a peculiar colour.
Page 170
Numerous other species have been described by De Man from the coast of
Holland. It is probable that some of them are the free stages of parasitic
forms; a brackish water species found in the East Indies (Dorylaimus
palustris) is regarded by Carter as the larva of Filaria medinensis.
Oncholaimus echini Leyd. is parasitic in the intestine of the sea-urchin
Echinus esculentus. Tricoma cincta[197] has a strongly striated cuticle,
which gives it almost the appearance of segmentation. Fimbria tenuis has
numerous hairs on the tail, and the mouth is surrounded by bristle-bearing
papillae.
Here must be mentioned two families closely allied to the true Nematodes.
(i.) Chaetosomatidae.—This family includes three genera: Chaetosoma,
Rhabdogaster, and Tristicochaeta. According to Metschnikoff,[198] although
they are not true Nematodes, they have a great likeness to the group. He
distinguishes them from the swimming members of the group as "creeping
Nematoda." Chaetosoma, of which two species are known, C.
ophicephalum and C. claparedii, has a head distinct from the body (Fig.
79). The mouth is at the anterior end, surrounded by a double semicircle of
movable spicules; the whole body is covered by fine hairs, and on the
ventral surface, just in front of the anus, is a double row of about fifteen
cylindrical projections, by whose agency the animal creeps. The female C.
claparedii is 1.5 mm. long, the male 1.14 mm. They were found creeping
about on sea-weeds in the neighbourhood of Salerno.
Fig. 79.—Mature female of Chaetosoma claparedii Metschni., × 57. (From
Metschnikoff.) a, Oesophagus; b, intestine; c, anus; d, ovary; e, generative pore;
f, ventral bristles.
Holland. It is probable that some of them are the free stages of parasitic
forms; a brackish water species found in the East Indies (Dorylaimus
palustris) is regarded by Carter as the larva of Filaria medinensis.
Oncholaimus echini Leyd. is parasitic in the intestine of the sea-urchin
Echinus esculentus. Tricoma cincta[197] has a strongly striated cuticle,
which gives it almost the appearance of segmentation. Fimbria tenuis has
numerous hairs on the tail, and the mouth is surrounded by bristle-bearing
papillae.
Here must be mentioned two families closely allied to the true Nematodes.
(i.) Chaetosomatidae.—This family includes three genera: Chaetosoma,
Rhabdogaster, and Tristicochaeta. According to Metschnikoff,[198] although
they are not true Nematodes, they have a great likeness to the group. He
distinguishes them from the swimming members of the group as "creeping
Nematoda." Chaetosoma, of which two species are known, C.
ophicephalum and C. claparedii, has a head distinct from the body (Fig.
79). The mouth is at the anterior end, surrounded by a double semicircle of
movable spicules; the whole body is covered by fine hairs, and on the
ventral surface, just in front of the anus, is a double row of about fifteen
cylindrical projections, by whose agency the animal creeps. The female C.
claparedii is 1.5 mm. long, the male 1.14 mm. They were found creeping
about on sea-weeds in the neighbourhood of Salerno.
Fig. 79.—Mature female of Chaetosoma claparedii Metschni., × 57. (From
Metschnikoff.) a, Oesophagus; b, intestine; c, anus; d, ovary; e, generative pore;
f, ventral bristles.
Page 171
The genus Tristicochaeta[199] differs from the foregoing in having three
rows of locomotor projections instead of two.
Fig. 80.—Tristicochaeta inarimense Panceri, in one of its most usual positions,
showing the triple row of ventral bristles, × 100. (From Panceri.)
Rhabdogaster has no head distinct from the body, though the anterior part
of the body is swollen. A second swelling occurs, as is also the case with
Chaetosoma, in the region of the opening of the genital ducts. The female in
Rh. cygnoides attains a length of 0.36 mm. In this genus the hairs are
confined to the dorsal middle line. The locomotor projections are hooked,
and are much finer than those of Chaetosoma, and they are situated farther
forward than in the last-named genus. Rhabdogaster occurs in the same
surroundings as Chaetosoma. Ch. ophicephalum is recorded from the
English Channel.
(ii.) Desmoscolecidae.—The members of this family are minute, and are
characterised by the presence of well-marked ridges which surround the
body and give it an appearance of segmentation. The head, which is
somewhat swollen, bears four bristles, and single pairs are borne by a
certain number of the ridges, some on the dorsal and some on the ventral
surface. These hairs can be moved independently of one another. Two red
eye-spots are described between the fourth and fifth rings. The sexes are
distinct, and the internal organs generally have a marked resemblance to
those of the true Nematoda. The Desmoscolecidae move by looping their
bodies after the manner of the Geometrid caterpillars, as well as by creeping
with their bristles. The genus contains numerous species[200]: D. minutus
Clap. (English Channel), D. nematoides Greef, D. adelphus Greef, D.
chaetogaster Greef, D. elongatus Panceri, and D. lanuginosa Panceri. They
are exclusively marine.
rows of locomotor projections instead of two.
Fig. 80.—Tristicochaeta inarimense Panceri, in one of its most usual positions,
showing the triple row of ventral bristles, × 100. (From Panceri.)
Rhabdogaster has no head distinct from the body, though the anterior part
of the body is swollen. A second swelling occurs, as is also the case with
Chaetosoma, in the region of the opening of the genital ducts. The female in
Rh. cygnoides attains a length of 0.36 mm. In this genus the hairs are
confined to the dorsal middle line. The locomotor projections are hooked,
and are much finer than those of Chaetosoma, and they are situated farther
forward than in the last-named genus. Rhabdogaster occurs in the same
surroundings as Chaetosoma. Ch. ophicephalum is recorded from the
English Channel.
(ii.) Desmoscolecidae.—The members of this family are minute, and are
characterised by the presence of well-marked ridges which surround the
body and give it an appearance of segmentation. The head, which is
somewhat swollen, bears four bristles, and single pairs are borne by a
certain number of the ridges, some on the dorsal and some on the ventral
surface. These hairs can be moved independently of one another. Two red
eye-spots are described between the fourth and fifth rings. The sexes are
distinct, and the internal organs generally have a marked resemblance to
those of the true Nematoda. The Desmoscolecidae move by looping their
bodies after the manner of the Geometrid caterpillars, as well as by creeping
with their bristles. The genus contains numerous species[200]: D. minutus
Clap. (English Channel), D. nematoides Greef, D. adelphus Greef, D.
chaetogaster Greef, D. elongatus Panceri, and D. lanuginosa Panceri. They
are exclusively marine.
Page 172
Fig. 81.—Female Desmoscolex elongatus Panceri, ventral view, × 260. a, Ovary. (From
Panceri.)
Trichoderma oxycaudatum Greef[201] is a minute animal, 0.3 mm. long,
which has no head or ventral spines, but whose body is ringed and covered
with long hair-like bristles. The male has two spicules, and the internal
organisation recalls that of other Nematodes; still its ringed body has
induced some authorities to place it near to Desmoscolex.
The Life-History of Nematodes.
Although, considering the enormous number of species of Nematodes and
the remarkable diversity of the conditions under which they live, their
bodily structure shows a very striking uniformity, the same is by no means
the case with their life-history, which exhibits an astounding variety. Von
Linstow[202] has arranged the various modifications, which occur under
fourteen heads. He includes in his list the Gordian worms, which we have
placed under a different heading. The following account has been taken
from his paper, with a few alterations:—
1. The embryos develop, with a larval stage and without any change of
medium, directly into the mature sexual forms. They live in fresh, brackish,
or salt water, in plants, in the earth or in decaying organic matter: examples,
Dorylaimus, Enoplus, Plectus, Monhystera.
Panceri.)
Trichoderma oxycaudatum Greef[201] is a minute animal, 0.3 mm. long,
which has no head or ventral spines, but whose body is ringed and covered
with long hair-like bristles. The male has two spicules, and the internal
organisation recalls that of other Nematodes; still its ringed body has
induced some authorities to place it near to Desmoscolex.
The Life-History of Nematodes.
Although, considering the enormous number of species of Nematodes and
the remarkable diversity of the conditions under which they live, their
bodily structure shows a very striking uniformity, the same is by no means
the case with their life-history, which exhibits an astounding variety. Von
Linstow[202] has arranged the various modifications, which occur under
fourteen heads. He includes in his list the Gordian worms, which we have
placed under a different heading. The following account has been taken
from his paper, with a few alterations:—
1. The embryos develop, with a larval stage and without any change of
medium, directly into the mature sexual forms. They live in fresh, brackish,
or salt water, in plants, in the earth or in decaying organic matter: examples,
Dorylaimus, Enoplus, Plectus, Monhystera.
Page 173
2. The larvae live in the earth, the sexual forms in plants: examples,
Tylenchus tritici and T. devastatrix, Heterodera schachtii (Figs. 77 and 78).
3. The larvae live in animals, after whose death and decay they are set free
and develop into the sexual animals in the earth: example, Rhabditis pellio.
4. The bisexual forms live in the earth, and the fertilised females bore into
animals (insects), and here produce embryos: example, Sphaerularia bombi
(Fig. 76).
5. The bisexual forms live in the earth; the females do not develop, but the
males make their way into Insects (Beetles), and becoming hermaphrodite,
develop ova which give rise to the bisexual form: example, Bradynema
rigidum.
6. The larvae live in the earth, the sexual form in Vertebrates: examples,
Dochmius, Strongylus.
7. The Nematode lives as a hermaphrodite in animals, the offspring of this,
by an alternation of generations, become sexual in the earth: example,
Rhabdonema in Frog.
8. A bisexual free form gives origin to a bisexual parasitic form living in an
animal: example, Leptodera appendiculata in Snails.
9. The eggs develop in the earth, and give rise to embryos which are
transferred whilst still in the egg-cell to the body of an animal. The embryos
hatch out and form bisexual parasites: examples, Oxyuris, Trichocephalus.
10. The larvae live in insects, the sexual worms in water or in the earth:
example, Mermis.
11. The larva lives encapsuled and is passively transferred to a second
animal: examples, Ollulanus, from Mouse to Cat; Cucullanus elegans, from
Cyclops to Perch; Spiroptera obtusa, from Meal-worm to Mouse.
Tylenchus tritici and T. devastatrix, Heterodera schachtii (Figs. 77 and 78).
3. The larvae live in animals, after whose death and decay they are set free
and develop into the sexual animals in the earth: example, Rhabditis pellio.
4. The bisexual forms live in the earth, and the fertilised females bore into
animals (insects), and here produce embryos: example, Sphaerularia bombi
(Fig. 76).
5. The bisexual forms live in the earth; the females do not develop, but the
males make their way into Insects (Beetles), and becoming hermaphrodite,
develop ova which give rise to the bisexual form: example, Bradynema
rigidum.
6. The larvae live in the earth, the sexual form in Vertebrates: examples,
Dochmius, Strongylus.
7. The Nematode lives as a hermaphrodite in animals, the offspring of this,
by an alternation of generations, become sexual in the earth: example,
Rhabdonema in Frog.
8. A bisexual free form gives origin to a bisexual parasitic form living in an
animal: example, Leptodera appendiculata in Snails.
9. The eggs develop in the earth, and give rise to embryos which are
transferred whilst still in the egg-cell to the body of an animal. The embryos
hatch out and form bisexual parasites: examples, Oxyuris, Trichocephalus.
10. The larvae live in insects, the sexual worms in water or in the earth:
example, Mermis.
11. The larva lives encapsuled and is passively transferred to a second
animal: examples, Ollulanus, from Mouse to Cat; Cucullanus elegans, from
Cyclops to Perch; Spiroptera obtusa, from Meal-worm to Mouse.
Page 174
12. The sexual form lives for a short time in the intestine of a Vertebrate,
and produces larvae which bore through the intestinal wall and become
encapsuled in the tissues: example, Trichina spiralis.
13. The sexual animal lives in the trachea of birds; the ova containing
embryos are coughed up and are taken into other birds with food. They quit
the egg-shell and wander into the air-sacs, and finally into the trachea:
example, Syngamus.
14. There are two larval forms; the first lives in water, the second in the
lungs of Amphibia, whence they wander into the intestine and become
sexually mature: example, Nematoxys longicauda in Triton alpestris.
Parasitism.
1. Effect of Parasitism on the Parasite.—The usual effect of parasitism on
the parasitic organism is that the various organs necessary for a free life
tend to degenerate, whilst there is a multiplication and development of
organs of adhesion, by means of which the parasite maintains its hold on its
host. There is further an immense increase in the powers of reproduction,
which may take the form of an increase in the number of fertilised eggs
produced, or the parasite may at some time of its life reproduce asexually,
by budding, or fission, or parthenogetically.
Of the various classes of animals which are more or less parasitic, the
Nematodes show less difference between the free-living and parasitic
members of the group than obtains in any other class. With few exceptions,
such as Sphaerularia, Allantonema, and one or two others, the parasitic
forms have undergone but little degeneration. It is true that they have no
eyes such as the free forms often possess, but in other respects, such as in
the nervous, muscular, and digestive systems, they do not show any marked
retrogression; further, the mouth-armature is developed in many free forms,
and is not confined to the parasites.
and produces larvae which bore through the intestinal wall and become
encapsuled in the tissues: example, Trichina spiralis.
13. The sexual animal lives in the trachea of birds; the ova containing
embryos are coughed up and are taken into other birds with food. They quit
the egg-shell and wander into the air-sacs, and finally into the trachea:
example, Syngamus.
14. There are two larval forms; the first lives in water, the second in the
lungs of Amphibia, whence they wander into the intestine and become
sexually mature: example, Nematoxys longicauda in Triton alpestris.
Parasitism.
1. Effect of Parasitism on the Parasite.—The usual effect of parasitism on
the parasitic organism is that the various organs necessary for a free life
tend to degenerate, whilst there is a multiplication and development of
organs of adhesion, by means of which the parasite maintains its hold on its
host. There is further an immense increase in the powers of reproduction,
which may take the form of an increase in the number of fertilised eggs
produced, or the parasite may at some time of its life reproduce asexually,
by budding, or fission, or parthenogetically.
Of the various classes of animals which are more or less parasitic, the
Nematodes show less difference between the free-living and parasitic
members of the group than obtains in any other class. With few exceptions,
such as Sphaerularia, Allantonema, and one or two others, the parasitic
forms have undergone but little degeneration. It is true that they have no
eyes such as the free forms often possess, but in other respects, such as in
the nervous, muscular, and digestive systems, they do not show any marked
retrogression; further, the mouth-armature is developed in many free forms,
and is not confined to the parasites.
Page 175
The group has developed no methods of asexual reproduction by budding or
fission, such as are found in Platyhelminthes; and the cases of an alternation
of generations in which a sexual form alternates with a parthenogenetic
form, are rare, e.g. Rhabdonema nigrovenosum; and it seems possible that
even when parthenogenesis has been described, further observation may
show that the parthenogenetic stage is really a protandrous hermaphrodite,
in which case the alternation of generations in Nematodes, i.e. the
hermaphrodite alternating with the dioecious form, is a case of heterogamy
or the alternation of two sexual generations.
On the other hand, parasitic Nematodes produce enormous numbers of
eggs. Van Beneden states that 60,000,000 have been computed in a single
Nematode, and this multiplication of ova is absolutely necessary, for the
chance of the embryo reaching the right host, in which alone it can develop,
is always a small one.
It is a common thing to find that parasites are either hermaphrodite or that
the male is degenerate, as is the case with many of the parasitic Crustacea,
but with one or two exceptions the Nematoda are bisexual, and although, as
a rule, the males are smaller than the females, they show no other trace of
degeneracy.
In spite of the fact that the class as a whole shows but few special
modifications consequent on a parasitic mode of life, it is clear that the
Nematoda are peculiarly adapted for such a mode of life. Their elongated
thread-like bodies afford little resistance to the passage of the food, which,
as it passes through the intestine of the host, might tend to carry the
parasites out of the body. At the same time their shape enables them to
pierce and wriggle through the various tissues without making any very
serious lesions such as might prove fatal to their host. Their extraordinary
power of resisting desiccation both in the egg and in the adult state vastly
increases their chances of ultimately hitting on the right host. They are
capable of living in a state of suspended animation for months, and even
years when dried (vide p. 136), and of resuming their activity on being
moistened.
fission, such as are found in Platyhelminthes; and the cases of an alternation
of generations in which a sexual form alternates with a parthenogenetic
form, are rare, e.g. Rhabdonema nigrovenosum; and it seems possible that
even when parthenogenesis has been described, further observation may
show that the parthenogenetic stage is really a protandrous hermaphrodite,
in which case the alternation of generations in Nematodes, i.e. the
hermaphrodite alternating with the dioecious form, is a case of heterogamy
or the alternation of two sexual generations.
On the other hand, parasitic Nematodes produce enormous numbers of
eggs. Van Beneden states that 60,000,000 have been computed in a single
Nematode, and this multiplication of ova is absolutely necessary, for the
chance of the embryo reaching the right host, in which alone it can develop,
is always a small one.
It is a common thing to find that parasites are either hermaphrodite or that
the male is degenerate, as is the case with many of the parasitic Crustacea,
but with one or two exceptions the Nematoda are bisexual, and although, as
a rule, the males are smaller than the females, they show no other trace of
degeneracy.
In spite of the fact that the class as a whole shows but few special
modifications consequent on a parasitic mode of life, it is clear that the
Nematoda are peculiarly adapted for such a mode of life. Their elongated
thread-like bodies afford little resistance to the passage of the food, which,
as it passes through the intestine of the host, might tend to carry the
parasites out of the body. At the same time their shape enables them to
pierce and wriggle through the various tissues without making any very
serious lesions such as might prove fatal to their host. Their extraordinary
power of resisting desiccation both in the egg and in the adult state vastly
increases their chances of ultimately hitting on the right host. They are
capable of living in a state of suspended animation for months, and even
years when dried (vide p. 136), and of resuming their activity on being
moistened.
Page 176
The great faculty this group shows for living parasitically is evinced by the
extraordinary variety of life-history presented by the different species.
There is scarcely a stage which may not be parasitic; the eggs, the larvae,
the adults are all in some cases free, in others parasitic, and in many cases
first the one and then the other.
2. Occurrence and Effect of the Parasite on the Host.—Von Linstow
states that the only law that can be derived inductively from the study of the
life-history of Nematodes is that those that live in animals never pass
through all their stages of development in the same organ; consequently, in
considering the distribution of the parasites within the body of their host we
have a double habitat to consider. Many forms, such as Trichina spiralis,
wander from the intestine to the muscles; others, such as Filaria
medinensis, from the alimentary canal to the lymphatics or blood vessels or
subcutaneous tissues. Others pass from the body-cavity to the intestine, as
the Mermithidae, which infest Insects, or from the stem and leaves of a
plant to its flower, as in the case of Tylenchus tritici.
With regard to their occurrence in the different classes of the animal
kingdom, they have been most frequently observed in Vertebrates and in
Insects. They are comparatively rare in the other large divisions. Many
genera are confined to certain hosts: thus Ascaris, Filaria, Trichosoma
occur only in Vertebrates; Spiroptera (with one exception) in Mammals and
Birds; Cucullanus in Fishes and Amphibia; Strongylus and Physaloptera in
Mammals, Birds, and Reptiles; Dochmius, Pseudalius, Trichocephalus in
Mammals; Dispharagus, Hystrichis, Syngamus in Birds; Nematoxys,
Hedruris in Amphibia and Reptiles; Ichthyonema in Fishes; and Isacis and
Mermis in Insects.
Twenty-two species have been described as parasitic in man, of which
perhaps the most dangerous are Filaria medinensis, the three varieties of F.
sanguinis hominis; Dochmius (Ancylostomum) duodenalis, and Trichina
spiralis. The Ascaridae, as Ascaris lumbricoides and Oxyuris vermicularis,
though painful, seldom cause death.
extraordinary variety of life-history presented by the different species.
There is scarcely a stage which may not be parasitic; the eggs, the larvae,
the adults are all in some cases free, in others parasitic, and in many cases
first the one and then the other.
2. Occurrence and Effect of the Parasite on the Host.—Von Linstow
states that the only law that can be derived inductively from the study of the
life-history of Nematodes is that those that live in animals never pass
through all their stages of development in the same organ; consequently, in
considering the distribution of the parasites within the body of their host we
have a double habitat to consider. Many forms, such as Trichina spiralis,
wander from the intestine to the muscles; others, such as Filaria
medinensis, from the alimentary canal to the lymphatics or blood vessels or
subcutaneous tissues. Others pass from the body-cavity to the intestine, as
the Mermithidae, which infest Insects, or from the stem and leaves of a
plant to its flower, as in the case of Tylenchus tritici.
With regard to their occurrence in the different classes of the animal
kingdom, they have been most frequently observed in Vertebrates and in
Insects. They are comparatively rare in the other large divisions. Many
genera are confined to certain hosts: thus Ascaris, Filaria, Trichosoma
occur only in Vertebrates; Spiroptera (with one exception) in Mammals and
Birds; Cucullanus in Fishes and Amphibia; Strongylus and Physaloptera in
Mammals, Birds, and Reptiles; Dochmius, Pseudalius, Trichocephalus in
Mammals; Dispharagus, Hystrichis, Syngamus in Birds; Nematoxys,
Hedruris in Amphibia and Reptiles; Ichthyonema in Fishes; and Isacis and
Mermis in Insects.
Twenty-two species have been described as parasitic in man, of which
perhaps the most dangerous are Filaria medinensis, the three varieties of F.
sanguinis hominis; Dochmius (Ancylostomum) duodenalis, and Trichina
spiralis. The Ascaridae, as Ascaris lumbricoides and Oxyuris vermicularis,
though painful, seldom cause death.
Page 177
The enormous number of parasites harboured by one host is shown by the
fact mentioned in Leuckart's Parasites of Man, that Nathusius[203] took
from a single black stork 24 specimens of Filaria labiata from the lungs, 16
Syngamus trachealis from the trachea, more than 100 Spiroptera alata from
the coats of the stomach, besides several hundred Trematodes belonging to
several different species (see p. 63). Even this has been surpassed in the
case of a young horse, in whose body Krause found 500 Ascaris
megalocephala, 190 Oxyuris curvula, several millions of Strongylus
tetracanthus, 214 Sclerostomum armatum, 287 Filaria papillosa, 69 Taenia
perfoliata, and 6 Cysticercus forms.
It is impossible here to enter into a full description of the destruction caused
to domesticated animals and crops by the presence of these parasites; full
details will be found in books dealing especially with this question, such as
Neumann's Parasites and Parasitic Diseases of Domesticated Animals. A
couple of cases will show how important this matter is to the farmer. Crisp
estimates that Syngamus trachealis causes the death of half a million pullets
in England every year, and Mégnin states that in a single pheasantry 1200
victims died daily; again, the loss of one-third the crop of beetroot is by no
means uncommon when it is infested with Heterodera schachtii. These
show the practical importance of what at first sight seem quite insignificant
animals, and the necessity for the minutest observation, for only when we
are fully acquainted with all the details of the life-history of a parasite are
we in a position to successfully combat it.
Sub-Order II. Nematomorpha.
Until the last few years it has been customary to regard the Gordiidae as a
family of Nematodes. Although in external appearance and life-history they
closely resemble the members of this group, yet recent research has shown
so many important morphological differences between them and the
Nematoda, that most zoologists are now agreed in placing them in a
different sub-Order, the Nematomorpha, a name first suggested by
Vejdovsky.[204]
fact mentioned in Leuckart's Parasites of Man, that Nathusius[203] took
from a single black stork 24 specimens of Filaria labiata from the lungs, 16
Syngamus trachealis from the trachea, more than 100 Spiroptera alata from
the coats of the stomach, besides several hundred Trematodes belonging to
several different species (see p. 63). Even this has been surpassed in the
case of a young horse, in whose body Krause found 500 Ascaris
megalocephala, 190 Oxyuris curvula, several millions of Strongylus
tetracanthus, 214 Sclerostomum armatum, 287 Filaria papillosa, 69 Taenia
perfoliata, and 6 Cysticercus forms.
It is impossible here to enter into a full description of the destruction caused
to domesticated animals and crops by the presence of these parasites; full
details will be found in books dealing especially with this question, such as
Neumann's Parasites and Parasitic Diseases of Domesticated Animals. A
couple of cases will show how important this matter is to the farmer. Crisp
estimates that Syngamus trachealis causes the death of half a million pullets
in England every year, and Mégnin states that in a single pheasantry 1200
victims died daily; again, the loss of one-third the crop of beetroot is by no
means uncommon when it is infested with Heterodera schachtii. These
show the practical importance of what at first sight seem quite insignificant
animals, and the necessity for the minutest observation, for only when we
are fully acquainted with all the details of the life-history of a parasite are
we in a position to successfully combat it.
Sub-Order II. Nematomorpha.
Until the last few years it has been customary to regard the Gordiidae as a
family of Nematodes. Although in external appearance and life-history they
closely resemble the members of this group, yet recent research has shown
so many important morphological differences between them and the
Nematoda, that most zoologists are now agreed in placing them in a
different sub-Order, the Nematomorpha, a name first suggested by
Vejdovsky.[204]
Page 178
Fig. 82.—A water plant around which a female Gordius is twining and laying eggs. a,
a, Clump and string of eggs. (From von Linstow.[205])
The Gordiidae comprise but two genera, Gordius and Nectonema. The latter
has but one species, N. agile Verr., and is marine; the former, on the other
hand, is exclusively fresh-water, and contains a very large number of
species. Gordian worms are frequently to be found in ditches, ponds, or
large puddles, moving with an undulating motion through the water, or
twining and writhing round water-plants; they are scarcer in running water.
In shape they are like a piece of thin whip-cord, slightly tapering at each
end; the male, however, is easily distinguished from the female by its
forked tail (Fig. 89). Not unfrequently a considerable number are found
inextricably tangled together into a knot, and the name of the genus refers
to this fact. Where numbers have suddenly appeared in water hitherto free
from them, legends have sprung up which attribute their presence to a rain
of worms; in reality they have come out of the bodies of Insects in which
they are parasitic for the greater part of their life.
The genus Gordius passes through three distinct stages, of which the first
two are larval and parasitic; the third is sexually mature and lives in water.
The second larval stage closely resembles the adult, but the reproductive
organs are not developed. The following account of the structure of this
larval form and of the adult is in the main taken from von Linstow.[206]
The whole body is covered with a well-developed two-layered cuticle,
which in the adult is marked out into areas, and bears numerous minute
sensory bristles, which are especially developed in the neighbourhood of
the cloaca of the male. Beneath this is a hypodermis which differs markedly
from the sub-cuticle of Nematodes, inasmuch as it consists of a single layer
of polygonal nucleated cells. Within this lies a single layer of longitudinal
muscle-cells, which differ from the corresponding layer of Nematodes in
having that part of their medulla which is not surrounded by the contractile
a, Clump and string of eggs. (From von Linstow.[205])
The Gordiidae comprise but two genera, Gordius and Nectonema. The latter
has but one species, N. agile Verr., and is marine; the former, on the other
hand, is exclusively fresh-water, and contains a very large number of
species. Gordian worms are frequently to be found in ditches, ponds, or
large puddles, moving with an undulating motion through the water, or
twining and writhing round water-plants; they are scarcer in running water.
In shape they are like a piece of thin whip-cord, slightly tapering at each
end; the male, however, is easily distinguished from the female by its
forked tail (Fig. 89). Not unfrequently a considerable number are found
inextricably tangled together into a knot, and the name of the genus refers
to this fact. Where numbers have suddenly appeared in water hitherto free
from them, legends have sprung up which attribute their presence to a rain
of worms; in reality they have come out of the bodies of Insects in which
they are parasitic for the greater part of their life.
The genus Gordius passes through three distinct stages, of which the first
two are larval and parasitic; the third is sexually mature and lives in water.
The second larval stage closely resembles the adult, but the reproductive
organs are not developed. The following account of the structure of this
larval form and of the adult is in the main taken from von Linstow.[206]
The whole body is covered with a well-developed two-layered cuticle,
which in the adult is marked out into areas, and bears numerous minute
sensory bristles, which are especially developed in the neighbourhood of
the cloaca of the male. Beneath this is a hypodermis which differs markedly
from the sub-cuticle of Nematodes, inasmuch as it consists of a single layer
of polygonal nucleated cells. Within this lies a single layer of longitudinal
muscle-cells, which differ from the corresponding layer of Nematodes in
having that part of their medulla which is not surrounded by the contractile
Page 179
portion directed outwards towards the hypodermis, and not inwards towards
the body-cavity.
Fig. 83.—Transverse section through a young male Gordius tolosanus Duj. (From von
Linstow.) Highly magnified. a, Cuticle; b, hypodermis; c, muscular layer; d,
parenchyma; e, alimentary canal; f, nervous system; g, cells of the testis.
The body is in the younger stages practically solid, the interior being filled
with clearly defined polygonal cells which are arranged in definite rows; in
later life certain splits arise in this tissue which subserve various functions;
between these splits strands of tissue are left which form mesenteries, and
some of the cells remain lining the muscular layer (Fig. 86). These cells
have been described by Vejdovsky as a definite somatic, peritoneal
epithelium, but this was not found by von Linstow. Besides forming the
mesenteries, and acting as packing between the various organs of the body,
these cells also form the ova and the spermatozoa.
The splits which have appeared when the animal has reached the second
larval stage, are two dorsal and a ventral; the latter contains the alimentary
canal, and may be termed the body-cavity, the former will develop the
generative organs. The mouth is occluded in the older larvae, and in the
adults there is a distinct but solid oesophagus which passes into a tubular
intestine. The intestine consists of a single layer of cells surrounding a
lumen; it runs straight to the hinder end of the body, where it opens in both
sexes with the ducts of the reproductive organs.
The nervous system consists of a well-defined circumoesophageal ring with
two dorsal swellings, and, arising from this, a median ventral cord which
runs the whole length of the body. The cord consists of three longitudinal
strands with ganglionic cells below them; the latter, though they lie within
the muscle layer, maintain a connexion with the hypodermis. Behind, the
nerve-cord splits in the male, one half passing into each caudal fork. In the
the body-cavity.
Fig. 83.—Transverse section through a young male Gordius tolosanus Duj. (From von
Linstow.) Highly magnified. a, Cuticle; b, hypodermis; c, muscular layer; d,
parenchyma; e, alimentary canal; f, nervous system; g, cells of the testis.
The body is in the younger stages practically solid, the interior being filled
with clearly defined polygonal cells which are arranged in definite rows; in
later life certain splits arise in this tissue which subserve various functions;
between these splits strands of tissue are left which form mesenteries, and
some of the cells remain lining the muscular layer (Fig. 86). These cells
have been described by Vejdovsky as a definite somatic, peritoneal
epithelium, but this was not found by von Linstow. Besides forming the
mesenteries, and acting as packing between the various organs of the body,
these cells also form the ova and the spermatozoa.
The splits which have appeared when the animal has reached the second
larval stage, are two dorsal and a ventral; the latter contains the alimentary
canal, and may be termed the body-cavity, the former will develop the
generative organs. The mouth is occluded in the older larvae, and in the
adults there is a distinct but solid oesophagus which passes into a tubular
intestine. The intestine consists of a single layer of cells surrounding a
lumen; it runs straight to the hinder end of the body, where it opens in both
sexes with the ducts of the reproductive organs.
The nervous system consists of a well-defined circumoesophageal ring with
two dorsal swellings, and, arising from this, a median ventral cord which
runs the whole length of the body. The cord consists of three longitudinal
strands with ganglionic cells below them; the latter, though they lie within
the muscle layer, maintain a connexion with the hypodermis. Behind, the
nerve-cord splits in the male, one half passing into each caudal fork. In the
Page 180
adult a pair of black eyes can be detected on the head; the only other sense
organs are the tactile bristles mentioned above. Excretory organs are
unknown.
Fig. 84.—Section through a young female Gordius tolosanus. (From von Linstow.) a,
Cuticle; b, hypodermis; c, muscular layer; d, parenchyma; e, alimentary canal; f,
nervous system; g, egg-sac; h, ovary.
The generative organs only attain maturity in the adult, which is, in fact,
exclusively devoted to reproduction. No trace of testes is found in the larva,
though the two dorsal splits from the walls of which the spermatozoa will
arise are present. They are lined by a definite epithelium (Fig. 83), and this
serves at once to distinguish them from the body-cavity. Posteriorly the
splits narrow and become the two vasa deferentia which open one on each
side into the cloaca. The cells lining the lumen give rise to secondary cells,
and these become spermatozoa, the process extending from behind
forwards. The external organs—bursa, etc.—described by Vejdovsky were
not found by von Linstow.
Fig. 85.—Section through a mature female Gordius tolosanus. (From von Linstow.)
Lettering as in Fig. 84; g, egg-sac; h, ovary.
organs are the tactile bristles mentioned above. Excretory organs are
unknown.
Fig. 84.—Section through a young female Gordius tolosanus. (From von Linstow.) a,
Cuticle; b, hypodermis; c, muscular layer; d, parenchyma; e, alimentary canal; f,
nervous system; g, egg-sac; h, ovary.
The generative organs only attain maturity in the adult, which is, in fact,
exclusively devoted to reproduction. No trace of testes is found in the larva,
though the two dorsal splits from the walls of which the spermatozoa will
arise are present. They are lined by a definite epithelium (Fig. 83), and this
serves at once to distinguish them from the body-cavity. Posteriorly the
splits narrow and become the two vasa deferentia which open one on each
side into the cloaca. The cells lining the lumen give rise to secondary cells,
and these become spermatozoa, the process extending from behind
forwards. The external organs—bursa, etc.—described by Vejdovsky were
not found by von Linstow.
Fig. 85.—Section through a mature female Gordius tolosanus. (From von Linstow.)
Lettering as in Fig. 84; g, egg-sac; h, ovary.
Page 181
Fig. 86.—Section through a female Gordius tolosanus when the deposition of ova is
almost complete. a, b, c, d, e, and f, as in Fig. 84; g, egg-sac; h, ovary almost
empty; i, dorsal canal containing eggs; j, receptaculum seminis.
In the female larva two similar splits are present; these form the egg-sacs.
Posteriorly they end in two short oviducts which open into a uterus, in
which fertilisation takes place, and in which the secretion arises which
cements the eggs together. In the adult the ovaries and a receptaculum
seminis are found, in addition to the organs present in the larva. The ovaries
are formed from modifications of the packing tissue; they begin close
behind the head, and soon attain such dimensions as to compress the egg-
sacs and body-cavity to small slits. After a time the wall between the ovary
and the egg-sacs becomes absorbed, and the eggs grow into the latter. In the
old females, where the egg sacs are empty, there is a considerable space
round the exhausted ovary, into which eggs continue to fall off; there is also
a median dorsal canal which contains a few eggs. By this time the wall
between the ovary and the egg-sac has again appeared.
One of the most interesting points about the female is that, according to
Vejdovsky, the ovary is segmented, the cells which form the ova being
heaped up in segmentally-arranged masses. This observation, if correct, is
almost the only instance of segmentation recorded in the group
Nemathelminthes.
Fig. 87.—Nectonema agile Verrill. A, The adult. Magnified. (After Fewkes.) B,
Longitudinal section through the head. × about 20. (From Bürger.) a, Mouth; b,
circumoesophageal commissure (dorsal); c, cell of salivary gland; d, septum
cutting off head from rest of body; e, testis; f, ventral cord; g, oesophageal cells;
h, lumen of oesophagus; i, cerebral ganglion (ventral).
almost complete. a, b, c, d, e, and f, as in Fig. 84; g, egg-sac; h, ovary almost
empty; i, dorsal canal containing eggs; j, receptaculum seminis.
In the female larva two similar splits are present; these form the egg-sacs.
Posteriorly they end in two short oviducts which open into a uterus, in
which fertilisation takes place, and in which the secretion arises which
cements the eggs together. In the adult the ovaries and a receptaculum
seminis are found, in addition to the organs present in the larva. The ovaries
are formed from modifications of the packing tissue; they begin close
behind the head, and soon attain such dimensions as to compress the egg-
sacs and body-cavity to small slits. After a time the wall between the ovary
and the egg-sacs becomes absorbed, and the eggs grow into the latter. In the
old females, where the egg sacs are empty, there is a considerable space
round the exhausted ovary, into which eggs continue to fall off; there is also
a median dorsal canal which contains a few eggs. By this time the wall
between the ovary and the egg-sac has again appeared.
One of the most interesting points about the female is that, according to
Vejdovsky, the ovary is segmented, the cells which form the ova being
heaped up in segmentally-arranged masses. This observation, if correct, is
almost the only instance of segmentation recorded in the group
Nemathelminthes.
Fig. 87.—Nectonema agile Verrill. A, The adult. Magnified. (After Fewkes.) B,
Longitudinal section through the head. × about 20. (From Bürger.) a, Mouth; b,
circumoesophageal commissure (dorsal); c, cell of salivary gland; d, septum
cutting off head from rest of body; e, testis; f, ventral cord; g, oesophageal cells;
h, lumen of oesophagus; i, cerebral ganglion (ventral).
Page 182
The only other genus which is associated with Gordius in the group
Nematomorpha is Nectonema, of which there is as yet but one species
known, Nectonema agile Verr.[207] Our knowledge of the anatomy of this
worm is due mainly to Bürger[208] and Ward.[209] Nectonema is a marine
worm found swimming near the surface of the sea with rapid undulatory
motion. The males are from 50 to 200 mm. long, the females from 30 to 60
mm. The body is faintly ringed, and bears two rows of fine bristles on each
side. Owing to a curious torsion of the body through a right angle, the
lateral bristles of the anterior third seem to be placed in the ventral and
dorsal middle line. They are very easily broken off. The body is divided into
a small anterior and a large posterior chamber by a transverse septum
placed a little way behind the head. The anterior chamber contains the brain
and is lined by a definite epithelium, the posterior is not. The layers of the
skin correspond with those of Nematodes or of Gordius, but the hypodermal
cells show no cell outlines; still they are not so modified as in the former
group. The hypodermis is thickened in the median dorsal and ventral line,
and the single nerve-cord lies in the latter.
The alimentary canal is degenerate, as in Gordius. A mouth exists, but it is
minute, and opens into a very fine tube lined with chitin, which pierces
through the substance of a single elongated cell. This minute oesophagus,
with its coextensive cell, reaches back to the transverse partition, but behind
this a few other cells become associated with it, and ultimately the lumen of
the alimentary canal is surrounded by four cells; but the number diminishes
behind, and soon only two cells surround the tube at any one level, and the
intestine dwindles away some little distance in front of the tail. There is no
sign of an anus. A circumoesophageal nerve-ring exists, of which the
ventral part is by far the larger (Fig. 87); it gives off a ventral nerve-cord,
which swells posteriorly in the male into a large anal ganglion, far bigger
than the brain, and larger in the male than in the female.
The testes consist of a dorsally placed sac, continuous behind with a vas
deferens; this opens at the posterior end, which is pointed and slightly
curved ventrally. The ovary is unknown; but females have been found with
their body-cavity crammed with ova; these escape, like the spermatozoa,
from a genital pore at the posterior end of the body.
Nematomorpha is Nectonema, of which there is as yet but one species
known, Nectonema agile Verr.[207] Our knowledge of the anatomy of this
worm is due mainly to Bürger[208] and Ward.[209] Nectonema is a marine
worm found swimming near the surface of the sea with rapid undulatory
motion. The males are from 50 to 200 mm. long, the females from 30 to 60
mm. The body is faintly ringed, and bears two rows of fine bristles on each
side. Owing to a curious torsion of the body through a right angle, the
lateral bristles of the anterior third seem to be placed in the ventral and
dorsal middle line. They are very easily broken off. The body is divided into
a small anterior and a large posterior chamber by a transverse septum
placed a little way behind the head. The anterior chamber contains the brain
and is lined by a definite epithelium, the posterior is not. The layers of the
skin correspond with those of Nematodes or of Gordius, but the hypodermal
cells show no cell outlines; still they are not so modified as in the former
group. The hypodermis is thickened in the median dorsal and ventral line,
and the single nerve-cord lies in the latter.
The alimentary canal is degenerate, as in Gordius. A mouth exists, but it is
minute, and opens into a very fine tube lined with chitin, which pierces
through the substance of a single elongated cell. This minute oesophagus,
with its coextensive cell, reaches back to the transverse partition, but behind
this a few other cells become associated with it, and ultimately the lumen of
the alimentary canal is surrounded by four cells; but the number diminishes
behind, and soon only two cells surround the tube at any one level, and the
intestine dwindles away some little distance in front of the tail. There is no
sign of an anus. A circumoesophageal nerve-ring exists, of which the
ventral part is by far the larger (Fig. 87); it gives off a ventral nerve-cord,
which swells posteriorly in the male into a large anal ganglion, far bigger
than the brain, and larger in the male than in the female.
The testes consist of a dorsally placed sac, continuous behind with a vas
deferens; this opens at the posterior end, which is pointed and slightly
curved ventrally. The ovary is unknown; but females have been found with
their body-cavity crammed with ova; these escape, like the spermatozoa,
from a genital pore at the posterior end of the body.
Page 183
Classification.—The separation of the Nematomorpha from the Nematoda
depends mainly on the character of the nervous system, the absence of the
lateral lines and of the dorsal line, the character of the contents of the body-
cavity, and the character of the reproductive organs. In Gordiidae the latter
are always placed dorsal to the intestine, and ovaries and testes open alike
at the hinder end of the body. The importance of the differences in the
organs just enumerated has been considered sufficient to justify the removal
of the Gordiidae from the Nematoda, and the establishment of the special
sub-Order Nematomorpha for their reception; and although Nectonema has
a dorsal line, and is in some other respects intermediate between the two
groups, there can be little doubt that it is more closely allied to Gordius than
to any member of the Nematoda, and it must therefore be placed with it in
the Nematomorpha.
On the other hand, it ought to be mentioned that Camerano[210] found that
the chief details of the fertilisation and development of the egg in Gordius
closely conform with what is known of the same processes in Nematodes,
and he is of opinion that these resemblances are sufficiently important to
justify the retention of the group among the Nematoda.
Life-History.—The life-history of Gordius comprises four stages—the
early development of the egg, the first larval form, the second larval form,
and the sexually mature form. Both larval forms are parasitic, and during
their life they are actively engaged in feeding; the free form, on the other
hand, takes in no nourishment, and is exclusively engaged in reproduction.
Fig. 88.—Abdomen of Pterostichus niger with the terga removed to expose the Gordius
larva within. Slightly magnified. (From von Linstow.)
Von Linstow[211] gives the following account of the life-history of G.
tolosanus, a form which has been more fully worked out than any other. In
depends mainly on the character of the nervous system, the absence of the
lateral lines and of the dorsal line, the character of the contents of the body-
cavity, and the character of the reproductive organs. In Gordiidae the latter
are always placed dorsal to the intestine, and ovaries and testes open alike
at the hinder end of the body. The importance of the differences in the
organs just enumerated has been considered sufficient to justify the removal
of the Gordiidae from the Nematoda, and the establishment of the special
sub-Order Nematomorpha for their reception; and although Nectonema has
a dorsal line, and is in some other respects intermediate between the two
groups, there can be little doubt that it is more closely allied to Gordius than
to any member of the Nematoda, and it must therefore be placed with it in
the Nematomorpha.
On the other hand, it ought to be mentioned that Camerano[210] found that
the chief details of the fertilisation and development of the egg in Gordius
closely conform with what is known of the same processes in Nematodes,
and he is of opinion that these resemblances are sufficiently important to
justify the retention of the group among the Nematoda.
Life-History.—The life-history of Gordius comprises four stages—the
early development of the egg, the first larval form, the second larval form,
and the sexually mature form. Both larval forms are parasitic, and during
their life they are actively engaged in feeding; the free form, on the other
hand, takes in no nourishment, and is exclusively engaged in reproduction.
Fig. 88.—Abdomen of Pterostichus niger with the terga removed to expose the Gordius
larva within. Slightly magnified. (From von Linstow.)
Von Linstow[211] gives the following account of the life-history of G.
tolosanus, a form which has been more fully worked out than any other. In
Page 184
the month of April numerous specimens of the beetle Pterostichus niger
were found floating on the surface of the ditches and small ponds in the
fields surrounding Göttingen. Some were found dead or dying; others
appeared quite healthy, and these were swimming actively, endeavouring to
reach land. Within the abdomen of these beetles, in about 20 per cent of
those collected, the second larval form of the G. tolosanus was found. The
longest larvae were 122 mm. in length, and very soft, partly snow-white and
partly brown in colour; traces of the boring apparatus of the first larval form
were still to be seen, but in other respects the larva only differed from the
free form in the immaturity of its sexual organs. Besides the parasite hardly
anything was to be found in the abdomen of the beetle, the larva having
eaten up all trace of the fat body and the generative organs of its host. The
larvae bored their way out of the body of the beetle and became adult
animals.
It is rather difficult to say what brings these essentially terrestrial beetles to
the water, but von Linstow suggests that, as they live partly on snails, and at
this time of year there are not many land-snails about, they may be in search
of water-snails such as Limnaea. They may also be sometimes blown into
the water by wind storms, but, whatever the cause is, their presence in water
is essential for the continuance of the life of their parasites.
Once free in the water the Gordius is soon sexually mature; the fertilisation
takes place in April, and then the female may be seen twisting and writhing
round the stems of water-plants and laying the long bead-like strands of
eggs (Fig. 82). The first deposition observed by von Linstow took place on
14th April, the last on 2nd August, and the period of egg-laying for each
female extended over four weeks. At first the eggs are snow-white, but
within twenty-four hours they turn brown in colour.
The development of the first larva within the egg takes about a month.
When it emerges from the egg-shell it is minute, .065 mm. long, ringed
anteriorly, and provided with a protrusible and retractile boring apparatus
consisting of three chitinous rods; round the base of this piercing proboscis
is a double crown of papillae, each bearing a spine (Fig. 90).
were found floating on the surface of the ditches and small ponds in the
fields surrounding Göttingen. Some were found dead or dying; others
appeared quite healthy, and these were swimming actively, endeavouring to
reach land. Within the abdomen of these beetles, in about 20 per cent of
those collected, the second larval form of the G. tolosanus was found. The
longest larvae were 122 mm. in length, and very soft, partly snow-white and
partly brown in colour; traces of the boring apparatus of the first larval form
were still to be seen, but in other respects the larva only differed from the
free form in the immaturity of its sexual organs. Besides the parasite hardly
anything was to be found in the abdomen of the beetle, the larva having
eaten up all trace of the fat body and the generative organs of its host. The
larvae bored their way out of the body of the beetle and became adult
animals.
It is rather difficult to say what brings these essentially terrestrial beetles to
the water, but von Linstow suggests that, as they live partly on snails, and at
this time of year there are not many land-snails about, they may be in search
of water-snails such as Limnaea. They may also be sometimes blown into
the water by wind storms, but, whatever the cause is, their presence in water
is essential for the continuance of the life of their parasites.
Once free in the water the Gordius is soon sexually mature; the fertilisation
takes place in April, and then the female may be seen twisting and writhing
round the stems of water-plants and laying the long bead-like strands of
eggs (Fig. 82). The first deposition observed by von Linstow took place on
14th April, the last on 2nd August, and the period of egg-laying for each
female extended over four weeks. At first the eggs are snow-white, but
within twenty-four hours they turn brown in colour.
The development of the first larva within the egg takes about a month.
When it emerges from the egg-shell it is minute, .065 mm. long, ringed
anteriorly, and provided with a protrusible and retractile boring apparatus
consisting of three chitinous rods; round the base of this piercing proboscis
is a double crown of papillae, each bearing a spine (Fig. 90).
Page 185
Fig. 89.—The tail ends of a female Gordius (a) and a male (b) in copula. × 1.5. (From
G. Meissner.[212])
This first larval form breaks through the egg-shell and sinks to the bottom
of the water, where it moves about sluggishly and awaits the arrival of the
right host in which to take up its abode. This host is the larva of the Alder-
fly, Sialis lutaria Lin. (vide vol. v. p. 444), and into this it bores and comes
to rest in the muscles or the fat body. It does not form distinct capsules. It
remains in this larva during the following winter, and in the spring passes
over into the imago Sialis. The complete insect frequents the small plants
growing along the water's edge, and falls an easy prey to the predaceous
beetle Pt. niger. The larva is eaten, and undergoing a change becomes the
second larval form mentioned above. It remains in the body of the beetle
during the second winter, and finally returns to the water as the adult some
eighteen or twenty months after it has been hatched from the egg.
Fig. 90.—Embryo or first larval form of Gordius tolosanus taken from the egg. Highly
magnified. a and b, The bristle-bearing papillae on the head; c, the boring
apparatus. (From von Linstow.)
From the above account of the life-history of Gordius it will be seen that the
chances of an egg reaching maturity are comparatively small, and to
compensate for this a very large number of eggs are laid. In addition to the
risk of the larvae not finding the right host at the right time, and of the first
host not being eaten by the second, and the second not being drowned, there
is the danger that the ditches and ponds in which the adults live may dry up,
and, in fact, great numbers of worms perish by this taking place.
G. Meissner.[212])
This first larval form breaks through the egg-shell and sinks to the bottom
of the water, where it moves about sluggishly and awaits the arrival of the
right host in which to take up its abode. This host is the larva of the Alder-
fly, Sialis lutaria Lin. (vide vol. v. p. 444), and into this it bores and comes
to rest in the muscles or the fat body. It does not form distinct capsules. It
remains in this larva during the following winter, and in the spring passes
over into the imago Sialis. The complete insect frequents the small plants
growing along the water's edge, and falls an easy prey to the predaceous
beetle Pt. niger. The larva is eaten, and undergoing a change becomes the
second larval form mentioned above. It remains in the body of the beetle
during the second winter, and finally returns to the water as the adult some
eighteen or twenty months after it has been hatched from the egg.
Fig. 90.—Embryo or first larval form of Gordius tolosanus taken from the egg. Highly
magnified. a and b, The bristle-bearing papillae on the head; c, the boring
apparatus. (From von Linstow.)
From the above account of the life-history of Gordius it will be seen that the
chances of an egg reaching maturity are comparatively small, and to
compensate for this a very large number of eggs are laid. In addition to the
risk of the larvae not finding the right host at the right time, and of the first
host not being eaten by the second, and the second not being drowned, there
is the danger that the ditches and ponds in which the adults live may dry up,
and, in fact, great numbers of worms perish by this taking place.
Page 186
The sex of the adults may be told from their colour, the males being of a
blackish brown, the females of a light clay brown; the former average 120
mm. in length, the latter 170 mm. The males are also more numerous, the
proportion being seven to three. Camerano[213] has drawn attention to the
fact that there is a certain polymorphism in size, form, and colour which is
especially common amongst the males; dwarf forms with mature
reproductive organs exist, and he is of opinion that these differences depend
both on the size of the second host and on the duration of the parasitic life.
In addition to the larva of Sialis lutaria, the first larval stage has also been
found in the larva of Ephemera, Tanypus, Corethra, and Chironomus; the
second in Carabus hortensis Fabr., Procerus (Carabus) coriaceus Linn.,
Calathus fuscipes Goeze, Molops elatus Fabr., several species of
Pterostichus, and a number of other beetles. It is probable that its normal
hosts are S. lutaria and Pt. niger, but it is clear that it often comes to rest in
other insects. The view that the Gordiidae have no special hosts, but may
either pass the whole of their life-history within one and the same animal,
or, on the other hand, may inhabit animals belonging to very different
groups, is held by Villot, who has paid great attention to the subject. He
finds the first larval form encysted in the walls of the alimentary canal in
fishes, such as Leuciscus phoxinus, the minnow, Cobitis barbatula, the
loach, and Petromyzon planeri, the lamprey; in the larvae of Diptera,
Ephemera, and beetles, in Planorbis (a water snail), in Enchytraeus (an
Oligochaet); the second larval form in all kinds of insects, spiders,
Crustacea, fish, frogs, birds (Otis), and in man, and these various habitats
lead him to the conclusion that "Les Gordiens n'ont pas d'hôtes spéciaux."
On the other hand, as von Linstow points out, it is contrary to our
knowledge of parasites that a single species should develop equally well in
the body of warm and cold-blooded Vertebrates and of Insects, and the
explanation of the presence of the larvae in these various forms may either
be that they belong to different species of Gordius or, more probably, that
they are accidentally present, having passed into their hosts with drinking
water.
blackish brown, the females of a light clay brown; the former average 120
mm. in length, the latter 170 mm. The males are also more numerous, the
proportion being seven to three. Camerano[213] has drawn attention to the
fact that there is a certain polymorphism in size, form, and colour which is
especially common amongst the males; dwarf forms with mature
reproductive organs exist, and he is of opinion that these differences depend
both on the size of the second host and on the duration of the parasitic life.
In addition to the larva of Sialis lutaria, the first larval stage has also been
found in the larva of Ephemera, Tanypus, Corethra, and Chironomus; the
second in Carabus hortensis Fabr., Procerus (Carabus) coriaceus Linn.,
Calathus fuscipes Goeze, Molops elatus Fabr., several species of
Pterostichus, and a number of other beetles. It is probable that its normal
hosts are S. lutaria and Pt. niger, but it is clear that it often comes to rest in
other insects. The view that the Gordiidae have no special hosts, but may
either pass the whole of their life-history within one and the same animal,
or, on the other hand, may inhabit animals belonging to very different
groups, is held by Villot, who has paid great attention to the subject. He
finds the first larval form encysted in the walls of the alimentary canal in
fishes, such as Leuciscus phoxinus, the minnow, Cobitis barbatula, the
loach, and Petromyzon planeri, the lamprey; in the larvae of Diptera,
Ephemera, and beetles, in Planorbis (a water snail), in Enchytraeus (an
Oligochaet); the second larval form in all kinds of insects, spiders,
Crustacea, fish, frogs, birds (Otis), and in man, and these various habitats
lead him to the conclusion that "Les Gordiens n'ont pas d'hôtes spéciaux."
On the other hand, as von Linstow points out, it is contrary to our
knowledge of parasites that a single species should develop equally well in
the body of warm and cold-blooded Vertebrates and of Insects, and the
explanation of the presence of the larvae in these various forms may either
be that they belong to different species of Gordius or, more probably, that
they are accidentally present, having passed into their hosts with drinking
water.
Page 187
Fig. 91.—Tarsal joint of an Ephemerid larva into which two Gordius larvae (a, a) have
penetrated. Magnified. (From G. Meissner.)
The number of species of Gordius is large; over 100 are enumerated in the
Compendium der Helminthologie,[214] the great majority of which inhabit
insects.
The life-history of Nectonema is practically unknown; the adults have been
found swimming near the surface of the sea at two places only: Newport,
R.I., and Wood's Holl, Mass., on the south coast of New England. It has
been fished close to the shore, from the end of June to the beginning of
October, when the tide is going out at evening and there is no moon. This
seems to indicate that it avoids the light. When first caught the worms move
actively about, coiling themselves into figures of eight and then uncoiling;
at the same time there is a rhythmical movement caused by waves of
muscular contraction passing down each side of the body alternately; by
this kind of motion they make rapid and definite progress through the water.
It seems probable that the adult Nectonema is preceded by one or more
larval stages, and what appears to be a young form has been obtained from
the thoracic cavity of a prawn, Palaemonetes,[215] which has thus some
claim to be regarded as the host of this species, but nothing is known about
its early life-history.
Sub-Order III. Acanthocephala.
The Acanthocephala, which form the third class of the Nemathelminthes,
consists of but few genera; there are, however, numerous species of very
different size, varying from 10 to 65 cm. long in the female
Gigantorhynchus (Echinorhynchus) gigas, to quite minute forms a few
penetrated. Magnified. (From G. Meissner.)
The number of species of Gordius is large; over 100 are enumerated in the
Compendium der Helminthologie,[214] the great majority of which inhabit
insects.
The life-history of Nectonema is practically unknown; the adults have been
found swimming near the surface of the sea at two places only: Newport,
R.I., and Wood's Holl, Mass., on the south coast of New England. It has
been fished close to the shore, from the end of June to the beginning of
October, when the tide is going out at evening and there is no moon. This
seems to indicate that it avoids the light. When first caught the worms move
actively about, coiling themselves into figures of eight and then uncoiling;
at the same time there is a rhythmical movement caused by waves of
muscular contraction passing down each side of the body alternately; by
this kind of motion they make rapid and definite progress through the water.
It seems probable that the adult Nectonema is preceded by one or more
larval stages, and what appears to be a young form has been obtained from
the thoracic cavity of a prawn, Palaemonetes,[215] which has thus some
claim to be regarded as the host of this species, but nothing is known about
its early life-history.
Sub-Order III. Acanthocephala.
The Acanthocephala, which form the third class of the Nemathelminthes,
consists of but few genera; there are, however, numerous species of very
different size, varying from 10 to 65 cm. long in the female
Gigantorhynchus (Echinorhynchus) gigas, to quite minute forms a few
Page 188
millimetres in length. The adult stage occurs in the alimentary canal of
Vertebrates, as a rule in those which live in, or frequent water; the larvae are
found in the bodies of certain Invertebrates, very frequently small
Crustacea.
Fig. 92.—Two specimens of Echinorhynchus proteus Westrumb., with their anterior
ends embedded in the wall of the intestine of a Pike. Magnified with a lens.
(From Hamann.)
Anatomy.—The body of the mature forms can usually be divided into three
sections—the proboscis, the neck, and the trunk, but the middle region is
not always discernible. The proboscis is armed with rings of hooks (Fig. 93)
arranged in longitudinal rows; they are usually of two kinds, but in E.
proteus of three. They have a certain specific value, but not much stress can
be laid on the number of rings, e.g. in E. angustatus the number varies from
eight to twenty-four. The recurved hooks serve to fasten the parasite very
firmly to the tissues of the host. The proboscis is hollow and retractile; it
can be withdrawn into the body by means of muscles attached internally to
its tip. It does not, however, pass straight into the body-cavity, but is
retracted into a special cavity—the proboscis sheath—with a double
muscular wall. The proboscis sheath may perhaps be looked upon as a
septum, such as is found in some of the Nematomorpha, dividing the body-
cavity into two parts. It is inserted into the body-wall at the junction of the
neck and trunk or of the proboscis and trunk. In addition to the muscles
which withdraw the proboscis into its sheath, there are two retractors
running from the outside of the sheath to the body-wall; these serve to
retract the whole sheath and its contents into the body-cavity of the trunk.
The structure of the skin is essentially like that of Nematodes, but the
details are much more complicated. The whole body is covered by a thin
cuticle secreted by the epidermis, which, as in the other groups, breaks
down and forms a syncytium called the sub-cuticle. The minute fibrils
which penetrate this layer are much more definitely arranged than in
Vertebrates, as a rule in those which live in, or frequent water; the larvae are
found in the bodies of certain Invertebrates, very frequently small
Crustacea.
Fig. 92.—Two specimens of Echinorhynchus proteus Westrumb., with their anterior
ends embedded in the wall of the intestine of a Pike. Magnified with a lens.
(From Hamann.)
Anatomy.—The body of the mature forms can usually be divided into three
sections—the proboscis, the neck, and the trunk, but the middle region is
not always discernible. The proboscis is armed with rings of hooks (Fig. 93)
arranged in longitudinal rows; they are usually of two kinds, but in E.
proteus of three. They have a certain specific value, but not much stress can
be laid on the number of rings, e.g. in E. angustatus the number varies from
eight to twenty-four. The recurved hooks serve to fasten the parasite very
firmly to the tissues of the host. The proboscis is hollow and retractile; it
can be withdrawn into the body by means of muscles attached internally to
its tip. It does not, however, pass straight into the body-cavity, but is
retracted into a special cavity—the proboscis sheath—with a double
muscular wall. The proboscis sheath may perhaps be looked upon as a
septum, such as is found in some of the Nematomorpha, dividing the body-
cavity into two parts. It is inserted into the body-wall at the junction of the
neck and trunk or of the proboscis and trunk. In addition to the muscles
which withdraw the proboscis into its sheath, there are two retractors
running from the outside of the sheath to the body-wall; these serve to
retract the whole sheath and its contents into the body-cavity of the trunk.
The structure of the skin is essentially like that of Nematodes, but the
details are much more complicated. The whole body is covered by a thin
cuticle secreted by the epidermis, which, as in the other groups, breaks
down and forms a syncytium called the sub-cuticle. The minute fibrils
which penetrate this layer are much more definitely arranged than in
Page 189
Nematodes; the largest of them run from without inwards, others run
concentrically round the body. Large oval or spherical nuclei are scattered
in the sub-cuticle, which is further honeycombed by a number of lacunae or
spaces which are described below.
Fig. 93.—A, Five specimens of Echinorhynchus acus Rud. attached to a piece of
intestinal wall, × 4; B, the proboscis of one still more highly magnified.
Within the sub-cuticular layer is found a sheath of circularly-arranged
muscle-fibres, and within this again a sheath of longitudinal muscles which
do not extend into the proboscis; this inner layer lines the body-cavity, there
being no epithelium within it. In their minute structure the muscle-cells
resemble those of Nematodes.
The canals in the sub-cuticle form a very curious system of anastomosing
spaces, in which a clear fluid containing fat globules circulates. The extent
to which the system is developed varies in different species, but in all there
is a pair of longitudinal canals which are situated laterally, and which give
off the subsidiary channels in their course. The above description applies to
the lacunar spaces in the skin of the trunk; those of the proboscis are quite
distinct, and there is no communication between the two sets of spaces; in
fact, the sub-cuticle in which the lacunae are formed is not continuous
across the line of junction of the proboscis and the neck, or, when the latter
is absent, of the proboscis and the trunk, but it is interrupted by the
ingrowth of a thin ring of cuticle which reaches down to the muscular layers
(Fig. 94).
concentrically round the body. Large oval or spherical nuclei are scattered
in the sub-cuticle, which is further honeycombed by a number of lacunae or
spaces which are described below.
Fig. 93.—A, Five specimens of Echinorhynchus acus Rud. attached to a piece of
intestinal wall, × 4; B, the proboscis of one still more highly magnified.
Within the sub-cuticular layer is found a sheath of circularly-arranged
muscle-fibres, and within this again a sheath of longitudinal muscles which
do not extend into the proboscis; this inner layer lines the body-cavity, there
being no epithelium within it. In their minute structure the muscle-cells
resemble those of Nematodes.
The canals in the sub-cuticle form a very curious system of anastomosing
spaces, in which a clear fluid containing fat globules circulates. The extent
to which the system is developed varies in different species, but in all there
is a pair of longitudinal canals which are situated laterally, and which give
off the subsidiary channels in their course. The above description applies to
the lacunar spaces in the skin of the trunk; those of the proboscis are quite
distinct, and there is no communication between the two sets of spaces; in
fact, the sub-cuticle in which the lacunae are formed is not continuous
across the line of junction of the proboscis and the neck, or, when the latter
is absent, of the proboscis and the trunk, but it is interrupted by the
ingrowth of a thin ring of cuticle which reaches down to the muscular layers
(Fig. 94).
Page 190
Fig. 94.—A longitudinal section through the anterior end of Echinorhynchus haeruca
Rud. (From Hamann.) a, The proboscis not fully expanded; b, proboscis-sheath;
c, retractor muscles of the proboscis; d, cerebral ganglion; e, retinaculum
enclosing a nerve; f, one of the retractors of the sheath; g, a lemniscus; h, one of
the spaces in the sub-cuticular tissue; i, longitudinal muscular layer; j, circular
muscular layer; k, line of division between the sub-cuticular tissue of the trunk
and that of the proboscis with the lemnisci.
All the spaces in the skin of the proboscis open ultimately into a circular
canal situated round its base; on each side the canal opens into a sac-like
structure which extends through the body-cavity towards the posterior end
of the animal. These two lateral diverticula are termed the lemnisci. They
have always attracted considerable attention from the workers at the group,
and numerous functions have from time to time been attributed to them.
They are more or less hollow, and their walls consist of sub-cuticular tissue
surrounded with a scanty muscular coat; they contain the same fluid as the
lacunae of the skin of the proboscis, with which they are placed in
communication by means of the circular canal; and it seems most probable
that, as Hamann[216] suggests, they act as reservoirs into which the lacunar
fluid retires when the proboscis is retracted, and which, by means of the
contractions of their muscular coat, force the fluid into the lacunae when the
proboscis is everted, and thus aid in its protrusion.
The parasitic habits of Echinorhynchus have had a deeper influence on the
structure of the body than is the case with the Nematoda. All traces of an
alimentary canal have disappeared, and the animals live entirely by the
imbibition through the skin of the already elaborated fluids of their hosts.
The power of absorbing fluids is shown by the fact that they swell up and
become tense when placed in fresh water.
Rud. (From Hamann.) a, The proboscis not fully expanded; b, proboscis-sheath;
c, retractor muscles of the proboscis; d, cerebral ganglion; e, retinaculum
enclosing a nerve; f, one of the retractors of the sheath; g, a lemniscus; h, one of
the spaces in the sub-cuticular tissue; i, longitudinal muscular layer; j, circular
muscular layer; k, line of division between the sub-cuticular tissue of the trunk
and that of the proboscis with the lemnisci.
All the spaces in the skin of the proboscis open ultimately into a circular
canal situated round its base; on each side the canal opens into a sac-like
structure which extends through the body-cavity towards the posterior end
of the animal. These two lateral diverticula are termed the lemnisci. They
have always attracted considerable attention from the workers at the group,
and numerous functions have from time to time been attributed to them.
They are more or less hollow, and their walls consist of sub-cuticular tissue
surrounded with a scanty muscular coat; they contain the same fluid as the
lacunae of the skin of the proboscis, with which they are placed in
communication by means of the circular canal; and it seems most probable
that, as Hamann[216] suggests, they act as reservoirs into which the lacunar
fluid retires when the proboscis is retracted, and which, by means of the
contractions of their muscular coat, force the fluid into the lacunae when the
proboscis is everted, and thus aid in its protrusion.
The parasitic habits of Echinorhynchus have had a deeper influence on the
structure of the body than is the case with the Nematoda. All traces of an
alimentary canal have disappeared, and the animals live entirely by the
imbibition through the skin of the already elaborated fluids of their hosts.
The power of absorbing fluids is shown by the fact that they swell up and
become tense when placed in fresh water.
Page 191
Until recently no definite excretory organs had been recognised, and the
function of excreting the nitrogenous matter was by some assigned to the
lemnisci. In 1893 Kaiser[217] described in G. gigas two organs which he
called nephridia, placed dorsally to the ducts of the male and female
reproductive organs. Each nephridium, which somewhat resembles a
cauliflower, consists of a stalk or duct, opening at one end into the
reproductive ducts, and at the other branching and breaking up into a
number of secondary and tertiary twigs. The end of each twig is closed by a
membrane pierced with a number of most minute pores, by means of which
it communicates with the body-cavity; on the inner side the membrane
bears a number of long cilia, which keep up an active flickering. The
presence of these cilia is interesting, as elsewhere they are unknown
throughout the Nemathelminthes.
Fig. 95.—A, A longitudinal section through the terminal twigs of the nephridium of
Gigantorhynchus gigas. (From J. E. Kaiser.) Highly magnified. a, Nucleus. B, A
terminal twig more highly magnified; b, the porous membrane.
The nervous system consists of a central ganglion situated in the proboscis
sheath; it is oval and flattened in shape. The ganglion gives off nerves to the
proboscis, and two main trunks which pierce the proboscis-sheath and run
backward surrounded by a cluster of muscle-fibres, the whole being termed
the retinaculum; in the male they are in connexion with a special genital
ganglion which lies near the ductus ejaculatorius.
With the exception of certain sensory papillae in the neighbourhood of the
male genital orifice, and of three similar papillae mentioned by Kaiser on
the proboscis, the Acanthocephala are devoid of sense organs.
The Acanthocephala are dioecious; their generative organs are developed in
connexion with the ligament, a cord-like structure which arises between the
inner and outer layer of the hinder end of the proboscis sheath and traverses
function of excreting the nitrogenous matter was by some assigned to the
lemnisci. In 1893 Kaiser[217] described in G. gigas two organs which he
called nephridia, placed dorsally to the ducts of the male and female
reproductive organs. Each nephridium, which somewhat resembles a
cauliflower, consists of a stalk or duct, opening at one end into the
reproductive ducts, and at the other branching and breaking up into a
number of secondary and tertiary twigs. The end of each twig is closed by a
membrane pierced with a number of most minute pores, by means of which
it communicates with the body-cavity; on the inner side the membrane
bears a number of long cilia, which keep up an active flickering. The
presence of these cilia is interesting, as elsewhere they are unknown
throughout the Nemathelminthes.
Fig. 95.—A, A longitudinal section through the terminal twigs of the nephridium of
Gigantorhynchus gigas. (From J. E. Kaiser.) Highly magnified. a, Nucleus. B, A
terminal twig more highly magnified; b, the porous membrane.
The nervous system consists of a central ganglion situated in the proboscis
sheath; it is oval and flattened in shape. The ganglion gives off nerves to the
proboscis, and two main trunks which pierce the proboscis-sheath and run
backward surrounded by a cluster of muscle-fibres, the whole being termed
the retinaculum; in the male they are in connexion with a special genital
ganglion which lies near the ductus ejaculatorius.
With the exception of certain sensory papillae in the neighbourhood of the
male genital orifice, and of three similar papillae mentioned by Kaiser on
the proboscis, the Acanthocephala are devoid of sense organs.
The Acanthocephala are dioecious; their generative organs are developed in
connexion with the ligament, a cord-like structure which arises between the
inner and outer layer of the hinder end of the proboscis sheath and traverses
Page 192
the body-cavity, ending posteriorly in connexion with the genital ducts. The
testes lie in this ligament; they are paired oval bodies which open each into
a vas deferens. The vasa deferentia each bear three lateral diverticula, the
vesiculae seminales; and three pairs of cement glands pour their secretion
into a duct which opens into the vasa deferentia; the latter unite and open by
a penis which is withdrawn into a genital bursa, but is capable of being
extruded.
Fig. 96.—An optical section through a male Neorhynchus clavaeceps Zed. (From
Hamann.) a, Proboscis; b, proboscis sheath; c, retractor of the proboscis; d,
cerebral ganglion; f, f, retractors of the proboscis sheath; g, g, lemnisci, each with
two giant nuclei; h, space in sub-cuticular layer of the skin; l, ligament; m, m,
testes; o, glands on vas deferens; p, giant nucleus in skin; q, opening of vas
deferens.
The two ovaries are formed in the ligament of the female in a corresponding
position to that occupied by the testes in the male, but at an early stage they
break down into packets of cells, of which those of the peripheral layer
develop into ova at the cost of the central cells, which serve them as a food
supply. As these masses grow and increase in number they rupture the walls
of the ligament, and escape into the body-cavity, in which they float. The
ova are fertilised whilst floating in the fluid of the body-cavity. The eggs
segment and the embryo is formed whilst still in the body of the mother.
The embryos escape by means of a complicated apparatus the details of
which vary in the different species, but which, like many of the organs in
these animals, consists of very few cells with very large nuclei. This
testes lie in this ligament; they are paired oval bodies which open each into
a vas deferens. The vasa deferentia each bear three lateral diverticula, the
vesiculae seminales; and three pairs of cement glands pour their secretion
into a duct which opens into the vasa deferentia; the latter unite and open by
a penis which is withdrawn into a genital bursa, but is capable of being
extruded.
Fig. 96.—An optical section through a male Neorhynchus clavaeceps Zed. (From
Hamann.) a, Proboscis; b, proboscis sheath; c, retractor of the proboscis; d,
cerebral ganglion; f, f, retractors of the proboscis sheath; g, g, lemnisci, each with
two giant nuclei; h, space in sub-cuticular layer of the skin; l, ligament; m, m,
testes; o, glands on vas deferens; p, giant nucleus in skin; q, opening of vas
deferens.
The two ovaries are formed in the ligament of the female in a corresponding
position to that occupied by the testes in the male, but at an early stage they
break down into packets of cells, of which those of the peripheral layer
develop into ova at the cost of the central cells, which serve them as a food
supply. As these masses grow and increase in number they rupture the walls
of the ligament, and escape into the body-cavity, in which they float. The
ova are fertilised whilst floating in the fluid of the body-cavity. The eggs
segment and the embryo is formed whilst still in the body of the mother.
The embryos escape by means of a complicated apparatus the details of
which vary in the different species, but which, like many of the organs in
these animals, consists of very few cells with very large nuclei. This
Page 193
apparatus consists of three parts: the bell, the uterus, and the oviduct. The
bell is a large funnel-shaped structure, which opens into the body-cavity,
and is connected with the end of the ligament; near its lower end, where it is
continuous with the uterus, is a second smaller opening situated dorsally.
By the contraction and expansion of its lips the oval embryos are swallowed
and pass on through the uterus to the oviduct, which opens at the posterior
end of the body. If the bell takes in any of the less mature eggs which are
spherical in shape, they are passed back into the body-cavity through the
above-mentioned dorsal opening, and the same orifice permits the passage
of the spermatozoa even when the bell is full of embryos.
Fig. 97.—An egg of Echinorhynchus acus Rud. surrounded by three egg-shells. Highly
magnified. The egg has segmented, and the cells are differentiated into a, the
entoblast, and b, the ectoblast; c, spines. (From Hamann.)
Embryology.—After fertilisation the egg surrounds itself with several egg-
shells, three of which are usually distinguished; the embryo is already far
advanced in its development by the time it leaves the body of the mother
and passes out into the alimentary canal of the Vertebrate host. It leaves the
body of this second host with the faeces, and is eaten by the first or larval
host, usually a small Crustacean or water-insect, but in some cases a fish,
within whose alimentary canal it casts its membranes and becomes actively
mobile. By means of a ring of hooks developed round the anterior end it
bores its way through the wall of the alimentary canal, and after some time
—three weeks in E. proteus—comes to rest in the body-cavity of its host.
bell is a large funnel-shaped structure, which opens into the body-cavity,
and is connected with the end of the ligament; near its lower end, where it is
continuous with the uterus, is a second smaller opening situated dorsally.
By the contraction and expansion of its lips the oval embryos are swallowed
and pass on through the uterus to the oviduct, which opens at the posterior
end of the body. If the bell takes in any of the less mature eggs which are
spherical in shape, they are passed back into the body-cavity through the
above-mentioned dorsal opening, and the same orifice permits the passage
of the spermatozoa even when the bell is full of embryos.
Fig. 97.—An egg of Echinorhynchus acus Rud. surrounded by three egg-shells. Highly
magnified. The egg has segmented, and the cells are differentiated into a, the
entoblast, and b, the ectoblast; c, spines. (From Hamann.)
Embryology.—After fertilisation the egg surrounds itself with several egg-
shells, three of which are usually distinguished; the embryo is already far
advanced in its development by the time it leaves the body of the mother
and passes out into the alimentary canal of the Vertebrate host. It leaves the
body of this second host with the faeces, and is eaten by the first or larval
host, usually a small Crustacean or water-insect, but in some cases a fish,
within whose alimentary canal it casts its membranes and becomes actively
mobile. By means of a ring of hooks developed round the anterior end it
bores its way through the wall of the alimentary canal, and after some time
—three weeks in E. proteus—comes to rest in the body-cavity of its host.
Page 194
By this time most of the organs of the adult, with the exception of the
reproductive glands, are already well established; the latter only attain
maturity when the first host is eaten by the second, and the larvae find
themselves in the intestine of a Vertebrate.
Fig. 98.—A, A larval Echinorhynchus proteus Westrumb. further developed than in Fig.
97. Highly magnified. The entoblast has developed inside it the proboscis a; b, b,
the giant nuclei of the ectoblast. B, The entoblast at a more advanced stage, the
ectoblast is not shown. The outermost layer of cells will form the muscles of the
body-wall; the body-cavity has appeared; a, proboscis; b, cerebral ganglion; c,
body-cavity; d, d, the testes beginning to appear in the ligament; e, cells which
will form the generative ducts.
Some of the details of the development are very remarkable, and a short
account of them may be given. The segmentation of the egg is unequal; it
results in the formation of a central biscuit-shaped mass of small cells and a
peripheral mass of larger cells; the former is called by Hamann[218] the
entoblast, the latter the ectoblast. From the entoblast arise all the organs of
the body but the sub-cuticle and the associated lemnisci, which are formed
from the ectoblast. The latter has a remarkable history; the cells begin to
break down and lose their outlines, whilst their nuclei fuse together and
form a small number of giant nuclei, which lie scattered throughout the
syncytium thus formed. The syncytium surrounds the entoblast on all sides;
by this time the anteriorly-placed hooks have appeared; in E. proteus there
are ten of these, but the number is not the same in all species. The
syncytium is in a fluid state, with a few gigantic nuclei floating in it; these
now lose their spherical shape, and throwing out processes become
amoeboid; in this way they bud off small portions of their substance, and
from these the oval nuclei of the sub-cuticle and the lemnisci arise. The rest
of the syncytium hardens into the fibrillar matrix of the sub-cuticle, leaving,
however, scattered spaces which form the sub-cuticular sinuses of the adult.
reproductive glands, are already well established; the latter only attain
maturity when the first host is eaten by the second, and the larvae find
themselves in the intestine of a Vertebrate.
Fig. 98.—A, A larval Echinorhynchus proteus Westrumb. further developed than in Fig.
97. Highly magnified. The entoblast has developed inside it the proboscis a; b, b,
the giant nuclei of the ectoblast. B, The entoblast at a more advanced stage, the
ectoblast is not shown. The outermost layer of cells will form the muscles of the
body-wall; the body-cavity has appeared; a, proboscis; b, cerebral ganglion; c,
body-cavity; d, d, the testes beginning to appear in the ligament; e, cells which
will form the generative ducts.
Some of the details of the development are very remarkable, and a short
account of them may be given. The segmentation of the egg is unequal; it
results in the formation of a central biscuit-shaped mass of small cells and a
peripheral mass of larger cells; the former is called by Hamann[218] the
entoblast, the latter the ectoblast. From the entoblast arise all the organs of
the body but the sub-cuticle and the associated lemnisci, which are formed
from the ectoblast. The latter has a remarkable history; the cells begin to
break down and lose their outlines, whilst their nuclei fuse together and
form a small number of giant nuclei, which lie scattered throughout the
syncytium thus formed. The syncytium surrounds the entoblast on all sides;
by this time the anteriorly-placed hooks have appeared; in E. proteus there
are ten of these, but the number is not the same in all species. The
syncytium is in a fluid state, with a few gigantic nuclei floating in it; these
now lose their spherical shape, and throwing out processes become
amoeboid; in this way they bud off small portions of their substance, and
from these the oval nuclei of the sub-cuticle and the lemnisci arise. The rest
of the syncytium hardens into the fibrillar matrix of the sub-cuticle, leaving,
however, scattered spaces which form the sub-cuticular sinuses of the adult.
Page 195
An interesting feature of N. clavaeceps and Arhynchus hemignathi is that
the skin of the adult retains the larval features, and it and the lemnisci
consist of a syncytium with a very few giant nuclei scattered through it.
Hamann counted only eight in the skin and two in each lemniscus in the
example figured on p. 178.
Fig. 99.—A, The larva of Echinorhynchus proteus from the body-cavity of Phoxinus
laevis, with the proboscis retracted and the whole still enclosed in a capsule. B,
A section through the same; a, the invaginated proboscis; b, proboscis sheath; c,
beginning of the neck; d, lemniscus. Highly magnified. (Both from Hamann.)
The whole of the rest of the body is formed by the entoblast. Within the
latter a circular split arises which separates a single layer of outermost cells
from an axial strand of many cells (Fig. 98, B). The split is the future body-
cavity; the axial strand forms the proboscis, its sheath, the cerebral
ganglion, muscles, etc., and the ligament with the contained generative
organs; the outermost layer of cells forms the muscular lining to the skin. It
is interesting to note that these cells destined to become muscle-fibres are at
first arranged as a single layer of cubical epithelial cells lining the body-
cavity; most of them become circular muscle-fibres, but a few are pushed
inwards so as to lie next the body-cavity, and these become the longitudinal
fibres.
Classification.—Until recently the Acanthocephala were supposed to
include but one genus, Echinorhynchus, with several hundred species, but
Hamann[219] has pointed out that these species present differences which
enabled him to divide the group into three families, each with a
corresponding genus. To these I have ventured to add a fourth family, to
include a remarkable species, Arhynchus hemignathi, described below. The
characters of the first three families in the account given below are taken
from Hamann's paper.
the skin of the adult retains the larval features, and it and the lemnisci
consist of a syncytium with a very few giant nuclei scattered through it.
Hamann counted only eight in the skin and two in each lemniscus in the
example figured on p. 178.
Fig. 99.—A, The larva of Echinorhynchus proteus from the body-cavity of Phoxinus
laevis, with the proboscis retracted and the whole still enclosed in a capsule. B,
A section through the same; a, the invaginated proboscis; b, proboscis sheath; c,
beginning of the neck; d, lemniscus. Highly magnified. (Both from Hamann.)
The whole of the rest of the body is formed by the entoblast. Within the
latter a circular split arises which separates a single layer of outermost cells
from an axial strand of many cells (Fig. 98, B). The split is the future body-
cavity; the axial strand forms the proboscis, its sheath, the cerebral
ganglion, muscles, etc., and the ligament with the contained generative
organs; the outermost layer of cells forms the muscular lining to the skin. It
is interesting to note that these cells destined to become muscle-fibres are at
first arranged as a single layer of cubical epithelial cells lining the body-
cavity; most of them become circular muscle-fibres, but a few are pushed
inwards so as to lie next the body-cavity, and these become the longitudinal
fibres.
Classification.—Until recently the Acanthocephala were supposed to
include but one genus, Echinorhynchus, with several hundred species, but
Hamann[219] has pointed out that these species present differences which
enabled him to divide the group into three families, each with a
corresponding genus. To these I have ventured to add a fourth family, to
include a remarkable species, Arhynchus hemignathi, described below. The
characters of the first three families in the account given below are taken
from Hamann's paper.
Page 196
Fig. 100.—Fully formed larva of Echinorhynchus proteus from the body-cavity of
Phoxinus laevis. (From Hamann.) Highly magnified. a, Proboscis; b, bulla; c,
neck; d, trunk; e, e, lemnisci.
Family I. Echinorhynchidae.—The body is elongated and smooth. The
proboscis-sheath has a double wall, and the proboscis is invaginated into it.
The central nerve-ganglion lies in the middle line, as a rule on the posterior
blind end of the proboscis-sheath. The papillae which bear the hooks are
only covered with a chitinous cap at their apex, and the hooks have a
process below. This family is by far the largest; a few species only can be
mentioned. Echinorhynchus proteus lives in its mature form in fishes; the
young forms, up to a centimetre in length, are found living freely in the
intestine of numerous fresh-water fishes. Those found in Gobio fluviatilis,
the gudgeon; Leuciscus virgo; Lota vulgaris, the burbot or eel-pout; young
trout; Thymallus vulgaris, the grayling, seldom surpass this size, but those
found in Acerina cernua, the pope fish; in Abramis bipunctatus; in Esox
lucius,the pike, and in older trout, attain or surpass double the length. As the
parasites grow older they bury their proboscis and neck in the wall of the
intestine, the inner surface of which is studded with the orange-coloured
bodies of the parasites. The proboscis is so deeply sunk in the wall of the
alimentary canal as to form a papilla on its outer surface (Fig. 92). The
larvae of E. proteus are found in the body-cavity of Gammarus pulex, one
of the Amphipod Crustacea, and also in the same position in numerous
fresh-water fishes; they must have passed into this first host by the mouth
and alimentary canal. If the liver of an infested minnow, Leuciscus
phoxinus, be examined, it will be found to contain on its surface numerous
spherical or egg-shaped capsules of an orange colour, 2 to 2.5 mm. in
length; these contain the larval forms of the parasite. They develop into the
adult form when the first host is eaten by a carnivorous fish, but a
complication may take place when the larval form is found in Gammarus,
Phoxinus laevis. (From Hamann.) Highly magnified. a, Proboscis; b, bulla; c,
neck; d, trunk; e, e, lemnisci.
Family I. Echinorhynchidae.—The body is elongated and smooth. The
proboscis-sheath has a double wall, and the proboscis is invaginated into it.
The central nerve-ganglion lies in the middle line, as a rule on the posterior
blind end of the proboscis-sheath. The papillae which bear the hooks are
only covered with a chitinous cap at their apex, and the hooks have a
process below. This family is by far the largest; a few species only can be
mentioned. Echinorhynchus proteus lives in its mature form in fishes; the
young forms, up to a centimetre in length, are found living freely in the
intestine of numerous fresh-water fishes. Those found in Gobio fluviatilis,
the gudgeon; Leuciscus virgo; Lota vulgaris, the burbot or eel-pout; young
trout; Thymallus vulgaris, the grayling, seldom surpass this size, but those
found in Acerina cernua, the pope fish; in Abramis bipunctatus; in Esox
lucius,the pike, and in older trout, attain or surpass double the length. As the
parasites grow older they bury their proboscis and neck in the wall of the
intestine, the inner surface of which is studded with the orange-coloured
bodies of the parasites. The proboscis is so deeply sunk in the wall of the
alimentary canal as to form a papilla on its outer surface (Fig. 92). The
larvae of E. proteus are found in the body-cavity of Gammarus pulex, one
of the Amphipod Crustacea, and also in the same position in numerous
fresh-water fishes; they must have passed into this first host by the mouth
and alimentary canal. If the liver of an infested minnow, Leuciscus
phoxinus, be examined, it will be found to contain on its surface numerous
spherical or egg-shaped capsules of an orange colour, 2 to 2.5 mm. in
length; these contain the larval forms of the parasite. They develop into the
adult form when the first host is eaten by a carnivorous fish, but a
complication may take place when the larval form is found in Gammarus,
Page 197
as the latter, the first host, may be eaten by a fish (intermediate host) in
which the larva does not become mature, and only develops sexual organs
when eaten by a carnivorous fish (second host). The larval form is also
found in Nemachilus barbatulus, Gobio fluviatilis, and the sticklebacks
Gasterosteus aculeatus and G. pungitius.
E. clavula Duj. is found in Salmo fario, Abramis brama, Cyprinus carpio,
Gobius niger, Lepadogaster gouanii, etc.; E. linstowi Ham. in Leuciscus
idus, Abramis ballerus, Abramis bipunctatus, and Acipenser huso; E. lutzii
Ham. was found by Dr. Lutz in Brazil in the intestine of Bufo agua; E.
angustatus Rud. occurs in such numbers in the perch, Perca fluviatilis, as to
almost occlude the lumen of the intestine, and one out of every three or four
fish in certain districts is infested by it. It is also found in the pike, Esox
lucius, and the barbel, Barbus vulgaris. The first or larval host of this
species is the Isopod Asellus aquaticus. E. moniliformis Brews. is stated to
attain maturity in the human intestine. Except for the fact that G. gigas has
once been observed in the same place, this is the only human parasite
amongst the Acanthocephala. Its normal second hosts are Mus decumanus
and Myoxus quercinus, and its first or larval host, the larvae of the beetle
Blaps mucronata. E. porrigens Rud. is found in considerable numbers in the
small intestine of a fin-whale (Balaenoptera sibbaldii), and E. strumosus
Rud., in the small intestine of a seal (Phoca vitulina), and in the body-
cavity of the angler fish (Lophius piscatorius). E. acus is common in the
whiting, Gadus merlangus.
Family II. Gigantorhynchidae.—Large forms with ringed, flattened, and
Taenia-like bodies. The hook-papillae are covered all over with transparent
chitinous sheaths with two root-like processes. The proboscis-sheath is
muscular and without a lumen. The central nervous system is excentrically
placed below the middle of the so-called sheath. The lemnisci are long
twisted tubes with a central canal.
Hamann places three species in this family: Gigantorhynchus echinodiscus,
G. spira, and G. taenioides; but as he points out that E. gigas resembles
these in its more important structural features, it seems advisable to include
it here under the name G. gigas. The members of the first family often
which the larva does not become mature, and only develops sexual organs
when eaten by a carnivorous fish (second host). The larval form is also
found in Nemachilus barbatulus, Gobio fluviatilis, and the sticklebacks
Gasterosteus aculeatus and G. pungitius.
E. clavula Duj. is found in Salmo fario, Abramis brama, Cyprinus carpio,
Gobius niger, Lepadogaster gouanii, etc.; E. linstowi Ham. in Leuciscus
idus, Abramis ballerus, Abramis bipunctatus, and Acipenser huso; E. lutzii
Ham. was found by Dr. Lutz in Brazil in the intestine of Bufo agua; E.
angustatus Rud. occurs in such numbers in the perch, Perca fluviatilis, as to
almost occlude the lumen of the intestine, and one out of every three or four
fish in certain districts is infested by it. It is also found in the pike, Esox
lucius, and the barbel, Barbus vulgaris. The first or larval host of this
species is the Isopod Asellus aquaticus. E. moniliformis Brews. is stated to
attain maturity in the human intestine. Except for the fact that G. gigas has
once been observed in the same place, this is the only human parasite
amongst the Acanthocephala. Its normal second hosts are Mus decumanus
and Myoxus quercinus, and its first or larval host, the larvae of the beetle
Blaps mucronata. E. porrigens Rud. is found in considerable numbers in the
small intestine of a fin-whale (Balaenoptera sibbaldii), and E. strumosus
Rud., in the small intestine of a seal (Phoca vitulina), and in the body-
cavity of the angler fish (Lophius piscatorius). E. acus is common in the
whiting, Gadus merlangus.
Family II. Gigantorhynchidae.—Large forms with ringed, flattened, and
Taenia-like bodies. The hook-papillae are covered all over with transparent
chitinous sheaths with two root-like processes. The proboscis-sheath is
muscular and without a lumen. The central nervous system is excentrically
placed below the middle of the so-called sheath. The lemnisci are long
twisted tubes with a central canal.
Hamann places three species in this family: Gigantorhynchus echinodiscus,
G. spira, and G. taenioides; but as he points out that E. gigas resembles
these in its more important structural features, it seems advisable to include
it here under the name G. gigas. The members of the first family often
Page 198
present a transversely ringed appearance after death, but the
Gigantorhynchidae are ringed when alive, and the circular canals in the skin
show a certain regularity, being arranged one between each two rings. There
is no lumen in the proboscis-sheath, which is not attached to the boundary
between the proboscis and the trunk, but to the inner surface of the
proboscis, and the whole can be retracted within the anterior portion of the
body, which is invaginable. There are always eight cement-glands, and
other differences exist in the musculature, hooks, and position of the
nervous system.
G. gigas occurs in the adult state in the small intestine of swine; in Europe
its first or larval host is believed to be the grubs of Melolontha vulgaris and
Cetonia aurata, but these beetles are absent from America, though the
parasite infests American hogs. Stiles[220] has recently made some
experiments which tend to show that in the United States the source of
infection is some species of the beetle Lachnosterna, and he has succeeded
in infecting the grub of L. arcuata by feeding it on the eggs of the parasite;
from one larva he took 300 parasites six weeks after feeding it. L. arcuata
is, like M. vulgaris, phytophagous, but the grubs of both the beetles are fond
of frequenting manure heaps and patches of dung, and thus are much
exposed to the dangers of infection.
G. echinodiscus inhabits the intestine of ant-eaters, having been found in
Myrmecophaga jubata and Cycloturus didactylus. G. spira lives in the king
vulture Sarcorhampus papa, and G. taenioides in Dicholophus cristatus, a
species of Cariama.
Family III. Neorhynchidae.—Sexual maturity is reached in the larval
stage. The proboscis-sheath has a single wall. A few giant nuclei only are
found in the sub-cuticle and in the lemnisci. The circular muscle layer is
very simply developed. The longitudinal muscle-cells are only present in
certain places.
This family includes two species, Neorhynchus clavaeceps and N. agilis,
which afford interesting examples of paedogenesis. The sub-cuticle and the
lemnisci are dominated by a few giant nuclei, which remain in the
Gigantorhynchidae are ringed when alive, and the circular canals in the skin
show a certain regularity, being arranged one between each two rings. There
is no lumen in the proboscis-sheath, which is not attached to the boundary
between the proboscis and the trunk, but to the inner surface of the
proboscis, and the whole can be retracted within the anterior portion of the
body, which is invaginable. There are always eight cement-glands, and
other differences exist in the musculature, hooks, and position of the
nervous system.
G. gigas occurs in the adult state in the small intestine of swine; in Europe
its first or larval host is believed to be the grubs of Melolontha vulgaris and
Cetonia aurata, but these beetles are absent from America, though the
parasite infests American hogs. Stiles[220] has recently made some
experiments which tend to show that in the United States the source of
infection is some species of the beetle Lachnosterna, and he has succeeded
in infecting the grub of L. arcuata by feeding it on the eggs of the parasite;
from one larva he took 300 parasites six weeks after feeding it. L. arcuata
is, like M. vulgaris, phytophagous, but the grubs of both the beetles are fond
of frequenting manure heaps and patches of dung, and thus are much
exposed to the dangers of infection.
G. echinodiscus inhabits the intestine of ant-eaters, having been found in
Myrmecophaga jubata and Cycloturus didactylus. G. spira lives in the king
vulture Sarcorhampus papa, and G. taenioides in Dicholophus cristatus, a
species of Cariama.
Family III. Neorhynchidae.—Sexual maturity is reached in the larval
stage. The proboscis-sheath has a single wall. A few giant nuclei only are
found in the sub-cuticle and in the lemnisci. The circular muscle layer is
very simply developed. The longitudinal muscle-cells are only present in
certain places.
This family includes two species, Neorhynchus clavaeceps and N. agilis,
which afford interesting examples of paedogenesis. The sub-cuticle and the
lemnisci are dominated by a few giant nuclei, which remain in the
Page 199
embryonic state and do not break up into numerous nuclei as in other forms.
The musculature is but little developed and the longitudinal sheath hardly
exists. The proboscis-sheath consists of a simple muscular layer, and the
short proboscis has few hooks and presents an embryonic appearance.
The sexually-mature form lives in the carp, Cyprinus carpio; the larval
form is found, according to Villot,[221] encysted in the fat bodies of the larva
of Sialis lutaria, one of the Neuroptera, and in the alimentary canal of the
leech Nephelis octocula, and successful experiments have been made in
infecting some species of the water snail Limnaea. N. agilis occurs in Mugil
auratus and M. cephalus.
Family IV. Arhynchidae.—Short forms with the body divided into three
well-marked regions—head, collar, and trunk. The head is pitted, the collar
smooth, and the trunk wrinkled, not annulated, in spirit specimens. There is
no eversible introvert, and no introvert sheath and no hooks. The sub-cuticle
and the lemnisci have a few giant nuclei, and the lemnisci are long and
coiled.[222]
This family resembles the Gigantorhynchidae in the length and curvature of
its lemnisci, and the Neorhynchidae in the persistence of the embryonic
condition of the nuclei in the sub-cuticle and the lemnisci; but in the shape
of the body, its division into three well-marked regions, the absence of
eversible proboscis, proboscis sheath, and hooks it stands alone, though it is
nearer to the Neorhynchidae than to either of the other families.
The single species Arhynchus hemignathi was found attached to the skin
around the anus of a Sandwich Island bird, Hemignathus proceros. The bird
is a member of a family Drepanididae, which is entirely confined to the
Sandwich Island group. Professor Newton tells me that it is probable that
the "food of Hemignathus consists entirely of insects which it finds in or
under the bark of trees," hence it is probable that the second host of this
parasite, if such exists, must be looked for amongst the Insecta.
The musculature is but little developed and the longitudinal sheath hardly
exists. The proboscis-sheath consists of a simple muscular layer, and the
short proboscis has few hooks and presents an embryonic appearance.
The sexually-mature form lives in the carp, Cyprinus carpio; the larval
form is found, according to Villot,[221] encysted in the fat bodies of the larva
of Sialis lutaria, one of the Neuroptera, and in the alimentary canal of the
leech Nephelis octocula, and successful experiments have been made in
infecting some species of the water snail Limnaea. N. agilis occurs in Mugil
auratus and M. cephalus.
Family IV. Arhynchidae.—Short forms with the body divided into three
well-marked regions—head, collar, and trunk. The head is pitted, the collar
smooth, and the trunk wrinkled, not annulated, in spirit specimens. There is
no eversible introvert, and no introvert sheath and no hooks. The sub-cuticle
and the lemnisci have a few giant nuclei, and the lemnisci are long and
coiled.[222]
This family resembles the Gigantorhynchidae in the length and curvature of
its lemnisci, and the Neorhynchidae in the persistence of the embryonic
condition of the nuclei in the sub-cuticle and the lemnisci; but in the shape
of the body, its division into three well-marked regions, the absence of
eversible proboscis, proboscis sheath, and hooks it stands alone, though it is
nearer to the Neorhynchidae than to either of the other families.
The single species Arhynchus hemignathi was found attached to the skin
around the anus of a Sandwich Island bird, Hemignathus proceros. The bird
is a member of a family Drepanididae, which is entirely confined to the
Sandwich Island group. Professor Newton tells me that it is probable that
the "food of Hemignathus consists entirely of insects which it finds in or
under the bark of trees," hence it is probable that the second host of this
parasite, if such exists, must be looked for amongst the Insecta.
Page 200
CHAPTER VII
CHAETOGNATHA
STRUCTURE—REPRODUCTION—HABITS—FOOD—CLASSIFICATION TABLE OF
IDENTIFICATION
At certain seasons and at certain times of the day the naturalist who is
investigating the fauna of the surface of the sea is apt to find his tow-net
crammed with innumerable transparent spindle-shaped animals, which by
their number and the way in which they become entangled with rarer
objects, often render useless the result of his labours. These animals belong
to the class Chaetognatha, which includes three genera, Sagitta, Spadella,
and Krohnia. Amongst them are divided about twenty species, some of
which, however, are of doubtful value.
Anatomy.—The body of these animals is as transparent as crystal; it is
elongated, and bears a resemblance to certain torpedos, except that the head
forms a somewhat blunt termination to the spindle-shaped body. The tail
bears a caudal fin, and Spadella and Krohnia have a single pair, and Sagitta
two pairs, of lateral fins; all of which are flattened horizontally.
The body is externally divisible into three regions—head, trunk, and tail—
and these correspond with the arrangement of the internal organs.
Fig. 101.—Sagitta bipunctata. a, Vesicula seminalis. × 4. (After Hertwig.)
The head is surrounded by a fold of skin, forming a hood, which is most
prominent at the sides (Fig. 102, g); within the hood the head bears from
CHAETOGNATHA
STRUCTURE—REPRODUCTION—HABITS—FOOD—CLASSIFICATION TABLE OF
IDENTIFICATION
At certain seasons and at certain times of the day the naturalist who is
investigating the fauna of the surface of the sea is apt to find his tow-net
crammed with innumerable transparent spindle-shaped animals, which by
their number and the way in which they become entangled with rarer
objects, often render useless the result of his labours. These animals belong
to the class Chaetognatha, which includes three genera, Sagitta, Spadella,
and Krohnia. Amongst them are divided about twenty species, some of
which, however, are of doubtful value.
Anatomy.—The body of these animals is as transparent as crystal; it is
elongated, and bears a resemblance to certain torpedos, except that the head
forms a somewhat blunt termination to the spindle-shaped body. The tail
bears a caudal fin, and Spadella and Krohnia have a single pair, and Sagitta
two pairs, of lateral fins; all of which are flattened horizontally.
The body is externally divisible into three regions—head, trunk, and tail—
and these correspond with the arrangement of the internal organs.
Fig. 101.—Sagitta bipunctata. a, Vesicula seminalis. × 4. (After Hertwig.)
The head is surrounded by a fold of skin, forming a hood, which is most
prominent at the sides (Fig. 102, g); within the hood the head bears from
Page 201
two to four rows of short spines, and outside these a right and left row of
sickle-shaped hooks, the free ends of which in a state of rest converge round
the mouth, but when disturbed these hooks can be widely divaricated.
The cavity of the body, or coelom, is divided into three distinct chambers by
the presence of two thin transverse walls or septa, one situated between the
head and the trunk, the other between the trunk and the tail (Figs. 104, 105).
In the head, this cavity is much reduced by the presence of special muscles
which move the spines, hooks, etc.; and in the small species, such as
Spadella cephaloptera, the other two cavities are almost entirely occupied
by the digestive and reproductive organs[223]; but in the large species, e.g.
Sagitta hexaptera, a considerable space is left between the internal organs
and the skin, and this is occupied by a coelomic fluid. If the skin of one of
these larger species be punctured the fluid escapes and the animal shrivels
up. A longitudinal partition or mesentery, with numerous pores in it, runs
through these spaces, dividing the body-cavity into a right and left half; in
the region of the trunk this mesentery supports the alimentary canal.
In addition to certain muscles in the head, which move the hooks, etc., there
is a muscular lining to the body-wall. This is divided into two dorsal and
two ventral bands, much in the same way as in Nematodes. The muscle
fibres are striated.
The mouth, situated either terminally—Spadella marioni[224]—or below the
head, leads into a pharynx; this passes into an intestine lined by a single
layer of ciliated cells with a few glandular ones intermingled. The intestine
runs straight through the body without loop or coil, and opens by an anus
situated at the junction of the trunk and the tail. In most cases the anus is
ventral or on the lower surface, but Gourret asserts that in Spadella marioni
it is on the upper surface.
There are no special respiratory, excretory, or circulatory organs, unless a
glandular structure described by Gourret in the head of Spadella marioni be
a real kidney.
sickle-shaped hooks, the free ends of which in a state of rest converge round
the mouth, but when disturbed these hooks can be widely divaricated.
The cavity of the body, or coelom, is divided into three distinct chambers by
the presence of two thin transverse walls or septa, one situated between the
head and the trunk, the other between the trunk and the tail (Figs. 104, 105).
In the head, this cavity is much reduced by the presence of special muscles
which move the spines, hooks, etc.; and in the small species, such as
Spadella cephaloptera, the other two cavities are almost entirely occupied
by the digestive and reproductive organs[223]; but in the large species, e.g.
Sagitta hexaptera, a considerable space is left between the internal organs
and the skin, and this is occupied by a coelomic fluid. If the skin of one of
these larger species be punctured the fluid escapes and the animal shrivels
up. A longitudinal partition or mesentery, with numerous pores in it, runs
through these spaces, dividing the body-cavity into a right and left half; in
the region of the trunk this mesentery supports the alimentary canal.
In addition to certain muscles in the head, which move the hooks, etc., there
is a muscular lining to the body-wall. This is divided into two dorsal and
two ventral bands, much in the same way as in Nematodes. The muscle
fibres are striated.
The mouth, situated either terminally—Spadella marioni[224]—or below the
head, leads into a pharynx; this passes into an intestine lined by a single
layer of ciliated cells with a few glandular ones intermingled. The intestine
runs straight through the body without loop or coil, and opens by an anus
situated at the junction of the trunk and the tail. In most cases the anus is
ventral or on the lower surface, but Gourret asserts that in Spadella marioni
it is on the upper surface.
There are no special respiratory, excretory, or circulatory organs, unless a
glandular structure described by Gourret in the head of Spadella marioni be
a real kidney.
Page 202
The nervous system consists of a supra-oesophageal ganglion or brain
situated in the head, and of a ventral ganglion lying in the trunk; both these
nerve centres are embedded in the epidermis, and are connected with one
another by means of two stout peri-oesophageal nerves (Figs. 102, 104).
The brain also gives off a pair of nerves to the eyes, another pair to the
olfactory organ, and a pair which ultimately meet one another and so form a
ring; on this are certain ganglia giving off nerves which supply the muscles
of the head. Both the chief ganglia give off numerous nerves, which divide
and split up into a network of fibres which permeate the whole skin.
The sense organs are comparatively simple. A pair of very small eyes lie in
the skin of the head; they are of complex structure, and to some extent
remind one of the simple eyes of certain Crustacea. Behind the eyes and
also on the upper surface of the animal is an unpaired organ which is
usually described as olfactory in function (Figs. 103, 105). This is a ring-
shaped modification of the epidermis drawn out into different shapes in the
various species. The modified epidermal cells bear long cilia. The
remaining sensory organs found in the group consist of clumps of modified
cells scattered in round groups over the surface of the body and of the fins.
The central cells of each group bear long tactile hairs, and are surrounded
by supporting cells.
Fig. 102.—Head of Sagitta bipunctata. A, Dorsal view; B, ventral view. × about 33.
(From Hertwig.) A, a, spines; b, nerves to lateral cephalic ganglia; c, hooks; d,
cephalic ganglion; e, olfactory nerve; f, optic nerve; g, hood; h, commissure to
ventral ganglion; j, olfactory organ: B, a, c, and g as in A; k, mouth.
The Chaetognatha are hermaphrodite, and carry the female organs in the
trunk, the male in the tail. In a mature specimen the two ovaries occupy
almost all the space in the trunk between the alimentary canal and the skin,
situated in the head, and of a ventral ganglion lying in the trunk; both these
nerve centres are embedded in the epidermis, and are connected with one
another by means of two stout peri-oesophageal nerves (Figs. 102, 104).
The brain also gives off a pair of nerves to the eyes, another pair to the
olfactory organ, and a pair which ultimately meet one another and so form a
ring; on this are certain ganglia giving off nerves which supply the muscles
of the head. Both the chief ganglia give off numerous nerves, which divide
and split up into a network of fibres which permeate the whole skin.
The sense organs are comparatively simple. A pair of very small eyes lie in
the skin of the head; they are of complex structure, and to some extent
remind one of the simple eyes of certain Crustacea. Behind the eyes and
also on the upper surface of the animal is an unpaired organ which is
usually described as olfactory in function (Figs. 103, 105). This is a ring-
shaped modification of the epidermis drawn out into different shapes in the
various species. The modified epidermal cells bear long cilia. The
remaining sensory organs found in the group consist of clumps of modified
cells scattered in round groups over the surface of the body and of the fins.
The central cells of each group bear long tactile hairs, and are surrounded
by supporting cells.
Fig. 102.—Head of Sagitta bipunctata. A, Dorsal view; B, ventral view. × about 33.
(From Hertwig.) A, a, spines; b, nerves to lateral cephalic ganglia; c, hooks; d,
cephalic ganglion; e, olfactory nerve; f, optic nerve; g, hood; h, commissure to
ventral ganglion; j, olfactory organ: B, a, c, and g as in A; k, mouth.
The Chaetognatha are hermaphrodite, and carry the female organs in the
trunk, the male in the tail. In a mature specimen the two ovaries occupy
almost all the space in the trunk between the alimentary canal and the skin,
Page 203
and each is supported by a narrow lateral mesentery. The ovary is traversed
by a oviduct which often contains spermatozoa; it is not clear how the eggs
make their way into the oviduct, which seems to have no internal opening
and to act largely as a receptaculum seminis. The oviducts open externally
on the upper side at the base of the lateral fin, close to the junction of the
tail and the trunk.
The cavity of the tail is divided into two lateral chambers by the extension
backward of the median vertical mesentery. In each of these a testis and a
vas deferens are found. The testes are solid ridges formed by the growth of
the lining cells of this part of the body-cavity; the cells mature into
spermatozoa, which break off and float freely in the coelomic fluid. At the
breeding season the whole tail may be crowded with masses of
spermatozoa, which are kept in a more or less regular circulation by the
ciliated cells lining the body-wall. The vas deferens opens internally into
the space where the spermatozoa lie, and at the other end into a vesicula
seminis, which opens to the exterior. The position of the latter structure
varies, and is of some systematic value.
The eggs are laid in the water and as a rule float at the surface of the sea.
Spadella cephaloptera is, however, an exception to this rule, as it attaches
its eggs by means of a gelatinous stalk to sea-weeds. The segmentation of
the ovum is regular, and gives rise to a two-layered stage or gastrula, which
opens by a pore, the blastopore. This does not, however, become the mouth,
but closes up and the mouth arises at the opposite pole. Perhaps the most
interesting feature of the development of Sagitta is that the cells destined to
form the reproductive organs separate from the other cells of the embryo at
a very early date, whilst it is still in the gastrula stage. There is no larval
form, but the young hatch out from the egg in a state resembling the adult in
all respects but that of size.
by a oviduct which often contains spermatozoa; it is not clear how the eggs
make their way into the oviduct, which seems to have no internal opening
and to act largely as a receptaculum seminis. The oviducts open externally
on the upper side at the base of the lateral fin, close to the junction of the
tail and the trunk.
The cavity of the tail is divided into two lateral chambers by the extension
backward of the median vertical mesentery. In each of these a testis and a
vas deferens are found. The testes are solid ridges formed by the growth of
the lining cells of this part of the body-cavity; the cells mature into
spermatozoa, which break off and float freely in the coelomic fluid. At the
breeding season the whole tail may be crowded with masses of
spermatozoa, which are kept in a more or less regular circulation by the
ciliated cells lining the body-wall. The vas deferens opens internally into
the space where the spermatozoa lie, and at the other end into a vesicula
seminis, which opens to the exterior. The position of the latter structure
varies, and is of some systematic value.
The eggs are laid in the water and as a rule float at the surface of the sea.
Spadella cephaloptera is, however, an exception to this rule, as it attaches
its eggs by means of a gelatinous stalk to sea-weeds. The segmentation of
the ovum is regular, and gives rise to a two-layered stage or gastrula, which
opens by a pore, the blastopore. This does not, however, become the mouth,
but closes up and the mouth arises at the opposite pole. Perhaps the most
interesting feature of the development of Sagitta is that the cells destined to
form the reproductive organs separate from the other cells of the embryo at
a very early date, whilst it is still in the gastrula stage. There is no larval
form, but the young hatch out from the egg in a state resembling the adult in
all respects but that of size.
Page 204
Fig. 103.—Spadella cephaloptera. Dorsal view. x 30. (From Hertwig.) a, Cephalic
ganglion; b, commissure to ventral ganglion; c, olfactory organ; d, alimentary
canal; e, ovary; f, oviduct; g, testis; h, vesicula seminalis.
Habits.—The Chaetognatha are essentially pelagic, and resemble many
other creatures that dwell at the surface of the ocean in being almost
completely transparent. Most species have been taken far out at sea, but
some are perhaps rather more numerous near the coast, and one species,
Spadella cephaloptera, is littoral. They swim by means of muscular
movements of the whole body; the fins have no movement of their own,
and seem to serve as balancers, and not as locomotory organs. Although
usually found at the surface of the water, many species have been taken at
considerable depths. Chun[225] states that they are found in countless
numbers at depths of from 100 metres to 1300 metres. The commonest
species at these depths are Sagitta hexaptera and Sagitta serratodentata.
Sagitta bipunctata, according to the same authority, confines itself to the
surface. Whether the change of depth is diurnal, or whether it has any
relation to sexual maturity, or to any other cause, has not been satisfactorily
determined.
The food of the Chaetognatha consists of floating diatoms, Infusoria, small
larvae, and such Copepods as Calanus finmarchicus, and small Amphipods
as Phoxus plumosus.[226] At times they also devour small larval or post-
larval fishes, and owing to their incredible numbers, they doubtless do
considerable damage to sea fisheries. It is also recorded that they eat one
another, and specimens have been taken which have ingested the whole
body of another Sagitta except the head, which hangs out of the mouth of
the eater, and gives it the appearance of a double-headed monster.[227] It has
ganglion; b, commissure to ventral ganglion; c, olfactory organ; d, alimentary
canal; e, ovary; f, oviduct; g, testis; h, vesicula seminalis.
Habits.—The Chaetognatha are essentially pelagic, and resemble many
other creatures that dwell at the surface of the ocean in being almost
completely transparent. Most species have been taken far out at sea, but
some are perhaps rather more numerous near the coast, and one species,
Spadella cephaloptera, is littoral. They swim by means of muscular
movements of the whole body; the fins have no movement of their own,
and seem to serve as balancers, and not as locomotory organs. Although
usually found at the surface of the water, many species have been taken at
considerable depths. Chun[225] states that they are found in countless
numbers at depths of from 100 metres to 1300 metres. The commonest
species at these depths are Sagitta hexaptera and Sagitta serratodentata.
Sagitta bipunctata, according to the same authority, confines itself to the
surface. Whether the change of depth is diurnal, or whether it has any
relation to sexual maturity, or to any other cause, has not been satisfactorily
determined.
The food of the Chaetognatha consists of floating diatoms, Infusoria, small
larvae, and such Copepods as Calanus finmarchicus, and small Amphipods
as Phoxus plumosus.[226] At times they also devour small larval or post-
larval fishes, and owing to their incredible numbers, they doubtless do
considerable damage to sea fisheries. It is also recorded that they eat one
another, and specimens have been taken which have ingested the whole
body of another Sagitta except the head, which hangs out of the mouth of
the eater, and gives it the appearance of a double-headed monster.[227] It has
Page 205
been said that they attack hydroid polypes, but here at any rate they do not
have it all their own way. Masterman[228] has figured the apical group of
five polypes of Obelia, three of which are engaged in ingesting as many
young Sagitta.
They exist in incredible numbers; Grassi describes the surface of the sea at
Messina on certain days as being literally covered with them, and they must
form the food supply of numerous animals which prey upon the pelagic
fauna. The immense number of individuals is probably accounted for to
some extent by the fact that they lay eggs all the year round, and pass
through a very short and rapid development. They are not known to be
phosphorescent.
Classification.—The features of the Chaetognatha which have most
systematic value are the size of the adult, the relations of the length to the
breadth, and of the three divisions to one another; the size, number, and
position of the lateral fins, and of the hooks and spines on the head; the
thickness of the epidermis, and the structure of the olfactory organ; and,
finally, the form of the reproductive organs.
Strodtmann,[229] who gives the latest and most complete account of the
species of Chaetognatha, arranges them under three genera, which he
characterises as follows:—
(i.) Sagitta Slabber.—Two pairs of lateral fins, two rows of spines on the
head. The lateral thickening of the epidermis absent or insignificant.
Under this genus are included nine definite species and five others—S.
gracilis Verrill, S. elegans Verrill, S. darwini Grassi, S. diptera d'Orbigny,
and S. triptera d'Orbigny—whose position, owing to the inadequacy of their
description, is of doubtful validity.
have it all their own way. Masterman[228] has figured the apical group of
five polypes of Obelia, three of which are engaged in ingesting as many
young Sagitta.
They exist in incredible numbers; Grassi describes the surface of the sea at
Messina on certain days as being literally covered with them, and they must
form the food supply of numerous animals which prey upon the pelagic
fauna. The immense number of individuals is probably accounted for to
some extent by the fact that they lay eggs all the year round, and pass
through a very short and rapid development. They are not known to be
phosphorescent.
Classification.—The features of the Chaetognatha which have most
systematic value are the size of the adult, the relations of the length to the
breadth, and of the three divisions to one another; the size, number, and
position of the lateral fins, and of the hooks and spines on the head; the
thickness of the epidermis, and the structure of the olfactory organ; and,
finally, the form of the reproductive organs.
Strodtmann,[229] who gives the latest and most complete account of the
species of Chaetognatha, arranges them under three genera, which he
characterises as follows:—
(i.) Sagitta Slabber.—Two pairs of lateral fins, two rows of spines on the
head. The lateral thickening of the epidermis absent or insignificant.
Under this genus are included nine definite species and five others—S.
gracilis Verrill, S. elegans Verrill, S. darwini Grassi, S. diptera d'Orbigny,
and S. triptera d'Orbigny—whose position, owing to the inadequacy of their
description, is of doubtful validity.
Page 206
Fig. 104.—Sagitta hexaptera. Ventral view. × 4. (From Hertwig.) a, Mouth; b, hooks; c,
anterior septum; d, alimentary canal; e, commissure from the brain to the ventral
ganglion; f, ventral ganglion; g, ovary; h, oviduct; i, posterior septum; j, testis; k,
vesicula seminalis.
The distribution of the other species may be mentioned. S. hexaptera is the
largest Chaetognath known, and reaches in the adult stage a length of 7 cm.
It is very widely distributed, being found in practically all the temperate and
warm seas, usually at the surface of the water, though at times it is found at
a depth of one metre, or even deeper. S. lyra, Mediterranean, very rare. S.
tricuspidata, widely distributed. S. magna, Mediterranean and Madeiran,
living at the surface. S. bipunctata, the most frequently described form,
smaller than the preceding species, 1-2 cm. in length, widely distributed,
and as a rule living near the coast line. S. serratodentata, Mediterranean. S.
enflata, on the surface of the sea, Mediterranean and Madeiran. S. minima, a
very small species, 1 cm. in length, Mediterranean. S. falcidens, Atlantic,
off the coast of New Jersey.
(ii.) Krohnia Langerhans.—A single lateral fin extending on to both trunk
and tail segment, no lateral epidermal extensions behind the head, only one
row of spines on the head. Trunk longer than the tail.
Krohnia has but two species: K. hamata Möbius, with a length of 3-4 cm.,
found in the North Atlantic and at considerable depths, 200 to 300 fathoms;
and K. subtilis Grassi, 1.5 cm. long, with an extraordinary slender body and
a relatively large head, found at Messina, but very rare; as a rule only one
specimen has been found at a time.
anterior septum; d, alimentary canal; e, commissure from the brain to the ventral
ganglion; f, ventral ganglion; g, ovary; h, oviduct; i, posterior septum; j, testis; k,
vesicula seminalis.
The distribution of the other species may be mentioned. S. hexaptera is the
largest Chaetognath known, and reaches in the adult stage a length of 7 cm.
It is very widely distributed, being found in practically all the temperate and
warm seas, usually at the surface of the water, though at times it is found at
a depth of one metre, or even deeper. S. lyra, Mediterranean, very rare. S.
tricuspidata, widely distributed. S. magna, Mediterranean and Madeiran,
living at the surface. S. bipunctata, the most frequently described form,
smaller than the preceding species, 1-2 cm. in length, widely distributed,
and as a rule living near the coast line. S. serratodentata, Mediterranean. S.
enflata, on the surface of the sea, Mediterranean and Madeiran. S. minima, a
very small species, 1 cm. in length, Mediterranean. S. falcidens, Atlantic,
off the coast of New Jersey.
(ii.) Krohnia Langerhans.—A single lateral fin extending on to both trunk
and tail segment, no lateral epidermal extensions behind the head, only one
row of spines on the head. Trunk longer than the tail.
Krohnia has but two species: K. hamata Möbius, with a length of 3-4 cm.,
found in the North Atlantic and at considerable depths, 200 to 300 fathoms;
and K. subtilis Grassi, 1.5 cm. long, with an extraordinary slender body and
a relatively large head, found at Messina, but very rare; as a rule only one
specimen has been found at a time.
Page 207
(iii.) Spadella Langerhans.—A single pair of lateral fins; these are situated
on the tail segment. Behind the head a thickening of the epidermis extends
down each side of the body to the fin, or even farther. Two rows of spines
on the head. Small animals, not longer than 1 cm.
Fig. 105.—Spadella draco. Dorsal view. × 12. (From Hertwig.) a, Cephalic ganglion; b,
commissure between the cephalic ganglion and the ventral; c, eye; d, olfactory
organ; e, alimentary canal; f, ovary; g, oviduct (the line goes a little beyond the
duct); h, testis; j, vesicula seminalis.
S. cephaloptera Busch is the smallest species of Chaetognatha, attaining at
most a length of .5 cm. The body is not so transparent as in other species,
and is of a yellowish colour. It has been found from the Orkney Islands to
the Mediterranean. Strodtmann is of the opinion that the three species S.
mariana Lewes, S. batziana Giard, and S. gallica Pagenstecher differ from
the above-named only in size, or that their description is too indefinite to
permit of accurate characterisation. He recognises three other distinct
species: S. pontica Uljanin, from the Black Sea; S. marioni Gourret, from
the Gulf of Lyons; and S. draco Krohn, Mediterranean and Madeiran, and
from the Canaries.
Much confusion has been introduced into the classification of the
Chaetognatha by Grassi,[230] who calls some—but not all—of what other
writers term Sagitta, Spadella, and vice versâ. The following table was
compiled by Strodtmann,[231] but I have incorporated in it two species
recently described from Amboyna by Béraneck,[232] and called by him
Sagitta bedoti and Spadella vougai respectively:—
on the tail segment. Behind the head a thickening of the epidermis extends
down each side of the body to the fin, or even farther. Two rows of spines
on the head. Small animals, not longer than 1 cm.
Fig. 105.—Spadella draco. Dorsal view. × 12. (From Hertwig.) a, Cephalic ganglion; b,
commissure between the cephalic ganglion and the ventral; c, eye; d, olfactory
organ; e, alimentary canal; f, ovary; g, oviduct (the line goes a little beyond the
duct); h, testis; j, vesicula seminalis.
S. cephaloptera Busch is the smallest species of Chaetognatha, attaining at
most a length of .5 cm. The body is not so transparent as in other species,
and is of a yellowish colour. It has been found from the Orkney Islands to
the Mediterranean. Strodtmann is of the opinion that the three species S.
mariana Lewes, S. batziana Giard, and S. gallica Pagenstecher differ from
the above-named only in size, or that their description is too indefinite to
permit of accurate characterisation. He recognises three other distinct
species: S. pontica Uljanin, from the Black Sea; S. marioni Gourret, from
the Gulf of Lyons; and S. draco Krohn, Mediterranean and Madeiran, and
from the Canaries.
Much confusion has been introduced into the classification of the
Chaetognatha by Grassi,[230] who calls some—but not all—of what other
writers term Sagitta, Spadella, and vice versâ. The following table was
compiled by Strodtmann,[231] but I have incorporated in it two species
recently described from Amboyna by Béraneck,[232] and called by him
Sagitta bedoti and Spadella vougai respectively:—
Page 208
CHAETOGNATHA
I. Two pairs of lateral fins; two rows of spines on the head; slender
forms.
(i.) Number of spines in posterior row greater than in anterior.
a. Border of hooks smooth, their point not curved.
α. No interval between the two fins on each side. 3.5 cm. long; 4-
7 anterior spines, 8-11 posterior spines; olfactory organ lying
entirely on the trunk. The anterior nerves of the ventral ganglion
lie close to one another as far as the head.—Sagitta lyra.
β. A distinct interval between the two fins on each side.
aa. Adult animals large; hooks 6-7; anterior spines 3-4;
posterior spines 5-7; tail ¼ or ⅕ of the total length; lateral
areas relatively larger.—Sagitta hexaptera.
bb. Greatest length 1-2 cm.
αα. Thickening of the epidermis behind the head;
prominently projecting vesiculae seminales; olfactory organ
very long; hooks 8-10; anterior spines 4-6; posterior spines
10-15.—Sagitta bipunctata.
ββ. No epidermal thickening; two caeca on the anterior end
of intestine; length 1 cm.; hooks 6-9; anterior spines 3-4;
posterior spines 7-8; point of the hooks somewhat bent
round.—Sagitta minima.
γγ. Epidermis thin; no caeca; hooks 8-9, their ends not bent;
anterior spines 3-4; posterior spines 7-8; length 2 cm.; small
head; trunk proportionately thick.—Sagitta enflata.
I. Two pairs of lateral fins; two rows of spines on the head; slender
forms.
(i.) Number of spines in posterior row greater than in anterior.
a. Border of hooks smooth, their point not curved.
α. No interval between the two fins on each side. 3.5 cm. long; 4-
7 anterior spines, 8-11 posterior spines; olfactory organ lying
entirely on the trunk. The anterior nerves of the ventral ganglion
lie close to one another as far as the head.—Sagitta lyra.
β. A distinct interval between the two fins on each side.
aa. Adult animals large; hooks 6-7; anterior spines 3-4;
posterior spines 5-7; tail ¼ or ⅕ of the total length; lateral
areas relatively larger.—Sagitta hexaptera.
bb. Greatest length 1-2 cm.
αα. Thickening of the epidermis behind the head;
prominently projecting vesiculae seminales; olfactory organ
very long; hooks 8-10; anterior spines 4-6; posterior spines
10-15.—Sagitta bipunctata.
ββ. No epidermal thickening; two caeca on the anterior end
of intestine; length 1 cm.; hooks 6-9; anterior spines 3-4;
posterior spines 7-8; point of the hooks somewhat bent
round.—Sagitta minima.
γγ. Epidermis thin; no caeca; hooks 8-9, their ends not bent;
anterior spines 3-4; posterior spines 7-8; length 2 cm.; small
head; trunk proportionately thick.—Sagitta enflata.
Page 209
δδ. Hooks 11-14, usually 12; length 1.8 cm.; anterior spines
6-7; posterior spines 18.—Sagitta falcidens.
εε. Hooks 7 on each side; length 1.3 cm.; anterior spines 8-
10, posterior spines 18-22; no olfactory organ.—Sagitta
bedoti.
b. Edge of hooks toothed and their point bent round; hooks 6-8;
anterior spines 6-8; posterior spines 10-12; length 1.5 cm.; slender;
conspicuously projecting vesiculae seminales.—Sagitta
serratodentata.
(ii.) Number of the spines in posterior row smaller than in anterior.
a. Anterior spines 3; posterior spine 1; hooks 8; length 3.5 cm.—
Sagitta tricuspidata.
b. Anterior spines 4; posterior spines 3; hooks 10-13; length 4.1
cm.; tail ⅕ of the total length.—Sagitta magna.
II. One pair of lateral fins lying on the trunk and tail; one row of
spines; body slender; epidermis not thickened.
(i.) Hooks 8-9, bent like an elbow at the point, serrated in the young;
20-25 spines in a row; ovary reddish; length 3-4 cm.—Krohnia
hamata.
(ii.) Hooks 8, broad at their base but very sharply pointed; spines in a
curved row, about 18, with a constriction below like the neck of a
bottle; body thin; length 1-1.5 cm.—Krohnia subtilis.
III. One pair of lateral fins, these lie on the tail; body relatively very
broad in consequence of the thickening of the epidermis lying behind
the head; two rows of spines; greatest length 1 cm.; tail and trunk
usually the same length.
6-7; posterior spines 18.—Sagitta falcidens.
εε. Hooks 7 on each side; length 1.3 cm.; anterior spines 8-
10, posterior spines 18-22; no olfactory organ.—Sagitta
bedoti.
b. Edge of hooks toothed and their point bent round; hooks 6-8;
anterior spines 6-8; posterior spines 10-12; length 1.5 cm.; slender;
conspicuously projecting vesiculae seminales.—Sagitta
serratodentata.
(ii.) Number of the spines in posterior row smaller than in anterior.
a. Anterior spines 3; posterior spine 1; hooks 8; length 3.5 cm.—
Sagitta tricuspidata.
b. Anterior spines 4; posterior spines 3; hooks 10-13; length 4.1
cm.; tail ⅕ of the total length.—Sagitta magna.
II. One pair of lateral fins lying on the trunk and tail; one row of
spines; body slender; epidermis not thickened.
(i.) Hooks 8-9, bent like an elbow at the point, serrated in the young;
20-25 spines in a row; ovary reddish; length 3-4 cm.—Krohnia
hamata.
(ii.) Hooks 8, broad at their base but very sharply pointed; spines in a
curved row, about 18, with a constriction below like the neck of a
bottle; body thin; length 1-1.5 cm.—Krohnia subtilis.
III. One pair of lateral fins, these lie on the tail; body relatively very
broad in consequence of the thickening of the epidermis lying behind
the head; two rows of spines; greatest length 1 cm.; tail and trunk
usually the same length.
Page 210
(i.) A great extension of the epidermis behind the head, consisting of
very large cells; amongst these, at the level of the ventral ganglion,
lies a bundle of stiff hairs; tactile organ on papillae; hooks 9-10;
anterior spines 6-8; posterior spines 12-18.—Spadella draco.
(ii.) Lateral extension of the epidermis not so conspicuous, and the
cells composing it smaller. Tactile organs in little depressions.
Transverse as well as longitudinal muscles in the trunk. Adhesive
cells on the ventral surface of the body. No interval between the
lateral fins and the tail fin. Two papillae on the head-hood elongated
into club-shaped tentacles. Hooks 8-9, slightly serrated; anterior
spines 3-4; posterior spines 3-4.—Spadella cephaloptera.
(iii.) Similar to the last-mentioned species, but the tail segment is
larger than the trunk; in the above it is of the same size. No adhesive
cells. The fins are covered with papillae, and with a number of
serrated spines pointed at both ends.—Spadella pontica.
(iv.) Tactile organs and adhesive cells are unmodified epidermal
cells. Anus dorsal. Orifice of oviducts ventral. No olfactory organ.
Epidermis colourless. Lateral fins without rays. A pair of ganglia at
the postero-lateral angle of the brain.—Spadella marioni.
(v.) Tactile organs well developed on the head, trunk, and fins; tail
segment a little shorter than the trunk. Body short, length 3-4 mm.
Hooks 9; anterior spines 4-5, posterior spines 6-7.—Spadella
vougai.
very large cells; amongst these, at the level of the ventral ganglion,
lies a bundle of stiff hairs; tactile organ on papillae; hooks 9-10;
anterior spines 6-8; posterior spines 12-18.—Spadella draco.
(ii.) Lateral extension of the epidermis not so conspicuous, and the
cells composing it smaller. Tactile organs in little depressions.
Transverse as well as longitudinal muscles in the trunk. Adhesive
cells on the ventral surface of the body. No interval between the
lateral fins and the tail fin. Two papillae on the head-hood elongated
into club-shaped tentacles. Hooks 8-9, slightly serrated; anterior
spines 3-4; posterior spines 3-4.—Spadella cephaloptera.
(iii.) Similar to the last-mentioned species, but the tail segment is
larger than the trunk; in the above it is of the same size. No adhesive
cells. The fins are covered with papillae, and with a number of
serrated spines pointed at both ends.—Spadella pontica.
(iv.) Tactile organs and adhesive cells are unmodified epidermal
cells. Anus dorsal. Orifice of oviducts ventral. No olfactory organ.
Epidermis colourless. Lateral fins without rays. A pair of ganglia at
the postero-lateral angle of the brain.—Spadella marioni.
(v.) Tactile organs well developed on the head, trunk, and fins; tail
segment a little shorter than the trunk. Body short, length 3-4 mm.
Hooks 9; anterior spines 4-5, posterior spines 6-7.—Spadella
vougai.
Page 211
ROTIFERA, GASTROTRICHA, AND
KINORHYNCHA
BY
MARCUS HARTOG, M.A., Trinity College (D.Sc. Lond.)
Professor of Natural History in the Queen's College, Cork.
CHAPTER VIII
ROTIFERA, GASTROTRICHA, AND KINORHYNCHA
ROTIFERA—HISTORY—EXTERNAL FEATURES—MOVEMENT—ANATOMY—
REPRODUCTION—EMBRYOLOGY—CLASSIFICATION—DISTRIBUTION—AFFINITIES—
GASTROTRICHA—KINORHYNCHA
The Rotifera are microscopic animals, the largest not exceeding one-eighth
of an inch in length. According to Hudson and Gosse,[233] they are first
recorded in an observation of the Rev. John Harris, in 1696, of "an Animal
like a large Maggot which could contract itself into a Spherical Figure, and
then stretch itself out again; the end of its Tail appeared with a Forceps like
that of an Ear-wig."[234] This was certainly a Bdelloid Rotifer.
In 1703 Leeuwenhoek[235] gave a fuller description of a tubicolous form,
probably Limnias, and noted the peculiar appearance of the ciliary wreath
as "two wheels thickset with teeth as the wheel of a watch." He also noted a
little later[236] the way in which Melicerta (see p. 206) builds its tube, and
was the first to observe the revivification of certain species after drying.[237]
Joblot, a French professor of mathematics, in 1718 figured and described a
large number of new genera and species with more or less fantastic details.
Baker's figures[238] are a considerable advance on Joblot's, and his
descriptions of habits are still fresh and accurate. Eichhorn found a number
KINORHYNCHA
BY
MARCUS HARTOG, M.A., Trinity College (D.Sc. Lond.)
Professor of Natural History in the Queen's College, Cork.
CHAPTER VIII
ROTIFERA, GASTROTRICHA, AND KINORHYNCHA
ROTIFERA—HISTORY—EXTERNAL FEATURES—MOVEMENT—ANATOMY—
REPRODUCTION—EMBRYOLOGY—CLASSIFICATION—DISTRIBUTION—AFFINITIES—
GASTROTRICHA—KINORHYNCHA
The Rotifera are microscopic animals, the largest not exceeding one-eighth
of an inch in length. According to Hudson and Gosse,[233] they are first
recorded in an observation of the Rev. John Harris, in 1696, of "an Animal
like a large Maggot which could contract itself into a Spherical Figure, and
then stretch itself out again; the end of its Tail appeared with a Forceps like
that of an Ear-wig."[234] This was certainly a Bdelloid Rotifer.
In 1703 Leeuwenhoek[235] gave a fuller description of a tubicolous form,
probably Limnias, and noted the peculiar appearance of the ciliary wreath
as "two wheels thickset with teeth as the wheel of a watch." He also noted a
little later[236] the way in which Melicerta (see p. 206) builds its tube, and
was the first to observe the revivification of certain species after drying.[237]
Joblot, a French professor of mathematics, in 1718 figured and described a
large number of new genera and species with more or less fantastic details.
Baker's figures[238] are a considerable advance on Joblot's, and his
descriptions of habits are still fresh and accurate. Eichhorn found a number
Page 212
of new and interesting forms; and O. F. Müller, influenced by the new
discipline of Linnaeus, not only figured many species, but gave good short
diagnoses of their characters. Ehrenberg in 1838 brought out his
magnificent Infusionsthierchen, which contains descriptions and figures of
what are now divided into Protophyta, Protozoa, Rotifera, and Gastrotricha.
Dujardin's monograph on the "Infusoires," in the Suites à Buffon,[239] was in
several respects an advance on Ehrenberg, whose power of observation was
so great as to render his mistakes the more inexplicable. But Ehrenberg ever
adhered to his errors as firmly as to his facts.
The occurrence of Rotifers among microscopic plants induced the botanists
Cohn and Williamson[240] to work at their structure; the group has been
studied by men engrossed in other professional cares, such as Gosse,
Bedwell, Moxon, Rousselet, and Maupas. Huxley,[241] Leydig,[242] and
Cohn[243] studied Rotifers in the '50's and early '60's with a precision the
more remarkable when we remember the imperfect methods then available.
This period was closed by the valuable monograph published in Arlidge's
(4th) edition of Pritchard's Infusoria,[244] under the supervision of W. C.
Williamson. Leidy began the study of the American Rotifers. Eckstein[245]
gave a careful and interesting account of the species about Giessen in a
richly illustrated paper. In recent times the modern methods of histological
and embryological research have been applied by Vallentin,[246] Plate,[247]
Tessin,[248] and Zelinka,[249] the three Studien ueber Rotatorien of the last
author being indispensable to every student, and containing a full
bibliography.
Hudson and Gosse's Monograph (1886-89) contains a history of the class to
which, as to the whole book, we are deeply indebted; and a full systematic
account of all published species.[250] C. Rousselet has introduced a
method[251] of preparation of Rotifers in microscopic slides which enables
workers to preserve the types they figure and describe for future
identification and comparison. Gunson Thorpe has collected and studied
Rotifera in China and Australia. It would be unfair not to record here the
invaluable services of the late Thomas Bolton, and his son of the same
name, both of Birmingham, and of J. Hood of Dundee, who have found and
widely distributed living specimens of new, rare, and interesting species.
discipline of Linnaeus, not only figured many species, but gave good short
diagnoses of their characters. Ehrenberg in 1838 brought out his
magnificent Infusionsthierchen, which contains descriptions and figures of
what are now divided into Protophyta, Protozoa, Rotifera, and Gastrotricha.
Dujardin's monograph on the "Infusoires," in the Suites à Buffon,[239] was in
several respects an advance on Ehrenberg, whose power of observation was
so great as to render his mistakes the more inexplicable. But Ehrenberg ever
adhered to his errors as firmly as to his facts.
The occurrence of Rotifers among microscopic plants induced the botanists
Cohn and Williamson[240] to work at their structure; the group has been
studied by men engrossed in other professional cares, such as Gosse,
Bedwell, Moxon, Rousselet, and Maupas. Huxley,[241] Leydig,[242] and
Cohn[243] studied Rotifers in the '50's and early '60's with a precision the
more remarkable when we remember the imperfect methods then available.
This period was closed by the valuable monograph published in Arlidge's
(4th) edition of Pritchard's Infusoria,[244] under the supervision of W. C.
Williamson. Leidy began the study of the American Rotifers. Eckstein[245]
gave a careful and interesting account of the species about Giessen in a
richly illustrated paper. In recent times the modern methods of histological
and embryological research have been applied by Vallentin,[246] Plate,[247]
Tessin,[248] and Zelinka,[249] the three Studien ueber Rotatorien of the last
author being indispensable to every student, and containing a full
bibliography.
Hudson and Gosse's Monograph (1886-89) contains a history of the class to
which, as to the whole book, we are deeply indebted; and a full systematic
account of all published species.[250] C. Rousselet has introduced a
method[251] of preparation of Rotifers in microscopic slides which enables
workers to preserve the types they figure and describe for future
identification and comparison. Gunson Thorpe has collected and studied
Rotifera in China and Australia. It would be unfair not to record here the
invaluable services of the late Thomas Bolton, and his son of the same
name, both of Birmingham, and of J. Hood of Dundee, who have found and
widely distributed living specimens of new, rare, and interesting species.
Page 213
Fig. 106.—Hydatina senta, ventral view. (After Plate.) al, Lateral antenna; bl, bladder;
ci, cingulum; e, e, eggs in uterus; fg, foot gland; g, gizzard; gg, gastric gland; gm,
germarium or ovary; gr, ciliated lobes of "groove"; i, intestine; k, k, kidneys; m,
mouth; ns, nephrostome; oe, oesophagus; rc, renal commissure, transverse tube
uniting kidneys above mouth; s, stomach overlaid by reproductive organs; tr,
trochus; u, uterus; vm, vitellarium or yolk-gland.
Definition of the Class.—We may define Rotifera as a class of minute
bilaterally symmetrical animals, with a chitinous integument, a soft terminal
"disc" fringed by a complex ciliary "wreath," an anterior or subventral
mouth, and a dorsal cloacal aperture, beyond which the body is usually
prolonged into the "foot" or process bearing cement glands, and serving for
attachment, temporary or permanent. The body-cavity has no epithelial
lining, and is traversed by nerves and muscles. The alimentary canal
possesses a chitinous gizzard or mastax of peculiar arrangement, and it
usually opens into a cloaca. The nervous centre consists of a ganglion on
the dorsal side of the pharynx, to which a second one on the ventral side is
sometimes connected to form a complete ring; eyes and bristle-bearing
feelers are usually present as sense-organs. A paired system of renal tubes
serves for excretion, opening through a median contractile bladder into the
ventral side of the cloaca. The sexes are distinct; but the males (Fig. 107),
which mostly lack digestive organs, occur rarely, and the females are
usually viviparous, or carry about the eggs till they are hatched; while,
owing to the rarity of the males, parthenogenesis is habitual. Fission and
budding are alike unknown. The fertilised eggs are of the kind termed
"winter" or "resting" eggs, and resist conditions adverse to life.
ci, cingulum; e, e, eggs in uterus; fg, foot gland; g, gizzard; gg, gastric gland; gm,
germarium or ovary; gr, ciliated lobes of "groove"; i, intestine; k, k, kidneys; m,
mouth; ns, nephrostome; oe, oesophagus; rc, renal commissure, transverse tube
uniting kidneys above mouth; s, stomach overlaid by reproductive organs; tr,
trochus; u, uterus; vm, vitellarium or yolk-gland.
Definition of the Class.—We may define Rotifera as a class of minute
bilaterally symmetrical animals, with a chitinous integument, a soft terminal
"disc" fringed by a complex ciliary "wreath," an anterior or subventral
mouth, and a dorsal cloacal aperture, beyond which the body is usually
prolonged into the "foot" or process bearing cement glands, and serving for
attachment, temporary or permanent. The body-cavity has no epithelial
lining, and is traversed by nerves and muscles. The alimentary canal
possesses a chitinous gizzard or mastax of peculiar arrangement, and it
usually opens into a cloaca. The nervous centre consists of a ganglion on
the dorsal side of the pharynx, to which a second one on the ventral side is
sometimes connected to form a complete ring; eyes and bristle-bearing
feelers are usually present as sense-organs. A paired system of renal tubes
serves for excretion, opening through a median contractile bladder into the
ventral side of the cloaca. The sexes are distinct; but the males (Fig. 107),
which mostly lack digestive organs, occur rarely, and the females are
usually viviparous, or carry about the eggs till they are hatched; while,
owing to the rarity of the males, parthenogenesis is habitual. Fission and
budding are alike unknown. The fertilised eggs are of the kind termed
"winter" or "resting" eggs, and resist conditions adverse to life.
Page 214
The Rotifera are of cosmopolitan distribution; most of the species inhabit
fresh water, whilst some are brackish, and a few are marine; 84 genera and
about 700 species have been described.
Fig. 107.—Male Rotifers. (After Hudson.[252]) 1, Floscularia campanulata; 2,
Lacinularia socialis; 3, Notops brachionus; 4, Synchaeta tremula; 5, Asplanchna
ebbesbornii; 6, Brachionus urceolaris; 7, Salpina mucronata; 8, Pedalion mirum.
External Features.[253]—The body is divided into three regions: (1) the
head, ending in the disc, which bears the ciliary wreath; (2) the trunk,
containing the viscera; (3) the foot, which only contains muscles, nerves,
and cement-glands. The general form of the BODY varies greatly: it is
spherical in Trochosphaera, ovoid in Asplanchnidae, conical in Scirtopoda,
Triarthridae, and Synchaeta; moderately elongated in the majority of the
Ploima, among which some forms are very flat, like Pterodina, Metopidia,
and Brachionus; shortly elongated and cylindrical in Hydatina (Fig. 106),
Notommatidae, and many others. In Taphrocampa it is cylindrical and
segmented, while the segments are telescopic in the Bdelloida, both ends
being retractile into the middle segment. In most attached, tube-dwelling
forms the body is ovate, tapering behind into the elongated stalk-like foot.
The FOOT at the hinder end of the body is usually more or less jointed; in
Pterodina and Brachionus it is long, transversely wrinkled, and retractile.
Usually it terminates in a couple of acute, mobile toes, perforated at the tips
by the ducts of the pedal glands (Fig. 106, fg), whose viscid secretion serves
to anchor the animal. In Rotifer there are three of these toes, which are
retractile, and in addition there are in this genus, as in most of the
Bdelloida, toe-like pointed spurs in pairs on the more proximal joints of the
foot. In Callidina the spurs are often perforated, and the toes are replaced
by numerous openings on the last joint of the foot (Fig. 109, A); while in
fresh water, whilst some are brackish, and a few are marine; 84 genera and
about 700 species have been described.
Fig. 107.—Male Rotifers. (After Hudson.[252]) 1, Floscularia campanulata; 2,
Lacinularia socialis; 3, Notops brachionus; 4, Synchaeta tremula; 5, Asplanchna
ebbesbornii; 6, Brachionus urceolaris; 7, Salpina mucronata; 8, Pedalion mirum.
External Features.[253]—The body is divided into three regions: (1) the
head, ending in the disc, which bears the ciliary wreath; (2) the trunk,
containing the viscera; (3) the foot, which only contains muscles, nerves,
and cement-glands. The general form of the BODY varies greatly: it is
spherical in Trochosphaera, ovoid in Asplanchnidae, conical in Scirtopoda,
Triarthridae, and Synchaeta; moderately elongated in the majority of the
Ploima, among which some forms are very flat, like Pterodina, Metopidia,
and Brachionus; shortly elongated and cylindrical in Hydatina (Fig. 106),
Notommatidae, and many others. In Taphrocampa it is cylindrical and
segmented, while the segments are telescopic in the Bdelloida, both ends
being retractile into the middle segment. In most attached, tube-dwelling
forms the body is ovate, tapering behind into the elongated stalk-like foot.
The FOOT at the hinder end of the body is usually more or less jointed; in
Pterodina and Brachionus it is long, transversely wrinkled, and retractile.
Usually it terminates in a couple of acute, mobile toes, perforated at the tips
by the ducts of the pedal glands (Fig. 106, fg), whose viscid secretion serves
to anchor the animal. In Rotifer there are three of these toes, which are
retractile, and in addition there are in this genus, as in most of the
Bdelloida, toe-like pointed spurs in pairs on the more proximal joints of the
foot. In Callidina the spurs are often perforated, and the toes are replaced
by numerous openings on the last joint of the foot (Fig. 109, A); while in
Page 215
Discopus the end of the foot expands into a large disc, with numerous pores
for the exudation of the pedal cement, and there are no spurs. In Pedalion
mirum the foot is represented by two tubular processes ciliated at the apex
and at the outer side near the base (Fig. 117, f). These are inconstant in size
and form, that of one side being sometimes reduced or absent, while both
are absent in the closely allied species P. fennicum.
In Melicertidae and Flosculariidae the long foot ends in an expanded disc,
which is cupped and ciliated in the larva (Fig. 112, B) and in the larva-like
male (Fig. 107); but in two species it is prolonged into a long flexible thread
which is not contractile. The foot is also elongated in the Bdelloid genus
Actinurus and the Ploimal genus Scaridium. It forms a mere ventral disc in
Apsilus (and Atrochus?), and is absent in Asplanchnidae (except
Asplanchnopus), Triarthridae, and Anuraeidae, and in the genera
Trochosphaera (Melicertaceae) and Pompholyx (Pterodinidae).
The fringed spines of Triarthridae are jointed appendages moved by
powerful muscles; in Triarthra one is median and ventral, the others being
attached to the shoulders. In Polyarthra, there are twelve flattened and
serrated spines, a bunch of three being attached to the dorsal and ventral
faces of either shoulder. An easy transition leads to the hollow appendages
of Scirtopoda, which end in a fringe of bristly hairs, themselves feathered
with finer hairs (Fig. 117). These processes are in Pedalion six in number,
two median (respectively dorsal and ventral), two antero-lateral, and two
postero-lateral. As they contain proper muscles, and the postero-lateral pair
contain part of the nephridia and bear the lateral antennae, they are true
outgrowths of the body, and are not homologous with the spines of
Triarthridae.
Fig. 108.—Diagrammatic views of disc of Rotifers. Cingulum represented by a black
line, groove shaded; trochus dotted; the black spot represents the mouth. 1,
Simple disc of Microcodon; 2, Bdelloid disc of Rotifer or Callidina, the star
for the exudation of the pedal cement, and there are no spurs. In Pedalion
mirum the foot is represented by two tubular processes ciliated at the apex
and at the outer side near the base (Fig. 117, f). These are inconstant in size
and form, that of one side being sometimes reduced or absent, while both
are absent in the closely allied species P. fennicum.
In Melicertidae and Flosculariidae the long foot ends in an expanded disc,
which is cupped and ciliated in the larva (Fig. 112, B) and in the larva-like
male (Fig. 107); but in two species it is prolonged into a long flexible thread
which is not contractile. The foot is also elongated in the Bdelloid genus
Actinurus and the Ploimal genus Scaridium. It forms a mere ventral disc in
Apsilus (and Atrochus?), and is absent in Asplanchnidae (except
Asplanchnopus), Triarthridae, and Anuraeidae, and in the genera
Trochosphaera (Melicertaceae) and Pompholyx (Pterodinidae).
The fringed spines of Triarthridae are jointed appendages moved by
powerful muscles; in Triarthra one is median and ventral, the others being
attached to the shoulders. In Polyarthra, there are twelve flattened and
serrated spines, a bunch of three being attached to the dorsal and ventral
faces of either shoulder. An easy transition leads to the hollow appendages
of Scirtopoda, which end in a fringe of bristly hairs, themselves feathered
with finer hairs (Fig. 117). These processes are in Pedalion six in number,
two median (respectively dorsal and ventral), two antero-lateral, and two
postero-lateral. As they contain proper muscles, and the postero-lateral pair
contain part of the nephridia and bear the lateral antennae, they are true
outgrowths of the body, and are not homologous with the spines of
Triarthridae.
Fig. 108.—Diagrammatic views of disc of Rotifers. Cingulum represented by a black
line, groove shaded; trochus dotted; the black spot represents the mouth. 1,
Simple disc of Microcodon; 2, Bdelloid disc of Rotifer or Callidina, the star
Page 216
represents the ciliated proboscis; 3, disc of Hydatina, groove represented by
lobes bearing ciliated styles; 4, disc of Melicerta, the star represents the ciliated
ventral cup with openings into it from the groove; 5, disc of Conochilus; 6, disc
of Stephanoceros, cingulum (?) of setose lobes, trochus horseshoe-shaped, mouth
central.
The front of the body constitutes the HEAD, which is scarcely distinct,
though usually separated by a slight neck-like constriction. The DISC, which
terminates the head, varies greatly in shape and in the arrangement of its
parts. Imagine a circular funnel, finely ciliated within, and with the mouth
at the bottom, the prominent rim bearing two zones of cilia, the inner or
anterior being the coarser, and termed the "trochus" or hoop; the outer finer,
and termed the "cingulum" or girdle, while a very finely ciliated groove lies
between the two zones. Either or both of these zones may be interrupted on
the dorsal or ventral median line, or both; and the funnel-shaped mouth may
be shifted—usually ventrally, so that it forms only a dilatation of the
ciliated groove. Again, the wreath as a whole may be festooned or lobed; or
the lobing may be confined to the area between the cingulum and trochus,
as in most Ploima (Figs. 106 and 108, 3). Very frequently on these lobes
adjacent cilia are fused together during life, producing "vibratile styles,"
whose true nature is only revealed after death. In Microcodonidae the
structure of the disc (Fig. 108, 1) nearly conforms to the primitive type; but
the ciliated groove is absent, and the "trochus" is in two separate half-
elliptical bands. In the Flosculariaceae (Fig. 108, 6) the mouth is also
central, the disc is funnel-shaped, and the trochus is a horseshoe-shaped
ridge, with its ends dorsal and raised into prominent knobs. The margin of
the funnel is in Flosculariidae (Fig. 115) usually lobed, and furnished either
with exceptionally strong cilia, or else with very long bristles which are
usually passive. However, by the retraction of the lobes that bear them they
are clasped together like casting-nets to enclose prey brought into the funnel
by the action of the trochal cilia. An external ring of cilia in Floscularia
mutabilis and F. pelagica serves for swimming. In Apsilidae the margin of
the disc bears neither cilia nor bristles, but is either simple and ring-like, or
is produced into tentacles (Fig. 112, C). The oral funnel is probably
represented in Flosculariaceae by the continuation of the small central
mouth into a ciliated tube (Fig. 115, C, tf), open below, and hanging freely
down into the crop.
lobes bearing ciliated styles; 4, disc of Melicerta, the star represents the ciliated
ventral cup with openings into it from the groove; 5, disc of Conochilus; 6, disc
of Stephanoceros, cingulum (?) of setose lobes, trochus horseshoe-shaped, mouth
central.
The front of the body constitutes the HEAD, which is scarcely distinct,
though usually separated by a slight neck-like constriction. The DISC, which
terminates the head, varies greatly in shape and in the arrangement of its
parts. Imagine a circular funnel, finely ciliated within, and with the mouth
at the bottom, the prominent rim bearing two zones of cilia, the inner or
anterior being the coarser, and termed the "trochus" or hoop; the outer finer,
and termed the "cingulum" or girdle, while a very finely ciliated groove lies
between the two zones. Either or both of these zones may be interrupted on
the dorsal or ventral median line, or both; and the funnel-shaped mouth may
be shifted—usually ventrally, so that it forms only a dilatation of the
ciliated groove. Again, the wreath as a whole may be festooned or lobed; or
the lobing may be confined to the area between the cingulum and trochus,
as in most Ploima (Figs. 106 and 108, 3). Very frequently on these lobes
adjacent cilia are fused together during life, producing "vibratile styles,"
whose true nature is only revealed after death. In Microcodonidae the
structure of the disc (Fig. 108, 1) nearly conforms to the primitive type; but
the ciliated groove is absent, and the "trochus" is in two separate half-
elliptical bands. In the Flosculariaceae (Fig. 108, 6) the mouth is also
central, the disc is funnel-shaped, and the trochus is a horseshoe-shaped
ridge, with its ends dorsal and raised into prominent knobs. The margin of
the funnel is in Flosculariidae (Fig. 115) usually lobed, and furnished either
with exceptionally strong cilia, or else with very long bristles which are
usually passive. However, by the retraction of the lobes that bear them they
are clasped together like casting-nets to enclose prey brought into the funnel
by the action of the trochal cilia. An external ring of cilia in Floscularia
mutabilis and F. pelagica serves for swimming. In Apsilidae the margin of
the disc bears neither cilia nor bristles, but is either simple and ring-like, or
is produced into tentacles (Fig. 112, C). The oral funnel is probably
represented in Flosculariaceae by the continuation of the small central
mouth into a ciliated tube (Fig. 115, C, tf), open below, and hanging freely
down into the crop.
Page 217
In all other cases the mouth is displaced, and lies in the groove and on its
ventral side (except in Conochilus, where it is dorsal, Fig. 108, 5). In the
Bdelloida the disc is prolonged into two great lobes like kettle-drums, round
the posterior, external, and ventral edges of which run the trochus,
cingulum, and ciliated groove (Fig. 108, 2). All three are interrupted behind
in the median line; ventrally the groove widens into the oral funnel, the
cingulum is continued into a sort of spout-like lower lip (Fig. 109, C, D, l),
and the trochus is absent. The body is prolonged dorsally above the lobes
into a two-jointed proboscis, ending in a ciliated cup overhung by two
dorsal flaps: this we regard as a detached portion of the wreath.
This "Bdelloid" type of wreath occurs also in Scirtopoda (Fig. 117), and in
the Ploimal genera Triarthra, Pterodina, and Pompholyx. A simpler wreath
of essentially the same type occurs in Asplanchnaceae and Melicertaceae;
the disc is not prolonged into drum-shaped lobes, but is thin at the rim,
where it bears the triple ciliated zone, interrupted on the dorsal median line
and depressed ventrally into the oral funnel. In the Melicertidae, moreover,
the disc is widened into a great plate-like extension, often beautifully lobed;
and in many of the species a ciliated cup lies ventral to the lips, and is
connected with the groove by a short ciliated channel on either side (Figs.
108, 4, and 116). Even the simpler wreath of Asplanchnidae is complicated
by stronger lobes on either side bearing vibratile styles.
The most complex discs are found in Ploima, especially in Brachionus,
Hydatina, and Synchaeta, since the groove is replaced by a zone of lappets,
as above mentioned. In Proales the whole face of the disc is strongly
ciliated. The wreath is reduced in the parasitic genera Drilophagus,
Albertia, Balatro, and the Seisonaceae; in Adineta and Taphrocampa it is
only represented by a general but scanty ciliation of the disc.
ventral side (except in Conochilus, where it is dorsal, Fig. 108, 5). In the
Bdelloida the disc is prolonged into two great lobes like kettle-drums, round
the posterior, external, and ventral edges of which run the trochus,
cingulum, and ciliated groove (Fig. 108, 2). All three are interrupted behind
in the median line; ventrally the groove widens into the oral funnel, the
cingulum is continued into a sort of spout-like lower lip (Fig. 109, C, D, l),
and the trochus is absent. The body is prolonged dorsally above the lobes
into a two-jointed proboscis, ending in a ciliated cup overhung by two
dorsal flaps: this we regard as a detached portion of the wreath.
This "Bdelloid" type of wreath occurs also in Scirtopoda (Fig. 117), and in
the Ploimal genera Triarthra, Pterodina, and Pompholyx. A simpler wreath
of essentially the same type occurs in Asplanchnaceae and Melicertaceae;
the disc is not prolonged into drum-shaped lobes, but is thin at the rim,
where it bears the triple ciliated zone, interrupted on the dorsal median line
and depressed ventrally into the oral funnel. In the Melicertidae, moreover,
the disc is widened into a great plate-like extension, often beautifully lobed;
and in many of the species a ciliated cup lies ventral to the lips, and is
connected with the groove by a short ciliated channel on either side (Figs.
108, 4, and 116). Even the simpler wreath of Asplanchnidae is complicated
by stronger lobes on either side bearing vibratile styles.
The most complex discs are found in Ploima, especially in Brachionus,
Hydatina, and Synchaeta, since the groove is replaced by a zone of lappets,
as above mentioned. In Proales the whole face of the disc is strongly
ciliated. The wreath is reduced in the parasitic genera Drilophagus,
Albertia, Balatro, and the Seisonaceae; in Adineta and Taphrocampa it is
only represented by a general but scanty ciliation of the disc.
Page 218
Fig. 109.—Callidina symbiotica. (After Zelinka.) A, Ventral view, with the disc half
expanded, proboscis extended; B, lateral view, proboscis extended; C, ventral
view of anterior segments with expanded disc; D, lateral view of same
(proboscis retracted). a, Antenna; bl, bladder (enlargement of rectum); c, ciliated
cup of the proboscis; ci, cingulum; cl, cloaca; cp, group of pores, the openings of
cement glands; di, disc; g, gizzard; gm, germarium (that of the opposite side seen
at a higher level); gr, ciliated groove; k, kidney; l, lip; m, mouth; pr, proboscis;
sp, spurs of foot; tr, large cilia of trochus, showing vertical movements; vm,
yolk-gland. The body muscles are represented by shaded bands.
The head is very frequently retractile, as a whole, by strong muscles. In
Bdelloida the disc proper is retracted when the animal crawls, while the
proboscis is exserted (Fig. 109). Ciliated patches occurring outside the
region of the disc point to a primitive condition when the whole surface of
the body was ciliated, as does the partial ciliation of the foot in certain
groups. Synchaeta and many Notommatidae possess a pair of lateral,
hollow, ciliated pits on the body, which can be everted to serve as additional
swimming organs; these are termed "auricles."
The cuticle varies much in texture. It may be smooth and flexible, dotted or
shagreened, or in the Loricata firm and of definite shape, constituting a
lorica, which may be more or less distinctly divided up into areas or
separated into distinct pieces. In this case it resists decomposition, and
several species are only known by this "skeleton." In Ploesoma it is much
thickened and looks like a honeycomb. A regular alternation of harder and
softer zones effects the annulation of the body in certain genera.
The hypoderm or protoplasmic layer of the skin has no cellular boundaries,
though it contains large and distinct nuclei; it is usually somewhat granular.
expanded, proboscis extended; B, lateral view, proboscis extended; C, ventral
view of anterior segments with expanded disc; D, lateral view of same
(proboscis retracted). a, Antenna; bl, bladder (enlargement of rectum); c, ciliated
cup of the proboscis; ci, cingulum; cl, cloaca; cp, group of pores, the openings of
cement glands; di, disc; g, gizzard; gm, germarium (that of the opposite side seen
at a higher level); gr, ciliated groove; k, kidney; l, lip; m, mouth; pr, proboscis;
sp, spurs of foot; tr, large cilia of trochus, showing vertical movements; vm,
yolk-gland. The body muscles are represented by shaded bands.
The head is very frequently retractile, as a whole, by strong muscles. In
Bdelloida the disc proper is retracted when the animal crawls, while the
proboscis is exserted (Fig. 109). Ciliated patches occurring outside the
region of the disc point to a primitive condition when the whole surface of
the body was ciliated, as does the partial ciliation of the foot in certain
groups. Synchaeta and many Notommatidae possess a pair of lateral,
hollow, ciliated pits on the body, which can be everted to serve as additional
swimming organs; these are termed "auricles."
The cuticle varies much in texture. It may be smooth and flexible, dotted or
shagreened, or in the Loricata firm and of definite shape, constituting a
lorica, which may be more or less distinctly divided up into areas or
separated into distinct pieces. In this case it resists decomposition, and
several species are only known by this "skeleton." In Ploesoma it is much
thickened and looks like a honeycomb. A regular alternation of harder and
softer zones effects the annulation of the body in certain genera.
The hypoderm or protoplasmic layer of the skin has no cellular boundaries,
though it contains large and distinct nuclei; it is usually somewhat granular.
Page 219
It forms the wall of the body-cavity, which contains a transparent liquid
without corpuscles.
The principal external glands are the pedal or cement-glands, which secrete
a viscid substance that sets in water and serves to anchor the animal. They
are formed from an ingrowth of the hypoderm, are usually paired, and open
by fine ducts on or near the apex of the toes, when these processes of the
foot are present (Fig. 106, fg). These glands are mostly absent when there is
no foot, as in most Asplanchnidae and in Anuraeidae, but in Asplanchna
herrickii a small gland on the ventral side of the cloacal aperture appears to
represent the last rudiment of the foot.
In addition to these, the ciliated ventral cup below the disc of many
Melicertidae secretes a viscid substance (Fig. 116, p); and possibly the
whole surface of the body is secretory in those species of this group, and of
the Flosculariidae, whose tube (Fig. 115, A) is uniform and not made of
pellets. In several other species belonging to Bdelloida and Ploima-
Illoricata a viscid secretion of the surface of the body renders it "sordid"
with adherent particles of dirt.
When the secretion takes the form of a tube, the body can be wholly
withdrawn into it by the contraction of the foot. In Floscularia,
Stephanoceros, and Conochilus the tube is hyaline and thin-walled; in
Oecistes and Cephalosiphon it is more or less floccose; and in Limnias it is
thin, firm, and annulated. In Melicerta and some species of Oecistes the
tube thus secreted by the body is only formed in a very young state. In M.
janus and M. pilula it is increased by the successive deposition of ovoid
faecal pellets on to the rim. In M. ringens (Fig. 116) and M. conifera pellets
are formed of the excess of the food particles brought to the disc by the
ciliary current; they are carried through the gutters on either side of the
projecting ventral lip or "chin" into the ciliated glandular cup on that side of
the head. Here, as they revolve, they are cemented together into a pellet
which is spheroidal in the former species, cylindro-conoidal with a basal
hollow like a rifle-bullet in the latter. After a pellet is completed the animal
stoops down and deposits it on the edge of the tube. This may easily be
verified by furnishing a young Melicerta with water containing solid
without corpuscles.
The principal external glands are the pedal or cement-glands, which secrete
a viscid substance that sets in water and serves to anchor the animal. They
are formed from an ingrowth of the hypoderm, are usually paired, and open
by fine ducts on or near the apex of the toes, when these processes of the
foot are present (Fig. 106, fg). These glands are mostly absent when there is
no foot, as in most Asplanchnidae and in Anuraeidae, but in Asplanchna
herrickii a small gland on the ventral side of the cloacal aperture appears to
represent the last rudiment of the foot.
In addition to these, the ciliated ventral cup below the disc of many
Melicertidae secretes a viscid substance (Fig. 116, p); and possibly the
whole surface of the body is secretory in those species of this group, and of
the Flosculariidae, whose tube (Fig. 115, A) is uniform and not made of
pellets. In several other species belonging to Bdelloida and Ploima-
Illoricata a viscid secretion of the surface of the body renders it "sordid"
with adherent particles of dirt.
When the secretion takes the form of a tube, the body can be wholly
withdrawn into it by the contraction of the foot. In Floscularia,
Stephanoceros, and Conochilus the tube is hyaline and thin-walled; in
Oecistes and Cephalosiphon it is more or less floccose; and in Limnias it is
thin, firm, and annulated. In Melicerta and some species of Oecistes the
tube thus secreted by the body is only formed in a very young state. In M.
janus and M. pilula it is increased by the successive deposition of ovoid
faecal pellets on to the rim. In M. ringens (Fig. 116) and M. conifera pellets
are formed of the excess of the food particles brought to the disc by the
ciliary current; they are carried through the gutters on either side of the
projecting ventral lip or "chin" into the ciliated glandular cup on that side of
the head. Here, as they revolve, they are cemented together into a pellet
which is spheroidal in the former species, cylindro-conoidal with a basal
hollow like a rifle-bullet in the latter. After a pellet is completed the animal
stoops down and deposits it on the edge of the tube. This may easily be
verified by furnishing a young Melicerta with water containing solid
Page 220
particles of carmine. M. tubicolaria forms a thick tube which is laminated,
the laminae being directed upwards and outwards, and having diatom
shells, etc., between the layers. In this case we have observed that the faeces
are pellucid, and sometimes are so ejected as to lie in a sheet against the
funnel-shaped mouth of the tube, and we are inclined to believe that the
tube itself is formed altogether in this way. A similar process probably
occurs in Oecistes crystallinus and Oe. umbella.
The muscles are simple elongated fibres, usually having near the middle a
mass of granular protoplasm containing a nucleus; they may be smooth or
striated. The principal muscles of the body are conspicuously striated in
many active free-swimming forms (Pedalion, Synchaeta, Pterodina,
Triarthra).
The muscles of the body-wall are transverse and longitudinal. They are best
seen in Bdelloida. The principal muscles of the body-cavity are
longitudinal; the most conspicuous and constant are the retractors of the
disc and of the foot, protraction of these organs being usually accomplished
by the contraction of the transverse muscles. Special muscles effect the
vigorous springing of the Triarthridae and Scirtopoda; in the former group
the muscles only raise the spines, and their elastic recoil is the actual
mechanism of progression; but in the latter (Fig. 117) special flexor muscles
of the limbs are the effective agents of the leaping movements.
Movements.—The Rotifera vary very greatly in their movements. The cilia
of the disc, and especially of the trochus, are the principal organs of
prehension of food, and also of swimming when the animal is not fixed by
its foot. In some cases, as in Bdelloida, the cilia lash downwards
successively in the longitudinal plane of the body (Fig. 109, C, D); this
motion during fixation produces a hollow vortex ring, like the rings of a
skilled cigarette-smoker, but when the animal is free it determines a simple
forward progression through the water. In other cases the animal rotates on
its long axis, or may even turn somersaults (Synchaeta). The appearance of
the spokes of a wheel is a pure illusion due to the greater visibility of the
cilia in their slow recovery than in their instantaneous down-lash. The finer
cilia of the groove and cingulum play a very minor part in the act of
the laminae being directed upwards and outwards, and having diatom
shells, etc., between the layers. In this case we have observed that the faeces
are pellucid, and sometimes are so ejected as to lie in a sheet against the
funnel-shaped mouth of the tube, and we are inclined to believe that the
tube itself is formed altogether in this way. A similar process probably
occurs in Oecistes crystallinus and Oe. umbella.
The muscles are simple elongated fibres, usually having near the middle a
mass of granular protoplasm containing a nucleus; they may be smooth or
striated. The principal muscles of the body are conspicuously striated in
many active free-swimming forms (Pedalion, Synchaeta, Pterodina,
Triarthra).
The muscles of the body-wall are transverse and longitudinal. They are best
seen in Bdelloida. The principal muscles of the body-cavity are
longitudinal; the most conspicuous and constant are the retractors of the
disc and of the foot, protraction of these organs being usually accomplished
by the contraction of the transverse muscles. Special muscles effect the
vigorous springing of the Triarthridae and Scirtopoda; in the former group
the muscles only raise the spines, and their elastic recoil is the actual
mechanism of progression; but in the latter (Fig. 117) special flexor muscles
of the limbs are the effective agents of the leaping movements.
Movements.—The Rotifera vary very greatly in their movements. The cilia
of the disc, and especially of the trochus, are the principal organs of
prehension of food, and also of swimming when the animal is not fixed by
its foot. In some cases, as in Bdelloida, the cilia lash downwards
successively in the longitudinal plane of the body (Fig. 109, C, D); this
motion during fixation produces a hollow vortex ring, like the rings of a
skilled cigarette-smoker, but when the animal is free it determines a simple
forward progression through the water. In other cases the animal rotates on
its long axis, or may even turn somersaults (Synchaeta). The appearance of
the spokes of a wheel is a pure illusion due to the greater visibility of the
cilia in their slow recovery than in their instantaneous down-lash. The finer
cilia of the groove and cingulum play a very minor part in the act of
Page 221
swimming, and in the production of the great vortices at the edge of the disc
when the animal is fixed; they serve to direct the particles brought by the
vortices to the edge of the disc onwards towards the mouth. It is easy to see
that the stream must be in opposite directions on opposite sides of the
groove; its prolongation across the dorsal median line would be useless,
which explains the existence of the dorsal median gap. At the ventral side
we usually find a prominent ciliated lip, whose cilia work outwards, and
carry off the excess of food particles as by an overflow spout. In many
cases among the Notommatidae, Coluridae, etc., the disc serves as much for
creeping over organic débris as for swimming.
We have already noticed the springing bristles and limbs of the Triarthridae
and Scirtopoda respectively; the great foot of Scaridium is also used for
leaping. The Bdelloida have the power of retracting their disc and
progressing in loops like a leech or looper (Geometrid) caterpillar.
Baker, in a letter addressed to Martin Folkes, Esq., President of the Royal
Society, dated London, 16th January 1744-5,[254] gives the following lively
account of the aspect and movements of Philodina roseola belonging to this
group, with figures, some of which we reproduce from the original copper-
plate engraving:—"I call it a Water Animal, because its Appearance as a
living Creature is only in that Element. I give it also for Distinction Sake
the Name of Wheeler, Wheel Insect or Animal; from its being furnished
with a Pair of Instruments, which in Figure and Motion appear much to
resemble Wheels. It can, however, continue many Months out of Water, and
dry as Dust; in which Condition its Shape is globular, its Bigness exceeds
not a Grain of Sand, and no Signs of Life appear. Notwithstanding, being
put into Water, in the Space of Half an Hour a languid Motion begins, the
Globule turns itself about, lengthens by slow Degrees, becomes in the Form
of a lively Maggot, and most commonly in a few Minutes afterwards puts
out its Wheels, and swims vigorously through the Water in Search of Food;
or else, fixing by its Tail, works them in such a Manner as to bring its Food
to it. But sometimes it will remain a long While in the Maggot Form and
not shew its Wheels at all....
when the animal is fixed; they serve to direct the particles brought by the
vortices to the edge of the disc onwards towards the mouth. It is easy to see
that the stream must be in opposite directions on opposite sides of the
groove; its prolongation across the dorsal median line would be useless,
which explains the existence of the dorsal median gap. At the ventral side
we usually find a prominent ciliated lip, whose cilia work outwards, and
carry off the excess of food particles as by an overflow spout. In many
cases among the Notommatidae, Coluridae, etc., the disc serves as much for
creeping over organic débris as for swimming.
We have already noticed the springing bristles and limbs of the Triarthridae
and Scirtopoda respectively; the great foot of Scaridium is also used for
leaping. The Bdelloida have the power of retracting their disc and
progressing in loops like a leech or looper (Geometrid) caterpillar.
Baker, in a letter addressed to Martin Folkes, Esq., President of the Royal
Society, dated London, 16th January 1744-5,[254] gives the following lively
account of the aspect and movements of Philodina roseola belonging to this
group, with figures, some of which we reproduce from the original copper-
plate engraving:—"I call it a Water Animal, because its Appearance as a
living Creature is only in that Element. I give it also for Distinction Sake
the Name of Wheeler, Wheel Insect or Animal; from its being furnished
with a Pair of Instruments, which in Figure and Motion appear much to
resemble Wheels. It can, however, continue many Months out of Water, and
dry as Dust; in which Condition its Shape is globular, its Bigness exceeds
not a Grain of Sand, and no Signs of Life appear. Notwithstanding, being
put into Water, in the Space of Half an Hour a languid Motion begins, the
Globule turns itself about, lengthens by slow Degrees, becomes in the Form
of a lively Maggot, and most commonly in a few Minutes afterwards puts
out its Wheels, and swims vigorously through the Water in Search of Food;
or else, fixing by its Tail, works them in such a Manner as to bring its Food
to it. But sometimes it will remain a long While in the Maggot Form and
not shew its Wheels at all....
Page 222
Fig. 110.—Philodina roseola. (After Baker.) A, B, Crawling, with extended proboscis,
and showing antenna; C, D, E, attached, with "wheels" extended for catching
food; F, attached, with anterior end retracted.
"If the Water standing in Gutters of Lead, or the slimy Sediment it leaves
behind, has any Thing of a red Colour, one may be almost certain of finding
them therein,[255] and, if in Summer, when all the Water is dried away, and
nothing but Dust remains, that Dust appears red, or of a dark brown, one
shall seldom fail, on putting it into Water, to discover Multitudes of minute
reddish Globules, which are indeed the Animals, and will soon change their
Appearance, in the Manner just now mentioned....
"A Couple of circular Bodies, armed with small Teeth like those of the
Balance-Wheel of a Watch, appear projecting forwards beyond the Head,
and extending sideways somewhat wider than the Diameter thereof. They
have very much the Similitude of Wheels, and seem to turn round with a
considerable Degree of Velocity, by which Means a pretty rapid Current of
Water is brought from a great Distance to the very Mouth of the Creature,
who is thereby supplied with many little Animalcules and various Particles
of Matter that the Waters are furnished with.
"As these Wheels (for so from their Appearance I shall beg Leave to call
them) are every where excessively transparent, except about their circular
Rim or Edge on which the Cogs or Teeth appear, it is very difficult to
determine by what Contrivance they are turned about, or what their real
Figure is, though they seem exactly to resemble Wheels moving round upon
an Axis....
and showing antenna; C, D, E, attached, with "wheels" extended for catching
food; F, attached, with anterior end retracted.
"If the Water standing in Gutters of Lead, or the slimy Sediment it leaves
behind, has any Thing of a red Colour, one may be almost certain of finding
them therein,[255] and, if in Summer, when all the Water is dried away, and
nothing but Dust remains, that Dust appears red, or of a dark brown, one
shall seldom fail, on putting it into Water, to discover Multitudes of minute
reddish Globules, which are indeed the Animals, and will soon change their
Appearance, in the Manner just now mentioned....
"A Couple of circular Bodies, armed with small Teeth like those of the
Balance-Wheel of a Watch, appear projecting forwards beyond the Head,
and extending sideways somewhat wider than the Diameter thereof. They
have very much the Similitude of Wheels, and seem to turn round with a
considerable Degree of Velocity, by which Means a pretty rapid Current of
Water is brought from a great Distance to the very Mouth of the Creature,
who is thereby supplied with many little Animalcules and various Particles
of Matter that the Waters are furnished with.
"As these Wheels (for so from their Appearance I shall beg Leave to call
them) are every where excessively transparent, except about their circular
Rim or Edge on which the Cogs or Teeth appear, it is very difficult to
determine by what Contrivance they are turned about, or what their real
Figure is, though they seem exactly to resemble Wheels moving round upon
an Axis....
Page 223
"As the Animal is capable of thrusting these Parts out, or drawing them in,
somewhat in the Way that Snails do their Horns, the Figure of them is
different in their several Degrees of Extension and Contraction, or
according to their Position to the Eye of the Observer, whereby they not
only appear in all the various Forms before represented, but seem at certain
Times as if the circular Rim of the Wheel or Funnel were of some
Thickness, and had two Rows of Cogs or Teeth, one above and the other
below that Rim."
Digestive Organs.—The pharynx is usually a narrow ciliated tube, which
varies in length from genus to genus, but in no other important point, save
in Flosculariidae, where it assumes the form of a crop, into which the mouth
hangs freely down as a narrow ciliated tube. At its lower end is an
enlargement, the mastax or gizzard.[256] This is a strong muscular sac
containing the trophi or hard chitinous chewing organs, with an antero-
ventral inlet from the pharynx, and a postero-dorsal outlet through which
the food passes into the stomach either directly or through a slender gullet
(Fig. 106, oe). In the ventral wall of the gizzard of most Ploima is a median
piece, the fulcrum, from which run forwards and upwards two pieces, the
rami, which are hinged on the fulcrum. The Y-shaped structure formed of
these three pieces is called the incus (anvil). At either side of the gizzard
and at a higher level is a paired piece, the malleus, so called from its
resemblance to a hammer, of which the manubrium (handle) looks
backwards, and is embedded in the side walls of the mastax, while the
toothed claw or uncus looks forwards and inwards, and is hinged at its inner
side with the tip of the ramus. As the unci and rami are usually strongly
toothed, this gizzard forms a very efficient apparatus for chewing. In some
cases, when the pharynx is short and dilatable, the points of the unci and
rami may be protruded for biting, for clinging to the host (in the parasitic
genera Albertia and Drilophagus), or for the prehension of food (Rattulidae,
etc.).
somewhat in the Way that Snails do their Horns, the Figure of them is
different in their several Degrees of Extension and Contraction, or
according to their Position to the Eye of the Observer, whereby they not
only appear in all the various Forms before represented, but seem at certain
Times as if the circular Rim of the Wheel or Funnel were of some
Thickness, and had two Rows of Cogs or Teeth, one above and the other
below that Rim."
Digestive Organs.—The pharynx is usually a narrow ciliated tube, which
varies in length from genus to genus, but in no other important point, save
in Flosculariidae, where it assumes the form of a crop, into which the mouth
hangs freely down as a narrow ciliated tube. At its lower end is an
enlargement, the mastax or gizzard.[256] This is a strong muscular sac
containing the trophi or hard chitinous chewing organs, with an antero-
ventral inlet from the pharynx, and a postero-dorsal outlet through which
the food passes into the stomach either directly or through a slender gullet
(Fig. 106, oe). In the ventral wall of the gizzard of most Ploima is a median
piece, the fulcrum, from which run forwards and upwards two pieces, the
rami, which are hinged on the fulcrum. The Y-shaped structure formed of
these three pieces is called the incus (anvil). At either side of the gizzard
and at a higher level is a paired piece, the malleus, so called from its
resemblance to a hammer, of which the manubrium (handle) looks
backwards, and is embedded in the side walls of the mastax, while the
toothed claw or uncus looks forwards and inwards, and is hinged at its inner
side with the tip of the ramus. As the unci and rami are usually strongly
toothed, this gizzard forms a very efficient apparatus for chewing. In some
cases, when the pharynx is short and dilatable, the points of the unci and
rami may be protruded for biting, for clinging to the host (in the parasitic
genera Albertia and Drilophagus), or for the prehension of food (Rattulidae,
etc.).
Page 224
Fig. 111.—Diagram of trophi. (After Hudson.) A, Malleate; B, submalleate; C, virgate;
D, forcipate; E, malleoramate (Melicerta); F, incudate (Asplanchna); G,
uncinate (Stephanoceros); H, ramate (Rotifer). f, Fulcrum; i, incus; ma,
manubrium (malleus in G); r, ramus; un, uncus.
The type we have just described is termed the "malleate" type (Fig. 111, A).
If all the trophi are slender and scarcely toothed, we have the "virgate" type
(C), which is frequently asymmetrical. In the "submalleate" type (B) the
mallei only are slender; in the "forcipate" type (D) both the unci and rami
are slender and sharply pointed.[257] In the "malleoramate" type (E) the
manubrium is a curious looped structure, while the uncus is formed of a
number of parallel slender elongated teeth; this characterises the family
Melicertidae, and the genera Triarthra, Pterodina, and Pedalion. In the
"uncinate" type (G) the mallei are simply incurved hooks with a few teeth at
the free end, the rami are simple or absent, and there is no fulcrum; this type
occurs in Flosculariaceae only. In Asplanchnidae the rami are large and
hooked, constituting the "incudate" mastax (F); but here reduced mallei are
often present, and in Asplanchnopus they are almost as well developed as in
Melicertidae, affording a transition to the malleoramate type. In this group
too the mastax has a very peculiar form; it is divided into two chambers,
dorsal and ventral. The dorsal chamber forms a great purse-like sac or crop,
with a framework of four longitudinal bars: into this the gullet and pharynx
open. The ventral pouch is much smaller, and in its base the large rami are
inserted, so that they can be protruded into the crop. This ventral sac with
the rami may even be everted through the crop and the mouth, to swallow
the small Rotifers and Entomostraca which form the food of this group, or
to eject the undigested remains of the food. Two lateral sacs open at the
junction of the ventral pouch and the crop, but whether they play a part in
the deglutition of food or in the disgorging of faeces is uncertain. The fact
that the whole of this apparatus is lined by a non-ciliated chitinous cuticle
D, forcipate; E, malleoramate (Melicerta); F, incudate (Asplanchna); G,
uncinate (Stephanoceros); H, ramate (Rotifer). f, Fulcrum; i, incus; ma,
manubrium (malleus in G); r, ramus; un, uncus.
The type we have just described is termed the "malleate" type (Fig. 111, A).
If all the trophi are slender and scarcely toothed, we have the "virgate" type
(C), which is frequently asymmetrical. In the "submalleate" type (B) the
mallei only are slender; in the "forcipate" type (D) both the unci and rami
are slender and sharply pointed.[257] In the "malleoramate" type (E) the
manubrium is a curious looped structure, while the uncus is formed of a
number of parallel slender elongated teeth; this characterises the family
Melicertidae, and the genera Triarthra, Pterodina, and Pedalion. In the
"uncinate" type (G) the mallei are simply incurved hooks with a few teeth at
the free end, the rami are simple or absent, and there is no fulcrum; this type
occurs in Flosculariaceae only. In Asplanchnidae the rami are large and
hooked, constituting the "incudate" mastax (F); but here reduced mallei are
often present, and in Asplanchnopus they are almost as well developed as in
Melicertidae, affording a transition to the malleoramate type. In this group
too the mastax has a very peculiar form; it is divided into two chambers,
dorsal and ventral. The dorsal chamber forms a great purse-like sac or crop,
with a framework of four longitudinal bars: into this the gullet and pharynx
open. The ventral pouch is much smaller, and in its base the large rami are
inserted, so that they can be protruded into the crop. This ventral sac with
the rami may even be everted through the crop and the mouth, to swallow
the small Rotifers and Entomostraca which form the food of this group, or
to eject the undigested remains of the food. Two lateral sacs open at the
junction of the ventral pouch and the crop, but whether they play a part in
the deglutition of food or in the disgorging of faeces is uncertain. The fact
that the whole of this apparatus is lined by a non-ciliated chitinous cuticle
Page 225
justifies our view that it is simply an enlargement and specialisation of the
mastax.
The trophi in Bdelloids also are only represented by the rami, which have
the form of segments of a sphere, excavated on the curved sides for the
attachment of muscles, and transversely ridged on the two flat sides; the
gizzard is here called "ramate" (H).
It will be seen that the characters of the gizzard are very useful for
classification, only breaking down indeed in the Ploima; for though the
majority of these present one or other of the four varieties of the malleate
type, Triarthra and Pterodina (but not the other genera of their respective
families) have the gizzard malleoramate.
The oesophagus is, when present, a contractile ciliated tube in which the
food makes no sojourn on its way to the stomach.
The stomach may be nearly spherical, ovoid, or elongated and cylindrical.
Its walls are formed of large cells, often granular and sometimes brownish,
whence a hepatic function has been assigned to them. Its apertures are both
surrounded by constricting muscular fibres. The intestine may be simple or
divided by a similar constriction into intestine proper and rectum. The
whole of the alimentary tract, with the exception of the mastax, is richly
ciliated within. The rectum opens into the slender non-ciliated cloaca. The
intestine is sharply bent upwards and towards the back in the tubicolous
forms, but is nearly straight elsewhere; in Trochosphaera and Apsilus it is
bent ventrally. In Asplanchnaceae and in Paraseison there is no rectum, the
stomach being a blind sac.
The so-called salivary glands, usually two in number, open into the pharynx
or mastax; and the paired gastric glands (Fig. 106, gg) open into the
oesophagus or stomach. While the prehension of food is usually
accomplished by the ciliary current of the disc and pharynx, we have seen
that a more active swallowing action takes place in Flosculariaceae and
Asplanchnidae, which devour whole Algae, Infusoria, and even other
Rotifers, the long spines of Triarthra not availing as a protection. Many
mastax.
The trophi in Bdelloids also are only represented by the rami, which have
the form of segments of a sphere, excavated on the curved sides for the
attachment of muscles, and transversely ridged on the two flat sides; the
gizzard is here called "ramate" (H).
It will be seen that the characters of the gizzard are very useful for
classification, only breaking down indeed in the Ploima; for though the
majority of these present one or other of the four varieties of the malleate
type, Triarthra and Pterodina (but not the other genera of their respective
families) have the gizzard malleoramate.
The oesophagus is, when present, a contractile ciliated tube in which the
food makes no sojourn on its way to the stomach.
The stomach may be nearly spherical, ovoid, or elongated and cylindrical.
Its walls are formed of large cells, often granular and sometimes brownish,
whence a hepatic function has been assigned to them. Its apertures are both
surrounded by constricting muscular fibres. The intestine may be simple or
divided by a similar constriction into intestine proper and rectum. The
whole of the alimentary tract, with the exception of the mastax, is richly
ciliated within. The rectum opens into the slender non-ciliated cloaca. The
intestine is sharply bent upwards and towards the back in the tubicolous
forms, but is nearly straight elsewhere; in Trochosphaera and Apsilus it is
bent ventrally. In Asplanchnaceae and in Paraseison there is no rectum, the
stomach being a blind sac.
The so-called salivary glands, usually two in number, open into the pharynx
or mastax; and the paired gastric glands (Fig. 106, gg) open into the
oesophagus or stomach. While the prehension of food is usually
accomplished by the ciliary current of the disc and pharynx, we have seen
that a more active swallowing action takes place in Flosculariaceae and
Asplanchnidae, which devour whole Algae, Infusoria, and even other
Rotifers, the long spines of Triarthra not availing as a protection. Many
Page 226
Ploima put out the tips of their trophi to nibble at débris, or, in the case of
Diglena and Distemma, to attack Desmids, or the Infusorian Stentor. But
this use of the trophi is most efficient in Ploesoma. Bilfinger[258] writes: "It
has the courage to attack larger Rotifers; thus I was able to observe under
the microscope how it fell upon a Rattulus but little smaller than itself and
destroyed it. First it plunged the sharp prongs of its mastax deep into the
tender frontal area of its unhappy victim; then followed a pumping action of
the gizzard, and stroke by stroke the whole contents of the victim's body
passed into the brigand's stomach." From this it is an easy transition to the
ectoparasitism of Drilophagus, Balatro, and some species of Albertia,
which cling to their host by the exserted trophi.
Renal Organs.—The kidneys consist of a pair of convoluted tubes, formed
of a succession of perforated, so-called "drainpipe" cells (Fig. 106, k); they
open directly or indirectly into the cloaca. Their walls are thin in the straight
parts, but thick and glandular in the coils which occur at intervals. These
tubes bear little tag-like appendages, hanging freely into the body-cavity,
often widening towards the free end, and flattened or circular in section
(Fig. 106, ns). They show during life a peculiar flickering motion in their
interior, like the equivalent "flame-cells" of many Platyhelminthes (see p.
25), and are in function the representatives of the multicellular renal funnels
of Annelids. On one side, especially on the edge of the flattened tags, the
appearance is as of a tapering whip-like lash, attached by its base to the free
end of the tag and waving in its cavity; but the side view of the flattened
tags shows an appearance of successive transverse or oblique waves. In
many if not all cases the free end of the tag is closed by a vacuolated plug
of protoplasm, which sometimes at least bears two flagella waving freely in
the body-cavity. The probable explanation of the two distinct wave
appearances within the tag is that the protoplasmic plug bears on its inner
face a row or tuft of long cilia hanging down into the cavity of the tag. The
tags probably keep up a current of liquid through the kidneys, while the
contents of the body-cavity are constantly replenished by osmosis.
The two renal tubes may end blindly below the disc, or else join by a short
transverse dorsal communication in front of the brain, as in Stephanoceros,
Atrochus (Fig. 112, C), and Apsilus among Flosculariaceae, Lacinularia
among Melicertidae, and Hydatina among the Illoricate Ploima (Fig. 106,
Diglena and Distemma, to attack Desmids, or the Infusorian Stentor. But
this use of the trophi is most efficient in Ploesoma. Bilfinger[258] writes: "It
has the courage to attack larger Rotifers; thus I was able to observe under
the microscope how it fell upon a Rattulus but little smaller than itself and
destroyed it. First it plunged the sharp prongs of its mastax deep into the
tender frontal area of its unhappy victim; then followed a pumping action of
the gizzard, and stroke by stroke the whole contents of the victim's body
passed into the brigand's stomach." From this it is an easy transition to the
ectoparasitism of Drilophagus, Balatro, and some species of Albertia,
which cling to their host by the exserted trophi.
Renal Organs.—The kidneys consist of a pair of convoluted tubes, formed
of a succession of perforated, so-called "drainpipe" cells (Fig. 106, k); they
open directly or indirectly into the cloaca. Their walls are thin in the straight
parts, but thick and glandular in the coils which occur at intervals. These
tubes bear little tag-like appendages, hanging freely into the body-cavity,
often widening towards the free end, and flattened or circular in section
(Fig. 106, ns). They show during life a peculiar flickering motion in their
interior, like the equivalent "flame-cells" of many Platyhelminthes (see p.
25), and are in function the representatives of the multicellular renal funnels
of Annelids. On one side, especially on the edge of the flattened tags, the
appearance is as of a tapering whip-like lash, attached by its base to the free
end of the tag and waving in its cavity; but the side view of the flattened
tags shows an appearance of successive transverse or oblique waves. In
many if not all cases the free end of the tag is closed by a vacuolated plug
of protoplasm, which sometimes at least bears two flagella waving freely in
the body-cavity. The probable explanation of the two distinct wave
appearances within the tag is that the protoplasmic plug bears on its inner
face a row or tuft of long cilia hanging down into the cavity of the tag. The
tags probably keep up a current of liquid through the kidneys, while the
contents of the body-cavity are constantly replenished by osmosis.
The two renal tubes may end blindly below the disc, or else join by a short
transverse dorsal communication in front of the brain, as in Stephanoceros,
Atrochus (Fig. 112, C), and Apsilus among Flosculariaceae, Lacinularia
among Melicertidae, and Hydatina among the Illoricate Ploima (Fig. 106,
Page 227
rc). In some species of Asplanchna, if not all, a recurrent branch occurs
opening at either end into the main tube of its own side.
The kidneys unite to discharge into the cloaca near its orifice, and on its
distal (primitively ventral) side in many Melicertidae. In Bdelloida the
common duct formed by their fusion opens into the ventral side of a dilated
bladder-like section of the cloaca (Fig. 109, A, bl), which contracts
rhythmically to discharge the liquid; while in the majority of the class they
open singly or by a common duct into a separate contractile vesicle or
bladder, which also discharges at regular intervals into the cloaca on its
ventral or distal side (Figs. 106, bl and 112).
Fig. 112.—Apsilidae: A, Apsilus lentiformis, ♀, dorsal view (after Metschnikoff); the
square brain is seen with nerves to the lateral antennae; B, larva of A. lentiformis
(?), showing the paired eyes and ciliated cupped foot; C, adult of Atrochus
appendiculatus, ♂ (after Wierzejski). al, Lateral antennae; am, median antenna
(just in front is seen the renal commissure); an, anus; br, brain, below which the
paired eyes are seen; c, cloaca; em, embryo; em', em', em''', three successive
stages of embryos in the uterus of C; k, kidney. The coarser muscles are striated.
This bladder may reach when expanded one-third the diameter of the whole
animal, and contract as often as three times per minute; so that in a period
of nine minutes a bulk of water equal to that of the animal must have
diffused through the body-wall, to be removed by the kidneys. It is obvious
that while the function of the kidneys is primitively excretory, the passage
of the water through the body must bring in the oxygen dissolved in the
external medium, and carry off the carbonic acid formed in the tissues, and
opening at either end into the main tube of its own side.
The kidneys unite to discharge into the cloaca near its orifice, and on its
distal (primitively ventral) side in many Melicertidae. In Bdelloida the
common duct formed by their fusion opens into the ventral side of a dilated
bladder-like section of the cloaca (Fig. 109, A, bl), which contracts
rhythmically to discharge the liquid; while in the majority of the class they
open singly or by a common duct into a separate contractile vesicle or
bladder, which also discharges at regular intervals into the cloaca on its
ventral or distal side (Figs. 106, bl and 112).
Fig. 112.—Apsilidae: A, Apsilus lentiformis, ♀, dorsal view (after Metschnikoff); the
square brain is seen with nerves to the lateral antennae; B, larva of A. lentiformis
(?), showing the paired eyes and ciliated cupped foot; C, adult of Atrochus
appendiculatus, ♂ (after Wierzejski). al, Lateral antennae; am, median antenna
(just in front is seen the renal commissure); an, anus; br, brain, below which the
paired eyes are seen; c, cloaca; em, embryo; em', em', em''', three successive
stages of embryos in the uterus of C; k, kidney. The coarser muscles are striated.
This bladder may reach when expanded one-third the diameter of the whole
animal, and contract as often as three times per minute; so that in a period
of nine minutes a bulk of water equal to that of the animal must have
diffused through the body-wall, to be removed by the kidneys. It is obvious
that while the function of the kidneys is primitively excretory, the passage
of the water through the body must bring in the oxygen dissolved in the
external medium, and carry off the carbonic acid formed in the tissues, and
Page 228
so fulfil the act of respiration. This mechanism is physiologically
comparable with that of the contractile vacuole of fresh-water Protozoa. In
a few genera (Conochilus, Lacinularia, Pterodina) the kidneys open
separately after a slight dilatation into the cloaca.
Nervous System.—The nervous centre of the Rotifera is the brain (Fig.
112, C, br), a ganglion lying dorsal to the pharynx; and when this is short it
may be immediately below the surface of the disc (Microcodon). In
Bdelloida a second ganglion is present below the pharynx, and is connected
with the former by lateral cords which contain ganglion cells. From the
brain, nerves are given off to the disc, to the muscles, and to the integument
of the body, as well as to the sense organs. The largest nerves are two given
off from the sides of the brain, each of which divides into a lateral and a
ventral trunk, which run nearly the whole length of the animal.
The brain of several Notommatidae has a curious appendage, white by
reflected light and very opaque; it is a sac full of chalky mineral matter,
which dissolves readily in dilute acids.
Sense Organs.—The most widely diffused sense organs are the antennae or
feelers, which may serve for touch or smell, or possibly both. Each antenna
is a conical or tubular outgrowth of the skin; from its apex projects a fine
pencil of sense hairs borne on a protoplasmic cushion, which receives a
nerve. Often the antenna is elongated, and may then contain a muscle by
which it is retractile (lateral antennae of Melicerta); sometimes it is reduced
to a slight prominence bearing the setae (dorsal antenna of this genus).
There are usually three antennae—a median dorsal (Figs. 109, B, a, and
112, C, am) and two lateral (Figs. 106, 112, C, and 115, A, al), often
approximated towards the ventral surface, and sometimes all but fused on
the middle line, or completely united (Conochilus dossuarius, Copeus
caudatus).[259]
Most Rotifers possess an organ of sight. This in its simplest form is a
refractive globule seated in a red pigmented cup through which the nerve
passes; in other cases it lies directly on the brain. Very frequently the eye is
paired (Figs. 112, B, and 115, A); and these paired eyes may lie on the
comparable with that of the contractile vacuole of fresh-water Protozoa. In
a few genera (Conochilus, Lacinularia, Pterodina) the kidneys open
separately after a slight dilatation into the cloaca.
Nervous System.—The nervous centre of the Rotifera is the brain (Fig.
112, C, br), a ganglion lying dorsal to the pharynx; and when this is short it
may be immediately below the surface of the disc (Microcodon). In
Bdelloida a second ganglion is present below the pharynx, and is connected
with the former by lateral cords which contain ganglion cells. From the
brain, nerves are given off to the disc, to the muscles, and to the integument
of the body, as well as to the sense organs. The largest nerves are two given
off from the sides of the brain, each of which divides into a lateral and a
ventral trunk, which run nearly the whole length of the animal.
The brain of several Notommatidae has a curious appendage, white by
reflected light and very opaque; it is a sac full of chalky mineral matter,
which dissolves readily in dilute acids.
Sense Organs.—The most widely diffused sense organs are the antennae or
feelers, which may serve for touch or smell, or possibly both. Each antenna
is a conical or tubular outgrowth of the skin; from its apex projects a fine
pencil of sense hairs borne on a protoplasmic cushion, which receives a
nerve. Often the antenna is elongated, and may then contain a muscle by
which it is retractile (lateral antennae of Melicerta); sometimes it is reduced
to a slight prominence bearing the setae (dorsal antenna of this genus).
There are usually three antennae—a median dorsal (Figs. 109, B, a, and
112, C, am) and two lateral (Figs. 106, 112, C, and 115, A, al), often
approximated towards the ventral surface, and sometimes all but fused on
the middle line, or completely united (Conochilus dossuarius, Copeus
caudatus).[259]
Most Rotifers possess an organ of sight. This in its simplest form is a
refractive globule seated in a red pigmented cup through which the nerve
passes; in other cases it lies directly on the brain. Very frequently the eye is
paired (Figs. 112, B, and 115, A); and these paired eyes may lie on the
Page 229
brain, and then are so close together that the pigment-cups have the shape
of an x, or else they are seated in the dorsal region of the head behind the
disc. In some cases they lie just under the ciliary wreath, or even within the
region of the disc, and pass towards its ventral side in Pedalion (Fig. 117,
A, e). In Rotifer they lie just under the dorsal side of the proboscis just
below its apex. The median and two lateral eyes often exist together, as in
Eosphora; and sometimes additional paired eyes exist. In Furcularia
longiseta, var. grandis a pair of pigment spots (eyes?) occurs at the hinder
end of the body just in front of the foot.
The active Ploima show a spontaneity of movement and marked power of
avoiding obstacles, etc. This is still more marked in the very active
Pedalion, which, as Rousselet notes, clearly avoids capture by the dropping
tube, aided by its sense of sight, as he suggests, or by the tactile or olfactory
powers of the antennae. They must rank as psychically high in the scale of
creatures of simple organisation.
Reproductive Organs and Reproduction.—The most conspicuous organ
in the female is the large yolk-gland or vitellarium (Figs. 106 and 109, A,
vm), which was regarded as the ovary by all the older observers. It consists
usually of eight cells, with conspicuous nuclei, lying on the ventral side of
the stomach, and frequently displaced to one side; but in most
Asplanchnidae it forms a broad transverse band of numerous cells. In
Pterodina it is horseshoe-shaped, while in Seisonaceae and Bdelloida it is
paired, either gland containing four or eight cells. The true ovary or
germarium (Fig. 106, gm) lies more or less hidden between the yolk-gland
and the stomach; it is composed of numerous minute rounded cells, of
which the hindmost for the time being enlarges by nutrition from the yolk-
gland, and finally receives a membranous shell. This true ovary is
somewhat lateral in most Rotifers, but is median in Asplanchnidae, and
paired in Pterodina, Bdelloida, and Seisonaceae. A membranous covering is
common to the ovary and yolk-gland (paired when these are paired); it is
continued into a thin-walled tube or oviduct, which opens into the cloaca on
its ventral side beyond the bladder or common renal duct. In the viviparous
species the mature ovum (Fig. 112, em) usually lies in the oviduct, dilating
it into a sort of "uterus" until the birth of the young. The ordinary eggs or
"summer eggs" are formed without any fertilisation, and develop
of an x, or else they are seated in the dorsal region of the head behind the
disc. In some cases they lie just under the ciliary wreath, or even within the
region of the disc, and pass towards its ventral side in Pedalion (Fig. 117,
A, e). In Rotifer they lie just under the dorsal side of the proboscis just
below its apex. The median and two lateral eyes often exist together, as in
Eosphora; and sometimes additional paired eyes exist. In Furcularia
longiseta, var. grandis a pair of pigment spots (eyes?) occurs at the hinder
end of the body just in front of the foot.
The active Ploima show a spontaneity of movement and marked power of
avoiding obstacles, etc. This is still more marked in the very active
Pedalion, which, as Rousselet notes, clearly avoids capture by the dropping
tube, aided by its sense of sight, as he suggests, or by the tactile or olfactory
powers of the antennae. They must rank as psychically high in the scale of
creatures of simple organisation.
Reproductive Organs and Reproduction.—The most conspicuous organ
in the female is the large yolk-gland or vitellarium (Figs. 106 and 109, A,
vm), which was regarded as the ovary by all the older observers. It consists
usually of eight cells, with conspicuous nuclei, lying on the ventral side of
the stomach, and frequently displaced to one side; but in most
Asplanchnidae it forms a broad transverse band of numerous cells. In
Pterodina it is horseshoe-shaped, while in Seisonaceae and Bdelloida it is
paired, either gland containing four or eight cells. The true ovary or
germarium (Fig. 106, gm) lies more or less hidden between the yolk-gland
and the stomach; it is composed of numerous minute rounded cells, of
which the hindmost for the time being enlarges by nutrition from the yolk-
gland, and finally receives a membranous shell. This true ovary is
somewhat lateral in most Rotifers, but is median in Asplanchnidae, and
paired in Pterodina, Bdelloida, and Seisonaceae. A membranous covering is
common to the ovary and yolk-gland (paired when these are paired); it is
continued into a thin-walled tube or oviduct, which opens into the cloaca on
its ventral side beyond the bladder or common renal duct. In the viviparous
species the mature ovum (Fig. 112, em) usually lies in the oviduct, dilating
it into a sort of "uterus" until the birth of the young. The ordinary eggs or
"summer eggs" are formed without any fertilisation, and develop
Page 230
immediately; they are often hatched within the tube of the tubicolous
species.
Under certain conditions the unfertilised females produce exclusively
smaller eggs, which develop into males. Maupas[260] has demonstrated that
a rise in temperature to a minimum of 26° C. (79° F.) is the efficient factor.
But as Bergendal points out,[261] the critical temperature probably varies
with the antecedent conditions of the race, since males occur in Greenland
at a very much lower temperature; and it would seem probable that a
temperature approaching that at which the pools habitually dry up is what is
necessary for the production of males, as a provision for those fertilised
eggs, which, having a hard shell often adorned with prickly prominences,
and usually remaining for some time before development, are capable of
withstanding drought; such eggs are termed "winter eggs," but a better term
would be "resting eggs" (German, "Dauereier").[262]
Fig. 113.—Diglena catellina. (After Weber.) A, Male; B, the pair in copula; C, female,
p, Penis; te, testis.
The male organs consist of a testis (Fig. 113, A, te) with accessory glands, a
large seminal vesicle, and a protrusible or projecting penis (p). In
Notommata and Diglena true intromission at the cloaca (B) has been seen
by many observers; but it appears equally certain that in many cases the
male bores into the body-wall of the female at any point, and deposits the
spermatozoa in the body-cavity, so that they must pass through the wall of
the oviduct to effect fertilisation. Maupas finds that the process of
fertilisation is ineffective except upon such newly-hatched females as
would otherwise be the parents of small male eggs; that fertilisation is
inoperative even for these at a later age when their eggs have begun to
species.
Under certain conditions the unfertilised females produce exclusively
smaller eggs, which develop into males. Maupas[260] has demonstrated that
a rise in temperature to a minimum of 26° C. (79° F.) is the efficient factor.
But as Bergendal points out,[261] the critical temperature probably varies
with the antecedent conditions of the race, since males occur in Greenland
at a very much lower temperature; and it would seem probable that a
temperature approaching that at which the pools habitually dry up is what is
necessary for the production of males, as a provision for those fertilised
eggs, which, having a hard shell often adorned with prickly prominences,
and usually remaining for some time before development, are capable of
withstanding drought; such eggs are termed "winter eggs," but a better term
would be "resting eggs" (German, "Dauereier").[262]
Fig. 113.—Diglena catellina. (After Weber.) A, Male; B, the pair in copula; C, female,
p, Penis; te, testis.
The male organs consist of a testis (Fig. 113, A, te) with accessory glands, a
large seminal vesicle, and a protrusible or projecting penis (p). In
Notommata and Diglena true intromission at the cloaca (B) has been seen
by many observers; but it appears equally certain that in many cases the
male bores into the body-wall of the female at any point, and deposits the
spermatozoa in the body-cavity, so that they must pass through the wall of
the oviduct to effect fertilisation. Maupas finds that the process of
fertilisation is ineffective except upon such newly-hatched females as
would otherwise be the parents of small male eggs; that fertilisation is
inoperative even for these at a later age when their eggs have begun to
Page 231
mature; and that it is wholly useless for those that lay ordinary summer
eggs. The parent of male or winter eggs would thus be comparable to the
queen bee, which if not fertilised produces drones. These sexual relations
find a close parallel in the Ostracod and Phyllopod Crustacea, as well as in
many plant-lice (Homoptera).
Development.—This has only been fully studied in the summer egg; in
Brachionus by Salensky,[263] in Melicerta by Joliet[264]; in Eosphora
digitata and several other species by Tessin[265]; in Callidina and Melicerta
by Zelinka,[266] the last two observers having utilised modern methods of
research.[267] We shall base our account on Zelinka's observations. As in the
case of most "parthenogenetic" eggs, the ovarian egg begins by a very
uneven division to form two cells: the minute "first polar body" which
undergoes no further development; and the definitive egg, which by its
repeated divisions gives rise to the tissues and organs.
Segmentation is very unequal, and recalls that of Molluscs in several
respects. The first division gives rise to a smaller and a larger cell. Both of
these divide again, the latter unequally, so that now there are three smaller
cells and one large one; and after repeated divisions of the small cells and
unequal divisions of the larger one, a stage is reached where there are a
number of small cells and one large one, which sinks in and is overgrown
by the small ones. Just prior to this the large cell undergoes equal divisions;
its cells are the "hypoblast" cells (Fig. 114, hyp), and give rise to the gullet,
stomach, and intestine, with their appendages, and the generative organs;
while the smaller cells constitute the "epiblast" (ep), which gives rise to the
body-wall and muscles, to the cement glands, nervous system, pharynx and
mastax, and probably to the kidneys.
eggs. The parent of male or winter eggs would thus be comparable to the
queen bee, which if not fertilised produces drones. These sexual relations
find a close parallel in the Ostracod and Phyllopod Crustacea, as well as in
many plant-lice (Homoptera).
Development.—This has only been fully studied in the summer egg; in
Brachionus by Salensky,[263] in Melicerta by Joliet[264]; in Eosphora
digitata and several other species by Tessin[265]; in Callidina and Melicerta
by Zelinka,[266] the last two observers having utilised modern methods of
research.[267] We shall base our account on Zelinka's observations. As in the
case of most "parthenogenetic" eggs, the ovarian egg begins by a very
uneven division to form two cells: the minute "first polar body" which
undergoes no further development; and the definitive egg, which by its
repeated divisions gives rise to the tissues and organs.
Segmentation is very unequal, and recalls that of Molluscs in several
respects. The first division gives rise to a smaller and a larger cell. Both of
these divide again, the latter unequally, so that now there are three smaller
cells and one large one; and after repeated divisions of the small cells and
unequal divisions of the larger one, a stage is reached where there are a
number of small cells and one large one, which sinks in and is overgrown
by the small ones. Just prior to this the large cell undergoes equal divisions;
its cells are the "hypoblast" cells (Fig. 114, hyp), and give rise to the gullet,
stomach, and intestine, with their appendages, and the generative organs;
while the smaller cells constitute the "epiblast" (ep), which gives rise to the
body-wall and muscles, to the cement glands, nervous system, pharynx and
mastax, and probably to the kidneys.
Page 232
Fig. 114.—Development of Callidina. (After Zelinka.) A, Early stage showing
involution of granular cells (g), to form the mastax or gizzard. B, Involution
complete. C, Second involution of epiblast cells to form pharynx. D, The embryo
bent on itself at ventral fold (vf). E, Showing ingrowth of epiblast to form brain
(br): an, involution of epiblast to form cloaca; br, brain; ep, epiblast; fg,
involution to form cement glands of foot; g, granular cells; gi, gizzard; hyp,
hypoblast; m, mouth; o, ovary; sp, salivary glands; vf, limiting body from foot.
Owing to the elongation of the body within the narrow space of the egg the
hinder part is bent up on the ventral surface (D, E); and this part, narrower
than the rest, forms the foot, the centre of which is at first occupied by a
column of hypoblast. The cloaca is now formed by a dorsal ingrowth of
epiblast (the "proctodaeum") at the junction of the foot and the body (an).
The hypoblast in the body anterior to the cloacal ingrowth forms the
digestive apparatus; the part immediately behind forms the reproductive
organs (o); and the hindmost part apparently disappears. An ingrowth of
epiblast at the extreme tip of the foot gives rise to the cement glands (fg).
The muscles arise from the epiblast cells. The disc arises from the
modification of epiblast cells lateral to and behind the mouth, enclosing a
so-called "polar area"; it is completed by the transformation of cells on the
ventral side of the mouth. The brain (br) is formed by the multiplication of
epiblast cells; and in Bdelloida a ventral ingrowth below the mouth forms
the sub-oesophageal ganglion. The ciliated cup in Melicerta is formed as a
ventral hollow, only later on united with the ciliated furrow of the wreath by
the lateral grooves.[268] In Melicerta the two eyes are formed in the polar
area. The young as hatched differs from the adult in the greater simplicity of
its ciliary wreath; and in the tubicolous forms the cupped end of the foot-
gland is ciliated, and two eyes are present on the polar area, which later sink
in, and often disappear more or less completely. It is stated that the young
hatched from winter eggs do not pass through this larval state.
involution of granular cells (g), to form the mastax or gizzard. B, Involution
complete. C, Second involution of epiblast cells to form pharynx. D, The embryo
bent on itself at ventral fold (vf). E, Showing ingrowth of epiblast to form brain
(br): an, involution of epiblast to form cloaca; br, brain; ep, epiblast; fg,
involution to form cement glands of foot; g, granular cells; gi, gizzard; hyp,
hypoblast; m, mouth; o, ovary; sp, salivary glands; vf, limiting body from foot.
Owing to the elongation of the body within the narrow space of the egg the
hinder part is bent up on the ventral surface (D, E); and this part, narrower
than the rest, forms the foot, the centre of which is at first occupied by a
column of hypoblast. The cloaca is now formed by a dorsal ingrowth of
epiblast (the "proctodaeum") at the junction of the foot and the body (an).
The hypoblast in the body anterior to the cloacal ingrowth forms the
digestive apparatus; the part immediately behind forms the reproductive
organs (o); and the hindmost part apparently disappears. An ingrowth of
epiblast at the extreme tip of the foot gives rise to the cement glands (fg).
The muscles arise from the epiblast cells. The disc arises from the
modification of epiblast cells lateral to and behind the mouth, enclosing a
so-called "polar area"; it is completed by the transformation of cells on the
ventral side of the mouth. The brain (br) is formed by the multiplication of
epiblast cells; and in Bdelloida a ventral ingrowth below the mouth forms
the sub-oesophageal ganglion. The ciliated cup in Melicerta is formed as a
ventral hollow, only later on united with the ciliated furrow of the wreath by
the lateral grooves.[268] In Melicerta the two eyes are formed in the polar
area. The young as hatched differs from the adult in the greater simplicity of
its ciliary wreath; and in the tubicolous forms the cupped end of the foot-
gland is ciliated, and two eyes are present on the polar area, which later sink
in, and often disappear more or less completely. It is stated that the young
hatched from winter eggs do not pass through this larval state.
Page 233
Fig. 115.—Stephanoceros eichhornii. (After Cubitt.) A, Dorsal view of the upper part
in its tube: al, lateral antenna; e, eye; em, developing embryo in uterus; g,
gizzard; s.g, median salivary gland. B, Extremity of foot. C, Lateral view of base
of disc: am, median antenna; of, oral funnel; s.g, median salivary gland; tf, in the
crop, indicates the ciliated tube prolonging the funnel; tr, horseshoe-shaped
trochus.
Classification.[269]
Order I. Flosculariaceae.—Females mostly tubicolous, attached by a long
contractile foot. Disc produced into a wide funnel-shaped contractile cup,
produced into lobes with long setae (Floscularia) or coarse cilia
(Stephanoceros), or entire (Apsilidae); an outer row of fine cilia rarely
present; trochus a horseshoe, open behind. Oral funnel a slender tube
hanging freely into a large pharyngeal crop; trophi uncinate projecting
freely into the crop. Kidneys often united by an anterior cross-piece. Body-
wall often containing a definite system of canals, filled with refractive
granules, and serving by their contraction to dilate the disc. Males (Fig.
107, 1) and larvae vermiform with a ciliated pedal cup, and a simple
wreath, with two eyes on the disc.
Fam. 1. Flosculariidae: Floscularia Oken, Stephanoceros E. (Fig. 115).
Fam. 2. Apsilidae: Apsilus Metschnikoff (Fig. 112, A), Acyclus Leidy,
Atrochus Wierzejski (Fig. 112, C).
The family Flosculariidae contains some most exquisite forms;
Stephanoceros, the "Crown Animalcule," being probably the most lovely of
the Class, and many of the Floscules coming not far behind. The Apsilidae
are mostly mud-dwellers.
in its tube: al, lateral antenna; e, eye; em, developing embryo in uterus; g,
gizzard; s.g, median salivary gland. B, Extremity of foot. C, Lateral view of base
of disc: am, median antenna; of, oral funnel; s.g, median salivary gland; tf, in the
crop, indicates the ciliated tube prolonging the funnel; tr, horseshoe-shaped
trochus.
Classification.[269]
Order I. Flosculariaceae.—Females mostly tubicolous, attached by a long
contractile foot. Disc produced into a wide funnel-shaped contractile cup,
produced into lobes with long setae (Floscularia) or coarse cilia
(Stephanoceros), or entire (Apsilidae); an outer row of fine cilia rarely
present; trochus a horseshoe, open behind. Oral funnel a slender tube
hanging freely into a large pharyngeal crop; trophi uncinate projecting
freely into the crop. Kidneys often united by an anterior cross-piece. Body-
wall often containing a definite system of canals, filled with refractive
granules, and serving by their contraction to dilate the disc. Males (Fig.
107, 1) and larvae vermiform with a ciliated pedal cup, and a simple
wreath, with two eyes on the disc.
Fam. 1. Flosculariidae: Floscularia Oken, Stephanoceros E. (Fig. 115).
Fam. 2. Apsilidae: Apsilus Metschnikoff (Fig. 112, A), Acyclus Leidy,
Atrochus Wierzejski (Fig. 112, C).
The family Flosculariidae contains some most exquisite forms;
Stephanoceros, the "Crown Animalcule," being probably the most lovely of
the Class, and many of the Floscules coming not far behind. The Apsilidae
are mostly mud-dwellers.
Page 234
Order II. Melicertaceae.—Females (except in Trochosphaera) attached or
tubicolous; tube variable. Disc with a dorsal gap (except Conochilus) often
two-lobed or corolla-like; a ventral lip often separating off a ventral ciliated
cup continuous by a pair of gutters with the ciliated groove; trochus of
stronger cilia than the cingulum. Trophi malleoramate in a distinct mastax.
Intestine much curved dorsally, cloaca long eversible (except
Trochosphaera). Males and larvae as in Order I.
Fig. 116.—Melicerta ringens. (After Joliet). A, Side view; B, dorsal view. al, Lateral
antennae; ci, cingulum seen by transparency; g, gizzard; p, pellet in ciliated cup,
about to be deposited on edge of tube; tr, trochus.
Fam. 3. Melicertidae: Melicerta E. (Fig. 116), Limnias Schrank,
Cephalosiphon E., Oecistes E., Lacinularia E., Megalotrocha E.,
Conochilus E., Octotrocha Thorpe.
Fam. 4. Trochosphaeridae: Trochosphaera Semper (Fig. 118, D).
The Melicertidae embrace a large number of tubicolous forms, many of
which are social. This habit is especially noticeable in Lacinularia socialis,
which forms a gelatinous incrustation easily seen by the naked eye; and in
Conochilus volvox, which forms free-swimming globular aggregates, the
young attaching themselves when hatched to the centre of the ball, and the
ball splitting up into two as soon as undue pressure is exerted at the
periphery by overcrowding. In this genus the eyes are very conspicuous in
the adult, as they are in the similar free-swimming aggregates of
Lacinularia racemovata.
Trochosphaera (Fig. 118, D) is remarkable for its peculiar spherical shape,
the absence of a foot, the limitation of the viscera to the lower hemisphere,
and the dorsal position of the ovary. But a reference to the figure will show
tubicolous; tube variable. Disc with a dorsal gap (except Conochilus) often
two-lobed or corolla-like; a ventral lip often separating off a ventral ciliated
cup continuous by a pair of gutters with the ciliated groove; trochus of
stronger cilia than the cingulum. Trophi malleoramate in a distinct mastax.
Intestine much curved dorsally, cloaca long eversible (except
Trochosphaera). Males and larvae as in Order I.
Fig. 116.—Melicerta ringens. (After Joliet). A, Side view; B, dorsal view. al, Lateral
antennae; ci, cingulum seen by transparency; g, gizzard; p, pellet in ciliated cup,
about to be deposited on edge of tube; tr, trochus.
Fam. 3. Melicertidae: Melicerta E. (Fig. 116), Limnias Schrank,
Cephalosiphon E., Oecistes E., Lacinularia E., Megalotrocha E.,
Conochilus E., Octotrocha Thorpe.
Fam. 4. Trochosphaeridae: Trochosphaera Semper (Fig. 118, D).
The Melicertidae embrace a large number of tubicolous forms, many of
which are social. This habit is especially noticeable in Lacinularia socialis,
which forms a gelatinous incrustation easily seen by the naked eye; and in
Conochilus volvox, which forms free-swimming globular aggregates, the
young attaching themselves when hatched to the centre of the ball, and the
ball splitting up into two as soon as undue pressure is exerted at the
periphery by overcrowding. In this genus the eyes are very conspicuous in
the adult, as they are in the similar free-swimming aggregates of
Lacinularia racemovata.
Trochosphaera (Fig. 118, D) is remarkable for its peculiar spherical shape,
the absence of a foot, the limitation of the viscera to the lower hemisphere,
and the dorsal position of the ovary. But a reference to the figure will show
Page 235
that the outgrowth of a foot in the quadrant between the mouth and anus
and the flattening of the upper hemisphere would bring its organs on the
whole into close correspondence with those of the rest of the Order. It is
recorded from South China, the Philippines, and North-East Australia, and
has only been seen by Semper, the founder of the genus, and by Thorpe,
who saw the male of the first species, and described a second.[270]
Order III. Bdelloida.—Females creeping like a leech, as well as
swimming (males unknown), susceptible of desiccation and revival
("anabiotic"). Body telescopic at both ends. Disc (except in Adineta) chiefly
composed of two dorsal lobes like kettle-drums, wholly retractile; a dorsal
proboscis or trunk-like prolongation of the body ends in a ciliated, sensory,
and adhesive cup used in crawling, and overhung by a pair of membranous
flaps. Trophi ramate; brain with a ventral ganglion, forming a complete
ring. Eyes, two on the proboscis or brain, or absent. Bladder a mere
dilatation of the rectum. Foot often possessing blind spurs, as well as two or
three retractile perforated toes, or forming a terminal disc perforated by
numerous pores of the cement glands, rarely ciliated.[271]
Fam. 5. Philodinidae: Philodina E. (Fig. 110), Rotifer Schrank,
Actinurus E., Callidina E. (Fig. 109), Adineta H.
This group is remarkable for the great resisting powers of its members to
drought and to heat and cold when dried, a fact which may explain the
absence of males, though Janson records the occurrence of winter eggs in
four species of Callidina and in Adineta vaga. The body is often strongly
pigmented; red in Philodina roseola, Callidina scarlatina, and C. russeola,
yellow in P. citrina, Rotifer citrinus, and Discopus synaptae. Most of the
species are dust- or moss-dwellers; some, such as Rotifer vulgaris, are
equally common in organic débris in infusions, pools, and ditches. Discopus
adheres to the skin of the Holothurian Synapta.
Order IV. Asplanchnaceae.—Females ovoid, footless except in
Asplanchnopus. Disc often bearing a pair of antennae; circular, often
prolonged at the margin into two rounded lobes, interrupted dorsally,
depressed at the ventral side into a deep ventral funnel. Trophi incudate
and the flattening of the upper hemisphere would bring its organs on the
whole into close correspondence with those of the rest of the Order. It is
recorded from South China, the Philippines, and North-East Australia, and
has only been seen by Semper, the founder of the genus, and by Thorpe,
who saw the male of the first species, and described a second.[270]
Order III. Bdelloida.—Females creeping like a leech, as well as
swimming (males unknown), susceptible of desiccation and revival
("anabiotic"). Body telescopic at both ends. Disc (except in Adineta) chiefly
composed of two dorsal lobes like kettle-drums, wholly retractile; a dorsal
proboscis or trunk-like prolongation of the body ends in a ciliated, sensory,
and adhesive cup used in crawling, and overhung by a pair of membranous
flaps. Trophi ramate; brain with a ventral ganglion, forming a complete
ring. Eyes, two on the proboscis or brain, or absent. Bladder a mere
dilatation of the rectum. Foot often possessing blind spurs, as well as two or
three retractile perforated toes, or forming a terminal disc perforated by
numerous pores of the cement glands, rarely ciliated.[271]
Fam. 5. Philodinidae: Philodina E. (Fig. 110), Rotifer Schrank,
Actinurus E., Callidina E. (Fig. 109), Adineta H.
This group is remarkable for the great resisting powers of its members to
drought and to heat and cold when dried, a fact which may explain the
absence of males, though Janson records the occurrence of winter eggs in
four species of Callidina and in Adineta vaga. The body is often strongly
pigmented; red in Philodina roseola, Callidina scarlatina, and C. russeola,
yellow in P. citrina, Rotifer citrinus, and Discopus synaptae. Most of the
species are dust- or moss-dwellers; some, such as Rotifer vulgaris, are
equally common in organic débris in infusions, pools, and ditches. Discopus
adheres to the skin of the Holothurian Synapta.
Order IV. Asplanchnaceae.—Females ovoid, footless except in
Asplanchnopus. Disc often bearing a pair of antennae; circular, often
prolonged at the margin into two rounded lobes, interrupted dorsally,
depressed at the ventral side into a deep ventral funnel. Trophi incudate
Page 236
(virgate in Ascomorpha), mastax enlarged dorsally into a wide crop;
stomach large, blind. Kidneys large, with a "recurrent duct" and numerous
tags; bladder large. Brain large, with a median eye, and frequently paired
smaller eyes at the base of the marginal processes of the disc; anterior
antennae paired, relatively far back on dorsal surface. Males (Fig. 107, 5)
relatively large, frequently found.
Fam. 6. Asplanchnidae: Asplanchna G., Asplanchnopus De Guerne, (?)
Ascomorpha, Perty, (?) Dinops Western.
Order V. Scirtopoda.—Females of conical shape, with the body prolonged
into hollow limb-like expansions (see p. 201) moved by strong muscles, and
ending in branched setose fins like the limbs of Crustacea. Disc as in
Bdelloids, but not retractile. Foot represented by two subventral toes,
ciliated, inconstant or absent. Trophi malleoramate. Eyes two, latero-
ventral, on the disc. Male (Fig. 107, 8) conical, with simple setae.
Fam. 7. Pedalionidae: Pedalion H. (Fig. 117),[272] Hexarthra
Schmarda.[273]
Order VI. Ploima.—Free-swimming forms, more rarely parasites, often
adherent by their trophi to a host. Disc variable, often bearing within the
cingulum a number of lobes fringed with coarse compound cilia. Foot
rarely absent, marked off by a sharp constriction. Mastax variable, rarely
malleoramate, never incudate or uncinate. Intestine not blind. Males small.
[274]
Sub-Order A. Illoricata.—Ploima with a soft flexible integument; disc
variable; ciliated auricles sometimes present (Synchaetidae,
Notommatidae); foot rarely absent; trophi usually malleate.
Fam. 8. Microcodonidae: Microcodon E., Microcodides Bergendal.
Fam. 9. Rhinopidae: Rhinops H.
stomach large, blind. Kidneys large, with a "recurrent duct" and numerous
tags; bladder large. Brain large, with a median eye, and frequently paired
smaller eyes at the base of the marginal processes of the disc; anterior
antennae paired, relatively far back on dorsal surface. Males (Fig. 107, 5)
relatively large, frequently found.
Fam. 6. Asplanchnidae: Asplanchna G., Asplanchnopus De Guerne, (?)
Ascomorpha, Perty, (?) Dinops Western.
Order V. Scirtopoda.—Females of conical shape, with the body prolonged
into hollow limb-like expansions (see p. 201) moved by strong muscles, and
ending in branched setose fins like the limbs of Crustacea. Disc as in
Bdelloids, but not retractile. Foot represented by two subventral toes,
ciliated, inconstant or absent. Trophi malleoramate. Eyes two, latero-
ventral, on the disc. Male (Fig. 107, 8) conical, with simple setae.
Fam. 7. Pedalionidae: Pedalion H. (Fig. 117),[272] Hexarthra
Schmarda.[273]
Order VI. Ploima.—Free-swimming forms, more rarely parasites, often
adherent by their trophi to a host. Disc variable, often bearing within the
cingulum a number of lobes fringed with coarse compound cilia. Foot
rarely absent, marked off by a sharp constriction. Mastax variable, rarely
malleoramate, never incudate or uncinate. Intestine not blind. Males small.
[274]
Sub-Order A. Illoricata.—Ploima with a soft flexible integument; disc
variable; ciliated auricles sometimes present (Synchaetidae,
Notommatidae); foot rarely absent; trophi usually malleate.
Fam. 8. Microcodonidae: Microcodon E., Microcodides Bergendal.
Fam. 9. Rhinopidae: Rhinops H.
Page 237
Fam. 10. Hydatinidae: Hydatina E. (Fig. 106), Notops H., Hudsonella
Zach., Cyrtonia Rouss.
Fam. 11. Synchaetidae: Synchaeta E.
Fam. 12. Notommatidae: Notommata E., Pleurotrocha E., Copeus G.,
Proales G., Furcularia G., Eosphora G., Triophthalmus E., Diglena E.
(Fig. 113), Distemma E., Triphylus E., Taphrocampa G., Albertia Duj.,
Balatro Clap.
Fam. 13. Drilophagidae: Drilophagus Vejdovsky.
Fam. 14. Triarthridae: Triarthra E., Polyarthra E., Pteroessa G.,
Pedetes G.
Fig. 117.—Pedalion mirum, female. (After Hudson.) A, Ventral view; B, side view. a,
Median antenna; al, antero-lateral limb; an, anus; ci, cingulum; dl, dorso-median
limb; e, eye; f, ciliated pedal processes; l, lip; m, mouth; pl, postero-lateral limb;
tr, trochus; vl, ventro-median limb.
To this group belongs the eyeless Hydatina, a classical object of study,
common in greenish pools, whose male was the first male Rotifer to be
figured by Ehrenberg (1838), though he did not recognise its nature, and
gave it the name of Enteroploea hydatina. Rhinops has the back of the
corona curiously prolonged forwards into a sort of proboscis bearing two
eyes. Some species of Notommata and Proales are distinctly annulated; in
Taphrocampa the segmentation is so marked as to give the appearance of
mesenteric septa extending inwards from the body-wall to the intestine.
Microcodon has a wreath which is very peculiar in its extreme simplicity,
with the mouth nearly central, and the eye lying just dorsal to the mouth.
Zach., Cyrtonia Rouss.
Fam. 11. Synchaetidae: Synchaeta E.
Fam. 12. Notommatidae: Notommata E., Pleurotrocha E., Copeus G.,
Proales G., Furcularia G., Eosphora G., Triophthalmus E., Diglena E.
(Fig. 113), Distemma E., Triphylus E., Taphrocampa G., Albertia Duj.,
Balatro Clap.
Fam. 13. Drilophagidae: Drilophagus Vejdovsky.
Fam. 14. Triarthridae: Triarthra E., Polyarthra E., Pteroessa G.,
Pedetes G.
Fig. 117.—Pedalion mirum, female. (After Hudson.) A, Ventral view; B, side view. a,
Median antenna; al, antero-lateral limb; an, anus; ci, cingulum; dl, dorso-median
limb; e, eye; f, ciliated pedal processes; l, lip; m, mouth; pl, postero-lateral limb;
tr, trochus; vl, ventro-median limb.
To this group belongs the eyeless Hydatina, a classical object of study,
common in greenish pools, whose male was the first male Rotifer to be
figured by Ehrenberg (1838), though he did not recognise its nature, and
gave it the name of Enteroploea hydatina. Rhinops has the back of the
corona curiously prolonged forwards into a sort of proboscis bearing two
eyes. Some species of Notommata and Proales are distinctly annulated; in
Taphrocampa the segmentation is so marked as to give the appearance of
mesenteric septa extending inwards from the body-wall to the intestine.
Microcodon has a wreath which is very peculiar in its extreme simplicity,
with the mouth nearly central, and the eye lying just dorsal to the mouth.
Page 238
The Triarthridae, which resemble the Scirtopoda in having strong leaping
spines fringed by fine bristles, should perhaps be placed in the next sub-
Order.
Sub-Order B. Loricata.—Ploima with a firm elastic cuticle of definite
form, persistent after death, continuous, or divided by thinner strips into
plates or shields, which again may be areolated. The cuticle may also be
shagreened or embossed in various ways.
Fam. 15. Rattulidae: Rattulus E., Mastigocerca E., Coelopus G.,
Diurella (?) Eyfurth.
Fam. 16. Dinocharididae: Dinocharis E., Scaridium E., Stephanops E.
Fam. 17. Salpinidae: Salpina E., Diaschiza G., Ploesoma Herrick,
Diplax G., Diplois G.
Fam. 18. Euchlanididae: Euchlanis E., Dapidia G., Apodoides Joseph.
Fam. 19. Cathypnidae: Cathypna G., Distyla Eckstein, Monostyla E.
Fam. 20. Coluridae: Colurus E., Metopidia E., Monura E., Mytilia G.,
Cochleare G., Dispinthera G.
Fam. 21. Pterodinidae: Pterodina E., Pompholyx G.
Fam. 22. Brachionidae: Brachionus E., Noteus E., Schizocerca Daday.
Fam. 23. Anuraeidae: Anuraea E., Notholca G., Eretmia G.
The group includes a number of very minute forms, besides others
conspicuous both for size and beauty. A soft dorsal flap above the head
occurs in Stephanops; also in Coluridae, a large family of minute species,
where the flap is movable, and looks in profile like a hook overhanging the
forehead. The genus Pterodina, like Pedalion and Triarthra, combines a
spines fringed by fine bristles, should perhaps be placed in the next sub-
Order.
Sub-Order B. Loricata.—Ploima with a firm elastic cuticle of definite
form, persistent after death, continuous, or divided by thinner strips into
plates or shields, which again may be areolated. The cuticle may also be
shagreened or embossed in various ways.
Fam. 15. Rattulidae: Rattulus E., Mastigocerca E., Coelopus G.,
Diurella (?) Eyfurth.
Fam. 16. Dinocharididae: Dinocharis E., Scaridium E., Stephanops E.
Fam. 17. Salpinidae: Salpina E., Diaschiza G., Ploesoma Herrick,
Diplax G., Diplois G.
Fam. 18. Euchlanididae: Euchlanis E., Dapidia G., Apodoides Joseph.
Fam. 19. Cathypnidae: Cathypna G., Distyla Eckstein, Monostyla E.
Fam. 20. Coluridae: Colurus E., Metopidia E., Monura E., Mytilia G.,
Cochleare G., Dispinthera G.
Fam. 21. Pterodinidae: Pterodina E., Pompholyx G.
Fam. 22. Brachionidae: Brachionus E., Noteus E., Schizocerca Daday.
Fam. 23. Anuraeidae: Anuraea E., Notholca G., Eretmia G.
The group includes a number of very minute forms, besides others
conspicuous both for size and beauty. A soft dorsal flap above the head
occurs in Stephanops; also in Coluridae, a large family of minute species,
where the flap is movable, and looks in profile like a hook overhanging the
forehead. The genus Pterodina, like Pedalion and Triarthra, combines a
Page 239
Bdelloid disc with malleoramate trophi, while its exsertile wrinkled foot
ends in a ciliated cup like that of a larval tubicolous species.
Brachionus, a large, often flat, transparent form, with a long wrinkled foot,
is a very common genus, known to the earlier observers, and repeatedly
figured by them. Pompholyx has a sack-like lorica, no foot, and carries its
immense egg suspended by an elastic thread from the cloaca. The
Anuraeidae lack the foot, and often have great spines or bristles projecting
from the lorica, which no doubt facilitate floating. They are abundant in the
"plankton" or floating fauna of large lakes far from the shore. Many marine
species belong to this family.
Order VII. Seisonaceae.—Marine Rotifers parasitic on the Crustacean
Nebalia; males resembling the females. Body elongated, with a slender
retractile neck, a much reduced disc, an elongated foot with a terminal
perforated disc as in Callidina. Trophi virgate exsertile. Genito-urinary
cloaca opening at the base of the neck in the male, at the hinder end of the
body in the female. Intestine complete (Seison) or blind (Paraseison).[275]
Fam. 24. Seisonidae: Seison Grube; Paraseison Plate; Saccobdella Van
Beneden and Hesse.
Habits.—The habitat of Rotifers is well known to the student of pond life.
Every dip from a greenish pool will give us a supply, if there be not an
excessive contamination by manure; and such pools give us some of the
largest and most beautiful forms, such as Hydatina and Brachionus,
swimming about among the fibrous Algae and feeding on the organic débris
among them. Almost any organic infusions freely exposed to the open air
will yield Ploima shortly after the active putrefaction is completed. The
finer water-weeds yield most of the beautiful tubicolous forms. A whole
group of species and genera are quasi-pelagic in fresh and salt water,
constituting a large proportion of the "plankton" or floating life near the
surface; and some of these are found in deep water or in the depths of the
lakes. Among them are the Asplanchnidae, Triarthridae, and Anuraeidae. A
number of Loricates, such as Notholca and Eretmia, are armed with long
spines, which doubtless render floating easier.
ends in a ciliated cup like that of a larval tubicolous species.
Brachionus, a large, often flat, transparent form, with a long wrinkled foot,
is a very common genus, known to the earlier observers, and repeatedly
figured by them. Pompholyx has a sack-like lorica, no foot, and carries its
immense egg suspended by an elastic thread from the cloaca. The
Anuraeidae lack the foot, and often have great spines or bristles projecting
from the lorica, which no doubt facilitate floating. They are abundant in the
"plankton" or floating fauna of large lakes far from the shore. Many marine
species belong to this family.
Order VII. Seisonaceae.—Marine Rotifers parasitic on the Crustacean
Nebalia; males resembling the females. Body elongated, with a slender
retractile neck, a much reduced disc, an elongated foot with a terminal
perforated disc as in Callidina. Trophi virgate exsertile. Genito-urinary
cloaca opening at the base of the neck in the male, at the hinder end of the
body in the female. Intestine complete (Seison) or blind (Paraseison).[275]
Fam. 24. Seisonidae: Seison Grube; Paraseison Plate; Saccobdella Van
Beneden and Hesse.
Habits.—The habitat of Rotifers is well known to the student of pond life.
Every dip from a greenish pool will give us a supply, if there be not an
excessive contamination by manure; and such pools give us some of the
largest and most beautiful forms, such as Hydatina and Brachionus,
swimming about among the fibrous Algae and feeding on the organic débris
among them. Almost any organic infusions freely exposed to the open air
will yield Ploima shortly after the active putrefaction is completed. The
finer water-weeds yield most of the beautiful tubicolous forms. A whole
group of species and genera are quasi-pelagic in fresh and salt water,
constituting a large proportion of the "plankton" or floating life near the
surface; and some of these are found in deep water or in the depths of the
lakes. Among them are the Asplanchnidae, Triarthridae, and Anuraeidae. A
number of Loricates, such as Notholca and Eretmia, are armed with long
spines, which doubtless render floating easier.
Page 240
Among tubicolous forms Conochilus volvox and Lacinularia racemovata
have this pelagic habit, forming floating globular or ovoid colonies, and two
species of Floscularia also float freely in their tubes.
The following forms occur in salt or brackish water,[276] those marked with
an asterisk (*) also occurring in fresh water:—
Floscularia campanulata.* Melicerta tubicolaria.* Rotifer citrinus.*
Discopus synaptae. Synchaeta baltica, S. monopus, S. apus, S.
tremula,* S. longipes, S. tavina. Asplanchna girodi.* Asplanchnopus
syringoides. Hexarthra polyptera. Notommata naias, N. reinhardti.
Proales decipiens. Furcularia forficula,* F. gracilis, F. reinhardti, F.
marina, F. neapolitana. Diglena catellina,* D. suilla, D. putrida.
Pleurotrocha leptura. Distemma raptor, D. marinum, D. platyceps.*
Bothriocerca longicauda. Polyarthra platyptera.* Triarthra longiseta.*
Rattulus calyptus. Diurella marina, D. brevidactylus, D. brevis.
Diaschiza fretalis. Euchlanis luna. Monostyla quadridentata, M.
lunaris. Colurus amblytelus, C. uncinatus,* C. dactylotus, C.
coelopinus, C. pedatus, C. rotundatus, C. truncatus, C. caudatus.*
Mytilia tavina. Pterodina clypeata. Brachionus bakeri,* B. mülleri.
Anuraea valga,* A. biremis,* A. aculeata,* A. tecta,* A. cochlearis.*
Notholca striata,* N. scapha,* N. thalassia, N. spinifera, N. inermis, N.
jugosa, N. rhomboidea. Seison grubei, S. annulatus. Paraseison
asplanchnus, P. nudus, P. proboscideus, P. ciliatus. Discobdella
nebaliae.
Thus about seventy species are recorded as marine. Synchaeta baltica is
truly pelagic, and contributes to the phosphorescence of the ocean.
Other forms again are parasitic. Proales werneckii is found in Vaucheria, a
coarse, dark green, thread-like Alga found in fresh water; and the closely
allied P. parasita is not uncommon in the beautiful floating green spheres of
Volvox.[277] Albertia, Drilophagus, and Balatro are parasitic on or in fresh-
water Oligochaetes; the curious Seisonaceae are parasitic on Nebalia, a
small Crustacean easily obtained in masses of whelk's eggs; the aberrant
Bdelloid Discopus attaches itself to the surface of the Holothurian Synapta.
have this pelagic habit, forming floating globular or ovoid colonies, and two
species of Floscularia also float freely in their tubes.
The following forms occur in salt or brackish water,[276] those marked with
an asterisk (*) also occurring in fresh water:—
Floscularia campanulata.* Melicerta tubicolaria.* Rotifer citrinus.*
Discopus synaptae. Synchaeta baltica, S. monopus, S. apus, S.
tremula,* S. longipes, S. tavina. Asplanchna girodi.* Asplanchnopus
syringoides. Hexarthra polyptera. Notommata naias, N. reinhardti.
Proales decipiens. Furcularia forficula,* F. gracilis, F. reinhardti, F.
marina, F. neapolitana. Diglena catellina,* D. suilla, D. putrida.
Pleurotrocha leptura. Distemma raptor, D. marinum, D. platyceps.*
Bothriocerca longicauda. Polyarthra platyptera.* Triarthra longiseta.*
Rattulus calyptus. Diurella marina, D. brevidactylus, D. brevis.
Diaschiza fretalis. Euchlanis luna. Monostyla quadridentata, M.
lunaris. Colurus amblytelus, C. uncinatus,* C. dactylotus, C.
coelopinus, C. pedatus, C. rotundatus, C. truncatus, C. caudatus.*
Mytilia tavina. Pterodina clypeata. Brachionus bakeri,* B. mülleri.
Anuraea valga,* A. biremis,* A. aculeata,* A. tecta,* A. cochlearis.*
Notholca striata,* N. scapha,* N. thalassia, N. spinifera, N. inermis, N.
jugosa, N. rhomboidea. Seison grubei, S. annulatus. Paraseison
asplanchnus, P. nudus, P. proboscideus, P. ciliatus. Discobdella
nebaliae.
Thus about seventy species are recorded as marine. Synchaeta baltica is
truly pelagic, and contributes to the phosphorescence of the ocean.
Other forms again are parasitic. Proales werneckii is found in Vaucheria, a
coarse, dark green, thread-like Alga found in fresh water; and the closely
allied P. parasita is not uncommon in the beautiful floating green spheres of
Volvox.[277] Albertia, Drilophagus, and Balatro are parasitic on or in fresh-
water Oligochaetes; the curious Seisonaceae are parasitic on Nebalia, a
small Crustacean easily obtained in masses of whelk's eggs; the aberrant
Bdelloid Discopus attaches itself to the surface of the Holothurian Synapta.
Page 241
Similarly among this last Order Callidina parasitica attaches itself to the
limbs of the fresh-water Crustacea Gammarus and Asellus. These are rather
commensals than true parasites. The species of Brachionus often attach
themselves temporarily to the common water-flea Daphnia.
Besides a few Ploima, the vast majority of the Bdelloids live in or among
mosses and their roots. Many Callidina inhabit cup-like hollows in the
leaves of the scale mosses (Jungermanniaceae), especially of the genus
Frullania. Almost all the members of this Order are susceptible of
desiccation and revival; certain species, such as Rotifer vulgaris, Philodina
roseola, Adineta vaga, etc., can be readily obtained by moistening gutter
dust. The mechanism of the process is as follows: when desiccation is
gradual the animals close up their telescopic bodies and excrete gelatinous
plugs at either end, which effectually seal them against further drying; if,
however, they be dried on a slide without any débris, the process is too
rapid for them to protect themselves, and they therefore die. This was dimly
seen by others, and clearly demonstrated by H. Davis,[278] who records the
following experiment:—The Rev. E. J. Holloway, having found Philodina
roseola in gutters, placed strips of paper there in the rainy season, and
succeeded in obtaining clean gatherings, taking dry groups of a hundred
together, having a varnish-like covering all over; and being glued to one
another, mostly in one plane, and to the paper, forming a pavement. In the
dry condition they resist extremes of temperature; thus Zelinka found
Callidina revive after an exposure of -20° C. (-4° F. or 36° of frost), and
immersion in hot water at 70° C. (158° F.). They will also resist deprivation
of air in a vacuum of an ordinary air-pump, but not the all but perfect
exhaustion of the Sprengel pump.
A very curious fact in relation to this Class is that often when a new form is
once described from a single locality, fresh and widely distant stations for it
rapidly become known.[279] Thus Pedalion mirum, first found at Clifton in
1872 by Hudson, was a few years after captured in a small pool above tide-
marks on a rocky islet in Torres Straits. Since then it has been recorded
from many different European stations, and a second closely allied species
has been found in Finland. So a species of Ehrenberg's[280] was not seen
again till within the last decade or so; but since then it has been
limbs of the fresh-water Crustacea Gammarus and Asellus. These are rather
commensals than true parasites. The species of Brachionus often attach
themselves temporarily to the common water-flea Daphnia.
Besides a few Ploima, the vast majority of the Bdelloids live in or among
mosses and their roots. Many Callidina inhabit cup-like hollows in the
leaves of the scale mosses (Jungermanniaceae), especially of the genus
Frullania. Almost all the members of this Order are susceptible of
desiccation and revival; certain species, such as Rotifer vulgaris, Philodina
roseola, Adineta vaga, etc., can be readily obtained by moistening gutter
dust. The mechanism of the process is as follows: when desiccation is
gradual the animals close up their telescopic bodies and excrete gelatinous
plugs at either end, which effectually seal them against further drying; if,
however, they be dried on a slide without any débris, the process is too
rapid for them to protect themselves, and they therefore die. This was dimly
seen by others, and clearly demonstrated by H. Davis,[278] who records the
following experiment:—The Rev. E. J. Holloway, having found Philodina
roseola in gutters, placed strips of paper there in the rainy season, and
succeeded in obtaining clean gatherings, taking dry groups of a hundred
together, having a varnish-like covering all over; and being glued to one
another, mostly in one plane, and to the paper, forming a pavement. In the
dry condition they resist extremes of temperature; thus Zelinka found
Callidina revive after an exposure of -20° C. (-4° F. or 36° of frost), and
immersion in hot water at 70° C. (158° F.). They will also resist deprivation
of air in a vacuum of an ordinary air-pump, but not the all but perfect
exhaustion of the Sprengel pump.
A very curious fact in relation to this Class is that often when a new form is
once described from a single locality, fresh and widely distant stations for it
rapidly become known.[279] Thus Pedalion mirum, first found at Clifton in
1872 by Hudson, was a few years after captured in a small pool above tide-
marks on a rocky islet in Torres Straits. Since then it has been recorded
from many different European stations, and a second closely allied species
has been found in Finland. So a species of Ehrenberg's[280] was not seen
again till within the last decade or so; but since then it has been
Page 242
independently found and described by six observers, who have given it as
many distinct generic names. In the case of Pedalion it may well be that, as
Hudson suggests, the species is of southern origin and has followed the
flag, the winter egg being conveyed in dust by ships or travellers.
The above account of the habits gives the key to the collection of the
various forms. The weed-loving species are collected with the weeds, and
will keep with these in vessels if screened from direct sunlight and
protected against dust. The free-swimming forms may be collected by
sweeping with a net of fine gauze, with a bottle fixed in the bottom.
Except for their power of resisting desiccation, Rotifera are not very long-
lived, and the males are especially short-lived; the most exact observations
are those of Maupas on Hydatina. He found that the greatest age of the
unfertilised female was thirteen days, during which it could produce some
fifty eggs; the fertilised female lives for seven or eight days, producing
about sixteen eggs; while the male dies in two or three days.
The preservation of Rotifers has been recently reduced to a fine art by
Rousselet, who uses a solution consisting of cocaine hydrochlorate, 1
gramme; water, 50 cc.; and methylated spirit, 12 cc. This will keep without
deterioration. When in use it must be diluted in the proportion of two
volumes to three of water. This solution is added cautiously to the capsule
in which the Rotifers lie, and they are watched till their ciliary motions
slacken; when this happens a drop or two of osmic acid solution (½ to 1 per
cent) is added; the Rotifers are then sucked up by a capillary pipette, and
transferred to fresh water; and then into a solution of "Formaline" diluted to
contain 2½ per cent of formic aldehyde. In this solution they are transferred
to shallow cells, ground out of the centre of an ordinary glass slide, covered
with thin glass, and sealed.[281] Other methods of preparing Rotifers for
minute study will be found in the papers of Plate, Tessin, and Zelinka.
The zoological affinities of the Rotifers have long been a subject of keen
interest. As early as 1851 Huxley[282] suggested that they represent a
primitive form, preserved, with modifications, in the larva of Molluscs,
Annelids and other worms, and Echinoderms. Similar views were later
many distinct generic names. In the case of Pedalion it may well be that, as
Hudson suggests, the species is of southern origin and has followed the
flag, the winter egg being conveyed in dust by ships or travellers.
The above account of the habits gives the key to the collection of the
various forms. The weed-loving species are collected with the weeds, and
will keep with these in vessels if screened from direct sunlight and
protected against dust. The free-swimming forms may be collected by
sweeping with a net of fine gauze, with a bottle fixed in the bottom.
Except for their power of resisting desiccation, Rotifera are not very long-
lived, and the males are especially short-lived; the most exact observations
are those of Maupas on Hydatina. He found that the greatest age of the
unfertilised female was thirteen days, during which it could produce some
fifty eggs; the fertilised female lives for seven or eight days, producing
about sixteen eggs; while the male dies in two or three days.
The preservation of Rotifers has been recently reduced to a fine art by
Rousselet, who uses a solution consisting of cocaine hydrochlorate, 1
gramme; water, 50 cc.; and methylated spirit, 12 cc. This will keep without
deterioration. When in use it must be diluted in the proportion of two
volumes to three of water. This solution is added cautiously to the capsule
in which the Rotifers lie, and they are watched till their ciliary motions
slacken; when this happens a drop or two of osmic acid solution (½ to 1 per
cent) is added; the Rotifers are then sucked up by a capillary pipette, and
transferred to fresh water; and then into a solution of "Formaline" diluted to
contain 2½ per cent of formic aldehyde. In this solution they are transferred
to shallow cells, ground out of the centre of an ordinary glass slide, covered
with thin glass, and sealed.[281] Other methods of preparing Rotifers for
minute study will be found in the papers of Plate, Tessin, and Zelinka.
The zoological affinities of the Rotifers have long been a subject of keen
interest. As early as 1851 Huxley[282] suggested that they represent a
primitive form, preserved, with modifications, in the larva of Molluscs,
Annelids and other worms, and Echinoderms. Similar views were later
Page 243
maintained by Lankester,[283] who termed the larva of Polychaets, etc., a
"trochosphere," for which "trochophore" has been substituted in order to
avoid confusion with the Rotifer Trochosphaera; Balfour,[284] Hatschek,[285]
Kleinenberg,[286] and others have developed these views. Serious
difficulties, however, arise in the detailed comparison of Rotifers with this
type; and the special students of this Class have found it practically
impossible to agree in the identification of the various parts, a difficulty
especially felt in the case of the Rotiferan genus Trochosphaera, though this
is just the one which presents the closest superficial resemblance to the
Trochophore larva. I have been induced to take a view of the structure of
Rotifers that brings it into close relationship with the lower
Platyhelminthes, and with the more primitive larva of the Nemertines
termed Pilidium (Fig. 60, p. 113). This is hemispherical, ciliated all over,
with the mouth in a ventral funnel lined by fine cilia; while the edge is
fringed with two rows of strong cilia, separated by a finely ciliated groove,
like those of the ciliary wreath of a Rotifer.
"trochosphere," for which "trochophore" has been substituted in order to
avoid confusion with the Rotifer Trochosphaera; Balfour,[284] Hatschek,[285]
Kleinenberg,[286] and others have developed these views. Serious
difficulties, however, arise in the detailed comparison of Rotifers with this
type; and the special students of this Class have found it practically
impossible to agree in the identification of the various parts, a difficulty
especially felt in the case of the Rotiferan genus Trochosphaera, though this
is just the one which presents the closest superficial resemblance to the
Trochophore larva. I have been induced to take a view of the structure of
Rotifers that brings it into close relationship with the lower
Platyhelminthes, and with the more primitive larva of the Nemertines
termed Pilidium (Fig. 60, p. 113). This is hemispherical, ciliated all over,
with the mouth in a ventral funnel lined by fine cilia; while the edge is
fringed with two rows of strong cilia, separated by a finely ciliated groove,
like those of the ciliary wreath of a Rotifer.
Page 244
Fig. 118.—Diagram explaining the possible relations of Rotifers. A, Pilidium; B, hypothetical
Rotifer modified from Asplanchnopus; C, a Ploimal Rotifer; D, Trochosphaera
aequatorialis (modified from Semper, the extension of the ovary into the posterior
ventral quadrant being omitted); E, Mollusc larva (Veliger); F, Trochophore larva of
Annelid. a, Anus; ap, apical organ; at, median antenna (near which, in B, is a black
spot, the brain); bl, bladder (receiving the ramified kidney in B, C, and D); br, brain; f,
foot; fg, cement-glands, replacing apical organ; g, ovary; k, kidney; m, mouth; n, supra-
oesophageal ganglion; nap, nerve of apical organ; nr, nerve-ring in section; pot,
praeoral portion of trochus; s.g, shell-gland; s.n, sub-oesophageal ganglion; t, trochus or
ciliary wreath; tt, posterior ciliated ring; v, velum, or expanded praeoral part of trochus.
The sides are produced on either side into lappets, which we do not take into
account. A cup-shaped depression at the apical pole is lined by sense-cells, bearing
long cilia which are probably sensory. A ring of nerve-cells passes within the
ciliated rim of the hemisphere, and the stomach is a blind sac. If we compare this
organism with a Rotifer, we find that the wreath corresponds in both, the funnel of
the disc in such forms as Flosculariidae and Microcodon leading to the mouth of
Pilidium, while the gut is blind in Asplanchnidae and in some of the highly
developed Seisonidae. The circular nerve-ring of Pilidium is in many Rotifers only
represented by its anterior part, the brain; though in Bdelloids a sub-oesophageal
ganglion completes the ring. This leaves a difficulty with regard to the apical sense
organ; but it is easy to understand that an organ of sensation should become an
organ of fixation. In this case the foot with its glands would correspond to the
sense organ of the Trochophore larva; and it retains its primitive ciliated character
in the larvae and males of many Rotifera, and the adult female of Pterodina and
Callidina tetraodon. Embryology tells us that the anus of Rotifers cannot be
homologous with that of Annelids, etc., for it is formed outside the area of the
blastopore: it is an independent formation, probably due to the coalescence of the
originally blind intestine at its extremity with the earlier genito-urinary cloaca. On
this view we must change the orientation of the Rotifer, and place it, like a
Cuttlefish, mouth downwards: for "anterior and posterior" we must substitute oral
(or basal) and apical; for "dorsal" and "ventral" we must use anterior and
posterior; while "right" and "left" are unchanged. And this correctly expresses the
actual space-relations in those Ploima like Rattulus that swim with their disc in
Rotifer modified from Asplanchnopus; C, a Ploimal Rotifer; D, Trochosphaera
aequatorialis (modified from Semper, the extension of the ovary into the posterior
ventral quadrant being omitted); E, Mollusc larva (Veliger); F, Trochophore larva of
Annelid. a, Anus; ap, apical organ; at, median antenna (near which, in B, is a black
spot, the brain); bl, bladder (receiving the ramified kidney in B, C, and D); br, brain; f,
foot; fg, cement-glands, replacing apical organ; g, ovary; k, kidney; m, mouth; n, supra-
oesophageal ganglion; nap, nerve of apical organ; nr, nerve-ring in section; pot,
praeoral portion of trochus; s.g, shell-gland; s.n, sub-oesophageal ganglion; t, trochus or
ciliary wreath; tt, posterior ciliated ring; v, velum, or expanded praeoral part of trochus.
The sides are produced on either side into lappets, which we do not take into
account. A cup-shaped depression at the apical pole is lined by sense-cells, bearing
long cilia which are probably sensory. A ring of nerve-cells passes within the
ciliated rim of the hemisphere, and the stomach is a blind sac. If we compare this
organism with a Rotifer, we find that the wreath corresponds in both, the funnel of
the disc in such forms as Flosculariidae and Microcodon leading to the mouth of
Pilidium, while the gut is blind in Asplanchnidae and in some of the highly
developed Seisonidae. The circular nerve-ring of Pilidium is in many Rotifers only
represented by its anterior part, the brain; though in Bdelloids a sub-oesophageal
ganglion completes the ring. This leaves a difficulty with regard to the apical sense
organ; but it is easy to understand that an organ of sensation should become an
organ of fixation. In this case the foot with its glands would correspond to the
sense organ of the Trochophore larva; and it retains its primitive ciliated character
in the larvae and males of many Rotifera, and the adult female of Pterodina and
Callidina tetraodon. Embryology tells us that the anus of Rotifers cannot be
homologous with that of Annelids, etc., for it is formed outside the area of the
blastopore: it is an independent formation, probably due to the coalescence of the
originally blind intestine at its extremity with the earlier genito-urinary cloaca. On
this view we must change the orientation of the Rotifer, and place it, like a
Cuttlefish, mouth downwards: for "anterior and posterior" we must substitute oral
(or basal) and apical; for "dorsal" and "ventral" we must use anterior and
posterior; while "right" and "left" are unchanged. And this correctly expresses the
actual space-relations in those Ploima like Rattulus that swim with their disc in
Page 245
contact with the organic débris on which they feed, with the foot turned outwards
and backwards. As these views are now published for the first time, I have thought
it wiser to keep to the accepted relations in the general description, a course which
has the advantage of avoiding difficulties in the study of the literature of the Class.
The supposed resemblance of Pedalion to the Crustacea is probably the result of
convergence, not of consanguinity. The Polyzoa are a group of freely-budding
organisms whose structure otherwise recalls in many respects that of the attached
Rotifers; but a close investigation reveals so many differences in structure,
orientation, and development, that we cannot regard the two groups as at all
closely allied.
Thus the Rotifers may be regarded as a group apart, but probably representing an
early offshoot from a free-swimming Platyhelminth, probably a Rhabdocoele; the
modifications being the loss of the general ciliation of the surface, the arching of
the back into an elongated vault, the conversion of the inner half of the pharynx
into a gizzard, the change of position of the genital and urinary apertures to the
antero-dorsal surface, and the opening of the intestine into the genito-urinary
cloaca.
Gastrotricha.
This small and very homogeneous group consists of minute fresh-water
organisms, closely resembling many Ciliate Infusoria in their movements, habit
and habitat. They were first described in detail by Ehrenberg, and placed by him
and Dujardin in the neighbourhood of Rotifers. In recent years A. C. Stokes[287] in
America and C. Zelinka[288] in Germany have contributed, the former a careful
description of a number of new species and their habits, the latter a complete
monograph of everything that is known of the Order.
The Gastrotricha dwell among filamentous Algae and organic débris, and are of
frequent occurrence with Protozoa and Rotifera of similar habit. The largest
known measures only 400 µ (1⁄60 in.) in length, and the smallest run as low as 74
µ (1⁄300 in.).
and backwards. As these views are now published for the first time, I have thought
it wiser to keep to the accepted relations in the general description, a course which
has the advantage of avoiding difficulties in the study of the literature of the Class.
The supposed resemblance of Pedalion to the Crustacea is probably the result of
convergence, not of consanguinity. The Polyzoa are a group of freely-budding
organisms whose structure otherwise recalls in many respects that of the attached
Rotifers; but a close investigation reveals so many differences in structure,
orientation, and development, that we cannot regard the two groups as at all
closely allied.
Thus the Rotifers may be regarded as a group apart, but probably representing an
early offshoot from a free-swimming Platyhelminth, probably a Rhabdocoele; the
modifications being the loss of the general ciliation of the surface, the arching of
the back into an elongated vault, the conversion of the inner half of the pharynx
into a gizzard, the change of position of the genital and urinary apertures to the
antero-dorsal surface, and the opening of the intestine into the genito-urinary
cloaca.
Gastrotricha.
This small and very homogeneous group consists of minute fresh-water
organisms, closely resembling many Ciliate Infusoria in their movements, habit
and habitat. They were first described in detail by Ehrenberg, and placed by him
and Dujardin in the neighbourhood of Rotifers. In recent years A. C. Stokes[287] in
America and C. Zelinka[288] in Germany have contributed, the former a careful
description of a number of new species and their habits, the latter a complete
monograph of everything that is known of the Order.
The Gastrotricha dwell among filamentous Algae and organic débris, and are of
frequent occurrence with Protozoa and Rotifera of similar habit. The largest
known measures only 400 µ (1⁄60 in.) in length, and the smallest run as low as 74
µ (1⁄300 in.).
Page 246
Fig. 119.—Gastrotricha. (From Zelinka.) A, Chaetonotus bogdanovii, side view (after
Schimkewitsch); B, Gossea antenniger (after Gosse); C, Dasydetes goniathrix (after
Gosse); D, Dasydetes saltitans (after Stokes); E, D. longisetosum (after Metschnikoff);
F, Chaetonotus spinulosus (after Stokes); G, Chaetonotus schultzei (after Gosse and
Bütschli). (Magnified.) B-F, × about 390; G, × about 125.
We shall follow Zelinka in his description of the common species Chaetonotus
larus as a type. The body is nearly circular in section, flattened a little on the
ventral side. The apertures are the terminal mouth; the anus, nearly terminal and
slightly dorsal; the two kidney openings, ventral, nearly half-way down the trunk;
besides the pore of a cement-gland on either terminal process. The short ventral
and post-anal portion of the trunk with its processes therefore corresponds to the
foot of a Rotifer. The integument of the body is a thin nucleated hypoderm, not
distinctly divided into cells, covered by a chitinised cuticle; it bears cilia, sensory
hairs, and peculiar scale-like processes, sometimes produced into long bristles.
The cilia are chiefly arranged in two ventral bands, each extending nearly the
whole length of the body, and composed of a series of transverse rows of single
cilia; along these bands the hypoderm is thickened and more richly nucleated. The
sides of the head also bear numerous long cilia.
The scales are hollow processes of the cuticle overlapping from before backwards.
A ventral row lies between the ciliary bands; two series of alternating dorsal rows
lie on the back and sides of the animal, and in the hirsute species it is these that are
produced backward into bristles. A single large scale, the "frontal shield," protects
the head above and behind, but does not extend down to the ventral surface. On
either side of the head is a pair of flattened oval areas, the "lateral fields." From
between these on either side springs a tuft of motile sensory hairs. Two pairs of
similar tufts arise dorsally on the front margin of the frontal shield, and a fourth
pair spring from the ventral surface a little behind the mouth. These hairs are
distinguished from ordinary cilia by their length, and their insertion on large
nucleated cells receiving nerves; two pairs of similar hairs lie farther back on the
Schimkewitsch); B, Gossea antenniger (after Gosse); C, Dasydetes goniathrix (after
Gosse); D, Dasydetes saltitans (after Stokes); E, D. longisetosum (after Metschnikoff);
F, Chaetonotus spinulosus (after Stokes); G, Chaetonotus schultzei (after Gosse and
Bütschli). (Magnified.) B-F, × about 390; G, × about 125.
We shall follow Zelinka in his description of the common species Chaetonotus
larus as a type. The body is nearly circular in section, flattened a little on the
ventral side. The apertures are the terminal mouth; the anus, nearly terminal and
slightly dorsal; the two kidney openings, ventral, nearly half-way down the trunk;
besides the pore of a cement-gland on either terminal process. The short ventral
and post-anal portion of the trunk with its processes therefore corresponds to the
foot of a Rotifer. The integument of the body is a thin nucleated hypoderm, not
distinctly divided into cells, covered by a chitinised cuticle; it bears cilia, sensory
hairs, and peculiar scale-like processes, sometimes produced into long bristles.
The cilia are chiefly arranged in two ventral bands, each extending nearly the
whole length of the body, and composed of a series of transverse rows of single
cilia; along these bands the hypoderm is thickened and more richly nucleated. The
sides of the head also bear numerous long cilia.
The scales are hollow processes of the cuticle overlapping from before backwards.
A ventral row lies between the ciliary bands; two series of alternating dorsal rows
lie on the back and sides of the animal, and in the hirsute species it is these that are
produced backward into bristles. A single large scale, the "frontal shield," protects
the head above and behind, but does not extend down to the ventral surface. On
either side of the head is a pair of flattened oval areas, the "lateral fields." From
between these on either side springs a tuft of motile sensory hairs. Two pairs of
similar tufts arise dorsally on the front margin of the frontal shield, and a fourth
pair spring from the ventral surface a little behind the mouth. These hairs are
distinguished from ordinary cilia by their length, and their insertion on large
nucleated cells receiving nerves; two pairs of similar hairs lie farther back on the
Page 247
dorsal surface, one in the front of the neck, one near the base of the pedal
processes.
The muscles lie some in the body-wall, and some traverse the body-cavity; only
six pairs occur, simple, unstriated, and longitudinal. There are neither transverse
nor circular muscles.
The alimentary canal is very simple and nearly straight from mouth to anus; it
may be divided into pharynx, gullet, stomach, and rectum. The mouth is circular,
and looks forwards and a little downwards. From the mouth opens the pharynx, a
short chitinous tube, capable of eversion by being pushed forwards by the gullet; it
bears half-way down a circlet of curved hooks, which open out when it is everted;
within these are tooth-like thickenings.
The oesophagus or gullet is thick and muscular, extending through the whole of
the neck of the animal; its cavity, as well as the opening from the pharynx, is
triradiate like a leech-bite, but can be dilated by the action of the muscular walls,
inserted into a firm external cuticle; the internal wall is also cuticulised, not
ciliated as in Rotifers. The hinder end of the gullet is produced into a short, wide,
membranous funnel projecting freely into the midgut or stomach. The latter is
elongated and oval, composed of four rows of hexagonal cells, with large nuclei.
This is separated by a distinct constriction or sphincter from the short pear-shaped
rectum, which opens by a minute anus on the back just in front of the pedal
processes.
The food is chiefly organic débris; but Gastrotricha have been seen to attack large
Infusoria by nibbling, and to swallow the protoplasm as it exudes from the wound
in their prey.
The nervous system is chiefly composed of the large brain, a ganglion lying like a
saddle above and on the sides of the gullet, and in direct continuity with the nerve-
cells of the cephalic sense-hairs. A pair of dorsal nerve-trunks extend along the
whole length of the gullet. The sense-hairs described with the general integument
may be organs of external taste ("smell") or of touch. Eyes have been described in
several species; and though Zelinka has failed to verify this, I have myself seen a
pair of minute red eyes in the back of the head of an animal (probably a
Chaetonotus), whose hasty escape into a mass of débris prevented my determining
its species.
processes.
The muscles lie some in the body-wall, and some traverse the body-cavity; only
six pairs occur, simple, unstriated, and longitudinal. There are neither transverse
nor circular muscles.
The alimentary canal is very simple and nearly straight from mouth to anus; it
may be divided into pharynx, gullet, stomach, and rectum. The mouth is circular,
and looks forwards and a little downwards. From the mouth opens the pharynx, a
short chitinous tube, capable of eversion by being pushed forwards by the gullet; it
bears half-way down a circlet of curved hooks, which open out when it is everted;
within these are tooth-like thickenings.
The oesophagus or gullet is thick and muscular, extending through the whole of
the neck of the animal; its cavity, as well as the opening from the pharynx, is
triradiate like a leech-bite, but can be dilated by the action of the muscular walls,
inserted into a firm external cuticle; the internal wall is also cuticulised, not
ciliated as in Rotifers. The hinder end of the gullet is produced into a short, wide,
membranous funnel projecting freely into the midgut or stomach. The latter is
elongated and oval, composed of four rows of hexagonal cells, with large nuclei.
This is separated by a distinct constriction or sphincter from the short pear-shaped
rectum, which opens by a minute anus on the back just in front of the pedal
processes.
The food is chiefly organic débris; but Gastrotricha have been seen to attack large
Infusoria by nibbling, and to swallow the protoplasm as it exudes from the wound
in their prey.
The nervous system is chiefly composed of the large brain, a ganglion lying like a
saddle above and on the sides of the gullet, and in direct continuity with the nerve-
cells of the cephalic sense-hairs. A pair of dorsal nerve-trunks extend along the
whole length of the gullet. The sense-hairs described with the general integument
may be organs of external taste ("smell") or of touch. Eyes have been described in
several species; and though Zelinka has failed to verify this, I have myself seen a
pair of minute red eyes in the back of the head of an animal (probably a
Chaetonotus), whose hasty escape into a mass of débris prevented my determining
its species.
Page 248
The kidneys are paired tubes lying at the sides of the front of the stomach, and
sending a simple loop into the neck. Each tube is much convoluted, and ends at
the one extremity in a long "flame-cell," like that of a Rotifer much drawn out, and
at the other by a minute pore on the outer side of the ventral row of scales.
Reproductive Organs.—Only the female is with certainty known to occur; and
the eggs, though recalling in their thick ornamented shell the fertilised winter eggs
of Rotifers, are probably unfertilised and parthenogenetic like the summer eggs.
The ovaries are two minute patches of cells lying at the junction of the stomach
and rectum. The eggs, as they mature and enlarge, press against the side and back
of the stomach, where they attain a length of one-third to one-half that of the
mother. The extrusion of the egg has not been observed; but it is laid in the angles
of weeds, the moulted shells of Entomostraca, etc., where its development may be
studied. The sculpture of the shell serves to anchor it if laid among weeds. When
hatched the head, trunk, and pedal processes are of the full adult size, all
subsequent growth being limited to the neck.
The function of testis has been ascribed by Ludwig to a minute granular organ
between the ovaries above the rectum; if this view be correct the Gastrotricha are
hermaphrodite.
The movements of the Gastrotricha are very elegant, recalling those of the long-
necked Ciliate Infusoria, like Amphileptus, Lacrymaria, etc., with the
characteristic exception that they always swim forwards; the grace of their
movements being due to the bending of the head and neck on the body. Those
which are provided with long motile bristles like Dasydetes, alternate their gliding
with leaps, like the springing Rotifers.
The Gastrotricha are divided into two sub-Orders—Euichthydina, with two pedal
appendages, containing the genera Ichthydium Ehr., Lepidoderma Zel.,
Chaetonotus Ehr., and Chaetura Metsch.; and the Apodina, with no pedal
appendages, comprising Dasydetes G. and Gossea Zel.
Their geographical distribution, like that of most microscopic fresh-water
organisms, is cosmopolitan. Few observers have enumerated the members of this
group; of their extra-temperate occurrence we have only the single observations of
Ehrenberg, Schmarda, and Voeltzkow for Nubia, Ceylon, and Madagascar
respectively.
sending a simple loop into the neck. Each tube is much convoluted, and ends at
the one extremity in a long "flame-cell," like that of a Rotifer much drawn out, and
at the other by a minute pore on the outer side of the ventral row of scales.
Reproductive Organs.—Only the female is with certainty known to occur; and
the eggs, though recalling in their thick ornamented shell the fertilised winter eggs
of Rotifers, are probably unfertilised and parthenogenetic like the summer eggs.
The ovaries are two minute patches of cells lying at the junction of the stomach
and rectum. The eggs, as they mature and enlarge, press against the side and back
of the stomach, where they attain a length of one-third to one-half that of the
mother. The extrusion of the egg has not been observed; but it is laid in the angles
of weeds, the moulted shells of Entomostraca, etc., where its development may be
studied. The sculpture of the shell serves to anchor it if laid among weeds. When
hatched the head, trunk, and pedal processes are of the full adult size, all
subsequent growth being limited to the neck.
The function of testis has been ascribed by Ludwig to a minute granular organ
between the ovaries above the rectum; if this view be correct the Gastrotricha are
hermaphrodite.
The movements of the Gastrotricha are very elegant, recalling those of the long-
necked Ciliate Infusoria, like Amphileptus, Lacrymaria, etc., with the
characteristic exception that they always swim forwards; the grace of their
movements being due to the bending of the head and neck on the body. Those
which are provided with long motile bristles like Dasydetes, alternate their gliding
with leaps, like the springing Rotifers.
The Gastrotricha are divided into two sub-Orders—Euichthydina, with two pedal
appendages, containing the genera Ichthydium Ehr., Lepidoderma Zel.,
Chaetonotus Ehr., and Chaetura Metsch.; and the Apodina, with no pedal
appendages, comprising Dasydetes G. and Gossea Zel.
Their geographical distribution, like that of most microscopic fresh-water
organisms, is cosmopolitan. Few observers have enumerated the members of this
group; of their extra-temperate occurrence we have only the single observations of
Ehrenberg, Schmarda, and Voeltzkow for Nubia, Ceylon, and Madagascar
respectively.
Page 249
Of the thirty-two species described, twelve are recorded by A. C. Stokes from
Maine and New Jersey only, besides five others that occur also in Europe. In
Europe nineteen species are recorded, one of which, Ichthydium podura, has also
been found in Nubia and Ceylon. One species, Chaetonotus tabulatus Schmarda,
has been recorded by its author from Colombia (in South America). As of the
nineteen European species only seven have been recorded as British, we may
expect to find that careful study will well repay the student in these islands.
The affinities of this group are probably with the Turbellarians and the
Nematodes; they differ from the former in the highly developed alimentary canal,
and from the latter in the possession of the ciliated ventral bands and wreath. The
general chitinisation of the skin, the primitive body-cavity, the character of the
alimentary canal, the ventral opening of the renal canals far in front of the anus are
characters shared by the Nematodes, many of which possess bristles like this
group. But their affinity must be rather to some hypothetical ancestral group than
to any living Nematodes, which are destitute of cilia. To the Rotifers the affinity,
dwelt on by Zelinka, is less close.
Kinorhyncha.
This Class and Order comprises but one genus, Echinoderes (Fig. 120), founded in
1851 by Dujardin.[289] Reinhard's monograph[290] is the generally accepted
authority on this subject, and contains a full bibliography, with diagnoses of the
individual species, eighteen in number.
Fig. 120.—Echinoderes dujardinii (?), drawn from a preserved specimen taken at Worthing. ×
about 210. b, Bristle; c.s, caudal spine; ph, pharynx; s and s', the spines on the two
segments of the proboscis; s.g, salivary glands; st, stomach.
The animals of this group are found in shallow seas with muddy bottom, below
low-water mark, and feed on organic débris. They have been taken in the Black
Sea, Mediterranean, British Channel, and North Sea, and off the Canary Islands
Maine and New Jersey only, besides five others that occur also in Europe. In
Europe nineteen species are recorded, one of which, Ichthydium podura, has also
been found in Nubia and Ceylon. One species, Chaetonotus tabulatus Schmarda,
has been recorded by its author from Colombia (in South America). As of the
nineteen European species only seven have been recorded as British, we may
expect to find that careful study will well repay the student in these islands.
The affinities of this group are probably with the Turbellarians and the
Nematodes; they differ from the former in the highly developed alimentary canal,
and from the latter in the possession of the ciliated ventral bands and wreath. The
general chitinisation of the skin, the primitive body-cavity, the character of the
alimentary canal, the ventral opening of the renal canals far in front of the anus are
characters shared by the Nematodes, many of which possess bristles like this
group. But their affinity must be rather to some hypothetical ancestral group than
to any living Nematodes, which are destitute of cilia. To the Rotifers the affinity,
dwelt on by Zelinka, is less close.
Kinorhyncha.
This Class and Order comprises but one genus, Echinoderes (Fig. 120), founded in
1851 by Dujardin.[289] Reinhard's monograph[290] is the generally accepted
authority on this subject, and contains a full bibliography, with diagnoses of the
individual species, eighteen in number.
Fig. 120.—Echinoderes dujardinii (?), drawn from a preserved specimen taken at Worthing. ×
about 210. b, Bristle; c.s, caudal spine; ph, pharynx; s and s', the spines on the two
segments of the proboscis; s.g, salivary glands; st, stomach.
The animals of this group are found in shallow seas with muddy bottom, below
low-water mark, and feed on organic débris. They have been taken in the Black
Sea, Mediterranean, British Channel, and North Sea, and off the Canary Islands
Page 250
(Lanzarote, Porto Pi, Palma di Mallorca). Their size varies from 0.86 mm. × 0.22
mm. in Echinoderes spinosus, to 0.14 mm. × 0.03 mm. in E. kowalevskii.[291]
The body is protected by a strong chitinous cuticle distinctly annulated, forming
eleven rings, besides a retractile proboscis obscurely divided into two segments at
the apex of which the mouth opens. The anus opens on the extreme end of the last
segment, which is frequently retracted; the genital pores open right and left of the
anus; and the renal pores lie on either side of the back of the ninth segment. The
first ring may be undivided, or else distinctly divided into four plates, one dorsal,
two latero-ventral, and one ventral. In the remaining segments each ring has only
three plates, one dorsal and two ventral, the two latter being sometimes more or
less fused in the last or ventral segment. These plates all overlap from before
backwards.
As the name Echinoderes implies (Thorn-skin), the cuticle is produced into points,
bristles, or spines. The last segment frequently bears a large pair of these, which
have been compared, on the flimsiest grounds, with the furcal processes of
Crustacea and the perforated toes of Rotifers and Gastrotricha.
The proboscis when extruded has the form of a truncated cone, obscurely divided
into two segments, a ring of strong spines marking the boundary between them,
and a second double ring of spines surrounding the apex. The eversion is of the
type termed by Lankester pleurembolic or acrecbolic, the sides being first
withdrawn, the apex first extruded.
As in so many Invertebrata, the epidermis is not separated by boundaries into
distinct cells. This layer sends out processes each of which lies in a hollow in the
thick cuticle, and perforates it to end in a fine bristle. Minute orange pigment-
granules occur at irregular intervals in this hypoderm.
The muscles of Echinoderes are simple striated bands. Numerous bands lie within
and attached to the body-wall, extending its whole length; paired dorsi-ventral
muscles separate the intestine from the reproductive organ on either side, and a
complex system effect the movements of the proboscis.
Alimentary Canal.—The pore at the tip of the proboscis leads into a short thin-
walled tube, which is rarely evaginated; into the base of this tube projects the short
bluntly conical apex of the large ovoid muscular pharynx (or gullet?); this is lined
by an epithelial layer of nucleated protoplasm, which secretes a strong cuticle. The
mm. in Echinoderes spinosus, to 0.14 mm. × 0.03 mm. in E. kowalevskii.[291]
The body is protected by a strong chitinous cuticle distinctly annulated, forming
eleven rings, besides a retractile proboscis obscurely divided into two segments at
the apex of which the mouth opens. The anus opens on the extreme end of the last
segment, which is frequently retracted; the genital pores open right and left of the
anus; and the renal pores lie on either side of the back of the ninth segment. The
first ring may be undivided, or else distinctly divided into four plates, one dorsal,
two latero-ventral, and one ventral. In the remaining segments each ring has only
three plates, one dorsal and two ventral, the two latter being sometimes more or
less fused in the last or ventral segment. These plates all overlap from before
backwards.
As the name Echinoderes implies (Thorn-skin), the cuticle is produced into points,
bristles, or spines. The last segment frequently bears a large pair of these, which
have been compared, on the flimsiest grounds, with the furcal processes of
Crustacea and the perforated toes of Rotifers and Gastrotricha.
The proboscis when extruded has the form of a truncated cone, obscurely divided
into two segments, a ring of strong spines marking the boundary between them,
and a second double ring of spines surrounding the apex. The eversion is of the
type termed by Lankester pleurembolic or acrecbolic, the sides being first
withdrawn, the apex first extruded.
As in so many Invertebrata, the epidermis is not separated by boundaries into
distinct cells. This layer sends out processes each of which lies in a hollow in the
thick cuticle, and perforates it to end in a fine bristle. Minute orange pigment-
granules occur at irregular intervals in this hypoderm.
The muscles of Echinoderes are simple striated bands. Numerous bands lie within
and attached to the body-wall, extending its whole length; paired dorsi-ventral
muscles separate the intestine from the reproductive organ on either side, and a
complex system effect the movements of the proboscis.
Alimentary Canal.—The pore at the tip of the proboscis leads into a short thin-
walled tube, which is rarely evaginated; into the base of this tube projects the short
bluntly conical apex of the large ovoid muscular pharynx (or gullet?); this is lined
by an epithelial layer of nucleated protoplasm, which secretes a strong cuticle. The
Page 251
stomach is a wide tube, somewhat dilated in each segment between the paired
dorsi-ventral muscles, and tapering behind to end in the terminal anus. Four
minute glands open at the junction of the pharynx and stomach.
Kidneys.—These are a pair of blind pear-shaped sacs, ciliated within (the only
case of ciliation in Echinoderes), lying in the eighth segment, and opening by the
taper ends right and left on the back of the ninth segment.
Nervous System.—All that has been clearly defined of this is a small brain or
ganglion lying dorsally at the junction of the pharynx and stomach. From two to
eight eye-spots have been described by earlier writers, but Reinhard was unable to
find them in the (distinct) species which he principally worked at, though he noted
their existence in the solitary specimen of the original species, E. dujardini, which
he obtained.
Reproductive Organs.—The sexes are distinct. The reproductive glands form a
pair of tubular sacs, opening ventrally on either side of the anus, and extending
forwards beside the gut as far forwards as the fifth to the second segment in the
male, but only to the fourth at furthest in the female. The ova are large nucleated
cells embedded in the protoplasmic lining of the ovarian sac, and acquiring a
distinct shell as they approach its opening. Three-quarters of the testis sac is
occupied with granular protoplasm containing a quantity of small nuclei; the lower
part alone contains mature spermatozoa. Adjoining each external opening in the
male are a pair of short hollowed spines, which may perhaps serve as organs of
copulation; but nothing is really known of this process or of the development of
the egg. It is almost certain, from the absence of developing eggs within
Echinoderes, that the genus is not viviparous.
From the foregoing description it is obvious that Echinoderes approaches the
Nematoda very closely: the two main points of difference are its ciliated kidneys
and its bilaterally paired sexual organs. Possibly the study of such forms as
Desmoscolex (Fig. 81, p. 159) may reveal closer affinities.
[Zelinka (Verh. D. Zool. Ges., 1894 and 1898), has given a preliminary
account of a new research on this group. The principal addition is the
discovery of a ventral nerve-cord, with a ganglionic dilatation in each
segment, lying in the ectoderm of the body-wall, as indeed do the brain and
nerve-collar. He divides the genus into two Orders according as the orifice of
dorsi-ventral muscles, and tapering behind to end in the terminal anus. Four
minute glands open at the junction of the pharynx and stomach.
Kidneys.—These are a pair of blind pear-shaped sacs, ciliated within (the only
case of ciliation in Echinoderes), lying in the eighth segment, and opening by the
taper ends right and left on the back of the ninth segment.
Nervous System.—All that has been clearly defined of this is a small brain or
ganglion lying dorsally at the junction of the pharynx and stomach. From two to
eight eye-spots have been described by earlier writers, but Reinhard was unable to
find them in the (distinct) species which he principally worked at, though he noted
their existence in the solitary specimen of the original species, E. dujardini, which
he obtained.
Reproductive Organs.—The sexes are distinct. The reproductive glands form a
pair of tubular sacs, opening ventrally on either side of the anus, and extending
forwards beside the gut as far forwards as the fifth to the second segment in the
male, but only to the fourth at furthest in the female. The ova are large nucleated
cells embedded in the protoplasmic lining of the ovarian sac, and acquiring a
distinct shell as they approach its opening. Three-quarters of the testis sac is
occupied with granular protoplasm containing a quantity of small nuclei; the lower
part alone contains mature spermatozoa. Adjoining each external opening in the
male are a pair of short hollowed spines, which may perhaps serve as organs of
copulation; but nothing is really known of this process or of the development of
the egg. It is almost certain, from the absence of developing eggs within
Echinoderes, that the genus is not viviparous.
From the foregoing description it is obvious that Echinoderes approaches the
Nematoda very closely: the two main points of difference are its ciliated kidneys
and its bilaterally paired sexual organs. Possibly the study of such forms as
Desmoscolex (Fig. 81, p. 159) may reveal closer affinities.
[Zelinka (Verh. D. Zool. Ges., 1894 and 1898), has given a preliminary
account of a new research on this group. The principal addition is the
discovery of a ventral nerve-cord, with a ganglionic dilatation in each
segment, lying in the ectoderm of the body-wall, as indeed do the brain and
nerve-collar. He divides the genus into two Orders according as the orifice of
Page 252
the retracted fore-part of the body is slit-like or circular. The former
(Homalorhagae) retract the first two segments with the proboscis; they are
mud-dwellers, sluggish, eyeless: the latter group (Cyclorhagae) only retract
the first segment with the proboscis; they crawl among algae, and mostly
have paired pigmented eye-spots, each with a lens, imbedded in the brain.—
M. H., Jan. 1901.]
(Homalorhagae) retract the first two segments with the proboscis; they are
mud-dwellers, sluggish, eyeless: the latter group (Cyclorhagae) only retract
the first segment with the proboscis; they crawl among algae, and mostly
have paired pigmented eye-spots, each with a lens, imbedded in the brain.—
M. H., Jan. 1901.]
Page 253
ARCHIANNELIDA, POLYCHAETA, AND
MYZOSTOMARIA
BY
W. BLAXLAND BENHAM, D.Sc. (Lond.), Hon. M.A. (Oxon.)
CHAPTER IX
THE CHAETOPODOUS WORMS—THE ARCHIANNELIDA—ANATOMY OF NEREIS, AS TYPICAL
OF THE POLYCHAETA
Those animals which possess lateral bundles of bristles (technically termed
"chaetae") for use in locomotion constitute the group of "Bristle-worms," or
Chaetopoda. The body of these animals is made up of a preoral lobe or
prostomium, and a number of more or less distinct segments following one
another in a line, and repeating one another in their internal and external structure.
The Chaetopoda embrace the following smaller groups or Orders:—I.
Archiannelida, II. Polychaeta, III. Myzostomaria, IV. Oligochaeta. The
Archiannelida, although without the characteristic chaetae, are yet anatomically so
similar to the true Chaetopoda that they must be included in the group, just as
certain fishes are classed as "Vertebrata," although they do not possess vertebrae.
The old term Annelida is sometimes used to include the above-mentioned groups,
together with the Gephyrea[292] and the Hirudinea or leeches.
Order I. Archiannelida.
The Archiannelida are very simple worms, but simplicity may be, and very
frequently is, the result of degeneration; and it is not always possible to determine
whether a simple animal is primitively, i.e. ancestrally simple, or whether it is
secondarily simplified. Hence the term Haplodrili has been employed by
Professor Lankester as the name of the group; a term which does not prejudge the
question as to whether or not the worms are "primitive." It is quite possible, and
even probable, that Dinophilus is ancestrally simple; whilst many features in
Polygordius appear to be the result of simplification. For this reason it would be
MYZOSTOMARIA
BY
W. BLAXLAND BENHAM, D.Sc. (Lond.), Hon. M.A. (Oxon.)
CHAPTER IX
THE CHAETOPODOUS WORMS—THE ARCHIANNELIDA—ANATOMY OF NEREIS, AS TYPICAL
OF THE POLYCHAETA
Those animals which possess lateral bundles of bristles (technically termed
"chaetae") for use in locomotion constitute the group of "Bristle-worms," or
Chaetopoda. The body of these animals is made up of a preoral lobe or
prostomium, and a number of more or less distinct segments following one
another in a line, and repeating one another in their internal and external structure.
The Chaetopoda embrace the following smaller groups or Orders:—I.
Archiannelida, II. Polychaeta, III. Myzostomaria, IV. Oligochaeta. The
Archiannelida, although without the characteristic chaetae, are yet anatomically so
similar to the true Chaetopoda that they must be included in the group, just as
certain fishes are classed as "Vertebrata," although they do not possess vertebrae.
The old term Annelida is sometimes used to include the above-mentioned groups,
together with the Gephyrea[292] and the Hirudinea or leeches.
Order I. Archiannelida.
The Archiannelida are very simple worms, but simplicity may be, and very
frequently is, the result of degeneration; and it is not always possible to determine
whether a simple animal is primitively, i.e. ancestrally simple, or whether it is
secondarily simplified. Hence the term Haplodrili has been employed by
Professor Lankester as the name of the group; a term which does not prejudge the
question as to whether or not the worms are "primitive." It is quite possible, and
even probable, that Dinophilus is ancestrally simple; whilst many features in
Polygordius appear to be the result of simplification. For this reason it would be
Page 254
well to separate Dinophilus from the other two genera, on account of its much less
elaborate and more generalised structure,—so generalised, in fact, that the worm is
by some authorities placed amongst the Planarians; for the present, however, the
group Archiannelida may be regarded as containing three genera: Dinophilus,
Protodrilus, and Polygordius.[293]
Fig. 121.—Dinophilus taeniatus. (From Harmer.) The left figure represents the dorsal surface
of a young individual, × 76; the mouth and alimentary tract are seen by transparency: p,
prostomium, with two bands of cilia and a pair of eyes; a, anus; t, tail; 1 to 5, the
segments with ciliated bands. The right figure shows the anatomy of the male, × 38: b,
rectum; c, body-cavity; d, vas deferens; m, muscular organ (pharynx); n', the first
nephridium; oe, entrance to oesophagus; p, penis; st, intestine (stomach); s.x, seminal
vesicle (5th nephridium).
Dinophilus is represented on our coasts by at least two species: D. gigas
Weldon[294] and D. taeniatus Harmer.[295] The latter is about one-twelfth of an
inch in length, bright orange in colour, and more or less abundant, at springtime, in
the rock pools around Plymouth, where it may be found amongst green algae, or
on the mud at the bottom of the pools.
The animal consists of a broad prostomium, with a pair of eyes; and of a body,
distinctly constricted in immature specimens into five or six segments, followed
by a short conical tail. There are neither chaetae nor tentacles; locomotion is
chiefly effected by means of the bands of cilia which encircle the body in a regular
fashion, two bands round the head, and two round each segment in D. taeniatus; in
some species there is only a single band on each segment. The whole of the
ventral surface is covered with cilia, by the aid of which the animal probably
"creeps" along the weeds.
The alimentary canal is straight, and divisible into the regions shown in Fig. 121; a
muscular protrusible organ, which is a ventral outgrowth of the foregut, is
employed as a "sucker." The coelom is more or less obliterated (or ill developed).
elaborate and more generalised structure,—so generalised, in fact, that the worm is
by some authorities placed amongst the Planarians; for the present, however, the
group Archiannelida may be regarded as containing three genera: Dinophilus,
Protodrilus, and Polygordius.[293]
Fig. 121.—Dinophilus taeniatus. (From Harmer.) The left figure represents the dorsal surface
of a young individual, × 76; the mouth and alimentary tract are seen by transparency: p,
prostomium, with two bands of cilia and a pair of eyes; a, anus; t, tail; 1 to 5, the
segments with ciliated bands. The right figure shows the anatomy of the male, × 38: b,
rectum; c, body-cavity; d, vas deferens; m, muscular organ (pharynx); n', the first
nephridium; oe, entrance to oesophagus; p, penis; st, intestine (stomach); s.x, seminal
vesicle (5th nephridium).
Dinophilus is represented on our coasts by at least two species: D. gigas
Weldon[294] and D. taeniatus Harmer.[295] The latter is about one-twelfth of an
inch in length, bright orange in colour, and more or less abundant, at springtime, in
the rock pools around Plymouth, where it may be found amongst green algae, or
on the mud at the bottom of the pools.
The animal consists of a broad prostomium, with a pair of eyes; and of a body,
distinctly constricted in immature specimens into five or six segments, followed
by a short conical tail. There are neither chaetae nor tentacles; locomotion is
chiefly effected by means of the bands of cilia which encircle the body in a regular
fashion, two bands round the head, and two round each segment in D. taeniatus; in
some species there is only a single band on each segment. The whole of the
ventral surface is covered with cilia, by the aid of which the animal probably
"creeps" along the weeds.
The alimentary canal is straight, and divisible into the regions shown in Fig. 121; a
muscular protrusible organ, which is a ventral outgrowth of the foregut, is
employed as a "sucker." The coelom is more or less obliterated (or ill developed).
Page 255
The excretory system in the genus is varied: in some species, as in D. gigas, it is
stated to be constructed on the Planarian plan; in others, as in D. taeniatus, the
organs are definite nephridia. Of these tubes there are five pairs, the last pair in the
male serving as a seminal vesicle. Each nephridium is a ciliated tube, the internal
end of which lies in the body-cavity and appears to be blocked by a ciliated
tongue-shaped appendage. The first pair corresponds to the "larval nephridia" of
Trochosphere larvae.
The nervous system, which is in contact with the epidermis, consists of a brain in
the prostomium, and, on each side of the body, a ventral cord with five ganglia,
connected by transverse commissures in as many segments.
The sexes are separate, and are usually similar; the male of D. gyrociliatus is,
however, much smaller than the female. The generative organs occupy the greater
part of the body-cavity; in the male the testes communicate, by means of the pair
of seminal vesicles, with a median eversible apparatus. In the female the paired
ovaries communicate with a median sac which serves as a spermatheca.
The development is simple:[296] the worm itself is more like a larval Polychaete
than a full-grown worm. Dinophilus is an extremely interesting form, and it has
been suggested that, while still possessing certain Planarian characteristics, it may
be looked upon as closely resembling the ancestor from which the Chaetopoda
have arisen.
Protodrilus and Polygordius are distinctly Annelidan in character. Protodrilus[297]
is found in the mud of the "Pantano," an inlet of the sea near Messina; whilst of
Polygordius[298] one species at least occurs on our shores, and several others in the
Mediterranean and elsewhere. The worms are cylindrical, with many segments,
but these segments are only indistinctly marked externally—by girdles of cilia in
Protodrilus, or by faint grooves in Polygordius; but there are none of the
characteristic Chaetopod bristles or chaetae. The small prostomium which
overhangs the mouth is provided with a pair of ciliated pits, and carries a pair of
tentacles, serving as sensory organs, which, in Protodrilus, are also respiratory.
The anus is surrounded by glandular papillae in Polygordius, by means of which
the animal can fix itself; these are represented in Protodrilus by a couple of
processes.
The nervous system lies entirely in the epidermis. The body-cavity is regularly
segmented by transverse septa passing from the body-wall to the intestinal wall.
stated to be constructed on the Planarian plan; in others, as in D. taeniatus, the
organs are definite nephridia. Of these tubes there are five pairs, the last pair in the
male serving as a seminal vesicle. Each nephridium is a ciliated tube, the internal
end of which lies in the body-cavity and appears to be blocked by a ciliated
tongue-shaped appendage. The first pair corresponds to the "larval nephridia" of
Trochosphere larvae.
The nervous system, which is in contact with the epidermis, consists of a brain in
the prostomium, and, on each side of the body, a ventral cord with five ganglia,
connected by transverse commissures in as many segments.
The sexes are separate, and are usually similar; the male of D. gyrociliatus is,
however, much smaller than the female. The generative organs occupy the greater
part of the body-cavity; in the male the testes communicate, by means of the pair
of seminal vesicles, with a median eversible apparatus. In the female the paired
ovaries communicate with a median sac which serves as a spermatheca.
The development is simple:[296] the worm itself is more like a larval Polychaete
than a full-grown worm. Dinophilus is an extremely interesting form, and it has
been suggested that, while still possessing certain Planarian characteristics, it may
be looked upon as closely resembling the ancestor from which the Chaetopoda
have arisen.
Protodrilus and Polygordius are distinctly Annelidan in character. Protodrilus[297]
is found in the mud of the "Pantano," an inlet of the sea near Messina; whilst of
Polygordius[298] one species at least occurs on our shores, and several others in the
Mediterranean and elsewhere. The worms are cylindrical, with many segments,
but these segments are only indistinctly marked externally—by girdles of cilia in
Protodrilus, or by faint grooves in Polygordius; but there are none of the
characteristic Chaetopod bristles or chaetae. The small prostomium which
overhangs the mouth is provided with a pair of ciliated pits, and carries a pair of
tentacles, serving as sensory organs, which, in Protodrilus, are also respiratory.
The anus is surrounded by glandular papillae in Polygordius, by means of which
the animal can fix itself; these are represented in Protodrilus by a couple of
processes.
The nervous system lies entirely in the epidermis. The body-cavity is regularly
segmented by transverse septa passing from the body-wall to the intestinal wall.
Page 256
The foregut presents a slight eversible portion in Polygordius, whilst in
Protodrilus it has a peculiar U-shaped muscular diverticulum on its ventral
surface, corresponding with the similar apparatus in Dinophilus; it is capable of
eversion, and aids the worm in burrowing, as well as in seizing and swallowing
the mud. The vascular system is represented by a dorsal and a ventral vessel,
neither of which, however, is contractile. In Protodrilus the dorsal vessel divides
into two branches in the first segment, each of which passes to the tip of the
tentacle, and returning, joins its fellow to form the ventral vessel. In some species
of Polygordius there is a pair of vessels connecting the dorsal and ventral vessels
in every segment, but no vessel to the tentacle. The blood is colourless in some
species of Polygordius, but may be yellow (P. neapolitanus), red (P. lacteus), or
green (P. erythrophthalmus). Paired nephridia, with distinct funnels, occur
regularly throughout the body.
The sexes are separate in Polygordius, whilst Protodrilus is hermaphrodite,
bearing ova in the first seven segments and testes in the remaining segments. The
genital cells are produced from the body-wall in every segment; their mode of
discharge is unknown in the male Polygordius, though probably the nephridia
convey the spermatozoa to the exterior; but in the female the body-wall ruptures to
allow the ova to escape, and then the animal dies. The development of Polygordius
has been made the subject of very careful study; the larva has long been known,
and is a typical "trochosphere" of rather a depressed form. This "trochosphere"
larva is of considerable importance, as it makes its appearance in sundry groups of
animals in some form or another. Here, in Polygordius, it has the appearance of a
couple of wide but low cones united together by their bases, which form the
equator of the larva. This equator carries a double girdle of cilia, dividing the
animal into a preoral and postoral region; for the mouth is placed on one side of
the animal between the two girdles, while the anus lies at the apex of the postoral
cone, and is surrounded by another girdle of cilia. The alimentary canal is divisible
into three regions; it is separated from the body-wall by an extensive space, which
contains cells destined to give rise to muscles and nephridia. A nervous system
(apical plate) is present at the apex of the preoral cone. This little larva swims
freely on the surface of the sea, moving, balancing, and feeding by means of the
girdle of cilia. It soon increases in length by the active growth of the apex of the
postoral cone, which becomes cylindrical and then segmented externally and
internally. The greater part of the original larva remains of the same shape as
before, and forms the head (prostomium and peristomium): small tentacles grow
out of the preoral lobe, and after a gradual reduction in the relative size of the
"head" by the growth of the segmented "body," the animal becomes worm-like and
develops into a Polygordius.[299]
Protodrilus it has a peculiar U-shaped muscular diverticulum on its ventral
surface, corresponding with the similar apparatus in Dinophilus; it is capable of
eversion, and aids the worm in burrowing, as well as in seizing and swallowing
the mud. The vascular system is represented by a dorsal and a ventral vessel,
neither of which, however, is contractile. In Protodrilus the dorsal vessel divides
into two branches in the first segment, each of which passes to the tip of the
tentacle, and returning, joins its fellow to form the ventral vessel. In some species
of Polygordius there is a pair of vessels connecting the dorsal and ventral vessels
in every segment, but no vessel to the tentacle. The blood is colourless in some
species of Polygordius, but may be yellow (P. neapolitanus), red (P. lacteus), or
green (P. erythrophthalmus). Paired nephridia, with distinct funnels, occur
regularly throughout the body.
The sexes are separate in Polygordius, whilst Protodrilus is hermaphrodite,
bearing ova in the first seven segments and testes in the remaining segments. The
genital cells are produced from the body-wall in every segment; their mode of
discharge is unknown in the male Polygordius, though probably the nephridia
convey the spermatozoa to the exterior; but in the female the body-wall ruptures to
allow the ova to escape, and then the animal dies. The development of Polygordius
has been made the subject of very careful study; the larva has long been known,
and is a typical "trochosphere" of rather a depressed form. This "trochosphere"
larva is of considerable importance, as it makes its appearance in sundry groups of
animals in some form or another. Here, in Polygordius, it has the appearance of a
couple of wide but low cones united together by their bases, which form the
equator of the larva. This equator carries a double girdle of cilia, dividing the
animal into a preoral and postoral region; for the mouth is placed on one side of
the animal between the two girdles, while the anus lies at the apex of the postoral
cone, and is surrounded by another girdle of cilia. The alimentary canal is divisible
into three regions; it is separated from the body-wall by an extensive space, which
contains cells destined to give rise to muscles and nephridia. A nervous system
(apical plate) is present at the apex of the preoral cone. This little larva swims
freely on the surface of the sea, moving, balancing, and feeding by means of the
girdle of cilia. It soon increases in length by the active growth of the apex of the
postoral cone, which becomes cylindrical and then segmented externally and
internally. The greater part of the original larva remains of the same shape as
before, and forms the head (prostomium and peristomium): small tentacles grow
out of the preoral lobe, and after a gradual reduction in the relative size of the
"head" by the growth of the segmented "body," the animal becomes worm-like and
develops into a Polygordius.[299]
Page 257
Order II. Polychaeta.
Anatomy of Nereis.—In order to obtain a general idea of a Polychaete worm, it is
well to study a concrete example, and for this purpose the common Nereis serves
excellently. Several species (see p. 315) occur more or less commonly on our
coasts, and the general remarks will apply to one as well as to another.
Nereis pelagica Linnaeus reaches a length of 5 to 6 inches, and is about ¼ inch
across. It is convex above, nearly flat below. Its colour is brown or bronze. The
worm, which is to be found in shallow water, is made up of a considerable number
of rings or segments, constituting the "trunk" or "body," terminated at each end by
modified segments known as "head" and "tail" (Fig. 122). The segments
composing the trunk are all alike, except for small proportional differences, and it
will be convenient to describe a "typical segment" before referring to the head or
tail.
A typical body segment carries on each side a muscular lobed outgrowth, bearing
bundles of bristles or "chaetae," and filamentous sensory organs known as "cirri."
To this lateral locomotor organ Huxley gave the name "parapodium" (Fig. 124).
Each parapodium or foot consists of a basal portion, supporting a dorsal and a
ventral process, the "notopodium" (ntp) and "neuropodium" (nrp) respectively,
each of which is bilobed. The lobes are very vascular and glandular, and probably
serve as respiratory organs or "gills."
Fig. 122.—Nereis pelagica L., natural size. (From Ehlers.)
Anatomy of Nereis.—In order to obtain a general idea of a Polychaete worm, it is
well to study a concrete example, and for this purpose the common Nereis serves
excellently. Several species (see p. 315) occur more or less commonly on our
coasts, and the general remarks will apply to one as well as to another.
Nereis pelagica Linnaeus reaches a length of 5 to 6 inches, and is about ¼ inch
across. It is convex above, nearly flat below. Its colour is brown or bronze. The
worm, which is to be found in shallow water, is made up of a considerable number
of rings or segments, constituting the "trunk" or "body," terminated at each end by
modified segments known as "head" and "tail" (Fig. 122). The segments
composing the trunk are all alike, except for small proportional differences, and it
will be convenient to describe a "typical segment" before referring to the head or
tail.
A typical body segment carries on each side a muscular lobed outgrowth, bearing
bundles of bristles or "chaetae," and filamentous sensory organs known as "cirri."
To this lateral locomotor organ Huxley gave the name "parapodium" (Fig. 124).
Each parapodium or foot consists of a basal portion, supporting a dorsal and a
ventral process, the "notopodium" (ntp) and "neuropodium" (nrp) respectively,
each of which is bilobed. The lobes are very vascular and glandular, and probably
serve as respiratory organs or "gills."
Fig. 122.—Nereis pelagica L., natural size. (From Ehlers.)
Page 258
Fig. 123.—Chaetae of Nereis; enlarged. A, from neuropodium; B, from notopodium of N.
diversicolor; C, swimming chaeta of Heteronereid stage of N. dumerilii.
The chaetae, or bristles, of each bundle project from the mouth of a great sac, the
lips of which are particularly prominent in Nereis. Each chaeta arises from a single
cell situated at the bottom of the sac. The chaetae of Nereis, as of many other
Polychaetes, are of a kind usually termed compound or "jointed," each being
composed of a long stalk and a small "appendix" articulated in a cup at its
extremity (Fig. 123). The shape of the cup varies; it is in some cases of equal
height all round, or it is higher on one side than on the other. Further, the appendix
may be short and curved, or more elongate and spear-like; it is generally notched
or finely toothed on one side.
Fig. 124.—Nereis. Somewhat diagrammatic transverse section through the body. On the left
the chief constituents of the vascular system are represented; on the right side the
chaetae and their muscles, as well as the distribution of the lateral nerve, etc., are
shown. ac, aciculum; bv, network of blood-vessels; ch, chaetae (only a few are shown)
in two bundles; ch.l, lips of the chaetigerous sac; cil.org, dorsal ciliated organ; cir,
circular muscular coat; coe, coelom; d.cir, dorsal cirrus; d.long, dorsal bundle of
longitudinal muscles; d.ve, dorsal blood trunk; ep, epidermis; INT, intestine; int.cap,
blood capillaries in its wall; m.ch, muscles which move the chaetae; N.c, ventral nerve
cord; ner, lateral sensory nerve, dividing into a ventral branch entering the ventral
cirrus, and a dorsal branch (n.cir) for the dorsal cirrus; neph, nephridium, seen through
the oblique muscle through which its funnel passes; nrp, neuropodium; nrp.lig,
diversicolor; C, swimming chaeta of Heteronereid stage of N. dumerilii.
The chaetae, or bristles, of each bundle project from the mouth of a great sac, the
lips of which are particularly prominent in Nereis. Each chaeta arises from a single
cell situated at the bottom of the sac. The chaetae of Nereis, as of many other
Polychaetes, are of a kind usually termed compound or "jointed," each being
composed of a long stalk and a small "appendix" articulated in a cup at its
extremity (Fig. 123). The shape of the cup varies; it is in some cases of equal
height all round, or it is higher on one side than on the other. Further, the appendix
may be short and curved, or more elongate and spear-like; it is generally notched
or finely toothed on one side.
Fig. 124.—Nereis. Somewhat diagrammatic transverse section through the body. On the left
the chief constituents of the vascular system are represented; on the right side the
chaetae and their muscles, as well as the distribution of the lateral nerve, etc., are
shown. ac, aciculum; bv, network of blood-vessels; ch, chaetae (only a few are shown)
in two bundles; ch.l, lips of the chaetigerous sac; cil.org, dorsal ciliated organ; cir,
circular muscular coat; coe, coelom; d.cir, dorsal cirrus; d.long, dorsal bundle of
longitudinal muscles; d.ve, dorsal blood trunk; ep, epidermis; INT, intestine; int.cap,
blood capillaries in its wall; m.ch, muscles which move the chaetae; N.c, ventral nerve
cord; ner, lateral sensory nerve, dividing into a ventral branch entering the ventral
cirrus, and a dorsal branch (n.cir) for the dorsal cirrus; neph, nephridium, seen through
the oblique muscle through which its funnel passes; nrp, neuropodium; nrp.lig,
Page 259
neuropodial lobe or ligule; ntp, notopodium; ntp.lig, notopodial ligule; obl, oblique
transverse muscle (muscle of the parapodium); pv, peripheral blood-vessel; v.cir, ventral
cirrus; v.long, ventral bundle of longitudinal muscles; v.ve, ventral blood trunk.
In addition to these projecting locomotor chaetae, there is embedded in each of the
two chaetigerous lobes a much stouter and dark-coloured, needle-shaped bristle
known as an "aciculum," whose point only just projects beyond the surface. This
aciculum extends into the interior of the body much farther than do the locomotor
chaetae, and it is to it that the muscles serving to move the whole bundle of
chaetae are attached. The acicula thus serve as an internal skeleton to the
parapodium. The shape of the parapodium, the relative lengths of cirri and lobes,
the shape and arrangement of the chaetae, are all employed as specific characters.
The head consists of a preoral portion above the mouth, the "prostomium," and a
postoral region surrounding the mouth, the "peristomium" (Fig. 125). The
prostomium varies in shape in different species of Nereis; but it always carries on
its dorsal surface two pairs of eyes. From its narrower anterior end there arises a
pair of short, somewhat conical, sensory processes known as the "prostomial
tentacles." A second pair of processes springs from the under surface, and rather to
the side of the prostomium; these are known as the "palps," and in Nereis are
much more conspicuous than the tentacles; each is composed of two parts, a large
basal piece and a smaller terminal joint, capable of being withdrawn into the
former. The palps are highly muscular, and though they are sensory organs, act
also as great lateral lips.
Fig. 125.—Nereis diversicolor Müll. × 4. Head, with buccal region everted. A, Dorsal view; B,
ventral view. a, Prostomium; B, everted buccal region; c, c', peristomial cirri, 1, 2, 3, 4;
d, denticles or paragnaths; e, eyes; E, lower lip; P, palp in A, entrance to pharynx in B;
J, jaw; T, tentacle; I, peristomium; II, foot of apparent second segment.
The peristomium is in many species of Nereis (as in N. pelagica) considerably
larger than the trunk segments; it carries at its anterior edge four filiform cirri on
each side, which are directed forwards and used as feelers. They are arranged in
couples; a more anterior couple of dorsal and ventral cirri, and a more posterior
couple of dorsal and ventral cirri.
transverse muscle (muscle of the parapodium); pv, peripheral blood-vessel; v.cir, ventral
cirrus; v.long, ventral bundle of longitudinal muscles; v.ve, ventral blood trunk.
In addition to these projecting locomotor chaetae, there is embedded in each of the
two chaetigerous lobes a much stouter and dark-coloured, needle-shaped bristle
known as an "aciculum," whose point only just projects beyond the surface. This
aciculum extends into the interior of the body much farther than do the locomotor
chaetae, and it is to it that the muscles serving to move the whole bundle of
chaetae are attached. The acicula thus serve as an internal skeleton to the
parapodium. The shape of the parapodium, the relative lengths of cirri and lobes,
the shape and arrangement of the chaetae, are all employed as specific characters.
The head consists of a preoral portion above the mouth, the "prostomium," and a
postoral region surrounding the mouth, the "peristomium" (Fig. 125). The
prostomium varies in shape in different species of Nereis; but it always carries on
its dorsal surface two pairs of eyes. From its narrower anterior end there arises a
pair of short, somewhat conical, sensory processes known as the "prostomial
tentacles." A second pair of processes springs from the under surface, and rather to
the side of the prostomium; these are known as the "palps," and in Nereis are
much more conspicuous than the tentacles; each is composed of two parts, a large
basal piece and a smaller terminal joint, capable of being withdrawn into the
former. The palps are highly muscular, and though they are sensory organs, act
also as great lateral lips.
Fig. 125.—Nereis diversicolor Müll. × 4. Head, with buccal region everted. A, Dorsal view; B,
ventral view. a, Prostomium; B, everted buccal region; c, c', peristomial cirri, 1, 2, 3, 4;
d, denticles or paragnaths; e, eyes; E, lower lip; P, palp in A, entrance to pharynx in B;
J, jaw; T, tentacle; I, peristomium; II, foot of apparent second segment.
The peristomium is in many species of Nereis (as in N. pelagica) considerably
larger than the trunk segments; it carries at its anterior edge four filiform cirri on
each side, which are directed forwards and used as feelers. They are arranged in
couples; a more anterior couple of dorsal and ventral cirri, and a more posterior
couple of dorsal and ventral cirri.
Page 260
The Tail.—As the most anterior segment is perforated by the mouth, and is
modified as described above, so the last or anal segment, which carries the anus,
differs from the rest. It is more or less elongated, cylindrical, and without
parapodia or chaetae. It retains, however, its pair of ventral cirri, which are very
long.
Internal Anatomy.—In correspondence with the external metamerism there is an
internal repetition of parts. For, except in the anterior segments, where the
powerful protrusible pharynx is situated, the body-cavity or "coelom" is divided
into a series of chambers, by means of muscular septa inserted, on the one hand,
into the body-wall at the level of the grooves between the external segments, and,
on the other, into the wall of the alimentary canal. Each of these coelomic
chambers contains a pair of nephridia, a portion of the intestine, of the vascular
system, and of the nervous system, as will be seen in Fig. 124.
The epidermis, which forms the outer part of the body-wall, consists of a single
layer of cells, covered externally by a thin, tough cuticle. The latter is usually
stated to consist of the chemical substance known as chitin, but since the cuticle
differs from true chitin by dissolving in caustic potash after a time, Eisig[300] has
suggested that its substance is merely a stage in the formation of chitin. The
epidermis contains gland-cells, which are especially abundant on the lobes of the
parapodia. Below the epidermis lies the circular coat of muscles by whose
contraction the worm diminishes its diameter: it is interrupted on each side at the
junction of the parapodium with the body. Deeper still lie the longitudinal
muscles, which form four great bundles, two dorsal, separated by the insertion of a
small mesentery and dorsal blood-vessel, and two ventral bundles separated in the
middle line by the nerve-cords. These longitudinal muscles, by their contraction,
bend the worm from side to side, and are continuous from segment to segment. A
very characteristic muscle, present in all the Polychaeta, is an obliquely transverse
sheet of fibres passing from the body-wall at the side of the nerve-cord to the
parapodium, where it spreads out and serves to move the parapodium (Fig. 124).
All these muscles consist of smooth fibres, as in the earthworm.
The alimentary canal may be divided into the following four regions:—(1)
buccal or eversible region, (2) pharynx, carrying the great jaws, (3) oesophagus,
(4) intestine.
The first two regions constitute an "introvert" (Lankester[301]). When fully everted
the whole of the buccal region is turned inside out, and the terminal aperture leads
modified as described above, so the last or anal segment, which carries the anus,
differs from the rest. It is more or less elongated, cylindrical, and without
parapodia or chaetae. It retains, however, its pair of ventral cirri, which are very
long.
Internal Anatomy.—In correspondence with the external metamerism there is an
internal repetition of parts. For, except in the anterior segments, where the
powerful protrusible pharynx is situated, the body-cavity or "coelom" is divided
into a series of chambers, by means of muscular septa inserted, on the one hand,
into the body-wall at the level of the grooves between the external segments, and,
on the other, into the wall of the alimentary canal. Each of these coelomic
chambers contains a pair of nephridia, a portion of the intestine, of the vascular
system, and of the nervous system, as will be seen in Fig. 124.
The epidermis, which forms the outer part of the body-wall, consists of a single
layer of cells, covered externally by a thin, tough cuticle. The latter is usually
stated to consist of the chemical substance known as chitin, but since the cuticle
differs from true chitin by dissolving in caustic potash after a time, Eisig[300] has
suggested that its substance is merely a stage in the formation of chitin. The
epidermis contains gland-cells, which are especially abundant on the lobes of the
parapodia. Below the epidermis lies the circular coat of muscles by whose
contraction the worm diminishes its diameter: it is interrupted on each side at the
junction of the parapodium with the body. Deeper still lie the longitudinal
muscles, which form four great bundles, two dorsal, separated by the insertion of a
small mesentery and dorsal blood-vessel, and two ventral bundles separated in the
middle line by the nerve-cords. These longitudinal muscles, by their contraction,
bend the worm from side to side, and are continuous from segment to segment. A
very characteristic muscle, present in all the Polychaeta, is an obliquely transverse
sheet of fibres passing from the body-wall at the side of the nerve-cord to the
parapodium, where it spreads out and serves to move the parapodium (Fig. 124).
All these muscles consist of smooth fibres, as in the earthworm.
The alimentary canal may be divided into the following four regions:—(1)
buccal or eversible region, (2) pharynx, carrying the great jaws, (3) oesophagus,
(4) intestine.
The first two regions constitute an "introvert" (Lankester[301]). When fully everted
the whole of the buccal region is turned inside out, and the terminal aperture leads
Page 261
directly into the pharynx, which is not everted but merely protruded. Throughout
the following chapters the word "buccal" region is used for that part—if any—
which is thus everted (Figs. 125, 126).
Both the buccal and pharyngeal regions are wrapped round by several coats of
muscle, to form apparently a single muscular organ (Fig. 127, sh), which occupies
about eight segments in a condition of complete introversion. The septa are absent
from the anterior part of the body.
Fig. 126.—Diagrams to illustrate the action of the Chaetopodan "introvert." (From Lang.) A
shows the apparatus at rest; the mouth leads into the buccal cavity (B), with paragnaths
in its wall; P, the pharynx, with jaws at its anterior end; c, brain; p, protractor muscles;
r, retractors. B, the pharynx has been brought forward or protruded by the eversion, or
turning inside out, of the buccal region, so that the jaws (j) now lie some way in front of
the head, which is represented by the brain.
The buccal region is lined with chitin, which is specially thickened at certain
definite spots, forming small "denticles" or "paragnaths" (Fig. 125), which have a
different arrangement in the various species.
The cavity of the pharynx is narrow and the walls thick and muscular; each side
wall carries a large, dark, chitinous "jaw" (Fig. 127, J), which is hollow at the
base, into which the muscles serving to move it are inserted, whilst the apex is
solid, curved, and more or less notched. These two great jaws are used not only for
tearing prey, but for seizing it; for when the pharynx is entirely protruded the two
jaws are wide apart, and when retraction takes place they come together and grasp
the prey.
Eversion of the apparatus is partly effected by protractor muscles (Fig. 126, A, p)
and partly by the pressure of the coelomic fluid, compressed by the muscles of the
body-wall; the eversion is stopped at a certain stage by a sheet of muscular tissue
or "diaphragm" (Fig. 127, diaph) inserted round the buccal region and attached to
the body-wall in the second segment. The introversion is effected partly by the
contraction of this diaphragm and partly by the action of powerful retractor
muscles (Fig. 126, r) inserted into the hinder end of the pharynx and passing to the
the following chapters the word "buccal" region is used for that part—if any—
which is thus everted (Figs. 125, 126).
Both the buccal and pharyngeal regions are wrapped round by several coats of
muscle, to form apparently a single muscular organ (Fig. 127, sh), which occupies
about eight segments in a condition of complete introversion. The septa are absent
from the anterior part of the body.
Fig. 126.—Diagrams to illustrate the action of the Chaetopodan "introvert." (From Lang.) A
shows the apparatus at rest; the mouth leads into the buccal cavity (B), with paragnaths
in its wall; P, the pharynx, with jaws at its anterior end; c, brain; p, protractor muscles;
r, retractors. B, the pharynx has been brought forward or protruded by the eversion, or
turning inside out, of the buccal region, so that the jaws (j) now lie some way in front of
the head, which is represented by the brain.
The buccal region is lined with chitin, which is specially thickened at certain
definite spots, forming small "denticles" or "paragnaths" (Fig. 125), which have a
different arrangement in the various species.
The cavity of the pharynx is narrow and the walls thick and muscular; each side
wall carries a large, dark, chitinous "jaw" (Fig. 127, J), which is hollow at the
base, into which the muscles serving to move it are inserted, whilst the apex is
solid, curved, and more or less notched. These two great jaws are used not only for
tearing prey, but for seizing it; for when the pharynx is entirely protruded the two
jaws are wide apart, and when retraction takes place they come together and grasp
the prey.
Eversion of the apparatus is partly effected by protractor muscles (Fig. 126, A, p)
and partly by the pressure of the coelomic fluid, compressed by the muscles of the
body-wall; the eversion is stopped at a certain stage by a sheet of muscular tissue
or "diaphragm" (Fig. 127, diaph) inserted round the buccal region and attached to
the body-wall in the second segment. The introversion is effected partly by the
contraction of this diaphragm and partly by the action of powerful retractor
muscles (Fig. 126, r) inserted into the hinder end of the pharynx and passing to the
Page 262
body-wall (these are removed in Fig. 127). The movement of the jaws themselves
and of the wall of the apparatus is due to other muscles.
The oesophagus is quite short; into it opens a pair of sacculated diverticula or
glands. Then follows the intestine, which extends through the rest of the body as a
thin-walled tube, slightly dilated at the insertion of the septa.
Fig. 127.—Nereis, laid open by removal of the dorsal body-wall. br, Cerebral ganglion, from
which three pairs of nerves are represented as arising; a pair to the tentacles, a pair to
the palps, and a pair (con) passing one on each side of the buccal region, to join the
ventral nerve-cord; mo, mouth, exposed by removal of the dorsal wall of the buccal
region (Buc); pgn, the paragnaths in its wall; Ph, pharynx; J, the large "jaws" embedded
in its wall; J.mus, the muscles which work the jaws; sh, the muscular sheath; diaph, the
"diaphragm"; oes, oesophagus; gl, its glands; st, stomach; int, intestine; Sept, septum;
d.v, dorsal blood trunk; p.v, perivisceral branches, one pair in each segment; P, palp; t,
tentacle; per, peristomium; per.ci, two of the four peristomial cirri; ppIII, the first
parapodium which belongs to the third true, but second apparent, segment; cir.m,
circular muscular coat; lg.m, longitudinal muscular coat of the body-wall.
The vascular system consists of a contractile dorsal vessel and of a non-
contractile ventral vessel extending along the whole length of the body, from each
of which paired and segmentally-arranged vessels pass to the intestinal wall and to
the body-wall, and here form extensive capillary networks (Fig. 124, p. 247). This
type of vascular system is pretty generally adhered to throughout the Order, but in
the Terebelliformia, Scoleciformia, and Cryptocephala the dorsal vessel and
capillary plexus on the intestine are replaced by a continuous blood sinus, situated
in the substance of the gut-wall. This "perienteric sinus" has the same relation to
the segmental vessels as the dorsal vessel has in the Nereidiformia, and from it a
and of the wall of the apparatus is due to other muscles.
The oesophagus is quite short; into it opens a pair of sacculated diverticula or
glands. Then follows the intestine, which extends through the rest of the body as a
thin-walled tube, slightly dilated at the insertion of the septa.
Fig. 127.—Nereis, laid open by removal of the dorsal body-wall. br, Cerebral ganglion, from
which three pairs of nerves are represented as arising; a pair to the tentacles, a pair to
the palps, and a pair (con) passing one on each side of the buccal region, to join the
ventral nerve-cord; mo, mouth, exposed by removal of the dorsal wall of the buccal
region (Buc); pgn, the paragnaths in its wall; Ph, pharynx; J, the large "jaws" embedded
in its wall; J.mus, the muscles which work the jaws; sh, the muscular sheath; diaph, the
"diaphragm"; oes, oesophagus; gl, its glands; st, stomach; int, intestine; Sept, septum;
d.v, dorsal blood trunk; p.v, perivisceral branches, one pair in each segment; P, palp; t,
tentacle; per, peristomium; per.ci, two of the four peristomial cirri; ppIII, the first
parapodium which belongs to the third true, but second apparent, segment; cir.m,
circular muscular coat; lg.m, longitudinal muscular coat of the body-wall.
The vascular system consists of a contractile dorsal vessel and of a non-
contractile ventral vessel extending along the whole length of the body, from each
of which paired and segmentally-arranged vessels pass to the intestinal wall and to
the body-wall, and here form extensive capillary networks (Fig. 124, p. 247). This
type of vascular system is pretty generally adhered to throughout the Order, but in
the Terebelliformia, Scoleciformia, and Cryptocephala the dorsal vessel and
capillary plexus on the intestine are replaced by a continuous blood sinus, situated
in the substance of the gut-wall. This "perienteric sinus" has the same relation to
the segmental vessels as the dorsal vessel has in the Nereidiformia, and from it a
Page 263
tubular dorsal vessel arises anteriorly. In Arenicola the sinus is preceded in the
young stage by a network the branches of which gradually enlarge, meet, and fuse
to form the sinus.[302] Whether it is in all cases secondary is a moot point.
This system of vessels in the majority of Chaetopoda contains a respiratory fluid
coloured red[303] by haemoglobin in solution; in it float a very few small oval
nucleated non-amoeboid corpuscles. But the place of this red pigment is taken by
a green one, named "chlorocruorin," in the Chlorhaemidae and many
Sabelliformia;[304] whilst in Magelona[305] the blood is tinted madder-pink by a
number of globules of "haemerythrin." The blood (or "haemal fluid") is driven
forwards in the dorsal vessel, and passes backwards in the ventral vessel.
Respiration in Nereis is carried on by the whole surface of the body, but naturally
with greater activity in the surface of the parapodia, the lobes of which, with their
extensive vascular plexus, may be termed "gills"; but it must be borne in mind that
these organs have other functions as well.
The coelomic fluid, which fills the general body-cavity, is colourless, and contains
amoeboid corpuscles or "leucocytes." It corresponds to the lymph of Vertebrates,
being nutritive in function, in that it conveys absorbed material from the wall of
the intestine to the organs of the body, and at the same time removes any waste
substances from these organs; these waste substances contain nitrogen, and are
ultimately removed by the nephridia. In Ophelia many of the corpuscles contain a
curious dumb-bell-shaped rod of chitin, and it has been shown[306] that this
substance is a highly complex form of excretory material,—more complex than
guanin, for instance, which exists in the corpuscles of the Capitelliformia.
In Glyceridae, Capitelliformia, and Polycirrus haematodes (a Terebellid), the
vascular system is absent, and the coelomic corpuscles become coloured by
haemoglobin, and in order that the coelomic fluid may be distributed to the organs
of the body, the peritoneum is ciliated along certain definite tracts. The fluid in
these "anangian" worms thus combines originally separate functions, and behaves
like the "blood" of Vertebrates.
The excretory system is represented by a pair of nephridia in each segment, with
the exception of a few anteriorly and a few posteriorly. The nephridium of Nereis
differs from that of most other Polychaetes hitherto examined carefully, and rather
resembles that of the Oligochaetous Enchytraeids. It consists of a compact gland-
like organ, containing a much coiled tube, ciliated for the greater part of its length,
but deprived of cilia in its last coils; this latter part—or duct—leaves the "gland"
young stage by a network the branches of which gradually enlarge, meet, and fuse
to form the sinus.[302] Whether it is in all cases secondary is a moot point.
This system of vessels in the majority of Chaetopoda contains a respiratory fluid
coloured red[303] by haemoglobin in solution; in it float a very few small oval
nucleated non-amoeboid corpuscles. But the place of this red pigment is taken by
a green one, named "chlorocruorin," in the Chlorhaemidae and many
Sabelliformia;[304] whilst in Magelona[305] the blood is tinted madder-pink by a
number of globules of "haemerythrin." The blood (or "haemal fluid") is driven
forwards in the dorsal vessel, and passes backwards in the ventral vessel.
Respiration in Nereis is carried on by the whole surface of the body, but naturally
with greater activity in the surface of the parapodia, the lobes of which, with their
extensive vascular plexus, may be termed "gills"; but it must be borne in mind that
these organs have other functions as well.
The coelomic fluid, which fills the general body-cavity, is colourless, and contains
amoeboid corpuscles or "leucocytes." It corresponds to the lymph of Vertebrates,
being nutritive in function, in that it conveys absorbed material from the wall of
the intestine to the organs of the body, and at the same time removes any waste
substances from these organs; these waste substances contain nitrogen, and are
ultimately removed by the nephridia. In Ophelia many of the corpuscles contain a
curious dumb-bell-shaped rod of chitin, and it has been shown[306] that this
substance is a highly complex form of excretory material,—more complex than
guanin, for instance, which exists in the corpuscles of the Capitelliformia.
In Glyceridae, Capitelliformia, and Polycirrus haematodes (a Terebellid), the
vascular system is absent, and the coelomic corpuscles become coloured by
haemoglobin, and in order that the coelomic fluid may be distributed to the organs
of the body, the peritoneum is ciliated along certain definite tracts. The fluid in
these "anangian" worms thus combines originally separate functions, and behaves
like the "blood" of Vertebrates.
The excretory system is represented by a pair of nephridia in each segment, with
the exception of a few anteriorly and a few posteriorly. The nephridium of Nereis
differs from that of most other Polychaetes hitherto examined carefully, and rather
resembles that of the Oligochaetous Enchytraeids. It consists of a compact gland-
like organ, containing a much coiled tube, ciliated for the greater part of its length,
but deprived of cilia in its last coils; this latter part—or duct—leaves the "gland"
Page 264
and pierces the body-wall, opening to the exterior at the base of the parapodium.
The ciliated canal passes forwards into the next segment, where it opens by a
funnel into the coelom. The lip of the funnel is extremely curious, for the cells
constituting it are drawn out into very long, delicate processes covered with cilia.
[307]
Fig. 128.—Nephridium of Nereis. (From Goodrich.) f, Funnel; n, neck, which passes through a
septum; t, coiled tubule; c, connective tissue; d, duct.
In most Polychaetes the nephridium is a wide, sac-like tube as in Arenicola[308]
(Fig. 129). Its walls are covered by a dense network of blood-vessels, and it not
only acts as an excretory organ, but also as a genital duct (see p. 273).
Excretion, in the strict sense of the word, is carried out by the cells forming the
wall of the tube; they remove waste materials from the blood distributed over the
surface of the organ. But, in addition, there is a removal from the coelom, by
means of the funnel, of any dead or dying coelomic corpuscles which in their turn
have eaten up or otherwise destroyed foreign bodies (such as Bacteria, etc.) that
may have entered the animal.
In Nereis there is in each segment, in addition to the pair of nephridia, a pair of
"dorsal ciliated organs" (Goodrich) (cil.org in Fig. 124). Each appears as a wide-
mouthed funnel, greatly folded, and without any permanent outlet. But it is
possible that these organs function as genital ducts, and that the external aperture
will make its appearance temporarily at the period of maturity. This "dorsal
ciliated organ" has not been met with in allied genera—such as Eunice, Nephthys,
Polynoë, Glycera—where the nephridium is a wide tube, and serves as a genital
duct.
Fig. 129.—Nephridium of Arenicola. (From Benham.) × 4. d, Dorsal lip of funnel; v, ventral
lip of funnel; b, blood-vessel (all the black lines are blood-vessels); m, dilated bladder;
x, part cut away from body-wall where the nephridium is passing to the exterior.
The ciliated canal passes forwards into the next segment, where it opens by a
funnel into the coelom. The lip of the funnel is extremely curious, for the cells
constituting it are drawn out into very long, delicate processes covered with cilia.
[307]
Fig. 128.—Nephridium of Nereis. (From Goodrich.) f, Funnel; n, neck, which passes through a
septum; t, coiled tubule; c, connective tissue; d, duct.
In most Polychaetes the nephridium is a wide, sac-like tube as in Arenicola[308]
(Fig. 129). Its walls are covered by a dense network of blood-vessels, and it not
only acts as an excretory organ, but also as a genital duct (see p. 273).
Excretion, in the strict sense of the word, is carried out by the cells forming the
wall of the tube; they remove waste materials from the blood distributed over the
surface of the organ. But, in addition, there is a removal from the coelom, by
means of the funnel, of any dead or dying coelomic corpuscles which in their turn
have eaten up or otherwise destroyed foreign bodies (such as Bacteria, etc.) that
may have entered the animal.
In Nereis there is in each segment, in addition to the pair of nephridia, a pair of
"dorsal ciliated organs" (Goodrich) (cil.org in Fig. 124). Each appears as a wide-
mouthed funnel, greatly folded, and without any permanent outlet. But it is
possible that these organs function as genital ducts, and that the external aperture
will make its appearance temporarily at the period of maturity. This "dorsal
ciliated organ" has not been met with in allied genera—such as Eunice, Nephthys,
Polynoë, Glycera—where the nephridium is a wide tube, and serves as a genital
duct.
Fig. 129.—Nephridium of Arenicola. (From Benham.) × 4. d, Dorsal lip of funnel; v, ventral
lip of funnel; b, blood-vessel (all the black lines are blood-vessels); m, dilated bladder;
x, part cut away from body-wall where the nephridium is passing to the exterior.
Page 265
The nervous system, as in all Chaetopods, consists of a dorsal cerebral ganglion
or "brain" (Fig. 127, br), connected by circum-buccal commissures with the
anterior end of a ventral chain of ganglia. The brain occupies the prostomium,[309]
and from it nerves pass away to the prostomial tentacles and palps. The circum-
buccal commissures spring from the outer corner of the brain, and from each
arises a nerve to the first pair of peristomial cirri. The first ventral ganglion lies in
the third segment, and represents at least two ganglion-pairs fused together, for
from it arise (1) a pair of nerves to the second pair of peristomial cirri and (2) a
pair to the first parapodium. In the remainder of the body there is a ganglion in
each segment, whence nerves pass outwards to the parapodium and muscles of the
segment (Fig. 124).
In Nereis the apparently single ganglion in each segment really consists of two
halves, and the apparently single cord which traverses the whole length of the
body consists of two closely apposed cords. In some worms, such as Serpulidae,
the two cords are more or less widely separated, and the two ganglia of each
segment are thus distinct, and connected by a transverse commissure. In Nereis, as
well as in many other Polychaeta, the nerve-cords lie within the body-wall, but in
other cases they lie in the epidermis, as they do in Archiannelida.
The visceral nervous system, supplying the muscles of the pharynx, is frequently
highly developed. In Nereis it arises on each side by two roots, one from the brain,
the second from the circum-buccal commissure.
Fig. 130.—Eye of Nereis. (After Andrews.) × 150. A, Section through the entire eye; c,
cuticle; e, epidermis; l, lens; h, rods; r, retina; n, optic nerve: B, isolated retinal element;
c, cell; p, pigment; h, rod: f, nerve-fibre.
The organs of sense in Nereis are eyes, tentacles, palps, and cirri. The four eyes,
which rest upon the brain, have the structure represented in Fig. 130. The retina
consists of a single layer of cells containing pigment; each cell is drawn out
peripherally into a nerve-fibre, whilst centrally it forms a cuticular product—the
"rod" (h). The edges of the retina are continuous with the surrounding epidermis,
and the cup thus formed remains widely opened to the cuticle in a few
Polychaetes, e.g. Autolytus, and in the young of Nereis, but more usually it has the
or "brain" (Fig. 127, br), connected by circum-buccal commissures with the
anterior end of a ventral chain of ganglia. The brain occupies the prostomium,[309]
and from it nerves pass away to the prostomial tentacles and palps. The circum-
buccal commissures spring from the outer corner of the brain, and from each
arises a nerve to the first pair of peristomial cirri. The first ventral ganglion lies in
the third segment, and represents at least two ganglion-pairs fused together, for
from it arise (1) a pair of nerves to the second pair of peristomial cirri and (2) a
pair to the first parapodium. In the remainder of the body there is a ganglion in
each segment, whence nerves pass outwards to the parapodium and muscles of the
segment (Fig. 124).
In Nereis the apparently single ganglion in each segment really consists of two
halves, and the apparently single cord which traverses the whole length of the
body consists of two closely apposed cords. In some worms, such as Serpulidae,
the two cords are more or less widely separated, and the two ganglia of each
segment are thus distinct, and connected by a transverse commissure. In Nereis, as
well as in many other Polychaeta, the nerve-cords lie within the body-wall, but in
other cases they lie in the epidermis, as they do in Archiannelida.
The visceral nervous system, supplying the muscles of the pharynx, is frequently
highly developed. In Nereis it arises on each side by two roots, one from the brain,
the second from the circum-buccal commissure.
Fig. 130.—Eye of Nereis. (After Andrews.) × 150. A, Section through the entire eye; c,
cuticle; e, epidermis; l, lens; h, rods; r, retina; n, optic nerve: B, isolated retinal element;
c, cell; p, pigment; h, rod: f, nerve-fibre.
The organs of sense in Nereis are eyes, tentacles, palps, and cirri. The four eyes,
which rest upon the brain, have the structure represented in Fig. 130. The retina
consists of a single layer of cells containing pigment; each cell is drawn out
peripherally into a nerve-fibre, whilst centrally it forms a cuticular product—the
"rod" (h). The edges of the retina are continuous with the surrounding epidermis,
and the cup thus formed remains widely opened to the cuticle in a few
Polychaetes, e.g. Autolytus, and in the young of Nereis, but more usually it has the
Page 266
relations represented in the figure. The lens is produced by the retinal cells
(according to Andrews[310]), and is in some cases (Eunice, Amphinome)
continuous with the cuticle. It appears to be composed in other cases
(Lepidonotus) of continuations of the retinal rods. The structure of the other sense
organs indicates their adaptation to a tactile function; in each case a nerve
traverses the axis of the organ, and the nerve-fibrils terminate in sensory cells.
Very probably the palps have a certain power of testing the food—a combination
of the senses of taste and smell.
The Generative System.—In all the Polychaeta, with very few exceptions, the
sexes are separate; and the reproductive cells—ova and spermatozoa—are
produced at certain seasons of the year by the rapid proliferation and modification
of coelomic epithelial cells surrounding the blood-vessels in the parapodium and
its immediate neighbourhood. The sexual cells remain in the coelom till they are
ripe.
The egg-cells become filled with yolk globules; a vitelline membrane is present,
and an outer coat of albuminous material. It is doubtful by what means these
sexual cells are discharged in Nereis. There is some evidence that the "dorsal
ciliated organ" may act as a genital duct. In some other worms the nephridia serve
this purpose, whilst in others a rupture of the body-wall allows the products to
escape into the sea. According to Wistinghausen,[311] at the time of discharge the
females of Nereis dumerilii become surrounded by a kind of gelatinous tube
formed from a secretion of the parapodial glands, and into this tube the ova are
discharged, and arranged in a single layer round its wall.
The common species Nereis diversicolor is viviparous. In a large number of
species of Nereis the sexually-mature individuals undergo very marked changes in
various parts of their body, so that they differ very greatly from the immature
individuals.
These changes resulting in the "heteronereid" condition will be dealt with at some
length in Chap. X. p. 276. The larvae of Polychaetes and other facts connected
with reproduction are described in the same chapter.
CHAPTER X
(according to Andrews[310]), and is in some cases (Eunice, Amphinome)
continuous with the cuticle. It appears to be composed in other cases
(Lepidonotus) of continuations of the retinal rods. The structure of the other sense
organs indicates their adaptation to a tactile function; in each case a nerve
traverses the axis of the organ, and the nerve-fibrils terminate in sensory cells.
Very probably the palps have a certain power of testing the food—a combination
of the senses of taste and smell.
The Generative System.—In all the Polychaeta, with very few exceptions, the
sexes are separate; and the reproductive cells—ova and spermatozoa—are
produced at certain seasons of the year by the rapid proliferation and modification
of coelomic epithelial cells surrounding the blood-vessels in the parapodium and
its immediate neighbourhood. The sexual cells remain in the coelom till they are
ripe.
The egg-cells become filled with yolk globules; a vitelline membrane is present,
and an outer coat of albuminous material. It is doubtful by what means these
sexual cells are discharged in Nereis. There is some evidence that the "dorsal
ciliated organ" may act as a genital duct. In some other worms the nephridia serve
this purpose, whilst in others a rupture of the body-wall allows the products to
escape into the sea. According to Wistinghausen,[311] at the time of discharge the
females of Nereis dumerilii become surrounded by a kind of gelatinous tube
formed from a secretion of the parapodial glands, and into this tube the ova are
discharged, and arranged in a single layer round its wall.
The common species Nereis diversicolor is viviparous. In a large number of
species of Nereis the sexually-mature individuals undergo very marked changes in
various parts of their body, so that they differ very greatly from the immature
individuals.
These changes resulting in the "heteronereid" condition will be dealt with at some
length in Chap. X. p. 276. The larvae of Polychaetes and other facts connected
with reproduction are described in the same chapter.
CHAPTER X
Page 267
CLASSIFICATION OF THE POLYCHAETA—SHAPE—HEAD—PARAPODIA—CHAETAE—GILLS—
INTERNAL ORGANS—JAWS—SENSE ORGANS—REPRODUCTION—LARVAL FORMS—BUDDING
—FISSION—BRANCHING—REGENERATION.
The Polychaeta are marine worms whose bodies are usually elongated and
cylindrical; they either lead a free life, swimming in the open sea, or crawling
along the bottom; or they pass their life in burrows or definite tubes of various
kinds.
Each segment is normally provided on each side with a single or a couple of
bundles of chaetae, by means of which locomotion is effected. These, in the free-
living forms, are carried at the ends of lateral muscular outgrowths of the body,
known as "parapodia," which are practically limbs.
The "head" of the worm generally carries eyes, and frequently more or less
elongated tactile organs, the "tentacles" dorsally and "palps" ventrally. The foregut
is frequently provided with a masticating apparatus in its anterior region, which is
capable of protrusion; but this apparatus is absent in many burrowing and
tubicolous forms. The sexes are separate, so that there is no such complicated
system of generative organs as occurs in the Oligochaeta. The nephridia usually
act as genital ducts. In the majority of cases the egg develops into a larva, the
"Trochosphere," which leads a free life and undergoes a greater or less
metamorphosis into the adult condition.
The classification of Polychaeta adopted in this work is as follows:[312]—
Branch A. Phanerocephala.
Sub-Order 1. Nereidiformia [= Errantia, auctt. + Ariciidae].
Family 1. Syllidae see p. 306 Family 8. Amphinomidae see p. 318
" 2. Hesionidae " 308 " 9. Eunicidae " 318
" 3. Aphroditidae " 309 " 10. Glyceridae " 320
" 4. Phyllodocidae " 313 " 11. Sphaerodoridae " 320
" 5. Tomopteridae " 315 " 12. Ariciidae " 321
" 6. Nereidae " 315 " 13. Typhloscolecidae " 321
" 7. Nephthydidae " 317
Sub-Order 2. Spioniformia.
Family 1. Spionidae see p. 321 Family 4. Magelonidae see p. 325
INTERNAL ORGANS—JAWS—SENSE ORGANS—REPRODUCTION—LARVAL FORMS—BUDDING
—FISSION—BRANCHING—REGENERATION.
The Polychaeta are marine worms whose bodies are usually elongated and
cylindrical; they either lead a free life, swimming in the open sea, or crawling
along the bottom; or they pass their life in burrows or definite tubes of various
kinds.
Each segment is normally provided on each side with a single or a couple of
bundles of chaetae, by means of which locomotion is effected. These, in the free-
living forms, are carried at the ends of lateral muscular outgrowths of the body,
known as "parapodia," which are practically limbs.
The "head" of the worm generally carries eyes, and frequently more or less
elongated tactile organs, the "tentacles" dorsally and "palps" ventrally. The foregut
is frequently provided with a masticating apparatus in its anterior region, which is
capable of protrusion; but this apparatus is absent in many burrowing and
tubicolous forms. The sexes are separate, so that there is no such complicated
system of generative organs as occurs in the Oligochaeta. The nephridia usually
act as genital ducts. In the majority of cases the egg develops into a larva, the
"Trochosphere," which leads a free life and undergoes a greater or less
metamorphosis into the adult condition.
The classification of Polychaeta adopted in this work is as follows:[312]—
Branch A. Phanerocephala.
Sub-Order 1. Nereidiformia [= Errantia, auctt. + Ariciidae].
Family 1. Syllidae see p. 306 Family 8. Amphinomidae see p. 318
" 2. Hesionidae " 308 " 9. Eunicidae " 318
" 3. Aphroditidae " 309 " 10. Glyceridae " 320
" 4. Phyllodocidae " 313 " 11. Sphaerodoridae " 320
" 5. Tomopteridae " 315 " 12. Ariciidae " 321
" 6. Nereidae " 315 " 13. Typhloscolecidae " 321
" 7. Nephthydidae " 317
Sub-Order 2. Spioniformia.
Family 1. Spionidae see p. 321 Family 4. Magelonidae see p. 325
Page 268
" 2. Polydoridae " 323 " 5. Ammocharidae " 325
" 3. Chaetopteridae " 323
Sub-Order 3. Terebelliformia.
Family 1. Cirratulidae see p. 325 Family 3. Ampharetidae see p. 330
" 2. Terebellidae " 327 " 4. Amphictenidae " 330
Sub-Order 4. Capitelliformia.
Family. Capitellidae, see p. 331.
Sub-Order 5. Scoleciformia.
Family 1. Opheliidae see p. 331 Family 4. Scalibregmidae see p. 334
" 2. Maldanidae " 332 " 5. Chlorhaemidae " 334
" 3. Arenicolidae " 333 " 6. Sternaspidae " 335
Branch B. Cryptocephala.
Sub-Order 1. Sabelliformia.
Family 1. Sabellidae see p. 336 Family 3. Amphicorinidae see p. 339
" 2. Eriographidae " 338 " 4. Serpulidae " 339
Sub-Order 2. Hermelliformia.
Family. Hermellidae, see p. 341.
Comparative Anatomy of the Polychaeta.
General Shape of the Body.—The majority of the Polychaeta have an elongated
and very mobile body, like that of Nereis, consisting of an indefinite and usually of
a considerable number of segments; a few, however, have a shorter body, with
fewer segments, definite in number, for instance Aphrodite and Polynoë, which
have thirty to forty segments; and some Hesionids, with only some seventeen to
twenty segments.
In Aphroditidae and certain Amphinomidae the body is more or less oval in shape.
In Lipobranchius and Sternaspis it is grub-like, short, and cylindrical, with
rounded ends; in the former it is difficult to distinguish head and tail, or dorsal and
ventral surfaces.
" 3. Chaetopteridae " 323
Sub-Order 3. Terebelliformia.
Family 1. Cirratulidae see p. 325 Family 3. Ampharetidae see p. 330
" 2. Terebellidae " 327 " 4. Amphictenidae " 330
Sub-Order 4. Capitelliformia.
Family. Capitellidae, see p. 331.
Sub-Order 5. Scoleciformia.
Family 1. Opheliidae see p. 331 Family 4. Scalibregmidae see p. 334
" 2. Maldanidae " 332 " 5. Chlorhaemidae " 334
" 3. Arenicolidae " 333 " 6. Sternaspidae " 335
Branch B. Cryptocephala.
Sub-Order 1. Sabelliformia.
Family 1. Sabellidae see p. 336 Family 3. Amphicorinidae see p. 339
" 2. Eriographidae " 338 " 4. Serpulidae " 339
Sub-Order 2. Hermelliformia.
Family. Hermellidae, see p. 341.
Comparative Anatomy of the Polychaeta.
General Shape of the Body.—The majority of the Polychaeta have an elongated
and very mobile body, like that of Nereis, consisting of an indefinite and usually of
a considerable number of segments; a few, however, have a shorter body, with
fewer segments, definite in number, for instance Aphrodite and Polynoë, which
have thirty to forty segments; and some Hesionids, with only some seventeen to
twenty segments.
In Aphroditidae and certain Amphinomidae the body is more or less oval in shape.
In Lipobranchius and Sternaspis it is grub-like, short, and cylindrical, with
rounded ends; in the former it is difficult to distinguish head and tail, or dorsal and
ventral surfaces.
Page 269
The segments composing the trunk may be all alike, or may constitute two more
or less sharply marked regions, the thorax and abdomen, differing in the character
of the chaetae, or in their arrangement, or in some other way, as in the
Sabelliformia and the Capitelliformia.
As peculiar cuticular structures, the curious shields of Sternaspis, and of certain of
the Maldanidae may be mentioned.
The posterior extremity is generally more or less narrowed, and most of the
Nereidiformia are provided with special elongated cirri, borne by the anal
segment. In the Maldanidae and others the body terminates in a funnel, at the
bottom of which is placed the anus. Only in a few cases is the anus not terminal; in
Notopygos and other Amphinomidae, as well as in some species of Polynoë, it is
dorsal.[313] In Sabellaria and Pectinaria the hinder end of the body undergoes
great degeneration; in the former it is achaetous, but cylindrical and bent forwards
alongside the body (Fig. 131). In Pectinaria (Fig. 177), this region, which is called
the "scapha," is leaf-like, and serves to close the narrower end of the tube in which
the worm lives. Arenicola marina, and some Terebellids have no chaetae in the
hinder, narrower part of the body.
Fig. 131.—Sabellaria alveolata L. × 3. (After Malmgren.) a, Anus.
The Head.—The prostomium is, in the majority of cases, rounded or conical,
though it may be square (Nephthys) or elongated and jointed (Glycera), or even
hammer-shaped (Tomopteris); or it may be fused with the peristomium, and
apparently absent (Arenicola). In the great group Cryptocephala, the peristomium
grows forwards so as to hide the prostomium entirely.
In a few of the Nereidiformia the prostomium is compressed, and in the
Amphinomidae it is provided with a dorsal ridge or "caruncle," which is a leaf-like
process overlapping three or more segments. In many Aphroditidae (as well as in
or less sharply marked regions, the thorax and abdomen, differing in the character
of the chaetae, or in their arrangement, or in some other way, as in the
Sabelliformia and the Capitelliformia.
As peculiar cuticular structures, the curious shields of Sternaspis, and of certain of
the Maldanidae may be mentioned.
The posterior extremity is generally more or less narrowed, and most of the
Nereidiformia are provided with special elongated cirri, borne by the anal
segment. In the Maldanidae and others the body terminates in a funnel, at the
bottom of which is placed the anus. Only in a few cases is the anus not terminal; in
Notopygos and other Amphinomidae, as well as in some species of Polynoë, it is
dorsal.[313] In Sabellaria and Pectinaria the hinder end of the body undergoes
great degeneration; in the former it is achaetous, but cylindrical and bent forwards
alongside the body (Fig. 131). In Pectinaria (Fig. 177), this region, which is called
the "scapha," is leaf-like, and serves to close the narrower end of the tube in which
the worm lives. Arenicola marina, and some Terebellids have no chaetae in the
hinder, narrower part of the body.
Fig. 131.—Sabellaria alveolata L. × 3. (After Malmgren.) a, Anus.
The Head.—The prostomium is, in the majority of cases, rounded or conical,
though it may be square (Nephthys) or elongated and jointed (Glycera), or even
hammer-shaped (Tomopteris); or it may be fused with the peristomium, and
apparently absent (Arenicola). In the great group Cryptocephala, the peristomium
grows forwards so as to hide the prostomium entirely.
In a few of the Nereidiformia the prostomium is compressed, and in the
Amphinomidae it is provided with a dorsal ridge or "caruncle," which is a leaf-like
process overlapping three or more segments. In many Aphroditidae (as well as in
Page 270
Polydora) there is a peculiar "frontal" ridge passing forwards from the prostomial
tentacle, and downwards into the mouth (Figs. 132, c, and 133, A, x).
Fig. 132.—Aphrodite aculeata L. Ventral view of anterior region, × 6. a, Prostomium; c,
frontal ridge on prostomium; d, neuropodial cirrus; l, lower lip; m, mouth; p, palp; s,
intersegmental groove; t, tentacle; I, foot of peristomium, which has shifted forwards so
as to lie in front of the mouth; II to V, successive feet.
In all the Nereidiformia, as well as in Sabelliformia and Chlorhaemidae, the
prostomium bears sensory processes of two kinds, viz. dorsal tentacles and ventral
palps. The latter are invariably two in number, and are particularly well developed
in Aphroditidae, Nereidae, Syllidae, some of the Eunicidae, and in Chlorhaemidae.
Even when they are apparently absent, as in Nephthys, it is possible that they are
represented by certain lobes at the sides of the mouth, for in many Syllidae they
are so fused with the prostomium as to be scarcely distinguishable. In the
Chlorhaemids the palps[314] are grooved, and in the Sabelliformia they become
considerably branched, and extend round the prostomium so as to nearly meet
dorsally and ventrally. Each palp is, in this sub-Order, represented by a greater or
smaller number of long, mobile filaments, arising from a common base; they are
grooved along the inner side, ciliated, and provided with secondary processes. The
crown of "gills," in fact, is nothing more than the greatly subdivided and
enormously elongated palps, as both Pruvot[315] and Meyer[316] have shown. In
such forms as Haplobranchus and Amphicorine the process of subdivision
(branching) has only gone a short way. In all the Sabelliformia each filament, in
addition to its sensory function, aids in conveying food to the mouth by the action
of the cilia, and has a blood-vessel within, thus acting as a respiratory organ. The
filament may carry compound eyes (Fig. 143) either at its apex (Branchiomma) or
at intervals along its course (Dasychone).
tentacle, and downwards into the mouth (Figs. 132, c, and 133, A, x).
Fig. 132.—Aphrodite aculeata L. Ventral view of anterior region, × 6. a, Prostomium; c,
frontal ridge on prostomium; d, neuropodial cirrus; l, lower lip; m, mouth; p, palp; s,
intersegmental groove; t, tentacle; I, foot of peristomium, which has shifted forwards so
as to lie in front of the mouth; II to V, successive feet.
In all the Nereidiformia, as well as in Sabelliformia and Chlorhaemidae, the
prostomium bears sensory processes of two kinds, viz. dorsal tentacles and ventral
palps. The latter are invariably two in number, and are particularly well developed
in Aphroditidae, Nereidae, Syllidae, some of the Eunicidae, and in Chlorhaemidae.
Even when they are apparently absent, as in Nephthys, it is possible that they are
represented by certain lobes at the sides of the mouth, for in many Syllidae they
are so fused with the prostomium as to be scarcely distinguishable. In the
Chlorhaemids the palps[314] are grooved, and in the Sabelliformia they become
considerably branched, and extend round the prostomium so as to nearly meet
dorsally and ventrally. Each palp is, in this sub-Order, represented by a greater or
smaller number of long, mobile filaments, arising from a common base; they are
grooved along the inner side, ciliated, and provided with secondary processes. The
crown of "gills," in fact, is nothing more than the greatly subdivided and
enormously elongated palps, as both Pruvot[315] and Meyer[316] have shown. In
such forms as Haplobranchus and Amphicorine the process of subdivision
(branching) has only gone a short way. In all the Sabelliformia each filament, in
addition to its sensory function, aids in conveying food to the mouth by the action
of the cilia, and has a blood-vessel within, thus acting as a respiratory organ. The
filament may carry compound eyes (Fig. 143) either at its apex (Branchiomma) or
at intervals along its course (Dasychone).
Page 271
Fig. 133.—A, Anterior end of Polydora enlarged. a, Prostomium; x, frontal ridge; I,
peristomium; c', its long cirrus; II, III, etc., the following segments; c, gill; B, head of
Sabellid; P, palps (branchial crown); t, position of tentacles; l, processes of upper lip
membrane; I, peristomium raised into a collar; II, III, IV, following segments.
In the family Serpulidae one (rarely two) of the most dorsally placed gill filaments
is enlarged terminally, and acts as a stopper or "operculum," which closes the
mouth of the tube when the animal withdraws into it. Further, in Spirorbis this
operculum is grooved on one side, and serves as a brood pouch in which the eggs
undergo development (Fig. 184, p. 341). It will be seen, therefore, that the palps
may be very important organs for the life of the worm, and they are no less
interesting to the comparative anatomist, serving as they do as an excellent
illustration of the various uses which Nature finds for one and the same organ.
In the other sub-Orders the prostomium carries neither palps nor tentacles.
Fig. 134.—Heads of various Polychaeta (diagrammatic). A, Polynoid; B, Syllid; C, Nephthys;
D, Eunice; E, Phyllodoce; F, Trophonia: a, prostomium; c, normal cirrus; c1,
peristomial cirri; c2, cirrus of second segment; c3, cirrus of third segment; el1 point of
attachment of elytron; p, palp: s, nuchal organ (ciliated pit); t, tentacle; I, peristomium;
II, III, IV, segments.
The tentacles in the Nereidiformia present a wide variation in number; probably
the typical number is three, one of which is median and two lateral—as in
Polynoids, Syllidae, and some Eunicidae. Further, there is a certain amount of
peristomium; c', its long cirrus; II, III, etc., the following segments; c, gill; B, head of
Sabellid; P, palps (branchial crown); t, position of tentacles; l, processes of upper lip
membrane; I, peristomium raised into a collar; II, III, IV, following segments.
In the family Serpulidae one (rarely two) of the most dorsally placed gill filaments
is enlarged terminally, and acts as a stopper or "operculum," which closes the
mouth of the tube when the animal withdraws into it. Further, in Spirorbis this
operculum is grooved on one side, and serves as a brood pouch in which the eggs
undergo development (Fig. 184, p. 341). It will be seen, therefore, that the palps
may be very important organs for the life of the worm, and they are no less
interesting to the comparative anatomist, serving as they do as an excellent
illustration of the various uses which Nature finds for one and the same organ.
In the other sub-Orders the prostomium carries neither palps nor tentacles.
Fig. 134.—Heads of various Polychaeta (diagrammatic). A, Polynoid; B, Syllid; C, Nephthys;
D, Eunice; E, Phyllodoce; F, Trophonia: a, prostomium; c, normal cirrus; c1,
peristomial cirri; c2, cirrus of second segment; c3, cirrus of third segment; el1 point of
attachment of elytron; p, palp: s, nuchal organ (ciliated pit); t, tentacle; I, peristomium;
II, III, IV, segments.
The tentacles in the Nereidiformia present a wide variation in number; probably
the typical number is three, one of which is median and two lateral—as in
Polynoids, Syllidae, and some Eunicidae. Further, there is a certain amount of
Page 272
evidence in the nerve supply of the median tentacle to show that it was originally
double. The presence of four tentacles, then, as in Nephthys, Phyllodoce, and
Glycera, may be a primitive condition. By the disappearance of the paired lateral
tentacles the worm possesses a single median one, as in Aphrodite and
Amphinomids;[317] whilst a duplication of these lateral ones leads to the condition
of Eunice and Hyalinoecia, which have five tentacles. In the Chlorhaemidae the
number is further increased to five or more on each side,[318] and in the
Terebellidae these prostomial processes become very numerous.
In the Cryptocephala there is never more than a single pair of tentacles, and these
are generally reduced to a group of sensory cells, though in Sabellaria they retain
a considerable size.
In a few genera, such as Aphrodite, Nephthys, Capitella, the first postoral segment
is distinguished from the succeeding segments only by its position with regard to
the mouth (Fig. 132) and by its smaller size. But in the remainder of the
Polychaeta, with here and there an exception, the peristomium is achaetous in the
adult.[319]
Except in the Nereidiformia, peristomial or tentacular cirri are rare, being
represented in the Spioniformia by the very long "tentacles." In the Nereidiformia
one or more of the following segments may be added to the peristomium, and
share in the "cephalisation," which is so characteristic a feature in this group. In
Amphinomids the first three or four chaetigerous segments are incomplete
ventrally, owing to the shifting of the mouth backwards; these segments form
lateral lips, but they are not otherwise modified. In Phyllodoce, however, there are
four cirri on each side of the mouth, and from the arrangement in the Alciopids we
are justified in concluding that the segment which carries the four pairs of cirri is
really made up of three segments (Fig. 134, E). Among the Hesionids there are
four such "cephalised" achaetous segments with long cirri.
double. The presence of four tentacles, then, as in Nephthys, Phyllodoce, and
Glycera, may be a primitive condition. By the disappearance of the paired lateral
tentacles the worm possesses a single median one, as in Aphrodite and
Amphinomids;[317] whilst a duplication of these lateral ones leads to the condition
of Eunice and Hyalinoecia, which have five tentacles. In the Chlorhaemidae the
number is further increased to five or more on each side,[318] and in the
Terebellidae these prostomial processes become very numerous.
In the Cryptocephala there is never more than a single pair of tentacles, and these
are generally reduced to a group of sensory cells, though in Sabellaria they retain
a considerable size.
In a few genera, such as Aphrodite, Nephthys, Capitella, the first postoral segment
is distinguished from the succeeding segments only by its position with regard to
the mouth (Fig. 132) and by its smaller size. But in the remainder of the
Polychaeta, with here and there an exception, the peristomium is achaetous in the
adult.[319]
Except in the Nereidiformia, peristomial or tentacular cirri are rare, being
represented in the Spioniformia by the very long "tentacles." In the Nereidiformia
one or more of the following segments may be added to the peristomium, and
share in the "cephalisation," which is so characteristic a feature in this group. In
Amphinomids the first three or four chaetigerous segments are incomplete
ventrally, owing to the shifting of the mouth backwards; these segments form
lateral lips, but they are not otherwise modified. In Phyllodoce, however, there are
four cirri on each side of the mouth, and from the arrangement in the Alciopids we
are justified in concluding that the segment which carries the four pairs of cirri is
really made up of three segments (Fig. 134, E). Among the Hesionids there are
four such "cephalised" achaetous segments with long cirri.
Page 273
Fig. 135.—Sabellaria alveolata L. Ventral view of anterior region, × 10. a, Notopodial cirrus;
b, notopodium; c, neuropodium; ch, peristomial chaetae; d, neuropodial cirrus; m,
mouth; P, multifid palp (gill filaments); P', ridges after removal of gill filaments; s,
ventral (tubiparous) gland shield; T, tentacle; I, hood formed by peristomium; II to VI,
following segments.
In a few cases, such as the Chlorhaemids and Sternaspis, and to a slight degree in
Arenicola, the "head" and even the anterior part of the worm is capable of being
withdrawn into the body.
The Parapodia and Chaetae.—The typical parts of a parapodium have been
described in the preceding chapter; here it is only necessary to refer to the series of
diagrams (Figs. 136, 137) representing the parapodia of the more common
Polychaetes, and to add a few remarks about them.
Fig. 136.—Parapodia. A, Nephthys; B, Amphinome; C, Glycera (the unlettered lobe above g is
the notopodial cirrus); D, Syllis; E, Eunice; F, Phyllodoce. a, Notopodial cirrus; b,
notopodium; c, neuropodium; d, neuropodial cirrus; g, special gill; n, aciculum (omitted
in B); x, cirriform lip of chaetigerous sac.
In most Annelids the chaetae are in two bundles on each side, but there are certain
families in which the dorsal bundle, and even the notopodium itself, is absent, as
in the Eunicidae, Syllidae, and Phyllodocidae; or the dorsal bundle may be absent
only in certain regions of the body, as in the hind-body of Terebellids. In some
Amphinomidae and Aphroditidae the notopodium is scarcely distinct as a separate
lobe, being a slight tubercle on the upper surface of the neuropodium; but the
notopodial chaetae are present, and indeed particularly well developed in many
cases.
But whilst, in the Nereidiformia, the parapodia, whether consisting of two lobes or
only one, are always well developed, and project to a more or less pronounced
degree from the sides of the body, it is otherwise in the rest of the group, where the
chaetigerous lobes are usually reduced to mere tubercles or ridges, no doubt in
b, notopodium; c, neuropodium; ch, peristomial chaetae; d, neuropodial cirrus; m,
mouth; P, multifid palp (gill filaments); P', ridges after removal of gill filaments; s,
ventral (tubiparous) gland shield; T, tentacle; I, hood formed by peristomium; II to VI,
following segments.
In a few cases, such as the Chlorhaemids and Sternaspis, and to a slight degree in
Arenicola, the "head" and even the anterior part of the worm is capable of being
withdrawn into the body.
The Parapodia and Chaetae.—The typical parts of a parapodium have been
described in the preceding chapter; here it is only necessary to refer to the series of
diagrams (Figs. 136, 137) representing the parapodia of the more common
Polychaetes, and to add a few remarks about them.
Fig. 136.—Parapodia. A, Nephthys; B, Amphinome; C, Glycera (the unlettered lobe above g is
the notopodial cirrus); D, Syllis; E, Eunice; F, Phyllodoce. a, Notopodial cirrus; b,
notopodium; c, neuropodium; d, neuropodial cirrus; g, special gill; n, aciculum (omitted
in B); x, cirriform lip of chaetigerous sac.
In most Annelids the chaetae are in two bundles on each side, but there are certain
families in which the dorsal bundle, and even the notopodium itself, is absent, as
in the Eunicidae, Syllidae, and Phyllodocidae; or the dorsal bundle may be absent
only in certain regions of the body, as in the hind-body of Terebellids. In some
Amphinomidae and Aphroditidae the notopodium is scarcely distinct as a separate
lobe, being a slight tubercle on the upper surface of the neuropodium; but the
notopodial chaetae are present, and indeed particularly well developed in many
cases.
But whilst, in the Nereidiformia, the parapodia, whether consisting of two lobes or
only one, are always well developed, and project to a more or less pronounced
degree from the sides of the body, it is otherwise in the rest of the group, where the
chaetigerous lobes are usually reduced to mere tubercles or ridges, no doubt in
Page 274
relation to their burrowing or tubicolous habits. In Sternaspis the chaetae issue
directly from the body-wall.
Amongst the Nereidiformia we find examples in which the parapodia, instead of
being more or less conical "legs," are flattened fore and aft so as to serve as
efficient "fins," as in the active swimmers, Nereis virens and Nephthys caeca, and
in the pelagic Phyllodocids, Alciopids, Typhloscolecids, and Tomopteris.
Fig. 137.—Parapodia. A, Polynoë; B, Scoloplos; C, Euphrosyne. (Transverse section of body.)
a', Accessory cirrus; y, doubtful branchiae; D, Sabella (thoracic). a, Notopodial cirrus
("elytron" in A, "gill" in B); b, notopodium; c, neuropodium; d, neuropodial cirrus; n,
aciculum (accidentally omitted in C).
Of the typical dorsal and ventral cirri, the ventral is only absent in some
Amphinomids amongst the Nereidiformia; the dorsal is absent in Nephthys and
degenerate in Glycera, whilst in a very large number of families of the other sub-
Orders neither cirrus is present. These cirri, though originally filamentous and
sensory, may, by virtue of special blood supply, become "gills," and this occurs in
several families of different sub-Orders. Thus in Eunice this gill is comb-like; in
Amphinome and in Arenicola (on certain segments) it is arborescent, as it is also in
one to three segments in Terebellids; whilst in Ariciidae, Spioniformia,
Cirratulidae, Opheliidae, and Sabellaria it remains more or less finger-shaped or
filamentous. In the family Serpulidae the thoracic cirri, both dorsal and ventral,
become flattened and extended antero-posteriorly, and unite with one another to
form the "thoracic membrane."[320] In Phyllodocidae the cirri are foliaceous and
natatory, and they contain a great quantity of glands of a peculiar character. The
Aphroditidae are distinguished from other Annelids by the possession of "elytra"
or dorsal scales, which appear to be the dorso-ventrally flattened cirri, retaining
their sensory nature, but adding to this function several others.[321]
The chaetae or bristles are mainly used in locomotion, but it is not unreasonable
to believe that some of the stronger, serrated kinds may be used as weapons of
directly from the body-wall.
Amongst the Nereidiformia we find examples in which the parapodia, instead of
being more or less conical "legs," are flattened fore and aft so as to serve as
efficient "fins," as in the active swimmers, Nereis virens and Nephthys caeca, and
in the pelagic Phyllodocids, Alciopids, Typhloscolecids, and Tomopteris.
Fig. 137.—Parapodia. A, Polynoë; B, Scoloplos; C, Euphrosyne. (Transverse section of body.)
a', Accessory cirrus; y, doubtful branchiae; D, Sabella (thoracic). a, Notopodial cirrus
("elytron" in A, "gill" in B); b, notopodium; c, neuropodium; d, neuropodial cirrus; n,
aciculum (accidentally omitted in C).
Of the typical dorsal and ventral cirri, the ventral is only absent in some
Amphinomids amongst the Nereidiformia; the dorsal is absent in Nephthys and
degenerate in Glycera, whilst in a very large number of families of the other sub-
Orders neither cirrus is present. These cirri, though originally filamentous and
sensory, may, by virtue of special blood supply, become "gills," and this occurs in
several families of different sub-Orders. Thus in Eunice this gill is comb-like; in
Amphinome and in Arenicola (on certain segments) it is arborescent, as it is also in
one to three segments in Terebellids; whilst in Ariciidae, Spioniformia,
Cirratulidae, Opheliidae, and Sabellaria it remains more or less finger-shaped or
filamentous. In the family Serpulidae the thoracic cirri, both dorsal and ventral,
become flattened and extended antero-posteriorly, and unite with one another to
form the "thoracic membrane."[320] In Phyllodocidae the cirri are foliaceous and
natatory, and they contain a great quantity of glands of a peculiar character. The
Aphroditidae are distinguished from other Annelids by the possession of "elytra"
or dorsal scales, which appear to be the dorso-ventrally flattened cirri, retaining
their sensory nature, but adding to this function several others.[321]
The chaetae or bristles are mainly used in locomotion, but it is not unreasonable
to believe that some of the stronger, serrated kinds may be used as weapons of
Page 275
offence and defence; certainly the Polynoids, bristling as they do with stiff chaetae
along each side, must be rather unpleasant to their smaller enemies.
The various bristles may be placed in three chief groups, viz. (1) simple; (2)
jointed; (3) uncini (see Fig. 138).
(1) The simple chaetae may be smooth and hair-shaped, i.e. "capillary," such as are
present in nearly all families: or they may be forked (Amphinomidae), comb-
shaped (Eunice), notched or serrated, or provided with a series of frills at right
angles to their length, as in Aphroditidae; or fringed along one or both sides with a
membranous expansion, as in Terebellids and Sabellids. The simple chaetae may
also be short and spine-like, as in the ventral bundles of Arenicola; or they may be
slightly curved at the end and notched, forming what are generally termed
"crotchets," such as are common amongst Oligochaeta. These "crotchets" may be
simple, or have numerous denticulations at the end (Maldanidae), or be provided
with a membranous hood (Spioniformia, Capitelliformia). In Hermione peculiar
sheathed, spear-like bristles occur (Fig. 138, N).
(2) Jointed chaetae have already been described (p. 246); they are confined to the
sub-Order Nereidiformia, and occur only in certain families.
(3) The uncini are very short chaetae, which are simply embedded in the skin, and
do not extend beyond the body-wall into the body-cavity. An uncinus is a sharply
curved hook, which may have more or less numerous secondary teeth on it. They
are characteristic of the Sabelliformia and the Terebelliformia.
The chaetae appear as solid, usually fibrillated structures, of a yellow or golden
tint, transparent and refringent. Chemically they consist of chitin, and each chaeta
is the product of a single cell. The chaetae of Euphrosyne are hollow and
calcareous, being peculiar in both characters.
along each side, must be rather unpleasant to their smaller enemies.
The various bristles may be placed in three chief groups, viz. (1) simple; (2)
jointed; (3) uncini (see Fig. 138).
(1) The simple chaetae may be smooth and hair-shaped, i.e. "capillary," such as are
present in nearly all families: or they may be forked (Amphinomidae), comb-
shaped (Eunice), notched or serrated, or provided with a series of frills at right
angles to their length, as in Aphroditidae; or fringed along one or both sides with a
membranous expansion, as in Terebellids and Sabellids. The simple chaetae may
also be short and spine-like, as in the ventral bundles of Arenicola; or they may be
slightly curved at the end and notched, forming what are generally termed
"crotchets," such as are common amongst Oligochaeta. These "crotchets" may be
simple, or have numerous denticulations at the end (Maldanidae), or be provided
with a membranous hood (Spioniformia, Capitelliformia). In Hermione peculiar
sheathed, spear-like bristles occur (Fig. 138, N).
(2) Jointed chaetae have already been described (p. 246); they are confined to the
sub-Order Nereidiformia, and occur only in certain families.
(3) The uncini are very short chaetae, which are simply embedded in the skin, and
do not extend beyond the body-wall into the body-cavity. An uncinus is a sharply
curved hook, which may have more or less numerous secondary teeth on it. They
are characteristic of the Sabelliformia and the Terebelliformia.
The chaetae appear as solid, usually fibrillated structures, of a yellow or golden
tint, transparent and refringent. Chemically they consist of chitin, and each chaeta
is the product of a single cell. The chaetae of Euphrosyne are hollow and
calcareous, being peculiar in both characters.
Page 276
Fig. 138.—Chaetae of various Polychaetes (the magnification is not the same in all cases). A,
Doubly-fringed capillary, from Terebellid; B, hooded crotchet, from Polydora; C, a
fork, from Euphrosyne; D, jointed chaeta, from Phyllodoce; E, simple chaeta, with
serrated ridges or frills, from a Polynoid; F, jointed chaeta, from Eunice; G, uncinus,
from Pomatoceros (Serpulid); H, one of the outer series of paleae from the hood of
Sabellaria spinulosa; I, jointed chaeta, from a Syllid; J, multidenticulate crotchet, from
a Maldanid; K, comb-shaped chaeta, from Eunice; L, uncinus of a Sabellid; M, uncinus
of Terebellid (Amphitrite Johnstoni); a, edgewise; b, side view; m, attachments of
muscles into ba, basal plate; x, accessory teeth. N, Sheathed spear of Hermione; a, the
spear-shaped capillary removed from its sheath; b, the same, with sheath.
Certain modifications of the chaetae presented by various worms deserve mention.
In Polydora (Fig. 133, A) and in Chaetopterus (Fig. 173, p. 324) those of one
segment are especially strong, but their significance is uncertain. In Capitella
those of the notopodium of the eighth and ninth segments are specially modified;
they are analogous to the copulatory chaetae of Oligochaeta. In Aphrodite, in
addition to the ordinary locomotor chaetae, there are brilliant, iridescent bristles
and peculiar felting threads arising from the indistinct notopodium; these latter,
however, are not true "chaetae," but are separate chitinous filaments similar to the
constituent fibres of an ordinary chaeta.[322]
While the chaetae in the Nereidiformia and others are grouped in bundles, those of
many other families are in vertical, transverse rows, as in Maldanidae and in
Arenicola. The uncini are always embedded in such rows, usually slightly raised
from the general level of the body surface, each being termed a "torus
uncinigerus." These tori are usually limited to the sides of the body, but in
Myxicola and in Notomastus they encroach upon the dorsal surface, and in
Doubly-fringed capillary, from Terebellid; B, hooded crotchet, from Polydora; C, a
fork, from Euphrosyne; D, jointed chaeta, from Phyllodoce; E, simple chaeta, with
serrated ridges or frills, from a Polynoid; F, jointed chaeta, from Eunice; G, uncinus,
from Pomatoceros (Serpulid); H, one of the outer series of paleae from the hood of
Sabellaria spinulosa; I, jointed chaeta, from a Syllid; J, multidenticulate crotchet, from
a Maldanid; K, comb-shaped chaeta, from Eunice; L, uncinus of a Sabellid; M, uncinus
of Terebellid (Amphitrite Johnstoni); a, edgewise; b, side view; m, attachments of
muscles into ba, basal plate; x, accessory teeth. N, Sheathed spear of Hermione; a, the
spear-shaped capillary removed from its sheath; b, the same, with sheath.
Certain modifications of the chaetae presented by various worms deserve mention.
In Polydora (Fig. 133, A) and in Chaetopterus (Fig. 173, p. 324) those of one
segment are especially strong, but their significance is uncertain. In Capitella
those of the notopodium of the eighth and ninth segments are specially modified;
they are analogous to the copulatory chaetae of Oligochaeta. In Aphrodite, in
addition to the ordinary locomotor chaetae, there are brilliant, iridescent bristles
and peculiar felting threads arising from the indistinct notopodium; these latter,
however, are not true "chaetae," but are separate chitinous filaments similar to the
constituent fibres of an ordinary chaeta.[322]
While the chaetae in the Nereidiformia and others are grouped in bundles, those of
many other families are in vertical, transverse rows, as in Maldanidae and in
Arenicola. The uncini are always embedded in such rows, usually slightly raised
from the general level of the body surface, each being termed a "torus
uncinigerus." These tori are usually limited to the sides of the body, but in
Myxicola and in Notomastus they encroach upon the dorsal surface, and in
Page 277
Chaetozone, also upon the ventral, so as nearly to encircle the body, recalling the
"perichaetous" condition of some earth-worms.
Fig. 139.—Aphrodite. Foot, × 2. a, Elytron; b, notopodium; c, neuropodium; d, neuropodial
cirrus; n, aciculum; 1, iridescent bristles; 2, stiff chaetae; 3, felt.
Gills.—We have already seen that several different organs, e.g. the palps in
Sabelliformia, the prostomial tentacles of Chlorhaemidae, and the notopodial cirri
of sundry other Polychaetes, may take on a respiratory function. There are,
however, certain "gills" developed either on the parapodium itself or elsewhere on
the body which it is difficult to homologise. Such are the retractile gills on the
parapodia of the Glyceridae (Fig. 136, C); those of Dasybranchus, near the
abdominal neuropodia; those of Mastobranchus, near the notopodia. Nephthys has
a sickle-shaped gill on the under surface of the notopodium. The long gill
filaments at the posterior end of Sternaspis, again, are only doubtfully interpreted
as the dorsal cirri of some of the posterior segments.
Since primitively the whole skin of the worm is respiratory, any part of the skin
may become more or less specialised for this function, and chiefly, of course, on
the more actively moving parapodia. The blood-vessels constituting the essential
part of the "gill" may make use of any already existing outgrowth (such as a cirrus
or a tentacle), or may push the body-wall out on their own account.
Internal Anatomy.
Probably those organs which have the greatest effect in modifying the shape of the
body are the septa, for we find in the long, free-swimming worms that these are
regularly present throughout the body, and external "segmentation" of the body is
well marked. In burrowing and tubicolous forms the septa are frequently
incompletely developed, or more or fewer may be absent; and the body becomes
less distinctly segmented externally, tends to vary greatly in diameter during
movement, or becomes plumper. With the disappearance of the septa there is also
a diminution in the number of nephridia, as in Arenicola, with only six pairs.
Further, there is frequently a dimorphism of these organs; instead of all of them
serving equally as excretory organs and as genital ducts, some of the most anterior
"perichaetous" condition of some earth-worms.
Fig. 139.—Aphrodite. Foot, × 2. a, Elytron; b, notopodium; c, neuropodium; d, neuropodial
cirrus; n, aciculum; 1, iridescent bristles; 2, stiff chaetae; 3, felt.
Gills.—We have already seen that several different organs, e.g. the palps in
Sabelliformia, the prostomial tentacles of Chlorhaemidae, and the notopodial cirri
of sundry other Polychaetes, may take on a respiratory function. There are,
however, certain "gills" developed either on the parapodium itself or elsewhere on
the body which it is difficult to homologise. Such are the retractile gills on the
parapodia of the Glyceridae (Fig. 136, C); those of Dasybranchus, near the
abdominal neuropodia; those of Mastobranchus, near the notopodia. Nephthys has
a sickle-shaped gill on the under surface of the notopodium. The long gill
filaments at the posterior end of Sternaspis, again, are only doubtfully interpreted
as the dorsal cirri of some of the posterior segments.
Since primitively the whole skin of the worm is respiratory, any part of the skin
may become more or less specialised for this function, and chiefly, of course, on
the more actively moving parapodia. The blood-vessels constituting the essential
part of the "gill" may make use of any already existing outgrowth (such as a cirrus
or a tentacle), or may push the body-wall out on their own account.
Internal Anatomy.
Probably those organs which have the greatest effect in modifying the shape of the
body are the septa, for we find in the long, free-swimming worms that these are
regularly present throughout the body, and external "segmentation" of the body is
well marked. In burrowing and tubicolous forms the septa are frequently
incompletely developed, or more or fewer may be absent; and the body becomes
less distinctly segmented externally, tends to vary greatly in diameter during
movement, or becomes plumper. With the disappearance of the septa there is also
a diminution in the number of nephridia, as in Arenicola, with only six pairs.
Further, there is frequently a dimorphism of these organs; instead of all of them
serving equally as excretory organs and as genital ducts, some of the most anterior
Page 278
in the Sabelliformia and Terebelliformia become greatly enlarged, and take on
practically the whole of the former function; whilst more or fewer of the posterior
nephridia dwindle in size, and become genital ducts. The absence of septa allows a
free communication between the successive segments, and thus a freer flow of
coelomic fluid for the distension of the anterior end of the worm during
burrowing.
The alimentary system presents certain modifications of a systematic value. In
the Nereidiformia the muscular pharynx, which is always protrusible and is
preceded by an eversible buccal region, frequently encloses thickened cuticular
plates which serve as crushing and grasping organs. The form, number, and
arrangement of these "jaws" vary in the different families. They form valuable
fossil records of extinct worms.
In the Scoleciformia and Capitelliformia the buccal region exists, but there are no
jaws. In the Sabelliformia and Terebelliformia eversion does not take place and
jaws are absent.
Amongst the Nereidiformia the jaws are absent in the Phyllodocidae and
Hesionidae; when present they are usually set in the direct course of the food.
There may be one small tooth used for stabbing, as in some Syllids (Fig. 141, A);
or a circle of such denticles (Autolytus, Fig. 140, D). To these are added powerful
grasping jaws in Nereis (E); or the latter may alone be present, as in Glycera (F).
In Polynoë the four jaws are carried by hard pieces, to which the muscles are
attached (C and G). In Nephthys there is a dorsal and a ventral jaw.
Fig. 140.—Jaws of various Chaetopods. A, Transverse section of the anterior end of Eunice; a,
b, c, d, various parts of the upper series of denticles lying in a special chamber; g,
oesophagus; k, lower jaw: B, the denticles of Eunice separated; U, upper series; a,
grinder; b, forceps; c, rasping plates; d, grater; L, lower series; j, tooth; k, base into
which muscles are inserted: C, Polynoid; U, upper, and L, lower jaws; j, tooth; k, base:
D, Diagrammatic section across pharynx of Autolytus; E, of Nereis; F, of Glycera; G,
of Polynoë.
practically the whole of the former function; whilst more or fewer of the posterior
nephridia dwindle in size, and become genital ducts. The absence of septa allows a
free communication between the successive segments, and thus a freer flow of
coelomic fluid for the distension of the anterior end of the worm during
burrowing.
The alimentary system presents certain modifications of a systematic value. In
the Nereidiformia the muscular pharynx, which is always protrusible and is
preceded by an eversible buccal region, frequently encloses thickened cuticular
plates which serve as crushing and grasping organs. The form, number, and
arrangement of these "jaws" vary in the different families. They form valuable
fossil records of extinct worms.
In the Scoleciformia and Capitelliformia the buccal region exists, but there are no
jaws. In the Sabelliformia and Terebelliformia eversion does not take place and
jaws are absent.
Amongst the Nereidiformia the jaws are absent in the Phyllodocidae and
Hesionidae; when present they are usually set in the direct course of the food.
There may be one small tooth used for stabbing, as in some Syllids (Fig. 141, A);
or a circle of such denticles (Autolytus, Fig. 140, D). To these are added powerful
grasping jaws in Nereis (E); or the latter may alone be present, as in Glycera (F).
In Polynoë the four jaws are carried by hard pieces, to which the muscles are
attached (C and G). In Nephthys there is a dorsal and a ventral jaw.
Fig. 140.—Jaws of various Chaetopods. A, Transverse section of the anterior end of Eunice; a,
b, c, d, various parts of the upper series of denticles lying in a special chamber; g,
oesophagus; k, lower jaw: B, the denticles of Eunice separated; U, upper series; a,
grinder; b, forceps; c, rasping plates; d, grater; L, lower series; j, tooth; k, base into
which muscles are inserted: C, Polynoid; U, upper, and L, lower jaws; j, tooth; k, base:
D, Diagrammatic section across pharynx of Autolytus; E, of Nereis; F, of Glycera; G,
of Polynoë.
Page 279
In the Eunicidae, however, the numerous denticles are carried in a special pouch
below the food tract, with which it communicates anteriorly.[323] They are
arranged in an upper and lower series. The lower series (L) consists of a pair of
flat plates (k) on each side partially embedded in and acted upon by muscles, with
a harder enamelled piece—the actual lower "tooth" (j)—at its anterior end. The
upper series (U) consists of several pieces, varying in shape and size in the various
genera of this family; but developmentally they result from modifications of two
rows of small, similar pieces.[324]
The intestine is generally straight and cylindrical, and is usually constricted by the
septa, if these are present. In the Polynoids the intervening sacculations become so
long as to receive the name of "caeca," which, in Aphrodite, become enormously
elongated (Fig. 142); there are eighteen pairs of them (c), each being a slender
tube bent upon itself, giving off short branches and dilated distally, where it lies in
the base of the parapodium.
Fig. 141.—A, Alimentary canal of Syllid: B, transverse section of pharynx of the same; b,
buccal region; d, oesophageal outgrowth; g, salivary glands; i, intestine; j, tooth; p,
pharynx; s, gizzard: C, alimentary canal of Petta (after Wirén); i, intestine; o,
oesophagus; r, rectum; s, stomach.
Fig. 142.—Alimentary canal of Aphrodite. × 1. (From Gegenbaur.) a, Anus; b, pharynx; c,
caeca; o, mouth.
below the food tract, with which it communicates anteriorly.[323] They are
arranged in an upper and lower series. The lower series (L) consists of a pair of
flat plates (k) on each side partially embedded in and acted upon by muscles, with
a harder enamelled piece—the actual lower "tooth" (j)—at its anterior end. The
upper series (U) consists of several pieces, varying in shape and size in the various
genera of this family; but developmentally they result from modifications of two
rows of small, similar pieces.[324]
The intestine is generally straight and cylindrical, and is usually constricted by the
septa, if these are present. In the Polynoids the intervening sacculations become so
long as to receive the name of "caeca," which, in Aphrodite, become enormously
elongated (Fig. 142); there are eighteen pairs of them (c), each being a slender
tube bent upon itself, giving off short branches and dilated distally, where it lies in
the base of the parapodium.
Fig. 141.—A, Alimentary canal of Syllid: B, transverse section of pharynx of the same; b,
buccal region; d, oesophageal outgrowth; g, salivary glands; i, intestine; j, tooth; p,
pharynx; s, gizzard: C, alimentary canal of Petta (after Wirén); i, intestine; o,
oesophagus; r, rectum; s, stomach.
Fig. 142.—Alimentary canal of Aphrodite. × 1. (From Gegenbaur.) a, Anus; b, pharynx; c,
caeca; o, mouth.
Page 280
The intestine is looped in a few genera only, as in Trophonia, or coiled, as in
Sternaspis, Petta (Amphictenid, Fig. 141, C), and Ammotrypane. In the course of
the tube there may be a thick-walled muscular gizzard, with hard chitinous lining,
as in certain Terebellids, where it appears to replace, in function, the pharynx of
the Nereidiformia; in the Syllidae the gizzard is present in addition to the pharynx
(Fig. 141, A).
Glandular appendages of the oesophagus are present in many worms. Amongst the
Nereidiformia, the Syllidae and Hesionidae possess oesophageal diverticula (Fig.
141, A, d), which are used, not for secreting a digestive fluid, but as reservoirs for
water and air swallowed by the worms; and are provided with muscular walls, by
which their contents can be driven out. They appear, in fact, to be used like the
swim-bladder of fishes.[325] Many Chaetopods take in water by the anus—no
doubt for respiratory purposes—and pass it forwards along the intestine. In the
Capitelliformia a special groove conducts the water for some distance, then the
groove becomes closed to form a canal, which, after a course forwards as a free
tube below the intestine, again enters the latter, constituting a "siphonal
apparatus," similar to that of the Echiuroids and the sea urchins.
Sense Organs.—In addition to the prostomial eyes, which are present in nearly all
the Nereidiformia and Spioniformia, eyes may exist elsewhere on the body: thus
Myxicola infundibulum and Fabricia possess a pair on the anal segment; in M.
aesthetica Clap. there is a pair to every segment; in Branchiomma there is a
compound eye near the tip of each gill filament (i.e. palp); whilst in Dasychone a
series occurs along each gill filament. All these examples belong to the
Cryptocephala, in which, owing to certain peculiar modes of life, these sense
organs are required in correspondingly peculiar positions. It is usually stated that
Polyophthalmus possesses, in addition to the usual prostomial eyes, twelve pairs
on as many successive segments; but the minute structure of these organs points
rather to their function as light-producing organs.
Fig. 143.—A gill filament, A, of Branchiomma, B, of Dasychone. a, Axis; f, secondary
filaments; o, compound eye; x, lappets.
Sternaspis, Petta (Amphictenid, Fig. 141, C), and Ammotrypane. In the course of
the tube there may be a thick-walled muscular gizzard, with hard chitinous lining,
as in certain Terebellids, where it appears to replace, in function, the pharynx of
the Nereidiformia; in the Syllidae the gizzard is present in addition to the pharynx
(Fig. 141, A).
Glandular appendages of the oesophagus are present in many worms. Amongst the
Nereidiformia, the Syllidae and Hesionidae possess oesophageal diverticula (Fig.
141, A, d), which are used, not for secreting a digestive fluid, but as reservoirs for
water and air swallowed by the worms; and are provided with muscular walls, by
which their contents can be driven out. They appear, in fact, to be used like the
swim-bladder of fishes.[325] Many Chaetopods take in water by the anus—no
doubt for respiratory purposes—and pass it forwards along the intestine. In the
Capitelliformia a special groove conducts the water for some distance, then the
groove becomes closed to form a canal, which, after a course forwards as a free
tube below the intestine, again enters the latter, constituting a "siphonal
apparatus," similar to that of the Echiuroids and the sea urchins.
Sense Organs.—In addition to the prostomial eyes, which are present in nearly all
the Nereidiformia and Spioniformia, eyes may exist elsewhere on the body: thus
Myxicola infundibulum and Fabricia possess a pair on the anal segment; in M.
aesthetica Clap. there is a pair to every segment; in Branchiomma there is a
compound eye near the tip of each gill filament (i.e. palp); whilst in Dasychone a
series occurs along each gill filament. All these examples belong to the
Cryptocephala, in which, owing to certain peculiar modes of life, these sense
organs are required in correspondingly peculiar positions. It is usually stated that
Polyophthalmus possesses, in addition to the usual prostomial eyes, twelve pairs
on as many successive segments; but the minute structure of these organs points
rather to their function as light-producing organs.
Fig. 143.—A gill filament, A, of Branchiomma, B, of Dasychone. a, Axis; f, secondary
filaments; o, compound eye; x, lappets.
Page 281
The Capitelliformia and Opheliidae possess a pair of peculiar "ciliated pits" or
"nuchal organs" at the upper side of the head, between the prostomium and
peristomium, and capable of eversion (Fig. 144). They are most characteristically
developed in the Capitelliformia, where each organ abuts upon a special lobe of
the brain. The function of these "ciliated organs," which bear a great resemblance
to those of the Nemertines, is a matter of speculation. Similar organs, in the form
of simple pits or grooves, occur in many of the Nereidiformia, Terebelliformia,
and others.[326]
Otocysts are rare. Arenicola possesses a pair at the base of the prostomium, each
of which in some species retains an opening to the exterior.[327] They probably
serve as "organs of direction" rather than of "hearing." Aricia and Polyophthalmus
likewise have such organs on the prostomium; whilst Fabricia, Myxicola,
Terebella, and a few others possess them in the peristomium, or in some other
segment of the body.
Fig. 144.—Ammotrypane aulogaster Rathke, enlarged. (From Cuningham.) Anterior end. a,
Prostomium; b, everted buccal region; c, notopodial cirrus; X, ciliated organ everted; I,
II, III, first three segments.
Reproductive Phenomena.—With a few exceptions mentioned below, the
Polychaeta are unisexual. The sexual cells are developed in all cases from the
lining epithelium of the body-cavity. The exact spot at which this occurs varies in
different cases; it may be, though rarely, on the floor of the body-cavity; it is more
usually on the wall of some blood-vessel, either the ventral vessel or on branches
of it; or on the many blind blood-vessels of Aphrodite. The number of such genital
organs is very great in most worms, but in those presenting two regions of the
body they are confined to the posterior segments (Sabelliformia, Terebelliformia,
Capitelliformia). The number is very limited in Arenicola and other worms
presenting but few nephridia: in the former genus there being six pairs, in
Trophonia only one pair.
The following genera are hermaphrodite:—Amphiglena, Salmacina, Protula,
Spirorbis, belonging to the Sabelliformia, to which must be added some
Hesionidae. In this family ova and spermatozoa are developed around the same
"nuchal organs" at the upper side of the head, between the prostomium and
peristomium, and capable of eversion (Fig. 144). They are most characteristically
developed in the Capitelliformia, where each organ abuts upon a special lobe of
the brain. The function of these "ciliated organs," which bear a great resemblance
to those of the Nemertines, is a matter of speculation. Similar organs, in the form
of simple pits or grooves, occur in many of the Nereidiformia, Terebelliformia,
and others.[326]
Otocysts are rare. Arenicola possesses a pair at the base of the prostomium, each
of which in some species retains an opening to the exterior.[327] They probably
serve as "organs of direction" rather than of "hearing." Aricia and Polyophthalmus
likewise have such organs on the prostomium; whilst Fabricia, Myxicola,
Terebella, and a few others possess them in the peristomium, or in some other
segment of the body.
Fig. 144.—Ammotrypane aulogaster Rathke, enlarged. (From Cuningham.) Anterior end. a,
Prostomium; b, everted buccal region; c, notopodial cirrus; X, ciliated organ everted; I,
II, III, first three segments.
Reproductive Phenomena.—With a few exceptions mentioned below, the
Polychaeta are unisexual. The sexual cells are developed in all cases from the
lining epithelium of the body-cavity. The exact spot at which this occurs varies in
different cases; it may be, though rarely, on the floor of the body-cavity; it is more
usually on the wall of some blood-vessel, either the ventral vessel or on branches
of it; or on the many blind blood-vessels of Aphrodite. The number of such genital
organs is very great in most worms, but in those presenting two regions of the
body they are confined to the posterior segments (Sabelliformia, Terebelliformia,
Capitelliformia). The number is very limited in Arenicola and other worms
presenting but few nephridia: in the former genus there being six pairs, in
Trophonia only one pair.
The following genera are hermaphrodite:—Amphiglena, Salmacina, Protula,
Spirorbis, belonging to the Sabelliformia, to which must be added some
Hesionidae. In this family ova and spermatozoa are developed around the same
Page 282
blood-vessel. But in the former group of worms (as also in Ophryotrocha) the two
kinds of cells are produced in different regions of the body. Thus in Protula the
anterior abdominal segments are male, the posterior ones female, while in
Spirorbis the reverse arrangement holds; and in Syllis corruscans the anterior
segments of the body contain eggs, whilst the posterior region contains
spermatozoa, and this region separates and becomes a male worm.
The eggs and spermatozoa in the Polychaeta are discharged into the sea either by
rupture of the body-wall or through the nephridia; the male and female elements
unite, and the resulting fertilised eggs undergo development, either floating
separately in the water, or embedded in jelly, or attached to the body or to the tube
of the worm.
The result of the segmentation of the egg is a free-swimming larva known as a
"Trochosphere," similar to that of Polygordius. The larvae of different species
present various more or less marked departures from this type, for instead of the
two girdles of cilia there may be only the anterior girdle, or there may be several
complete or incomplete girdles between the two typical ones, or there may be
(Chaetopterids) only a single girdle of cilia about the middle of the body, the two
typical girdles being absent.[328] The postoral region, after elongation, generally
becomes marked out into three segments, and these segments develop chaetae,
which are usually temporary and specially long.
The little animal is thus equipped for an independent life: the provisional chaetae
help in keeping it balanced; and in some cases (Spionidae) serve to protect the
little soft creature, for when it is touched it curls up, and its chaetae stick out at the
sides, so that it looks like a hairy caterpillar. But the larva is quite at the mercy of
the sea, for it is carried hither and thither by currents, and in this way the species is
disseminated. The larvae of the Polychaetes, like those of other animals, occur at
certain periods of the year in large quantities at the surface of the sea, and serve as
food for various larger animals.
Fig. 145.—A, Trochosphere of Nephthys. × 65. a, Anus; b, apical plate (brain); c, apical tuft of
cilia; c', girdle of cilia; i, intestine; m, mouth; st, stomach. B, Larva of Spio, with three
kinds of cells are produced in different regions of the body. Thus in Protula the
anterior abdominal segments are male, the posterior ones female, while in
Spirorbis the reverse arrangement holds; and in Syllis corruscans the anterior
segments of the body contain eggs, whilst the posterior region contains
spermatozoa, and this region separates and becomes a male worm.
The eggs and spermatozoa in the Polychaeta are discharged into the sea either by
rupture of the body-wall or through the nephridia; the male and female elements
unite, and the resulting fertilised eggs undergo development, either floating
separately in the water, or embedded in jelly, or attached to the body or to the tube
of the worm.
The result of the segmentation of the egg is a free-swimming larva known as a
"Trochosphere," similar to that of Polygordius. The larvae of different species
present various more or less marked departures from this type, for instead of the
two girdles of cilia there may be only the anterior girdle, or there may be several
complete or incomplete girdles between the two typical ones, or there may be
(Chaetopterids) only a single girdle of cilia about the middle of the body, the two
typical girdles being absent.[328] The postoral region, after elongation, generally
becomes marked out into three segments, and these segments develop chaetae,
which are usually temporary and specially long.
The little animal is thus equipped for an independent life: the provisional chaetae
help in keeping it balanced; and in some cases (Spionidae) serve to protect the
little soft creature, for when it is touched it curls up, and its chaetae stick out at the
sides, so that it looks like a hairy caterpillar. But the larva is quite at the mercy of
the sea, for it is carried hither and thither by currents, and in this way the species is
disseminated. The larvae of the Polychaetes, like those of other animals, occur at
certain periods of the year in large quantities at the surface of the sea, and serve as
food for various larger animals.
Fig. 145.—A, Trochosphere of Nephthys. × 65. a, Anus; b, apical plate (brain); c, apical tuft of
cilia; c', girdle of cilia; i, intestine; m, mouth; st, stomach. B, Larva of Spio, with three
Page 283
segments, eight days old. × 100. c, Preoral girdle of cilia; c', preanal girdle; ch, long
provisional chaetae; pr, prostomium with eyes. (From Claparède and Metschnikoff.)
These larvae are at first very different from the adult animal, and the necessary
changes to be passed through are more or less great according to the species. It is
not our intention to describe these changes in detail.[329] The larva increases in
size, the permanent chaetae make their appearance in regular order, and the body
exhibits segmentation, the new segments always appearing just in front of the anal
segment. The internal organs gradually develop, and the prostomial and parapodial
appendages grow out in their turn. In the Sabelliformia the multifilamentous
"gills" arise by the continued branching of an at first simple process (the palp)
arising from the latero-ventral surface of each side of the preoral lobe.[330] These
gradually encroach dorsally and ventrally till the prostomium is more or less
encircled; meanwhile the peristomium grows forwards so as to conceal the
prostomium, which no longer increases at the same rate as does the rest of the
body.
Although most worms appear to discharge their ova directly into the sea and take
no further care of them, some make provision for their offspring either by laying
the eggs in a jelly, which will serve as food for the young larvae—Aricia, Ophelia,
Protula, Phyllodoce—or by attaching them to their body. In certain Polynoids the
eggs are attached by means of a secretion to the back, under the elytra, where they
undergo development up to a certain stage. In Exogone and some other Syllids
they are attached to the ventral cirri, or in Grubea limbata, all over the back. In the
female Autolytus (Sacconereis) a ventrally-placed brood sac is formed by the
hardening of a secretion; the eggs develop into embryos inside the brood sac, and
then become free, with head appendages and three pairs of parapodia. Enormous
numbers of such embryos may occur; for instance, some 300 were counted in a
brood sac of Autolytus ebiensis. In the case of tubicolous worms, the eggs are
frequently attached to the tube, either inside or outside. In Spirorbis and
Salmacina the operculum serves as a brood pouch.
Only a very few species are known to be viviparous, viz. Syllis vivipara Kr.,
Cirratulus chrysoderma Clap., Marphysa sanguinea Mont., and Nereis
diversicolor Müll.
In most genera there is no external difference between a mature worm filled with
generative products and an immature one, except, it may be, in the colour; for the
yolk of the eggs is frequently tinted yellow, or pink, or bluish, while the
spermatozoa in mass are white; so that the normal colouring of the worm may be
provisional chaetae; pr, prostomium with eyes. (From Claparède and Metschnikoff.)
These larvae are at first very different from the adult animal, and the necessary
changes to be passed through are more or less great according to the species. It is
not our intention to describe these changes in detail.[329] The larva increases in
size, the permanent chaetae make their appearance in regular order, and the body
exhibits segmentation, the new segments always appearing just in front of the anal
segment. The internal organs gradually develop, and the prostomial and parapodial
appendages grow out in their turn. In the Sabelliformia the multifilamentous
"gills" arise by the continued branching of an at first simple process (the palp)
arising from the latero-ventral surface of each side of the preoral lobe.[330] These
gradually encroach dorsally and ventrally till the prostomium is more or less
encircled; meanwhile the peristomium grows forwards so as to conceal the
prostomium, which no longer increases at the same rate as does the rest of the
body.
Although most worms appear to discharge their ova directly into the sea and take
no further care of them, some make provision for their offspring either by laying
the eggs in a jelly, which will serve as food for the young larvae—Aricia, Ophelia,
Protula, Phyllodoce—or by attaching them to their body. In certain Polynoids the
eggs are attached by means of a secretion to the back, under the elytra, where they
undergo development up to a certain stage. In Exogone and some other Syllids
they are attached to the ventral cirri, or in Grubea limbata, all over the back. In the
female Autolytus (Sacconereis) a ventrally-placed brood sac is formed by the
hardening of a secretion; the eggs develop into embryos inside the brood sac, and
then become free, with head appendages and three pairs of parapodia. Enormous
numbers of such embryos may occur; for instance, some 300 were counted in a
brood sac of Autolytus ebiensis. In the case of tubicolous worms, the eggs are
frequently attached to the tube, either inside or outside. In Spirorbis and
Salmacina the operculum serves as a brood pouch.
Only a very few species are known to be viviparous, viz. Syllis vivipara Kr.,
Cirratulus chrysoderma Clap., Marphysa sanguinea Mont., and Nereis
diversicolor Müll.
In most genera there is no external difference between a mature worm filled with
generative products and an immature one, except, it may be, in the colour; for the
yolk of the eggs is frequently tinted yellow, or pink, or bluish, while the
spermatozoa in mass are white; so that the normal colouring of the worm may be
Page 284
modified when filled with these elements. But in a few instances striking
anatomical peculiarities are exhibited by the mature worm.[331] In many species of
Nereis, for instance, those segments containing the generative products undergo
more or less extensive changes, while the anterior ones remain unaltered. The
body of the ripe Nereis is then distinguishable into an anterior non-sexual region
and a posterior sexual region; and so great are these changes in certain species that
the mature worms were for a long time believed to belong to a different genus, and
received the name Heteronereis. But we now know their true relations, thanks to
the work of Claparède and others. The males in the Heteronereid phase have fewer
unaltered anterior segments than the females, so that there is a sexual dimorphism.
Fig. 146.—Male "Heteronereis" of N. pelagica L. × 1. A, Non-sexual region; B, sexual,
modified region. (From Ehlers.)
The changes which Nereis undergoes in its transformation affect chiefly (a) the
shape of the parapodia, and (b) the form of the chaetae of these parapodia. Other
organs may also be affected, though less noticeably; thus the eyes become
enlarged, the intestine may become so compressed by the generative products as to
be functionless, and the tail develops special sensory papillae.[332]
In the parapodia an increase in size and a sharper delineation of the various parts
take place; then flattened foliaceous outgrowths (Fig. 147, x, y) arise from certain
lobes of the feet, in which, too, the blood supply becomes greatly increased. The
old chaetae are pushed out by the development of new ones of quite a different
shape; these are jointed like the old ones, but the appendix is, in many species at
least, flattened and oar-shaped (Fig. 123, C, p. 246); and the chaetae are arranged
in a fan-like manner. Both these modifications are in evident relation to the free-
swimming habit which the Heteronereid now adopts. The new foot serves as a
swimming organ, the old one was a walking appendage.
anatomical peculiarities are exhibited by the mature worm.[331] In many species of
Nereis, for instance, those segments containing the generative products undergo
more or less extensive changes, while the anterior ones remain unaltered. The
body of the ripe Nereis is then distinguishable into an anterior non-sexual region
and a posterior sexual region; and so great are these changes in certain species that
the mature worms were for a long time believed to belong to a different genus, and
received the name Heteronereis. But we now know their true relations, thanks to
the work of Claparède and others. The males in the Heteronereid phase have fewer
unaltered anterior segments than the females, so that there is a sexual dimorphism.
Fig. 146.—Male "Heteronereis" of N. pelagica L. × 1. A, Non-sexual region; B, sexual,
modified region. (From Ehlers.)
The changes which Nereis undergoes in its transformation affect chiefly (a) the
shape of the parapodia, and (b) the form of the chaetae of these parapodia. Other
organs may also be affected, though less noticeably; thus the eyes become
enlarged, the intestine may become so compressed by the generative products as to
be functionless, and the tail develops special sensory papillae.[332]
In the parapodia an increase in size and a sharper delineation of the various parts
take place; then flattened foliaceous outgrowths (Fig. 147, x, y) arise from certain
lobes of the feet, in which, too, the blood supply becomes greatly increased. The
old chaetae are pushed out by the development of new ones of quite a different
shape; these are jointed like the old ones, but the appendix is, in many species at
least, flattened and oar-shaped (Fig. 123, C, p. 246); and the chaetae are arranged
in a fan-like manner. Both these modifications are in evident relation to the free-
swimming habit which the Heteronereid now adopts. The new foot serves as a
swimming organ, the old one was a walking appendage.
Page 285
Fig. 147.—Parapodium of male "Heteronereis" of N. pelagica L. × 10. (From Ehlers.) a,
Notopodial cirrus; b, notopodium; c, neuropodium with new chaetae; c', foliaceous
outgrowth; d, neuropodial cirrus; x, y, foliaceous outgrowths.
Whilst some species, such as the common British N. diversicolor, undergo no
change, and others become modified as just described, others, again, are
polymorphic. Claparède was the first to show that N. dumerilii may occur in at
least five different mature forms; these differ from one another in size, colour,
mode of life, character of the eggs, etc. The immature forms may become ripe and
lay eggs while still retaining the "Nereid" characteristics, or these immature forms
may become "Heteronereids"[333] whilst the sexual elements are ripening. There
are then three different kinds of males and of females in this one species, some
being found at the bottom of the sea, as the large Heteronereid form, while the
small Heteronereid swims on the surface. The relations of these various forms to
one another, and the causes leading to the assumption of a Heteronereid condition
in some cases and not in others, are unknown.
A somewhat similar phenomenon is exhibited by members of the family Syllidae.
[334]
In this family sexual reproduction is frequently accompanied by the asexual
modes of fission and gemmation. In some genera, such as Eusyllis, Odontosyllis,
and Exogone, there occur changes quite similar to those characterising
"Heteronereis"—that is, the posterior segments in which the genital organs exist
become altered, so that the worm consists of two distinct regions, and is termed a
"Heterosyllis." The most marked change is the appearance of a dorsal bundle of
long capilliform chaetae in each of the genital segments (Fig. 148, I).
But in other genera the hinder genital region of the body becomes separated, on
maturity, from the anterior non-sexual region. Various stages of this "schizogamy,"
or fission into a sexual and a non-sexual zooid, have been observed in different
genera. In the genus Syllis the first segment of the sexual zooid, after its separation
from the asexual zooid, proceeds to bud forth a head. The character of the head is
alike in both sexes, though different species present heads of different shapes; and
as the worms were originally described as distinct genera, the names then given
are retained as descriptive terms. Thus the "Chaetosyllis" form has only two
Notopodial cirrus; b, notopodium; c, neuropodium with new chaetae; c', foliaceous
outgrowth; d, neuropodial cirrus; x, y, foliaceous outgrowths.
Whilst some species, such as the common British N. diversicolor, undergo no
change, and others become modified as just described, others, again, are
polymorphic. Claparède was the first to show that N. dumerilii may occur in at
least five different mature forms; these differ from one another in size, colour,
mode of life, character of the eggs, etc. The immature forms may become ripe and
lay eggs while still retaining the "Nereid" characteristics, or these immature forms
may become "Heteronereids"[333] whilst the sexual elements are ripening. There
are then three different kinds of males and of females in this one species, some
being found at the bottom of the sea, as the large Heteronereid form, while the
small Heteronereid swims on the surface. The relations of these various forms to
one another, and the causes leading to the assumption of a Heteronereid condition
in some cases and not in others, are unknown.
A somewhat similar phenomenon is exhibited by members of the family Syllidae.
[334]
In this family sexual reproduction is frequently accompanied by the asexual
modes of fission and gemmation. In some genera, such as Eusyllis, Odontosyllis,
and Exogone, there occur changes quite similar to those characterising
"Heteronereis"—that is, the posterior segments in which the genital organs exist
become altered, so that the worm consists of two distinct regions, and is termed a
"Heterosyllis." The most marked change is the appearance of a dorsal bundle of
long capilliform chaetae in each of the genital segments (Fig. 148, I).
But in other genera the hinder genital region of the body becomes separated, on
maturity, from the anterior non-sexual region. Various stages of this "schizogamy,"
or fission into a sexual and a non-sexual zooid, have been observed in different
genera. In the genus Syllis the first segment of the sexual zooid, after its separation
from the asexual zooid, proceeds to bud forth a head. The character of the head is
alike in both sexes, though different species present heads of different shapes; and
as the worms were originally described as distinct genera, the names then given
are retained as descriptive terms. Thus the "Chaetosyllis" form has only two
Page 286
tentacles; the "Ioda" form has three tentacles and a pair of palps. One and the same
species (e.g. S. hyalina) may successively pass through these stages.
With regard to the asexual portion, there is a regeneration of the tail segments after
the sexual zooid has separated; and the number of segments so regenerated is
usually equal to those that have become sexual. After a time these newly formed
segments will produce generative organs, and take on the characteristic natatory
chaetae, and this region will in its turn separate.
But in other genera, such as Autolytus, the regeneration of segments may
commence before the separation of the sexual zooid; and the head of the sexual
zooid becomes budded out before separation from the asexual portion. So that the
animal now consists of two worms, each with its own head, separated by a region
or zone of proliferation (Fig. 148, IV). Moreover, in some species not only is the
hinder part of the body converted into a sexual zooid, but the zone of proliferation
becomes very active, and produces by gemmation a large number of segments,
which become marked out, by the appearance of heads at intervals, into a number
of zooids, in which genital organs will later make their appearance. A chain of as
many as sixteen zooids may be formed in Autolytus (Fig. 148, V)—the hindermost
by conversion of the hinder part of the body of the original "stock," the
intervening zooids by gemmation.
Fig. 148.—Diagrams illustrating the various stages in the asexual formation of a chain of
zooids. (Modified from Malaquin.)
I, Heteronereid or Heterosyllid stage. A, Non-sexual; A', sexual region of the body, with
modified parapodia.
II, Syllis. The hinder sexual region, B, is similarly modified, and will separate from the parent
zooid, A, and become an independent zooid.
species (e.g. S. hyalina) may successively pass through these stages.
With regard to the asexual portion, there is a regeneration of the tail segments after
the sexual zooid has separated; and the number of segments so regenerated is
usually equal to those that have become sexual. After a time these newly formed
segments will produce generative organs, and take on the characteristic natatory
chaetae, and this region will in its turn separate.
But in other genera, such as Autolytus, the regeneration of segments may
commence before the separation of the sexual zooid; and the head of the sexual
zooid becomes budded out before separation from the asexual portion. So that the
animal now consists of two worms, each with its own head, separated by a region
or zone of proliferation (Fig. 148, IV). Moreover, in some species not only is the
hinder part of the body converted into a sexual zooid, but the zone of proliferation
becomes very active, and produces by gemmation a large number of segments,
which become marked out, by the appearance of heads at intervals, into a number
of zooids, in which genital organs will later make their appearance. A chain of as
many as sixteen zooids may be formed in Autolytus (Fig. 148, V)—the hindermost
by conversion of the hinder part of the body of the original "stock," the
intervening zooids by gemmation.
Fig. 148.—Diagrams illustrating the various stages in the asexual formation of a chain of
zooids. (Modified from Malaquin.)
I, Heteronereid or Heterosyllid stage. A, Non-sexual; A', sexual region of the body, with
modified parapodia.
II, Syllis. The hinder sexual region, B, is similarly modified, and will separate from the parent
zooid, A, and become an independent zooid.
Page 287
III, Autolytus. The hinder zooid, B, develops a head by budding before separation.
IV, Autolytus, etc. A zone of budding (z) makes its appearance in front of the head of B, and by
its growth will give rise to a series of new segments in the middle of the body.
V, Myrianida, Autolytus, etc. From this zone of budding a very large number of segments have
been formed, which have, further, become grouped so as to form three individuals, C,
D, E; B is the hindmost zooid, which is either formed from the hinder segments of the
parent zooid or is produced by budding, like C, D, E.
One original "stock," or asexual zooid, thus produces several sexual zooids, but
these are only of one sex for a given stock. The males differ in several important
characters from the females; so different, indeed, are the two sexes that before
their history was worked out by Agassiz[335] they were placed in different genera.
The male zooid has thus come to be known as Polybostrichus (Fig. 149, B). It has
three tentacles and two bifid palps; there are two pairs of peristomial cirri; the
testes are confined to the four anterior segments, which are without natatory
chaetae. The female is termed Sacconereis, owing to the possession of a great
ventral brood sac; its head possesses no separate palps; the peristomium carries
only one cirrus on each side; ova occur in every segment of the body, and may
even extend into the hinder segments of the asexual zooid (Fig. 149, C).
Fig. 149.—Myrianida fasciata. (From Malaquin.) The bright red markings of the living animal
are here represented black. A, An asexual individual which has produced by budding
from the zone (z) a chain of twenty-nine zooids, the oldest being labelled 1, the
youngest 29. B, A ripe male zooid (Polybostrichus), with three tentacles and a pair of
forked palps (p). There are five unaltered anterior segments. C, A ripe female zooid
(Sacconereis) with the palps fused with the prostomium; s, the ventral brood pouch
projecting on each side; t, tentacles.
A further development of this process of gemmiparity is exhibited by Myrianida.
Here, there is no conversion of the hinder segments, but the normal preanal zone
of proliferation gives rise to a large number of new segments. After a time the
most anterior of these becomes a head, and thus a new zooid is marked out. The
IV, Autolytus, etc. A zone of budding (z) makes its appearance in front of the head of B, and by
its growth will give rise to a series of new segments in the middle of the body.
V, Myrianida, Autolytus, etc. From this zone of budding a very large number of segments have
been formed, which have, further, become grouped so as to form three individuals, C,
D, E; B is the hindmost zooid, which is either formed from the hinder segments of the
parent zooid or is produced by budding, like C, D, E.
One original "stock," or asexual zooid, thus produces several sexual zooids, but
these are only of one sex for a given stock. The males differ in several important
characters from the females; so different, indeed, are the two sexes that before
their history was worked out by Agassiz[335] they were placed in different genera.
The male zooid has thus come to be known as Polybostrichus (Fig. 149, B). It has
three tentacles and two bifid palps; there are two pairs of peristomial cirri; the
testes are confined to the four anterior segments, which are without natatory
chaetae. The female is termed Sacconereis, owing to the possession of a great
ventral brood sac; its head possesses no separate palps; the peristomium carries
only one cirrus on each side; ova occur in every segment of the body, and may
even extend into the hinder segments of the asexual zooid (Fig. 149, C).
Fig. 149.—Myrianida fasciata. (From Malaquin.) The bright red markings of the living animal
are here represented black. A, An asexual individual which has produced by budding
from the zone (z) a chain of twenty-nine zooids, the oldest being labelled 1, the
youngest 29. B, A ripe male zooid (Polybostrichus), with three tentacles and a pair of
forked palps (p). There are five unaltered anterior segments. C, A ripe female zooid
(Sacconereis) with the palps fused with the prostomium; s, the ventral brood pouch
projecting on each side; t, tentacles.
A further development of this process of gemmiparity is exhibited by Myrianida.
Here, there is no conversion of the hinder segments, but the normal preanal zone
of proliferation gives rise to a large number of new segments. After a time the
most anterior of these becomes a head, and thus a new zooid is marked out. The
Page 288
zone of proliferation immediately in front of the new head now proceeds to form
new segments, and a second zooid results. This process goes on till a considerable
number of new worms have been formed at the tail of the original one, the oldest
of these new ones being the most posterior, the youngest next the original "stock."
In each zooid there is a zone of activity which adds to its number of segments, so
that as we pass backwards the zooids increase in size. As many as twenty-nine
such zooids may be formed in this way entirely by gemmation; and as each zooid
becomes completed, genital organs make their appearance, and when these are
ripe the zooid separates from the "colony" and leads an independent life. Here, as
in Autolytus, the sexes are dimorphic, the male and female resembling those of
that genus.
The process of gemmation, as seen in Autolytus, closely resembles that exhibited
by certain Oligochaeta (Naididae), where there exists a definite alternation of
generations; the production of new individuals by gemmation occurring
throughout the greater part of the year, and sexual reproduction recurring only at
certain intervals. In the Polychaeta such alternation exists in Myrianida; but it is
only the terminal link of a series, which takes its starting-point in the process
exhibited by the majority of Annelids, where no sexual character marks maturity.
The next stage is presented by "epigamous" forms like Heteronereis and
Heterosyllis; then "schizogamy" makes its appearance in certain Syllidae,
resulting in the formation of two morphologically and physiologically distinct
individuals which lead independent lives. The appearance of a head and of a zone
of proliferation leading to the formation of a chain of sexual zooids is
accompanied by a delay in the appearance of the genital organs, for in Autolytus
these arise during the formation of the new individuals, as part of the general
process of new formation; whilst in Myrianida the delay is prolonged, and the
generative elements do not make their appearance till after the new individuals
have reached some size.
More simple cases of the separation of the body into two parts, sexual and asexual,
occur also in some of the Serpulidae. Thus in Filigrana and Salmacina the
generative elements make their appearance in the hinder segments, as they do
throughout the Sabelliformia; and this hinder part of the body separates from the
anterior region after the formation of a new head between the two regions.[336]
Another modification of the process of budding and fission is exhibited by Syllis
ramosa, one of the most interesting forms of animal life which was obtained by
the "Challenger." This worm consists of a main stem, whence arise a number of
lateral branches, which may also branch so as to give rise to an arborescent colony
new segments, and a second zooid results. This process goes on till a considerable
number of new worms have been formed at the tail of the original one, the oldest
of these new ones being the most posterior, the youngest next the original "stock."
In each zooid there is a zone of activity which adds to its number of segments, so
that as we pass backwards the zooids increase in size. As many as twenty-nine
such zooids may be formed in this way entirely by gemmation; and as each zooid
becomes completed, genital organs make their appearance, and when these are
ripe the zooid separates from the "colony" and leads an independent life. Here, as
in Autolytus, the sexes are dimorphic, the male and female resembling those of
that genus.
The process of gemmation, as seen in Autolytus, closely resembles that exhibited
by certain Oligochaeta (Naididae), where there exists a definite alternation of
generations; the production of new individuals by gemmation occurring
throughout the greater part of the year, and sexual reproduction recurring only at
certain intervals. In the Polychaeta such alternation exists in Myrianida; but it is
only the terminal link of a series, which takes its starting-point in the process
exhibited by the majority of Annelids, where no sexual character marks maturity.
The next stage is presented by "epigamous" forms like Heteronereis and
Heterosyllis; then "schizogamy" makes its appearance in certain Syllidae,
resulting in the formation of two morphologically and physiologically distinct
individuals which lead independent lives. The appearance of a head and of a zone
of proliferation leading to the formation of a chain of sexual zooids is
accompanied by a delay in the appearance of the genital organs, for in Autolytus
these arise during the formation of the new individuals, as part of the general
process of new formation; whilst in Myrianida the delay is prolonged, and the
generative elements do not make their appearance till after the new individuals
have reached some size.
More simple cases of the separation of the body into two parts, sexual and asexual,
occur also in some of the Serpulidae. Thus in Filigrana and Salmacina the
generative elements make their appearance in the hinder segments, as they do
throughout the Sabelliformia; and this hinder part of the body separates from the
anterior region after the formation of a new head between the two regions.[336]
Another modification of the process of budding and fission is exhibited by Syllis
ramosa, one of the most interesting forms of animal life which was obtained by
the "Challenger." This worm consists of a main stem, whence arise a number of
lateral branches, which may also branch so as to give rise to an arborescent colony
Page 289
(Fig. 150). The branches of the first and second and higher orders arise by budding
from the sides of the original form or branches of lower order; and some of these
branches develop generative products, and bud forth a head near the point of
attachment. These sexual branches, no doubt, separate from the colony and
distribute the ova. The worm lives in a Hexactinellid sponge, Crateromorpha
meyeri, living in depths of 95 to 140 fathoms in the Eastern seas.[337]
from the sides of the original form or branches of lower order; and some of these
branches develop generative products, and bud forth a head near the point of
attachment. These sexual branches, no doubt, separate from the colony and
distribute the ova. The worm lives in a Hexactinellid sponge, Crateromorpha
meyeri, living in depths of 95 to 140 fathoms in the Eastern seas.[337]
Page 290
Fig. 150.—Portion of Syllis ramosa. (Reduced from M‘Intosh.)
Regeneration of lost Parts.—The process of budding and fission of the worm
into two parts is merely an extension of that resulting in the formation of new
segments when the worm is injured. In most of the Nereidiform Polychaetes
the number of segments forming the body continues to increase throughout
life by the formation of new segments between the anal segment and the one
in front of it; that is to say, there is normally a process of budding taking place
at this point. Now in many of the longer worms it may be noticed that the
segments of the hinder end suddenly become smaller than the rest; these are
segments newly formed to replace those lost by the worm. But this
"regeneration," though the same in principle as ordinary growth at the
penultimate segment, is due to activity in a segment (any segment) further
forwards; in other words, in the less modified worms every segment has the
power of forming new tissues, just as each of the joints of a crab's leg has the
power of forming the remaining joints when injured. It is not therefore
surprising that a "zone of budding" arises in an uninjured worm at certain
seasons, viz. that of reproduction; it is a property that each worm possesses,
though generally it remains latent till injury provides the stimulus.
Moreover, not only can new segments arise at the hinder end, but a new head
can be formed at the anterior end, as has been observed in worms belonging to
many families—in the less modified Syllidae,[338] in others of the
Nereidiformia, and even in Sabellids, where the greatly specialised gill
filaments can be reproduced. Thus Sir J. Dalyell[339] noted in Dasychone that
the crown of branchiae was regenerated in about a month in springtime, while
in winter the process occupied 116 days. He cut a Dasychone into three pieces;
the hindermost produced a head, the anterior piece developed an anus, and the
middle portion formed both a head and tail!
These regenerated heads are of course at first smaller than the rest of the body,
but soon grow to a normal size. Naturally this extensive power of regeneration
Regeneration of lost Parts.—The process of budding and fission of the worm
into two parts is merely an extension of that resulting in the formation of new
segments when the worm is injured. In most of the Nereidiform Polychaetes
the number of segments forming the body continues to increase throughout
life by the formation of new segments between the anal segment and the one
in front of it; that is to say, there is normally a process of budding taking place
at this point. Now in many of the longer worms it may be noticed that the
segments of the hinder end suddenly become smaller than the rest; these are
segments newly formed to replace those lost by the worm. But this
"regeneration," though the same in principle as ordinary growth at the
penultimate segment, is due to activity in a segment (any segment) further
forwards; in other words, in the less modified worms every segment has the
power of forming new tissues, just as each of the joints of a crab's leg has the
power of forming the remaining joints when injured. It is not therefore
surprising that a "zone of budding" arises in an uninjured worm at certain
seasons, viz. that of reproduction; it is a property that each worm possesses,
though generally it remains latent till injury provides the stimulus.
Moreover, not only can new segments arise at the hinder end, but a new head
can be formed at the anterior end, as has been observed in worms belonging to
many families—in the less modified Syllidae,[338] in others of the
Nereidiformia, and even in Sabellids, where the greatly specialised gill
filaments can be reproduced. Thus Sir J. Dalyell[339] noted in Dasychone that
the crown of branchiae was regenerated in about a month in springtime, while
in winter the process occupied 116 days. He cut a Dasychone into three pieces;
the hindermost produced a head, the anterior piece developed an anus, and the
middle portion formed both a head and tail!
These regenerated heads are of course at first smaller than the rest of the body,
but soon grow to a normal size. Naturally this extensive power of regeneration
Page 291
is of extreme value to the Polychaetes, for if a fish or other enemy bites the
head off a worm, a new one can form; and it is not difficult to see in this the
origin of the reproduction by fission as a normal process.
CHAPTER XI
NATURAL HISTORY OF POLYCHAETES—GENERAL HABITS—CHARACTER OF TUBE AND
ITS FORMATION—COLOURING—PROTECTIVE AND MIMETIC DEVICES—
PHOSPHORESCENCE—FOOD—USES—ASSOCIATED WORMS—WORMS AS HOSTS—
DISTRIBUTION—FOSSIL REMAINS.
All the many hundreds of species of Polychaetes are marine, with a very few
exceptions, which have been in recent years recorded from fresh (i.e.
drinkable) water, viz. a species of Nereis from a lake in Mingrelia, another
Nereis and a Lumbriconereis from running water in Trinidad,[340] a Sabellid,
Manayunkia speciosa,[341] from Philadelphia; and another Sabellid,
Coabangia,[342] from fresh water at Tonquin, which lives in borings in shells
of Melania; and it is by no means improbable that other fresh-water
Polychaetes exist in Lake Tanganyika in Africa, where a Medusa has recently
been discovered.
In brackish water of various densities many Polychaetes live; Arenicola
especially is regardless of the character of the medium, and Nereis
diversicolor appears to withstand considerable admixture of fresh water.
The majority of the Polychaetes occur "inshore," that is, between tide-marks
and in shallow water down to 20 fathoms; but they occur at all depths more or
less abundantly, and some have been dredged from depths of more than 3000
fathoms.
The nature of the soil composing the shore has a good deal to do with the
number of worms to be found there; thus in calcareous districts they are fewer
than in places where harder rocks, such as granite, form the shore line, for the
chalk or limestone wears away more quickly, and exposes to destruction the
worms which may have sheltered in its crevices: further, it does not give so
head off a worm, a new one can form; and it is not difficult to see in this the
origin of the reproduction by fission as a normal process.
CHAPTER XI
NATURAL HISTORY OF POLYCHAETES—GENERAL HABITS—CHARACTER OF TUBE AND
ITS FORMATION—COLOURING—PROTECTIVE AND MIMETIC DEVICES—
PHOSPHORESCENCE—FOOD—USES—ASSOCIATED WORMS—WORMS AS HOSTS—
DISTRIBUTION—FOSSIL REMAINS.
All the many hundreds of species of Polychaetes are marine, with a very few
exceptions, which have been in recent years recorded from fresh (i.e.
drinkable) water, viz. a species of Nereis from a lake in Mingrelia, another
Nereis and a Lumbriconereis from running water in Trinidad,[340] a Sabellid,
Manayunkia speciosa,[341] from Philadelphia; and another Sabellid,
Coabangia,[342] from fresh water at Tonquin, which lives in borings in shells
of Melania; and it is by no means improbable that other fresh-water
Polychaetes exist in Lake Tanganyika in Africa, where a Medusa has recently
been discovered.
In brackish water of various densities many Polychaetes live; Arenicola
especially is regardless of the character of the medium, and Nereis
diversicolor appears to withstand considerable admixture of fresh water.
The majority of the Polychaetes occur "inshore," that is, between tide-marks
and in shallow water down to 20 fathoms; but they occur at all depths more or
less abundantly, and some have been dredged from depths of more than 3000
fathoms.
The nature of the soil composing the shore has a good deal to do with the
number of worms to be found there; thus in calcareous districts they are fewer
than in places where harder rocks, such as granite, form the shore line, for the
chalk or limestone wears away more quickly, and exposes to destruction the
worms which may have sheltered in its crevices: further, it does not give so
Page 292
permanent a place of attachment to seaweeds, on which many Polychaetes
feed. The calcareous rocks, too, are more likely to be traversed by springs of
fresh water, which is not to the taste of the worms. The sand resulting from the
destruction of the rocks, whether hard or soft, is of itself unsuitable to the
majority of worms, which are most abundant where mud containing decaying
vegetable matter is mixed with the sand: this, which gives a firmer consistency
to the soil, so that the burrows retain their form better, supplies food for the
burrowers.
General Habits.—The division of the Polychaetes into the "Errantia" or free-
swimming and wandering forms, and "Sedentaria" or tubicolous and sedentary
forms, is a misleading mode of classification, for as a matter of fact only a
comparatively few forms are really free-swimming throughout life; the
majority, even if they do not form definite tubes, burrow galleries for
themselves in the soil, and these burrows are in many cases only rarely left;
this is true of both groups. Amongst the "errant" Polychaetes nearly all the
Eunicidae secrete a parchment-like tube, and some Polynoids form mud tubes.
Among the "sedentary worms" there are forms which merely burrow; while
Myxicola readily leaves its gelatinous tube and swims freely; Pectinaria
carries its house with it as it moves about, and Polycirrus, a Terebellid, does
not form any tube at all.
Owing to their sedentary habits, quite a representative collection of genera
may be made, especially at a spring tide, at any seaside place which is
provided with a sandy shore, and with rocks and seaweed. The larger species,
however, require to be dredged, and the best time is at night, for then many
forms which during the day are concealed in their burrows, will be issuing
forth to obtain food.
It may be useful to give instances of worms occurring in various situations
between tide-marks. Throughout pretty well the whole of the area left
uncovered by the tide, even up to nearly high-water mark in many parts of the
coast, the cylindrical "castings" of sand and mud, forming little heaps, indicate
the burrows of Arenicola, the common "lug-worm"; these "castings" have
passed through the worm's body, having been swallowed during the process of
burrowing as well as for the purpose of obtaining food, as in the case of the
earthworms. Rather nearer the water may be seen little tufts of sand-threads,
about an inch high, springing from a short piece of cylindrical, sandy tube
feed. The calcareous rocks, too, are more likely to be traversed by springs of
fresh water, which is not to the taste of the worms. The sand resulting from the
destruction of the rocks, whether hard or soft, is of itself unsuitable to the
majority of worms, which are most abundant where mud containing decaying
vegetable matter is mixed with the sand: this, which gives a firmer consistency
to the soil, so that the burrows retain their form better, supplies food for the
burrowers.
General Habits.—The division of the Polychaetes into the "Errantia" or free-
swimming and wandering forms, and "Sedentaria" or tubicolous and sedentary
forms, is a misleading mode of classification, for as a matter of fact only a
comparatively few forms are really free-swimming throughout life; the
majority, even if they do not form definite tubes, burrow galleries for
themselves in the soil, and these burrows are in many cases only rarely left;
this is true of both groups. Amongst the "errant" Polychaetes nearly all the
Eunicidae secrete a parchment-like tube, and some Polynoids form mud tubes.
Among the "sedentary worms" there are forms which merely burrow; while
Myxicola readily leaves its gelatinous tube and swims freely; Pectinaria
carries its house with it as it moves about, and Polycirrus, a Terebellid, does
not form any tube at all.
Owing to their sedentary habits, quite a representative collection of genera
may be made, especially at a spring tide, at any seaside place which is
provided with a sandy shore, and with rocks and seaweed. The larger species,
however, require to be dredged, and the best time is at night, for then many
forms which during the day are concealed in their burrows, will be issuing
forth to obtain food.
It may be useful to give instances of worms occurring in various situations
between tide-marks. Throughout pretty well the whole of the area left
uncovered by the tide, even up to nearly high-water mark in many parts of the
coast, the cylindrical "castings" of sand and mud, forming little heaps, indicate
the burrows of Arenicola, the common "lug-worm"; these "castings" have
passed through the worm's body, having been swallowed during the process of
burrowing as well as for the purpose of obtaining food, as in the case of the
earthworms. Rather nearer the water may be seen little tufts of sand-threads,
about an inch high, springing from a short piece of cylindrical, sandy tube
Page 293
rising up out of the sand; this is the head end of the tube of Terebella
conchilega (Fig. 153).
Amongst the rocks may be found loose stones of different sizes; on lifting
them up, various kinds of worms may be brought to light, according to the
locality, the time of year, the position with respect to the sea, and so on.
Polynoë is pretty sure to be present somewhere near low-tide mark; the
number of species is considerable, and their colouring very varied: but as the
worms have a habit of remaining still on the under surface of the uplifted
stone, the observer may easily overlook them.
Other worms occur below the stones, more or less buried in the sand or mud;
for instance, a small Nereis may be lying in its temporary burrow immediately
underneath, and will at once withdraw from the now injured part of the
burrow; while deeper in the mud or sand, especially in rather highly-smelling
mud, little red worms are abundant, such as Scoloplos, Nerine, Capitella, and
others. By digging near low water one may find Nephthys, Glycera, and others
burrowing or hiding in the soil.
In rock pools, or sandy stretches amongst rocks kept moist and cool by
abundant Fucus, one may see under stones the red or yellow gill filaments of
Cirratulus and of Terebellids protruding from their burrows and tubes, while
other worms are to be met with in clefts of the rocks, and amongst the roots of
Laminaria.
Still farther out, below low-water mark, where one must wade, can be seen the
beautiful branchial crowns of various Sabellids protruding from their tubes;
but care is necessary on approaching these worms, as eyes are, in many cases,
present on the branchiae and a shadow is readily perceived; then the brightly-
coloured tuft disappears, and only a piece of sandy or muddy cylindrical
tubing remains to tell where the Sabella has withdrawn. In order to obtain the
worms one must dig quickly and deeply before they have been disturbed; for
the tube is of considerable length, and the inhabitant withdraws to the bottom
of it. Some of these soft-skinned worms have the power of boring into hard
rocks,[343] though by what means they do so is uncertain.[344] Polydora ciliata
makes a tube of mud projecting from the mouth of U-shaped galleries in
chalk, limestone, shells, and even shale; it has no hard jaws or other structures
conchilega (Fig. 153).
Amongst the rocks may be found loose stones of different sizes; on lifting
them up, various kinds of worms may be brought to light, according to the
locality, the time of year, the position with respect to the sea, and so on.
Polynoë is pretty sure to be present somewhere near low-tide mark; the
number of species is considerable, and their colouring very varied: but as the
worms have a habit of remaining still on the under surface of the uplifted
stone, the observer may easily overlook them.
Other worms occur below the stones, more or less buried in the sand or mud;
for instance, a small Nereis may be lying in its temporary burrow immediately
underneath, and will at once withdraw from the now injured part of the
burrow; while deeper in the mud or sand, especially in rather highly-smelling
mud, little red worms are abundant, such as Scoloplos, Nerine, Capitella, and
others. By digging near low water one may find Nephthys, Glycera, and others
burrowing or hiding in the soil.
In rock pools, or sandy stretches amongst rocks kept moist and cool by
abundant Fucus, one may see under stones the red or yellow gill filaments of
Cirratulus and of Terebellids protruding from their burrows and tubes, while
other worms are to be met with in clefts of the rocks, and amongst the roots of
Laminaria.
Still farther out, below low-water mark, where one must wade, can be seen the
beautiful branchial crowns of various Sabellids protruding from their tubes;
but care is necessary on approaching these worms, as eyes are, in many cases,
present on the branchiae and a shadow is readily perceived; then the brightly-
coloured tuft disappears, and only a piece of sandy or muddy cylindrical
tubing remains to tell where the Sabella has withdrawn. In order to obtain the
worms one must dig quickly and deeply before they have been disturbed; for
the tube is of considerable length, and the inhabitant withdraws to the bottom
of it. Some of these soft-skinned worms have the power of boring into hard
rocks,[343] though by what means they do so is uncertain.[344] Polydora ciliata
makes a tube of mud projecting from the mouth of U-shaped galleries in
chalk, limestone, shells, and even shale; it has no hard jaws or other structures
Page 294
sufficient to account for the holes, but it is possible that the specially strong
chaetae on the sixth segment may be of some use in this work. Other
lithodomous worms are Sabella saxicava and Dodecaceria concharum, which
is a common little borer, forming galleries in oyster-shells, etc.
The tubes formed by these Polychaetes are very varied in constitution.[345] In
some cases a mucus, which hardens to form a firm protective envelope, is
secreted from special parts (e.g. the ventral gland shields of Terebellids and
Sabelliformia), or from the greater part of the general surface of the body; in
other cases the secretion serves to stick together particles of mud or sand, or
shelly fragments, so as to form a more or less cylindrical tube (rarely
branched), which is lined internally by the hardened "mucus," having the
appearance of silk.
Fig. 151.—Clymene ebiensis in its tube (t) (from Règne Animal). a, Anterior, p, posterior
end, which is, however, injured.
But the process of tube-making is not a simple one, for in many cases, at least,
the worms exhibit definite powers of choice. Thus some species of Sabella
choose only the very finest particles of mud; Terebella conchilega chooses
fragments of shell and grains of sand; Onuphis conchylega employs small
stones more or less of a size; Sabellaria makes use only of sand grains. Whilst
some worms, like Terebella, Nicomache, and others, make a very irregular
tube, Pectinaria builds a most remarkably neat house, open at each end, which
it carries about with it, the narrow end uppermost (Fig. 152); the grains of
sand are nearly all of the same size and only one layer in thickness, embedded
in abundant "mucus," and with the outer surface quite smooth.
Sir J. Dalyell[346] made some most interesting observations on the method
followed by sundry tube-formers in the building of their tenements, and these
observations, though made nearly half a century ago, have required very little
addition or correction in modern times. In speaking of Sabella, he writes as
follows:—
chaetae on the sixth segment may be of some use in this work. Other
lithodomous worms are Sabella saxicava and Dodecaceria concharum, which
is a common little borer, forming galleries in oyster-shells, etc.
The tubes formed by these Polychaetes are very varied in constitution.[345] In
some cases a mucus, which hardens to form a firm protective envelope, is
secreted from special parts (e.g. the ventral gland shields of Terebellids and
Sabelliformia), or from the greater part of the general surface of the body; in
other cases the secretion serves to stick together particles of mud or sand, or
shelly fragments, so as to form a more or less cylindrical tube (rarely
branched), which is lined internally by the hardened "mucus," having the
appearance of silk.
Fig. 151.—Clymene ebiensis in its tube (t) (from Règne Animal). a, Anterior, p, posterior
end, which is, however, injured.
But the process of tube-making is not a simple one, for in many cases, at least,
the worms exhibit definite powers of choice. Thus some species of Sabella
choose only the very finest particles of mud; Terebella conchilega chooses
fragments of shell and grains of sand; Onuphis conchylega employs small
stones more or less of a size; Sabellaria makes use only of sand grains. Whilst
some worms, like Terebella, Nicomache, and others, make a very irregular
tube, Pectinaria builds a most remarkably neat house, open at each end, which
it carries about with it, the narrow end uppermost (Fig. 152); the grains of
sand are nearly all of the same size and only one layer in thickness, embedded
in abundant "mucus," and with the outer surface quite smooth.
Sir J. Dalyell[346] made some most interesting observations on the method
followed by sundry tube-formers in the building of their tenements, and these
observations, though made nearly half a century ago, have required very little
addition or correction in modern times. In speaking of Sabella, he writes as
follows:—
Page 295
Fig. 152.—The tube of Pectinaria auricoma. × 3. (From M‘Intosh.) This is its natural
position as carried about by the animal.
Fig. 153.—The upper end of the tube of Terebella conchilega. Slightly enlarged. (From
M‘Intosh.)
"Let a tall and ample crystal jar containing a Sabella be emptied of its contents
and speedily replenished with sea-water; the animal, if in view, has retreated
during the short interval; the orifice of the tube is closed, all is at rest. But
soon after replenishment it rises, to display its branchial plume still more
vigorously than before, and remains stationary, as if enjoying the freshness of
the renovated element, always so grateful—the harbinger of health and
strength to those whose dwelling is there. The passing spectator would
conclude that he now beholds only a beautiful flower, completely expanded,
inclining towards the light like some of those ornaments of nature decorating
position as carried about by the animal.
Fig. 153.—The upper end of the tube of Terebella conchilega. Slightly enlarged. (From
M‘Intosh.)
"Let a tall and ample crystal jar containing a Sabella be emptied of its contents
and speedily replenished with sea-water; the animal, if in view, has retreated
during the short interval; the orifice of the tube is closed, all is at rest. But
soon after replenishment it rises, to display its branchial plume still more
vigorously than before, and remains stationary, as if enjoying the freshness of
the renovated element, always so grateful—the harbinger of health and
strength to those whose dwelling is there. The passing spectator would
conclude that he now beholds only a beautiful flower, completely expanded,
inclining towards the light like some of those ornaments of nature decorating
Page 296
our gardens. He pauses in admiration. But if a drop of liquid mud falls amidst
the element from above, disturbing its purity, then, while the plume unfolds to
its utmost capacity, does the animal commence a slow revolution, the body
also passing around within the tube. Now are the thousands of cilia fringing
the ribs [i.e. the secondary filaments] of the branchiae discovered to be in
vigorous activity, and their office to be wondrous. A loose muddy mass is soon
afterwards visibly accumulating in the bottom of the funnel; meantime the
neck or first segment of the body, rising unusually high above the orifice of
the tube, exhibits two trowels beating down the thin edge as they fold and
clasp over the margin, like our fingers pressing a flattened cake against the
palm of the hand. [This refers to the lappets of the peristomial collar.] During
these operations muddy collections are seen descending between the roots of
the fans [right and left gills] towards the trowels, while another organ, perhaps
the mouth, is also occupied, it may be, in compounding the preparation with
adhesive matter. Still does the partial or complete revolution of the plume
above, and of the body within the tube, continue; the bulk of the muddy mass
diminishes, activity abates; it is succeeded by repose, when the tube is found
to have received evident prolongation."
Fig. 154.—Terebella conchilega Pall. Upper end of the tube (s) showing the anterior end
of the worm. h, Its head; t, tentacles collecting sand grains (y) in their grooves; x,
sand grains in mouth of worm; f, filamentous fringe of tube. (After Watson.)
The Terebellids use their numerous tentacles in searching for particles of sand,
etc.; each tentacle is grooved along its ventral surface, and the particle is
conveyed along the furrow to the mouth. These particles are actually taken
into the mouth, and mixed with some sort of secretion; on ejection again, each
particle is placed by another tentacle in its position at the edge of the tube, and
by means of its lower lip the Terebellid works it into place.[347]
the element from above, disturbing its purity, then, while the plume unfolds to
its utmost capacity, does the animal commence a slow revolution, the body
also passing around within the tube. Now are the thousands of cilia fringing
the ribs [i.e. the secondary filaments] of the branchiae discovered to be in
vigorous activity, and their office to be wondrous. A loose muddy mass is soon
afterwards visibly accumulating in the bottom of the funnel; meantime the
neck or first segment of the body, rising unusually high above the orifice of
the tube, exhibits two trowels beating down the thin edge as they fold and
clasp over the margin, like our fingers pressing a flattened cake against the
palm of the hand. [This refers to the lappets of the peristomial collar.] During
these operations muddy collections are seen descending between the roots of
the fans [right and left gills] towards the trowels, while another organ, perhaps
the mouth, is also occupied, it may be, in compounding the preparation with
adhesive matter. Still does the partial or complete revolution of the plume
above, and of the body within the tube, continue; the bulk of the muddy mass
diminishes, activity abates; it is succeeded by repose, when the tube is found
to have received evident prolongation."
Fig. 154.—Terebella conchilega Pall. Upper end of the tube (s) showing the anterior end
of the worm. h, Its head; t, tentacles collecting sand grains (y) in their grooves; x,
sand grains in mouth of worm; f, filamentous fringe of tube. (After Watson.)
The Terebellids use their numerous tentacles in searching for particles of sand,
etc.; each tentacle is grooved along its ventral surface, and the particle is
conveyed along the furrow to the mouth. These particles are actually taken
into the mouth, and mixed with some sort of secretion; on ejection again, each
particle is placed by another tentacle in its position at the edge of the tube, and
by means of its lower lip the Terebellid works it into place.[347]
Page 297
But whereas the greater number of tubicolous worms make use of adventitious
material wherewith to strengthen the wall of their tube, the Serpulidae secrete
carbonate of lime from their tube-glands, and mould a tube of this substance.
Amongst the Eunicidae the secreted substance is of itself strong enough to
protect the animal; for in Hyalinoecia and species of Eunice the tube consists
of a translucent, tough, parchment-like material.
Chemical analysis has been employed in a few cases to determine the
substance composing the tube. In the case of Hyalinoecia (sometimes
erroneously called Onuphis) the material consists of a phosphoric salt
containing magnesia and a characteristic organic substance "onuphin"[348]; in
Spirographis, a Sabellid, the name "spirographin" is given to its special
secretion, whilst in Serpulids the organic base of the calcareous tube is
"conchiolin."
Fig. 155.—Eunice tibiana Pourt. × ½. The branching tube (t) with the worm (w)
protruding its head through one of several openings. (From Ehlers.)
The majority of worms are solitary, but there are a few instances of social
worms—not that there is any co-operation or distribution of labour amongst
the individuals, but they merely occur together in quantities; thus the sandy
tubes of Sabellaria may form compact masses of several cubic feet, which,
left uncovered by the receding tide, look like rocks upon the shore; as, for
instance, at Paignton and Torquay. Filigrana implexa and Serpula uncinata
similarly intertwine their calcareous tubes to form masses.
Whereas most worms live at the bottom of the sea, at various depths, a few are
to be found at the surface. Purely pelagic habits are confined to a few families,
viz. Tomopteridae, Typhloscolecidae, and the Alciopids and others amongst
the Phyllodocidae; though Nectochaeta, one of the Polynoidae, and
material wherewith to strengthen the wall of their tube, the Serpulidae secrete
carbonate of lime from their tube-glands, and mould a tube of this substance.
Amongst the Eunicidae the secreted substance is of itself strong enough to
protect the animal; for in Hyalinoecia and species of Eunice the tube consists
of a translucent, tough, parchment-like material.
Chemical analysis has been employed in a few cases to determine the
substance composing the tube. In the case of Hyalinoecia (sometimes
erroneously called Onuphis) the material consists of a phosphoric salt
containing magnesia and a characteristic organic substance "onuphin"[348]; in
Spirographis, a Sabellid, the name "spirographin" is given to its special
secretion, whilst in Serpulids the organic base of the calcareous tube is
"conchiolin."
Fig. 155.—Eunice tibiana Pourt. × ½. The branching tube (t) with the worm (w)
protruding its head through one of several openings. (From Ehlers.)
The majority of worms are solitary, but there are a few instances of social
worms—not that there is any co-operation or distribution of labour amongst
the individuals, but they merely occur together in quantities; thus the sandy
tubes of Sabellaria may form compact masses of several cubic feet, which,
left uncovered by the receding tide, look like rocks upon the shore; as, for
instance, at Paignton and Torquay. Filigrana implexa and Serpula uncinata
similarly intertwine their calcareous tubes to form masses.
Whereas most worms live at the bottom of the sea, at various depths, a few are
to be found at the surface. Purely pelagic habits are confined to a few families,
viz. Tomopteridae, Typhloscolecidae, and the Alciopids and others amongst
the Phyllodocidae; though Nectochaeta, one of the Polynoidae, and
Page 298
Ophryotrocha, one of the Eunicidae, are modified for this mode of life.[349]
Several genera become pelagic during the breeding season. All these forms are
excellent swimmers, and many of them are transparent.
The Colouring of Polychaetes.—The majority of Polychaetes quickly lose
their colour in spirits, and become uniformly dull or light brown in museums.
There are a few, however, which retain their brilliancy, like Aphrodite and
Chloeia, but in both cases the coloration is due to the beautiful hair-like
bristles ranged along each side of the animal; in the former the colours of the
rainbow flash from specimens which have been kept in spirit for any length of
time. The Polynoids, too, with their golden chaetae and pigmented scales,
retain to some extent their characteristic colouring. But the colours of most
Annelids are due to pigments in the skin, together with the haemoglobin of the
blood, which are soluble, or otherwise changed, in alcohol; for instance, the
bright greenish-blue tint of the common Phyllodoce of our coasts is changed
to a rich chocolate brown; but such cases are rare, most worms becoming
more or less decolorised.
The varied colouring in the Polychaetes, as in other animals, is due to a variety
of causes. The red is in many cases due to haemoglobin of the vascular system
showing through the transparent body; the green of the tentacles of the
Sabellids and Chlorhaemids is similarly due to chlorocruorin. In other cases
the contents of the intestine or the tint of the coelomic fluid may affect the
colour of the worm. In Capitella the coloured excretory products are regained
in the skin; in an Eunicid living in a yellow sponge, on which it feeds, the
colouring matter is extracted and stored in the skin; in the same kind of way
green caterpillars may owe their tint to feeding on green leaves. But many of
the Polychaetes possess distinct pigments in the skin; thus in Arenicola the
dark pigment melanin has been recognised; in Cirratulus and Nereis certain
lipochromes; whilst Eulalia viridis contains a pigment allied to bonellein.
These various pigments yield different absorption bands when a solution is
examined with the spectroscope; others, however, give no bands, but are
distinguished by different chemical reactions.[350] The colour of the intestine
of Chaetopterus has been stated to be due to "modified chlorophyll," but it is
quite a different substance.
When seen in the living and healthy condition, however, these Polychaete
worms vie with the very butterflies in their brilliant and beautiful colourings,
Several genera become pelagic during the breeding season. All these forms are
excellent swimmers, and many of them are transparent.
The Colouring of Polychaetes.—The majority of Polychaetes quickly lose
their colour in spirits, and become uniformly dull or light brown in museums.
There are a few, however, which retain their brilliancy, like Aphrodite and
Chloeia, but in both cases the coloration is due to the beautiful hair-like
bristles ranged along each side of the animal; in the former the colours of the
rainbow flash from specimens which have been kept in spirit for any length of
time. The Polynoids, too, with their golden chaetae and pigmented scales,
retain to some extent their characteristic colouring. But the colours of most
Annelids are due to pigments in the skin, together with the haemoglobin of the
blood, which are soluble, or otherwise changed, in alcohol; for instance, the
bright greenish-blue tint of the common Phyllodoce of our coasts is changed
to a rich chocolate brown; but such cases are rare, most worms becoming
more or less decolorised.
The varied colouring in the Polychaetes, as in other animals, is due to a variety
of causes. The red is in many cases due to haemoglobin of the vascular system
showing through the transparent body; the green of the tentacles of the
Sabellids and Chlorhaemids is similarly due to chlorocruorin. In other cases
the contents of the intestine or the tint of the coelomic fluid may affect the
colour of the worm. In Capitella the coloured excretory products are regained
in the skin; in an Eunicid living in a yellow sponge, on which it feeds, the
colouring matter is extracted and stored in the skin; in the same kind of way
green caterpillars may owe their tint to feeding on green leaves. But many of
the Polychaetes possess distinct pigments in the skin; thus in Arenicola the
dark pigment melanin has been recognised; in Cirratulus and Nereis certain
lipochromes; whilst Eulalia viridis contains a pigment allied to bonellein.
These various pigments yield different absorption bands when a solution is
examined with the spectroscope; others, however, give no bands, but are
distinguished by different chemical reactions.[350] The colour of the intestine
of Chaetopterus has been stated to be due to "modified chlorophyll," but it is
quite a different substance.
When seen in the living and healthy condition, however, these Polychaete
worms vie with the very butterflies in their brilliant and beautiful colourings,
Page 299
and though our own worms are not lacking in beauty, many tropical and
southern forms exceed them in gayness of tint. Bright reds, orange, yellows,
greens, blues, rich violets, and sombre browns are all displayed.[351]
The handsome Terebella nebulosa of our own coasts is coloured bright red,
sprinkled with white spots. Nicomache lumbricalis is pink, with red girdles.
Eunicids are frequently red or brown, and the red gills along each side,
together with a brilliant iridescence, render these worms very beautiful.
Nereids present a great range of coloration, from light green to sundry tints of
brown and red in various combinations. Amongst the Serpulids our common S.
vermicularis is a very showy little worm, with its orange body, its red gills
splashed with orange, and its orange operculum streaked with red; and a
Southern form, Placostegus coeruleus, occurring at the Cape of Good Hope, is
provided with beautiful lavender-blue gills. Our own Sabellids present
examples of beautiful markings on the gills, in different colours or in different
shades of the same colour. Amongst Polynoids, P. leucohyba, from the
Antilles, has blue elytra; Hemilepidia erythrotaenia, a long worm from the
Cape of Good Hope, has the anterior end of its body covered with light blue
elytra, whilst the uncovered part is orange, with a broad magenta-red band
along the dorsal surface.
The Phyllodocids are mostly very brightly coloured. The common P.
lamelligera of our coast has a bluish-green body, with olive-green parapodia;
but Lopadorhynchus erythrophyllum, from Jamaica, has a blue body with red
parapodia; whilst Notophyllum myriacyclum has a brown body with
longitudinal dark-brown stripes and yellow parapodia. Both these worms live
in coral reefs, where brilliancy of colour is one of the characteristic features of
the fauna. Other worms are of various shades of green: the dark green
Arenicola with red gills; the bright green Eulalia viridis; the deep green
Amphinome smaragdina, from Jamaica; Gnathosyllis diplodonta, with its
green and yellow body, serve as examples.
Patterns or "markings" may be exemplified by Lepidasthenia elegans (Fig.
156), and Myrianida fasciata, which has a bright red band on each segment
(Fig. 149, p. 280). From this brief list of examples it will be seen that
beautiful, and even brilliant, coloration is not confined to any particular mode
of life; many of the most typically tubicolous forms, like the Terebellids and
Serpulids, are as brilliantly coloured as the most typically free-swimming
southern forms exceed them in gayness of tint. Bright reds, orange, yellows,
greens, blues, rich violets, and sombre browns are all displayed.[351]
The handsome Terebella nebulosa of our own coasts is coloured bright red,
sprinkled with white spots. Nicomache lumbricalis is pink, with red girdles.
Eunicids are frequently red or brown, and the red gills along each side,
together with a brilliant iridescence, render these worms very beautiful.
Nereids present a great range of coloration, from light green to sundry tints of
brown and red in various combinations. Amongst the Serpulids our common S.
vermicularis is a very showy little worm, with its orange body, its red gills
splashed with orange, and its orange operculum streaked with red; and a
Southern form, Placostegus coeruleus, occurring at the Cape of Good Hope, is
provided with beautiful lavender-blue gills. Our own Sabellids present
examples of beautiful markings on the gills, in different colours or in different
shades of the same colour. Amongst Polynoids, P. leucohyba, from the
Antilles, has blue elytra; Hemilepidia erythrotaenia, a long worm from the
Cape of Good Hope, has the anterior end of its body covered with light blue
elytra, whilst the uncovered part is orange, with a broad magenta-red band
along the dorsal surface.
The Phyllodocids are mostly very brightly coloured. The common P.
lamelligera of our coast has a bluish-green body, with olive-green parapodia;
but Lopadorhynchus erythrophyllum, from Jamaica, has a blue body with red
parapodia; whilst Notophyllum myriacyclum has a brown body with
longitudinal dark-brown stripes and yellow parapodia. Both these worms live
in coral reefs, where brilliancy of colour is one of the characteristic features of
the fauna. Other worms are of various shades of green: the dark green
Arenicola with red gills; the bright green Eulalia viridis; the deep green
Amphinome smaragdina, from Jamaica; Gnathosyllis diplodonta, with its
green and yellow body, serve as examples.
Patterns or "markings" may be exemplified by Lepidasthenia elegans (Fig.
156), and Myrianida fasciata, which has a bright red band on each segment
(Fig. 149, p. 280). From this brief list of examples it will be seen that
beautiful, and even brilliant, coloration is not confined to any particular mode
of life; many of the most typically tubicolous forms, like the Terebellids and
Serpulids, are as brilliantly coloured as the most typically free-swimming
Page 300
genera, like the Phyllodocids. Carnivorous forms like Amphinomids and
Syllids present as wide a range of tint as the limivorous forms like Cirratulus,
Sabella, or Maldanids. Shore-lovers, and deep-sea dwellers, and surface-
swimmers, all exhibit equally bright or equally sombre tints; it is therefore
difficult and rash to dogmatise on the "use" of these colourings to these
animals, or to point to this worm as being protectively, to the other as being
warningly, coloured; for we are too ignorant as to the habits of the worms.
Fig. 156.—Lepidasthenia elegans Gr., × 2, to illustrate colour-markings: the dark bands in
the anterior part of the body occupy two elytriferous, and the intermediate
segments. In the hinder region, where the elytra are in every third segment, this one
is dark. el.12, The twelfth elytron.
Protective and Mimetic Devices.—From the point of view of "protection" in
the evolutionist's sense of the word, we can say but little. Protective
resemblance there is undoubtedly amongst the Polynoids, for the scales of
these forms resemble more or less closely the stones or sand amongst which
they live; in the same species there is great variety in coloration. This
protective habit is carried still further in the case of Psammolyce by the
attachment of sand grains to little cups on the elytra, so that the back of the
animal is concealed. Certain commensals, such as Polynoë arenicolae, P.
Syllids present as wide a range of tint as the limivorous forms like Cirratulus,
Sabella, or Maldanids. Shore-lovers, and deep-sea dwellers, and surface-
swimmers, all exhibit equally bright or equally sombre tints; it is therefore
difficult and rash to dogmatise on the "use" of these colourings to these
animals, or to point to this worm as being protectively, to the other as being
warningly, coloured; for we are too ignorant as to the habits of the worms.
Fig. 156.—Lepidasthenia elegans Gr., × 2, to illustrate colour-markings: the dark bands in
the anterior part of the body occupy two elytriferous, and the intermediate
segments. In the hinder region, where the elytra are in every third segment, this one
is dark. el.12, The twelfth elytron.
Protective and Mimetic Devices.—From the point of view of "protection" in
the evolutionist's sense of the word, we can say but little. Protective
resemblance there is undoubtedly amongst the Polynoids, for the scales of
these forms resemble more or less closely the stones or sand amongst which
they live; in the same species there is great variety in coloration. This
protective habit is carried still further in the case of Psammolyce by the
attachment of sand grains to little cups on the elytra, so that the back of the
animal is concealed. Certain commensals, such as Polynoë arenicolae, P.
Page 301
pentactes, are coloured so as to resemble their associates. In a few cases it is
possible that the gills of Sabelliformia are protectively coloured; for in Sabella
pavonia they vary from a light yellowish tint to a deep violet-brown, and the
dark markings on them are therefore more or less distinct. Spread out as the
gills are in life, they are in many cases difficult to recognise; it is rather their
movement as they are withdrawn that attracts one's attention to them, as the
tubes of these worms frequently serve for the attachment of brownish
seaweeds, to which the gills bear resemblance. But, as a matter of fact, little
work has been done in this direction, and speculation on the matter without
evidence is worthless. Many pelagic forms, being transparent, such as
Tomopteris and Alciopids, are no doubt protected by their lack of colour; yet
these forms present brightly-coloured spots,—the light-producing organs in
the parapodia of the former, and the large dark eyes of the latter.
Semper[352] mentions a case of possible mimicry in a species of Myxicola
which lives in the clefts of a coral, Cladocora. The branchial funnel, when
expanded, resembles very closely the expanded coral in size, colour, etc.; but
he points out that the species occurs in other situations, where its colouring is
not protective. Probably the "mimicry" is in other instances merely accidental.
No doubt many Polychaetes may be "warningly coloured," but experimental
evidence is incomplete. Polycirrus aurantiacus is bright red, with orange
tentacles; these worms were rejected by certain fish.[353] The animal has given
up living in tubes as all its allies do, and it is the tentacles which appear to be
distasteful to its enemies, for when irritated it coils itself up and wraps itself
round with its tentacles. Moreover, when the tentacles were cut off the fish did
not reject the body of the worm. The tentacles are thus coloured in such a way
that fish recognise them, and associate with the colour some distasteful
property.
possible that the gills of Sabelliformia are protectively coloured; for in Sabella
pavonia they vary from a light yellowish tint to a deep violet-brown, and the
dark markings on them are therefore more or less distinct. Spread out as the
gills are in life, they are in many cases difficult to recognise; it is rather their
movement as they are withdrawn that attracts one's attention to them, as the
tubes of these worms frequently serve for the attachment of brownish
seaweeds, to which the gills bear resemblance. But, as a matter of fact, little
work has been done in this direction, and speculation on the matter without
evidence is worthless. Many pelagic forms, being transparent, such as
Tomopteris and Alciopids, are no doubt protected by their lack of colour; yet
these forms present brightly-coloured spots,—the light-producing organs in
the parapodia of the former, and the large dark eyes of the latter.
Semper[352] mentions a case of possible mimicry in a species of Myxicola
which lives in the clefts of a coral, Cladocora. The branchial funnel, when
expanded, resembles very closely the expanded coral in size, colour, etc.; but
he points out that the species occurs in other situations, where its colouring is
not protective. Probably the "mimicry" is in other instances merely accidental.
No doubt many Polychaetes may be "warningly coloured," but experimental
evidence is incomplete. Polycirrus aurantiacus is bright red, with orange
tentacles; these worms were rejected by certain fish.[353] The animal has given
up living in tubes as all its allies do, and it is the tentacles which appear to be
distasteful to its enemies, for when irritated it coils itself up and wraps itself
round with its tentacles. Moreover, when the tentacles were cut off the fish did
not reject the body of the worm. The tentacles are thus coloured in such a way
that fish recognise them, and associate with the colour some distasteful
property.
Page 302
Fig. 157.—Chaetopterus variopedatus Ren. × ½. On the left the entire animal, with the
three regions A, B, C. c, Peristomial cirrus; d, "sucker"; e, the great "wings"; f,
"fan"; m, mouth. On the right the animal is represented in the dark, under
stimulation, so as to exhibit the phosphorescent portions of the body. (From
Panceri.)
Phosphorescence.—Many worms of very different habits have the power of
emitting a light from some parts of the body, and they are then said to be
"phosphorescent."[354] Probably Chaetopterus is most eminently photogenic;
the base of the great "wings," the "fans," and other parts emit, on stimulation,
an azure blue to greenish light, so bright that one may read one's watch by it.
Several species of Polynoë exhibit a similar phenomenon, each elytron, with
the exception of the area of attachment, being brilliantly illuminated. In these
species the phosphorescent elytra are frequently thrown off by the animal, so
that possibly they deceive enemies. Polycirrus aurantiacus produces a
beautiful violet phosphorescence; usually its many tentacles alone show the
light, but under strong stimulation the entire body takes part in the display, and
no doubt the phosphorescence has, like the colour, a "warning" purpose.
The production of the light in these various forms is apparently due to two
different processes. In some cases, e.g. Chaetopterus, Syllids, Terebellids, it
appears to be due to the oxidation of certain cell contents which are discharged
more or less freely on irritation of the nerves; whilst in Polynoids the
phenomenon is due to some purely nervous process, for the elytra have no
glands, but are provided with ganglia and a nervous network.
In other worms, however, there are definite light-producing organs. In
Tomopteris there is on each parapodium, above and below, a brightly-coloured
spherical organ, which for a long time was regarded as an eye, but from its
structure appears to be a "photogen" (Fig. 167, p. 315). The same is very likely
the true explanation of the segmental "eyes" of Polyophthalmus, for their
structure recalls that of the light-organs of deep-sea fishes.
As many of the phosphorescent Polynoids are commensals, while
Chaetopterus inhabits tubes, and close allies of other phosphorescent worms
have no power of emitting light, it is impossible to apply the same explanation
of its purpose to all cases alike; in some it may be "accidental," though in
others it may be of definite use in warning enemies or in attracting prey.
three regions A, B, C. c, Peristomial cirrus; d, "sucker"; e, the great "wings"; f,
"fan"; m, mouth. On the right the animal is represented in the dark, under
stimulation, so as to exhibit the phosphorescent portions of the body. (From
Panceri.)
Phosphorescence.—Many worms of very different habits have the power of
emitting a light from some parts of the body, and they are then said to be
"phosphorescent."[354] Probably Chaetopterus is most eminently photogenic;
the base of the great "wings," the "fans," and other parts emit, on stimulation,
an azure blue to greenish light, so bright that one may read one's watch by it.
Several species of Polynoë exhibit a similar phenomenon, each elytron, with
the exception of the area of attachment, being brilliantly illuminated. In these
species the phosphorescent elytra are frequently thrown off by the animal, so
that possibly they deceive enemies. Polycirrus aurantiacus produces a
beautiful violet phosphorescence; usually its many tentacles alone show the
light, but under strong stimulation the entire body takes part in the display, and
no doubt the phosphorescence has, like the colour, a "warning" purpose.
The production of the light in these various forms is apparently due to two
different processes. In some cases, e.g. Chaetopterus, Syllids, Terebellids, it
appears to be due to the oxidation of certain cell contents which are discharged
more or less freely on irritation of the nerves; whilst in Polynoids the
phenomenon is due to some purely nervous process, for the elytra have no
glands, but are provided with ganglia and a nervous network.
In other worms, however, there are definite light-producing organs. In
Tomopteris there is on each parapodium, above and below, a brightly-coloured
spherical organ, which for a long time was regarded as an eye, but from its
structure appears to be a "photogen" (Fig. 167, p. 315). The same is very likely
the true explanation of the segmental "eyes" of Polyophthalmus, for their
structure recalls that of the light-organs of deep-sea fishes.
As many of the phosphorescent Polynoids are commensals, while
Chaetopterus inhabits tubes, and close allies of other phosphorescent worms
have no power of emitting light, it is impossible to apply the same explanation
of its purpose to all cases alike; in some it may be "accidental," though in
others it may be of definite use in warning enemies or in attracting prey.
Page 303
The Food of Worms.—The Nereidiformia are mostly carnivorous, and feed
on small Crustacea, Mollusca, sponges, and other animals; and Polynoids are
even said to eat one another. Many worms do not disdain various seaweeds,
whilst the Spioniformia and Scoleciformia, which burrow in mud and sand,
and are without biting organs, swallow the mud and digest what animal or
vegetable débris it may contain. The Terebellids and Cryptocephala depend on
minute organisms which may be driven into the mouth by the action of the
cilia of the gills or tentacles.
In the case of deep-sea forms, it is an interesting fact that the intestines are not
unfrequently crammed with Radiolaria and Foraminifera in a fairly fresh,
uninjured condition, indicating that these Rhizopods do not merely sink to the
bottom, but must actually live there.[355]
The economic purposes to which Polychaetes are put are few; they are used
either as bait for fishes or as food for man.
One of the commonest baits used for certain fish, as all who have done any
sea-fishing off the piers of our coasts know, is the common lug-worm
(Arenicola marina), whilst Nephthys caeca and Nereis fucata are also used in
some places; and for whiting Nereis cultrifera and N. diversicolor. Marphysa
sanguinea, known to the fishermen in some parts as "varme," is less
frequently used.
A peculiar worm—Palolo viridis—is used as food by the natives of Samoa
and Fiji. The worm is similar to our Eunicid Lysidice ninetta, and lives in
fissures among corals on the reefs, at a depth of about two fathoms. At certain
days in October and November they leave the reefs and swim to the shores of
the above islands, probably to spawn; and this occurs on two days in each of
the above months—the day on which the moon is in her last quarter, and the
day before. The natives, who call the worm "Mbalolo," give the name
"Mbalolo lailai" (little) to October, and "Mbalolo levu" (large) to November,
thereby indicating the relative abundance of the worms in these two months.
The natives eat them either alive or baked, tied up in leaves; and they are
esteemed so great a delicacy that presents of them are sent by the chiefs who
live on shore to those living inland. A dark green-blue Phyllodocid, which is
on small Crustacea, Mollusca, sponges, and other animals; and Polynoids are
even said to eat one another. Many worms do not disdain various seaweeds,
whilst the Spioniformia and Scoleciformia, which burrow in mud and sand,
and are without biting organs, swallow the mud and digest what animal or
vegetable débris it may contain. The Terebellids and Cryptocephala depend on
minute organisms which may be driven into the mouth by the action of the
cilia of the gills or tentacles.
In the case of deep-sea forms, it is an interesting fact that the intestines are not
unfrequently crammed with Radiolaria and Foraminifera in a fairly fresh,
uninjured condition, indicating that these Rhizopods do not merely sink to the
bottom, but must actually live there.[355]
The economic purposes to which Polychaetes are put are few; they are used
either as bait for fishes or as food for man.
One of the commonest baits used for certain fish, as all who have done any
sea-fishing off the piers of our coasts know, is the common lug-worm
(Arenicola marina), whilst Nephthys caeca and Nereis fucata are also used in
some places; and for whiting Nereis cultrifera and N. diversicolor. Marphysa
sanguinea, known to the fishermen in some parts as "varme," is less
frequently used.
A peculiar worm—Palolo viridis—is used as food by the natives of Samoa
and Fiji. The worm is similar to our Eunicid Lysidice ninetta, and lives in
fissures among corals on the reefs, at a depth of about two fathoms. At certain
days in October and November they leave the reefs and swim to the shores of
the above islands, probably to spawn; and this occurs on two days in each of
the above months—the day on which the moon is in her last quarter, and the
day before. The natives, who call the worm "Mbalolo," give the name
"Mbalolo lailai" (little) to October, and "Mbalolo levu" (large) to November,
thereby indicating the relative abundance of the worms in these two months.
The natives eat them either alive or baked, tied up in leaves; and they are
esteemed so great a delicacy that presents of them are sent by the chiefs who
live on shore to those living inland. A dark green-blue Phyllodocid, which is
Page 304
called "A'oon," occurs in abundance off Mota Island, amongst the New
Hebrides, has similar habits, and is also eaten.[356]
Associated Worms.—A considerable number of worms live in association
with other animals, either as commensals or as parasites, and it is not in every
case possible to decide in what relation the two animals stand. Labrorostratus
parasiticus, a Eunicid, is parasitic in the body-cavity of Odontosyllis
ctenostomatus (Fig. 158); such an association between two members of the
same group of animals is peculiar; but still more exceptional is the occurrence
of Haematocleptes terebellides, as a parasite in Marphysa sanguinea, for both
parasite and host are members of the same family, the Eunicidae. Another
Eunicid, Oligognathus bonelliae, occurs in the body-cavity of the Gephyrean
Bonellia.
The Polynoid Acholoe astericola and the Hesionid Ophiodromus flexuosus
occur as ectoparasites (or perhaps commensals) in the ambulacral grooves of
the starfish Astropecten aurantiacus. An Amphinomid is stated to live in the
branchial chamber of the barnacle, Lepas anatifera. Alciopina parasitica lives,
during the early stages of its life-history, within Cydippe, and it is possible that
most of the Alciopids thus make use of Ctenophores as their nurseries.
A considerable number of the Polynoids are ectoparasitic: P. castanea lodges
in the peri-oral region of Spatangus purpureus, and in the ambulacral grooves
of Astropecten; P. (Halosydna) bairdi lives between the mantle and foot of the
mollusc Fissurella cratitia; P. pentactes is found on the body of the
Holothurian Cucumaria pentactes, and appears to be protectively coloured. P.
(Antinoë) parasitica lives under the elytra of another Polynoid, and P.
acanellae on the coral Acanella normani.[357]
Hebrides, has similar habits, and is also eaten.[356]
Associated Worms.—A considerable number of worms live in association
with other animals, either as commensals or as parasites, and it is not in every
case possible to decide in what relation the two animals stand. Labrorostratus
parasiticus, a Eunicid, is parasitic in the body-cavity of Odontosyllis
ctenostomatus (Fig. 158); such an association between two members of the
same group of animals is peculiar; but still more exceptional is the occurrence
of Haematocleptes terebellides, as a parasite in Marphysa sanguinea, for both
parasite and host are members of the same family, the Eunicidae. Another
Eunicid, Oligognathus bonelliae, occurs in the body-cavity of the Gephyrean
Bonellia.
The Polynoid Acholoe astericola and the Hesionid Ophiodromus flexuosus
occur as ectoparasites (or perhaps commensals) in the ambulacral grooves of
the starfish Astropecten aurantiacus. An Amphinomid is stated to live in the
branchial chamber of the barnacle, Lepas anatifera. Alciopina parasitica lives,
during the early stages of its life-history, within Cydippe, and it is possible that
most of the Alciopids thus make use of Ctenophores as their nurseries.
A considerable number of the Polynoids are ectoparasitic: P. castanea lodges
in the peri-oral region of Spatangus purpureus, and in the ambulacral grooves
of Astropecten; P. (Halosydna) bairdi lives between the mantle and foot of the
mollusc Fissurella cratitia; P. pentactes is found on the body of the
Holothurian Cucumaria pentactes, and appears to be protectively coloured. P.
(Antinoë) parasitica lives under the elytra of another Polynoid, and P.
acanellae on the coral Acanella normani.[357]
Page 305
Fig. 158.—Odontosyllis ctenostomatus, with (L) Labrorostratus parasiticus in its body-
cavity. The parapodia and cirri are omitted from the greater part of the body. (After
St. Joseph.) × 4.
As commensals there may be mentioned Nereis fucata, which lives in the
upper coil of whelk-shells which are inhabited by a hermit crab. The same
shell usually bears a particular sea-anemone, so that there are three animals
living together in or upon the cast-off house of a fourth. Siphonostoma is
found in the "nests" made by the mollusc Lima. A Eunice is constantly
associated with the coral Lophohelia prolifera, amongst the branches of which
the worm twines its tube; whilst another Polychaete inhabits a tube formed by
the interweaving of the fine branches of the coral Antipathes filix,[358] found in
the West Indian seas. A species of Polydora forms its tube in Heliopora. The
Polynoids present many instances of commensalism, a few of which may be
here mentioned. P. johnstoni Marenz. is only found in the tubes of Terebella
nebulosa; other species occur in the tubes of other Terebellids. P. marphysae
lives in tubes of the Eunicid Marphysa sanguinea. Two species live in the
tubes of Chaetopterus. P. extenuata has been found in tubes of Serpula
vermicularis, while P. arenicolae occurs on the body of the common lug-
worm, with the colouring of which it closely harmonises.
Worms as Hosts.—The Polychaeta serve not only as food for fishes,
Crustacea, and other predatory animals of larger size, but are also liable to be
the hosts of parasites[359] such as Gregarines, and even, as we have seen, of
other members of their own group. Sundry ectoparasitic Copepoda have been
found attached to worms between the parapodia or to the sides of the feet, and
an unnamed Copepod occurs attached, sometimes in considerable numbers, to
the sides of Nereis cultrifera. The Polychaeta also act as protectors to other
animals, for on the under surface of elytra of sundry Polynoids may very
cavity. The parapodia and cirri are omitted from the greater part of the body. (After
St. Joseph.) × 4.
As commensals there may be mentioned Nereis fucata, which lives in the
upper coil of whelk-shells which are inhabited by a hermit crab. The same
shell usually bears a particular sea-anemone, so that there are three animals
living together in or upon the cast-off house of a fourth. Siphonostoma is
found in the "nests" made by the mollusc Lima. A Eunice is constantly
associated with the coral Lophohelia prolifera, amongst the branches of which
the worm twines its tube; whilst another Polychaete inhabits a tube formed by
the interweaving of the fine branches of the coral Antipathes filix,[358] found in
the West Indian seas. A species of Polydora forms its tube in Heliopora. The
Polynoids present many instances of commensalism, a few of which may be
here mentioned. P. johnstoni Marenz. is only found in the tubes of Terebella
nebulosa; other species occur in the tubes of other Terebellids. P. marphysae
lives in tubes of the Eunicid Marphysa sanguinea. Two species live in the
tubes of Chaetopterus. P. extenuata has been found in tubes of Serpula
vermicularis, while P. arenicolae occurs on the body of the common lug-
worm, with the colouring of which it closely harmonises.
Worms as Hosts.—The Polychaeta serve not only as food for fishes,
Crustacea, and other predatory animals of larger size, but are also liable to be
the hosts of parasites[359] such as Gregarines, and even, as we have seen, of
other members of their own group. Sundry ectoparasitic Copepoda have been
found attached to worms between the parapodia or to the sides of the feet, and
an unnamed Copepod occurs attached, sometimes in considerable numbers, to
the sides of Nereis cultrifera. The Polychaeta also act as protectors to other
animals, for on the under surface of elytra of sundry Polynoids may very
Page 306
frequently be found specimens of Loxosoma, which may also be attached to
gills of Eunicids; whilst below those of Aphrodite echidna and Hermadion
pellucidum, Pedicellina belgica occurs. Under the felt of A. aculeata the
Sabellid Branchiomma vigilans forms its tube, and Vorticellids may be found
on chaetae, gills, or other parts of the body of sundry worms.
Distribution.—Very little can be said in a brief way of the geographical
distribution of these worms, for many of the genera are cosmopolitan,
although only a few species occur in all the great oceans, e.g. Polynoë
imbricata, Hyalinoecia tubicola, Nerine (Scolecolepis) cirrata, and
Terebellides stroemi.
As for species, it can be said generally that the different oceanic areas and
even different coasts present different species, but we know practically
nothing of variation amongst Polychaeta, and many so called species may be
mere local varieties, for frequently the descriptions of "new species" are
scarcely intelligible. At any rate we know that certain species occur at widely
separated localities, for two or three species of Polynoids occur in Japan, and
again at Dinard on the French coast. A considerable number of species are
common to both sides of the North Atlantic ocean, having been obtained off
Norway and in the Gulf of the St. Lawrence. A few of these which are
common on our coasts may be enumerated:—Nereis pelagica, Nicomache
lumbricalis, Glycera capitata, Thelepus cincinnatus, Scoloplos armiger,
Sabella pavonia, Ophelia limacina, Aphrodite aculeata, Trophonia plumosa,
Polynoë squamata, Capitella capitata, Sthenelais limicola.
As for bathymetrical distribution,[360] many genera occur at all depths, though
Polychaetes appear to be most abundant, as far as we know at present, in
"shallow water"—that is, down to twenty fathoms or so; but this may be due
to the greater facility of collection on shore and in these slight depths, for the
"Challenger" obtained considerable numbers of new species at greater depths.
The "deep-sea" forms are chiefly tubicolous, and since these tubes are fixed
and partially embedded in the bottom, probably comparatively few are brought
up. Some genera occur at very great depths; thus the Terebellid Leaena
abyssorum and the Serpulid Placostegus benthalianus were brought up from
3125 fathoms—the greatest depth from which Polychaetes were obtained by
gills of Eunicids; whilst below those of Aphrodite echidna and Hermadion
pellucidum, Pedicellina belgica occurs. Under the felt of A. aculeata the
Sabellid Branchiomma vigilans forms its tube, and Vorticellids may be found
on chaetae, gills, or other parts of the body of sundry worms.
Distribution.—Very little can be said in a brief way of the geographical
distribution of these worms, for many of the genera are cosmopolitan,
although only a few species occur in all the great oceans, e.g. Polynoë
imbricata, Hyalinoecia tubicola, Nerine (Scolecolepis) cirrata, and
Terebellides stroemi.
As for species, it can be said generally that the different oceanic areas and
even different coasts present different species, but we know practically
nothing of variation amongst Polychaeta, and many so called species may be
mere local varieties, for frequently the descriptions of "new species" are
scarcely intelligible. At any rate we know that certain species occur at widely
separated localities, for two or three species of Polynoids occur in Japan, and
again at Dinard on the French coast. A considerable number of species are
common to both sides of the North Atlantic ocean, having been obtained off
Norway and in the Gulf of the St. Lawrence. A few of these which are
common on our coasts may be enumerated:—Nereis pelagica, Nicomache
lumbricalis, Glycera capitata, Thelepus cincinnatus, Scoloplos armiger,
Sabella pavonia, Ophelia limacina, Aphrodite aculeata, Trophonia plumosa,
Polynoë squamata, Capitella capitata, Sthenelais limicola.
As for bathymetrical distribution,[360] many genera occur at all depths, though
Polychaetes appear to be most abundant, as far as we know at present, in
"shallow water"—that is, down to twenty fathoms or so; but this may be due
to the greater facility of collection on shore and in these slight depths, for the
"Challenger" obtained considerable numbers of new species at greater depths.
The "deep-sea" forms are chiefly tubicolous, and since these tubes are fixed
and partially embedded in the bottom, probably comparatively few are brought
up. Some genera occur at very great depths; thus the Terebellid Leaena
abyssorum and the Serpulid Placostegus benthalianus were brought up from
3125 fathoms—the greatest depth from which Polychaetes were obtained by
Page 307
H.M.S. "Challenger"; and it is interesting to note that species of each of these
two genera occur in shallow water, the Serpulid being represented in our own
coast fauna by P. tricuspidata.
Amongst our own fauna, a few examples may be given of the "replacement of
species."[361] The littoral Sthenelais boa is represented by S. limicola in deeper
water; Sabellaria alveolata by S. spinulosa; Polynoë imbricata by several
deep-water species. Similarly with genera: the littoral Pomatoceros is replaced
by Serpula in deeper water; and the Hesionid Psamathe by Castalia.
The limitation of species to certain regions, or to certain depths of an ocean,
may appear at first sight peculiar, in view of the unrestricted communication
between all its parts; but there are as efficient "barriers" there as on land, for
generally a particular worm can live only in a certain temperature and at a
certain pressure, and is dependent for its food on particular organisms, which
in their turn depend on the depth and its accompaniments. It is, in fact, so
much the more peculiar that certain species are more or less cosmopolitan, or
occur at widely distant points. It is less peculiar, of course, to find different
species of the same genus at different depths or in different areas, for any
slight variation in a species advantageous to new conditions would readily be
fixed, and give rise to a new species.
The distribution of the Polychaeta depends probably on the pelagic larvae,
which are carried by currents from one part of an ocean to another. There can
be little doubt that many Polychaetes are very "plastic," and can adapt
themselves to changed conditions of life with considerable ease; for Nereis
diversicolor, Arenicola marina, and others live equally well in water of very
different densities, and with a different food supply. The great variety in the
"habitats," and presumably therefore in their food supply, etc., exhibited by
many Polychaetes, as well as the great variation observable in some species of
Polynoina, and the close affinity of the species and genera of this sub-family,
lead us to the same conclusion.
Extinct Polychaetes.—The most numerous fossil records of the Polychaetes
are calcareous tubes of various shapes and sizes; they are irregularly or
spirally curved, and are very usually attached at one end, or by one surface, to
two genera occur in shallow water, the Serpulid being represented in our own
coast fauna by P. tricuspidata.
Amongst our own fauna, a few examples may be given of the "replacement of
species."[361] The littoral Sthenelais boa is represented by S. limicola in deeper
water; Sabellaria alveolata by S. spinulosa; Polynoë imbricata by several
deep-water species. Similarly with genera: the littoral Pomatoceros is replaced
by Serpula in deeper water; and the Hesionid Psamathe by Castalia.
The limitation of species to certain regions, or to certain depths of an ocean,
may appear at first sight peculiar, in view of the unrestricted communication
between all its parts; but there are as efficient "barriers" there as on land, for
generally a particular worm can live only in a certain temperature and at a
certain pressure, and is dependent for its food on particular organisms, which
in their turn depend on the depth and its accompaniments. It is, in fact, so
much the more peculiar that certain species are more or less cosmopolitan, or
occur at widely distant points. It is less peculiar, of course, to find different
species of the same genus at different depths or in different areas, for any
slight variation in a species advantageous to new conditions would readily be
fixed, and give rise to a new species.
The distribution of the Polychaeta depends probably on the pelagic larvae,
which are carried by currents from one part of an ocean to another. There can
be little doubt that many Polychaetes are very "plastic," and can adapt
themselves to changed conditions of life with considerable ease; for Nereis
diversicolor, Arenicola marina, and others live equally well in water of very
different densities, and with a different food supply. The great variety in the
"habitats," and presumably therefore in their food supply, etc., exhibited by
many Polychaetes, as well as the great variation observable in some species of
Polynoina, and the close affinity of the species and genera of this sub-family,
lead us to the same conclusion.
Extinct Polychaetes.—The most numerous fossil records of the Polychaetes
are calcareous tubes of various shapes and sizes; they are irregularly or
spirally curved, and are very usually attached at one end, or by one surface, to
Page 308
stones or to fossils. These tubes belong to the Serpulidae, and are referred to
the genera Serpula, Spirorbis, Ditrupa, and others.[362]
Spirorbis is the oldest unequivocal representative of the Polychaetes, as its
tubes are found more or less abundantly in the Silurian and other Palaeozoic
strata. In Palaeozoic times Serpula was rare, as it was too in the Trias and
Lias, but in the Jurassic strata it becomes abundant. In the chalk, S. socialis
may occur in masses like S. uncinata of the present day, forming "Serpulite
chalk." In the older tertiaries the genus is represented by Spirulaea.
Terebella lapilloides occurs in the Lias as a cylindrical, more or less curved
tube of sand-grains.
Fig. 159.—Eunicites avitus Ehl. A fossil worm from the lithographic slate of Solenhofen:
the jaws are seen in front, and the acicula along each side. (From Ehlers.) Natural
size.
Amongst the Nereidiformia the remains are fewer, but the acicula and the hard
jaws are preserved in certain rocks, and can be referred to existing families.
Eunicites avitus[363] is represented by a double series of acicula, indicating the
parapodia of the two sides; and by remains of both upper and lower jaws (Fig.
159). Four different species of the worm have been described from the
lithographic slate of Bavaria, of Jurassic age; and several upper jaws of other
Eunicids have been discovered in the Palaeozoic beds of Canada and Scotland,
and have received the names Lumbriconereites, Oenonites, and Arabellites, in
reference to their nearest allies amongst living genera.
the genera Serpula, Spirorbis, Ditrupa, and others.[362]
Spirorbis is the oldest unequivocal representative of the Polychaetes, as its
tubes are found more or less abundantly in the Silurian and other Palaeozoic
strata. In Palaeozoic times Serpula was rare, as it was too in the Trias and
Lias, but in the Jurassic strata it becomes abundant. In the chalk, S. socialis
may occur in masses like S. uncinata of the present day, forming "Serpulite
chalk." In the older tertiaries the genus is represented by Spirulaea.
Terebella lapilloides occurs in the Lias as a cylindrical, more or less curved
tube of sand-grains.
Fig. 159.—Eunicites avitus Ehl. A fossil worm from the lithographic slate of Solenhofen:
the jaws are seen in front, and the acicula along each side. (From Ehlers.) Natural
size.
Amongst the Nereidiformia the remains are fewer, but the acicula and the hard
jaws are preserved in certain rocks, and can be referred to existing families.
Eunicites avitus[363] is represented by a double series of acicula, indicating the
parapodia of the two sides; and by remains of both upper and lower jaws (Fig.
159). Four different species of the worm have been described from the
lithographic slate of Bavaria, of Jurassic age; and several upper jaws of other
Eunicids have been discovered in the Palaeozoic beds of Canada and Scotland,
and have received the names Lumbriconereites, Oenonites, and Arabellites, in
reference to their nearest allies amongst living genera.
Page 309
There are, however, numerous remains, in the forms of tracks or casts, in the
earlier rocks, which have been referred to the Polychaeta. The names
Crossopodia, Myrianites, Nereites, Phyllodocites, have been given to some of
these traces, though they are open to numerous other interpretations. Some of
the "tracks" are similar to those made by living Crustacea in walking over wet
sand; others appear to be the casts of some animals. Tubular burrows in rocks
or fossils, some straight, others U-shaped, have received such names as
Arenicolites, Scolithus, Histioderma; whilst under the name Lumbricaria
certain cylindrical, coiled structures, resembling worm "castings," are met
with in this same lithographic stone of Solenhofen. Many of the tubes referred
to Polychaetes by the earlier palaeontologists have been transferred to other
groups; thus Cornulites is now believed to be a Pteropod shell.
This very meagre geological record is quite insufficient to form any basis for a
phylogeny of the group. And this poor supply of remains is not surprising,
when we consider the soft nature of the tissues, the absence, in the majority of
families, of skeleton and of other parts which could have been fossilised; yet
we might have expected a greater abundance of fossilised jaws than is
represented at present. But it must be borne in mind that the conditions of life
of these soft-bodied animals are not conducive to their leaving abundant
fossilised remains.
CHAPTER XII
CHARACTERS OF THE SUB-ORDERS OF POLYCHAETES—CHARACTERS OF THE FAMILIES
—DESCRIPTION OF BRITISH GENERA AND SPECIES—THE MYZOSTOMARIA.
Systematic.—The Order Polychaeta may be divided into two branches, in one
of which, the Phanerocephala, the prostomium retains its ancestral condition
as a lobe overhanging the mouth, and frequently carries, in addition to paired
eyes, certain sensory processes of a simple structure, the tentacles and palps;
the body-segments are more or less alike, and (except in some Spioniformia,
some of the Terebelliformia, and the Capitelliformia) do not present two
sharply marked regions, owing to the differential arrangement or character of
the chaetae. In the second branch, the Cryptocephala, the peristomium grows
earlier rocks, which have been referred to the Polychaeta. The names
Crossopodia, Myrianites, Nereites, Phyllodocites, have been given to some of
these traces, though they are open to numerous other interpretations. Some of
the "tracks" are similar to those made by living Crustacea in walking over wet
sand; others appear to be the casts of some animals. Tubular burrows in rocks
or fossils, some straight, others U-shaped, have received such names as
Arenicolites, Scolithus, Histioderma; whilst under the name Lumbricaria
certain cylindrical, coiled structures, resembling worm "castings," are met
with in this same lithographic stone of Solenhofen. Many of the tubes referred
to Polychaetes by the earlier palaeontologists have been transferred to other
groups; thus Cornulites is now believed to be a Pteropod shell.
This very meagre geological record is quite insufficient to form any basis for a
phylogeny of the group. And this poor supply of remains is not surprising,
when we consider the soft nature of the tissues, the absence, in the majority of
families, of skeleton and of other parts which could have been fossilised; yet
we might have expected a greater abundance of fossilised jaws than is
represented at present. But it must be borne in mind that the conditions of life
of these soft-bodied animals are not conducive to their leaving abundant
fossilised remains.
CHAPTER XII
CHARACTERS OF THE SUB-ORDERS OF POLYCHAETES—CHARACTERS OF THE FAMILIES
—DESCRIPTION OF BRITISH GENERA AND SPECIES—THE MYZOSTOMARIA.
Systematic.—The Order Polychaeta may be divided into two branches, in one
of which, the Phanerocephala, the prostomium retains its ancestral condition
as a lobe overhanging the mouth, and frequently carries, in addition to paired
eyes, certain sensory processes of a simple structure, the tentacles and palps;
the body-segments are more or less alike, and (except in some Spioniformia,
some of the Terebelliformia, and the Capitelliformia) do not present two
sharply marked regions, owing to the differential arrangement or character of
the chaetae. In the second branch, the Cryptocephala, the peristomium grows
Page 310
forwards during development, so as to compress or even hide the prostomium,
which thus becomes a very insignificant organ. The tentacles are reduced, but
the palps become greatly developed and take on sundry new functions. The
body in this group, by the character and arrangement of the chaetae, is
distinguishable into a thorax and abdomen, presenting certain internal
differences.
These two branches may be supposed to have arisen from a common ancestor
having a general resemblance to a nereidiform worm, such as Syllis,
possessing palps and tentacles on the prostomium, definite parapodia and cirri
on the body, and internally, a well-marked and regular repetition of organs.
The branch Phanerocephala contains the following five sub-Orders, though it
is possible that the Capitelliformia deserves a more important position in the
system:—
Sub-Order 1.—The Nereidiformia have well-developed tentacles and palps;
the peristomium almost invariably possesses special cirri; the parapodia are
well-marked locomotor organs, supported by acicula, and carry dorsal and
ventral cirri. The chaetae are usually jointed, though unjointed ones may
coexist with these; uncini are never present. An eversible buccal region leads
into a muscular pharynx, which in the majority is armed with chitinous jaws;
the septa and nephridia are regularly repeated throughout the body. The worms
lead a predaceous life, and are mostly carnivorous; a few form tubes.
Sub-Order 2.—The Spioniformia possess neither tentacles nor palps; the
peristomium usually carries a pair of long tentacular cirri, and extends
forwards at the sides of the prostomium. The parapodia project only to a slight
degree; the dorsal cirri may attain a considerable size, and act as gills
throughout the greater part of the body. The chaetae are unjointed; uncini are
only present in the aberrant Chaetopterus.[364] The body may present two
regions more or less distinctly marked externally, but without corresponding
internal differences. The buccal region may be eversible, but there are no jaws.
Septa and nephridia are regularly developed. The worms are burrowers, or
tubicolous.
which thus becomes a very insignificant organ. The tentacles are reduced, but
the palps become greatly developed and take on sundry new functions. The
body in this group, by the character and arrangement of the chaetae, is
distinguishable into a thorax and abdomen, presenting certain internal
differences.
These two branches may be supposed to have arisen from a common ancestor
having a general resemblance to a nereidiform worm, such as Syllis,
possessing palps and tentacles on the prostomium, definite parapodia and cirri
on the body, and internally, a well-marked and regular repetition of organs.
The branch Phanerocephala contains the following five sub-Orders, though it
is possible that the Capitelliformia deserves a more important position in the
system:—
Sub-Order 1.—The Nereidiformia have well-developed tentacles and palps;
the peristomium almost invariably possesses special cirri; the parapodia are
well-marked locomotor organs, supported by acicula, and carry dorsal and
ventral cirri. The chaetae are usually jointed, though unjointed ones may
coexist with these; uncini are never present. An eversible buccal region leads
into a muscular pharynx, which in the majority is armed with chitinous jaws;
the septa and nephridia are regularly repeated throughout the body. The worms
lead a predaceous life, and are mostly carnivorous; a few form tubes.
Sub-Order 2.—The Spioniformia possess neither tentacles nor palps; the
peristomium usually carries a pair of long tentacular cirri, and extends
forwards at the sides of the prostomium. The parapodia project only to a slight
degree; the dorsal cirri may attain a considerable size, and act as gills
throughout the greater part of the body. The chaetae are unjointed; uncini are
only present in the aberrant Chaetopterus.[364] The body may present two
regions more or less distinctly marked externally, but without corresponding
internal differences. The buccal region may be eversible, but there are no jaws.
Septa and nephridia are regularly developed. The worms are burrowers, or
tubicolous.
Page 311
Sub-Order 3. Terebelliformia.—The prostomium is a more or less prominent
lobe (upper lip) with or without tentacles but without palps. The peristomium
may carry cirri or "tentacular filaments."[365] The parapodia are feebly
developed; there are no ventral cirri; the dorsal cirri may exist and function as
gills on more or fewer of the anterior segments. The chaetae are unjointed, and
uncini are usually present. The buccal region is not eversible; there are no
jaws. The septa are usually incomplete, with the exception of one strongly-
developed "diaphragm" anteriorly; the nephridia are dimorphic, those of the
anterior (prediaphragmatic) segments are of large size and are excretory; the
posterior series are mere funnels, and act as genital ducts. These worms are
burrowers or tube-formers, and in the majority the tube-forming glands are
grouped on the ventral surface of the anterior segments to form "gland-
shields."
Sub-Order 4.—The Capitelliformia have no prostomial processes, but possess
a pair of large retractile "ciliated organs." The parapodia do not project; the
chaetae are unjointed, and are hair-like in the anterior segments and hooded
"crotchets" posteriorly; this external division of the body does not correspond
with definite internal differences. There are no cirri, though special "gills,"
often retractile, are frequently present. The buccal region is eversible; there is
no armed pharynx. An "accessory gut" or "siphon" exists. The nephridia are
small, and sometimes more than one pair in a segment; special genital funnels
exist in more or fewer of the anterior segments of the hind body. There is no
system of blood-vessels; the coelomic corpuscles are red. The worms are
burrowers.
Sub-Order 5.—The Scoleciformia possess a prostomium, which rarely
(Chlorhaemidae) carries any sensory processes; the peristomium is without
cirri (except, perhaps, in the Chlorhaemidae). The parapodia are ill developed,
and may be absent; only rarely are dorsal cirri present, acting as gills; ventral
cirri are absent. The chaetae are unjointed; true uncini are not present. The
buccal region is eversible, but there is no armed pharynx. The septa are not
regularly developed, as more or fewer are absent, and the nephridia are
considerably reduced in number, it may be to a single pair (Sternaspidae and
some Chlorhaemidae), but they are all alike.[366] The worms are mostly
burrowers.
The branch Cryptocephala contains two sub-Orders:—
lobe (upper lip) with or without tentacles but without palps. The peristomium
may carry cirri or "tentacular filaments."[365] The parapodia are feebly
developed; there are no ventral cirri; the dorsal cirri may exist and function as
gills on more or fewer of the anterior segments. The chaetae are unjointed, and
uncini are usually present. The buccal region is not eversible; there are no
jaws. The septa are usually incomplete, with the exception of one strongly-
developed "diaphragm" anteriorly; the nephridia are dimorphic, those of the
anterior (prediaphragmatic) segments are of large size and are excretory; the
posterior series are mere funnels, and act as genital ducts. These worms are
burrowers or tube-formers, and in the majority the tube-forming glands are
grouped on the ventral surface of the anterior segments to form "gland-
shields."
Sub-Order 4.—The Capitelliformia have no prostomial processes, but possess
a pair of large retractile "ciliated organs." The parapodia do not project; the
chaetae are unjointed, and are hair-like in the anterior segments and hooded
"crotchets" posteriorly; this external division of the body does not correspond
with definite internal differences. There are no cirri, though special "gills,"
often retractile, are frequently present. The buccal region is eversible; there is
no armed pharynx. An "accessory gut" or "siphon" exists. The nephridia are
small, and sometimes more than one pair in a segment; special genital funnels
exist in more or fewer of the anterior segments of the hind body. There is no
system of blood-vessels; the coelomic corpuscles are red. The worms are
burrowers.
Sub-Order 5.—The Scoleciformia possess a prostomium, which rarely
(Chlorhaemidae) carries any sensory processes; the peristomium is without
cirri (except, perhaps, in the Chlorhaemidae). The parapodia are ill developed,
and may be absent; only rarely are dorsal cirri present, acting as gills; ventral
cirri are absent. The chaetae are unjointed; true uncini are not present. The
buccal region is eversible, but there is no armed pharynx. The septa are not
regularly developed, as more or fewer are absent, and the nephridia are
considerably reduced in number, it may be to a single pair (Sternaspidae and
some Chlorhaemidae), but they are all alike.[366] The worms are mostly
burrowers.
The branch Cryptocephala contains two sub-Orders:—
Page 312
Sub-Order 1. Sabelliformia.—The prostomium is entirely hidden by the
forward extension of the peristomium; the tentacles are very small, being
frequently represented merely by small knobs of sense-cells; the palps, on the
other hand, are greatly developed, branched, and contain blood-vessels, acting
as respiratory as well as sensory organs. The peristomium never carries cirri or
chaetae, and it is usually raised up into a projecting collar, used in fashioning
the lip of the animal's tube. The parapodia are but feebly developed; cirri are
absent, except in the Serpulidae, where the dorsal and ventral cirri become
united to form the "thoracic membrane" (Meyer). The chaetae are of two kinds
—unjointed, hair-like, fringed bristles and "uncini." By their arrangement the
body is divided into a thorax of nine segments and an abdomen; in the former
the capillary chaetae are dorsal, and in the latter ventral. The buccal region is
not eversible; there is no pharynx. The septa are regularly developed in the
abdomen, but are absent in the thorax; the nephridia are dimorphic; there are
two large ones in the thorax opening by a median dorsal pore just above the
brain; those of the abdomen are small funnels, and act as genital ducts. The
worms are tubicolous; "gland-shields" are present on the thoracic segments.
Sub-Order 2. Hermelliformia.—The peristomium (Fig. 135) is enormously
developed, and forms a bilobed hood capable of closing over the mouth; the
truncated free end of each lobe carries three semicircles of peculiar chaetae,
which act as an efficient protection when the worm is withdrawn into its tube.
The prostomium is very small, but retains a pair of well-developed tentacles;
the palps, which are subdivided as in the Sabelliformia, have become fused
with the ventral edges of the peristomium, and appear as a series of ridges on
each side, carrying numerous filaments. The thorax consists of five segments,
the notopodia of three of which are well developed and bear strong chaetae;
dorsal cirri are present along the greater part of the body, and act as gills. The
arrangement of the chaetae and of the internal organs is as in the
Sabelliformia. The worms form tubes of sand.
BRANCH A. PHANEROCEPHALA.
Sub-Order 1. Nereidiformia.[367]
Fam. 1. Syllidae.—These are small worms, the majority being less than an
inch long, so that they are not easily observed. The body consists of a fair
forward extension of the peristomium; the tentacles are very small, being
frequently represented merely by small knobs of sense-cells; the palps, on the
other hand, are greatly developed, branched, and contain blood-vessels, acting
as respiratory as well as sensory organs. The peristomium never carries cirri or
chaetae, and it is usually raised up into a projecting collar, used in fashioning
the lip of the animal's tube. The parapodia are but feebly developed; cirri are
absent, except in the Serpulidae, where the dorsal and ventral cirri become
united to form the "thoracic membrane" (Meyer). The chaetae are of two kinds
—unjointed, hair-like, fringed bristles and "uncini." By their arrangement the
body is divided into a thorax of nine segments and an abdomen; in the former
the capillary chaetae are dorsal, and in the latter ventral. The buccal region is
not eversible; there is no pharynx. The septa are regularly developed in the
abdomen, but are absent in the thorax; the nephridia are dimorphic; there are
two large ones in the thorax opening by a median dorsal pore just above the
brain; those of the abdomen are small funnels, and act as genital ducts. The
worms are tubicolous; "gland-shields" are present on the thoracic segments.
Sub-Order 2. Hermelliformia.—The peristomium (Fig. 135) is enormously
developed, and forms a bilobed hood capable of closing over the mouth; the
truncated free end of each lobe carries three semicircles of peculiar chaetae,
which act as an efficient protection when the worm is withdrawn into its tube.
The prostomium is very small, but retains a pair of well-developed tentacles;
the palps, which are subdivided as in the Sabelliformia, have become fused
with the ventral edges of the peristomium, and appear as a series of ridges on
each side, carrying numerous filaments. The thorax consists of five segments,
the notopodia of three of which are well developed and bear strong chaetae;
dorsal cirri are present along the greater part of the body, and act as gills. The
arrangement of the chaetae and of the internal organs is as in the
Sabelliformia. The worms form tubes of sand.
BRANCH A. PHANEROCEPHALA.
Sub-Order 1. Nereidiformia.[367]
Fam. 1. Syllidae.—These are small worms, the majority being less than an
inch long, so that they are not easily observed. The body consists of a fair
Page 313
number of segments.[368] In many genera a dorsal bundle of unjointed,
natatory chaetae makes its appearance at maturity. The palps, which are
grooved, are in some cases so united with one another and with the
prostomium as to be scarcely recognisable. (For head see p. 262, and for feet
see p. 264.) The pharynx is armed with one or more teeth. There is a special
gizzard, following the pharynx, and provided with thick, muscular walls of
peculiar structure. Following the gizzard, the oesophagus receives in many
genera a pair of T-shaped diverticula, that are used for storing water, which is
swallowed with food. These diverticula are absent in Autolytus and other free-
swimming forms. The reproduction of the members of this family is
interesting, and has already been described (p. 278).
Fig. 160.—Syllis armillaris Müll. × 2. (From Johnston.) The head is towards the right.
Syllis.—The tentacles and cirri are moniliform; the palps large; there is a
single dorsal tooth, which is provided with a poison gland, the duct of which
opens near its apex; it is used rather for stabbing its prey than for grasping and
tearing. S. krohnii Ehlers, is abundant under stones, and forms tubes of sand; it
is nearly an inch long, and consists of some eighty-five to ninety-five
segments marked with yellow bands. It may readily be identified by longer
dorsal cirri, terminally dilated, alternating with shorter ones. S. cornuta
Rathke, has a translucent green body, about half an inch long; no alternation of
cirri. Mediterranean, Atlantic, on the Norwegian coast, off Spitzbergen, and on
the Madeira coast. S. armillaris Müll. is very common at low water; it is pale
yellowish-brown, with a couple of dusky marks on each segment; and
measures 2 inches. The dorsal cirri are quite short, consisting of only eight to
ten joints. In Pionosyllis the tentacles and cirri are not moniliform; a single
dorsal tooth. P. malmgreni M‘I. under stones. Sphaerosyllis.—The dorsal cirri
are swollen at the base, and are not moniliform; the long palps are fused along
nearly their whole extent. S. hystrix Clap. is only about one-eighth of an inch
in length. Exogone Oerst. Grubea Qfg.
Autolytus.—The small palps are entirely fused with the prostomium; the
pharynx, which is bent upon itself, is armed with a circle of denticles. Dorsal
cirri somewhat foliaceous. There are no ventral cirri. The male and female
differ from one another and from the asexual "stock" (see p. 279). A. pictus
natatory chaetae makes its appearance at maturity. The palps, which are
grooved, are in some cases so united with one another and with the
prostomium as to be scarcely recognisable. (For head see p. 262, and for feet
see p. 264.) The pharynx is armed with one or more teeth. There is a special
gizzard, following the pharynx, and provided with thick, muscular walls of
peculiar structure. Following the gizzard, the oesophagus receives in many
genera a pair of T-shaped diverticula, that are used for storing water, which is
swallowed with food. These diverticula are absent in Autolytus and other free-
swimming forms. The reproduction of the members of this family is
interesting, and has already been described (p. 278).
Fig. 160.—Syllis armillaris Müll. × 2. (From Johnston.) The head is towards the right.
Syllis.—The tentacles and cirri are moniliform; the palps large; there is a
single dorsal tooth, which is provided with a poison gland, the duct of which
opens near its apex; it is used rather for stabbing its prey than for grasping and
tearing. S. krohnii Ehlers, is abundant under stones, and forms tubes of sand; it
is nearly an inch long, and consists of some eighty-five to ninety-five
segments marked with yellow bands. It may readily be identified by longer
dorsal cirri, terminally dilated, alternating with shorter ones. S. cornuta
Rathke, has a translucent green body, about half an inch long; no alternation of
cirri. Mediterranean, Atlantic, on the Norwegian coast, off Spitzbergen, and on
the Madeira coast. S. armillaris Müll. is very common at low water; it is pale
yellowish-brown, with a couple of dusky marks on each segment; and
measures 2 inches. The dorsal cirri are quite short, consisting of only eight to
ten joints. In Pionosyllis the tentacles and cirri are not moniliform; a single
dorsal tooth. P. malmgreni M‘I. under stones. Sphaerosyllis.—The dorsal cirri
are swollen at the base, and are not moniliform; the long palps are fused along
nearly their whole extent. S. hystrix Clap. is only about one-eighth of an inch
in length. Exogone Oerst. Grubea Qfg.
Autolytus.—The small palps are entirely fused with the prostomium; the
pharynx, which is bent upon itself, is armed with a circle of denticles. Dorsal
cirri somewhat foliaceous. There are no ventral cirri. The male and female
differ from one another and from the asexual "stock" (see p. 279). A. pictus
Page 314
Ehl. is abundant under stones. It measures about two-thirds of an inch in
length, is darkly coloured with a median lighter band; the anterior dorsal cirri
are long. A. prolifer Müll. is common.
Myrianida fasciata Milne Edwards, with its foliaceous cirri, occurs off our
coasts (see Fig. 149, p. 280). Atlantic, Mediterranean.
Fam. 2. Hesionidae.—The body is relatively short, with only a few segments
(sixteen to fifty, according to the genus); in the larger forms it is cylindrical.
The parapodium is usually uniramous; the dorsal cirri are long and
multiarticulate; the chaetae are jointed. The prostomium carries, in addition to
four eyes, two or three tentacles, and generally a pair of jointed palps. The
peristomium and two or more of the following segments are achaetous, and
carry long "peristomial" cirri. The pharynx is very long but unarmed.
Psamathe Johnston, has many segments; head with two tentacles and a pair of
three-jointed palps. P. fusca Jnstn. occurs amongst coralline Algae, to which it
bears some resemblance, which is heightened by the moniliform cirri. It is a
small worm, less than an inch in length. Mediterranean. Castalia punctata
Müll. is dirty green or brownish, with a narrow purplish band on each side. It
occurs in deeper water than the preceding. In Ophiodromus the head has three
tentacles; the palps are two-jointed; there are six pairs of peristomial cirri; the
parapodia are biramous. O. vittatus Sars is dredged in numbers off the Scotch
coast, and is found also at low tides. It measures 2 inches in length. A closely
allied species lives in the ambulacral grooves of the starfish Astropecten.
Fam. 3. Aphroditidae.[369]—The most characteristic feature of this family, and
one by which its members are absolutely distinguished from all other
Chaetopods, is the possession of scales or "elytra" on the back. These flattened
dorsal cirri are of a somewhat horny texture, and are carried, generally, on
alternate segments of the body; filamentous cirri occurring on the other
segments. In the sub-families Hermionina and Polynoina the elytriferous
segments are 2, 4, 5, 7, 9, etc., up to 23; then every third segment. The worms
are usually short, with some thirty-five to forty-five segments, though
Sthenelais and a few others have many more. (For head see p. 262, and for
parapodium see pp. 265, 268.) The pharynx is very thick walled, and furnished
with two pairs of jaws, which are, however, not hardened in the sub-family
length, is darkly coloured with a median lighter band; the anterior dorsal cirri
are long. A. prolifer Müll. is common.
Myrianida fasciata Milne Edwards, with its foliaceous cirri, occurs off our
coasts (see Fig. 149, p. 280). Atlantic, Mediterranean.
Fam. 2. Hesionidae.—The body is relatively short, with only a few segments
(sixteen to fifty, according to the genus); in the larger forms it is cylindrical.
The parapodium is usually uniramous; the dorsal cirri are long and
multiarticulate; the chaetae are jointed. The prostomium carries, in addition to
four eyes, two or three tentacles, and generally a pair of jointed palps. The
peristomium and two or more of the following segments are achaetous, and
carry long "peristomial" cirri. The pharynx is very long but unarmed.
Psamathe Johnston, has many segments; head with two tentacles and a pair of
three-jointed palps. P. fusca Jnstn. occurs amongst coralline Algae, to which it
bears some resemblance, which is heightened by the moniliform cirri. It is a
small worm, less than an inch in length. Mediterranean. Castalia punctata
Müll. is dirty green or brownish, with a narrow purplish band on each side. It
occurs in deeper water than the preceding. In Ophiodromus the head has three
tentacles; the palps are two-jointed; there are six pairs of peristomial cirri; the
parapodia are biramous. O. vittatus Sars is dredged in numbers off the Scotch
coast, and is found also at low tides. It measures 2 inches in length. A closely
allied species lives in the ambulacral grooves of the starfish Astropecten.
Fam. 3. Aphroditidae.[369]—The most characteristic feature of this family, and
one by which its members are absolutely distinguished from all other
Chaetopods, is the possession of scales or "elytra" on the back. These flattened
dorsal cirri are of a somewhat horny texture, and are carried, generally, on
alternate segments of the body; filamentous cirri occurring on the other
segments. In the sub-families Hermionina and Polynoina the elytriferous
segments are 2, 4, 5, 7, 9, etc., up to 23; then every third segment. The worms
are usually short, with some thirty-five to forty-five segments, though
Sthenelais and a few others have many more. (For head see p. 262, and for
parapodium see pp. 265, 268.) The pharynx is very thick walled, and furnished
with two pairs of jaws, which are, however, not hardened in the sub-family
Page 315
Hermionina. The intestine is provided with a number of paired longer or
shorter caeca (Fig. 142). A considerable number of this family are commensal
or parasitic (see p. 297). The family is well represented on our own coasts, so
that only a few of the more readily distinguishable species can be here
described.
Fig. 161.—Polynoë squamata L. Nat. size. c, Notopodial cirrus; e, elytron; f, parapodium;
p, palp; t, tentacle. (From Johnston.)
Sub-Fam. 1. Polynoina.—Body flattened, with nearly parallel sides, usually
short, more rarely worm-like; three tentacles; peristomium with long dorsal
and ventral cirri; the ventral cirri of the next segment are also elongated. Jaws
are present. Elytra, usually twelve to eighteen pairs, the surface of which is
more or less papillose, and may be "fringed" along the outer border, with long
processes. The colouring of the elytra is characteristic in most cases, though
liable to considerable variation in some species. The chaetae are generally
strong, and of bright golden colour: they are all unjointed. The Polynoina are
generally but feeble swimmers, and are mostly found under stones at low tide.
Some species have a very wide geographical range.
Polynoë.[370]—The body is short; none or only a few segments at the end of
the body are uncovered by the elytra, except in the long body of P. johnstoni.
A. With twelve pairs of elytra.—In P. squamata Linn. the elytra entirely cover
the body and conceal the head, each elytron overlapping the next posterior
one, and those of the two sides overlapping. General colour sandy-brown,
speckled, lighter or darker. The fringed elytra are very firmly fixed to the
body. The notopodial chaetae scarcely project from below the elytra. The
worm is common between tide-marks and in the coralline region, is about one
to one and a half inches in length, and about one-third of an inch in width.
Atlantic. P. clava Montagu, may attain a larger size, though it is generally
shorter caeca (Fig. 142). A considerable number of this family are commensal
or parasitic (see p. 297). The family is well represented on our own coasts, so
that only a few of the more readily distinguishable species can be here
described.
Fig. 161.—Polynoë squamata L. Nat. size. c, Notopodial cirrus; e, elytron; f, parapodium;
p, palp; t, tentacle. (From Johnston.)
Sub-Fam. 1. Polynoina.—Body flattened, with nearly parallel sides, usually
short, more rarely worm-like; three tentacles; peristomium with long dorsal
and ventral cirri; the ventral cirri of the next segment are also elongated. Jaws
are present. Elytra, usually twelve to eighteen pairs, the surface of which is
more or less papillose, and may be "fringed" along the outer border, with long
processes. The colouring of the elytra is characteristic in most cases, though
liable to considerable variation in some species. The chaetae are generally
strong, and of bright golden colour: they are all unjointed. The Polynoina are
generally but feeble swimmers, and are mostly found under stones at low tide.
Some species have a very wide geographical range.
Polynoë.[370]—The body is short; none or only a few segments at the end of
the body are uncovered by the elytra, except in the long body of P. johnstoni.
A. With twelve pairs of elytra.—In P. squamata Linn. the elytra entirely cover
the body and conceal the head, each elytron overlapping the next posterior
one, and those of the two sides overlapping. General colour sandy-brown,
speckled, lighter or darker. The fringed elytra are very firmly fixed to the
body. The notopodial chaetae scarcely project from below the elytra. The
worm is common between tide-marks and in the coralline region, is about one
to one and a half inches in length, and about one-third of an inch in width.
Atlantic. P. clava Montagu, may attain a larger size, though it is generally
Page 316
smaller. The elytra are dark, usually grey, mottled with white or light grey,
unfringed, and do not overlap to so great an extent as in P. squamata, so that
the middle of the back and the hinder part of the body is more or less exposed.
This is never the case in the preceding species, but even here it is subject to
variation in extent, depending on the amount of food contained by the worm
or on the ripeness of the genital products. It occurs in the Mediterranean.[371]
Fig. 162.—Elytra, A, of Polynoë squamata L.; B, of P. clava Mont. × 10. a, Area of
attachment; e, external margin; f, fringe (the letter is at the posterior side of the
elytron); i, internal margin. (From Bourne.)
B. With fifteen pairs of elytra.—P. imbricata L. is probably the commonest
species of the genus, occurring nearly everywhere under stones at low tide. It
is about an inch in length; the elytra are deciduous, and are very variously
coloured and marked; sometimes uniformly grey or even black, sometimes
mottled with brown: in other specimens each elytron has its outer half pale or
white, while its inner half is darker, usually some tint of brown or olive green,
so that the worm appears to have a dark band along the middle of its back.
Other patterns occur. The body is entirely covered by the elytra. The chaetae
project considerably, and are nearly as long as half the width of the body;
those of the notopodium are brown and are directed upwards, being nearly as
long as the golden neuropodial chaetae. This species has a very wide range,
occurring on both sides of the Atlantic, even on the shores of Nova Zembla,
and reappearing again at Japan. P. semisculptus Leach is rather larger than the
foregoing. The elytra are very readily detached: they are light in colour,
without a fringe, but with large papillae near the margin. The notopodial
chaetae are thicker than those of the neuropodium. Several other species are
also common, but P. johnstoni v. Marenz.[372] differs from the rest in having
an elongated body of some seventy segments, so that the posterior half is
uncovered by the elytra, which are small, greenish-grey, speckled, and have no
fringe. It is common and widely distributed, but appears to be only found in
the tubes of Terebella nebulosa.
unfringed, and do not overlap to so great an extent as in P. squamata, so that
the middle of the back and the hinder part of the body is more or less exposed.
This is never the case in the preceding species, but even here it is subject to
variation in extent, depending on the amount of food contained by the worm
or on the ripeness of the genital products. It occurs in the Mediterranean.[371]
Fig. 162.—Elytra, A, of Polynoë squamata L.; B, of P. clava Mont. × 10. a, Area of
attachment; e, external margin; f, fringe (the letter is at the posterior side of the
elytron); i, internal margin. (From Bourne.)
B. With fifteen pairs of elytra.—P. imbricata L. is probably the commonest
species of the genus, occurring nearly everywhere under stones at low tide. It
is about an inch in length; the elytra are deciduous, and are very variously
coloured and marked; sometimes uniformly grey or even black, sometimes
mottled with brown: in other specimens each elytron has its outer half pale or
white, while its inner half is darker, usually some tint of brown or olive green,
so that the worm appears to have a dark band along the middle of its back.
Other patterns occur. The body is entirely covered by the elytra. The chaetae
project considerably, and are nearly as long as half the width of the body;
those of the notopodium are brown and are directed upwards, being nearly as
long as the golden neuropodial chaetae. This species has a very wide range,
occurring on both sides of the Atlantic, even on the shores of Nova Zembla,
and reappearing again at Japan. P. semisculptus Leach is rather larger than the
foregoing. The elytra are very readily detached: they are light in colour,
without a fringe, but with large papillae near the margin. The notopodial
chaetae are thicker than those of the neuropodium. Several other species are
also common, but P. johnstoni v. Marenz.[372] differs from the rest in having
an elongated body of some seventy segments, so that the posterior half is
uncovered by the elytra, which are small, greenish-grey, speckled, and have no
fringe. It is common and widely distributed, but appears to be only found in
the tubes of Terebella nebulosa.
Page 317
Fig. 163.—Elytron of Polynoë imbricata. a, Area of attachment to body; e, outer border; i,
inner border.
C. With eighteen pairs of elytra.—P. gelatinosa Sars, may attain a length of 2
inches. The elytra are very faintly coloured, transparent and soft, attached by
rather long peduncles. In spirit they become swollen and folded, giving the
worm a very untidy appearance. The prostomium is partly overlapped by a
peculiar collar-like fold of the peristomium.
D. With numerous pairs of elytra.—Lepidasthenia has a very long body,
consisting of more than eighty segments. The elytra are quite small, and occur
throughout the body on the usual segments. There are no notopodial chaetae.
L. elegans Gr. is a very elegantly marked worm, which, however, has not been
recorded from the British area; it occurs in the Mediterranean (see Fig. 156, p.
293).
Sub-Fam. 2. Hermionina.—The body is short, oval and depressed; the
particularly strong notopodial chaetae are directed upwards and backwards so
as to protect the elytra. The neuropodial chaetae are also strong. The
prostomium carries a single tentacle and two long palps; the prostomial ridge
may be well developed. The peristomium is chaetigerous, with long cirri. The
jaws are represented merely by thickened prominences.
Fig. 164.—Aphrodite aculeata L. (from Règne Animal). Nat. size. c, Neuropodial chaetae;
p, palps; 1, iridescent bristles; 2, stiff chaetae; 3, felting bristles of notopodium.
inner border.
C. With eighteen pairs of elytra.—P. gelatinosa Sars, may attain a length of 2
inches. The elytra are very faintly coloured, transparent and soft, attached by
rather long peduncles. In spirit they become swollen and folded, giving the
worm a very untidy appearance. The prostomium is partly overlapped by a
peculiar collar-like fold of the peristomium.
D. With numerous pairs of elytra.—Lepidasthenia has a very long body,
consisting of more than eighty segments. The elytra are quite small, and occur
throughout the body on the usual segments. There are no notopodial chaetae.
L. elegans Gr. is a very elegantly marked worm, which, however, has not been
recorded from the British area; it occurs in the Mediterranean (see Fig. 156, p.
293).
Sub-Fam. 2. Hermionina.—The body is short, oval and depressed; the
particularly strong notopodial chaetae are directed upwards and backwards so
as to protect the elytra. The neuropodial chaetae are also strong. The
prostomium carries a single tentacle and two long palps; the prostomial ridge
may be well developed. The peristomium is chaetigerous, with long cirri. The
jaws are represented merely by thickened prominences.
Fig. 164.—Aphrodite aculeata L. (from Règne Animal). Nat. size. c, Neuropodial chaetae;
p, palps; 1, iridescent bristles; 2, stiff chaetae; 3, felting bristles of notopodium.
Page 318
Aphrodite.—The fifteen pairs of elytra, arranged as in Polynoë, are concealed
by a "felting" of hair-like chitinous threads arising from the notopodium (Fig.
139, p. 268). A. aculeata L.—The "sea-mouse" is one of the most beautiful of
the Polychaetes. The small tentacle is very readily detached; the palps are very
long; the parapodia of the peristomium are directed forwards so as to form
lateral lips; and its cirri are not especially modified (see Fig. 132, p. 260). The
body, which measures 3 to 6 inches, consists of thirty-five to forty segments,
and is broadest in the middle, the last dozen segments being very small; the
body terminates in a point. Some of the notopodial chaetae are brilliantly
iridescent, and give the worm its characteristic coloration. It is fairly common
in the coralline regions, and is frequently thrown ashore after storms. Atlantic
and Mediterranean.
In Hermione the "felt" is absent, so that the elytra are exposed. H. hystrix Sav.
occurs in ten to thirty fathoms of water all over the British area and
Mediterranean. It resembles in its general appearance a fat Polynoid, with
strong chaetae. Laetmonice filicornis Kinb. also occurs on our north-west
coasts, and L. producta Gr. has been dredged in 500 fathoms off the west coast
of Ireland; it has been recorded also from Kerguelen and from Japan, so that it
has a very wide distribution.[373]
Sub-Fam. 3. Acoetina.[374]—The long, vermiform body has some thirty-nine
to ninety-three pairs of elytra, placed on every alternate segment throughout. It
is represented in the British area by Panthalis from 75 fms., which forms a
tube of black mud.
Sub-Fam. 4. Sigalionina.—This sub-family includes forms with a long,
vermiform body; anteriorly the elytra are on alternate segments, up to the
twenty-sixth, and posteriorly on every succeeding segment; "gills" here
coexist with elytra; cirri are absent. The prostomium in Sthenelais Kinb. has a
median tentacle, which is absent in Sigalion Aud. and Edw. Sth. boa Jnstn. is
common off our coasts near low-water mark, where it burrows in the loose
sand with rapidity. It is an elegant worm, and may attain a length of 8 inches,
though it is generally smaller; it is narrow, flat, and only slightly tapering at
each end; the elytra, which may be more than a hundred pairs, are greyish or
slightly brownish, some being lighter than others; the margin is fringed with
simple processes (which in Sigalion are pinnate). Atlantic and Mediterranean.
by a "felting" of hair-like chitinous threads arising from the notopodium (Fig.
139, p. 268). A. aculeata L.—The "sea-mouse" is one of the most beautiful of
the Polychaetes. The small tentacle is very readily detached; the palps are very
long; the parapodia of the peristomium are directed forwards so as to form
lateral lips; and its cirri are not especially modified (see Fig. 132, p. 260). The
body, which measures 3 to 6 inches, consists of thirty-five to forty segments,
and is broadest in the middle, the last dozen segments being very small; the
body terminates in a point. Some of the notopodial chaetae are brilliantly
iridescent, and give the worm its characteristic coloration. It is fairly common
in the coralline regions, and is frequently thrown ashore after storms. Atlantic
and Mediterranean.
In Hermione the "felt" is absent, so that the elytra are exposed. H. hystrix Sav.
occurs in ten to thirty fathoms of water all over the British area and
Mediterranean. It resembles in its general appearance a fat Polynoid, with
strong chaetae. Laetmonice filicornis Kinb. also occurs on our north-west
coasts, and L. producta Gr. has been dredged in 500 fathoms off the west coast
of Ireland; it has been recorded also from Kerguelen and from Japan, so that it
has a very wide distribution.[373]
Sub-Fam. 3. Acoetina.[374]—The long, vermiform body has some thirty-nine
to ninety-three pairs of elytra, placed on every alternate segment throughout. It
is represented in the British area by Panthalis from 75 fms., which forms a
tube of black mud.
Sub-Fam. 4. Sigalionina.—This sub-family includes forms with a long,
vermiform body; anteriorly the elytra are on alternate segments, up to the
twenty-sixth, and posteriorly on every succeeding segment; "gills" here
coexist with elytra; cirri are absent. The prostomium in Sthenelais Kinb. has a
median tentacle, which is absent in Sigalion Aud. and Edw. Sth. boa Jnstn. is
common off our coasts near low-water mark, where it burrows in the loose
sand with rapidity. It is an elegant worm, and may attain a length of 8 inches,
though it is generally smaller; it is narrow, flat, and only slightly tapering at
each end; the elytra, which may be more than a hundred pairs, are greyish or
slightly brownish, some being lighter than others; the margin is fringed with
simple processes (which in Sigalion are pinnate). Atlantic and Mediterranean.
Page 319
In Psammolyce the elytra are covered with sand grains. British and
Mediterranean.
Fam. 4. Phyllodocidae.—The members of this family make use of the
foliaceous cirri (Fig. 136, F) in their very active movements. The rounded
prostomium bears four or five tentacles; there are four long peristomial cirri
on each side (see Fig. 134, E).
Sub-Fam. 1. Phyllodocina.—The body is elongated, with numerous segments;
the eyes are small; the chaetae are jointed; the dorsal and ventral cirri are
foliaceous; the pharynx is covered with papillae externally, but contains no
"jaws."
Phyllodoce has a more or less depressed body; four prostomial tentacles; four
pairs of peristomial cirri. P. lamelligera Jnstn.[375] (the "paddle-worm") may
reach a length of 24 inches, but is usually 8 to 12 inches long and ½ inch
across. The general colour is bright bluish-green or yellowish-green, with
metallic iridescence; the parapodia olive-green or brown, the sensory
processes yellow. It lurks, during day, under stones and shells, etc., in the
Laminarian zone. The green egg masses, so frequently referred to as belonging
to Arenicola, are laid by Phyllodocids.[376]
Fig. 165.—Phyllodoce paretti Blv. × ½. (From Règne Animal.)
In Eulalia an additional (fifth) tentacle arises from the middle of the back of
the prostomium. E. viridis Müll. is a dark green worm smaller than the
preceding; common between tide-marks, hiding in cavities and tunnels in
limestone rocks, which have been bored by the mollusc Saxicava; it is rare
where such rocks are absent. It might have been thought that its vivid colour
would harmonise with its surroundings, but it is most abundant in regions
where Fucus abounds and Ulva is absent. It is evident then that the colour is
not protective; it may perhaps be of warning significance, for the mucus
secreted in quantities by glands on the cirri of the Phyllodocids is probably
Mediterranean.
Fam. 4. Phyllodocidae.—The members of this family make use of the
foliaceous cirri (Fig. 136, F) in their very active movements. The rounded
prostomium bears four or five tentacles; there are four long peristomial cirri
on each side (see Fig. 134, E).
Sub-Fam. 1. Phyllodocina.—The body is elongated, with numerous segments;
the eyes are small; the chaetae are jointed; the dorsal and ventral cirri are
foliaceous; the pharynx is covered with papillae externally, but contains no
"jaws."
Phyllodoce has a more or less depressed body; four prostomial tentacles; four
pairs of peristomial cirri. P. lamelligera Jnstn.[375] (the "paddle-worm") may
reach a length of 24 inches, but is usually 8 to 12 inches long and ½ inch
across. The general colour is bright bluish-green or yellowish-green, with
metallic iridescence; the parapodia olive-green or brown, the sensory
processes yellow. It lurks, during day, under stones and shells, etc., in the
Laminarian zone. The green egg masses, so frequently referred to as belonging
to Arenicola, are laid by Phyllodocids.[376]
Fig. 165.—Phyllodoce paretti Blv. × ½. (From Règne Animal.)
In Eulalia an additional (fifth) tentacle arises from the middle of the back of
the prostomium. E. viridis Müll. is a dark green worm smaller than the
preceding; common between tide-marks, hiding in cavities and tunnels in
limestone rocks, which have been bored by the mollusc Saxicava; it is rare
where such rocks are absent. It might have been thought that its vivid colour
would harmonise with its surroundings, but it is most abundant in regions
where Fucus abounds and Ulva is absent. It is evident then that the colour is
not protective; it may perhaps be of warning significance, for the mucus
secreted in quantities by glands on the cirri of the Phyllodocids is probably
Page 320
objectionable to their enemies. Phalacrophorus Grf. and Pontodora Grf. may
be mentioned as pelagic genera.
Sub-Fam. 2. Lopadorhynchina.—This includes small forms, Lopadorhynchus
Gr., Pelagobia Grf., and other pelagic genera.
Fig. 166.—Nauphanta celox R. Grf. × 4. (From Greef.) e, The large eye.
Sub-Fam. 3. Alciopina.—These are surface forms, and, like most pelagic
animals, are colourless and transparent; the eyes, however, are very large, and,
with certain brown spots in each segment,[377] are the only coloured parts in
the body; in structure the eyes are much more complicated than those of other
Polychaetes. The prostomium has five tentacles; there are long peristomial
cirri, and in general their anatomy agrees most closely with that of
Phyllodocids. Alciope, Asterope, Vanadis, Nauphanta are genera of the family;
[378]
none have been recorded from the British area.
Fam. 5. Tomopteridae.[379]—This includes but one genus, Tomopteris, which is
pelagic. The transparent, colourless body consists of only a few (eighteen to
twenty) segments; the parapodia are as long as the body is wide, and carry no
chaetae; each is bilobed, and fringed with a membrane; each of these lobes
contains a yellow rosette-shaped photogenic organ. The only chaetae present
in the worm are on the "head." The prostomium is hammer-shaped, and
appears to carry a pair of short filaments ventrally (Fig. 167, x) each with a
single chaeta within it; and a longer filament laterally (y), supported by a long,
very delicate chaeta. The mouth is behind these, and they probably are the first
pair of parapodia which have shifted forwards. T. onisciformis Eschscholtz is
not unfrequently obtained off our shores in the tow-net.
be mentioned as pelagic genera.
Sub-Fam. 2. Lopadorhynchina.—This includes small forms, Lopadorhynchus
Gr., Pelagobia Grf., and other pelagic genera.
Fig. 166.—Nauphanta celox R. Grf. × 4. (From Greef.) e, The large eye.
Sub-Fam. 3. Alciopina.—These are surface forms, and, like most pelagic
animals, are colourless and transparent; the eyes, however, are very large, and,
with certain brown spots in each segment,[377] are the only coloured parts in
the body; in structure the eyes are much more complicated than those of other
Polychaetes. The prostomium has five tentacles; there are long peristomial
cirri, and in general their anatomy agrees most closely with that of
Phyllodocids. Alciope, Asterope, Vanadis, Nauphanta are genera of the family;
[378]
none have been recorded from the British area.
Fam. 5. Tomopteridae.[379]—This includes but one genus, Tomopteris, which is
pelagic. The transparent, colourless body consists of only a few (eighteen to
twenty) segments; the parapodia are as long as the body is wide, and carry no
chaetae; each is bilobed, and fringed with a membrane; each of these lobes
contains a yellow rosette-shaped photogenic organ. The only chaetae present
in the worm are on the "head." The prostomium is hammer-shaped, and
appears to carry a pair of short filaments ventrally (Fig. 167, x) each with a
single chaeta within it; and a longer filament laterally (y), supported by a long,
very delicate chaeta. The mouth is behind these, and they probably are the first
pair of parapodia which have shifted forwards. T. onisciformis Eschscholtz is
not unfrequently obtained off our shores in the tow-net.
Page 321
Fig. 167.—Tomopteris rolasi Grf. × 10. From Guinea Isles. pr, Hammer-shaped
prostomium; x, first chaetigerous process; y, second chaetigerous process; c, rosette
(photogenic) organ on first two parapodia; b, similar organ in the lobes of the
following parapodia; d, pigment spots; f, parapodium. (From Greef.)
Fam. 6. Nereidae (Lycoridae).—This family contains a very large number of
species, differing from one another in small and not readily recognisable
characters, such as the relative lengths of the various processes of the head, of
the lobes of the feet, the arrangement of the "paragnaths" (see Fig. 125, d) and
so forth. The general features of the family have been already described. The
genus Nereis is represented by six fairly common species on our coast, which
are almost world-wide in distribution.
N. diversicolor Müll. is about 3 to 4 inches in length, of a general fleshy-red
colour, though tending in some cases to yellowish-brown or even greenish. It
may be distinguished by two diverging brown bands, which start on the
peristomium and pass backward one along each side of the body for several
segments. The prostomium is broader than it is long. The worm burrows in
mud or sand, all round our coast between tide-marks. It has a very wide
distribution, being met with on this side of the Atlantic, and off the coast of
Greenland, and off Japan. It is even found in brackish water at Bembridge, Isle
of Wight.
N. cultrifera Gr. is green or greenish-grey, with a series of small rectangular
light spots along the mid-dorsal surface, and oblique light lines at the sides of
each segment. Posteriorly the greenish pigment becomes less and less till the
hinder segments are flesh-coloured. The prostomium is as long as it is broad.
This species attains a length of 6 inches. Southern coasts: locally known as
"Red Cat."
prostomium; x, first chaetigerous process; y, second chaetigerous process; c, rosette
(photogenic) organ on first two parapodia; b, similar organ in the lobes of the
following parapodia; d, pigment spots; f, parapodium. (From Greef.)
Fam. 6. Nereidae (Lycoridae).—This family contains a very large number of
species, differing from one another in small and not readily recognisable
characters, such as the relative lengths of the various processes of the head, of
the lobes of the feet, the arrangement of the "paragnaths" (see Fig. 125, d) and
so forth. The general features of the family have been already described. The
genus Nereis is represented by six fairly common species on our coast, which
are almost world-wide in distribution.
N. diversicolor Müll. is about 3 to 4 inches in length, of a general fleshy-red
colour, though tending in some cases to yellowish-brown or even greenish. It
may be distinguished by two diverging brown bands, which start on the
peristomium and pass backward one along each side of the body for several
segments. The prostomium is broader than it is long. The worm burrows in
mud or sand, all round our coast between tide-marks. It has a very wide
distribution, being met with on this side of the Atlantic, and off the coast of
Greenland, and off Japan. It is even found in brackish water at Bembridge, Isle
of Wight.
N. cultrifera Gr. is green or greenish-grey, with a series of small rectangular
light spots along the mid-dorsal surface, and oblique light lines at the sides of
each segment. Posteriorly the greenish pigment becomes less and less till the
hinder segments are flesh-coloured. The prostomium is as long as it is broad.
This species attains a length of 6 inches. Southern coasts: locally known as
"Red Cat."
Page 322
N. dumerilii Aud. and Edw. is rather smaller and narrower than the two
preceding species; it is reddish-violet in colour, marked with darker transverse
lines in each segment. It is readily recognised by the two dark brown spots on
the upper surface of the base of the notopodium in most of the segments, and
by the great length of the peristomial cirri, the longest of which reaches the
fifteenth segment. It is sometimes found enclosed in a cocoon-like tube of
hardened grey mucus, more or less covered with foreign particles, such as
sand grains. Atlantic, Mediterranean, Japan.
Fig. 168.—Nereis cultrifera Gr. × 6. Head with buccal region everted, to show the
arrangement of the jaws. (From Ehlers.) Cf. N. diversicolor, Fig. 125, p. 248.
N. pelagica L. is red-brown or bronze in colour, and is generally larger than
the other species, from which it is distinguished by being widest about the
middle of the body (see Fig. 122, p. 246); whilst in the preceding species the
greatest breadth occurs at the segments immediately following the head.
Further, the palps are long, the peristomium is twice as long as the next
segment, and the back of the worm is strongly arched. At all depths on rocky
and stony ground. Northern coasts.
N. (Nereilepas) fucata Sav. lives in the topmost whorls of empty whelk shells
and in those occupied by hermit crabs. The ground colour is tile-red, with two
milk-white bands along the dorsal surface. The dorsal lobe of the foot is
slightly foliaceous, glandular, and vascular.
N. (Alitta) virens Sars. is a giant amongst Polychaetes, reaching a length of 18
inches. Its name suggests its colour; it is very plentiful at certain times at St.
Andrews, and between tide-marks along the shore of the Mersey estuary, as
well as elsewhere. It forms a burrow in the clay, etc., of the shore, and lines it
with mucus, which is abundantly secreted by the great foliaceous lobes of the
parapodia. These great leaf-like lobes of the foot recall the modification which
the foot of many species of Nereis undergoes in transformation into
Heteronereis: they are so greatly developed that, at first sight, the worm might
be mistaken for a large Phyllodoce. The worm is known as the "Creeper," and
is much esteemed as bait on some parts of our coast.
preceding species; it is reddish-violet in colour, marked with darker transverse
lines in each segment. It is readily recognised by the two dark brown spots on
the upper surface of the base of the notopodium in most of the segments, and
by the great length of the peristomial cirri, the longest of which reaches the
fifteenth segment. It is sometimes found enclosed in a cocoon-like tube of
hardened grey mucus, more or less covered with foreign particles, such as
sand grains. Atlantic, Mediterranean, Japan.
Fig. 168.—Nereis cultrifera Gr. × 6. Head with buccal region everted, to show the
arrangement of the jaws. (From Ehlers.) Cf. N. diversicolor, Fig. 125, p. 248.
N. pelagica L. is red-brown or bronze in colour, and is generally larger than
the other species, from which it is distinguished by being widest about the
middle of the body (see Fig. 122, p. 246); whilst in the preceding species the
greatest breadth occurs at the segments immediately following the head.
Further, the palps are long, the peristomium is twice as long as the next
segment, and the back of the worm is strongly arched. At all depths on rocky
and stony ground. Northern coasts.
N. (Nereilepas) fucata Sav. lives in the topmost whorls of empty whelk shells
and in those occupied by hermit crabs. The ground colour is tile-red, with two
milk-white bands along the dorsal surface. The dorsal lobe of the foot is
slightly foliaceous, glandular, and vascular.
N. (Alitta) virens Sars. is a giant amongst Polychaetes, reaching a length of 18
inches. Its name suggests its colour; it is very plentiful at certain times at St.
Andrews, and between tide-marks along the shore of the Mersey estuary, as
well as elsewhere. It forms a burrow in the clay, etc., of the shore, and lines it
with mucus, which is abundantly secreted by the great foliaceous lobes of the
parapodia. These great leaf-like lobes of the foot recall the modification which
the foot of many species of Nereis undergoes in transformation into
Heteronereis: they are so greatly developed that, at first sight, the worm might
be mistaken for a large Phyllodoce. The worm is known as the "Creeper," and
is much esteemed as bait on some parts of our coast.
Page 323
Fig. 169.—Parapodium of N. virens Sars. ×4. a, Notopodial cirrus; b, notopodium; c,
neuropodium; d, neuropodial cirrus; l, foliaceous appendage. (From Ehlers.)
Fam. 7. Nephthydidae.—The elongated body is quadrangular in section, the
dorsal and ventral surfaces being almost flat. (For head see p. 262, and for
parapodium, p. 264.) The two lobes of the parapodium are widely separated,
and each is fringed with a membrane, while a sickle-shaped "gill" hangs down
from the under surface of the notopodium. The pharynx is enormous. Of the
genus Nephthys two species, called the "Lurg" or "White Cat" by fishermen,
occur on our coasts. Their active movements and beautiful mother-of-pearl tint
are characteristic. N. hombergii Aud. and Edw. occurs on the shore, and down
to 20 fathoms; it is 3 or 4 inches long, and may be found burrowing in the
sand; the chaetae exceed in length those of N. caeca Fabricius, which occurs
less frequently and in deeper water, and is larger than the preceding. Both are
Atlantic forms.
Fam. 8. Amphinomidae.—The body in this family is either vermiform, as in
Eurythoe, or oval and flattened, as in Euphrosyne and Spinther. The head
carries a peculiar sense organ, the "caruncle," consisting of a smooth axis with
the sides folded so as to look like a number of lamellae. The parapodia carry
gills. Most of the Amphinomids are tropical and Southern forms.
Eurythoe borealis Oerst. measuring 6 inches, occurs all round the British area,
from the Shetlands, where it occurs in deep water, to the Channel Isles, where
it lives on shore, under stones, etc. (For parapodium of Amphinome see p.
264.)
Euphrosyne.—The body is short, oval, and flattened. The parapodia are not
distinct processes, but the chaetae extend from each side of each segment
nearly to the middle dorsal line, and are absent ventrally (Fig. 137, C, p. 265).
The dorsal and ventral cirri are more or less filiform, and there is an
intermediate similar process on the back (? = lip of chaetigerous sac).
Amongst the chaetae are a number of curious branched processes—usually
called "gills."[380] The presence of these and of the chaetae give the upper
neuropodium; d, neuropodial cirrus; l, foliaceous appendage. (From Ehlers.)
Fam. 7. Nephthydidae.—The elongated body is quadrangular in section, the
dorsal and ventral surfaces being almost flat. (For head see p. 262, and for
parapodium, p. 264.) The two lobes of the parapodium are widely separated,
and each is fringed with a membrane, while a sickle-shaped "gill" hangs down
from the under surface of the notopodium. The pharynx is enormous. Of the
genus Nephthys two species, called the "Lurg" or "White Cat" by fishermen,
occur on our coasts. Their active movements and beautiful mother-of-pearl tint
are characteristic. N. hombergii Aud. and Edw. occurs on the shore, and down
to 20 fathoms; it is 3 or 4 inches long, and may be found burrowing in the
sand; the chaetae exceed in length those of N. caeca Fabricius, which occurs
less frequently and in deeper water, and is larger than the preceding. Both are
Atlantic forms.
Fam. 8. Amphinomidae.—The body in this family is either vermiform, as in
Eurythoe, or oval and flattened, as in Euphrosyne and Spinther. The head
carries a peculiar sense organ, the "caruncle," consisting of a smooth axis with
the sides folded so as to look like a number of lamellae. The parapodia carry
gills. Most of the Amphinomids are tropical and Southern forms.
Eurythoe borealis Oerst. measuring 6 inches, occurs all round the British area,
from the Shetlands, where it occurs in deep water, to the Channel Isles, where
it lives on shore, under stones, etc. (For parapodium of Amphinome see p.
264.)
Euphrosyne.—The body is short, oval, and flattened. The parapodia are not
distinct processes, but the chaetae extend from each side of each segment
nearly to the middle dorsal line, and are absent ventrally (Fig. 137, C, p. 265).
The dorsal and ventral cirri are more or less filiform, and there is an
intermediate similar process on the back (? = lip of chaetigerous sac).
Amongst the chaetae are a number of curious branched processes—usually
called "gills."[380] The presence of these and of the chaetae give the upper
Page 324
surface of the body a fluffy appearance. E. foliosa Aud. and Edw. is fairly
common under stones on our southern shores. It is about an inch in length and
is of a cinnamon-red colour.
Fam. 9. Eunicidae.—The elongated body is provided with parapodial gills in
more or fewer segments (except in Lumbriconereis). The "gills" may be
cirriform (Hyalinoecia), pectinate (Eunice, Onuphis), or more complex
(Diopatra). The notopodium is represented by a lobe (usually called "cirrus")
into which an aciculum projects; in some cases it even contains a few chaetae;
most of the neuropodial chaetae are jointed (Fig. 138, F). The prostomial
tentacles vary in number; they may be three or five, or five and two short
"frontal palps," or they may be absent. Peristomial cirri are absent, though in
Eunice, Diopatra, and Onuphis "nuchal cirri" are present on the dorsal surface
of the second segment (Fig. 134, D). One of the most characteristic features in
the anatomy of the Eunicids is the peculiar jaw apparatus (see p. 270). The
majority of the genera form permanent tubes of parchment-like consistency,
which may be further strengthened by the addition of grains of sand, small
pebbles, etc.; the tubes may be branched.
Eunice has five tentacles, two great palps, and a pair of nuchal cirri; the gills
are pectinate, and there are four anal cirri. E. harassii Aud. and Edw. is about
8 inches long. It is reddish-brown, with white spots down the back, one to
each segment, and others at the sides. The gills begin at the sixth segment, and
when fully developed have eleven branches. The dorsal cirrus is not longer
than the gill. E. philocorallia Buch.[381] forms its tube amongst the branches
of Lophohelia prolifera, in 200 fathoms, off the west coast of Ireland.
Marphysa resembles Eunice, but has no nuchal cirri. M. sanguinea Mont. is a
fine bronze colour, with bright red gills, which commence on the twentieth
segment, and have only four or five branches. The worm, which measures 12
to 18 inches, and is as thick as one's finger, hides in clefts in rocks and under
stones below low water. Mediterranean. It is known as "Rockworm" in the
Channel Islands.
Hyalinoecia Mgrn., in addition to the five prostomial tentacles and palps,
possesses a pair of small "frontal palps" arising from the anterior border of the
prostomium; there are no nuchal cirri, and the gills are simple filiform
common under stones on our southern shores. It is about an inch in length and
is of a cinnamon-red colour.
Fam. 9. Eunicidae.—The elongated body is provided with parapodial gills in
more or fewer segments (except in Lumbriconereis). The "gills" may be
cirriform (Hyalinoecia), pectinate (Eunice, Onuphis), or more complex
(Diopatra). The notopodium is represented by a lobe (usually called "cirrus")
into which an aciculum projects; in some cases it even contains a few chaetae;
most of the neuropodial chaetae are jointed (Fig. 138, F). The prostomial
tentacles vary in number; they may be three or five, or five and two short
"frontal palps," or they may be absent. Peristomial cirri are absent, though in
Eunice, Diopatra, and Onuphis "nuchal cirri" are present on the dorsal surface
of the second segment (Fig. 134, D). One of the most characteristic features in
the anatomy of the Eunicids is the peculiar jaw apparatus (see p. 270). The
majority of the genera form permanent tubes of parchment-like consistency,
which may be further strengthened by the addition of grains of sand, small
pebbles, etc.; the tubes may be branched.
Eunice has five tentacles, two great palps, and a pair of nuchal cirri; the gills
are pectinate, and there are four anal cirri. E. harassii Aud. and Edw. is about
8 inches long. It is reddish-brown, with white spots down the back, one to
each segment, and others at the sides. The gills begin at the sixth segment, and
when fully developed have eleven branches. The dorsal cirrus is not longer
than the gill. E. philocorallia Buch.[381] forms its tube amongst the branches
of Lophohelia prolifera, in 200 fathoms, off the west coast of Ireland.
Marphysa resembles Eunice, but has no nuchal cirri. M. sanguinea Mont. is a
fine bronze colour, with bright red gills, which commence on the twentieth
segment, and have only four or five branches. The worm, which measures 12
to 18 inches, and is as thick as one's finger, hides in clefts in rocks and under
stones below low water. Mediterranean. It is known as "Rockworm" in the
Channel Islands.
Hyalinoecia Mgrn., in addition to the five prostomial tentacles and palps,
possesses a pair of small "frontal palps" arising from the anterior border of the
prostomium; there are no nuchal cirri, and the gills are simple filiform
Page 325
processes. H. tubicola Müll., about 3 inches long, is yellowish-brown, and
forms a transparent, parchment-like tube. Atlantic and Mediterranean.
Fig. 170.—Ophryotrocha puerilis Clap., Metsch. × 25. ci, Bands of cilia; cp, ciliated pit
(nuchal organ); J, jaws. (From Korschelt.)
Onuphis Oerst. has a head like the preceding, from which it differs in having
pectinated gills and two nuchal cirri like Eunice. In making its tube it employs
small pebbles, bits of shell, and even echinid spines, which it glues together
with mucus, so that it bears a general resemblance to its surroundings. O.
conchylega Sars, has a flattened, scabbard-like tube, which can be carried
about by its owner. Atlantic.
Lumbriconereis has a more or less conical prostomium, without any tentacles,
but with large palps: segments without gills. L. fragilis Müll. is reddish or
brownish, with a beautiful iridescence; it is cylindrical, very narrow, and some
5 or 6 inches long; L. tricolor Jnstn. is much larger.
Ophryotrocha (Fig. 170) is a small form often occurring in aquaria; it is
chiefly remarkable for the possession of segmentally-arranged girdles of cilia
—a permanent larval feature. Lysidice ninetta Aud. and Edw. belongs here.
Fam. 10. Glyceridae.—Elongated worms with numerous segments. The
prostomium, though narrow, is long, conical, annulated, and carries at its apex
four very small tentacles; at its base a pair of palps. Special retractile gills are
present. The armed pharynx is very long, and when protruded appears wider
than the animal. The members of this family are without any system of blood-
forms a transparent, parchment-like tube. Atlantic and Mediterranean.
Fig. 170.—Ophryotrocha puerilis Clap., Metsch. × 25. ci, Bands of cilia; cp, ciliated pit
(nuchal organ); J, jaws. (From Korschelt.)
Onuphis Oerst. has a head like the preceding, from which it differs in having
pectinated gills and two nuchal cirri like Eunice. In making its tube it employs
small pebbles, bits of shell, and even echinid spines, which it glues together
with mucus, so that it bears a general resemblance to its surroundings. O.
conchylega Sars, has a flattened, scabbard-like tube, which can be carried
about by its owner. Atlantic.
Lumbriconereis has a more or less conical prostomium, without any tentacles,
but with large palps: segments without gills. L. fragilis Müll. is reddish or
brownish, with a beautiful iridescence; it is cylindrical, very narrow, and some
5 or 6 inches long; L. tricolor Jnstn. is much larger.
Ophryotrocha (Fig. 170) is a small form often occurring in aquaria; it is
chiefly remarkable for the possession of segmentally-arranged girdles of cilia
—a permanent larval feature. Lysidice ninetta Aud. and Edw. belongs here.
Fam. 10. Glyceridae.—Elongated worms with numerous segments. The
prostomium, though narrow, is long, conical, annulated, and carries at its apex
four very small tentacles; at its base a pair of palps. Special retractile gills are
present. The armed pharynx is very long, and when protruded appears wider
than the animal. The members of this family are without any system of blood-
Page 326
vessels, but the coelomic corpuscles are coloured red. Glycera has four jaws,
the parapodia are all alike (Fig. 136, C). G. capitata Oerst. is 2 or 3 inches in
length, is yellowish in colour, with a dark-red median line. It may be found
burrowing in sand. The setigerous lobes of each foot are coalesced to form one
large lobe with pointed apex. The dorsal cirrus is a small wart above the base
of the foot. Atlantic and Mediterranean. A second species, which is much
larger and flesh-coloured, also occurs.
Fig. 171.—Glycera meckelii Aud. and Edw. with pharynx everted, × 1. (Règne Animal.)
Goniada is distinguished from the preceding by the fact that the parapodia
suddenly change in size and character at about one-third the length of the
body. The pharynx has numerous paragnaths. G. maculata Oerst. occurs off
our coasts.
Fam. 11. Sphaerodoridae.—The dorsal and ventral cirri of each segment are
spherical. The chaetae are usually jointed, and there is an aciculum to each
parapodium. Ephesia Rthke. (E. gracilis R. = Sphaerodorum peripatus Jnstn.)
is exceptional in having unjointed chaetae. North Sea, Arctic Ocean, and the
Channel. The family, which is much modified, is allied in some respects to the
Syllidae.
Fam. 12. Ariciidae.—These worms burrow in sand between tide-marks. The
body consists of many short segments, and is nearly cylindrical. The
the parapodia are all alike (Fig. 136, C). G. capitata Oerst. is 2 or 3 inches in
length, is yellowish in colour, with a dark-red median line. It may be found
burrowing in sand. The setigerous lobes of each foot are coalesced to form one
large lobe with pointed apex. The dorsal cirrus is a small wart above the base
of the foot. Atlantic and Mediterranean. A second species, which is much
larger and flesh-coloured, also occurs.
Fig. 171.—Glycera meckelii Aud. and Edw. with pharynx everted, × 1. (Règne Animal.)
Goniada is distinguished from the preceding by the fact that the parapodia
suddenly change in size and character at about one-third the length of the
body. The pharynx has numerous paragnaths. G. maculata Oerst. occurs off
our coasts.
Fam. 11. Sphaerodoridae.—The dorsal and ventral cirri of each segment are
spherical. The chaetae are usually jointed, and there is an aciculum to each
parapodium. Ephesia Rthke. (E. gracilis R. = Sphaerodorum peripatus Jnstn.)
is exceptional in having unjointed chaetae. North Sea, Arctic Ocean, and the
Channel. The family, which is much modified, is allied in some respects to the
Syllidae.
Fam. 12. Ariciidae.—These worms burrow in sand between tide-marks. The
body consists of many short segments, and is nearly cylindrical. The
Page 327
prostomium is more or less pointed; the chaetae are all capillary; in the first
few segments they project laterally but soon come to lie dorsally, and are
carried by slight conical papillae (supported by acicula), which are longer in
the middle of the body. Most of the segments carry filiform "gills,"
representing the dorsal cirri (Fig. 137, B).
Scoloplos armiger Müll. is extremely common on our coast. It is about an inch
long, yellowish, with red gills, commencing about the twelfth segment. Each
of the lobes of the parapodium possesses an aciculum, and the chaetae are bent
in a peculiar way. The everted buccal region has the form of a six- or eight-
rayed star. The spawn of this species may be found on the shore in spring as
brown, pear-shaped, jelly-like masses, each with a long stalk, by which the
mass is fixed to the sand. In the jelly are the eggs, which may be watched
passing through the earlier stages of development. Atlantic on both shores,
even off Spitzbergen, and Nova Zembla. Another representative is Theodisca
mamillata Clap., which occurs amongst the roots of Laminaria.
Fam. 13. Typhloscolecidae.[382]—Pelagic, greatly modified forms, apparently
related to the Phyllodocidae, but with very uncertain affinities. The
prostomium is pointed and carries a pair of foliaceous tentacles; each of the
first two segments bears a pair of foliaceous cirri; the remaining segments
possess a dorsal and a ventral pair of foliaceous cirri, with a small bunch of
chaetae and a single aciculum. All the cirri have peculiar rod-cells.
Typhloscolex Busch, Sagitella Wagner, and Travisiopsis Uljanin: all small
worms. North Sea Atlantic.
Sub-Order 2. Spioniformia.
Fam. 1. Spionidae.—Mostly small worms, with small ridge-like prostomium
carrying a pair of eyes, but no tentacles or palps. The peristomium, which
extends forwards on each side of the prostomium, bears a pair of very long
cirri (usually termed "tentacles") normally directed backwards, very mobile,
and more or less coiled. They are readily thrown off by the animal. The
notopodial cirri are long, finger-shaped, and curved over the back; they are
vascular and ciliated, and function as "gills." The neuropodia project laterally.
Both are usually provided with a "podal membrane" along their outer margin.
There are no ventral cirri; the dorsal chaetae are fringed capillaries; the ventral
few segments they project laterally but soon come to lie dorsally, and are
carried by slight conical papillae (supported by acicula), which are longer in
the middle of the body. Most of the segments carry filiform "gills,"
representing the dorsal cirri (Fig. 137, B).
Scoloplos armiger Müll. is extremely common on our coast. It is about an inch
long, yellowish, with red gills, commencing about the twelfth segment. Each
of the lobes of the parapodium possesses an aciculum, and the chaetae are bent
in a peculiar way. The everted buccal region has the form of a six- or eight-
rayed star. The spawn of this species may be found on the shore in spring as
brown, pear-shaped, jelly-like masses, each with a long stalk, by which the
mass is fixed to the sand. In the jelly are the eggs, which may be watched
passing through the earlier stages of development. Atlantic on both shores,
even off Spitzbergen, and Nova Zembla. Another representative is Theodisca
mamillata Clap., which occurs amongst the roots of Laminaria.
Fam. 13. Typhloscolecidae.[382]—Pelagic, greatly modified forms, apparently
related to the Phyllodocidae, but with very uncertain affinities. The
prostomium is pointed and carries a pair of foliaceous tentacles; each of the
first two segments bears a pair of foliaceous cirri; the remaining segments
possess a dorsal and a ventral pair of foliaceous cirri, with a small bunch of
chaetae and a single aciculum. All the cirri have peculiar rod-cells.
Typhloscolex Busch, Sagitella Wagner, and Travisiopsis Uljanin: all small
worms. North Sea Atlantic.
Sub-Order 2. Spioniformia.
Fam. 1. Spionidae.—Mostly small worms, with small ridge-like prostomium
carrying a pair of eyes, but no tentacles or palps. The peristomium, which
extends forwards on each side of the prostomium, bears a pair of very long
cirri (usually termed "tentacles") normally directed backwards, very mobile,
and more or less coiled. They are readily thrown off by the animal. The
notopodial cirri are long, finger-shaped, and curved over the back; they are
vascular and ciliated, and function as "gills." The neuropodia project laterally.
Both are usually provided with a "podal membrane" along their outer margin.
There are no ventral cirri; the dorsal chaetae are fringed capillaries; the ventral
Page 328
are "crotchets." The buccal region is eversible. The worms burrow in mud and
sand.
Spio seticornis Fabr. is a small worm less than an inch in length, colourless
except for the red blood in its vessels. It builds long and flexible tubes of sand
in the clefts of rocks and under stones in the upper part of the littoral zone.
The prostomium is notched at the anterior margin. The gills commence on the
twelfth segment, and do not extend to the end of the body. A membrane-like
cirrus exists also on the second chaetigerous segment. The podal membrane is
adnate to the gill throughout its extent. Four short anal cirri occur. Greenland
and Scandinavia.
Fig. 172.—Nerine vulgaris Jnstn., enlarged. (From Cunningham.) a, Prostomium; c1,
cirrus of peristomium; c2, "gill"; l, lobes; m, podal membrane; I, peristomium; II,
III, IV, following segments.
Nerine is represented by two species, sometimes called "Ragworms." The
genus is very similar to Spio, but the worms are of larger size. The
prostomium is compressed by the forward growth of the peristomium, and
appears as a ridge on the latter segment, extending downwards in front
towards the mouth. The "gills" commence on the second segment, and are
continued in every segment except the hindmost. Nerine (Scolecolepis)
vulgaris Jnstn. is readily distinguished from other species by its somewhat T-
shaped prostomium. It is an extremely common worm under stones and
amongst seaweed at low water. It is some 3 or 4 inches in length and more
slender than the following species. Its colour is yellowish-brown, and the red
gills directed upwards and backwards give the appearance of oblique red lines.
The podal membrane does not reach the tip of the gill. North Atlantic. It is said
to ascend rivers and live in brackish water. N. coniocephala Jnstn. is much the
same colour, but reaches a length of 8 inches, and a diameter of ¼ inch. The
prostomium is conical. The podal membrane reaches to the tip of the gill in the
anterior segments. The worm burrows rather more deeply and nearer low-
water mark than the preceding species.
sand.
Spio seticornis Fabr. is a small worm less than an inch in length, colourless
except for the red blood in its vessels. It builds long and flexible tubes of sand
in the clefts of rocks and under stones in the upper part of the littoral zone.
The prostomium is notched at the anterior margin. The gills commence on the
twelfth segment, and do not extend to the end of the body. A membrane-like
cirrus exists also on the second chaetigerous segment. The podal membrane is
adnate to the gill throughout its extent. Four short anal cirri occur. Greenland
and Scandinavia.
Fig. 172.—Nerine vulgaris Jnstn., enlarged. (From Cunningham.) a, Prostomium; c1,
cirrus of peristomium; c2, "gill"; l, lobes; m, podal membrane; I, peristomium; II,
III, IV, following segments.
Nerine is represented by two species, sometimes called "Ragworms." The
genus is very similar to Spio, but the worms are of larger size. The
prostomium is compressed by the forward growth of the peristomium, and
appears as a ridge on the latter segment, extending downwards in front
towards the mouth. The "gills" commence on the second segment, and are
continued in every segment except the hindmost. Nerine (Scolecolepis)
vulgaris Jnstn. is readily distinguished from other species by its somewhat T-
shaped prostomium. It is an extremely common worm under stones and
amongst seaweed at low water. It is some 3 or 4 inches in length and more
slender than the following species. Its colour is yellowish-brown, and the red
gills directed upwards and backwards give the appearance of oblique red lines.
The podal membrane does not reach the tip of the gill. North Atlantic. It is said
to ascend rivers and live in brackish water. N. coniocephala Jnstn. is much the
same colour, but reaches a length of 8 inches, and a diameter of ¼ inch. The
prostomium is conical. The podal membrane reaches to the tip of the gill in the
anterior segments. The worm burrows rather more deeply and nearer low-
water mark than the preceding species.
Page 329
Fam. 2. Polydoridae.—Polydora Bosc (= Leucodore Jnstn.) is readily
distinguished from the other Spionids, and, indeed, from any other Polychaet
(except Chaetopterus), by possessing specially strong chaetae in the enlarged
fifth chaetigerous segment. The anterior segments differ from the rest in the
absence of gills and in the character of the chaetae (Fig. 133, A, p. 261).
P. ciliata Jnstn. inhabits soft mud tubes near low water; it also makes U-
shaped galleries in stones and shells, and the tube projects from each mouth.
The worm is about ½ inch long, consists of some forty segments, and is
yellowish or flesh-coloured. The prostomium resembles that of Spio; the
peristomium is raised into a slight collar at each side. The anus is surrounded
by an incomplete funnel. The species has almost a world-wide distribution,
having been recorded from Iceland, Australia, the Philippine Islands, as well
as from the European seas. P. coeca Oerst. often lives commensally with a
sponge, having a protective odour.
Fam. 3. Chaetopteridae.—The family is represented on our coasts by
Chaetopterus variopedatus Ren.,[383] which is found at the Channel Islands,
the Scilly Isles, the Isle of Man, and the west Scottish coast, and probably at
various other places, at low water and down to a depth of some 15 fathoms. It
occurs in all European seas. The animal builds a long tube, the basis of which
is a tough, parchment-like substance; this is coated externally with sand, small
pebbles, and other débris: it is of considerable length and about ¾ inch in
diameter, is U-shaped and open at both ends, the greater part of it being
embedded in sand or in crevices of rocks. The animal, whose body-wall is thin
and delicate, never leaves its tube. The body has a bizarre appearance; three
regions are readily distinguishable, which may be denoted by the letters A, B,
and C. The most anterior region, A, is flattened, and carries nine pairs of
conical lobes with delicate chaetae, though the fourth lobe possesses special
stouter chaetae (as in Polydora). The anterior end of the body terminates in a
wide funnel, the boundary of which is formed chiefly by the peristomium; on
its dorsal surface is a pair of tentacle-like processes (peristomial cirri); the
region between which represents the prostomium.
distinguished from the other Spionids, and, indeed, from any other Polychaet
(except Chaetopterus), by possessing specially strong chaetae in the enlarged
fifth chaetigerous segment. The anterior segments differ from the rest in the
absence of gills and in the character of the chaetae (Fig. 133, A, p. 261).
P. ciliata Jnstn. inhabits soft mud tubes near low water; it also makes U-
shaped galleries in stones and shells, and the tube projects from each mouth.
The worm is about ½ inch long, consists of some forty segments, and is
yellowish or flesh-coloured. The prostomium resembles that of Spio; the
peristomium is raised into a slight collar at each side. The anus is surrounded
by an incomplete funnel. The species has almost a world-wide distribution,
having been recorded from Iceland, Australia, the Philippine Islands, as well
as from the European seas. P. coeca Oerst. often lives commensally with a
sponge, having a protective odour.
Fam. 3. Chaetopteridae.—The family is represented on our coasts by
Chaetopterus variopedatus Ren.,[383] which is found at the Channel Islands,
the Scilly Isles, the Isle of Man, and the west Scottish coast, and probably at
various other places, at low water and down to a depth of some 15 fathoms. It
occurs in all European seas. The animal builds a long tube, the basis of which
is a tough, parchment-like substance; this is coated externally with sand, small
pebbles, and other débris: it is of considerable length and about ¾ inch in
diameter, is U-shaped and open at both ends, the greater part of it being
embedded in sand or in crevices of rocks. The animal, whose body-wall is thin
and delicate, never leaves its tube. The body has a bizarre appearance; three
regions are readily distinguishable, which may be denoted by the letters A, B,
and C. The most anterior region, A, is flattened, and carries nine pairs of
conical lobes with delicate chaetae, though the fourth lobe possesses special
stouter chaetae (as in Polydora). The anterior end of the body terminates in a
wide funnel, the boundary of which is formed chiefly by the peristomium; on
its dorsal surface is a pair of tentacle-like processes (peristomial cirri); the
region between which represents the prostomium.
Page 330
Fig. 173.—Chaetopterus. (From Panceri.) Natural size of a young specimen. A is the
anterior region of the body; B, the middle region; C, the hinder region. c,
Peristomial cirri; d, "sucker"; e, the great "wings"; f, the first of the three "fans"; m,
mouth.
The second region, B, is very curiously modified; it is formed of five
segments. The most anterior is produced on either side into a great wing-like
process, which in life is directed forwards above the region A. Each is grooved
on its inner side, the ciliated grooves being continuous with a median groove
running forwards along the back of A; this apparatus serves to bring food to
the great funnel-like mouth. The next segment (twelfth) carries a dorsal and
ventral "sucker," representing the parapodia. Each of the segments 13, 14, 15
carries a membranous fold encircling the body. By the constant movement of
these "fans," which have nearly the same diameter as the tube, a current of
water is constantly washed over the animal. The fans represent the notopodia;
the neuropodia are bilobed rounded knobs. The region C consists in the adult
of about thirty segments, all alike, and less modified than the preceding. The
animal is the most truly tubicolous of the Polychaetes, and is much modified
on this account. No locomotor chaetae are present, though the great wings and
notopodial processes of region C contains chitinous bristles, which, however,
do not project;[384] the anterior region with its stiff chaetae, and the
neuropodial uncinal plates of the rest of the body serve in its movements up
and down the tube, while the "suckers" fix the worm temporarily to the wall of
its house.
Chaetopterus is highly phosphorescent (see p. 295). It is further interesting on
account of the green colouring-matter, which is extracted by alcohol. Two
commensal Polynoids occur in the tube, viz. Polynoë glabra and P. cirrosa.
The larva is "mesotrochal" (with a ciliated ring round its middle), that region
of the body lying in front of the cilia giving rise to the region A, whilst the rest
of the body gives rise to regions B and C.
anterior region of the body; B, the middle region; C, the hinder region. c,
Peristomial cirri; d, "sucker"; e, the great "wings"; f, the first of the three "fans"; m,
mouth.
The second region, B, is very curiously modified; it is formed of five
segments. The most anterior is produced on either side into a great wing-like
process, which in life is directed forwards above the region A. Each is grooved
on its inner side, the ciliated grooves being continuous with a median groove
running forwards along the back of A; this apparatus serves to bring food to
the great funnel-like mouth. The next segment (twelfth) carries a dorsal and
ventral "sucker," representing the parapodia. Each of the segments 13, 14, 15
carries a membranous fold encircling the body. By the constant movement of
these "fans," which have nearly the same diameter as the tube, a current of
water is constantly washed over the animal. The fans represent the notopodia;
the neuropodia are bilobed rounded knobs. The region C consists in the adult
of about thirty segments, all alike, and less modified than the preceding. The
animal is the most truly tubicolous of the Polychaetes, and is much modified
on this account. No locomotor chaetae are present, though the great wings and
notopodial processes of region C contains chitinous bristles, which, however,
do not project;[384] the anterior region with its stiff chaetae, and the
neuropodial uncinal plates of the rest of the body serve in its movements up
and down the tube, while the "suckers" fix the worm temporarily to the wall of
its house.
Chaetopterus is highly phosphorescent (see p. 295). It is further interesting on
account of the green colouring-matter, which is extracted by alcohol. Two
commensal Polynoids occur in the tube, viz. Polynoë glabra and P. cirrosa.
The larva is "mesotrochal" (with a ciliated ring round its middle), that region
of the body lying in front of the cilia giving rise to the region A, whilst the rest
of the body gives rise to regions B and C.
Page 331
Fam. 4. Magelonidae.—This family includes only the very peculiar worm,
Magelona papillicornis Fr. Müll., which lives buried in sand, between tide-
marks, in various parts of our coast and that of the United States. Its chief
features are the large, flat, spoon-shaped prostomium; the long peristomial
cirri, slightly expanded terminally, carrying papillae along one side; the
enormous, eversible buccal region, which is an important respiratory organ.
The blood is of a madder-pink colour, and the blood-vessels in the thorax are
greatly dilated. The body of the worm is divisible into two well-marked
regions, owing to differences in the chaetae.[385]
Fam. 5. Ammocharidae.—This family contains only one species, Owenia
filiformis D. Ch. Some of the anterior segments are longer than the hinder
ones, though the arrangement of chaetae is alike throughout. The mouth is
wide, like that of Chaetopterus, and is surrounded, except ventrally, by a
membrane, so deeply notched as to give rise to flattened filaments containing
blood-vessels. These "gills" appear to belong to the peristomium. The small
worm in its sandy tube is plentiful on our coasts in about 20 fathoms. Off
Greenland and the Mediterranean.
Sub-Order 3. Terebelliformia.
Fam. 1. Cirratulidae.—These worms have a cylindrical body, more or less
attenuated at each end; the segments are distinct, and similar throughout, with
capillary chaetae on each side in two bundles, carried by small papillae. The
prostomium is conical, the peristomium usually without cirri. On more or
fewer segments the dorsal cirri are long and filamentous, and function as gills.
There is a single pair of anterior nephridia: the septa and genital ducts are
repeated throughout the hinder part of the body. The worms usually live in
burrows.
Cirratulus.—The prostomium is long, sometimes annulated. In addition to the
segmental filamentous "gills" there is a transverse row of long "tentacular
filaments" across one of the anterior segments, and it has been suggested that
they are really prostomial tentacles which have shifted backwards. They and
the gills twist about in a very active fashion during life, and look like small
independent worms, especially when they are detached. C. cirratus Müll, is a
brown or dirty yellowish worm about 4 to 6 inches in length, usually to be
Magelona papillicornis Fr. Müll., which lives buried in sand, between tide-
marks, in various parts of our coast and that of the United States. Its chief
features are the large, flat, spoon-shaped prostomium; the long peristomial
cirri, slightly expanded terminally, carrying papillae along one side; the
enormous, eversible buccal region, which is an important respiratory organ.
The blood is of a madder-pink colour, and the blood-vessels in the thorax are
greatly dilated. The body of the worm is divisible into two well-marked
regions, owing to differences in the chaetae.[385]
Fam. 5. Ammocharidae.—This family contains only one species, Owenia
filiformis D. Ch. Some of the anterior segments are longer than the hinder
ones, though the arrangement of chaetae is alike throughout. The mouth is
wide, like that of Chaetopterus, and is surrounded, except ventrally, by a
membrane, so deeply notched as to give rise to flattened filaments containing
blood-vessels. These "gills" appear to belong to the peristomium. The small
worm in its sandy tube is plentiful on our coasts in about 20 fathoms. Off
Greenland and the Mediterranean.
Sub-Order 3. Terebelliformia.
Fam. 1. Cirratulidae.—These worms have a cylindrical body, more or less
attenuated at each end; the segments are distinct, and similar throughout, with
capillary chaetae on each side in two bundles, carried by small papillae. The
prostomium is conical, the peristomium usually without cirri. On more or
fewer segments the dorsal cirri are long and filamentous, and function as gills.
There is a single pair of anterior nephridia: the septa and genital ducts are
repeated throughout the hinder part of the body. The worms usually live in
burrows.
Cirratulus.—The prostomium is long, sometimes annulated. In addition to the
segmental filamentous "gills" there is a transverse row of long "tentacular
filaments" across one of the anterior segments, and it has been suggested that
they are really prostomial tentacles which have shifted backwards. They and
the gills twist about in a very active fashion during life, and look like small
independent worms, especially when they are detached. C. cirratus Müll, is a
brown or dirty yellowish worm about 4 to 6 inches in length, usually to be
Page 332
found under stones, partially embedded in the mud or sand. The prostomium
carries a pair of linear groups of "eye-spots"; the first chaetigerous segment
carries a transverse row of tentacular filaments, and the red gill-filaments
commence on the same segment. Common. C. tentaculatus Mont. is a larger
worm, dark red in colour, and is distinguished from the preceding by the
absence of eyes and by the fact that the tentacular filaments are on the seventh
chaetigerous segment, while the gills commence more anteriorly. Atlantic and
the Mediterranean.
Fig. 174.—Cirratulus tentaculatus Mont. (½ nat. size). (From Règne Animal.)
Chaetozone setosa Mgrn. occurs in the North Atlantic. Dodecaceria
concharum Oerst. is about an inch in length, olive-green or brownish in
colour, and is not uncommon amongst roots of Laminaria. It is stated to live
also in tortuous tubes bored in shells and stones, but whether it makes these
tubes is uncertain. The worm has two thick tentacular filaments, and the
thinner gills are only on four segments. Hekaterobranchus shrubsolii Buch.
[386] is a small worm some ½ inch long, found at Sheerness, where it occurs at
low tide in soft mud; here it forms a loosely coherent tube, though it also
moves freely in the mud. Its chief features are (1) a pair of long, ciliated
"cephalic tentacles," probably peristomial, and similar to the "tentacular
filaments" of Dodecaceria; (2) a pair of filamentous gills (dorsal cirri) on the
first chaetigerous segment; (3) a pair of large green nephridia in the anterior
segments. The describer placed it amongst the Spionids, but the above and
other features point to Cirratulid affinities.
Fam. 2. Terebellidae.—The body is cylindrical, and generally larger in front
than behind. The prostomium is generally flattened, and forms a mobile upper
lip, which always carries a transverse series of many tentacles; it may bear
carries a pair of linear groups of "eye-spots"; the first chaetigerous segment
carries a transverse row of tentacular filaments, and the red gill-filaments
commence on the same segment. Common. C. tentaculatus Mont. is a larger
worm, dark red in colour, and is distinguished from the preceding by the
absence of eyes and by the fact that the tentacular filaments are on the seventh
chaetigerous segment, while the gills commence more anteriorly. Atlantic and
the Mediterranean.
Fig. 174.—Cirratulus tentaculatus Mont. (½ nat. size). (From Règne Animal.)
Chaetozone setosa Mgrn. occurs in the North Atlantic. Dodecaceria
concharum Oerst. is about an inch in length, olive-green or brownish in
colour, and is not uncommon amongst roots of Laminaria. It is stated to live
also in tortuous tubes bored in shells and stones, but whether it makes these
tubes is uncertain. The worm has two thick tentacular filaments, and the
thinner gills are only on four segments. Hekaterobranchus shrubsolii Buch.
[386] is a small worm some ½ inch long, found at Sheerness, where it occurs at
low tide in soft mud; here it forms a loosely coherent tube, though it also
moves freely in the mud. Its chief features are (1) a pair of long, ciliated
"cephalic tentacles," probably peristomial, and similar to the "tentacular
filaments" of Dodecaceria; (2) a pair of filamentous gills (dorsal cirri) on the
first chaetigerous segment; (3) a pair of large green nephridia in the anterior
segments. The describer placed it amongst the Spionids, but the above and
other features point to Cirratulid affinities.
Fam. 2. Terebellidae.—The body is cylindrical, and generally larger in front
than behind. The prostomium is generally flattened, and forms a mobile upper
lip, which always carries a transverse series of many tentacles; it may bear
Page 333
"eye-spots," but never palps; the lower lip is formed by the peristomium.
There are one to three pairs of gills, which are usually more or less branched,
on as many segments.[387]
The chaetigerous lobes are small; the dorsal ones contain capillary chaetae,
which are frequently confined to the anterior segments, whilst the ventral
chaetae are uncini. The ventral surface of the anterior segments is thickened
by glands which secrete the mucus employed in tube-building; the number of
these "shields" and of the dorsal bundles of chaetae have to be noted in
identifying the worms. There are one to three pairs of large anterior nephridia.
A very strong "diaphragm"—usually more or less pouched—cuts off this
anterior region of the body-cavity from the rest, and is the only complete
septum in the body; from three to twelve pairs of small generative ducts occur
behind it. The family is tubicolous, foreign materials being generally used in
the formation of the tube.
Fig. 175.—Amphitrite johnstoni (½ nat. size). g, Gills; t, prostomial tentacles. (From
Cunningham and Ramage.)
There are six genera which are fairly common round our coast, and their
identification may be facilitated by means of the following table[388]:—
A. Capillary Gills Amphitrite.
equal in size.
chaetae ramose. 3 pairs, 24 notopodia.
confined to which are Terebella.
unequal in size.
the anterior 17 notopodia.
part of body; 2 pairs. Gills equal.
commencing Nicolea.
17 notopodia. Eye-spots.
There are one to three pairs of gills, which are usually more or less branched,
on as many segments.[387]
The chaetigerous lobes are small; the dorsal ones contain capillary chaetae,
which are frequently confined to the anterior segments, whilst the ventral
chaetae are uncini. The ventral surface of the anterior segments is thickened
by glands which secrete the mucus employed in tube-building; the number of
these "shields" and of the dorsal bundles of chaetae have to be noted in
identifying the worms. There are one to three pairs of large anterior nephridia.
A very strong "diaphragm"—usually more or less pouched—cuts off this
anterior region of the body-cavity from the rest, and is the only complete
septum in the body; from three to twelve pairs of small generative ducts occur
behind it. The family is tubicolous, foreign materials being generally used in
the formation of the tube.
Fig. 175.—Amphitrite johnstoni (½ nat. size). g, Gills; t, prostomial tentacles. (From
Cunningham and Ramage.)
There are six genera which are fairly common round our coast, and their
identification may be facilitated by means of the following table[388]:—
A. Capillary Gills Amphitrite.
equal in size.
chaetae ramose. 3 pairs, 24 notopodia.
confined to which are Terebella.
unequal in size.
the anterior 17 notopodia.
part of body; 2 pairs. Gills equal.
commencing Nicolea.
17 notopodia. Eye-spots.
Page 334
on the fourth Gills unequal and of
Pista.
segment. peculiar shape.
B. Capillary
chaetae arborescent; 3 pairs. Leprea.
throughout
the body; Gills
commencing filiform; in transverse series in
Thelepus.
on the third two segments.
segment.
Amphitrite johnstoni Mgrn. (Fig. 175) is brown in colour, about 4 to 6 inches
in length, and nearly ½ inch in breadth anteriorly. Each of the gills consists of
a curved stem; from the convex side of which arise a number of branches,
themselves dichotomously divided, the final branches being long (Fig. 176,
A). There are twelve ventral "gland shields." The worm is fairly common
between tide-marks, below stones in muddy places: the end of its tube of mud
projects above the surface. Atlantic.
Terebella (Polymnia) nebulosa Mont. is distinguished by its bright red colour,
spotted with white; it is 6 or 7 inches in length, and ½ inch across. Large
specimens of this beautiful worm may be obtained at Weymouth and
elsewhere on the south coast, where it lives in about 14 fathoms. Each gill
appears much more arborescent than in the preceding (Fig. 176, B); it consists
of a main stem, from which comparatively few branches arise; these subdivide
frequently, and the terminal branchlets are quite short. The "gland shields" are
fourteen to sixteen in number. The tube is of mud. North Sea and
Mediterranean. T. (Leprea) lapidaria L. is 1 inch in length, orange-red in
colour; and has 12 ventral shields. The tube, of fine mud, lies horizontally on
the under surface of stones.
T. (Lanice) conchilega Pall. (the "sand mason") forms a very characteristic
tube of sandy particles, small pebbles, and pieces of shell. It is buried in the
sand, but a short portion protrudes, and bears, set round its edge, a fringe of
branching sandy threads (Fig. 153) commonly seen on sandy shores between
tide-marks. The worm may be distinguished from the preceding species by the
fact that the series of fourteen to seventeen gland shields are red, and
continuous from segment to segment. The gill is shown in Fig. 176, C. North
Sea, Atlantic, and Mediterranean.
Pista.
segment. peculiar shape.
B. Capillary
chaetae arborescent; 3 pairs. Leprea.
throughout
the body; Gills
commencing filiform; in transverse series in
Thelepus.
on the third two segments.
segment.
Amphitrite johnstoni Mgrn. (Fig. 175) is brown in colour, about 4 to 6 inches
in length, and nearly ½ inch in breadth anteriorly. Each of the gills consists of
a curved stem; from the convex side of which arise a number of branches,
themselves dichotomously divided, the final branches being long (Fig. 176,
A). There are twelve ventral "gland shields." The worm is fairly common
between tide-marks, below stones in muddy places: the end of its tube of mud
projects above the surface. Atlantic.
Terebella (Polymnia) nebulosa Mont. is distinguished by its bright red colour,
spotted with white; it is 6 or 7 inches in length, and ½ inch across. Large
specimens of this beautiful worm may be obtained at Weymouth and
elsewhere on the south coast, where it lives in about 14 fathoms. Each gill
appears much more arborescent than in the preceding (Fig. 176, B); it consists
of a main stem, from which comparatively few branches arise; these subdivide
frequently, and the terminal branchlets are quite short. The "gland shields" are
fourteen to sixteen in number. The tube is of mud. North Sea and
Mediterranean. T. (Leprea) lapidaria L. is 1 inch in length, orange-red in
colour; and has 12 ventral shields. The tube, of fine mud, lies horizontally on
the under surface of stones.
T. (Lanice) conchilega Pall. (the "sand mason") forms a very characteristic
tube of sandy particles, small pebbles, and pieces of shell. It is buried in the
sand, but a short portion protrudes, and bears, set round its edge, a fringe of
branching sandy threads (Fig. 153) commonly seen on sandy shores between
tide-marks. The worm may be distinguished from the preceding species by the
fact that the series of fourteen to seventeen gland shields are red, and
continuous from segment to segment. The gill is shown in Fig. 176, C. North
Sea, Atlantic, and Mediterranean.
Page 335
Fig. 176.—Gills of various Terebellids. × 4. A, Amphitrite johnstoni Mgrn.; B, Terebella
nebulosa Mont.; C, T. conchilega Pall.; D, Nicolea Mgrn. (the finer branches are
not indicated); E, Pista Mgrn.; F, Terebellides Sars (after Malmgren). g, Gill; m,
mouth; t, tentacles.
Nicolea venustula Mont. has only two pairs of equal, arborescent gills (Fig.
176, D); the tentacles are comparatively few. The animal, which is about an
inch in length, is cinnamon-yellow with white spots, and has seventeen gland
shields. 20 fathoms, North Sea and Mediterranean. Pista cristata Müll. is
readily recognised by the shape of the gills (Fig. 176, E), of which there are
only two pairs. Each consists of a long peduncle, bearing a number of
dichotomously dividing, rather spirally-arranged branches, the whole having
the appearance of a "bottle-brush." The worm is 2 to 4 inches long, of greyish-
red to yellow colour. Atlantic east and west (even at the mouth of the Congo),
and Mediterranean. Thelepus cincinnatus Fabr. is about the same length, pale
red in colour, marked on its back with clear areas, giving the appearance of
lacework. The gills are represented by numerous unbranched filaments arising
separately in two transverse rows. The tube, which is adherent to shells, etc.,
along its whole length, is of thin, transparent, and flexible material like mica,
covered with foreign bodies, and even with Polyzoa and Hydrozoa. 30
fathoms, Atlantic and Mediterranean.
Polycirrus aurantiacus Gr. is sometimes placed in a special sub-family, as it
has no gills. The numerous tentacles are very long, and arise from a great hood
over the mouth; the capillary chaetae commence in the first segment and
extend for about half the length of the body; the uncini commence in the ninth
segment. The ventral "shields" are paired. The animal is highly coloured; its
phosphorescence and its distastefulness have already been mentioned on p.
294. In Terebellides stroemi Sars, four comb-like gills arise from a single
common thick peduncle on the back of the second segment (Fig. 176, F). The
ventral surface of the body bends upwards anteriorly so as to bring the mouth
nebulosa Mont.; C, T. conchilega Pall.; D, Nicolea Mgrn. (the finer branches are
not indicated); E, Pista Mgrn.; F, Terebellides Sars (after Malmgren). g, Gill; m,
mouth; t, tentacles.
Nicolea venustula Mont. has only two pairs of equal, arborescent gills (Fig.
176, D); the tentacles are comparatively few. The animal, which is about an
inch in length, is cinnamon-yellow with white spots, and has seventeen gland
shields. 20 fathoms, North Sea and Mediterranean. Pista cristata Müll. is
readily recognised by the shape of the gills (Fig. 176, E), of which there are
only two pairs. Each consists of a long peduncle, bearing a number of
dichotomously dividing, rather spirally-arranged branches, the whole having
the appearance of a "bottle-brush." The worm is 2 to 4 inches long, of greyish-
red to yellow colour. Atlantic east and west (even at the mouth of the Congo),
and Mediterranean. Thelepus cincinnatus Fabr. is about the same length, pale
red in colour, marked on its back with clear areas, giving the appearance of
lacework. The gills are represented by numerous unbranched filaments arising
separately in two transverse rows. The tube, which is adherent to shells, etc.,
along its whole length, is of thin, transparent, and flexible material like mica,
covered with foreign bodies, and even with Polyzoa and Hydrozoa. 30
fathoms, Atlantic and Mediterranean.
Polycirrus aurantiacus Gr. is sometimes placed in a special sub-family, as it
has no gills. The numerous tentacles are very long, and arise from a great hood
over the mouth; the capillary chaetae commence in the first segment and
extend for about half the length of the body; the uncini commence in the ninth
segment. The ventral "shields" are paired. The animal is highly coloured; its
phosphorescence and its distastefulness have already been mentioned on p.
294. In Terebellides stroemi Sars, four comb-like gills arise from a single
common thick peduncle on the back of the second segment (Fig. 176, F). The
ventral surface of the body bends upwards anteriorly so as to bring the mouth
Page 336
to the dorsal surface. 13 to 16 fathoms, muddy bottoms, North Sea and
Mediterranean.
Fam. 3. Ampharetidae.—This family differs from the Terebellids chiefly in the
shape of the head and in the presence of a bundle of strong chaetae (or paleae)
on each side of the head in front of the gills, of which there are four on each
side. Each gill is a simple filiform process, considerably longer than the
tentacles, which are very few in number. Amphicteis gunneri Sars, Ampharete
gracilis Mgrn., and Melinna cristata Sars, occur on our coasts.
Fig. 177.—Pectinaria belgica Pall. Slightly enlarged. a, Neuropodial chaetae; b,
notopodium; ch, paleae; g, gills; sc, scapha; t, prostomial tentacles; I, peristomium.
(From Malmgren.)
Fam. 4. Amphictenidae.—This contains the interesting genus Pectinaria, in
which the head is protected by great golden chaetae on the second segment;
they are flattened, curved, and pointed, and are arranged in a single transverse
row on each side, serving as an operculum to the tube. The posterior end of the
worm has undergone great degeneration, and is represented by a small leaf-
like "scapha" which serves to close the tube posteriorly. The worm is 1½
inches in length and consists of only twenty segments, of which seventeen are
chaetigerous. The tube is nearly cylindrical, but wider anteriorly than
posteriorly (Fig. 152, p. 288); the sand grains are uniform in size, and are
embedded in the secreted mucus in a very regular way, the surface being
smooth both inside and out. These tubes can be carried about by the worm, but
may be found projecting from the sand at very low tides. P. belgica Pall. forms
a straight tube, whilst in P. auricoma Müll. the tube is larger and slightly
curved. The former species appears to be confined to the North Sea; the latter
occurs in deeper water, and is also present in the Mediterranean.
Mediterranean.
Fam. 3. Ampharetidae.—This family differs from the Terebellids chiefly in the
shape of the head and in the presence of a bundle of strong chaetae (or paleae)
on each side of the head in front of the gills, of which there are four on each
side. Each gill is a simple filiform process, considerably longer than the
tentacles, which are very few in number. Amphicteis gunneri Sars, Ampharete
gracilis Mgrn., and Melinna cristata Sars, occur on our coasts.
Fig. 177.—Pectinaria belgica Pall. Slightly enlarged. a, Neuropodial chaetae; b,
notopodium; ch, paleae; g, gills; sc, scapha; t, prostomial tentacles; I, peristomium.
(From Malmgren.)
Fam. 4. Amphictenidae.—This contains the interesting genus Pectinaria, in
which the head is protected by great golden chaetae on the second segment;
they are flattened, curved, and pointed, and are arranged in a single transverse
row on each side, serving as an operculum to the tube. The posterior end of the
worm has undergone great degeneration, and is represented by a small leaf-
like "scapha" which serves to close the tube posteriorly. The worm is 1½
inches in length and consists of only twenty segments, of which seventeen are
chaetigerous. The tube is nearly cylindrical, but wider anteriorly than
posteriorly (Fig. 152, p. 288); the sand grains are uniform in size, and are
embedded in the secreted mucus in a very regular way, the surface being
smooth both inside and out. These tubes can be carried about by the worm, but
may be found projecting from the sand at very low tides. P. belgica Pall. forms
a straight tube, whilst in P. auricoma Müll. the tube is larger and slightly
curved. The former species appears to be confined to the North Sea; the latter
occurs in deeper water, and is also present in the Mediterranean.
Page 337
Sub-Order 4. Capitelliformia.
Fam. Capitellidae.[389]—Capitella capitata v. Ben. occurs pretty frequently in
the sand under stones near low tide-mark. It is a red worm, about 1½ to 2
inches long, greatly resembling a Tubificid Oligochaete. It may readily be
distinguished from other Polychaeta by the strong genital chaetae in the male,
which replace the notopodial chaetae of segments 8 and 9; those in the former
segment are pointed backwards, and in the latter forwards. There is but a
single pair of generative ducts in either sex in the eighth segment. North Sea,
Mediterranean.
Notomastus latericeus Sars is a longer worm, living in shallow water, off our
coast and in the Mediterranean. The anterior twelve segments are wider than
the rest of the body. The notopodial chaetae of the anterior segments of the
hind body form a ring. Dasybranchus caducus Gr., which occurs in the
Mediterranean, but not on our coast, reaches a length of 2 or 3 feet. It has gills
on the hinder segments above the neuropodia.
Mastobranchus Eis. is found in the Mediterranean.
Sub-Order 5. Scoleciformia.
Fam. 1. Opheliidae.—Comparatively short, rather ugly worms of a pearly
colour, no prostomial processes: parapodia obscure. The family is represented
in British waters by four species, occurring in shallow water.
Ammotrypane aulogaster Rathke, is about 2 inches long; the nearly cylindrical
body has a ridge running along each side below the chaetae. The conical
prostomium is tipped with a small knob, and carries at each side a ciliated pit
(Fig. 144, p. 273). Every segment, except the first chaetigerous, is provided
with a filamentous gill (dorsal cirrus). The segmentation is very obscurely
marked, for internally there are only three complete septa, placed far forwards.
The intestine is bent upon itself. In Ophelia limacina Rthk. the gills
commence in the eighth segment, and the longitudinal ridge does not extend in
front of this segment. The worm is about 1½ inches long, and occurs between
tide-marks. Travisia forbesi Jnstn., North Sea. Polyophthalmus pictus[390] Duj.
Fam. Capitellidae.[389]—Capitella capitata v. Ben. occurs pretty frequently in
the sand under stones near low tide-mark. It is a red worm, about 1½ to 2
inches long, greatly resembling a Tubificid Oligochaete. It may readily be
distinguished from other Polychaeta by the strong genital chaetae in the male,
which replace the notopodial chaetae of segments 8 and 9; those in the former
segment are pointed backwards, and in the latter forwards. There is but a
single pair of generative ducts in either sex in the eighth segment. North Sea,
Mediterranean.
Notomastus latericeus Sars is a longer worm, living in shallow water, off our
coast and in the Mediterranean. The anterior twelve segments are wider than
the rest of the body. The notopodial chaetae of the anterior segments of the
hind body form a ring. Dasybranchus caducus Gr., which occurs in the
Mediterranean, but not on our coast, reaches a length of 2 or 3 feet. It has gills
on the hinder segments above the neuropodia.
Mastobranchus Eis. is found in the Mediterranean.
Sub-Order 5. Scoleciformia.
Fam. 1. Opheliidae.—Comparatively short, rather ugly worms of a pearly
colour, no prostomial processes: parapodia obscure. The family is represented
in British waters by four species, occurring in shallow water.
Ammotrypane aulogaster Rathke, is about 2 inches long; the nearly cylindrical
body has a ridge running along each side below the chaetae. The conical
prostomium is tipped with a small knob, and carries at each side a ciliated pit
(Fig. 144, p. 273). Every segment, except the first chaetigerous, is provided
with a filamentous gill (dorsal cirrus). The segmentation is very obscurely
marked, for internally there are only three complete septa, placed far forwards.
The intestine is bent upon itself. In Ophelia limacina Rthk. the gills
commence in the eighth segment, and the longitudinal ridge does not extend in
front of this segment. The worm is about 1½ inches long, and occurs between
tide-marks. Travisia forbesi Jnstn., North Sea. Polyophthalmus pictus[390] Duj.
Page 338
is very abundant at some parts of the coast. There are two bundles of chaetae
on each side of every segment; each bundle contains three chaetae, of which
only one projects to any distance. Paired eye-like spots exist on the sides of
twelve segments. The worm is about an inch in length.
Fam. 2. Maldanidae (= Clymenidae).—Represented on our coasts by four
fairly common species. They form sandy tubes, which are embedded in the
sand with a short portion projecting. In some places they are so abundant that
at low water the sand has quite a rough appearance. The prostomium is
frequently truncated and depressed, and is always fused with the peristomium.
A horny plate may be developed on the upper surface of the head, and the skin
at the side of the prostomium is frequently raised into a more or less
prominent fold. The hinder end of the body carries a funnel surrounding the
anus. There are no gills or sensory processes on the body. Some of the
segments towards the middle of the body may be longer than the rest. Peculiar
serrated hooks of characteristic shape constitute the neuropodial "torus." The
buccal region is eversible.
Nicomache lumbricalis Fabr. is a rosy-pink worm with white spots anteriorly;
the chaetigerous ridges are red. The worm consists of twenty-six segments,
and measures 2 or 3 inches. It is very narrow and readily breaks in pieces. The
prostomium is laterally compressed; the anal funnel is fringed with a number
of short equal processes. Under stones in the Laminarian zone.
Fig. 178.—Anal funnel of Nicomache lumbricalis. (From Malmgren.)
Axiothea catenata Mgrn., which may reach a length of 3 or 4 inches,
resembles the above in general colour, though of a deeper tint. There are only
eighteen chaetigerous segments. The head has a membranous fold of skin on
each side, and the anal funnel is produced into longer and shorter processes.
Both these species are also found on the west side of the Atlantic. Clymene
lumbricoides Qfg. is about 8 inches long; pink, with a light ring round each
segment; the seventh segment is larger and reddish-brown. The prostomium is
laterally compressed. Anus on a cone, which rises from the bottom of a funnel,
the margin of which is entire. Atlantic.
on each side of every segment; each bundle contains three chaetae, of which
only one projects to any distance. Paired eye-like spots exist on the sides of
twelve segments. The worm is about an inch in length.
Fam. 2. Maldanidae (= Clymenidae).—Represented on our coasts by four
fairly common species. They form sandy tubes, which are embedded in the
sand with a short portion projecting. In some places they are so abundant that
at low water the sand has quite a rough appearance. The prostomium is
frequently truncated and depressed, and is always fused with the peristomium.
A horny plate may be developed on the upper surface of the head, and the skin
at the side of the prostomium is frequently raised into a more or less
prominent fold. The hinder end of the body carries a funnel surrounding the
anus. There are no gills or sensory processes on the body. Some of the
segments towards the middle of the body may be longer than the rest. Peculiar
serrated hooks of characteristic shape constitute the neuropodial "torus." The
buccal region is eversible.
Nicomache lumbricalis Fabr. is a rosy-pink worm with white spots anteriorly;
the chaetigerous ridges are red. The worm consists of twenty-six segments,
and measures 2 or 3 inches. It is very narrow and readily breaks in pieces. The
prostomium is laterally compressed; the anal funnel is fringed with a number
of short equal processes. Under stones in the Laminarian zone.
Fig. 178.—Anal funnel of Nicomache lumbricalis. (From Malmgren.)
Axiothea catenata Mgrn., which may reach a length of 3 or 4 inches,
resembles the above in general colour, though of a deeper tint. There are only
eighteen chaetigerous segments. The head has a membranous fold of skin on
each side, and the anal funnel is produced into longer and shorter processes.
Both these species are also found on the west side of the Atlantic. Clymene
lumbricoides Qfg. is about 8 inches long; pink, with a light ring round each
segment; the seventh segment is larger and reddish-brown. The prostomium is
laterally compressed. Anus on a cone, which rises from the bottom of a funnel,
the margin of which is entire. Atlantic.
Page 339
Fig. 179.—Axiothea catenata. × ½. a, Anterior end; b, notopodial and c, neuropodial
chaetae; p, perianal funnel. (From Malmgren.)
Fig. 180.—Arenicola marina. × 1. Dorsal view. The anterior end is seen partly from the
side. III, The first chaetigerous segment; IX, the ninth chaetigerous, and first
branchial segment; XXI, the last branchial segment; b, notopodial and c,
neuropodial chaetae; g', g, the first and last gills; t, the non-chaetigerous tail.
Fam. 3. Arenicolidae.—Here belongs the common "lug-worm" Arenicola
marina L., which occurs all round our coasts between tide-marks, and is so
generally used as bait in fishing. The worm, which measures 5 to 8 inches, is
of a dark tint, usually brownish-green. It burrows to a depth of some 18 inches
or 2 feet, and throws up a considerable quantity of "castings" or "sand-ropes,"
which are noticeable on every shore consisting of mud or muddy sand. The
body of the worm is cylindrical, thicker anteriorly; the segments are indistinct,
owing to the secondary groovings and furrows on the skin. The prostomium is
in the adult fused with the peristomium; this and the second segment are
achaetous. Then follow twenty chaetigerous segments with dorsal bundles of
capillary chaetae and ventral rows of short crotchets. The hinder region of the
body is achaetous and narrower than the rest, forming a "tail." There are
twelve (sometimes thirteen) pairs of arborescent red gills on segments 9 to 20
chaetae; p, perianal funnel. (From Malmgren.)
Fig. 180.—Arenicola marina. × 1. Dorsal view. The anterior end is seen partly from the
side. III, The first chaetigerous segment; IX, the ninth chaetigerous, and first
branchial segment; XXI, the last branchial segment; b, notopodial and c,
neuropodial chaetae; g', g, the first and last gills; t, the non-chaetigerous tail.
Fam. 3. Arenicolidae.—Here belongs the common "lug-worm" Arenicola
marina L., which occurs all round our coasts between tide-marks, and is so
generally used as bait in fishing. The worm, which measures 5 to 8 inches, is
of a dark tint, usually brownish-green. It burrows to a depth of some 18 inches
or 2 feet, and throws up a considerable quantity of "castings" or "sand-ropes,"
which are noticeable on every shore consisting of mud or muddy sand. The
body of the worm is cylindrical, thicker anteriorly; the segments are indistinct,
owing to the secondary groovings and furrows on the skin. The prostomium is
in the adult fused with the peristomium; this and the second segment are
achaetous. Then follow twenty chaetigerous segments with dorsal bundles of
capillary chaetae and ventral rows of short crotchets. The hinder region of the
body is achaetous and narrower than the rest, forming a "tail." There are
twelve (sometimes thirteen) pairs of arborescent red gills on segments 9 to 20
Page 340
(21). Internally there are only four complete septa, and six pairs of nephridia,
which are of large size: the fore-gut is eversible. Atlantic and Mediterranean.
A second and smaller species, A. ecaudata Jnstn., occurs on our southern
coasts; it is readily distinguished by the absence of a "tail," the chaetae and
gills being continued to the end of the body.
Fam. 4. Scalibregmidae.—Prostomium ill-marked, fringed with small
processes. Parapodia represented by slight papillae; two bundles of chaetae;
usually cirriform lobes above and below them. Lipobranchius jeffreysii M‘I.
has a grub-like body pointed at each end; forms tubes of mud. Firth of Clyde
and elsewhere in North Sea. Sclerocheilus Gr. in old oyster shells. Channel,
Mediterranean. Eumenia crassa Oerst. has gills on first six segments. North
Sea. Scalibregma inflata Rthke. has arborescent gills on segments 4 to 7. The
anterior part of the body is dilated. North Sea.
Fam. 5. Chlorhaemidae.—The family derives its name from the green colour
of the blood, due to chlorocruorin. The representatives are comparatively short
worms, with capillary chaetae on all the segments, the limits of which are not
evident. The prostomium carries a pair of long grooved yellowish processes,
which are perhaps palps, and several green tentacles, acting as "gills,"
arranged in a transverse series above the mouth (Fig. 134, F, p. 262). The
peristomium is achaetous; the whole "head" can be withdrawn into the body.
The chaetae of the anterior segments are especially long, and directed
forwards so as to form a "cage" for the head. The body-wall is covered with
longer or shorter papillae. Internally, the chief points of interest are the
presence of only two septa (Trophonia) or only one septum (Siphonostoma),
situated somewhere in front of the middle of the body, and forming a great
backwardly-directed pouch, which contains a part of the looped intestine, and
the nephridia, of which there are only two or four.
Trophonia plumosa Müll. is about 2 to 4 inches long, yellowish-brown in
colour, with a rough skin; the head is usually retracted. It lives in the mud
amongst Laminarian roots down to 50 fathoms. North Atlantic. Siphonostoma
(Flabelligera) diplochaitos Otto, has a transparent body-wall, so that the
coloured viscera are visible. The skin carries long papillae, which traverse a
thick jelly-like envelope secreted by it, in which numerous diatoms live
(symbiotically?); the surface is covered by particles of mud, etc. This species,
which are of large size: the fore-gut is eversible. Atlantic and Mediterranean.
A second and smaller species, A. ecaudata Jnstn., occurs on our southern
coasts; it is readily distinguished by the absence of a "tail," the chaetae and
gills being continued to the end of the body.
Fam. 4. Scalibregmidae.—Prostomium ill-marked, fringed with small
processes. Parapodia represented by slight papillae; two bundles of chaetae;
usually cirriform lobes above and below them. Lipobranchius jeffreysii M‘I.
has a grub-like body pointed at each end; forms tubes of mud. Firth of Clyde
and elsewhere in North Sea. Sclerocheilus Gr. in old oyster shells. Channel,
Mediterranean. Eumenia crassa Oerst. has gills on first six segments. North
Sea. Scalibregma inflata Rthke. has arborescent gills on segments 4 to 7. The
anterior part of the body is dilated. North Sea.
Fam. 5. Chlorhaemidae.—The family derives its name from the green colour
of the blood, due to chlorocruorin. The representatives are comparatively short
worms, with capillary chaetae on all the segments, the limits of which are not
evident. The prostomium carries a pair of long grooved yellowish processes,
which are perhaps palps, and several green tentacles, acting as "gills,"
arranged in a transverse series above the mouth (Fig. 134, F, p. 262). The
peristomium is achaetous; the whole "head" can be withdrawn into the body.
The chaetae of the anterior segments are especially long, and directed
forwards so as to form a "cage" for the head. The body-wall is covered with
longer or shorter papillae. Internally, the chief points of interest are the
presence of only two septa (Trophonia) or only one septum (Siphonostoma),
situated somewhere in front of the middle of the body, and forming a great
backwardly-directed pouch, which contains a part of the looped intestine, and
the nephridia, of which there are only two or four.
Trophonia plumosa Müll. is about 2 to 4 inches long, yellowish-brown in
colour, with a rough skin; the head is usually retracted. It lives in the mud
amongst Laminarian roots down to 50 fathoms. North Atlantic. Siphonostoma
(Flabelligera) diplochaitos Otto, has a transparent body-wall, so that the
coloured viscera are visible. The skin carries long papillae, which traverse a
thick jelly-like envelope secreted by it, in which numerous diatoms live
(symbiotically?); the surface is covered by particles of mud, etc. This species,
Page 341
which may be found under stones at low tide, occurs also in the
Mediterranean.
Mediterranean.
Page 342
Fig. 181.—Sternaspis scutata Ranz. × 2. (From Vejdovsky.) The left figure shows the
ventral surface; the right represents the internal organs as seen when the body-
wall is pinned aside, having been slit up along its dorsal surface. a, Anus; c, gills;
ch, anterior strong chaetae; ch1, bundles of chaetae along the lateral margin of
the shield; ch2, the posterior marginal chaetae; d, oviduct; g, the external tube
carrying genital pore; i, coiled intestine; n, nephridium ("brown tube"); o, ovary,
amongst the coils of the alimentary canal; p, pharynx; pr, prostomium, with
mouth just behind it; s, shield (on left figure); s, stomach (on right); sh, outline of
shield seen through the ventral body-wall (in right figure); x, chaetae embedded
in the body-wall, with nerves passing by them.
Fam. 6. Sternaspidae.—The single genus, Sternaspis, has not been recorded
on our coasts, but is of so peculiar a structure as to deserve a description.
[391] S. scutata Ranzani, occurring in the Mediterranean, is rather less than
an inch in length, and derives its name from the possession of a pair of
peculiar "horny" plates or shields on the ventral surface posteriorly. Around
their margins are set about thirty bundles of long capillary chaetae. There
are three half rings of stronger chaetae on each side near the anterior end of
the body. The mouth is overhung by a very small rounded knob
(prostomium), which in S. spinosa Sluiter, is prolonged outwards on each
side to form a grooved palp-like organ, recalling that of Bonellia. The anus
is placed posteriorly; and in front of it, on the dorsal surface, are two
bundles of many long thread-like gills. On the ventro-lateral surface, in
front of the middle of the body, is a pair of finger-shaped processes
containing the genital ducts. The anterior segments of the body can be
withdrawn into the body, as in the Chlorhaemidae. Further examination
leads to the conclusion that the body of Sternaspis consists of about thirty
segments, most of them provided with paired bundles of capillary
(neuropodial?) chaetae, distributed as follows:—Each of the segments 2, 3,
4 has a half ring of strong chaetae on each side; segments 5 to 7 are without
chaetae; segments 8 to 14 have chaetae embedded in the body-wall, but not
ventral surface; the right represents the internal organs as seen when the body-
wall is pinned aside, having been slit up along its dorsal surface. a, Anus; c, gills;
ch, anterior strong chaetae; ch1, bundles of chaetae along the lateral margin of
the shield; ch2, the posterior marginal chaetae; d, oviduct; g, the external tube
carrying genital pore; i, coiled intestine; n, nephridium ("brown tube"); o, ovary,
amongst the coils of the alimentary canal; p, pharynx; pr, prostomium, with
mouth just behind it; s, shield (on left figure); s, stomach (on right); sh, outline of
shield seen through the ventral body-wall (in right figure); x, chaetae embedded
in the body-wall, with nerves passing by them.
Fam. 6. Sternaspidae.—The single genus, Sternaspis, has not been recorded
on our coasts, but is of so peculiar a structure as to deserve a description.
[391] S. scutata Ranzani, occurring in the Mediterranean, is rather less than
an inch in length, and derives its name from the possession of a pair of
peculiar "horny" plates or shields on the ventral surface posteriorly. Around
their margins are set about thirty bundles of long capillary chaetae. There
are three half rings of stronger chaetae on each side near the anterior end of
the body. The mouth is overhung by a very small rounded knob
(prostomium), which in S. spinosa Sluiter, is prolonged outwards on each
side to form a grooved palp-like organ, recalling that of Bonellia. The anus
is placed posteriorly; and in front of it, on the dorsal surface, are two
bundles of many long thread-like gills. On the ventro-lateral surface, in
front of the middle of the body, is a pair of finger-shaped processes
containing the genital ducts. The anterior segments of the body can be
withdrawn into the body, as in the Chlorhaemidae. Further examination
leads to the conclusion that the body of Sternaspis consists of about thirty
segments, most of them provided with paired bundles of capillary
(neuropodial?) chaetae, distributed as follows:—Each of the segments 2, 3,
4 has a half ring of strong chaetae on each side; segments 5 to 7 are without
chaetae; segments 8 to 14 have chaetae embedded in the body-wall, but not
Page 343
projecting. The shields cover the remaining segments; and along the outer
edge of each are some ten bundles of chaetae, and along the hinder edge
some five or six bundles, representing as many segments. Thus the worm
consists of about thirty segments whose outlines are nearly obliterated (as in
the Chlorhaemidae), and whose chaetae, except those which are specially
developed, are disappearing: while posteriorly a great shortening of the
body brings the bundles close together. A continuation of this process,
involving a further disappearance of chaetae, leads readily to the condition
met with in Echiurus, one of the chaetigerous Gephyrea. Internally, further
evidence of the relation between Sternaspis and the Chlorhaemids with the
Gephyrea is afforded by the absence of septa, by the coiled alimentary
canal, and by the presence of a single pair of nephridia, which in the latter
group act both as excretory organs and as genital ducts.
BRANCH B. CRYPTOCEPHALA.
Sub-Order 1. Sabelliformia.[392]
Fam. 1. Sabellidae.—The branchial crown consists of a usually
considerable number of filaments arising from a semicircular base. The
peristomium may be reflexed to form a collar, which is frequently notched,
so that a lateral and a ventral lobe on each side may be distinguished (Fig.
133, B, p. 261). The thorax consists of nine segments, and is provided with
ventral "gland shields," which are continued along the abdomen, where they
are subdivided into two by a ciliated "faecal groove," which sometimes
bends to one side on reaching the thorax, and may extend forwards along
the dorsal surface to the head: this groove serves to carry the faeces out of
the tube. The gill filaments are always provided with secondary processes,
and may be provided with compound eyes.[393] The tubes of the Sabellidae
are always of fine mud or of sand.
Sabella pavonia Sav. is about 10 to 12 inches long and about ¼ inch across;
the tube of fine mud is considerably longer and embedded deeply in the
mud, with its free end projecting to some 2 or more inches, where it serves
for the attachment of seaweed, Polyzoa, Hydrozoa, etc. The colour of the
edge of each are some ten bundles of chaetae, and along the hinder edge
some five or six bundles, representing as many segments. Thus the worm
consists of about thirty segments whose outlines are nearly obliterated (as in
the Chlorhaemidae), and whose chaetae, except those which are specially
developed, are disappearing: while posteriorly a great shortening of the
body brings the bundles close together. A continuation of this process,
involving a further disappearance of chaetae, leads readily to the condition
met with in Echiurus, one of the chaetigerous Gephyrea. Internally, further
evidence of the relation between Sternaspis and the Chlorhaemids with the
Gephyrea is afforded by the absence of septa, by the coiled alimentary
canal, and by the presence of a single pair of nephridia, which in the latter
group act both as excretory organs and as genital ducts.
BRANCH B. CRYPTOCEPHALA.
Sub-Order 1. Sabelliformia.[392]
Fam. 1. Sabellidae.—The branchial crown consists of a usually
considerable number of filaments arising from a semicircular base. The
peristomium may be reflexed to form a collar, which is frequently notched,
so that a lateral and a ventral lobe on each side may be distinguished (Fig.
133, B, p. 261). The thorax consists of nine segments, and is provided with
ventral "gland shields," which are continued along the abdomen, where they
are subdivided into two by a ciliated "faecal groove," which sometimes
bends to one side on reaching the thorax, and may extend forwards along
the dorsal surface to the head: this groove serves to carry the faeces out of
the tube. The gill filaments are always provided with secondary processes,
and may be provided with compound eyes.[393] The tubes of the Sabellidae
are always of fine mud or of sand.
Sabella pavonia Sav. is about 10 to 12 inches long and about ¼ inch across;
the tube of fine mud is considerably longer and embedded deeply in the
mud, with its free end projecting to some 2 or more inches, where it serves
for the attachment of seaweed, Polyzoa, Hydrozoa, etc. The colour of the
Page 344
animal is orange-brown; the gills, which are about 1½ inches long, are
green (due to contained blood) marked with more or less extensive brown
or purple-brown spots, which may even hide the green tint. There is a pair
of dark filaments arising between the dorsalmost gill filaments, which have
been erroneously regarded as "prostomial tentacles"; they are, in fact,
prolongations of a peculiar membrane or lip round the base of the gills,
which bounds a groove leading to the mouth. These lip-processes (Fig. 133,
B, l) occur in other Sabellids. Atlantic, North Sea, and Mediterranean.
Fig. 182.—A, A gill filament of Branchiomma; B, of Dasychone. a, Axis; f, secondary
filaments; o, eye; x, dorsal appendices.
Branchiomma vesiculosum Mont. forms a sandy tube near low tide-mark.
The animal, measuring 6-7 inches, is rich brown, darker anteriorly,
abundantly speckled with white; the ventral surface is pink; the gills are
green or olive-brown, marked with white bands in a fairly regular fashion.
Each gill filament has, just below its tip, a compound eye, consisting of
several lenses and retinae. North Sea and Mediterranean.
Dasychone bombyx Dalyl. is a short, comparatively stout worm usually 1 to
1½ inches long; reddish-brown in colour, with a darker spot on each side of
every segment. The gills are lighter with greenish marks. This worm may
readily be recognised, for each of the gill filaments carries some six to ten
pairs of dark compound eyes at intervals along its length, and near to each
pair there arise two short processes from the outer side of the filament,
which are known as "dorsal appendices." The worm forms a tube of mud,
more or less mixed with sand. It occurs at low water and to some depth
round the coasts of the Atlantic, North Sea, and Mediterranean.
Chone infundibuliformis Kröyer may be recognised by the absence of lobes
on the collar, the presence of a membrane connecting the gill filaments, and
green (due to contained blood) marked with more or less extensive brown
or purple-brown spots, which may even hide the green tint. There is a pair
of dark filaments arising between the dorsalmost gill filaments, which have
been erroneously regarded as "prostomial tentacles"; they are, in fact,
prolongations of a peculiar membrane or lip round the base of the gills,
which bounds a groove leading to the mouth. These lip-processes (Fig. 133,
B, l) occur in other Sabellids. Atlantic, North Sea, and Mediterranean.
Fig. 182.—A, A gill filament of Branchiomma; B, of Dasychone. a, Axis; f, secondary
filaments; o, eye; x, dorsal appendices.
Branchiomma vesiculosum Mont. forms a sandy tube near low tide-mark.
The animal, measuring 6-7 inches, is rich brown, darker anteriorly,
abundantly speckled with white; the ventral surface is pink; the gills are
green or olive-brown, marked with white bands in a fairly regular fashion.
Each gill filament has, just below its tip, a compound eye, consisting of
several lenses and retinae. North Sea and Mediterranean.
Dasychone bombyx Dalyl. is a short, comparatively stout worm usually 1 to
1½ inches long; reddish-brown in colour, with a darker spot on each side of
every segment. The gills are lighter with greenish marks. This worm may
readily be recognised, for each of the gill filaments carries some six to ten
pairs of dark compound eyes at intervals along its length, and near to each
pair there arise two short processes from the outer side of the filament,
which are known as "dorsal appendices." The worm forms a tube of mud,
more or less mixed with sand. It occurs at low water and to some depth
round the coasts of the Atlantic, North Sea, and Mediterranean.
Chone infundibuliformis Kröyer may be recognised by the absence of lobes
on the collar, the presence of a membrane connecting the gill filaments, and
Page 345
the passage of the faecal groove along the dorsal surface of the thorax. The
worm is 6 inches long, with purple gills, spotted with yellowish-white. The
tube is formed of yellowish membrane covered with sand, and is fixed to
stones and other objects. Potamilla reniformis Müll. is about 3 inches long,
with about twelve brown gill filaments, some of which have eyes near the
base. The tube is transparent and horny, with sometimes a slight covering of
sand. Found in old oyster shells. North Sea, Atlantic, Mediterranean.
The genus Spirographis contains one of the largest European Sabellids, S.
spallanzanii Viv., which occurs off the Channel Islands and in the
Mediterranean. The two gill plumes are unequal; the large rone forms an
upright, spirally-coiled column.
Fam. 2. Eriographidae.—Myxicola infundibulum Mont. has its gill
filaments connected by a membrane reaching nearly to their tips. Each gill
plume forms a semicircle; there are no eyes; the peristomium does not form
a collar; no gland shields. The worm requires neither of these structures,
since it is practically a free-swimmer, envelopes itself in mucus, and moves
tail first. The faecal groove is not well marked, though continued dorsally.
In the abdomen the tori uncinigeri extend dorsally and ventrally (beyond
the neuropodial chaetae) and nearly encircle the body. The animal is 4 or 5
inches long, dull green, with purplish gills. Between tide-marks. North Sea
and Mediterranean.
Amphiglena mediterranea Leyd. is only about ¼ inch long, hermaphrodite,
and has eyes on the peristomium and on the anal segment. It is a very
elegant little worm, and as a living object under the microscope, with the
cilia on the gills, is very beautiful. The gills consist of six filaments on each
side, provided with the usual double row of ciliated processes.
Fam. 3. Amphicorinidae.—Small hermaphrodite Sabellids in which each
gill tuft contains only a few branching filaments. The simplest form is
Haplobranchus aestuarinus Bourne,[394] which occurs in the rather foul
mud at low tide in the estuaries of the Thames, the Liffey, and other rivers.
The animal is about ¼ inch long, with four finger-shaped processes on each
side, and a pair of larger, vascular processes on the ventral surface. These
worm is 6 inches long, with purple gills, spotted with yellowish-white. The
tube is formed of yellowish membrane covered with sand, and is fixed to
stones and other objects. Potamilla reniformis Müll. is about 3 inches long,
with about twelve brown gill filaments, some of which have eyes near the
base. The tube is transparent and horny, with sometimes a slight covering of
sand. Found in old oyster shells. North Sea, Atlantic, Mediterranean.
The genus Spirographis contains one of the largest European Sabellids, S.
spallanzanii Viv., which occurs off the Channel Islands and in the
Mediterranean. The two gill plumes are unequal; the large rone forms an
upright, spirally-coiled column.
Fam. 2. Eriographidae.—Myxicola infundibulum Mont. has its gill
filaments connected by a membrane reaching nearly to their tips. Each gill
plume forms a semicircle; there are no eyes; the peristomium does not form
a collar; no gland shields. The worm requires neither of these structures,
since it is practically a free-swimmer, envelopes itself in mucus, and moves
tail first. The faecal groove is not well marked, though continued dorsally.
In the abdomen the tori uncinigeri extend dorsally and ventrally (beyond
the neuropodial chaetae) and nearly encircle the body. The animal is 4 or 5
inches long, dull green, with purplish gills. Between tide-marks. North Sea
and Mediterranean.
Amphiglena mediterranea Leyd. is only about ¼ inch long, hermaphrodite,
and has eyes on the peristomium and on the anal segment. It is a very
elegant little worm, and as a living object under the microscope, with the
cilia on the gills, is very beautiful. The gills consist of six filaments on each
side, provided with the usual double row of ciliated processes.
Fam. 3. Amphicorinidae.—Small hermaphrodite Sabellids in which each
gill tuft contains only a few branching filaments. The simplest form is
Haplobranchus aestuarinus Bourne,[394] which occurs in the rather foul
mud at low tide in the estuaries of the Thames, the Liffey, and other rivers.
The animal is about ¼ inch long, with four finger-shaped processes on each
side, and a pair of larger, vascular processes on the ventral surface. These
Page 346
five branches are gills (palps), although, owing to the small size of the
worm and simple vascular system, the four lateral filaments have no blood-
vessels. The animal consists of only eleven chaetigerous segments, and
lives in a tube made of mud particles.[395] Fabricia sabella Ehrenb.
(Amphicora fabricia Müll.) has three gills on each side, each with a number
of secondary branches of different sizes, but so arranged as all to reach the
same level. It has eyes in its tail and swims backwards.
Fam. 4. Serpulidae.—The thorax is provided with an undulated membrane
on each side, chiefly employed in smoothing the inside of the tube; it
represents the dorsal and ventral cirri of these segments. The gland shields
are confined to the thoracic segments. In many genera the dorsalmost gill
filament on one or both sides is terminally dilated and serves as an
operculum. The tube is calcareous, and attached to rocks, shells, etc., for a
greater or smaller part of its extent.
Serpula vermicularis L. forms a pinkish tapering tube about 3 inches long;
the narrower fixed end is coiled. It is marked at irregular intervals with
encircling ridges, indicating cessation in formation, and has a circular
aperture. The worm itself is about 1½ inches long. The horny operculum is
conical, with its base upwards, fringed with short processes. 20 fathoms in
the North Sea and Mediterranean; also from 275 fathoms off the west coast
of Ireland.
Pomatoceros triqueter L.—The white shell is adherent, with a distinct keel
along its upper surface; the aperture is overhung by a spine. The tubes are
abundant everywhere, attached to rocks, stones, shells, etc., between tide-
marks and down to 18 fathoms. The animal is very handsome, the thorax
being deep blue, the abdomen red in the female, whitish in the ripe male.
The branchiae are barred and spotted with blue, orange, and white; the
operculum is calcareous, and furnished with a couple of horn-like
processes.
worm and simple vascular system, the four lateral filaments have no blood-
vessels. The animal consists of only eleven chaetigerous segments, and
lives in a tube made of mud particles.[395] Fabricia sabella Ehrenb.
(Amphicora fabricia Müll.) has three gills on each side, each with a number
of secondary branches of different sizes, but so arranged as all to reach the
same level. It has eyes in its tail and swims backwards.
Fam. 4. Serpulidae.—The thorax is provided with an undulated membrane
on each side, chiefly employed in smoothing the inside of the tube; it
represents the dorsal and ventral cirri of these segments. The gland shields
are confined to the thoracic segments. In many genera the dorsalmost gill
filament on one or both sides is terminally dilated and serves as an
operculum. The tube is calcareous, and attached to rocks, shells, etc., for a
greater or smaller part of its extent.
Serpula vermicularis L. forms a pinkish tapering tube about 3 inches long;
the narrower fixed end is coiled. It is marked at irregular intervals with
encircling ridges, indicating cessation in formation, and has a circular
aperture. The worm itself is about 1½ inches long. The horny operculum is
conical, with its base upwards, fringed with short processes. 20 fathoms in
the North Sea and Mediterranean; also from 275 fathoms off the west coast
of Ireland.
Pomatoceros triqueter L.—The white shell is adherent, with a distinct keel
along its upper surface; the aperture is overhung by a spine. The tubes are
abundant everywhere, attached to rocks, stones, shells, etc., between tide-
marks and down to 18 fathoms. The animal is very handsome, the thorax
being deep blue, the abdomen red in the female, whitish in the ripe male.
The branchiae are barred and spotted with blue, orange, and white; the
operculum is calcareous, and furnished with a couple of horn-like
processes.
Page 347
Fig. 183.—A group of tubes of Serpula vermicularis L., from the mouths of two of
which the animals are protruding, that on the right being seen from above. br,
The gill plume; m, thoracic membrane; op, operculum; op1, corresponding gill
filament of the opposite side; t, tube. (From Cuvier's Règne Animal.) Nat. size.
Filigrana implexa Berkeley is a small worm, but the slender white tubes
intertwine and adhere together in masses 3 or 4 inches high, occurring at
low tide and down to 18 fathoms in the North Sea and Mediterranean. The
animal has only eight gill filaments on each side, one of which on each side
is slightly expanded to serve as an operculum. The worm multiplies by
transverse division.
Spirorbis borealis Daudin is a still smaller worm, the tube of which is
coiled in a flat spiral about 1⁄16 to ⅛ inch across; it is common, adhering to
Fucus, shells, and other objects. It is represented by fossils in the
Palaeozoic rocks. Cosmopolitan.
Protula (Psygmobranchus) tubularia Mont. is a Serpulid without an
operculum; it forms a straight or slightly and irregularly curved tube.
Atlantic and Mediterranean. Salmacina dysteri Huxley has no operculum; it
is a small worm incrusting seaweeds, or forming masses like Filigrana.
Sub-Order 2. Hermelliformia.
The single family Hermellidae is represented by two species—Sabellaria
alveolata L., which is littoral, and S. spinulosa Leuck., occurring in 10 to 30
which the animals are protruding, that on the right being seen from above. br,
The gill plume; m, thoracic membrane; op, operculum; op1, corresponding gill
filament of the opposite side; t, tube. (From Cuvier's Règne Animal.) Nat. size.
Filigrana implexa Berkeley is a small worm, but the slender white tubes
intertwine and adhere together in masses 3 or 4 inches high, occurring at
low tide and down to 18 fathoms in the North Sea and Mediterranean. The
animal has only eight gill filaments on each side, one of which on each side
is slightly expanded to serve as an operculum. The worm multiplies by
transverse division.
Spirorbis borealis Daudin is a still smaller worm, the tube of which is
coiled in a flat spiral about 1⁄16 to ⅛ inch across; it is common, adhering to
Fucus, shells, and other objects. It is represented by fossils in the
Palaeozoic rocks. Cosmopolitan.
Protula (Psygmobranchus) tubularia Mont. is a Serpulid without an
operculum; it forms a straight or slightly and irregularly curved tube.
Atlantic and Mediterranean. Salmacina dysteri Huxley has no operculum; it
is a small worm incrusting seaweeds, or forming masses like Filigrana.
Sub-Order 2. Hermelliformia.
The single family Hermellidae is represented by two species—Sabellaria
alveolata L., which is littoral, and S. spinulosa Leuck., occurring in 10 to 30
Page 348
fathoms.
S. alveolata[396] is about an inch long; the thorax is purple, the abdomen
yellow to red. The narrow caudal region is bent sharply forwards, so that
the anus, situated at its tip, comes to lie at the orifice of the tube, which is
irregular and sandy. Great numbers of the animals live together, so that the
masses of their tubes may be 2 or 3 feet thick and several feet long. They
are well seen on the shore, at Paignton, near Torquay, and on Hilbre Island,
off the Cheshire coast. North Sea, Atlantic, Mediterranean.
Fig. 184.—Spirorbis. A, the shell, enlarged. B, the animal, × 50. c, Peristomial collar; e,
eggs in the brood pouch at the end of the operculum; g, gills; m, thoracic
membrane (characteristic of Serpulidae); n, the single pair of thoracic nephridia
opening by a median dorsal pore beneath the collar (common to all
Sabelliformia); o, ova in the anterior abdominal segments; op, operculum; s,
spermatozoa in the hinder abdominal segments; st, stomach. (From Claparède.)
Order III. Myzostomaria.[397]
These animals are parasitic on Crinoids or Asteroids.[398] The single family,
Myzostomatidae, contains but two genera, Myzostoma F. S. Lkt. and
Stelechopus v. Gr.
Some of them move, more or less actively, on the surface of their hosts,
others live in a sessile condition between the joints of the arms or pinnules,
causing a greater or less malformation thereof, sometimes leading to the
formation of a more or less globular cyst like a plant-gall, due to
overgrowths of the joint, as in M. deformator v. Gr. and M. cysticola v. Gr.:
while M. pulvinar v. Gr. is endoparasitic in the intestine. Two species occur
S. alveolata[396] is about an inch long; the thorax is purple, the abdomen
yellow to red. The narrow caudal region is bent sharply forwards, so that
the anus, situated at its tip, comes to lie at the orifice of the tube, which is
irregular and sandy. Great numbers of the animals live together, so that the
masses of their tubes may be 2 or 3 feet thick and several feet long. They
are well seen on the shore, at Paignton, near Torquay, and on Hilbre Island,
off the Cheshire coast. North Sea, Atlantic, Mediterranean.
Fig. 184.—Spirorbis. A, the shell, enlarged. B, the animal, × 50. c, Peristomial collar; e,
eggs in the brood pouch at the end of the operculum; g, gills; m, thoracic
membrane (characteristic of Serpulidae); n, the single pair of thoracic nephridia
opening by a median dorsal pore beneath the collar (common to all
Sabelliformia); o, ova in the anterior abdominal segments; op, operculum; s,
spermatozoa in the hinder abdominal segments; st, stomach. (From Claparède.)
Order III. Myzostomaria.[397]
These animals are parasitic on Crinoids or Asteroids.[398] The single family,
Myzostomatidae, contains but two genera, Myzostoma F. S. Lkt. and
Stelechopus v. Gr.
Some of them move, more or less actively, on the surface of their hosts,
others live in a sessile condition between the joints of the arms or pinnules,
causing a greater or less malformation thereof, sometimes leading to the
formation of a more or less globular cyst like a plant-gall, due to
overgrowths of the joint, as in M. deformator v. Gr. and M. cysticola v. Gr.:
while M. pulvinar v. Gr. is endoparasitic in the intestine. Two species occur
Page 349
on our common Antedon (Comatula) rosacea; one, M. cirriferum Lkt.,
creeps about the oral surface, especially along the food grooves of the disc
and arms; the other, M. glabrum Lkt., lives close to the mouth of the
Crinoid, so that its pharynx can be inserted into the oesophagus of the host;
this species rarely moves from this position, and carries a young one on its
back.
Fig. 185.—Myzostoma glabrum Lkt., on the disc of Antedon rosacea. The
hermaphrodite individual (⚥) lies over the mouth of the Antedon, and carries on
its back at the anterior end a young one ( ♂ ) with only male organs fully
developed. ap, The anal papilla of Antedon. × 4.
The Myzostomaria are circular or oval, more or less markedly convex
dorsally, flat ventrally; Stelechopus, however, which lives on Hyocrinus, is
elongated. The margin of the body is provided with ten or more pairs of
cirri, short (M. glabrum) or long (M. cirriferum), and the general
appearance of the animal is greatly changed in some species by the great
elongation of the hinder cirri, into which the viscera may extend (M.
filicauda v. Gr.). On the ventral surface are five pairs of small conical
"parapodia," arranged, like the internal organs, in a radiate manner. Each
parapodium carries a couple of chaetae; one a hook, the other serving as a
"guide" for this hook. The four "suckers" on each side are either glandular
or sensory organs; and Wheeler considers them homologous with the lateral
organs of Capitellids; they are usually little developed in those species
which live inside cysts.
creeps about the oral surface, especially along the food grooves of the disc
and arms; the other, M. glabrum Lkt., lives close to the mouth of the
Crinoid, so that its pharynx can be inserted into the oesophagus of the host;
this species rarely moves from this position, and carries a young one on its
back.
Fig. 185.—Myzostoma glabrum Lkt., on the disc of Antedon rosacea. The
hermaphrodite individual (⚥) lies over the mouth of the Antedon, and carries on
its back at the anterior end a young one ( ♂ ) with only male organs fully
developed. ap, The anal papilla of Antedon. × 4.
The Myzostomaria are circular or oval, more or less markedly convex
dorsally, flat ventrally; Stelechopus, however, which lives on Hyocrinus, is
elongated. The margin of the body is provided with ten or more pairs of
cirri, short (M. glabrum) or long (M. cirriferum), and the general
appearance of the animal is greatly changed in some species by the great
elongation of the hinder cirri, into which the viscera may extend (M.
filicauda v. Gr.). On the ventral surface are five pairs of small conical
"parapodia," arranged, like the internal organs, in a radiate manner. Each
parapodium carries a couple of chaetae; one a hook, the other serving as a
"guide" for this hook. The four "suckers" on each side are either glandular
or sensory organs; and Wheeler considers them homologous with the lateral
organs of Capitellids; they are usually little developed in those species
which live inside cysts.
Page 350
Fig. 186.—Myzostoma cirriferum. (After Lang and v. Graff.) The organs are supposed
to be seen by transparency. On the right side the more dorsal organs are shown,
and on the left, those lying more ventrally. a, Anus; c, ten pairs of marginal cirri;
f1 to f5, the five parapodia of the left side, each with two chaetae; i, the branches
of the intestine on the right side; m, mouth; o, the opening of the oviduct (od)
into the rectum; ov, the uterus or coelom, filled with eggs, occupying the spaces
between the lobes of the intestine; p, the pharynx (acrecbolic introvert) lying in
the pharyngeal sac; r, rectum; s, the four "suckers" of the left side; these, like the
parapodia, really lie on the ventral surface; st, stomach; t, the branching testis; ♂,
the pore of the sperm-duct.
The mouth and anus are usually ventral; but in M. glabrum the anus is
dorsal, and in a few species both apertures are carried on to the back by the
great development of the ventral surface. The alimentary canal is provided
with a protrusible pharynx; the intestine is branched; amongst its branches
is the coelom, packed with eggs, and functioning as a uterus (usually called
"ovary"). The true ovary is a small mass of cells on each side, a
proliferation of the coelomic epithelium covering the intestinal wall. A
median continuation of the uterus passes backwards above the rectum, and
opens either into it or by an independent pore dorsal to the anus. The
"lateral oviducts" of Nansen are nephridia with ciliated funnels opening into
the coelom (uterus), and with pores leading into the cloaca on its ventral
surface; or, in M. belli Wheeler, opening to the exterior. The two testes are
branched, and each sperm-duct opens laterally on a papilla, just outside the
third parapodium of each side. Wheeler[399] has recently shown that in the
young Myzostoma the spermatozoa ripen before the ova, so that it is
functionally a male; before the spermatozoa are all discharged the ova
mature, and the animal is for a time hermaphrodite; later on, however, when
all the spermatozoa are used up, the worm is a female. Beard's "dwarf
males" are therefore merely the young of hermaphrodite forms. In
to be seen by transparency. On the right side the more dorsal organs are shown,
and on the left, those lying more ventrally. a, Anus; c, ten pairs of marginal cirri;
f1 to f5, the five parapodia of the left side, each with two chaetae; i, the branches
of the intestine on the right side; m, mouth; o, the opening of the oviduct (od)
into the rectum; ov, the uterus or coelom, filled with eggs, occupying the spaces
between the lobes of the intestine; p, the pharynx (acrecbolic introvert) lying in
the pharyngeal sac; r, rectum; s, the four "suckers" of the left side; these, like the
parapodia, really lie on the ventral surface; st, stomach; t, the branching testis; ♂,
the pore of the sperm-duct.
The mouth and anus are usually ventral; but in M. glabrum the anus is
dorsal, and in a few species both apertures are carried on to the back by the
great development of the ventral surface. The alimentary canal is provided
with a protrusible pharynx; the intestine is branched; amongst its branches
is the coelom, packed with eggs, and functioning as a uterus (usually called
"ovary"). The true ovary is a small mass of cells on each side, a
proliferation of the coelomic epithelium covering the intestinal wall. A
median continuation of the uterus passes backwards above the rectum, and
opens either into it or by an independent pore dorsal to the anus. The
"lateral oviducts" of Nansen are nephridia with ciliated funnels opening into
the coelom (uterus), and with pores leading into the cloaca on its ventral
surface; or, in M. belli Wheeler, opening to the exterior. The two testes are
branched, and each sperm-duct opens laterally on a papilla, just outside the
third parapodium of each side. Wheeler[399] has recently shown that in the
young Myzostoma the spermatozoa ripen before the ova, so that it is
functionally a male; before the spermatozoa are all discharged the ova
mature, and the animal is for a time hermaphrodite; later on, however, when
all the spermatozoa are used up, the worm is a female. Beard's "dwarf
males" are therefore merely the young of hermaphrodite forms. In
Page 351
cysticolous species each cyst usually contains a large female individual and
a small male. In these cases the young one (male) discharges all its
spermatozoa before the ova ripen, so that a period of immaturity intervenes
and a true hermaphrodite condition is omitted; the animal is at first male,
and later female. The Myzostomaria are thus "protandric hermaphrodites."
The affinity of these animals has been much discussed; they superficially
resemble the Tardigrada in many anatomical features, and differ greatly
from Chaetopoda, but as they possess the characteristic chaetae or
parapodia, and pass through a larval stage[400] similar to that of the
Polychaetes, there is no doubt that they are closely allied to the group, and
indeed may be regarded as degenerate Chaetopods. It has been suggested
that they form a passage group between them and the Tardigrada; and von
Graff forms a group Stelechopoda, to include the Myzostomaria, the
Tardigrada, and the Linguatulida.
a small male. In these cases the young one (male) discharges all its
spermatozoa before the ova ripen, so that a period of immaturity intervenes
and a true hermaphrodite condition is omitted; the animal is at first male,
and later female. The Myzostomaria are thus "protandric hermaphrodites."
The affinity of these animals has been much discussed; they superficially
resemble the Tardigrada in many anatomical features, and differ greatly
from Chaetopoda, but as they possess the characteristic chaetae or
parapodia, and pass through a larval stage[400] similar to that of the
Polychaetes, there is no doubt that they are closely allied to the group, and
indeed may be regarded as degenerate Chaetopods. It has been suggested
that they form a passage group between them and the Tardigrada; and von
Graff forms a group Stelechopoda, to include the Myzostomaria, the
Tardigrada, and the Linguatulida.
Page 352
OLIGOCHAETA (EARTHWORMS, ETC.) AND
HIRUDINEA (LEECHES)
BY
F. E. BEDDARD, M.A. (Oxon.), F.R.S.
Prosector to the Zoological Society
CHAPTER XIII
OLIGOCHAETA (EARTHWORMS AND THEIR ALLIES)
INTRODUCTION—ANATOMY—REPRODUCTION—BIONOMICS—DISTRIBUTION—
CLASSIFICATION—MICRODRILI AND MEGADRILI
The Oligochaeta form a well-marked branch of that exceedingly large
assortment of animals vaguely spoken of as worms, and embracing a
number of types many of which have no near relationship to each other.
From this great and unnatural group, which has survived as "Vermes" even
in some quite modern text-books, we can separate off those forms which
show a plain segmentation or division of the body internally as well as
externally into a series of more or less similar rings, as a Class Chaetopoda.
This Class, consisting of the Orders mentioned on p. 241, includes the
worms which form the subject of the present chapter—the Oligochaeta, as
they were originally called by Grube, on account of the fewness of their
chaetae as compared with the number possessed by the majority of the
Polychaeta.
Our knowledge of this group, as of so many others, dates from Aristotle,
who called the earthworms the "intestines of the earth." But it is only very
recently that the numerous and remarkable genera of exotic earthworms
have been anatomically investigated; indeed the common British species
HIRUDINEA (LEECHES)
BY
F. E. BEDDARD, M.A. (Oxon.), F.R.S.
Prosector to the Zoological Society
CHAPTER XIII
OLIGOCHAETA (EARTHWORMS AND THEIR ALLIES)
INTRODUCTION—ANATOMY—REPRODUCTION—BIONOMICS—DISTRIBUTION—
CLASSIFICATION—MICRODRILI AND MEGADRILI
The Oligochaeta form a well-marked branch of that exceedingly large
assortment of animals vaguely spoken of as worms, and embracing a
number of types many of which have no near relationship to each other.
From this great and unnatural group, which has survived as "Vermes" even
in some quite modern text-books, we can separate off those forms which
show a plain segmentation or division of the body internally as well as
externally into a series of more or less similar rings, as a Class Chaetopoda.
This Class, consisting of the Orders mentioned on p. 241, includes the
worms which form the subject of the present chapter—the Oligochaeta, as
they were originally called by Grube, on account of the fewness of their
chaetae as compared with the number possessed by the majority of the
Polychaeta.
Our knowledge of this group, as of so many others, dates from Aristotle,
who called the earthworms the "intestines of the earth." But it is only very
recently that the numerous and remarkable genera of exotic earthworms
have been anatomically investigated; indeed the common British species
Page 353
was not really well known before the publication of the memoirs of
Lankester[401] and Claparède[402] in 1864 and 1868, in spite of the elaborate
quarto devoted to it by Morren,[403] the botanist, in 1826. Some of the
aquatic species afforded material to Bonnet and Spallanzani for their
experiments upon the powers of regeneration of the animals when cut into
fragments, while the work of O. F. Müller[404] upon various Naids is a
monument of careful anatomical description. Our knowledge of the aquatic
Oligochaeta does not appear to have advanced so rapidly as has that of the
earthworms.
External Characters.—The most salient external characteristic of this
group of worms, which vary from 1 mm. to 2 metres in length, is of course
the segmentation. The entire body is divided into a number of rings, which
are for the most part similar to each other; a fragment of an earthworm's
body could not be accurately replaced unless it had been cut from the
anterior region. There is precisely the same regular segmentation in the
aquatic representatives of the Order. At the anterior end of the body in the
common earthworm (and in nearly all Oligochaeta) is a small unpaired
lobe, which overhangs the mouth, and is usually termed the prostomium;
the mouth itself is surrounded by the first segment of the body, which never
bears any chaetae in any Oligochaete. The prostomium is occasionally
greatly developed, and in such cases doubtless forms a tactile organ of
importance. This is especially the case with the South American genus
Rhinodrilus, where the lengthy prostomium can be retracted at will. The
aquatic Nais lacustris (= Stylaria proboscidea) has also an exceedingly long
prostomium, which cannot, however, be retracted, though it is contractile.
At a certain distance from the anterior end of the body, fixed for the species,
but varying greatly from genus to genus and from species to species, is the
clitellum. This region of the body (popularly believed to mark the spot
where a worm divided by the gardener's spade has come together again) is
associated with the reproductive function, and serves to secrete the cocoon
in which the creature's eggs are deposited. It has in the earthworm a thick
glandular appearance. A more minute examination of the worm's body will
show the orifices of the reproductive ducts and of the excretory organs
which will be found described below. In addition to these, all British
earthworms and a large percentage of the tropical forms have a row of pores
along the back, which are between the successive segments in the median
Lankester[401] and Claparède[402] in 1864 and 1868, in spite of the elaborate
quarto devoted to it by Morren,[403] the botanist, in 1826. Some of the
aquatic species afforded material to Bonnet and Spallanzani for their
experiments upon the powers of regeneration of the animals when cut into
fragments, while the work of O. F. Müller[404] upon various Naids is a
monument of careful anatomical description. Our knowledge of the aquatic
Oligochaeta does not appear to have advanced so rapidly as has that of the
earthworms.
External Characters.—The most salient external characteristic of this
group of worms, which vary from 1 mm. to 2 metres in length, is of course
the segmentation. The entire body is divided into a number of rings, which
are for the most part similar to each other; a fragment of an earthworm's
body could not be accurately replaced unless it had been cut from the
anterior region. There is precisely the same regular segmentation in the
aquatic representatives of the Order. At the anterior end of the body in the
common earthworm (and in nearly all Oligochaeta) is a small unpaired
lobe, which overhangs the mouth, and is usually termed the prostomium;
the mouth itself is surrounded by the first segment of the body, which never
bears any chaetae in any Oligochaete. The prostomium is occasionally
greatly developed, and in such cases doubtless forms a tactile organ of
importance. This is especially the case with the South American genus
Rhinodrilus, where the lengthy prostomium can be retracted at will. The
aquatic Nais lacustris (= Stylaria proboscidea) has also an exceedingly long
prostomium, which cannot, however, be retracted, though it is contractile.
At a certain distance from the anterior end of the body, fixed for the species,
but varying greatly from genus to genus and from species to species, is the
clitellum. This region of the body (popularly believed to mark the spot
where a worm divided by the gardener's spade has come together again) is
associated with the reproductive function, and serves to secrete the cocoon
in which the creature's eggs are deposited. It has in the earthworm a thick
glandular appearance. A more minute examination of the worm's body will
show the orifices of the reproductive ducts and of the excretory organs
which will be found described below. In addition to these, all British
earthworms and a large percentage of the tropical forms have a row of pores
along the back, which are between the successive segments in the median
Page 354
line. These "dorsal pores" open directly into the body-cavity, and are mere
perforations of the body-wall, not tubes lined by a special layer of cells.
Professor Spencer of Melbourne[405] has observed a giant earthworm
(Megascolides australis) of Gippsland which, when held in the hand, spurts
out, to a height of several inches, the fluid of the body-cavity through its
dorsal pores. The burrows, he remarks, are coated over with the same fluid,
which is regarded by him as a lubricant. This, however, considering that the
glandular cells of the epidermis can secrete a mucous fluid, seems to be an
expensive use to which to put the important fluids of the interior of the
body. It is more probable that the dorsal pores are a means of getting rid of
waste products. Lim Boon Keng[406] suggests that the coelomic fluid
possesses a bactericidal function. The dorsal pores are missing in many
earthworms, and without exception in those Oligochaeta which live in
water; but these latter worms have a pore upon the head, which appears to
be wanting in the earthworms. Dr. Michaelsen has thought that the head-
pore serves to relieve the brain from undue watery pressure—to act, in fact,
as a kind of safety-valve for the liberation of superfluous fluid.
In some foreign worms the pores of the reproductive ducts are conspicuous
external features (Fig. 197); even in our British species the turgescent male
apertures upon the fifteenth segment are sometimes quite obvious.
Structure of the Body-Wall.—The body-wall consists in all Oligochaeta of
three recognisable sheets of tissue. Outside is the epidermis, which always
consists of a single layer of cells, except in the clitellar region of
earthworms. It is a point of difference between the aquatic genera and the
terrestrial forms that in the former the clitellum is only one cell thick, while
in the higher Oligochaeta it is made up of more than one layer of cells. The
epidermis is ciliated only in the genus Aeolosoma, and there only on the
prostomium. It secretes a thin layer of chitin, which is defective opposite to
the glandular cells, and becomes therefore perforated by numerous pores.
The structure of the epidermis of Lumbricus has been studied by
Cerfontaine, whose recent account[407] of the same is the fullest and most
accurate that exists.
perforations of the body-wall, not tubes lined by a special layer of cells.
Professor Spencer of Melbourne[405] has observed a giant earthworm
(Megascolides australis) of Gippsland which, when held in the hand, spurts
out, to a height of several inches, the fluid of the body-cavity through its
dorsal pores. The burrows, he remarks, are coated over with the same fluid,
which is regarded by him as a lubricant. This, however, considering that the
glandular cells of the epidermis can secrete a mucous fluid, seems to be an
expensive use to which to put the important fluids of the interior of the
body. It is more probable that the dorsal pores are a means of getting rid of
waste products. Lim Boon Keng[406] suggests that the coelomic fluid
possesses a bactericidal function. The dorsal pores are missing in many
earthworms, and without exception in those Oligochaeta which live in
water; but these latter worms have a pore upon the head, which appears to
be wanting in the earthworms. Dr. Michaelsen has thought that the head-
pore serves to relieve the brain from undue watery pressure—to act, in fact,
as a kind of safety-valve for the liberation of superfluous fluid.
In some foreign worms the pores of the reproductive ducts are conspicuous
external features (Fig. 197); even in our British species the turgescent male
apertures upon the fifteenth segment are sometimes quite obvious.
Structure of the Body-Wall.—The body-wall consists in all Oligochaeta of
three recognisable sheets of tissue. Outside is the epidermis, which always
consists of a single layer of cells, except in the clitellar region of
earthworms. It is a point of difference between the aquatic genera and the
terrestrial forms that in the former the clitellum is only one cell thick, while
in the higher Oligochaeta it is made up of more than one layer of cells. The
epidermis is ciliated only in the genus Aeolosoma, and there only on the
prostomium. It secretes a thin layer of chitin, which is defective opposite to
the glandular cells, and becomes therefore perforated by numerous pores.
The structure of the epidermis of Lumbricus has been studied by
Cerfontaine, whose recent account[407] of the same is the fullest and most
accurate that exists.
Page 355
Underneath the epidermis comes a layer of circular muscle-fibres, and
underneath this again a layer of longitudinal muscles. In both layers the
fibres have a softer core, outside which lies the radially striated muscular
substance. The fibres are embedded in a granular matrix. It used to be
considered at one time that such medullated fibres were distinctive of
leeches as opposed to Oligochaeta. Their existence has been really known
in the Oligochaeta since the researches of Ratzel; but Cerfontaine has fully
described them, and emphasised the fact that the fibres of both circular and
longitudinal coats are alike in this respect.
Fig. 187.—Chaetae of Oligochaeta. × 10. (After Michaelsen, Stolc, and Vejdovsky). 1,
2, Penial chaetae of Acanthodrilus georgianus; 3, Spirosperma; 4, Ilyodrilus; 5,
Lophochaeta; 6, Tubifex; 7, 8, Nais; 9, Bohemilla. Figs. 3-9 are ordinary chaetae.
Chaetae.—The passive organs of locomotion in these animals are the
chaetae, which are absent in only one family, Discodrilidae, and in one
other genus, Anachaeta. In this latter worm the chaetae are represented by
large glandular cells, which seem to correspond to the cells from which the
chaetae arise in other forms. They are in this case, as in the others, cells of
the epidermis. The chaetae of the Oligochaeta are not quite so variable in
form as in the marine Polychaeta (see Fig. 138, p. 267). Figs. 187 and 188
illustrate some of the principal shapes which these bristles assume. The
most prevalent form is an elongated S, which has been aptly compared to
the mathematical sign ∫. This kind of chaeta is found in all earthworms, and
in not a few aquatic genera such as the Lumbriculidae. In some of the latter
and in the Tubificidae and Naids there is the same form of chaeta, which is
cleft at the free end, and possibly enables the worm to grasp the leaves of
aquatic plants, and otherwise facilitates progression in a laxer medium than
the stiff soil frequented by the earthworms. Even earthworms, at any rate
the genus Pontoscolex, have chaetae of this kind; some of the aquatic
Oligochaeta have elongated and hair-like bristles, such as that of Tubifex.
underneath this again a layer of longitudinal muscles. In both layers the
fibres have a softer core, outside which lies the radially striated muscular
substance. The fibres are embedded in a granular matrix. It used to be
considered at one time that such medullated fibres were distinctive of
leeches as opposed to Oligochaeta. Their existence has been really known
in the Oligochaeta since the researches of Ratzel; but Cerfontaine has fully
described them, and emphasised the fact that the fibres of both circular and
longitudinal coats are alike in this respect.
Fig. 187.—Chaetae of Oligochaeta. × 10. (After Michaelsen, Stolc, and Vejdovsky). 1,
2, Penial chaetae of Acanthodrilus georgianus; 3, Spirosperma; 4, Ilyodrilus; 5,
Lophochaeta; 6, Tubifex; 7, 8, Nais; 9, Bohemilla. Figs. 3-9 are ordinary chaetae.
Chaetae.—The passive organs of locomotion in these animals are the
chaetae, which are absent in only one family, Discodrilidae, and in one
other genus, Anachaeta. In this latter worm the chaetae are represented by
large glandular cells, which seem to correspond to the cells from which the
chaetae arise in other forms. They are in this case, as in the others, cells of
the epidermis. The chaetae of the Oligochaeta are not quite so variable in
form as in the marine Polychaeta (see Fig. 138, p. 267). Figs. 187 and 188
illustrate some of the principal shapes which these bristles assume. The
most prevalent form is an elongated S, which has been aptly compared to
the mathematical sign ∫. This kind of chaeta is found in all earthworms, and
in not a few aquatic genera such as the Lumbriculidae. In some of the latter
and in the Tubificidae and Naids there is the same form of chaeta, which is
cleft at the free end, and possibly enables the worm to grasp the leaves of
aquatic plants, and otherwise facilitates progression in a laxer medium than
the stiff soil frequented by the earthworms. Even earthworms, at any rate
the genus Pontoscolex, have chaetae of this kind; some of the aquatic
Oligochaeta have elongated and hair-like bristles, such as that of Tubifex.
Page 356
Fig. 188.—Chaetae. × 10. 1, Onychochaeta; 2, Pontoscolex; 3, Trichochaeta; 3b, the
same, more highly magnified.
In the Tubificid Lophochaeta (Fig. 187, 5) the chaetae are ornamented on
both sides with delicate processes, which give them the appearance of
Crustacean hairs. Among earthworms the simple S-like form is sometimes
complicated by the development of sinuous ridges upon the distal end. No
doubt these bristles enable their possessor to get a firmer grip of adjacent
objects; they are very commonly found, in the family Geoscolicidae, upon
the segments of the clitellum, and permit of a firmer union during sexual
congress. In no Oligochaeta are the chaetae borne upon parapodia, as is the
case with the Polychaeta; but in many of the aquatic forms there are a
considerable number to each bundle. In earthworms the number of chaetae
varies greatly. The common earthworms of this country, belonging to the
genera Lumbricus, Allolobophora, and Allurus, have only eight chaetae
upon each segment of the body, and these are then, as a rule, arranged in
pairs or rather couples, two of each on each side of the body. The genus
Perichaeta and some of its allies have a much larger number of chaetae to
each segment, disposed in a continuous row round the middle of the
segment. The intermediate condition is to be seen in the genus Deinodrilus,
where there are twelve in each segment, and in certain members of the
genus Megascolex, where there are eight in each segment in the anterior
region of the body, the number increasing in the posterior segments. The
four bundles of chaetae in the Naids and Tubificids have been likened to the
notopodia and neuropodia of the Polychaetes; but it does not seem certain
that this comparison is justifiable. It was at one time thought that the
continuous circle of chaetae of the Perichaetidae was the primitive
condition; but Professor Bourne has lately found that in Perichaeta the
young embryos have not got this continuous circle; it is only acquired later.
Branchiae.—The Oligochaeta were called by Cuvier the "Annélides
abranches sétigères." But the epithet "abranches" is now known to be
same, more highly magnified.
In the Tubificid Lophochaeta (Fig. 187, 5) the chaetae are ornamented on
both sides with delicate processes, which give them the appearance of
Crustacean hairs. Among earthworms the simple S-like form is sometimes
complicated by the development of sinuous ridges upon the distal end. No
doubt these bristles enable their possessor to get a firmer grip of adjacent
objects; they are very commonly found, in the family Geoscolicidae, upon
the segments of the clitellum, and permit of a firmer union during sexual
congress. In no Oligochaeta are the chaetae borne upon parapodia, as is the
case with the Polychaeta; but in many of the aquatic forms there are a
considerable number to each bundle. In earthworms the number of chaetae
varies greatly. The common earthworms of this country, belonging to the
genera Lumbricus, Allolobophora, and Allurus, have only eight chaetae
upon each segment of the body, and these are then, as a rule, arranged in
pairs or rather couples, two of each on each side of the body. The genus
Perichaeta and some of its allies have a much larger number of chaetae to
each segment, disposed in a continuous row round the middle of the
segment. The intermediate condition is to be seen in the genus Deinodrilus,
where there are twelve in each segment, and in certain members of the
genus Megascolex, where there are eight in each segment in the anterior
region of the body, the number increasing in the posterior segments. The
four bundles of chaetae in the Naids and Tubificids have been likened to the
notopodia and neuropodia of the Polychaetes; but it does not seem certain
that this comparison is justifiable. It was at one time thought that the
continuous circle of chaetae of the Perichaetidae was the primitive
condition; but Professor Bourne has lately found that in Perichaeta the
young embryos have not got this continuous circle; it is only acquired later.
Branchiae.—The Oligochaeta were called by Cuvier the "Annélides
abranches sétigères." But the epithet "abranches" is now known to be
Page 357
inaccurate. In fact it really was so when Cuvier wrote; for naturalists were
at that time well acquainted, chiefly through the elaborate work of O. F.
Müller, with the little fresh-water Naid Dero, the posterior extremity of
which is provided with a varying number of branchial processes. These are
furnished with looped blood-vessels and are covered externally by cilia, so
that the water containing oxygen is constantly renovated. The second
instance of a gilled Oligochaete was discovered in the very same family.
Professor Bourne[408] of Madras found in "tanks" a Naid which he named
Chaetobranchus, in which the head segments, to the number of fifty or so,
are provided with long ciliated processes, which as a rule enclose the dorsal
chaetae of their segments, and in addition a capillary loop. Curiously
enough, this very same worm made its appearance in the Victoria regia tank
at the Botanical Gardens in the Regent's Park, whither it had in all
probability been accidentally imported. Two members of the family
Tubificidae were the next examples of gilled Oligochaeta made known to
science; one of these, Branchiura sowerbyi,[409] appeared also in the
Botanical Gardens, so that its native home is unknown. It differs from
Chaetobranchus in that the gills are at the posterior end of the body, and are
contractile; during the life of the worm they are in continual motion. A
species of the South American genus Hesperodrilus,[410] H. branchiatus, is
also gilled, and, so far as can be made out from a spirit-preserved specimen,
the gills are precisely of the same pattern and contractility as those of its
ally Branchiura. Possibly Branchiura ought to be included in the same
genus with Hesperodrilus. A worm which was originally described by
Grube as Alma nilotica, should really have been placed before the three
last-mentioned instances; but as this worm was only known from a
fragment, and as the description was not by any means full, it was not
thoroughly believed in; it was surmised that it might be a member of some
marine genus, perhaps of the Capitellidae. Oddly enough, the same worm
was independently described by a different name, Digitibranchus niloticus,
a few years later by Levinsen. Quite recently Michaelsen has found by a
reference to the original types that this worm is really gilled, and that it is
specifically identical with a worm which had been given a totally different
name, viz. Siphonogaster. The fact that the gills of the latter had been
overlooked was readily explained by the circumstance that they are
retractile, and not merely contractile. But all the species of the genus
Siphonogaster, or Alma, as it ought really, following the rules of priority, to
at that time well acquainted, chiefly through the elaborate work of O. F.
Müller, with the little fresh-water Naid Dero, the posterior extremity of
which is provided with a varying number of branchial processes. These are
furnished with looped blood-vessels and are covered externally by cilia, so
that the water containing oxygen is constantly renovated. The second
instance of a gilled Oligochaete was discovered in the very same family.
Professor Bourne[408] of Madras found in "tanks" a Naid which he named
Chaetobranchus, in which the head segments, to the number of fifty or so,
are provided with long ciliated processes, which as a rule enclose the dorsal
chaetae of their segments, and in addition a capillary loop. Curiously
enough, this very same worm made its appearance in the Victoria regia tank
at the Botanical Gardens in the Regent's Park, whither it had in all
probability been accidentally imported. Two members of the family
Tubificidae were the next examples of gilled Oligochaeta made known to
science; one of these, Branchiura sowerbyi,[409] appeared also in the
Botanical Gardens, so that its native home is unknown. It differs from
Chaetobranchus in that the gills are at the posterior end of the body, and are
contractile; during the life of the worm they are in continual motion. A
species of the South American genus Hesperodrilus,[410] H. branchiatus, is
also gilled, and, so far as can be made out from a spirit-preserved specimen,
the gills are precisely of the same pattern and contractility as those of its
ally Branchiura. Possibly Branchiura ought to be included in the same
genus with Hesperodrilus. A worm which was originally described by
Grube as Alma nilotica, should really have been placed before the three
last-mentioned instances; but as this worm was only known from a
fragment, and as the description was not by any means full, it was not
thoroughly believed in; it was surmised that it might be a member of some
marine genus, perhaps of the Capitellidae. Oddly enough, the same worm
was independently described by a different name, Digitibranchus niloticus,
a few years later by Levinsen. Quite recently Michaelsen has found by a
reference to the original types that this worm is really gilled, and that it is
specifically identical with a worm which had been given a totally different
name, viz. Siphonogaster. The fact that the gills of the latter had been
overlooked was readily explained by the circumstance that they are
retractile, and not merely contractile. But all the species of the genus
Siphonogaster, or Alma, as it ought really, following the rules of priority, to
Page 358
be called, have not got gills, as is the case too with the genus Hesperodrilus.
The gills of Alma are branched, and there is therefore no longer any
justification whatever for defining the Oligochaeta as a group of Annelids
without gills. The simple gill-like processes of Chaetobranchus might have
been held to be not accurately comparable to the more complex structures
which we find in the marine worms.
Fig. 189.—Transverse section through Branchiura sowerbyi. × 20. d.br, Dorsal
branchia; i, intestine; n, nerve-cord; v.br, ventral branchia.
Nervous System.—The central nervous system of the Oligochaeta is very
uniform in its structure in the entire group. The only family which is at all
anomalous is that of the Aphaneura. In Aeolosoma there appears to be only
a pair of cerebral ganglia, which retain the primitive position of these
organs in being still in direct connexion with the epidermis. In all other
Oligochaeta there are a pair of cerebral ganglia, connected by a
circumoesophageal commissure with a ventral ganglionated cord. From the
cerebral ganglia arises a system of nerve-fibres and nerve-cells, which
represents the stomatogastric nerves of other Invertebrates.
Senses and Sense-Organs.—The only organs that can be regarded with
anything like probability as sense-organs are the pigmented eyes of certain
Naids and the tactile cells of many worms. The latter are usually elongated
cells provided at their free extremity with a stiff process; they occur
associated in groups, and often these bundles of cells have a segmental
arrangement. The head end of many of the lower Oligochaeta, for instance
the genus Aeolosoma, has delicate processes projecting here and there;
The gills of Alma are branched, and there is therefore no longer any
justification whatever for defining the Oligochaeta as a group of Annelids
without gills. The simple gill-like processes of Chaetobranchus might have
been held to be not accurately comparable to the more complex structures
which we find in the marine worms.
Fig. 189.—Transverse section through Branchiura sowerbyi. × 20. d.br, Dorsal
branchia; i, intestine; n, nerve-cord; v.br, ventral branchia.
Nervous System.—The central nervous system of the Oligochaeta is very
uniform in its structure in the entire group. The only family which is at all
anomalous is that of the Aphaneura. In Aeolosoma there appears to be only
a pair of cerebral ganglia, which retain the primitive position of these
organs in being still in direct connexion with the epidermis. In all other
Oligochaeta there are a pair of cerebral ganglia, connected by a
circumoesophageal commissure with a ventral ganglionated cord. From the
cerebral ganglia arises a system of nerve-fibres and nerve-cells, which
represents the stomatogastric nerves of other Invertebrates.
Senses and Sense-Organs.—The only organs that can be regarded with
anything like probability as sense-organs are the pigmented eyes of certain
Naids and the tactile cells of many worms. The latter are usually elongated
cells provided at their free extremity with a stiff process; they occur
associated in groups, and often these bundles of cells have a segmental
arrangement. The head end of many of the lower Oligochaeta, for instance
the genus Aeolosoma, has delicate processes projecting here and there;
Page 359
these appear to be also of a tactile nature, and are of course connected with
cells of the epidermis. The eyes of certain Naids are little more than
lenticular bodies embedded in a mass of pigment. In the genus Eudrilus and
in many Eudrilidae are peculiar integumental bodies, which were
independently discovered by Dr. Horst[411] and myself, and compared by us
to the Pacinian bodies of Mammals. Whether these structures are connected
with nerves or not is doubtful. In spite of the poor development and the
simplicity of their sense organs, the higher Oligochaeta at any rate can feel,
and can distinguish light from darkness. Darwin[412] came to the conclusion
that "light affects worms by its intensity and its duration." And furthermore,
it is only the anterior end of the body which is thus affected. Of the sense of
hearing these animals appear to be utterly devoid. Some kept by Darwin
"took not the least notice of the shrill notes from a metal whistle, which was
repeatedly sounded near them; nor did they of the deepest and loudest tones
of a bassoon." But it is always necessary to discriminate between sound and
vibrations passing through any solid body, which would appeal rather to a
sense of touch. Here worms are most sensitive. It is quite easy, by digging
with some vigour, to arouse the worms in the neighbourhood, who will
crawl to the surface and away from the scene of action; a proceeding on
their part which is sometimes put down to a desire to escape from their
enemy the mole.
Smell appears to be another sense which is somewhat deficient. But worms
are epicures, and exhibit a decided taste and preference for certain articles
of diet. Like their fellow tiller of the soil, the agricultural labourer, worms
have a keen relish for onions, which, however, they must recognise by the
smell. They prefer green cabbage to red, celery to both, and raw meat
appears to be the greatest delicacy that can be offered to them. It is only
substances they are not likely to meet with, such as perfumes, tobacco, and
paraffin, that produce no impression upon the worm's sense of smell.
Coelom and Vascular System.—When an earthworm is dissected the
various organs are seen to lie in a fairly spacious cavity, which is
interrupted and divided into a series of chambers by the mesenteries or
septa which stretch across from wall to wall of the body, and correspond
roughly in their position to the grooves which separate the body externally.
cells of the epidermis. The eyes of certain Naids are little more than
lenticular bodies embedded in a mass of pigment. In the genus Eudrilus and
in many Eudrilidae are peculiar integumental bodies, which were
independently discovered by Dr. Horst[411] and myself, and compared by us
to the Pacinian bodies of Mammals. Whether these structures are connected
with nerves or not is doubtful. In spite of the poor development and the
simplicity of their sense organs, the higher Oligochaeta at any rate can feel,
and can distinguish light from darkness. Darwin[412] came to the conclusion
that "light affects worms by its intensity and its duration." And furthermore,
it is only the anterior end of the body which is thus affected. Of the sense of
hearing these animals appear to be utterly devoid. Some kept by Darwin
"took not the least notice of the shrill notes from a metal whistle, which was
repeatedly sounded near them; nor did they of the deepest and loudest tones
of a bassoon." But it is always necessary to discriminate between sound and
vibrations passing through any solid body, which would appeal rather to a
sense of touch. Here worms are most sensitive. It is quite easy, by digging
with some vigour, to arouse the worms in the neighbourhood, who will
crawl to the surface and away from the scene of action; a proceeding on
their part which is sometimes put down to a desire to escape from their
enemy the mole.
Smell appears to be another sense which is somewhat deficient. But worms
are epicures, and exhibit a decided taste and preference for certain articles
of diet. Like their fellow tiller of the soil, the agricultural labourer, worms
have a keen relish for onions, which, however, they must recognise by the
smell. They prefer green cabbage to red, celery to both, and raw meat
appears to be the greatest delicacy that can be offered to them. It is only
substances they are not likely to meet with, such as perfumes, tobacco, and
paraffin, that produce no impression upon the worm's sense of smell.
Coelom and Vascular System.—When an earthworm is dissected the
various organs are seen to lie in a fairly spacious cavity, which is
interrupted and divided into a series of chambers by the mesenteries or
septa which stretch across from wall to wall of the body, and correspond
roughly in their position to the grooves which separate the body externally.
Page 360
This cavity, common to all the higher animals, is known as the coelom; it is
lined by cells, which cover the intestines as well as the inside of the body-
wall; and upon the intestine assume the form so characteristic of the group,
namely, that of large yellow cells loaded with secreted matters, and called
"chloragogen-cells" by Claparède. The coelom communicates with the
exterior by means of the dorsal pores, the nephridia, and the ducts of the
reproductive organs. As in all animals which possess a coelom, the
reproductive tissues, ova and sperm, are developed on its walls.
Fig. 190.—Sparganophilus tamesis; general anatomy, × 3. (After Benham.) I-XVIII,
segments. 1, 4, 6, Perivisceral vessels (6 is one of the hearts); 2, 3, 7, dorsal
vessel; 5, spermatheca; 8, sperm sacs; 9, intestino-tegumentary vessels; 10,
ovary; 11, 12, integumentary vessels.
The vascular system of the Oligochaeta forms a system of perfectly closed
vessels, which ramify into fine capillary networks in the body-wall, in the
coats of the alimentary canal, and upon the other organs of the body. The
main trunks are a dorsal and a ventral longitudinal, which communicate
directly in the anterior end of the body by large transverse contractile
trunks, the so-called hearts (see Fig. 190, 6). The dorsal vessel is also
contractile, but not the ventral, or, when it occurs, the subnervian. The
vascular system has many degrees of complexity in different families; it is
simpler in the smaller aquatic forms. The blood is usually red, and the
pigment which is suspended in the plasma is haemoglobin. The blood is
corpusculated.
lined by cells, which cover the intestines as well as the inside of the body-
wall; and upon the intestine assume the form so characteristic of the group,
namely, that of large yellow cells loaded with secreted matters, and called
"chloragogen-cells" by Claparède. The coelom communicates with the
exterior by means of the dorsal pores, the nephridia, and the ducts of the
reproductive organs. As in all animals which possess a coelom, the
reproductive tissues, ova and sperm, are developed on its walls.
Fig. 190.—Sparganophilus tamesis; general anatomy, × 3. (After Benham.) I-XVIII,
segments. 1, 4, 6, Perivisceral vessels (6 is one of the hearts); 2, 3, 7, dorsal
vessel; 5, spermatheca; 8, sperm sacs; 9, intestino-tegumentary vessels; 10,
ovary; 11, 12, integumentary vessels.
The vascular system of the Oligochaeta forms a system of perfectly closed
vessels, which ramify into fine capillary networks in the body-wall, in the
coats of the alimentary canal, and upon the other organs of the body. The
main trunks are a dorsal and a ventral longitudinal, which communicate
directly in the anterior end of the body by large transverse contractile
trunks, the so-called hearts (see Fig. 190, 6). The dorsal vessel is also
contractile, but not the ventral, or, when it occurs, the subnervian. The
vascular system has many degrees of complexity in different families; it is
simpler in the smaller aquatic forms. The blood is usually red, and the
pigment which is suspended in the plasma is haemoglobin. The blood is
corpusculated.
Page 361
Excretory Organs.—There appears to be a great deal more variation in the
structure of the excretory system than there is in many other groups. For a
long time only Lumbricus and a few of the aquatic genera were known as
regards their excretory systems. In these there is a pair of excretory organs
or nephridia in nearly all the segments. These are much coiled tubes, in
which it is always possible to recognise three divisions. The nephridium
commences with an orifice of a funnel-like character, fringed with long
cilia, and opening into the body-cavity; from this springs a tube, which
immediately perforates the septum lying between the segment which
contains the funnel and the following one; this tube has the peculiarity first
pointed out by Claparède of being excavated in the substance of cells; the
glandular part of the nephridium is a row of cells which are bored through
by a continuous canal, the walls of which are here and there furnished with
cilia. It often happens that the main canal gives off minute lateral
ramifications, which may even form a kind of network round the principal
canal. The terminal section of the nephridium is a muscular sac which
opens on to the exterior by a pore, and from which the products of excretion
are from time to time evacuated by contractions of its walls. This is a brief
statement of the main facts in the structure of those Oligochaeta in which
there is a single pair of nephridia to each segment of the body; small
differences of more or less importance occur. In Chaetogaster, for example,
there is no trace of a funnel; in some genera the terminal sac is much
reduced or unusually extended, being even sometimes provided with a
caecum of moderate dimensions. In Acanthodrilus novae-zelandiae and a
few other species the point of opening of the nephridia varies from segment
to segment, though it always bears some relation to the chaetae. In these
species the nephridia which open more dorsally are a little different in
structure from those which open more ventrally. One set have a caecum,
and the other have not.
The nephridia of the terrestrial forms are enveloped by a richly developed
network of blood capillaries, which is absent in the smaller aquatic genera.
A very remarkable genus, Brachydrilus, has lately been described by Dr.
Benham,[413] in which each segment has two pairs of nephridia instead of a
single pair. More recently, certain Australian forms, which I propose to
structure of the excretory system than there is in many other groups. For a
long time only Lumbricus and a few of the aquatic genera were known as
regards their excretory systems. In these there is a pair of excretory organs
or nephridia in nearly all the segments. These are much coiled tubes, in
which it is always possible to recognise three divisions. The nephridium
commences with an orifice of a funnel-like character, fringed with long
cilia, and opening into the body-cavity; from this springs a tube, which
immediately perforates the septum lying between the segment which
contains the funnel and the following one; this tube has the peculiarity first
pointed out by Claparède of being excavated in the substance of cells; the
glandular part of the nephridium is a row of cells which are bored through
by a continuous canal, the walls of which are here and there furnished with
cilia. It often happens that the main canal gives off minute lateral
ramifications, which may even form a kind of network round the principal
canal. The terminal section of the nephridium is a muscular sac which
opens on to the exterior by a pore, and from which the products of excretion
are from time to time evacuated by contractions of its walls. This is a brief
statement of the main facts in the structure of those Oligochaeta in which
there is a single pair of nephridia to each segment of the body; small
differences of more or less importance occur. In Chaetogaster, for example,
there is no trace of a funnel; in some genera the terminal sac is much
reduced or unusually extended, being even sometimes provided with a
caecum of moderate dimensions. In Acanthodrilus novae-zelandiae and a
few other species the point of opening of the nephridia varies from segment
to segment, though it always bears some relation to the chaetae. In these
species the nephridia which open more dorsally are a little different in
structure from those which open more ventrally. One set have a caecum,
and the other have not.
The nephridia of the terrestrial forms are enveloped by a richly developed
network of blood capillaries, which is absent in the smaller aquatic genera.
A very remarkable genus, Brachydrilus, has lately been described by Dr.
Benham,[413] in which each segment has two pairs of nephridia instead of a
single pair. More recently, certain Australian forms, which I propose to
Page 362
unite on this account into a genus Trinephrus, have been discovered which
have no less than three distinct and separate pairs in each segment.[414]
Fig. 191.—Section through body-wall of Megascolides australis, highly magnified.
(After Spencer.) 1, 4, 5, 6, Coils of nephridia; 2, funnel; 3, septum; 7, external
apertures.
In many Megascolicidae there is a nephridial system of a different
character. In Perichaeta when dissected the nephridia appear, on account of
their minute size, to be altogether absent. There is, however, in most
Perichaetidae, in many Acanthodrilidae, and in many Cryptodrilidae a mass
of minute tubules which cover the inside of the body-wall, and open on to
the exterior by innumerable openings; there may be in a single segment one
hundred or more of these external orifices, which are scattered about
irregularly. It is at present uncertain whether these minute tubes are
connected among themselves, thus forming a network passing through the
septum and from segment to segment, or whether each tube is isolated from
its fellows, and forms a distinct nephridium, of which there are many in
each segment and entirely separate. This is, however, certain, that the
complex nephridial systems of at any rate Octochaetus and Megascolides
are derived from the multiplication of a single pair of tubes which are alone
present in the embryo. In Perichaeta the minute nephridia are furnished
with coelomic funnels; in Octochaetus they are not, except in the case of
certain nephridia which open into the terminal section of the intestine.
have no less than three distinct and separate pairs in each segment.[414]
Fig. 191.—Section through body-wall of Megascolides australis, highly magnified.
(After Spencer.) 1, 4, 5, 6, Coils of nephridia; 2, funnel; 3, septum; 7, external
apertures.
In many Megascolicidae there is a nephridial system of a different
character. In Perichaeta when dissected the nephridia appear, on account of
their minute size, to be altogether absent. There is, however, in most
Perichaetidae, in many Acanthodrilidae, and in many Cryptodrilidae a mass
of minute tubules which cover the inside of the body-wall, and open on to
the exterior by innumerable openings; there may be in a single segment one
hundred or more of these external orifices, which are scattered about
irregularly. It is at present uncertain whether these minute tubes are
connected among themselves, thus forming a network passing through the
septum and from segment to segment, or whether each tube is isolated from
its fellows, and forms a distinct nephridium, of which there are many in
each segment and entirely separate. This is, however, certain, that the
complex nephridial systems of at any rate Octochaetus and Megascolides
are derived from the multiplication of a single pair of tubes which are alone
present in the embryo. In Perichaeta the minute nephridia are furnished
with coelomic funnels; in Octochaetus they are not, except in the case of
certain nephridia which open into the terminal section of the intestine.
Page 363
Both at the anterior and at the posterior end the nephridia occasionally open
into the alimentary canal. In various genera the first pair of nephridia are
larger than the others, and open into the buccal cavity; it seems likely that
they serve as salivary glands. A somewhat similar condition of things exists
in Peripatus (vol. v, p. 17). In Octochaetus multiporus, for example, there is
a large tuft of nephridial tubes in the anterior region of the body, which
opens by a long muscular duct into the buccal cavity. In the same species a
good many of the nephridial tubes open into the posterior section of the
intestine, reminding one of the anal vesicles of the Gephyrea (p. 436) and of
the Malpighian tubes of the Arthropods.
In many Eudrilidae the ducts of the paired nephridia form a network in the
body-wall, which opens on to the exterior by many pores.
Alimentary Canal.—The digestive tube is perfectly straight in nearly all
Oligochaeta. Only in Plagiochaeta and a species of Digaster is it twisted in
the intestinal region in a corkscrew-like fashion. The mouth is under the
buccal lobe (where, as in the majority of cases, this is present); the anus is
mostly terminal, or rarely, e.g. Criodrilus, a little in advance of the end of
the body on the ventral side. In the simpler forms three regions can be
distinguished, which are themselves simple in structure. The mouth leads
into a buccal cavity, which in its turn opens into the pharynx; the latter is
muscular, with thick walls. The narrower oesophagus opens into the wider
intestine, which opens posteriorly, as already stated. In the earthworms
there is as a rule some complication. The oesophagus bears certain
glandular appendages, the calciferous glands; and a part of it is modified
into a gizzard. The gizzard is merely a portion of the oesophagus with very
much thickened muscular walls and with a stout lining of chitin. It is not
universally present among earthworms, and when present varies much in
position. The rule is that one gizzard only is present. In Digaster, as is
implied by the name, and in some other forms there are two in successive
segments; in Trigaster, as the name also indicates, there are three gizzards;
in Moniligaster and the Eudrilids Hyperiodrilus and Heliodrilus there are
four to six; and a few other forms also have a considerable number of
gizzards. The calciferous glands are diverticula of the oesophagus with
folded and sometimes ciliated walls; their epithelium secretes calcareous
particles, which are frequently of crystalline form. Darwin supposed that
into the alimentary canal. In various genera the first pair of nephridia are
larger than the others, and open into the buccal cavity; it seems likely that
they serve as salivary glands. A somewhat similar condition of things exists
in Peripatus (vol. v, p. 17). In Octochaetus multiporus, for example, there is
a large tuft of nephridial tubes in the anterior region of the body, which
opens by a long muscular duct into the buccal cavity. In the same species a
good many of the nephridial tubes open into the posterior section of the
intestine, reminding one of the anal vesicles of the Gephyrea (p. 436) and of
the Malpighian tubes of the Arthropods.
In many Eudrilidae the ducts of the paired nephridia form a network in the
body-wall, which opens on to the exterior by many pores.
Alimentary Canal.—The digestive tube is perfectly straight in nearly all
Oligochaeta. Only in Plagiochaeta and a species of Digaster is it twisted in
the intestinal region in a corkscrew-like fashion. The mouth is under the
buccal lobe (where, as in the majority of cases, this is present); the anus is
mostly terminal, or rarely, e.g. Criodrilus, a little in advance of the end of
the body on the ventral side. In the simpler forms three regions can be
distinguished, which are themselves simple in structure. The mouth leads
into a buccal cavity, which in its turn opens into the pharynx; the latter is
muscular, with thick walls. The narrower oesophagus opens into the wider
intestine, which opens posteriorly, as already stated. In the earthworms
there is as a rule some complication. The oesophagus bears certain
glandular appendages, the calciferous glands; and a part of it is modified
into a gizzard. The gizzard is merely a portion of the oesophagus with very
much thickened muscular walls and with a stout lining of chitin. It is not
universally present among earthworms, and when present varies much in
position. The rule is that one gizzard only is present. In Digaster, as is
implied by the name, and in some other forms there are two in successive
segments; in Trigaster, as the name also indicates, there are three gizzards;
in Moniligaster and the Eudrilids Hyperiodrilus and Heliodrilus there are
four to six; and a few other forms also have a considerable number of
gizzards. The calciferous glands are diverticula of the oesophagus with
folded and sometimes ciliated walls; their epithelium secretes calcareous
particles, which are frequently of crystalline form. Darwin supposed that
Page 364
this secretion was provided in order to negative the humus-acids of the soil
which is the food of earthworms. These organs are usually paired, but in the
Eudrilidae there are unpaired as well as paired glands; the unpaired
calciferous glands lie ventrally. These glands are totally wanting among the
aquatic families, with the sole exception of the Enchytraeidae. In a few of
these there are either paired or single glands of a very similar nature; Dr.
Michaelsen has suggested that the function of these is rather absorptive than
secretory. From the median unpaired gland of Buchholzia arises the dorsal
vessel, which at first forms a sinus round the glandular epithelium; the
epithelium, like that of the nephridia, is perforated by the ducts. In certain
Oligochaeta there are some curious modifications of the calciferous glands.
In Stuhlmannia and a few other Eudrilidae the oesophagus is beset with a
larger number of paired structures than in any other genera of the family,
where the calciferous glands are more limited in number. These glands
consist of a short tube lined with epithelium opening into the oesophagus.
Round this is a mass of cellular tissue, but the outlines of the constituent
cells are lost; the whole is permeated with abundant blood-vessels. This
layer seems to be peritoneal, and the entire gland seems to have lost its
function as a secretory organ, and to have taken on some function in
connexion with the vascular system. An analogous modification is to be
found among the Enchytraeidae. In certain forms there is a structure known
as the cardiac body; this is a chord of cells lying in the dorsal blood-vessel
at the point where it springs from the intestine. It is tempting to regard this
cellular rod as being the altered dorsal glandular pouch already spoken of,
which is surrounded by a blood sinus.
Reproductive Organs.—All the Oligochaeta are hermaphrodite animals.
But, as is the case with other hermaphrodites, the male and female organs
are in many cases mature at different times, thus leading to a practical
unisexuality. Many of the aquatic forms appear to have fixed times for
breeding, which may be in the winter or in the summer; but the earthworms
are as a rule sexually mature the whole year round. Various accessory
organs are developed in the majority of cases. In all, the reproductive glands
lie in successive segments and are attached to the septa, from the peritoneal
covering of which they originate. Their actual position differs greatly in
different genera; the position is constant only in the earthworms, where the
testes are in the tenth and eleventh segments and the ovaries in the
which is the food of earthworms. These organs are usually paired, but in the
Eudrilidae there are unpaired as well as paired glands; the unpaired
calciferous glands lie ventrally. These glands are totally wanting among the
aquatic families, with the sole exception of the Enchytraeidae. In a few of
these there are either paired or single glands of a very similar nature; Dr.
Michaelsen has suggested that the function of these is rather absorptive than
secretory. From the median unpaired gland of Buchholzia arises the dorsal
vessel, which at first forms a sinus round the glandular epithelium; the
epithelium, like that of the nephridia, is perforated by the ducts. In certain
Oligochaeta there are some curious modifications of the calciferous glands.
In Stuhlmannia and a few other Eudrilidae the oesophagus is beset with a
larger number of paired structures than in any other genera of the family,
where the calciferous glands are more limited in number. These glands
consist of a short tube lined with epithelium opening into the oesophagus.
Round this is a mass of cellular tissue, but the outlines of the constituent
cells are lost; the whole is permeated with abundant blood-vessels. This
layer seems to be peritoneal, and the entire gland seems to have lost its
function as a secretory organ, and to have taken on some function in
connexion with the vascular system. An analogous modification is to be
found among the Enchytraeidae. In certain forms there is a structure known
as the cardiac body; this is a chord of cells lying in the dorsal blood-vessel
at the point where it springs from the intestine. It is tempting to regard this
cellular rod as being the altered dorsal glandular pouch already spoken of,
which is surrounded by a blood sinus.
Reproductive Organs.—All the Oligochaeta are hermaphrodite animals.
But, as is the case with other hermaphrodites, the male and female organs
are in many cases mature at different times, thus leading to a practical
unisexuality. Many of the aquatic forms appear to have fixed times for
breeding, which may be in the winter or in the summer; but the earthworms
are as a rule sexually mature the whole year round. Various accessory
organs are developed in the majority of cases. In all, the reproductive glands
lie in successive segments and are attached to the septa, from the peritoneal
covering of which they originate. Their actual position differs greatly in
different genera; the position is constant only in the earthworms, where the
testes are in the tenth and eleventh segments and the ovaries in the
Page 365
thirteenth, in exactly corresponding situations. A few earthworms have only
one pair of testes. The only exception, among terrestrial forms, to the
position of the generative organs is in the family Moniligastridae, which
show so many other affinities to the lower forms of Oligochaeta. In this
family the ovaries have moved one or two segments forward. Among the
fresh-water families the position of the testes and of the ovaries is not so
uniform. They are generally more anterior than in the terrestrial genera,
particularly the ovaries.
One of the chief differences between the Oligochaeta and the Polychaeta is
that the reproductive organs of the former have special ducts to convey their
products to the exterior. In Aeolosoma, the only exception to this rule, Dr.
Stolc[415] has shown some reasons for believing that certain nephridia, but
slightly altered in form, serve as the conduits of the spermatozoa, whilst the
ova are extruded through a pore upon the ventral surface of the body. In the
Enchytraeidae the same pore for the extrusion of the ova appears to exist;
but a nearer examination shows that it is really not a mere perforation of the
integument, like the dorsal pores, for example, but that its internal orifice is
fringed with cells which seem to represent a rudimentary oviduct; perhaps
Aeolosoma typifies a last stage in the reduction. Even so high in the scale as
in the genus Nemertodrilus (Eudrilidae), there is an oviduct which can only
be compared with that of the Enchytraeidae. Elsewhere the oviducts are a
pair of tubes with a wide, funnel-shaped, and ciliated mouth, which leads to
the exterior by way of a ciliated tube of varying length.
The sperm-ducts are of an essentially similar structure; but they are
commonly much longer, passing through a variable number of segments on
their way to the exterior. In most earthworms there are, moreover, two of
them on each side instead of only a single pair, as is the case with the
oviducts. Among the Tubificidae, Naids, and other aquatic families there are
only two sperm-ducts, one on each side of the body. But this is not a
character of the aquatic families, for the Lumbriculidae have generally two
pairs, as in the earthworms. It is, however, a rule with hardly an exception,
that among the aquatic Oligochaets the sperm-ducts open, as do the
oviducts in all Oligochaets, upon the segments following that which bears
internally the ciliated funnel. It is only in the Moniligastridae among
earthworms that the sperm-duct only traverses two segments in its course.
one pair of testes. The only exception, among terrestrial forms, to the
position of the generative organs is in the family Moniligastridae, which
show so many other affinities to the lower forms of Oligochaeta. In this
family the ovaries have moved one or two segments forward. Among the
fresh-water families the position of the testes and of the ovaries is not so
uniform. They are generally more anterior than in the terrestrial genera,
particularly the ovaries.
One of the chief differences between the Oligochaeta and the Polychaeta is
that the reproductive organs of the former have special ducts to convey their
products to the exterior. In Aeolosoma, the only exception to this rule, Dr.
Stolc[415] has shown some reasons for believing that certain nephridia, but
slightly altered in form, serve as the conduits of the spermatozoa, whilst the
ova are extruded through a pore upon the ventral surface of the body. In the
Enchytraeidae the same pore for the extrusion of the ova appears to exist;
but a nearer examination shows that it is really not a mere perforation of the
integument, like the dorsal pores, for example, but that its internal orifice is
fringed with cells which seem to represent a rudimentary oviduct; perhaps
Aeolosoma typifies a last stage in the reduction. Even so high in the scale as
in the genus Nemertodrilus (Eudrilidae), there is an oviduct which can only
be compared with that of the Enchytraeidae. Elsewhere the oviducts are a
pair of tubes with a wide, funnel-shaped, and ciliated mouth, which leads to
the exterior by way of a ciliated tube of varying length.
The sperm-ducts are of an essentially similar structure; but they are
commonly much longer, passing through a variable number of segments on
their way to the exterior. In most earthworms there are, moreover, two of
them on each side instead of only a single pair, as is the case with the
oviducts. Among the Tubificidae, Naids, and other aquatic families there are
only two sperm-ducts, one on each side of the body. But this is not a
character of the aquatic families, for the Lumbriculidae have generally two
pairs, as in the earthworms. It is, however, a rule with hardly an exception,
that among the aquatic Oligochaets the sperm-ducts open, as do the
oviducts in all Oligochaets, upon the segments following that which bears
internally the ciliated funnel. It is only in the Moniligastridae among
earthworms that the sperm-duct only traverses two segments in its course.
Page 366
But where it is short as regards the actual distance traversed between the
two extremities, the tube itself is commonly long and coiled.
Sometimes, as in our common earthworms, the sperm-duct opens directly
on to the exterior of the body, the lips of the external orifice being swollen
by the development of cutaneous gland-cells. In the majority of cases the
sperm-duct or ducts open near or into a glandular structure which in
earthworms has been called "prostate"; in the aquatic forms, on the other
hand, "atrium." As these terms are objectionable from the different way in
which they have been used for structures of Vertebrates, I have suggested
for both the term "spermiducal glands," indicating the identity of the
structure in all Oligochaeta. The number of pairs of these glands varies, as
does also their shape and size. The typical form is perhaps illustrated in the
lower Oligochaeta, where there is but a single pair into which the sperm-
duct or ducts of the same side open. The Naids, Tubificidae, Lumbriculidae,
and Moniligastridae have a simple gland of this description on each side of
the body. These glands may consist of a tuft of pear-shaped glandular cells
attached to the organ at one side, as in most Tubificidae, or of a complete
investment of gland-cells, as in Branchiura. Among earthworms it is only
the Moniligastridae and the Eudrilidae in which the sperm-duct opens
directly into the end of the spermiducal gland; in the Perichaetidae the
gland is differentiated into two sections; there is a muscular duct leading to
the exterior, and a lobate glandular part, which is formed by a complicated
branching of a single sac such as exists in the Tubificidae; in the
Acanthodrilidae and in many Cryptodrilidae the spermiducal glands are of a
tubular form and are not branched, though there is the same differentiation
into a duct and a secreting portion. There are in the Acanthodrilidae two
pairs of these, and as many as three pairs in Dichogaster; in the latter case
in three successive segments. In the Acanthodrilidae the glands are upon the
seventeenth and nineteenth segments. In most Cryptodrilidae the sperm-
ducts do not open into the duct of the spermiducal gland, but on to the
body-wall near to its orifice, the distance varying in different genera. In the
Acanthodrilidae the male pore is on the eighteenth segment, removed
therefore by the distance of a segment from the aperture of either of the
glands. It may be that a large series of structures which exist in Microchaeta
benhami[416] and in other Geoscolecids, and which have been termed
copulatory glands, are the equivalents of the spermiducal glands.
two extremities, the tube itself is commonly long and coiled.
Sometimes, as in our common earthworms, the sperm-duct opens directly
on to the exterior of the body, the lips of the external orifice being swollen
by the development of cutaneous gland-cells. In the majority of cases the
sperm-duct or ducts open near or into a glandular structure which in
earthworms has been called "prostate"; in the aquatic forms, on the other
hand, "atrium." As these terms are objectionable from the different way in
which they have been used for structures of Vertebrates, I have suggested
for both the term "spermiducal glands," indicating the identity of the
structure in all Oligochaeta. The number of pairs of these glands varies, as
does also their shape and size. The typical form is perhaps illustrated in the
lower Oligochaeta, where there is but a single pair into which the sperm-
duct or ducts of the same side open. The Naids, Tubificidae, Lumbriculidae,
and Moniligastridae have a simple gland of this description on each side of
the body. These glands may consist of a tuft of pear-shaped glandular cells
attached to the organ at one side, as in most Tubificidae, or of a complete
investment of gland-cells, as in Branchiura. Among earthworms it is only
the Moniligastridae and the Eudrilidae in which the sperm-duct opens
directly into the end of the spermiducal gland; in the Perichaetidae the
gland is differentiated into two sections; there is a muscular duct leading to
the exterior, and a lobate glandular part, which is formed by a complicated
branching of a single sac such as exists in the Tubificidae; in the
Acanthodrilidae and in many Cryptodrilidae the spermiducal glands are of a
tubular form and are not branched, though there is the same differentiation
into a duct and a secreting portion. There are in the Acanthodrilidae two
pairs of these, and as many as three pairs in Dichogaster; in the latter case
in three successive segments. In the Acanthodrilidae the glands are upon the
seventeenth and nineteenth segments. In most Cryptodrilidae the sperm-
ducts do not open into the duct of the spermiducal gland, but on to the
body-wall near to its orifice, the distance varying in different genera. In the
Acanthodrilidae the male pore is on the eighteenth segment, removed
therefore by the distance of a segment from the aperture of either of the
glands. It may be that a large series of structures which exist in Microchaeta
benhami[416] and in other Geoscolecids, and which have been termed
copulatory glands, are the equivalents of the spermiducal glands.
Page 367
Fig. 192.—Diagrammatic longitudinal section of Lumbricus, showing the generative
segments. × 3. (After Hesse.) sp, Spermathecal pore; t, testis; s.s, seminal sac;
sp.s, sperm-sac; o, ovary; e.s, egg-sac; ♀, female pore; ♂, male pore.
In many earthworms there are, at the external opening of the male ducts,
bundles of specially modified chaetae, which have been called, from their
supposed function, penial chaetae; they are usually ornamented at the free
end with spinelets or ridges, and frequently offer valuable specific
characters. In the Lumbricidae and the Geoscolicidae there are modified
chaetae upon the clitellum; in a few forms, such as, for example,
Acanthodrilus schmardae, the spermathecae have bundles of similar
chaetae in their neighbourhood, often associated with glands not unlike the
spermiducal glands.
In most, perhaps in all Oligochaeta the sperm is not matured in the testes, or
even in the body-cavity; it is received into special sacs which are called
sperm-sacs, and there ripens. These sacs, the vesiculae seminales, have been
shown to be outgrowths of the septa; their cavity is thus a portion of the
body-cavity shut off more or less completely from the general body-cavity.
The reproductive organs of the Eudrilidae, and particularly the female
organs, are so divergent in many particulars from those of other Oligochaeta
that it is convenient to treat them separately. The testes are normal, save that
they are often adherent to the posterior wall of their segment, as, however,
is the case with some other earthworms. In many Eudrilidae, for instance in
the genus Hyperiodrilus, the funnels of the sperm-ducts are dependent from
the anterior wall of the segment which contains them; the narrow tube
which follows projects into the segment in front, and is there immediately
dilated into a wide chamber, which again narrows, and bending round, re-
segments. × 3. (After Hesse.) sp, Spermathecal pore; t, testis; s.s, seminal sac;
sp.s, sperm-sac; o, ovary; e.s, egg-sac; ♀, female pore; ♂, male pore.
In many earthworms there are, at the external opening of the male ducts,
bundles of specially modified chaetae, which have been called, from their
supposed function, penial chaetae; they are usually ornamented at the free
end with spinelets or ridges, and frequently offer valuable specific
characters. In the Lumbricidae and the Geoscolicidae there are modified
chaetae upon the clitellum; in a few forms, such as, for example,
Acanthodrilus schmardae, the spermathecae have bundles of similar
chaetae in their neighbourhood, often associated with glands not unlike the
spermiducal glands.
In most, perhaps in all Oligochaeta the sperm is not matured in the testes, or
even in the body-cavity; it is received into special sacs which are called
sperm-sacs, and there ripens. These sacs, the vesiculae seminales, have been
shown to be outgrowths of the septa; their cavity is thus a portion of the
body-cavity shut off more or less completely from the general body-cavity.
The reproductive organs of the Eudrilidae, and particularly the female
organs, are so divergent in many particulars from those of other Oligochaeta
that it is convenient to treat them separately. The testes are normal, save that
they are often adherent to the posterior wall of their segment, as, however,
is the case with some other earthworms. In many Eudrilidae, for instance in
the genus Hyperiodrilus, the funnels of the sperm-ducts are dependent from
the anterior wall of the segment which contains them; the narrow tube
which follows projects into the segment in front, and is there immediately
dilated into a wide chamber, which again narrows, and bending round, re-
Page 368
traverses the same septum; the two ducts of each side (if there are two,
which is not invariably the case) remain separate and open separately into
the glandular part of the spermiducal gland. There is occasionally only a
single median gland; and as a general rule the two glands open by a median
unpaired orifice. Penial chaetae may or may not be present.
Fig. 193.—Female reproductive organs of Hyperiodrilus. XII-XV, Segments of the
body; 1, spermathecal sac; 2, egg-sac; 3, spermatheca; 4, ovary.
The structure of the female organs differs considerably in detail in the
different genera. But Hyperiodrilus may be taken as an instance of a genus
in which these organs are as complicated as they are anywhere. The ovaries
(Fig. 193, 4) are perfectly normal in structure and in position. So also are
the oviducts; but both are enclosed in sacs which communicate in rather an
elaborate fashion. Each ovisac is somewhat rounded in form, and the two
communicate by a narrow tube; from the ovisac also arises another narrow
tube, which soon dilates into a chamber lying in the thirteenth segment; this
contains the mouth of the oviduct and is continuous with the egg-sac; the
latter is quite normal in position. Beyond the egg-sacs the two tubes unite
round the intestine and open into a large median sac, which contains sperm
and may be called the spermathecal sac (1). There is, however, a true
spermatheca, single and median. This opens on to the exterior in the middle
of the thirteenth segment, but lies chiefly in the right-hand sac behind the
ovarian portion of the same. I never found this spermatheca to contain
sperm. Dr. Rosa inferred on anatomical grounds, and I have been able to
prove developmentally (in Libyodrilus), that these sacs which involve the
ovaries and oviducts, and which also contain sperm, are derivatives of the
septa; that in fact the spaces which they enclose are coelomic. In some
Eudrilids these sacs are the only "spermathecae"; in others, as in
Hyperiodrilus, there are in addition blind pouches lying within them which
which is not invariably the case) remain separate and open separately into
the glandular part of the spermiducal gland. There is occasionally only a
single median gland; and as a general rule the two glands open by a median
unpaired orifice. Penial chaetae may or may not be present.
Fig. 193.—Female reproductive organs of Hyperiodrilus. XII-XV, Segments of the
body; 1, spermathecal sac; 2, egg-sac; 3, spermatheca; 4, ovary.
The structure of the female organs differs considerably in detail in the
different genera. But Hyperiodrilus may be taken as an instance of a genus
in which these organs are as complicated as they are anywhere. The ovaries
(Fig. 193, 4) are perfectly normal in structure and in position. So also are
the oviducts; but both are enclosed in sacs which communicate in rather an
elaborate fashion. Each ovisac is somewhat rounded in form, and the two
communicate by a narrow tube; from the ovisac also arises another narrow
tube, which soon dilates into a chamber lying in the thirteenth segment; this
contains the mouth of the oviduct and is continuous with the egg-sac; the
latter is quite normal in position. Beyond the egg-sacs the two tubes unite
round the intestine and open into a large median sac, which contains sperm
and may be called the spermathecal sac (1). There is, however, a true
spermatheca, single and median. This opens on to the exterior in the middle
of the thirteenth segment, but lies chiefly in the right-hand sac behind the
ovarian portion of the same. I never found this spermatheca to contain
sperm. Dr. Rosa inferred on anatomical grounds, and I have been able to
prove developmentally (in Libyodrilus), that these sacs which involve the
ovaries and oviducts, and which also contain sperm, are derivatives of the
septa; that in fact the spaces which they enclose are coelomic. In some
Eudrilids these sacs are the only "spermathecae"; in others, as in
Hyperiodrilus, there are in addition blind pouches lying within them which
Page 369
must be regarded as true spermathecae; these are smaller in some than in
others. In fact there are various transitions in the entire replacement of true
spermathecae apparently homologous with those of other earthworms by
pouches which are derived from the septa, and which are therefore of an
entirely different morphological significance; here is an excellent case of
the substitution of organs, analogous to the replacement of the primitive
notochord of the Vertebrate by the vertebral column.
So far as is known, all the Oligochaeta deposit their eggs in special
chitinous cases, the cocoons. They share this peculiarity with the Hirudinea.
The cocoons have long been known, but were originally mistaken for the
eggs themselves. The cocoons contain several eggs and a variable quantity
of albumen for the nutrition of the growing embryos. In the majority of
earthworms they are more or less oval with projections at the two ends, and
are of a brownish colour. In others the tint is rather to be described as green.
The genera Criodrilus and Sparganophilus have a cocoon which is greatly
elongated. These structures seem to be undoubtedly formed by the
clitellum, the earlier opinion of D'Udekem being that they were the product
of certain glands developed in Lumbricus at the breeding season, which he
thence called the capsulogenous glands. It is more probable that these
glands, which have been up to the present but little investigated, are the seat
of the formation of the albumen which is found within the cocoons. The
cocoons are deposited at varying depths in the ground, or on the surface.
Among the aquatic genera they are often attached to aquatic plants. The
process of formation has been carefully watched by Vejdovsky[417] in the
genus Rhynchelmis. The worm throws off the cocoon over its head,
crawling backwards to free itself therefrom. The eggs, spermatozoa and
albumen, reach the interior of the cocoon as it passes over the orifices of the
respective ducts. Out of the numerous eggs which a single cocoon
originally contains, only a few, sometimes only one, reaches to maturity.
Among the Enchytraeidae, however, quite a large number of young emerge
from a single cocoon. The development of all the Oligochaeta is direct,
there being no free larval stage. It seems to be the rule for a process of
fission to take place in the embryos of Allolobophora trapezoides[418] at
least, according to the observations of Vejdovsky, in warm weather. In cold
weather he found in each cocoon as a rule single embryos, and only 10 per
cent of double embryos.
others. In fact there are various transitions in the entire replacement of true
spermathecae apparently homologous with those of other earthworms by
pouches which are derived from the septa, and which are therefore of an
entirely different morphological significance; here is an excellent case of
the substitution of organs, analogous to the replacement of the primitive
notochord of the Vertebrate by the vertebral column.
So far as is known, all the Oligochaeta deposit their eggs in special
chitinous cases, the cocoons. They share this peculiarity with the Hirudinea.
The cocoons have long been known, but were originally mistaken for the
eggs themselves. The cocoons contain several eggs and a variable quantity
of albumen for the nutrition of the growing embryos. In the majority of
earthworms they are more or less oval with projections at the two ends, and
are of a brownish colour. In others the tint is rather to be described as green.
The genera Criodrilus and Sparganophilus have a cocoon which is greatly
elongated. These structures seem to be undoubtedly formed by the
clitellum, the earlier opinion of D'Udekem being that they were the product
of certain glands developed in Lumbricus at the breeding season, which he
thence called the capsulogenous glands. It is more probable that these
glands, which have been up to the present but little investigated, are the seat
of the formation of the albumen which is found within the cocoons. The
cocoons are deposited at varying depths in the ground, or on the surface.
Among the aquatic genera they are often attached to aquatic plants. The
process of formation has been carefully watched by Vejdovsky[417] in the
genus Rhynchelmis. The worm throws off the cocoon over its head,
crawling backwards to free itself therefrom. The eggs, spermatozoa and
albumen, reach the interior of the cocoon as it passes over the orifices of the
respective ducts. Out of the numerous eggs which a single cocoon
originally contains, only a few, sometimes only one, reaches to maturity.
Among the Enchytraeidae, however, quite a large number of young emerge
from a single cocoon. The development of all the Oligochaeta is direct,
there being no free larval stage. It seems to be the rule for a process of
fission to take place in the embryos of Allolobophora trapezoides[418] at
least, according to the observations of Vejdovsky, in warm weather. In cold
weather he found in each cocoon as a rule single embryos, and only 10 per
cent of double embryos.
Page 370
Fig. 194.—Cocoons of Lumbricidae. (After Vejdovsky.) A, Lumbricus rubellus, nat.
size and × 3; B, Allurus, nat. size and × 6; C, Allolobophora foetida, nat. size
and × 3.
Habitat.—Earthworms are found in almost every part of the world where
they have been looked for. They occur far to the north, in Siberia and Nova
Zembla,[419] while South Georgia and Kerguelen mark their southern limits.
From arid tracts of country they are naturally absent, and also, which is
more curious, from certain districts of North America. In the tropics these
animals seem to be on the whole less abundant than in more temperate
climates. But this deficiency of individuals is counterbalanced by the
greater variety of generic and specific types. From tropical Africa, little
explored as it has been from this point of view, no less than thirty genera,
including about ninety species, have been recorded; whereas in Great
Britain only four genera and seventeen species occur, and in all probability
but few remain to be discovered. The vertical range of these Annelids is
also considerable. Several species have been met with in Europe and
elsewhere at an altitude of 10,000 feet.
For the bulk of the species the term earthworm is an accurate description of
their habitat. But there are not a few which occasionally or habitually prefer
other localities. The genus Allurus is equally at home in soil or in water; I
have taken it in the fast-flowing river Plym in Devonshire. The genus
Acanthodrilus includes a few species which have at present only been met
with in water; A. schmardae comes from fresh water in Queensland, A.
stagnalis from ponds in South America; A. dalei is like Allurus in that it is
to be found both on land and in streams and ponds. The Enchytraeidae are
just as amphibious; Criodrilus and Sparganophilus appear to be purely
aquatic. A more curious locality for a creature that is so characteristically
terrestrial is the margin of the sea. For a long time a species belonging to a
peculiar genus Pontodrilus has been known from the shores of the
Mediterranean in the neighbourhood of Nice. It lives there among seaweed
size and × 3; B, Allurus, nat. size and × 6; C, Allolobophora foetida, nat. size
and × 3.
Habitat.—Earthworms are found in almost every part of the world where
they have been looked for. They occur far to the north, in Siberia and Nova
Zembla,[419] while South Georgia and Kerguelen mark their southern limits.
From arid tracts of country they are naturally absent, and also, which is
more curious, from certain districts of North America. In the tropics these
animals seem to be on the whole less abundant than in more temperate
climates. But this deficiency of individuals is counterbalanced by the
greater variety of generic and specific types. From tropical Africa, little
explored as it has been from this point of view, no less than thirty genera,
including about ninety species, have been recorded; whereas in Great
Britain only four genera and seventeen species occur, and in all probability
but few remain to be discovered. The vertical range of these Annelids is
also considerable. Several species have been met with in Europe and
elsewhere at an altitude of 10,000 feet.
For the bulk of the species the term earthworm is an accurate description of
their habitat. But there are not a few which occasionally or habitually prefer
other localities. The genus Allurus is equally at home in soil or in water; I
have taken it in the fast-flowing river Plym in Devonshire. The genus
Acanthodrilus includes a few species which have at present only been met
with in water; A. schmardae comes from fresh water in Queensland, A.
stagnalis from ponds in South America; A. dalei is like Allurus in that it is
to be found both on land and in streams and ponds. The Enchytraeidae are
just as amphibious; Criodrilus and Sparganophilus appear to be purely
aquatic. A more curious locality for a creature that is so characteristically
terrestrial is the margin of the sea. For a long time a species belonging to a
peculiar genus Pontodrilus has been known from the shores of the
Mediterranean in the neighbourhood of Nice. It lives there among seaweed
Page 371
above high-water mark, but it must at least occasionally be splashed by the
waves. Another species of the same genus occurs on the coast of Brazil and
some of the West Indian islands; Pontoscolex corethrurus and Diachaeta
littoralis were described by Schmarda[420] from the shores of Jamaica. The
former species is one of the most widely distributed of earthworms, and,
except in this particular part of the world, has been always taken on the land
far from the sea. There are also partly marine forms among the Tubificidae;
Clitellio arenarius is common on our coasts.
While there are several kinds of earthworms that are thus met with in fresh
water, others will live for some time submerged in water. Perrier found by
experiment that various species could undergo with impunity a prolonged
immersion in water, and I confirmed his experiments myself with a
common species of Allolobophora. A correspondent of "Nature" stated that
a certain number of species (not particularised) of earthworms in Ceylon
could suffer with impunity the effects of sea-water. The importance of this
fact will be again dealt with in considering the geographical distribution of
the group.
Among the aquatic genera of Oligochaeta we do not as a rule meet with
amphibious species. The Enchytraeidae however, as already mentioned, are
an exception; so too appears to be the genus Phreoryctes, which in its
structure is to some extent intermediate between the earthworms and the
aquatic families.
Terrestrial and Aquatic Forms.—There are many obvious structural
peculiarities which would prevent the normally aquatic worms from being
thoroughly at home on dry land. The gills of Branchiura and the other
gilled species would be injured, in all probability, by friction with the earth;
the delicate and long chaetae of Naids and Tubifex are also most unsuited
for progression through dry soil; and it is to be noted that those
Oligochaeta, which, belonging to aquatic groups, are yet found away from
water, have chaetae of the simple sigmoid pattern which characterises the
earthworms.
waves. Another species of the same genus occurs on the coast of Brazil and
some of the West Indian islands; Pontoscolex corethrurus and Diachaeta
littoralis were described by Schmarda[420] from the shores of Jamaica. The
former species is one of the most widely distributed of earthworms, and,
except in this particular part of the world, has been always taken on the land
far from the sea. There are also partly marine forms among the Tubificidae;
Clitellio arenarius is common on our coasts.
While there are several kinds of earthworms that are thus met with in fresh
water, others will live for some time submerged in water. Perrier found by
experiment that various species could undergo with impunity a prolonged
immersion in water, and I confirmed his experiments myself with a
common species of Allolobophora. A correspondent of "Nature" stated that
a certain number of species (not particularised) of earthworms in Ceylon
could suffer with impunity the effects of sea-water. The importance of this
fact will be again dealt with in considering the geographical distribution of
the group.
Among the aquatic genera of Oligochaeta we do not as a rule meet with
amphibious species. The Enchytraeidae however, as already mentioned, are
an exception; so too appears to be the genus Phreoryctes, which in its
structure is to some extent intermediate between the earthworms and the
aquatic families.
Terrestrial and Aquatic Forms.—There are many obvious structural
peculiarities which would prevent the normally aquatic worms from being
thoroughly at home on dry land. The gills of Branchiura and the other
gilled species would be injured, in all probability, by friction with the earth;
the delicate and long chaetae of Naids and Tubifex are also most unsuited
for progression through dry soil; and it is to be noted that those
Oligochaeta, which, belonging to aquatic groups, are yet found away from
water, have chaetae of the simple sigmoid pattern which characterises the
earthworms.
Page 372
There are other peculiarities found only in the aquatic species which have
not so obvious a relation to their habitat. In no genus that is mainly aquatic
in habit are the ova small and nearly unprovided with yolk as in Lumbricus;
the ova of aquatic forms are invariably large and filled with abundant yolk.
The more delicate organisation of the aquatic Oligochaeta is not so hard to
understand. The comparatively unresisting nature of the medium in which
they live, water or fine mud, does not necessitate so strong a development
of the layers of the body-wall as is essential to the earth-living forms, which
have also thick septa in the anterior region, to protect the organs of
reproduction as the strong muscular contractions of the body force the
worm's way through the dense soil. With the weak structure of the
integument are perhaps also correlated the simplicity of other organs of the
body in the aquatic Oligochaeta. With thin body-walls, through which gases
can diffuse with great ease, there would seem to be less need for the
development of a system of integumental blood capillaries. These are
indeed for the most part absent in the aquatic forms, being only faintly
developed in a few, an example possibly of degeneration.
Earthworms and the Soil.—Darwin has explained the enormous effects
which these soft-bodied and small creatures have had upon the superficial
structure of the earth. Their castings, brought up to the surface, are blown
about by the wind when dry, and are thus spread over the ground in a fine
layer. It has been calculated that in the space of an acre .2 of an inch in
thickness of earth is annually brought to the surface. It is clear therefore that
in a long period of years there would be a very large effect produced. On
the sides of a hill this matter brought up from below would tend to roll
down the slopes when dry, and would increase the débris carried away to
the sea by streams and rivers, so that continents formerly deposited under
the sea may owe no small proportion of their size to the continued work of
earthworms in past ages.
Darwin has also pointed out the benefits to the agriculturist which accrue
from the industry of these Annelids. The soil is thoroughly mixed and
submitted to the action of the atmosphere. The secretions of the worms
themselves cannot but have a good effect upon its fertility, while the
not so obvious a relation to their habitat. In no genus that is mainly aquatic
in habit are the ova small and nearly unprovided with yolk as in Lumbricus;
the ova of aquatic forms are invariably large and filled with abundant yolk.
The more delicate organisation of the aquatic Oligochaeta is not so hard to
understand. The comparatively unresisting nature of the medium in which
they live, water or fine mud, does not necessitate so strong a development
of the layers of the body-wall as is essential to the earth-living forms, which
have also thick septa in the anterior region, to protect the organs of
reproduction as the strong muscular contractions of the body force the
worm's way through the dense soil. With the weak structure of the
integument are perhaps also correlated the simplicity of other organs of the
body in the aquatic Oligochaeta. With thin body-walls, through which gases
can diffuse with great ease, there would seem to be less need for the
development of a system of integumental blood capillaries. These are
indeed for the most part absent in the aquatic forms, being only faintly
developed in a few, an example possibly of degeneration.
Earthworms and the Soil.—Darwin has explained the enormous effects
which these soft-bodied and small creatures have had upon the superficial
structure of the earth. Their castings, brought up to the surface, are blown
about by the wind when dry, and are thus spread over the ground in a fine
layer. It has been calculated that in the space of an acre .2 of an inch in
thickness of earth is annually brought to the surface. It is clear therefore that
in a long period of years there would be a very large effect produced. On
the sides of a hill this matter brought up from below would tend to roll
down the slopes when dry, and would increase the débris carried away to
the sea by streams and rivers, so that continents formerly deposited under
the sea may owe no small proportion of their size to the continued work of
earthworms in past ages.
Darwin has also pointed out the benefits to the agriculturist which accrue
from the industry of these Annelids. The soil is thoroughly mixed and
submitted to the action of the atmosphere. The secretions of the worms
themselves cannot but have a good effect upon its fertility, while the
Page 373
burrows open up the deeper-lying layers to the rain. Mr. Alvan Millson,[421]
in detailing the labours of the remarkable Yoruba worm (Siphonogaster
millsoni Beddard), hints that they may serve as a check upon the fatal
malaria of the west coast of Africa. By their incessant burrowings and
ejecting of the undigested remains of their food many poisonous germs may
be brought up from below, where they flourish in the absence of sunlight
and oxygen, and submitted to the purifying influence of sun and air.
Phosphorescence.—Phosphorescence has been observed in several species
of Oligochaeta. The most noteworthy instance of recent times is the
discovery by Giard of the small worm which he called Photodrilus
phosphoreus at Wimereux. During damp weather it was sufficient to disturb
the gravel upon the walks of a certain garden to excite the luminosity of
these Annelids. In all probability this species is identical with one whose
luminosity had been noticed some years before (in 1837) by Dugès, and
named by him Lumbricus phosphoreus. According to Giard, the light is
produced by a series of glands in the anterior region of the body debouching
upon the exterior. This same worm has since been found in other localities,
where it has been shown to be phosphorescent, by Moniez[422] and by
Matzdorf[423]. It is remarkable that in some other cases the luminosity,
though it exists, is very rarely seen. The exceedingly common Brandling
(Allolobophora foetida) of dunghills has been observed on occasions to
emit a phosphorescent light. This observation is due to Professor Vejdovsky,
[424]
and was made "upon a warm July night of 1881." He thinks that the
seat of the light is in the secretion of the glandular cells of the epidermis,
for when this and other worms are handled the phosphorescence clings to
the fingers, as of course does the mucous secretion voided by the glands.
Phosphorescence has been observed also in some other families of
Oligochaetes. The late Professor Allen Harker noticed a small worm in
marshy ground in Northumberland which emitted a distinct light, and which
was subsequently identified as a member of the family Enchytraeidae.
Geographical Distribution.[425]—In the succeeding pages some of the
details of the geographical range of the Oligochaeta will be found. The
in detailing the labours of the remarkable Yoruba worm (Siphonogaster
millsoni Beddard), hints that they may serve as a check upon the fatal
malaria of the west coast of Africa. By their incessant burrowings and
ejecting of the undigested remains of their food many poisonous germs may
be brought up from below, where they flourish in the absence of sunlight
and oxygen, and submitted to the purifying influence of sun and air.
Phosphorescence.—Phosphorescence has been observed in several species
of Oligochaeta. The most noteworthy instance of recent times is the
discovery by Giard of the small worm which he called Photodrilus
phosphoreus at Wimereux. During damp weather it was sufficient to disturb
the gravel upon the walks of a certain garden to excite the luminosity of
these Annelids. In all probability this species is identical with one whose
luminosity had been noticed some years before (in 1837) by Dugès, and
named by him Lumbricus phosphoreus. According to Giard, the light is
produced by a series of glands in the anterior region of the body debouching
upon the exterior. This same worm has since been found in other localities,
where it has been shown to be phosphorescent, by Moniez[422] and by
Matzdorf[423]. It is remarkable that in some other cases the luminosity,
though it exists, is very rarely seen. The exceedingly common Brandling
(Allolobophora foetida) of dunghills has been observed on occasions to
emit a phosphorescent light. This observation is due to Professor Vejdovsky,
[424]
and was made "upon a warm July night of 1881." He thinks that the
seat of the light is in the secretion of the glandular cells of the epidermis,
for when this and other worms are handled the phosphorescence clings to
the fingers, as of course does the mucous secretion voided by the glands.
Phosphorescence has been observed also in some other families of
Oligochaetes. The late Professor Allen Harker noticed a small worm in
marshy ground in Northumberland which emitted a distinct light, and which
was subsequently identified as a member of the family Enchytraeidae.
Geographical Distribution.[425]—In the succeeding pages some of the
details of the geographical range of the Oligochaeta will be found. The
Page 374
present section deals with a few generalities, which appear to result from an
examination of the facts.
As to the aquatic genera but little is known at present with regard to their
range; they have not been widely collected in extra-European countries.
What little is known points to the conclusion that while many parts of the
world have their peculiar genera (such as Hesperodrilus in South America,
Phreodrilus and Pelodrilus in New Zealand), some of the common
European species are widely distributed. I have, for example, received
Henlea ventriculosa from Kirghiz Tartary, and from New Zealand; and a
New Zealand Tubifex appeared to me to be indistinguishable from the
common T. rivulorum of our rivers and ponds. It is possible that these and
similar instances may, at least in some cases, be due to accidental
importation at the hands of man, a matter into which we shall enter later.
But the aquatic genera have, many of them, facilities for extending their
range in a natural fashion, which are greater than those possessed by
earthworms. It has been pointed out that the chaetae of the aquatic
Oligochaeta are generally hooked at the extremity and bifid, which would
give them a greater chance of holding on to the feet or feathers of aquatic
birds; I am not myself disposed to lay much stress on the possibilities of
migration by these means, since the tender bodies of the small worms
would be liable to be soon dried up by wind while in the act of migration.
More likely in every way is a migration when enclosed in the cocoon. The
cocoons being small, and often deposited at the edges of ponds frequented
by aquatic birds, there would be many chances of their being carried away
with tolerable frequency; moreover, as Dr. Michaelsen has pointed out, the
cocoons of some species, particularly among the Enchytraeidae, contain a
large number of embryos; so that when such a cocoon reached a foreign
shore there would be a better chance of the species establishing itself there.
I have referred elsewhere[426] to the singular habit of forming a temporary
cyst which characterises one species of the genus Aeolosoma; this would
perhaps tend to facilitate its transference in the way indicated from one spot
to another.
Earthworms, on the other hand, have not such easy means of travelling
from country to country; the assistance which the cocoons in all probability
give to the smaller aquatic Oligochaeta cannot be held to be of much
examination of the facts.
As to the aquatic genera but little is known at present with regard to their
range; they have not been widely collected in extra-European countries.
What little is known points to the conclusion that while many parts of the
world have their peculiar genera (such as Hesperodrilus in South America,
Phreodrilus and Pelodrilus in New Zealand), some of the common
European species are widely distributed. I have, for example, received
Henlea ventriculosa from Kirghiz Tartary, and from New Zealand; and a
New Zealand Tubifex appeared to me to be indistinguishable from the
common T. rivulorum of our rivers and ponds. It is possible that these and
similar instances may, at least in some cases, be due to accidental
importation at the hands of man, a matter into which we shall enter later.
But the aquatic genera have, many of them, facilities for extending their
range in a natural fashion, which are greater than those possessed by
earthworms. It has been pointed out that the chaetae of the aquatic
Oligochaeta are generally hooked at the extremity and bifid, which would
give them a greater chance of holding on to the feet or feathers of aquatic
birds; I am not myself disposed to lay much stress on the possibilities of
migration by these means, since the tender bodies of the small worms
would be liable to be soon dried up by wind while in the act of migration.
More likely in every way is a migration when enclosed in the cocoon. The
cocoons being small, and often deposited at the edges of ponds frequented
by aquatic birds, there would be many chances of their being carried away
with tolerable frequency; moreover, as Dr. Michaelsen has pointed out, the
cocoons of some species, particularly among the Enchytraeidae, contain a
large number of embryos; so that when such a cocoon reached a foreign
shore there would be a better chance of the species establishing itself there.
I have referred elsewhere[426] to the singular habit of forming a temporary
cyst which characterises one species of the genus Aeolosoma; this would
perhaps tend to facilitate its transference in the way indicated from one spot
to another.
Earthworms, on the other hand, have not such easy means of travelling
from country to country; the assistance which the cocoons in all probability
give to the smaller aquatic Oligochaeta cannot be held to be of much
Page 375
importance in facilitating the migrations of the earthworms. In the first
place, the animals themselves are of greater bulk, and their cocoons are
naturally larger, and thus less easy of transportation. Secondly, they are
deposited as a rule upon dry land, where the chances of their sticking to the
feet of birds would be less; and thirdly, they are often deposited deep in the
ground, which is a further bar to their being taken up. Another possible
method by which earthworms could cross the sea is by the help of floating
tree-trunks; it is, however, the case with many species that they are fatally
injured by the contact of salt water. There are, it is true, a few species, such
as Pontodrilus of the Mediterranean coast, which habitually live within
reach of the waves; but with the majority any such passage across the sea
seems to be impossible.[427] On the other hand, rivers and lakes are not a
barrier to the dispersal of the group. There are a few species, such as
Allurus tetragonurus, which live indifferently on land and in fresh water;
and even some habitually terrestrial species can be kept in water for many
weeks with impunity. A desert, on the other hand, is a complete barrier; the
animals are absolutely dependent upon moisture, and though in dry weather
the worms of tropical countries bury themselves deep in the soil, and even
make temporary cysts by the aid of their mucous secretions, this would be
of no avail except in countries where there were at least occasional spells of
wet weather.
The range of the existing genera and species is quite in keeping with the
suggestions and facts already put forward. But in considering them we must
first of all eliminate the direct influence of man. Every one who studies this
group of animals knows perfectly well that importations of plants
frequently contain accidentally-included earthworms; and there are other
ways in which the transference of species from one country to another
could be effected by man. There are various considerations which enable us
to form a fair opinion as to the probability of a given species being really
indigenous or imported. Oceanic islands afford one test. There are species
of earthworms known from a good many, but with a few exceptions they
are the same species as those which occur on the nearest mainland; in those
cases where it is supposed that the animal inhabitants have reached an
oceanic island by natural means of transit, it is a rule that the species are
different, and even the genera are frequently different. That the bulk of
them are the same seems to argue either frequent natural communication
place, the animals themselves are of greater bulk, and their cocoons are
naturally larger, and thus less easy of transportation. Secondly, they are
deposited as a rule upon dry land, where the chances of their sticking to the
feet of birds would be less; and thirdly, they are often deposited deep in the
ground, which is a further bar to their being taken up. Another possible
method by which earthworms could cross the sea is by the help of floating
tree-trunks; it is, however, the case with many species that they are fatally
injured by the contact of salt water. There are, it is true, a few species, such
as Pontodrilus of the Mediterranean coast, which habitually live within
reach of the waves; but with the majority any such passage across the sea
seems to be impossible.[427] On the other hand, rivers and lakes are not a
barrier to the dispersal of the group. There are a few species, such as
Allurus tetragonurus, which live indifferently on land and in fresh water;
and even some habitually terrestrial species can be kept in water for many
weeks with impunity. A desert, on the other hand, is a complete barrier; the
animals are absolutely dependent upon moisture, and though in dry weather
the worms of tropical countries bury themselves deep in the soil, and even
make temporary cysts by the aid of their mucous secretions, this would be
of no avail except in countries where there were at least occasional spells of
wet weather.
The range of the existing genera and species is quite in keeping with the
suggestions and facts already put forward. But in considering them we must
first of all eliminate the direct influence of man. Every one who studies this
group of animals knows perfectly well that importations of plants
frequently contain accidentally-included earthworms; and there are other
ways in which the transference of species from one country to another
could be effected by man. There are various considerations which enable us
to form a fair opinion as to the probability of a given species being really
indigenous or imported. Oceanic islands afford one test. There are species
of earthworms known from a good many, but with a few exceptions they
are the same species as those which occur on the nearest mainland; in those
cases where it is supposed that the animal inhabitants have reached an
oceanic island by natural means of transit, it is a rule that the species are
different, and even the genera are frequently different. That the bulk of
them are the same seems to argue either frequent natural communication
Page 376
with the mainland or a great stability on the part of the species themselves.
It is more probable that the identity is in this case to be ascribed to
accidental transference.
Another argument comes from the distribution of the family Lumbricidae.
This family forms the bulk of the earthworms of the European and North
American continents. But they are also found all over the world. With one
or two exceptions, such as Allolobophora moebii, from Madeira, the extra-
north-temperate species are identical with those found within that region.
Now, if the migration had been by natural means there would surely in the
lapse of time been some differentiation of species. Furthermore, Dr.
Michaelsen has pointed out that in South America the presumably European
forms (i.e. Lumbricus and Allolobophora) are found upon the coast and in
cultivated ground; it is inland that the presumably indigenous species are
met with. This again looks very like accidental transference.
A mapping of the world in regions indicative of the distribution of
earthworms produces a result which is slightly different from the accepted
division. North America, Europe, and Northern Asia so far as is known
agree in having as their distinctive earthworms the family Lumbricidae,
which is very nearly the only one represented in these parts of the world.
The majority of the species are common to the two continents; there cannot,
in fact, be a separation of Nearctic and Palaearctic; we must accept the
Holarctic region of Professor Newton. The Ethiopian region, on the other
hand, is quite as it is in other groups, being bounded to the north by the
desert of Sahara. The Neotropical region is quite distinct, and includes
Central as well as South America, and the West Indian islands, even the
Bermudas. It is, however, a question whether the more southern portions of
the continent should not be cut off from the rest and joined with New
Zealand, to form an Antarctic region. In these two countries, and also in
Kerguelen and Marion Islands, the prevailing genera are Acanthodrilus and
Microscolex. In America Acanthodrilus is found nowhere but in the more
southern regions of the southern continent, as well as in the Falklands and
South Georgia. New Zealand is characterised by other genera of
Acanthodrilids besides Acanthodrilus itself; but the bulk of the species
belong to the latter genus. Acanthodrilus also occurs (three species only) in
Queensland and at the Cape of Good Hope. Microscolex is rather more
It is more probable that the identity is in this case to be ascribed to
accidental transference.
Another argument comes from the distribution of the family Lumbricidae.
This family forms the bulk of the earthworms of the European and North
American continents. But they are also found all over the world. With one
or two exceptions, such as Allolobophora moebii, from Madeira, the extra-
north-temperate species are identical with those found within that region.
Now, if the migration had been by natural means there would surely in the
lapse of time been some differentiation of species. Furthermore, Dr.
Michaelsen has pointed out that in South America the presumably European
forms (i.e. Lumbricus and Allolobophora) are found upon the coast and in
cultivated ground; it is inland that the presumably indigenous species are
met with. This again looks very like accidental transference.
A mapping of the world in regions indicative of the distribution of
earthworms produces a result which is slightly different from the accepted
division. North America, Europe, and Northern Asia so far as is known
agree in having as their distinctive earthworms the family Lumbricidae,
which is very nearly the only one represented in these parts of the world.
The majority of the species are common to the two continents; there cannot,
in fact, be a separation of Nearctic and Palaearctic; we must accept the
Holarctic region of Professor Newton. The Ethiopian region, on the other
hand, is quite as it is in other groups, being bounded to the north by the
desert of Sahara. The Neotropical region is quite distinct, and includes
Central as well as South America, and the West Indian islands, even the
Bermudas. It is, however, a question whether the more southern portions of
the continent should not be cut off from the rest and joined with New
Zealand, to form an Antarctic region. In these two countries, and also in
Kerguelen and Marion Islands, the prevailing genera are Acanthodrilus and
Microscolex. In America Acanthodrilus is found nowhere but in the more
southern regions of the southern continent, as well as in the Falklands and
South Georgia. New Zealand is characterised by other genera of
Acanthodrilids besides Acanthodrilus itself; but the bulk of the species
belong to the latter genus. Acanthodrilus also occurs (three species only) in
Queensland and at the Cape of Good Hope. Microscolex is rather more
Page 377
widely dispersed, being found in other parts of America and in Europe, the
island of Madeira (? accidentally imported); but it is undoubtedly chiefly
concentrated in South America and in New Zealand. Apart from New
Zealand, which, as already said, can only be doubtfully referred to the
Australian region, the latter appears to form one with the Oriental region (to
which, on account of its Perichaetidae, Japan should be added) of other
writers. There is, so far as earthworms are concerned, no "Wallace's line" at
all. The characteristic genera Perichaeta and Megascolex range from one
extremity of the Indo-Australian region to the other. It is true that
Cryptodrilus and Megascolides are limited to Australia itself (with the
apparent exception of a species or two in America, for I can hardly separate
Argilophilus of Eisen from Megascolides); but they are not at all well-
defined genera, and indeed the generic distinctions of the whole family
Cryptodrilidae are not in a satisfactory condition.
Classification.—The Oligochaeta do not shade into the Polychaeta so
imperceptibly as might be inferred from the current schemes of
classification. Apart from minor points, which are not universally
characteristic of the two groups, though never found except in one or the
other, the Oligochaeta are to be defined by the complicated reproductive
system; although in a few undoubted Polychaets there is a faint approach to
this in the specialisation of some of the nephridia as sperm-receptacles and
even as sperm-ducts. But nowhere among the Polychaeta are there the
diversified sperm-ducts and oviducts, spermathecae and sperm-sacs, that
are universal among the Oligochaeta. Moreover, no Polychaet has a
clitellum, which is so distinctive of the Oligochaeta, and of their near allies
the Leeches. Dr. Eisig has compared the glandular modification of the
integument at the mouths of the sperm-ducts in the Capitellidae to the
beginnings of a clitellum. This may be the case, but it is, in my opinion,
more comparable to the similar glandular spots at the male pores in
earthworms. The reproductive glands in the Oligochaeta (save for a few
apparently abnormal cases) are restricted to at most two pairs of each,
which occur in the same individual; the Polychaeta being dioecious. There
is, in short, no form known which cannot be definitely referred to either the
Polychaeta or the Oligochaeta, excepting perhaps Ctenodrilus, the anatomy
of whose reproductive organs is at present unknown.
island of Madeira (? accidentally imported); but it is undoubtedly chiefly
concentrated in South America and in New Zealand. Apart from New
Zealand, which, as already said, can only be doubtfully referred to the
Australian region, the latter appears to form one with the Oriental region (to
which, on account of its Perichaetidae, Japan should be added) of other
writers. There is, so far as earthworms are concerned, no "Wallace's line" at
all. The characteristic genera Perichaeta and Megascolex range from one
extremity of the Indo-Australian region to the other. It is true that
Cryptodrilus and Megascolides are limited to Australia itself (with the
apparent exception of a species or two in America, for I can hardly separate
Argilophilus of Eisen from Megascolides); but they are not at all well-
defined genera, and indeed the generic distinctions of the whole family
Cryptodrilidae are not in a satisfactory condition.
Classification.—The Oligochaeta do not shade into the Polychaeta so
imperceptibly as might be inferred from the current schemes of
classification. Apart from minor points, which are not universally
characteristic of the two groups, though never found except in one or the
other, the Oligochaeta are to be defined by the complicated reproductive
system; although in a few undoubted Polychaets there is a faint approach to
this in the specialisation of some of the nephridia as sperm-receptacles and
even as sperm-ducts. But nowhere among the Polychaeta are there the
diversified sperm-ducts and oviducts, spermathecae and sperm-sacs, that
are universal among the Oligochaeta. Moreover, no Polychaet has a
clitellum, which is so distinctive of the Oligochaeta, and of their near allies
the Leeches. Dr. Eisig has compared the glandular modification of the
integument at the mouths of the sperm-ducts in the Capitellidae to the
beginnings of a clitellum. This may be the case, but it is, in my opinion,
more comparable to the similar glandular spots at the male pores in
earthworms. The reproductive glands in the Oligochaeta (save for a few
apparently abnormal cases) are restricted to at most two pairs of each,
which occur in the same individual; the Polychaeta being dioecious. There
is, in short, no form known which cannot be definitely referred to either the
Polychaeta or the Oligochaeta, excepting perhaps Ctenodrilus, the anatomy
of whose reproductive organs is at present unknown.
Page 378
It is a difficult task to classify the different families of the Oligochaeta; and
to enter into the historical aspect of the matter would take too much space. I
am myself disposed to divide them first of all into two main groups, for
which I use Dr. Benham's[428] names of Microdrili and Megadrili.
The Microdrili are, as a rule, small and aquatic in habit; they have short
sperm-ducts which open on to the exterior in the segment which
immediately follows that which contains the internal aperture; the clitellum
is only one cell thick; the egg-sacs are large; the epoch of sexual maturity is
at a fixed period. This group, to my thinking, includes the Moniligastridae;
although Professor Bourne has denied my statement with regard to the
clitellum, and in this case it is not so easy to decide their systematic
position.
The Megadrili are characterised by the precisely opposite characters. The
sperm-ducts are longer; the clitellum is composed of many layers of cells;
the egg-sacs are rudimentary; sexual maturity appears to be more or less
continuous.
There is, however, a substantial agreement about the families which I here
adopt, which may be fairly taken to express our present knowledge of the
Order. For fuller details the reader is referred to my Monograph of the
Order Oligochaeta.[429]
Fig. 195.—Aeolosoma hemprichii dividing transversely, × 30. (After Lankester.)
I. Microdrili.
to enter into the historical aspect of the matter would take too much space. I
am myself disposed to divide them first of all into two main groups, for
which I use Dr. Benham's[428] names of Microdrili and Megadrili.
The Microdrili are, as a rule, small and aquatic in habit; they have short
sperm-ducts which open on to the exterior in the segment which
immediately follows that which contains the internal aperture; the clitellum
is only one cell thick; the egg-sacs are large; the epoch of sexual maturity is
at a fixed period. This group, to my thinking, includes the Moniligastridae;
although Professor Bourne has denied my statement with regard to the
clitellum, and in this case it is not so easy to decide their systematic
position.
The Megadrili are characterised by the precisely opposite characters. The
sperm-ducts are longer; the clitellum is composed of many layers of cells;
the egg-sacs are rudimentary; sexual maturity appears to be more or less
continuous.
There is, however, a substantial agreement about the families which I here
adopt, which may be fairly taken to express our present knowledge of the
Order. For fuller details the reader is referred to my Monograph of the
Order Oligochaeta.[429]
Fig. 195.—Aeolosoma hemprichii dividing transversely, × 30. (After Lankester.)
I. Microdrili.
Page 379
Fam. 1. Aphaneura.[430]—This name was originally given to the present
family by Vejdovsky; the family contains a single genus, Aeolosoma, of
which there are some seven species. The name is taken from, perhaps, the
most important though not the most salient characteristic of the worms. The
central nervous system appears in all of them to be reduced to the cerebral
ganglia, which, moreover, retain the embryonic connexion with the
epidermis. The worms of the genus are fairly common in fresh waters of
this country, and they have been also met with in North and South America,
and in Egypt, India, America, and tropical Africa. They are all small,
generally minute (1 to 2 mm. long), and have a transparent body variously
ornamented by brightly-coloured oil globules secreted by the epidermis.
These are reddish brown in A. quaternarium, bright green in A. variegatum
and A. headleyi, in the latter even with a tinge of blue. In the largest species
of the genus, A. tenebrarum they are olive green. In A. niveum the spots are
colourless, and A. variegatum has colourless droplets mixed with the bright
green ones. Fig. 195 shows very well the general appearance of the species
of this genus. The body has less fixed outlines than in most worms, and the
movement of the creatures is not unsuggestive of a Planarian. As the under
side of the prostomium is ciliated, and as the movements of these cilia
conduce towards the general movement of the body, the resemblance is
intelligible. One species of Aeolosoma, at any rate, has a curious habit
which is unique in the Order. At certain times, for some reason at present
unknown, the worm secretes a chitinous capsule, inside which it moves
about with considerable freedom; these capsules when first observed were
mistaken for the cocoons of the worms; they are really homologous with the
viscid secretion which the common earthworm throws off when in too dry
soil, and with which it lines the chamber excavated in the earth in which it
is lying. The worms of this genus multiply by fission; sexual reproduction
has been but rarely observed.
Fam. 2. Enchytraeidae.[431]—This family consists at present of rather over
fifty well-characterised species, which are distributed into eleven genera. It
is common in this country and in Europe generally; it has been met with in
Spitzbergen and the extreme north; it occurs in the American continent from
the north to the extreme south; it is also an inhabitant of New Zealand. The
worms of this family are nearly always of small size, sometimes minute;
they never exceed an inch or so in length, and that is a rare occurrence.
family by Vejdovsky; the family contains a single genus, Aeolosoma, of
which there are some seven species. The name is taken from, perhaps, the
most important though not the most salient characteristic of the worms. The
central nervous system appears in all of them to be reduced to the cerebral
ganglia, which, moreover, retain the embryonic connexion with the
epidermis. The worms of the genus are fairly common in fresh waters of
this country, and they have been also met with in North and South America,
and in Egypt, India, America, and tropical Africa. They are all small,
generally minute (1 to 2 mm. long), and have a transparent body variously
ornamented by brightly-coloured oil globules secreted by the epidermis.
These are reddish brown in A. quaternarium, bright green in A. variegatum
and A. headleyi, in the latter even with a tinge of blue. In the largest species
of the genus, A. tenebrarum they are olive green. In A. niveum the spots are
colourless, and A. variegatum has colourless droplets mixed with the bright
green ones. Fig. 195 shows very well the general appearance of the species
of this genus. The body has less fixed outlines than in most worms, and the
movement of the creatures is not unsuggestive of a Planarian. As the under
side of the prostomium is ciliated, and as the movements of these cilia
conduce towards the general movement of the body, the resemblance is
intelligible. One species of Aeolosoma, at any rate, has a curious habit
which is unique in the Order. At certain times, for some reason at present
unknown, the worm secretes a chitinous capsule, inside which it moves
about with considerable freedom; these capsules when first observed were
mistaken for the cocoons of the worms; they are really homologous with the
viscid secretion which the common earthworm throws off when in too dry
soil, and with which it lines the chamber excavated in the earth in which it
is lying. The worms of this genus multiply by fission; sexual reproduction
has been but rarely observed.
Fam. 2. Enchytraeidae.[431]—This family consists at present of rather over
fifty well-characterised species, which are distributed into eleven genera. It
is common in this country and in Europe generally; it has been met with in
Spitzbergen and the extreme north; it occurs in the American continent from
the north to the extreme south; it is also an inhabitant of New Zealand. The
worms of this family are nearly always of small size, sometimes minute;
they never exceed an inch or so in length, and that is a rare occurrence.
Page 380
They are equally at home in water and in soil, some species being common
to the two media; a few are marine or littoral in habit, while others are
parasitic in vegetable tissues. Like most earthworms, and unlike the
majority of aquatic worms, the chaetae are without a bifid termination; the
body-wall, too, is comparatively thick. The perivisceral fluid is often (as in
certain Naids) loaded with elliptical or rounded corpuscles. Resemblances
to earthworms rather than to the aquatic families of Oligochaeta are
suggested by the long distance which separates the spermathecae from the
male pores (segments 5 and 12), and by the paired or unpaired glands that
have been already compared to the calciferous glands so universally present
among earthworms. On the other hand, the male ducts are confined, as in
the lower Oligochaeta, to two segments, upon one of which the internal,
upon the other the external orifice is situated, and the oviduct is reduced to
a simple pore, as in Naids; but this may be merely a matter of convergence
by degeneration. Perhaps the most remarkable genus in the family is
Anachaeta, which has no chaetae, but in their place a large cell projecting
into the body-cavity, which appears to represent the formative cell of the
chaeta. The integument of this genus contains true chlorophyll, according to
Vejdovsky.
A singular character, found, however, also in Rhynchelmis and Sutroa
among the Lumbriculidae, is the opening of the spermathecae into the
alimentary canal. This was originally discovered by Dr. Michaelsen, but has
been abundantly confirmed.
Stercutus is a singular genus which was originally found in manure, and has
the peculiarity that the alimentary canal is often aborted; this degeneration
seems to bear some relation to the food and conditions of life.
Fam. 3. Discodrilidae.[432]—This family consists of small parasitic forms
which were at one time assigned to the Hirudinea; there seems, however, to
be no doubt that they are rightly included in the present Order.
Branchiobdella is found upon the gills of the Crayfish, Astacus fluviatilis;
the American Bdellodrilus upon Cambarus. The chief reason for the former
inclusion of these worms among the leeches was due to the absence of
chaetae and to the presence of chitinous jaws and of suckers; apart from
to the two media; a few are marine or littoral in habit, while others are
parasitic in vegetable tissues. Like most earthworms, and unlike the
majority of aquatic worms, the chaetae are without a bifid termination; the
body-wall, too, is comparatively thick. The perivisceral fluid is often (as in
certain Naids) loaded with elliptical or rounded corpuscles. Resemblances
to earthworms rather than to the aquatic families of Oligochaeta are
suggested by the long distance which separates the spermathecae from the
male pores (segments 5 and 12), and by the paired or unpaired glands that
have been already compared to the calciferous glands so universally present
among earthworms. On the other hand, the male ducts are confined, as in
the lower Oligochaeta, to two segments, upon one of which the internal,
upon the other the external orifice is situated, and the oviduct is reduced to
a simple pore, as in Naids; but this may be merely a matter of convergence
by degeneration. Perhaps the most remarkable genus in the family is
Anachaeta, which has no chaetae, but in their place a large cell projecting
into the body-cavity, which appears to represent the formative cell of the
chaeta. The integument of this genus contains true chlorophyll, according to
Vejdovsky.
A singular character, found, however, also in Rhynchelmis and Sutroa
among the Lumbriculidae, is the opening of the spermathecae into the
alimentary canal. This was originally discovered by Dr. Michaelsen, but has
been abundantly confirmed.
Stercutus is a singular genus which was originally found in manure, and has
the peculiarity that the alimentary canal is often aborted; this degeneration
seems to bear some relation to the food and conditions of life.
Fam. 3. Discodrilidae.[432]—This family consists of small parasitic forms
which were at one time assigned to the Hirudinea; there seems, however, to
be no doubt that they are rightly included in the present Order.
Branchiobdella is found upon the gills of the Crayfish, Astacus fluviatilis;
the American Bdellodrilus upon Cambarus. The chief reason for the former
inclusion of these worms among the leeches was due to the absence of
chaetae and to the presence of chitinous jaws and of suckers; apart from
Page 381
these structures there is nothing whatever leech-like about the worms.
Bdellodrilus has two pairs of testes in segments 5 and 6; there are two pairs
of sperm-ducts, all opening, however, by a common "atrium" on the sixth
segment; on the fifth open a pair of spermathecae, likewise by a common
pore. The ovaries are in segment 7, and the ova escape by a pair of pores
apparently like the single pore of the Enchytraeidae. The entire worm
consists of only eleven segments.
Fam. 4. Phreoryctidae.[433]—This family contains only two genera,
Phreoryctes and Pelodrilus. The former is widely spread, occurring in
Europe, North America, and New Zealand. Pelodrilus is limited to New
Zealand. Most species of Phreoryctes are distinguished by their
extraordinary length and thinness, and there is frequently a tendency to the
disappearance of the chaetae. The most important anatomical fact about
Phreoryctes (at any rate P. smithii) is that there are two pairs of ovaries as
well as two pairs of testes, and that the ducts of all are simple and very
much alike. This seems to argue the low position of the family in the series.
Fam. 5. Naidomorpha.[434]—This family contains eight or nine genera,
perhaps more; they are all of them aquatic and of small size, and they
multiply by fission as well as sexually. The most noticeable peculiarity of
the family is the "cephalisation" which occurs in the head segments. In
some genera, in Pristina for example, there is no such cephalisation to be
observed; but in others the dorsal bundles of chaetae commence a few
segments farther back than the ventral, the segment where they commence
being different and characteristic in the various genera. Thus in Dero the
first four segments are without dorsal chaetae, and in Nais the first five are
in this condition. There is thus a kind of "head" formed, whence the
expression "cephalisation." Dero, Nais, and Pristina are commonly to be
met with in ponds, lakes, etc., in this country. Bohemilla is rarer, and is to
be distinguished by the remarkable serrated chaetae of the dorsal bundles.
Of Dero and Nais there are a considerable number of different species;
indeed it is usual perhaps to regard as distributable among three genera,
Nais, Stylaria, and Slavina, the species which I am disposed to place in one
genus, Nais. Stylaria is defined on this view by its extremely long
prostomium, which has given rise to both its popular and technical names.
Bdellodrilus has two pairs of testes in segments 5 and 6; there are two pairs
of sperm-ducts, all opening, however, by a common "atrium" on the sixth
segment; on the fifth open a pair of spermathecae, likewise by a common
pore. The ovaries are in segment 7, and the ova escape by a pair of pores
apparently like the single pore of the Enchytraeidae. The entire worm
consists of only eleven segments.
Fam. 4. Phreoryctidae.[433]—This family contains only two genera,
Phreoryctes and Pelodrilus. The former is widely spread, occurring in
Europe, North America, and New Zealand. Pelodrilus is limited to New
Zealand. Most species of Phreoryctes are distinguished by their
extraordinary length and thinness, and there is frequently a tendency to the
disappearance of the chaetae. The most important anatomical fact about
Phreoryctes (at any rate P. smithii) is that there are two pairs of ovaries as
well as two pairs of testes, and that the ducts of all are simple and very
much alike. This seems to argue the low position of the family in the series.
Fam. 5. Naidomorpha.[434]—This family contains eight or nine genera,
perhaps more; they are all of them aquatic and of small size, and they
multiply by fission as well as sexually. The most noticeable peculiarity of
the family is the "cephalisation" which occurs in the head segments. In
some genera, in Pristina for example, there is no such cephalisation to be
observed; but in others the dorsal bundles of chaetae commence a few
segments farther back than the ventral, the segment where they commence
being different and characteristic in the various genera. Thus in Dero the
first four segments are without dorsal chaetae, and in Nais the first five are
in this condition. There is thus a kind of "head" formed, whence the
expression "cephalisation." Dero, Nais, and Pristina are commonly to be
met with in ponds, lakes, etc., in this country. Bohemilla is rarer, and is to
be distinguished by the remarkable serrated chaetae of the dorsal bundles.
Of Dero and Nais there are a considerable number of different species;
indeed it is usual perhaps to regard as distributable among three genera,
Nais, Stylaria, and Slavina, the species which I am disposed to place in one
genus, Nais. Stylaria is defined on this view by its extremely long
prostomium, which has given rise to both its popular and technical names.
Page 382
"Die gezungelte Naide" was the term applied by one of its earliest
investigators, and the name Stylaria proboscidea signifies the same
peculiarity. But as the same inordinately long "proboscis" occurs in the
South American Pristina proboscidea, belonging to a genus of which the
other member does not possess so well developed a prostomium, it seems
too variable a character upon which to differentiate a genus. Chaetogaster
and Amphichaeta have been placed by some systematists in a separate
family. The first named contains four species which are fairly common. It is
one of those worms in which the chaetae are not exactly related to the
segmentation of other organs, which moreover sometimes show an
independence in their segmentation; thus there are more nerve ganglia in
the anterior segments of the body than there are septa.
Fam. 6. Tubificidae.—The worms belonging to this family are of small size,
and are all inhabitants of fresh or salt water, or the margins of pools and the
sea. They differ from the last family in that asexual reproduction never
occurs, and that the reproductive organs are situated rather farther back in
the body. The male pores are upon segment 11, and the oviduct-pores upon
the following segment. This family differs from the Lumbriculidae in the
fact that there are only a single pair of sperm-ducts.
The earliest known Tubificid was the common Tubifex rivulorum, so widely
dispersed in this country and elsewhere; but with it was at first confounded
the somewhat similar genus Limnodrilus, which only differs in that the
chaetae are all of the cleft variety, and never capilliform, as in Tubifex. The
genera are mainly distinguished by the characters of the chaetae and of the
male ducts. At the base of the series perhaps lies Ilyodrilus, which has many
points in common with the Naids. The form of the terminal chamber into
which the sperm-duct opens has the same simplicity as in that group, and
the intestine is surrounded with a network of blood-vessels as in the Naids,
a structure which is otherwise wanting in the Tubificidae. The development
of the ova also is upon a plan which is met with in the Naids. The atrium
(see p. 361) becomes more complicated in other Tubificidae. The extremity
also is as a rule modified into a retractile penis. The discrete "prostate," of
which we have already spoken, marks out a considerable number of genera,
such as Tubifex, Limnodrilus, Spirosperma, Hemitubifex. In the marine
Clitellio there is no such structure at all, and it is also wanting in the South
investigators, and the name Stylaria proboscidea signifies the same
peculiarity. But as the same inordinately long "proboscis" occurs in the
South American Pristina proboscidea, belonging to a genus of which the
other member does not possess so well developed a prostomium, it seems
too variable a character upon which to differentiate a genus. Chaetogaster
and Amphichaeta have been placed by some systematists in a separate
family. The first named contains four species which are fairly common. It is
one of those worms in which the chaetae are not exactly related to the
segmentation of other organs, which moreover sometimes show an
independence in their segmentation; thus there are more nerve ganglia in
the anterior segments of the body than there are septa.
Fam. 6. Tubificidae.—The worms belonging to this family are of small size,
and are all inhabitants of fresh or salt water, or the margins of pools and the
sea. They differ from the last family in that asexual reproduction never
occurs, and that the reproductive organs are situated rather farther back in
the body. The male pores are upon segment 11, and the oviduct-pores upon
the following segment. This family differs from the Lumbriculidae in the
fact that there are only a single pair of sperm-ducts.
The earliest known Tubificid was the common Tubifex rivulorum, so widely
dispersed in this country and elsewhere; but with it was at first confounded
the somewhat similar genus Limnodrilus, which only differs in that the
chaetae are all of the cleft variety, and never capilliform, as in Tubifex. The
genera are mainly distinguished by the characters of the chaetae and of the
male ducts. At the base of the series perhaps lies Ilyodrilus, which has many
points in common with the Naids. The form of the terminal chamber into
which the sperm-duct opens has the same simplicity as in that group, and
the intestine is surrounded with a network of blood-vessels as in the Naids,
a structure which is otherwise wanting in the Tubificidae. The development
of the ova also is upon a plan which is met with in the Naids. The atrium
(see p. 361) becomes more complicated in other Tubificidae. The extremity
also is as a rule modified into a retractile penis. The discrete "prostate," of
which we have already spoken, marks out a considerable number of genera,
such as Tubifex, Limnodrilus, Spirosperma, Hemitubifex. In the marine
Clitellio there is no such structure at all, and it is also wanting in the South
Page 383
American Hesperodrilus. In Branchiura there is a complete prostatic
investment of the atrium, and in Telmatodrilus a large number of separate
aggregations forming as many distinct prostates. Vermiculus, a genus
consisting of but one species, found by Mr. Goodrich on the sea-shore in the
neighbourhood of Plymouth, is remarkable for the unpaired character of the
generative organs, a peculiarity which is shared by Stolc's genus
Bothrioneuron. The gills upon the posterior segments of Branchiura
sowerbyi and Hesperodrilus branchiatus have been already noticed above
(p. 352). A very aberrant genus, perhaps not rightly referable to this family,
is Phreodrilus,[435] from New Zealand, first collected in water from a
subterranean spring. It differs from all other Tubificids except
Hesperodrilus in that the spermathecae lie behind the male pores, a state of
affairs which is met with in the Lumbriculidae. Another singularity of
structure concerns the sperm-duct, which is wrapped in a thin-walled sac,
which has every appearance of being simply the outer muscular wall of the
duct. Within this are the complicated coils of the duct, and also a quantity of
free spermatozoa, whose mode of ingress is difficult to understand. Many of
the Tubificidae live in tubes fabricated by themselves, whence the tail end
protrudes. The integument in more than one species is vascular. This
integumental blood system, universal among the earthworms, appears to be
restricted to the present group among the Limicolae of Claparède.
Fam. 7. Lumbriculidae.[436]—This family is not a large one, and is nearly
limited in range to Europe and North America; indeed, if we omit the
doubtful Alluroides, entirely to the Palaearctic region. There are only
fourteen species, which are referred to eight genera. A number of dubious
forms, as is the case with other families, may possibly ultimately swell this
list. The type genus of the family, viz. Lumbriculus, upon which Bonnet
made his experiments in section and subsequent regeneration, has only
within the last year been thoroughly explored anatomically. But all the other
genera are well known. The Lumbriculidae are of small or moderate size,
and all of them aquatic in habitat. There are three characters which are
nearly or quite universal in the genera of the family. In all of them the
chaetae are only eight to each segment, arranged in couples, and are either
cleft at the extremity or simple. As a rule which has but two exceptions, the
genera Alluroides and Lumbriculus, there are two pairs of sperm-ducts,
investment of the atrium, and in Telmatodrilus a large number of separate
aggregations forming as many distinct prostates. Vermiculus, a genus
consisting of but one species, found by Mr. Goodrich on the sea-shore in the
neighbourhood of Plymouth, is remarkable for the unpaired character of the
generative organs, a peculiarity which is shared by Stolc's genus
Bothrioneuron. The gills upon the posterior segments of Branchiura
sowerbyi and Hesperodrilus branchiatus have been already noticed above
(p. 352). A very aberrant genus, perhaps not rightly referable to this family,
is Phreodrilus,[435] from New Zealand, first collected in water from a
subterranean spring. It differs from all other Tubificids except
Hesperodrilus in that the spermathecae lie behind the male pores, a state of
affairs which is met with in the Lumbriculidae. Another singularity of
structure concerns the sperm-duct, which is wrapped in a thin-walled sac,
which has every appearance of being simply the outer muscular wall of the
duct. Within this are the complicated coils of the duct, and also a quantity of
free spermatozoa, whose mode of ingress is difficult to understand. Many of
the Tubificidae live in tubes fabricated by themselves, whence the tail end
protrudes. The integument in more than one species is vascular. This
integumental blood system, universal among the earthworms, appears to be
restricted to the present group among the Limicolae of Claparède.
Fam. 7. Lumbriculidae.[436]—This family is not a large one, and is nearly
limited in range to Europe and North America; indeed, if we omit the
doubtful Alluroides, entirely to the Palaearctic region. There are only
fourteen species, which are referred to eight genera. A number of dubious
forms, as is the case with other families, may possibly ultimately swell this
list. The type genus of the family, viz. Lumbriculus, upon which Bonnet
made his experiments in section and subsequent regeneration, has only
within the last year been thoroughly explored anatomically. But all the other
genera are well known. The Lumbriculidae are of small or moderate size,
and all of them aquatic in habitat. There are three characters which are
nearly or quite universal in the genera of the family. In all of them the
chaetae are only eight to each segment, arranged in couples, and are either
cleft at the extremity or simple. As a rule which has but two exceptions, the
genera Alluroides and Lumbriculus, there are two pairs of sperm-ducts,
Page 384
which, however, communicate with the exterior through a single terminal
chamber on each side of the body.
The dorsal blood-vessel has in the Lumbriculidae a series of contractile and
blind appendages, which were at first mistaken for caeca of the intestine
itself. There are two genera of this family in North America, which are not
very different anatomically from their European representatives. The genera
described by Eisen are Sutroa[437] and Eclipidrilus.[438] The latter lives in
cold torrents at a great height in the mountains of the Sierra Nevada of
California.
Fam. 8. Moniligastridae.—This family, terrestrial in habit, is probably
Oriental in range; but I have described a single species from the Bahamas
which may possibly be referable to the category of accidentally introduced
specimens. Our knowledge of this family is conveniently summed up in
Professor Bourne's paper[439] upon the genus Moniligaster. There are some
eighteen species, which range in size from an inch or so in length (M.
bahamensis) to about two feet; this last measurement is that of the huge M.
grandis, of which, together with many others, Professor Bourne gives
coloured drawings. There is a second genus, Desmogaster, which is mainly
characterised by the doubling of the reproductive organs. This was
described by Rosa from Burmah. The family is noteworthy on account of
the fact that every species belonging to it has at least four distinct gizzards,
sometimes more; but as this multiplication of the gizzards has been also
found in Heliodrilus among the Eudrilidae, and indeed elsewhere, it is
insufficient to define the family. More characteristic is the fact that the
sperm-ducts open on to the next segment to, or even the same segment as,
that which contains their funnels; consequently the apertures of the oviducts
are behind instead of in front of them. These pores are also situated in a
very anterior position, the male pores being upon the tenth segment or
between the tenth and eleventh, and the oviducal pores upon the following
one. In these features the family presents resemblance to the aquatic
Oligochaeta, from which, however, its stoutly-built gizzards, and vascular
nephridia differentiate it.
II. Megadrili.
chamber on each side of the body.
The dorsal blood-vessel has in the Lumbriculidae a series of contractile and
blind appendages, which were at first mistaken for caeca of the intestine
itself. There are two genera of this family in North America, which are not
very different anatomically from their European representatives. The genera
described by Eisen are Sutroa[437] and Eclipidrilus.[438] The latter lives in
cold torrents at a great height in the mountains of the Sierra Nevada of
California.
Fam. 8. Moniligastridae.—This family, terrestrial in habit, is probably
Oriental in range; but I have described a single species from the Bahamas
which may possibly be referable to the category of accidentally introduced
specimens. Our knowledge of this family is conveniently summed up in
Professor Bourne's paper[439] upon the genus Moniligaster. There are some
eighteen species, which range in size from an inch or so in length (M.
bahamensis) to about two feet; this last measurement is that of the huge M.
grandis, of which, together with many others, Professor Bourne gives
coloured drawings. There is a second genus, Desmogaster, which is mainly
characterised by the doubling of the reproductive organs. This was
described by Rosa from Burmah. The family is noteworthy on account of
the fact that every species belonging to it has at least four distinct gizzards,
sometimes more; but as this multiplication of the gizzards has been also
found in Heliodrilus among the Eudrilidae, and indeed elsewhere, it is
insufficient to define the family. More characteristic is the fact that the
sperm-ducts open on to the next segment to, or even the same segment as,
that which contains their funnels; consequently the apertures of the oviducts
are behind instead of in front of them. These pores are also situated in a
very anterior position, the male pores being upon the tenth segment or
between the tenth and eleventh, and the oviducal pores upon the following
one. In these features the family presents resemblance to the aquatic
Oligochaeta, from which, however, its stoutly-built gizzards, and vascular
nephridia differentiate it.
II. Megadrili.
Page 385
Fam. 9. Perichaetidae.[440]—The Perichaetidae comprise a larger number of
species than any other family of earthworms; but it is a matter of
considerable difficulty to divide the family satisfactorily into genera. The
family as a whole may be defined as having numerous chaetae in most of
the segments of the body.
There is no other definition which will distinguish this family from the next
two families, and even this definition is not absolutely distinctive. There are
Acanthodrilids which have a large number of chaetae in each segment. The
only difference is that in this case—in the genus Plagiochaeta—the chaetae
are implanted in twos; this is not the case in the Perichaetidae. In all
Perichaetidae that are known the sperm-ducts open in common with the
ducts of the spermiducal glands; they generally open into them at some
distance from the common external pore. In Megascolex, Perichaeta, and
Pleionogaster the nephridia are of the diffuse type so widely spread among
these worms, and the spermiducal glands are lobate. Megascolex differs
from the others in the fact that in addition to the small scattered nephridia
there are a pair of large nephridia in each segment, and the chaetae do not
form absolutely continuous circles, but are interrupted above and below.
Pleionogaster has more than one gizzard but otherwise agrees with
Perichaeta; it is confined to the East. Perichaeta is tropical and occurs—no
doubt introduced—in Europe and America. Megascolex is Old World only,
and, like Perichaeta, Australian as well as Oriental. But whereas Perichaeta
is rare in the Australian region, Megascolex is common there. Perionyx and
Diporochaeta are the other genera which it is possible to recognise. Both of
them have paired nephridia, and neither of them have intestinal caeca, a
peculiarity which they both share with Megascolex and Pleionogaster.
Perionyx principally differs from Diporochaeta in that the spermiducal
glands are lobate, whereas in the latter they are as in the Acanthodrilidae.
Perionyx is Oriental; Diporochaeta occurs in Australia and New Zealand.
species than any other family of earthworms; but it is a matter of
considerable difficulty to divide the family satisfactorily into genera. The
family as a whole may be defined as having numerous chaetae in most of
the segments of the body.
There is no other definition which will distinguish this family from the next
two families, and even this definition is not absolutely distinctive. There are
Acanthodrilids which have a large number of chaetae in each segment. The
only difference is that in this case—in the genus Plagiochaeta—the chaetae
are implanted in twos; this is not the case in the Perichaetidae. In all
Perichaetidae that are known the sperm-ducts open in common with the
ducts of the spermiducal glands; they generally open into them at some
distance from the common external pore. In Megascolex, Perichaeta, and
Pleionogaster the nephridia are of the diffuse type so widely spread among
these worms, and the spermiducal glands are lobate. Megascolex differs
from the others in the fact that in addition to the small scattered nephridia
there are a pair of large nephridia in each segment, and the chaetae do not
form absolutely continuous circles, but are interrupted above and below.
Pleionogaster has more than one gizzard but otherwise agrees with
Perichaeta; it is confined to the East. Perichaeta is tropical and occurs—no
doubt introduced—in Europe and America. Megascolex is Old World only,
and, like Perichaeta, Australian as well as Oriental. But whereas Perichaeta
is rare in the Australian region, Megascolex is common there. Perionyx and
Diporochaeta are the other genera which it is possible to recognise. Both of
them have paired nephridia, and neither of them have intestinal caeca, a
peculiarity which they both share with Megascolex and Pleionogaster.
Perionyx principally differs from Diporochaeta in that the spermiducal
glands are lobate, whereas in the latter they are as in the Acanthodrilidae.
Perionyx is Oriental; Diporochaeta occurs in Australia and New Zealand.
Page 386
Fig. 196.—Perichaeta everetti F. E. B. × 1. sp, Spermathecal pores; cl, clitellum; ♀,
female pore; ♂, male pore.
A very distinctive feature of Perichaeta—perhaps only of the genus sensu
stricto—is its exceeding activity. The first specimens ever noticed in this
country, or at least of whose existence printed notice was taken, were
exhibited by the late Dr. Baird of the British Museum, at a meeting of the
Zoological Society. He remarked in that communication upon the agile
fashion in which these tropical Annelids will spring off a table when
touched or in any way interfered with. Numerous other observers have seen
the same manifestations, and the name of "eel-worm" has been given to
these Perichaeta by gardeners. It is worth putting on record here that in a
species of Acanthodrilus (A. capensis) the same irritable behaviour is
visible. When a Perichaeta moves it helps itself greatly by extending, or
rather protruding, the buccal cavity, which serves as a sucker, and grips the
ground in front until the rest of the body is brought forward. It is possibly
on account of this extra facility for movement that the genus can climb trees
with such ease. A species of Perichaeta has been recorded by Mr. Willey
upon an epiphyte of a palm, and Dr. Benham has found that it is a new
species, to which the name of Perichaeta willeyi has been given. The
Lumbricid genus (if it be admitted as a genus), Dendrobaena, was so named
on account of a similar habit of climbing trees. Very singular in its habit is
the not inaptly-named Perichaeta musica of Java. It is a monster of its kind,
several feet in length, and during the night makes "a sharp interrupted
sound," apparently by the friction of the chaetae against stones. The species
figured (p. 381) is, as are a few others, remarkable for the presence of
twelve or seventeen spermathecae in segments 6 and 7.
Fam. 10. Cryptodrilidae.[441]—This family is one of the largest of the
Oligochaeta; there are rather over 120 different species, which can be
arranged in at least sixteen genera. They are found in most parts of the
female pore; ♂, male pore.
A very distinctive feature of Perichaeta—perhaps only of the genus sensu
stricto—is its exceeding activity. The first specimens ever noticed in this
country, or at least of whose existence printed notice was taken, were
exhibited by the late Dr. Baird of the British Museum, at a meeting of the
Zoological Society. He remarked in that communication upon the agile
fashion in which these tropical Annelids will spring off a table when
touched or in any way interfered with. Numerous other observers have seen
the same manifestations, and the name of "eel-worm" has been given to
these Perichaeta by gardeners. It is worth putting on record here that in a
species of Acanthodrilus (A. capensis) the same irritable behaviour is
visible. When a Perichaeta moves it helps itself greatly by extending, or
rather protruding, the buccal cavity, which serves as a sucker, and grips the
ground in front until the rest of the body is brought forward. It is possibly
on account of this extra facility for movement that the genus can climb trees
with such ease. A species of Perichaeta has been recorded by Mr. Willey
upon an epiphyte of a palm, and Dr. Benham has found that it is a new
species, to which the name of Perichaeta willeyi has been given. The
Lumbricid genus (if it be admitted as a genus), Dendrobaena, was so named
on account of a similar habit of climbing trees. Very singular in its habit is
the not inaptly-named Perichaeta musica of Java. It is a monster of its kind,
several feet in length, and during the night makes "a sharp interrupted
sound," apparently by the friction of the chaetae against stones. The species
figured (p. 381) is, as are a few others, remarkable for the presence of
twelve or seventeen spermathecae in segments 6 and 7.
Fam. 10. Cryptodrilidae.[441]—This family is one of the largest of the
Oligochaeta; there are rather over 120 different species, which can be
arranged in at least sixteen genera. They are found in most parts of the
Page 387
world, but abound principally in the tropics. Australia may be considered to
be the headquarters of the family, which form its principal earthworm-
inhabitants. Peculiar to this continent, or at least mainly confined to it, are
the genera Megascolides, Cryptodrilus, Fletcherodrilus, Trinephrus, and
Digaster. Microscolex, though occurring in many parts of the world, is
characteristic of the more southern regions of South America and of New
Zealand. Tropical Africa has the genera Nannodrilus and Millsonia limited
to itself, and has besides nearly all the species of the genus Gordiodrilus.
This family is one which it is exceedingly difficult to define and to split up
into different genera. It shades almost imperceptibly into the Perichaetidae
on the one hand, and is very hard to differentiate from the Acanthodrilidae
on the other. A Cryptodrilid, like any member of the genus Cryptodrilus,
with complete circles of chaetae would be a Perichaetid; and as there are
species of Perichaeta in which the anterior segments have only a few
chaetae in each segment, it is perhaps wrong to separate the two families at
all. Apart from the chaetae, there is no peculiarity in the organisation of the
family Perichaetidae that is not also met with in the Cryptodrilidae. Even
the highly characteristic intestinal caeca so distinctive of the genus
Perichaeta itself, as contrasted with Megascolex and the other genera,
occur, though more numerously, in the African Millsonia, where there are
forty or fifty pairs of them. A fairly common feature in the family is the
presence of two, or even three, pairs of gizzards, a character which is also
met with in the genus Benhamia among the Acanthodrilidae, and occurs
also in some other families. The names Digaster, Didymogaster,
Perissogaster, and Dichogaster have been founded upon this character. The
excretory organs may be paired (in Trinephrus there are three pairs to each
segment) or of the diffuse kind. The male pores are usually upon the
eighteenth segment, but not unfrequently upon the seventeenth, and are
often armed with long and ornamented chaetae. Spermiducal glands are
invariably present, and may be lobate or tubular. There are two groups of
small-sized genera, which in their simplicity of organisation stand at the
base of the series; but it is very possible that the simplification is rather due
to degeneration than to primitive position. One of these groups includes the
semi-marine genus Pontodrilus (with which I include the phosphorescent
Photodrilus) and Microscolex. In these forms the gizzard has disappeared,
or is represented by a rudimentary structure, and the male pores are upon
the seventeenth segment. In the other group are the genera Ocnerodrilus,
be the headquarters of the family, which form its principal earthworm-
inhabitants. Peculiar to this continent, or at least mainly confined to it, are
the genera Megascolides, Cryptodrilus, Fletcherodrilus, Trinephrus, and
Digaster. Microscolex, though occurring in many parts of the world, is
characteristic of the more southern regions of South America and of New
Zealand. Tropical Africa has the genera Nannodrilus and Millsonia limited
to itself, and has besides nearly all the species of the genus Gordiodrilus.
This family is one which it is exceedingly difficult to define and to split up
into different genera. It shades almost imperceptibly into the Perichaetidae
on the one hand, and is very hard to differentiate from the Acanthodrilidae
on the other. A Cryptodrilid, like any member of the genus Cryptodrilus,
with complete circles of chaetae would be a Perichaetid; and as there are
species of Perichaeta in which the anterior segments have only a few
chaetae in each segment, it is perhaps wrong to separate the two families at
all. Apart from the chaetae, there is no peculiarity in the organisation of the
family Perichaetidae that is not also met with in the Cryptodrilidae. Even
the highly characteristic intestinal caeca so distinctive of the genus
Perichaeta itself, as contrasted with Megascolex and the other genera,
occur, though more numerously, in the African Millsonia, where there are
forty or fifty pairs of them. A fairly common feature in the family is the
presence of two, or even three, pairs of gizzards, a character which is also
met with in the genus Benhamia among the Acanthodrilidae, and occurs
also in some other families. The names Digaster, Didymogaster,
Perissogaster, and Dichogaster have been founded upon this character. The
excretory organs may be paired (in Trinephrus there are three pairs to each
segment) or of the diffuse kind. The male pores are usually upon the
eighteenth segment, but not unfrequently upon the seventeenth, and are
often armed with long and ornamented chaetae. Spermiducal glands are
invariably present, and may be lobate or tubular. There are two groups of
small-sized genera, which in their simplicity of organisation stand at the
base of the series; but it is very possible that the simplification is rather due
to degeneration than to primitive position. One of these groups includes the
semi-marine genus Pontodrilus (with which I include the phosphorescent
Photodrilus) and Microscolex. In these forms the gizzard has disappeared,
or is represented by a rudimentary structure, and the male pores are upon
the seventeenth segment. In the other group are the genera Ocnerodrilus,
Page 388
[442] Gordiodrilus,[443] and Nannodrilus, which are of even smaller size, and
have in the same way the male pores upon the seventeenth segment. The
species of this group are often aquatic, and there is not only no gizzard (in
most of the species), but the calciferous glands have been reduced to a
single pair, which lie in the ninth segment. The latter character is also found
in the Acanthodrilid Kerria, which has been associated with the above
named. Gordiodrilus has the peculiarity that there are, as in Acanthodrilids,
two pairs of tubular spermiducal glands.
Fam. 11. Acanthodrilidae.[444]—This family is only with difficulty to be
distinguished from the last. The following definition applies to all the
members of the family with one exception, and does not apply to any
Cryptodrilid with, so far as is known, one exception only. There are two
pairs of spermiducal glands, opening upon the segments in front of and
behind that which bears the apertures of the sperm-ducts.
The one exception to this definition is the species Acanthodrilus
monocystis, which I formerly placed in a distinct genus, Neodrilus.
Microscolex modestus is the exception among the Cryptodrilidae; in that
worm the male pores are upon the segment which follows that upon which
the spermiducal glands open. The Acanthodrilidae show a considerable
range of structural variation. This enables them to be separated into several
well-marked genera. The type genus Acanthodrilus has a pair of nephridia
in each segment. It contains thirty-five species, which are all from the
southern hemisphere. These species show but little variation among
themselves. Benhamia is a genus that differs from Acanthodrilus in the fact
that the nephridia are of the complex type, so often met with in earthworms
with many external pores. The segment that bears the male pores is entirely
without any traces of the ventral chaetae. Here again there are a large
number of species which are nearly confined to the continent of Africa. Dr.
Michaelsen is indeed of opinion that the few species found in the East
Indies and America are accidental importations. I have proposed to separate
some of the New Zealand Acanthodrilids into a distinct genus, Octochaetus,
which is somewhat intermediate between Acanthodrilus and Benhamia.
They have multiple nephridia, but only a single gizzard. Plagiochaeta of
Benham, from New Zealand, is in any case clearly a distinct form. It is
have in the same way the male pores upon the seventeenth segment. The
species of this group are often aquatic, and there is not only no gizzard (in
most of the species), but the calciferous glands have been reduced to a
single pair, which lie in the ninth segment. The latter character is also found
in the Acanthodrilid Kerria, which has been associated with the above
named. Gordiodrilus has the peculiarity that there are, as in Acanthodrilids,
two pairs of tubular spermiducal glands.
Fam. 11. Acanthodrilidae.[444]—This family is only with difficulty to be
distinguished from the last. The following definition applies to all the
members of the family with one exception, and does not apply to any
Cryptodrilid with, so far as is known, one exception only. There are two
pairs of spermiducal glands, opening upon the segments in front of and
behind that which bears the apertures of the sperm-ducts.
The one exception to this definition is the species Acanthodrilus
monocystis, which I formerly placed in a distinct genus, Neodrilus.
Microscolex modestus is the exception among the Cryptodrilidae; in that
worm the male pores are upon the segment which follows that upon which
the spermiducal glands open. The Acanthodrilidae show a considerable
range of structural variation. This enables them to be separated into several
well-marked genera. The type genus Acanthodrilus has a pair of nephridia
in each segment. It contains thirty-five species, which are all from the
southern hemisphere. These species show but little variation among
themselves. Benhamia is a genus that differs from Acanthodrilus in the fact
that the nephridia are of the complex type, so often met with in earthworms
with many external pores. The segment that bears the male pores is entirely
without any traces of the ventral chaetae. Here again there are a large
number of species which are nearly confined to the continent of Africa. Dr.
Michaelsen is indeed of opinion that the few species found in the East
Indies and America are accidental importations. I have proposed to separate
some of the New Zealand Acanthodrilids into a distinct genus, Octochaetus,
which is somewhat intermediate between Acanthodrilus and Benhamia.
They have multiple nephridia, but only a single gizzard. Plagiochaeta of
Benham, from New Zealand, is in any case clearly a distinct form. It is
Page 389
mainly to be distinguished by the numerous chaetae in each segment.
Trigaster Benham, is West Indian. Deinodrilus (New Zealand) has twelve
chaetae in each segment. Diplocardia, from North America, has the male
pores on segments 18, 19, 20.
Fam. 12. Eudrilidae.[445]—This is perhaps the most remarkable family of
terrestrial Oligochaeta. Its distribution is no less curious than its structure.
Up to the present it is not known outside tropical Africa, with the exception
of the genus Eudrilus itself, which is almost world-wide in range. As,
however, but one species of Eudrilus is found out of Africa, and as that
species is so common in gatherings from various tropical countries, it seems
to be an instance of a species with large capacities for accidental
transference from country to country. The type genus, Eudrilus, has been
known since 1871, when it was originally described by M. Perrier.[446]
Since that date nineteen other genera have been described from Africa by
Dr. Michaelsen, Dr. Rosa, and myself. The most salient external character
of the group, not universal but general, is the unpaired male and female
orifices. The orifices are commonly very conspicuous (see Fig. 197).
Fig. 197.—Libyodrilus violaceus F. E. B. × 2. sp, Spermathecal pore; cl, clitellum; ♂,
male pore.
The peculiarities of internal structure mainly concern the reproductive
organs, the differences in which from genus to genus are often very great.
We have already referred to the remarkable branching of the nephridial duct
Trigaster Benham, is West Indian. Deinodrilus (New Zealand) has twelve
chaetae in each segment. Diplocardia, from North America, has the male
pores on segments 18, 19, 20.
Fam. 12. Eudrilidae.[445]—This is perhaps the most remarkable family of
terrestrial Oligochaeta. Its distribution is no less curious than its structure.
Up to the present it is not known outside tropical Africa, with the exception
of the genus Eudrilus itself, which is almost world-wide in range. As,
however, but one species of Eudrilus is found out of Africa, and as that
species is so common in gatherings from various tropical countries, it seems
to be an instance of a species with large capacities for accidental
transference from country to country. The type genus, Eudrilus, has been
known since 1871, when it was originally described by M. Perrier.[446]
Since that date nineteen other genera have been described from Africa by
Dr. Michaelsen, Dr. Rosa, and myself. The most salient external character
of the group, not universal but general, is the unpaired male and female
orifices. The orifices are commonly very conspicuous (see Fig. 197).
Fig. 197.—Libyodrilus violaceus F. E. B. × 2. sp, Spermathecal pore; cl, clitellum; ♂,
male pore.
The peculiarities of internal structure mainly concern the reproductive
organs, the differences in which from genus to genus are often very great.
We have already referred to the remarkable branching of the nephridial duct
Page 390
in the body-wall, and to the much modified calciferous glands of
Stuhlmannia and some other genera. These structural variations perhaps
permit the family to be divided into two sub-families. In one there are
calciferous glands of the normal type, though peculiar in that one or more
are median and ventral in position, and are unpaired; there is no branching
of the nephridium in the body-wall; there are always, so far as is known, the
Pacinian-corpuscle-like bodies in the integument. In the other sub-family
the calciferous glands, if present (they are absent, for instance, in
Libyodrilus), have undergone much modification in structure; the nephridia,
where they have been investigated, have been found to branch copiously in
the body-wall; the peculiar integumental bodies hardly ever occur.
Fam. 13. Geoscolicidae.[447]—This family is essentially tropical, being
found in South America and the West Indies, in tropical Africa, in India, and
in some of the islands of the Malay Archipelago. But it also occurs
(Sparganophilus and Criodrilus) in Europe and in America. A good many of
the genera are aquatic. This is the case with the two already mentioned; the
genera Glyphidrilus and Annadrilus of the Malay Archipelago can live in
water. The family is easily definable if we take the more typical forms; but
at one end of the series it fades into the next family, that of the
Lumbricidae. Criodrilus is one of the genera which is difficult to place. As
is the case with many Geoscolicidae, Criodrilus has ornamented chaetae not
only upon the clitellum, but upon the other segments of the body. This
character was until recently unknown among the Lumbricidae; it has been
lately found in Allolobophora moebii and A. lonnbergi. The absence of
spermathecae characterises Criodrilus as well as other Geoscolicidae; but
here again the character is not by any means distinctive, for in
Allolobophora constricta there is the same absence of these organs. In
Criodrilus the male pores are upon segment 15, as in the Lumbricidae, but a
species of Kynotus, which is certainly a Geoscolecid, has these pores upon
precisely the same segment. The only point in which Criodrilus is definitely
a Geoscolecid, or rather not a Lumbricid, is in the forward position of the
clitellum, which begins upon the fifteenth segment, far earlier than it does
in any undoubted Lumbricid. The peculiar elongated cocoon, which much
resembles that of Sparganophilus, is another character which favours its
Geoscolecine affinities. Dr. Michaelsen has proposed to unite Criodrilus
Stuhlmannia and some other genera. These structural variations perhaps
permit the family to be divided into two sub-families. In one there are
calciferous glands of the normal type, though peculiar in that one or more
are median and ventral in position, and are unpaired; there is no branching
of the nephridium in the body-wall; there are always, so far as is known, the
Pacinian-corpuscle-like bodies in the integument. In the other sub-family
the calciferous glands, if present (they are absent, for instance, in
Libyodrilus), have undergone much modification in structure; the nephridia,
where they have been investigated, have been found to branch copiously in
the body-wall; the peculiar integumental bodies hardly ever occur.
Fam. 13. Geoscolicidae.[447]—This family is essentially tropical, being
found in South America and the West Indies, in tropical Africa, in India, and
in some of the islands of the Malay Archipelago. But it also occurs
(Sparganophilus and Criodrilus) in Europe and in America. A good many of
the genera are aquatic. This is the case with the two already mentioned; the
genera Glyphidrilus and Annadrilus of the Malay Archipelago can live in
water. The family is easily definable if we take the more typical forms; but
at one end of the series it fades into the next family, that of the
Lumbricidae. Criodrilus is one of the genera which is difficult to place. As
is the case with many Geoscolicidae, Criodrilus has ornamented chaetae not
only upon the clitellum, but upon the other segments of the body. This
character was until recently unknown among the Lumbricidae; it has been
lately found in Allolobophora moebii and A. lonnbergi. The absence of
spermathecae characterises Criodrilus as well as other Geoscolicidae; but
here again the character is not by any means distinctive, for in
Allolobophora constricta there is the same absence of these organs. In
Criodrilus the male pores are upon segment 15, as in the Lumbricidae, but a
species of Kynotus, which is certainly a Geoscolecid, has these pores upon
precisely the same segment. The only point in which Criodrilus is definitely
a Geoscolecid, or rather not a Lumbricid, is in the forward position of the
clitellum, which begins upon the fifteenth segment, far earlier than it does
in any undoubted Lumbricid. The peculiar elongated cocoon, which much
resembles that of Sparganophilus, is another character which favours its
Geoscolecine affinities. Dr. Michaelsen has proposed to unite Criodrilus
Page 391
and Alma into a family intermediate between the Geoscolicidae and the
Lumbricidae.
Fig. 198.—Alma millsoni F. E. B. × 1.
Perhaps the most remarkable genus in the whole family is Alma. One
species lives in the Nile mud; another is the "Yoruba worm" of West Africa,
whose habits have been described by Mr. Millson. The most marked
character of this genus, apart from the branchiae (see p. 352) which
apparently may be present or absent according to the species, is in the two
enormous processes of the body-wall, which are illustrated in Fig. 198.
These contain the sperm-ducts, which, however, open some way in front of
the free end; they are provided on the ventral surface with a series of
sucker-like structures and with peculiar chaetae. Another interesting genus
is Pontoscolex, which was originally described from the sea-shore of
Jamaica by Schmarda; there are only two species which are certainly
characterised, though a variety from the Hawaian Islands may be a "good"
species. It possesses the remarkable peculiarity that the chaetae at the end of
the body are disposed in a perfectly irregular fashion, which earned for it
the name of brush-tail at the hands of its discoverer, Fritz Müller. This
worm, which is universal, or nearly so, in its range, doubtless having been
transferred accidentally from country to country, invariably shows a light
spot not far from the tail; when this is examined with the microscope it is
seen that the chaetae are here absent or very small, and that the muscular
structure of the body-wall is slightly different; it was thought that this spot
was a zone of growth where fresh segments could be added after the fashion
of some of the aquatic Oligochaeta, to which, it may be remarked, the
present genus shows a curious point of likeness in the bifid character of the
chaetae. It seems, however, that there are really no grounds for the
supposition, and it is possible that we have here a "weak" spot, such as that
Lumbricidae.
Fig. 198.—Alma millsoni F. E. B. × 1.
Perhaps the most remarkable genus in the whole family is Alma. One
species lives in the Nile mud; another is the "Yoruba worm" of West Africa,
whose habits have been described by Mr. Millson. The most marked
character of this genus, apart from the branchiae (see p. 352) which
apparently may be present or absent according to the species, is in the two
enormous processes of the body-wall, which are illustrated in Fig. 198.
These contain the sperm-ducts, which, however, open some way in front of
the free end; they are provided on the ventral surface with a series of
sucker-like structures and with peculiar chaetae. Another interesting genus
is Pontoscolex, which was originally described from the sea-shore of
Jamaica by Schmarda; there are only two species which are certainly
characterised, though a variety from the Hawaian Islands may be a "good"
species. It possesses the remarkable peculiarity that the chaetae at the end of
the body are disposed in a perfectly irregular fashion, which earned for it
the name of brush-tail at the hands of its discoverer, Fritz Müller. This
worm, which is universal, or nearly so, in its range, doubtless having been
transferred accidentally from country to country, invariably shows a light
spot not far from the tail; when this is examined with the microscope it is
seen that the chaetae are here absent or very small, and that the muscular
structure of the body-wall is slightly different; it was thought that this spot
was a zone of growth where fresh segments could be added after the fashion
of some of the aquatic Oligochaeta, to which, it may be remarked, the
present genus shows a curious point of likeness in the bifid character of the
chaetae. It seems, however, that there are really no grounds for the
supposition, and it is possible that we have here a "weak" spot, such as that
Page 392
in the foot of certain land snails, which readily gives way when the worm is
picked up by a bird, and allows the "better half" of the creature to escape.
The Bermudian genus Onychochaeta offers a very strange peculiarity in
that the chaetae on the hinder segments of the body are enormously larger
than those in front, and end in strong hooks; it seems likely that their
function is to maintain a tight hold of the ground while the worm is leaning
out of its burrow, as every one has seen the common earthworms of this
country do. Onychochaeta has the same irregular arrangement of the
chaetae upon the greater part of the body, as has Pontoscolex. This family,
like so many others, has its giants and its dwarfs. At one extreme is the
great Antaeus of South America, several feet in length; at the other the inch-
long Ilyogenia of Africa. The American Urobenus has a pair of intestinal
caeca like those of Perichaeta, and placed in the same segment.
Fam. 14.9 Lumbricidae.[448]—This family is to be distinguished by the
following assemblage of characters.
The male pores are usually upon segment 15, and never behind that
segment; the clitellum commences some way behind the male pores. The
gizzard, which is invariably single, is equally invariably at the end of the
oesophagus. There are three pairs of calciferous glands. The nephridia are
always paired. The spermathecae never have a diverticulum.
This family only contains three well-known genera, viz. Lumbricus,
Allolobophora, and Allurus. The American Bimastos may be distinct.
Tetragonurus, not allowed by some, is at present unknown except as
regards external characters; it differs from the other Lumbricidae in the fact
that the male pores are upon the twelfth segment. In Allurus they are upon
segment 13, and in the remaining genera upon the fifteenth. Lumbricus is to
be distinguished from Allolobophora by its prostomium, which is continued
by grooves on to the buccal segment, so as to cut the latter in half. It has
also median sperm reservoirs, as well as the paired sperm sacs which are
alone present in Allolobophora.
picked up by a bird, and allows the "better half" of the creature to escape.
The Bermudian genus Onychochaeta offers a very strange peculiarity in
that the chaetae on the hinder segments of the body are enormously larger
than those in front, and end in strong hooks; it seems likely that their
function is to maintain a tight hold of the ground while the worm is leaning
out of its burrow, as every one has seen the common earthworms of this
country do. Onychochaeta has the same irregular arrangement of the
chaetae upon the greater part of the body, as has Pontoscolex. This family,
like so many others, has its giants and its dwarfs. At one extreme is the
great Antaeus of South America, several feet in length; at the other the inch-
long Ilyogenia of Africa. The American Urobenus has a pair of intestinal
caeca like those of Perichaeta, and placed in the same segment.
Fam. 14.9 Lumbricidae.[448]—This family is to be distinguished by the
following assemblage of characters.
The male pores are usually upon segment 15, and never behind that
segment; the clitellum commences some way behind the male pores. The
gizzard, which is invariably single, is equally invariably at the end of the
oesophagus. There are three pairs of calciferous glands. The nephridia are
always paired. The spermathecae never have a diverticulum.
This family only contains three well-known genera, viz. Lumbricus,
Allolobophora, and Allurus. The American Bimastos may be distinct.
Tetragonurus, not allowed by some, is at present unknown except as
regards external characters; it differs from the other Lumbricidae in the fact
that the male pores are upon the twelfth segment. In Allurus they are upon
segment 13, and in the remaining genera upon the fifteenth. Lumbricus is to
be distinguished from Allolobophora by its prostomium, which is continued
by grooves on to the buccal segment, so as to cut the latter in half. It has
also median sperm reservoirs, as well as the paired sperm sacs which are
alone present in Allolobophora.
Page 393
Fig. 199.—Allolobophora chlorotica Savigny. × 4. The clitellar segments are marked in
Roman numerals. t.p, Tubercula pubertatis; ♂, male pore.
Fig. 200.—Allolobophora putris Vejd. × 5. Lettering as in Fig. 199. The black dots
represent the chaetae in both figures.
This is the only family of earthworms which, so far as is known, can brave
the ice and snow, and what is still more difficult to understand, the
perpetually frozen undersoil of the Arctic regions. Eisen has described a
number of species from Spitzbergen, and Colonel Feilden recently sent me
an example of Allolobophora octoedra from Kolguiev, where Mr. Trevor-
Battye also saw another specimen. The family is characteristic of the
Nearctic and Palaearctic regions, and though found beyond them, is
probably elsewhere an accidental importation (see p. 371). There are at least
fifteen species of this family found in England and Ireland, and probably
more will be identified.
Roman numerals. t.p, Tubercula pubertatis; ♂, male pore.
Fig. 200.—Allolobophora putris Vejd. × 5. Lettering as in Fig. 199. The black dots
represent the chaetae in both figures.
This is the only family of earthworms which, so far as is known, can brave
the ice and snow, and what is still more difficult to understand, the
perpetually frozen undersoil of the Arctic regions. Eisen has described a
number of species from Spitzbergen, and Colonel Feilden recently sent me
an example of Allolobophora octoedra from Kolguiev, where Mr. Trevor-
Battye also saw another specimen. The family is characteristic of the
Nearctic and Palaearctic regions, and though found beyond them, is
probably elsewhere an accidental importation (see p. 371). There are at least
fifteen species of this family found in England and Ireland, and probably
more will be identified.
Page 394
There does not exist at present any comprehensive account of the British
species of earthworms, though all of them are included in Dr. Rosa's recent
revision of the family. Most of the British forms belong to the genus
Allolobophora, which may be divided into two series according to whether
the chaetae are quite close together or further apart. The extent of the
clitellum and the position of those swollen eminences which appear earlier
than the clitellum, and are known as tubercula pubertatis, offer further
characters. In the following tables, extracted from those of Rosa, the known
British species of this genus are grouped according to these three
characters. With the help of these tables and Figs. 199 and 200, any of the
species ought to be easily identified.
With Chaetae Distant.[449]
25 26 27 28 29 30 31 32 33 34 35 36
A. putris ··· — — — — — — ···
··· — —
A. — — — — — —
constricta
A. veneta ··· — — — — — — —
— —
A. — — — — ···
octoedra — — —
A. cyanea — — — — — —
(subsp. — — — —
profuga)
A. rubida — — — — — —
— — — — — —
A. — — — — — —
mammalis — —
species of earthworms, though all of them are included in Dr. Rosa's recent
revision of the family. Most of the British forms belong to the genus
Allolobophora, which may be divided into two series according to whether
the chaetae are quite close together or further apart. The extent of the
clitellum and the position of those swollen eminences which appear earlier
than the clitellum, and are known as tubercula pubertatis, offer further
characters. In the following tables, extracted from those of Rosa, the known
British species of this genus are grouped according to these three
characters. With the help of these tables and Figs. 199 and 200, any of the
species ought to be easily identified.
With Chaetae Distant.[449]
25 26 27 28 29 30 31 32 33 34 35 36
A. putris ··· — — — — — — ···
··· — —
A. — — — — — —
constricta
A. veneta ··· — — — — — — —
— —
A. — — — — ···
octoedra — — —
A. cyanea — — — — — —
(subsp. — — — —
profuga)
A. rubida — — — — — —
— — — — — —
A. — — — — — —
mammalis — —
Page 395
With Chaetae Paired.
24 25 26 27 28 29 30 31 32 33 34 35 36 37
A. rosea ··· — — — — — — — —
— — ···
A. foetida ··· ··· — — — — — — —
— — — ···
A. eiseni ··· — — — — — — — —
A. caliginosa ··· — — — — — — — ···
— ··· —
A. terrestris ··· — — — — — — — —
— — —
A. chlorotica ··· — — — — — — — — —
— — —
A. georgii ··· — — — — — — —
— —
There are of course other points by which the different species can be distinguished.
Colour in a few cases enables a species to be named at once without any further aid.
One of the most striking of these cases is the Brandling, so common upon dunghills,
and so dear to some anglers. This worm is ringed with brownish purple upon a
yellowish ground. The greenish A. chlorotica is often found under stones, and curls
itself round into nearly a complete circle when disturbed. A. cyanea, of a bluish grey
colour, is one of the earthworms very commonly met with in the early morning in
London and the neighbourhood. More generally, however, the colour is of a paler or
darker red, verging towards and attaining brown, or even blackish brown; and is so
variable that nothing in the way of identification can be attempted from the colour
alone, even with the most elaborate description.
Lumbricus, as already mentioned, is distinguished from all Allolobophora except A.
eiseni, by the complete dovetailing of the prostomium into the first segment. There are
five species in this country which may be thus distinguished by the position of the
tubercula pubertatis. The most familiar species is the common L. rubellus.
L. rubellus Hoff. tubercula pubertatis are on 28, 29, 30, 31
L. castaneus Sav. " " " 29, 30, 31, 32
L. herculeus Sav. " " " 33, 34, 35, 36
24 25 26 27 28 29 30 31 32 33 34 35 36 37
A. rosea ··· — — — — — — — —
— — ···
A. foetida ··· ··· — — — — — — —
— — — ···
A. eiseni ··· — — — — — — — —
A. caliginosa ··· — — — — — — — ···
— ··· —
A. terrestris ··· — — — — — — — —
— — —
A. chlorotica ··· — — — — — — — — —
— — —
A. georgii ··· — — — — — — —
— —
There are of course other points by which the different species can be distinguished.
Colour in a few cases enables a species to be named at once without any further aid.
One of the most striking of these cases is the Brandling, so common upon dunghills,
and so dear to some anglers. This worm is ringed with brownish purple upon a
yellowish ground. The greenish A. chlorotica is often found under stones, and curls
itself round into nearly a complete circle when disturbed. A. cyanea, of a bluish grey
colour, is one of the earthworms very commonly met with in the early morning in
London and the neighbourhood. More generally, however, the colour is of a paler or
darker red, verging towards and attaining brown, or even blackish brown; and is so
variable that nothing in the way of identification can be attempted from the colour
alone, even with the most elaborate description.
Lumbricus, as already mentioned, is distinguished from all Allolobophora except A.
eiseni, by the complete dovetailing of the prostomium into the first segment. There are
five species in this country which may be thus distinguished by the position of the
tubercula pubertatis. The most familiar species is the common L. rubellus.
L. rubellus Hoff. tubercula pubertatis are on 28, 29, 30, 31
L. castaneus Sav. " " " 29, 30, 31, 32
L. herculeus Sav. " " " 33, 34, 35, 36
Page 396
L. papillosus " " " 34, 35, 36, 37
Friend
L. festivus Sav. " " " 35, 36, 37,
38.
CHAPTER XIV
HIRUDINEA (LEECHES)
INTRODUCTION—ANATOMY—REPRODUCTION—CLASSIFICATION—RHYNCHOBDELLAE AND
GNATHOBDELLAE
"The external appearance of the Hirudinea," remarks Professor Vaillant,[450] "permits
us, save for rare exceptions, to recognise at once the animals which belong to that
group." The leeches are distinguished as a rule by the possession of two suckers, one
at each end of the body; their general shape usually differs from that of other Annelids
by its oval contour and its dorso-ventral flattening. Cyclicobdella lumbricoides of
Grube, which Blanchard has stated to be the same species as Nephelis tergestina, has,
however, almost the form of an earthworm by reason of its cylindrical shape and the
inconspicuousness of the suckers, while Lumbricobdella also resembles an earthworm
and has no posterior sucker at all.[451] The Oligochaet family Discodrilidae (see p.
376) agree with the leeches in their parasitism, in their general shape, in the presence
of two suckers, and, furthermore, in the existence of jaws, which are found in no other
Oligochaet, but occur in a large number of the Hirudinea. These facts, indeed, though
not perhaps important by themselves, are indications of the really close resemblance
of the Hirudinea to the Oligochaeta, a group which they approach not merely in such
habits as the formation of a cocoon in which the eggs are enclosed, but also in many
important points of internal and external structure. Indeed, the fundamental differences
between the two groups are not numerous, and are not of such importance as has been
given them by some writers.
Leeches are to be found in most parts of the world, in situations which are sufficiently
damp for their comfort. But we do not at present possess enough knowledge to state
much as to the facts of their distribution. The structure of leeches is not so well known
as is that of the earthworms; for they have not been to so great an extent collected in
extra-European countries. It would even be desirable to ascertain precisely the species
which inhabit these islands, the most recent enumeration (1865) being that contained
in the British Museum Catalogue of non-parasitical worms by the late Dr. George
Johnston. For Italy this has been lately done by Dr. Blanchard, and a good many of the
Friend
L. festivus Sav. " " " 35, 36, 37,
38.
CHAPTER XIV
HIRUDINEA (LEECHES)
INTRODUCTION—ANATOMY—REPRODUCTION—CLASSIFICATION—RHYNCHOBDELLAE AND
GNATHOBDELLAE
"The external appearance of the Hirudinea," remarks Professor Vaillant,[450] "permits
us, save for rare exceptions, to recognise at once the animals which belong to that
group." The leeches are distinguished as a rule by the possession of two suckers, one
at each end of the body; their general shape usually differs from that of other Annelids
by its oval contour and its dorso-ventral flattening. Cyclicobdella lumbricoides of
Grube, which Blanchard has stated to be the same species as Nephelis tergestina, has,
however, almost the form of an earthworm by reason of its cylindrical shape and the
inconspicuousness of the suckers, while Lumbricobdella also resembles an earthworm
and has no posterior sucker at all.[451] The Oligochaet family Discodrilidae (see p.
376) agree with the leeches in their parasitism, in their general shape, in the presence
of two suckers, and, furthermore, in the existence of jaws, which are found in no other
Oligochaet, but occur in a large number of the Hirudinea. These facts, indeed, though
not perhaps important by themselves, are indications of the really close resemblance
of the Hirudinea to the Oligochaeta, a group which they approach not merely in such
habits as the formation of a cocoon in which the eggs are enclosed, but also in many
important points of internal and external structure. Indeed, the fundamental differences
between the two groups are not numerous, and are not of such importance as has been
given them by some writers.
Leeches are to be found in most parts of the world, in situations which are sufficiently
damp for their comfort. But we do not at present possess enough knowledge to state
much as to the facts of their distribution. The structure of leeches is not so well known
as is that of the earthworms; for they have not been to so great an extent collected in
extra-European countries. It would even be desirable to ascertain precisely the species
which inhabit these islands, the most recent enumeration (1865) being that contained
in the British Museum Catalogue of non-parasitical worms by the late Dr. George
Johnston. For Italy this has been lately done by Dr. Blanchard, and a good many of the
Page 397
species are common to the two countries. Johnston enumerates altogether (after
subtracting what are probably synonyms) twenty-one species, distributed among the
genera Branchellion, Pontobdella, Piscicola, Nephelis, Trocheta, Haemopis, Hirudo,
and Glossiphonia (= Clepsine), which number will be possibly still further reduced.
The first two genera are marine, the remainder being fresh water or terrestrial;
Trocheta has been probably introduced.
Fig. 201.—Anterior end of Macrobdella sestertia, to show eyes and sense bodies. (After
Whitman.)
The use of Hirudo medicinalis is well known to many of us from personal experience.
So extensively was this leech formerly made use of that it is now far from being a
common species either in this country or in France. Those who desire full information
as to Hirudiniculture should consult the work of Dr. Ebrard, published in 1857.[452]
The former extensive use of the leech has led to the transfer of its name to the doctor
who employs it, the authors of the sixteenth century constantly terming a physician a
leech; it has been suggested, however, that the term was applied rather by way of
analogy. The useful blood-sucking habits of the medicinal leech have been wrongly
attributed to the innocent horseleech (Aulastomum)—innocent, that is to say, of the
blood of Vertebrates, for it has been described as "a cruel and greedy worm,"
engulfing earthworms and even smaller specimens of its own species. "Horsleches,"
said an old writer, "are wholesome to drawe foorthe foule blood, if thei are put into a
hollowe rede, and one of their endes cutte of, whereby the blood maie run forthe." But
it is clearly not easy for a creature destitute of jaws and teeth to bite, and the similarity
of general aspect has doubtless led to a confusion with the savagely biting medicinal
leech.
subtracting what are probably synonyms) twenty-one species, distributed among the
genera Branchellion, Pontobdella, Piscicola, Nephelis, Trocheta, Haemopis, Hirudo,
and Glossiphonia (= Clepsine), which number will be possibly still further reduced.
The first two genera are marine, the remainder being fresh water or terrestrial;
Trocheta has been probably introduced.
Fig. 201.—Anterior end of Macrobdella sestertia, to show eyes and sense bodies. (After
Whitman.)
The use of Hirudo medicinalis is well known to many of us from personal experience.
So extensively was this leech formerly made use of that it is now far from being a
common species either in this country or in France. Those who desire full information
as to Hirudiniculture should consult the work of Dr. Ebrard, published in 1857.[452]
The former extensive use of the leech has led to the transfer of its name to the doctor
who employs it, the authors of the sixteenth century constantly terming a physician a
leech; it has been suggested, however, that the term was applied rather by way of
analogy. The useful blood-sucking habits of the medicinal leech have been wrongly
attributed to the innocent horseleech (Aulastomum)—innocent, that is to say, of the
blood of Vertebrates, for it has been described as "a cruel and greedy worm,"
engulfing earthworms and even smaller specimens of its own species. "Horsleches,"
said an old writer, "are wholesome to drawe foorthe foule blood, if thei are put into a
hollowe rede, and one of their endes cutte of, whereby the blood maie run forthe." But
it is clearly not easy for a creature destitute of jaws and teeth to bite, and the similarity
of general aspect has doubtless led to a confusion with the savagely biting medicinal
leech.
Page 398
Fig. 202.—Sense body of Macrobdella sestertia. (After Whitman.) ep, Epidermis; s, clear cells.
Highly magnified.
Fig. 203.—Section through eye of Haemadipsa japonica. (After Whitman.) ep, Epidermis; n,
nerve. Highly magnified.
The Hirudinea are all distinctly segmented animals, but the segmentation differs from
that of the Oligochaeta in two points. In the first place the number of segments is
much smaller in a leech than in an Oligochaete, although the difference does not
appear great at first sight.
A leech's body may seem to be composed of seventy, eighty, or one hundred segments,
a number quite as great as is found, for example, in the genus Perichaeta among the
earthworms; but the apparent number of segments in the leech is produced by a very
marked annulation of the real segments; and this is indeed the second point of
difference referred to above. But there are earthworms which show frequently a
secondary annulation,—secondary because it appears late and does not affect other
organs of the body. A segment of an earthworm may indeed have five or six distinct
annulations, but it will be bounded internally by two septa, and will bear only one set
of chaetae externally. In the leech external clues to the definition of a segment were
until recently wanting. They appear now to have been found in the sensory organs of
the skin (Figs. 201 and 202), which are, according to Whitman,[453] disposed in a
perfectly metameric fashion. Judged by this, and also by the nephridia and nerve-
ganglia, the number of segments in a leech does not appear to exceed twenty-six,
independently of the sucker, which may represent a few fused segments, seven (in the
medicinal leech) according to Leuckart.
Highly magnified.
Fig. 203.—Section through eye of Haemadipsa japonica. (After Whitman.) ep, Epidermis; n,
nerve. Highly magnified.
The Hirudinea are all distinctly segmented animals, but the segmentation differs from
that of the Oligochaeta in two points. In the first place the number of segments is
much smaller in a leech than in an Oligochaete, although the difference does not
appear great at first sight.
A leech's body may seem to be composed of seventy, eighty, or one hundred segments,
a number quite as great as is found, for example, in the genus Perichaeta among the
earthworms; but the apparent number of segments in the leech is produced by a very
marked annulation of the real segments; and this is indeed the second point of
difference referred to above. But there are earthworms which show frequently a
secondary annulation,—secondary because it appears late and does not affect other
organs of the body. A segment of an earthworm may indeed have five or six distinct
annulations, but it will be bounded internally by two septa, and will bear only one set
of chaetae externally. In the leech external clues to the definition of a segment were
until recently wanting. They appear now to have been found in the sensory organs of
the skin (Figs. 201 and 202), which are, according to Whitman,[453] disposed in a
perfectly metameric fashion. Judged by this, and also by the nephridia and nerve-
ganglia, the number of segments in a leech does not appear to exceed twenty-six,
independently of the sucker, which may represent a few fused segments, seven (in the
medicinal leech) according to Leuckart.
Page 399
The eyes, which are so useful in the systematic arrangement of the group, appear to
have been evolved from these sensory organs by a further exaggeration of their
peculiarities. Figs. 202 and 203 show this point convincingly. The segmental sense
organ is shown in Fig. 202; to the outside of certain sense cells, below which are a
mass of ganglion cells, are certain peculiar transparent cells very similar to the clear
cells found in the interior of the eye (Fig. 203). The segmental disposal of the sensory
bodies and of the eyes is shown in Fig. 201.
Fig. 204.—Branchellion torpedinis. (From the "Règne Animal.") ×1.
Some Hirudinea are furnished with external branchiae; this is the case with
Branchellion, in which genus the branchiae (Fig. 204) have an arborescent form; in
Cystibranchus there are a series of paired simple vesicles which take the place of these
more complicated respiratory organs of Branchellion. The Hirudinea do not, save for
one exception (Acanthobdella), possess chaetae; but it must be borne in mind that the
Discodrilidae and the genus Anachaeta among the Oligochaeta are in the same
condition. In Acanthobdella[454] there are two pairs of chaetae upon each side of the
anterior five segments of the body. According to the figure which Grube, the original
describer of the genus, gives of these chaetae, the part implanted in the body is
straight, while the part extending freely beyond the body is sharply hooked.
The body of the leeches is never ciliated externally; there is, as in the higher
Oligochaeta, a cuticle secreted by the underlying epidermis. The Hirudinea have, like
the Oligochaeta, a clitellum which, as in some of the lower members of that group, is
limited to a very few segments in the immediate neighbourhood of the generative
openings. It occupies in Hirudo segments 9, 10, and 11. The epidermis gives rise to
many unicellular glands which either remain in situ or get moved to a deeper position.
In this the leeches exactly resemble the earthworms. There is generally a great deal of
connective tissue in the body-wall. The muscles consist of circular, longitudinal, and
radial series. The individual fibres have the same structure as those of the Oligochaeta,
consisting of a soft and undifferentiated core, round which is a radially-striated sheath
of contractile substance.
have been evolved from these sensory organs by a further exaggeration of their
peculiarities. Figs. 202 and 203 show this point convincingly. The segmental sense
organ is shown in Fig. 202; to the outside of certain sense cells, below which are a
mass of ganglion cells, are certain peculiar transparent cells very similar to the clear
cells found in the interior of the eye (Fig. 203). The segmental disposal of the sensory
bodies and of the eyes is shown in Fig. 201.
Fig. 204.—Branchellion torpedinis. (From the "Règne Animal.") ×1.
Some Hirudinea are furnished with external branchiae; this is the case with
Branchellion, in which genus the branchiae (Fig. 204) have an arborescent form; in
Cystibranchus there are a series of paired simple vesicles which take the place of these
more complicated respiratory organs of Branchellion. The Hirudinea do not, save for
one exception (Acanthobdella), possess chaetae; but it must be borne in mind that the
Discodrilidae and the genus Anachaeta among the Oligochaeta are in the same
condition. In Acanthobdella[454] there are two pairs of chaetae upon each side of the
anterior five segments of the body. According to the figure which Grube, the original
describer of the genus, gives of these chaetae, the part implanted in the body is
straight, while the part extending freely beyond the body is sharply hooked.
The body of the leeches is never ciliated externally; there is, as in the higher
Oligochaeta, a cuticle secreted by the underlying epidermis. The Hirudinea have, like
the Oligochaeta, a clitellum which, as in some of the lower members of that group, is
limited to a very few segments in the immediate neighbourhood of the generative
openings. It occupies in Hirudo segments 9, 10, and 11. The epidermis gives rise to
many unicellular glands which either remain in situ or get moved to a deeper position.
In this the leeches exactly resemble the earthworms. There is generally a great deal of
connective tissue in the body-wall. The muscles consist of circular, longitudinal, and
radial series. The individual fibres have the same structure as those of the Oligochaeta,
consisting of a soft and undifferentiated core, round which is a radially-striated sheath
of contractile substance.
Page 400
Alimentary Canal.—The leeches are divided into the Rhynchobdellae, which have a
proboscis but no jaws, and the Gnathobdellae, which possess a series of jaws but have
no proboscis. But the division is not a hard and fast one, for we have Whitman's genus
Leptostoma, which should belong to the jawed division, but which has quite
rudimentary jaws without the sharp denticles so characteristic of Hirudo. The pharynx
is furnished with salivary glands. The oesophagus is followed by the proventriculus,
which has a varying number of pairs of caeca; then comes the intestine and the rectum.
The anus is, as a general rule, placed dorsally to the sucker, but there are a few rare
exceptions where the anus is within the sucker. The caeca are totally absent in
Trocheta.
Vascular System.—As will be seen from Fig. 205, the vascular system of the
Hirudinea is constructed on a plan which closely resembles that of the Oligochaeta.
The diagram represents Glossiphonia, one of the Rhynchobdellae, the group which
comes nearer to the Oligochaeta in many particulars than the Gnathobdellae. We can
recognise a dorsal and a ventral vessel, which are united in the anterior part of the
body by three perioesophageal rings, the elongation of which, particularly of the last
pair (v), from before backwards is very marked. In the region of the sucker the dorsal
and ventral vessels are united by fourteen shorter loops, the number of which has an
interesting relation to the number of segments out of which this portion of the body is
possibly formed. It will be observed also that the dorsal vessel is double in this region,
a condition which obtains along its whole length in Branchellion—a repetition of what
has been described in more than one species of Oligochaete. In the region of the last
pair of digestive caeca the dorsal vessel has appended to it copious sinuses which
embrace the intestine and supply its walls with blood. In Hirudo there are only a pair
of lateral vessels, and neither dorsal nor ventral vessels; in this leech and in the
Gnathobdellae generally there are intra-epidermic capillaries, a fact first discovered by
Professor Lankester, and now known to occur also in the Oligochaeta.
The development of the blood-vessels shows that they have no relation whatever to
the coelom, in spite of their subsequent connexion with it. The two longitudinal stems
of Hirudo arise as cavities in the somatic layer of the mesoblast after the formation of
the coelom. In Nephelis, but not in Hirudo, Dr. Bürger thinks that there is some reason
for regarding the vascular system as the remains of the primitive segmentation-cavity
of the embryo, an opinion which is held in respect of the vascular system of many
other animals.
proboscis but no jaws, and the Gnathobdellae, which possess a series of jaws but have
no proboscis. But the division is not a hard and fast one, for we have Whitman's genus
Leptostoma, which should belong to the jawed division, but which has quite
rudimentary jaws without the sharp denticles so characteristic of Hirudo. The pharynx
is furnished with salivary glands. The oesophagus is followed by the proventriculus,
which has a varying number of pairs of caeca; then comes the intestine and the rectum.
The anus is, as a general rule, placed dorsally to the sucker, but there are a few rare
exceptions where the anus is within the sucker. The caeca are totally absent in
Trocheta.
Vascular System.—As will be seen from Fig. 205, the vascular system of the
Hirudinea is constructed on a plan which closely resembles that of the Oligochaeta.
The diagram represents Glossiphonia, one of the Rhynchobdellae, the group which
comes nearer to the Oligochaeta in many particulars than the Gnathobdellae. We can
recognise a dorsal and a ventral vessel, which are united in the anterior part of the
body by three perioesophageal rings, the elongation of which, particularly of the last
pair (v), from before backwards is very marked. In the region of the sucker the dorsal
and ventral vessels are united by fourteen shorter loops, the number of which has an
interesting relation to the number of segments out of which this portion of the body is
possibly formed. It will be observed also that the dorsal vessel is double in this region,
a condition which obtains along its whole length in Branchellion—a repetition of what
has been described in more than one species of Oligochaete. In the region of the last
pair of digestive caeca the dorsal vessel has appended to it copious sinuses which
embrace the intestine and supply its walls with blood. In Hirudo there are only a pair
of lateral vessels, and neither dorsal nor ventral vessels; in this leech and in the
Gnathobdellae generally there are intra-epidermic capillaries, a fact first discovered by
Professor Lankester, and now known to occur also in the Oligochaeta.
The development of the blood-vessels shows that they have no relation whatever to
the coelom, in spite of their subsequent connexion with it. The two longitudinal stems
of Hirudo arise as cavities in the somatic layer of the mesoblast after the formation of
the coelom. In Nephelis, but not in Hirudo, Dr. Bürger thinks that there is some reason
for regarding the vascular system as the remains of the primitive segmentation-cavity
of the embryo, an opinion which is held in respect of the vascular system of many
other animals.
Page 401
Fig. 205.—Glossiphonia marginata, vascular and alimentary system. ×4. (After Oka.) a, Dorsal
vessel; g, intestinal caecum; v, one of the hearts.
Body-Cavity.—One of the most marked differences between the leeches and the
Oligochaeta is in the body-cavity. In the latter there are a series of cavities
corresponding to the segments, which are bounded in front and behind by the
intersegmental septa, and in which all the viscera lie. In leeches such an arrangement
is not recognisable save in Acanthobdella, where Kowalevsky[455] has quite recently
described a typical coelom divided by septa into twenty segments. In transverse
sections the body of other leeches appears at first sight to be solid, owing to the
growth of the muscles and connective tissue. A more careful study, however, has
revealed the fact that there are considerable remains of the body-cavity or coelom
which form a complicated system of spaces and channels. What has happened, in fact,
in the leech is that the coelom has become gradually and partially obliterated by
proliferation of the cells in the interior of the body, a process of obliteration which has
already commenced in the Oligochaeta. In many of the latter, some of the principal
blood-vessels have become surrounded by a space cut off from the general body-
cavity, while in the majority a special cavity surrounds the testes and the funnels of the
sperm-ducts. This process of the formation of separate cavities for the inclusion of the
several viscera culminates in the leeches with the marked obliteration of the greater
part of the coelom. This has become so much reduced to the condition of narrow tubes
that there has been a tendency to confuse it with the vascular system, more especially
perhaps in those forms in which the blood is tinged with haemoglobin, and in which
there is a connexion between the two systems of spaces. This confusion has been
further increased by the plan of injecting the vascular system, a method of
investigation which must be employed with great care in delicately-organised
creatures whose tissues can be easily ruptured, and so lead to a flow of the injecting
fluid into places and in directions impossible during life.
vessel; g, intestinal caecum; v, one of the hearts.
Body-Cavity.—One of the most marked differences between the leeches and the
Oligochaeta is in the body-cavity. In the latter there are a series of cavities
corresponding to the segments, which are bounded in front and behind by the
intersegmental septa, and in which all the viscera lie. In leeches such an arrangement
is not recognisable save in Acanthobdella, where Kowalevsky[455] has quite recently
described a typical coelom divided by septa into twenty segments. In transverse
sections the body of other leeches appears at first sight to be solid, owing to the
growth of the muscles and connective tissue. A more careful study, however, has
revealed the fact that there are considerable remains of the body-cavity or coelom
which form a complicated system of spaces and channels. What has happened, in fact,
in the leech is that the coelom has become gradually and partially obliterated by
proliferation of the cells in the interior of the body, a process of obliteration which has
already commenced in the Oligochaeta. In many of the latter, some of the principal
blood-vessels have become surrounded by a space cut off from the general body-
cavity, while in the majority a special cavity surrounds the testes and the funnels of the
sperm-ducts. This process of the formation of separate cavities for the inclusion of the
several viscera culminates in the leeches with the marked obliteration of the greater
part of the coelom. This has become so much reduced to the condition of narrow tubes
that there has been a tendency to confuse it with the vascular system, more especially
perhaps in those forms in which the blood is tinged with haemoglobin, and in which
there is a connexion between the two systems of spaces. This confusion has been
further increased by the plan of injecting the vascular system, a method of
investigation which must be employed with great care in delicately-organised
creatures whose tissues can be easily ruptured, and so lead to a flow of the injecting
fluid into places and in directions impossible during life.
Page 402
Fig. 206.—Coelomic canals of Glossiphonia complanata. × 10. (After Oka.) a, Dorsal canal
containing dorsal blood-vessel; b, ventral canal containing ventral blood-vessel; l, lateral
canal; n, nerve-cord.
In transverse sections of leeches it may be seen in successful preparations that the
various organs of the body are enclosed in spaces. The funnels of the nephridia open
into lacunae which could hardly in any case be regarded as blood spaces, while the
blood-vessels themselves with their muscular walls cannot be confounded, at least in
the case of the larger trunks, with the spaces not having muscular walls which
surround them. Furthermore, it will be pointed out immediately that the reproductive
organs are produced on the walls of spaces which are the commencement in the
embryo of the reduced coelom of the adult worm. These spaces therefore conform in
every particular to the general conditions which have been laid down about the
characters of a true coelom. As to the complexity of this system, attention may be
directed, to the accompanying diagram (Fig. 206) of the coelom of a segment of
Glossiphonia, which has been lately worked out in detail.[456] It will be observed that
there are four main longitudinal sinuses which are connected by a complicated system
of transverse tubes and spaces. In the anterior part of the body, before the point where
the intestinal caeca arise, the dorsal and ventral lacunae fuse to form one larger so-
called median lacuna. The cavity of this is interrupted, in correspondence with the
segmentation of the body, by septa exactly comparable to those of Oligochaeta; but the
septa in Glossiphonia are not present at every segment. So far our account of the
coelom is chiefly derived from the genus Glossiphonia. In Hirudo, which is an
example of the Gnathobdellae, the coelom is still further reduced; the lateral sinuses in
them appear to be absent. But on the other hand there is formed a series of cavities in a
form of connective tissue which has been termed botryoidal tissue. The cells of this
tissue become hollowed out, and form channels which are in communication on the
one hand with the remains of the coelom and on the other with the vascular system.
This system has certain analogies with the lymphatic vessels of Vertebrates, and, like
them, is an intermediary between the body-cavity and the blood. Originally, however,
these botryoidal vessels have nothing whatever to do with either the vascular or the
coelomic system; their connexion with both is a purely secondary affair, and only
appears, comparatively speaking, late in life.
The development of the spaces here spoken of collectively as coelom confirms this
interpretation of their nature. In the embryos of Hirudo, Aulastomum, and Nephelis
there is a ventral space,[457] which includes the nerve-cord. Into this open a series of
paired and segmentally-disposed lateral cavities, a pair to each segment. The ventral
containing dorsal blood-vessel; b, ventral canal containing ventral blood-vessel; l, lateral
canal; n, nerve-cord.
In transverse sections of leeches it may be seen in successful preparations that the
various organs of the body are enclosed in spaces. The funnels of the nephridia open
into lacunae which could hardly in any case be regarded as blood spaces, while the
blood-vessels themselves with their muscular walls cannot be confounded, at least in
the case of the larger trunks, with the spaces not having muscular walls which
surround them. Furthermore, it will be pointed out immediately that the reproductive
organs are produced on the walls of spaces which are the commencement in the
embryo of the reduced coelom of the adult worm. These spaces therefore conform in
every particular to the general conditions which have been laid down about the
characters of a true coelom. As to the complexity of this system, attention may be
directed, to the accompanying diagram (Fig. 206) of the coelom of a segment of
Glossiphonia, which has been lately worked out in detail.[456] It will be observed that
there are four main longitudinal sinuses which are connected by a complicated system
of transverse tubes and spaces. In the anterior part of the body, before the point where
the intestinal caeca arise, the dorsal and ventral lacunae fuse to form one larger so-
called median lacuna. The cavity of this is interrupted, in correspondence with the
segmentation of the body, by septa exactly comparable to those of Oligochaeta; but the
septa in Glossiphonia are not present at every segment. So far our account of the
coelom is chiefly derived from the genus Glossiphonia. In Hirudo, which is an
example of the Gnathobdellae, the coelom is still further reduced; the lateral sinuses in
them appear to be absent. But on the other hand there is formed a series of cavities in a
form of connective tissue which has been termed botryoidal tissue. The cells of this
tissue become hollowed out, and form channels which are in communication on the
one hand with the remains of the coelom and on the other with the vascular system.
This system has certain analogies with the lymphatic vessels of Vertebrates, and, like
them, is an intermediary between the body-cavity and the blood. Originally, however,
these botryoidal vessels have nothing whatever to do with either the vascular or the
coelomic system; their connexion with both is a purely secondary affair, and only
appears, comparatively speaking, late in life.
The development of the spaces here spoken of collectively as coelom confirms this
interpretation of their nature. In the embryos of Hirudo, Aulastomum, and Nephelis
there is a ventral space,[457] which includes the nerve-cord. Into this open a series of
paired and segmentally-disposed lateral cavities, a pair to each segment. The ventral
Page 403
cavity itself is formed by fusion of the median parts of the lateral cavities. There is
here clear evidence of a coelom, developed on a plan fundamentally identical with that
of the Oligochaeta in that it is formed as a paired series of chambers corresponding to
the segmentation of the body.
Nephridia.—The "segmental organs" or nephridia are seen in their simplest form in
such a type as Glossiphonia—the Rhynchobdellae, to which this genus belongs, being
indeed in most particulars less specialised than the Gnathobdellae. Here we have a
distinct funnel opening freely into the median or ventral coelomic space, which is
immediately followed by a rounded swelling termed by Oka[458] the capsule; this is
filled with cells, in the interstices of which the ductules are situated and meander.
There is in this capsule a very strong likeness to the glandular brownish swelling
which immediately follows the funnel in the nephridia of certain of the aquatic
Oligochaeta, for example the Naids, where, as Vejdovsky has shown, there is a similar
"rete mirabile" of the nephridial duct. After the capsule is a single row of cells which
are disposed in a complicated coil. These cells are perforated by the duct, which is
thus, as in the Oligochaeta, intracellular. In the first set of cells the duct is single, and
gives off numerous branchlets into the interior of each cell, a condition which has also
been observed in many Oligochaeta. Afterwards the cells are perforated by two, or
even three, main ducts, for the duct returns upon itself and traverses the row of cells
more than once; there are also branchlets developed from one or other of the main
ducts. The terminal part of the nephridium is a short invagination from the exterior,
which is lined by cells. There is clearly a close resemblance here with the nephridium
of an Oligochaete. The nephridium, however, except for the funnel and the narrow
tube immediately following it, does not appear to be ciliated.
Fig. 207.—Nephridium of Hirudo medicinalis. × 10. (After Bourne.) f, Funnel; v, distal vesicle.
There is, however, some difference of opinion as to the portions of the nephridium
where there are two ducts in a single cell. Bourne[459] thinks that where there are two
ducts there are two cells, one lying inside the other, and that there is sometimes also a
telescoping of cell within cell where the duct is single. In Hirudo the same writer has
described the nephridial funnel, which has lost the simple character of that of
Glossiphonia. The funnel is represented by a cabbage-head-like mass (Fig. 207, f) of
ciliated cells with no single definite outlet to the exterior as in Glossiphonia. It appears
to be an organ which has lost its proper function—a degeneration of the funnel being,
here clear evidence of a coelom, developed on a plan fundamentally identical with that
of the Oligochaeta in that it is formed as a paired series of chambers corresponding to
the segmentation of the body.
Nephridia.—The "segmental organs" or nephridia are seen in their simplest form in
such a type as Glossiphonia—the Rhynchobdellae, to which this genus belongs, being
indeed in most particulars less specialised than the Gnathobdellae. Here we have a
distinct funnel opening freely into the median or ventral coelomic space, which is
immediately followed by a rounded swelling termed by Oka[458] the capsule; this is
filled with cells, in the interstices of which the ductules are situated and meander.
There is in this capsule a very strong likeness to the glandular brownish swelling
which immediately follows the funnel in the nephridia of certain of the aquatic
Oligochaeta, for example the Naids, where, as Vejdovsky has shown, there is a similar
"rete mirabile" of the nephridial duct. After the capsule is a single row of cells which
are disposed in a complicated coil. These cells are perforated by the duct, which is
thus, as in the Oligochaeta, intracellular. In the first set of cells the duct is single, and
gives off numerous branchlets into the interior of each cell, a condition which has also
been observed in many Oligochaeta. Afterwards the cells are perforated by two, or
even three, main ducts, for the duct returns upon itself and traverses the row of cells
more than once; there are also branchlets developed from one or other of the main
ducts. The terminal part of the nephridium is a short invagination from the exterior,
which is lined by cells. There is clearly a close resemblance here with the nephridium
of an Oligochaete. The nephridium, however, except for the funnel and the narrow
tube immediately following it, does not appear to be ciliated.
Fig. 207.—Nephridium of Hirudo medicinalis. × 10. (After Bourne.) f, Funnel; v, distal vesicle.
There is, however, some difference of opinion as to the portions of the nephridium
where there are two ducts in a single cell. Bourne[459] thinks that where there are two
ducts there are two cells, one lying inside the other, and that there is sometimes also a
telescoping of cell within cell where the duct is single. In Hirudo the same writer has
described the nephridial funnel, which has lost the simple character of that of
Glossiphonia. The funnel is represented by a cabbage-head-like mass (Fig. 207, f) of
ciliated cells with no single definite outlet to the exterior as in Glossiphonia. It appears
to be an organ which has lost its proper function—a degeneration of the funnel being,
Page 404
as a matter of fact, not unknown in the Oligochaeta, where it may be carried to
absolute extinction (Chaetogaster). In Branchellion and Pontobdella the simple
metameric arrangement of the nephridia is to some extent lost, owing to the formation
of a network continuous from segment to segment. It will be borne in mind that the
Oligochaeta are the only other Chaetopods in which such a nephridial network has
been stated to exist.
Male Reproductive Organs.—In Hirudo medicinalis there are nine, occasionally ten,
pairs of testes, which are round white bodies arranged segmentally, i.e. a pair to each
segment. From each arises a slender, somewhat sinuous tube, which enters the
common collecting tube of its own side; each of these is much contorted at the upper
end, the coiled portion being termed the epididymis. From this they enter a muscular
penis which can be protruded. This is the arrangement met with in all leeches, save for
the fact that the penis is absent in some; in Glossiphonia (see Fig. 208) this is the case.
The number of pairs of testes also varies; and in Nephelis they are no longer arranged
metamerically.
Fig. 208.—Nervous system and reproductive organs of Glossiphonia plana. × 2. (After Whitman.)
gl, Prostate glands; n, nerve-cord; o, ovary; t, testes.
The testes arise as local proliferations of the epithelium of the lateral coelomic
cavities, but from the somatic wall, not from the splanchnic, as in the case of the
ovaries to be described later. A portion of the tissue which is to form the testis grows
out laterally into a thin cord, which is to become the vas efferens of that testis. Later
both testis and duct become hollowed out with a common cavity. The main portion of
the vas deferens of each side, as well as the terminal copulatory apparatus, is an
ingrowth from the epidermis which meets the downgrowths from the testes.
That there are considerable differences between the reproductive organs of the leeches
and those of Oligochaeta will be apparent from the above description. There are,
however, to begin with, certain obvious similarities. In the first place, the origin of the
reproductive glands is identical; in both groups also the efferent ducts consist of two
absolute extinction (Chaetogaster). In Branchellion and Pontobdella the simple
metameric arrangement of the nephridia is to some extent lost, owing to the formation
of a network continuous from segment to segment. It will be borne in mind that the
Oligochaeta are the only other Chaetopods in which such a nephridial network has
been stated to exist.
Male Reproductive Organs.—In Hirudo medicinalis there are nine, occasionally ten,
pairs of testes, which are round white bodies arranged segmentally, i.e. a pair to each
segment. From each arises a slender, somewhat sinuous tube, which enters the
common collecting tube of its own side; each of these is much contorted at the upper
end, the coiled portion being termed the epididymis. From this they enter a muscular
penis which can be protruded. This is the arrangement met with in all leeches, save for
the fact that the penis is absent in some; in Glossiphonia (see Fig. 208) this is the case.
The number of pairs of testes also varies; and in Nephelis they are no longer arranged
metamerically.
Fig. 208.—Nervous system and reproductive organs of Glossiphonia plana. × 2. (After Whitman.)
gl, Prostate glands; n, nerve-cord; o, ovary; t, testes.
The testes arise as local proliferations of the epithelium of the lateral coelomic
cavities, but from the somatic wall, not from the splanchnic, as in the case of the
ovaries to be described later. A portion of the tissue which is to form the testis grows
out laterally into a thin cord, which is to become the vas efferens of that testis. Later
both testis and duct become hollowed out with a common cavity. The main portion of
the vas deferens of each side, as well as the terminal copulatory apparatus, is an
ingrowth from the epidermis which meets the downgrowths from the testes.
That there are considerable differences between the reproductive organs of the leeches
and those of Oligochaeta will be apparent from the above description. There are,
however, to begin with, certain obvious similarities. In the first place, the origin of the
reproductive glands is identical; in both groups also the efferent ducts consist of two
Page 405
portions—an invagination from the outside, and a formation of the proximal part of
the ducts near to the glands. In Moniligaster, where—exceptionally—the testes
develop on the posterior wall of their segment in close contact with the funnels of the
sperm-ducts, there is no very hard and fast line to be observed between the tissues of
the two. The hollowing out of the testis in the leech, and the continuity of the cavity
thus formed with the duct, is a specialty of the leeches not found among the
Oligochaeta.
Like many Oligochaeta, the leeches may form spermatophores in which the sperm is
packed for its conveyance from one individual to another. Glossiphonia (Clepsine)
plana, where the structure in question has been elaborately described by Whitman,[460]
may be selected as an example. The spermatophore (Fig. 209) is about 8 mm. long,
and is clearly formed of two halves, each of which is formed separately in one ductus
ejaculatorius, the soldering together being effected in the common part of the male
ducts, where also a basal portion with a single lumen is added. The spermatophore has
a double wall. It is deposited not in the neighbourhood of the generative pores, but
upon the back; and Whitman has discovered the extraordinary fact that the
spermatozoa find their way through the body-wall of the leech into the interior of its
body, where fertilisation presumably occurs.
Fig. 209.—Spermatophore of Glossiphonia plana. × 22. (After Whitman.)
Female Reproductive Organs.—The ovaries of the Hirudinea appear to differ from
those of the Oligochaeta in that the ovaries are continuous with their ducts. In Hirudo,
however, the real ovary of each side consists of masses of germinal tissue lying freely
within a sac which communicates with a duct; the two ducts unite to form a much
convoluted tube which opens into a thick-walled vagina, itself opening again on to the
exterior by a median unpaired opening on the seventh segment. The muscular vagina
is not always present.
The median unpaired female aperture offers now no particular difficulty, since in
many earthworms, e.g. Perichaeta, this orifice is in the same condition; nor does the
the ducts near to the glands. In Moniligaster, where—exceptionally—the testes
develop on the posterior wall of their segment in close contact with the funnels of the
sperm-ducts, there is no very hard and fast line to be observed between the tissues of
the two. The hollowing out of the testis in the leech, and the continuity of the cavity
thus formed with the duct, is a specialty of the leeches not found among the
Oligochaeta.
Like many Oligochaeta, the leeches may form spermatophores in which the sperm is
packed for its conveyance from one individual to another. Glossiphonia (Clepsine)
plana, where the structure in question has been elaborately described by Whitman,[460]
may be selected as an example. The spermatophore (Fig. 209) is about 8 mm. long,
and is clearly formed of two halves, each of which is formed separately in one ductus
ejaculatorius, the soldering together being effected in the common part of the male
ducts, where also a basal portion with a single lumen is added. The spermatophore has
a double wall. It is deposited not in the neighbourhood of the generative pores, but
upon the back; and Whitman has discovered the extraordinary fact that the
spermatozoa find their way through the body-wall of the leech into the interior of its
body, where fertilisation presumably occurs.
Fig. 209.—Spermatophore of Glossiphonia plana. × 22. (After Whitman.)
Female Reproductive Organs.—The ovaries of the Hirudinea appear to differ from
those of the Oligochaeta in that the ovaries are continuous with their ducts. In Hirudo,
however, the real ovary of each side consists of masses of germinal tissue lying freely
within a sac which communicates with a duct; the two ducts unite to form a much
convoluted tube which opens into a thick-walled vagina, itself opening again on to the
exterior by a median unpaired opening on the seventh segment. The muscular vagina
is not always present.
The median unpaired female aperture offers now no particular difficulty, since in
many earthworms, e.g. Perichaeta, this orifice is in the same condition; nor does the
Page 406
fusion of the oviducts and the so-called ovaries; for in Eudrilus, for example, and in
many Eudrilidae, the ovary is contained in a sac into which the oviduct also opens. It
will be noticed too that the existence of short oviducts as compared with the long
sperm-ducts is a further point of likeness to at any rate the higher Oligochaeta. But a
further comparison needs first to be based upon a consideration of the development of
the different sections of the apparatus in the leech. The independence of the ovaries
and their ducts has been proved by several observers; quite recently Bürger has dealt
with the matter in Nephelis, Hirudo, and Aulastomum gulo.[461] He has found that the
ovaries arise from the splanchnic wall of the lateral coelomic cavities; they are
therefore proliferations of the coelomic epithelium, as in Oligochaeta and all
Coelomates so far as is known. The peripheral layer of the mass of indifferent cells
which constitutes the ovary becomes somewhat modified; its cells are flattened, and it
at length separates itself and forms a capsule surrounding the other cells, which are in
fact, or become, the ovary. This capsule meets and fuses with the ducts, which are
invaginations from the exterior of the body.
There are clearly differences between the ovary of a leech and that of a typical
Oligochaete like Lumbricus. The only point of agreement, in fact, is the origin of the
reproductive gland itself from the walls of the body-cavity. In Lumbricus and allied
forms, whatever may be held with regard to their homologies, the oviducts as a matter
of fact appear first as funnels, which afterwards bore their way to the exterior. They
are purely mesoblastic structures, not—except perhaps the very extremity—derived
from an ingrowth from the epidermis. We have, however, other Oligochaeta in which
there are closer resemblances to what has just been described in the Hirudinea. In
more than one point the aberrant family of the Eudrilidae come nearer to the Hirudinea
than any other Oligochaeta, in spite of Branchiobdella with its jaws and sucker. Now
in Eudrilus the ovary is enclosed in a capsule which becomes continuous with the duct
of the great sperm-holding pouch, itself an invagination from the exterior; there is no
reason in this Annelid why the ova should not reach the exterior by this system of
ducts, although there is no actual experimental proof that they do so. In any case there
is also an oviduct corresponding to that of Lumbricus, which opens into the opposite
side of the duct of the spermathecal pouch on the one hand, and into the receptaculum
ovorum on the other; it has no direct connexion whatever with the sac containing the
ovary. If we were to cut off the receptaculum and the oviduct and reduce the
spermathecal sac to its duct, the result would be much the same as we find it in the
leech.
Cocoon.—The practice of forming a cocoon for the shelter of the eggs and of the
developing young is shared with the Oligochaeta; but not all leeches deposit their eggs
in this manner. Glossiphonia, for instance, carries its eggs upon the ventral face of the
body, where the young remain for some time after they are hatched attached by the
posterior sucker to their parent's body, and from which situation of safety they make
many Eudrilidae, the ovary is contained in a sac into which the oviduct also opens. It
will be noticed too that the existence of short oviducts as compared with the long
sperm-ducts is a further point of likeness to at any rate the higher Oligochaeta. But a
further comparison needs first to be based upon a consideration of the development of
the different sections of the apparatus in the leech. The independence of the ovaries
and their ducts has been proved by several observers; quite recently Bürger has dealt
with the matter in Nephelis, Hirudo, and Aulastomum gulo.[461] He has found that the
ovaries arise from the splanchnic wall of the lateral coelomic cavities; they are
therefore proliferations of the coelomic epithelium, as in Oligochaeta and all
Coelomates so far as is known. The peripheral layer of the mass of indifferent cells
which constitutes the ovary becomes somewhat modified; its cells are flattened, and it
at length separates itself and forms a capsule surrounding the other cells, which are in
fact, or become, the ovary. This capsule meets and fuses with the ducts, which are
invaginations from the exterior of the body.
There are clearly differences between the ovary of a leech and that of a typical
Oligochaete like Lumbricus. The only point of agreement, in fact, is the origin of the
reproductive gland itself from the walls of the body-cavity. In Lumbricus and allied
forms, whatever may be held with regard to their homologies, the oviducts as a matter
of fact appear first as funnels, which afterwards bore their way to the exterior. They
are purely mesoblastic structures, not—except perhaps the very extremity—derived
from an ingrowth from the epidermis. We have, however, other Oligochaeta in which
there are closer resemblances to what has just been described in the Hirudinea. In
more than one point the aberrant family of the Eudrilidae come nearer to the Hirudinea
than any other Oligochaeta, in spite of Branchiobdella with its jaws and sucker. Now
in Eudrilus the ovary is enclosed in a capsule which becomes continuous with the duct
of the great sperm-holding pouch, itself an invagination from the exterior; there is no
reason in this Annelid why the ova should not reach the exterior by this system of
ducts, although there is no actual experimental proof that they do so. In any case there
is also an oviduct corresponding to that of Lumbricus, which opens into the opposite
side of the duct of the spermathecal pouch on the one hand, and into the receptaculum
ovorum on the other; it has no direct connexion whatever with the sac containing the
ovary. If we were to cut off the receptaculum and the oviduct and reduce the
spermathecal sac to its duct, the result would be much the same as we find it in the
leech.
Cocoon.—The practice of forming a cocoon for the shelter of the eggs and of the
developing young is shared with the Oligochaeta; but not all leeches deposit their eggs
in this manner. Glossiphonia, for instance, carries its eggs upon the ventral face of the
body, where the young remain for some time after they are hatched attached by the
posterior sucker to their parent's body, and from which situation of safety they make
Page 407
short excursions. Other leeches deposit their eggs singly, but agglutinated together
upon stones, etc. In the medicinal leech the cocoon is ovoid in shape, and from the
end, which is closed by a temporary plug, the young when ready escape. This cocoon
is deposited, as is that of an earthworm, in soil near to the borders of a marsh or pond,
so that the young, while enjoying the requisite degree of moisture, may not be injured
by a too wet environment. On the other hand Pontobdella and some other leeches lay
their cocoons attached to bodies actually submerged in the water. The cocoon is
secreted, as in Oligochaeta, by the clitellum, and as in them, is drawn off over the
head, the ova and sperm probably flowing into it during the process. The elasticity of
the slightly hardened mucus causes the two ends of the cocoon to close up when it is
free from the body; it is then whitish and soft, and the leech fixes it, and appears to
polish the surface with its buccal sucker. In a few hours the cocoon becomes amber
brown, a colour which characterises the cocoons of a great many earthworms and
other Oligochaeta. The medicinal leech forms its cocoon in the same way as does
Nephelis, to which the above description refers; but when the cocoon is formed the
leech covers it with another layer of mucus, which Vaillant, from whose work the
foregoing notes are extracted,[462] thinks may be produced from the so-called salivary
glands.
Classification.—The number of different kinds of leeches is at present uncertain.
Seeing that no less than sixty-four varieties of the common Hirudo medicinalis—
colour varieties, it is true—are said to exist, it is not wonderful that the labours of
some systematists have been severe, and have provoked much criticism and alteration
on the part of others.[463] As to genera, Vaillant, in his recent continuation of de
Quatrefages' "Annelés" in the Suites à Buffon, which includes the literature up to the
year 1886, allows thirty-seven, some (three) of which, however, are admitted to be
incertae sedis. Blanchard, who has paid a great deal of attention to the group, reduces
these by six, which he considers to be synonyms; but on the other hand he has added
or rescued from oblivion six or seven others, and Whitman has instituted several
Japanese and Australian genera. Most of these generic types are, however, only
imperfectly known, and from external characters only. It is quite problematical how
many valid genera should be retained; in the meantime those that are fairly well
known are divided by Blanchard[464] in the following way:—
Sub-Order 1. Rhynchobdellae.—Hirudinea with an exsertile proboscis, without
jaws, and with colourless blood.
Fam. 1. Ichthyobdellidae.—Body formed of two regions, a narrower anterior portion
and a wider "abdomen," both anterior and posterior suckers distinct from the body.
upon stones, etc. In the medicinal leech the cocoon is ovoid in shape, and from the
end, which is closed by a temporary plug, the young when ready escape. This cocoon
is deposited, as is that of an earthworm, in soil near to the borders of a marsh or pond,
so that the young, while enjoying the requisite degree of moisture, may not be injured
by a too wet environment. On the other hand Pontobdella and some other leeches lay
their cocoons attached to bodies actually submerged in the water. The cocoon is
secreted, as in Oligochaeta, by the clitellum, and as in them, is drawn off over the
head, the ova and sperm probably flowing into it during the process. The elasticity of
the slightly hardened mucus causes the two ends of the cocoon to close up when it is
free from the body; it is then whitish and soft, and the leech fixes it, and appears to
polish the surface with its buccal sucker. In a few hours the cocoon becomes amber
brown, a colour which characterises the cocoons of a great many earthworms and
other Oligochaeta. The medicinal leech forms its cocoon in the same way as does
Nephelis, to which the above description refers; but when the cocoon is formed the
leech covers it with another layer of mucus, which Vaillant, from whose work the
foregoing notes are extracted,[462] thinks may be produced from the so-called salivary
glands.
Classification.—The number of different kinds of leeches is at present uncertain.
Seeing that no less than sixty-four varieties of the common Hirudo medicinalis—
colour varieties, it is true—are said to exist, it is not wonderful that the labours of
some systematists have been severe, and have provoked much criticism and alteration
on the part of others.[463] As to genera, Vaillant, in his recent continuation of de
Quatrefages' "Annelés" in the Suites à Buffon, which includes the literature up to the
year 1886, allows thirty-seven, some (three) of which, however, are admitted to be
incertae sedis. Blanchard, who has paid a great deal of attention to the group, reduces
these by six, which he considers to be synonyms; but on the other hand he has added
or rescued from oblivion six or seven others, and Whitman has instituted several
Japanese and Australian genera. Most of these generic types are, however, only
imperfectly known, and from external characters only. It is quite problematical how
many valid genera should be retained; in the meantime those that are fairly well
known are divided by Blanchard[464] in the following way:—
Sub-Order 1. Rhynchobdellae.—Hirudinea with an exsertile proboscis, without
jaws, and with colourless blood.
Fam. 1. Ichthyobdellidae.—Body formed of two regions, a narrower anterior portion
and a wider "abdomen," both anterior and posterior suckers distinct from the body.
Page 408
These leeches are parasites of fishes and of some other animals such as tortoises. The
family contains a number of genera. Branchellion (Fig. 204) has a series of leaf-like
branchiae on both sides; in Cystibranchus the respiratory organs are reduced to a
series of round vesicles. The latter genus occurs in Europe and North America, and is
parasitic upon marine and fresh-water fishes. Piscicola is a common leech which
confines its attacks to the inhabitants of fresh water. Pontobdella (Fig. 210) is marine,
and affects rays and sharks; the best known species, P. muricata, is usually of a green
colour.
To the family Ichthyobdellidae also belongs the large Chilian leech Macrobdella
valdiviana, of which there is or are also species in North America. Philippi's figure of
this leech[465] shows the distinct neck; and as it has no jaws, it should be referred to
the present family. It has got an undue reputation for size, 2½ feet[466] having been
assigned to it. As a matter of fact Philippi's illustration depicts an Annelid of about 7
inches in length, with a greatest diameter of about an inch. But doubtless when
extended in walking it would be longer—1½ feet, Philippi thinks. It has no eyes, a
failing which is not unusual among the leeches.
Fam. 2. Glossiphoniidae.—Anterior sucker fused with the body, posterior sucker
distinct. No cocoon.
Fig. 210.—Pontobdella muricata. × 1. (After Bourne.)
The members of this family all inhabit fresh water; they have the habit of depositing
the eggs separately, which are then fixed to the ventral surface of the body, and the
young when hatched are still protected by the parent, returning to its body for shelter.
The type genus Glossiphonia ( = Clepsine) is common in Europe, and has many
species. The Mexican and Amazonian Haementeria contains a number of species, of
which the Mexican H. officinalis is used in medicine; but according to Miguel
family contains a number of genera. Branchellion (Fig. 204) has a series of leaf-like
branchiae on both sides; in Cystibranchus the respiratory organs are reduced to a
series of round vesicles. The latter genus occurs in Europe and North America, and is
parasitic upon marine and fresh-water fishes. Piscicola is a common leech which
confines its attacks to the inhabitants of fresh water. Pontobdella (Fig. 210) is marine,
and affects rays and sharks; the best known species, P. muricata, is usually of a green
colour.
To the family Ichthyobdellidae also belongs the large Chilian leech Macrobdella
valdiviana, of which there is or are also species in North America. Philippi's figure of
this leech[465] shows the distinct neck; and as it has no jaws, it should be referred to
the present family. It has got an undue reputation for size, 2½ feet[466] having been
assigned to it. As a matter of fact Philippi's illustration depicts an Annelid of about 7
inches in length, with a greatest diameter of about an inch. But doubtless when
extended in walking it would be longer—1½ feet, Philippi thinks. It has no eyes, a
failing which is not unusual among the leeches.
Fam. 2. Glossiphoniidae.—Anterior sucker fused with the body, posterior sucker
distinct. No cocoon.
Fig. 210.—Pontobdella muricata. × 1. (After Bourne.)
The members of this family all inhabit fresh water; they have the habit of depositing
the eggs separately, which are then fixed to the ventral surface of the body, and the
young when hatched are still protected by the parent, returning to its body for shelter.
The type genus Glossiphonia ( = Clepsine) is common in Europe, and has many
species. The Mexican and Amazonian Haementeria contains a number of species, of
which the Mexican H. officinalis is used in medicine; but according to Miguel
Page 409
Jimenez, its use is apt to be attended with unpleasant symptoms. Drowsiness, a
buzzing in the ears, and the development of a painful rash are some of the effects
produced by its bite. It is disputed whether the animal's saliva or foreign matter
introduced by it into the wound are the cause of the symptoms.
Mesobdella of Blanchard[467] is said to be intermediate between this family and the
next. Each segment has three annuli, as in this family, but the leech has three jaws, as
in Hirudo.
Sub-Order 2. Gnathobdellae.—Hirudinea without a proboscis, generally with jaws;
the blood is red; the eggs are invariably deposited in cocoons.
Fam. 1. Gnathobdellidae.—Pharynx with three denticulate jaws.
This family as well as the next is terrestrial or fresh-water in habit. It contains a
number of generic types, including the medicinal leech, Hirudo medicinalis, and the
horseleech, Haemopis (Aulastomum) gulo. The former can be distinguished from the
latter by its power of contracting itself into an oval olive-shaped form, which power is
not possessed by the horseleech; the latter has, moreover, only two caeca, while the
common leech has ten pairs of these appendages of the intestine. The genus Limnatis
is called after the Greek word λιμνῆτις, which Theocritus applied to the leech. It is
found in the Nile, and caused serious inconvenience to the army of Napoleon. His
soldiers in drinking at pools sucked up the small leeches not thicker than a horse's hair,
whose presence in the hinder part of the mouth cavity produced divers objectionable
results, such as spitting of blood and hindered respiration.
Fam. 2. Herpobdellidae.—Pharynx without denticulate jaws, with three unarmed
chitinous plates.
A characteristic genus of this family is Trocheta, which is so common at the
Zoological Society's Gardens and in the Regent's Park, and which has been met with
in other places near London; it is in this country an introduced species, but is found in
many parts of the continent. It is a land-leech, and lives upon earthworms.
The genus Haemadipsa, which M. Blanchard places in a special sub-family, contains a
number of species which are for the most part land-leeches. Land-leeches occur in
many parts of the world, but chiefly in the tropics—in India, Ceylon, Java, South
America, etc. They lie in wait for their prey, upon the ground as a rule; but they may
ascend herbs and shrubs to gain a better outlook when they are aware of an
approaching footstep. A vivid account of the ferocity of these tiny Annelids in Ceylon
can be read in Sir J. E. Tennent's Natural History of Ceylon. They have been said to be
buzzing in the ears, and the development of a painful rash are some of the effects
produced by its bite. It is disputed whether the animal's saliva or foreign matter
introduced by it into the wound are the cause of the symptoms.
Mesobdella of Blanchard[467] is said to be intermediate between this family and the
next. Each segment has three annuli, as in this family, but the leech has three jaws, as
in Hirudo.
Sub-Order 2. Gnathobdellae.—Hirudinea without a proboscis, generally with jaws;
the blood is red; the eggs are invariably deposited in cocoons.
Fam. 1. Gnathobdellidae.—Pharynx with three denticulate jaws.
This family as well as the next is terrestrial or fresh-water in habit. It contains a
number of generic types, including the medicinal leech, Hirudo medicinalis, and the
horseleech, Haemopis (Aulastomum) gulo. The former can be distinguished from the
latter by its power of contracting itself into an oval olive-shaped form, which power is
not possessed by the horseleech; the latter has, moreover, only two caeca, while the
common leech has ten pairs of these appendages of the intestine. The genus Limnatis
is called after the Greek word λιμνῆτις, which Theocritus applied to the leech. It is
found in the Nile, and caused serious inconvenience to the army of Napoleon. His
soldiers in drinking at pools sucked up the small leeches not thicker than a horse's hair,
whose presence in the hinder part of the mouth cavity produced divers objectionable
results, such as spitting of blood and hindered respiration.
Fam. 2. Herpobdellidae.—Pharynx without denticulate jaws, with three unarmed
chitinous plates.
A characteristic genus of this family is Trocheta, which is so common at the
Zoological Society's Gardens and in the Regent's Park, and which has been met with
in other places near London; it is in this country an introduced species, but is found in
many parts of the continent. It is a land-leech, and lives upon earthworms.
The genus Haemadipsa, which M. Blanchard places in a special sub-family, contains a
number of species which are for the most part land-leeches. Land-leeches occur in
many parts of the world, but chiefly in the tropics—in India, Ceylon, Java, South
America, etc. They lie in wait for their prey, upon the ground as a rule; but they may
ascend herbs and shrubs to gain a better outlook when they are aware of an
approaching footstep. A vivid account of the ferocity of these tiny Annelids in Ceylon
can be read in Sir J. E. Tennent's Natural History of Ceylon. They have been said to be
Page 410
so pugnacious and so poisonous that persons surprised in their sleep by the pests have
succumbed to their united efforts. A whole battalion of English soldiers decamped on
one occasion from a wood which was overflowing with land-leeches. The familiar
misquotation "lethalis hirudo" might well be applied to this species. Professor
Whitman has written much upon the habits of the land-leech of Japan (Haemadipsa
japonica), which bites so softly that its presence cannot be detected except for the
stream of blood which trickles from the wound. While it is feeding it emits from the
pores of the nephridia a clear fluid, which, as it appears, is used to keep the skin moist;
when unduly dried the same phenomenon occurs. It is curious that in this and other
leeches the nephridia should play a part which in the earthworm is played by the
dorsal pores; in both animals the glands of the skin are also concerned with the same
duty.
The purely aquatic leeches swim by undulations, and also crawl by the help of the two
suckers, like a "Geometer" caterpillar. But when a land-leech is dropped into the water
it at once sinks to the bottom and crawls out; it does not swim, but can survive
immersion for a long period. In this it resembles the earthworms, which can also
survive a prolonged immersion, and even in the case of some are indifferent to the
medium, land or water, in which they live; the land-leech, however, is entirely
dependent upon damp surroundings; a dry air is fatal to it. The land-leech of Japan
leaves a slimy trail behind it as it crawls, in this respect recalling the land Planarian
Bipalium kewense.
succumbed to their united efforts. A whole battalion of English soldiers decamped on
one occasion from a wood which was overflowing with land-leeches. The familiar
misquotation "lethalis hirudo" might well be applied to this species. Professor
Whitman has written much upon the habits of the land-leech of Japan (Haemadipsa
japonica), which bites so softly that its presence cannot be detected except for the
stream of blood which trickles from the wound. While it is feeding it emits from the
pores of the nephridia a clear fluid, which, as it appears, is used to keep the skin moist;
when unduly dried the same phenomenon occurs. It is curious that in this and other
leeches the nephridia should play a part which in the earthworm is played by the
dorsal pores; in both animals the glands of the skin are also concerned with the same
duty.
The purely aquatic leeches swim by undulations, and also crawl by the help of the two
suckers, like a "Geometer" caterpillar. But when a land-leech is dropped into the water
it at once sinks to the bottom and crawls out; it does not swim, but can survive
immersion for a long period. In this it resembles the earthworms, which can also
survive a prolonged immersion, and even in the case of some are indifferent to the
medium, land or water, in which they live; the land-leech, however, is entirely
dependent upon damp surroundings; a dry air is fatal to it. The land-leech of Japan
leaves a slimy trail behind it as it crawls, in this respect recalling the land Planarian
Bipalium kewense.
Page 411
GEPHYREA AND PHORONIS
BY
ARTHUR E. SHIPLEY, M.A.
Fellow and Tutor of Christ's College, Cambridge
CHAPTER XV
GEPHYREA
INTRODUCTION—ANATOMY—DEVELOPMENT—SIPUNCULOIDEA—PRIAPULOIDEA—
ECHIUROIDEA—EPITHETOSOMATOIDEA—AFFINITIES OF THE GROUP.
The animals included in the above-named group were formerly associated with the
Echinodermata. Delle Chiaje[468] states that Bohadsch of Prague in 1757 was the first
to give an accurate description of Sipunculus under the name of Syrinx, but Linnaeus,
who noted that in captivity the animal always kept its anus directed upwards, re-
named it Sipunculus. Lamarck[469] placed the Gephyrea near the Holothurians; and
Cuvier[470] also assigned them a position amongst the Echinoderms. He mentions
Bonellia, Thalassema, Echiurus, Sternaspis, and three species of Sipunculus, one of
which, S. edulis, "sert de nourriture aux Chinois qui habitent Java, et qui vont la
chercher dans le sable au moyen de petits bambous préparés."
The name Gephyrea[471] was first used by Quatrefages, who regarded these animals as
bridging the gulf between the Worms and the Echinoderms. He included in this group
the genus Sternaspis (vide p. 335), now more usually classed with the Chaetopoda.
The Gephyrea are exclusively marine. They are subcylindrical animals, which can
either retract the anterior end of their body—the introvert—carrying the mouth into
the interior; or are provided with a long flexible but non-retractile proboscis. The latter
is easily cast off. They usually bear spines or hooks of a hard chitinous character,
secreted by the epidermis or outermost layer of cells. The mouth is at the base of the
proboscis or at the end of the protractile part, the anus is at the other end of the body
or on the dorsal surface. The nervous system consists of a ring round the mouth and of
a ventral nerve-cord. A vascular system is present as a rule. Nephridia are found which
BY
ARTHUR E. SHIPLEY, M.A.
Fellow and Tutor of Christ's College, Cambridge
CHAPTER XV
GEPHYREA
INTRODUCTION—ANATOMY—DEVELOPMENT—SIPUNCULOIDEA—PRIAPULOIDEA—
ECHIUROIDEA—EPITHETOSOMATOIDEA—AFFINITIES OF THE GROUP.
The animals included in the above-named group were formerly associated with the
Echinodermata. Delle Chiaje[468] states that Bohadsch of Prague in 1757 was the first
to give an accurate description of Sipunculus under the name of Syrinx, but Linnaeus,
who noted that in captivity the animal always kept its anus directed upwards, re-
named it Sipunculus. Lamarck[469] placed the Gephyrea near the Holothurians; and
Cuvier[470] also assigned them a position amongst the Echinoderms. He mentions
Bonellia, Thalassema, Echiurus, Sternaspis, and three species of Sipunculus, one of
which, S. edulis, "sert de nourriture aux Chinois qui habitent Java, et qui vont la
chercher dans le sable au moyen de petits bambous préparés."
The name Gephyrea[471] was first used by Quatrefages, who regarded these animals as
bridging the gulf between the Worms and the Echinoderms. He included in this group
the genus Sternaspis (vide p. 335), now more usually classed with the Chaetopoda.
The Gephyrea are exclusively marine. They are subcylindrical animals, which can
either retract the anterior end of their body—the introvert—carrying the mouth into
the interior; or are provided with a long flexible but non-retractile proboscis. The latter
is easily cast off. They usually bear spines or hooks of a hard chitinous character,
secreted by the epidermis or outermost layer of cells. The mouth is at the base of the
proboscis or at the end of the protractile part, the anus is at the other end of the body
or on the dorsal surface. The nervous system consists of a ring round the mouth and of
a ventral nerve-cord. A vascular system is present as a rule. Nephridia are found which
Page 412
act as excretory organs, and in most cases also as ducts for the generative cells. The
Gephyrea are bisexual, and the male is sometimes degenerate.
The group may be divided into four Orders:—(i.) Sipunculoidea; (ii.) Priapuloidea;
(iii.) Echiuroidea; (iv.) Epithetosomatoidea; of these the first is by far the largest, both
in number of genera and of species.
The Anatomy of Sipunculus nudus.
External Characters.—The body of S. nudus when fully extended may attain a
length of a foot, or even a little more; in this condition it is seen to consist of two
portions, the anterior of which is, however, retracted into the other when the animal is
disturbed. The retractile portion is sometimes termed the proboscis, but as its nature is
entirely different from that of the proboscis of the Echiuroidea, it is better to refer to it
as the introvert. Special retractor muscles are attached on the one hand to the body-
wall about half-way down the body, and on the other hand are fused into a muscular
sheath which surrounds the gullet, just behind the mouth. When these muscles
contract, they withdraw the introvert into the rest of the body or trunk in much the
same way as the finger of a glove may be drawn into the hand, by a thread fastened to
the inside of its apex. The introvert is protruded by the contraction of the circular
muscles of the body-wall. These exert a pressure on the fluid which fills the body-
cavity, and by this means the sides of the introvert are forced forward until finally the
head is exposed.
The introvert occupies about one-sixth or one-fifth of the total body length. It is
somewhat narrower than the trunk, and is covered by a number of small flattened
papillae, some of which lie with their free ends directed backward, overlapping one
another like tiles on a roof. In some other genera, as Phymosoma, the introvert bears
rows of horny hooks, which are apt to fall off as the animal grows old.
The trunk has from thirty to thirty-two longitudinal furrows, the elevations between
which correspond with a similar number of muscles lying in the skin. This
longitudinal marking is crossed at right angles by a circular marking of similar origin,
the elevations of which correspond with the circular muscles in the skin. These two
sets of markings thus divide the skin of the trunk into a number of small square areas,
very regularly arranged (Fig. 212).
The outline of the trunk is more or less uniform, but it is capable of considerable
change according to the state of contraction of its muscles. The circular muscles, for
Gephyrea are bisexual, and the male is sometimes degenerate.
The group may be divided into four Orders:—(i.) Sipunculoidea; (ii.) Priapuloidea;
(iii.) Echiuroidea; (iv.) Epithetosomatoidea; of these the first is by far the largest, both
in number of genera and of species.
The Anatomy of Sipunculus nudus.
External Characters.—The body of S. nudus when fully extended may attain a
length of a foot, or even a little more; in this condition it is seen to consist of two
portions, the anterior of which is, however, retracted into the other when the animal is
disturbed. The retractile portion is sometimes termed the proboscis, but as its nature is
entirely different from that of the proboscis of the Echiuroidea, it is better to refer to it
as the introvert. Special retractor muscles are attached on the one hand to the body-
wall about half-way down the body, and on the other hand are fused into a muscular
sheath which surrounds the gullet, just behind the mouth. When these muscles
contract, they withdraw the introvert into the rest of the body or trunk in much the
same way as the finger of a glove may be drawn into the hand, by a thread fastened to
the inside of its apex. The introvert is protruded by the contraction of the circular
muscles of the body-wall. These exert a pressure on the fluid which fills the body-
cavity, and by this means the sides of the introvert are forced forward until finally the
head is exposed.
The introvert occupies about one-sixth or one-fifth of the total body length. It is
somewhat narrower than the trunk, and is covered by a number of small flattened
papillae, some of which lie with their free ends directed backward, overlapping one
another like tiles on a roof. In some other genera, as Phymosoma, the introvert bears
rows of horny hooks, which are apt to fall off as the animal grows old.
The trunk has from thirty to thirty-two longitudinal furrows, the elevations between
which correspond with a similar number of muscles lying in the skin. This
longitudinal marking is crossed at right angles by a circular marking of similar origin,
the elevations of which correspond with the circular muscles in the skin. These two
sets of markings thus divide the skin of the trunk into a number of small square areas,
very regularly arranged (Fig. 212).
The outline of the trunk is more or less uniform, but it is capable of considerable
change according to the state of contraction of its muscles. The circular muscles, for
Page 413
instance, may be contracted at one level, thus causing a constriction at this spot. The
colour of S. nudus is a somewhat glistening greyish-white.
Fig. 211.—Right half of the anterior end of Sipunculus nudus L., seen from the inner side and
magnified. a, Funnel-shaped grooved tentacular crown leading to the mouth; b, oesophagus;
c, strands breaking up the cavity of the tentacular crown into vascular spaces; c', heart; d,
brain; e, ventral, and e', dorsal retractor muscles; f, ventral nerve-cord; G, vascular spaces in
tentacular crown.
The anterior end of the fully-expanded Sipunculus may be termed the head; here the
skin is produced into a frayed fringe which stands up in the shape of a funnel round
the mouth. This fringe is grooved on its internal surface with numerous little gutters,
all of them lined with cilia, which by their constant motion keep up a current which
sweeps food into the mouth. The fringe may be in the form of a simple ring round the
mouth, or the ring may be folded in at the dorsal side so as to take the form of a
double horse-shoe (Figs. 211 and 212).
Body-wall.—The glistening appearance of Sipunculus is due to the cuticle, a chitinoid
layer which is secreted by the external layer of cells, the epidermis. Beneath this lies a
layer of connective tissue, which is not always present in other Gephyrea; within this
lies a layer of circular muscles arranged in bundles, then comes a very thin sheath of
oblique muscular fibres, then a thicker layer of longitudinal muscles, and finally a
layer of peritoneal epithelial cells, which in Sipunculus are for the most part ciliated.
Scattered over the surface of the body, and opening by narrow tubes which pierce the
cuticle, are a number of glandular bodies which may be either bi- or multi-cellular.
The glandular cells are apparently enlarged and modified epidermal cells; they are
arranged in a cup-shaped manner, with their apices directed towards the orifice. They
are crowded with granules, which are presumably poured out over the cuticle, but the
exact function of the secretion is entirely unknown. They have a well-developed nerve
supply.
colour of S. nudus is a somewhat glistening greyish-white.
Fig. 211.—Right half of the anterior end of Sipunculus nudus L., seen from the inner side and
magnified. a, Funnel-shaped grooved tentacular crown leading to the mouth; b, oesophagus;
c, strands breaking up the cavity of the tentacular crown into vascular spaces; c', heart; d,
brain; e, ventral, and e', dorsal retractor muscles; f, ventral nerve-cord; G, vascular spaces in
tentacular crown.
The anterior end of the fully-expanded Sipunculus may be termed the head; here the
skin is produced into a frayed fringe which stands up in the shape of a funnel round
the mouth. This fringe is grooved on its internal surface with numerous little gutters,
all of them lined with cilia, which by their constant motion keep up a current which
sweeps food into the mouth. The fringe may be in the form of a simple ring round the
mouth, or the ring may be folded in at the dorsal side so as to take the form of a
double horse-shoe (Figs. 211 and 212).
Body-wall.—The glistening appearance of Sipunculus is due to the cuticle, a chitinoid
layer which is secreted by the external layer of cells, the epidermis. Beneath this lies a
layer of connective tissue, which is not always present in other Gephyrea; within this
lies a layer of circular muscles arranged in bundles, then comes a very thin sheath of
oblique muscular fibres, then a thicker layer of longitudinal muscles, and finally a
layer of peritoneal epithelial cells, which in Sipunculus are for the most part ciliated.
Scattered over the surface of the body, and opening by narrow tubes which pierce the
cuticle, are a number of glandular bodies which may be either bi- or multi-cellular.
The glandular cells are apparently enlarged and modified epidermal cells; they are
arranged in a cup-shaped manner, with their apices directed towards the orifice. They
are crowded with granules, which are presumably poured out over the cuticle, but the
exact function of the secretion is entirely unknown. They have a well-developed nerve
supply.
Page 414
Digestive System.—The mouth lies in the centre of the fringe, and is not provided
with any kind of jaw or biting armature; it leads directly into the thin-walled
alimentary canal, the first part of which is ciliated. The alimentary canal is not marked
out into definite regions, but passes as a thin-walled semi-transparent tube to the
posterior end of the body, and then turns forward again and opens to the exterior by an
anus situated about an inch below the junction of the introvert with the trunk, on the
median dorsal line. The descending and ascending limbs of the alimentary canal are
coiled together in a spiral, which may be more or less close in different individuals.
The whole is supported by numerous fine muscular strands, which pass from the walls
of the intestine to the skin, and by a spindle-muscle, which runs from the extreme
posterior end of the trunk up the axis of the spiral and terminates in the skin close to
the anus.
No glands open into the alimentary canal at any point of its course, but near the anus a
simple diverticulum, or pocket, of unknown function arises. The size of this outgrowth
differs enormously in different individuals. The alimentary canal near the anus also
bears two tuft-like organs, which, however, do not open into the intestine, but
probably have some function in connexion with the fluid in the body-cavity.
Along the whole course of the alimentary canal there runs a ciliated groove, into
which the food does not pass, but the cilia of which probably keep in motion a current
of water whose function may be respiratory.
with any kind of jaw or biting armature; it leads directly into the thin-walled
alimentary canal, the first part of which is ciliated. The alimentary canal is not marked
out into definite regions, but passes as a thin-walled semi-transparent tube to the
posterior end of the body, and then turns forward again and opens to the exterior by an
anus situated about an inch below the junction of the introvert with the trunk, on the
median dorsal line. The descending and ascending limbs of the alimentary canal are
coiled together in a spiral, which may be more or less close in different individuals.
The whole is supported by numerous fine muscular strands, which pass from the walls
of the intestine to the skin, and by a spindle-muscle, which runs from the extreme
posterior end of the trunk up the axis of the spiral and terminates in the skin close to
the anus.
No glands open into the alimentary canal at any point of its course, but near the anus a
simple diverticulum, or pocket, of unknown function arises. The size of this outgrowth
differs enormously in different individuals. The alimentary canal near the anus also
bears two tuft-like organs, which, however, do not open into the intestine, but
probably have some function in connexion with the fluid in the body-cavity.
Along the whole course of the alimentary canal there runs a ciliated groove, into
which the food does not pass, but the cilia of which probably keep in motion a current
of water whose function may be respiratory.
Page 415
Fig. 212.—Sipunculus nudus L., with introvert and head fully extended, laid open by an incision
along the right side to show the internal organs. × 2. a, Mouth; b, ventral nerve-cord; c,
heart; d, oesophagus; e, intestine; f, position of anus; g, tuft-like organs; h, right nephridium;
i, retractor muscles; j, diverticulum on rectum. The spindle-muscle is seen overlying the
rectum.
Vascular System.—On the dorsal surface of the anterior end of the alimentary canal
lies a contractile vessel, usually termed the heart. It is a tube about an inch long,
ending blindly behind, but opening in front into a ring-shaped space surrounding the
mouth and partially enveloping the brain. From this ring-like vessel numerous
branches are given off which pass into the fringe round the mouth, and probably the
chief function of the heart is by its contraction to force fluid into this fringe, and so to
extend it. The heart contains a corpusculated fluid. A similar but shorter tube is found
on the ventral surface of the anterior end of the alimentary canal in the species in
question; it also opens into the ring which surrounds the mouth.
Respiratory System.—There are no special respiratory organs, and it has long been a
matter of dispute where the respiration of Gephyrea is carried on. The oxygenation of
the blood probably takes place to some extent through the walls of the oral fringe, but
the blood which receives its oxygen at this spot is limited in its distribution, and could
only supply the brain and head. It seems probable that the remaining organs are
supplied with oxygen by the fluid of the body-cavity, which bathes them on all sides.
This might obtain its oxygen from the blood in the heart, or more probably, through
along the right side to show the internal organs. × 2. a, Mouth; b, ventral nerve-cord; c,
heart; d, oesophagus; e, intestine; f, position of anus; g, tuft-like organs; h, right nephridium;
i, retractor muscles; j, diverticulum on rectum. The spindle-muscle is seen overlying the
rectum.
Vascular System.—On the dorsal surface of the anterior end of the alimentary canal
lies a contractile vessel, usually termed the heart. It is a tube about an inch long,
ending blindly behind, but opening in front into a ring-shaped space surrounding the
mouth and partially enveloping the brain. From this ring-like vessel numerous
branches are given off which pass into the fringe round the mouth, and probably the
chief function of the heart is by its contraction to force fluid into this fringe, and so to
extend it. The heart contains a corpusculated fluid. A similar but shorter tube is found
on the ventral surface of the anterior end of the alimentary canal in the species in
question; it also opens into the ring which surrounds the mouth.
Respiratory System.—There are no special respiratory organs, and it has long been a
matter of dispute where the respiration of Gephyrea is carried on. The oxygenation of
the blood probably takes place to some extent through the walls of the oral fringe, but
the blood which receives its oxygen at this spot is limited in its distribution, and could
only supply the brain and head. It seems probable that the remaining organs are
supplied with oxygen by the fluid of the body-cavity, which bathes them on all sides.
This might obtain its oxygen from the blood in the heart, or more probably, through
Page 416
the thin walls of the intestine, from the stream of water which is maintained by the
ciliated groove described above. Quite recently a form—S. mundanus, var. branchiata
—has been described[472] with thin-walled papillae covering parts of the skin. These
papillae are full of corpuscles, and are regarded by their discoverer as branchiae.
Body-Cavity.—The pinkish fluid of the body-cavity contains numerous corpuscles,
the products of the reproductive organs (either ova or spermatozoa), and some curious
unicellular bodies known as "urns." The latter are shaped like a bowl with a ciliated
rim, and are formed from the budding of certain cells on the walls of the dorsal blood-
vessel.[473] Their function is unknown, but they resemble certain multicellular bodies
found in the body-cavity of Phascolosoma. The generative cells found in the body-
cavity are further considered below. The true corpuscles are either biconcave round
corpuscles coloured with a chemical substance, the haemerythrin of Krukenberg,
which apparently plays the same rôle as haemoglobin in other animals; or amoeboid
corpuscles, which, though rare in Sipunculus, are very numerous in Phascolosoma.
Nervous System.—The nervous system of Sipunculus consists of a brain or cerebral
ganglion, a circumoesophageal ring surrounding the gullet, and a ventral nerve-cord.
The brain is a small bi-lobed nervous mass situated on the dorsal surface of the
oesophagus, in the angle between the right and left dorsal retractor muscles close to
their point of insertion. Numerous nerves arise from it, and pass to the fringe
surrounding the mouth and to neighbouring parts. At the sides, the brain is continued
into two stout nerve-cords which encircle the oesophagus, and meeting, fuse together
in the median ventral line to form the ventral nerve-cord (Fig. 211). The latter is of the
same diameter throughout, and shows no signs of segmentation; it is oval in section,
and consists of small ganglion cells heaped up on the ventral surface, i.e. next the skin,
and of numerous fibres situated dorsally. The cord gives off many nerves, which
usually arise in pairs. These pass into the skin, and forming rings, run round the body,
and give off finer nerves as they go.
The nerve-cord is supported by numerous strands of muscle which pass to it from the
skin. These are especially long in the region where the introvert joins the trunk, and
thus allow free play to the nerve-cord when the former is being protruded or retracted.
Sipunculus is not well provided with sense-organs, but in an animal which lives buried
in sand we should not expect to find these very highly developed. On the introvert
there are certain patches of epithelium bearing long stout cilia, which have been
regarded as tactile in function, and there is a tubular infolding reaching the brain,
which almost certainly has some sensory function. Ward[474] has termed this "the
cerebral organ." It consists of a duct lined with ciliated cells, which opens to the
exterior in the middle dorsal line outside the tentacular fringe. The duct leads down to
ciliated groove described above. Quite recently a form—S. mundanus, var. branchiata
—has been described[472] with thin-walled papillae covering parts of the skin. These
papillae are full of corpuscles, and are regarded by their discoverer as branchiae.
Body-Cavity.—The pinkish fluid of the body-cavity contains numerous corpuscles,
the products of the reproductive organs (either ova or spermatozoa), and some curious
unicellular bodies known as "urns." The latter are shaped like a bowl with a ciliated
rim, and are formed from the budding of certain cells on the walls of the dorsal blood-
vessel.[473] Their function is unknown, but they resemble certain multicellular bodies
found in the body-cavity of Phascolosoma. The generative cells found in the body-
cavity are further considered below. The true corpuscles are either biconcave round
corpuscles coloured with a chemical substance, the haemerythrin of Krukenberg,
which apparently plays the same rôle as haemoglobin in other animals; or amoeboid
corpuscles, which, though rare in Sipunculus, are very numerous in Phascolosoma.
Nervous System.—The nervous system of Sipunculus consists of a brain or cerebral
ganglion, a circumoesophageal ring surrounding the gullet, and a ventral nerve-cord.
The brain is a small bi-lobed nervous mass situated on the dorsal surface of the
oesophagus, in the angle between the right and left dorsal retractor muscles close to
their point of insertion. Numerous nerves arise from it, and pass to the fringe
surrounding the mouth and to neighbouring parts. At the sides, the brain is continued
into two stout nerve-cords which encircle the oesophagus, and meeting, fuse together
in the median ventral line to form the ventral nerve-cord (Fig. 211). The latter is of the
same diameter throughout, and shows no signs of segmentation; it is oval in section,
and consists of small ganglion cells heaped up on the ventral surface, i.e. next the skin,
and of numerous fibres situated dorsally. The cord gives off many nerves, which
usually arise in pairs. These pass into the skin, and forming rings, run round the body,
and give off finer nerves as they go.
The nerve-cord is supported by numerous strands of muscle which pass to it from the
skin. These are especially long in the region where the introvert joins the trunk, and
thus allow free play to the nerve-cord when the former is being protruded or retracted.
Sipunculus is not well provided with sense-organs, but in an animal which lives buried
in sand we should not expect to find these very highly developed. On the introvert
there are certain patches of epithelium bearing long stout cilia, which have been
regarded as tactile in function, and there is a tubular infolding reaching the brain,
which almost certainly has some sensory function. Ward[474] has termed this "the
cerebral organ." It consists of a duct lined with ciliated cells, which opens to the
exterior in the middle dorsal line outside the tentacular fringe. The duct leads down to
Page 417
the brain, and expands at its lower end into a saucer-shaped space, covering that
portion of the brain where its substance is continuous with the external epithelium. In
Phymosoma this cavity is produced into two finger-shaped processes, which are sunk
into the brain and are lined by cells crowded with a dense black pigment.[475] They are
probably rudimentary eyes, perhaps distinguishing only between darkness and light.
The pits appear to be absent in Sipunculus nudus, but Andrews states they are found,
although without pigment, in S. gouldii.[476]
Excretory System.—The excretory organs or "brown tubes" are typical nephridia,
that is to say, they consist of tubes with glandular walls which open on the one side to
the exterior, and on the other by means of a ciliated funnel-shaped opening into the
body-cavity. In Gephyrea one wall of the tube is produced into a long diverticulum or
sac which hangs down into the body-cavity, and is usually supported by muscle-fibres
running to the body-wall. The lower end of the sac is broken up into a number of
crypts or pits, lined by large glandular cells crowded with brown pigment. The
pigment-granules are secreted into the cavity of the sac, and leave the body through
the external opening; they probably consist of the nitrogenous excreta of the animal.
The upper end of the sac, into which both the external and internal orifices open, is
usually enlarged, and its walls are very muscular. As in so many other animals, the
nephridia serve as ducts through which the reproductive cells leave the body of the
parent.
Reproductive System.—The Gephyrea are bisexual. In Sipunculus the testes and
ovaries are found in the same position in the two sexes, and are indistinguishable
without microscopic investigation. They each consist of small ridges situated at the
lower end of the ventral retractor muscles, just where the latter take their origin from
the longitudinal muscles of the skin. At this level the cells which line the body-cavity
on the inside of the skin are heaped up, and become modified in the one case into ova
or eggs, and in the other into the mother-cells of the spermatozoa. This method of
forming the reproductive organs from modified cells lining the body-cavity is very
common in the higher animals; but it is seen in its simplest and least modified form in
the Sipunculidae.
The eggs break away from the ovary in a very undeveloped condition, but whilst
floating about in the body-cavity they increase in size and secrete a thick membrane
around them. They have a well-marked nucleus, and are oval in outline.
The mother-cells of the spermatozoa also break away in an immature condition, and
complete their development in the nutritive fluid of the body-cavity. They divide into a
number of spermatozoa, usually eight or sixteen, which remain in contact. They each
develop a tail, which projects outwards, and aids the cluster in swimming along. These
portion of the brain where its substance is continuous with the external epithelium. In
Phymosoma this cavity is produced into two finger-shaped processes, which are sunk
into the brain and are lined by cells crowded with a dense black pigment.[475] They are
probably rudimentary eyes, perhaps distinguishing only between darkness and light.
The pits appear to be absent in Sipunculus nudus, but Andrews states they are found,
although without pigment, in S. gouldii.[476]
Excretory System.—The excretory organs or "brown tubes" are typical nephridia,
that is to say, they consist of tubes with glandular walls which open on the one side to
the exterior, and on the other by means of a ciliated funnel-shaped opening into the
body-cavity. In Gephyrea one wall of the tube is produced into a long diverticulum or
sac which hangs down into the body-cavity, and is usually supported by muscle-fibres
running to the body-wall. The lower end of the sac is broken up into a number of
crypts or pits, lined by large glandular cells crowded with brown pigment. The
pigment-granules are secreted into the cavity of the sac, and leave the body through
the external opening; they probably consist of the nitrogenous excreta of the animal.
The upper end of the sac, into which both the external and internal orifices open, is
usually enlarged, and its walls are very muscular. As in so many other animals, the
nephridia serve as ducts through which the reproductive cells leave the body of the
parent.
Reproductive System.—The Gephyrea are bisexual. In Sipunculus the testes and
ovaries are found in the same position in the two sexes, and are indistinguishable
without microscopic investigation. They each consist of small ridges situated at the
lower end of the ventral retractor muscles, just where the latter take their origin from
the longitudinal muscles of the skin. At this level the cells which line the body-cavity
on the inside of the skin are heaped up, and become modified in the one case into ova
or eggs, and in the other into the mother-cells of the spermatozoa. This method of
forming the reproductive organs from modified cells lining the body-cavity is very
common in the higher animals; but it is seen in its simplest and least modified form in
the Sipunculidae.
The eggs break away from the ovary in a very undeveloped condition, but whilst
floating about in the body-cavity they increase in size and secrete a thick membrane
around them. They have a well-marked nucleus, and are oval in outline.
The mother-cells of the spermatozoa also break away in an immature condition, and
complete their development in the nutritive fluid of the body-cavity. They divide into a
number of spermatozoa, usually eight or sixteen, which remain in contact. They each
develop a tail, which projects outwards, and aids the cluster in swimming along. These
Page 418
clusters of spermatozoa are about the same size as the ova of the female, and, like
them, make their way into the "brown tubes." The exact way in which this is
accomplished is not very clear, but the cilia on the funnel-shaped internal opening of
the tube seem to have some power of selecting the generative cells when they come
within their reach, and of passing them on, whilst they reject the much smaller
corpuscles of the perivisceral fluid, which are never found in the nephridia.[477] Once
inside the internal opening, the clusters break up and the spermatozoa escape singly
into the sea. Here they meet with and fertilise the eggs which have escaped from the
body of the female.
Fig. 213.—Larva of Sipunculus nudus L. × 150. (After Hatschek.) a, Mouth; b, anus; c, excretory
organ; d, glandular appendage of oesophagus; e, wall of stomach over which the retractor
muscle runs; f, invaginated sense-organ at aboral pole.
Development.—Hatschek,[478] who investigated the development of Sipunculus nudus
at Pantano, an inlet of the sea near Messina, states that the spawning takes place
during the night, and ceases about July 10. The rate of development depends upon the
temperature, but the larvae usually free themselves from the egg-membrane during the
third day. When hatched the embryos lengthen out a good deal, and take the form
represented in Fig. 213. The larva swims actively by means of a ring of stout cilia,
which encircle the body just behind the mouth. Other shorter cilia are found on the
head, continuing into the lining of the mouth, and a little bunch of them is situated at
the extreme posterior end. The alimentary canal is already formed, and is twisted, so
that the anus lies dorsally, but not so far forward as it does in the adult. A glandular
structure opens into the mouth, and another body of unknown function is connected
with the oesophagus; both these disappear during larval life. A pair of excretory
tubules, the forerunners of the brown tubes, are found, and the chief muscle tracts are
already established. The nervous system is still in close connexion with the skin, from
the outer part of which it is derived; the cerebral thickening bears two eye-spots.
The fluid of the body-cavity contains corpuscles, which are kept in active circulation
by the constant contractions of the body-wall, and by numerous tufts of cilia which are
them, make their way into the "brown tubes." The exact way in which this is
accomplished is not very clear, but the cilia on the funnel-shaped internal opening of
the tube seem to have some power of selecting the generative cells when they come
within their reach, and of passing them on, whilst they reject the much smaller
corpuscles of the perivisceral fluid, which are never found in the nephridia.[477] Once
inside the internal opening, the clusters break up and the spermatozoa escape singly
into the sea. Here they meet with and fertilise the eggs which have escaped from the
body of the female.
Fig. 213.—Larva of Sipunculus nudus L. × 150. (After Hatschek.) a, Mouth; b, anus; c, excretory
organ; d, glandular appendage of oesophagus; e, wall of stomach over which the retractor
muscle runs; f, invaginated sense-organ at aboral pole.
Development.—Hatschek,[478] who investigated the development of Sipunculus nudus
at Pantano, an inlet of the sea near Messina, states that the spawning takes place
during the night, and ceases about July 10. The rate of development depends upon the
temperature, but the larvae usually free themselves from the egg-membrane during the
third day. When hatched the embryos lengthen out a good deal, and take the form
represented in Fig. 213. The larva swims actively by means of a ring of stout cilia,
which encircle the body just behind the mouth. Other shorter cilia are found on the
head, continuing into the lining of the mouth, and a little bunch of them is situated at
the extreme posterior end. The alimentary canal is already formed, and is twisted, so
that the anus lies dorsally, but not so far forward as it does in the adult. A glandular
structure opens into the mouth, and another body of unknown function is connected
with the oesophagus; both these disappear during larval life. A pair of excretory
tubules, the forerunners of the brown tubes, are found, and the chief muscle tracts are
already established. The nervous system is still in close connexion with the skin, from
the outer part of which it is derived; the cerebral thickening bears two eye-spots.
The fluid of the body-cavity contains corpuscles, which are kept in active circulation
by the constant contractions of the body-wall, and by numerous tufts of cilia which are
Page 419
borne on the inner surface of the skin. The dorsal blood-vessel is one of the latest
organs to arise.
The larva swims actively about for a month, during which time it increases greatly in
size; it then undergoes a somewhat sudden metamorphosis. The ciliated ring and the
structures related to the oesophagus begin to disappear, the distinction between the
head and the rest of the body is obliterated, and the head becomes relatively small. The
mouth changes its position, and becomes terminal instead of being somewhat ventral,
and the tentacular membrane begins to appear. At the same time the larva relinquishes
its free-swimming life, and sinks to the bottom; it begins creeping amongst the sand
by protruding and retracting the anterior part of its body, and takes on all the
characters and habits of the adult.
I. Order Sipunculoidea.
Besides the genus Sipunculus, the Order Sipunculoidea includes ten other genera. A
key to these, taken for the most part from Selenka's admirable monograph, is given on
page 424.
Phascolosoma contains, in comparison with Sipunculus, only small species, and it is
easily distinguished by the fact that the longitudinal muscles are fused into a
continuous sheath. As a rule the skin is smooth. A few species bear hooks, which are
generally scattered irregularly and not arranged in transverse rows, as in Phymosoma
(Fig. 214) and most of the other genera.
The fold which in S. nudus surrounds the mouth may be in the same species bent in so
as to take the form of a double horse-shoe, the opening of which is always dorsal, just
above the brain; in this case the mouth is crescentiform. In other genera the fold is
broken up into discrete tentacles, and these are variously arranged; in Dendrostoma
they are grouped together in four or six bundles round the mouth, but the more usual
arrangement is the horse-shoe-like row of tentacles which overhang the crescentiform
mouth, as in Phymosoma and some species of Aspidosiphon.
The ventral side of each tentacle is grooved and ciliated, and the grooves are
continued into the ciliated mouth. Their dorsal surface is pigmented, and in the hollow
of the horse-shoe lies a deeply pigmented epithelium covering the brain.
A blood-vessel courses up each tentacle, and usually two channels return the blood to
the vascular ring which surrounds the mouth. In those forms which possess tentacles
organs to arise.
The larva swims actively about for a month, during which time it increases greatly in
size; it then undergoes a somewhat sudden metamorphosis. The ciliated ring and the
structures related to the oesophagus begin to disappear, the distinction between the
head and the rest of the body is obliterated, and the head becomes relatively small. The
mouth changes its position, and becomes terminal instead of being somewhat ventral,
and the tentacular membrane begins to appear. At the same time the larva relinquishes
its free-swimming life, and sinks to the bottom; it begins creeping amongst the sand
by protruding and retracting the anterior part of its body, and takes on all the
characters and habits of the adult.
I. Order Sipunculoidea.
Besides the genus Sipunculus, the Order Sipunculoidea includes ten other genera. A
key to these, taken for the most part from Selenka's admirable monograph, is given on
page 424.
Phascolosoma contains, in comparison with Sipunculus, only small species, and it is
easily distinguished by the fact that the longitudinal muscles are fused into a
continuous sheath. As a rule the skin is smooth. A few species bear hooks, which are
generally scattered irregularly and not arranged in transverse rows, as in Phymosoma
(Fig. 214) and most of the other genera.
The fold which in S. nudus surrounds the mouth may be in the same species bent in so
as to take the form of a double horse-shoe, the opening of which is always dorsal, just
above the brain; in this case the mouth is crescentiform. In other genera the fold is
broken up into discrete tentacles, and these are variously arranged; in Dendrostoma
they are grouped together in four or six bundles round the mouth, but the more usual
arrangement is the horse-shoe-like row of tentacles which overhang the crescentiform
mouth, as in Phymosoma and some species of Aspidosiphon.
The ventral side of each tentacle is grooved and ciliated, and the grooves are
continued into the ciliated mouth. Their dorsal surface is pigmented, and in the hollow
of the horse-shoe lies a deeply pigmented epithelium covering the brain.
A blood-vessel courses up each tentacle, and usually two channels return the blood to
the vascular ring which surrounds the mouth. In those forms which possess tentacles
Page 420
on the dorsal side of the mouth only, the ventral part of the vascular ring lies in the
lower lip, which is tumid and swollen. The brain supplies a nerve to each tentacle.
When the introvert is retracted the tentacular ring is withdrawn and to some extent
collapsed; in this condition it would be almost touching the rough external surface of
the introvert. In some species of Phymosoma the delicate appendages of the head are
guarded from the hooks on the introvert by a thin membrane or collar,[479] which
completely ensheaths the retracted head.
Fig. 214.—A, Phymosoma granulatum F. S. Leuck. × 2. B, Head of the same. × 4. a, Pigmented pit
leading to brain. The crescentiform mouth on the lower side of the figure is overhung by the
tentacles.
When the introvert is fully extended the dorsal blood-vessel contracts and sends its
blood forward into the vascular ring, and thence into the tentacles or tentacular fold,
which are thus erected. In several species of Sipunculus, as S. nudus, S. norvegicus, S.
robustus, S. tesselatus, there is a ventral blind tube as well as a dorsal, into which the
blood is withdrawn when the head is retracted. In many other species in various
genera, such as Phymosoma weldonii and Ph. asser, Dendrostoma signifer, S. vastus,
the lumen of the dorsal vessel is increased by numerous hollow blind processes which
it bears, hanging freely into the body-cavity. Three very small genera of Sipunculids—
Onchnesoma, Petalostoma, and Tylosoma—are devoid of all trace of vascular system
and of tentacles; the mouth opens in the centre of the anterior end of the introvert. In
Onchnesoma the dorsal part of the lip is somewhat produced, so that the head has
somewhat the shape of a Doge's cap, and in Petalostoma there are two leaf-like
processes of the body-wall which guard the mouth.
The extent to which the intestine is coiled varies very much even in the same species;
the axis of the coil is often supported by a spindle-muscle, but this is sometimes
lower lip, which is tumid and swollen. The brain supplies a nerve to each tentacle.
When the introvert is retracted the tentacular ring is withdrawn and to some extent
collapsed; in this condition it would be almost touching the rough external surface of
the introvert. In some species of Phymosoma the delicate appendages of the head are
guarded from the hooks on the introvert by a thin membrane or collar,[479] which
completely ensheaths the retracted head.
Fig. 214.—A, Phymosoma granulatum F. S. Leuck. × 2. B, Head of the same. × 4. a, Pigmented pit
leading to brain. The crescentiform mouth on the lower side of the figure is overhung by the
tentacles.
When the introvert is fully extended the dorsal blood-vessel contracts and sends its
blood forward into the vascular ring, and thence into the tentacles or tentacular fold,
which are thus erected. In several species of Sipunculus, as S. nudus, S. norvegicus, S.
robustus, S. tesselatus, there is a ventral blind tube as well as a dorsal, into which the
blood is withdrawn when the head is retracted. In many other species in various
genera, such as Phymosoma weldonii and Ph. asser, Dendrostoma signifer, S. vastus,
the lumen of the dorsal vessel is increased by numerous hollow blind processes which
it bears, hanging freely into the body-cavity. Three very small genera of Sipunculids—
Onchnesoma, Petalostoma, and Tylosoma—are devoid of all trace of vascular system
and of tentacles; the mouth opens in the centre of the anterior end of the introvert. In
Onchnesoma the dorsal part of the lip is somewhat produced, so that the head has
somewhat the shape of a Doge's cap, and in Petalostoma there are two leaf-like
processes of the body-wall which guard the mouth.
The extent to which the intestine is coiled varies very much even in the same species;
the axis of the coil is often supported by a spindle-muscle, but this is sometimes
Page 421
absent. The caecum, which opens into the rectum of S. nudus, is again a very variable
structure, and when it is present varies remarkably in size.
The food of Sipunculids seems to consist almost entirely of sand, and their only
nourishment must be such small microscopic organisms or particles of animal and
vegetable débris as are to be found mixed with the sand. The alimentary canal is, as a
rule, quite full of sand, and yet in spite of the tenuity of its walls they never seem to be
ruptured. If the contents of the digestive tube be washed out with a pipette, it will be
found that it requires considerable force to dislodge many of the sand-particles lying
next the wall. These are more or less embedded in crypts or pockets of the wall, and as
the sand passes along the intestine they probably serve as more or less fixed hard
points, against which the sharp edges of the sand particles are worn off. Amongst the
sand are usually to be found pieces of shell, sometimes with a diameter equal to that of
the alimentary canal; these are usually rounded, but their angles may have been
removed by attrition before they entered the mouth of the Sipunculid.
In S. tesselatus the sand is to some extent held together by a mucous deposit; in those
cases where there is no sand in the intestine, there is always a coagulum of mucus, and
the walls are contracted and thick; when full of sand the walls are tensely stretched
and very thin. This thinness of the wall of the alimentary canal seems ill-adapted to a
diet of sand, nevertheless it is also met with in other great sand-eating groups of
animals, such as the Echinids and the Holothurians.
The enormous amount of sand and mud which passes through the bodies of the
Sipunculids shows that they must take a considerable part in modifying the mineral
substances which form the bottom of the sea. Just as earthworms, as shown by
Darwin, play a considerable rôle in the formation of soil, so must these animals, in
conjunction with Echinids and Holothurians, effect considerable modifications in the
sand and mud which pass through their bodies. Mr. J. Y. Buchanan[480] is "led to
believe that the principal agent in the comminution of the mineral matter found at the
bottom of both deep and shallow seas and oceans, is the ground fauna of the sea,
which depends for its subsistence on the organic matter which it can extract from the
mud." The minerals at the bottom of the sea are exposed to a reducing process in
passing through the bodies of the animals which eat them, and subsequently to an
oxidising process due to the oxygen dissolved in the sea-water acting on the minerals
extruded from the animals' bodies.
The rate at which the sand passes through the body of Sipunculus is unfortunately
unknown, but that at any one moment a considerable quantity is contained in the
intestine is shown by the fact that the average weight of five specimens of S. nudus
from Naples, taken at random, was 19.08 grms., whilst the average weight of sand
structure, and when it is present varies remarkably in size.
The food of Sipunculids seems to consist almost entirely of sand, and their only
nourishment must be such small microscopic organisms or particles of animal and
vegetable débris as are to be found mixed with the sand. The alimentary canal is, as a
rule, quite full of sand, and yet in spite of the tenuity of its walls they never seem to be
ruptured. If the contents of the digestive tube be washed out with a pipette, it will be
found that it requires considerable force to dislodge many of the sand-particles lying
next the wall. These are more or less embedded in crypts or pockets of the wall, and as
the sand passes along the intestine they probably serve as more or less fixed hard
points, against which the sharp edges of the sand particles are worn off. Amongst the
sand are usually to be found pieces of shell, sometimes with a diameter equal to that of
the alimentary canal; these are usually rounded, but their angles may have been
removed by attrition before they entered the mouth of the Sipunculid.
In S. tesselatus the sand is to some extent held together by a mucous deposit; in those
cases where there is no sand in the intestine, there is always a coagulum of mucus, and
the walls are contracted and thick; when full of sand the walls are tensely stretched
and very thin. This thinness of the wall of the alimentary canal seems ill-adapted to a
diet of sand, nevertheless it is also met with in other great sand-eating groups of
animals, such as the Echinids and the Holothurians.
The enormous amount of sand and mud which passes through the bodies of the
Sipunculids shows that they must take a considerable part in modifying the mineral
substances which form the bottom of the sea. Just as earthworms, as shown by
Darwin, play a considerable rôle in the formation of soil, so must these animals, in
conjunction with Echinids and Holothurians, effect considerable modifications in the
sand and mud which pass through their bodies. Mr. J. Y. Buchanan[480] is "led to
believe that the principal agent in the comminution of the mineral matter found at the
bottom of both deep and shallow seas and oceans, is the ground fauna of the sea,
which depends for its subsistence on the organic matter which it can extract from the
mud." The minerals at the bottom of the sea are exposed to a reducing process in
passing through the bodies of the animals which eat them, and subsequently to an
oxidising process due to the oxygen dissolved in the sea-water acting on the minerals
extruded from the animals' bodies.
The rate at which the sand passes through the body of Sipunculus is unfortunately
unknown, but that at any one moment a considerable quantity is contained in the
intestine is shown by the fact that the average weight of five specimens of S. nudus
from Naples, taken at random, was 19.08 grms., whilst the average weight of sand
Page 422
washed out of their alimentary canal was 10.03 grms. The sand contained in five other
specimens of the same species measured respectively 6 c.c., 7 c.c., 6.5 c.c., 7.5 c.c.,
and 7.5 c.c., giving an average of 6.9 c.c. for each individual.
Onchnesoma and Tylosoma have only one retractor muscle; Aspidosiphon and
Phascolion have, as a rule, two; Phymosoma and Sipunculus have four, and perhaps
this is the more usual number.
Phascolion, Tylosoma, and Onchnesoma have but one "brown tube"; in Phascolion
this is the right, in Onchnesoma it is sometimes the right and sometimes the left that
persists. Most other genera retain two, but there are many exceptions; for instance,
Phascolosoma squamatum has but one, and so has Aspidosiphon tortus, and in both
cases it is that of the left side. No Sipunculid has more than two. It has been pointed
out by Selenka that those species which have but one brown tube are, as a rule,
inhabitants of tubes or shells, and do not move actively about in the sand.
The eggs of all members of the family, with the exception of the genus Phymosoma,
are spherical, but those of the last-named genus are elliptical. They are always
surrounded by a thick membrane, the "zona radiata," pierced by numerous pores.
Aspidosiphon (Fig. 215) is easily recognised by the presence of two symmetrically-
arranged cuticular shields, one at each end of the trunk. These are formed by the
fusion of minute cuticular plates, such as exist in the skin of most Sipunculids. The
posterior shield is radially symmetrical, but the anterior is somewhat like the shell of a
Pecten, and symmetrical only about one plane. The introvert is protruded from the
acute angle of the anterior shield, and when extended lies almost at right angles to the
trunk, instead of being, as is usually the case, in the same straight line with it. In many
specimens, and these seem as a rule to be the older ones, a deposit of calcium
carbonate takes place over these shields, covering over and concealing their external
markings.
Cloeosiphon (Echinosiphon) has a calcareous ring, consisting of four or five rows of
lozenge-shaped calcareous bodies forming a close mosaic, arranged round the base of
the introvert, which when extended is in the same straight line as the trunk. Each piece
bears a brown spot, which is said to be the pore of a gland (Fig. 217). Golfingia
Lankester, has a cylindrical horny thickening at the anterior end of the trunk and
another at the posterior.
specimens of the same species measured respectively 6 c.c., 7 c.c., 6.5 c.c., 7.5 c.c.,
and 7.5 c.c., giving an average of 6.9 c.c. for each individual.
Onchnesoma and Tylosoma have only one retractor muscle; Aspidosiphon and
Phascolion have, as a rule, two; Phymosoma and Sipunculus have four, and perhaps
this is the more usual number.
Phascolion, Tylosoma, and Onchnesoma have but one "brown tube"; in Phascolion
this is the right, in Onchnesoma it is sometimes the right and sometimes the left that
persists. Most other genera retain two, but there are many exceptions; for instance,
Phascolosoma squamatum has but one, and so has Aspidosiphon tortus, and in both
cases it is that of the left side. No Sipunculid has more than two. It has been pointed
out by Selenka that those species which have but one brown tube are, as a rule,
inhabitants of tubes or shells, and do not move actively about in the sand.
The eggs of all members of the family, with the exception of the genus Phymosoma,
are spherical, but those of the last-named genus are elliptical. They are always
surrounded by a thick membrane, the "zona radiata," pierced by numerous pores.
Aspidosiphon (Fig. 215) is easily recognised by the presence of two symmetrically-
arranged cuticular shields, one at each end of the trunk. These are formed by the
fusion of minute cuticular plates, such as exist in the skin of most Sipunculids. The
posterior shield is radially symmetrical, but the anterior is somewhat like the shell of a
Pecten, and symmetrical only about one plane. The introvert is protruded from the
acute angle of the anterior shield, and when extended lies almost at right angles to the
trunk, instead of being, as is usually the case, in the same straight line with it. In many
specimens, and these seem as a rule to be the older ones, a deposit of calcium
carbonate takes place over these shields, covering over and concealing their external
markings.
Cloeosiphon (Echinosiphon) has a calcareous ring, consisting of four or five rows of
lozenge-shaped calcareous bodies forming a close mosaic, arranged round the base of
the introvert, which when extended is in the same straight line as the trunk. Each piece
bears a brown spot, which is said to be the pore of a gland (Fig. 217). Golfingia
Lankester, has a cylindrical horny thickening at the anterior end of the trunk and
another at the posterior.
Page 423
Fig. 215.—Aspidosiphon truncatus Kef. × 2. a, Introvert partially extended, but not sufficiently to
show the head.
Key to the Genera of Sipunculoidea.[481]
I. The longitudinal muscles in the body-wall divided into 17-41 distinct bundles.
Four retractor muscles.
A. Body covered with papillae. Numerous filiform tentacles which seldom (or
never?) surround the mouth, but stand above and dorsal to it in a horse-shoe,
with the opening dorsal. No rectal caecum. Hooks usually present. Four
retractors (in Ph. Rupellii only two?). Heart almost always without caeca. Eye-
spots always present. Eggs oval, flat, reddish. Almost entirely small tropical
species
1. Phymosoma
B. Body devoid of papillae. Tentacular membrane surrounds the mouth in a
circlet. Rectum with one or more caeca (except S. edulis?). Hooks absent
except in S. australis. Eggs spherical. The tentacular membrane contains a
vascular network. A ventral contractile vessel usually present in addition to the
heart. Mostly large forms. Found in all seas
2. Sipunculus
II. The longitudinal muscles in the body-wall form a continuous sheath, and are
not split up into bundles.
A. Two brown tubes. Numerous tentacles form a wreath round the mouth.
Alimentary canal forms a complete spiral, free behind except in Ph. Hanseni.
Spindle-muscle usually present. One or more ligaments present, but only on
the anterior convolutions of the intestine. Adhesive papillae always absent.
Hooks very frequently absent. Eggs spherical. Found in all seas.
3. Phascolosoma
show the head.
Key to the Genera of Sipunculoidea.[481]
I. The longitudinal muscles in the body-wall divided into 17-41 distinct bundles.
Four retractor muscles.
A. Body covered with papillae. Numerous filiform tentacles which seldom (or
never?) surround the mouth, but stand above and dorsal to it in a horse-shoe,
with the opening dorsal. No rectal caecum. Hooks usually present. Four
retractors (in Ph. Rupellii only two?). Heart almost always without caeca. Eye-
spots always present. Eggs oval, flat, reddish. Almost entirely small tropical
species
1. Phymosoma
B. Body devoid of papillae. Tentacular membrane surrounds the mouth in a
circlet. Rectum with one or more caeca (except S. edulis?). Hooks absent
except in S. australis. Eggs spherical. The tentacular membrane contains a
vascular network. A ventral contractile vessel usually present in addition to the
heart. Mostly large forms. Found in all seas
2. Sipunculus
II. The longitudinal muscles in the body-wall form a continuous sheath, and are
not split up into bundles.
A. Two brown tubes. Numerous tentacles form a wreath round the mouth.
Alimentary canal forms a complete spiral, free behind except in Ph. Hanseni.
Spindle-muscle usually present. One or more ligaments present, but only on
the anterior convolutions of the intestine. Adhesive papillae always absent.
Hooks very frequently absent. Eggs spherical. Found in all seas.
3. Phascolosoma
Page 424
B. Two free brown tubes. Only four or six plumed tentacles. A complete
intestinal spiral, not attached behind. Spindle-muscle always present. One or
more ligaments present, but only on the anterior convolutions of the intestine.
Hooks are present, but sometimes fall off early in life. Heart usually bears
caeca. Found only in the tropics.
4. Dendrostoma
C. Only one brown tube, that of the right side, present; it is attached to the
body-wall throughout its entire length. Numerous tentacles form a circle round
the mouth. The alimentary canal forms no spiral, or an incomplete one. No
spindle-muscle, but the intestine is attached to the body-wall throughout its
length by numerous ligaments. Adhesive papillae often present. Not more than
two retractors. Spherical eggs. Inhabits Mollusc shells or tubes. Found in all
seas
5. Phascolion
III. At both ends of the trunk a distinct horny shield, or tube-like cornification, or
a calcareous ring at the anterior end of the trunk. Hooks sometimes present.
Longitudinal muscles continuous or split up into bundles.
A. A shield at both ends of the trunk. Introvert excentric, arising from the
ventral side of the anterior shield. Tentacles small and few in number, arranged
in a horse-shoe above the mouth. A spindle-muscle, which arises from the
posterior end of the body, traverses the intestinal coil. Two retractors only,
these are the ventral; they are frequently fused together from their point of
origin.
6. Aspidosiphon
B. A calcareous ring surrounds the anterior end of the trunk, from the middle
of which the introvert is extruded. Longitudinal muscles continuous. Hooks
bifid. Tropical.
7. Cloeosiphon
C. A corneous ring, from which the introvert issues, surrounds the anterior end
of the trunk, and the posterior end of the trunk is produced into a corneous
spike. Six pinnate tentacles encircle the mouth. Four retractors. Hooks present
on the introvert. Longitudinal muscles continuous. Intestine not coiled
throughout in a spiral nor fastened posteriorly. Spindle muscle present.
8. Golfingia
intestinal spiral, not attached behind. Spindle-muscle always present. One or
more ligaments present, but only on the anterior convolutions of the intestine.
Hooks are present, but sometimes fall off early in life. Heart usually bears
caeca. Found only in the tropics.
4. Dendrostoma
C. Only one brown tube, that of the right side, present; it is attached to the
body-wall throughout its entire length. Numerous tentacles form a circle round
the mouth. The alimentary canal forms no spiral, or an incomplete one. No
spindle-muscle, but the intestine is attached to the body-wall throughout its
length by numerous ligaments. Adhesive papillae often present. Not more than
two retractors. Spherical eggs. Inhabits Mollusc shells or tubes. Found in all
seas
5. Phascolion
III. At both ends of the trunk a distinct horny shield, or tube-like cornification, or
a calcareous ring at the anterior end of the trunk. Hooks sometimes present.
Longitudinal muscles continuous or split up into bundles.
A. A shield at both ends of the trunk. Introvert excentric, arising from the
ventral side of the anterior shield. Tentacles small and few in number, arranged
in a horse-shoe above the mouth. A spindle-muscle, which arises from the
posterior end of the body, traverses the intestinal coil. Two retractors only,
these are the ventral; they are frequently fused together from their point of
origin.
6. Aspidosiphon
B. A calcareous ring surrounds the anterior end of the trunk, from the middle
of which the introvert is extruded. Longitudinal muscles continuous. Hooks
bifid. Tropical.
7. Cloeosiphon
C. A corneous ring, from which the introvert issues, surrounds the anterior end
of the trunk, and the posterior end of the trunk is produced into a corneous
spike. Six pinnate tentacles encircle the mouth. Four retractors. Hooks present
on the introvert. Longitudinal muscles continuous. Intestine not coiled
throughout in a spiral nor fastened posteriorly. Spindle muscle present.
8. Golfingia
Page 425
IV. No tentacles, but two leaf-like extensions of the body-wall guard the mouth.
Four retractors. Few intestinal loops, quite free. No vascular system.
9. Petalostoma
V. No tentacles, no vascular system. One retractor, and one segmental organ.
A. Introvert long. Body small, pear-shaped.
10. Onchnesoma
B. No introvert (?). Body cylindrical, thickly covered with papillae, which are
larger and more crowded at both ends of the trunk.
11. Tylosoma
Species of Sipunculoidea.—The genus Phymosoma (Fig. 214) contains more species
than any other genus of Sipunculoidea, and they are all of fair size. Twenty-seven
species are known, of which seventeen occur in the Malay Archipelago, thirteen being
found there alone. Phymosoma affects shallow water, the deepest specimens being
taken at a depth of about 50 fathoms; this may be due to the fact that they flourish only
in comparatively warm water. With very few exceptions, they are found only in
tropical seas, very often living in tubular excavations made in soft coral rock.
The genus Sipunculus contains sixteen species. They are the largest and the most
conspicuous members of the group. They have a very wide distribution, some species,
as S. nudus (Fig. 212) and S. australis, being almost cosmopolitan. They are most
common in temperate and tropical seas, but S. norvegicus and S. priapuloides are
found far north, but always at considerable depths, 100 to 200 fathoms.
The following account of the habits of Sipunculus gouldii is taken from Mr.
Andrews'[482] paper on that species:—
"This Sipunculus is very abundant in certain small areas of compact, fine sand
darkened by organic matter and not laid bare at ordinary low tide. In such places, only
a few square metres in extent, they pierce the sand in all directions to a depth of more
than half a metre, making burrows with persistent lumen running from the surface
downward and then laterally, but with no regularity in direction.
"Kept in aquaria, the dependence of the animal upon the nature of the sand and its
method of locomotion may be readily observed. A vigorous individual buries itself in a
few moments in the following manner: Running out the introvert to nearly its full
extent, and applying it to the surface of the sand till some spot of less resistance is
Four retractors. Few intestinal loops, quite free. No vascular system.
9. Petalostoma
V. No tentacles, no vascular system. One retractor, and one segmental organ.
A. Introvert long. Body small, pear-shaped.
10. Onchnesoma
B. No introvert (?). Body cylindrical, thickly covered with papillae, which are
larger and more crowded at both ends of the trunk.
11. Tylosoma
Species of Sipunculoidea.—The genus Phymosoma (Fig. 214) contains more species
than any other genus of Sipunculoidea, and they are all of fair size. Twenty-seven
species are known, of which seventeen occur in the Malay Archipelago, thirteen being
found there alone. Phymosoma affects shallow water, the deepest specimens being
taken at a depth of about 50 fathoms; this may be due to the fact that they flourish only
in comparatively warm water. With very few exceptions, they are found only in
tropical seas, very often living in tubular excavations made in soft coral rock.
The genus Sipunculus contains sixteen species. They are the largest and the most
conspicuous members of the group. They have a very wide distribution, some species,
as S. nudus (Fig. 212) and S. australis, being almost cosmopolitan. They are most
common in temperate and tropical seas, but S. norvegicus and S. priapuloides are
found far north, but always at considerable depths, 100 to 200 fathoms.
The following account of the habits of Sipunculus gouldii is taken from Mr.
Andrews'[482] paper on that species:—
"This Sipunculus is very abundant in certain small areas of compact, fine sand
darkened by organic matter and not laid bare at ordinary low tide. In such places, only
a few square metres in extent, they pierce the sand in all directions to a depth of more
than half a metre, making burrows with persistent lumen running from the surface
downward and then laterally, but with no regularity in direction.
"Kept in aquaria, the dependence of the animal upon the nature of the sand and its
method of locomotion may be readily observed. A vigorous individual buries itself in a
few moments in the following manner: Running out the introvert to nearly its full
extent, and applying it to the surface of the sand till some spot of less resistance is
Page 426
found, the animal still further expands the introvert so that it penetrates the sand,
provided this is not too dense and firm, for then the body is merely shoved backward.
When the introvert is inserted, the contraction of the longitudinal muscles of the body-
wall brings the whole body forward somewhat, in case the introvert is fixed in the
sand. In case soft ooze was present, this fixation did not take place, and the introvert
was merely pulled out again, but when the sand was of the right consistency the
introvert was fixed by becoming much swollen at the tip, and then constricted just
posterior to this swollen area. This bulb-like area exerts lateral pressure on the sand, as
could be seen by movements of the grains. The swelling of the anterior end of the
introvert is brought about by the body-wall contracting elsewhere, and forcing in
liquid to distend that end. Owing to the curved form assumed by the body in the
normal contracted state when first removed from its burrow, the entrance of the
introvert may often be nearly vertical, and hence the entire body is soon raised nearly
upright in the water above the sand. If the body has thus been warped forward
sufficiently to become somewhat fixed in the sand, the introvert is rolled in and again
thrust forward from this new point of resistance, and so on till the animal is entirely
buried. This locomotion increases in speed as the creature becomes more completely
surrounded by sand, and is the only means of moving from place to place.
"On a smooth surface, or on one not presenting the right degree of resistance, the
Sipunculus does not change its position, but remains till death finally occurs, rolling
its introvert in and out and contracting its body-wall to no purpose.
"The essential factors in the mechanism bringing about this hydrostatic locomotion are
an elongated contractile sac filled with liquid, and some means of definitely co-
ordinating the contractions of the sac.
"In natural environment the animals are found with sometimes one, sometimes the
other end nearer the surface of the sand: in the aquaria the same was observed, but
when the water became stagnant and impure the anterior end with expanded branchiae
was often protruded somewhat above the surface of the sand."
The genus Phascolosoma contains at least twenty-five species, for the most part small.
Ph. margaritaceum, however, measures[483] 10 cm. in length, and Ph. flagriferum, 13
cm. The latter is produced at the hinder end of its trunk into a long whip-like process,
which recalls the horny spike of Golfingia. Most species live free, but a few inhabit
the shells of dead Gasteropods or of Dentalium, or the abandoned tubes of worms.
They occur in practically all seas.
provided this is not too dense and firm, for then the body is merely shoved backward.
When the introvert is inserted, the contraction of the longitudinal muscles of the body-
wall brings the whole body forward somewhat, in case the introvert is fixed in the
sand. In case soft ooze was present, this fixation did not take place, and the introvert
was merely pulled out again, but when the sand was of the right consistency the
introvert was fixed by becoming much swollen at the tip, and then constricted just
posterior to this swollen area. This bulb-like area exerts lateral pressure on the sand, as
could be seen by movements of the grains. The swelling of the anterior end of the
introvert is brought about by the body-wall contracting elsewhere, and forcing in
liquid to distend that end. Owing to the curved form assumed by the body in the
normal contracted state when first removed from its burrow, the entrance of the
introvert may often be nearly vertical, and hence the entire body is soon raised nearly
upright in the water above the sand. If the body has thus been warped forward
sufficiently to become somewhat fixed in the sand, the introvert is rolled in and again
thrust forward from this new point of resistance, and so on till the animal is entirely
buried. This locomotion increases in speed as the creature becomes more completely
surrounded by sand, and is the only means of moving from place to place.
"On a smooth surface, or on one not presenting the right degree of resistance, the
Sipunculus does not change its position, but remains till death finally occurs, rolling
its introvert in and out and contracting its body-wall to no purpose.
"The essential factors in the mechanism bringing about this hydrostatic locomotion are
an elongated contractile sac filled with liquid, and some means of definitely co-
ordinating the contractions of the sac.
"In natural environment the animals are found with sometimes one, sometimes the
other end nearer the surface of the sand: in the aquaria the same was observed, but
when the water became stagnant and impure the anterior end with expanded branchiae
was often protruded somewhat above the surface of the sand."
The genus Phascolosoma contains at least twenty-five species, for the most part small.
Ph. margaritaceum, however, measures[483] 10 cm. in length, and Ph. flagriferum, 13
cm. The latter is produced at the hinder end of its trunk into a long whip-like process,
which recalls the horny spike of Golfingia. Most species live free, but a few inhabit
the shells of dead Gasteropods or of Dentalium, or the abandoned tubes of worms.
They occur in practically all seas.
Page 427
Fig. 216.—Specimens of the Coral Heteropsammia cochlea, with Aspidosiphon
heteropsammiarum or A. michelini living in a state of commensalism with them. (From
Bouvier.)
Dendrostoma contains but five species, which are all found within the tropics in the
Pacific or in the West Atlantic. They are shallow-water forms, and some are found
between tide-marks.
Phascolion is a smaller genus, containing but ten species, which may have been
derived independently from different species of Phascolosoma, and in this case the
genus should be broken up. The members of this genus live in Mollusc shells, such as
Dentalium, Turritella, Buccinum, Chenopus (Aporrhais), Nassa, Strombus, and
generally acquire the coiled shape of their host. They are usually attached to the shell
by means of certain adhesive papillae found on their posterior end. Ph. strombi fills its
shell with mud, which must be kept together by some secretion of the animal. The
body lies in a tube in this mud, and the introvert projects from the small round opening
at the end of the tube, and explores the ground in every direction. They are found in all
seas, but more especially in the colder waters.
Fig. 217.—Cloeosiphon aspergillum Quatr. × ½. a, Introvert covered with spines and partially
extended, but not sufficiently to show the head; b, calcareous plates surrounding the point of
origin of the introvert.
The genus Aspidosiphon includes nineteen species, which are, with few exceptions,
exclusively confined to the Indian Ocean and neighbouring seas, including the Red
Sea. The exceptions are A. armatus from the Norwegian coast, and A. mülleri from the
heteropsammiarum or A. michelini living in a state of commensalism with them. (From
Bouvier.)
Dendrostoma contains but five species, which are all found within the tropics in the
Pacific or in the West Atlantic. They are shallow-water forms, and some are found
between tide-marks.
Phascolion is a smaller genus, containing but ten species, which may have been
derived independently from different species of Phascolosoma, and in this case the
genus should be broken up. The members of this genus live in Mollusc shells, such as
Dentalium, Turritella, Buccinum, Chenopus (Aporrhais), Nassa, Strombus, and
generally acquire the coiled shape of their host. They are usually attached to the shell
by means of certain adhesive papillae found on their posterior end. Ph. strombi fills its
shell with mud, which must be kept together by some secretion of the animal. The
body lies in a tube in this mud, and the introvert projects from the small round opening
at the end of the tube, and explores the ground in every direction. They are found in all
seas, but more especially in the colder waters.
Fig. 217.—Cloeosiphon aspergillum Quatr. × ½. a, Introvert covered with spines and partially
extended, but not sufficiently to show the head; b, calcareous plates surrounding the point of
origin of the introvert.
The genus Aspidosiphon includes nineteen species, which are, with few exceptions,
exclusively confined to the Indian Ocean and neighbouring seas, including the Red
Sea. The exceptions are A. armatus from the Norwegian coast, and A. mülleri from the
Page 428
Mediterranean and Adriatic. A. truncatus is also stated to occur at Panama, the
Bahamas, and at Mauritius. The remaining species almost all occur in the Malay
Archipelago and neighbouring islands, and as was the case with Phymosoma, this part
of the world seems to be the headquarters of the genus. A. mülleri lives in the
interstices of rocks and stones, and occasionally in disused Mollusc shells.
Two species of Aspidosiphon have been described by Bouvier[484] living in a state of
commensalism with two species of Madreporarian corals, Stephanoceris rousseaui
and Heteropsammia cochlea, which live on and surrounding the shells of certain
Molluscs at Aden (Fig. 216). Apparently the Gephyrean takes up its abode within its
house at a tender age, and according to Bouvier, it provides for its increasing bulk by
secreting a coiled calcareous tube, the outer surface of which affords space for the
growth of the coral.
The genus Cloeosiphon, the Echinosiphon of Sluiter, includes three species: C.
aspergillum (Fig. 217), C. molle, and C. javanicum. The first named occurs at
Mauritius, the Malay Archipelago, and neighbouring islands; the others are confined
to the last-named area, which thus again forms the headquarters of a genus.
Golfingia, described by Lankester from a single specimen, was dredged in St.
Andrews Bay, at the depth of 10 fathoms.
Petalostoma comprises but one species, P. minutum, which is found in the English
Channel.
Onchnesoma comprises two species, O. steenstrupii and O. sarsii, both found off the
coast of Norway at considerable depths between 200 and 300 fathoms.
Tylosoma comprises one species, T. lütkenii, also from the Norwegian coast. It is
dredged from stony ground in 50 to 80 fathoms.
II. Order Priapuloidea.
Anatomy.—This Order consists of the two genera Priapulus and Halicryptus. Both
are cylindrical animals with the mouth at one end and the anus at the other. The
introvert is short, and is covered with rows of chitinous spines, which are continued to
some extent over the body.
The skin is folded in a series of rings, and the body is usually somewhat swollen
posteriorly. P. caudatus bears a curious caudal appendage, beset with a number of
Bahamas, and at Mauritius. The remaining species almost all occur in the Malay
Archipelago and neighbouring islands, and as was the case with Phymosoma, this part
of the world seems to be the headquarters of the genus. A. mülleri lives in the
interstices of rocks and stones, and occasionally in disused Mollusc shells.
Two species of Aspidosiphon have been described by Bouvier[484] living in a state of
commensalism with two species of Madreporarian corals, Stephanoceris rousseaui
and Heteropsammia cochlea, which live on and surrounding the shells of certain
Molluscs at Aden (Fig. 216). Apparently the Gephyrean takes up its abode within its
house at a tender age, and according to Bouvier, it provides for its increasing bulk by
secreting a coiled calcareous tube, the outer surface of which affords space for the
growth of the coral.
The genus Cloeosiphon, the Echinosiphon of Sluiter, includes three species: C.
aspergillum (Fig. 217), C. molle, and C. javanicum. The first named occurs at
Mauritius, the Malay Archipelago, and neighbouring islands; the others are confined
to the last-named area, which thus again forms the headquarters of a genus.
Golfingia, described by Lankester from a single specimen, was dredged in St.
Andrews Bay, at the depth of 10 fathoms.
Petalostoma comprises but one species, P. minutum, which is found in the English
Channel.
Onchnesoma comprises two species, O. steenstrupii and O. sarsii, both found off the
coast of Norway at considerable depths between 200 and 300 fathoms.
Tylosoma comprises one species, T. lütkenii, also from the Norwegian coast. It is
dredged from stony ground in 50 to 80 fathoms.
II. Order Priapuloidea.
Anatomy.—This Order consists of the two genera Priapulus and Halicryptus. Both
are cylindrical animals with the mouth at one end and the anus at the other. The
introvert is short, and is covered with rows of chitinous spines, which are continued to
some extent over the body.
The skin is folded in a series of rings, and the body is usually somewhat swollen
posteriorly. P. caudatus bears a curious caudal appendage, beset with a number of
Page 429
hollow lobes somewhat grape-like in appearance. This is situated ventral to the anus;
its lumen is continuous with that of the body-cavity, but it can be separated from it by
the action of a sphincter muscle. Two such appendages exist in P. bicaudatus.
There cannot be said to be any head in the Priapuloidea; they have no tentacles or
tentacular fringe, no proboscis, and no distinct brain; simply a round aperture, the
mouth, which is surrounded by a groove in the skin, at the bottom of which the
circumoesophageal nerve-cord lies. The mouth leads into a very muscular pharynx
lined with stout chitinous teeth; this passes into an intestine, which is as a rule straight,
but in P. glandifer it has a single loop.
The Priapuloidea possess no vascular system and no brown tubes. Their skin has in the
main the same structure as that of the Sipunculids, with spines, glandular bodies, and
papillae with sensory hairs which resemble similar structures on Phymosoma varians.
Retractor muscles arise from the longitudinal muscles of the skin, and are inserted into
the pharynx; they are short and not constant in number.
The nervous system has retained throughout its primitive connexion with the
epidermis. In almost all animals the nervous system is formed from the epiblast or
outermost cellular layer of the embryo; it usually, however, breaks away from this and
sinks into the body. Thus in Sipunculus it lies within the body-cavity, and has retained
its primitive connexion with the outer layers of the skin only in the region of the brain;
but in the Priapulids the nervous system, which consists of a ring round the mouth and
of a ventral cord, lies embedded in the skin, and the nerve cells are directly continuous
with the cells of the epidermis. The nerve-ring lies at the base of a groove in the skin,
which forms a kind of gutter round the mouth; the ventral nerve-cord is visible
exteriorly as a light line which marks the ventral surface of the animal. In no place is
the ring or cord differentiated in any way, and there cannot be said to be any brain or
special sense-organs. Numerous nerves are given off from the ring to the pharynx and
intestine, and from the cord to the body-wall.
Fig. 218.—Priapulus caudatus Lam. Nat. size. a, Mouth surrounded by spines.
its lumen is continuous with that of the body-cavity, but it can be separated from it by
the action of a sphincter muscle. Two such appendages exist in P. bicaudatus.
There cannot be said to be any head in the Priapuloidea; they have no tentacles or
tentacular fringe, no proboscis, and no distinct brain; simply a round aperture, the
mouth, which is surrounded by a groove in the skin, at the bottom of which the
circumoesophageal nerve-cord lies. The mouth leads into a very muscular pharynx
lined with stout chitinous teeth; this passes into an intestine, which is as a rule straight,
but in P. glandifer it has a single loop.
The Priapuloidea possess no vascular system and no brown tubes. Their skin has in the
main the same structure as that of the Sipunculids, with spines, glandular bodies, and
papillae with sensory hairs which resemble similar structures on Phymosoma varians.
Retractor muscles arise from the longitudinal muscles of the skin, and are inserted into
the pharynx; they are short and not constant in number.
The nervous system has retained throughout its primitive connexion with the
epidermis. In almost all animals the nervous system is formed from the epiblast or
outermost cellular layer of the embryo; it usually, however, breaks away from this and
sinks into the body. Thus in Sipunculus it lies within the body-cavity, and has retained
its primitive connexion with the outer layers of the skin only in the region of the brain;
but in the Priapulids the nervous system, which consists of a ring round the mouth and
of a ventral cord, lies embedded in the skin, and the nerve cells are directly continuous
with the cells of the epidermis. The nerve-ring lies at the base of a groove in the skin,
which forms a kind of gutter round the mouth; the ventral nerve-cord is visible
exteriorly as a light line which marks the ventral surface of the animal. In no place is
the ring or cord differentiated in any way, and there cannot be said to be any brain or
special sense-organs. Numerous nerves are given off from the ring to the pharynx and
intestine, and from the cord to the body-wall.
Fig. 218.—Priapulus caudatus Lam. Nat. size. a, Mouth surrounded by spines.
Page 430
The sexes are distinct, but they differ from the other Gephyrea in the nature of their
reproductive organs. In mature specimens the ovaries or testes are easily recognisable,
lying to the right and left of the alimentary canal. The reproductive glands are
continuous with ducts, which act as oviducts and vasa deferentia respectively. Both
glands and ducts are attached to the body-wall by a mesentery.
The excretory function is performed in the Priapuloidea by the ducts of the generative
organs. These are primarily connected with a number of branching canals of small size
which project into the body-cavity. According to Schauinsland,[485] one or more pear-
shaped cells are found at the end of each branch, and each is continued into a long
cilium which hangs down into the lumen of the canal, and by its movement produces a
flickering motion. Beyond the free end of the large cilium the canal is lined with
ciliated cells. The remarkable resemblance this form of excretory organ presents to
that of the Platyhelminthes (vide p. 25) and of certain Chaetopods is worthy of
attention. In the young Priapuloidea the duct with its branching canals is not masked
by the generative organs, but as the animals become mature, diverticula from the duct
arise, and the cells covering these become modified into ova in the female, and into
spermatozoa in the male. The presence of these follicles masks the excretory part of
the gland. The ova and spermatozoa escape through the ciliated ducts which open to
the exterior one on each side of the anus, and, contrary to what is the case with other
Gephyrea, leave the body without having ever been in the body-cavity.
Nothing is known of the embryology of either member of this family, but both genera
appear to be sexually mature from the end of May until October.
Classification.—The two genera which make up the Order Priapuloidea are
characterised as follows:—
Priapulus.—The body is continued into one or two caudal appendages, beset with
hollow papillae; these are ventral to the anus. The introvert forms ¼ to ⅓ of the total
body-length; it is covered with spines in conspicuous longitudinal rows, the rest of the
body being ringed. The retractor muscles are numerous, and are attached to the body-
wall, some anteriorly and some posteriorly.
The genus includes the following five species:—
P. caudatus Lam. (Fig. 218). Hab. Coasts of Greenland, Norway, Great Britain,
the North Sea, and the Baltic.
P. bicaudatus Dan. Hab. North Sea and Arctic Ocean.
reproductive organs. In mature specimens the ovaries or testes are easily recognisable,
lying to the right and left of the alimentary canal. The reproductive glands are
continuous with ducts, which act as oviducts and vasa deferentia respectively. Both
glands and ducts are attached to the body-wall by a mesentery.
The excretory function is performed in the Priapuloidea by the ducts of the generative
organs. These are primarily connected with a number of branching canals of small size
which project into the body-cavity. According to Schauinsland,[485] one or more pear-
shaped cells are found at the end of each branch, and each is continued into a long
cilium which hangs down into the lumen of the canal, and by its movement produces a
flickering motion. Beyond the free end of the large cilium the canal is lined with
ciliated cells. The remarkable resemblance this form of excretory organ presents to
that of the Platyhelminthes (vide p. 25) and of certain Chaetopods is worthy of
attention. In the young Priapuloidea the duct with its branching canals is not masked
by the generative organs, but as the animals become mature, diverticula from the duct
arise, and the cells covering these become modified into ova in the female, and into
spermatozoa in the male. The presence of these follicles masks the excretory part of
the gland. The ova and spermatozoa escape through the ciliated ducts which open to
the exterior one on each side of the anus, and, contrary to what is the case with other
Gephyrea, leave the body without having ever been in the body-cavity.
Nothing is known of the embryology of either member of this family, but both genera
appear to be sexually mature from the end of May until October.
Classification.—The two genera which make up the Order Priapuloidea are
characterised as follows:—
Priapulus.—The body is continued into one or two caudal appendages, beset with
hollow papillae; these are ventral to the anus. The introvert forms ¼ to ⅓ of the total
body-length; it is covered with spines in conspicuous longitudinal rows, the rest of the
body being ringed. The retractor muscles are numerous, and are attached to the body-
wall, some anteriorly and some posteriorly.
The genus includes the following five species:—
P. caudatus Lam. (Fig. 218). Hab. Coasts of Greenland, Norway, Great Britain,
the North Sea, and the Baltic.
P. bicaudatus Dan. Hab. North Sea and Arctic Ocean.
Page 431
P. glandifer Ehlers. Hab. Coast of Greenland, North Sea.
P. brevicaudatus Ehlers. Hab. North Sea and Baltic, from ten fathoms.
P. tuberculato-spinosus Baird. Hab. Falkland Islands.
Halicryptus.—No caudal appendages. Introvert ⅒ to 1⁄12 of the total body length,
with numerous spines arranged in close circles. Retractors numerous and all attached
to the body-wall anteriorly.
H. spinulosus v. Sieb. (Fig. 219). Hab. North Sea, Arctic Ocean, and Baltic, in
from two to fifty fathoms.
It will be noticed that with the exception of P. tuberculato-spinosus, described by
Baird from a single specimen, the whole family is confined to northern seas.
Habits.—The newly-captured specimens of both P. caudatus and H. spinulosus are of
a flesh colour, with a somewhat metallic sheen. According to Apel, the latter lived in
an aquarium for more than five months, whilst the former died during the first month.
When first introduced into the aquarium they immediately began to busy themselves
in the mud or sand at its bottom, and very seldom showed themselves above it. They
forced their way into the sand by alternately contracting and extending their introvert,
and the Priapulus arranged itself so that a portion, often a very small one, of its caudal
appendage was exposed to the water; this fact supports the view that the appendage is
respiratory in function. When the animal buries itself deeply, the appendage does not
relinquish its position at the surface of the sand, but stretches itself until it in some
cases surpasses the length of the body. On the other hand, Halicryptus (Fig. 219),
according to the same observer, lies with the anterior end, the mouth, projecting from
the surface of the sand, or else it curves itself, so that both ends project into the water.
Fig. 219.—Halicryptus spinulosus v. Sieb. × 6. a, Dark line indicating the position of the ventral
nerve-cord; d, mouth surrounded by spines.
P. brevicaudatus Ehlers. Hab. North Sea and Baltic, from ten fathoms.
P. tuberculato-spinosus Baird. Hab. Falkland Islands.
Halicryptus.—No caudal appendages. Introvert ⅒ to 1⁄12 of the total body length,
with numerous spines arranged in close circles. Retractors numerous and all attached
to the body-wall anteriorly.
H. spinulosus v. Sieb. (Fig. 219). Hab. North Sea, Arctic Ocean, and Baltic, in
from two to fifty fathoms.
It will be noticed that with the exception of P. tuberculato-spinosus, described by
Baird from a single specimen, the whole family is confined to northern seas.
Habits.—The newly-captured specimens of both P. caudatus and H. spinulosus are of
a flesh colour, with a somewhat metallic sheen. According to Apel, the latter lived in
an aquarium for more than five months, whilst the former died during the first month.
When first introduced into the aquarium they immediately began to busy themselves
in the mud or sand at its bottom, and very seldom showed themselves above it. They
forced their way into the sand by alternately contracting and extending their introvert,
and the Priapulus arranged itself so that a portion, often a very small one, of its caudal
appendage was exposed to the water; this fact supports the view that the appendage is
respiratory in function. When the animal buries itself deeply, the appendage does not
relinquish its position at the surface of the sand, but stretches itself until it in some
cases surpasses the length of the body. On the other hand, Halicryptus (Fig. 219),
according to the same observer, lies with the anterior end, the mouth, projecting from
the surface of the sand, or else it curves itself, so that both ends project into the water.
Fig. 219.—Halicryptus spinulosus v. Sieb. × 6. a, Dark line indicating the position of the ventral
nerve-cord; d, mouth surrounded by spines.
Page 432
Leckenby, who described specimens of P. caudatus which were found by fishermen
searching for worms for bait in the outer harbour at Scarborough at half tide, states
that they live in sandy clay in U-shaped tubes, at a depth of about 9 inches, the tubes
opening at each end on to the surface of the sand. The fishermen of this district call
them "sea mushrooms."
Halicryptus casts its cuticle in May and September; it becomes loose first at the hinder
end, and the split between it and the skin grows forward until the animal lies free in a
cuticular mantle. After some days this is split, and the animal frees itself from it; the
cast-off cuticle includes for a short distance the lining of the mouth, the anus, and the
two generative pores.
III. Order Echiuroidea.
Anatomy.—The most striking peculiarity of the Echiuroidea, as opposed to the other
two families of the Gephyrea, is the presence of a solid dorsal outgrowth of a portion
of the head, forming the proboscis. The nature of this proboscis is something quite
different from that of the introvert of the Sipunculoidea; it would appear to correspond
to an extension, in the members of the last-named Order, of that part of the head which
is dorsal to the mouth and is covered by a peculiar pigment-epithelium, often in
continuity with the brain. In its outgrowth this portion of the body has carried with it
the nerve-ring and the vascular ring, which both surround the mouth. The proboscis is
found in all the genera with the exception of the aberrant genus Saccosoma.
Fig. 220.—A, Bonellia viridis Rol., ♀; B, B. fuliginosa. Both nat. size. a, Grooved proboscis; b,
mouth; c, ventral hooks; d, anus.
The body of the female Bonellia viridis, one of the best known species of Echiurids, is
shaped like a small sausage, and is usually about 2 inches long. The proboscis arises
from the anterior end, and is extremely extensible. At the distal end the proboscis
searching for worms for bait in the outer harbour at Scarborough at half tide, states
that they live in sandy clay in U-shaped tubes, at a depth of about 9 inches, the tubes
opening at each end on to the surface of the sand. The fishermen of this district call
them "sea mushrooms."
Halicryptus casts its cuticle in May and September; it becomes loose first at the hinder
end, and the split between it and the skin grows forward until the animal lies free in a
cuticular mantle. After some days this is split, and the animal frees itself from it; the
cast-off cuticle includes for a short distance the lining of the mouth, the anus, and the
two generative pores.
III. Order Echiuroidea.
Anatomy.—The most striking peculiarity of the Echiuroidea, as opposed to the other
two families of the Gephyrea, is the presence of a solid dorsal outgrowth of a portion
of the head, forming the proboscis. The nature of this proboscis is something quite
different from that of the introvert of the Sipunculoidea; it would appear to correspond
to an extension, in the members of the last-named Order, of that part of the head which
is dorsal to the mouth and is covered by a peculiar pigment-epithelium, often in
continuity with the brain. In its outgrowth this portion of the body has carried with it
the nerve-ring and the vascular ring, which both surround the mouth. The proboscis is
found in all the genera with the exception of the aberrant genus Saccosoma.
Fig. 220.—A, Bonellia viridis Rol., ♀; B, B. fuliginosa. Both nat. size. a, Grooved proboscis; b,
mouth; c, ventral hooks; d, anus.
The body of the female Bonellia viridis, one of the best known species of Echiurids, is
shaped like a small sausage, and is usually about 2 inches long. The proboscis arises
from the anterior end, and is extremely extensible. At the distal end the proboscis
Page 433
splits into two short arms, which are often recurved; along the whole ventral surface
runs a groove lined with cilia, which by the approximation of its edges can be
converted into a tube. At the bottom of the proboscis the groove opens into the mouth.
Echiurus; Thalassema, and the female Hamingia have short proboscides, which do not
bifurcate but otherwise resemble those of the female Bonellia.
Fig. 221.—View of a female Bonellia viridis Rol., opened along the left side, × 2. a, Proboscis cut
short; b, a bristle passed through the mouth into the pharynx; c, convoluted intestine; d, anal
tufts or vesicles; e, ventral nerve-cord; f, ovary borne on ventral vessel running parallel with
e; g, position of anus; h, points to position of external opening of nephridium; i, nephridium.
This line is on a level with the internal funnel-shaped opening.
The green colour of B. viridis is due to a special pigment, "Bonellein," which at one
time was thought to be identical with chlorophyll. A similar green colour is found in
Hamingia arctica, Thalassema baronii, and the larvae of many forms.
A short distance behind the mouth, on the ventral surface, the female Bonellia and
both sexes of Thalassema and Echiurus bear two incurved stout chitinous hooks; these
gave the name Gephyrea Armata to the above-mentioned genera. In addition to these,
Echiurus has a row of chitinous bristles surrounding the posterior end of the body; the
row is single in E. unicinctus, double in E. pallasii. These bristles are formed, like the
hooks on the introvert of the Sipunculoidea, by epidermal cells; those of B. minor and
of the posterior rings in Echiurus are said to arise each from a single cell, just as the
bristles do in Chaetopods.
The skin consists of very much the same layers as does that of Sipunculus; the cuticle
is thin, the epidermis is modified into numerous glandular cells, papillae, and pits,
from which the bristles arise. A third layer of oblique or circular fibres is usually found
runs a groove lined with cilia, which by the approximation of its edges can be
converted into a tube. At the bottom of the proboscis the groove opens into the mouth.
Echiurus; Thalassema, and the female Hamingia have short proboscides, which do not
bifurcate but otherwise resemble those of the female Bonellia.
Fig. 221.—View of a female Bonellia viridis Rol., opened along the left side, × 2. a, Proboscis cut
short; b, a bristle passed through the mouth into the pharynx; c, convoluted intestine; d, anal
tufts or vesicles; e, ventral nerve-cord; f, ovary borne on ventral vessel running parallel with
e; g, position of anus; h, points to position of external opening of nephridium; i, nephridium.
This line is on a level with the internal funnel-shaped opening.
The green colour of B. viridis is due to a special pigment, "Bonellein," which at one
time was thought to be identical with chlorophyll. A similar green colour is found in
Hamingia arctica, Thalassema baronii, and the larvae of many forms.
A short distance behind the mouth, on the ventral surface, the female Bonellia and
both sexes of Thalassema and Echiurus bear two incurved stout chitinous hooks; these
gave the name Gephyrea Armata to the above-mentioned genera. In addition to these,
Echiurus has a row of chitinous bristles surrounding the posterior end of the body; the
row is single in E. unicinctus, double in E. pallasii. These bristles are formed, like the
hooks on the introvert of the Sipunculoidea, by epidermal cells; those of B. minor and
of the posterior rings in Echiurus are said to arise each from a single cell, just as the
bristles do in Chaetopods.
The skin consists of very much the same layers as does that of Sipunculus; the cuticle
is thin, the epidermis is modified into numerous glandular cells, papillae, and pits,
from which the bristles arise. A third layer of oblique or circular fibres is usually found
Page 434
inside the longitudinal muscle-layer. The proboscis is solid, and contains much
connective-tissue and numerous muscle-fibres running in all directions; the ventral
groove is ciliated.
The alimentary canal in the Echiuroidea consists of a long thin-walled tube with
numerous convolutions; it is not coiled as in Sipunculids, but the loops are irregularly
arranged, and are supported by numerous fine muscular strands which run from the
skin. There is a ciliated groove running along one side of the intestine, as in the
Sipunculids. The anus is terminal. The most striking peculiarity of the alimentary
canal of the Echiurids is the existence of a collateral intestine or "siphon." This is a
narrow tube which arises from the main canal not very far from the mouth, and re-
enters it again lower down. A similar structure occurs in some Echinids, and in the
Capitelliformia (pp. 272, 305). Its function is not certainly known.
Another characteristic feature of the Echiurids is the presence of "anal vesicles,"
branching structures which unite into a common stem opening into the intestine close
to the anus. The free end of each of the branches terminates in a ciliated funnel-shaped
opening. The function of these structures may be excretory, or they may control the
amount of fluid in the body-cavity.
A closed vascular system exists in Echiurids, consisting of a contractile dorsal vessel
running along the dorsal surface of the anterior end of the alimentary canal, and
continued along the axis of the proboscis. At the tip of the proboscis it bifurcates, and
each branch descends along the edge until it reaches the base where, having encircled
the oesophagus, the two unite, and are continued as the ventral vessel which runs
along the dorsal surface of the nerve-cord, and eventually ends blindly. There is also a
vessel which passes from the ventral vessel and encircles the intestine, opening into
the posterior end of the dorsal vessel. In Echiurus the same vessel encircles a stout
muscle which runs from the base of one of the ventral bristles to the other. In
Thalassema Lankester states that the fluid within the vessels is colourless, and does
not contain corpuscles similar to those in the body-cavity fluid.
The "brown tubes" or nephridia vary in number in the Echiurids. In the female
Bonellia there is but one; in B. viridis the right, in B. minor the left usually persists. In
shape, colour, contractility, and minute structure they closely resemble those of
Sipunculus. Hamingia is said to have a pair of brown tubes; Echiurus has two pairs,
except E. chilensis, which has three; their internal openings are produced into long
coiled slits in some genera. Thalassema gigas has one pair; Th. neptuni, Th. baronii,
Th. formosulum, and Th. exilii, two; whilst Th. vegrande, Th. moebii, Th.
erythrogrammon, Th. caudex, and Th. sorbillans have three pairs.
connective-tissue and numerous muscle-fibres running in all directions; the ventral
groove is ciliated.
The alimentary canal in the Echiuroidea consists of a long thin-walled tube with
numerous convolutions; it is not coiled as in Sipunculids, but the loops are irregularly
arranged, and are supported by numerous fine muscular strands which run from the
skin. There is a ciliated groove running along one side of the intestine, as in the
Sipunculids. The anus is terminal. The most striking peculiarity of the alimentary
canal of the Echiurids is the existence of a collateral intestine or "siphon." This is a
narrow tube which arises from the main canal not very far from the mouth, and re-
enters it again lower down. A similar structure occurs in some Echinids, and in the
Capitelliformia (pp. 272, 305). Its function is not certainly known.
Another characteristic feature of the Echiurids is the presence of "anal vesicles,"
branching structures which unite into a common stem opening into the intestine close
to the anus. The free end of each of the branches terminates in a ciliated funnel-shaped
opening. The function of these structures may be excretory, or they may control the
amount of fluid in the body-cavity.
A closed vascular system exists in Echiurids, consisting of a contractile dorsal vessel
running along the dorsal surface of the anterior end of the alimentary canal, and
continued along the axis of the proboscis. At the tip of the proboscis it bifurcates, and
each branch descends along the edge until it reaches the base where, having encircled
the oesophagus, the two unite, and are continued as the ventral vessel which runs
along the dorsal surface of the nerve-cord, and eventually ends blindly. There is also a
vessel which passes from the ventral vessel and encircles the intestine, opening into
the posterior end of the dorsal vessel. In Echiurus the same vessel encircles a stout
muscle which runs from the base of one of the ventral bristles to the other. In
Thalassema Lankester states that the fluid within the vessels is colourless, and does
not contain corpuscles similar to those in the body-cavity fluid.
The "brown tubes" or nephridia vary in number in the Echiurids. In the female
Bonellia there is but one; in B. viridis the right, in B. minor the left usually persists. In
shape, colour, contractility, and minute structure they closely resemble those of
Sipunculus. Hamingia is said to have a pair of brown tubes; Echiurus has two pairs,
except E. chilensis, which has three; their internal openings are produced into long
coiled slits in some genera. Thalassema gigas has one pair; Th. neptuni, Th. baronii,
Th. formosulum, and Th. exilii, two; whilst Th. vegrande, Th. moebii, Th.
erythrogrammon, Th. caudex, and Th. sorbillans have three pairs.
Page 435
The nervous system consists of a ventral cord lying in the body-cavity, as in the
Sipunculoidea, but attached to the skin, and of a circumoesophageal ring. With the
growth of the proboscis this ring is drawn out, and the two branches run along the
sides of the proboscis and unite at the tip. There is no specialisation of brain, nor are
any special sense organs present, but the ventral cord gives off paired nerves at regular
intervals, which, uniting dorsally, form rings in the skin in some and probably in all
species.
The perivisceral fluid is of a dark brown colour in Thalassema, containing numerous
spherical corpuscles deeply impregnated, according to Lankester, with haemoglobin,
and also containing granules of a brown pigment. Haemoglobin is also found in
certain of the muscles and in part of the epithelial lining of the body-cavity. Lankester
also describes the presence of haemoglobin in the corpuscles of the perivisceral fluid
in Hamingia.
The genital glands are, like those of the Sipunculoidea, formed by a special
development of the cells lining the body-cavity. These cells are massed together along
the wall of the ventral blood-vessel. In Echiurus and in Thalassema the cells break off
and float in the body-cavity, developing into ova and spermatozoa. In Bonellia each
cell does not become an egg, but a mass of cells breaks off, one of which increases in
size at the expense of the others and forms the ovum. The mature sexual cells leave the
body through the nephridia.
Fig. 222.—An adult male Bonellia viridis Rol. The original was 1.5 mm. long. The nervous system
is not shown. (After Selenka.). a, Generative pore with spermatozoa coming out; b, anterior
blind end of intestine attached to the parenchymatous tissue by muscular strands; c, green
wandering cells containing chlorophyll; d, parenchymatous connective-tissue; e, epidermis;
i, intestine; j, vas deferens; l, internal opening of vas deferens; m, the left anal vesicle; n,
spermatozoa in the body-cavity.
Sipunculoidea, but attached to the skin, and of a circumoesophageal ring. With the
growth of the proboscis this ring is drawn out, and the two branches run along the
sides of the proboscis and unite at the tip. There is no specialisation of brain, nor are
any special sense organs present, but the ventral cord gives off paired nerves at regular
intervals, which, uniting dorsally, form rings in the skin in some and probably in all
species.
The perivisceral fluid is of a dark brown colour in Thalassema, containing numerous
spherical corpuscles deeply impregnated, according to Lankester, with haemoglobin,
and also containing granules of a brown pigment. Haemoglobin is also found in
certain of the muscles and in part of the epithelial lining of the body-cavity. Lankester
also describes the presence of haemoglobin in the corpuscles of the perivisceral fluid
in Hamingia.
The genital glands are, like those of the Sipunculoidea, formed by a special
development of the cells lining the body-cavity. These cells are massed together along
the wall of the ventral blood-vessel. In Echiurus and in Thalassema the cells break off
and float in the body-cavity, developing into ova and spermatozoa. In Bonellia each
cell does not become an egg, but a mass of cells breaks off, one of which increases in
size at the expense of the others and forms the ovum. The mature sexual cells leave the
body through the nephridia.
Fig. 222.—An adult male Bonellia viridis Rol. The original was 1.5 mm. long. The nervous system
is not shown. (After Selenka.). a, Generative pore with spermatozoa coming out; b, anterior
blind end of intestine attached to the parenchymatous tissue by muscular strands; c, green
wandering cells containing chlorophyll; d, parenchymatous connective-tissue; e, epidermis;
i, intestine; j, vas deferens; l, internal opening of vas deferens; m, the left anal vesicle; n,
spermatozoa in the body-cavity.
Page 436
Bonellia and Hamingia present very interesting cases of sexual dimorphism. In both
genera the female is an animal of considerable size with the normal structure of the
Echiuroidea, but the male (Fig. 222) is a microscopic Planarian-like animal, which
lives in the mouth and in the nephridia of the female. Both in Bonellia[486] and in
Hamingia the male is provided with a pair of hook-like ventral bristles; these are
wanting in the female Hamingia. The surface of the male is ciliated, and the skin
contains circular and longitudinal muscle-fibres. The body-cavity is developed, but
does not reach to either end of the body. The alimentary canal is closed, neither mouth
nor anus existing; it is supported by regularly arranged dorso-ventral muscle strands.
A nerve-ring and a ventral cord exist. There are also two rudimentary organs
corresponding with the anal vesicles of the female, and a single nephridium which acts
as a duct for the spermatozoa; the latter arise from modified cells lining the body-
cavity.
In both sexes the larvae develop to a certain stage without showing any trace of sexual
differentiation, but after this stage, the development of the male is to a certain extent
arrested; in some respects, indeed, it undergoes retrogressive changes. At this time it is
found clinging to the proboscis of the female, thence it makes its way to the mouth,
where it undergoes its final change; and then creeping out, finds its way into the
nephridium of the female, and spends the rest of its life there in a special recess cut off
by a fold from the excretory part of this organ. In Hamingia, however, Lankester, who
first described the male, did not find any in the nephridia, but found five specimens,
each 1⁄12 inch long, within the dilated pharynx of the female.
Development.—In Bonellia and Hamingia it seems probable that the ova are fertilised
in the nephridium of the female; in the other genera they are fertilised in the water
after leaving the body of the mother.
In Thalassema and Echiurus the growth of the embryo results in the formation of a
typical Trochosphere larva, a type widely spread in the animal kingdom, being found
in the Chaetopoda (Fig. 145, A), Polyzoa (p. 510), and Mollusca. The large prae-oral
lobe persists in the Echiuroidea as the proboscis; the mouth is ventral in position, with
usually a ring of cilia encircling the body in front of and behind it; the anus is
posterior and terminal. A pair of larval excretory organs are present, and a special
nervous aggregation of cells at the apex of the prae-oral lobe is usually indicated by
the presence of a bunch of long cilia.
The trunk of the Trochosphere is unsegmented, and in certain groups of animals it
remains so, but in Chaetopods, and in Echiurus and Thalassema, it elongates and
becomes divided up into a series of somites or segments. Of these there are fifteen in
Echiurus, and apparently eleven in Th. mellita; in this stage the Gephyrean larvae have
genera the female is an animal of considerable size with the normal structure of the
Echiuroidea, but the male (Fig. 222) is a microscopic Planarian-like animal, which
lives in the mouth and in the nephridia of the female. Both in Bonellia[486] and in
Hamingia the male is provided with a pair of hook-like ventral bristles; these are
wanting in the female Hamingia. The surface of the male is ciliated, and the skin
contains circular and longitudinal muscle-fibres. The body-cavity is developed, but
does not reach to either end of the body. The alimentary canal is closed, neither mouth
nor anus existing; it is supported by regularly arranged dorso-ventral muscle strands.
A nerve-ring and a ventral cord exist. There are also two rudimentary organs
corresponding with the anal vesicles of the female, and a single nephridium which acts
as a duct for the spermatozoa; the latter arise from modified cells lining the body-
cavity.
In both sexes the larvae develop to a certain stage without showing any trace of sexual
differentiation, but after this stage, the development of the male is to a certain extent
arrested; in some respects, indeed, it undergoes retrogressive changes. At this time it is
found clinging to the proboscis of the female, thence it makes its way to the mouth,
where it undergoes its final change; and then creeping out, finds its way into the
nephridium of the female, and spends the rest of its life there in a special recess cut off
by a fold from the excretory part of this organ. In Hamingia, however, Lankester, who
first described the male, did not find any in the nephridia, but found five specimens,
each 1⁄12 inch long, within the dilated pharynx of the female.
Development.—In Bonellia and Hamingia it seems probable that the ova are fertilised
in the nephridium of the female; in the other genera they are fertilised in the water
after leaving the body of the mother.
In Thalassema and Echiurus the growth of the embryo results in the formation of a
typical Trochosphere larva, a type widely spread in the animal kingdom, being found
in the Chaetopoda (Fig. 145, A), Polyzoa (p. 510), and Mollusca. The large prae-oral
lobe persists in the Echiuroidea as the proboscis; the mouth is ventral in position, with
usually a ring of cilia encircling the body in front of and behind it; the anus is
posterior and terminal. A pair of larval excretory organs are present, and a special
nervous aggregation of cells at the apex of the prae-oral lobe is usually indicated by
the presence of a bunch of long cilia.
The trunk of the Trochosphere is unsegmented, and in certain groups of animals it
remains so, but in Chaetopods, and in Echiurus and Thalassema, it elongates and
becomes divided up into a series of somites or segments. Of these there are fifteen in
Echiurus, and apparently eleven in Th. mellita; in this stage the Gephyrean larvae have
Page 437
again so close a resemblance to the segmenting Chaetopod larvae as to be easily
mistaken for them. The segmentation is shown in the following way: (i.) the middle
layer of cells or mesoblast is typically segmented, and forms septa, which separate
each segment from its neighbours; (ii.) the ventral nerve-cord arises as segmentally-
arranged thickenings of the epiblast, which fuse together, but retain their segmented
appearance for some time; (iii.) the skin shows the segmentation of the body both by
the arrangement of the pigment and by bands of cilia. The latter are replaced in the
adult by rows of spines, and on the fourteenth and fifteenth segments in Echiurus
pallasii by the two peri-anal circles of bristles. Each bristle, like those of Chaetopods,
originates from a single cell.
The anal vesicles arise quite late in the development; when they have acquired their
openings into the body-cavity, they seem to take in water. In Thalassema, as described
by Conn, this is accompanied by remarkable changes, amounting almost to a
metamorphosis. The body increases in bulk fourfold, the cilia of the prae-oral ring
disappear, and the animal now moves only by means of its proboscis; the pigment is
absorbed, and all traces of segmentation disappear. A similar intaking of water is
described by Spengel in Bonellia. In this genus the larva, which is coloured bright
green, and has two brown eye-spots, is not such a typical Trochosphere as is that of
Echiurus and Thalassema.
Fig. 223.—Echiurus pallasii Guér. × ½. a, Mouth at the end of the grooved proboscis; b, ventral
hooks; c, anus.
Nothing is known of the development of Hamingia or of Saccosoma.
Species of Echiuroidea.—Echiurus. Proboscis not bifurcated at the end. Two ventral
hooks and a single or double peri-anal ring of bristles. The body is to a varying extent
marked by rings bearing spines. Two or three (E. chilensis) pairs of nephridia, their
external orifice often lengthened and spirally coiled. Both sexes alike.
mistaken for them. The segmentation is shown in the following way: (i.) the middle
layer of cells or mesoblast is typically segmented, and forms septa, which separate
each segment from its neighbours; (ii.) the ventral nerve-cord arises as segmentally-
arranged thickenings of the epiblast, which fuse together, but retain their segmented
appearance for some time; (iii.) the skin shows the segmentation of the body both by
the arrangement of the pigment and by bands of cilia. The latter are replaced in the
adult by rows of spines, and on the fourteenth and fifteenth segments in Echiurus
pallasii by the two peri-anal circles of bristles. Each bristle, like those of Chaetopods,
originates from a single cell.
The anal vesicles arise quite late in the development; when they have acquired their
openings into the body-cavity, they seem to take in water. In Thalassema, as described
by Conn, this is accompanied by remarkable changes, amounting almost to a
metamorphosis. The body increases in bulk fourfold, the cilia of the prae-oral ring
disappear, and the animal now moves only by means of its proboscis; the pigment is
absorbed, and all traces of segmentation disappear. A similar intaking of water is
described by Spengel in Bonellia. In this genus the larva, which is coloured bright
green, and has two brown eye-spots, is not such a typical Trochosphere as is that of
Echiurus and Thalassema.
Fig. 223.—Echiurus pallasii Guér. × ½. a, Mouth at the end of the grooved proboscis; b, ventral
hooks; c, anus.
Nothing is known of the development of Hamingia or of Saccosoma.
Species of Echiuroidea.—Echiurus. Proboscis not bifurcated at the end. Two ventral
hooks and a single or double peri-anal ring of bristles. The body is to a varying extent
marked by rings bearing spines. Two or three (E. chilensis) pairs of nephridia, their
external orifice often lengthened and spirally coiled. Both sexes alike.
Page 438
Greef[487] mentions six species of Echiurus, viz. E. pallasii, E. forcipatus, E.
sitchaensis, E. chilensis, E. carabaicus, and E. chrysacanthophorus; to these must be
added E. unicinctus. It seems probable that E. forcipatus of Reinhardt is identical with
E. pallasii, although bigger, whilst E. sitchaensis, E. carabaicus, and E.
chrysacanthophorus are inadequately described. The distribution of the remaining
three species is as follows:—
E. pallasii Guérin (Fig. 223). North Sea, Atlantic, English Channel.
E. unicinctus Drasche. Japan.
E. chilensis Max Müller. Chili.
Thalassema.—Proboscis rather pointed at the end, not bifurcated. No peri-anal
bristles, but two ventral hook-like bristles placed anteriorly. One to three or four pairs
of nephridia. The sexes resemble each other.
Greef mentions eight species of Thalassema and Rietsch thirteen; three of these,
however, Th. grohmanni, Th. lessonii, and Th. pelzelnii, were not seen by either
author, and their description is taken from Diesing. There is some reason for thinking
that the two first-named species are identical with Th. neptuni. Conn has established a
new species for the specimens whose embryology he worked out at Beaufort, Virginia,
and Selenka described a new species from the Challenger material.
With the exception of the three doubtful species mentioned above, the list of species of
Thalassema is as follows:—
Th. neptuni Gaertner (Fig. 224). English Channel (Devonshire coast),
Concarneau, Mediterranean (Gulf of Marseilles), Irish coast (Dungarvan).
Th. gigas Max Müller. Trieste.
Th. vegrande Lampert. Philippine Islands.
Th. baronii Greef. Canary Islands (Lanzarote).
Th. formosulum Lampert. Shanghai and Philippine Islands.
Th. exilii Fr. Müller. Brazil (Desterro).
sitchaensis, E. chilensis, E. carabaicus, and E. chrysacanthophorus; to these must be
added E. unicinctus. It seems probable that E. forcipatus of Reinhardt is identical with
E. pallasii, although bigger, whilst E. sitchaensis, E. carabaicus, and E.
chrysacanthophorus are inadequately described. The distribution of the remaining
three species is as follows:—
E. pallasii Guérin (Fig. 223). North Sea, Atlantic, English Channel.
E. unicinctus Drasche. Japan.
E. chilensis Max Müller. Chili.
Thalassema.—Proboscis rather pointed at the end, not bifurcated. No peri-anal
bristles, but two ventral hook-like bristles placed anteriorly. One to three or four pairs
of nephridia. The sexes resemble each other.
Greef mentions eight species of Thalassema and Rietsch thirteen; three of these,
however, Th. grohmanni, Th. lessonii, and Th. pelzelnii, were not seen by either
author, and their description is taken from Diesing. There is some reason for thinking
that the two first-named species are identical with Th. neptuni. Conn has established a
new species for the specimens whose embryology he worked out at Beaufort, Virginia,
and Selenka described a new species from the Challenger material.
With the exception of the three doubtful species mentioned above, the list of species of
Thalassema is as follows:—
Th. neptuni Gaertner (Fig. 224). English Channel (Devonshire coast),
Concarneau, Mediterranean (Gulf of Marseilles), Irish coast (Dungarvan).
Th. gigas Max Müller. Trieste.
Th. vegrande Lampert. Philippine Islands.
Th. baronii Greef. Canary Islands (Lanzarote).
Th. formosulum Lampert. Shanghai and Philippine Islands.
Th. exilii Fr. Müller. Brazil (Desterro).
Page 439
Th. moebii Greef. Mauritius.
Th. erythrogrammon Max Müller. Red Sea and East Indies (Billiton).
Th. caudex Lampert. Red Sea and Indian Ocean.
Th. sorbillans Lampert. Philippine Islands.
Th. mellita Conn. West Atlantic (Beaufort).
Th. faex Selenka. North of the Faroe Islands.
Bonellia.—Proboscis very extensible and bifurcated at the end. The body and
proboscis are coloured a bright green. Two ventral hook-like bristles, but no peri-anal
ring. A single nephridium. The above applies to the female; the males are degenerate,
and live in the nephridium or pharynx of the female.
Three (or four?) species of this genus are known.
B. viridis Rolando (Fig. 220). Mediterranean, Adriatic, North Sea (Bergen).
B. minor Marion. Mediterranean (Gulf of Marseilles, Naples).
B. suhmii Selenka. Off Nova Scotia. Male not known.
B. fuliginosa Rolando? (Fig. 220). Mediterranean (Naples).
Hamingia.—Proboscis not bifurcated, about as long as body. No ventral hook-like
bristles. One or two nephridia, which open at the apex of one or two well-marked
papillae. The above applies to the female; as in the genus Bonellia, the male is minute
and parasitic. It has two well-marked hook-like bristles situated behind the genital
pore.
This genus was first described by Koren and Danielssen as H. arctica. Two specimens
were afterwards described by Horst as H. glacialis. Later Lankester described two
other specimens; he was the first to find the male in the pharynx of the female. He is
of the opinion that all three descriptions apply to the same species, and for this the
original name H. arctica must be retained.
Th. erythrogrammon Max Müller. Red Sea and East Indies (Billiton).
Th. caudex Lampert. Red Sea and Indian Ocean.
Th. sorbillans Lampert. Philippine Islands.
Th. mellita Conn. West Atlantic (Beaufort).
Th. faex Selenka. North of the Faroe Islands.
Bonellia.—Proboscis very extensible and bifurcated at the end. The body and
proboscis are coloured a bright green. Two ventral hook-like bristles, but no peri-anal
ring. A single nephridium. The above applies to the female; the males are degenerate,
and live in the nephridium or pharynx of the female.
Three (or four?) species of this genus are known.
B. viridis Rolando (Fig. 220). Mediterranean, Adriatic, North Sea (Bergen).
B. minor Marion. Mediterranean (Gulf of Marseilles, Naples).
B. suhmii Selenka. Off Nova Scotia. Male not known.
B. fuliginosa Rolando? (Fig. 220). Mediterranean (Naples).
Hamingia.—Proboscis not bifurcated, about as long as body. No ventral hook-like
bristles. One or two nephridia, which open at the apex of one or two well-marked
papillae. The above applies to the female; as in the genus Bonellia, the male is minute
and parasitic. It has two well-marked hook-like bristles situated behind the genital
pore.
This genus was first described by Koren and Danielssen as H. arctica. Two specimens
were afterwards described by Horst as H. glacialis. Later Lankester described two
other specimens; he was the first to find the male in the pharynx of the female. He is
of the opinion that all three descriptions apply to the same species, and for this the
original name H. arctica must be retained.
Page 440
Hamingia arctica K. and D. Two hundred miles north of North Cape and in the
Hardanger Fjord.
Saccosoma.—No proboscis. The body is flask-shaped. The mouth and anus are
terminal. The ovary is anterior, and there is only one nephridium. No bristles.
Our knowledge of this remarkable Gephyrean is very incomplete, but such as it is, it is
due to the careful investigations of Koren and Danielssen, who had only a single
specimen at their disposition.
Saccosoma vitreum K. and D. North of the Faroe Islands.
Habits of the Echiuroidea.—As a rule the members of this group conceal their
bodies in clefts and fissures of rocks and stones, keeping up communication with the
outer world by means of their proboscis. Rietsch[488] describes a specimen of Bonellia
minor, which he placed in an aquarium, exploring with its proboscis the nature of the
bottom; when the animal had found a convenient crevice, it fixed its proboscis in it by
means of the bifurcated end, and by its contraction drew the body up, and entered the
hole, proboscis first. It then turned round, and during this operation doubtless the
ventral hooks came into play; and then stretching out its proboscis, it began to explore
the neighbourhood. The proboscis is evidently very sensitive, and in addition to being
a locomotor organ, it is also used for the prehension of food. If cut off near the mouth,
the animal does not long survive, but if a considerable portion is left the scar heals,
and the lost part is probably regenerated. In captivity the animals frequently change
their place of residence.
Eisig some years ago described the great extensibility of the proboscis of B. viridis
when confined in the tanks of the Zoological Station at Naples. When contracted the
proboscis was but a few inches long, but at times it was extended till it reached the
length of 1½ metre, shining through the water as a transparent green thread. The body
of the Bonellia was hidden under stones, but the proboscis could be seen seizing
between its two ends the bodies of certain Ascidians which covered the inside of the
tank, tearing them off the walls, and conveying them to the mouth along its grooved
ventral surface.
The food of the Echiuroidea consists of organic matter, in the main of animal nature,
but the group differs from the Sipunculoidea in not eating sand.
Rietsch describes Thalassema neptuni as being more active in its movements and less
sedentary than B. minor. The proboscis is still the chief organ of locomotion, but the
trunk plays a greater part in the movements of the animal than it does in the last-
Hardanger Fjord.
Saccosoma.—No proboscis. The body is flask-shaped. The mouth and anus are
terminal. The ovary is anterior, and there is only one nephridium. No bristles.
Our knowledge of this remarkable Gephyrean is very incomplete, but such as it is, it is
due to the careful investigations of Koren and Danielssen, who had only a single
specimen at their disposition.
Saccosoma vitreum K. and D. North of the Faroe Islands.
Habits of the Echiuroidea.—As a rule the members of this group conceal their
bodies in clefts and fissures of rocks and stones, keeping up communication with the
outer world by means of their proboscis. Rietsch[488] describes a specimen of Bonellia
minor, which he placed in an aquarium, exploring with its proboscis the nature of the
bottom; when the animal had found a convenient crevice, it fixed its proboscis in it by
means of the bifurcated end, and by its contraction drew the body up, and entered the
hole, proboscis first. It then turned round, and during this operation doubtless the
ventral hooks came into play; and then stretching out its proboscis, it began to explore
the neighbourhood. The proboscis is evidently very sensitive, and in addition to being
a locomotor organ, it is also used for the prehension of food. If cut off near the mouth,
the animal does not long survive, but if a considerable portion is left the scar heals,
and the lost part is probably regenerated. In captivity the animals frequently change
their place of residence.
Eisig some years ago described the great extensibility of the proboscis of B. viridis
when confined in the tanks of the Zoological Station at Naples. When contracted the
proboscis was but a few inches long, but at times it was extended till it reached the
length of 1½ metre, shining through the water as a transparent green thread. The body
of the Bonellia was hidden under stones, but the proboscis could be seen seizing
between its two ends the bodies of certain Ascidians which covered the inside of the
tank, tearing them off the walls, and conveying them to the mouth along its grooved
ventral surface.
The food of the Echiuroidea consists of organic matter, in the main of animal nature,
but the group differs from the Sipunculoidea in not eating sand.
Rietsch describes Thalassema neptuni as being more active in its movements and less
sedentary than B. minor. The proboscis is still the chief organ of locomotion, but the
trunk plays a greater part in the movements of the animal than it does in the last-
Page 441
named species. Th. neptuni is found in cavities of stones or in the chambers worn out
by the Mollusc Gastrochaena; when withdrawn from its house the body is found to be
covered by a thick layer of tenacious viscid mucus.
by the Mollusc Gastrochaena; when withdrawn from its house the body is found to be
covered by a thick layer of tenacious viscid mucus.
Page 442
Fig. 224.—Thalassema neptuni Gaert. × 2. A, The animal lying on its ventral surface.
B, Ventral view of the anterior end, showing the grooved proboscis ending
behind in the mouth, and the ventral hooks.
Th. mellita was so named by Conn because it is found sheltering in the
Echinid Mellita. "It enters the shell at the oral opening while yet very small,
but once within its house it grows to its adult size, and is obliged therefore
to remain during the rest of its life a prisoner." Each shell thus inhabited
acquires a reddish brown horse-shoe-shaped marking, which affords a
conspicuous signal that the shell contains a Thalassema.
Thalassema is seldom found living in sand, and Bonellia never, but
Echiurus is almost always found in U-shaped tubes or passages in the sand,
which it digs out for itself by the rapid contractions of its body-wall aided
by its bristles. It, like the other two genera named above, does not long
remain in the same hole, but frequently changes its home. As a rule the
Echiurus sits near the mouth of its tube, which is often a foot or even two in
depth, and sends out its proboscis in every direction; at the least sign of
disturbance it withdraws into the deeper recesses. The walls of the tube are
kept from falling in by a layer of mucus, which makes a smooth lining to
the passage. The peri-anal bristles, which can be withdrawn or protruded at
will, enable the animal to fix itself at any level in the tube.
The Echiuroidea are sometimes used by fishermen as bait. In Echiurus
pallasii Greef found three parasites, all of them new species. One, a
Gregarine, he named Conorhynchus gibbosus; the others were
Platyhelminthes, and were named by him Distomum echiuri and
Nemertoscolex parasiticus respectively.
IV. Order Epithetosomatoidea.
This Order includes the single Family Epithetosomatidae, which was
established by Koren and Danielssen to contain the remarkable Gephyrean
B, Ventral view of the anterior end, showing the grooved proboscis ending
behind in the mouth, and the ventral hooks.
Th. mellita was so named by Conn because it is found sheltering in the
Echinid Mellita. "It enters the shell at the oral opening while yet very small,
but once within its house it grows to its adult size, and is obliged therefore
to remain during the rest of its life a prisoner." Each shell thus inhabited
acquires a reddish brown horse-shoe-shaped marking, which affords a
conspicuous signal that the shell contains a Thalassema.
Thalassema is seldom found living in sand, and Bonellia never, but
Echiurus is almost always found in U-shaped tubes or passages in the sand,
which it digs out for itself by the rapid contractions of its body-wall aided
by its bristles. It, like the other two genera named above, does not long
remain in the same hole, but frequently changes its home. As a rule the
Echiurus sits near the mouth of its tube, which is often a foot or even two in
depth, and sends out its proboscis in every direction; at the least sign of
disturbance it withdraws into the deeper recesses. The walls of the tube are
kept from falling in by a layer of mucus, which makes a smooth lining to
the passage. The peri-anal bristles, which can be withdrawn or protruded at
will, enable the animal to fix itself at any level in the tube.
The Echiuroidea are sometimes used by fishermen as bait. In Echiurus
pallasii Greef found three parasites, all of them new species. One, a
Gregarine, he named Conorhynchus gibbosus; the others were
Platyhelminthes, and were named by him Distomum echiuri and
Nemertoscolex parasiticus respectively.
IV. Order Epithetosomatoidea.
This Order includes the single Family Epithetosomatidae, which was
established by Koren and Danielssen to contain the remarkable Gephyrean
Page 443
they described in 1881 under the name Epithetosoma norvegicum (Fig.
225).
Unfortunately only two specimens were at their disposition, and these were
badly preserved, so that many details of their structure could not be made
out. The animals are of an olive-green colour, and consist of a trunk about
12 mm. long, and of a proboscis 30 mm. in length; the latter differs
essentially from the proboscis of the Echiuroidea inasmuch as it is hollow,
and seems to be a whip-like tubular extension of the skin. Its lumen opens
into the body-cavity. Ventral to the base of the proboscis is the mouth; the
intestine is straight, and terminates in the anus, which is posterior. The
nervous system lies between the circular and the longitudinal muscles of the
body-wall, and contains a tube, the nature of which is obscure. No vascular
system is known. The ovary is attached to a mesentery ventral to the
anterior part of the alimentary canal, and there is a single nephridium. No
anal vesicles exist.
The most remarkable feature of the genus is a series of pore-like openings,
which are stated to lead from the outside into the body-cavity (Fig. 225, a).
These are arranged four on each side, at the bottom of two slit-like
depressions in the skin, which lie one on each side of the base of the
proboscis, slightly dorsal to it.
These remarkable structures are without parallel amongst the Gephyrea,
and, together with the peculiar character of the proboscis, justify the
Norwegian naturalists in adding a new family to the group.
225).
Unfortunately only two specimens were at their disposition, and these were
badly preserved, so that many details of their structure could not be made
out. The animals are of an olive-green colour, and consist of a trunk about
12 mm. long, and of a proboscis 30 mm. in length; the latter differs
essentially from the proboscis of the Echiuroidea inasmuch as it is hollow,
and seems to be a whip-like tubular extension of the skin. Its lumen opens
into the body-cavity. Ventral to the base of the proboscis is the mouth; the
intestine is straight, and terminates in the anus, which is posterior. The
nervous system lies between the circular and the longitudinal muscles of the
body-wall, and contains a tube, the nature of which is obscure. No vascular
system is known. The ovary is attached to a mesentery ventral to the
anterior part of the alimentary canal, and there is a single nephridium. No
anal vesicles exist.
The most remarkable feature of the genus is a series of pore-like openings,
which are stated to lead from the outside into the body-cavity (Fig. 225, a).
These are arranged four on each side, at the bottom of two slit-like
depressions in the skin, which lie one on each side of the base of the
proboscis, slightly dorsal to it.
These remarkable structures are without parallel amongst the Gephyrea,
and, together with the peculiar character of the proboscis, justify the
Norwegian naturalists in adding a new family to the group.
Page 444
Fig. 225.—A, Epithetosoma norvegicum K. and D., magnified. a, a, Right and left slits
leading to the pores; b, mouth; c, proboscis: B, the same animal opened dorsally;
a, pores; b, oesophagus; c, proboscis; d, brown tube. (After Danielssen and
Koren.)
Affinities of the Gephyrea.
Before considering to what other groups of animals the Gephyrea may be
allied, it is advisable to discuss the relationship of the four Orders which
compose the group.
Quatrefages, in the year 1865, divided the Gephyrea into I. Gephyrea
Armata, with which he included the Echiuroidea and Sternaspis,[489] and II.
Gephyrea Inermia or Sipunculoidea. The Gephyrea Inermia, sometimes
called the Achaeta, have been extended to include the Order Priapuloidea,
and opposed to the smaller sub-group the Gephyrea Armata or Chaetifera.
In my opinion, however, these names now are no longer in accordance with
our knowledge of the structure of the animals they attempt to describe, and
they should be given up. Both names had reference to the presence or
absence of the two hook-like bristles described on the ventral surface of
some of the Echiuroidea, but of the five genera of this family, two,
Saccosoma and Hamingia (the latter in the female or normal form), are
without these bristles, and can therefore be described neither as Armata nor
as Chaetifera. On the other hand, hook-like chitinous bristles of somewhat
the same nature, though smaller in size and varying in position, are very
common on the introvert of Sipunculoidea and on the body of the
Priapuloidea.
leading to the pores; b, mouth; c, proboscis: B, the same animal opened dorsally;
a, pores; b, oesophagus; c, proboscis; d, brown tube. (After Danielssen and
Koren.)
Affinities of the Gephyrea.
Before considering to what other groups of animals the Gephyrea may be
allied, it is advisable to discuss the relationship of the four Orders which
compose the group.
Quatrefages, in the year 1865, divided the Gephyrea into I. Gephyrea
Armata, with which he included the Echiuroidea and Sternaspis,[489] and II.
Gephyrea Inermia or Sipunculoidea. The Gephyrea Inermia, sometimes
called the Achaeta, have been extended to include the Order Priapuloidea,
and opposed to the smaller sub-group the Gephyrea Armata or Chaetifera.
In my opinion, however, these names now are no longer in accordance with
our knowledge of the structure of the animals they attempt to describe, and
they should be given up. Both names had reference to the presence or
absence of the two hook-like bristles described on the ventral surface of
some of the Echiuroidea, but of the five genera of this family, two,
Saccosoma and Hamingia (the latter in the female or normal form), are
without these bristles, and can therefore be described neither as Armata nor
as Chaetifera. On the other hand, hook-like chitinous bristles of somewhat
the same nature, though smaller in size and varying in position, are very
common on the introvert of Sipunculoidea and on the body of the
Priapuloidea.
Page 445
Again, the association of the two last-named Orders in one sub-group is, to
my mind, an error. The Priapuloidea have little in common with the
Sipunculoidea; almost the only real point of resemblance is the power of
protruding the anterior part of the alimentary canal, and withdrawing it by
the aid of retractor muscles. But in the Priapuloidea this power exists to a
very small extent, and it is a power shared by very many animals besides
the Gephyrea. The terminal anus of the former is a feature shared by the
Echiuroidea and by Epithetosoma, but these have little else in common with
the Priapuloidea. On the other hand, the entire absence of any head
appendages, such as the proboscis of the Echiuroidea and the tentacles or
tentacular membrane of the Sipunculoidea, the absence of a vascular
system, of nephridia or anal vesicles, taken together with the straight
intestine which occurs elsewhere only in Epithetosoma, the persistent
connexion of the nervous system with the epidermis, the unique character
of their excretory system and of the reproductive organs, are all features in
which the Priapuloidea differ from the more normal members of the other
three Orders. These constitute a list of peculiarities which are at least as
important, and probably even more important, than those which characterise
the Sipunculoidea and the Echiuroidea. Thus the Priapuloidea should, I
think, be regarded as a distinct Order, which occupies a very isolated
position in the group.
Until we know something about the development of Halicryptus and of
Priapulus, it will be difficult to say whether the Order is more nearly allied
to one or the other of the two great Orders of Gephyrea, whether it is very
primitive or very specialised. The connexion of the entire nervous system
with the epidermis and the absence of a vascular system are both rather
primitive features, and so is the Platyhelminthine character of the excretory
organs. With regard to the vascular system, however, it should be pointed
out that it arises very late in the larva of those Gephyrea whose
development is known, and that it does not seem to correspond with the
vascular system of other animals; it has no fine vessels or capillaries
connected with it, and apparently does not act so much as the channel of the
circulatory medium, but more as a mechanism for the expansion of the head
appendages, the tentacles in the Sipunculoidea and the proboscis in the
Echiuroidea; moreover, it is absent in some genera of the former, such as
Onchnesoma, Tylosoma, and Petalostoma, where there are no tentacles.
my mind, an error. The Priapuloidea have little in common with the
Sipunculoidea; almost the only real point of resemblance is the power of
protruding the anterior part of the alimentary canal, and withdrawing it by
the aid of retractor muscles. But in the Priapuloidea this power exists to a
very small extent, and it is a power shared by very many animals besides
the Gephyrea. The terminal anus of the former is a feature shared by the
Echiuroidea and by Epithetosoma, but these have little else in common with
the Priapuloidea. On the other hand, the entire absence of any head
appendages, such as the proboscis of the Echiuroidea and the tentacles or
tentacular membrane of the Sipunculoidea, the absence of a vascular
system, of nephridia or anal vesicles, taken together with the straight
intestine which occurs elsewhere only in Epithetosoma, the persistent
connexion of the nervous system with the epidermis, the unique character
of their excretory system and of the reproductive organs, are all features in
which the Priapuloidea differ from the more normal members of the other
three Orders. These constitute a list of peculiarities which are at least as
important, and probably even more important, than those which characterise
the Sipunculoidea and the Echiuroidea. Thus the Priapuloidea should, I
think, be regarded as a distinct Order, which occupies a very isolated
position in the group.
Until we know something about the development of Halicryptus and of
Priapulus, it will be difficult to say whether the Order is more nearly allied
to one or the other of the two great Orders of Gephyrea, whether it is very
primitive or very specialised. The connexion of the entire nervous system
with the epidermis and the absence of a vascular system are both rather
primitive features, and so is the Platyhelminthine character of the excretory
organs. With regard to the vascular system, however, it should be pointed
out that it arises very late in the larva of those Gephyrea whose
development is known, and that it does not seem to correspond with the
vascular system of other animals; it has no fine vessels or capillaries
connected with it, and apparently does not act so much as the channel of the
circulatory medium, but more as a mechanism for the expansion of the head
appendages, the tentacles in the Sipunculoidea and the proboscis in the
Echiuroidea; moreover, it is absent in some genera of the former, such as
Onchnesoma, Tylosoma, and Petalostoma, where there are no tentacles.
Page 446
The conclusion of the whole matter seems to be that the Priapuloidea are an
isolated Order retaining many primitive features, and having no closer
affinities to the Sipunculoidea than to the Echiuroidea.
Hatschek came to the conclusion, from his work on the development of
Echiurus, that the Echiuroidea are true "Annelids," and from the presence
and mode of formation of the bristles, that they are related to the
Chaetopods. In this view he is confirmed by Conn, who worked out the
development of Thalassema. This relationship is further confirmed by the
discovery of Sluiter's that Sternaspis, the genus of Chaetopods which in
other respects most nearly resembles the Gephyrea, has in one of its species
(S. spinosa) a well-marked bifid proboscis, which, like that of the
Echiuroidea, is thrown off at the least disturbance. Thus it seems fairly well
established that the Echiuroidea are closely connected with the Chaetopoda,
for although the only traces of segmentation they retain in the adult are the
serially-repeated nephridia of Thalassema and Echiurus pallasii, and the
two rows of peri-anal bristles in the latter, and possibly the circular nerves
given off from the ventral cord, yet the larva is fully segmented, and in
other respects is almost typically Chaetopodan.
The relationship of the Sipunculoidea to the Echiuroidea is a more doubtful
point. Hatschek is inclined to separate them, and in this he is again
supported by Conn. Embryology unfortunately does not help us much. The
early stages and larvae of Sipunculus nudus and of Phascolosoma
elongatum have been investigated by Hatschek and by Selenka respectively.
In neither genus is there any trace of segmentation or of Annelid features,
with the possible exception of the bristles on the larval Phascolosoma. On
the other hand, it must be remembered that the development of Sipunculus
is remarkably abbreviated, and that such stages may have dropped out, the
larvae hardly differing more from the Trochosphere of Echiurus and
Thalassema than does that of Bonellia, an undoubted Echiurid. Still the
facts that there is never a head-kidney present, that there is no trace of
segmentation, and that at no stage is the anus terminal, must have a certain
weight.
isolated Order retaining many primitive features, and having no closer
affinities to the Sipunculoidea than to the Echiuroidea.
Hatschek came to the conclusion, from his work on the development of
Echiurus, that the Echiuroidea are true "Annelids," and from the presence
and mode of formation of the bristles, that they are related to the
Chaetopods. In this view he is confirmed by Conn, who worked out the
development of Thalassema. This relationship is further confirmed by the
discovery of Sluiter's that Sternaspis, the genus of Chaetopods which in
other respects most nearly resembles the Gephyrea, has in one of its species
(S. spinosa) a well-marked bifid proboscis, which, like that of the
Echiuroidea, is thrown off at the least disturbance. Thus it seems fairly well
established that the Echiuroidea are closely connected with the Chaetopoda,
for although the only traces of segmentation they retain in the adult are the
serially-repeated nephridia of Thalassema and Echiurus pallasii, and the
two rows of peri-anal bristles in the latter, and possibly the circular nerves
given off from the ventral cord, yet the larva is fully segmented, and in
other respects is almost typically Chaetopodan.
The relationship of the Sipunculoidea to the Echiuroidea is a more doubtful
point. Hatschek is inclined to separate them, and in this he is again
supported by Conn. Embryology unfortunately does not help us much. The
early stages and larvae of Sipunculus nudus and of Phascolosoma
elongatum have been investigated by Hatschek and by Selenka respectively.
In neither genus is there any trace of segmentation or of Annelid features,
with the possible exception of the bristles on the larval Phascolosoma. On
the other hand, it must be remembered that the development of Sipunculus
is remarkably abbreviated, and that such stages may have dropped out, the
larvae hardly differing more from the Trochosphere of Echiurus and
Thalassema than does that of Bonellia, an undoubted Echiurid. Still the
facts that there is never a head-kidney present, that there is no trace of
segmentation, and that at no stage is the anus terminal, must have a certain
weight.
Page 447
If we leave out of account the larval history, which, although pointing to a
difference in the nature of the two families, is by no means decisive, and
consider the adult structures, we find very considerable evidences of
affinity. Taking firstly the main points of difference, we find these to be (i.)
the nature of the cephalic appendages, either a proboscis or some
modification of tentacles; (ii.) the position of the anus; (iii.) the presence of
anal vesicles; (iv.) the number of the nephridia, never more than one pair in
Sipunculids; and (v.) the difference in origin of the chaetae. Of these most
undoubtedly the first is the most important. The Echiuroidea have retained
the prae-oral lobe of the larva in the form of a solid outgrowth of the body,
which outgrowth has carried with it the nerve-ring and vascular ring which
surround the mouth. This has been lost in the Sipunculoidea, but is, I think,
represented by a modified patch of epidermis which lies dorsal to the mouth
and just above the brain. A solid extension of the skin in this region, which
involved the nervous and vascular systems, would bring about the same
relation of parts as is found in the Echiuroidea. The tentacular membrane or
tentacles of the Sipunculoidea have such a variety of form and arrangement,
whilst all subserving the same end, that I am inclined to believe that they
have originated within the limits of the family.
The position of the anus in the Sipunculoidea is one common to very many
animals which live embedded in sand or in tubular holes; it is probably not
primitive, as in the larva of Sipunculus it is near the posterior end, and
becomes more dorsal as the larva elongates.
The anal vesicles of the Echiuroidea probably have no representative in the
Sipunculoidea. In appearance and position they are very like the little tufts
which are found on the rectum of Sipunculus, but since these open neither
into the body-cavity nor into the alimentary canal, it is hardly fair to
compare them.
The resemblances between the Orders seem to me, on the whole, to
outweigh the differences. The general structure of the skin, the coiled
alimentary canal, with its ciliated groove, supported by strands of muscles,
the vascular system which gives off no capillaries, the structure of the
brown tubes, the existence of chitinous hooks or bristles, the nervous
difference in the nature of the two families, is by no means decisive, and
consider the adult structures, we find very considerable evidences of
affinity. Taking firstly the main points of difference, we find these to be (i.)
the nature of the cephalic appendages, either a proboscis or some
modification of tentacles; (ii.) the position of the anus; (iii.) the presence of
anal vesicles; (iv.) the number of the nephridia, never more than one pair in
Sipunculids; and (v.) the difference in origin of the chaetae. Of these most
undoubtedly the first is the most important. The Echiuroidea have retained
the prae-oral lobe of the larva in the form of a solid outgrowth of the body,
which outgrowth has carried with it the nerve-ring and vascular ring which
surround the mouth. This has been lost in the Sipunculoidea, but is, I think,
represented by a modified patch of epidermis which lies dorsal to the mouth
and just above the brain. A solid extension of the skin in this region, which
involved the nervous and vascular systems, would bring about the same
relation of parts as is found in the Echiuroidea. The tentacular membrane or
tentacles of the Sipunculoidea have such a variety of form and arrangement,
whilst all subserving the same end, that I am inclined to believe that they
have originated within the limits of the family.
The position of the anus in the Sipunculoidea is one common to very many
animals which live embedded in sand or in tubular holes; it is probably not
primitive, as in the larva of Sipunculus it is near the posterior end, and
becomes more dorsal as the larva elongates.
The anal vesicles of the Echiuroidea probably have no representative in the
Sipunculoidea. In appearance and position they are very like the little tufts
which are found on the rectum of Sipunculus, but since these open neither
into the body-cavity nor into the alimentary canal, it is hardly fair to
compare them.
The resemblances between the Orders seem to me, on the whole, to
outweigh the differences. The general structure of the skin, the coiled
alimentary canal, with its ciliated groove, supported by strands of muscles,
the vascular system which gives off no capillaries, the structure of the
brown tubes, the existence of chitinous hooks or bristles, the nervous
Page 448
system with its single unsegmented ventral cord, the formation of the
generative organs, all point to a sufficiently close resemblance to justify us
in classing the two Orders together. In addition to these there are
considerable histological resemblances which cannot be discussed here, but
which have a certain weight.
To sum up, it seems probable that the Echiuroidea are derived from the
Chaetopoda, and that their nearest ally in this group is Sternaspis; and that
the Sipunculoidea are allied to the Echiuroidea, but have further departed
from the Annelid stock, and have lost even those traces of affinity with the
parent group which have been preserved in the development of Echiurus
and Thalassema.
So little is known of Epithetosoma that it is difficult to discuss its affinities.
The presence of the hollow proboscis and the pores leading into the body-
cavity undoubtedly justify its being placed in a separate Order, but beyond
the presence of a terminal anus, in which it resembles the Echiuroidea, there
is nothing in its structure which connects it more nearly with one than with
the other of the three larger Orders of Gephyrea.
List of Gephyrea found in the British Area as defined by Canon
Norman.
Phascolosoma vulgare English Channel and North Sea.
Blainv.
" elongatum English Channel.
Kef.
" papillosum English coast.
Thom.
" eremita Sars North Sea.
" procerum Bass Rock.
Moeb.
Phascolion strombi Mont. English coast (Plymouth).
Sipunculus nudus L. North Sea, English Channel (Paignton,
Teignmouth).
generative organs, all point to a sufficiently close resemblance to justify us
in classing the two Orders together. In addition to these there are
considerable histological resemblances which cannot be discussed here, but
which have a certain weight.
To sum up, it seems probable that the Echiuroidea are derived from the
Chaetopoda, and that their nearest ally in this group is Sternaspis; and that
the Sipunculoidea are allied to the Echiuroidea, but have further departed
from the Annelid stock, and have lost even those traces of affinity with the
parent group which have been preserved in the development of Echiurus
and Thalassema.
So little is known of Epithetosoma that it is difficult to discuss its affinities.
The presence of the hollow proboscis and the pores leading into the body-
cavity undoubtedly justify its being placed in a separate Order, but beyond
the presence of a terminal anus, in which it resembles the Echiuroidea, there
is nothing in its structure which connects it more nearly with one than with
the other of the three larger Orders of Gephyrea.
List of Gephyrea found in the British Area as defined by Canon
Norman.
Phascolosoma vulgare English Channel and North Sea.
Blainv.
" elongatum English Channel.
Kef.
" papillosum English coast.
Thom.
" eremita Sars North Sea.
" procerum Bass Rock.
Moeb.
Phascolion strombi Mont. English coast (Plymouth).
Sipunculus nudus L. North Sea, English Channel (Paignton,
Teignmouth).
Page 449
Golfingia macintoshii East coast of Scotland (St. Andrews Bay).
Lank.
Petalostoma minutum Kef. English Channel (Plymouth).
Priapulus caudatus Lam. Scarborough, Outer Hebrides.
Echiurus pallasii Guérin Coast of Scotland, English Channel.
Thalassema neptuni English Channel (Coast of Devonshire).
Gaertner
CHAPTER XVI
PHORONIS
HISTORY—HABITS—STRUCTURE—REPRODUCTION—LARVA—METAMORPHOSIS—
LIST OF SPECIES AND LOCALITIES—SYSTEMATIC POSITION.
This interesting genus was discovered and first described by Dr. Strethill
Wright of Edinburgh, who in the year 1856 found specimens of it living on
a stone with Caryophyllia sent to him from Ilfracombe. He christened the
form Phoronis hippocrepia,[490] the generic name being apparently taken
from an epithet applied to Io, the specific name having reference to the
beautiful horseshoe shape of its tentacular crown. Two years later a closely
allied or identical form was described by Professor P. J. van Beneden under
the name of Crepina gracilis.[491]
Phoronis is a sedentary animal living in "colonies," but each member of the
colony is distinct, and has no organic connexion with the others, from
which it is isolated by the presence of a tube in which it lives, and into
which it can be completely withdrawn. The tube is formed from a secretion
which probably has its origin from the anterior end of the body-wall. The
secretion hardens and forms at first a transparent coating, but it soon
becomes opaque, and numerous sand particles, small pieces of shell, sponge
spicules, and other marine objects adhere to the outside of the tubes, giving
them a very characteristic appearance, and doubtless serving to protect the
inhabitants from predatory animals.
Lank.
Petalostoma minutum Kef. English Channel (Plymouth).
Priapulus caudatus Lam. Scarborough, Outer Hebrides.
Echiurus pallasii Guérin Coast of Scotland, English Channel.
Thalassema neptuni English Channel (Coast of Devonshire).
Gaertner
CHAPTER XVI
PHORONIS
HISTORY—HABITS—STRUCTURE—REPRODUCTION—LARVA—METAMORPHOSIS—
LIST OF SPECIES AND LOCALITIES—SYSTEMATIC POSITION.
This interesting genus was discovered and first described by Dr. Strethill
Wright of Edinburgh, who in the year 1856 found specimens of it living on
a stone with Caryophyllia sent to him from Ilfracombe. He christened the
form Phoronis hippocrepia,[490] the generic name being apparently taken
from an epithet applied to Io, the specific name having reference to the
beautiful horseshoe shape of its tentacular crown. Two years later a closely
allied or identical form was described by Professor P. J. van Beneden under
the name of Crepina gracilis.[491]
Phoronis is a sedentary animal living in "colonies," but each member of the
colony is distinct, and has no organic connexion with the others, from
which it is isolated by the presence of a tube in which it lives, and into
which it can be completely withdrawn. The tube is formed from a secretion
which probably has its origin from the anterior end of the body-wall. The
secretion hardens and forms at first a transparent coating, but it soon
becomes opaque, and numerous sand particles, small pieces of shell, sponge
spicules, and other marine objects adhere to the outside of the tubes, giving
them a very characteristic appearance, and doubtless serving to protect the
inhabitants from predatory animals.
Page 450
What little we know about the habits of Phoronis is in the main due to the
observations of Cori,[492] who studied Ph. psammophila at Faro, an inlet of
the sea near Messina. The least disturbance causes the animal to withdraw
its head with lightning rapidity into the tube, from which after a time it re-
emerges very slowly, and does not expand its tentacular crown until its
body is completely extended. Cori states that not unfrequently individuals
are found either without the crown of tentacles or with the latter in process
of regeneration. These may have been bitten off by fish, etc.; but, on the
other hand, van Beneden describes in Crepina gracilis (Ph. hippocrepia) the
throwing off and regeneration of the crown of tentacles; and Cori confirms
his observation, at any rate as far as concerns those individuals kept in
captivity, and whose surroundings were presumably somewhat
unfavourable. He further observed the interesting fact that the cast-off
crown of tentacles continued to live, and suggests that possibly it may
develop a new body, in which case the phenomenon would be an interesting
case of binary fission producing two new animals.
Fig. 226.—A piece of a matted colony of Ph. kowalevskii Cald. Slightly magnified. In
most cases the tentacular head is protruding from the tube.
With regard to the habitation of Ph. australis, the largest species known,
some discrepancies have crept into the literature of the genus, and to
prevent their recurring again it may be worth while to quote the statements
of its discoverer, Mr. Haswell.[493] He says: "Phoronis australis occurs in
communities of twenty to thirty, in spaces in the substance of the wall of the
tube inhabited and formed by a species of Cerianthus. Each worm has a
tube of its own, very delicate and transparent, made up of several layers, the
mouth opening on the outer surface of the tube of the Cerianthus. The
Cerianthus tubes sometimes come up empty, as we should naturally expect,
the animal having dropped out; but a sufficient number of occupied tubes
are found to show that, under ordinary circumstances, a living Cerianthus
occupies the interior of the tube and a community of Phoronis live in its
wall. This species of Phoronis is never found anywhere else, and the
species of Cerianthus is very rarely found without the Phoronis."
observations of Cori,[492] who studied Ph. psammophila at Faro, an inlet of
the sea near Messina. The least disturbance causes the animal to withdraw
its head with lightning rapidity into the tube, from which after a time it re-
emerges very slowly, and does not expand its tentacular crown until its
body is completely extended. Cori states that not unfrequently individuals
are found either without the crown of tentacles or with the latter in process
of regeneration. These may have been bitten off by fish, etc.; but, on the
other hand, van Beneden describes in Crepina gracilis (Ph. hippocrepia) the
throwing off and regeneration of the crown of tentacles; and Cori confirms
his observation, at any rate as far as concerns those individuals kept in
captivity, and whose surroundings were presumably somewhat
unfavourable. He further observed the interesting fact that the cast-off
crown of tentacles continued to live, and suggests that possibly it may
develop a new body, in which case the phenomenon would be an interesting
case of binary fission producing two new animals.
Fig. 226.—A piece of a matted colony of Ph. kowalevskii Cald. Slightly magnified. In
most cases the tentacular head is protruding from the tube.
With regard to the habitation of Ph. australis, the largest species known,
some discrepancies have crept into the literature of the genus, and to
prevent their recurring again it may be worth while to quote the statements
of its discoverer, Mr. Haswell.[493] He says: "Phoronis australis occurs in
communities of twenty to thirty, in spaces in the substance of the wall of the
tube inhabited and formed by a species of Cerianthus. Each worm has a
tube of its own, very delicate and transparent, made up of several layers, the
mouth opening on the outer surface of the tube of the Cerianthus. The
Cerianthus tubes sometimes come up empty, as we should naturally expect,
the animal having dropped out; but a sufficient number of occupied tubes
are found to show that, under ordinary circumstances, a living Cerianthus
occupies the interior of the tube and a community of Phoronis live in its
wall. This species of Phoronis is never found anywhere else, and the
species of Cerianthus is very rarely found without the Phoronis."
Page 451
Ph. australis is sluggish in its movements, but other species are capable of
very active movement, and withdraw their heads in a moment at the
approach of danger. A Neapolitan species, Ph. kowalevskii—known to the
fishermen of that place as "Ficchetelli bianchi" or "Vermi di ceppa"—lives
chiefly on submarine posts and piles; its tubes, closely interlacing, form a
dense feltwork, upon which Ascidians and Sea-anemones often settle, and
over which Ophiurids and Polychaets creep. The tubes of this species are
rendered opaque by the excreta ejected from the body, and they do not
attach foreign substances to the outside to anything like the same degree as
Ph. psammophila, which live in sandy places, and are termed by the Sicilian
fishermen "Tubi di sabbia." The feltwork of Ph. kowalevskii attains a
thickness of 5 to 8 cm. In each case the tube is much longer than the animal
it shelters, and is so entangled with its neighbours, to which it frequently
adheres, that it is a matter of considerable difficulty to isolate it.
Fig. 227.—A piece of a colony of Ph. psammophila Cori. Slightly magnified. The tubes
are covered by particles of sand, small shells, etc.
The various species of Phoronis differ a good deal in size; Cori gives the
average length as varying from 1.5 to 7.9 mm. in Ph. hippocrepia and up to
127 mm. (6 inches) in Ph. australis. Probably the very short individuals of
the first-named species had not attained their adult stature. Ph. australis has
recently formed the subject of a memoir by Dr. W. B. Benham,[494] from
whom the following account is mainly taken.
The length of the individuals varied from three to six inches, and their
diameter, which is not very uniform, averaged one-eighth of an inch. At one
end, which, since it bears the mouth, we may call the oral end, is the very
characteristic tentacular crown surrounding the mouth on all sides but one,
where there is a slight break in its continuity. The crown of tentacles or
lophophore is flattened, and the two ends drawn out, and each is coiled into
a spiral (Fig. 229); between the bases of these two spirals three ridges can
very active movement, and withdraw their heads in a moment at the
approach of danger. A Neapolitan species, Ph. kowalevskii—known to the
fishermen of that place as "Ficchetelli bianchi" or "Vermi di ceppa"—lives
chiefly on submarine posts and piles; its tubes, closely interlacing, form a
dense feltwork, upon which Ascidians and Sea-anemones often settle, and
over which Ophiurids and Polychaets creep. The tubes of this species are
rendered opaque by the excreta ejected from the body, and they do not
attach foreign substances to the outside to anything like the same degree as
Ph. psammophila, which live in sandy places, and are termed by the Sicilian
fishermen "Tubi di sabbia." The feltwork of Ph. kowalevskii attains a
thickness of 5 to 8 cm. In each case the tube is much longer than the animal
it shelters, and is so entangled with its neighbours, to which it frequently
adheres, that it is a matter of considerable difficulty to isolate it.
Fig. 227.—A piece of a colony of Ph. psammophila Cori. Slightly magnified. The tubes
are covered by particles of sand, small shells, etc.
The various species of Phoronis differ a good deal in size; Cori gives the
average length as varying from 1.5 to 7.9 mm. in Ph. hippocrepia and up to
127 mm. (6 inches) in Ph. australis. Probably the very short individuals of
the first-named species had not attained their adult stature. Ph. australis has
recently formed the subject of a memoir by Dr. W. B. Benham,[494] from
whom the following account is mainly taken.
The length of the individuals varied from three to six inches, and their
diameter, which is not very uniform, averaged one-eighth of an inch. At one
end, which, since it bears the mouth, we may call the oral end, is the very
characteristic tentacular crown surrounding the mouth on all sides but one,
where there is a slight break in its continuity. The crown of tentacles or
lophophore is flattened, and the two ends drawn out, and each is coiled into
a spiral (Fig. 229); between the bases of these two spirals three ridges can
Page 452
be seen, each ending in a pore; the median opening is the anus, the two
lateral are the openings of the nephridia or kidneys, which also serve as
ducts for the reproductive organs. The anus is thus approximated to the
mouth, and since the continuity of the tentacular crown is broken at a spot
just between the two, there would be nothing to separate these orifices if it
were not for the presence of the epistome, a projection or flap of the body-
wall which overhangs the mouth between it and part of the crown of
tentacles.
The extent to which the ridge bearing the tentacles is incurved at each side
varies in different species. In Ph. kowalevskii and Ph. psammophila the
ends are only slightly turned in, so that the crown of tentacles is truly horse-
shoe shaped; but in Ph. australis they are turned in and form three coils on
each side. The number of tentacles also varies, being very numerous in Ph.
australis and Ph. buskii—the latter having as many as 300, whilst the other
species as a rule have from 60 to 90. The bases of the tentacles are fused for
a short distance with one another, forming a thin membrane.
Fig. 228.—A specimen of Ph. buskii M‘Int. removed from its tube and seen from
behind, × about 2. (After M‘Intosh.)
The rest of each tentacle is free, and its inner surface, or that turned towards
the mouth, is covered with long cilia, which, by the currents they set up,
doubtless serve to bring food to the mouth. The tentacles are hollow, and
their cavity is kept open by a stiffening of the tissue, which almost
resembles an internal skeleton; the cavity communicates with the anterior
part of the general body-cavity, and up it runs a single blood-vessel
containing red blood. A single nerve is also distributed to each tentacle.
lateral are the openings of the nephridia or kidneys, which also serve as
ducts for the reproductive organs. The anus is thus approximated to the
mouth, and since the continuity of the tentacular crown is broken at a spot
just between the two, there would be nothing to separate these orifices if it
were not for the presence of the epistome, a projection or flap of the body-
wall which overhangs the mouth between it and part of the crown of
tentacles.
The extent to which the ridge bearing the tentacles is incurved at each side
varies in different species. In Ph. kowalevskii and Ph. psammophila the
ends are only slightly turned in, so that the crown of tentacles is truly horse-
shoe shaped; but in Ph. australis they are turned in and form three coils on
each side. The number of tentacles also varies, being very numerous in Ph.
australis and Ph. buskii—the latter having as many as 300, whilst the other
species as a rule have from 60 to 90. The bases of the tentacles are fused for
a short distance with one another, forming a thin membrane.
Fig. 228.—A specimen of Ph. buskii M‘Int. removed from its tube and seen from
behind, × about 2. (After M‘Intosh.)
The rest of each tentacle is free, and its inner surface, or that turned towards
the mouth, is covered with long cilia, which, by the currents they set up,
doubtless serve to bring food to the mouth. The tentacles are hollow, and
their cavity is kept open by a stiffening of the tissue, which almost
resembles an internal skeleton; the cavity communicates with the anterior
part of the general body-cavity, and up it runs a single blood-vessel
containing red blood. A single nerve is also distributed to each tentacle.
Page 453
At the base of the two spirals of the tentacular crown lie two ciliated pits,
regarded by Caldwell and M‘Intosh[495] as sensory organs, but Benham
looks upon them as glandular in structure and function. Perhaps they secrete
the substance from which the tubes are formed.
The skin is covered by a delicate cuticle secreted by the underlying
epidermis; within the latter is a well-marked basement membrane, and
beneath this a layer of circular muscle fibres; these surround a layer of
longitudinally-arranged fibres, which do not form a continuous sheet but are
arranged in bundles. In both layers the fibres are unstriated. The
longitudinal fibres are covered on their inner side by a layer of flat
pavement cells, which line the general cavity of the body.
This space, the body-cavity, is divided into two parts by the presence of a
diaphragm or septum which runs across from one side of the body to the
other about the level of the ridge bearing the tentacular crown. The anterior
space is continuous with the cavities of the tentacles and of the epistome.
The partition is pierced by the blood-vessels and the oesophagus, but the
rest of the alimentary canal, including the anus, the kidneys, and the
reproductive organs, all lie in the posterior half of the body-cavity behind
the diaphragm. This portion of the body-cavity is further subdivided by the
presence of three longitudinal mesenteries supporting the alimentary canal
and running between it and the body-wall. One of these mesenteries runs
along the outside of the alimentary canal throughout its whole length,
attaching both the descending and ascending limbs of the U-shaped tube to
the body-wall. The other two are lateral mesenteries, which pass from the
body-wall to the sides of the oesophagus. These mesenteries therefore
divide the body-cavity into three spaces—one in which the rectum lies,
which may be called the rectal, and two lateral; owing to the fact that the
lateral mesenteries end before they reach the bend of the alimentary canal,
the three chambers are in free communication one with another. The body-
cavity is further traversed by irregular strands of tissue which run from the
body-wall to the various organs. It contains a corpusculated fluid.
The alimentary canal (Fig. 230) consists of a U-shaped tube which may be
divided into four regions. The mouth (m) leads into the oesophagus (oe),
regarded by Caldwell and M‘Intosh[495] as sensory organs, but Benham
looks upon them as glandular in structure and function. Perhaps they secrete
the substance from which the tubes are formed.
The skin is covered by a delicate cuticle secreted by the underlying
epidermis; within the latter is a well-marked basement membrane, and
beneath this a layer of circular muscle fibres; these surround a layer of
longitudinally-arranged fibres, which do not form a continuous sheet but are
arranged in bundles. In both layers the fibres are unstriated. The
longitudinal fibres are covered on their inner side by a layer of flat
pavement cells, which line the general cavity of the body.
This space, the body-cavity, is divided into two parts by the presence of a
diaphragm or septum which runs across from one side of the body to the
other about the level of the ridge bearing the tentacular crown. The anterior
space is continuous with the cavities of the tentacles and of the epistome.
The partition is pierced by the blood-vessels and the oesophagus, but the
rest of the alimentary canal, including the anus, the kidneys, and the
reproductive organs, all lie in the posterior half of the body-cavity behind
the diaphragm. This portion of the body-cavity is further subdivided by the
presence of three longitudinal mesenteries supporting the alimentary canal
and running between it and the body-wall. One of these mesenteries runs
along the outside of the alimentary canal throughout its whole length,
attaching both the descending and ascending limbs of the U-shaped tube to
the body-wall. The other two are lateral mesenteries, which pass from the
body-wall to the sides of the oesophagus. These mesenteries therefore
divide the body-cavity into three spaces—one in which the rectum lies,
which may be called the rectal, and two lateral; owing to the fact that the
lateral mesenteries end before they reach the bend of the alimentary canal,
the three chambers are in free communication one with another. The body-
cavity is further traversed by irregular strands of tissue which run from the
body-wall to the various organs. It contains a corpusculated fluid.
The alimentary canal (Fig. 230) consists of a U-shaped tube which may be
divided into four regions. The mouth (m) leads into the oesophagus (oe),
Page 454
which gradually enlarges into the stomach (st) situated just before the bend;
a constriction just at the bend separates the stomach from the intestine (int),
and this leads into the rectum (r), which terminates in the anus (an). The
first three divisions of the alimentary canal are ciliated, but the rectum is
not; the walls of the stomach also contain glandular cells, but there are no
special glands opening into any part of the tract.
Fig. 229.—The dorsal surface of Ph. australis Has., looking down on the head. The
tentacles are cut away on the left side, and the innermost are shortened on the
right side to show the arrangement; in reality they are of the same length
throughout. a, Mouth; b, anus; c, pore of left nephridium; d, epistome; e, break in
the inner series of tentacles. The drawing is to some extent diagrammatic, and is
considerably enlarged. (After Benham.)
One of the most interesting features of Phoronis is the presence of a closed
system of blood-vessels containing red blood. There are two main blood-
vessels; one, lying in the rectal chamber between the two limbs of the U-
shaped alimentary canal, has been named the afferent vessel. Just below the
diaphragm this splits into two, and each branch, after piercing this partition,
runs in a spiral course along the base of the crown of tentacles, giving off a
single blood-vessel into each tentacle. At its base each tentacular vessel
opens not only into the above-mentioned "distributing" vessel, but also into
a "recipient" vessel which takes a course parallel with the former. The two
recipient vessels pierce the diaphragm, and after running for some distance
apart, fuse to form the efferent vessel, which continues down the body on
the left side of the oesophagus. At the aboral end of the body the efferent
vessel turns forward and becomes the afferent. Both the main vessels give
off numerous blood diverticula, which are developed into plexiform sinuses
on the walls of the stomach, and in this region they are covered with the
reproductive cells. All the vessels are contractile, and Strethill Wright
a constriction just at the bend separates the stomach from the intestine (int),
and this leads into the rectum (r), which terminates in the anus (an). The
first three divisions of the alimentary canal are ciliated, but the rectum is
not; the walls of the stomach also contain glandular cells, but there are no
special glands opening into any part of the tract.
Fig. 229.—The dorsal surface of Ph. australis Has., looking down on the head. The
tentacles are cut away on the left side, and the innermost are shortened on the
right side to show the arrangement; in reality they are of the same length
throughout. a, Mouth; b, anus; c, pore of left nephridium; d, epistome; e, break in
the inner series of tentacles. The drawing is to some extent diagrammatic, and is
considerably enlarged. (After Benham.)
One of the most interesting features of Phoronis is the presence of a closed
system of blood-vessels containing red blood. There are two main blood-
vessels; one, lying in the rectal chamber between the two limbs of the U-
shaped alimentary canal, has been named the afferent vessel. Just below the
diaphragm this splits into two, and each branch, after piercing this partition,
runs in a spiral course along the base of the crown of tentacles, giving off a
single blood-vessel into each tentacle. At its base each tentacular vessel
opens not only into the above-mentioned "distributing" vessel, but also into
a "recipient" vessel which takes a course parallel with the former. The two
recipient vessels pierce the diaphragm, and after running for some distance
apart, fuse to form the efferent vessel, which continues down the body on
the left side of the oesophagus. At the aboral end of the body the efferent
vessel turns forward and becomes the afferent. Both the main vessels give
off numerous blood diverticula, which are developed into plexiform sinuses
on the walls of the stomach, and in this region they are covered with the
reproductive cells. All the vessels are contractile, and Strethill Wright
Page 455
counted about fifteen pulsations a minute. The blood contains numerous
nucleated, disc-shaped corpuscles differing in appearance from those of the
fluid in the body-cavity. The corpuscles contain haemoglobin, which gives
the red colour to the blood.
The two nephridia or kidneys are essentially tubes which open on the one
side into the body-cavity, and on the other to the exterior. The position of
the external pores has already been described, one being on each side of the
anus. Each pore leads into a tube which passes into that part of the body-
cavity situated below the diaphragm, where it divides, and each of the two
branches terminates in a ciliated funnel-shaped opening. The smaller of
these two funnels pierces the lateral mesentery and opens into the lateral
chamber, whilst the larger, whose opening is very much drawn out
longitudinally, opens into the rectal chamber. The whole organ is ciliated
internally.
The nervous system lies in the skin immediately below the epidermis. This
position is very primitive, and forms one of the most interesting anatomical
peculiarities of the genus. The nervous tissue is probably diffused all over
the body, but there is a special concentration or thickening in the form of a
ring which surrounds the mouth, following the base of the tentacular spirals
and giving off a nerve to each tentacle. The ring lies at the outside of the
base of the tentacles, the anus is not included in it. Caldwell[496] has
described in Ph. kowalevskii an asymmetrical nerve-cord given off from the
ring and running along the left side of the body; associated with which is a
tubular structure of unknown function. In Ph. australis Benham mentions
two such tubes, one on each side of the body; their precise value is obscure.
The epithelium covering the nerve-ring is slightly modified in the
neighbourhood of the kidney pore, and may have some special sensory
function; no other organs of sense are known (but see p. 454).
nucleated, disc-shaped corpuscles differing in appearance from those of the
fluid in the body-cavity. The corpuscles contain haemoglobin, which gives
the red colour to the blood.
The two nephridia or kidneys are essentially tubes which open on the one
side into the body-cavity, and on the other to the exterior. The position of
the external pores has already been described, one being on each side of the
anus. Each pore leads into a tube which passes into that part of the body-
cavity situated below the diaphragm, where it divides, and each of the two
branches terminates in a ciliated funnel-shaped opening. The smaller of
these two funnels pierces the lateral mesentery and opens into the lateral
chamber, whilst the larger, whose opening is very much drawn out
longitudinally, opens into the rectal chamber. The whole organ is ciliated
internally.
The nervous system lies in the skin immediately below the epidermis. This
position is very primitive, and forms one of the most interesting anatomical
peculiarities of the genus. The nervous tissue is probably diffused all over
the body, but there is a special concentration or thickening in the form of a
ring which surrounds the mouth, following the base of the tentacular spirals
and giving off a nerve to each tentacle. The ring lies at the outside of the
base of the tentacles, the anus is not included in it. Caldwell[496] has
described in Ph. kowalevskii an asymmetrical nerve-cord given off from the
ring and running along the left side of the body; associated with which is a
tubular structure of unknown function. In Ph. australis Benham mentions
two such tubes, one on each side of the body; their precise value is obscure.
The epithelium covering the nerve-ring is slightly modified in the
neighbourhood of the kidney pore, and may have some special sensory
function; no other organs of sense are known (but see p. 454).
Page 456
Fig. 230.—A schematic view of the interior of the body of Phoronis. The middle seven-
eighths of the body are omitted, af, Afferent blood-vessel; an, anus; ef, efferent
blood-vessel; ep, epistome; gl, glandular pit; int, intestine or "second stomach";
k, large funnel of the left nephridium; ko, opening of right nephridium, the
opening of the left is seen immediately below in section; m, mouth; n, nerve
concentration; oe, oesophagus; oem, oesophageal mesentery; ov, ovary; r,
rectum; rm, rectal mesentery; rv, right recipient blood-vessel; s, septum; st,
stomach; t, testis; tm, right lateral mesentery. (From Benham.)
Phoronis is hermaphrodite, male and female reproductive cells being
formed in the same individual. The testes and ovaries form two white
masses lying on the left side of the stomach, one on one side and the other
on the other side of the efferent blood-vessel. The glands are traversed in all
directions by the diverticula given off from this trunk, and are thus well
supplied with blood; in fact both the ovary and the testis are formed by the
multiplication and growth of the epithelial cells which cover these
diverticula. When ripe the ova and spermatozoa drop off into the body-
cavity and make their way to the exterior through the duct of the kidney.
eighths of the body are omitted, af, Afferent blood-vessel; an, anus; ef, efferent
blood-vessel; ep, epistome; gl, glandular pit; int, intestine or "second stomach";
k, large funnel of the left nephridium; ko, opening of right nephridium, the
opening of the left is seen immediately below in section; m, mouth; n, nerve
concentration; oe, oesophagus; oem, oesophageal mesentery; ov, ovary; r,
rectum; rm, rectal mesentery; rv, right recipient blood-vessel; s, septum; st,
stomach; t, testis; tm, right lateral mesentery. (From Benham.)
Phoronis is hermaphrodite, male and female reproductive cells being
formed in the same individual. The testes and ovaries form two white
masses lying on the left side of the stomach, one on one side and the other
on the other side of the efferent blood-vessel. The glands are traversed in all
directions by the diverticula given off from this trunk, and are thus well
supplied with blood; in fact both the ovary and the testis are formed by the
multiplication and growth of the epithelial cells which cover these
diverticula. When ripe the ova and spermatozoa drop off into the body-
cavity and make their way to the exterior through the duct of the kidney.
Page 457
Fig. 231.—Three stages in the metamorphosis of the Actinotrocha into Phoronis. A,
Actinotrocha larva with the invagination (c), which will form the trunk of the
Phoronis larva beginning to appear. B, Stage with the invagination partly
extruded. C, Stage when the extrusion is complete and the alimentary canal has
passed into it. C is after Metschnikoff. a, Mouth; b, anus; c, invagination which
ultimately forms the greater part of the body of the adult.
The ova are probably fertilised in the sea-water; they undergo the early
stages of their development whilst entangled amongst the tentacles of the
parent. The larval form to which they give rise was known long before its
connexion with the adult was demonstrated by Kowalevsky.[497] It is known
as the Actinotrocha (Fig. 231, A), and according to Caldwell has the
following structure in Ph. kowalevskii. The mouth is anterior, and the anus
terminal and posterior; the mouth is overhung by an immense prae-oral
lobe, which bears a special larval nerve ganglion, and in some species four
eye-spots; at the base of this, but behind the mouth, is a ring of larval
tentacles. The prae-oral lobe and the tentacles are ciliated; the margin of the
lobe bears, however, specially long cilia, and there is also a ring of long
cilia around the anus.
Before the Actinotrocha stage has been reached the larva has forsaken the
shelter of its parent's tentacles, and swims actively about in the open sea. As
it grows older a finger-like involution of the skin (c) arises just behind the
tentacles on the ventral surface and grows into the body, increasing greatly
in length and becoming much folded. The larva now sinks to the bottom of
the sea, and after swimming round many times on its axis, undergoes a very
astonishing metamorphosis (Fig. 231, B, C). The finger-like involution is
Actinotrocha larva with the invagination (c), which will form the trunk of the
Phoronis larva beginning to appear. B, Stage with the invagination partly
extruded. C, Stage when the extrusion is complete and the alimentary canal has
passed into it. C is after Metschnikoff. a, Mouth; b, anus; c, invagination which
ultimately forms the greater part of the body of the adult.
The ova are probably fertilised in the sea-water; they undergo the early
stages of their development whilst entangled amongst the tentacles of the
parent. The larval form to which they give rise was known long before its
connexion with the adult was demonstrated by Kowalevsky.[497] It is known
as the Actinotrocha (Fig. 231, A), and according to Caldwell has the
following structure in Ph. kowalevskii. The mouth is anterior, and the anus
terminal and posterior; the mouth is overhung by an immense prae-oral
lobe, which bears a special larval nerve ganglion, and in some species four
eye-spots; at the base of this, but behind the mouth, is a ring of larval
tentacles. The prae-oral lobe and the tentacles are ciliated; the margin of the
lobe bears, however, specially long cilia, and there is also a ring of long
cilia around the anus.
Before the Actinotrocha stage has been reached the larva has forsaken the
shelter of its parent's tentacles, and swims actively about in the open sea. As
it grows older a finger-like involution of the skin (c) arises just behind the
tentacles on the ventral surface and grows into the body, increasing greatly
in length and becoming much folded. The larva now sinks to the bottom of
the sea, and after swimming round many times on its axis, undergoes a very
astonishing metamorphosis (Fig. 231, B, C). The finger-like involution is
Page 458
suddenly turned inside out, and forms a large projection on the ventral
surface, into which the alimentary canal passes, assuming a U-shape, as in
the adult. This ventral process in fact forms all the body of the adult behind
the line of tentacles, and subsequently contains, not only the alimentary
canal, but the kidneys, the reproductive organs, and a large part of the
vascular system. At the same time the prae-oral lobe breaks off, and,
together with its ganglia and eye-spots, passes into the mouth and is
digested in the stomach; the larval tentacles follow the prae-oral lobe, and
are similarly digested. Their place is taken by a ring of adult tentacles which
commence to appear just behind the larval tentacles before they fall off. The
animal is now practically adult.[498]
It is obvious that this astonishing metamorphosis is accompanied by the
rotation of the axes of the animal. The adult practically lives at right angles
to the larva. In the latter the anus marked the posterior end, and the prae-
oral lobe the anterior. The prae-oral lobe has disappeared in the adult, but its
position is marked by the mouth. The ventral surface has enormously
increased, and corresponds with the whole surface of the trunk. To be
consistent we must therefore regard the mouth of the adult as marking the
anterior end of the animal, the anus the posterior. The short line between the
mouth and anus across the centre of the tentacular crown marks the dorsal
surface; and the line running all round the trunk from anus to mouth, the
ventral. In fact, in its usual position in its tube Phoronis is lying on its
ventral surface, its back faces upwards, and the anterior and posterior ends
lie on one side or the other.
Species and Affinities.—In his exhaustive memoir on the anatomy and
histology of Phoronis, Cori enumerates seven different species, and quotes
the characters of each as enumerated by eight different authors. He,
however, reserves his opinion as to the identity or distinctness of some of
these species. Benham in his account of Ph. australis enumerates five
species, including amongst them Ph. ovalis, which, however, he regards as
probably a young form, an opinion in which Cori coincides. The latter
regards it as possibly a young form of Ph. hippocrepia.
surface, into which the alimentary canal passes, assuming a U-shape, as in
the adult. This ventral process in fact forms all the body of the adult behind
the line of tentacles, and subsequently contains, not only the alimentary
canal, but the kidneys, the reproductive organs, and a large part of the
vascular system. At the same time the prae-oral lobe breaks off, and,
together with its ganglia and eye-spots, passes into the mouth and is
digested in the stomach; the larval tentacles follow the prae-oral lobe, and
are similarly digested. Their place is taken by a ring of adult tentacles which
commence to appear just behind the larval tentacles before they fall off. The
animal is now practically adult.[498]
It is obvious that this astonishing metamorphosis is accompanied by the
rotation of the axes of the animal. The adult practically lives at right angles
to the larva. In the latter the anus marked the posterior end, and the prae-
oral lobe the anterior. The prae-oral lobe has disappeared in the adult, but its
position is marked by the mouth. The ventral surface has enormously
increased, and corresponds with the whole surface of the trunk. To be
consistent we must therefore regard the mouth of the adult as marking the
anterior end of the animal, the anus the posterior. The short line between the
mouth and anus across the centre of the tentacular crown marks the dorsal
surface; and the line running all round the trunk from anus to mouth, the
ventral. In fact, in its usual position in its tube Phoronis is lying on its
ventral surface, its back faces upwards, and the anterior and posterior ends
lie on one side or the other.
Species and Affinities.—In his exhaustive memoir on the anatomy and
histology of Phoronis, Cori enumerates seven different species, and quotes
the characters of each as enumerated by eight different authors. He,
however, reserves his opinion as to the identity or distinctness of some of
these species. Benham in his account of Ph. australis enumerates five
species, including amongst them Ph. ovalis, which, however, he regards as
probably a young form, an opinion in which Cori coincides. The latter
regards it as possibly a young form of Ph. hippocrepia.
Page 459
Without comparing specimens of each of the alleged species, it is difficult
to come to any very satisfactory solution of the problem of how many
distinct species are at present known, but it seems probable that there are at
least six.
(i.) Phoronis hippocrepia Wright.—Under this name is included the
first form, described and named by Wright in 1856; also Ph. ovalis,
described two years later by the same observer as a distinct form,
though it now seems probable that it is but a young form of Ph.
hippocrepia. The Crepina gracilis of van Beneden is probably identical
with this species.
This species occurs in membranous tubes embedded in limestone,
corals, or oyster shells. Its length varies from 1.5 to 15 mm. The
number of tentacles varies from 16 to 86. It has been found off the
coast of Devonshire and in the Firth of Forth.
(ii.) Phoronis kowalevskii Caldwell.—This name is given by Benham
to the species from Naples described by Caldwell, and replaces the
name Ph. caespitosa, which was given by Cori. This species is found in
the Bay of Naples, living in considerable colonies on submarine piles
and posts. It is not firmly attached to its substratum. The tube may be
coated with sand or other foreign particles. The length of the
individuals varies from 3 to 39 mm. The lophophore is simple, with
from 50 to 100 tentacles.
(iii.) Phoronis australis Haswell.—This is the giant of the genus, the
length of the individuals being from 3 to 5 (76-127 mm.) or rarely 6
inches. It lives in delicate transparent tubes, interlacing the walls of the
tube of a sea-anemone, Cerianthus. The arms of the lophophore coil
into two spirals. The colour is reddish or purple. Found in Port Jackson.
(iv.) Phoronis buskii M‘Intosh.—This species was dredged by the
Challenger from a sandy bottom at a depth of 10 to 20 fathoms off the
Philippines. Its tube is covered with particles of sand, sponge spicules,
etc. Its length is 52 mm. or more (more than two inches). The anatomy
to come to any very satisfactory solution of the problem of how many
distinct species are at present known, but it seems probable that there are at
least six.
(i.) Phoronis hippocrepia Wright.—Under this name is included the
first form, described and named by Wright in 1856; also Ph. ovalis,
described two years later by the same observer as a distinct form,
though it now seems probable that it is but a young form of Ph.
hippocrepia. The Crepina gracilis of van Beneden is probably identical
with this species.
This species occurs in membranous tubes embedded in limestone,
corals, or oyster shells. Its length varies from 1.5 to 15 mm. The
number of tentacles varies from 16 to 86. It has been found off the
coast of Devonshire and in the Firth of Forth.
(ii.) Phoronis kowalevskii Caldwell.—This name is given by Benham
to the species from Naples described by Caldwell, and replaces the
name Ph. caespitosa, which was given by Cori. This species is found in
the Bay of Naples, living in considerable colonies on submarine piles
and posts. It is not firmly attached to its substratum. The tube may be
coated with sand or other foreign particles. The length of the
individuals varies from 3 to 39 mm. The lophophore is simple, with
from 50 to 100 tentacles.
(iii.) Phoronis australis Haswell.—This is the giant of the genus, the
length of the individuals being from 3 to 5 (76-127 mm.) or rarely 6
inches. It lives in delicate transparent tubes, interlacing the walls of the
tube of a sea-anemone, Cerianthus. The arms of the lophophore coil
into two spirals. The colour is reddish or purple. Found in Port Jackson.
(iv.) Phoronis buskii M‘Intosh.—This species was dredged by the
Challenger from a sandy bottom at a depth of 10 to 20 fathoms off the
Philippines. Its tube is covered with particles of sand, sponge spicules,
etc. Its length is 52 mm. or more (more than two inches). The anatomy
Page 460
of this species closely resembles that of Ph. australis, and Benham
thinks that, in spite of the difference in their habitat, they may belong
to the same species.
(v.) Phoronis architecta Andrews.—A species recently described by
Andrews from Beaufort, N.C. Its distinctive features are: "the
formation of isolated tubes covered by definite collections of sand
grains; the presence of special prostomial organs, possibly of use in the
formation of these tubes; the great development of the longitudinal
muscles; the presence of a ciliated groove in the digestive tract; the
apparent separation of the sexes."
(vi.) Phoronis psammophila Cori.—Found in Faro, near Messina. The
tube is hyaline, and is covered by numerous grains of sand, some of
considerable size. The length of the individuals is 25 to 50 mm. There
are 60 to 90 tentacles. The colour is a fleshy red. A second species
discovered by Haswell in Port Jackson had no points of importance to
distinguish it from Ph. psammophila, except that no sand adheres to its
tube and the number of tentacles is slightly greater.
In addition to the various species of Phoronis, several distinct forms of
its larva, Actinotrocha, are known, and have been named without
having been traced into their corresponding adult form.
The position of Phoronis in the animal kingdom has formed the matter of
considerable divergence of opinion amongst the naturalists who have
studied it. The earlier writers regarded Phoronis as allied to the Gephyrea,
and it was for a long time classed with these animals, but placed in a
separate sub-Order, the Gephyrea tubicola, which was opposed to the
Gephyrea nuda, which comprised the true Gephyrea.
Caldwell referred Phoronis, the Brachiopoda, the Polyzoa, and the
Gephyrea to the same type of body structure, and Lankester subsequently
suggested the provisional name Podaxonia for this miscellaneous collection
of animals. Lankester divided his phylum Podaxonia into three classes: (i.)
the Sipunculoidea (Gephyrea), (ii.) the Brachiopoda, and (iii.) the Polyzoa.
thinks that, in spite of the difference in their habitat, they may belong
to the same species.
(v.) Phoronis architecta Andrews.—A species recently described by
Andrews from Beaufort, N.C. Its distinctive features are: "the
formation of isolated tubes covered by definite collections of sand
grains; the presence of special prostomial organs, possibly of use in the
formation of these tubes; the great development of the longitudinal
muscles; the presence of a ciliated groove in the digestive tract; the
apparent separation of the sexes."
(vi.) Phoronis psammophila Cori.—Found in Faro, near Messina. The
tube is hyaline, and is covered by numerous grains of sand, some of
considerable size. The length of the individuals is 25 to 50 mm. There
are 60 to 90 tentacles. The colour is a fleshy red. A second species
discovered by Haswell in Port Jackson had no points of importance to
distinguish it from Ph. psammophila, except that no sand adheres to its
tube and the number of tentacles is slightly greater.
In addition to the various species of Phoronis, several distinct forms of
its larva, Actinotrocha, are known, and have been named without
having been traced into their corresponding adult form.
The position of Phoronis in the animal kingdom has formed the matter of
considerable divergence of opinion amongst the naturalists who have
studied it. The earlier writers regarded Phoronis as allied to the Gephyrea,
and it was for a long time classed with these animals, but placed in a
separate sub-Order, the Gephyrea tubicola, which was opposed to the
Gephyrea nuda, which comprised the true Gephyrea.
Caldwell referred Phoronis, the Brachiopoda, the Polyzoa, and the
Gephyrea to the same type of body structure, and Lankester subsequently
suggested the provisional name Podaxonia for this miscellaneous collection
of animals. Lankester divided his phylum Podaxonia into three classes: (i.)
the Sipunculoidea (Gephyrea), (ii.) the Brachiopoda, and (iii.) the Polyzoa.
Page 461
The last-named class he divided into three sections: (a) the Vermiformia,
this includes the single genus Phoronis; (b) the Pterobranchia, including the
forms Cephalodiscus and Rhabdopleura, whose affinities with
Balanoglossus were subsequently demonstrated; and (c) the Eupolyzoa,
including the forms treated as Polyzoa in the following pages.
Masterman's recent researches[499] on Phoronis seem to indicate that the
Vermiformia, like the Pterobranchia, must in future be grouped with the
Hemichordata. He finds three well-defined coelomic spaces corresponding
with the epistome, the collar, and the trunk, and also representatives of the
collar pores, and is further inclined to believe that structures representing
the notochord exist in Actinotrocha.
Should Masterman's researches be confirmed, Phoronis will be removed
from its present isolated and enigmatical position, and placed with
Cephalodiscus and Rhabdopleura amongst the Hemichordata, which will be
described in Vol. VII. of this work.
this includes the single genus Phoronis; (b) the Pterobranchia, including the
forms Cephalodiscus and Rhabdopleura, whose affinities with
Balanoglossus were subsequently demonstrated; and (c) the Eupolyzoa,
including the forms treated as Polyzoa in the following pages.
Masterman's recent researches[499] on Phoronis seem to indicate that the
Vermiformia, like the Pterobranchia, must in future be grouped with the
Hemichordata. He finds three well-defined coelomic spaces corresponding
with the epistome, the collar, and the trunk, and also representatives of the
collar pores, and is further inclined to believe that structures representing
the notochord exist in Actinotrocha.
Should Masterman's researches be confirmed, Phoronis will be removed
from its present isolated and enigmatical position, and placed with
Cephalodiscus and Rhabdopleura amongst the Hemichordata, which will be
described in Vol. VII. of this work.
Page 462
POLYZOA
BY
SIDNEY F. HARMER, M.A.
Fellow of King's College, Cambridge
CHAPTER XVII
POLYZOA
INTRODUCTION—GENERAL CHARACTERS AND TERMINOLOGY—BROWN BODIES—
HISTORY—OUTLINES OF CLASSIFICATION—MARINE POLYZOA—OCCURRENCE—
FORMS OF COLONY AND OF ZOOECIA—OVICELLS—AVICULARIA—VIBRACULA—
ENTOPROCTA.
The following pages[500] deal with animals whose very existence is hardly
known to those who are not professed naturalists. There are but few
Polyzoa which have earned the distinction of possessing a popular name,
and most of such names as do exist cannot be found outside treatises on
Natural History. It is true that many of the members of this group have been
vaguely termed "Zoophytes"; but this term implies no more than that they
possess a superficial resemblance to certain plants, and it must be
remembered that this habit of growth is assumed by many animals which
have nothing to do with the Polyzoa. The term "Coralline" is sometimes
applied to those calcareous Polyzoa which grow into coral-like forms; and
the Tertiary deposit known as the "Coralline Crag" is so called from the
large number of fossil Polyzoa which it contains.
The Polyzoa are none the less a most attractive group. Let any one examine
a dry piece of a brown paper-like substance (Fig. 232, A), which may be
found thrown up on the beach on many parts of our coasts. Of this species
(Flustra foliacea), the so-called "sea-mat," an old writer says: "For curiosity
BY
SIDNEY F. HARMER, M.A.
Fellow of King's College, Cambridge
CHAPTER XVII
POLYZOA
INTRODUCTION—GENERAL CHARACTERS AND TERMINOLOGY—BROWN BODIES—
HISTORY—OUTLINES OF CLASSIFICATION—MARINE POLYZOA—OCCURRENCE—
FORMS OF COLONY AND OF ZOOECIA—OVICELLS—AVICULARIA—VIBRACULA—
ENTOPROCTA.
The following pages[500] deal with animals whose very existence is hardly
known to those who are not professed naturalists. There are but few
Polyzoa which have earned the distinction of possessing a popular name,
and most of such names as do exist cannot be found outside treatises on
Natural History. It is true that many of the members of this group have been
vaguely termed "Zoophytes"; but this term implies no more than that they
possess a superficial resemblance to certain plants, and it must be
remembered that this habit of growth is assumed by many animals which
have nothing to do with the Polyzoa. The term "Coralline" is sometimes
applied to those calcareous Polyzoa which grow into coral-like forms; and
the Tertiary deposit known as the "Coralline Crag" is so called from the
large number of fossil Polyzoa which it contains.
The Polyzoa are none the less a most attractive group. Let any one examine
a dry piece of a brown paper-like substance (Fig. 232, A), which may be
found thrown up on the beach on many parts of our coasts. Of this species
(Flustra foliacea), the so-called "sea-mat," an old writer says: "For curiosity
Page 463
and beauty, I have not, among all the plants or vegetables I have yet
observed, seen any one comparable to this seaweed."[501] Viewed with the
microscope, the frond is seen to consist of two layers, placed back to back,
of oblong chambers, each of which is the dried body-wall of a single
individual. The whole is obviously a colony, and to this fact the term
Polyzoa refers.
The chambers just noticed are termed "zooecia." Each is rounded at one
end, near which is the "orifice," through which the tentacles of the living
animal can be pushed out. Two short, stiff spines usually occur on each side
of the orifice; and the symmetry of this forest of spines fully justifies the
above-quoted remark.
Fig. 232.—Flustra foliacea L., Cromer. A, Natural size, B' indicating the portion
magnified in B (× 30): a, avicularium with closed mouth, to the left of which are
seen two avicularia with open months; o, ovicell, forming the upper part of a
zooecium. Ovicells are seen on three consecutive zooecia. The operculum, which
closes the orifice of the zooecium, is seen in different positions in the individuals
figured.
The upper part of some of the zooecia is somewhat swollen, these swellings
representing the conspicuous "ovicells" of many other genera. In the early
part of the year each ovicell protects an orange-coloured egg or embryo,
and the larvae are readily liberated if the fresh colony be placed in clean
sea-water. "At least ten thousand" were hatched out in three hours from a
colony placed in a glass by Sir John Dalyell.[502] The larva swims freely in
the water for a short time, and should it find a suitable resting-place, it fixes
itself and forms the starting-point of a colony, the number of whose
individuals is continually increased by the production of buds at the
growing edge. The "avicularia" of this species will be alluded to later (see
p. 482).
observed, seen any one comparable to this seaweed."[501] Viewed with the
microscope, the frond is seen to consist of two layers, placed back to back,
of oblong chambers, each of which is the dried body-wall of a single
individual. The whole is obviously a colony, and to this fact the term
Polyzoa refers.
The chambers just noticed are termed "zooecia." Each is rounded at one
end, near which is the "orifice," through which the tentacles of the living
animal can be pushed out. Two short, stiff spines usually occur on each side
of the orifice; and the symmetry of this forest of spines fully justifies the
above-quoted remark.
Fig. 232.—Flustra foliacea L., Cromer. A, Natural size, B' indicating the portion
magnified in B (× 30): a, avicularium with closed mouth, to the left of which are
seen two avicularia with open months; o, ovicell, forming the upper part of a
zooecium. Ovicells are seen on three consecutive zooecia. The operculum, which
closes the orifice of the zooecium, is seen in different positions in the individuals
figured.
The upper part of some of the zooecia is somewhat swollen, these swellings
representing the conspicuous "ovicells" of many other genera. In the early
part of the year each ovicell protects an orange-coloured egg or embryo,
and the larvae are readily liberated if the fresh colony be placed in clean
sea-water. "At least ten thousand" were hatched out in three hours from a
colony placed in a glass by Sir John Dalyell.[502] The larva swims freely in
the water for a short time, and should it find a suitable resting-place, it fixes
itself and forms the starting-point of a colony, the number of whose
individuals is continually increased by the production of buds at the
growing edge. The "avicularia" of this species will be alluded to later (see
p. 482).
Page 464
F. foliacea has long been known to possess in the fresh state a remarkable
odour, which is described, according to the fancy of the observer, as a
strong odour of fish, or as the smell of violets after a shower. Others have
compared it to that of the orange or verbena, or to that of a mixture of roses
and geranium.
Flustrella hispida, another of our commonest Polyzoa, which may be found
between tide-marks on the stalks of Fucus, consists of a softish brown
encrustation, about one-sixteenth of an inch thick, covered by numerous
spines. If examined undisturbed in a rock-pool, or transferred to a glass of
sea-water, the brown mass will be seen to become surrounded by a delicate
bluish halo, which is about as thick as the encrusting mass itself, and
consists of the tentacles of the numerous individuals of the colony. The
microscope shows that each individual is provided with a circlet of some
thirty or more long, delicate tentacles, which together form a graceful
funnel (as in Fig. 233). At the bottom of the funnel is the mouth, to which
Diatoms or other minute organic particles are conveyed by the cilia which
fringe the tentacles. If the tentacles be touched with a needle, the whole
funnel is retracted with great rapidity, and in this retracted condition we see
no more than the body-walls of the animals. After an interval the tips of the
tentacles are cautiously protruded; the tentacles are gradually pushed out, at
first in a close bundle, but finally separating from one another to form the
funnel which we have already noticed.
There is hardly a more surprising spectacle in the whole animal kingdom
than a living fragment of the genus Bugula. The colony grows in the shape
of a small tree, whose height may amount to several inches; and is
characterised, in many species, by a spiral arrangement of the branches,
which makes the genus easy to recognise at first sight (Fig. 233, A). The
stem and branches are composed of a single layer of zooecia, arranged two
or more abreast. Each zooecium bears, on its outer side, a most singular
body termed an avicularium, from its resemblance to a bird's head. Imagine
a minute eagle's head attached by a short but flexible neck to the zooecium.
Suppose further that this structure moves backwards and forwards in a
deliberate but determined fashion, its lower jaw usually widely open so as
to be nearly 180° distant from its position when closed. Suppose that the
lower jaw is moved by powerful muscles which can be distinctly seen
odour, which is described, according to the fancy of the observer, as a
strong odour of fish, or as the smell of violets after a shower. Others have
compared it to that of the orange or verbena, or to that of a mixture of roses
and geranium.
Flustrella hispida, another of our commonest Polyzoa, which may be found
between tide-marks on the stalks of Fucus, consists of a softish brown
encrustation, about one-sixteenth of an inch thick, covered by numerous
spines. If examined undisturbed in a rock-pool, or transferred to a glass of
sea-water, the brown mass will be seen to become surrounded by a delicate
bluish halo, which is about as thick as the encrusting mass itself, and
consists of the tentacles of the numerous individuals of the colony. The
microscope shows that each individual is provided with a circlet of some
thirty or more long, delicate tentacles, which together form a graceful
funnel (as in Fig. 233). At the bottom of the funnel is the mouth, to which
Diatoms or other minute organic particles are conveyed by the cilia which
fringe the tentacles. If the tentacles be touched with a needle, the whole
funnel is retracted with great rapidity, and in this retracted condition we see
no more than the body-walls of the animals. After an interval the tips of the
tentacles are cautiously protruded; the tentacles are gradually pushed out, at
first in a close bundle, but finally separating from one another to form the
funnel which we have already noticed.
There is hardly a more surprising spectacle in the whole animal kingdom
than a living fragment of the genus Bugula. The colony grows in the shape
of a small tree, whose height may amount to several inches; and is
characterised, in many species, by a spiral arrangement of the branches,
which makes the genus easy to recognise at first sight (Fig. 233, A). The
stem and branches are composed of a single layer of zooecia, arranged two
or more abreast. Each zooecium bears, on its outer side, a most singular
body termed an avicularium, from its resemblance to a bird's head. Imagine
a minute eagle's head attached by a short but flexible neck to the zooecium.
Suppose further that this structure moves backwards and forwards in a
deliberate but determined fashion, its lower jaw usually widely open so as
to be nearly 180° distant from its position when closed. Suppose that the
lower jaw is moved by powerful muscles which can be distinctly seen
Page 465
inside the transparent head of the avicularium, and that every now and then
it closes with a snap, seizing any unfortunate worm which may happen to
be within reach with a grasp of iron. The above gives a very faint idea of
the appearance of a living Bugula colony, with its hundreds of swaying
avicularia, and with its tentacular funnels protruding from their zooecia, and
withdrawing themselves capriciously from time to time.
Fig. 233.—Bugula turbinata Alder, Plymouth. A, A small colony (natural size); B,
portion of a branch (× 50): a, a', avicularia, in different positions; ap, "aperture"
(see p. 524); b, polypide-bud, attached by its stomach to b.b, brown body; m,
mouth, surrounded by the circle of tentacles; two individuals to the right show
the tentacles partially expanded; o, ovicell; s, marginal spine. The avicularia of
some of the zooecia have been omitted in B.
General Characters.—The Polyzoa are colonies, leaf-like or tree-like in
form, and often strongly resembling seaweeds, or forming encrustations on
the surface of stones and water-plants, or taking on other shapes. The units
of the colony are complete individuals (Fig. 234). The zooecium or body-
wall encloses a body-cavity, in which lies a digestive canal, with which are
closely connected the central nervous system and the retractile, ciliated
tentacles. The structures other than the zooecium constitute the "polypide."
The mouth (m) leads into the ciliated pharynx (ph) which is followed by the
oesophagus (oe) which again passes into the stomach (s), whose walls are
coloured by a characteristic yellowish pigment. The stomach gives off the
intestine (in), which is lined by strong cilia, by means of which a rotatory
movement is given to the faeces contained in it. This communicates by a
narrow passage with the rectum (r), which opens by means of the anus (a).
it closes with a snap, seizing any unfortunate worm which may happen to
be within reach with a grasp of iron. The above gives a very faint idea of
the appearance of a living Bugula colony, with its hundreds of swaying
avicularia, and with its tentacular funnels protruding from their zooecia, and
withdrawing themselves capriciously from time to time.
Fig. 233.—Bugula turbinata Alder, Plymouth. A, A small colony (natural size); B,
portion of a branch (× 50): a, a', avicularia, in different positions; ap, "aperture"
(see p. 524); b, polypide-bud, attached by its stomach to b.b, brown body; m,
mouth, surrounded by the circle of tentacles; two individuals to the right show
the tentacles partially expanded; o, ovicell; s, marginal spine. The avicularia of
some of the zooecia have been omitted in B.
General Characters.—The Polyzoa are colonies, leaf-like or tree-like in
form, and often strongly resembling seaweeds, or forming encrustations on
the surface of stones and water-plants, or taking on other shapes. The units
of the colony are complete individuals (Fig. 234). The zooecium or body-
wall encloses a body-cavity, in which lies a digestive canal, with which are
closely connected the central nervous system and the retractile, ciliated
tentacles. The structures other than the zooecium constitute the "polypide."
The mouth (m) leads into the ciliated pharynx (ph) which is followed by the
oesophagus (oe) which again passes into the stomach (s), whose walls are
coloured by a characteristic yellowish pigment. The stomach gives off the
intestine (in), which is lined by strong cilia, by means of which a rotatory
movement is given to the faeces contained in it. This communicates by a
narrow passage with the rectum (r), which opens by means of the anus (a).
Page 466
Fig. 234.—Alcyonidium albidum Alder, Banyuls-sur-Mer. Diagram showing the
structure of a single zooecium with its polypide retracted: a, anus; d, diaphragm;
e, ectocyst; em, ectoderm; f, funiculus; g, ganglion; i, intertentacular organ; in,
intestine; m, mouth; mm, mesoderm of body-wall; o, orifice; oe, oesophagus; ov,
ovary; p, parietal muscles; ph, pharynx; p.v, parieto-vaginal muscles; r, rectum;
r.m, retractor muscles (contracted); s, stomach; t, testis; tn, tentacles; t.s, tentacle-
sheath or kamptoderm. (After Prouho.[503])
In the retracted condition the tentacles (tn) lie in a cavity which opens to the
exterior by the orifice (o). The cavity is bounded by a thin membrane
termed the "tentacle-sheath" (ts), and it is incompletely subdivided, near its
upper end, by a diaphragm (d), perforated by a circular hole through which
the tentacles can be protruded. The diaphragm bears the thin folded collar
characteristic of the Ctenostomata, the group to which the species figured
belongs (see p. 477).
Fig. 238, B, shows the tentacles of Bowerbankia in their fully expanded and
partially expanded condition. Comparing this with Fig. 234, it will be clear
that when protrusion is taking place, the tentacles are forced in a bundle,
tips first, through the diaphragm and next through the orifice of the
zooecium, the alimentary canal offering no resistance to this movement,
owing to the length of the oesophagus. A moment's consideration will show
that the bases of the tentacles, in passing through the orifice, will carry with
them that part of the flexible tentacle-sheath to which they are attached; and
it will further be clear that so much of the tentacle-sheath as is thus
protruded will be turned inside out. This process of "evagination" continues
structure of a single zooecium with its polypide retracted: a, anus; d, diaphragm;
e, ectocyst; em, ectoderm; f, funiculus; g, ganglion; i, intertentacular organ; in,
intestine; m, mouth; mm, mesoderm of body-wall; o, orifice; oe, oesophagus; ov,
ovary; p, parietal muscles; ph, pharynx; p.v, parieto-vaginal muscles; r, rectum;
r.m, retractor muscles (contracted); s, stomach; t, testis; tn, tentacles; t.s, tentacle-
sheath or kamptoderm. (After Prouho.[503])
In the retracted condition the tentacles (tn) lie in a cavity which opens to the
exterior by the orifice (o). The cavity is bounded by a thin membrane
termed the "tentacle-sheath" (ts), and it is incompletely subdivided, near its
upper end, by a diaphragm (d), perforated by a circular hole through which
the tentacles can be protruded. The diaphragm bears the thin folded collar
characteristic of the Ctenostomata, the group to which the species figured
belongs (see p. 477).
Fig. 238, B, shows the tentacles of Bowerbankia in their fully expanded and
partially expanded condition. Comparing this with Fig. 234, it will be clear
that when protrusion is taking place, the tentacles are forced in a bundle,
tips first, through the diaphragm and next through the orifice of the
zooecium, the alimentary canal offering no resistance to this movement,
owing to the length of the oesophagus. A moment's consideration will show
that the bases of the tentacles, in passing through the orifice, will carry with
them that part of the flexible tentacle-sheath to which they are attached; and
it will further be clear that so much of the tentacle-sheath as is thus
protruded will be turned inside out. This process of "evagination" continues
Page 467
until its further progress is stopped by the retractor-muscles (r.m), and by
the parieto-vaginal muscles (p.v), which pass from the interior of the body-
wall to the upper part of the tentacle-sheath. The latter has now become the
delicate layer which connects the expanded tentacles with the zooecium;
and the anus (Fig. 238, C, a) opens directly to the exterior. Since the name
"tentacle-sheath" is thus descriptive of the condition of retraction only, the
term "kamptoderm"[504] has been suggested as an alternative name.
The presence of a complete digestive canal and the ciliation of the tentacles
in Polyzoa are conspicuous differences between these animals and the
Hydroids, with some of which the Polyzoa may have a marked external
similarity.
The outermost[505] layer of the body-wall is known as the "ectocyst" (Fig.
234, e). This may be densely calcareous, in which case the dried Polyzoon
differs little in appearance from the living animal with its tentacles
retracted; or it may be partially calcified, or it may consist entirely of a
flexible cuticle, as in Fig. 234. The ectocyst is prolonged through the orifice
(o) as far as the diaphragm (d).
Forms with a calcareous ectocyst are commonly ornamented with ridges or
other patterns, which are often of great beauty. The ectocyst in these cases
is commonly interrupted at intervals by pores (Fig. 239, C), into which
processes of the "endocyst"—the living, internal part of the body-wall—
extend. These may appear as superficial pores, which apparently open to the
exterior in the dried condition, or they may perforate the septa between
adjacent individuals. This may be strikingly demonstrated by decalcifying a
branch of Crisia (Fig. 237), in which the zooecia then appear connected by
numerous strands of tissue. In many marine forms the communications
between the individuals are in the form of small sieve-like plates known as
"rosette-plates."
The endocyst may consist of definite layers of ectoderm (em) and
mesoderm (mm), as in Fig. 234, but the mesoderm is commonly in the form
of a loose network, some of which is attached to the body-wall, some to the
alimentary canal, some forming connecting strands between these two
the parieto-vaginal muscles (p.v), which pass from the interior of the body-
wall to the upper part of the tentacle-sheath. The latter has now become the
delicate layer which connects the expanded tentacles with the zooecium;
and the anus (Fig. 238, C, a) opens directly to the exterior. Since the name
"tentacle-sheath" is thus descriptive of the condition of retraction only, the
term "kamptoderm"[504] has been suggested as an alternative name.
The presence of a complete digestive canal and the ciliation of the tentacles
in Polyzoa are conspicuous differences between these animals and the
Hydroids, with some of which the Polyzoa may have a marked external
similarity.
The outermost[505] layer of the body-wall is known as the "ectocyst" (Fig.
234, e). This may be densely calcareous, in which case the dried Polyzoon
differs little in appearance from the living animal with its tentacles
retracted; or it may be partially calcified, or it may consist entirely of a
flexible cuticle, as in Fig. 234. The ectocyst is prolonged through the orifice
(o) as far as the diaphragm (d).
Forms with a calcareous ectocyst are commonly ornamented with ridges or
other patterns, which are often of great beauty. The ectocyst in these cases
is commonly interrupted at intervals by pores (Fig. 239, C), into which
processes of the "endocyst"—the living, internal part of the body-wall—
extend. These may appear as superficial pores, which apparently open to the
exterior in the dried condition, or they may perforate the septa between
adjacent individuals. This may be strikingly demonstrated by decalcifying a
branch of Crisia (Fig. 237), in which the zooecia then appear connected by
numerous strands of tissue. In many marine forms the communications
between the individuals are in the form of small sieve-like plates known as
"rosette-plates."
The endocyst may consist of definite layers of ectoderm (em) and
mesoderm (mm), as in Fig. 234, but the mesoderm is commonly in the form
of a loose network, some of which is attached to the body-wall, some to the
alimentary canal, some forming connecting strands between these two
Page 468
layers, and other cells floating about freely in the body-cavity. These
mesodermic structures are often spoken of as the "funicular tissue," since
one or more strands of it commonly take on the form of a definite
"funiculus" (f). This structure may bear the ovary (ov), while the testes (t)
are found, commonly in the same zooecium, attached to various parts of the
body-wall. The eggs and spermatozoa, when ripe, break off and float freely
in the body-cavity.
The funicular tissue was at one time described as a "colonial nervous
system." The idea expressed by this term must be considered erroneous
from the fact that no nervous co-ordination of the individuals is known to
exist, in the vast majority of cases. The actual nervous system consists of a
ganglion (g) placed between the mouth and anus of each polypide, and
lying in a small circular canal (not shown in Fig. 234) which immediately
surrounds the oesophagus. This canal is developed in the bud as a part of
the body-cavity, from which it becomes completely separated in marine
forms. The Polyzoa have no vascular system.
Brown Bodies.—In the majority of cases, an extraordinary process of
regeneration takes place periodically during the life of each zooecium. The
tentacles, alimentary canal, and nervous system break down, and the
tentacles cease to be capable of being protruded (Fig. 235, 1). The
degenerating organs become compacted into a rounded mass (Fig. 235, 2
and 3, b.b), known from its colour as the "brown body." This structure may
readily be seen in a large proportion of the zooecia of transparent species. In
active parts of the colony the body-wall next develops an internal bud-like
structure (Fig. 235, 1, b), which rapidly acquires the form of a new polypide
(Fig. 235, 2 and 3). This takes the place originally occupied by the old
polypide, while the latter may either remain in the zooecium in the
permanent form of a "brown body," or pass to the exterior. In Flustra the
young polypide-bud becomes connected with the "brown body" by a
funiculus (Fig. 235, 1, 2). The apex of the blind pouch or "caecum" of the
young stomach is guided by this strand to the "brown body," which it
partially surrounds (3). The "brown body" then breaks up, and its fragments
pass into the cavity of the stomach, from which they reach the exterior by
means of the anus.
mesodermic structures are often spoken of as the "funicular tissue," since
one or more strands of it commonly take on the form of a definite
"funiculus" (f). This structure may bear the ovary (ov), while the testes (t)
are found, commonly in the same zooecium, attached to various parts of the
body-wall. The eggs and spermatozoa, when ripe, break off and float freely
in the body-cavity.
The funicular tissue was at one time described as a "colonial nervous
system." The idea expressed by this term must be considered erroneous
from the fact that no nervous co-ordination of the individuals is known to
exist, in the vast majority of cases. The actual nervous system consists of a
ganglion (g) placed between the mouth and anus of each polypide, and
lying in a small circular canal (not shown in Fig. 234) which immediately
surrounds the oesophagus. This canal is developed in the bud as a part of
the body-cavity, from which it becomes completely separated in marine
forms. The Polyzoa have no vascular system.
Brown Bodies.—In the majority of cases, an extraordinary process of
regeneration takes place periodically during the life of each zooecium. The
tentacles, alimentary canal, and nervous system break down, and the
tentacles cease to be capable of being protruded (Fig. 235, 1). The
degenerating organs become compacted into a rounded mass (Fig. 235, 2
and 3, b.b), known from its colour as the "brown body." This structure may
readily be seen in a large proportion of the zooecia of transparent species. In
active parts of the colony the body-wall next develops an internal bud-like
structure (Fig. 235, 1, b), which rapidly acquires the form of a new polypide
(Fig. 235, 2 and 3). This takes the place originally occupied by the old
polypide, while the latter may either remain in the zooecium in the
permanent form of a "brown body," or pass to the exterior. In Flustra the
young polypide-bud becomes connected with the "brown body" by a
funiculus (Fig. 235, 1, 2). The apex of the blind pouch or "caecum" of the
young stomach is guided by this strand to the "brown body," which it
partially surrounds (3). The "brown body" then breaks up, and its fragments
pass into the cavity of the stomach, from which they reach the exterior by
means of the anus.
Page 469
Fig. 235.—Flustra papyrea Pall. Naples. × 50. Illustrating the development of a new
polypide after the formation of a "brown body." In 1, a, two masses formed from
the alimentary canal; b, young polypide-bud; b.b, degenerating tentacles; c,
connective tissue: 2, another zooecium, later stage; b.b, brown body; r.m,
retractor muscles; s, stomach; t, tentacles of new polypide; t.s, tentacle-sheath: 3,
the same zooecium, 191 hours later; letters as in 2. 1 and 2 are seen from the
front, 3 from the back.[506]
There is some reason to believe[507] that these remarkable processes are
connected with the removal of waste nitrogenous matters. The Marine
Polyzoa are not known to be, in most cases, provided with definite
excretory organs, although it is possible that the intertentacular organ (Fig.
234, i) described on p. 508 may in some cases perform excretory functions.
There can, however, be little doubt that some kind of excretion takes place
in the Polyzoa; and in considering what organs could possibly perform this
work, our attention is arrested by the alimentary canal. The digestive organs
of the young bud are perfectly colourless. As growth proceeds, certain parts
acquire a yellowish, and later a brown colour. The degeneration of the
polypide is followed by the grouping of large numbers of the free cells of
the body-cavity into a mass which closely surrounds the incipient "brown
body." Under their action, the latter becomes considerably smaller, probably
as the result of the absorption of matters of nutritive value into other tissues.
The final result is the formation of the compact "brown body," whose
colour is principally derived from the pigment formerly present in the
alimentary canal. Experiments made by introducing into the tissues of the
Polyzoa certain artificial pigments which are known to be excreted by the
kidneys when injected into the bodies of other animals, have given some
reason for believing that the appearance of the brown pigment in the wall of
the digestive organs is, in part, a normal process of excretion; although that
process is not entirely carried out by the organs in question.
polypide after the formation of a "brown body." In 1, a, two masses formed from
the alimentary canal; b, young polypide-bud; b.b, degenerating tentacles; c,
connective tissue: 2, another zooecium, later stage; b.b, brown body; r.m,
retractor muscles; s, stomach; t, tentacles of new polypide; t.s, tentacle-sheath: 3,
the same zooecium, 191 hours later; letters as in 2. 1 and 2 are seen from the
front, 3 from the back.[506]
There is some reason to believe[507] that these remarkable processes are
connected with the removal of waste nitrogenous matters. The Marine
Polyzoa are not known to be, in most cases, provided with definite
excretory organs, although it is possible that the intertentacular organ (Fig.
234, i) described on p. 508 may in some cases perform excretory functions.
There can, however, be little doubt that some kind of excretion takes place
in the Polyzoa; and in considering what organs could possibly perform this
work, our attention is arrested by the alimentary canal. The digestive organs
of the young bud are perfectly colourless. As growth proceeds, certain parts
acquire a yellowish, and later a brown colour. The degeneration of the
polypide is followed by the grouping of large numbers of the free cells of
the body-cavity into a mass which closely surrounds the incipient "brown
body." Under their action, the latter becomes considerably smaller, probably
as the result of the absorption of matters of nutritive value into other tissues.
The final result is the formation of the compact "brown body," whose
colour is principally derived from the pigment formerly present in the
alimentary canal. Experiments made by introducing into the tissues of the
Polyzoa certain artificial pigments which are known to be excreted by the
kidneys when injected into the bodies of other animals, have given some
reason for believing that the appearance of the brown pigment in the wall of
the digestive organs is, in part, a normal process of excretion; although that
process is not entirely carried out by the organs in question.
Page 470
Little is known with regard to the duration of life of a single polypide; but
some information bearing on this question may be obtained from a set of
observations made on Flustra papyrea.[508] The table gives the number of
days from the time at which the polypides were noticed to commence their
degeneration:—
Days.
2 "Brown body" partially formed, the parts of the polypide being still
easily recognisable.
5 Tentacles still just recognisable: appearance of new polypide-bud.
8 Stage shown in Fig. 235, 2.
11 Union of apex of stomach with "brown body."
16 "Brown body" half surrounded by stomach, and preparing to break
up (Fig. 235, 3).
21 "Brown body" broken up into numerous fragments, contained in the
alimentary canal of the new polypide.
35 "Brown body" almost completely absorbed.[509]
These results did not hold good for all the zooecia in a single colony. In
some, the "brown body" was not completely got rid of at the end of sixty-
eight days, the conclusion of the experiment.
So striking are the facts relating to the "brown bodies" that it has been
believed[510] that what we have above described as the individual really
consists of two kinds of individuals: firstly, the "polypide" or complex of
tentacles and digestive organs; and secondly, the "zooecium," or house of
the zooid or polypide, corresponding with what has been described above as
the body-wall. The one individual, the zooecium, is on this view provided
with successive generations of the second kind of individual, the polypide;
and these latter function as the digestive organs of the two-fold organism.
This view, though fascinating at first sight, is not borne out by an
examination of all the facts of the case, especially when the Entoprocta are
taken into account.
some information bearing on this question may be obtained from a set of
observations made on Flustra papyrea.[508] The table gives the number of
days from the time at which the polypides were noticed to commence their
degeneration:—
Days.
2 "Brown body" partially formed, the parts of the polypide being still
easily recognisable.
5 Tentacles still just recognisable: appearance of new polypide-bud.
8 Stage shown in Fig. 235, 2.
11 Union of apex of stomach with "brown body."
16 "Brown body" half surrounded by stomach, and preparing to break
up (Fig. 235, 3).
21 "Brown body" broken up into numerous fragments, contained in the
alimentary canal of the new polypide.
35 "Brown body" almost completely absorbed.[509]
These results did not hold good for all the zooecia in a single colony. In
some, the "brown body" was not completely got rid of at the end of sixty-
eight days, the conclusion of the experiment.
So striking are the facts relating to the "brown bodies" that it has been
believed[510] that what we have above described as the individual really
consists of two kinds of individuals: firstly, the "polypide" or complex of
tentacles and digestive organs; and secondly, the "zooecium," or house of
the zooid or polypide, corresponding with what has been described above as
the body-wall. The one individual, the zooecium, is on this view provided
with successive generations of the second kind of individual, the polypide;
and these latter function as the digestive organs of the two-fold organism.
This view, though fascinating at first sight, is not borne out by an
examination of all the facts of the case, especially when the Entoprocta are
taken into account.
Page 471
History.—The history of the Polyzoa, as far as 1856, has been fully treated
by Allman in his great work on the Fresh-water Polyzoa;[511] but a few
words may be said on this subject.
The Polyzoa attracted comparatively little attention before the beginning of
the present century. Originally passed over as seaweeds, their real nature
was established in connexion with the discovery of the animal nature of
corals. So great a revolution could hardly be accepted without a struggle,
and even Linnaeus went no further in this direction than to place them in a
kind of half-way group of "zoophytes," whose nature was partly animal and
partly vegetable. It is hardly necessary to point out that this view has now
been abandoned by common consent; and indeed there is no more reason
for regarding an animal as showing an approach to the plants because it
grows in the external semblance of a seaweed than there would be for
supposing a bee-orchid to be allied to the animal kingdom because of the
form of its flowers.
But the claims of the Polyzoa to rank as a separate class were by no means
admitted with the discovery that they were animals. They were still
confounded with Hydroids, Alcyonarians, or Corals until their possession of
a complete alimentary canal was recognised as a feature distinguishing
them from those animals. This was principally due to the observations of J.
V. Thompson[512] in Ireland, who introduced the term Polyzoa; and of C. G.
Ehrenberg[513] in Germany, who proposed the class-name Bryozoa, or
moss-like animals.
It is impossible to avoid all mention of the controversy which has raged
with regard to these two rival terms. The controversy is for the present at
rest, the name Polyzoa being employed by the majority of English writers,
amongst whom must be mentioned Allman, Busk, Hincks, and Norman,
admittedly authorities of the first rank; while Bryozoa is employed by
practically all the Continental writers.
The priority of Thompson's name is unquestioned. While Ehrenberg,
however, definitely introduced Bryozoa as the name of a group, Thompson
was less precise in this respect, although he states[514] that his discovery
by Allman in his great work on the Fresh-water Polyzoa;[511] but a few
words may be said on this subject.
The Polyzoa attracted comparatively little attention before the beginning of
the present century. Originally passed over as seaweeds, their real nature
was established in connexion with the discovery of the animal nature of
corals. So great a revolution could hardly be accepted without a struggle,
and even Linnaeus went no further in this direction than to place them in a
kind of half-way group of "zoophytes," whose nature was partly animal and
partly vegetable. It is hardly necessary to point out that this view has now
been abandoned by common consent; and indeed there is no more reason
for regarding an animal as showing an approach to the plants because it
grows in the external semblance of a seaweed than there would be for
supposing a bee-orchid to be allied to the animal kingdom because of the
form of its flowers.
But the claims of the Polyzoa to rank as a separate class were by no means
admitted with the discovery that they were animals. They were still
confounded with Hydroids, Alcyonarians, or Corals until their possession of
a complete alimentary canal was recognised as a feature distinguishing
them from those animals. This was principally due to the observations of J.
V. Thompson[512] in Ireland, who introduced the term Polyzoa; and of C. G.
Ehrenberg[513] in Germany, who proposed the class-name Bryozoa, or
moss-like animals.
It is impossible to avoid all mention of the controversy which has raged
with regard to these two rival terms. The controversy is for the present at
rest, the name Polyzoa being employed by the majority of English writers,
amongst whom must be mentioned Allman, Busk, Hincks, and Norman,
admittedly authorities of the first rank; while Bryozoa is employed by
practically all the Continental writers.
The priority of Thompson's name is unquestioned. While Ehrenberg,
however, definitely introduced Bryozoa as the name of a group, Thompson
was less precise in this respect, although he states[514] that his discovery
Page 472
"must be the cause of extensive alterations and dismemberments in the class
with which they [the Polyzoa] have hitherto been associated." Thompson, in
fact, clearly understood that the Polyzoa could no longer rank with the
Hydroids. The controversy has been summarised by Hincks, in his History
of the British Marine Polyzoa,[515] where references to other papers on the
same subject are given.
The Polyzoa were associated by H. Milne-Edwards with the Tunicata in the
group Molluscoidea (Molluscoïdes[516]), to which the Brachiopoda were
afterwards added by Huxley.[517] A knowledge of the development of the
Tunicata has, however, shown that these animals must be withdrawn from
any association with the other two groups; while there is little real evidence
that even the Brachiopods have anything to do with the Polyzoa.
Classification.—The Polyzoa are divided into two sub-classes:—I, the
Entoprocta; and II, the Ectoprocta.[518] Although the character referred to
by these terms is merely the position of the anus with relation to the
tentacles,[519] there can be no doubt that the two groups differ widely from
one another in many important respects. I do not, however, accept the view,
maintained by some authors, that the Entoprocta and the Ectoprocta are two
separate classes which are not nearly related.
The base from which the whole set of tentacles springs is known as the
"lophophore."[520] In the Entoprocta (Fig. 236, 1) the lophophore is circular;
the mouth is situated near the margin of the area surrounded by the
tentacles; and the anus is found within the circlet, near the end opposite to
the mouth.
In (2) and (3), representing the Ectoprocta, the anus is outside the series of
tentacles. In the majority of cases, including all the marine Ectoprocta and
one or two of the fresh-water forms, the lophophore is circular (2), the
mouth occurring at the centre of the circle, and not being provided with a
lip. These forms of Ectoprocta constitute the Order Gymnolaemata,[521] the
dominant group of the Polyzoa in respect of number of genera and species.
The remaining Ectoprocta belong to the exclusively fresh-water Order
with which they [the Polyzoa] have hitherto been associated." Thompson, in
fact, clearly understood that the Polyzoa could no longer rank with the
Hydroids. The controversy has been summarised by Hincks, in his History
of the British Marine Polyzoa,[515] where references to other papers on the
same subject are given.
The Polyzoa were associated by H. Milne-Edwards with the Tunicata in the
group Molluscoidea (Molluscoïdes[516]), to which the Brachiopoda were
afterwards added by Huxley.[517] A knowledge of the development of the
Tunicata has, however, shown that these animals must be withdrawn from
any association with the other two groups; while there is little real evidence
that even the Brachiopods have anything to do with the Polyzoa.
Classification.—The Polyzoa are divided into two sub-classes:—I, the
Entoprocta; and II, the Ectoprocta.[518] Although the character referred to
by these terms is merely the position of the anus with relation to the
tentacles,[519] there can be no doubt that the two groups differ widely from
one another in many important respects. I do not, however, accept the view,
maintained by some authors, that the Entoprocta and the Ectoprocta are two
separate classes which are not nearly related.
The base from which the whole set of tentacles springs is known as the
"lophophore."[520] In the Entoprocta (Fig. 236, 1) the lophophore is circular;
the mouth is situated near the margin of the area surrounded by the
tentacles; and the anus is found within the circlet, near the end opposite to
the mouth.
In (2) and (3), representing the Ectoprocta, the anus is outside the series of
tentacles. In the majority of cases, including all the marine Ectoprocta and
one or two of the fresh-water forms, the lophophore is circular (2), the
mouth occurring at the centre of the circle, and not being provided with a
lip. These forms of Ectoprocta constitute the Order Gymnolaemata,[521] the
dominant group of the Polyzoa in respect of number of genera and species.
The remaining Ectoprocta belong to the exclusively fresh-water Order
Page 473
Phylactolaemata,[522] in which the mouth is protected by an overhanging
lip or "epistome"; the ground-plan of the tentacles is, except in Fredericella,
horse-shoe shaped (Fig. 236, 3), and the tentacles themselves are usually
much more numerous than in the other cases.
Fig. 236.—Ground-plan of the lophophore in (1) Entoprocta, (2) Gymnolaemata, (3)
Phylactolaemata: a, anus; ep, epistome; m, mouth. The tentacles are represented
by shaded circles.
The general characters of these divisions will be more easily understood by
referring to the figures given of living representatives of the groups. The
Entoprocta are illustrated by Figs. 243-245; the Gymnolaemata by Figs.
238, 240; and the Phylactolaemata by Figs. 247, 248.
The Gymnolaemata include three Sub-Orders:—
1. Cyclostomata.[523]—Body-wall densely calcareous, the zooecia
being more or less tubular, usually with a circular orifice (Fig. 237).
2. Cheilostomata.[524]—Body-wall of varying consistency. The orifice
is closed, in the retracted state of the polypide, by a chitinous lip or
"operculum," which is more or less semicircular (Figs. 239, 241).
3. Ctenostomata.[525]—Body-wall always soft. The cavity into which
the tentacles are retracted is closed by a frill-like membrane, the edges
of whose folds have some resemblance to the teeth of a comb. This
membrane, the "collar," is seen in different conditions of protrusion or
retraction in Figs. 234, 238. The stomach may, in this group, be
preceded by a muscular gizzard (Fig. 238, C, g).
lip or "epistome"; the ground-plan of the tentacles is, except in Fredericella,
horse-shoe shaped (Fig. 236, 3), and the tentacles themselves are usually
much more numerous than in the other cases.
Fig. 236.—Ground-plan of the lophophore in (1) Entoprocta, (2) Gymnolaemata, (3)
Phylactolaemata: a, anus; ep, epistome; m, mouth. The tentacles are represented
by shaded circles.
The general characters of these divisions will be more easily understood by
referring to the figures given of living representatives of the groups. The
Entoprocta are illustrated by Figs. 243-245; the Gymnolaemata by Figs.
238, 240; and the Phylactolaemata by Figs. 247, 248.
The Gymnolaemata include three Sub-Orders:—
1. Cyclostomata.[523]—Body-wall densely calcareous, the zooecia
being more or less tubular, usually with a circular orifice (Fig. 237).
2. Cheilostomata.[524]—Body-wall of varying consistency. The orifice
is closed, in the retracted state of the polypide, by a chitinous lip or
"operculum," which is more or less semicircular (Figs. 239, 241).
3. Ctenostomata.[525]—Body-wall always soft. The cavity into which
the tentacles are retracted is closed by a frill-like membrane, the edges
of whose folds have some resemblance to the teeth of a comb. This
membrane, the "collar," is seen in different conditions of protrusion or
retraction in Figs. 234, 238. The stomach may, in this group, be
preceded by a muscular gizzard (Fig. 238, C, g).
Page 474
Occurrence.—By far the larger number of the Polyzoa are inhabitants of
the sea. A recently published catalogue[526] of marine Polyzoa includes
nearly 1700 living species; and of these, the great majority belong to the
Gymnolaemata. This group is further known to include an enormous
number of fossil forms. Not only do we find that in living Polyzoa the
members of a single Order largely outnumber the remainder of the Polyzoa,
but we may further notice that the Cheilostomata, one of the sub-Orders of
the dominant group, are at present largely in excess of the whole of the rest
of the Polyzoa taken together.
Polyzoa may be collected with ease on almost any part of our coasts. The
fronds of the "sea-mat" (Flustra foliacea) are thrown up by the waves in
thousands in places where the bottom is shallow and sandy. The bases of the
larger seaweeds growing on rocks between tide-marks are nearly always
thickly covered with encrustations of Flustrella hispida or of species of
Alcyonidium, in places where they are kept moist by being covered with a
sufficiently thick layer of other algae. Rocks which are protected from the
sun may be coated with calcareous Cheilostomes; and these are also found,
in company with branching Polyzoa of various kinds, on the bases of the
Laminaria thrown up by gales or exposed at spring tides. The graceful
spirals of Bugula turbinata (Fig. 233, A) may be found hanging from the
rocks at extreme low water; while colonies of Scrupocellaria, remarkable
for their vibracula (see p. 484), are common in many places between tide-
marks. Certain species affect the mouths of estuaries.
Membranipora membranacea commonly covers many square inches of the
frond of Laminaria with its delicate lace-like encrustation. Nitsche[527] has
shown that this species has its calcareous matter deposited in plates,
separated by intervals of uncalcified ectocyst. The effect of this
arrangement is to make the colony flexible, and to enable it to adapt its
shape to the movements of the Laminaria, which is swayed to and fro by
the action of the waves. Many of the calcareous forms growing on
Laminaria have no special arrangement of this kind, and they accordingly
grow in colonies whose area is so small that the greatest movements to
which the seaweed is liable are not sufficient to crack or break the colony.
the sea. A recently published catalogue[526] of marine Polyzoa includes
nearly 1700 living species; and of these, the great majority belong to the
Gymnolaemata. This group is further known to include an enormous
number of fossil forms. Not only do we find that in living Polyzoa the
members of a single Order largely outnumber the remainder of the Polyzoa,
but we may further notice that the Cheilostomata, one of the sub-Orders of
the dominant group, are at present largely in excess of the whole of the rest
of the Polyzoa taken together.
Polyzoa may be collected with ease on almost any part of our coasts. The
fronds of the "sea-mat" (Flustra foliacea) are thrown up by the waves in
thousands in places where the bottom is shallow and sandy. The bases of the
larger seaweeds growing on rocks between tide-marks are nearly always
thickly covered with encrustations of Flustrella hispida or of species of
Alcyonidium, in places where they are kept moist by being covered with a
sufficiently thick layer of other algae. Rocks which are protected from the
sun may be coated with calcareous Cheilostomes; and these are also found,
in company with branching Polyzoa of various kinds, on the bases of the
Laminaria thrown up by gales or exposed at spring tides. The graceful
spirals of Bugula turbinata (Fig. 233, A) may be found hanging from the
rocks at extreme low water; while colonies of Scrupocellaria, remarkable
for their vibracula (see p. 484), are common in many places between tide-
marks. Certain species affect the mouths of estuaries.
Membranipora membranacea commonly covers many square inches of the
frond of Laminaria with its delicate lace-like encrustation. Nitsche[527] has
shown that this species has its calcareous matter deposited in plates,
separated by intervals of uncalcified ectocyst. The effect of this
arrangement is to make the colony flexible, and to enable it to adapt its
shape to the movements of the Laminaria, which is swayed to and fro by
the action of the waves. Many of the calcareous forms growing on
Laminaria have no special arrangement of this kind, and they accordingly
grow in colonies whose area is so small that the greatest movements to
which the seaweed is liable are not sufficient to crack or break the colony.
Page 475
Many species show a decided, or even exclusive, preference for particular
situations; as, for instance, species of Triticella, which are only found on
certain Crustacea. Many encrusting forms prefer the inside of dead shells of
Pecten, Cyprina, etc., to any other habitat. Terebripora[528] excavates
tubular cavities in the substance of the shells of Molluscs. Hypophorella[529]
inhabits passages which it forms in the walls of the tubes of the Polychaets,
Lanice and Chaetopterus. Lepralia foliacea, one of the Cheilostomata,
forms masses which may reach a circumference of several feet, simulating a
small coral-reef. Its contorted plates are a regular museum of Polyzoa, so
numerous are the species which delight to find shelter in the quiet
interstices of the colony. The exquisite little colonies of Crisia eburnea are
commonly found on red seaweeds, or on the branches of the Hydroid
Sertularia.
The Polyzoa are found at all depths, certain Cheilostomes having been
recorded from 3000 fathoms. The Cyclostomes dredged by the "Challenger"
were all found in depths of 1600 fathoms or less, while the Ctenostomes are
a distinctly shallow water group, most having been found at less than 40
fathoms, and only three at so great a depth as 150 fathoms.[530]
A few forms (Membranipora pilosa, Scrupocellaria reptans, etc.) are
known to be phosphorescent;[531] but it is not known what is the purpose of
this phenomenon.
External Form.—The Polyzoa may be roughly divided into (1) encrusting
forms, usually calcareous, but sometimes soft; and (2) erect forms, which
are either rigid or flexible. This flexibility can coexist with a highly
calcified ectocyst, as in Crisia (Fig. 237), Cellaria, and others in which the
branches are interrupted at intervals by chitinous joints. The coral-like
forms may assume the most exquisite shapes, pre-eminent among which are
the lovely net-like colonies of Retepora. Polyzoa of this type are seldom
found between tide-marks, where their brittle branches would be liable to
be snapped off by the waves. The erect species which occur in such
positions are flexible, although flexible species are by no means restricted
to the zone between tide-marks.
situations; as, for instance, species of Triticella, which are only found on
certain Crustacea. Many encrusting forms prefer the inside of dead shells of
Pecten, Cyprina, etc., to any other habitat. Terebripora[528] excavates
tubular cavities in the substance of the shells of Molluscs. Hypophorella[529]
inhabits passages which it forms in the walls of the tubes of the Polychaets,
Lanice and Chaetopterus. Lepralia foliacea, one of the Cheilostomata,
forms masses which may reach a circumference of several feet, simulating a
small coral-reef. Its contorted plates are a regular museum of Polyzoa, so
numerous are the species which delight to find shelter in the quiet
interstices of the colony. The exquisite little colonies of Crisia eburnea are
commonly found on red seaweeds, or on the branches of the Hydroid
Sertularia.
The Polyzoa are found at all depths, certain Cheilostomes having been
recorded from 3000 fathoms. The Cyclostomes dredged by the "Challenger"
were all found in depths of 1600 fathoms or less, while the Ctenostomes are
a distinctly shallow water group, most having been found at less than 40
fathoms, and only three at so great a depth as 150 fathoms.[530]
A few forms (Membranipora pilosa, Scrupocellaria reptans, etc.) are
known to be phosphorescent;[531] but it is not known what is the purpose of
this phenomenon.
External Form.—The Polyzoa may be roughly divided into (1) encrusting
forms, usually calcareous, but sometimes soft; and (2) erect forms, which
are either rigid or flexible. This flexibility can coexist with a highly
calcified ectocyst, as in Crisia (Fig. 237), Cellaria, and others in which the
branches are interrupted at intervals by chitinous joints. The coral-like
forms may assume the most exquisite shapes, pre-eminent among which are
the lovely net-like colonies of Retepora. Polyzoa of this type are seldom
found between tide-marks, where their brittle branches would be liable to
be snapped off by the waves. The erect species which occur in such
positions are flexible, although flexible species are by no means restricted
to the zone between tide-marks.
Page 476
Fig. 237.—Crisia ramosa Harmer, Plymouth. A, End of a branch, × 1; B, another
branch, × 20, showing the chitinous joints, the tubular zooecia characteristic of
Cyclostomata, and the pear-shaped ovicell with a funnel-shaped orifice at its
upper end.
Although the form of the colony is very different in different Polyzoa, a
pocket-lens will usually show whether a given specimen belongs to the
group or not. The surface is nearly always more or less distinctly composed
of zooecia, or at least shows their orifices. The entire colony may be built
up of these zooecia; and this is by far the commonest arrangement, both in
encrusting and in erect forms. In certain genera, however, and particularly
in some Ctenostomes (Fig. 238), and in most of the Entoprocta, the
individuals grow out at intervals from a cylindrical stem or "stolon" (st),
which is not composed of zooecia.
The Cyclostomata may assume an erect or encrusting habit. Their zooecia
are always more or less cylindrical; the upper ends being often completely
free, although in many cases the whole zooecium is closely adnate to its
neighbours. In the breeding season the forms which belong to this group are
provided with curious "ovicells," which contain the embryos. These may
either be pear-shaped swellings on the branches (Crisia, Fig. 237), or they
branch, × 20, showing the chitinous joints, the tubular zooecia characteristic of
Cyclostomata, and the pear-shaped ovicell with a funnel-shaped orifice at its
upper end.
Although the form of the colony is very different in different Polyzoa, a
pocket-lens will usually show whether a given specimen belongs to the
group or not. The surface is nearly always more or less distinctly composed
of zooecia, or at least shows their orifices. The entire colony may be built
up of these zooecia; and this is by far the commonest arrangement, both in
encrusting and in erect forms. In certain genera, however, and particularly
in some Ctenostomes (Fig. 238), and in most of the Entoprocta, the
individuals grow out at intervals from a cylindrical stem or "stolon" (st),
which is not composed of zooecia.
The Cyclostomata may assume an erect or encrusting habit. Their zooecia
are always more or less cylindrical; the upper ends being often completely
free, although in many cases the whole zooecium is closely adnate to its
neighbours. In the breeding season the forms which belong to this group are
provided with curious "ovicells," which contain the embryos. These may
either be pear-shaped swellings on the branches (Crisia, Fig. 237), or they
Page 477
may form inflations of the surface, between the zooecia. The mature ovicell
is provided with one or more openings, through which the larvae escape.
Fig. 238.—Bowerbankia pustulosa Ell. and Sol., Plymouth. A, Fragment of a colony,
natural size, showing the branching stem, bearing tufts of zooecia: B, one of
these tufts, with the growing apex of the stem (st), × 27; b, young zooecia (buds);
c, the "collar" characteristic of Ctenostomata; t, tentacles; C, a single zooecium,
with expanded tentacles, more highly magnified; a, anus; c, collar; g, gizzard; i,
intestine; o, oesophagus; s, stomach.
The Ctenostomata rarely have even the slightest trace of calcareous matter.
Alcyonidium and its allies form soft encrustations, or may even grow into
erect masses six inches or more in height (A. gelatinosum). In this type the
zooecia are often so closely united that it may be difficult or impossible to
make out their limits in the living colony. Many of the dendritic or
branching Ctenostomes (Fig. 238) are characterised by an extreme delicacy
of habit. The zooecia in these cases are sharply marked off from the stem.
They are either cylindrical or ovoid, being commonly attached by a very
narrow base, so that in some species they readily fall off, and may thus be
completely absent in certain parts of the colony. In such forms as
Vesicularia spinosa, it requires considerable experience to recognise a stem
which has lost its zooecia as being part of a Polyzoon. In Mimosella the
zooecia possess a remarkable power of movement on the stem, similar to
that possessed by the leaflets of the Sensitive Plant.[532] In certain forms
(Bowerbankia, Amathia) the zooecia occur in groups separated by intervals
which are devoid of zooecia, but in other cases they may have a more
irregular arrangement. The collar to which this group owes its name is by
no means a conspicuous feature. Its position when retracted has been shown
in Fig. 234, while Fig. 238 further illustrates its relations.
is provided with one or more openings, through which the larvae escape.
Fig. 238.—Bowerbankia pustulosa Ell. and Sol., Plymouth. A, Fragment of a colony,
natural size, showing the branching stem, bearing tufts of zooecia: B, one of
these tufts, with the growing apex of the stem (st), × 27; b, young zooecia (buds);
c, the "collar" characteristic of Ctenostomata; t, tentacles; C, a single zooecium,
with expanded tentacles, more highly magnified; a, anus; c, collar; g, gizzard; i,
intestine; o, oesophagus; s, stomach.
The Ctenostomata rarely have even the slightest trace of calcareous matter.
Alcyonidium and its allies form soft encrustations, or may even grow into
erect masses six inches or more in height (A. gelatinosum). In this type the
zooecia are often so closely united that it may be difficult or impossible to
make out their limits in the living colony. Many of the dendritic or
branching Ctenostomes (Fig. 238) are characterised by an extreme delicacy
of habit. The zooecia in these cases are sharply marked off from the stem.
They are either cylindrical or ovoid, being commonly attached by a very
narrow base, so that in some species they readily fall off, and may thus be
completely absent in certain parts of the colony. In such forms as
Vesicularia spinosa, it requires considerable experience to recognise a stem
which has lost its zooecia as being part of a Polyzoon. In Mimosella the
zooecia possess a remarkable power of movement on the stem, similar to
that possessed by the leaflets of the Sensitive Plant.[532] In certain forms
(Bowerbankia, Amathia) the zooecia occur in groups separated by intervals
which are devoid of zooecia, but in other cases they may have a more
irregular arrangement. The collar to which this group owes its name is by
no means a conspicuous feature. Its position when retracted has been shown
in Fig. 234, while Fig. 238 further illustrates its relations.
Page 478
The Cheilostomata grow in a great variety of forms, and also show a wide
range of character in their zooecia. The orifice is commonly surrounded by
stiff spines (Fig. 257, p. 524), which perhaps have the function of protecting
the delicate polypides from the sudden impact of foreign bodies. These
spines may attain an enormous development, as in Bicellaria ciliata, and
some forms of Electra (Membranipora) pilosa (Fig. 256, A).
The operculum is usually, though by no means always, a conspicuous
feature of the Cheilostome zooecium. It is invariably of chitinous
consistency, and is more or less semicircular in outline, the straight edge
forming a hinge on which the operculum opens. In some cases the orifice is
surrounded by a raised margin or "peristome" (Fig. 255, B, C); the
operculum is then situated at the bottom of a depression of the surface, and
may be concealed from view. In others, in which the front wall of the
zooecium is membranous (Bugula, Fig. 233), the operculum is merely a
part of this membrane, and so is quite inconspicuous; and in cases of this
kind the membranous wall may be protected by an arched spine, the
"fornix," developed from one side of the zooecium (Fig. 254, f). The
ovicells are commonly a conspicuous feature of this group, although they
are believed to differ fundamentally from those of Cyclostomata. They have
the form of a helmet-like covering overhanging the orifice (Figs. 240, 241),
and may be either prominent or more or less concealed by the growth of
adjacent parts of the zooecia. The presence of ovicells of this description is
perfectly distinctive of the Cheilostomata.
Avicularia and Vibracula.—Most singular of the external appendages of
the Cheilostomata are the extraordinary "avicularia" and "vibracula" of
some genera.[533] By the comparison of a carefully selected series of genera,
it has been established that the avicularium is a special modification of a
zooecium. One of its least modified forms is found in Flustra foliacea (Fig.
232), where the avicularia (a) are small zooecia with a conspicuously large
operculum ("mandible"). Avicularia of a similar type occur in Cellaria (Fig.
239, A), Schizotheca, etc., the avicularium occupying the place of an
ordinary zooecium. These are the "vicarious" avicularia of Mr. Busk.[534]
range of character in their zooecia. The orifice is commonly surrounded by
stiff spines (Fig. 257, p. 524), which perhaps have the function of protecting
the delicate polypides from the sudden impact of foreign bodies. These
spines may attain an enormous development, as in Bicellaria ciliata, and
some forms of Electra (Membranipora) pilosa (Fig. 256, A).
The operculum is usually, though by no means always, a conspicuous
feature of the Cheilostome zooecium. It is invariably of chitinous
consistency, and is more or less semicircular in outline, the straight edge
forming a hinge on which the operculum opens. In some cases the orifice is
surrounded by a raised margin or "peristome" (Fig. 255, B, C); the
operculum is then situated at the bottom of a depression of the surface, and
may be concealed from view. In others, in which the front wall of the
zooecium is membranous (Bugula, Fig. 233), the operculum is merely a
part of this membrane, and so is quite inconspicuous; and in cases of this
kind the membranous wall may be protected by an arched spine, the
"fornix," developed from one side of the zooecium (Fig. 254, f). The
ovicells are commonly a conspicuous feature of this group, although they
are believed to differ fundamentally from those of Cyclostomata. They have
the form of a helmet-like covering overhanging the orifice (Figs. 240, 241),
and may be either prominent or more or less concealed by the growth of
adjacent parts of the zooecia. The presence of ovicells of this description is
perfectly distinctive of the Cheilostomata.
Avicularia and Vibracula.—Most singular of the external appendages of
the Cheilostomata are the extraordinary "avicularia" and "vibracula" of
some genera.[533] By the comparison of a carefully selected series of genera,
it has been established that the avicularium is a special modification of a
zooecium. One of its least modified forms is found in Flustra foliacea (Fig.
232), where the avicularia (a) are small zooecia with a conspicuously large
operculum ("mandible"). Avicularia of a similar type occur in Cellaria (Fig.
239, A), Schizotheca, etc., the avicularium occupying the place of an
ordinary zooecium. These are the "vicarious" avicularia of Mr. Busk.[534]
Page 479
Fig. 239.—Forms of avicularia. A, Cellaria fistulosa L., Plymouth, × 43; a.z,
avicularian zooecium, with closed mandible; o, operculum of zooecium: B,
Schizoporella unicornis Johnst., Scilly Is., × 43; zooecium bearing two
avicularia; m, opened mandible of avicularium; s, sinus of orifice: C, zooecium
of Smittia landsborovii Johnst., Plymouth, × 43; the operculum is seen at the
bottom of a depression surrounded by a thin collar or "peristome," in an
emargination of which is seen an avicularian zooecium (a.z); m, mandible
(opened); p, pores; t, tooth.
In the next stage (Figs. 239, B, 256, B) the avicularian zooecium is further
reduced; it has in most cases lost its place in the series of individuals, and is
found instead seated on some part of an ordinary zooecium ("adventitious"
avicularia). The avicularium now consists of a much reduced zooecium,
bearing the well-developed operculum or mandible.
Having arrived at this point, the avicularia seem to lose all sense of the
propriety of remaining in the positions once occupied by zooecia. They
have become degraded to the rank of appendages of the zooecia, and as
such they may occur in an astonishing variety of positions. Sometimes one
occurs on each zooecium in the middle line, or asymmetrically, or even on
the top of the ovicell; in other cases the orifice is flanked by an avicularium
on each side (Fig. 239, B). Sometimes (Cellepora) the avicularia are of
more than one kind, some being large and some small, some having a
pointed mandible and others a mandible with a rounded spoon-like end.
In the cases so far considered, the body of the avicularium is fixed. The
highest differentiation acquired by these structures occurs in cases like
Bugula, where they are borne on flexible stalks, which may even exceed the
avicularia in length.[535]
avicularian zooecium, with closed mandible; o, operculum of zooecium: B,
Schizoporella unicornis Johnst., Scilly Is., × 43; zooecium bearing two
avicularia; m, opened mandible of avicularium; s, sinus of orifice: C, zooecium
of Smittia landsborovii Johnst., Plymouth, × 43; the operculum is seen at the
bottom of a depression surrounded by a thin collar or "peristome," in an
emargination of which is seen an avicularian zooecium (a.z); m, mandible
(opened); p, pores; t, tooth.
In the next stage (Figs. 239, B, 256, B) the avicularian zooecium is further
reduced; it has in most cases lost its place in the series of individuals, and is
found instead seated on some part of an ordinary zooecium ("adventitious"
avicularia). The avicularium now consists of a much reduced zooecium,
bearing the well-developed operculum or mandible.
Having arrived at this point, the avicularia seem to lose all sense of the
propriety of remaining in the positions once occupied by zooecia. They
have become degraded to the rank of appendages of the zooecia, and as
such they may occur in an astonishing variety of positions. Sometimes one
occurs on each zooecium in the middle line, or asymmetrically, or even on
the top of the ovicell; in other cases the orifice is flanked by an avicularium
on each side (Fig. 239, B). Sometimes (Cellepora) the avicularia are of
more than one kind, some being large and some small, some having a
pointed mandible and others a mandible with a rounded spoon-like end.
In the cases so far considered, the body of the avicularium is fixed. The
highest differentiation acquired by these structures occurs in cases like
Bugula, where they are borne on flexible stalks, which may even exceed the
avicularia in length.[535]
Page 480
Fig. 240.—Bugula turbinata, showing avicularia (a, a'). The figure is explained on p.
468.
In Bugula turbinata (Fig. 240) each zooecium is provided with one of these
appendages, attached to the base of the outer of the two spines which border
its orifice. The avicularia of the two edges of the flattened branch are much
larger than those of the more internal zooecia. The upper jaw is
strengthened by a kind of buttress, or thickening of the ectocyst, which
passes on each side across the avicularium to the hinge-line of its mandible.
The upper part of the beak is strongly hooked, while the tip of the mandible
bears a prominent spike, which fits inside the upper beak when the jaw
snaps. A great part of the head is filled with a strong muscle, whose fibres
exhibit a distinct transverse striation, and converge into a median tendon.
The latter is inserted into the middle of the mandible. The muscle serves to
close the jaws, and is the representative of the muscles by which the
operculum is closed in an ordinary zooecium. The lower jaw is opened by
means of a pair of muscles which are situated immediately under the
ectocyst of the avicularium, and pass into the mandible close to its hinge.
468.
In Bugula turbinata (Fig. 240) each zooecium is provided with one of these
appendages, attached to the base of the outer of the two spines which border
its orifice. The avicularia of the two edges of the flattened branch are much
larger than those of the more internal zooecia. The upper jaw is
strengthened by a kind of buttress, or thickening of the ectocyst, which
passes on each side across the avicularium to the hinge-line of its mandible.
The upper part of the beak is strongly hooked, while the tip of the mandible
bears a prominent spike, which fits inside the upper beak when the jaw
snaps. A great part of the head is filled with a strong muscle, whose fibres
exhibit a distinct transverse striation, and converge into a median tendon.
The latter is inserted into the middle of the mandible. The muscle serves to
close the jaws, and is the representative of the muscles by which the
operculum is closed in an ordinary zooecium. The lower jaw is opened by
means of a pair of muscles which are situated immediately under the
ectocyst of the avicularium, and pass into the mandible close to its hinge.
Page 481
Fig. 241.—Illustrating the transition from avicularia to vibracula. A, Microporella
ciliata Pall., Scilly Is., × 62; a, avicularium with short mandible (closed); a',
avicularium with vibraculoid mandible (open); m.p, median pore; o, ovicell: B,
Mastigophora dutertrei Aud., Shetland Is., × 47; s, sinus of orifice; v, seta of
vibraculum (or vibraculoid avicularium).
Within the jaws, in the region which we may term the palate, is a rounded
knob, which bears a tuft of delicate sensory hairs, which doubtless enable
the avicularium to recognise the presence of any foreign body. The closure
of the mouth may, indeed, be instantaneously induced by touching it with
the point of a needle. It has been suggested that a small mass of cells which
bears these hairs may represent the rudiment of the polypide.
The "vibraculum" (Fig. 242) is regarded as an avicularium in which the
mandible has become elongated, so as to form a thin, chitinous "seta,"
which from time to time moves through the water. The part of the
vibraculum which represents the zooecium commonly bears a tubular
rootlet, used for attaching the colony to the substance on which it is
growing (Fig. 254, p. 517).
In Microporella ciliata (Fig. 241, A) the avicularia are very variable, and in
some cases take on a "vibraculoid" character. But in the fully-developed
vibraculum (Fig. 242) there is usually no such compromise of characters. It
may, however, be noted that Scrupocellaria scabra (Fig. 254), which
belongs to a genus characterised by its highly differentiated vibracula,
possesses structures (v.z) which could hardly be distinguished from
avicularia were it not for the presence of the rootlet (r).
In the course of some observations which I had the opportunity of making
on Bugula calathus at Naples, a fine hair offered to a small colony was
seized with such force by the avicularia that the entire colony was lifted out
of the water by the hair. The same colony had captured (1) a small Nereis,
which it held with several of its avicularia; (2) an Anisopod Crustacean, 2½
mm. long; and (3) a small Amphipod, which was held by one of its
antennae. The Anisopod was held by the tip of one leg with one
avicularium, and by the penultimate joint of one of its chelae with an
avicularium of another branch. It was captured in such a way that its chela,
the "hand" of which was about half as long as the avicularium, actually
ciliata Pall., Scilly Is., × 62; a, avicularium with short mandible (closed); a',
avicularium with vibraculoid mandible (open); m.p, median pore; o, ovicell: B,
Mastigophora dutertrei Aud., Shetland Is., × 47; s, sinus of orifice; v, seta of
vibraculum (or vibraculoid avicularium).
Within the jaws, in the region which we may term the palate, is a rounded
knob, which bears a tuft of delicate sensory hairs, which doubtless enable
the avicularium to recognise the presence of any foreign body. The closure
of the mouth may, indeed, be instantaneously induced by touching it with
the point of a needle. It has been suggested that a small mass of cells which
bears these hairs may represent the rudiment of the polypide.
The "vibraculum" (Fig. 242) is regarded as an avicularium in which the
mandible has become elongated, so as to form a thin, chitinous "seta,"
which from time to time moves through the water. The part of the
vibraculum which represents the zooecium commonly bears a tubular
rootlet, used for attaching the colony to the substance on which it is
growing (Fig. 254, p. 517).
In Microporella ciliata (Fig. 241, A) the avicularia are very variable, and in
some cases take on a "vibraculoid" character. But in the fully-developed
vibraculum (Fig. 242) there is usually no such compromise of characters. It
may, however, be noted that Scrupocellaria scabra (Fig. 254), which
belongs to a genus characterised by its highly differentiated vibracula,
possesses structures (v.z) which could hardly be distinguished from
avicularia were it not for the presence of the rootlet (r).
In the course of some observations which I had the opportunity of making
on Bugula calathus at Naples, a fine hair offered to a small colony was
seized with such force by the avicularia that the entire colony was lifted out
of the water by the hair. The same colony had captured (1) a small Nereis,
which it held with several of its avicularia; (2) an Anisopod Crustacean, 2½
mm. long; and (3) a small Amphipod, which was held by one of its
antennae. The Anisopod was held by the tip of one leg with one
avicularium, and by the penultimate joint of one of its chelae with an
avicularium of another branch. It was captured in such a way that its chela,
the "hand" of which was about half as long as the avicularium, actually
Page 482
closed on to the avicularium without being able to effect its escape. A little
later the other chela was caught by another avicularium. Curiously enough,
however, an avicularium did not necessarily close even when part of a
captured animal was actually in its mouth. The avicularia made no attempt
to place themselves in an advantageous position for catching fresh parts of
the Nereis, which they might easily have done. The avicularia which had
captured prey remained motionless. The others moved backwards and
forwards (cf. the various positions of the avicularia shown in Fig. 240) ten
times in ¾ to 1 minute, snapping their jaws perhaps once in that time. The
two Crustacea were still retained by the avicularia two days later. On the
next day they had both disappeared; but the colony had again caught the
Nereis, which had previously effected its escape with the loss of nearly all
its tentacular cirri.
These observations, and others which have been recorded, do not,
unfortunately, give any information as to the purpose of the movements of
the avicularia and vibracula. It is obvious that they may be defensive in
character; and it cannot be doubted that the avicularia can prevent
inquisitive worms from straying at will over the surface of the colony.
There is no evidence to show that animals are discouraged from interfering
with a Bugula owing to the presence of its defensive weapons.
Fig. 242.—Caberea ellisii Flem., Norway. × 40. Back view of part of a branch. The
large vibracular zooecia (v.z) occupy nearly the whole of the surface. s, Seta of
later the other chela was caught by another avicularium. Curiously enough,
however, an avicularium did not necessarily close even when part of a
captured animal was actually in its mouth. The avicularia made no attempt
to place themselves in an advantageous position for catching fresh parts of
the Nereis, which they might easily have done. The avicularia which had
captured prey remained motionless. The others moved backwards and
forwards (cf. the various positions of the avicularia shown in Fig. 240) ten
times in ¾ to 1 minute, snapping their jaws perhaps once in that time. The
two Crustacea were still retained by the avicularia two days later. On the
next day they had both disappeared; but the colony had again caught the
Nereis, which had previously effected its escape with the loss of nearly all
its tentacular cirri.
These observations, and others which have been recorded, do not,
unfortunately, give any information as to the purpose of the movements of
the avicularia and vibracula. It is obvious that they may be defensive in
character; and it cannot be doubted that the avicularia can prevent
inquisitive worms from straying at will over the surface of the colony.
There is no evidence to show that animals are discouraged from interfering
with a Bugula owing to the presence of its defensive weapons.
Fig. 242.—Caberea ellisii Flem., Norway. × 40. Back view of part of a branch. The
large vibracular zooecia (v.z) occupy nearly the whole of the surface. s, Seta of
Page 483
vibraculum; z, zooecia.
It is not, indeed, certain what are the enemies against which the Polyzoa
have specially to guard. Sea-urchins and certain Molluscs are known to
browse on Polyzoa. Fresh-water Polyzoa, in which avicularia and vibracula
are absent, are attacked by the larvae of Insects, and by Triclad Planarians. I
have found the latter with their long pharynx everted and completely buried
in a Cristatella colony. It is possible that some marine Cheilostomes may be
saved from attacks of this kind owing to the existence of their armoury of
avicularia and vibracula. It is also possible that these structures are of
service by removing foreign particles which might otherwise settle on the
colony, and tend to block up its orifices. It has further been suggested that
animals seized by the avicularia may be held until they die, and that their
disintegrating particles may then be carried to the mouths of the polypides
by the ciliary currents of the tentacles; but proofs of this suggestion are
wanting, and it must be admitted that the subject needs further elucidation.
The vibracula ordinarily remain stationary for some little time, every now
and then giving a sweep through the water. In the majority of cases these
structures, like the avicularia, act perfectly independently of one another, so
far as can be made out; but in Caberea (Fig. 242) the vibracula move in
unison, the simultaneous action of the whole series, after a period of quiet,
being described as "positively startling."[536]
It has been stated by Busk[537] that the entire colony in Selenaria and
Lunulites may be moved from place to place by the large vibracula which
these forms possess.
Fig. 243.—Pedicellina cernua Pall., Guernsey. Entire colony. × 27. The colony has
three growing ends, a; 1-8, individuals of colony; 1 and 8 are quite immature;
and 7 (tentacles retracted) is still young; 2, is seen in longitudinal section; g,
generative organ, and below it the ganglion; m, mouth; r, rectum; s, stomach;
between g and r are three embryos in the brood-pouch; the tentacles are
It is not, indeed, certain what are the enemies against which the Polyzoa
have specially to guard. Sea-urchins and certain Molluscs are known to
browse on Polyzoa. Fresh-water Polyzoa, in which avicularia and vibracula
are absent, are attacked by the larvae of Insects, and by Triclad Planarians. I
have found the latter with their long pharynx everted and completely buried
in a Cristatella colony. It is possible that some marine Cheilostomes may be
saved from attacks of this kind owing to the existence of their armoury of
avicularia and vibracula. It is also possible that these structures are of
service by removing foreign particles which might otherwise settle on the
colony, and tend to block up its orifices. It has further been suggested that
animals seized by the avicularia may be held until they die, and that their
disintegrating particles may then be carried to the mouths of the polypides
by the ciliary currents of the tentacles; but proofs of this suggestion are
wanting, and it must be admitted that the subject needs further elucidation.
The vibracula ordinarily remain stationary for some little time, every now
and then giving a sweep through the water. In the majority of cases these
structures, like the avicularia, act perfectly independently of one another, so
far as can be made out; but in Caberea (Fig. 242) the vibracula move in
unison, the simultaneous action of the whole series, after a period of quiet,
being described as "positively startling."[536]
It has been stated by Busk[537] that the entire colony in Selenaria and
Lunulites may be moved from place to place by the large vibracula which
these forms possess.
Fig. 243.—Pedicellina cernua Pall., Guernsey. Entire colony. × 27. The colony has
three growing ends, a; 1-8, individuals of colony; 1 and 8 are quite immature;
and 7 (tentacles retracted) is still young; 2, is seen in longitudinal section; g,
generative organ, and below it the ganglion; m, mouth; r, rectum; s, stomach;
between g and r are three embryos in the brood-pouch; the tentacles are
Page 484
retracted; in 5 and 6 the tentacles are expanded; in 6 two embryos are seen
within the circle of the tentacles, to the left of them is the rectum, and to the right
the mouth; 3 is in the act of losing its calyx, and has already developed the
beginning of a new polypide-bud; in 4 the primary calyx has been lost, and the
new calyx is clearly marked off from the stalk.
Entoprocta.—The Entoprocta, although a very small sub-class, deserve
special consideration, if for no other reason, from the fact that many writers
regard them as the most primitive group of Polyzoa, and consequently as
the forms which show most affinity to other classes of animals.
Their most obvious characteristic is, as we have already seen,[538] the
position of the anus within the circle of tentacles. The individuals formed
by budding always remain more separate from one another than those of
most Ectoprocta.
The commonest Entoproctous genus is Pedicellina, a graceful little animal,
which occurs on many parts of our coast. It may often be discovered by
looking carefully on the pink, jointed, calcareous alga, Corallina, which
may be found growing at the edges of deep and cool rock-pools not too far
above low-water mark. Its creeping stem or "stolon" is firmly attached to
the surface of the seaweed, and sends off vertical stems here and there.[539]
Each stem bears a "calyx," which is practically an individual of the colony.
The stolon terminates, at one or both ends, in a growing-point (a), from
which new individuals are budded off. The stalks bend from time to time in
a curious spasmodic manner, by which means the calyces are moved about
with an irritable and angry air. A good idea of the way in which the
tentacles are folded away when the animal is disturbed may be obtained by
putting the two wrists together, with the fingers spread out to represent the
tentacles, the retraction of which would be represented by turning the tips of
the fingers down into the space, the "vestibule," between the two palms. A
delicate fold of skin growing from the edge of the calyx closes over the
retracted tentacles, owing to the contraction of a sphincter muscle present in
its circular edge. The body-wall is not separated from the alimentary canal
by a definite body-cavity, so that there is no obvious distinction between the
polypide and the zooecium. The existence of the Entoprocta is in fact a
within the circle of the tentacles, to the left of them is the rectum, and to the right
the mouth; 3 is in the act of losing its calyx, and has already developed the
beginning of a new polypide-bud; in 4 the primary calyx has been lost, and the
new calyx is clearly marked off from the stalk.
Entoprocta.—The Entoprocta, although a very small sub-class, deserve
special consideration, if for no other reason, from the fact that many writers
regard them as the most primitive group of Polyzoa, and consequently as
the forms which show most affinity to other classes of animals.
Their most obvious characteristic is, as we have already seen,[538] the
position of the anus within the circle of tentacles. The individuals formed
by budding always remain more separate from one another than those of
most Ectoprocta.
The commonest Entoproctous genus is Pedicellina, a graceful little animal,
which occurs on many parts of our coast. It may often be discovered by
looking carefully on the pink, jointed, calcareous alga, Corallina, which
may be found growing at the edges of deep and cool rock-pools not too far
above low-water mark. Its creeping stem or "stolon" is firmly attached to
the surface of the seaweed, and sends off vertical stems here and there.[539]
Each stem bears a "calyx," which is practically an individual of the colony.
The stolon terminates, at one or both ends, in a growing-point (a), from
which new individuals are budded off. The stalks bend from time to time in
a curious spasmodic manner, by which means the calyces are moved about
with an irritable and angry air. A good idea of the way in which the
tentacles are folded away when the animal is disturbed may be obtained by
putting the two wrists together, with the fingers spread out to represent the
tentacles, the retraction of which would be represented by turning the tips of
the fingers down into the space, the "vestibule," between the two palms. A
delicate fold of skin growing from the edge of the calyx closes over the
retracted tentacles, owing to the contraction of a sphincter muscle present in
its circular edge. The body-wall is not separated from the alimentary canal
by a definite body-cavity, so that there is no obvious distinction between the
polypide and the zooecium. The existence of the Entoprocta is in fact a
Page 485
strong reason for refusing to admit that these two terms correspond with
two different kinds of individuals.
Let us now imagine the condition we should have if a large and continuous
cavity were developed between the alimentary canal and the body-wall. The
body-wall would clearly have the general relations of a zooecium, while the
alimentary canal and tentacles would obviously correspond with the
polypide. The existence of the body-cavity would make it possible for the
animal to retract its tentacles instead of merely turning them in. Regarded
in this way, there is but little difficulty in comparing the Ectoprocta with the
Entoprocta.
The calyces are deciduous, i.e. they are lost from time to time, the end of
the stalk then producing a polypide-bud, which forms the vestibule and
alimentary canal of a new calyx. Hence the phenomenon which may so
commonly be noticed in Pedicellina of a "young head on old shoulders."
The loss of the calyces may have some relation to the formation of the
"brown bodies" in the Ectoprocta.
Another Entoproct, Loxosoma (Fig. 245) is remarkable for being the only
Polyzoon which is not colonial. The buds, which are formed in two lateral
series, break off as soon as they are mature, and at once begin to lead an
independent existence. Loxosoma is further remarkable for being almost
invariably found commensally with other animals, where it may occur in
enormous numbers. L. phascolosomatum, common in the Channel Islands,
is only found on the tip of the tail of Phascolosoma (see p. 428), which
inhabits the mud of Zostera-beds. Other species are found on the external
surface of certain sponges (Tethya, Euspongia, Cacospongia); or on the
outside of a compound Ascidian, Leptoclinum, which may itself be carried
about as a detachable covering on the back of a crab (Dromia). Another
species is found on the ventral surface of the Polychaet Aphrodite, and of its
ally Hermione.
two different kinds of individuals.
Let us now imagine the condition we should have if a large and continuous
cavity were developed between the alimentary canal and the body-wall. The
body-wall would clearly have the general relations of a zooecium, while the
alimentary canal and tentacles would obviously correspond with the
polypide. The existence of the body-cavity would make it possible for the
animal to retract its tentacles instead of merely turning them in. Regarded
in this way, there is but little difficulty in comparing the Ectoprocta with the
Entoprocta.
The calyces are deciduous, i.e. they are lost from time to time, the end of
the stalk then producing a polypide-bud, which forms the vestibule and
alimentary canal of a new calyx. Hence the phenomenon which may so
commonly be noticed in Pedicellina of a "young head on old shoulders."
The loss of the calyces may have some relation to the formation of the
"brown bodies" in the Ectoprocta.
Another Entoproct, Loxosoma (Fig. 245) is remarkable for being the only
Polyzoon which is not colonial. The buds, which are formed in two lateral
series, break off as soon as they are mature, and at once begin to lead an
independent existence. Loxosoma is further remarkable for being almost
invariably found commensally with other animals, where it may occur in
enormous numbers. L. phascolosomatum, common in the Channel Islands,
is only found on the tip of the tail of Phascolosoma (see p. 428), which
inhabits the mud of Zostera-beds. Other species are found on the external
surface of certain sponges (Tethya, Euspongia, Cacospongia); or on the
outside of a compound Ascidian, Leptoclinum, which may itself be carried
about as a detachable covering on the back of a crab (Dromia). Another
species is found on the ventral surface of the Polychaet Aphrodite, and of its
ally Hermione.
Page 486
Fig. 244.—Side view of Loxosoma annelidicola Van Ben. and Hesse. × 50. (From
Prouho.)
L. annelidicola, an interesting species recently investigated by Prouho,[540]
was originally described in 1863 as a Trematode, under the name of
Cyclatella. It escaped further notice until it was again found in the
neighbourhood of Roscoff, in Brittany, on certain Polychaets belonging to
the family Maldanidae (see p. 332). The calyx has a very flattened form,
and is borne on a short stalk, which terminates in a large attaching disc,
formerly mistaken for the sucker of a Trematode. The features in which this
species differs from other members of the genus are shown by M. Prouho to
be correlated with its mode of life. The animal has the habit of lying flat on
its back, the disc at the end of its stalk being firmly attached to the skin of
the worm, and its short stalk being bent round into a curve so as to bring the
calyx into a supine position, with its lophophore directed upwards. This
habit, together with its flattened form, prevents it from being crushed
between the worm and its tube. But without some further provision its
position might be merely a source of danger. For supposing the calyx to be
directed backwards in relation to the worm, a sudden backward movement
of the latter into its tube might bring the Loxosoma into fatal contact with
the inner surface of the tube. There would obviously not be sufficient room
to turn round in a vertical plane, so as to bring the body into a position of
safety, i.e. into a position in which it moves stalk first. But by a beautiful
arrangement of the muscles of its stalk this movement is effected in a
horizontal plane; on touching the Loxosoma with the point of a needle it
would swing round in this way through 180° with "une rapidité qui étonne."
Urnatella[541] is a beautiful form with a segmented stalk, the stalks usually
arising in pairs from a common base. It has at present only been found in
fresh water in the United States.
Prouho.)
L. annelidicola, an interesting species recently investigated by Prouho,[540]
was originally described in 1863 as a Trematode, under the name of
Cyclatella. It escaped further notice until it was again found in the
neighbourhood of Roscoff, in Brittany, on certain Polychaets belonging to
the family Maldanidae (see p. 332). The calyx has a very flattened form,
and is borne on a short stalk, which terminates in a large attaching disc,
formerly mistaken for the sucker of a Trematode. The features in which this
species differs from other members of the genus are shown by M. Prouho to
be correlated with its mode of life. The animal has the habit of lying flat on
its back, the disc at the end of its stalk being firmly attached to the skin of
the worm, and its short stalk being bent round into a curve so as to bring the
calyx into a supine position, with its lophophore directed upwards. This
habit, together with its flattened form, prevents it from being crushed
between the worm and its tube. But without some further provision its
position might be merely a source of danger. For supposing the calyx to be
directed backwards in relation to the worm, a sudden backward movement
of the latter into its tube might bring the Loxosoma into fatal contact with
the inner surface of the tube. There would obviously not be sufficient room
to turn round in a vertical plane, so as to bring the body into a position of
safety, i.e. into a position in which it moves stalk first. But by a beautiful
arrangement of the muscles of its stalk this movement is effected in a
horizontal plane; on touching the Loxosoma with the point of a needle it
would swing round in this way through 180° with "une rapidité qui étonne."
Urnatella[541] is a beautiful form with a segmented stalk, the stalks usually
arising in pairs from a common base. It has at present only been found in
fresh water in the United States.
Page 487
Fig. 245.—Diagram of the structure of Loxosoma, seen from the oesophageal side. ×
about 70. a, Anus; b, buds; e, excretory organ; f, foot-gland; g, ganglion; gn,
generative organs; o, orifice of vestibule; oe, oesophagus; s, stomach; t, retracted
tentacles.
In Pedicellina the plane of the lophophore is at right angles to the stalk,
which is separated from its calyx by a marked constriction. In Loxosoma the
lophophore is set obliquely,[542] and there is no constriction at the base of
the calyx. In Urnatella we find an intermediate condition, the lophophore
resembling that of Loxosoma, while the constriction at the base of the calyx
is similar to that of Pedicellina. Since the latter is known to pass in its
development[543] through a stage with an oblique lophophore, it may be
presumed that Loxosoma is a more archaic form than Pedicellina. In other
respects, the structure of the Entoprocta is very constant, whatever the
genus.
A pair of ciliated excretory tubes open into the vestibule. These are similar
in structure to the "head-kidneys" of the larvae of Polychaet worms, or to
the excretory organs of adult Rotifers. Flame-cells have been described by
Davenport in the stalk of Urnatella, but it is not known whether they are
connected with the excretory tubes of the calyx. The animals are either
hermaphrodite or have separate sexes, and the generative organs open by
ducts of their own into the vestibule. The nervous system consists of a
ganglion placed between the mouth and the anus, giving off a set of nerves,
many of which end in delicate tactile hairs placed on the tentacles or other
parts of the body.[544]
CHAPTER XVIII
about 70. a, Anus; b, buds; e, excretory organ; f, foot-gland; g, ganglion; gn,
generative organs; o, orifice of vestibule; oe, oesophagus; s, stomach; t, retracted
tentacles.
In Pedicellina the plane of the lophophore is at right angles to the stalk,
which is separated from its calyx by a marked constriction. In Loxosoma the
lophophore is set obliquely,[542] and there is no constriction at the base of
the calyx. In Urnatella we find an intermediate condition, the lophophore
resembling that of Loxosoma, while the constriction at the base of the calyx
is similar to that of Pedicellina. Since the latter is known to pass in its
development[543] through a stage with an oblique lophophore, it may be
presumed that Loxosoma is a more archaic form than Pedicellina. In other
respects, the structure of the Entoprocta is very constant, whatever the
genus.
A pair of ciliated excretory tubes open into the vestibule. These are similar
in structure to the "head-kidneys" of the larvae of Polychaet worms, or to
the excretory organs of adult Rotifers. Flame-cells have been described by
Davenport in the stalk of Urnatella, but it is not known whether they are
connected with the excretory tubes of the calyx. The animals are either
hermaphrodite or have separate sexes, and the generative organs open by
ducts of their own into the vestibule. The nervous system consists of a
ganglion placed between the mouth and the anus, giving off a set of nerves,
many of which end in delicate tactile hairs placed on the tentacles or other
parts of the body.[544]
CHAPTER XVIII
Page 488
POLYZOA (continued)
FRESH-WATER POLYZOA—PHYLACTOLAEMATA—OCCURRENCE—STRUCTURE OF
CRISTATELLA—DIVISION OF COLONY—MOVEMENTS OF COLONY—RETRACTION AND
PROTRUSION OF POLYPIDES IN POLYZOA—STATOBLASTS—TABLE FOR
DETERMINATION OF GENERA OF FRESH-WATER POLYZOA—REPRODUCTIVE
PROCESSES OF POLYZOA—DEVELOPMENT—AFFINITIES—METAMORPHOSIS—
BUDDING.
Fresh-water Polyzoa.—Although the Gymnolaemata are ordinarily marine
animals, fresh-water examples from this Order are not altogether wanting.
The Ctenostomata among the typically marine groups show the most
tendency to stray into fresh-water.
Alcyonidium and Bowerbankia (Fig. 238) flourish in estuaries, while
Victorella and Paludicella (Fig. 250) are only known as fresh or brackish
water forms. Victorella was named after the Victoria Docks in London,
where it was first found; more recently it has also been discovered in other
parts of England and on the Continent.[545]
The systematic position of the genera Hislopia and Norodonia,[546] which
have been described from fresh water of India and China respectively, is at
present uncertain. The undoubted Cheilostome Membranipora has,
however, a British representative (M. monostachys), which occurs in
brackish water, in ditches on the coast of East Anglia. It is there known to
form "friable, irregularly-shaped, sponge-like masses," which grow on
water-plants.[547]
The Entoprocta, as we have seen, are represented in fresh water by the
genus Urnatella.
The Phylactolaemata are an exclusively fresh-water group, and they are
believed by Kraepelin[548] to have been derived from the Ctenostomata.
Many of their special peculiarities can, with great probability, be regarded
as adaptations to a fresh-water existence. This is particularly clear in the all
FRESH-WATER POLYZOA—PHYLACTOLAEMATA—OCCURRENCE—STRUCTURE OF
CRISTATELLA—DIVISION OF COLONY—MOVEMENTS OF COLONY—RETRACTION AND
PROTRUSION OF POLYPIDES IN POLYZOA—STATOBLASTS—TABLE FOR
DETERMINATION OF GENERA OF FRESH-WATER POLYZOA—REPRODUCTIVE
PROCESSES OF POLYZOA—DEVELOPMENT—AFFINITIES—METAMORPHOSIS—
BUDDING.
Fresh-water Polyzoa.—Although the Gymnolaemata are ordinarily marine
animals, fresh-water examples from this Order are not altogether wanting.
The Ctenostomata among the typically marine groups show the most
tendency to stray into fresh-water.
Alcyonidium and Bowerbankia (Fig. 238) flourish in estuaries, while
Victorella and Paludicella (Fig. 250) are only known as fresh or brackish
water forms. Victorella was named after the Victoria Docks in London,
where it was first found; more recently it has also been discovered in other
parts of England and on the Continent.[545]
The systematic position of the genera Hislopia and Norodonia,[546] which
have been described from fresh water of India and China respectively, is at
present uncertain. The undoubted Cheilostome Membranipora has,
however, a British representative (M. monostachys), which occurs in
brackish water, in ditches on the coast of East Anglia. It is there known to
form "friable, irregularly-shaped, sponge-like masses," which grow on
water-plants.[547]
The Entoprocta, as we have seen, are represented in fresh water by the
genus Urnatella.
The Phylactolaemata are an exclusively fresh-water group, and they are
believed by Kraepelin[548] to have been derived from the Ctenostomata.
Many of their special peculiarities can, with great probability, be regarded
as adaptations to a fresh-water existence. This is particularly clear in the all
Page 489
but universal habit of dying down in the winter, and in the occurrence of the
so-called statoblasts (Fig. 251), which are hard-shelled reproductive bodies,
absolutely restricted to the Phylactolaemata, and capable of resisting the
winter's cold and even a certain amount of drying up. Phylactolaemata have
indeed been recorded from the tropics; but it is not yet sufficiently clear
how they there behave in these respects. F. Müller[549] has found these
animals in Brazil, where they are said to be more common at certain periods
of the year than at others. Stuhlmann has found them in Tropical Africa
(Victoria Nyanza, etc.);[550] and Meissner[551] has discovered the sessile
statoblasts of Plumatella on the shells preserved in the Berlin Museum, of
species of the Mollusc Aetheria from various localities in Africa. Fresh-
water representatives of a considerable number of other groups of animals
agree with the Phylactolaemata in the possession of reproductive bodies
which are protected by hard coats. Such, for instance, are the ephippian ova
of Daphnia—bodies which have an extraordinary external similarity to
statoblasts—the gemmules of Spongillidae, the winter-eggs of Rhabdocoels
and Rotifers, and the cysts of Protozoa. The evolution of these bodies in so
many widely different cases may have been due to the selection of
variations calculated to minimise the dangers attendant on the drying up of
the water in summer, or on its freezing in winter.
The Phylactolaemata are by no means uncommon, although they can
seldom be found without a careful search. Their presence may often be
detected by taking advantage of the property of the free statoblasts of rising
to the top of the water, where they can be discovered by skimming the
surface with a fine hand-net.
The colonies themselves are usually found attached to water-plants, roots of
trees or stones. Most of them flourish best in a zone not more than two feet
below the surface. Certain species show a preference for floating leaves,
such as those of water-lilies, where they are not liable to be dried up by
alterations in the level of the water. Some forms (e.g. Plumatella, Fig. 246)
are, however, able to withstand being dried for some time. Most species
prefer shady places, and accordingly settle on the lower sides of leaves and
sticks. Others (e.g. Cristatella, Fig. 247) have no objection to the direct rays
so-called statoblasts (Fig. 251), which are hard-shelled reproductive bodies,
absolutely restricted to the Phylactolaemata, and capable of resisting the
winter's cold and even a certain amount of drying up. Phylactolaemata have
indeed been recorded from the tropics; but it is not yet sufficiently clear
how they there behave in these respects. F. Müller[549] has found these
animals in Brazil, where they are said to be more common at certain periods
of the year than at others. Stuhlmann has found them in Tropical Africa
(Victoria Nyanza, etc.);[550] and Meissner[551] has discovered the sessile
statoblasts of Plumatella on the shells preserved in the Berlin Museum, of
species of the Mollusc Aetheria from various localities in Africa. Fresh-
water representatives of a considerable number of other groups of animals
agree with the Phylactolaemata in the possession of reproductive bodies
which are protected by hard coats. Such, for instance, are the ephippian ova
of Daphnia—bodies which have an extraordinary external similarity to
statoblasts—the gemmules of Spongillidae, the winter-eggs of Rhabdocoels
and Rotifers, and the cysts of Protozoa. The evolution of these bodies in so
many widely different cases may have been due to the selection of
variations calculated to minimise the dangers attendant on the drying up of
the water in summer, or on its freezing in winter.
The Phylactolaemata are by no means uncommon, although they can
seldom be found without a careful search. Their presence may often be
detected by taking advantage of the property of the free statoblasts of rising
to the top of the water, where they can be discovered by skimming the
surface with a fine hand-net.
The colonies themselves are usually found attached to water-plants, roots of
trees or stones. Most of them flourish best in a zone not more than two feet
below the surface. Certain species show a preference for floating leaves,
such as those of water-lilies, where they are not liable to be dried up by
alterations in the level of the water. Some forms (e.g. Plumatella, Fig. 246)
are, however, able to withstand being dried for some time. Most species
prefer shady places, and accordingly settle on the lower sides of leaves and
sticks. Others (e.g. Cristatella, Fig. 247) have no objection to the direct rays
Page 490
of the sun. Most forms prefer still water, but one or two are found in
running water.
Fredericella is a common constituent of the deep-water fauna of Swiss
Lakes (down to over forty fathoms); and reaches there a size considerably
larger than the shallow-water form of the same species. Paludicella is
common at thirteen fathoms. These two genera, with Plumatella, have been
found in absolute darkness, under a pressure of 2½-5½ atmospheres, in the
Hamburg aqueduct. The Polyzoa and other organisms growing in the water-
supply of Hamburg were accused of being concerned in the spreading of
cholera, during the recent epidemic, by choking up the water-pipes, and
creating obstructions which formed a favourable nidus for the development
of cholera-germs.
The colony may take the form of a series of delicate, branching tubes
(Plumatella, Fredericella), of more massive aggregations of parallel tubes
(as in the Alcyonelloid forms of Plumatella), or of gelatinous masses of
varying size (Lophopus, Cristatella).
Fig. 246.—A, Plumatella (Alcyonella) fungosa Pall., Naples (fresh water), small part of
a mass, natural size; B, Plumatella repens L., R. Yare, on the leaf of a water-lily,
natural size.
Cristatella mucedo (Fig. 247) is remarkable for its power of moving from
place to place; it consists of an elongated mass of greenish, gelatinous
substance, which, in its fully developed state, may reach a length of eight
inches or more, with a transverse diameter of three-eighths of an inch. It has
a flattened sole on which it crawls, while the graceful plumes of its
numerous polypides protrude as a delicate fringe from its upper side.
running water.
Fredericella is a common constituent of the deep-water fauna of Swiss
Lakes (down to over forty fathoms); and reaches there a size considerably
larger than the shallow-water form of the same species. Paludicella is
common at thirteen fathoms. These two genera, with Plumatella, have been
found in absolute darkness, under a pressure of 2½-5½ atmospheres, in the
Hamburg aqueduct. The Polyzoa and other organisms growing in the water-
supply of Hamburg were accused of being concerned in the spreading of
cholera, during the recent epidemic, by choking up the water-pipes, and
creating obstructions which formed a favourable nidus for the development
of cholera-germs.
The colony may take the form of a series of delicate, branching tubes
(Plumatella, Fredericella), of more massive aggregations of parallel tubes
(as in the Alcyonelloid forms of Plumatella), or of gelatinous masses of
varying size (Lophopus, Cristatella).
Fig. 246.—A, Plumatella (Alcyonella) fungosa Pall., Naples (fresh water), small part of
a mass, natural size; B, Plumatella repens L., R. Yare, on the leaf of a water-lily,
natural size.
Cristatella mucedo (Fig. 247) is remarkable for its power of moving from
place to place; it consists of an elongated mass of greenish, gelatinous
substance, which, in its fully developed state, may reach a length of eight
inches or more, with a transverse diameter of three-eighths of an inch. It has
a flattened sole on which it crawls, while the graceful plumes of its
numerous polypides protrude as a delicate fringe from its upper side.
Page 491
The tentacles are about eighty to ninety in number, and they are, as in other
Phylactolaemata, united at their bases by a delicate web. The lophophore is
horse-shoe-shaped (Fig. 236, 3) throughout the group, with the exception of
Fredericella, in which genus it is circular.
In some Phylactolaemata the polypide has been observed to interlace its
tentacles, so that the plume becomes a kind of cage, in which the more
active Infusoria are imprisoned until their struggles have so far weakened
them that they are swept into the mouth by the action of the cilia of the
tentacles.[552]
Fig. 247.—Cristatella mucedo Cuv. (a small colony), R. Yare, above Norwich, × 24.
Around the edge of the Cristatella is found a zone of budding tissue, which
gives rise continuously to new individuals. Now, whereas in Gymnolaemata
the growing edge gives rise to zooecia, whose cavities become completely
cut off from that of the older ones; in Phylactolaemata the partitions
between the zooecia are never completed. The body-cavity of Cristatella is
thus a continuous space, interrupted at the margin only by vertical septa
(see Fig. 247), which represent the partitions between the zooecia of other
forms.
The body-wall consists of two epithelial layers of ectoderm and mesoderm,
between which is a layer of muscular fibres. Parts of the epithelium lining
the body-cavity are ciliated. Into the common body-cavity hang the
polypide-buds at the edge of the colony, and the mature polypides in the
more central regions. There are usually three rows of polypides on either
side of the middle line, in the neighbourhood of which is an area devoid of
polypides, but containing "brown bodies" and statoblasts. The polypides
Phylactolaemata, united at their bases by a delicate web. The lophophore is
horse-shoe-shaped (Fig. 236, 3) throughout the group, with the exception of
Fredericella, in which genus it is circular.
In some Phylactolaemata the polypide has been observed to interlace its
tentacles, so that the plume becomes a kind of cage, in which the more
active Infusoria are imprisoned until their struggles have so far weakened
them that they are swept into the mouth by the action of the cilia of the
tentacles.[552]
Fig. 247.—Cristatella mucedo Cuv. (a small colony), R. Yare, above Norwich, × 24.
Around the edge of the Cristatella is found a zone of budding tissue, which
gives rise continuously to new individuals. Now, whereas in Gymnolaemata
the growing edge gives rise to zooecia, whose cavities become completely
cut off from that of the older ones; in Phylactolaemata the partitions
between the zooecia are never completed. The body-cavity of Cristatella is
thus a continuous space, interrupted at the margin only by vertical septa
(see Fig. 247), which represent the partitions between the zooecia of other
forms.
The body-wall consists of two epithelial layers of ectoderm and mesoderm,
between which is a layer of muscular fibres. Parts of the epithelium lining
the body-cavity are ciliated. Into the common body-cavity hang the
polypide-buds at the edge of the colony, and the mature polypides in the
more central regions. There are usually three rows of polypides on either
side of the middle line, in the neighbourhood of which is an area devoid of
polypides, but containing "brown bodies" and statoblasts. The polypides
Page 492
nearest to the middle line pass in succession into the condition of "brown
bodies," while young buds near the margin grow up coincidently to form
new polypides.
The movement of the colony is in the direction of the long axis, although
either end may go first. Sir John Dalyell records an observation[553] on a
specimen (about one inch long) which was artificially divided into two
halves. The two halves "receded from each other as if by common consent,"
and were nearly an inch apart in twenty hours.
An observation made at Cambridge on a small colony of about 7 mm. in
greatest length gave the following results. The colony moved 13 mm.
(nearly twice its own length) in 8¼ hours: in the next 40 hours it moved 20
mm. (⅘ inch); while in the following 24 hours it moved only 6 mm. Large
colonies change their place only with reluctance.
The locomotive power possessed by Cristatella is not unique among
Phylactolaemata. Lophopus, the first fresh-water Polyzoon of which any
description was published, was originally described by Trembley in 1744
under the name of the "Polype à pannache." Trembley observed the
spontaneous division of the colony, followed by the gradual separation from
one another of the daughter-colonies.[554] The power of dividing
spontaneously is also possessed by colonies of Cristatella and of
Pectinatella.
The colonies of Lophopus are surrounded by an excessively hyaline
ectocyst, and are usually triangular, as shown by Fig. 248. When division is
about to occur, the base of the triangle becomes indented, and the
indentation travels towards the apex in such a way as to bisect the triangle.
The two halves diverge from one another during the process, so that before
division is complete, they are looking, in some cases, in opposite directions.
After a time the narrow connection breaks, and two new colonies are
formed.
Fig. 248 shows a colony shortly after division has taken place. The colony
had moved forwards, in a direction away from its apex, for three days in a
bodies," while young buds near the margin grow up coincidently to form
new polypides.
The movement of the colony is in the direction of the long axis, although
either end may go first. Sir John Dalyell records an observation[553] on a
specimen (about one inch long) which was artificially divided into two
halves. The two halves "receded from each other as if by common consent,"
and were nearly an inch apart in twenty hours.
An observation made at Cambridge on a small colony of about 7 mm. in
greatest length gave the following results. The colony moved 13 mm.
(nearly twice its own length) in 8¼ hours: in the next 40 hours it moved 20
mm. (⅘ inch); while in the following 24 hours it moved only 6 mm. Large
colonies change their place only with reluctance.
The locomotive power possessed by Cristatella is not unique among
Phylactolaemata. Lophopus, the first fresh-water Polyzoon of which any
description was published, was originally described by Trembley in 1744
under the name of the "Polype à pannache." Trembley observed the
spontaneous division of the colony, followed by the gradual separation from
one another of the daughter-colonies.[554] The power of dividing
spontaneously is also possessed by colonies of Cristatella and of
Pectinatella.
The colonies of Lophopus are surrounded by an excessively hyaline
ectocyst, and are usually triangular, as shown by Fig. 248. When division is
about to occur, the base of the triangle becomes indented, and the
indentation travels towards the apex in such a way as to bisect the triangle.
The two halves diverge from one another during the process, so that before
division is complete, they are looking, in some cases, in opposite directions.
After a time the narrow connection breaks, and two new colonies are
formed.
Fig. 248 shows a colony shortly after division has taken place. The colony
had moved forwards, in a direction away from its apex, for three days in a
Page 493
nearly straight line, the distances moved in each day being respectively 6,
8½, 8½ mm. These observations, for which I am indebted to Mr. Lister,
show a considerably higher speed than in those recorded by Trembley, who
observed no colony which moved more than half an inch (12.5 mm.) in
eight days.
The genus Pectinatella also has some power of locomotion. This
magnificent Polyzoon occurs in masses several feet in length (as much as
six feet in P. gelatinosa from Japan[555]), and four to eight inches in
thickness. The greater part of P. magnifica[556] consists of a thick, opaline,
and gelatinous ectocyst, the upper surface of which is covered by hundreds
of rosette-like colonies, which increase in number by division. The masses
are thus aggregations of colonies, which secrete a common basal ectocyst.
The latter decays in the autumn; and the separate rosettes, or groups of
them, may thus be set free, being found as floating masses, which may
again attach themselves to a solid object till the time of their death.
Pectinatella has not yet been recorded in England, although, considering
the ease with which statoblasts are transported, it is by no means
improbable that it will eventually be recorded as a British genus. It is at
present known to inhabit America, Japan, and Hamburg.
Fig. 248.—Lophopus crystallinus Pall., Cambridge, showing the rate of movement. The
colony and the distances moved are × 2.
It is by no means certain what is the mechanism by which movement takes
place in the above cases. The ectocyst of Cristatella is confined to the base
of the colony, and there forms a thin slimy film, which lubricates the
surface over which the animal moves. It has been stated[557] that
8½, 8½ mm. These observations, for which I am indebted to Mr. Lister,
show a considerably higher speed than in those recorded by Trembley, who
observed no colony which moved more than half an inch (12.5 mm.) in
eight days.
The genus Pectinatella also has some power of locomotion. This
magnificent Polyzoon occurs in masses several feet in length (as much as
six feet in P. gelatinosa from Japan[555]), and four to eight inches in
thickness. The greater part of P. magnifica[556] consists of a thick, opaline,
and gelatinous ectocyst, the upper surface of which is covered by hundreds
of rosette-like colonies, which increase in number by division. The masses
are thus aggregations of colonies, which secrete a common basal ectocyst.
The latter decays in the autumn; and the separate rosettes, or groups of
them, may thus be set free, being found as floating masses, which may
again attach themselves to a solid object till the time of their death.
Pectinatella has not yet been recorded in England, although, considering
the ease with which statoblasts are transported, it is by no means
improbable that it will eventually be recorded as a British genus. It is at
present known to inhabit America, Japan, and Hamburg.
Fig. 248.—Lophopus crystallinus Pall., Cambridge, showing the rate of movement. The
colony and the distances moved are × 2.
It is by no means certain what is the mechanism by which movement takes
place in the above cases. The ectocyst of Cristatella is confined to the base
of the colony, and there forms a thin slimy film, which lubricates the
surface over which the animal moves. It has been stated[557] that
Page 494
progression is produced in the following way. The polypides are withdrawn
by means of retractor muscles, which originate from the septa and inner
surface of the sole. Thus at each retraction of any polypide, the muscle pulls
on a portion of the sole. Should the expanded polypides place themselves in
a suitable position, the movement will be in the direction of the resultant of
the forces due to the separate retractor muscles; while it is probable that
their cilia assist in the onward movement. It should be noted that it is
definitely stated that a colony in which all the polypides are retracted can
alter its position,[558] although even then the retractor muscles might still
contract to some extent.
The movement probably depends on several causes. It must probably be
conceded that the sole itself has some effect on this process. Its outer cells
are contractile, and have the power of raising themselves from the
underlying ectocyst. They may then again attach themselves, and this new
attachment does not always take place in exactly the same place as the
former one. Any movement of the muscles of the sole, or of the retractor
muscles, will thus shift the skin to a new place.[559]
Protrusion of the Polypide.—While it is perfectly clear that retraction is
principally performed by the great retractor muscles acting directly on the
polypide, it is less easy to explain the converse movement. There can,
however, be little doubt that protrusion is effected by the pressure of the
fluid of the body-cavity, caused in large part by contractions of the common
body-wall.
Now since, in Cristatella, the body-cavity is a continuous space, any
pressure on the fluid must act uniformly on all its contents. The cause which
determines the protrusion of a polypide is thus to a large extent the
relaxation of the sphincter-muscle which surrounds its orifice, aided by
special muscles which dilate the orifice. Any polypide which is retracted
while the pressure of the fluid in the body-cavity is sufficient to keep other
polypides protruded, must therefore keep either its retractor-muscles or its
sphincter in a state of contraction in order to remain in that position. And as
a matter of fact, Cristatella and Lophopus differ from most other Polyzoa in
by means of retractor muscles, which originate from the septa and inner
surface of the sole. Thus at each retraction of any polypide, the muscle pulls
on a portion of the sole. Should the expanded polypides place themselves in
a suitable position, the movement will be in the direction of the resultant of
the forces due to the separate retractor muscles; while it is probable that
their cilia assist in the onward movement. It should be noted that it is
definitely stated that a colony in which all the polypides are retracted can
alter its position,[558] although even then the retractor muscles might still
contract to some extent.
The movement probably depends on several causes. It must probably be
conceded that the sole itself has some effect on this process. Its outer cells
are contractile, and have the power of raising themselves from the
underlying ectocyst. They may then again attach themselves, and this new
attachment does not always take place in exactly the same place as the
former one. Any movement of the muscles of the sole, or of the retractor
muscles, will thus shift the skin to a new place.[559]
Protrusion of the Polypide.—While it is perfectly clear that retraction is
principally performed by the great retractor muscles acting directly on the
polypide, it is less easy to explain the converse movement. There can,
however, be little doubt that protrusion is effected by the pressure of the
fluid of the body-cavity, caused in large part by contractions of the common
body-wall.
Now since, in Cristatella, the body-cavity is a continuous space, any
pressure on the fluid must act uniformly on all its contents. The cause which
determines the protrusion of a polypide is thus to a large extent the
relaxation of the sphincter-muscle which surrounds its orifice, aided by
special muscles which dilate the orifice. Any polypide which is retracted
while the pressure of the fluid in the body-cavity is sufficient to keep other
polypides protruded, must therefore keep either its retractor-muscles or its
sphincter in a state of contraction in order to remain in that position. And as
a matter of fact, Cristatella and Lophopus differ from most other Polyzoa in
Page 495
the readiness with which they expand their tentacles, after they have been
induced to retract themselves by mechanical irritation.
Plumatella and other forms have a chitinous ectocyst, which, however, is
sticky when it is first formed. By virtue of this property, the branches
become attached to the leaf on which the colony is growing, and may have
their natural transparency obscured by taking up foreign bodies. The
stiffness of the ectocyst naturally involves some modification of the process
by which the polypides are protruded. In some cases, this is effected by the
separation of the endocyst from the ectocyst in the lower parts of the tube.
The muscles of the body-wall can thus press on the fluid of the body-cavity
without being restrained by the inflexible ectocyst. In other cases, the tube
of ectocyst is rendered flexible by the presence of a thin line along one side
where the chitin is deficient.
Fig. 249.—Plumatella repens L., R. Yare, × 30. a, Anus; b, polypide-bud; c, caecum of
stomach; d, duplicature; e, epistome (see p. 476); f, funiculus; g, ganglion; m,
retractor muscle; p, parieto-vaginal muscles; ph, pharynx; s, statoblasts attached
to f.
The upper end of the retracted tentacle-sheath is connected with the body-
wall by bands known as the parieto-vaginal muscles (Fig. 249, p). These
serve not only to dilate the orifice when protrusion is commencing, but also
induced to retract themselves by mechanical irritation.
Plumatella and other forms have a chitinous ectocyst, which, however, is
sticky when it is first formed. By virtue of this property, the branches
become attached to the leaf on which the colony is growing, and may have
their natural transparency obscured by taking up foreign bodies. The
stiffness of the ectocyst naturally involves some modification of the process
by which the polypides are protruded. In some cases, this is effected by the
separation of the endocyst from the ectocyst in the lower parts of the tube.
The muscles of the body-wall can thus press on the fluid of the body-cavity
without being restrained by the inflexible ectocyst. In other cases, the tube
of ectocyst is rendered flexible by the presence of a thin line along one side
where the chitin is deficient.
Fig. 249.—Plumatella repens L., R. Yare, × 30. a, Anus; b, polypide-bud; c, caecum of
stomach; d, duplicature; e, epistome (see p. 476); f, funiculus; g, ganglion; m,
retractor muscle; p, parieto-vaginal muscles; ph, pharynx; s, statoblasts attached
to f.
The upper end of the retracted tentacle-sheath is connected with the body-
wall by bands known as the parieto-vaginal muscles (Fig. 249, p). These
serve not only to dilate the orifice when protrusion is commencing, but also
Page 496
to prevent the polypide from being forced out too far. They are arranged in
such a way that a circular fold, the duplicature (d), is never turned inside
out, even in the state of complete protrusion of the polypide.
The mechanism of the protrusion of the polypide in the Gymnolaemata is in
many cases obscure. The body-wall is not muscular in this group, in some
forms of which, however, short strands known as the parietal muscles (Fig.
234, p) pass across the body-cavity from one point to another of the
zooecium. As doubts have been thrown on the function of these muscles in
causing protrusion, it will be worth while to refer to the detailed and
convincing statements of Farre,[560] relating to this point.
Farre's observations were made on certain transparent Ctenostomes
(Bowerbankia and Farrella). He states that the parietal muscles "were
distinctly seen to contract whenever the protrusion of the animal took place,
and to become relaxed again upon its retiring into its cell." Their
contraction may indent the outline of the ectocyst, or may cause the
separation of the endocyst from the ectocyst. The endocyst is then drawn
into longitudinal lines at the origin and insertion of these fibres. It is further
suggested that some part is played in the process by the muscular walls of
the alimentary canal, which is a good deal bent in the retracted condition.
The effort to straighten itself is believed to have some share in forcing out
the polypide. The flexible, membranous character of the "aperture" (see p.
524) in Membranipora (Fig. 256, A) is said by Nitsche[561] to be an
arrangement for the protrusion of the polypides; the parietal muscles
passing from the lateral walls of the zooecium to the upper membranous
wall, which is accordingly depressed by their contraction.
Although it is hardly possible to doubt the accuracy of Farre's observations,
which have, moreover, been confirmed by Hincks, it is by no means certain
that this is the whole explanation in all cases. Oka,[562] for instance, states
that protrusion of the polypide in Phylactolaemata can be effected in a
branch whose body-wall has been cut open. Pergens[563] believes that the
diaphragm (Fig. 234, d) acts as a pump, introducing water from the
tentacle-sheath into the body-cavity, into which it is said by him to open,
and so forcing out the polypide. It is probable that many of the forms which
such a way that a circular fold, the duplicature (d), is never turned inside
out, even in the state of complete protrusion of the polypide.
The mechanism of the protrusion of the polypide in the Gymnolaemata is in
many cases obscure. The body-wall is not muscular in this group, in some
forms of which, however, short strands known as the parietal muscles (Fig.
234, p) pass across the body-cavity from one point to another of the
zooecium. As doubts have been thrown on the function of these muscles in
causing protrusion, it will be worth while to refer to the detailed and
convincing statements of Farre,[560] relating to this point.
Farre's observations were made on certain transparent Ctenostomes
(Bowerbankia and Farrella). He states that the parietal muscles "were
distinctly seen to contract whenever the protrusion of the animal took place,
and to become relaxed again upon its retiring into its cell." Their
contraction may indent the outline of the ectocyst, or may cause the
separation of the endocyst from the ectocyst. The endocyst is then drawn
into longitudinal lines at the origin and insertion of these fibres. It is further
suggested that some part is played in the process by the muscular walls of
the alimentary canal, which is a good deal bent in the retracted condition.
The effort to straighten itself is believed to have some share in forcing out
the polypide. The flexible, membranous character of the "aperture" (see p.
524) in Membranipora (Fig. 256, A) is said by Nitsche[561] to be an
arrangement for the protrusion of the polypides; the parietal muscles
passing from the lateral walls of the zooecium to the upper membranous
wall, which is accordingly depressed by their contraction.
Although it is hardly possible to doubt the accuracy of Farre's observations,
which have, moreover, been confirmed by Hincks, it is by no means certain
that this is the whole explanation in all cases. Oka,[562] for instance, states
that protrusion of the polypide in Phylactolaemata can be effected in a
branch whose body-wall has been cut open. Pergens[563] believes that the
diaphragm (Fig. 234, d) acts as a pump, introducing water from the
tentacle-sheath into the body-cavity, into which it is said by him to open,
and so forcing out the polypide. It is probable that many of the forms which
Page 497
have a stiff, unyielding ectocyst possess special arrangements for
introducing water in some way into the space bounded by the ectocyst,[564]
and so forcing out the polypide. Such, for instance, may be the median pore
which occurs beneath the orifice in Microporella (Fig. 241, A, mp), and in
certain other cases.
Reproduction of Phylactolaemata.—Sexual reproduction takes place in
Cristatella from June to August. The spermatozoa are ordinarily produced
on the funiculus. The ovaries usually occur on the inner side of the common
wall of the colony, not far below the orifice of a polypide. Each ovary
matures a single egg, which develops in situ, the free larva leaving the
colony by the orifice of one of the degenerated polypides.
A second method of reproduction takes place by means of the statoblasts,
which are developed on the funiculus (Fig. 249). According to Verworn,[565]
each statoblast arises from a single cell of the funiculus; and on this view,
the statoblast is, as supposed by the earlier observers, a special kind of
winter-egg. According to more recent researches,[566] the funiculus consists
of a central axis, formed from the ectoderm, and of an outer sheath of
mesoderm-cells; the statoblast is developed from the two kinds of cells of
which the funiculus is composed, and is consequently comparable in its
mode of origin to an ordinary bud. Its special peculiarities are: its origin as
an internal bud, its possession of a chitinous shell, and the fact that it is
destined to leave the parent colony, and to develop, after a period of rest,
into a new colony. Germination takes place by the formation of a polypide-
bud inside the statoblast, which finally splits along its equator into two
halves. The contents emerge as a young colony which possesses at least one
fully-formed polypide.
Remarkable structures known as "hibernacula" occur in the fresh-water
Ctenostomes, Paludicella and Victorella. These bodies are in the former
(Fig. 250, B) specially modified external buds, which persist through the
winter when the rest of the colony dies down. At the close of winter the
shell splits into two halves, exactly as takes place in the statoblasts, and a
young colony emerges. It is possible that the statoblasts may have been
evolved from a hibernaculum, which was at first produced externally, but
introducing water in some way into the space bounded by the ectocyst,[564]
and so forcing out the polypide. Such, for instance, may be the median pore
which occurs beneath the orifice in Microporella (Fig. 241, A, mp), and in
certain other cases.
Reproduction of Phylactolaemata.—Sexual reproduction takes place in
Cristatella from June to August. The spermatozoa are ordinarily produced
on the funiculus. The ovaries usually occur on the inner side of the common
wall of the colony, not far below the orifice of a polypide. Each ovary
matures a single egg, which develops in situ, the free larva leaving the
colony by the orifice of one of the degenerated polypides.
A second method of reproduction takes place by means of the statoblasts,
which are developed on the funiculus (Fig. 249). According to Verworn,[565]
each statoblast arises from a single cell of the funiculus; and on this view,
the statoblast is, as supposed by the earlier observers, a special kind of
winter-egg. According to more recent researches,[566] the funiculus consists
of a central axis, formed from the ectoderm, and of an outer sheath of
mesoderm-cells; the statoblast is developed from the two kinds of cells of
which the funiculus is composed, and is consequently comparable in its
mode of origin to an ordinary bud. Its special peculiarities are: its origin as
an internal bud, its possession of a chitinous shell, and the fact that it is
destined to leave the parent colony, and to develop, after a period of rest,
into a new colony. Germination takes place by the formation of a polypide-
bud inside the statoblast, which finally splits along its equator into two
halves. The contents emerge as a young colony which possesses at least one
fully-formed polypide.
Remarkable structures known as "hibernacula" occur in the fresh-water
Ctenostomes, Paludicella and Victorella. These bodies are in the former
(Fig. 250, B) specially modified external buds, which persist through the
winter when the rest of the colony dies down. At the close of winter the
shell splits into two halves, exactly as takes place in the statoblasts, and a
young colony emerges. It is possible that the statoblasts may have been
evolved from a hibernaculum, which was at first produced externally, but
Page 498
has become modified in such a way as to acquire an internal mode of origin.
[567]
The simplest known statoblast is that of Fredericella (Fig. 251, A), which
differs from that of other Phylactolaemata in having no ring of air-cells. In
Plumatella, the statoblast (Fig. 251, B) has a broad equatorial ring of air-
cells, which enable it to float at the surface of the water on the decay of the
parent tubes. In some species, certain statoblasts which are produced in the
adherent parts of the colony remain attached to the substratum. These
"sessile statoblasts" may have no trace of the ring of air-cells; but the fact
that many sessile statoblasts have rudiments of this structure suggests that
they are a secondary modification of the floating statoblast. In Lophopus
(Fig. 251, C) the ring of air-cells is very broad, and is pointed at each end;
while in Cristatella (Fig. 251, D) and in Pectinatella the statoblast is
circular, and possesses an armature of hooked spines. That of Cristatella,
measures about .75 mm. in its greatest length.
[567]
The simplest known statoblast is that of Fredericella (Fig. 251, A), which
differs from that of other Phylactolaemata in having no ring of air-cells. In
Plumatella, the statoblast (Fig. 251, B) has a broad equatorial ring of air-
cells, which enable it to float at the surface of the water on the decay of the
parent tubes. In some species, certain statoblasts which are produced in the
adherent parts of the colony remain attached to the substratum. These
"sessile statoblasts" may have no trace of the ring of air-cells; but the fact
that many sessile statoblasts have rudiments of this structure suggests that
they are a secondary modification of the floating statoblast. In Lophopus
(Fig. 251, C) the ring of air-cells is very broad, and is pointed at each end;
while in Cristatella (Fig. 251, D) and in Pectinatella the statoblast is
circular, and possesses an armature of hooked spines. That of Cristatella,
measures about .75 mm. in its greatest length.
Page 499
Fig. 250.—Paludicella ehrenbergi van Beneden, × about 3. A, Part of a colony with
expanded polypides; B, remains of part of a colony which has produced
hibernacula or winter-buds (h); z, zooecium. (From Kraepelin.)
Kraepelin has suggested that the above order of increasing complexity of
the statoblasts corresponds with the order in which the genera to which they
respectively belong would be placed, on the assumption that the
Phylactolaemata have been derived from the Ctenostomata. Thus, in
Fredericella, the form of the lophophore is circular, as in the
Gymnolaemata. The number of the tentacles is comparatively small (20-
24). The arborescent form of the colony resembles that of many
Ctenostomes, and the zooecia are more or less cut off from one another by
incomplete septa.
In Plumatella, the lophophore has become horse-shoe-shaped, and the
tentacles are more numerous (38-60). In general form and in the
arrangement of the septa this genus resembles Fredericella, with which it
may easily be confused.
In Cristatella we have the most highly modified of all the Phylactolaemata.
The individuality of the zooecium is here subordinated to that of the colony
as a whole. The branched arrangement of the zooecia is greatly obscured.
The body-cavities have become completely confluent, although rudiments
of the septa still exist. The ectocyst has been lost, with the exception of the
basal layer of the colony. The tentacles are more numerous (80-90); and in
accordance with the increase in the elaboration of the genus, its statoblasts
belong to the most complicated type known.
expanded polypides; B, remains of part of a colony which has produced
hibernacula or winter-buds (h); z, zooecium. (From Kraepelin.)
Kraepelin has suggested that the above order of increasing complexity of
the statoblasts corresponds with the order in which the genera to which they
respectively belong would be placed, on the assumption that the
Phylactolaemata have been derived from the Ctenostomata. Thus, in
Fredericella, the form of the lophophore is circular, as in the
Gymnolaemata. The number of the tentacles is comparatively small (20-
24). The arborescent form of the colony resembles that of many
Ctenostomes, and the zooecia are more or less cut off from one another by
incomplete septa.
In Plumatella, the lophophore has become horse-shoe-shaped, and the
tentacles are more numerous (38-60). In general form and in the
arrangement of the septa this genus resembles Fredericella, with which it
may easily be confused.
In Cristatella we have the most highly modified of all the Phylactolaemata.
The individuality of the zooecium is here subordinated to that of the colony
as a whole. The branched arrangement of the zooecia is greatly obscured.
The body-cavities have become completely confluent, although rudiments
of the septa still exist. The ectocyst has been lost, with the exception of the
basal layer of the colony. The tentacles are more numerous (80-90); and in
accordance with the increase in the elaboration of the genus, its statoblasts
belong to the most complicated type known.
Page 500
Fig. 251.—Statoblasts of Phylactolaemata. A, Fredericella sultana Blum., × 38; B,
Plumatella repens L., × 38; C, Lophopus crystallinus Pall., × 28; D, Cristatella
mucedo Cuv., × 28. (A, from Allman; B-D, from Kraepelin.)
The production of floating statoblasts may seem a strange adaptation to the
conditions of fresh-water life, since it might be assumed, a priori, that these
structures would be specially liable to be frozen during the winter. The
following experiments made by Braem[568] show, however, that the
germinating power of the statoblasts is improved by a certain amount of
frost. A number of statoblasts were taken; half of these were placed in
water, which was then frozen; and these were found to germinate readily
when afterwards exposed to suitable conditions. The other half were not
subjected to the action of frost; and these could not be made to germinate,
even although the water had been cooled to a point slightly above the
freezing point. It thus appears that the buoyancy, so far from being a risk, is
a means of exposing the statoblast to the conditions which are most
favourable to its later development.
Braem supposes that the beneficial action of frost is due to a lowering of the
vital energy of the statoblast. As in the case of reproductive bodies known
in many other fresh-water organisms, the statoblast germinates only after a
period of rest. Although this period is often shortened by a lowering of the
temperature, it can also be induced by the exclusion of air, as in an
experiment during which the statoblasts were enclosed in airtight tubes. The
respiratory processes were thereby lessened, and the germinating power
was materially improved.
Since the development of the statoblasts depends largely on the
temperature, the first warm weather in early spring will probably induce the
germination of those which are floating; and the young colony, leaving the
protection of the statoblast, will become susceptible to frost. But even if the
Plumatella repens L., × 38; C, Lophopus crystallinus Pall., × 28; D, Cristatella
mucedo Cuv., × 28. (A, from Allman; B-D, from Kraepelin.)
The production of floating statoblasts may seem a strange adaptation to the
conditions of fresh-water life, since it might be assumed, a priori, that these
structures would be specially liable to be frozen during the winter. The
following experiments made by Braem[568] show, however, that the
germinating power of the statoblasts is improved by a certain amount of
frost. A number of statoblasts were taken; half of these were placed in
water, which was then frozen; and these were found to germinate readily
when afterwards exposed to suitable conditions. The other half were not
subjected to the action of frost; and these could not be made to germinate,
even although the water had been cooled to a point slightly above the
freezing point. It thus appears that the buoyancy, so far from being a risk, is
a means of exposing the statoblast to the conditions which are most
favourable to its later development.
Braem supposes that the beneficial action of frost is due to a lowering of the
vital energy of the statoblast. As in the case of reproductive bodies known
in many other fresh-water organisms, the statoblast germinates only after a
period of rest. Although this period is often shortened by a lowering of the
temperature, it can also be induced by the exclusion of air, as in an
experiment during which the statoblasts were enclosed in airtight tubes. The
respiratory processes were thereby lessened, and the germinating power
was materially improved.
Since the development of the statoblasts depends largely on the
temperature, the first warm weather in early spring will probably induce the
germination of those which are floating; and the young colony, leaving the
protection of the statoblast, will become susceptible to frost. But even if the
Page 501
first-formed colonies are killed off by a subsequent frost, other statoblasts
which have remained in the mud during the winter are disentangled from
time to time, and germinate on reaching the surface.
Distribution.—The protective value of the shell is also shown by the fact
that the statoblast may be kept for some months in a dry condition without
losing its power of germination. There can be little doubt that the capability
of withstanding desiccation enables the species to enlarge its area of
distribution. It is asserted that fresh-water Polyzoa decrease in abundance in
proportion to the distance from the mouth of the river in which they are
found. The current will naturally tend to bring together the statoblasts from
the Polyzoa growing in the upper waters.
Nothing is more surprising than the wide geographical distribution of the
Phylactolaemata. The European genera are all recorded from North
America. Fredericella, Plumatella, and Lophopus are further recorded from
Australia; while Plumatella is known to occur also in Malacca, the
Philippine Islands, India, Japan, Africa, and South America, It is even stated
that some of the Australian species are identical with those found in Europe.
Some of the fresh-water Polyzoa are extremely variable, and observers are
by no means agreed in deciding whether certain well-known forms are to be
regarded as varieties or as species. While certain genera, such as Cristatella
and Lophopus, are comparatively constant in their form, Plumatella is
excessively variable. Plumatella has a number of species greater than that
of any other form, and the genus has a wider distribution than any other.
This greater variation of species of the dominant genus is in complete
accordance with the general law enunciated by Darwin that "wide-ranging,
much diffused, and common species vary most."
While the ordinary forms of Plumatella consist of branching colonies,
which are either completely adherent to their substratum, or grow in a more
or less erect manner, another habit which is assumed by this genus is so
different from the first that it has been considered to mark a distinct genus,
Alcyonella. The Alcyonelloid form (Fig. 246, A) consists of closely packed
tubes which stand more or less at right angles to their substratum, which
which have remained in the mud during the winter are disentangled from
time to time, and germinate on reaching the surface.
Distribution.—The protective value of the shell is also shown by the fact
that the statoblast may be kept for some months in a dry condition without
losing its power of germination. There can be little doubt that the capability
of withstanding desiccation enables the species to enlarge its area of
distribution. It is asserted that fresh-water Polyzoa decrease in abundance in
proportion to the distance from the mouth of the river in which they are
found. The current will naturally tend to bring together the statoblasts from
the Polyzoa growing in the upper waters.
Nothing is more surprising than the wide geographical distribution of the
Phylactolaemata. The European genera are all recorded from North
America. Fredericella, Plumatella, and Lophopus are further recorded from
Australia; while Plumatella is known to occur also in Malacca, the
Philippine Islands, India, Japan, Africa, and South America, It is even stated
that some of the Australian species are identical with those found in Europe.
Some of the fresh-water Polyzoa are extremely variable, and observers are
by no means agreed in deciding whether certain well-known forms are to be
regarded as varieties or as species. While certain genera, such as Cristatella
and Lophopus, are comparatively constant in their form, Plumatella is
excessively variable. Plumatella has a number of species greater than that
of any other form, and the genus has a wider distribution than any other.
This greater variation of species of the dominant genus is in complete
accordance with the general law enunciated by Darwin that "wide-ranging,
much diffused, and common species vary most."
While the ordinary forms of Plumatella consist of branching colonies,
which are either completely adherent to their substratum, or grow in a more
or less erect manner, another habit which is assumed by this genus is so
different from the first that it has been considered to mark a distinct genus,
Alcyonella. The Alcyonelloid form (Fig. 246, A) consists of closely packed
tubes which stand more or less at right angles to their substratum, which
Page 502
they may cover with a dense mass an inch thick, and with a superficial area
of several square inches. But in spite of this difference, it is possible that A.
fungosa is only a variety of an ordinary Plumatella form. Whether this is so
or not, a typical Plumatella may in places take on an Alcyonelloid habit;
and parts of an Alcyonella may become so lax in growth as to resemble a
Plumatella.
The British genera of fresh-water Polyzoa may be distinguished from one
another by means of the following table:—
1. Zooecia perfectly distinct from one another. Lophophore circular.
Statoblasts absent
2
Colony formed of branching tubes composed of confluent zooecia
3
Colony gelatinous, not obviously formed of branching tubes.
Lophophore horse-shoe shaped
4
2. Colony consisting of a stolon from which new zooecia originate.
These may give rise to new stolons, or directly to new zooecia
Victorella
Branches composed entirely of club-shaped zooecia, each of which
may give off two zooecia near its upper end
Paludicella (Fig. 250)
3. Tubes hyaline or opaque, usually containing numerous oval
statoblasts (Fig. 251, B), most of which have a ring of air-cells.
Lophophore horse-shoe shaped.
(a) Tubes divergent Plumatella (Fig. 246, B)
(b) Tubes parallel with one another
Alcyonella form of Plumatella (Fig. 246, A)
Tubes cylindrical, usually dark brown. Statoblasts (Fig. 251, A) few,
without air-cells. Lophophore circular
Fredericella
of several square inches. But in spite of this difference, it is possible that A.
fungosa is only a variety of an ordinary Plumatella form. Whether this is so
or not, a typical Plumatella may in places take on an Alcyonelloid habit;
and parts of an Alcyonella may become so lax in growth as to resemble a
Plumatella.
The British genera of fresh-water Polyzoa may be distinguished from one
another by means of the following table:—
1. Zooecia perfectly distinct from one another. Lophophore circular.
Statoblasts absent
2
Colony formed of branching tubes composed of confluent zooecia
3
Colony gelatinous, not obviously formed of branching tubes.
Lophophore horse-shoe shaped
4
2. Colony consisting of a stolon from which new zooecia originate.
These may give rise to new stolons, or directly to new zooecia
Victorella
Branches composed entirely of club-shaped zooecia, each of which
may give off two zooecia near its upper end
Paludicella (Fig. 250)
3. Tubes hyaline or opaque, usually containing numerous oval
statoblasts (Fig. 251, B), most of which have a ring of air-cells.
Lophophore horse-shoe shaped.
(a) Tubes divergent Plumatella (Fig. 246, B)
(b) Tubes parallel with one another
Alcyonella form of Plumatella (Fig. 246, A)
Tubes cylindrical, usually dark brown. Statoblasts (Fig. 251, A) few,
without air-cells. Lophophore circular
Fredericella
Page 503
4. Colony hyaline, usually divided into three or four short lobes.
Ectocyst thick. Statoblasts (Fig. 251, C) pointed at each end, with a
broad ring of air-cells
Lophopus (Fig. 248)
Colony slug-shaped, crawling on a flattened sole. Ectocyst
rudimentary. Statoblasts (Fig. 251, D) circular, with marginal
hooks
Cristatella (Fig. 247)
Colonies consisting of small rosettes, many of which are attached to
a thick basal layer of hyaline ectocyst. Statoblasts circular, with
marginal hooks. (Not recorded as British)
Pectinatella
Reproductive Processes of Polyzoa in general.
In studying the reproductive processes of Polyzoa, we have to deal with two
very distinct phenomena; firstly, with the development of eggs; and
secondly, with the formation of buds.
The process of budding usually does no more than increase the number of
individuals in a colony which already exists, and is seldom responsible for
the commencement of a new colony. In Loxosoma, however, the buds break
off and lead an independent existence; and in the Phylactolaemata a large
proportion of the colonies have their origin in the statoblasts. In certain
cases, again, new colonies may be formed by the detachment of parts of an
old one, as by the fission of Cristatella and Lophopus, or by the breaking up
of a richly-branched species into several colonies by the decay of the
proximal parts.
We may then in the majority of cases look to an embryo for the foundation
of a new colony. The embryo develops into a larva, which, after a period in
which it swims freely, settles down, and is metamorphosed into the first
zooecium. This primary individual forms the starting-point of a colony, and
often differs to a considerable extent from the other zooecia which arise
from it. In Cyclostomata, for instance, the proximal end of the primary
zooecium permanently retains the disc-like shape assumed by the young
Ectocyst thick. Statoblasts (Fig. 251, C) pointed at each end, with a
broad ring of air-cells
Lophopus (Fig. 248)
Colony slug-shaped, crawling on a flattened sole. Ectocyst
rudimentary. Statoblasts (Fig. 251, D) circular, with marginal
hooks
Cristatella (Fig. 247)
Colonies consisting of small rosettes, many of which are attached to
a thick basal layer of hyaline ectocyst. Statoblasts circular, with
marginal hooks. (Not recorded as British)
Pectinatella
Reproductive Processes of Polyzoa in general.
In studying the reproductive processes of Polyzoa, we have to deal with two
very distinct phenomena; firstly, with the development of eggs; and
secondly, with the formation of buds.
The process of budding usually does no more than increase the number of
individuals in a colony which already exists, and is seldom responsible for
the commencement of a new colony. In Loxosoma, however, the buds break
off and lead an independent existence; and in the Phylactolaemata a large
proportion of the colonies have their origin in the statoblasts. In certain
cases, again, new colonies may be formed by the detachment of parts of an
old one, as by the fission of Cristatella and Lophopus, or by the breaking up
of a richly-branched species into several colonies by the decay of the
proximal parts.
We may then in the majority of cases look to an embryo for the foundation
of a new colony. The embryo develops into a larva, which, after a period in
which it swims freely, settles down, and is metamorphosed into the first
zooecium. This primary individual forms the starting-point of a colony, and
often differs to a considerable extent from the other zooecia which arise
from it. In Cyclostomata, for instance, the proximal end of the primary
zooecium permanently retains the disc-like shape assumed by the young
Page 504
larva when it first fixed itself. The primary zooecium may be recognised
with equal ease in many Cheilostomata, and may differ from its successors
by possessing a richer development of marginal spines, or in other respects.
Reproductive Organs.—Eggs and spermatozoa are commonly found in the
same colony, either in different individuals, or else in the same zooecium
(see Fig. 234, p. 469). In some cases, the zooecium first develops
spermatozoa, and later eggs. The Entoprocta have a more marked separation
of the sexes than obtains in other Polyzoa. The genus Loxosoma is perhaps
always dioecious (i.e. with separate sexes). Pedicellina is sometimes found
with ovaries and testes in the same individual, sometimes with these organs
in different individuals; and it is not clear whether a given species always
behaves alike in these respects.
The reproductive organs of the Entoprocta open by ducts of their own into
the vestibule. In the Ectoprocta they are developed in the body-cavity, and
they have no ducts.
The fate of the ripe egg differs widely in different cases. In the Entoprocta it
develops in a kind of brood-pouch formed from part of the vestibule. The
fact that in Pedicellina (Fig. 243) the embryos grow largely during their
development, shows that nutritive material must be supplied to them from
the parent. There is reason to believe that the epithelium of the brood-pouch
is responsible for this process. The eggs are also known to develop at the
expense of nutritive substances prepared by the parent in the ovicells of the
Cyclostomata. In other cases, as in some species of Alcyonidium, the egg is
large, and its copious yolk doubtless supplies a large part of the material
required for development.
In the Ectoprocta, development takes place in a variety of places. In most
Cheilostomata a single egg passes into the globular ovicell, which is formed
above the orifice of many of the zooecia. In certain Ctenostomata,[569]
Phylactolaemata,[570] and Cyclostomata,[571] the ripe egg is taken up by a
rudimentary polypide-bud, which is specially formed for the purpose. In the
Ctenostomata and in the fresh-water Polyzoa these buds, if present, are
found in ordinary zooecia which do not become modified externally in any
with equal ease in many Cheilostomata, and may differ from its successors
by possessing a richer development of marginal spines, or in other respects.
Reproductive Organs.—Eggs and spermatozoa are commonly found in the
same colony, either in different individuals, or else in the same zooecium
(see Fig. 234, p. 469). In some cases, the zooecium first develops
spermatozoa, and later eggs. The Entoprocta have a more marked separation
of the sexes than obtains in other Polyzoa. The genus Loxosoma is perhaps
always dioecious (i.e. with separate sexes). Pedicellina is sometimes found
with ovaries and testes in the same individual, sometimes with these organs
in different individuals; and it is not clear whether a given species always
behaves alike in these respects.
The reproductive organs of the Entoprocta open by ducts of their own into
the vestibule. In the Ectoprocta they are developed in the body-cavity, and
they have no ducts.
The fate of the ripe egg differs widely in different cases. In the Entoprocta it
develops in a kind of brood-pouch formed from part of the vestibule. The
fact that in Pedicellina (Fig. 243) the embryos grow largely during their
development, shows that nutritive material must be supplied to them from
the parent. There is reason to believe that the epithelium of the brood-pouch
is responsible for this process. The eggs are also known to develop at the
expense of nutritive substances prepared by the parent in the ovicells of the
Cyclostomata. In other cases, as in some species of Alcyonidium, the egg is
large, and its copious yolk doubtless supplies a large part of the material
required for development.
In the Ectoprocta, development takes place in a variety of places. In most
Cheilostomata a single egg passes into the globular ovicell, which is formed
above the orifice of many of the zooecia. In certain Ctenostomata,[569]
Phylactolaemata,[570] and Cyclostomata,[571] the ripe egg is taken up by a
rudimentary polypide-bud, which is specially formed for the purpose. In the
Ctenostomata and in the fresh-water Polyzoa these buds, if present, are
found in ordinary zooecia which do not become modified externally in any
Page 505
special way. In the Cyclostomata (Crisia), on the contrary, the formation of
the polypide-bud is intimately bound up with the development of the
ovicell. The number of the zooecia which produce eggs that are capable of
development is greatly restricted in this group. The ovicell, which contains
numerous embryos, is not merely a portion of a zooecium, as in the
Cheilostomata; but it is probably to be regarded as a modification of the
entire fertile zooecium or zooecia. These take on an appearance widely
differing from that of the ordinary zooecia, and in course of time give rise
to the ovicells (see Fig. 237).
In all these cases the egg develops inside the parent, and it was hardly
known, before the publication of the interesting researches of M. Prouho,
[572]
that some of the Polyzoa lay eggs which develop externally. In these
cases a considerable number of eggs are produced simultaneously by a
single zooecium. M. Prouho further throws light on a much contested
subject; namely, the nature of the so-called "intertentacular organ" (i, Fig.
234, p. 469), described so long ago as 1837 by Farre,[573] but looked for in
vain by the majority of later observers.
The failure to find this organ, even in species which possess it, in certain
individuals, according to Farre's statements, is now satisfactorily explained
by M. Prouho, who shows that while it is absent in a large number of
polypides, it is normally present in those individuals which possess an
ovary, and in those only; and that its primary function is that of an oviduct.
The intertentacular organ is an unpaired ciliated tube, which is situated
between the two tentacles which are nearest to the ganglion. In the retracted
condition of the polypide, it opens from the body-cavity into the tentacle-
sheath; and in the expanded condition, directly to the exterior.
In the remarkable case of Alcyonidium duplex, each zooecium normally
possesses two sexual polypides. The first of these produces a testis and then
becomes a "brown body." The second is meanwhile developed, and
produces an ovary and an intertentacular organ, a structure which was not
present in the male polypide. The eggs pass through the intertentacular
the polypide-bud is intimately bound up with the development of the
ovicell. The number of the zooecia which produce eggs that are capable of
development is greatly restricted in this group. The ovicell, which contains
numerous embryos, is not merely a portion of a zooecium, as in the
Cheilostomata; but it is probably to be regarded as a modification of the
entire fertile zooecium or zooecia. These take on an appearance widely
differing from that of the ordinary zooecia, and in course of time give rise
to the ovicells (see Fig. 237).
In all these cases the egg develops inside the parent, and it was hardly
known, before the publication of the interesting researches of M. Prouho,
[572]
that some of the Polyzoa lay eggs which develop externally. In these
cases a considerable number of eggs are produced simultaneously by a
single zooecium. M. Prouho further throws light on a much contested
subject; namely, the nature of the so-called "intertentacular organ" (i, Fig.
234, p. 469), described so long ago as 1837 by Farre,[573] but looked for in
vain by the majority of later observers.
The failure to find this organ, even in species which possess it, in certain
individuals, according to Farre's statements, is now satisfactorily explained
by M. Prouho, who shows that while it is absent in a large number of
polypides, it is normally present in those individuals which possess an
ovary, and in those only; and that its primary function is that of an oviduct.
The intertentacular organ is an unpaired ciliated tube, which is situated
between the two tentacles which are nearest to the ganglion. In the retracted
condition of the polypide, it opens from the body-cavity into the tentacle-
sheath; and in the expanded condition, directly to the exterior.
In the remarkable case of Alcyonidium duplex, each zooecium normally
possesses two sexual polypides. The first of these produces a testis and then
becomes a "brown body." The second is meanwhile developed, and
produces an ovary and an intertentacular organ, a structure which was not
present in the male polypide. The eggs pass through the intertentacular
Page 506
organ into the tentacle-sheath, and attach themselves to the diaphragm (d,
Fig. 234), where they remain during their development.
Although the intertentacular organ has been found by Prouho in female
polypides only, it would perhaps be going too far to assert that it is confined
to polypides of that sex. Hincks[574] has observed the passage of
spermatozoa in enormous numbers through the organ, although it may be
noted that there is no sufficient proof that eggs were not present as well in
these zooecia. It further appears that in some cases waste matters may be
removed from the body-cavity through the same passage.
It may be presumed that the egg is normally fertilised by a spermatozoon,
although this is at present largely a matter of inference. It is believed by
Joliet[575] that fertilisation is reciprocal, although Prouho has come to the
opposite conclusion. Joliet has, however, very justly pointed out that the
enormous number of spermatozoa developed by a single individual would
be disproportionately large, if their function were merely to fertilise the
ovum in the same zooecium. According to his view, the egg is fertilised by
a spermatozoon after it has passed into the tentacle-sheath or ovicell, or
some other place where it is in free communication with the outside water.
Development and Affinities.—Few parts of the history of the Polyzoa are
more fascinating than that which deals with their development; and it is
probable that no other is capable of giving so much insight into the
affinities of the several groups to one another and to other groups of the
animal kingdom.
Fig. 234), where they remain during their development.
Although the intertentacular organ has been found by Prouho in female
polypides only, it would perhaps be going too far to assert that it is confined
to polypides of that sex. Hincks[574] has observed the passage of
spermatozoa in enormous numbers through the organ, although it may be
noted that there is no sufficient proof that eggs were not present as well in
these zooecia. It further appears that in some cases waste matters may be
removed from the body-cavity through the same passage.
It may be presumed that the egg is normally fertilised by a spermatozoon,
although this is at present largely a matter of inference. It is believed by
Joliet[575] that fertilisation is reciprocal, although Prouho has come to the
opposite conclusion. Joliet has, however, very justly pointed out that the
enormous number of spermatozoa developed by a single individual would
be disproportionately large, if their function were merely to fertilise the
ovum in the same zooecium. According to his view, the egg is fertilised by
a spermatozoon after it has passed into the tentacle-sheath or ovicell, or
some other place where it is in free communication with the outside water.
Development and Affinities.—Few parts of the history of the Polyzoa are
more fascinating than that which deals with their development; and it is
probable that no other is capable of giving so much insight into the
affinities of the several groups to one another and to other groups of the
animal kingdom.
Page 507
Fig. 252.—Diagrams of larvae. A, Loxosoma, × 208; a, anus; b, brain, with left eye and
ciliated pit; c, ciliated ring; ep, epistome; m, mouth; o, oesophagus; st, stomach;
x, aboral adhesive organ: B, Cyphonautes larva of Membranipora (Electra)
pilosa, × about 90; a, m, o, st as in A; c, anterior part, and c', posterior part of the
ciliated ring; e, epidermis; ms, adductor muscle of shells; p, pyriform organ, of
unknown function; sh, shell; v, vestibule; the "internal sac" or sucker, by which
fixation is effected, is seen between a and ms. (B, after Prouho.)
The comparative study of the larvae of the Polyzoa may be said to date
from 1877, when J. Barrois published an elaborate Monograph[576] on this
subject. Although some of Barrois' earlier opinions have been subsequently
modified, this work still gives the best figures of the external form of the
beautiful larvae of many genera. A detailed account of the larval forms of
Polyzoa must be omitted from want of space; and the general conclusions
only can be given.
The larvae of the Entoprocta (Fig. 252, A) resemble the so-called
"Trochosphere" of Polychaeta (see p. 274). The common characters shared
by the larvae of Chaetopoda, Echiuroid Gephyrea, Mollusca, and Polyzoa,
and by adult Rotifera, may well point to the derivation of these groups from
a common ancestor. On this assumption, it is possible that the Polyzoa have
been derived from forms which existed long ages ago, which combined the
common characters of these groups, and the structure of which we can
picture to ourselves only so far as the "Trochosphere" larva can be taken to
represent it in a much simplified condition. Such a view harmonises well
with the great antiquity of the Polyzoa. Certain Ectoproct forms have a
larva, known as Cyphonautes (Fig. 252, B), which closely resembles the
larval form of the Entoprocta; and it is a fact which probably has
considerable significance that this type of larva is known to occur only in
those species of Membranipora (Electra), Alcyonidium, and Hypophorella,
which lay eggs.[577] This may perhaps be regarded as a primitive form of
development which has been lost in species in which development takes
place inside the parent. Cyphonautes compressus (Fig. 252, B), one of the
commonest objects taken in the surface-net off our own coasts, is the larva
of Membranipora (Electra) pilosa. Whilst this larva is provided with a well-
developed alimentary canal, those of most other Ectoprocta possess a mere
rudiment of this structure, and depend for their nutrition either on yolk
present in the egg or on material supplied by the parent. In most cases the
ciliated pit; c, ciliated ring; ep, epistome; m, mouth; o, oesophagus; st, stomach;
x, aboral adhesive organ: B, Cyphonautes larva of Membranipora (Electra)
pilosa, × about 90; a, m, o, st as in A; c, anterior part, and c', posterior part of the
ciliated ring; e, epidermis; ms, adductor muscle of shells; p, pyriform organ, of
unknown function; sh, shell; v, vestibule; the "internal sac" or sucker, by which
fixation is effected, is seen between a and ms. (B, after Prouho.)
The comparative study of the larvae of the Polyzoa may be said to date
from 1877, when J. Barrois published an elaborate Monograph[576] on this
subject. Although some of Barrois' earlier opinions have been subsequently
modified, this work still gives the best figures of the external form of the
beautiful larvae of many genera. A detailed account of the larval forms of
Polyzoa must be omitted from want of space; and the general conclusions
only can be given.
The larvae of the Entoprocta (Fig. 252, A) resemble the so-called
"Trochosphere" of Polychaeta (see p. 274). The common characters shared
by the larvae of Chaetopoda, Echiuroid Gephyrea, Mollusca, and Polyzoa,
and by adult Rotifera, may well point to the derivation of these groups from
a common ancestor. On this assumption, it is possible that the Polyzoa have
been derived from forms which existed long ages ago, which combined the
common characters of these groups, and the structure of which we can
picture to ourselves only so far as the "Trochosphere" larva can be taken to
represent it in a much simplified condition. Such a view harmonises well
with the great antiquity of the Polyzoa. Certain Ectoproct forms have a
larva, known as Cyphonautes (Fig. 252, B), which closely resembles the
larval form of the Entoprocta; and it is a fact which probably has
considerable significance that this type of larva is known to occur only in
those species of Membranipora (Electra), Alcyonidium, and Hypophorella,
which lay eggs.[577] This may perhaps be regarded as a primitive form of
development which has been lost in species in which development takes
place inside the parent. Cyphonautes compressus (Fig. 252, B), one of the
commonest objects taken in the surface-net off our own coasts, is the larva
of Membranipora (Electra) pilosa. Whilst this larva is provided with a well-
developed alimentary canal, those of most other Ectoprocta possess a mere
rudiment of this structure, and depend for their nutrition either on yolk
present in the egg or on material supplied by the parent. In most cases the
Page 508
mature larva has no recognisable trace of a digestive system; and, although
it has a free-swimming period, it does not become truly pelagic.
The alimentary canal of the larva of Pedicellina is known to persist in the
primary individual of the colony. In all other known cases, even in that of
Cyphonautes, the larva at fixation loses practically all its internal organs,
and becomes a mere body-wall containing a mass of degenerated larval
tissues. It is in fact a zooecium containing a "brown body." A polypide-bud
is now developed, the body-cavity appears as the result of the shrinkage of
the "brown body," and the primary individual of the colony is thereby
established.
The larvae of the Ectoprocta form a tolerably complete series, starting from
Cyphonautes, itself allied to the larva of the Entoprocta, and ending with
the Phylactolaemata. Alcyonidium (Fig. 253, B) possesses a rudimentary
alimentary canal,[578] although the most conspicuous structures are those
connected with the fixation and other phenomena of larval life. The larvae
of many of the encrusting Cheilostomes (Fig. 253, A) resemble that of
Alcyonidium, while those of Bugula, Scrupocellaria, etc., belong to a type
easily derivable from that of the encrusting forms. The branching
Ctenostomes (Bowerbankia, etc.) have a larva which may be regarded as
derived, along slightly different lines, from that of Alcyonidium. The
Cyclostomata and the Phylactolaemata have the most modified forms of
larva. That of the former group may owe some of its peculiarities to the
occurrence of a remarkable process of embryonic fission, which takes place
in the ovicell, and as the result of which each egg gives rise to a large
number of larvae.[579] The Phylactolaemata have a larva which is not unlike
that of Bowerbankia.
it has a free-swimming period, it does not become truly pelagic.
The alimentary canal of the larva of Pedicellina is known to persist in the
primary individual of the colony. In all other known cases, even in that of
Cyphonautes, the larva at fixation loses practically all its internal organs,
and becomes a mere body-wall containing a mass of degenerated larval
tissues. It is in fact a zooecium containing a "brown body." A polypide-bud
is now developed, the body-cavity appears as the result of the shrinkage of
the "brown body," and the primary individual of the colony is thereby
established.
The larvae of the Ectoprocta form a tolerably complete series, starting from
Cyphonautes, itself allied to the larva of the Entoprocta, and ending with
the Phylactolaemata. Alcyonidium (Fig. 253, B) possesses a rudimentary
alimentary canal,[578] although the most conspicuous structures are those
connected with the fixation and other phenomena of larval life. The larvae
of many of the encrusting Cheilostomes (Fig. 253, A) resemble that of
Alcyonidium, while those of Bugula, Scrupocellaria, etc., belong to a type
easily derivable from that of the encrusting forms. The branching
Ctenostomes (Bowerbankia, etc.) have a larva which may be regarded as
derived, along slightly different lines, from that of Alcyonidium. The
Cyclostomata and the Phylactolaemata have the most modified forms of
larva. That of the former group may owe some of its peculiarities to the
occurrence of a remarkable process of embryonic fission, which takes place
in the ovicell, and as the result of which each egg gives rise to a large
number of larvae.[579] The Phylactolaemata have a larva which is not unlike
that of Bowerbankia.
Page 509
Fig. 253.—A, Aboral view of free larva of Lepralia foliacea Ell. and Sol.; a, long cilia
of pyriform organ; g, aboral groove: B, longitudinal section of embryo of
Alcyonidium, × 135; c, ciliated ring; g, aboral groove; m, mouth; n, nervous
system; p, "pyriform organ," of unknown function; s, "internal sac" or "sucker,"
by which fixation is effected; st, stomach.
We have seen that the larva at fixation becomes a zooecium, which in the
Gymnolaemata forms a polypide-bud after fixation. The peculiarities of the
Phylactolaematous larva may be explained by assuming that it becomes a
zooecium while it is still free-swimming. Thus the larva of Plumatella
develops one or sometimes two polypides, which actually reach maturity
before fixation takes place. That of Cristatella develops from two to
twenty[580] polypides or polypide-buds at the corresponding period, and it is
in fact a young colony while still free-swimming.
Now in most colonial animals, such as Coelenterates and Ascidians, the
larva metamorphoses itself into a temporarily solitary animal, which then
gives rise to the remainder of the colony by budding. The majority of the
Gymnolaemata behave in this way; while the Phylactolaemata may not only
develop a multiplicity of polypides in their larval stage, but the
individuality of the zooecia is then just as much obscured as in the adult
state. These facts are more easily explained if we assume that Cristatella is
the end-point in a series than if we suppose it to be a starting-point.
On the view maintained by many authorities, that the Polyzoa are related,
through Phoronis, with the Gephyrea and the Brachiopoda, we should
expect to find in those Polyzoa which most closely resemble Phoronis in
their adult state—that is to say in the Phylactolaemata—some indications of
affinity to that animal in their development. This is emphatically not the
of pyriform organ; g, aboral groove: B, longitudinal section of embryo of
Alcyonidium, × 135; c, ciliated ring; g, aboral groove; m, mouth; n, nervous
system; p, "pyriform organ," of unknown function; s, "internal sac" or "sucker,"
by which fixation is effected; st, stomach.
We have seen that the larva at fixation becomes a zooecium, which in the
Gymnolaemata forms a polypide-bud after fixation. The peculiarities of the
Phylactolaematous larva may be explained by assuming that it becomes a
zooecium while it is still free-swimming. Thus the larva of Plumatella
develops one or sometimes two polypides, which actually reach maturity
before fixation takes place. That of Cristatella develops from two to
twenty[580] polypides or polypide-buds at the corresponding period, and it is
in fact a young colony while still free-swimming.
Now in most colonial animals, such as Coelenterates and Ascidians, the
larva metamorphoses itself into a temporarily solitary animal, which then
gives rise to the remainder of the colony by budding. The majority of the
Gymnolaemata behave in this way; while the Phylactolaemata may not only
develop a multiplicity of polypides in their larval stage, but the
individuality of the zooecia is then just as much obscured as in the adult
state. These facts are more easily explained if we assume that Cristatella is
the end-point in a series than if we suppose it to be a starting-point.
On the view maintained by many authorities, that the Polyzoa are related,
through Phoronis, with the Gephyrea and the Brachiopoda, we should
expect to find in those Polyzoa which most closely resemble Phoronis in
their adult state—that is to say in the Phylactolaemata—some indications of
affinity to that animal in their development. This is emphatically not the
Page 510
case. The hypothesis that the Phylactolaemata are related to Phoronis leads,
moreover, to the improbable conclusion that the similarities between the
Entoproct-larva and Cyphonautes, on the one hand, and the Trochosphere
larva of Polychaeta, on the other hand, is entirely superficial and
meaningless. In spite, therefore, of the similarity between Phoronis and a
single individual of the Phylactolaemata, and in spite of the marked
resemblance between its nephridia and structures which have been
described in Cristatella[581] and Pectinatella[582] the comparative study of
the development appears to indicate that the resemblances between
Phoronis and the Phylactolaemata are the result of a coincidence rather than
of any close relationship.
A few points connected with the metamorphosis of the Polyzoa deserve
more special notice. There is generally great difficulty in persuading larvae
to fix themselves when kept in a small quantity of water, which becomes
over-heated in the air of a laboratory. The difficulty may be surmounted by
placing colonies containing embryos, together with some clean pieces of the
seaweed on which the adults are habitually found, in a vessel closed by a
piece of fine muslin, and by leaving the vessel attached to a buoy or in a
deep tide-pool. The larvae being without an alimentary canal, fix
themselves, after a very short free life, on the seaweed.
It is probable that a great struggle for existence normally takes place at the
commencement of the metamorphosis. Any one who will examine, in June
or July, rocks covered by Fucus on which Flustrella hispida is growing,
will probably find numerous young fronds of Fucus, from half an inch to an
inch or two in length, growing under the shelter of the older fronds. The
bivalve larvae of Flustrella show a marked preference for fixing on these
young fronds—perhaps in order that the duration of life of the colony may
coincide with that of the Fucus—and these young fronds are commonly
covered by very numerous recently-fixed larvae, and by young colonies of
various ages. Or, it is easy to observe, by placing pregnant colonies of
Bowerbankia in a vessel of water, that the larvae, which are hatched out in
thousands, fix themselves in dense masses on certain parts of the wall of the
vessel. It is clear that but a small proportion of these larvae will find room
for further development.
moreover, to the improbable conclusion that the similarities between the
Entoproct-larva and Cyphonautes, on the one hand, and the Trochosphere
larva of Polychaeta, on the other hand, is entirely superficial and
meaningless. In spite, therefore, of the similarity between Phoronis and a
single individual of the Phylactolaemata, and in spite of the marked
resemblance between its nephridia and structures which have been
described in Cristatella[581] and Pectinatella[582] the comparative study of
the development appears to indicate that the resemblances between
Phoronis and the Phylactolaemata are the result of a coincidence rather than
of any close relationship.
A few points connected with the metamorphosis of the Polyzoa deserve
more special notice. There is generally great difficulty in persuading larvae
to fix themselves when kept in a small quantity of water, which becomes
over-heated in the air of a laboratory. The difficulty may be surmounted by
placing colonies containing embryos, together with some clean pieces of the
seaweed on which the adults are habitually found, in a vessel closed by a
piece of fine muslin, and by leaving the vessel attached to a buoy or in a
deep tide-pool. The larvae being without an alimentary canal, fix
themselves, after a very short free life, on the seaweed.
It is probable that a great struggle for existence normally takes place at the
commencement of the metamorphosis. Any one who will examine, in June
or July, rocks covered by Fucus on which Flustrella hispida is growing,
will probably find numerous young fronds of Fucus, from half an inch to an
inch or two in length, growing under the shelter of the older fronds. The
bivalve larvae of Flustrella show a marked preference for fixing on these
young fronds—perhaps in order that the duration of life of the colony may
coincide with that of the Fucus—and these young fronds are commonly
covered by very numerous recently-fixed larvae, and by young colonies of
various ages. Or, it is easy to observe, by placing pregnant colonies of
Bowerbankia in a vessel of water, that the larvae, which are hatched out in
thousands, fix themselves in dense masses on certain parts of the wall of the
vessel. It is clear that but a small proportion of these larvae will find room
for further development.
Page 511
Next with regard to the mode of fixation. Attachment always takes place by
the surface on which the mouth or its rudiment is situated, and the
permanent alimentary canal opens on the opposite surface. In Pedicellina,
the one case in which the larval digestive organs are known to become
those of the first adult individual, this presupposes a rotation of the
alimentary canal, in order to bring it into its new position.
It is well known that the larvae of other fixed animals may undergo a
somewhat similar change. Thus those of Ascidians and of Barnacles fix
themselves by their anterior end, and ultimately reach their adult form by
performing a kind of a somersault. The process may perhaps be explained
by supposing that some part of the anterior end or of the oral surface is
specially sensitive, and that the larva fixes itself by that portion of its body
which is best fitted for ascertaining which is the proper substance on which
to fix.
Budding.—The formation of a new individual may take place by the
outgrowth of part of the body-wall, as in Pedicellina (Fig. 243, p. 487) and
in Bowerbankia (Fig. 238, p. 480). In Pedicellina a young stalk is formed
by an outgrowth near one of the growing points, and the upper part of this
outgrowth becomes constricted off to form the calyx. In other cases (cf. the
growing ends of the branches in Fig. 237) a partition grows across the
body-cavity at the growing edge of the colony, and so cuts off a part
destined to become a new zooecium.
The zooecium formed in one of these ways acquires an alimentary canal by
the formation of a polypide-bud, some stages in the growth of which are
shown in Fig. 235 (p. 472). Contrary to what happens in Coelenterates and
Tunicates, in which the endoderm takes part in the budding, there is good
reason for believing that in Polyzoa the polypide-bud is developed entirely
from ectoderm and mesoderm.[583] The bud is a two-layered vesicle,
attached to the inner side of the body-wall. Its inner layer is derived from
the ectoderm, which at first projects into the body-cavity in the form of a
solid knob surrounded by mesoderm-cells. A cavity appears in the inner,
ectodermic mass, and the upper part of the vesicle so developed becomes
excessively thin, forming the tentacle-sheath, which is always developed in
the surface on which the mouth or its rudiment is situated, and the
permanent alimentary canal opens on the opposite surface. In Pedicellina,
the one case in which the larval digestive organs are known to become
those of the first adult individual, this presupposes a rotation of the
alimentary canal, in order to bring it into its new position.
It is well known that the larvae of other fixed animals may undergo a
somewhat similar change. Thus those of Ascidians and of Barnacles fix
themselves by their anterior end, and ultimately reach their adult form by
performing a kind of a somersault. The process may perhaps be explained
by supposing that some part of the anterior end or of the oral surface is
specially sensitive, and that the larva fixes itself by that portion of its body
which is best fitted for ascertaining which is the proper substance on which
to fix.
Budding.—The formation of a new individual may take place by the
outgrowth of part of the body-wall, as in Pedicellina (Fig. 243, p. 487) and
in Bowerbankia (Fig. 238, p. 480). In Pedicellina a young stalk is formed
by an outgrowth near one of the growing points, and the upper part of this
outgrowth becomes constricted off to form the calyx. In other cases (cf. the
growing ends of the branches in Fig. 237) a partition grows across the
body-cavity at the growing edge of the colony, and so cuts off a part
destined to become a new zooecium.
The zooecium formed in one of these ways acquires an alimentary canal by
the formation of a polypide-bud, some stages in the growth of which are
shown in Fig. 235 (p. 472). Contrary to what happens in Coelenterates and
Tunicates, in which the endoderm takes part in the budding, there is good
reason for believing that in Polyzoa the polypide-bud is developed entirely
from ectoderm and mesoderm.[583] The bud is a two-layered vesicle,
attached to the inner side of the body-wall. Its inner layer is derived from
the ectoderm, which at first projects into the body-cavity in the form of a
solid knob surrounded by mesoderm-cells. A cavity appears in the inner,
ectodermic mass, and the upper part of the vesicle so developed becomes
excessively thin, forming the tentacle-sheath, which is always developed in
Page 512
the condition of retraction. The lower part becomes thicker; its inner layer
gives rise to the lining of the alimentary canal, to the nervous system, and to
the outer epithelium of the tentacles, which grow out into the tentacle-
sheath (cf. Fig. 235). The outer layer gives rise to the mesodermic
structures, such as the muscles, connective tissue, and generative organs.
These processes are fundamentally similar, whether in the metamorphosed
larva, in a young zooecium, in an old zooecium after the formation of a
"brown body," or in the germinating statoblast of the Phylactolaemata.
CHAPTER XIX
POLYZOA (continued)
CLASSIFICATION—GEOGRAPHICAL DISTRIBUTION—PALAEONTOLOGY—METHODS
FOR THE EXAMINATION OF SPECIFIC CHARACTERS—TERMINOLOGY—KEY FOR THE
DETERMINATION OF THE GENERA OF BRITISH MARINE POLYZOA
Our account of the Polyzoa would be manifestly incomplete without some
reference to the systematic arrangement of these animals. An outline of the
principal groups has been given on p. 475. So far, the classification is easy,
but it is otherwise when we attempt to subdivide most of the groups any
further.
Systems of classification which depend exclusively upon the external
characters of animals have been repeatedly shown to be unsatisfactory. Now
with regard to the Polyzoa, not only is it the case that the great majority of
forms are only known in their external characteristics, but current systems
of classification cannot be regarded as final, because it is not yet certain
which of the external features have most systematic value. Two obvious
points can be at once selected—namely, the character of the zooecium and
the character of the entire colony. One or two instances will serve to show
what different results are obtained by depending exclusively on either of
these characters by itself.
gives rise to the lining of the alimentary canal, to the nervous system, and to
the outer epithelium of the tentacles, which grow out into the tentacle-
sheath (cf. Fig. 235). The outer layer gives rise to the mesodermic
structures, such as the muscles, connective tissue, and generative organs.
These processes are fundamentally similar, whether in the metamorphosed
larva, in a young zooecium, in an old zooecium after the formation of a
"brown body," or in the germinating statoblast of the Phylactolaemata.
CHAPTER XIX
POLYZOA (continued)
CLASSIFICATION—GEOGRAPHICAL DISTRIBUTION—PALAEONTOLOGY—METHODS
FOR THE EXAMINATION OF SPECIFIC CHARACTERS—TERMINOLOGY—KEY FOR THE
DETERMINATION OF THE GENERA OF BRITISH MARINE POLYZOA
Our account of the Polyzoa would be manifestly incomplete without some
reference to the systematic arrangement of these animals. An outline of the
principal groups has been given on p. 475. So far, the classification is easy,
but it is otherwise when we attempt to subdivide most of the groups any
further.
Systems of classification which depend exclusively upon the external
characters of animals have been repeatedly shown to be unsatisfactory. Now
with regard to the Polyzoa, not only is it the case that the great majority of
forms are only known in their external characteristics, but current systems
of classification cannot be regarded as final, because it is not yet certain
which of the external features have most systematic value. Two obvious
points can be at once selected—namely, the character of the zooecium and
the character of the entire colony. One or two instances will serve to show
what different results are obtained by depending exclusively on either of
these characters by itself.
Page 513
According to the older writers, the habit of the colony was taken as the most
important generic character; and there can indeed be no doubt that this
feature has great importance within certain limits. Any one who has
examined different species of such genera as Flustra, Cellaria, Bugula,
Retepora, etc., must feel that the form of the colony goes for a good deal.
But a consideration of other cases shows that there is great risk in the
indiscriminate use of this method of arranging the Polyzoa. The old genus
Eschara, composed of forms with an erect coral-like habit,[584] included
species which are now placed in such different genera as Lepralia, Porella,
Microporella, etc. The older works on Polyzoa include all encrusting forms
of Cheilostomata, with a completely calcareous front wall, in the genus
Lepralia, the members of which are now distributed in numerous widely
separated genera.
As an instance of the converse arrangement—essential similarity of the
zooecia with great differences of the general habit—may be mentioned the
common Membranipora (Electra) pilosa.[585] Ordinarily growing in the
form of close encrustations on seaweeds, this species may take on entirely
different habits of growth. The zooecia are now dissociated, growing in
single lines over the substratum; now forming erect tufts, composed of
single lines of zooecia or of several rows. The erect, branching habit
appears to be induced in the first instance by the character of the seaweed
on which the colony begins life. Thus colonies which encrust the thin
branches of Corallina may have impressed on them something of the mode
of growth of the seaweed, so that when they extend beyond the tips of the
branches of the Corallina, they continue to grow in delicate branches,
which still retain more or less the same diameter as those which form their
base. An extreme variation results in the beautiful form known as Electra
verticillata, in which the zooecia are arranged with great regularity in
whorls, which together form erect branches.[586] But with all these
variations, the zooecia are so much alike that it is hardly possible to regard
the extreme forms as more than varieties of a single species. A careful
examination of this case would convince most observers that the characters
of the zooecium are a more trustworthy guide to classification than those of
the entire colony, a result which was first clearly stated by Smitt, and amply
confirmed by Hincks.[587]
important generic character; and there can indeed be no doubt that this
feature has great importance within certain limits. Any one who has
examined different species of such genera as Flustra, Cellaria, Bugula,
Retepora, etc., must feel that the form of the colony goes for a good deal.
But a consideration of other cases shows that there is great risk in the
indiscriminate use of this method of arranging the Polyzoa. The old genus
Eschara, composed of forms with an erect coral-like habit,[584] included
species which are now placed in such different genera as Lepralia, Porella,
Microporella, etc. The older works on Polyzoa include all encrusting forms
of Cheilostomata, with a completely calcareous front wall, in the genus
Lepralia, the members of which are now distributed in numerous widely
separated genera.
As an instance of the converse arrangement—essential similarity of the
zooecia with great differences of the general habit—may be mentioned the
common Membranipora (Electra) pilosa.[585] Ordinarily growing in the
form of close encrustations on seaweeds, this species may take on entirely
different habits of growth. The zooecia are now dissociated, growing in
single lines over the substratum; now forming erect tufts, composed of
single lines of zooecia or of several rows. The erect, branching habit
appears to be induced in the first instance by the character of the seaweed
on which the colony begins life. Thus colonies which encrust the thin
branches of Corallina may have impressed on them something of the mode
of growth of the seaweed, so that when they extend beyond the tips of the
branches of the Corallina, they continue to grow in delicate branches,
which still retain more or less the same diameter as those which form their
base. An extreme variation results in the beautiful form known as Electra
verticillata, in which the zooecia are arranged with great regularity in
whorls, which together form erect branches.[586] But with all these
variations, the zooecia are so much alike that it is hardly possible to regard
the extreme forms as more than varieties of a single species. A careful
examination of this case would convince most observers that the characters
of the zooecium are a more trustworthy guide to classification than those of
the entire colony, a result which was first clearly stated by Smitt, and amply
confirmed by Hincks.[587]
Page 514
The avicularia of the Cheilostomata afford useful help in classifying this
group; but while certain genera are always provided with avicularia, others
include some species with these organs, and other species without them.
Again, while the species of some genera (e.g. Cellepora) possess a great
variety of forms of avicularia, the same pattern of avicularium may
characterise several widely different genera. Further, the position of the
avicularium may be very different in species which are apparently closely
related. Well-developed vibracula, although constant in their occurrence in
such forms as Scrupocellaria (Fig. 254) and Caberea (Fig. 242), occur here
and there in species of encrusting forms which are ordinarily placed in very
different families.
Now although some of these discrepancies are perhaps due to errors in
classification, whereby species which are really allied have been wrongly
placed in distinct genera, this explanation would not prove satisfactory in
all cases. Thus in Bugula, a genus which is specially characterised by the
high development of its avicularia, these organs are normally absent in B.
neritina. The fact that this species was rightly placed in the genus has been
confirmed by the discovery made by Waters[588] that avicularia occur in
specimens which are believed to be identical with that species.
Fig. 254.—A, Front view, and B, back view of part of a branch of Scrupocellaria
scabra, Van Ben., Durham Coast, × 43; a, lateral avicularium; a', smaller median
avicularium; ap, membranous aperture; f, fornix; r, rootlet; s, seta of vibraculum;
v.z, vibracular zooecium.
1. The Cyclostomata appear to fall naturally into two main groups, (A) the
Articulata, including the Crisiidae (Fig. 237), distinguished by their erect
branches, divided at intervals by chitinous joints; and (B) the Inarticulata,
which include the remaining families, whether erect or encrusting, agreeing
in the negative character of being unjointed.
group; but while certain genera are always provided with avicularia, others
include some species with these organs, and other species without them.
Again, while the species of some genera (e.g. Cellepora) possess a great
variety of forms of avicularia, the same pattern of avicularium may
characterise several widely different genera. Further, the position of the
avicularium may be very different in species which are apparently closely
related. Well-developed vibracula, although constant in their occurrence in
such forms as Scrupocellaria (Fig. 254) and Caberea (Fig. 242), occur here
and there in species of encrusting forms which are ordinarily placed in very
different families.
Now although some of these discrepancies are perhaps due to errors in
classification, whereby species which are really allied have been wrongly
placed in distinct genera, this explanation would not prove satisfactory in
all cases. Thus in Bugula, a genus which is specially characterised by the
high development of its avicularia, these organs are normally absent in B.
neritina. The fact that this species was rightly placed in the genus has been
confirmed by the discovery made by Waters[588] that avicularia occur in
specimens which are believed to be identical with that species.
Fig. 254.—A, Front view, and B, back view of part of a branch of Scrupocellaria
scabra, Van Ben., Durham Coast, × 43; a, lateral avicularium; a', smaller median
avicularium; ap, membranous aperture; f, fornix; r, rootlet; s, seta of vibraculum;
v.z, vibracular zooecium.
1. The Cyclostomata appear to fall naturally into two main groups, (A) the
Articulata, including the Crisiidae (Fig. 237), distinguished by their erect
branches, divided at intervals by chitinous joints; and (B) the Inarticulata,
which include the remaining families, whether erect or encrusting, agreeing
in the negative character of being unjointed.
Page 515
2. The Cheilostomata consist of (A) the Cellularina, including the flexible,
erect forms, such as Bugula (Fig. 233) and Scrupocellaria (Fig. 254); (B)
the Flustrina, to which belong Flustra (Fig. 232), Membranipora (Fig.
256, A, B), Micropora (Fig. 256, C), and other forms in which the front
wall of the zooecium is either membranous, or depressed and marked off by
a ridge-like margin; (C) the Escharina, including the great majority of
forms, in which no part of the front wall remains membranous, the wall of
the zooecium being wholly calcified.
3. The Ctenostomata comprise (A) the Alcyonellea or encrusting forms;
and (B) the Vesicularina or branching forms. The zooecia in the latter
subdivision (Fig. 238) are given off from a tubular stem or stolon, which is
usually erect and branching.
We thus have the following arrangement of recent forms. The genera
mentioned are for the most part those which have already been alluded to in
the preceding account:—
Sub-class I. Entoprocta.
Loxosoma, Pedicellina, Urnatella.
Sub-class II. Ectoprocta.
Order 1. Gymnolaemata.
Sub-order 1. Cyclostomata.
A. Articulata. Crisia.
B. Inarticulata. Hornera, Idmonea, Tubulipora, Stomatopora,
Diastopora, Entalophora, Lichenopora.
Sub-order 2. Cheilostomata.
A. Cellularina. Aetea, Eucratea,[589] Catenicella,
Cellularia, Gemellaria, Menipea, Scrupocellaria,
Caberea, Notamia (= Epistomia), Bicellaria, Bugula,
Beania.
B. Flustrina. Cellaria, Flustra, Membranipora, Electra,
Lunulites, Membraniporella, Cribrilina, Micropora,
Selenaria.
C. Escharina. Retepora, Microporella, Lepralia, Porella,
Smittia, Mucronella, Schizoporella, Schizotheca,
erect forms, such as Bugula (Fig. 233) and Scrupocellaria (Fig. 254); (B)
the Flustrina, to which belong Flustra (Fig. 232), Membranipora (Fig.
256, A, B), Micropora (Fig. 256, C), and other forms in which the front
wall of the zooecium is either membranous, or depressed and marked off by
a ridge-like margin; (C) the Escharina, including the great majority of
forms, in which no part of the front wall remains membranous, the wall of
the zooecium being wholly calcified.
3. The Ctenostomata comprise (A) the Alcyonellea or encrusting forms;
and (B) the Vesicularina or branching forms. The zooecia in the latter
subdivision (Fig. 238) are given off from a tubular stem or stolon, which is
usually erect and branching.
We thus have the following arrangement of recent forms. The genera
mentioned are for the most part those which have already been alluded to in
the preceding account:—
Sub-class I. Entoprocta.
Loxosoma, Pedicellina, Urnatella.
Sub-class II. Ectoprocta.
Order 1. Gymnolaemata.
Sub-order 1. Cyclostomata.
A. Articulata. Crisia.
B. Inarticulata. Hornera, Idmonea, Tubulipora, Stomatopora,
Diastopora, Entalophora, Lichenopora.
Sub-order 2. Cheilostomata.
A. Cellularina. Aetea, Eucratea,[589] Catenicella,
Cellularia, Gemellaria, Menipea, Scrupocellaria,
Caberea, Notamia (= Epistomia), Bicellaria, Bugula,
Beania.
B. Flustrina. Cellaria, Flustra, Membranipora, Electra,
Lunulites, Membraniporella, Cribrilina, Micropora,
Selenaria.
C. Escharina. Retepora, Microporella, Lepralia, Porella,
Smittia, Mucronella, Schizoporella, Schizotheca,
Page 516
Mastigophora, Porina, Cellepora.
Sub-order 3. Ctenostomata.
A. Alcyonellea. Alcyonidium, Flustrella.
B. Vesicularina. Vesicularia, Amathia, Bowerbankia,
Farrella, Hypophorella, Triticella, Mimosella,
Victorella, Paludicella.
Order 2. Phylactolaemata.
Fredericella, Plumatella (including Alcyonella), Lophopus,
Cristatella, Pectinatella.
Even this classification, which deals only with the larger groups, must not
be made use of without a word of warning. The division of the
Cheilostomata is a matter of great difficulty; and no scheme which has yet
been suggested can be regarded as more than tentative. The great number of
forms included in this group makes its subdivision extremely desirable from
the point of view of convenience; but a further knowledge of the anatomy
and of the development of many of the forms of doubtful systematic
position is probably necessary before any scheme which is likely to be
permanent is put forward. Those who desire to make a further study of the
classification of the Polyzoa should refer to the works of Hincks,[590] Busk,
[591] MacGillivray,[592] and Gregory.[593]
The Polyzoa do not appear to lend any valuable assistance towards settling
the disputed problems of Geographical Distribution. They are not in any
case terrestrial, while the fresh-water species do not always respect the
limits between the great zoogeographical regions. It has already been
pointed out (p. 504) that Plumatella, Fredericella, and Lophopus are
believed to occur in Australia, and the first-named genus is practically
world-wide in its distribution.
Many marine forms also have a surprisingly wide distribution. Thus among
the British species which are described by Mr. Hincks as occurring from
Norway to New Zealand are Membranipora pilosa, Scrupocellaria
scruposa, Cellaria fistulosa, Microporella ciliata, and M. malusii. Even if it
should be proved that specific differences do exist between the southern
forms and our own, there can be no doubt of the wide distribution of certain
Sub-order 3. Ctenostomata.
A. Alcyonellea. Alcyonidium, Flustrella.
B. Vesicularina. Vesicularia, Amathia, Bowerbankia,
Farrella, Hypophorella, Triticella, Mimosella,
Victorella, Paludicella.
Order 2. Phylactolaemata.
Fredericella, Plumatella (including Alcyonella), Lophopus,
Cristatella, Pectinatella.
Even this classification, which deals only with the larger groups, must not
be made use of without a word of warning. The division of the
Cheilostomata is a matter of great difficulty; and no scheme which has yet
been suggested can be regarded as more than tentative. The great number of
forms included in this group makes its subdivision extremely desirable from
the point of view of convenience; but a further knowledge of the anatomy
and of the development of many of the forms of doubtful systematic
position is probably necessary before any scheme which is likely to be
permanent is put forward. Those who desire to make a further study of the
classification of the Polyzoa should refer to the works of Hincks,[590] Busk,
[591] MacGillivray,[592] and Gregory.[593]
The Polyzoa do not appear to lend any valuable assistance towards settling
the disputed problems of Geographical Distribution. They are not in any
case terrestrial, while the fresh-water species do not always respect the
limits between the great zoogeographical regions. It has already been
pointed out (p. 504) that Plumatella, Fredericella, and Lophopus are
believed to occur in Australia, and the first-named genus is practically
world-wide in its distribution.
Many marine forms also have a surprisingly wide distribution. Thus among
the British species which are described by Mr. Hincks as occurring from
Norway to New Zealand are Membranipora pilosa, Scrupocellaria
scruposa, Cellaria fistulosa, Microporella ciliata, and M. malusii. Even if it
should be proved that specific differences do exist between the southern
forms and our own, there can be no doubt of the wide distribution of certain
Page 517
species. It was pointed out by D'Orbigny that Bugula neritina has the habit
of attaching itself to the bottoms of ships, a fact which may possibly
account for the wide distribution of this species; although it would not be
safe to assume this explanation of the facts in all cases. Other Polyzoa, on
the contrary, have a more restricted range. Thus Catenicella is specially
characteristic of the Australian region.
It is perhaps surprising that marine Polyzoa should in so many cases have
so wide a range. Even though it is the rule for Polyzoa to have free larvae,
the period during which these larvae are free-swimming is, so far as is
known, a short one in most cases. Cyphonautes is a common pelagic form
(see p. 510), and probably remains for a considerable period in the larval
condition. Other Polyzoon-larvae appear to fix themselves very soon after
their birth; and this would not appear to give much time for them to be
carried to great distances by ocean-currents. It may, however, be suggested
that it does not follow that because we know that a larva may, under
favourable conditions fix itself a few minutes after it becomes free, we
should be justified in assuming that that larva would not retain for a long
period the power of undergoing a normal metamorphosis should it be
drifted away from suitable fixing-grounds.
Palaeontology.[594]—The number of fossil Polyzoa is enormous.
D'Orbigny devoted two hundred plates and more than a thousand octavo
pages[595] to a Monograph on the Cretaceous Polyzoa of France. Many of
the fossil forms are extraordinarily well preserved, and there is often no
difficulty in recognising the identity between certain fossil species
belonging to the more recent formations and living forms. It thus becomes
necessary to consult Palaeontological memoirs in working at recent
Polyzoa.
While the great majority of fossil Polyzoa do not differ in any essential
particular from recent species, this is not altogether the case with the
Palaeozoic forms. Leaving out of account the Stromatoporoids, which have
been variously referred to the Sponges, Hydrozoa, and Foraminifera, as
well as to the Polyzoa, the Palaeozoic strata contain large numbers of
peculiar Cyclostomata, together with members of the Trepostomata, a
of attaching itself to the bottoms of ships, a fact which may possibly
account for the wide distribution of this species; although it would not be
safe to assume this explanation of the facts in all cases. Other Polyzoa, on
the contrary, have a more restricted range. Thus Catenicella is specially
characteristic of the Australian region.
It is perhaps surprising that marine Polyzoa should in so many cases have
so wide a range. Even though it is the rule for Polyzoa to have free larvae,
the period during which these larvae are free-swimming is, so far as is
known, a short one in most cases. Cyphonautes is a common pelagic form
(see p. 510), and probably remains for a considerable period in the larval
condition. Other Polyzoon-larvae appear to fix themselves very soon after
their birth; and this would not appear to give much time for them to be
carried to great distances by ocean-currents. It may, however, be suggested
that it does not follow that because we know that a larva may, under
favourable conditions fix itself a few minutes after it becomes free, we
should be justified in assuming that that larva would not retain for a long
period the power of undergoing a normal metamorphosis should it be
drifted away from suitable fixing-grounds.
Palaeontology.[594]—The number of fossil Polyzoa is enormous.
D'Orbigny devoted two hundred plates and more than a thousand octavo
pages[595] to a Monograph on the Cretaceous Polyzoa of France. Many of
the fossil forms are extraordinarily well preserved, and there is often no
difficulty in recognising the identity between certain fossil species
belonging to the more recent formations and living forms. It thus becomes
necessary to consult Palaeontological memoirs in working at recent
Polyzoa.
While the great majority of fossil Polyzoa do not differ in any essential
particular from recent species, this is not altogether the case with the
Palaeozoic forms. Leaving out of account the Stromatoporoids, which have
been variously referred to the Sponges, Hydrozoa, and Foraminifera, as
well as to the Polyzoa, the Palaeozoic strata contain large numbers of
peculiar Cyclostomata, together with members of the Trepostomata, a
Page 518
fourth Sub-order of Gymnolaemata, allied to the Cyclostomata. The
Trepostomata are for the most part Palaeozoic, but a few survived as late as
the Jurassic period.[596] These, with the other Polyzoa from the same
formations, are considered by Dr. Gregory in his recently published
Catalogue of the Fossil Bryozoa in the British Museum (1896).
The number of Polyzoa recorded from the earlier secondary strata is small.
The majority of the known Jurassic forms belong to the Cyclostomata; and
one or two Cheilostomes are recorded from the same period. Recent papers
by Walford[597] on Jurassic Polyzoa contain the description of genera which
are believed to be intermediate between the Cyclostomata and
Cheilostomata, particularly with regard to the characters of their ovicells.
Although it is not impossible there may be a connection between the
ovicells of these two groups, it has yet to be proved that the two sets of
structures are homologous.
The Cretaceous period marks the commencement of a large number of
Cheilostome genera, although the Cyclostomes still remain numerous.
In the Tertiary formations the Cyclostomes gradually become less
numerous, and although in earlier geological periods they far outnumbered
the Cheilostomes, these relations are now reversed. Certain Tertiary strata,
and particularly the Coralline Crag (Pliocene), are remarkable for the
extremely large number of Polyzoa they contain. It will be noticed that no
mention has been made of the Entoprocta, the Ctenostomata, and the
Phylactolaemata. Their absence in the fossil condition[598] need not,
however, be a matter for surprise, as none of these forms are so well suited
for being fossilised as are the calcareous Cyclostomata and Cheilostomata.
There is consequently no adequate reason for assuming that the absence of
a palaeontological record implies that these groups have been recently
evolved.
Determination of Genera of Marine Polyzoa.—The species to which a
Polyzoon belongs can only be determined, in most cases, with the
assistance of the low powers of a microscope. There are very great
Trepostomata are for the most part Palaeozoic, but a few survived as late as
the Jurassic period.[596] These, with the other Polyzoa from the same
formations, are considered by Dr. Gregory in his recently published
Catalogue of the Fossil Bryozoa in the British Museum (1896).
The number of Polyzoa recorded from the earlier secondary strata is small.
The majority of the known Jurassic forms belong to the Cyclostomata; and
one or two Cheilostomes are recorded from the same period. Recent papers
by Walford[597] on Jurassic Polyzoa contain the description of genera which
are believed to be intermediate between the Cyclostomata and
Cheilostomata, particularly with regard to the characters of their ovicells.
Although it is not impossible there may be a connection between the
ovicells of these two groups, it has yet to be proved that the two sets of
structures are homologous.
The Cretaceous period marks the commencement of a large number of
Cheilostome genera, although the Cyclostomes still remain numerous.
In the Tertiary formations the Cyclostomes gradually become less
numerous, and although in earlier geological periods they far outnumbered
the Cheilostomes, these relations are now reversed. Certain Tertiary strata,
and particularly the Coralline Crag (Pliocene), are remarkable for the
extremely large number of Polyzoa they contain. It will be noticed that no
mention has been made of the Entoprocta, the Ctenostomata, and the
Phylactolaemata. Their absence in the fossil condition[598] need not,
however, be a matter for surprise, as none of these forms are so well suited
for being fossilised as are the calcareous Cyclostomata and Cheilostomata.
There is consequently no adequate reason for assuming that the absence of
a palaeontological record implies that these groups have been recently
evolved.
Determination of Genera of Marine Polyzoa.—The species to which a
Polyzoon belongs can only be determined, in most cases, with the
assistance of the low powers of a microscope. There are very great
Page 519
advantages in the use of a binocular instrument, by means of which a
microscopic preparation appears with its parts standing up in proper relief.
In the case of the calcareous forms, the external characters may be more
readily made out in a dry preparation than in any other way. For this
purpose, the colony should be washed with fresh water, in order to remove
the salts, which otherwise crystallise out on drying and obscure the surface.
Preparations of this kind must be looked at with the aid of reflected light.
Canada-balsam or glycerine preparations are also valuable, whether stained
or unstained; and are essential for the examination of the softer forms. In
the case of erect species, both surfaces of the branch should be looked at.
The opercula, avicularia, and rosette-plates afford important systematic
characters in the case of the Cheilostomata.
It must not be forgotten to take account of the condition of the zooecia at
different ages. The old zooecia often become entirely altered in form, by the
deposition of additional calcareous matter, or by the loss of certain parts
present in the younger zooecia. Thus the marginal spines may be entirely
lost in the older individuals, while in those forms which develop a
"peristome" (see Fig. 255 and p. 524), the characters of the orifice can often
be determined in the young zooecia only. It is thus essential to examine the
growing ends of the branches or the rim of the colony, as the case may be.
Fig. 255.—Illustrating the nature of a secondary orifice (Cheilostomata). A, Mucronella
coccinea Abildg., Scilly Is., × 40. The ovicell (o) overhangs the primary orifice,
which is concealed by the great development of the peristome, produced into the
mucro (mu); t, the three teeth (denticles) within the secondary orifice; a,
avicularium. B, Porella compressa Sowb., Norway, × 40; p.o. primary orifice,
above which is a concave lamina, the beginning of the ovicell. In the lower
zooecium the ovicell (o) is further grown. The primary orifice is still visible, but
it is partially concealed by the growth of the peristome, which encloses a minute
avicularium; m, mandible of avicularium. C, Older part of the same colony; pr,
peristome; s.o, secondary orifice; o', adult ovicell; p, pores.
microscopic preparation appears with its parts standing up in proper relief.
In the case of the calcareous forms, the external characters may be more
readily made out in a dry preparation than in any other way. For this
purpose, the colony should be washed with fresh water, in order to remove
the salts, which otherwise crystallise out on drying and obscure the surface.
Preparations of this kind must be looked at with the aid of reflected light.
Canada-balsam or glycerine preparations are also valuable, whether stained
or unstained; and are essential for the examination of the softer forms. In
the case of erect species, both surfaces of the branch should be looked at.
The opercula, avicularia, and rosette-plates afford important systematic
characters in the case of the Cheilostomata.
It must not be forgotten to take account of the condition of the zooecia at
different ages. The old zooecia often become entirely altered in form, by the
deposition of additional calcareous matter, or by the loss of certain parts
present in the younger zooecia. Thus the marginal spines may be entirely
lost in the older individuals, while in those forms which develop a
"peristome" (see Fig. 255 and p. 524), the characters of the orifice can often
be determined in the young zooecia only. It is thus essential to examine the
growing ends of the branches or the rim of the colony, as the case may be.
Fig. 255.—Illustrating the nature of a secondary orifice (Cheilostomata). A, Mucronella
coccinea Abildg., Scilly Is., × 40. The ovicell (o) overhangs the primary orifice,
which is concealed by the great development of the peristome, produced into the
mucro (mu); t, the three teeth (denticles) within the secondary orifice; a,
avicularium. B, Porella compressa Sowb., Norway, × 40; p.o. primary orifice,
above which is a concave lamina, the beginning of the ovicell. In the lower
zooecium the ovicell (o) is further grown. The primary orifice is still visible, but
it is partially concealed by the growth of the peristome, which encloses a minute
avicularium; m, mandible of avicularium. C, Older part of the same colony; pr,
peristome; s.o, secondary orifice; o', adult ovicell; p, pores.
Page 520
In order to make preparations with the tentacles expanded, hydrochlorate of
cocaine, chloral hydrate or spirit should be added gradually to the water.
When the animals are completely anaesthetised they may be killed by
means of a 7-10 p.c. solution of sulphate of copper (best made in distilled
water or in rain water). This method gives admirable results in the case of
both fresh-water and marine Polyzoa. The use of formaline (see p. 229) may
be strongly recommended for the Vesicularina.
The only recent work dealing with all the marine British forms is Mr.
Hincks' invaluable History of the British Marine Polyzoa.[599] As the use of
this book, unaided by any artificial help, is by no means easy to the
beginner, the following key has been compiled as an index to the genera.
The Entoproct forms, Loxosoma and Pedicellina (see pp. 488-491), are not
included in the table.
Fig. 256.—Illustrating the terminology of the front surface of the zooecium
(Cheilostomata). A, Membranipora (Electra) pilosa L., Cromer, × 47; ap, the
membranous "aperture;" o, orifice. B, Membranipora flemingii Busk, Plymouth,
× 60; ap, the aperture, enclosed in a calcareous "area" (a); av, avicularium; s,
marginal spines. C, Micropora coriacea Esper, Plymouth, × 43; a, area
(calcareous); o, operculum; ov, ovicell.
In order to facilitate the use of the table here given in conjunction with Mr.
Hincks' work, the nomenclature there adopted has been followed
throughout. References to other descriptions of the species may be obtained
by consulting Miss Jelly's admirable Synonymic Catalogue of the Recent
Marine Bryozoa.[600]
Terminology.—A few technical terms must of necessity be employed. The
colony is adherent when its zooecia are attached to the object on which the
colony is growing. The zooecium is the body-wall of a single individual;
cocaine, chloral hydrate or spirit should be added gradually to the water.
When the animals are completely anaesthetised they may be killed by
means of a 7-10 p.c. solution of sulphate of copper (best made in distilled
water or in rain water). This method gives admirable results in the case of
both fresh-water and marine Polyzoa. The use of formaline (see p. 229) may
be strongly recommended for the Vesicularina.
The only recent work dealing with all the marine British forms is Mr.
Hincks' invaluable History of the British Marine Polyzoa.[599] As the use of
this book, unaided by any artificial help, is by no means easy to the
beginner, the following key has been compiled as an index to the genera.
The Entoproct forms, Loxosoma and Pedicellina (see pp. 488-491), are not
included in the table.
Fig. 256.—Illustrating the terminology of the front surface of the zooecium
(Cheilostomata). A, Membranipora (Electra) pilosa L., Cromer, × 47; ap, the
membranous "aperture;" o, orifice. B, Membranipora flemingii Busk, Plymouth,
× 60; ap, the aperture, enclosed in a calcareous "area" (a); av, avicularium; s,
marginal spines. C, Micropora coriacea Esper, Plymouth, × 43; a, area
(calcareous); o, operculum; ov, ovicell.
In order to facilitate the use of the table here given in conjunction with Mr.
Hincks' work, the nomenclature there adopted has been followed
throughout. References to other descriptions of the species may be obtained
by consulting Miss Jelly's admirable Synonymic Catalogue of the Recent
Marine Bryozoa.[600]
Terminology.—A few technical terms must of necessity be employed. The
colony is adherent when its zooecia are attached to the object on which the
colony is growing. The zooecium is the body-wall of a single individual;
Page 521
and, except in transparent species, is the only part which can be seen from
the outside in the retracted condition of the polypide or tentacles with the
alimentary canal. The outermost layer of the zooecium is known as the
ectocyst; it may be simply membranous, or calcified, or may be rendered
opaque by foreign bodies; its surface in calcareous forms is often marked
by pores (Fig. 239, C, p), which are vacuities in the calcareous wall, closed
externally by membrane. A special median pore (Fig. 241, A, m.p) may
occur, and is in some cases at least a complete perforation through the
body-wall.
The tentacles are protruded through the orifice, which in Cheilostomata is
usually guarded by a movable chitinous lid, or operculum (Fig. 256, A, o).
Should the ectocyst be thickened or raised into a ridge surrounding the
orifice, a tubular passage results, known as the secondary orifice (Fig. 255),
at the deeper end of which is the true orifice. The peristome (Fig. 255, C,
pr) is the raised or thickened part which gives rise to the secondary orifice.
Should the zooecium be outlined by a raised ridge, the part so enclosed is
known as the area (Fig. 256, C, a), if calcareous. The aperture or opesia
(Fig. 256, A, B, ap) is a membranous part of the front surface; and may
consist of the whole or part of the area. The orifice or the aperture is
commonly provided with spines (Fig. 256, B, s).
Fig. 257.—A, Cribrilina annulata Fabr., Norway, × 33; c, calcareous bars concealing
the membranous aperture: B, Membraniporella nitida Johnst., Plymouth, × 45; a,
calcareous bars growing up round the margin of the aperture; b, the same, further
developed; c, the same, completely formed (as in A); av, avicularium; o,
immature, and o', mature, ovicell; s, marginal spines.
The avicularium and the vibraculum are specially modified zooecia (see p.
482), which occur in a great variety of forms, in certain Cheilostomata only.
The operculum of the ordinary zooecium is represented by the mandible
the outside in the retracted condition of the polypide or tentacles with the
alimentary canal. The outermost layer of the zooecium is known as the
ectocyst; it may be simply membranous, or calcified, or may be rendered
opaque by foreign bodies; its surface in calcareous forms is often marked
by pores (Fig. 239, C, p), which are vacuities in the calcareous wall, closed
externally by membrane. A special median pore (Fig. 241, A, m.p) may
occur, and is in some cases at least a complete perforation through the
body-wall.
The tentacles are protruded through the orifice, which in Cheilostomata is
usually guarded by a movable chitinous lid, or operculum (Fig. 256, A, o).
Should the ectocyst be thickened or raised into a ridge surrounding the
orifice, a tubular passage results, known as the secondary orifice (Fig. 255),
at the deeper end of which is the true orifice. The peristome (Fig. 255, C,
pr) is the raised or thickened part which gives rise to the secondary orifice.
Should the zooecium be outlined by a raised ridge, the part so enclosed is
known as the area (Fig. 256, C, a), if calcareous. The aperture or opesia
(Fig. 256, A, B, ap) is a membranous part of the front surface; and may
consist of the whole or part of the area. The orifice or the aperture is
commonly provided with spines (Fig. 256, B, s).
Fig. 257.—A, Cribrilina annulata Fabr., Norway, × 33; c, calcareous bars concealing
the membranous aperture: B, Membraniporella nitida Johnst., Plymouth, × 45; a,
calcareous bars growing up round the margin of the aperture; b, the same, further
developed; c, the same, completely formed (as in A); av, avicularium; o,
immature, and o', mature, ovicell; s, marginal spines.
The avicularium and the vibraculum are specially modified zooecia (see p.
482), which occur in a great variety of forms, in certain Cheilostomata only.
The operculum of the ordinary zooecium is represented by the mandible
Page 522
(Fig. 239, B, m) in the avicularium, and by the seta (Fig. 242, s) in the
vibraculum. The representative of the zooecium itself is known as the
avicularian (Fig. 239, A, a.z) or vibracular zooecium (Fig. 242, v.z).
An ovicell is a swelling in which the embryo develops, in certain
Cyclostomata (Fig. 237) and Cheilostomata (Fig. 241, A, o). A stolon (Fig.
238, B, st) is a stem, not formed of fused zooecia, from which new
individuals originate. An internode, in a jointed colony, is the part between
any two joints. The fornix or scutum (Fig. 254, A, f) is a modified spine
which in some Cheilostomata overhangs the aperture. A mucro (Fig. 255, A,
mu) is a spike or protuberance developed just below the orifice. A sinus
(Fig. 239, B, s) is a slight bay on the lower margin of the orifice.
The orifice opens at the upper end of the zooecium, on its front surface. The
length of the zooecium is the distance from the upper to the lower ends, and
the width the distance between its sides.
1. One or more of the following characters: orifice provided with an
operculum; avicularia or vibracula present; a globular ovicell
above the orifice of certain zooecia (Cheilostomata)
7
Opercula, avicularia, vibracula, and ovicells completely absent, or
inconspicuous. Calcareous or non-calcareous. If calcareous, the
orifice is not at the end of a free cylindrical portion
3
Calcareous; zooecia cylindrical, often united for the greater part of
their length, but usually ending in a free cylindrical portion, which
bears the terminal orifice. The zooecia may be much obscured by
calcifications surrounding their basal parts
2
2. Zooecia long, tubular, with a lateral membranous region at the upper
end, given off quite separately from a creeping stolon
Aetea
Zooecia more or less united to one another, orifice without chitinous
operculum (Cyclostomata[601])
vibraculum. The representative of the zooecium itself is known as the
avicularian (Fig. 239, A, a.z) or vibracular zooecium (Fig. 242, v.z).
An ovicell is a swelling in which the embryo develops, in certain
Cyclostomata (Fig. 237) and Cheilostomata (Fig. 241, A, o). A stolon (Fig.
238, B, st) is a stem, not formed of fused zooecia, from which new
individuals originate. An internode, in a jointed colony, is the part between
any two joints. The fornix or scutum (Fig. 254, A, f) is a modified spine
which in some Cheilostomata overhangs the aperture. A mucro (Fig. 255, A,
mu) is a spike or protuberance developed just below the orifice. A sinus
(Fig. 239, B, s) is a slight bay on the lower margin of the orifice.
The orifice opens at the upper end of the zooecium, on its front surface. The
length of the zooecium is the distance from the upper to the lower ends, and
the width the distance between its sides.
1. One or more of the following characters: orifice provided with an
operculum; avicularia or vibracula present; a globular ovicell
above the orifice of certain zooecia (Cheilostomata)
7
Opercula, avicularia, vibracula, and ovicells completely absent, or
inconspicuous. Calcareous or non-calcareous. If calcareous, the
orifice is not at the end of a free cylindrical portion
3
Calcareous; zooecia cylindrical, often united for the greater part of
their length, but usually ending in a free cylindrical portion, which
bears the terminal orifice. The zooecia may be much obscured by
calcifications surrounding their basal parts
2
2. Zooecia long, tubular, with a lateral membranous region at the upper
end, given off quite separately from a creeping stolon
Aetea
Zooecia more or less united to one another, orifice without chitinous
operculum (Cyclostomata[601])
Page 523
63
3. Zooecia without marginal spines; arising from a branching axis,
which is not formed of zooecia
74
Colony adherent; or erect, fleshy and slightly branched; or erect,
encrusted with earthy matter and repeatedly branched
72
Characters not as above 4
4. Zooecia minute, boat-shaped, united by a delicate tube. Aperture
large, with marginal spines
Beania mirabilis
Colony delicate, erect; zooecia wider above than below 5
5. No marginal spines 6
Zooecia uniserial; with marginal spines. Branches arising from the
top of a zooecium
Brettia
6. Zooecia uniserial; branches arising just below the large aperture. An
ovicell may be developed above the orifice of a modified
zooecium
Eucratea chelata
Zooecia somewhat pear-shaped; orifice small, semicircular
Huxleya fragilis
7. Colony erect 8
Zooecia in several layers forming confused masses 30
Colony entirely adherent, [602] the zooecia usually in a single layer
31
Erect Cheilostomata.
8. Branches cylindrical, calcareous, divided by chitinous joints.
Orifices arranged all round the branch
3. Zooecia without marginal spines; arising from a branching axis,
which is not formed of zooecia
74
Colony adherent; or erect, fleshy and slightly branched; or erect,
encrusted with earthy matter and repeatedly branched
72
Characters not as above 4
4. Zooecia minute, boat-shaped, united by a delicate tube. Aperture
large, with marginal spines
Beania mirabilis
Colony delicate, erect; zooecia wider above than below 5
5. No marginal spines 6
Zooecia uniserial; with marginal spines. Branches arising from the
top of a zooecium
Brettia
6. Zooecia uniserial; branches arising just below the large aperture. An
ovicell may be developed above the orifice of a modified
zooecium
Eucratea chelata
Zooecia somewhat pear-shaped; orifice small, semicircular
Huxleya fragilis
7. Colony erect 8
Zooecia in several layers forming confused masses 30
Colony entirely adherent, [602] the zooecia usually in a single layer
31
Erect Cheilostomata.
8. Branches cylindrical, calcareous, divided by chitinous joints.
Orifices arranged all round the branch
Page 524
Cellaria (Fig. 239, A)
Branches flexible, jointed or unjointed. Orifices not arranged all
round the branch.
9
Calcareous, unjointed, rigid 21
9. Branches leaf-like, flattened 10
Branches not leaf-like 11
10. Avicularia resembling birds' heads, movable
Bugula (Fig. 233)
Avicularia not resembling birds' heads, unstalked; or absent.
Colony broadly leaf-shaped, composed of a single layer or of two
layers of zooecia
Flustra (Fig. 232)
11. Zooecia in pairs, at the same level 12
Zooecia not obviously paired 13
12. Branches numerous, straight. Zooecia back to back, with an
oblique aperture. No avicularia
Gemellaria loricata
Branches delicate, curved. A pair of stalked avicularia between
each two pairs of zooecia
Notamia (= Epistomia) bursaria
13. Avicularia or vibracula conspicuous 14
Avicularia or vibracula inconspicuous or absent 17
14. Avicularia resembling birds' heads, movable. Vibracula absent
15
Avicularia large, unstalked. Vibracula present or absent
16
Avicularia inconspicuous. Setae of the vibracula large, very
conspicuous, on oblique vibracular zooecia, which almost cover
the backs of the branches
Caberea (Fig. 242)
Branches flexible, jointed or unjointed. Orifices not arranged all
round the branch.
9
Calcareous, unjointed, rigid 21
9. Branches leaf-like, flattened 10
Branches not leaf-like 11
10. Avicularia resembling birds' heads, movable
Bugula (Fig. 233)
Avicularia not resembling birds' heads, unstalked; or absent.
Colony broadly leaf-shaped, composed of a single layer or of two
layers of zooecia
Flustra (Fig. 232)
11. Zooecia in pairs, at the same level 12
Zooecia not obviously paired 13
12. Branches numerous, straight. Zooecia back to back, with an
oblique aperture. No avicularia
Gemellaria loricata
Branches delicate, curved. A pair of stalked avicularia between
each two pairs of zooecia
Notamia (= Epistomia) bursaria
13. Avicularia or vibracula conspicuous 14
Avicularia or vibracula inconspicuous or absent 17
14. Avicularia resembling birds' heads, movable. Vibracula absent
15
Avicularia large, unstalked. Vibracula present or absent
16
Avicularia inconspicuous. Setae of the vibracula large, very
conspicuous, on oblique vibracular zooecia, which almost cover
the backs of the branches
Caberea (Fig. 242)
Page 525
15. Zooecia in two series, alternate, with one or several conspicuously
long marginal spines
Bicellaria
Zooecia in two or more series. Aperture occupying most of the
front of the zooecium. Colony often spiral. Avicularia usually
large
Bugula (Fig. 233)
16. Zooecia long, narrow below, commonly in triplets, with two lateral
avicularia to each triplet. Fornix present.
Menipea ternata
Zooecia biserial, a considerable number forming an internode
separated by a joint (often inconspicuous) from the next
internode. Lateral avicularia usually large. Vibracular zooecia on
the back or sides of the branches
Scrupocellaria (Fig. 254)
17. Characters as in Scrupocellaria (No. 16), but with inconspicuous
avicularia. A branched fornix
Scrupocellaria reptans
Vibracula absent 18
18. A single, short, marginal spine; or none 19
Marginal spines present 20
19. Characters as in No. 6 Eucratea chelata, Huxleya fragilis
Zooecia biserial. Aperture large, the semicircular orifice at its
upper end, where there is commonly a short spine
Cellularia peachii
Zooecia in one or two series. Branches originating from the backs
of the zooecia, and facing in the opposite direction to the parent
branch. Aperture small
Scruparia clavata
20. One or more conspicuously long marginal spines. Avicularia
present or absent
long marginal spines
Bicellaria
Zooecia in two or more series. Aperture occupying most of the
front of the zooecium. Colony often spiral. Avicularia usually
large
Bugula (Fig. 233)
16. Zooecia long, narrow below, commonly in triplets, with two lateral
avicularia to each triplet. Fornix present.
Menipea ternata
Zooecia biserial, a considerable number forming an internode
separated by a joint (often inconspicuous) from the next
internode. Lateral avicularia usually large. Vibracular zooecia on
the back or sides of the branches
Scrupocellaria (Fig. 254)
17. Characters as in Scrupocellaria (No. 16), but with inconspicuous
avicularia. A branched fornix
Scrupocellaria reptans
Vibracula absent 18
18. A single, short, marginal spine; or none 19
Marginal spines present 20
19. Characters as in No. 6 Eucratea chelata, Huxleya fragilis
Zooecia biserial. Aperture large, the semicircular orifice at its
upper end, where there is commonly a short spine
Cellularia peachii
Zooecia in one or two series. Branches originating from the backs
of the zooecia, and facing in the opposite direction to the parent
branch. Aperture small
Scruparia clavata
20. One or more conspicuously long marginal spines. Avicularia
present or absent
Page 526
Bicellaria
Zooecia uniserial (see No. 5) Brettia
Zooecia biserial, in short internodes. An inconspicuous
avicularium below the aperture. Fornix present
Menipea jeffreysii
21. Colony consisting of a network of narrow branches, the zooecia
opening only on one of their surfaces
Retepora
Colony large, brittle, composed of contorted plates, uniting
irregularly, usually composed of two layers of zooecia. Orifice
large, indented laterally
Lepralia foliacea
Branches delicate, cylindrical 22
Branches or lobes coarser, not necessarily cylindrical 24
22. Branches composed of four rows of zooecia 23
Zooecia in more than four regular, longitudinal rows. Peristome
raised, and, with the ovicell, forming a swelling on the surface of
the branch
Escharoides quincuncialis
23. Orifice circular. A row of pores round the margin of the zooecium.
A median pore resembling a small orifice below the true orifice.
Small lateral avicularia
Porina borealis
Orifice surrounded by a peristome, produced into a mucro beneath
the orifice. No pores
Palmicellaria elegans
24. Zooecia arranged in regular series 25
Zooecia irregularly heaped, their long axes often perpendicular to
the surface of the colony. Mucro largely developed, concealing
the form of the orifice, and bearing an avicularium
Cellepora
Zooecia uniserial (see No. 5) Brettia
Zooecia biserial, in short internodes. An inconspicuous
avicularium below the aperture. Fornix present
Menipea jeffreysii
21. Colony consisting of a network of narrow branches, the zooecia
opening only on one of their surfaces
Retepora
Colony large, brittle, composed of contorted plates, uniting
irregularly, usually composed of two layers of zooecia. Orifice
large, indented laterally
Lepralia foliacea
Branches delicate, cylindrical 22
Branches or lobes coarser, not necessarily cylindrical 24
22. Branches composed of four rows of zooecia 23
Zooecia in more than four regular, longitudinal rows. Peristome
raised, and, with the ovicell, forming a swelling on the surface of
the branch
Escharoides quincuncialis
23. Orifice circular. A row of pores round the margin of the zooecium.
A median pore resembling a small orifice below the true orifice.
Small lateral avicularia
Porina borealis
Orifice surrounded by a peristome, produced into a mucro beneath
the orifice. No pores
Palmicellaria elegans
24. Zooecia arranged in regular series 25
Zooecia irregularly heaped, their long axes often perpendicular to
the surface of the colony. Mucro largely developed, concealing
the form of the orifice, and bearing an avicularium
Cellepora
Page 527
25. Orifice with a sinus; or peristome interrupted or extended below
into a sinus-like outgrowth, which usually includes a small
avicularium
26
Neither median sinus nor interrupted or extended peristome
28
26. Orifice with a sinus Schizoporella (Fig. 239, B)
Peristome interrupted or extended below 27
27. Branches of various forms. Surface of the older parts very even.
Secondary orifice rather long, usually wider above, enclosing a
small avicularium below, and appearing as a hole in the even
surface of the branch
Porella (Fig. 255, B, C)
A prominent tooth projects into the orifice from its lower side.
Zooecia with thin walls
Smittia landsborovii (Fig. 239, C)
No tooth in the orifice, at the side of which is a small avicularium.
Old zooecia with thick walls. Colony composed of a short stem
and flattened branches
Escharoides rosacea
28. A tooth projects from the lower side into the large, subcircular
orifice, on each side of which is a small oval avicularium (colony
erect or encrusting)
Mucronella pavonella
No tooth: mucro sometimes present 29
29. Branches cylindrical. Old zooecia with thick walls. Orifice in
young zooecia longer than broad; beneath it a median pore, and in
some cases a lateral avicularium with vibraculoid mandible
Diporula verrucosa
A distinct mucro, which may bear an avicularium above
Palmicellaria
Encrusting Cheilostomata.
into a sinus-like outgrowth, which usually includes a small
avicularium
26
Neither median sinus nor interrupted or extended peristome
28
26. Orifice with a sinus Schizoporella (Fig. 239, B)
Peristome interrupted or extended below 27
27. Branches of various forms. Surface of the older parts very even.
Secondary orifice rather long, usually wider above, enclosing a
small avicularium below, and appearing as a hole in the even
surface of the branch
Porella (Fig. 255, B, C)
A prominent tooth projects into the orifice from its lower side.
Zooecia with thin walls
Smittia landsborovii (Fig. 239, C)
No tooth in the orifice, at the side of which is a small avicularium.
Old zooecia with thick walls. Colony composed of a short stem
and flattened branches
Escharoides rosacea
28. A tooth projects from the lower side into the large, subcircular
orifice, on each side of which is a small oval avicularium (colony
erect or encrusting)
Mucronella pavonella
No tooth: mucro sometimes present 29
29. Branches cylindrical. Old zooecia with thick walls. Orifice in
young zooecia longer than broad; beneath it a median pore, and in
some cases a lateral avicularium with vibraculoid mandible
Diporula verrucosa
A distinct mucro, which may bear an avicularium above
Palmicellaria
Encrusting Cheilostomata.
Page 528
30. Usually growing on a small univalve shell. Orifice longer than
broad, indented laterally. Mucro present
Lepralia edax
One or two conspicuous processes, each bearing an avicularium,
near the orifice, which is often concealed. Avicularia in many
cases found on other parts of the colony
Cellepora
31. Zooecia distant; or in single rows 32
Zooecia forming continuous expansions 36
32. An oval aperture, larger than the orifice 33
No aperture 34
33. A tubular process below the aperture, in some cases: zooecia very
narrow below
Eucratea chelata, var. repens
No tubular process below the aperture Membranipora
34. Peristome much raised below, collar-like Phylactella
Peristome not much raised below 35
35. Zooecia minute, much narrowed below. Orifice small, usually with
a sinus
Hippothoa
Zooecia not narrowed below. Orifice with a sinus
Schizoporella
36. Zooecia partly separated by a thin calcareous crust. Colonies small
37
Zooecia contiguous 38
37. Zooecia pear-shaped. Orifice with a sinus
Hippothoa expansa
Zooecia ovoid. Orifice subcircular, with a tubular peristome
Lagenipora socialis
broad, indented laterally. Mucro present
Lepralia edax
One or two conspicuous processes, each bearing an avicularium,
near the orifice, which is often concealed. Avicularia in many
cases found on other parts of the colony
Cellepora
31. Zooecia distant; or in single rows 32
Zooecia forming continuous expansions 36
32. An oval aperture, larger than the orifice 33
No aperture 34
33. A tubular process below the aperture, in some cases: zooecia very
narrow below
Eucratea chelata, var. repens
No tubular process below the aperture Membranipora
34. Peristome much raised below, collar-like Phylactella
Peristome not much raised below 35
35. Zooecia minute, much narrowed below. Orifice small, usually with
a sinus
Hippothoa
Zooecia not narrowed below. Orifice with a sinus
Schizoporella
36. Zooecia partly separated by a thin calcareous crust. Colonies small
37
Zooecia contiguous 38
37. Zooecia pear-shaped. Orifice with a sinus
Hippothoa expansa
Zooecia ovoid. Orifice subcircular, with a tubular peristome
Lagenipora socialis
Page 529
38. Orifice close to the upper end of the zooecium (unless crowned by
an ovicell). Front of the zooecium marked by transverse or
radiating furrows or lines. The very young zooecium may possess
a membranous area, which becomes roofed in by the union of two
lateral series of converging bars (Fig. 257)
39
Characters not as above 40
39. Furrows with uniserial rows of pores (often minute), which are
rarely irregular
Cribrilina (Fig. 257, A)
No rows of pores. Distinct transverse lines or spaces and a median
longitudinal suture between the bars
Membraniporella (Fig. 257, B)
40. Zooecia arranged in regular series 41
Zooecia irregularly[603] heaped together (cf. No. 30)
Cellepora
41. Primary orifice conspicuous; with a sinus, or with a peristome
extended or interrupted below, and sometimes simulating a sinus
42
[604]
Neither sinus nor interrupted peristome 44
Surface of the old zooecia much thickened, so that the secondary
orifice does not project beyond the most prominent parts of the
zooecium. Secondary orifice concealing the primary orifice,
wider above, enclosing a small avicularium below
Porella (Fig. 255, B, C)
42. Primary orifice with a sinus, but no tooth 43
A prominent tooth projects into the orifice from its lower side.
Peristome interrupted or with a sinus. Surface of the old zooecia
not much thickened
Smittia
43. Orifice with a sinus and long spines. Peristome interrupted. Ovicell
with a wedge-shaped or linear longitudinal fissure. Avicularia
an ovicell). Front of the zooecium marked by transverse or
radiating furrows or lines. The very young zooecium may possess
a membranous area, which becomes roofed in by the union of two
lateral series of converging bars (Fig. 257)
39
Characters not as above 40
39. Furrows with uniserial rows of pores (often minute), which are
rarely irregular
Cribrilina (Fig. 257, A)
No rows of pores. Distinct transverse lines or spaces and a median
longitudinal suture between the bars
Membraniporella (Fig. 257, B)
40. Zooecia arranged in regular series 41
Zooecia irregularly[603] heaped together (cf. No. 30)
Cellepora
41. Primary orifice conspicuous; with a sinus, or with a peristome
extended or interrupted below, and sometimes simulating a sinus
42
[604]
Neither sinus nor interrupted peristome 44
Surface of the old zooecia much thickened, so that the secondary
orifice does not project beyond the most prominent parts of the
zooecium. Secondary orifice concealing the primary orifice,
wider above, enclosing a small avicularium below
Porella (Fig. 255, B, C)
42. Primary orifice with a sinus, but no tooth 43
A prominent tooth projects into the orifice from its lower side.
Peristome interrupted or with a sinus. Surface of the old zooecia
not much thickened
Smittia
43. Orifice with a sinus and long spines. Peristome interrupted. Ovicell
with a wedge-shaped or linear longitudinal fissure. Avicularia
Page 530
generally present, the avicularian zooecium conspicuous.
Schizotheca
Orifice semicircular. Vibracula present, near the orifice.
Mastigophora (Fig. 241, B)
Orifice semicircular or subcircular. No vibracula; avicularia with
vibraculoid mandibles may occur
Schizoporella (Fig. 239, B)
44. Zooecium with a median pore; or completely tubular above
45
Zooecium with no median pore. The orifice may be partially
surrounded by a collar-like development of the peristome, but it is
not completely tubular
49
45. Orifice not tubular. A median pore
Microporella (Fig. 241, A)
Orifice tubular 46
46. Zooecia narrow or small 47
Zooecia ovoid 48
47. Orifice markedly tubular. Median pore conspicuous
Porina tubulosa
Colony very small. Zooecia irregularly arranged, with no median
pore
Celleporella
48. Zooecia very convex, with a granular surface; ovicells set far back.
Orifice wider than long
Mucronella microstoma
Young zooecia with stellate pores. A minute avicularium, or merely
a pore, on the upper and lower sides of the orifice in some
zooecia.
Anarthropora monodon
49. Front of zooecium with an elevated margin, enclosing an area
Schizotheca
Orifice semicircular. Vibracula present, near the orifice.
Mastigophora (Fig. 241, B)
Orifice semicircular or subcircular. No vibracula; avicularia with
vibraculoid mandibles may occur
Schizoporella (Fig. 239, B)
44. Zooecium with a median pore; or completely tubular above
45
Zooecium with no median pore. The orifice may be partially
surrounded by a collar-like development of the peristome, but it is
not completely tubular
49
45. Orifice not tubular. A median pore
Microporella (Fig. 241, A)
Orifice tubular 46
46. Zooecia narrow or small 47
Zooecia ovoid 48
47. Orifice markedly tubular. Median pore conspicuous
Porina tubulosa
Colony very small. Zooecia irregularly arranged, with no median
pore
Celleporella
48. Zooecia very convex, with a granular surface; ovicells set far back.
Orifice wider than long
Mucronella microstoma
Young zooecia with stellate pores. A minute avicularium, or merely
a pore, on the upper and lower sides of the orifice in some
zooecia.
Anarthropora monodon
49. Front of zooecium with an elevated margin, enclosing an area
Page 531
50
Area not present 55
50. Front wall wholly calcareous 51
Front wall wholly or partly membranous 54
51. Avicularian or vibracular zooecia replacing an ordinary zooecium,
or at least situated between the zooecia
52
Avicularia and vibracula absent, or if present not replacing a
zooecium
53
52. Vibracula present. Colonies small. A pair of longitudinal slits
within the area
Setosella vulnerata
Very large avicularia present. Ovicell closed by a movable lid.
Orifice subcircular, with a minute lateral tooth on each side.
Thalamoporella[605] (Steganoporella) smittii
53. Orifice semicircular, quite at the upper end of the zooecium;
usually with a knob on each side
Micropora coriacea[606] (Fig. 256, C)
A transverse chitinous plate lies immediately below the operculum.
A vibraculoid spine may occur
Megapora ringens
54. Area entirely membranous, usually bordered by spines.
Membranipora (including Electra[607]) (Fig. 256, A)
Membranous portion reduced to a small portion, which may be
variously lobed, enclosing the orifice.
Membranipora (other species) (Fig. 256, B)
55. Peristome present. No mucro 56
Peristome absent; or if present, with a mucro 57
See also Mucronella pavonella, No. 28).
Area not present 55
50. Front wall wholly calcareous 51
Front wall wholly or partly membranous 54
51. Avicularian or vibracular zooecia replacing an ordinary zooecium,
or at least situated between the zooecia
52
Avicularia and vibracula absent, or if present not replacing a
zooecium
53
52. Vibracula present. Colonies small. A pair of longitudinal slits
within the area
Setosella vulnerata
Very large avicularia present. Ovicell closed by a movable lid.
Orifice subcircular, with a minute lateral tooth on each side.
Thalamoporella[605] (Steganoporella) smittii
53. Orifice semicircular, quite at the upper end of the zooecium;
usually with a knob on each side
Micropora coriacea[606] (Fig. 256, C)
A transverse chitinous plate lies immediately below the operculum.
A vibraculoid spine may occur
Megapora ringens
54. Area entirely membranous, usually bordered by spines.
Membranipora (including Electra[607]) (Fig. 256, A)
Membranous portion reduced to a small portion, which may be
variously lobed, enclosing the orifice.
Membranipora (other species) (Fig. 256, B)
55. Peristome present. No mucro 56
Peristome absent; or if present, with a mucro 57
See also Mucronella pavonella, No. 28).
Page 532
56. Peristome collar-like, much raised below and at the sides of the
orifice, deficient above. No avicularia
Phylactella
Orifice large, longer than broad. Peristome not deficient above the
orifice
Lepralia
57. Wall of zooecium thin, shiny, and without pores 58
Not agreeing with the characters given under No. 58 59
58. A minute avicularium above the orifice, or where an ovicell is
present, situated at the summit of that structure. Zooecia not quite
contiguous. Mucro sometimes present.
Chorizopora brongniartii
No avicularia. Ovicells on rudimentary zooecia, lying in a plane
superficial to that of the rest of the colony. Zooecia long.
Schizoporella hyalina
59. A more or less distinct mucro or prominence beneath the
orifice. 60
Mucro rarely present. Orifice nearly always longer than broad, or
nearly circular, usually large, and slightly indented laterally.
Lepralia
60. A tooth projects into the orifice from its lower side 61
No tooth 62
61. Colony glistening. Orifice much obscured by the mucro and by
stout spines developed from the peristome. Tooth (concealed in
old zooecia) large, strongly curved to one side.
Rhynchopora (Rhynchozoon[608]) bispinosa
Tooth of the lower margin of the orifice symmetrical, sometimes
bifid. Avicularia may be present laterally, but are not developed
on the mucro
Mucronella (Fig. 255, A)
orifice, deficient above. No avicularia
Phylactella
Orifice large, longer than broad. Peristome not deficient above the
orifice
Lepralia
57. Wall of zooecium thin, shiny, and without pores 58
Not agreeing with the characters given under No. 58 59
58. A minute avicularium above the orifice, or where an ovicell is
present, situated at the summit of that structure. Zooecia not quite
contiguous. Mucro sometimes present.
Chorizopora brongniartii
No avicularia. Ovicells on rudimentary zooecia, lying in a plane
superficial to that of the rest of the colony. Zooecia long.
Schizoporella hyalina
59. A more or less distinct mucro or prominence beneath the
orifice. 60
Mucro rarely present. Orifice nearly always longer than broad, or
nearly circular, usually large, and slightly indented laterally.
Lepralia
60. A tooth projects into the orifice from its lower side 61
No tooth 62
61. Colony glistening. Orifice much obscured by the mucro and by
stout spines developed from the peristome. Tooth (concealed in
old zooecia) large, strongly curved to one side.
Rhynchopora (Rhynchozoon[608]) bispinosa
Tooth of the lower margin of the orifice symmetrical, sometimes
bifid. Avicularia may be present laterally, but are not developed
on the mucro
Mucronella (Fig. 255, A)
Page 533
62. Orifice at least half the width of the zooecium, bordered below by
a well-developed prominence or "umbo." Surface of the
zooecium strongly areolated round the margin
Umbonula[609]
Orifice considerably less than half the width of the zooecium.
Schizoporella (Fig. 239, B)
Encrusting Cyclostomata.
63. Colony erect. Branches of two or one series of zooecia, divided at
intervals by chitinous joints. Ovicells pear-shaped.
Crisia (Fig. 237)
Colony erect, unjointed 69
Colony in the main adherent; or circular; or lobed 64
64. Colony more or less circular, discoidal or cup-shaped, sometimes
forming secondary colonies by marginal budding
65
Colonies not circular 68
65. Zooecia separated by calcified interspaces, which may contain
large pores, often difficult to distinguish from the orifices
66
No large pores as above. Orifices not spiny. Zooecia nearly always
contiguous, except where an ovicell is developed
67
66. Colony composed of one or more convex discs, bearing radial
ridges, each composed of many zooecia
Domopora
Colony encircled by a thin calcareous lamina, which gives rise to
new zooecia, its centre usually devoid of zooecia when adult, and
often bearing the orifice(s) of the ovicell. Zooecial orifices often
spiny.
Lichenopora
a well-developed prominence or "umbo." Surface of the
zooecium strongly areolated round the margin
Umbonula[609]
Orifice considerably less than half the width of the zooecium.
Schizoporella (Fig. 239, B)
Encrusting Cyclostomata.
63. Colony erect. Branches of two or one series of zooecia, divided at
intervals by chitinous joints. Ovicells pear-shaped.
Crisia (Fig. 237)
Colony erect, unjointed 69
Colony in the main adherent; or circular; or lobed 64
64. Colony more or less circular, discoidal or cup-shaped, sometimes
forming secondary colonies by marginal budding
65
Colonies not circular 68
65. Zooecia separated by calcified interspaces, which may contain
large pores, often difficult to distinguish from the orifices
66
No large pores as above. Orifices not spiny. Zooecia nearly always
contiguous, except where an ovicell is developed
67
66. Colony composed of one or more convex discs, bearing radial
ridges, each composed of many zooecia
Domopora
Colony encircled by a thin calcareous lamina, which gives rise to
new zooecia, its centre usually devoid of zooecia when adult, and
often bearing the orifice(s) of the ovicell. Zooecial orifices often
spiny.
Lichenopora
Page 534
67. Zooecia with a long, tubular, free portion, in some cases curved in
a horizontal plane. Colony fan-shaped until a late stage.
Tubulipora flabellaris
Tubular portion absent, or for the most part curved in a vertical
plane. Some of the orifices may be closed by a calcareous plate.
Colony circular or bluntly lobed
Diastopora
68. Zooecia in one or few series, forming a linear or branched colony,
which is closely adherent, but may give rise to short erect
portions. Branches narrow, but often broadening at their ends.
Zooecia usually with a free upper end
Stomatopora
Colony broadly lobed, some of the zooecia in transverse or oblique
ridges composed of contiguous zooecia, arranged like a row of
organ-pipes
Idmonea serpens
Colony broadly lobed, or fan-shaped; zooecia in many series,
which are not arranged like organ-pipes
Tubulipora
69. Well branched. Orifices confined to one surface of the colony
70
Not much branched 71
70. Zooecia in transverse rows, their upper ends united in the manner
of a row of organ-pipes. Ovicell (when present) an inflation of the
front of the branch
Idmonea atlantica
Zooecia not in regular transverse rows. Ovicell (when present)
large, mostly on the back of the branch
Hornera
71. Branches cylindrical, their ends massive and raised into radial
ridges, which carry the orifices
Domopora stellata
Ends of zooecia tubular, arranged all round the branch.
a horizontal plane. Colony fan-shaped until a late stage.
Tubulipora flabellaris
Tubular portion absent, or for the most part curved in a vertical
plane. Some of the orifices may be closed by a calcareous plate.
Colony circular or bluntly lobed
Diastopora
68. Zooecia in one or few series, forming a linear or branched colony,
which is closely adherent, but may give rise to short erect
portions. Branches narrow, but often broadening at their ends.
Zooecia usually with a free upper end
Stomatopora
Colony broadly lobed, some of the zooecia in transverse or oblique
ridges composed of contiguous zooecia, arranged like a row of
organ-pipes
Idmonea serpens
Colony broadly lobed, or fan-shaped; zooecia in many series,
which are not arranged like organ-pipes
Tubulipora
69. Well branched. Orifices confined to one surface of the colony
70
Not much branched 71
70. Zooecia in transverse rows, their upper ends united in the manner
of a row of organ-pipes. Ovicell (when present) an inflation of the
front of the branch
Idmonea atlantica
Zooecia not in regular transverse rows. Ovicell (when present)
large, mostly on the back of the branch
Hornera
71. Branches cylindrical, their ends massive and raised into radial
ridges, which carry the orifices
Domopora stellata
Ends of zooecia tubular, arranged all round the branch.
Page 535
Entalophora
Encrusting Ctenostomata.
72. Colony entirely adherent, or forming thick, soft, erect lobes
73
Colony erect, well-branched, dark and opaque, resembling
seaweed. Zooecia with a long tubular free portion
Anguinella palmata
73. Orifice large, with two distinct lips. A variable number of stout,
brown spines. Encrusting
Flustrella hispida
Orifice small, rounded, borne by a more or less distinct papilla.
Encrusting or erect. Zooecia crowded, rarely in single lines.
Alcyonidium
Orifice small, rounded. Zooecia widely separated, connected by
narrow tubes
Arachnidium
74. Axis of colony erect, usually branched 75
Axis creeping 79
75. Zooecia in elongated clusters, which occur at intervals 76
Zooecia not grouped; or in irregular groups; or in whorls 78
76. Zooecia regularly biserial 77
Zooecia long, less regularly arranged. Polypide with a gizzard.
Bowerbankia (Fig. 238)
77. Clusters of zooecia very regular, occurring immediately below a
bifurcation of the axis. Zooecium with a broad base, not movable.
Amathia lendigera
Zooecia arranged like the pinnules of a leaf, with a constricted
base, and movable on the branch
Mimosella gracilis
Encrusting Ctenostomata.
72. Colony entirely adherent, or forming thick, soft, erect lobes
73
Colony erect, well-branched, dark and opaque, resembling
seaweed. Zooecia with a long tubular free portion
Anguinella palmata
73. Orifice large, with two distinct lips. A variable number of stout,
brown spines. Encrusting
Flustrella hispida
Orifice small, rounded, borne by a more or less distinct papilla.
Encrusting or erect. Zooecia crowded, rarely in single lines.
Alcyonidium
Orifice small, rounded. Zooecia widely separated, connected by
narrow tubes
Arachnidium
74. Axis of colony erect, usually branched 75
Axis creeping 79
75. Zooecia in elongated clusters, which occur at intervals 76
Zooecia not grouped; or in irregular groups; or in whorls 78
76. Zooecia regularly biserial 77
Zooecia long, less regularly arranged. Polypide with a gizzard.
Bowerbankia (Fig. 238)
77. Clusters of zooecia very regular, occurring immediately below a
bifurcation of the axis. Zooecium with a broad base, not movable.
Amathia lendigera
Zooecia arranged like the pinnules of a leaf, with a constricted
base, and movable on the branch
Mimosella gracilis
Page 536
78. Main stem zigzag. Branchlets delicate, many ending in sharp
points. Zooecia small, ovoid
Vesicularia spinosa
Axis jointed. Zooecia small, in small clusters. Polypide without a
gizzard
Valkeria uva, var. cuscuta
Zooecia in whorls, attached to the axis by thread-like stalks, much
longer than themselves
Hippuraria egertoni
79. Zooecia pear-shaped, produced at the lower end into a distinct
stalk. Gizzard absent
80
Zooecia not distinctly stalked, although sometimes constricted at
the base
81
80. Stalk long. Zooecium movable on its stalk, compressed, with a
membranous area on one side. Twelve or more tentacles. Usually
found on Crustacea
Triticella
Stalk variable. Zooecium very transparent; orifice bilabiate. Ten to
sixteen tentacles
Farrella repens
Zooecium very small, much elongated and narrow. Eight tentacles.
Valkeria tremula
(See also Arachnidium, No. 73).
81. Zooecia short, minute, with a few short spines on each side of its
broadened base. Upper end tubular
Buskia nitens
Zooecia elongated 82
82. Zooecia transparent 84
Zooecia brown, often quite opaque 83
points. Zooecia small, ovoid
Vesicularia spinosa
Axis jointed. Zooecia small, in small clusters. Polypide without a
gizzard
Valkeria uva, var. cuscuta
Zooecia in whorls, attached to the axis by thread-like stalks, much
longer than themselves
Hippuraria egertoni
79. Zooecia pear-shaped, produced at the lower end into a distinct
stalk. Gizzard absent
80
Zooecia not distinctly stalked, although sometimes constricted at
the base
81
80. Stalk long. Zooecium movable on its stalk, compressed, with a
membranous area on one side. Twelve or more tentacles. Usually
found on Crustacea
Triticella
Stalk variable. Zooecium very transparent; orifice bilabiate. Ten to
sixteen tentacles
Farrella repens
Zooecium very small, much elongated and narrow. Eight tentacles.
Valkeria tremula
(See also Arachnidium, No. 73).
81. Zooecia short, minute, with a few short spines on each side of its
broadened base. Upper end tubular
Buskia nitens
Zooecia elongated 82
82. Zooecia transparent 84
Zooecia brown, often quite opaque 83
Page 537
83. Zooecia large (about 1⁄16 inch long), distant, constricted at the
base, bearing scattered bristles. Usually found on Crabs or
Hydroids.
Avenella fusca
Zooecia tall, cylindrical, not constricted at the base.
Cylindroecium
84. Zooecia minute. Axis dilating at intervals into swellings, from
which new zooecia originate. These may give rise to new stolons,
or directly to new zooecia. No gizzard. Found in brackish or fresh
water
Victorella pavida
Axis not dilated, as above 85
85. Zooecia small, in small groups. No gizzard Valkeria uva
Zooecia long, scattered or in groups. Gizzard present.
Bowerbankia (creeping forms)
It is highly probable that the Ctenostome genus Hypophorella[610] will
before long be added to the British Fauna. The animal consists of delicate
stolons, which give off small zooecia at intervals; and it is known to
excavate passages in the substance of the tubes of certain Polychaet worms
(Chaetopterus and Lanice).
base, bearing scattered bristles. Usually found on Crabs or
Hydroids.
Avenella fusca
Zooecia tall, cylindrical, not constricted at the base.
Cylindroecium
84. Zooecia minute. Axis dilating at intervals into swellings, from
which new zooecia originate. These may give rise to new stolons,
or directly to new zooecia. No gizzard. Found in brackish or fresh
water
Victorella pavida
Axis not dilated, as above 85
85. Zooecia small, in small groups. No gizzard Valkeria uva
Zooecia long, scattered or in groups. Gizzard present.
Bowerbankia (creeping forms)
It is highly probable that the Ctenostome genus Hypophorella[610] will
before long be added to the British Fauna. The animal consists of delicate
stolons, which give off small zooecia at intervals; and it is known to
excavate passages in the substance of the tubes of certain Polychaet worms
(Chaetopterus and Lanice).
Page 538
ADDENDUM TO CHAETOGNATHA
Since the Chapter on the Chaetognatha was printed the following list[611] of
"The Known Chaetognaths of American Waters" has appeared:—
1. Sagitta elegans Verr. This species resembles S. bipunctata (vide pp.
191 and 193), but differs in size, in the relative proportions of caudal
and body segments, and in the presence of diverticula from the
intestine.
2. Sagitta flaccida Con. This species resembles S. hexaptera (vide p.
193); it is, however, smaller (length, 1.3-1.8 cm.) and has more spines
(anterior, 7-8, posterior, 10-12), and its tail segment is relatively
smaller.
3. Sagitta tenuis Con. Length, 5.25 mm.; hooks, 7-8; anterior spines, 4-
5; posterior spines, 7-10.
4. Sagitta hispida[612] Con. Length, 7-11 mm.; hooks, 8-9; anterior
spines, 4-5; posterior spines, 8-15; tail segment one-third body length;
intestine with two diverticula; sensory hairs very numerous.
5. Sagitta hexaptera (vide p. 193).
6. Krohnia hamata (vide p. 194).
7. Spadella maxima Con. Length, 5.2 cm.; hooks, 6; anterior spines, 3-
5; posterior spines, 5-7; epidermal thickenings round the neck.
8. Spadella draco (vide p. 194).
9. Spadella schizoptera[612] Con. An opaque, yellowish-brown species
living among algae. Length, 4 mm.; hooks, 8; anterior spines, 4-6;
Since the Chapter on the Chaetognatha was printed the following list[611] of
"The Known Chaetognaths of American Waters" has appeared:—
1. Sagitta elegans Verr. This species resembles S. bipunctata (vide pp.
191 and 193), but differs in size, in the relative proportions of caudal
and body segments, and in the presence of diverticula from the
intestine.
2. Sagitta flaccida Con. This species resembles S. hexaptera (vide p.
193); it is, however, smaller (length, 1.3-1.8 cm.) and has more spines
(anterior, 7-8, posterior, 10-12), and its tail segment is relatively
smaller.
3. Sagitta tenuis Con. Length, 5.25 mm.; hooks, 7-8; anterior spines, 4-
5; posterior spines, 7-10.
4. Sagitta hispida[612] Con. Length, 7-11 mm.; hooks, 8-9; anterior
spines, 4-5; posterior spines, 8-15; tail segment one-third body length;
intestine with two diverticula; sensory hairs very numerous.
5. Sagitta hexaptera (vide p. 193).
6. Krohnia hamata (vide p. 194).
7. Spadella maxima Con. Length, 5.2 cm.; hooks, 6; anterior spines, 3-
5; posterior spines, 5-7; epidermal thickenings round the neck.
8. Spadella draco (vide p. 194).
9. Spadella schizoptera[612] Con. An opaque, yellowish-brown species
living among algae. Length, 4 mm.; hooks, 8; anterior spines, 4-6;
Page 539
posterior spines wanting. Caudal segment occupies one-half the body
length.
Professor Verrill states that the name S. gracilis (vide p. 191) was due to a
clerical error, the species really referred to being S. elegans.
A. E. S.
CHAPTER INDEX
Every reference is to the page: words in italics are names of genera or
species; figures in italics indicate that the reference relates to
systematic position; figures in thick type refer to an illustration; f. =
and in following page or pages; n. = note.
length.
Professor Verrill states that the name S. gracilis (vide p. 191) was due to a
clerical error, the species really referred to being S. elegans.
A. E. S.
CHAPTER INDEX
Every reference is to the page: words in italics are names of genera or
species; figures in italics indicate that the reference relates to
systematic position; figures in thick type refer to an illustration; f. =
and in following page or pages; n. = note.
Page 540
Acanella, as host, 298
Acanthobdella, 395
Acanthocephala, 123, 124, 174 f.;
embryology, 179;
classification, 181
Acanthocotyle, 73
Acanthodrilidae, 357, 362, 381, 383, 384
Acanthodrilus, 356, 363, 366, 372, 382, 384;
chaetae, 350
Acanthozoon, 20
Accessory gut, of Polychaeta, 305
Aceros, 19
Achaeta, 445
Acholoe, 297
Aciculum, 247; fossil, 302
Acmostoma, 50
Acoela, 42;
occurrence and habits, 43;
reproduction, 47;
classification, 49
Acotylea, 16 f., 17, 18
Acrorhynchus, 49;
occurrence, 44
Actinotrocha larva, 458
Actinurus, 201, 222
Acyclus, 221
Adaptation, of Trematodes, 52, 62;
of Cestodes, 74;
of Nematodes, 161
Adherent, 523
Adineta, 204, 222, 227
Adventitious avicularia, 482
Aeolosoma, 349, 353, 354, 360, 370, 374, 375
Aetea, 518, 525
Agassiz, on Syllidae, 280
Alaurina claparedii, 49
Albertia, 204, 210, 213, 224, 227
Acanthobdella, 395
Acanthocephala, 123, 124, 174 f.;
embryology, 179;
classification, 181
Acanthocotyle, 73
Acanthodrilidae, 357, 362, 381, 383, 384
Acanthodrilus, 356, 363, 366, 372, 382, 384;
chaetae, 350
Acanthozoon, 20
Accessory gut, of Polychaeta, 305
Aceros, 19
Achaeta, 445
Acholoe, 297
Aciculum, 247; fossil, 302
Acmostoma, 50
Acoela, 42;
occurrence and habits, 43;
reproduction, 47;
classification, 49
Acotylea, 16 f., 17, 18
Acrorhynchus, 49;
occurrence, 44
Actinotrocha larva, 458
Actinurus, 201, 222
Acyclus, 221
Adaptation, of Trematodes, 52, 62;
of Cestodes, 74;
of Nematodes, 161
Adherent, 523
Adineta, 204, 222, 227
Adventitious avicularia, 482
Aeolosoma, 349, 353, 354, 360, 370, 374, 375
Aetea, 518, 525
Agassiz, on Syllidae, 280
Alaurina claparedii, 49
Albertia, 204, 210, 213, 224, 227
Page 541
Alciope, 315
Alciopids (Alciopina), 314;
head, 263;
parapodium, 265;
habit, 291;
light-organs, 294
Alciopina parasitica, 298
Alcyonella, 494, 505, 518
Alcyonellea, 518
Alcyonidium, 477, 480, 492, 518, 532;
structure of zooecium, 469;
reproduction, 507, 508;
larva, 510, 511
Alimentary canal—see Digestive System
Alitta, 317
Allantonema, 131, 150, 151, 161
Allman, on Polyzoa, 474, 475
Alloeocoela, 43; habits, 46;
reproduction, 47;
classification, 50
Alloiogenesis, 66 n.
Allolobophora, 351, 367, 369, 371, 386, 389, 390 f.;
cocoons, 365
Allostoma pallidum, 50
Alluroides, 379
Allurus, 351, 366, 370, 389;
cocoons, 365
Alma, 352 f., 387
Alternation of generations, 66, 81, 281
Amathia, 481, 518, 532
Ammocharidae, 258, 325
Ammotrypane, 273, 331;
intestine, 271
Ampharete, 330
Ampharetidae, 258, 330
Amphibia, Trematodes of, 55, 62, 71, 72;
Nematodes of, 163
Alciopids (Alciopina), 314;
head, 263;
parapodium, 265;
habit, 291;
light-organs, 294
Alciopina parasitica, 298
Alcyonella, 494, 505, 518
Alcyonellea, 518
Alcyonidium, 477, 480, 492, 518, 532;
structure of zooecium, 469;
reproduction, 507, 508;
larva, 510, 511
Alimentary canal—see Digestive System
Alitta, 317
Allantonema, 131, 150, 151, 161
Allman, on Polyzoa, 474, 475
Alloeocoela, 43; habits, 46;
reproduction, 47;
classification, 50
Alloiogenesis, 66 n.
Allolobophora, 351, 367, 369, 371, 386, 389, 390 f.;
cocoons, 365
Allostoma pallidum, 50
Alluroides, 379
Allurus, 351, 366, 370, 389;
cocoons, 365
Alma, 352 f., 387
Alternation of generations, 66, 81, 281
Amathia, 481, 518, 532
Ammocharidae, 258, 325
Ammotrypane, 273, 331;
intestine, 271
Ampharete, 330
Ampharetidae, 258, 330
Amphibia, Trematodes of, 55, 62, 71, 72;
Nematodes of, 163
Page 542
Amphichaeta, 377
Amphicoerus, 49
Amphicora, 339
Amphicorine, gill, 261
Amphicorinidae, 258, 339
Amphicteis, 330
Amphictenidae, 258, 330
Amphiglena, 273, 339
Amphileptus, 235
Amphilina, 91
Amphinome, eye of, 255;
A. smaragdina, colour, 293
Amphinomidae, 258, 318;
shape, 259;
caruncle, 260, 273 n.;
head, 262, 263;
parapodium, 264;
cirri, 265;
chaetae, 267, 267;
in Lepas, 297
Amphiporus, 102, 114;
British species, 110
Amphiptyches, 77
Amphistomatidae, 73
Amphistomum, 71, 73;
A. hominis, 63
Amphitrite, 327, 328;
gill, 329
Ampullaria, Temnocephala with, 53
Anachaeta, 350, 376, 395
Anal, cirri, 259;
funnel, 259, 332, 333;
vesicles, 358, 436
Anangian worms, 253
Anarthropora, 529
Ancylostomum, 143, 163
Andrews, on Sipunculus, 417, 426
Amphicoerus, 49
Amphicora, 339
Amphicorine, gill, 261
Amphicorinidae, 258, 339
Amphicteis, 330
Amphictenidae, 258, 330
Amphiglena, 273, 339
Amphileptus, 235
Amphilina, 91
Amphinome, eye of, 255;
A. smaragdina, colour, 293
Amphinomidae, 258, 318;
shape, 259;
caruncle, 260, 273 n.;
head, 262, 263;
parapodium, 264;
cirri, 265;
chaetae, 267, 267;
in Lepas, 297
Amphiporus, 102, 114;
British species, 110
Amphiptyches, 77
Amphistomatidae, 73
Amphistomum, 71, 73;
A. hominis, 63
Amphitrite, 327, 328;
gill, 329
Ampullaria, Temnocephala with, 53
Anachaeta, 350, 376, 395
Anal, cirri, 259;
funnel, 259, 332, 333;
vesicles, 358, 436
Anangian worms, 253
Anarthropora, 529
Ancylostomum, 143, 163
Andrews, on Sipunculus, 417, 426
Page 543
Angiostomum, 134
Angler-fish, Trematodes of, 62, 72
Anguillula aceti, 125, 154;
A. tritici, 125;
A. diplogaster, 155
Anguillulidae, 137, 154
Anguinella, 532
Annadrilus, 386
Annelida, 241
Anocelis, 42
Anonymidae, 19
Anonymus, 16, 18, 19, 20;
penes, 27
Anopla, 109
Anoplocephala, 91;
characters, 90:
A. mamillana, 90;
A. perfoliata, life-history, 83;
specific characters, 90:
A. plicata, specific characters, 90
Anoplodiscus, 73
Anoplodium, 50;
A. parasiticum, occurrence, 45
Antaeus, 388
Antedon, as host, 342
Antenna, of Rotifers, 215
Anthobothrium, 76 n., 91
Anthocotyle, 73
Antinoë, 298
Antipathes, as host, 298
Anuraea, 225, 226
Anuraeidae, 201, 205, 225, 226
A'oon, an edible worm, 297
Apel, on Priapuloidea, 433
Aperture, of zooecium, 468, 517, 523, 524
Aphaneura, 353, 374
Aphanostoma, 49
Angler-fish, Trematodes of, 62, 72
Anguillula aceti, 125, 154;
A. tritici, 125;
A. diplogaster, 155
Anguillulidae, 137, 154
Anguinella, 532
Annadrilus, 386
Annelida, 241
Anocelis, 42
Anonymidae, 19
Anonymus, 16, 18, 19, 20;
penes, 27
Anopla, 109
Anoplocephala, 91;
characters, 90:
A. mamillana, 90;
A. perfoliata, life-history, 83;
specific characters, 90:
A. plicata, specific characters, 90
Anoplodiscus, 73
Anoplodium, 50;
A. parasiticum, occurrence, 45
Antaeus, 388
Antedon, as host, 342
Antenna, of Rotifers, 215
Anthobothrium, 76 n., 91
Anthocotyle, 73
Antinoë, 298
Antipathes, as host, 298
Anuraea, 225, 226
Anuraeidae, 201, 205, 225, 226
A'oon, an edible worm, 297
Apel, on Priapuloidea, 433
Aperture, of zooecium, 468, 517, 523, 524
Aphaneura, 353, 374
Aphanostoma, 49
Page 544
Aphanostomatidae, 49
Aphelenchus, 131, 155, 157
Aphrodite, 312;
shape, 258;
head, 260;
peristomium, 263;
chaetae, 268;
felting, 312;
intestine, 271;
genital cells, 273;
colour, 291:
A. aculeata, 312;
distribution, 299;
A. echidna, 299
Aphroditidae, 258, 309;
frontal ridge, 260;
parapodium, 264;
elytra, 266, 309;
chaetae, 266
Apical plate, of Trochosphere, 245
Apodina, 235
Apodoides, 225
Apogon, Scolex polymorphus in, 77
Apsilidae, 201, 203, 214, 220, 221
Apsilus, 201, 212, 213, 214, 221
Arabellites, 302
Arachnidium, 532
Archiannelida, 241;
anatomy, 243 f.;
nerve cords, 255;
development, 243, 245
Archigetes, 5, 74, 76, 91;
significance of, 77
Area, of zooecium, 523, 524
Arenicola, 333;
perienteric sinus, 252;
nephridium, 253, 254, 269;
Aphelenchus, 131, 155, 157
Aphrodite, 312;
shape, 258;
head, 260;
peristomium, 263;
chaetae, 268;
felting, 312;
intestine, 271;
genital cells, 273;
colour, 291:
A. aculeata, 312;
distribution, 299;
A. echidna, 299
Aphroditidae, 258, 309;
frontal ridge, 260;
parapodium, 264;
elytra, 266, 309;
chaetae, 266
Apical plate, of Trochosphere, 245
Apodina, 235
Apodoides, 225
Apogon, Scolex polymorphus in, 77
Apsilidae, 201, 203, 214, 220, 221
Apsilus, 201, 212, 213, 214, 221
Arabellites, 302
Arachnidium, 532
Archiannelida, 241;
anatomy, 243 f.;
nerve cords, 255;
development, 243, 245
Archigetes, 5, 74, 76, 91;
significance of, 77
Area, of zooecium, 523, 524
Arenicola, 333;
perienteric sinus, 252;
nephridium, 253, 254, 269;
Page 545
prostomium, 259;
body, 259;
head, 264;
gill, 265;
chaetae, 266 f.;
genital organs, 273;
otocyst, 273;
burrows, 285;
pigment, 291;
colour, 293;
A. marina, 333;
habits, 301;
in brackish water, 284;
as bait, 297;
eggs, 314
Arenicolidae, 258, 333
Argilophilus, 372
Arhynchidae, 185
Arhynchus hemignathi, 181, 185
Aricia, otocyst, 273;
eggs, 275
Ariciidae, 258, 321;
gill, 265
Aristotle, on Earthworms, 347
Armata, 445, 446
Arthropoda, absence of cilia in, 124
Articulata, 517, 518
Ascaridae, 131, 138, 163
Ascaris, 139, 163;
A. acus, 130;
A. alata, 140;
A. depressa, 141;
A. ferox, 141;
A. incurva, 141;
A. leptoptera, 141;
A. lumbricoides, 125, 134, 135, 139, 163;
A. megalocephala, 125, 127, 128, 131, 136, 140, 163;
body, 259;
head, 264;
gill, 265;
chaetae, 266 f.;
genital organs, 273;
otocyst, 273;
burrows, 285;
pigment, 291;
colour, 293;
A. marina, 333;
habits, 301;
in brackish water, 284;
as bait, 297;
eggs, 314
Arenicolidae, 258, 333
Argilophilus, 372
Arhynchidae, 185
Arhynchus hemignathi, 181, 185
Aricia, otocyst, 273;
eggs, 275
Ariciidae, 258, 321;
gill, 265
Aristotle, on Earthworms, 347
Armata, 445, 446
Arthropoda, absence of cilia in, 124
Articulata, 517, 518
Ascaridae, 131, 138, 163
Ascaris, 139, 163;
A. acus, 130;
A. alata, 140;
A. depressa, 141;
A. ferox, 141;
A. incurva, 141;
A. leptoptera, 141;
A. lumbricoides, 125, 134, 135, 139, 163;
A. megalocephala, 125, 127, 128, 131, 136, 140, 163;
Page 546
A. mucronata, 141;
A. mystax, 125, 130, 140;
A. nigrovenosa, 155;
A. rubicunda, 141;
A. suillae, 139;
A. sulcata, 141;
A. transfuga, 125, 126, 141
Ascodictyon, 521 n.
Ascomorpha, 223
Ascopodaria, 488 n.
Asellus, Rotifers attached to, 227
Asexual reproduction, in Triclads, 40;
in Rhabdocoels, 44;
in Cestodes, 80;
in Trichoplax and Salinella, 96;
in Polychaeta, 278 f., 279, 280, 282, 340;
in Oligochaeta, 374, 375, 377;
in Polyzoa, 496, 514
Aspidobothridae, 73
Aspidocotyle, 73
Aspidocotylea, 73
Aspidogaster, 63, 73
Aspidosiphon, 421, 423, 424, 425, 428;
commensalism of, 429
Asplanchna, 200, 205, 210, 213, 215 n., 223, 226
Asplanchnaceae, 203, 212, 220, 222
Asplanchnidae, 200, 201, 203, 205, 211, 212, 216, 223, 226, 230
Asplanchnopus, 201, 211, 222, 223, 226, 230
Ass, parasites of, 140
Association, of Rhabdocoels with Lamellibranchs and Sea-urchins, 45;
of Monotus fuscus with littoral animals, 46;
significance, in Turbellaria, 51—see also Commensal and Parasitic
Asteroids, as hosts, 341
Asterope, 315
Astropecten, as host, 297, 309
Atokous phase, 277 n.
Atractonema, 131, 150, 152, 153
A. mystax, 125, 130, 140;
A. nigrovenosa, 155;
A. rubicunda, 141;
A. suillae, 139;
A. sulcata, 141;
A. transfuga, 125, 126, 141
Ascodictyon, 521 n.
Ascomorpha, 223
Ascopodaria, 488 n.
Asellus, Rotifers attached to, 227
Asexual reproduction, in Triclads, 40;
in Rhabdocoels, 44;
in Cestodes, 80;
in Trichoplax and Salinella, 96;
in Polychaeta, 278 f., 279, 280, 282, 340;
in Oligochaeta, 374, 375, 377;
in Polyzoa, 496, 514
Aspidobothridae, 73
Aspidocotyle, 73
Aspidocotylea, 73
Aspidogaster, 63, 73
Aspidosiphon, 421, 423, 424, 425, 428;
commensalism of, 429
Asplanchna, 200, 205, 210, 213, 215 n., 223, 226
Asplanchnaceae, 203, 212, 220, 222
Asplanchnidae, 200, 201, 203, 205, 211, 212, 216, 223, 226, 230
Asplanchnopus, 201, 211, 222, 223, 226, 230
Ass, parasites of, 140
Association, of Rhabdocoels with Lamellibranchs and Sea-urchins, 45;
of Monotus fuscus with littoral animals, 46;
significance, in Turbellaria, 51—see also Commensal and Parasitic
Asteroids, as hosts, 341
Asterope, 315
Astropecten, as host, 297, 309
Atokous phase, 277 n.
Atractonema, 131, 150, 152, 153
Page 547
Atrium (genital), in Planaria, 38, 39;
in Oligochaeta, 361, 378
Atrochus, 201, 213, 214, 221
Auditory organs, of Turbellaria, 26;
of Hoplonemertea, 106, 110;
of Nematoda, 128;
of Polychaeta, 273
Aulastomum, 393, 399, 403
Auricles, of Rotifers, 205
Autolytus, 308;
eye, 255;
denticles, 270;
brood-sac, 275, 276;
reproduction, 278, 279;
sexual dimorphism, 281;
A. ebiensis, eggs, 276
Automolos, British species, 50
Avenella, 533
Avicularian zooecium, 482, 524
Avicularium, 466, 467, 468, 482 f., 482, 516, 517, 522 f., 524;
adventitious, 482;
vicarious, 482;
vibraculoid, 484, 485;
structure, 483;
movements, 485;
function, 486
Axine, 56, 73
Axiothea, 332, 333
Baely, on human parasites, 139
Baird, on Oligochaeta, 382
Bait, Polychaeta as, 297
Baker, on Rotifers, 197, 207; on Polyzoa,
496 n.
Balanoglossus, affinities of Nemertinea with, 120
Balatro, 204, 212, 224, 227
Balfour, on Trochosphere, 229
in Oligochaeta, 361, 378
Atrochus, 201, 213, 214, 221
Auditory organs, of Turbellaria, 26;
of Hoplonemertea, 106, 110;
of Nematoda, 128;
of Polychaeta, 273
Aulastomum, 393, 399, 403
Auricles, of Rotifers, 205
Autolytus, 308;
eye, 255;
denticles, 270;
brood-sac, 275, 276;
reproduction, 278, 279;
sexual dimorphism, 281;
A. ebiensis, eggs, 276
Automolos, British species, 50
Avenella, 533
Avicularian zooecium, 482, 524
Avicularium, 466, 467, 468, 482 f., 482, 516, 517, 522 f., 524;
adventitious, 482;
vicarious, 482;
vibraculoid, 484, 485;
structure, 483;
movements, 485;
function, 486
Axine, 56, 73
Axiothea, 332, 333
Baely, on human parasites, 139
Baird, on Oligochaeta, 382
Bait, Polychaeta as, 297
Baker, on Rotifers, 197, 207; on Polyzoa,
496 n.
Balanoglossus, affinities of Nemertinea with, 120
Balatro, 204, 212, 224, 227
Balfour, on Trochosphere, 229
Page 548
Barentsia, 488 n.
Barrois, on Polyzoa, 509
Basement-membrane, of Leptoplana, 11, 12;
of Nemertines, 102, 103, 110 f.
Bathymetrical distribution, of Polychaeta, 300
Bdellodrilus, 376
Bdelloida, 201, 203 f., 211, 213, 215, 216, 222, 227
Bdellouridae, 32, 42
Beania, 518, 525
Beddard, on Tetrastemma aquarium dulcium, 118;
on Oligochaeta, 347 f.;
on Leeches, 392 f.
Bedwell, on Rotifers, 198
Beneden, van, on Cestodes, 76;
on Nematodes, 162;
on Phoronis, 450
Benham, on a fresh-water Tetrastemma, 118;
on Archiannelida, 241 f.;
on Polychaeta, 245 f.;
on Myzostomaria, 341 f.;
on Oligochaeta, 357, 373, 382;
on Phoronis, 452 f.
Benhamia, 383 f.
Bicellaria, 481, 518, 526, 527
Bilfinger, on Rotifers, 212
Bilharzia, 4, 73;
B. crassa, 70;
B. haematobia, 63, 68 f., 69
Bimastos, 389
Bipaliidae, 35, 42
Bipalium, 33, 34, 42, 408
Birds, Trematodes of, 62, 63, 64, 72;
Cestodes of, 77 f., 84, 85;
Nematodes of, 144, 149, 163;
Gordius of, 173;
Acanthocephala of, 184, 185
Bisexual, Turbellaria, 44;
Barrois, on Polyzoa, 509
Basement-membrane, of Leptoplana, 11, 12;
of Nemertines, 102, 103, 110 f.
Bathymetrical distribution, of Polychaeta, 300
Bdellodrilus, 376
Bdelloida, 201, 203 f., 211, 213, 215, 216, 222, 227
Bdellouridae, 32, 42
Beania, 518, 525
Beddard, on Tetrastemma aquarium dulcium, 118;
on Oligochaeta, 347 f.;
on Leeches, 392 f.
Bedwell, on Rotifers, 198
Beneden, van, on Cestodes, 76;
on Nematodes, 162;
on Phoronis, 450
Benham, on a fresh-water Tetrastemma, 118;
on Archiannelida, 241 f.;
on Polychaeta, 245 f.;
on Myzostomaria, 341 f.;
on Oligochaeta, 357, 373, 382;
on Phoronis, 452 f.
Benhamia, 383 f.
Bicellaria, 481, 518, 526, 527
Bilfinger, on Rotifers, 212
Bilharzia, 4, 73;
B. crassa, 70;
B. haematobia, 63, 68 f., 69
Bimastos, 389
Bipaliidae, 35, 42
Bipalium, 33, 34, 42, 408
Birds, Trematodes of, 62, 63, 64, 72;
Cestodes of, 77 f., 84, 85;
Nematodes of, 144, 149, 163;
Gordius of, 173;
Acanthocephala of, 184, 185
Bisexual, Turbellaria, 44;
Page 549
Trematodes, 70 f.
Bladder, of Rotifers, 214
Bladder-worms, 5, 79 f., 89
Blanchard, on Cestoda, 91;
on Hirudinea, 392 f., 405, 408
Blastomeres, of egg of Distomum, 65
Blood, of Nemertinea, 108;
of Polygordius, 244;
of Chaetopoda, 252;
of Chlorhaemidae, 252, 334;
of Magelona, 252, 325;
of Sabelliformia, 252, 337
Blood-corpuscles, in Chaetopoda, 252
Body-cavity (including Coelom), of Nematoda, 130;
of Gordius, 166;
of Acanthocephala, 175, 178;
of Chaetognatha, 187;
of Archiannelids, 243, 244;
of Polychaeta, 249;
of Myzostoma, 343;
of Oligochaeta, 355;
of Leeches, 397;
of Gephyrea, 416;
of Phoronis, 454, 462;
of Polyzoa, 468, 488, 495
Body-wall, of Nemertinea, 102, 103;
of Nematodes, 125;
of Gordiidae, 165;
of Acanthocephala, 175;
of Chaetognatha, 187;
of Rotifers, 205;
of Nereis, 249;
of Oligochaeta, 349;
of Gephyrea, 414, 436;
of Phoronis, 454;
of Polyzoa, 470, 495, 500
Bohadsch, on Gephyrea, 411
Bladder, of Rotifers, 214
Bladder-worms, 5, 79 f., 89
Blanchard, on Cestoda, 91;
on Hirudinea, 392 f., 405, 408
Blastomeres, of egg of Distomum, 65
Blood, of Nemertinea, 108;
of Polygordius, 244;
of Chaetopoda, 252;
of Chlorhaemidae, 252, 334;
of Magelona, 252, 325;
of Sabelliformia, 252, 337
Blood-corpuscles, in Chaetopoda, 252
Body-cavity (including Coelom), of Nematoda, 130;
of Gordius, 166;
of Acanthocephala, 175, 178;
of Chaetognatha, 187;
of Archiannelids, 243, 244;
of Polychaeta, 249;
of Myzostoma, 343;
of Oligochaeta, 355;
of Leeches, 397;
of Gephyrea, 416;
of Phoronis, 454, 462;
of Polyzoa, 468, 488, 495
Body-wall, of Nemertinea, 102, 103;
of Nematodes, 125;
of Gordiidae, 165;
of Acanthocephala, 175;
of Chaetognatha, 187;
of Rotifers, 205;
of Nereis, 249;
of Oligochaeta, 349;
of Gephyrea, 414, 436;
of Phoronis, 454;
of Polyzoa, 470, 495, 500
Bohadsch, on Gephyrea, 411
Page 550
Bohemilla, 377;
chaeta, 350
Bonellein, 435, 292
Bonellia, 411, 434, 442;
anatomy, 434 f., 435;
male, 438;
development, 439;
habits of, 442;
as host, 297
Bonnet, on Oligochaeta, 348, 379
Boring Worms, 286, 287
Borlase, on Lineus marinus, 99
Borlasia elizabethae, 111, 114
Bothriocephalidae, 91
Bothriocephalinae, 91
Bothriocephalus, 91;
B. cordatus, 81, 91;
B. cristatus, 81, 91;
B. latus, in man, 81, 91;
life-history, 84;
reproductive organs, 87 f.;
larva, 87;
B. mansoni (= B. liguloides), 81, 91
Bothriocerca, 226
Bothrioneuron, 379
Bothrioplana, 46, 50
Bothrioplanidae, 42, 46, 50
Bothromesostoma personatum, 49
Bourne, on Oligochaeta, 352, 373, 377 n., 380;
on Leeches, 400
Bouvier, on commensal Gephyrea, 429
Bowerbankia, 470, 480, 481, 492, 500, 518, 532, 533;
larva, 511, 513;
budding, 514
Brachionidae, 225
Brachionus, 200, 201, 204, 218, 225, 226, 227
Brachydrilus, 357
chaeta, 350
Bonellein, 435, 292
Bonellia, 411, 434, 442;
anatomy, 434 f., 435;
male, 438;
development, 439;
habits of, 442;
as host, 297
Bonnet, on Oligochaeta, 348, 379
Boring Worms, 286, 287
Borlase, on Lineus marinus, 99
Borlasia elizabethae, 111, 114
Bothriocephalidae, 91
Bothriocephalinae, 91
Bothriocephalus, 91;
B. cordatus, 81, 91;
B. cristatus, 81, 91;
B. latus, in man, 81, 91;
life-history, 84;
reproductive organs, 87 f.;
larva, 87;
B. mansoni (= B. liguloides), 81, 91
Bothriocerca, 226
Bothrioneuron, 379
Bothrioplana, 46, 50
Bothrioplanidae, 42, 46, 50
Bothromesostoma personatum, 49
Bourne, on Oligochaeta, 352, 373, 377 n., 380;
on Leeches, 400
Bouvier, on commensal Gephyrea, 429
Bowerbankia, 470, 480, 481, 492, 500, 518, 532, 533;
larva, 511, 513;
budding, 514
Brachionidae, 225
Brachionus, 200, 201, 204, 218, 225, 226, 227
Brachydrilus, 357
Page 551
Brackish water, Rotifers, 226;
Polychaeta, 284;
Polyzoa, 492
Bradynema, 150, 151, 160
Braem, on statoblasts, 503 f.
Brain—see Nervous System
Branchellion, 393, 395, 397, 401, 406
Branchial crown, 336;
regeneration of, 283
Branchiobdella, 376
Branchiomma, 337;
gills, 261;
eyes, 272;
B. vigilans on Aphrodite, 299
Branchiura, 352, 361, 367, 378 f.;
transverse section, 353
Braun, on Platyhelminthes, etc., 6 n., 55 n., 62, 94
Brettia, 525, 527
Bristles = Chaetae, q.v.
Bristle-worms, 241
British, Polycladida, 19;
Tricladida, 42;
Rhabdocoelida, 49;
Nemertinea, 100, 110 f.;
Polychaeta, 306 f.;
Earthworms, 390;
Leeches, 393;
Gephyrea, 449;
Polyzoa, 488 n., 505, 523 f.
Brood-pouch, of Spirorbis, 261, 276, 341;
of Salmacina, 276;
of Entoprocta, 487, 507
Brood-sac, of Autolytus, 275;
of Myrianida, 280
Brown body, in Polyzoa, 468, 471 f., 472, 489, 496, 510, 514
Brown tubes (nephridia), of Sipunculoidea, 415, 417, 423, 425;
of Echiuroidea, 435, 437, 439, 441;
Polychaeta, 284;
Polyzoa, 492
Bradynema, 150, 151, 160
Braem, on statoblasts, 503 f.
Brain—see Nervous System
Branchellion, 393, 395, 397, 401, 406
Branchial crown, 336;
regeneration of, 283
Branchiobdella, 376
Branchiomma, 337;
gills, 261;
eyes, 272;
B. vigilans on Aphrodite, 299
Branchiura, 352, 361, 367, 378 f.;
transverse section, 353
Braun, on Platyhelminthes, etc., 6 n., 55 n., 62, 94
Brettia, 525, 527
Bristles = Chaetae, q.v.
Bristle-worms, 241
British, Polycladida, 19;
Tricladida, 42;
Rhabdocoelida, 49;
Nemertinea, 100, 110 f.;
Polychaeta, 306 f.;
Earthworms, 390;
Leeches, 393;
Gephyrea, 449;
Polyzoa, 488 n., 505, 523 f.
Brood-pouch, of Spirorbis, 261, 276, 341;
of Salmacina, 276;
of Entoprocta, 487, 507
Brood-sac, of Autolytus, 275;
of Myrianida, 280
Brown body, in Polyzoa, 468, 471 f., 472, 489, 496, 510, 514
Brown tubes (nephridia), of Sipunculoidea, 415, 417, 423, 425;
of Echiuroidea, 435, 437, 439, 441;
Page 552
of Epithetosomatoidea, 445;
used as generative ducts, 418, 438;
absent in Priapuloidea, 430
Bryozoa, 475
Buccal region, in Polychaeta, 249, 250, 269;
of Nereis diversicolor, 248;
of N. cultrifera, 316
Buchanan, on marine muds, 423
Buchholzia, 359
Budding, in Syllidae, 279, 283 (see also Gemmation);
in Polyzoa, 467, 514 (see also Polypide-bud)
Bugula, 467, 468, 477, 481, 515, 517, 518, 519, 526;
avicularia, 483, 485;
larva, 511
Bunge, on respiration in Nematoda, 130
Bürger, on Nemertinea, 109, 112;
on Nectonema, 168;
on Hirudinea, 397, 403
Burrows, of Polychaeta, 285, 304;
of Cirratulus, 286;
of Nereis, 286, 316, 317;
of Arenicola, 333;
fossil, 302;
of Earthworms, 368;
of Sipunculus, 426
Bursa seminalis, in Rhabdocoels, 48
Busk, on Polyzoa, 465 n., 475, 487, 519
Buskia, 533
Bütschli, on Nematoda, 137
Byrsophlebs, occurrence, 44;
British species, 49
Caberea, 487, 518, 526;
vibracula, 486, 517
Caecum, in Polyzoa, 499
Calathus, host of Gordius, 172
Calceostominae, 73
used as generative ducts, 418, 438;
absent in Priapuloidea, 430
Bryozoa, 475
Buccal region, in Polychaeta, 249, 250, 269;
of Nereis diversicolor, 248;
of N. cultrifera, 316
Buchanan, on marine muds, 423
Buchholzia, 359
Budding, in Syllidae, 279, 283 (see also Gemmation);
in Polyzoa, 467, 514 (see also Polypide-bud)
Bugula, 467, 468, 477, 481, 515, 517, 518, 519, 526;
avicularia, 483, 485;
larva, 511
Bunge, on respiration in Nematoda, 130
Bürger, on Nemertinea, 109, 112;
on Nectonema, 168;
on Hirudinea, 397, 403
Burrows, of Polychaeta, 285, 304;
of Cirratulus, 286;
of Nereis, 286, 316, 317;
of Arenicola, 333;
fossil, 302;
of Earthworms, 368;
of Sipunculus, 426
Bursa seminalis, in Rhabdocoels, 48
Busk, on Polyzoa, 465 n., 475, 487, 519
Buskia, 533
Bütschli, on Nematoda, 137
Byrsophlebs, occurrence, 44;
British species, 49
Caberea, 487, 518, 526;
vibracula, 486, 517
Caecum, in Polyzoa, 499
Calathus, host of Gordius, 172
Calceostominae, 73
Page 553
Calceostomum, 73
Caldwell, on Phoronis, 454, 456, 461
Calicotyle, 73
Callidina, 201, 202, 204, 218, 219, 222, 225, 227, 230
Calliobothrium, 76 n., 91;
larva, 77
Calotte, of Dicyemids, 93
Calyx, 488
Camerano, on development of Gordius, 170
Capitella, 331;
peristomium, 263;
special chaetae, 267, 268;
habitat, 286;
colour, 291;
O. capitata, distribution, 299
Capitellidae, 258, 331, 373
Capitelliformia, 258, 305;
guanin in, 253;
body, 259;
buccal region, 269;
siphon, 272;
ciliated organs, 272, 273;
genital organs, 273
Carabus, host of Gordius, 172
Carinella, 112;
British species, 112
Carinellidae, side organs of, 107
Caruncle, of Amphinomidae, 260, 273 n., 318
Caryophyllaeus, 91;
C. mutabilis, 77
Castalia, 308;
distribution of, 300
Castings, of Polychaeta, 285;
fossil, 302;
of Arenicola, 333
Castrada, 44, 49
Cat, parasites of, 80, 125, 130, 140, 143, 144, 145
Caldwell, on Phoronis, 454, 456, 461
Calicotyle, 73
Callidina, 201, 202, 204, 218, 219, 222, 225, 227, 230
Calliobothrium, 76 n., 91;
larva, 77
Calotte, of Dicyemids, 93
Calyx, 488
Camerano, on development of Gordius, 170
Capitella, 331;
peristomium, 263;
special chaetae, 267, 268;
habitat, 286;
colour, 291;
O. capitata, distribution, 299
Capitellidae, 258, 331, 373
Capitelliformia, 258, 305;
guanin in, 253;
body, 259;
buccal region, 269;
siphon, 272;
ciliated organs, 272, 273;
genital organs, 273
Carabus, host of Gordius, 172
Carinella, 112;
British species, 112
Carinellidae, side organs of, 107
Caruncle, of Amphinomidae, 260, 273 n., 318
Caryophyllaeus, 91;
C. mutabilis, 77
Castalia, 308;
distribution of, 300
Castings, of Polychaeta, 285;
fossil, 302;
of Arenicola, 333
Castrada, 44, 49
Cat, parasites of, 80, 125, 130, 140, 143, 144, 145
Page 554
Catenicella, 518, 519
Catenula, 49
Cathypna, 225
Cathypnidae, 225
Cellaria, 479, 515, 518, 519, 526;
zooecia and avicularium, 482
Cellepora, 518, 527, 528, 529;
avicularia, 483, 517
Celleporella, 529
Cellularia, 518, 527
Cellularina, 518
Cement-glands, of Rotifers, 205
Cephalic slits, of Nemertinea, 101, 104, 107, 111, 112
Cephalisation, in Polychaeta, 263;
in Oligochaeta, 377
Cephalodiscus, 461 f.
Cephalopods, parasites of, 78, 92;
list of, containing Dicyemids, 94
Cephalosiphon, 205, 221
Cephalothrix, 112
Cercaria, 13, 65, 67, 71 f.;
C. macrocerca, 72;
C. cystophora, 72
Cercyra, 42
Cerebral organ, of Nemertinea, 107;
of Gephyrea, 417
Cerebratulus, 101, 111, 114;
British species, 111
Cerfontaine, on Earthworms, 349, 350
Cestoda, characters of the group, 5, 74;
nature of, 76 f.;
occurrence, 77-82;
life-histories, 83;
structure and development, 84-89;
synoptic table of, 89 f.;
classification, 91
Cestodariidae (= Monozoa), 91
Catenula, 49
Cathypna, 225
Cathypnidae, 225
Cellaria, 479, 515, 518, 519, 526;
zooecia and avicularium, 482
Cellepora, 518, 527, 528, 529;
avicularia, 483, 517
Celleporella, 529
Cellularia, 518, 527
Cellularina, 518
Cement-glands, of Rotifers, 205
Cephalic slits, of Nemertinea, 101, 104, 107, 111, 112
Cephalisation, in Polychaeta, 263;
in Oligochaeta, 377
Cephalodiscus, 461 f.
Cephalopods, parasites of, 78, 92;
list of, containing Dicyemids, 94
Cephalosiphon, 205, 221
Cephalothrix, 112
Cercaria, 13, 65, 67, 71 f.;
C. macrocerca, 72;
C. cystophora, 72
Cercyra, 42
Cerebral organ, of Nemertinea, 107;
of Gephyrea, 417
Cerebratulus, 101, 111, 114;
British species, 111
Cerfontaine, on Earthworms, 349, 350
Cestoda, characters of the group, 5, 74;
nature of, 76 f.;
occurrence, 77-82;
life-histories, 83;
structure and development, 84-89;
synoptic table of, 89 f.;
classification, 91
Cestodariidae (= Monozoa), 91
Page 555
Cestoplana, 17, 18, 19
Cestoplanidae, 19
Chaetae, 241;
of Polychaeta, 266, 267;
provisional, 274;
of Nereis, 246, 247;
of Heteronereid, 276, 277;
jointed, 246;
natatory, in sexual Syllid, 278, 307;
iridescent, 268, 291, 312;
palmate, of Coabangia, 339 n.;
colour, 291;
genital, of Capitella, 331;
of Sternaspis, 336;
special, of Polydora, 261, 267;
of Chaetopterus, 267, 324;
of Myzostoma, 342;
of Oligochaeta, 347, 350, 351, 352;
penial, 362;
of Microdrili, 375 f.;
of Megadrili, 381 f.;
of Lumbricidae, 389, 390;
of Leeches, 395, 396;
(= hooks), of Echiuroid Gephyrea, 434, 435, 438, 440 f., 446
Chaetifera, 445, 446
Chaetobranchus, 352
Chaetogaster, 356, 377, 401
Chaetognatha, 186 f., 534;
anatomy, 186;
development, 189;
habits, 189;
classification, 191;
key to, 193;
American species, 534
Chaetonotus, 232, 235
Chaetopoda, 241 f.;
as food for Nemertinea, 115
Cestoplanidae, 19
Chaetae, 241;
of Polychaeta, 266, 267;
provisional, 274;
of Nereis, 246, 247;
of Heteronereid, 276, 277;
jointed, 246;
natatory, in sexual Syllid, 278, 307;
iridescent, 268, 291, 312;
palmate, of Coabangia, 339 n.;
colour, 291;
genital, of Capitella, 331;
of Sternaspis, 336;
special, of Polydora, 261, 267;
of Chaetopterus, 267, 324;
of Myzostoma, 342;
of Oligochaeta, 347, 350, 351, 352;
penial, 362;
of Microdrili, 375 f.;
of Megadrili, 381 f.;
of Lumbricidae, 389, 390;
of Leeches, 395, 396;
(= hooks), of Echiuroid Gephyrea, 434, 435, 438, 440 f., 446
Chaetifera, 445, 446
Chaetobranchus, 352
Chaetogaster, 356, 377, 401
Chaetognatha, 186 f., 534;
anatomy, 186;
development, 189;
habits, 189;
classification, 191;
key to, 193;
American species, 534
Chaetonotus, 232, 235
Chaetopoda, 241 f.;
as food for Nemertinea, 115
Page 556
Chaetopteridae, 258, 323
Chaetopterus, 304 n., 323;
anatomy, 323 f.;
special chaetae, 267;
larva, 274, 325;
pigment, 292;
phosphorescence, 295, 296;
commensals of, 298, 478, 533;
Ch. variopedatus, 324
Chaetosoma, 158
Chaetosomatidae, 158
Chaetosyllis, form of head, 278
Chaetozone, 326;
uncini, 268
Chaetura, 235
Chalk, Serpulids of, 301
Charles, on male guinea-worm, 148
Cheilostomata, 477, 506, 518, 519, 525, 526 f.;
occurrence, 478;
external characters (see also Avicularium and Vibraculum), 481;
ovicells, 507;
reproduction, 507 f.;
larva, 511;
fossil, 521
Chiaje, Delle, on Gephyrea, 411
Chickoff, on Triclads, 41
Chironomus, host of Gordius, 172
Chitin, 249, 267;
in coelomic corpuscles, 252
Chloeia, colour, 291
Chlorhaemidae, 258, 305, 334, 336;
chlorocruorin in, 252;
head, 260, 262, 264;
palps, 260;
tentacles, 262
Chlorocruorin, 252, 334;
colour due to, 291
Chaetopterus, 304 n., 323;
anatomy, 323 f.;
special chaetae, 267;
larva, 274, 325;
pigment, 292;
phosphorescence, 295, 296;
commensals of, 298, 478, 533;
Ch. variopedatus, 324
Chaetosoma, 158
Chaetosomatidae, 158
Chaetosyllis, form of head, 278
Chaetozone, 326;
uncini, 268
Chaetura, 235
Chalk, Serpulids of, 301
Charles, on male guinea-worm, 148
Cheilostomata, 477, 506, 518, 519, 525, 526 f.;
occurrence, 478;
external characters (see also Avicularium and Vibraculum), 481;
ovicells, 507;
reproduction, 507 f.;
larva, 511;
fossil, 521
Chiaje, Delle, on Gephyrea, 411
Chickoff, on Triclads, 41
Chironomus, host of Gordius, 172
Chitin, 249, 267;
in coelomic corpuscles, 252
Chloeia, colour, 291
Chlorhaemidae, 258, 305, 334, 336;
chlorocruorin in, 252;
head, 260, 262, 264;
palps, 260;
tentacles, 262
Chlorocruorin, 252, 334;
colour due to, 291
Page 557
Chone, 338
Chorizopora, 530
Cilia, 3;
of Leptoplana, 10, 11, 12, 15;
of Polyclads, 23, 25, 26;
of Müller's larva, 29;
of Land Planarians, 33;
of Planaria lactea, 35;
of Temnocephala, 53;
of Trematode-larvae, 3, 59, 60, 65;
of Cestode-larvae, 87;
absent in certain groups, 124, 396;
of Rotifers, 202 f.;
of Archiannelida, 243, 244;
of Echiuroidea, 434;
of Phoronis, 453;
of Polyzoa, 467, 470
Ciliated, lappets, of Pterosyllis, 273 n.;
pits, of Polygordius, 244;
pits (= nuchal organs), of Polychaeta, 272 f.;
organs, of Capitelliformia, 305
Cingulum, in Rotifers, 202
Cirratulidae, 258, 325;
gill, 265;
tentacular filaments, 304 n.
Cirratulus, 326;
burrows, 286;
pigment, 292;
colour, 293;
viviparous, 276;
C. tentaculatus, 326
Cirri, of Nereis, 246;
of Polychaeta, 265;
of Myzostoma, 342;
anal, 259;
nuchal, of Eunicidae, 318;
peristomial, of Nereis, 248;
Chorizopora, 530
Cilia, 3;
of Leptoplana, 10, 11, 12, 15;
of Polyclads, 23, 25, 26;
of Müller's larva, 29;
of Land Planarians, 33;
of Planaria lactea, 35;
of Temnocephala, 53;
of Trematode-larvae, 3, 59, 60, 65;
of Cestode-larvae, 87;
absent in certain groups, 124, 396;
of Rotifers, 202 f.;
of Archiannelida, 243, 244;
of Echiuroidea, 434;
of Phoronis, 453;
of Polyzoa, 467, 470
Ciliated, lappets, of Pterosyllis, 273 n.;
pits, of Polygordius, 244;
pits (= nuchal organs), of Polychaeta, 272 f.;
organs, of Capitelliformia, 305
Cingulum, in Rotifers, 202
Cirratulidae, 258, 325;
gill, 265;
tentacular filaments, 304 n.
Cirratulus, 326;
burrows, 286;
pigment, 292;
colour, 293;
viviparous, 276;
C. tentaculatus, 326
Cirri, of Nereis, 246;
of Polychaeta, 265;
of Myzostoma, 342;
anal, 259;
nuchal, of Eunicidae, 318;
peristomial, of Nereis, 248;
Page 558
nerves to, 254;
of Polychaeta, 263
Cladocora, with Myxicola, 294
Claparède, on Heteronereis, 276, 277;
on Earthworms, 347, 355, 356
Claus, on Nematoda, 138;
on Seisonaceae, 225 n.
Clepsine—see Glossiphonia
Clitellio, 366, 378
Cloeosiphon, 424, 425, 429
Clover sickness, 155
Clymene, 333;
C. ebiensis, tube of, 287
Clymenidae—see Maldanidae
Coabangia, 284, 339 n.
Cobb, on Nematoda, 131 n., 138
Cobbold, on Nematoda, 140
Cobitis, host of Gordius, 173
Cochleare, 225
Cocoons, of Triclads, 40;
of Oligochaeta, 364, 365;
of Leeches, 404
Coelom—see Body-cavity
Coelomic fluid, of Polychaeta, 252;
as cause of colour, 291
Coelopus, 225
Cohn, on Rotifers, 198
Collar, peristomial, of Sabellidae, 336;
of Gephyrea, 421;
of Ctenostomata, 470, 477, 480, 481
Colonial nervous system, 471
Colony, of Myrianida, 281;
of Syllis ramosa, 282;
of Polyzoa, 466
Colour of Polyclads, 20;
of Land Planarians, 33;
of Nemertinea, 102;
of Polychaeta, 263
Cladocora, with Myxicola, 294
Claparède, on Heteronereis, 276, 277;
on Earthworms, 347, 355, 356
Claus, on Nematoda, 138;
on Seisonaceae, 225 n.
Clepsine—see Glossiphonia
Clitellio, 366, 378
Cloeosiphon, 424, 425, 429
Clover sickness, 155
Clymene, 333;
C. ebiensis, tube of, 287
Clymenidae—see Maldanidae
Coabangia, 284, 339 n.
Cobb, on Nematoda, 131 n., 138
Cobbold, on Nematoda, 140
Cobitis, host of Gordius, 173
Cochleare, 225
Cocoons, of Triclads, 40;
of Oligochaeta, 364, 365;
of Leeches, 404
Coelom—see Body-cavity
Coelomic fluid, of Polychaeta, 252;
as cause of colour, 291
Coelopus, 225
Cohn, on Rotifers, 198
Collar, peristomial, of Sabellidae, 336;
of Gephyrea, 421;
of Ctenostomata, 470, 477, 480, 481
Colonial nervous system, 471
Colony, of Myrianida, 281;
of Syllis ramosa, 282;
of Polyzoa, 466
Colour of Polyclads, 20;
of Land Planarians, 33;
of Nemertinea, 102;
Page 559
of Polychaeta, 291, 314, 340
Coluridae, 207, 225
Colurus, 225, 226
Comatula, as host, 342
Commensal, Polychaeta, 297 f., 323, 325;
Gephyrea, 428, 429;
Polyzoa, 489
Conn, on development of Gephyrea, 419 n., 441, 444, 447
Conoceros, 19
Conochilus, 202, 203, 205, 215, 221, 226
Conocyema, hosts of, 94
Convoluta, 45;
British species, 43, 49;
C. henseni, pelagic habit, 43;
C. roscoffensis, assimilating tissue, 43
Copepoda, on Polychaeta, 299
Copeus, 215, 224
Coral reefs, Polychaeta in, 293
Corallina (= Coralline Alga), 14, 488, 516
Coralline, 465
Coralline Crag, 465, 521
Corallobothrium, 91
Corethra, host of Gordius, 172
Cori, on Phoronis, 451 f.
Cornulites, 302
Cotylea, 16 f., 17, 18
Cotylogaster, 73
Cotyloplana, 35
Crateromorpha, as host, 282
Crayfish, Temnocephala associated with, 53
Creeper, 317
Crepina, 450
Cretaceous, Polyzoa, 520, 521
Cribrilina, 518, 524, 528
Crinoids, as hosts, 341
Criodrilus, 358, 366, 386
Crisia, 471, 478, 479, 480, 507, 518, 531
Coluridae, 207, 225
Colurus, 225, 226
Comatula, as host, 342
Commensal, Polychaeta, 297 f., 323, 325;
Gephyrea, 428, 429;
Polyzoa, 489
Conn, on development of Gephyrea, 419 n., 441, 444, 447
Conoceros, 19
Conochilus, 202, 203, 205, 215, 221, 226
Conocyema, hosts of, 94
Convoluta, 45;
British species, 43, 49;
C. henseni, pelagic habit, 43;
C. roscoffensis, assimilating tissue, 43
Copepoda, on Polychaeta, 299
Copeus, 215, 224
Coral reefs, Polychaeta in, 293
Corallina (= Coralline Alga), 14, 488, 516
Coralline, 465
Coralline Crag, 465, 521
Corallobothrium, 91
Corethra, host of Gordius, 172
Cori, on Phoronis, 451 f.
Cornulites, 302
Cotylea, 16 f., 17, 18
Cotylogaster, 73
Cotyloplana, 35
Crateromorpha, as host, 282
Crayfish, Temnocephala associated with, 53
Creeper, 317
Crepina, 450
Cretaceous, Polyzoa, 520, 521
Cribrilina, 518, 524, 528
Crinoids, as hosts, 341
Criodrilus, 358, 366, 386
Crisia, 471, 478, 479, 480, 507, 518, 531
Page 560
Crisiidae, 517
Crisp, on Parasites, 164
Cristatella, 494 f., 495, 499, 501, 503-505, 512, 518;
attacked by Planarians, 486;
movements, 494, 496, 498;
fission, 496, 506;
statoblast, 502, 503;
larva, 512
Crossopodia, 302
Crotchets, 266, 267, 305, 322
Crustacea, parasites of, 174, 179, 182
Cryptocelis, 19, 24
Cryptocephala, 258, 303, 305;
vascular system, 252;
prostomium, 259;
tentacles, 263;
eyes, 272;
food, 296
Cryptodrilidae, 357, 362, 373, 382
Cryptodrilus, 372, 382 f.
Ctenodrilus, 373
Ctenophores, as hosts, 298
Ctenostomata, 470, 477, 479, 480, 518, 532;
occurrence, 478;
in fresh water, 492;
external characters, 480;
reproduction, 507;
larva, 511;
relation to Phylactolaemata, 493, 502 f.;
fossil, 521 n.
Cucullanus, 136, 142, 163;
C. elegans, 143, 161
Cucumaria, as host, 298
Cuénot, on Gephyrea, 416 n.
Cuticle, of Nemathelminthes, 125, 165, 175;
of Rotifera, etc., 205, 233, 236;
of Polyzoa, 470—see also Epidermis
Crisp, on Parasites, 164
Cristatella, 494 f., 495, 499, 501, 503-505, 512, 518;
attacked by Planarians, 486;
movements, 494, 496, 498;
fission, 496, 506;
statoblast, 502, 503;
larva, 512
Crossopodia, 302
Crotchets, 266, 267, 305, 322
Crustacea, parasites of, 174, 179, 182
Cryptocelis, 19, 24
Cryptocephala, 258, 303, 305;
vascular system, 252;
prostomium, 259;
tentacles, 263;
eyes, 272;
food, 296
Cryptodrilidae, 357, 362, 373, 382
Cryptodrilus, 372, 382 f.
Ctenodrilus, 373
Ctenophores, as hosts, 298
Ctenostomata, 470, 477, 479, 480, 518, 532;
occurrence, 478;
in fresh water, 492;
external characters, 480;
reproduction, 507;
larva, 511;
relation to Phylactolaemata, 493, 502 f.;
fossil, 521 n.
Cucullanus, 136, 142, 163;
C. elegans, 143, 161
Cucumaria, as host, 298
Cuénot, on Gephyrea, 416 n.
Cuticle, of Nemathelminthes, 125, 165, 175;
of Rotifera, etc., 205, 233, 236;
of Polyzoa, 470—see also Epidermis
Page 561
Cuvier, on Oligochaeta, 352;
on Gephyrea, 411
Cyclatella, 489
Cyclicobdella, 392
Cycloporus, 19, 22, 24
Cyclops, parasites of, 143, 148, 161
Cyclorhagae, 238
Cyclostomata, 477, 479, 506, 517, 518, 525, 531;
occurrence, 478;
external characters, 480;
ovicells, 507;
reproduction, 507, 511;
larva, 511; fossil, 520, 521
Cydippe, as host, 298
Cylindroecium, 533
Cylindrostoma, 46;
British species, 50
Cyphonautes, 509, 510, 512, 520
Cyprina, Malacobdella found on, 119
Cyrtonia, 224
Cyst, of Land-Planarians, 33;
of Myzostoma, 342, 343, 344;
(capsules), of Aeolosoma, 370, 375
Cystibranchus, 395, 406
Cysticercoid-larva, 83, 85, 88
Cysticercus-larva, 79, 80;
list of, 83;
C. cellulosae, 79, 80;
C. pisiformis, development, 81, 85, 89
Cysticolous, Myzostomaria, 344
Cystoidotaeninae, 91
Cystotaeninae, 91
Dactylogyrus, 73
Dalyell, on habits of Turbellaria, 6, 10, 20;
on regeneration in Polychaeta, 283;
on tubes of Polychaeta, 287;
on Gephyrea, 411
Cyclatella, 489
Cyclicobdella, 392
Cycloporus, 19, 22, 24
Cyclops, parasites of, 143, 148, 161
Cyclorhagae, 238
Cyclostomata, 477, 479, 506, 517, 518, 525, 531;
occurrence, 478;
external characters, 480;
ovicells, 507;
reproduction, 507, 511;
larva, 511; fossil, 520, 521
Cydippe, as host, 298
Cylindroecium, 533
Cylindrostoma, 46;
British species, 50
Cyphonautes, 509, 510, 512, 520
Cyprina, Malacobdella found on, 119
Cyrtonia, 224
Cyst, of Land-Planarians, 33;
of Myzostoma, 342, 343, 344;
(capsules), of Aeolosoma, 370, 375
Cystibranchus, 395, 406
Cysticercoid-larva, 83, 85, 88
Cysticercus-larva, 79, 80;
list of, 83;
C. cellulosae, 79, 80;
C. pisiformis, development, 81, 85, 89
Cysticolous, Myzostomaria, 344
Cystoidotaeninae, 91
Cystotaeninae, 91
Dactylogyrus, 73
Dalyell, on habits of Turbellaria, 6, 10, 20;
on regeneration in Polychaeta, 283;
on tubes of Polychaeta, 287;
Page 562
on Hirudinea, 405 n.;
on larvae of Flustra, 466;
on Cristatella, 496
Danielssen and Koren, on Gephyrea, 442, 444
Daphnia, Rotifers attached to, 227
Dapidia, 225
Darwin, on Earthworms, 354, 359, 368
Dasybranchus, 331;
gill, 268
Dasychone, 338;
gills, 261;
eyes, 272;
regeneration, 283
Dasydetes, 232, 235
Davaine, on Nematoda, 140, 145
Davainea, 91;
D. friedbergeri, 84;
D. madagascariensis, 80, 84;
D. proglottina, life-history, 84
Davenport, on Urnatella, 491
Davis, on Rotifers, 227
Deep-sea, Polychaeta, 300;
Polyzoa, 478
Deinodrilus, 351, 384
Delagia, 478 n.
Dendrobaena, 382
Dendrocoelum, 30, 35, 39
Dendrostoma, 422, 425, 428
Dendy, on Land Planarians, 33, 34, 38
Denticles, 248, 250, 316, 522
Dero, 352, 377
Derostoma, 44, 50
Desmogaster, 380
Desmoscolecidae, 159
Desmoscolex, 159, 258
Desor, on Nemertine development, 99;
Type of, larva, 113
on larvae of Flustra, 466;
on Cristatella, 496
Danielssen and Koren, on Gephyrea, 442, 444
Daphnia, Rotifers attached to, 227
Dapidia, 225
Darwin, on Earthworms, 354, 359, 368
Dasybranchus, 331;
gill, 268
Dasychone, 338;
gills, 261;
eyes, 272;
regeneration, 283
Dasydetes, 232, 235
Davaine, on Nematoda, 140, 145
Davainea, 91;
D. friedbergeri, 84;
D. madagascariensis, 80, 84;
D. proglottina, life-history, 84
Davenport, on Urnatella, 491
Davis, on Rotifers, 227
Deep-sea, Polychaeta, 300;
Polyzoa, 478
Deinodrilus, 351, 384
Delagia, 478 n.
Dendrobaena, 382
Dendrocoelum, 30, 35, 39
Dendrostoma, 422, 425, 428
Dendy, on Land Planarians, 33, 34, 38
Denticles, 248, 250, 316, 522
Dero, 352, 377
Derostoma, 44, 50
Desmogaster, 380
Desmoscolecidae, 159
Desmoscolex, 159, 258
Desor, on Nemertine development, 99;
Type of, larva, 113
Page 563
Development, of Polyclads, 28;
of Nemertinea, 99, 113;
of Nematoda, 135;
of Gordius, 171;
of Acanthocephala, 179;
of Chaetognatha, 189;
of Rotifers, 218;
of Archiannelida, 243, 245;
of Polychaeta, 274 f.;
of Oligochaeta, 365;
of Leeches, 399;
of Gephyrea, 419, 432, 439, 447;
of Phoronis, 458;
of Polyzoa, 506, 509—see also Life-history and Larva
Diachaeta, 366
Diaphragm, of Nereis introvert, 250, 251;
of Terebellidae, 304, 327;
of Polyzoa, 469, 470, 500, 508
Diaschiza, 225, 226
Diastopora, 518, 531
Dichogaster, 362, 383
Diclidophora, 73
Dicotylus, 32, 35, 36, 42
Dicranotaenia, 91;
D. coronula, life-history, 84
Dicyema, 93;
vermiform larva of, 92;
hosts of, 94
Dicyemennea, 93, 93;
hosts of, 94
Dicyemidae, 92 f.
Didymogaster, 383
Didymozoon, 73;
D. thynni (= Monostomum bipartitum), 71
Didymozoontidae, 73
Digaster, 358, 359, 382 f.
Digenea (Digenetic Trematodes), 5, 52, 62, 73;
of Nemertinea, 99, 113;
of Nematoda, 135;
of Gordius, 171;
of Acanthocephala, 179;
of Chaetognatha, 189;
of Rotifers, 218;
of Archiannelida, 243, 245;
of Polychaeta, 274 f.;
of Oligochaeta, 365;
of Leeches, 399;
of Gephyrea, 419, 432, 439, 447;
of Phoronis, 458;
of Polyzoa, 506, 509—see also Life-history and Larva
Diachaeta, 366
Diaphragm, of Nereis introvert, 250, 251;
of Terebellidae, 304, 327;
of Polyzoa, 469, 470, 500, 508
Diaschiza, 225, 226
Diastopora, 518, 531
Dichogaster, 362, 383
Diclidophora, 73
Dicotylus, 32, 35, 36, 42
Dicranotaenia, 91;
D. coronula, life-history, 84
Dicyema, 93;
vermiform larva of, 92;
hosts of, 94
Dicyemennea, 93, 93;
hosts of, 94
Dicyemidae, 92 f.
Didymogaster, 383
Didymozoon, 73;
D. thynni (= Monostomum bipartitum), 71
Didymozoontidae, 73
Digaster, 358, 359, 382 f.
Digenea (Digenetic Trematodes), 5, 52, 62, 73;
Page 564
occurrence and habits, 62;
life-histories, 63 f., 71 f.
Digestive system, of Leptoplana, 11, 12;
of Polyclads, 24;
of Triclads, 37, 39;
of Rhabdocoelida, 42 f.;
of Temnocephala, 53, 54;
of Polystomum, 57;
of Distomum, 62;
absence of, in Cestodes, 74;
life-histories, 63 f., 71 f.
Digestive system, of Leptoplana, 11, 12;
of Polyclads, 24;
of Triclads, 37, 39;
of Rhabdocoelida, 42 f.;
of Temnocephala, 53, 54;
of Polystomum, 57;
of Distomum, 62;
absence of, in Cestodes, 74;
Page 565
of Nemertinea, 103, 103, 104;
of Nematoda, 130;
of Gordiidae, 166, 169;
of Chaetognatha, 187;
of Rotifers, etc., 209, 233, 237;
of Archiannelida, 243;
of Polychaeta, 249, 269;
of Oligochaeta, 358;
of Hirudinea, 396;
of Gephyrea, 414;
of Phoronis, 454;
of Polyzoa, 468, 469, 487
Digitibranchus, 353
Diglena, 212, 217, 224, 226
Digonopora, 16
Dimorphism, in Polystomum, 59;
sexual, of Trematodes, 70;
of Orthonectida, 95;
of Dinophilus, 243;
of Polychaeta, 276, 279 f.;
of Gephyrea, 438
Dinocharididae, 225
Dinocharis, 225
Dinophilus, 242;
D. taeniatus, 242;
D. gyrociliatus, sexual dimorphism, 243
Dinops, 223
Diopatra, gill, 318
Diphyllinae, 91
Diplax, 225
Diplectanum, 73
Diplobothrium, 73
Diplocardia, 385
Diplodiscus, 73;
D. (Amphistomum) subclavatum, life-history, 71
Diplogaster, 154
Diplois, 225
of Nematoda, 130;
of Gordiidae, 166, 169;
of Chaetognatha, 187;
of Rotifers, etc., 209, 233, 237;
of Archiannelida, 243;
of Polychaeta, 249, 269;
of Oligochaeta, 358;
of Hirudinea, 396;
of Gephyrea, 414;
of Phoronis, 454;
of Polyzoa, 468, 469, 487
Digitibranchus, 353
Diglena, 212, 217, 224, 226
Digonopora, 16
Dimorphism, in Polystomum, 59;
sexual, of Trematodes, 70;
of Orthonectida, 95;
of Dinophilus, 243;
of Polychaeta, 276, 279 f.;
of Gephyrea, 438
Dinocharididae, 225
Dinocharis, 225
Dinophilus, 242;
D. taeniatus, 242;
D. gyrociliatus, sexual dimorphism, 243
Dinops, 223
Diopatra, gill, 318
Diphyllinae, 91
Diplax, 225
Diplectanum, 73
Diplobothrium, 73
Diplocardia, 385
Diplodiscus, 73;
D. (Amphistomum) subclavatum, life-history, 71
Diplogaster, 154
Diplois, 225
Page 566
Diplostomum, 73
Diplozoon, 55, 60, 73;
life-history, 60, 61;
reproductive organs, 60
Diporochaeta, 381
Diporpa, 60, 61
Diporula, 528
Dipylidium, 81, 91;
life-history, 83, 88, 89;
specific characters, 90
Disc, in Rotifers, 200, 202 f., 202
Discharge, of genital cells;
Nemertinea, 116;
Archiannelida, 244;
Polychaeta, 256, 274, 275
Discobdella, 226
Discocelis, 19, 23
Discodrilidae, 350, 376, 392, 395
Discopus, 201, 222, 226, 227
Dispharagus, 147, 149, 163
Dispinthera, 225
Distemma, 212, 224, 226
Distomatidae, 73
Distomum advena (= D. migrans), life-history, 71;
D. appendiculatum, life-history, 71;
D. ascidia, life-history, 71;
D. atriventre, life-history, 71;
D. brachysomum, life-history, 71;
D. buskii, 63;
D. caudatum, life-history, 71;
D. clavigerum, life-history, 72;
D. conjunctum, 63;
D. crassum, 63;
D. cygnoides, life-history, 72;
D. cylindraceum, 72;
D. dimorphum, 72;
D. echinatum, 63;
Diplozoon, 55, 60, 73;
life-history, 60, 61;
reproductive organs, 60
Diporochaeta, 381
Diporpa, 60, 61
Diporula, 528
Dipylidium, 81, 91;
life-history, 83, 88, 89;
specific characters, 90
Disc, in Rotifers, 200, 202 f., 202
Discharge, of genital cells;
Nemertinea, 116;
Archiannelida, 244;
Polychaeta, 256, 274, 275
Discobdella, 226
Discocelis, 19, 23
Discodrilidae, 350, 376, 392, 395
Discopus, 201, 222, 226, 227
Dispharagus, 147, 149, 163
Dispinthera, 225
Distemma, 212, 224, 226
Distomatidae, 73
Distomum advena (= D. migrans), life-history, 71;
D. appendiculatum, life-history, 71;
D. ascidia, life-history, 71;
D. atriventre, life-history, 71;
D. brachysomum, life-history, 71;
D. buskii, 63;
D. caudatum, life-history, 71;
D. clavigerum, life-history, 72;
D. conjunctum, 63;
D. crassum, 63;
D. cygnoides, life-history, 72;
D. cylindraceum, 72;
D. dimorphum, 72;
D. echinatum, 63;
Page 567
life-history, 72;
D. echiuri, 444;
D. endolobum, life-history, 72;
D. excavatum, 63;
D. ferox, 63;
D. globiporum, life-history, 72;
D. hians, 63;
D. hepaticum (liver-fluke), 3, 63, 67 f.,72;
D. heterophyes, 63;
D. hystrix, life-history, 72;
D. japonicum (= D. spathulatum), 63;
D. lanceolatum, 63;
D. luteum, excretory system of, 62;
D. macrostomum, life-history, 64, 65, 72;
D. magnum, 68;
D. militare, life-history, 72;
D. nodulosum, life-history, 72;
D. oculi-humani (= D. ophthalmobium), 63;
D. ovocaudatum, life-history, 72;
D. pulmonale, 63, 70;
D. rathouisi, 63, 70;
D. retusum, life-history, 72;
D. ringeri (= D. pulmonale), 63;
D. signatum, life-history, 72;
D. sinense, 70; D. spathulatum, 63;
D. squamula, life-history, 72;
D. trigonocephalum, life-history, 72;
D. westermanni (= D. pulmonale), 63
Distyla, 225
Dithyridium, 91
Ditrupa, 301
Diurella, 225, 226
Dochmius, 133, 135, 142, 160, 163;
D. cernua, 143;
D. duodenalis, 143, 163;
D. stenocephala, 143;
D. trigonocephala, 143
D. echiuri, 444;
D. endolobum, life-history, 72;
D. excavatum, 63;
D. ferox, 63;
D. globiporum, life-history, 72;
D. hians, 63;
D. hepaticum (liver-fluke), 3, 63, 67 f.,72;
D. heterophyes, 63;
D. hystrix, life-history, 72;
D. japonicum (= D. spathulatum), 63;
D. lanceolatum, 63;
D. luteum, excretory system of, 62;
D. macrostomum, life-history, 64, 65, 72;
D. magnum, 68;
D. militare, life-history, 72;
D. nodulosum, life-history, 72;
D. oculi-humani (= D. ophthalmobium), 63;
D. ovocaudatum, life-history, 72;
D. pulmonale, 63, 70;
D. rathouisi, 63, 70;
D. retusum, life-history, 72;
D. ringeri (= D. pulmonale), 63;
D. signatum, life-history, 72;
D. sinense, 70; D. spathulatum, 63;
D. squamula, life-history, 72;
D. trigonocephalum, life-history, 72;
D. westermanni (= D. pulmonale), 63
Distyla, 225
Dithyridium, 91
Ditrupa, 301
Diurella, 225, 226
Dochmius, 133, 135, 142, 160, 163;
D. cernua, 143;
D. duodenalis, 143, 163;
D. stenocephala, 143;
D. trigonocephala, 143
Page 568
Dodecaceria, 287, 326, 327
Dog, parasites of, 80 f., 90, 125, 140, 142, 143, 145
Dolichoplana, 37, 42
Domestic animals, Trematodes of, 67, 68, 70, 72;
Cestodes of, 81, 89;
Nematodes of, 139 f., 163;
Acanthocephala of, 184
Domopora, 531, 532
Dorsal ciliated organ, 247, 254, 256
Dorsal pores, 348
Dorylaimus, 131, 157, 160
Dracunculus, 131, 135, 147
Drepanidotaenia, 91;
D. anatina, life-history, 84, 85;
D. gracilis, D. infundibuliformis, D. setigera, life-history, 84
Drepanophorus, excretory system, 108;
British species, 110
Drilophagidae, 224
Drilophagus, 204, 210, 212, 224, 227
Dugès, on Planarians, 6, 10;
on Oligochaeta, 368
Dujardin, on Rotifers, 198;
on Gastrotricha, 231;
on Kinorhyncha, 236
Duplicature, 499, 500
Duthiersia, 91
Dwarf males, of Myzostoma, 344;
of Gephyrea, 438
Ear-cockle, 155
Earthworms, 347, 365;
senses, 354;
food, 359;
effect on the soil, 368;
distribution, 369 f.;
classification, 380 f.;
British, 390—see also Oligochaeta
Dog, parasites of, 80 f., 90, 125, 140, 142, 143, 145
Dolichoplana, 37, 42
Domestic animals, Trematodes of, 67, 68, 70, 72;
Cestodes of, 81, 89;
Nematodes of, 139 f., 163;
Acanthocephala of, 184
Domopora, 531, 532
Dorsal ciliated organ, 247, 254, 256
Dorsal pores, 348
Dorylaimus, 131, 157, 160
Dracunculus, 131, 135, 147
Drepanidotaenia, 91;
D. anatina, life-history, 84, 85;
D. gracilis, D. infundibuliformis, D. setigera, life-history, 84
Drepanophorus, excretory system, 108;
British species, 110
Drilophagidae, 224
Drilophagus, 204, 210, 212, 224, 227
Dugès, on Planarians, 6, 10;
on Oligochaeta, 368
Dujardin, on Rotifers, 198;
on Gastrotricha, 231;
on Kinorhyncha, 236
Duplicature, 499, 500
Duthiersia, 91
Dwarf males, of Myzostoma, 344;
of Gephyrea, 438
Ear-cockle, 155
Earthworms, 347, 365;
senses, 354;
food, 359;
effect on the soil, 368;
distribution, 369 f.;
classification, 380 f.;
British, 390—see also Oligochaeta
Page 569
Ebrard, on Hirudinea, 393
Echeneibothrium, 91
Echinella, 73
Echinobothrium, 74, 75, 85, 91
Echinococcus, 80, 83
Echinocotyle, 91
Echinoderes, 236 f., 236
Echinorhynchidae, 182
Echinorhynchus acus, 175, 179;
E. angustatus, 174, 183;
E. clavula, 183;
E. haeruca, 176;
E. linstowi, 183;
E. lutzii, 183;
E. moniliformis, 183;
E. proteus, 174, 180, 181, 182, 182
Echinosiphon, 424, 429
Echiuroidea, 241 n., 412, 434, 446;
anatomy, 434 f.;
classification, 440;
development, 439;
parasites, 444;
habits, 442
Echiurus, 336, 411, 435, 440, 441;
development, 439
Eckstein, on Rotifers, 198
Eclipidrilus, 380
Economic uses, of Polychaeta, 296, 297
Ectocyst, 469, 470, 523;
of Phylactolaemata, 496 f., 503
Ectoderm, of Mesozoa, 93, 95
Ectoparasitic Trematodes, 4, 52, 53
Ectoprocta, 475, 518;
structure, 469;
lophophore, 476;
reproduction, 506 f.;
larva, 509, 510, 511;
Echeneibothrium, 91
Echinella, 73
Echinobothrium, 74, 75, 85, 91
Echinococcus, 80, 83
Echinocotyle, 91
Echinoderes, 236 f., 236
Echinorhynchidae, 182
Echinorhynchus acus, 175, 179;
E. angustatus, 174, 183;
E. clavula, 183;
E. haeruca, 176;
E. linstowi, 183;
E. lutzii, 183;
E. moniliformis, 183;
E. proteus, 174, 180, 181, 182, 182
Echinosiphon, 424, 429
Echiuroidea, 241 n., 412, 434, 446;
anatomy, 434 f.;
classification, 440;
development, 439;
parasites, 444;
habits, 442
Echiurus, 336, 411, 435, 440, 441;
development, 439
Eckstein, on Rotifers, 198
Eclipidrilus, 380
Economic uses, of Polychaeta, 296, 297
Ectocyst, 469, 470, 523;
of Phylactolaemata, 496 f., 503
Ectoderm, of Mesozoa, 93, 95
Ectoparasitic Trematodes, 4, 52, 53
Ectoprocta, 475, 518;
structure, 469;
lophophore, 476;
reproduction, 506 f.;
larva, 509, 510, 511;
Page 570
compared with Entoprocta, 488
Effects, of parasites on their hosts, 56, 68, 69, 80, 94, 162
Eggs, of Leptoplana, 10, 16;
of Polyclads, 28;
of Triclads, 33, 40;
of Rhabdocoels, 47, 48;
of Termatodes, 52;
of ectoparasitic Trematodes, 54, 58, 60, 61;
of endoparasitic Trematodes, 63, 69;
of Cestodes, 87;
of Orthonectidae, 95;
of Nemertinea, 116;
of Nematoda, 135, 162;
of Gordius, 171;
of Acanthocephala, 179;
of Chaetognatha, 189;
of Rotifera, 200, 216 f.;
of Gastrotricha, 234;
of Nereis, 256;
of Polychaeta, 274, 275;
of Phyllodocids, 314;
of Scoloplos, 321;
of Myzostoma, 343;
of Polyzoa, 506, 507
Ehrenberg, on Turbellaria, 3, 6;
on Rotifers, 198, 220 n., 228;
on Gastrotricha, 231;
on Polyzoa (Bryozoa), 475
Eichhorn, on Rotifers, 197
Eisen, on Oligochaeta, 380, 390
Eisig, on Capitellidae, 373;
on Bonellia, 443
Electra, 481, 518, 523, 530;
larva, 509, 510;
variation, 516
Elytra, of Polynoids, 265, 292, 294, 298, 299, 309, 310, 311;
phosphorescent, 295, 296;
Effects, of parasites on their hosts, 56, 68, 69, 80, 94, 162
Eggs, of Leptoplana, 10, 16;
of Polyclads, 28;
of Triclads, 33, 40;
of Rhabdocoels, 47, 48;
of Termatodes, 52;
of ectoparasitic Trematodes, 54, 58, 60, 61;
of endoparasitic Trematodes, 63, 69;
of Cestodes, 87;
of Orthonectidae, 95;
of Nemertinea, 116;
of Nematoda, 135, 162;
of Gordius, 171;
of Acanthocephala, 179;
of Chaetognatha, 189;
of Rotifera, 200, 216 f.;
of Gastrotricha, 234;
of Nereis, 256;
of Polychaeta, 274, 275;
of Phyllodocids, 314;
of Scoloplos, 321;
of Myzostoma, 343;
of Polyzoa, 506, 507
Ehrenberg, on Turbellaria, 3, 6;
on Rotifers, 198, 220 n., 228;
on Gastrotricha, 231;
on Polyzoa (Bryozoa), 475
Eichhorn, on Rotifers, 197
Eisen, on Oligochaeta, 380, 390
Eisig, on Capitellidae, 373;
on Bonellia, 443
Electra, 481, 518, 523, 530;
larva, 509, 510;
variation, 516
Elytra, of Polynoids, 265, 292, 294, 298, 299, 309, 310, 311;
phosphorescent, 295, 296;
Page 571
as brood-pouch, 275;
of Aphroditidae, 266;
arrangement of, 309;
of Sigalionina, 313
Enantia, 16 n., 19
Enantiidae, 19
Enchelidium, 157
Enchytraeidae, 359, 360, 361, 366, 367, 370, 375
Enchytraeus, host of Gordius, 173
Encotylabe, 73;
eggs of E. pagelli, 58
Endocyst, 471
Endoderm, of Mesozoa, 93, 95
Endoparasitic Trematodes, 4, 52, 62
Enopla, 109
Enoplidae, 157
Enoplus, 157, 160
Entalophora, 518, 532
Enteroploea, 224
Enterostoma, 46;
British species, 50
Entoprocta, 475, 479, 487 f., 518;
lophophore, 476;
reproduction, 506;
larva, 509, 510
Eosphora, 216, 218, 224
Ephemera, host of Gordius, 172, 173
Ephesia, 321
Epibdella, 55, 73
Epidermis, of Leptoplana, 11, 12;
of Polyclads, 20, 25, 29;
of Trematodes, 56;
of Cestodes, 85;
of Nemertinea, 102;
of Nematoda, 125;
of Acanthocephala, 175;
of Nereis, 249;
of Aphroditidae, 266;
arrangement of, 309;
of Sigalionina, 313
Enantia, 16 n., 19
Enantiidae, 19
Enchelidium, 157
Enchytraeidae, 359, 360, 361, 366, 367, 370, 375
Enchytraeus, host of Gordius, 173
Encotylabe, 73;
eggs of E. pagelli, 58
Endocyst, 471
Endoderm, of Mesozoa, 93, 95
Endoparasitic Trematodes, 4, 52, 62
Enopla, 109
Enoplidae, 157
Enoplus, 157, 160
Entalophora, 518, 532
Enteroploea, 224
Enterostoma, 46;
British species, 50
Entoprocta, 475, 479, 487 f., 518;
lophophore, 476;
reproduction, 506;
larva, 509, 510
Eosphora, 216, 218, 224
Ephemera, host of Gordius, 172, 173
Ephesia, 321
Epibdella, 55, 73
Epidermis, of Leptoplana, 11, 12;
of Polyclads, 20, 25, 29;
of Trematodes, 56;
of Cestodes, 85;
of Nemertinea, 102;
of Nematoda, 125;
of Acanthocephala, 175;
of Nereis, 249;
Page 572
of Oligochaeta, 349;
of Leeches, 396;
of Gephyrea, 414;
of Phoronis, 454—see also Hypodermis
Epigamous, phase, of Nereis, 277 n.;
worms, 281
Epistome, in Phoronis, 453, 455;
in Phylactolaemata, 476, 476, 499;
in larva of Loxosoma, 509
Epistomia, 518, 526
Epithetosoma, 444, 445, 449
Epithetosomatoidea, 412, 444
Epitokous, phase, of Nereis, 277 n.
Eretmia, 225, 226
Eriographidae, 258, 338
Erpocotyle, 73
Errantia, 258, 285
Eschara, 516
Escharina, 518
Escharoides, 527
Euchlanididae, 225
Euchlanis, 225, 226
Eucratea, 518, 525, 527, 528
Eudrilidae, 359, 360, 380, 385, 403 f.
Eudrilus, 354, 385, 403 f.
Euichthydina, 235
Eulalia viridis, 314;
pigment, 292;
colour, 293;
eggs, 314 n.
Eumenia, 334
Eunice, 318, 319;
nephridium, 254;
eye, 255;
head, 262;
parapodium, 264;
gill, 265;
of Leeches, 396;
of Gephyrea, 414;
of Phoronis, 454—see also Hypodermis
Epigamous, phase, of Nereis, 277 n.;
worms, 281
Epistome, in Phoronis, 453, 455;
in Phylactolaemata, 476, 476, 499;
in larva of Loxosoma, 509
Epistomia, 518, 526
Epithetosoma, 444, 445, 449
Epithetosomatoidea, 412, 444
Epitokous, phase, of Nereis, 277 n.
Eretmia, 225, 226
Eriographidae, 258, 338
Erpocotyle, 73
Errantia, 258, 285
Eschara, 516
Escharina, 518
Escharoides, 527
Euchlanididae, 225
Euchlanis, 225, 226
Eucratea, 518, 525, 527, 528
Eudrilidae, 359, 360, 380, 385, 403 f.
Eudrilus, 354, 385, 403 f.
Euichthydina, 235
Eulalia viridis, 314;
pigment, 292;
colour, 293;
eggs, 314 n.
Eumenia, 334
Eunice, 318, 319;
nephridium, 254;
eye, 255;
head, 262;
parapodium, 264;
gill, 265;
Page 573
chaetae, 266, 267;
jaws, 270;
substance of tube, 290;
commensal, 298;
E. tibiana, 290
Eunicidae, 258, 318;
palps, 260;
tentacles, 262;
jaws, 270;
tube, 285, 290;
colour, 291, 292;
parasitic, 297;
tubes containing Polynoids, 298;
Palaeozoic, 302
Eunicites, 301, 302
Euphrosyne, 318;
parapodium, 265;
chaetae, 267
Eupolia, 113
Eupolyzoa, 461
Eurycercus, shell of, inhabited by Rotifers, 227 n.
Eurylepta, 19
Euryleptidae, 19
Eurythoe, 318
Eustrongylus gigas, 142;
E. tubifex, 142
Eusyllis, reproduction of, 278
Excretion, as cause of colour, 291
Excretory system, of Leptoplana, 13;
of Polyclads, 25;
of Triclads, 41;
absent in Acoela, 42;
of Temnocephala, 54;
of Digenea, 62;
of Cestodes, 86;
of Nemertinea, 108, 108, 120;
of Nematodes, 133;
jaws, 270;
substance of tube, 290;
commensal, 298;
E. tibiana, 290
Eunicidae, 258, 318;
palps, 260;
tentacles, 262;
jaws, 270;
tube, 285, 290;
colour, 291, 292;
parasitic, 297;
tubes containing Polynoids, 298;
Palaeozoic, 302
Eunicites, 301, 302
Euphrosyne, 318;
parapodium, 265;
chaetae, 267
Eupolia, 113
Eupolyzoa, 461
Eurycercus, shell of, inhabited by Rotifers, 227 n.
Eurylepta, 19
Euryleptidae, 19
Eurythoe, 318
Eustrongylus gigas, 142;
E. tubifex, 142
Eusyllis, reproduction of, 278
Excretion, as cause of colour, 291
Excretory system, of Leptoplana, 13;
of Polyclads, 25;
of Triclads, 41;
absent in Acoela, 42;
of Temnocephala, 54;
of Digenea, 62;
of Cestodes, 86;
of Nemertinea, 108, 108, 120;
of Nematodes, 133;
Page 574
of Acanthocephala, 177;
of Rotifers, 199, 213;
of Gastrotricha, 234;
of Kinorhyncha, 237;
of Polychaeta, 253;
of Polyzoa, 472 f.—see also Nephridium
Exogone, 308;
attachment of eggs, 275;
reproduction, 278
Eyes, of Leptoplana, 8, 15;
of Polyclads, 26, 27;
development of, 30;
of larval Polystomatidae, 59, 60;
of Nemertinea, 102, 106;
of Nematodes, 128;
of Gordius, 166;
of Chaetognatha, 188;
of Rotifera, 215;
of Gastrotricha, 234;
of Kinorhyncha, 238;
of Polychaeta, 255, 272, 314, 337, 339;
of Oligochaeta, 354;
of Leeches, 393, 394, 395;
of Gephyrea, 417;
of Polyzoon larva, 509
Fabricia, 339;
eyes, 272;
otocyst, 273
Faecal groove, of Sabellids, 337
Fans, of Chaetopterus, 295, 324
Faraday, on asexual reproduction of Planariae, 6, 40 n.
Farre, on Polyzoa, 500, 508
Farrella, 500, 518, 533
Fasciola, 67
Fecampia, life-history, 45
Felt, of Aphrodite, 268, 312
of Rotifers, 199, 213;
of Gastrotricha, 234;
of Kinorhyncha, 237;
of Polychaeta, 253;
of Polyzoa, 472 f.—see also Nephridium
Exogone, 308;
attachment of eggs, 275;
reproduction, 278
Eyes, of Leptoplana, 8, 15;
of Polyclads, 26, 27;
development of, 30;
of larval Polystomatidae, 59, 60;
of Nemertinea, 102, 106;
of Nematodes, 128;
of Gordius, 166;
of Chaetognatha, 188;
of Rotifera, 215;
of Gastrotricha, 234;
of Kinorhyncha, 238;
of Polychaeta, 255, 272, 314, 337, 339;
of Oligochaeta, 354;
of Leeches, 393, 394, 395;
of Gephyrea, 417;
of Polyzoon larva, 509
Fabricia, 339;
eyes, 272;
otocyst, 273
Faecal groove, of Sabellids, 337
Fans, of Chaetopterus, 295, 324
Faraday, on asexual reproduction of Planariae, 6, 40 n.
Farre, on Polyzoa, 500, 508
Farrella, 500, 518, 533
Fasciola, 67
Fecampia, life-history, 45
Felt, of Aphrodite, 268, 312
Page 575
Fertilisation, of Nemertinea, 117;
of Nematodes, 135;
of Gordiidae, 171;
of Acanthocephala, 179;
of Chaetognatha, 188;
of Rotifers, 217
Filaria, 147, 163;
F. attenuata, 134;
F. cystica, 142;
F. denticulata, 125;
F. immitis, 148;
F. labiata, 163;
F. laticaudata, 125;
F. loa, 149;
F. medinensis, 147, 157, 163;
F. sanguinis hominis, 149, 163;
F. papillosa, 163
Filariidae, 147
Filigrana, 340;
fission in, 281;
tubes, 290
Fimbria tenuis, 157
Fischer, on branchiae in Gephyrea, 416 n.
Fishes, Trematodes of, 4, 53, 55, 62, 64, 71, 72;
Cestodes of, 77, 84, 85;
Nemathelminthes of, 142, 143, 149, 163, 173, 182
Fission, in Bipalium, 34;
in Planariae, 40;
in Trichoplax, 96;
in Salinella, 96;
in Polychaeta, 278 f., 279, 280, 282, 340;
in Oligochaeta, 374, 375, 377;
in Phylactolaemata, 496;
in embryos, 365, 511
Fissurella, as host, 298
Flabelligera, 334
Flame-cells, in Leptoplana, 13;
of Nematodes, 135;
of Gordiidae, 171;
of Acanthocephala, 179;
of Chaetognatha, 188;
of Rotifers, 217
Filaria, 147, 163;
F. attenuata, 134;
F. cystica, 142;
F. denticulata, 125;
F. immitis, 148;
F. labiata, 163;
F. laticaudata, 125;
F. loa, 149;
F. medinensis, 147, 157, 163;
F. sanguinis hominis, 149, 163;
F. papillosa, 163
Filariidae, 147
Filigrana, 340;
fission in, 281;
tubes, 290
Fimbria tenuis, 157
Fischer, on branchiae in Gephyrea, 416 n.
Fishes, Trematodes of, 4, 53, 55, 62, 64, 71, 72;
Cestodes of, 77, 84, 85;
Nemathelminthes of, 142, 143, 149, 163, 173, 182
Fission, in Bipalium, 34;
in Planariae, 40;
in Trichoplax, 96;
in Salinella, 96;
in Polychaeta, 278 f., 279, 280, 282, 340;
in Oligochaeta, 374, 375, 377;
in Phylactolaemata, 496;
in embryos, 365, 511
Fissurella, as host, 298
Flabelligera, 334
Flame-cells, in Leptoplana, 13;
Page 576
in Thysanozoon, 25;
in Triclads, 41;
in Temnocephala, 54;
in Polystomatidae and Tristomatidae, 56;
in Distomum luteum, 62;
in Cestodes, 86;
in Nemertinea, 108, 109;
in Rotifers, 213;
in Urnatella, 491
Fletcherodrilus, 382
Floscularia, 200, 203, 205, 220, 221, 226
Flosculariaceae, 202, 211, 213, 220
Flosculariidae, 201, 203, 205, 220 n., 221, 230
Flukes, 51
Flustra, 465, 466, 467, 472, 473, 477, 515, 518, 526;
avicularia, 482
Flustrella, 467, 477, 518, 532;
larva, 513
Flustrina, 518
Food, of Turbellaria, 4;
of Leptoplana, 10;
of Polyclads, 24;
of Triclads, 37;
of Acoela, 43 f.;
of Rhabdocoela, 45;
of Trematodes, 4, 52, 62;
of Temnocephala, 53;
of Cestoda, 5;
of Nemertinea, 115;
of Nematodes, 131;
of Acanthocephala, 177;
of Chaetognatha, 190;
of Rotifera, 207, 212;
of Gastrotricha, 234;
of Polychaeta, 296;
of Earthworms, 359;
of Leeches, 393, 406 f.;
in Triclads, 41;
in Temnocephala, 54;
in Polystomatidae and Tristomatidae, 56;
in Distomum luteum, 62;
in Cestodes, 86;
in Nemertinea, 108, 109;
in Rotifers, 213;
in Urnatella, 491
Fletcherodrilus, 382
Floscularia, 200, 203, 205, 220, 221, 226
Flosculariaceae, 202, 211, 213, 220
Flosculariidae, 201, 203, 205, 220 n., 221, 230
Flukes, 51
Flustra, 465, 466, 467, 472, 473, 477, 515, 518, 526;
avicularia, 482
Flustrella, 467, 477, 518, 532;
larva, 513
Flustrina, 518
Food, of Turbellaria, 4;
of Leptoplana, 10;
of Polyclads, 24;
of Triclads, 37;
of Acoela, 43 f.;
of Rhabdocoela, 45;
of Trematodes, 4, 52, 62;
of Temnocephala, 53;
of Cestoda, 5;
of Nemertinea, 115;
of Nematodes, 131;
of Acanthocephala, 177;
of Chaetognatha, 190;
of Rotifera, 207, 212;
of Gastrotricha, 234;
of Polychaeta, 296;
of Earthworms, 359;
of Leeches, 393, 406 f.;
Page 577
of Gephyrea, 422, 443;
of Polyzoa, 467
Foot, in Rotifers, 200, 201
Foraminifera, as food of Polychaeta, 296
Forceps, of Eunice, 270
Forcipate, 210, 211
Formula, for Nematoda, 138
Fornix, 481, 517, 525
Fossil, Polychaeta, 301;
Polyzoa, 520;
Nemertinea, absence of, 119
Fredericella, 476, 494, 502-505, 518, 519;
lophophore, 495;
statoblast, 502, 503
Frenzel, on Trematoda, 62;
on Salinella, 96
Fresh-water, Turbellaria, compared with marine, 46;
Nemertinea, 101, 118;
Polychaeta, 284;
Polyzoa, 492
Friend, on Oligochaeta, 388 n.
Frogs, Trematodes of, 55, 58, 62, 71 f.;
Nematodes of, 140, 142, 160, 173
Frontal organ, of Nemertinea, 107
Frontal palps, of Eunicidae, 318 f.
Frontal ridge, 260
Frullania, inhabited by Rotifers, 227
Fulcrum, in Rotifers, 210
Funicular tissue, 471
Funiculus, 469, 471, 472, 499, 501
Furcularia, 216, 224, 226
Gamble, on Platyhelminthes, 3 f.;
on Mesozoa, 92 f.
Gammarus, Rotifers attached to, 227
Gapes, cause of, 144
Gardiner, on development of Acoela, 44 n.
of Polyzoa, 467
Foot, in Rotifers, 200, 201
Foraminifera, as food of Polychaeta, 296
Forceps, of Eunice, 270
Forcipate, 210, 211
Formula, for Nematoda, 138
Fornix, 481, 517, 525
Fossil, Polychaeta, 301;
Polyzoa, 520;
Nemertinea, absence of, 119
Fredericella, 476, 494, 502-505, 518, 519;
lophophore, 495;
statoblast, 502, 503
Frenzel, on Trematoda, 62;
on Salinella, 96
Fresh-water, Turbellaria, compared with marine, 46;
Nemertinea, 101, 118;
Polychaeta, 284;
Polyzoa, 492
Friend, on Oligochaeta, 388 n.
Frogs, Trematodes of, 55, 58, 62, 71 f.;
Nematodes of, 140, 142, 160, 173
Frontal organ, of Nemertinea, 107
Frontal palps, of Eunicidae, 318 f.
Frontal ridge, 260
Frullania, inhabited by Rotifers, 227
Fulcrum, in Rotifers, 210
Funicular tissue, 471
Funiculus, 469, 471, 472, 499, 501
Furcularia, 216, 224, 226
Gamble, on Platyhelminthes, 3 f.;
on Mesozoa, 92 f.
Gammarus, Rotifers attached to, 227
Gapes, cause of, 144
Gardiner, on development of Acoela, 44 n.
Page 578
Gasterostomatidae, 73
Gasterostomum, 73;
G. fimbriatum, life-history, 72;
G. gracilescens, 72
Gastrocotyle, 73
Gastrodiscus, 73
Gastrothylax, 73
Gastrotricha, 231 f.
Gegenbaur, on Nemertine development, 99
Gemellaria, 518, 526
Gemmation, 281;
in Syllidae, 278 f., 279, 280
Geobia, 37
Geodesmus, 34, 42
Geographical distribution, of Turbellaria, 32 f.;
of Nemertinea, 117;
of Chaetognatha, 191, 534;
of Gastrotricha, 235;
of Polychaeta, 299 f.;
of Oligochaeta, 369 f.;
of Leeches, 405;
of Gephyrea, 426 f., 432, 441 f.;
of Phoronis, 460;
of Polyzoa, 492 f., 504, 519
Geonemertes, 101;
description of G. chalicophora, 117
Geoplana, 33, 38, 42
Geoplanidae, 35, 42
Geoscolicidae, 351, 362, 386
Gephyrea, 411 f.;
history, 411;
external characters, 412, 420 f., 430 f., 434 f., 444;
body-wall, 414, 436;
digestive system, 414, 422, 430, 436, 445;
vascular system, 415, 421, 436;
respiratory system, 416;
body-cavity, 416, 437, 445;
Gasterostomum, 73;
G. fimbriatum, life-history, 72;
G. gracilescens, 72
Gastrocotyle, 73
Gastrodiscus, 73
Gastrothylax, 73
Gastrotricha, 231 f.
Gegenbaur, on Nemertine development, 99
Gemellaria, 518, 526
Gemmation, 281;
in Syllidae, 278 f., 279, 280
Geobia, 37
Geodesmus, 34, 42
Geographical distribution, of Turbellaria, 32 f.;
of Nemertinea, 117;
of Chaetognatha, 191, 534;
of Gastrotricha, 235;
of Polychaeta, 299 f.;
of Oligochaeta, 369 f.;
of Leeches, 405;
of Gephyrea, 426 f., 432, 441 f.;
of Phoronis, 460;
of Polyzoa, 492 f., 504, 519
Geonemertes, 101;
description of G. chalicophora, 117
Geoplana, 33, 38, 42
Geoplanidae, 35, 42
Geoscolicidae, 351, 362, 386
Gephyrea, 411 f.;
history, 411;
external characters, 412, 420 f., 430 f., 434 f., 444;
body-wall, 414, 436;
digestive system, 414, 422, 430, 436, 445;
vascular system, 415, 421, 436;
respiratory system, 416;
body-cavity, 416, 437, 445;
Page 579
nervous system, 416, 431, 437, 445;
excretory system, 417, 423, 431, 437, 445;
reproductive system, 418, 431, 437, 445;
development, 419, 439;
food, 422, 443;
commensalism, 429;
affinities, 241 n., 336, 445 f., 512;
British, 449
Germarium, of Rotifers, 216
Germ-yolk-gland, 47
Giard, on Oligochaeta, 368
Gid, induced by Coenurus, 82
Gigantorhynchidae, 183
Gigantorhynchus gigas, 174, 177, 184;
G. echinodiscus, G. spira, G. taenioides, 184
Gills, of Polychaeta, 252, 265, 268 f.;
of Arenicola, 333;
of Chlorhaemidae, 334;
of Cirratulus, 326;
of Euphrosyne, 265, 318;
of Eunicidae, 318;
of Nereis, 246;
of Sabelliformia, 260, 261;
development of, 275;
of Sabella, 286;
colour of, 294;
of Sabellaria, 263;
of Serpulidae, 261;
of Sternaspis, 336;
of Sigalionina, 313;
of Terebellidae, 329;
of Oligochaeta, 352, 353;
of Leeches, 395;
of Gephyrea, 416
Gizzard, in Rotifers, 199, 210;
in Polychaeta, 271, 307;
in Oligochaeta, 358;
excretory system, 417, 423, 431, 437, 445;
reproductive system, 418, 431, 437, 445;
development, 419, 439;
food, 422, 443;
commensalism, 429;
affinities, 241 n., 336, 445 f., 512;
British, 449
Germarium, of Rotifers, 216
Germ-yolk-gland, 47
Giard, on Oligochaeta, 368
Gid, induced by Coenurus, 82
Gigantorhynchidae, 183
Gigantorhynchus gigas, 174, 177, 184;
G. echinodiscus, G. spira, G. taenioides, 184
Gills, of Polychaeta, 252, 265, 268 f.;
of Arenicola, 333;
of Chlorhaemidae, 334;
of Cirratulus, 326;
of Euphrosyne, 265, 318;
of Eunicidae, 318;
of Nereis, 246;
of Sabelliformia, 260, 261;
development of, 275;
of Sabella, 286;
colour of, 294;
of Sabellaria, 263;
of Serpulidae, 261;
of Sternaspis, 336;
of Sigalionina, 313;
of Terebellidae, 329;
of Oligochaeta, 352, 353;
of Leeches, 395;
of Gephyrea, 416
Gizzard, in Rotifers, 199, 210;
in Polychaeta, 271, 307;
in Oligochaeta, 358;
Page 580
in Polyzoa, 477, 480, 532 f.
Glands, on parapodia, 249;
of Phyllodocids, 314;
oesophageal, 271, 272, 358;
tube-forming, 287, 304, 327
Gland shields, 287, 304, 306;
of Sabellids, 337;
of Terebellids, 327
Glandular papillae, of Polygordius, 244
Glossiphonia (= Clepsine), 393, 396, 399, 404, 407;
anatomy, 397, 398, 401;
spermatophore, 402
Glossiphoniidae, 406
Glycera, cirrus, 265;
habitat, 286;
jaws, 270;
nephridium, 254;
parapodium, 264;
prostomium, 259;
tentacles, 262;
G. capitata, distribution, 299;
G. meckelii, 320
Glyceridae, 258, 320;
gills, 268;
coelomic corpuscles, 253
Glyphidrilus, 386
Gnathobdellae, 396 f., 407
Gnathobdellidae, 407
Gnathosyllis, colour of, 293
Gobio, parasites of, 182, 183
Golfingia, 426, 428, 430
Goniada, 320
Goodrich, on Oligochaeta, 378
Gordiidae, 123, 164 f.
Gordiodrilus, 383 f.
Gordius, 164 f., 164;
G. tolosanus, 165 f., 170
Glands, on parapodia, 249;
of Phyllodocids, 314;
oesophageal, 271, 272, 358;
tube-forming, 287, 304, 327
Gland shields, 287, 304, 306;
of Sabellids, 337;
of Terebellids, 327
Glandular papillae, of Polygordius, 244
Glossiphonia (= Clepsine), 393, 396, 399, 404, 407;
anatomy, 397, 398, 401;
spermatophore, 402
Glossiphoniidae, 406
Glycera, cirrus, 265;
habitat, 286;
jaws, 270;
nephridium, 254;
parapodium, 264;
prostomium, 259;
tentacles, 262;
G. capitata, distribution, 299;
G. meckelii, 320
Glyceridae, 258, 320;
gills, 268;
coelomic corpuscles, 253
Glyphidrilus, 386
Gnathobdellae, 396 f., 407
Gnathobdellidae, 407
Gnathosyllis, colour of, 293
Gobio, parasites of, 182, 183
Golfingia, 426, 428, 430
Goniada, 320
Goodrich, on Oligochaeta, 378
Gordiidae, 123, 164 f.
Gordiodrilus, 383 f.
Gordius, 164 f., 164;
G. tolosanus, 165 f., 170
Page 581
Gosse, on Rotifers, 198, 209 n., 220
Gossea, 232, 235
Goujon, on Trichina, 146
Gourret, on Chaetognatha, 187
Graff, von, on Rhabdocoelida, 44;
on Geonemertes, 101, 117
Graffilla, 50;
occurrence, 45
Grassi, on Cestoda, 80 n., 89;
on Chaetognatha, 190, 193
Grater, of Eunicidae, 270
Greef, on Echiuroidea, 441, 444
Gregarines, in Polychaeta, 299;
in Gephyrea, 444
Gregory, on Polyzoa, 519, 520
Grinder, of Eunicidae, 270
Grube, on Oligochaeta, 347, 352;
on Hirudinea, 395
Grubea, 308;
attachment of eggs, 275
Guanin, in coelomic corpuscles, 253
Guinea-worm, 147
Gunda, 31, 41, 42
Gundidae, 42
Gymnolaemata, 476, 512, 518;
lophophore, 476;
in fresh water, 492
Gyrator hermaphroditus, 49
Gyrocotyle (= Amphiptyches), 91;
G. rugosa, 77;
G. urna, 77
Gyrodactylidae, 53, 61, 73
Gyrodactylinae, 73
Gyrodactylus, 55, 61, 73
Haberlandt, on Convoluta, 43
Habits, of Platyhelminthes, 3, 7, 21, 35, 43;
Gossea, 232, 235
Goujon, on Trichina, 146
Gourret, on Chaetognatha, 187
Graff, von, on Rhabdocoelida, 44;
on Geonemertes, 101, 117
Graffilla, 50;
occurrence, 45
Grassi, on Cestoda, 80 n., 89;
on Chaetognatha, 190, 193
Grater, of Eunicidae, 270
Greef, on Echiuroidea, 441, 444
Gregarines, in Polychaeta, 299;
in Gephyrea, 444
Gregory, on Polyzoa, 519, 520
Grinder, of Eunicidae, 270
Grube, on Oligochaeta, 347, 352;
on Hirudinea, 395
Grubea, 308;
attachment of eggs, 275
Guanin, in coelomic corpuscles, 253
Guinea-worm, 147
Gunda, 31, 41, 42
Gundidae, 42
Gymnolaemata, 476, 512, 518;
lophophore, 476;
in fresh water, 492
Gyrator hermaphroditus, 49
Gyrocotyle (= Amphiptyches), 91;
G. rugosa, 77;
G. urna, 77
Gyrodactylidae, 53, 61, 73
Gyrodactylinae, 73
Gyrodactylus, 55, 61, 73
Haberlandt, on Convoluta, 43
Habits, of Platyhelminthes, 3, 7, 21, 35, 43;
Page 582
of Nemertinea, 114;
of Gordiidae, 170 f.;
of Chaetognatha, 189;
of Rotifers, 206, 226;
of Gastrotricha, 232, 234, 235;
of Polychaeta, 285;
of Oligochaeta, 366;
of Gephyrea, 426, 433, 442;
of Phoronis, 451
Haemadipsa, 408;
eye, 394
Haemal fluid, 252
Haematocleptes, parasitic, 297
Haementeria, 407
Haemerythrin, 416;
in Magelona, 252
Haemoglobin, in Nemertinea, 107, 108;
in Chaetopoda, 252, 253, 291, 356;
in Gephyrea, 437;
in Phoronis, 456
Haemopis, 393, 407
Halicryptus, 432, 433;
anatomy, 430
Hallez, on Turbellaria, 7, 21, 40
Halosydna, 298
Hamann, on Nematoda, 131, 133, 136 n.;
on Acanthocephala, 176, 180
Hamingia, 435 f., 442;
males of, 438
Haplobranchus, 339;
gills, 261
Haplodiscus, 43, 49
Haplodrili, 241
Hares, parasites of, 141, 145
Harker, on Oligochaeta, 369
Harmer, on Polyzoa, 465 f.
Harris, on Rotifera, 197
of Gordiidae, 170 f.;
of Chaetognatha, 189;
of Rotifers, 206, 226;
of Gastrotricha, 232, 234, 235;
of Polychaeta, 285;
of Oligochaeta, 366;
of Gephyrea, 426, 433, 442;
of Phoronis, 451
Haemadipsa, 408;
eye, 394
Haemal fluid, 252
Haematocleptes, parasitic, 297
Haementeria, 407
Haemerythrin, 416;
in Magelona, 252
Haemoglobin, in Nemertinea, 107, 108;
in Chaetopoda, 252, 253, 291, 356;
in Gephyrea, 437;
in Phoronis, 456
Haemopis, 393, 407
Halicryptus, 432, 433;
anatomy, 430
Hallez, on Turbellaria, 7, 21, 40
Halosydna, 298
Hamann, on Nematoda, 131, 133, 136 n.;
on Acanthocephala, 176, 180
Hamingia, 435 f., 442;
males of, 438
Haplobranchus, 339;
gills, 261
Haplodiscus, 43, 49
Haplodrili, 241
Hares, parasites of, 141, 145
Harker, on Oligochaeta, 369
Harmer, on Polyzoa, 465 f.
Harris, on Rotifera, 197
Page 583
Hartog, on Rotifera, 197 f.;
on Gastrotricha, 231 f.;
on Kinorhyncha, 236 f.
Haswell, on Temnocephalidae, 53;
on Phoronis, 451
Hatschek, on affinities of Polyclads, 28 n.;
on nature of Cestodes, 76;
on Trochophore, 229;
on development of Gephyrea, 419, 447
Head, of Nereis, 246, 248;
of Polychaeta, 259 f.;
regeneration of, 283;
of Tomopteris, 315;
of Aphrodite, 260;
of Chlorhaemidae, 334;
of Eunice, 262;
of Nephthys, 262;
of Phyllodoce, 262;
of Polydora, 261;
of Polynoid, 262;
of Sabella, 261;
of Sabellaria, 263;
of Syllid, 262;
of Trophonia, 262
Hedruris, 163
Hekaterobranchus, 326
Heliodrilus, 359, 380
Heliopora, containing Polydora, 298
Heller, on human parasites, 139
Hemichordata, 462
Hemilepidia, colour of, 292
Hemistomum, 73
Hemitubifex, 378
Henlea, 369
Hermadion, 299
Hermaphrodite, Nemertinea, 109;
Polychaeta, 273 f.
on Gastrotricha, 231 f.;
on Kinorhyncha, 236 f.
Haswell, on Temnocephalidae, 53;
on Phoronis, 451
Hatschek, on affinities of Polyclads, 28 n.;
on nature of Cestodes, 76;
on Trochophore, 229;
on development of Gephyrea, 419, 447
Head, of Nereis, 246, 248;
of Polychaeta, 259 f.;
regeneration of, 283;
of Tomopteris, 315;
of Aphrodite, 260;
of Chlorhaemidae, 334;
of Eunice, 262;
of Nephthys, 262;
of Phyllodoce, 262;
of Polydora, 261;
of Polynoid, 262;
of Sabella, 261;
of Sabellaria, 263;
of Syllid, 262;
of Trophonia, 262
Hedruris, 163
Hekaterobranchus, 326
Heliodrilus, 359, 380
Heliopora, containing Polydora, 298
Heller, on human parasites, 139
Hemichordata, 462
Hemilepidia, colour of, 292
Hemistomum, 73
Hemitubifex, 378
Henlea, 369
Hermadion, 299
Hermaphrodite, Nemertinea, 109;
Polychaeta, 273 f.
Page 584
Hermellidae, 258, 341
Hermelliformia, 258, 306, 341
Hermione, 312;
chaetae, 266, 267
Hermionina, 309, 311
Herpobdellidae, 407
Hertwig, O., on Chaetognatha, 187 n.
Hesionidae, 258, 308;
segments, 258;
head, 263;
swim-bladder, 272;
genital organs, 274;
parasitic, 297
Hesperodrilus, 352 f., 369, 378 f.
Hesse, on nervous system of Nematoda, 127
Heterakis, 131, 139
Heterocotylea, 73
Heterodera, 155, 160, 164
Heterogamy, 66 n.
Heteronemertini, 113
Heteronereid phase, 276 f.;
chaetae, 246, 276;
parapodia, 276, 277
Heteronereis, 276, 281—see Heteronereid
Heteropora, 520 n.
Heterosyllis, 278, 279, 281
Hexacotyle, 73
Hexarthra, 223, 226
Hibernaculum, 501, 502
Hincks, on Polyzoa, 475, 500, 508, 516, 519, 523
Hippothoa, 528
Hippuraria, 533
Hirudinea, 241, 392 f.;
external characters, 392;
British species, 393;
eyes, 395;
branchiae, 395;
Hermelliformia, 258, 306, 341
Hermione, 312;
chaetae, 266, 267
Hermionina, 309, 311
Herpobdellidae, 407
Hertwig, O., on Chaetognatha, 187 n.
Hesionidae, 258, 308;
segments, 258;
head, 263;
swim-bladder, 272;
genital organs, 274;
parasitic, 297
Hesperodrilus, 352 f., 369, 378 f.
Hesse, on nervous system of Nematoda, 127
Heterakis, 131, 139
Heterocotylea, 73
Heterodera, 155, 160, 164
Heterogamy, 66 n.
Heteronemertini, 113
Heteronereid phase, 276 f.;
chaetae, 246, 276;
parapodia, 276, 277
Heteronereis, 276, 281—see Heteronereid
Heteropora, 520 n.
Heterosyllis, 278, 279, 281
Hexacotyle, 73
Hexarthra, 223, 226
Hibernaculum, 501, 502
Hincks, on Polyzoa, 475, 500, 508, 516, 519, 523
Hippothoa, 528
Hippuraria, 533
Hirudinea, 241, 392 f.;
external characters, 392;
British species, 393;
eyes, 395;
branchiae, 395;
Page 585
alimentary canal, 396;
vascular system, 396;
body-cavity, 397;
nephridia, 399;
reproductive organs, 401;
cocoons, 404;
classification, 405
Hirudiniculture, 393
Hirudo, 393, 396 f., 399, 403, 405, 407;
nephridium, 400
Hislopia, 492
Histioderma, 302
Histriobdella, 242 n.
Histriodrilus, 242 n.
Holloway, on Rotifers, 227
Holomyarii, 137
Holostomatidae, 63, 64, 73
Holostomum, 73;
H. excavatum, 63
Holothurian, as host, 298
Homalogaster, 73
Hood, of Sabellaria, 263, 306
Hooks, of Trematodes, 53, 56, 57;
of Cestodes, 75, 85;
of Cestode-larvae, 87, 88;
taxonomic value in Cestodes, 90 f.
Hoplonemertea, 106, 109, 110;
auditory organs, 106, 110;
British species, 110;
characters, 110;
development, 113;
proboscis, 110
Hornera, 518, 532
Horse, parasites of, 68, 83, 90, 125, 140, 142, 163
Horse-leeches, 393 f.
Horst, on Oligochaeta, 354
Hubrecht on Nemertinea, affinities, 120;
vascular system, 396;
body-cavity, 397;
nephridia, 399;
reproductive organs, 401;
cocoons, 404;
classification, 405
Hirudiniculture, 393
Hirudo, 393, 396 f., 399, 403, 405, 407;
nephridium, 400
Hislopia, 492
Histioderma, 302
Histriobdella, 242 n.
Histriodrilus, 242 n.
Holloway, on Rotifers, 227
Holomyarii, 137
Holostomatidae, 63, 64, 73
Holostomum, 73;
H. excavatum, 63
Holothurian, as host, 298
Homalogaster, 73
Hood, of Sabellaria, 263, 306
Hooks, of Trematodes, 53, 56, 57;
of Cestodes, 75, 85;
of Cestode-larvae, 87, 88;
taxonomic value in Cestodes, 90 f.
Hoplonemertea, 106, 109, 110;
auditory organs, 106, 110;
British species, 110;
characters, 110;
development, 113;
proboscis, 110
Hornera, 518, 532
Horse, parasites of, 68, 83, 90, 125, 140, 142, 163
Horse-leeches, 393 f.
Horst, on Oligochaeta, 354
Hubrecht on Nemertinea, affinities, 120;
Page 586
classification, 109;
excretory system, 108;
nervous system, 105
Hudson, on Rotifera, 197, 198, 215 n., 220 n., 223 n., 228
Hudsonella, 224
Huxley, on Rotifers, 198, 229;
on Polychaeta, 246;
on Molluscoidea, 475
Huxleya, 525, 527
Hyalinoecia, 299, 318, 319;
tentacles, 262;
composition of tube of, 290
Hydatina, 199, 200, 202, 204, 213, 224, 226, 228
Hydatinidae, 224
Hymenolepis, 91;
generic characters, 91;
H. diminuta (= Taenia flavopunctata), life-history, 83;
specific characters, 91;
H. murina (= Taenia murina), 70;
life-history, 83, 89, 91;
H. nana, 80;
life-history, 83;
specific characters, 91
Hyocrinus, as host, 342
Hyperiodrilus, 363 f.;
reproductive organs, 363
Hypodermic impregnation, 27, 218
Hypodermis (= Epidermis) of Gordius, 165;
of Rotifera, etc., 205, 232
Hypophorella, 478, 518, 533;
larva, 510
Hyporhynchus, 49
Hystrichis, 147, 149, 163
Ichthydium, 235
Ichthyobdellidae, 406
Ichthyonema, 131, 147, 149, 163
excretory system, 108;
nervous system, 105
Hudson, on Rotifera, 197, 198, 215 n., 220 n., 223 n., 228
Hudsonella, 224
Huxley, on Rotifers, 198, 229;
on Polychaeta, 246;
on Molluscoidea, 475
Huxleya, 525, 527
Hyalinoecia, 299, 318, 319;
tentacles, 262;
composition of tube of, 290
Hydatina, 199, 200, 202, 204, 213, 224, 226, 228
Hydatinidae, 224
Hymenolepis, 91;
generic characters, 91;
H. diminuta (= Taenia flavopunctata), life-history, 83;
specific characters, 91;
H. murina (= Taenia murina), 70;
life-history, 83, 89, 91;
H. nana, 80;
life-history, 83;
specific characters, 91
Hyocrinus, as host, 342
Hyperiodrilus, 363 f.;
reproductive organs, 363
Hypodermic impregnation, 27, 218
Hypodermis (= Epidermis) of Gordius, 165;
of Rotifera, etc., 205, 232
Hypophorella, 478, 518, 533;
larva, 510
Hyporhynchus, 49
Hystrichis, 147, 149, 163
Ichthydium, 235
Ichthyobdellidae, 406
Ichthyonema, 131, 147, 149, 163
Page 587
Ichthyotaenia, 91
Ichthyotaeninae, 85, 91
Idmonea, 518, 532
Iguana, parasites of, 142
Iijima, on yolk-glands, 38 n.
Illoricata, 223
Ilyodrilus, 378;
chaeta, 350
Ilyogenia, 388
Imogine, 19
Inarticulata, 517, 518
Incudate, 210, 211
Incus, in Rotifers, 210
Inermia, 445
Infusoriform embryos, 93
Insects, parasites of, 142, 150, 152, 153, 154, 160, 163, 179, 183, 184,
185
Internal sac, 509, 511
Internode, 525
Interproglottidal glands, 90
Intertentacular organ, 469, 473, 508
Introvert, in Polychaeta, 249, 250;
in Gephyrea, 412, 424
Investing membrane, in ectoparasitic Trematodes, 57;
in Cestodes, 85
Ioda, form of head, 278
Isacis, 163
Jammes, on skin of Nematoda, 126
Jaws, of Nereis, 248, 250, 270;
of Polychaeta, 269 f.;
of Eunicidae, 270;
of Polynoid, 270;
of Autolytus, 270;
fossil, 302;
of Glycera, 270
Jelly, Miss, on Polyzoa, 523
Ichthyotaeninae, 85, 91
Idmonea, 518, 532
Iguana, parasites of, 142
Iijima, on yolk-glands, 38 n.
Illoricata, 223
Ilyodrilus, 378;
chaeta, 350
Ilyogenia, 388
Imogine, 19
Inarticulata, 517, 518
Incudate, 210, 211
Incus, in Rotifers, 210
Inermia, 445
Infusoriform embryos, 93
Insects, parasites of, 142, 150, 152, 153, 154, 160, 163, 179, 183, 184,
185
Internal sac, 509, 511
Internode, 525
Interproglottidal glands, 90
Intertentacular organ, 469, 473, 508
Introvert, in Polychaeta, 249, 250;
in Gephyrea, 412, 424
Investing membrane, in ectoparasitic Trematodes, 57;
in Cestodes, 85
Ioda, form of head, 278
Isacis, 163
Jammes, on skin of Nematoda, 126
Jaws, of Nereis, 248, 250, 270;
of Polychaeta, 269 f.;
of Eunicidae, 270;
of Polynoid, 270;
of Autolytus, 270;
fossil, 302;
of Glycera, 270
Jelly, Miss, on Polyzoa, 523
Page 588
Jensenia, 50
Jimenez, on Leeches, 407
Joblot, on Rotifers, 197
Johnston, on Hirudinea, 393
Joliet, on development of Rotifers, 218;
on Polyzoa, 508
Jungermanniaceae, inhabited by Rotifers, 227
Jurassic, Serpulids, 301;
Polyzoa, 520 f.
Kaiser, on Acanthocephala, 177
Kamptoderm, 469, 470
Keferstein, on Polycladida, 7, 10
Kennel, von, on Nemertinea, 108;
on Malacobdella, 101 n., 119
Kerria, 384
Kinorhyncha, 236 f.
Kleinenberg, on Trochophore, 229
Koellikeria, 73
Kölliker, on Distomum okenii, 71
Koren and Danielssen, on Gephyrea, 442, 443
Kowalevsky, on Hirudinea, 397;
on Phoronis, 458
Kraepelin, on Polyzoa, 493, 502
Krause, on parasites, 163
Krohn, on Nemertine development, 99
Krohnia, 186;
species, 192, 194;
American species, 534
Krukenberg, on haemerythrin, 416
Kynotus, 386
Labrorostratus, 297
Lacinularia, 200, 213, 215, 221, 226
Lacrymaria, 235
Laetmonice, 312
Lagenipora, 528
Jimenez, on Leeches, 407
Joblot, on Rotifers, 197
Johnston, on Hirudinea, 393
Joliet, on development of Rotifers, 218;
on Polyzoa, 508
Jungermanniaceae, inhabited by Rotifers, 227
Jurassic, Serpulids, 301;
Polyzoa, 520 f.
Kaiser, on Acanthocephala, 177
Kamptoderm, 469, 470
Keferstein, on Polycladida, 7, 10
Kennel, von, on Nemertinea, 108;
on Malacobdella, 101 n., 119
Kerria, 384
Kinorhyncha, 236 f.
Kleinenberg, on Trochophore, 229
Koellikeria, 73
Kölliker, on Distomum okenii, 71
Koren and Danielssen, on Gephyrea, 442, 443
Kowalevsky, on Hirudinea, 397;
on Phoronis, 458
Kraepelin, on Polyzoa, 493, 502
Krause, on parasites, 163
Krohn, on Nemertine development, 99
Krohnia, 186;
species, 192, 194;
American species, 534
Krukenberg, on haemerythrin, 416
Kynotus, 386
Labrorostratus, 297
Lacinularia, 200, 213, 215, 221, 226
Lacrymaria, 235
Laetmonice, 312
Lagenipora, 528
Page 589
Lamarck, on Gephyrea, 411
Land, Planarians, 4, 30, 33, 34, 36;
Nemertines, 101, 117;
Oligochaeta, 347 f.;
Leeches, 408
Lang, on Polyclads, 7, 17, 21 f., 27, 28 n.;
on nature of Cestodes, 76
Lanice, 328;
Hypophorella in tubes of, 478, 533
Lankester, on Trochosphere, 229;
on Earthworms, 347;
on Hirudinea, 397;
on Gephyrea, 430, 437, 439;
on Podaxonia, 461
Larva, Müller's, 29;
of Polystomum, 59;
of Diplozoon, 60;
of Gyrodactylus, 61;
of Holostomatidae, 63, 64;
of Distomum 64, 65, 67;
hosts of larvae of digenetic Trematodes, 71 f.;
of Calliobothrium, 77;
of Cestodes, 79 f.;
table of Cestode larvae, 83, 85, 87;
of Schistocephalus, 84;
of Bothriocephalus, 87;
of Dipylidium (Cysticercoid), 83, 88 f.;
of Mesozoa, 92, 93;
of Nemertinea, 113;
Trochosphere, 229, 274, 439, 510;
of Polygordius, 245;
of Polychaeta, 274, 275;
of Chaetopterus, 325;
of Myzostoma, 344;
of Gephyrea, 419, 439;
of Phoronis, 458;
of Polyzoa, 466, 509, 511, 520
Land, Planarians, 4, 30, 33, 34, 36;
Nemertines, 101, 117;
Oligochaeta, 347 f.;
Leeches, 408
Lang, on Polyclads, 7, 17, 21 f., 27, 28 n.;
on nature of Cestodes, 76
Lanice, 328;
Hypophorella in tubes of, 478, 533
Lankester, on Trochosphere, 229;
on Earthworms, 347;
on Hirudinea, 397;
on Gephyrea, 430, 437, 439;
on Podaxonia, 461
Larva, Müller's, 29;
of Polystomum, 59;
of Diplozoon, 60;
of Gyrodactylus, 61;
of Holostomatidae, 63, 64;
of Distomum 64, 65, 67;
hosts of larvae of digenetic Trematodes, 71 f.;
of Calliobothrium, 77;
of Cestodes, 79 f.;
table of Cestode larvae, 83, 85, 87;
of Schistocephalus, 84;
of Bothriocephalus, 87;
of Dipylidium (Cysticercoid), 83, 88 f.;
of Mesozoa, 92, 93;
of Nemertinea, 113;
Trochosphere, 229, 274, 439, 510;
of Polygordius, 245;
of Polychaeta, 274, 275;
of Chaetopterus, 325;
of Myzostoma, 344;
of Gephyrea, 419, 439;
of Phoronis, 458;
of Polyzoa, 466, 509, 511, 520
Page 590
Lateral organs, of Capitellidae, 343—see also Ciliated pits
Laurer's Canal (= Laurer-Stieda canal), 57, 87
Laurer's Canal (= Laurer-Stieda canal), 57, 87
Page 591
Leaena, 300, 327 n.
Lecanocephalus, 131, 133
Leckenby, on Priapulus, 433
Leeches, 241, 392 f.—see also Hirudinea
Leeuwenhoek, on Rotifera, 197
Legrain, on Nematodes in deserts, 156
Legros, on Trichina, 146
Lehnert, on Bipalium, 36, 37
Leidy, on Rotifers, 198
Leimacopsis, 37, 42
Lemnisci, 176
Lepas, as host, 298
Lepidasthenia, 293, 311
Lepidoderma, 235
Lepidonotus (subgenus of Polynoe), eye, 255
Lepralia, 516, 518, 528, 530, 531 n.;
L. foliacea, 478, 527;
larva, 511
Leprea, 328
Leptodera, 129, 131, 133, 160
Leptoplana, 7, 8, 9, 11, 14, 17;
British species, 19;
habits, 8 f.;
anatomy, 11 f.
Leptoplanidae, 19
Leptostoma, 396
Lesson, on Polyclads, 24
Leuciscus, parasites of, 173, 182
Leuckart, on Platyhelminthes, 6, 64 f., 70, 76;
on Nemertinea, 99;
on Nematoda, 136, 139, 140, 142, 146, 163;
on Hirudinea, 395
Leucochloridium, 65, 66
Leucocytes, of Polychaeta, 252
Leucodore—see Polydora
Leydig, on Rotifers, 198
Lias, Serpulids in, 301
Lecanocephalus, 131, 133
Leckenby, on Priapulus, 433
Leeches, 241, 392 f.—see also Hirudinea
Leeuwenhoek, on Rotifera, 197
Legrain, on Nematodes in deserts, 156
Legros, on Trichina, 146
Lehnert, on Bipalium, 36, 37
Leidy, on Rotifers, 198
Leimacopsis, 37, 42
Lemnisci, 176
Lepas, as host, 298
Lepidasthenia, 293, 311
Lepidoderma, 235
Lepidonotus (subgenus of Polynoe), eye, 255
Lepralia, 516, 518, 528, 530, 531 n.;
L. foliacea, 478, 527;
larva, 511
Leprea, 328
Leptodera, 129, 131, 133, 160
Leptoplana, 7, 8, 9, 11, 14, 17;
British species, 19;
habits, 8 f.;
anatomy, 11 f.
Leptoplanidae, 19
Leptostoma, 396
Lesson, on Polyclads, 24
Leuciscus, parasites of, 173, 182
Leuckart, on Platyhelminthes, 6, 64 f., 70, 76;
on Nemertinea, 99;
on Nematoda, 136, 139, 140, 142, 146, 163;
on Hirudinea, 395
Leucochloridium, 65, 66
Leucocytes, of Polychaeta, 252
Leucodore—see Polydora
Leydig, on Rotifers, 198
Lias, Serpulids in, 301
Page 592
Libyodrilus, 364, 385, 386
Lichenopora, 518, 531
Life-history, of Trematodes, 4;
of Polystomatidae (Polystomum, Diplozoon, Gyrodactylus), 58 f.;
of digenetic Trematodes, 63 f.;
table of, 71;
of Cestodes, 5 f., 87;
table of life-histories of Cestodes, 83;
of Dipylidium, 88;
of Dicyemidae, 93;
of Nematoda, 159;
of Gordius, 170;
of Acanthocephala, 179—see also Development
Ligula, 91;
occurrence, 85
Ligulinae, 91
Lim Boon Keng, on Earthworms, 349
Lima, nests of, 298
Lime, secreted by Serpulidae, 290
Limnaea truncatula, host of larvae of Distomum hepaticum, 67, 72
Limnatis, 407
Limnias, 205, 221;
early description of, 197
Limnodrilus, 378
Lineus, 111;
L. marinus (= L. longissimus), 99, 100, 111, 114;
Borlase on, 99;
size of, 100;
L. gesserensis (= L. obscurus = L. sanguineus), recuperative powers
of, 116
Linguatulida, affinities of, 344
Linnaeus, on Cestodes, 78;
on Gephyrea, 411;
on Polyzoa, 474
Linstow, von, on classification of Nematodes, 137;
on life-history of Ascaris lumbricoides, 140;
on parasitism, 162;
Lichenopora, 518, 531
Life-history, of Trematodes, 4;
of Polystomatidae (Polystomum, Diplozoon, Gyrodactylus), 58 f.;
of digenetic Trematodes, 63 f.;
table of, 71;
of Cestodes, 5 f., 87;
table of life-histories of Cestodes, 83;
of Dipylidium, 88;
of Dicyemidae, 93;
of Nematoda, 159;
of Gordius, 170;
of Acanthocephala, 179—see also Development
Ligula, 91;
occurrence, 85
Ligulinae, 91
Lim Boon Keng, on Earthworms, 349
Lima, nests of, 298
Lime, secreted by Serpulidae, 290
Limnaea truncatula, host of larvae of Distomum hepaticum, 67, 72
Limnatis, 407
Limnias, 205, 221;
early description of, 197
Limnodrilus, 378
Lineus, 111;
L. marinus (= L. longissimus), 99, 100, 111, 114;
Borlase on, 99;
size of, 100;
L. gesserensis (= L. obscurus = L. sanguineus), recuperative powers
of, 116
Linguatulida, affinities of, 344
Linnaeus, on Cestodes, 78;
on Gephyrea, 411;
on Polyzoa, 474
Linstow, von, on classification of Nematodes, 137;
on life-history of Ascaris lumbricoides, 140;
on parasitism, 162;
Page 593
on Gordius, 166, 171, 173
Lip, lip-membrane, lip-processes, of Sabellidae, 261, 337
Lipobranchius, 334;
shape of body, 259
Lipochromes, in Polychaeta, 292
Lister, on Polyzoa, 497
Lithodomous, Polychaeta, 287
Lithographic slate, fossil Polychaeta from, 301, 302
Liver, -fluke, 51;
-rot, 68
Locomotion, of Planarians, 9, 10, 36;
of Polyclads, 22 f.;
of Nemertinea, 114, 115;
of Chaetognatha, 190;
of Rotifers, etc., 206, 235;
of Dinophilus, 243;
of Phylactolaemata, 496
Looss, on Trematoda, 62 n., 66, 70
Lopadorhynchina, 314
Lopadorhynchus, 314;
L. erythrophyllum, colour of, 292
Lophochaeta, 351;
chaeta, 350
Lophohelia, with Eunice, 298, 319
Lophophore, in Phoronis, 453;
in Polyzoa, 476, 476, 495
Lophopus, 494, 499, 504, 505, 518, 519;
movements, 496, 497;
fission, 496, 506;
statoblast, 502, 503
Lorica, in Rotifers, 205
Loricata, 205, 224
Lota, parasites of, 182
Loxosoma, 489 f., 489, 490, 506, 518;
on Polychaeta, 299, 489;
on other animals, 489;
buds, 489, 490, 506;
Lip, lip-membrane, lip-processes, of Sabellidae, 261, 337
Lipobranchius, 334;
shape of body, 259
Lipochromes, in Polychaeta, 292
Lister, on Polyzoa, 497
Lithodomous, Polychaeta, 287
Lithographic slate, fossil Polychaeta from, 301, 302
Liver, -fluke, 51;
-rot, 68
Locomotion, of Planarians, 9, 10, 36;
of Polyclads, 22 f.;
of Nemertinea, 114, 115;
of Chaetognatha, 190;
of Rotifers, etc., 206, 235;
of Dinophilus, 243;
of Phylactolaemata, 496
Looss, on Trematoda, 62 n., 66, 70
Lopadorhynchina, 314
Lopadorhynchus, 314;
L. erythrophyllum, colour of, 292
Lophochaeta, 351;
chaeta, 350
Lophohelia, with Eunice, 298, 319
Lophophore, in Phoronis, 453;
in Polyzoa, 476, 476, 495
Lophopus, 494, 499, 504, 505, 518, 519;
movements, 496, 497;
fission, 496, 506;
statoblast, 502, 503
Lorica, in Rotifers, 205
Loricata, 205, 224
Lota, parasites of, 182
Loxosoma, 489 f., 489, 490, 506, 518;
on Polychaeta, 299, 489;
on other animals, 489;
buds, 489, 490, 506;
Page 594
larva, 509
Lug-worm, castings of, 285;
as bait, 297
Lumbricaria, 302
Lumbricidae, 362, 371 f., 388
Lumbricobdella, 392
Lumbriconereis, 318, 320;
from fresh water, 284
Lumbriconereites (misprinted in text), 302
Lumbriculidae, 350, 361, 379
Lumbriculus, 379;
as host of Rotifer, 211 n.
Lumbricus, 349, 351, 356, 367, 368, 371, 389 f., 403 f.;
generative organs, 362;
cocoon, 365
Lunulites, 518;
vibracula, 487
Lurg, 317
Lycoridae, 315
Lysidice, 297, 320
MacGillivray, on Polyzoa, 519
M‘Intosh, on Nemertinea, 110 n., 115, 116;
on Phoronis, 454
Macraspis, 73
Macrobdella, 393, 406;
sense-body, 394
Macrorhynchus, 44, 47;
British species, 49
Macrostoma, 44, 47;
British species, 49
Macrostomatidae, 49
Magelona, 325;
haemerythrin in, 252
Magelonidae, 258, 325
Main-gut, of Leptoplana, 8, 13;
of Polyclads, 17
Lug-worm, castings of, 285;
as bait, 297
Lumbricaria, 302
Lumbricidae, 362, 371 f., 388
Lumbricobdella, 392
Lumbriconereis, 318, 320;
from fresh water, 284
Lumbriconereites (misprinted in text), 302
Lumbriculidae, 350, 361, 379
Lumbriculus, 379;
as host of Rotifer, 211 n.
Lumbricus, 349, 351, 356, 367, 368, 371, 389 f., 403 f.;
generative organs, 362;
cocoon, 365
Lunulites, 518;
vibracula, 487
Lurg, 317
Lycoridae, 315
Lysidice, 297, 320
MacGillivray, on Polyzoa, 519
M‘Intosh, on Nemertinea, 110 n., 115, 116;
on Phoronis, 454
Macraspis, 73
Macrobdella, 393, 406;
sense-body, 394
Macrorhynchus, 44, 47;
British species, 49
Macrostoma, 44, 47;
British species, 49
Macrostomatidae, 49
Magelona, 325;
haemerythrin in, 252
Magelonidae, 258, 325
Main-gut, of Leptoplana, 8, 13;
of Polyclads, 17
Page 595
Malacobdella, 101;
description of, 119;
M. grossa, 110, 119;
excretory system of, 108
Malacocotylea (= Digenea), 73
Maldanidae (= Clymenidae), 258, 332;
shields, 259;
anal funnel, 259;
chaetae, 266, 267, 268;
colour, 293
Male, of Rotifers, 199, 200, 217, 223 n.;
of Echiuroids, 438
Malleate, 210
Malleoramate, 210, 211
Malleus, 210
Mammals, Trematodes of, 62, 63, 67-70, 71 f.;
Cestodes of, 77-84, 89-91;
Nematodes of, 163;
Acanthocephala of, 183, 184
Man, Trematode-parasites of, 63, 68-70;
Cestodes of, 74, 78-81, 83, 89 f.;
Nematodes of, 125, 139, 140, 143, 145, 147, 163;
Gordius of, 173;
Echinorhynchus of, 183
Man, De, on free-living Nematodes, 157
Manayunkia, 284, 339 n.
Mandible, of avicularium, 482, 524
Manson, on Filaria, 149
Manubrium, 210
Marginal groove, of Leptoplana, 15
Maricola, 30, 32, 42
Marine, Rotifers, 226;
Oligochaeta, 366;
Leeches, 406
Marphysa, 276, 319;
as bait, 297;
as host, 297
description of, 119;
M. grossa, 110, 119;
excretory system of, 108
Malacocotylea (= Digenea), 73
Maldanidae (= Clymenidae), 258, 332;
shields, 259;
anal funnel, 259;
chaetae, 266, 267, 268;
colour, 293
Male, of Rotifers, 199, 200, 217, 223 n.;
of Echiuroids, 438
Malleate, 210
Malleoramate, 210, 211
Malleus, 210
Mammals, Trematodes of, 62, 63, 67-70, 71 f.;
Cestodes of, 77-84, 89-91;
Nematodes of, 163;
Acanthocephala of, 183, 184
Man, Trematode-parasites of, 63, 68-70;
Cestodes of, 74, 78-81, 83, 89 f.;
Nematodes of, 125, 139, 140, 143, 145, 147, 163;
Gordius of, 173;
Echinorhynchus of, 183
Man, De, on free-living Nematodes, 157
Manayunkia, 284, 339 n.
Mandible, of avicularium, 482, 524
Manson, on Filaria, 149
Manubrium, 210
Marginal groove, of Leptoplana, 15
Maricola, 30, 32, 42
Marine, Rotifers, 226;
Oligochaeta, 366;
Leeches, 406
Marphysa, 276, 319;
as bait, 297;
as host, 297
Page 596
Mastax, of Rotifers, 199, 210
Masterman, on Chaetognatha, 190;
on Phoronis, 461
Mastigocerca, 225
Mastigophora, 518, 529;
vibraculum, 484
Mastobranchus, gill of, 268, 331
Matzdorf, on Leeches, 369
Maupas, on Rotifers, 217
Mbalolo, 297
Meckelia asulcata, 111
Mecynostoma, 49
Median pore, in Cheilostomata, 484, 524
Megadrili, 373, 374, 380 f.
Megalotrocha, 221
Megapora, 530
Megascolex, 351, 372, 381, 383
Megascolides, 349, 358, 372, 382;
body-wall and nephridia, 357
Mégnin, on parasites, 164
Meissner, on Polyzoa, 493
Melania, Coabangia in shell of, 284
Melanin, 292
Melicerta, 202, 205, 206, 210, 215, 218, 219, 221, 226;
early description of, 197
Melicertaceae, 203, 221
Melicertidae, 201, 203, 205, 211, 213, 221
Melinna, 330
Membranipora, 481, 492, 518, 519, 523, 528, 530;
phosphorescence, 478;
function of aperture, 500;
larva, 509, 510;
variation, 516
Membraniporella, 518, 524, 528
Menipea, 518, 526, 527
Mermis, 131, 150, 160, 163
Mermithidae, 150, 163
Masterman, on Chaetognatha, 190;
on Phoronis, 461
Mastigocerca, 225
Mastigophora, 518, 529;
vibraculum, 484
Mastobranchus, gill of, 268, 331
Matzdorf, on Leeches, 369
Maupas, on Rotifers, 217
Mbalolo, 297
Meckelia asulcata, 111
Mecynostoma, 49
Median pore, in Cheilostomata, 484, 524
Megadrili, 373, 374, 380 f.
Megalotrocha, 221
Megapora, 530
Megascolex, 351, 372, 381, 383
Megascolides, 349, 358, 372, 382;
body-wall and nephridia, 357
Mégnin, on parasites, 164
Meissner, on Polyzoa, 493
Melania, Coabangia in shell of, 284
Melanin, 292
Melicerta, 202, 205, 206, 210, 215, 218, 219, 221, 226;
early description of, 197
Melicertaceae, 203, 221
Melicertidae, 201, 203, 205, 211, 213, 221
Melinna, 330
Membranipora, 481, 492, 518, 519, 523, 528, 530;
phosphorescence, 478;
function of aperture, 500;
larva, 509, 510;
variation, 516
Membraniporella, 518, 524, 528
Menipea, 518, 526, 527
Mermis, 131, 150, 160, 163
Mermithidae, 150, 163
Page 597
Meromyarii, 129, 137, 142
Mertens, on Polyclads, 6, 23
Mesobdella, 407
Mesocestoides, 91;
M. lineatus, life-history, 84;
specific characters, 90
Mesonemertini, 112
Mesostoma, 44, 45;
reproduction, 48;
British species, 49
Mesostomatidae, 49
Mesotrochal larva, 325
Mesozoa, 92 f.
Metamerism, 249
Metamorphosis, in Polycladida, 16, 28;
in Trematodes, 5, 66 f.;
in Cestodes, 5, 74, 76, 87-89;
in Phoronis, 459;
in Polyzoa, 512
Metanemertini, 112
Metastatica (= Holostomatidae), 73;
life-histories, 64
Metopidia, 200, 225
Metschnikoff, on Orthonectida, 94;
on Nemertines, 99;
on Chaetosomatidae, 158
Meyer, on Polychaeta, 261
Michaelsen, on Earthworms, 349, 353, 359, 370 f., 375, 385
Microchaeta, 362
Microcodides, 224
Microcodon, 202, 215, 224, 230
Microcodonidae, 202, 220 n., 224
Microcotyle, 73;
eggs of M. labracis, 58
Microcotylinae, 73
Microdrili, 373, 374 f.
Microplana, 34, 42
Mertens, on Polyclads, 6, 23
Mesobdella, 407
Mesocestoides, 91;
M. lineatus, life-history, 84;
specific characters, 90
Mesonemertini, 112
Mesostoma, 44, 45;
reproduction, 48;
British species, 49
Mesostomatidae, 49
Mesotrochal larva, 325
Mesozoa, 92 f.
Metamerism, 249
Metamorphosis, in Polycladida, 16, 28;
in Trematodes, 5, 66 f.;
in Cestodes, 5, 74, 76, 87-89;
in Phoronis, 459;
in Polyzoa, 512
Metanemertini, 112
Metastatica (= Holostomatidae), 73;
life-histories, 64
Metopidia, 200, 225
Metschnikoff, on Orthonectida, 94;
on Nemertines, 99;
on Chaetosomatidae, 158
Meyer, on Polychaeta, 261
Michaelsen, on Earthworms, 349, 353, 359, 370 f., 375, 385
Microchaeta, 362
Microcodides, 224
Microcodon, 202, 215, 224, 230
Microcodonidae, 202, 220 n., 224
Microcotyle, 73;
eggs of M. labracis, 58
Microcotylinae, 73
Microdrili, 373, 374 f.
Microplana, 34, 42
Page 598
Micropora, 518, 530;
zooecium, 523
Microporella, 516, 518, 519, 529;
avicularia, 484, 485;
median pore, 501
Microscolex, 372, 382, 383, 384
Microstoma, 44;
asexual reproduction, 44;
sexual organs, 47;
British species, 49
Microstomatidae, 49
Micrura, 101, 114;
British species, 111
Migrations, of Trematode-larvae, 5, 52, 63 f.;
of Cestode-larvae, 5, 74, 83, 87
Millson, on Oligochaeta, 368, 387
Millsonia, 382 f.
Milne-Edwards, on Polyzoa, 475
Mimicry, in Polychaeta, 293 f.
Mimosella, 518, 532;
movement of zooecia, 481
Molluscoidea, 475
Molops, host of Gordius, 172
Monhystera, 160
Moniez, on Cestodes, 84 n., 85;
on Earthworms, 369
Moniezia, 83, 91;
characters of genus, 90;
M. alba, M. benedeni, M. denticulata, 90;
M. expansa, 83, 90;
M. neumani, M. oblongiceps, M. planissima, M. trigonophora, 90
Moniligaster, 359, 380, 402
Moniligastridae, 361, 373, 380
Monkey, parasites of, 145
Monocotyle, 73
Monocotylinae, 73
Monogenea (Monogenetic Trematodes), 5, 53;
zooecium, 523
Microporella, 516, 518, 519, 529;
avicularia, 484, 485;
median pore, 501
Microscolex, 372, 382, 383, 384
Microstoma, 44;
asexual reproduction, 44;
sexual organs, 47;
British species, 49
Microstomatidae, 49
Micrura, 101, 114;
British species, 111
Migrations, of Trematode-larvae, 5, 52, 63 f.;
of Cestode-larvae, 5, 74, 83, 87
Millson, on Oligochaeta, 368, 387
Millsonia, 382 f.
Milne-Edwards, on Polyzoa, 475
Mimicry, in Polychaeta, 293 f.
Mimosella, 518, 532;
movement of zooecia, 481
Molluscoidea, 475
Molops, host of Gordius, 172
Monhystera, 160
Moniez, on Cestodes, 84 n., 85;
on Earthworms, 369
Moniezia, 83, 91;
characters of genus, 90;
M. alba, M. benedeni, M. denticulata, 90;
M. expansa, 83, 90;
M. neumani, M. oblongiceps, M. planissima, M. trigonophora, 90
Moniligaster, 359, 380, 402
Moniligastridae, 361, 373, 380
Monkey, parasites of, 145
Monocotyle, 73
Monocotylinae, 73
Monogenea (Monogenetic Trematodes), 5, 53;
Page 599
classification, 73
Mononchus, 154
Monoophorum striatum, 50
Monopora vivipara, 117
Monoporus rubropunctatus, 49;
reproductive organs of, 47
Monostomatidae, 73
Monostomum, 71, 73;
life-history, 72
Monostyla, 225, 226
Monotidae, 50
Monotus, 36;
British species, 50;
M. fuscus, 45;
habits, 46
Monozoa, 91
Montgomery, on Stichostemma eilhardii, 118
Monura, 225
Morren, on Earthworms, 347
Moseley, on Land Planarians, 7, 35 n., 37;
on Pelagonemertes, 101, 114
Movements, in Rotifers, etc., 206, 235
Moxon, on Rotifers, 198
Mucro, 522, 525
Mucronella, 518, 522, 528, 529, 530, 531
Müller, F., on Triclads, 37;
on Polyzoa, 493
Müller, O. F., on Turbellaria, 6;
on Rotifers, 197;
on Oligochaeta, 348, 352
Müller's larva, 16, 28, 29
Muscles, of Leptoplana, 12;
of intestine in Polyclads, 24;
of Nemertinea, 102, 103;
of Nematoda, 128;
of Gordiidae, 165;
of Chaetognatha, 187;
Mononchus, 154
Monoophorum striatum, 50
Monopora vivipara, 117
Monoporus rubropunctatus, 49;
reproductive organs of, 47
Monostomatidae, 73
Monostomum, 71, 73;
life-history, 72
Monostyla, 225, 226
Monotidae, 50
Monotus, 36;
British species, 50;
M. fuscus, 45;
habits, 46
Monozoa, 91
Montgomery, on Stichostemma eilhardii, 118
Monura, 225
Morren, on Earthworms, 347
Moseley, on Land Planarians, 7, 35 n., 37;
on Pelagonemertes, 101, 114
Movements, in Rotifers, etc., 206, 235
Moxon, on Rotifers, 198
Mucro, 522, 525
Mucronella, 518, 522, 528, 529, 530, 531
Müller, F., on Triclads, 37;
on Polyzoa, 493
Müller, O. F., on Turbellaria, 6;
on Rotifers, 197;
on Oligochaeta, 348, 352
Müller's larva, 16, 28, 29
Muscles, of Leptoplana, 12;
of intestine in Polyclads, 24;
of Nemertinea, 102, 103;
of Nematoda, 128;
of Gordiidae, 165;
of Chaetognatha, 187;
Page 600
of Rotifers, etc., 206, 233, 237;
of Nereis, 247, 249 f.;
of Polyzoa, 469, 470, 472, 499, 500—see also Body-wall
Musculo-glandular organ, in Triclads, 39, 40
Myrianida, 280, 308;
gemmiparity, 279, 280;
markings, 293
Myrianites, 302
Mytilia, 225, 226
Myxicola, 338;
tori uncinigeri, 268;
eyes, 272;
otocyst, 273;
tube, 285;
supposed mimicry, 294
Myzostoma, anatomy, 342 f.;
M. cirriferum, 343;
M. glabrum, 342
Myzostomaria, 241;
structure and affinities, 342 f.
Myzostomatidae, 342
Naidomorpha (= Naididae and Naids), 348, 352, 375 f., 377, 378, 400;
chaetae, 350, 367;
reproductive organs, 361;
asexual reproduction, 281, 377
Nais, 348, 377;
chaetae, 350
Nannodrilus, 382 f.
Natatory chaetae, of Nereidae, 277;
of Syllidae, 278, 307
Nathusius, on parasites, 63, 163
Nauphanta, 314, 315
Nebalia, Rotifers parasitic on, 225
Nectochaeta, 291
Nectonema agile, 164, 168, 169, 173
Nemathelminthes, 123 f., 168
of Nereis, 247, 249 f.;
of Polyzoa, 469, 470, 472, 499, 500—see also Body-wall
Musculo-glandular organ, in Triclads, 39, 40
Myrianida, 280, 308;
gemmiparity, 279, 280;
markings, 293
Myrianites, 302
Mytilia, 225, 226
Myxicola, 338;
tori uncinigeri, 268;
eyes, 272;
otocyst, 273;
tube, 285;
supposed mimicry, 294
Myzostoma, anatomy, 342 f.;
M. cirriferum, 343;
M. glabrum, 342
Myzostomaria, 241;
structure and affinities, 342 f.
Myzostomatidae, 342
Naidomorpha (= Naididae and Naids), 348, 352, 375 f., 377, 378, 400;
chaetae, 350, 367;
reproductive organs, 361;
asexual reproduction, 281, 377
Nais, 348, 377;
chaetae, 350
Nannodrilus, 382 f.
Natatory chaetae, of Nereidae, 277;
of Syllidae, 278, 307
Nathusius, on parasites, 63, 163
Nauphanta, 314, 315
Nebalia, Rotifers parasitic on, 225
Nectochaeta, 291
Nectonema agile, 164, 168, 169, 173
Nemathelminthes, 123 f., 168
Page 601
Nematobothrium, 4, 55, 71, 73
Nematoda, 123;
anatomy, 124 f.;
embryology, 135;
classification, 136;
life-history of, 159 f.
Nematogen, 94;
Secondary Nematogen, 94
Nematomorpha, 123, 164 f.
Nematoxys, 139, 142, 161, 163
Nematozoa, 137
Nemertes, British species, 110;
deposition of ova and spermatozoa in, 116
Nemertinea, affinities, 119;
anatomy, 102;
body-wall, 102;
breeding, 116;
cephalic slits and cerebral organs, 107, 273;
circulatory system, 106, 107;
classification, 109 f.;
colour, 102;
contractility, 102;
development, 113;
diagram, 104;
digestive system, 103;
excretory system, 108, 108;
external characters, 101;
food, 115;
fresh-water forms, 101, 118;
generative organs, 109;
geographical distribution, 117;
habitat, 100;
habits, 114;
land forms, 101, 117;
locomotion, 114, 115;
nervous system, 105, 106;
parasitic forms, 101, 119;
Nematoda, 123;
anatomy, 124 f.;
embryology, 135;
classification, 136;
life-history of, 159 f.
Nematogen, 94;
Secondary Nematogen, 94
Nematomorpha, 123, 164 f.
Nematoxys, 139, 142, 161, 163
Nematozoa, 137
Nemertes, British species, 110;
deposition of ova and spermatozoa in, 116
Nemertinea, affinities, 119;
anatomy, 102;
body-wall, 102;
breeding, 116;
cephalic slits and cerebral organs, 107, 273;
circulatory system, 106, 107;
classification, 109 f.;
colour, 102;
contractility, 102;
development, 113;
diagram, 104;
digestive system, 103;
excretory system, 108, 108;
external characters, 101;
food, 115;
fresh-water forms, 101, 118;
generative organs, 109;
geographical distribution, 117;
habitat, 100;
habits, 114;
land forms, 101, 117;
locomotion, 114, 115;
nervous system, 105, 106;
parasitic forms, 101, 119;
Page 602
pelagic forms, 101, 114;
proboscis, 100, 101 f., 103, 104, 110, 115;
regeneration, 115;
sense organs, 101, 106, 107;
size, 100
Nemertodrilus, 360
Nemertoscolex, 444
Neodrilus, 384
Neorhynchidae, 184
Neorhynchus clavaeceps, 178, 181, 184;
N. agilis, 184
Nephelis, 392 f., 397, 399, 401, 403, 405
Nephridium, of Archiannelida, 243, 244;
of Nereis, 253;
of Arenicola, 253, 254;
of Polychaeta, 253;
dimorphism of, in Polychaeta, 269;
thoracic, of Sabelliformia, 306;
of Terebellidae, 327;
of Chlorhaemidae, 334;
of Myzostoma, 344;
of Oligochaeta, 356 f., 381 f., 400;
of Leeches, 399;
of Gephyrea—see Brown tubes;
of Phoronis, 456
Nephthydidae, 258, 317
Nephthys, 317;
nephridium, 254;
prostomium, 259, 260;
head, 262;
tentacles, 262;
peristomium, 263;
parapodium, 264, 265;
cirrus, 265;
gill, 268;
jaws, 270;
habitat, 286;
proboscis, 100, 101 f., 103, 104, 110, 115;
regeneration, 115;
sense organs, 101, 106, 107;
size, 100
Nemertodrilus, 360
Nemertoscolex, 444
Neodrilus, 384
Neorhynchidae, 184
Neorhynchus clavaeceps, 178, 181, 184;
N. agilis, 184
Nephelis, 392 f., 397, 399, 401, 403, 405
Nephridium, of Archiannelida, 243, 244;
of Nereis, 253;
of Arenicola, 253, 254;
of Polychaeta, 253;
dimorphism of, in Polychaeta, 269;
thoracic, of Sabelliformia, 306;
of Terebellidae, 327;
of Chlorhaemidae, 334;
of Myzostoma, 344;
of Oligochaeta, 356 f., 381 f., 400;
of Leeches, 399;
of Gephyrea—see Brown tubes;
of Phoronis, 456
Nephthydidae, 258, 317
Nephthys, 317;
nephridium, 254;
prostomium, 259, 260;
head, 262;
tentacles, 262;
peristomium, 263;
parapodium, 264, 265;
cirrus, 265;
gill, 268;
jaws, 270;
habitat, 286;
Page 603
as bait, 297
Nereidae, 258, 315;
palps, 260;
colour, 292
Nereidiformia, 258, 303;
vascular system, 252;
anal cirri, 259;
prostomium, 259, 260;
tentacles, 262;
peristomial cirri, 263;
parapodium, 264 f.;
cirri, 265;
chaetae, 266;
jaws, 269;
eyes, 272;
ciliated organ, 273;
regeneration in, 283;
food, 296;
fossil, 301 f.
Nereilepas, 317
Nereis, 246, 299, 301, 316 f.;
anatomy, 245 f., 247 f.;
transverse section, 247;
parapodium, 246, 247, 265, 317;
chaetae, 246;
head, 246, 248, 316;
alimentary canal, 249 f., 251;
jaws, 248, 250, 270, 316;
nervous system, 254, 255;
eye, 255;
vascular system, 247, 251;
dorsal ciliated organ, 247, 254, 256;
nephridium, 253;
reproduction, 256;
sexually mature, 276, 276 f.;
sexual dimorphism and Heteroneid phase, 276 f.;
epitokous (= epigamous) and atokous phase, 277 n.;
Nereidae, 258, 315;
palps, 260;
colour, 292
Nereidiformia, 258, 303;
vascular system, 252;
anal cirri, 259;
prostomium, 259, 260;
tentacles, 262;
peristomial cirri, 263;
parapodium, 264 f.;
cirri, 265;
chaetae, 266;
jaws, 269;
eyes, 272;
ciliated organ, 273;
regeneration in, 283;
food, 296;
fossil, 301 f.
Nereilepas, 317
Nereis, 246, 299, 301, 316 f.;
anatomy, 245 f., 247 f.;
transverse section, 247;
parapodium, 246, 247, 265, 317;
chaetae, 246;
head, 246, 248, 316;
alimentary canal, 249 f., 251;
jaws, 248, 250, 270, 316;
nervous system, 254, 255;
eye, 255;
vascular system, 247, 251;
dorsal ciliated organ, 247, 254, 256;
nephridium, 253;
reproduction, 256;
sexually mature, 276, 276 f.;
sexual dimorphism and Heteroneid phase, 276 f.;
epitokous (= epigamous) and atokous phase, 277 n.;
Page 604
from fresh water, 284;
burrow, 286;
pigment, 292;
as bait, 297;
commensalism, 298;
as host, 299;
British species, 316 f.
Nereites, 302
Nerine, 299, 322;
habitat, 286;
N. vulgaris, head, 322
Nerve plexus of Nemertinea, 103, 105
Nervous system, of Leptoplana, 13, 14;
of Polyclads, 26, 30;
of Planaria lactea, 39;
reduced in parasitic Rhabdocoels, 45;
of Temnocephala, 54;
of Polystomatidae, 56;
of Cestodes, 75, 86;
of Nemertinea, 105, 106;
of Nematoda, 127;
of Gordiidae, 166;
of Acanthocephala, 177;
of Chaetognatha, 187;
of Rotifera, etc., 215, 234, 237;
of Archiannelida, 243, 244;
of Polychaeta, 254;
visceral, of Polychaeta, 255;
of Oligochaeta, 353, 374;
of Gephyrea, 416, 431, 437, 440, 445;
of Phoronis, 456;
of Polyzoa, 471
Neumann, on parasites, 164
Neuropodium, 246, 247, 264, 266, 268
Newton, on zoo-geographical regions, 372
Nicolea, 328;
gill, 329
burrow, 286;
pigment, 292;
as bait, 297;
commensalism, 298;
as host, 299;
British species, 316 f.
Nereites, 302
Nerine, 299, 322;
habitat, 286;
N. vulgaris, head, 322
Nerve plexus of Nemertinea, 103, 105
Nervous system, of Leptoplana, 13, 14;
of Polyclads, 26, 30;
of Planaria lactea, 39;
reduced in parasitic Rhabdocoels, 45;
of Temnocephala, 54;
of Polystomatidae, 56;
of Cestodes, 75, 86;
of Nemertinea, 105, 106;
of Nematoda, 127;
of Gordiidae, 166;
of Acanthocephala, 177;
of Chaetognatha, 187;
of Rotifera, etc., 215, 234, 237;
of Archiannelida, 243, 244;
of Polychaeta, 254;
visceral, of Polychaeta, 255;
of Oligochaeta, 353, 374;
of Gephyrea, 416, 431, 437, 440, 445;
of Phoronis, 456;
of Polyzoa, 471
Neumann, on parasites, 164
Neuropodium, 246, 247, 264, 266, 268
Newton, on zoo-geographical regions, 372
Nicolea, 328;
gill, 329
Page 605
Nicomache, 332;
tail, 332;
tube, 287;
N. lumbricalis, colour, 292;
distribution, 299
Nitsche, on Polyzoa, 475 n., 478, 500
Nitzschia, 56, 73
Norman, on Polyzoa, 475
Norodonia, 492
Notamia, 518, 526
Noteus, 225
Notholca, 225, 226
Notocotyle, 73
Notomastus, 331;
chaetae, 268
Notommata, 217, 224, 226
Notommatidae, 200, 205, 207, 215, 223, 224
Notophyllum, colour, 293
Notopodium, 246, 247, 264, 265, 268
Notops, 200, 224
Notopygos, 259
Nuchal cirri of Eunicidae, 318;
Nuchal organ—see Ciliated pits
Ocnerodrilus, 383
Octobothrium, 56, 73
Octochaetus, 358, 384
Octocotylinae, 73
Octotrocha, 221
Odontosyllis, reproduction of, 278;
as host, 297.
Oecistes, 205, 206, 221
Oenonites, 302
Oesophageal glands, 271, 358
Ogmogaster, 73
Oka, on Hirudinea, 399 f.;
on Polyzoa, 500
tail, 332;
tube, 287;
N. lumbricalis, colour, 292;
distribution, 299
Nitsche, on Polyzoa, 475 n., 478, 500
Nitzschia, 56, 73
Norman, on Polyzoa, 475
Norodonia, 492
Notamia, 518, 526
Noteus, 225
Notholca, 225, 226
Notocotyle, 73
Notomastus, 331;
chaetae, 268
Notommata, 217, 224, 226
Notommatidae, 200, 205, 207, 215, 223, 224
Notophyllum, colour, 293
Notopodium, 246, 247, 264, 265, 268
Notops, 200, 224
Notopygos, 259
Nuchal cirri of Eunicidae, 318;
Nuchal organ—see Ciliated pits
Ocnerodrilus, 383
Octobothrium, 56, 73
Octochaetus, 358, 384
Octocotylinae, 73
Octotrocha, 221
Odontosyllis, reproduction of, 278;
as host, 297.
Oecistes, 205, 206, 221
Oenonites, 302
Oesophageal glands, 271, 358
Ogmogaster, 73
Oka, on Hirudinea, 399 f.;
on Polyzoa, 500
Page 606
Olfactory pits, in Polyclads, 26;
in Triclads, 36
Oligocelis, 42
Oligochaeta, 241, 347 f.;
external characters, 348;
body-wall, 349;
chaetae, 350, 351;
branchiae, 352;
nervous system, 353;
sense-organs, 354;
coelom and vascular system, 355;
excretory organs, 356;
alimentary canal, 358;
reproductive organs, 360;
habitat, 365;
phosphorescence, 368;
distribution, 369;
classification, 373;
Rotifers parasitic on, 227
Oligocladus, 19, 22
Oligognathus, 297
Ollulanus, 142;
O. tricuspis, 144, 161
Omalostoma, 49
Onchnesoma, 422, 423, 426, 430, 447
Onchocotyle, 73
Oncholaimus, 157
Onchosphaera-larva of Cestodes, 87, 88
Onuphin, 290
Onuphis, 290, 318, 319;
O. conchylega, tube, 287
Onychochaeta, 388;
chaeta, 351
Onyx, 131
Ootype, in Polystomum, 59.
Operculum, of Serpulidae, 261, 276, 339;
of Spirorbis, as brood-pouch, 261, 276;
in Triclads, 36
Oligocelis, 42
Oligochaeta, 241, 347 f.;
external characters, 348;
body-wall, 349;
chaetae, 350, 351;
branchiae, 352;
nervous system, 353;
sense-organs, 354;
coelom and vascular system, 355;
excretory organs, 356;
alimentary canal, 358;
reproductive organs, 360;
habitat, 365;
phosphorescence, 368;
distribution, 369;
classification, 373;
Rotifers parasitic on, 227
Oligocladus, 19, 22
Oligognathus, 297
Ollulanus, 142;
O. tricuspis, 144, 161
Omalostoma, 49
Onchnesoma, 422, 423, 426, 430, 447
Onchocotyle, 73
Oncholaimus, 157
Onchosphaera-larva of Cestodes, 87, 88
Onuphin, 290
Onuphis, 290, 318, 319;
O. conchylega, tube, 287
Onychochaeta, 388;
chaeta, 351
Onyx, 131
Ootype, in Polystomum, 59.
Operculum, of Serpulidae, 261, 276, 339;
of Spirorbis, as brood-pouch, 261, 276;
Page 607
of Cheilostomata, 466, 477, 481, 482, 522, 524
Opesia, 524
Ophelia, 299, 332;
eggs, 275;
coelomic corpuscles, 252
Opheliidae, 258, 331;
gill, 265;
ciliated pits, 272
Ophiodromus, 308;
O. flexuosus, parasitic, 297
Ophryotrocha, 310, 320;
pelagic, 291;
genital organs, 274
Opisthotrema, 73
Opistoma, 50
Orbigny, D', on Polyzoa, 519, 520
Orifice, of zooecium, 466, 469, 470, 524;
secondary, 522, 524
Örley, on classification of Nematodes, 137
Orthonectidae, 13, 92, 94 f.
Otocyst (and Otolith), of Turbellaria, 26;
of Nemertinea, 106, 110;
of Polychaeta, 273
Otomesostoma, 46, 49
Otoplana, 50
Oudemans, on Nemertinea, 108
Ovary (and Oviduct), of Leptoplana, 11, 14, 16;
of Polyclads, 27;
of Planaria, 38, 39;
of Rhabdocoelida, 47;
of Temnocephala, 54;
of Polystomatidae, 57;
of Diplozoon, 60;
of Gyrodactylus, 61;
of Distomum macrostomum, 65;
of Calliobothrium, 75;
of Archigetes, 76;
Opesia, 524
Ophelia, 299, 332;
eggs, 275;
coelomic corpuscles, 252
Opheliidae, 258, 331;
gill, 265;
ciliated pits, 272
Ophiodromus, 308;
O. flexuosus, parasitic, 297
Ophryotrocha, 310, 320;
pelagic, 291;
genital organs, 274
Opisthotrema, 73
Opistoma, 50
Orbigny, D', on Polyzoa, 519, 520
Orifice, of zooecium, 466, 469, 470, 524;
secondary, 522, 524
Örley, on classification of Nematodes, 137
Orthonectidae, 13, 92, 94 f.
Otocyst (and Otolith), of Turbellaria, 26;
of Nemertinea, 106, 110;
of Polychaeta, 273
Otomesostoma, 46, 49
Otoplana, 50
Oudemans, on Nemertinea, 108
Ovary (and Oviduct), of Leptoplana, 11, 14, 16;
of Polyclads, 27;
of Planaria, 38, 39;
of Rhabdocoelida, 47;
of Temnocephala, 54;
of Polystomatidae, 57;
of Diplozoon, 60;
of Gyrodactylus, 61;
of Distomum macrostomum, 65;
of Calliobothrium, 75;
of Archigetes, 76;
Page 608
of Schistocephalus, 86;
of Rhopalura, 95;
of Myzostoma, 343—see also Reproductive organs
Ovicell, in Cheilostomata, 466, 466, 468, 481, 482, 484, 522 f., 525;
in Cyclostomata, 479, 480, 521, 525
Oviduct—see Ovary
Owenia, 325
Ox, parasites of, 79, 83, 125, 139, 140, 143
Oxysoma, 139, 142
Oxyuris, 129, 131, 135, 139, 141, 160;
O. ambigua, 141;
O. curvula, 141, 163;
O. diesingi, 141, 142;
O. vermicularis, 141, 163;
O. blattae, O. blatticola, O. hydrophili, O. megatyphlon,
O. spirotheca, 142
Paddle worm, 313
Paedogenesis, 151
Pagenstecher, on Nemertinea, 99
Palaemonetes, host of Nectonema, 174
Palaeonemertea, 109, 112;
characters, 111;
development, 113
Palaeozoic, Serpulidae, 301;
Eunicidae, 302;
Polyzoa, 520
Paleae, of Sabellaria, 267
Palmicellaria, 527, 528
Palolo viridis, as food, 297
Palps, of Nereis, 248, 255;
nerves to, 254;
of Polychaeta, 260 f.;
development of, in Sabelliformia, 275;
of Hermelliformia, 306;
of Syllidae, 307
Paludicella, 492, 494, 501, 502, 505, 518
of Rhopalura, 95;
of Myzostoma, 343—see also Reproductive organs
Ovicell, in Cheilostomata, 466, 466, 468, 481, 482, 484, 522 f., 525;
in Cyclostomata, 479, 480, 521, 525
Oviduct—see Ovary
Owenia, 325
Ox, parasites of, 79, 83, 125, 139, 140, 143
Oxysoma, 139, 142
Oxyuris, 129, 131, 135, 139, 141, 160;
O. ambigua, 141;
O. curvula, 141, 163;
O. diesingi, 141, 142;
O. vermicularis, 141, 163;
O. blattae, O. blatticola, O. hydrophili, O. megatyphlon,
O. spirotheca, 142
Paddle worm, 313
Paedogenesis, 151
Pagenstecher, on Nemertinea, 99
Palaemonetes, host of Nectonema, 174
Palaeonemertea, 109, 112;
characters, 111;
development, 113
Palaeozoic, Serpulidae, 301;
Eunicidae, 302;
Polyzoa, 520
Paleae, of Sabellaria, 267
Palmicellaria, 527, 528
Palolo viridis, as food, 297
Palps, of Nereis, 248, 255;
nerves to, 254;
of Polychaeta, 260 f.;
development of, in Sabelliformia, 275;
of Hermelliformia, 306;
of Syllidae, 307
Paludicella, 492, 494, 501, 502, 505, 518
Page 609
Paludicola, 30, 42
Panthalis, 313
Paragnaths, 248, 250, 316
Parapodium, of Nereis, 246, 247;
of Polychaeta, 264 f.;
of Heteronereid, 276, 277;
muscles of, 247;
glands of, 249, 314;
of Myzostoma, 342
Paraseison, 212, 225, 226
Parasitic, Turbellaria, 51;
Polyclads, 22;
Triclads, 32;
Rhabdocoela, 45, 51;
Nemertinea, 101, 119;
Rotifers, 204, 227;
Polychaeta, 297;
Leeches, 406
Parasitism, effect on the parasite, 161, 177;
effects on the host, 162
Parenchyma, in Leptoplana, 11, 12;
of Müller's larva, 29;
in Triclads, 41;
in Acoela, 42;
in Cestodes, 85, 86
Parovaria, of Phagocata, 38 n.
Parthenogenesis, amongst Rotifers, 200
Pectinaria, 330;
body, 259;
tube, 285, 287;
P. auricoma, tube, 288;
P. belgica, 330
Pectinatella, 496, 497, 505, 512, 518;
statoblast, 502
Pedalion, 200, 201, 206, 211, 216, 223, 224, 225, 228, 230
Pedalionidae, 223
Pedetes, 224
Panthalis, 313
Paragnaths, 248, 250, 316
Parapodium, of Nereis, 246, 247;
of Polychaeta, 264 f.;
of Heteronereid, 276, 277;
muscles of, 247;
glands of, 249, 314;
of Myzostoma, 342
Paraseison, 212, 225, 226
Parasitic, Turbellaria, 51;
Polyclads, 22;
Triclads, 32;
Rhabdocoela, 45, 51;
Nemertinea, 101, 119;
Rotifers, 204, 227;
Polychaeta, 297;
Leeches, 406
Parasitism, effect on the parasite, 161, 177;
effects on the host, 162
Parenchyma, in Leptoplana, 11, 12;
of Müller's larva, 29;
in Triclads, 41;
in Acoela, 42;
in Cestodes, 85, 86
Parovaria, of Phagocata, 38 n.
Parthenogenesis, amongst Rotifers, 200
Pectinaria, 330;
body, 259;
tube, 285, 287;
P. auricoma, tube, 288;
P. belgica, 330
Pectinatella, 496, 497, 505, 512, 518;
statoblast, 502
Pedalion, 200, 201, 206, 211, 216, 223, 224, 225, 228, 230
Pedalionidae, 223
Pedetes, 224
Page 610
Pedicellina, 487, 488, 490, 506, 507, 518;
larva, 510, 513;
budding, 514;
on Polychaeta, 299
Pelagic, Nemertinea, 101, 114;
Chaetognatha, 189; Rotifera, 226;
Polychaeta, 291, 294, 314;
larvae of Polychaeta, 300, of Polyzoa, 520
Pelagobia, 314
Pelagonemertes, 101, 114
Pelodera, 129, 131, 133
Pelodrilus, 369, 377
Pelodytes, 134
Penis, of Leptoplana, 14, 15;
of Polyclads, 27;
of Planaria, 38, 39;
of Rhabdocoelida, 47;
of Temnocephala, 54;
of Calliobothrium, 75;
of Schistocephalus (cirrus-sac), 86
Pennant, on Hirudinea, 406 n.
Pereyaslawzewa, on Acoela, 44 n.
Pergens, on Polyzoa, 500
Perichaeta, 351, 357, 358, 372, 381, 381 f., 388, 394, 403
Perichaetidae, 357, 362, 380
Perienteric, blood-sinus, 252
Perionyx, 381
Perissogaster, 383
Peristome, 481, 482, 522, 524
Peristomial (tentacular) cirri, of Nereis, 248;
of Polychaeta, 263;
nerves to, 254
Peristomium, of Nereis, 248;
of Polychaeta, 263;
of Sabellidae, 336
Perrier, on Oligochaeta, 367, 385
Petalostoma, 422, 426, 430, 447
larva, 510, 513;
budding, 514;
on Polychaeta, 299
Pelagic, Nemertinea, 101, 114;
Chaetognatha, 189; Rotifera, 226;
Polychaeta, 291, 294, 314;
larvae of Polychaeta, 300, of Polyzoa, 520
Pelagobia, 314
Pelagonemertes, 101, 114
Pelodera, 129, 131, 133
Pelodrilus, 369, 377
Pelodytes, 134
Penis, of Leptoplana, 14, 15;
of Polyclads, 27;
of Planaria, 38, 39;
of Rhabdocoelida, 47;
of Temnocephala, 54;
of Calliobothrium, 75;
of Schistocephalus (cirrus-sac), 86
Pennant, on Hirudinea, 406 n.
Pereyaslawzewa, on Acoela, 44 n.
Pergens, on Polyzoa, 500
Perichaeta, 351, 357, 358, 372, 381, 381 f., 388, 394, 403
Perichaetidae, 357, 362, 380
Perienteric, blood-sinus, 252
Perionyx, 381
Perissogaster, 383
Peristome, 481, 482, 522, 524
Peristomial (tentacular) cirri, of Nereis, 248;
of Polychaeta, 263;
nerves to, 254
Peristomium, of Nereis, 248;
of Polychaeta, 263;
of Sabellidae, 336
Perrier, on Oligochaeta, 367, 385
Petalostoma, 422, 426, 430, 447
Page 611
Petromyzon, host of Gordius, 173
Petta, intestine of, 271
Phagocata, 31, 32
Phalacrophorus, 314
Phanerocephala, 258, 303
Pharynx, 4;
of Leptoplana, 8, 9, 12, 14;
of Polyclads, 17, 24;
of Discocelis, 23;
development of, in Polyclads, 29, 30;
of Triclads, 31, 37, 39;
of Temnocephala, 53, 54;
of Polystomatidae, 56;
of Digenea, 62, 64;
of Nereis, 249, 250, 251;
of Polychaeta, 269
Phascolion, 423, 425, 428
Phascolosoma, 416, 420, 423, 425, 428, 447;
as host of Loxosoma, 489
Philippi, on Hirudinea, 406
Philodina, 208, 222, 227
Philodinidae, 222
Phoronis, 450 f., 451, 452, 453, 455;
habits, 451;
anatomy, 453 f., 457;
development, 458, 458;
species, 460;
affinities, 461, 512
Phosphorescence (and light-producing organs), in Rotifers, 226;
in Polychaeta, 272, 295, 296;
in Oligochaeta, 368;
in Polyzoa, 478
Photodrilus, 368, 383
Photogen (light-producing organ), of Polyophthalmus, 272;
of Tomopteris, 296, 315
Phreodrilus, 369, 379
Phreoryctes, 367, 377
Petta, intestine of, 271
Phagocata, 31, 32
Phalacrophorus, 314
Phanerocephala, 258, 303
Pharynx, 4;
of Leptoplana, 8, 9, 12, 14;
of Polyclads, 17, 24;
of Discocelis, 23;
development of, in Polyclads, 29, 30;
of Triclads, 31, 37, 39;
of Temnocephala, 53, 54;
of Polystomatidae, 56;
of Digenea, 62, 64;
of Nereis, 249, 250, 251;
of Polychaeta, 269
Phascolion, 423, 425, 428
Phascolosoma, 416, 420, 423, 425, 428, 447;
as host of Loxosoma, 489
Philippi, on Hirudinea, 406
Philodina, 208, 222, 227
Philodinidae, 222
Phoronis, 450 f., 451, 452, 453, 455;
habits, 451;
anatomy, 453 f., 457;
development, 458, 458;
species, 460;
affinities, 461, 512
Phosphorescence (and light-producing organs), in Rotifers, 226;
in Polychaeta, 272, 295, 296;
in Oligochaeta, 368;
in Polyzoa, 478
Photodrilus, 368, 383
Photogen (light-producing organ), of Polyophthalmus, 272;
of Tomopteris, 296, 315
Phreodrilus, 369, 379
Phreoryctes, 367, 377
Page 612
Phreoryctidae, 376
Phylactella, 528, 530
Phylactolaemata, 476, 493 f., 518;
lophophore, 476, 495;
occurrence, 493;
movements, 494, 496 f.;
reproduction, 501, 506, 507;
larva, 511, 512;
distribution, 493, 504;
affinities, 512
Phyllacanthinae, 91
Phyllobothrinae, 91
Phyllobothrium, 76 n., 91
Phyllocotyle, 73
Phyllodoce, 313, 314;
head, 262, 263:
eggs, 275, 314 n.;
colours, 291, 292;
parapodium, 264;
chaeta, 267
Phyllodocidae, 258, 313;
parapodial cirri, 266;
as food, 297;
eggs, 314;
colours, 292, 293
Phyllodocites, 302
Phyllonella, 73
Phymosoma, 413, 420, 421, 423 f., 425, 426
Physaloptera, 163
Pig, parasites of, 68, 79, 139, 147, 184
Pigments, of Polychaeta, 291 f.;
of Gephyrea, 435
Pike, Trematode of, 62;
Cestode of, 81, 84
Pilidium larva, 113, 113, 229, 230
Pionosyllis, 308
Piscicola, 393, 406
Phylactella, 528, 530
Phylactolaemata, 476, 493 f., 518;
lophophore, 476, 495;
occurrence, 493;
movements, 494, 496 f.;
reproduction, 501, 506, 507;
larva, 511, 512;
distribution, 493, 504;
affinities, 512
Phyllacanthinae, 91
Phyllobothrinae, 91
Phyllobothrium, 76 n., 91
Phyllocotyle, 73
Phyllodoce, 313, 314;
head, 262, 263:
eggs, 275, 314 n.;
colours, 291, 292;
parapodium, 264;
chaeta, 267
Phyllodocidae, 258, 313;
parapodial cirri, 266;
as food, 297;
eggs, 314;
colours, 292, 293
Phyllodocites, 302
Phyllonella, 73
Phymosoma, 413, 420, 421, 423 f., 425, 426
Physaloptera, 163
Pig, parasites of, 68, 79, 139, 147, 184
Pigments, of Polychaeta, 291 f.;
of Gephyrea, 435
Pike, Trematode of, 62;
Cestode of, 81, 84
Pilidium larva, 113, 113, 229, 230
Pionosyllis, 308
Piscicola, 393, 406
Page 613
Pista, 328;
gill of, 329
Pits, ciliated, of Polychaeta, 272, 273
Placostegus, colour, 292;
from deep sea, 300
Placunella, 73
Plagiochaeta, 358, 381, 384
Plagiostoma, 46;
British species, 50
Plagiostomatidae, 50
Planaria, 30, 31 f., 39;
British species, 42
Planarians, 3, 7;
Dinophilus, compared with, 242, 243
Planariidae, 42
Planctoplana, 19
Plankton, Rotifers in, 225
Planocera, 18, 19, 20
Planoceridae, 19, 23
Planorbis, host of Gordius, 173
Plants, parasites on, 154, 155, 157, 160
Plasmodium, nature of, in Orthonectids, 94
Plate, on Rotifers, 198, 225 n.
Platyaspis, 73
Platycotyle, 73
Platyhelminthes, 3 f.;
Nemertinea classed with, 119
Plectanocotyle, 73
Plectus, 160
Pleionogaster, 381
Plerocercoid larva, 84
Plessis, du, on Tetrastemma lacustre, 101 n., 118
Pleurocotyle, 73
Pleurotrocha, 224, 226
Ploesoma, 212, 225
Ploima, 202, 203, 212, 213, 216, 220, 223, 226, 227
Plumatella, 493, 494, 499, 503-505, 518, 519;
gill of, 329
Pits, ciliated, of Polychaeta, 272, 273
Placostegus, colour, 292;
from deep sea, 300
Placunella, 73
Plagiochaeta, 358, 381, 384
Plagiostoma, 46;
British species, 50
Plagiostomatidae, 50
Planaria, 30, 31 f., 39;
British species, 42
Planarians, 3, 7;
Dinophilus, compared with, 242, 243
Planariidae, 42
Planctoplana, 19
Plankton, Rotifers in, 225
Planocera, 18, 19, 20
Planoceridae, 19, 23
Planorbis, host of Gordius, 173
Plants, parasites on, 154, 155, 157, 160
Plasmodium, nature of, in Orthonectids, 94
Plate, on Rotifers, 198, 225 n.
Platyaspis, 73
Platycotyle, 73
Platyhelminthes, 3 f.;
Nemertinea classed with, 119
Plectanocotyle, 73
Plectus, 160
Pleionogaster, 381
Plerocercoid larva, 84
Plessis, du, on Tetrastemma lacustre, 101 n., 118
Pleurocotyle, 73
Pleurotrocha, 224, 226
Ploesoma, 212, 225
Ploima, 202, 203, 212, 213, 216, 220, 223, 226, 227
Plumatella, 493, 494, 499, 503-505, 518, 519;
Page 614
protrusion of polypides, 499;
statoblasts, 499, 502, 503;
larva, 512
Podal membrane, of Spionidae, 322
Podaxonia, 461
Polyarthra, 201, 224, 226
Polybostrichus, 280
Polycelis, 30, 31, 40, 42
Polychaeta, 241, 245 f.;
classification, 257, 258, 303 f,;
head, 248, 259 f.;
parapodium, 246, 264 f.;
chaetae, 246, 266 f.;
coelomic fluid, 252;
nervous system, 254;
sense-organs, 255, 272;
ciliated pits, 272;
alimentary canal, with pharynx, 249, 250, 251, 269, 270, 271;
oesophageal glands, 271 f.;
nephridium, 253, 254, 269, 274;
genital duct, 254, 269;
genital cells, 256, 273 f.;
hermaphrodite, 273;
regeneration, 278, 282;
habits, 285;
carnivorous, 304;
distribution, 299;
from fresh water, 284;
from deep sea, 300;
pelagic, 291, 314;
boring, 287;
tubes, 287;
pigments, 291;
colours, 291 f.;
warning colours, 294;
protective devices and mimicry, 293;
phosphorescent, 295;
statoblasts, 499, 502, 503;
larva, 512
Podal membrane, of Spionidae, 322
Podaxonia, 461
Polyarthra, 201, 224, 226
Polybostrichus, 280
Polycelis, 30, 31, 40, 42
Polychaeta, 241, 245 f.;
classification, 257, 258, 303 f,;
head, 248, 259 f.;
parapodium, 246, 264 f.;
chaetae, 246, 266 f.;
coelomic fluid, 252;
nervous system, 254;
sense-organs, 255, 272;
ciliated pits, 272;
alimentary canal, with pharynx, 249, 250, 251, 269, 270, 271;
oesophageal glands, 271 f.;
nephridium, 253, 254, 269, 274;
genital duct, 254, 269;
genital cells, 256, 273 f.;
hermaphrodite, 273;
regeneration, 278, 282;
habits, 285;
carnivorous, 304;
distribution, 299;
from fresh water, 284;
from deep sea, 300;
pelagic, 291, 314;
boring, 287;
tubes, 287;
pigments, 291;
colours, 291 f.;
warning colours, 294;
protective devices and mimicry, 293;
phosphorescent, 295;
Page 615
food of, 296, 299;
as bait, 296, 297;
as food for man, 297;
commensalism, 297 f.;
as bait, 296, 297;
as food for man, 297;
commensalism, 297 f.;
Page 616
parasitic, 297 f.;
as hosts, 299;
extinct, 301, 302;
larva, 274, 276, 300;
provisional chaetae, 274
Polychoerus, 49;
development of, 44 n.
Polycirrus, 330;
habits of, 285;
P. aurantiacus, warning colours, 294;
phosphorescence, 295;
P. haematodes, coelomic corpuscles, 253
Polycladida (Polyclads), 4 f., 7;
classification, 16 f.;
development, 28 f.;
British species, 19, 20, 22
Polycladus, 42
Polycotyle, 73
Polydora (= Leucodore), 323;
frontal ridge, 260;
head, 261;
special chaetae, 267;
with Heliopora, 298;
P. ciliata, borings, 287
Polydoridae, 258, 323
Polygordius, 242, 244;
development, 245
Polymnia, 328
Polymorphism, of Nereis, 277
Polymyarii, 137, 142
Polynoe 310;
segments 258;
parapodium, 265;
jaws, 270;
anus, 259;
nephridium, 254;
habits, 286;
as hosts, 299;
extinct, 301, 302;
larva, 274, 276, 300;
provisional chaetae, 274
Polychoerus, 49;
development of, 44 n.
Polycirrus, 330;
habits of, 285;
P. aurantiacus, warning colours, 294;
phosphorescence, 295;
P. haematodes, coelomic corpuscles, 253
Polycladida (Polyclads), 4 f., 7;
classification, 16 f.;
development, 28 f.;
British species, 19, 20, 22
Polycladus, 42
Polycotyle, 73
Polydora (= Leucodore), 323;
frontal ridge, 260;
head, 261;
special chaetae, 267;
with Heliopora, 298;
P. ciliata, borings, 287
Polydoridae, 258, 323
Polygordius, 242, 244;
development, 245
Polymnia, 328
Polymorphism, of Nereis, 277
Polymyarii, 137, 142
Polynoe 310;
segments 258;
parapodium, 265;
jaws, 270;
anus, 259;
nephridium, 254;
habits, 286;
Page 617
as ectoparasites or commensals, 294, 298, 325;
distribution, 299, 300;
British species, 299, 310 f.;
P. squamata, 309;
elytron, 310;
P. clava, elytron, 310;
P. imbricata, elytron, 311
Polynoina (= Polynoids), 309;
head, 262;
chaetae, 266, 267;
jaw, 270;
intestine, 271; eggs, 275;
sexual dimorphism, 276 n.;
tubes, 285;
colours, 291, 292;
protective resemblance, 294;
phosphorescence, 295, 296;
food, 296;
parasitic and commensal, 297, 325;
elytra, 275, 294, 295, 299, 309 f.
Polyodontes, 313 n.
Polyophthalmus, 332;
segmental eyes, 272, 296;
otocyst, 273
Polype à pannache, 496
Polypide, 468, 469, 474, 488, 523;
retraction and protrusion, 498 f.
Polypide-bud, 468, 472, 487, 496, 499, 501, 510;
connected with reproduction, 507
Polypostia, 19;
penes, 27
Polystomatidae, 53, 55, 73
Polystomatinae, 73
Polystomum, 55, 57;
life-history, 58, 59
Polyzoa, 465 f., 475;
external characters, 465 f., 479 f.;
distribution, 299, 300;
British species, 299, 310 f.;
P. squamata, 309;
elytron, 310;
P. clava, elytron, 310;
P. imbricata, elytron, 311
Polynoina (= Polynoids), 309;
head, 262;
chaetae, 266, 267;
jaw, 270;
intestine, 271; eggs, 275;
sexual dimorphism, 276 n.;
tubes, 285;
colours, 291, 292;
protective resemblance, 294;
phosphorescence, 295, 296;
food, 296;
parasitic and commensal, 297, 325;
elytra, 275, 294, 295, 299, 309 f.
Polyodontes, 313 n.
Polyophthalmus, 332;
segmental eyes, 272, 296;
otocyst, 273
Polype à pannache, 496
Polypide, 468, 469, 474, 488, 523;
retraction and protrusion, 498 f.
Polypide-bud, 468, 472, 487, 496, 499, 501, 510;
connected with reproduction, 507
Polypostia, 19;
penes, 27
Polystomatidae, 53, 55, 73
Polystomatinae, 73
Polystomum, 55, 57;
life-history, 58, 59
Polyzoa, 465 f., 475;
external characters, 465 f., 479 f.;
Page 618
anatomy, 468 f., 469;
brown bodies, 471 f., 472;
history, 474 f.;
classification, 475 f., 515, 517 f.;
occurrence, 477 f.;
avicularia and vibracula, 482;
enemies, 486;
Entoprocta, 487;
fresh water, 492 f.;
reproduction, 501, 506;
development, 509;
affinities, 461, 509, 510;
metamorphosis, 512;
budding, 514;
distribution, 493, 504, 519;
palaeontology, 520;
terminology, 523;
determination of British genera, 505, 521, 525
Pomatoceros, habitat, 300, 340
Pompholyx, 201, 203, 225
Pontobdella, 393, 401, 404, 406
Pontodora, 314
Pontodrilus, 366, 370, 383
Pontoscolex, 350, 366, 387 f.;
chaeta, 351
Pore, in Polyzoa, 471, 482, 522, 524;
median, 484, 524;
dorsal, 348
Porella, 516, 518, 522, 527, 529
Porina, 518, 527, 529
Potamilla, 338
Praeoral lobe (= Prostomium), 245, 439
Predaceous worms, 304
Priapuloidea, 412, 446;
anatomy, 430;
classification, 432;
habits, 433
brown bodies, 471 f., 472;
history, 474 f.;
classification, 475 f., 515, 517 f.;
occurrence, 477 f.;
avicularia and vibracula, 482;
enemies, 486;
Entoprocta, 487;
fresh water, 492 f.;
reproduction, 501, 506;
development, 509;
affinities, 461, 509, 510;
metamorphosis, 512;
budding, 514;
distribution, 493, 504, 519;
palaeontology, 520;
terminology, 523;
determination of British genera, 505, 521, 525
Pomatoceros, habitat, 300, 340
Pompholyx, 201, 203, 225
Pontobdella, 393, 401, 404, 406
Pontodora, 314
Pontodrilus, 366, 370, 383
Pontoscolex, 350, 366, 387 f.;
chaeta, 351
Pore, in Polyzoa, 471, 482, 522, 524;
median, 484, 524;
dorsal, 348
Porella, 516, 518, 522, 527, 529
Porina, 518, 527, 529
Potamilla, 338
Praeoral lobe (= Prostomium), 245, 439
Predaceous worms, 304
Priapuloidea, 412, 446;
anatomy, 430;
classification, 432;
habits, 433
Page 619
Priapulus, 430, 431, 432;
anatomy, 430 f.
Pristina, 377
Proales, 204, 224, 226, 227
Proboscidae, 49;
occurrence, 44
Proboscis, of Nemertinea, 100, 101 f., 103 f.;
of Hoplonemertea, 104, 110;
opening by mouth, 117, 119;
severance of, 116;
of Acanthocephala, 174 f.;
of Rotifers, 203;
of Kinorhyncha, 237;
of Echiuroidea, 434
Proboscis-pore of Nemertinea, 102, 103
Proboscis-sheath of Nemertinea, 103, 103 f.
Procerodes, 42
Procerodidae, 42
Procerus, host of Gordius, 172
Procotylea, 36, 42
Proglottis, 5, 74, 75, 79, 85
Promesostoma, occurrence, 44;
British species, 49
Proporidae, 49
Proporus venenosus, 49
Prorhynchidae, 49
Prorhynchus sphyrocephalus, terrestrial habit, 44;
P. stagnalis, 49
Prosorhochmus claparedii, 110, 114, 117
Prostate-gland, of Leptoplana, 16;
of Polyclads, 30;
of Planaria, 39;
of Rhabdocoela, 47;
of Oligochaeta, 361
Prostheceraeus, 19, 22;
spermatophores, 27
Prosthiostomatidae, 19
anatomy, 430 f.
Pristina, 377
Proales, 204, 224, 226, 227
Proboscidae, 49;
occurrence, 44
Proboscis, of Nemertinea, 100, 101 f., 103 f.;
of Hoplonemertea, 104, 110;
opening by mouth, 117, 119;
severance of, 116;
of Acanthocephala, 174 f.;
of Rotifers, 203;
of Kinorhyncha, 237;
of Echiuroidea, 434
Proboscis-pore of Nemertinea, 102, 103
Proboscis-sheath of Nemertinea, 103, 103 f.
Procerodes, 42
Procerodidae, 42
Procerus, host of Gordius, 172
Procotylea, 36, 42
Proglottis, 5, 74, 75, 79, 85
Promesostoma, occurrence, 44;
British species, 49
Proporidae, 49
Proporus venenosus, 49
Prorhynchidae, 49
Prorhynchus sphyrocephalus, terrestrial habit, 44;
P. stagnalis, 49
Prosorhochmus claparedii, 110, 114, 117
Prostate-gland, of Leptoplana, 16;
of Polyclads, 30;
of Planaria, 39;
of Rhabdocoela, 47;
of Oligochaeta, 361
Prostheceraeus, 19, 22;
spermatophores, 27
Prosthiostomatidae, 19
Page 620
Prosthiostomum, 17, 18, 19, 24
Prostomial tentacles, 248, 262
Prostomium, 241;
of Dinophilus, 243;
of Polygordius, 244;
of Trochosphere, 245;
of Nereis, 248;
of Polychaeta, 259;
of Glyceridae, 320;
of Terebellidae, 327;
of Oligochaeta, 348
Protodrilus, 242, 244
Protonemertini, 112
Protula, 341;
genital organs, 273, 274;
eggs, 275
Prouho, on Polyzoa, 489, 507 f.
Provisional chaetae, 274
Provortex, British species, 50
Proxenetes, 44;
British species, 49
Pruvot, on Polychaeta, 261
Psamathe, 300, 308
Psammolyce, 313;
elytra, 294, 313
Pseudalius, 135, 142, 163
Pseudaxine, 73
Pseudoceridae, 19, 20
Pseudoceros, 19, 20
Pseudocotyle, 73
Pseudorhynchus bifidus, 49
Psygmobranchus, 341
Pterobranchia, 461
Pterodina, 200, 201, 203, 206, 211, 215, 216, 225, 226, 230
Pterodinidae, 201, 225
Pteroessa, 224
Pteronella, 73
Prostomial tentacles, 248, 262
Prostomium, 241;
of Dinophilus, 243;
of Polygordius, 244;
of Trochosphere, 245;
of Nereis, 248;
of Polychaeta, 259;
of Glyceridae, 320;
of Terebellidae, 327;
of Oligochaeta, 348
Protodrilus, 242, 244
Protonemertini, 112
Protula, 341;
genital organs, 273, 274;
eggs, 275
Prouho, on Polyzoa, 489, 507 f.
Provisional chaetae, 274
Provortex, British species, 50
Proxenetes, 44;
British species, 49
Pruvot, on Polychaeta, 261
Psamathe, 300, 308
Psammolyce, 313;
elytra, 294, 313
Pseudalius, 135, 142, 163
Pseudaxine, 73
Pseudoceridae, 19, 20
Pseudoceros, 19, 20
Pseudocotyle, 73
Pseudorhynchus bifidus, 49
Psygmobranchus, 341
Pterobranchia, 461
Pterodina, 200, 201, 203, 206, 211, 215, 216, 225, 226, 230
Pterodinidae, 201, 225
Pteroessa, 224
Pteronella, 73
Page 621
Pterostichus niger, infested by Gordius, 170, 170, 172
Pterosyllis, ciliated lappets, 273 n.
Pyriform organ, 509, 511
Quatrefages, on Gephyrea, 411, 445
Rabbit, parasites of, 141, 145
Ragworm, 322
Railliet, on Cestodes, 91
Rami, in Rotifers, 210
Rasping plate, of Eunicidae, 270
Rattulidae, 210, 225
Rattulus, 212, 225, 226
Ratzel, on Earthworms, 350
Red Cat, 316
Regeneration of lost parts, in Polyclads, 26;
in Triclads, 40;
in Cestodes, 77;
in Nemertinea, 115;
in Polychaeta, 278, 282;
in Oligochaeta, 348, 379;
in Polyzoa, 471, 488
Repetition of parts, 249
Replacement of species, 300
Reproduction (and Reproductive organs), of Leptoplana, 14 f.;
of Polyclads, 26, 30;
of Triclads, 31, 38, 39;
of Rhabdocoelida, 45, 47 f.;
of Temnocephala, 54;
of Polystomatidae, 57 f.;
of Diplozoon, 60;
of Digenea, 65;
of Calliobothrium, 75;
of Schistocephalus, 86;
of Mesozoa, 93 f.;
of Nemertinea, 102, 103, 104, 109;
of Nematoda, 134;
Pterosyllis, ciliated lappets, 273 n.
Pyriform organ, 509, 511
Quatrefages, on Gephyrea, 411, 445
Rabbit, parasites of, 141, 145
Ragworm, 322
Railliet, on Cestodes, 91
Rami, in Rotifers, 210
Rasping plate, of Eunicidae, 270
Rattulidae, 210, 225
Rattulus, 212, 225, 226
Ratzel, on Earthworms, 350
Red Cat, 316
Regeneration of lost parts, in Polyclads, 26;
in Triclads, 40;
in Cestodes, 77;
in Nemertinea, 115;
in Polychaeta, 278, 282;
in Oligochaeta, 348, 379;
in Polyzoa, 471, 488
Repetition of parts, 249
Replacement of species, 300
Reproduction (and Reproductive organs), of Leptoplana, 14 f.;
of Polyclads, 26, 30;
of Triclads, 31, 38, 39;
of Rhabdocoelida, 45, 47 f.;
of Temnocephala, 54;
of Polystomatidae, 57 f.;
of Diplozoon, 60;
of Digenea, 65;
of Calliobothrium, 75;
of Schistocephalus, 86;
of Mesozoa, 93 f.;
of Nemertinea, 102, 103, 104, 109;
of Nematoda, 134;
Page 622
of Nematomorpha, 166, 169;
of Acanthocephala, 178;
of Chaetognatha, 188;
of Rotifera, etc., 216, 234, 238;
of Archiannelida, 243 f.;
of Polychaeta, 253, 254, 256, 269, 273;
of Myzostoma, 343;
of Oligochaeta, 360;
of Leeches, 401;
of Gephyrea, 418, 431, 437;
of Phoronis, 457;
of Polyzoa, 471, 490, 501, 506—see also Ovary and Asexual
reproduction
Reptiles, parasites of, 163
Respiration, in Nereis, 252;
in Chaetopoda, 272;
in Gephyrea, 416
Retepora, 479, 515, 518, 527
Rhabdites (rods), of Leptoplana, 11, 12;
in Polyclads, 29;
in Triclads, 37;
absent in parasitic Rhabdocoela, 45;
in Temnocephala, 53, 54
Rhabditiformae, 137
Rhabditis, 154, 160;
R. nigrovenosa, 140, 155
Rhabdocoelida, 4, 7, 36, 42 f.;
occurrence and habits, 43;
parasitic forms, 44;
reproduction, 47;
classification, 49;
British species, 43, 44, 49
Rhabdogaster, 158
Rhabdonema nigrovenosum, 134, 136, 140, 151, 160, 161
Rhabdopleura, 461 f.
Rhinodrilus, 348
Rhinopidae, 220 n., 224
of Acanthocephala, 178;
of Chaetognatha, 188;
of Rotifera, etc., 216, 234, 238;
of Archiannelida, 243 f.;
of Polychaeta, 253, 254, 256, 269, 273;
of Myzostoma, 343;
of Oligochaeta, 360;
of Leeches, 401;
of Gephyrea, 418, 431, 437;
of Phoronis, 457;
of Polyzoa, 471, 490, 501, 506—see also Ovary and Asexual
reproduction
Reptiles, parasites of, 163
Respiration, in Nereis, 252;
in Chaetopoda, 272;
in Gephyrea, 416
Retepora, 479, 515, 518, 527
Rhabdites (rods), of Leptoplana, 11, 12;
in Polyclads, 29;
in Triclads, 37;
absent in parasitic Rhabdocoela, 45;
in Temnocephala, 53, 54
Rhabditiformae, 137
Rhabditis, 154, 160;
R. nigrovenosa, 140, 155
Rhabdocoelida, 4, 7, 36, 42 f.;
occurrence and habits, 43;
parasitic forms, 44;
reproduction, 47;
classification, 49;
British species, 43, 44, 49
Rhabdogaster, 158
Rhabdonema nigrovenosum, 134, 136, 140, 151, 160, 161
Rhabdopleura, 461 f.
Rhinodrilus, 348
Rhinopidae, 220 n., 224
Page 623
Rhinops, 224;
male of, 223 n.
Rhizopoda, as food for Polychaeta, 296
Rhizota, 220 n.
Rhombogen (form of Dicyemid), 93
Rhopalonaria, 521 n.
Rhopalophorus, 73
Rhopalura giardii, occurrence and structure, 94, 95;
R. intoshii, 94
Rhynchelmis, 365, 376
Rhynchobdellae, 396 f., 405
Rhynchodemidae, 35, 42
Rhynchodemus, 34, 35, 42
Rhynchopora, 531
Rhynchozoon, 529 n., 531
Riches, on British Nemertinea, 110;
on Malacobdella, 119
Rietsch, on Gephyrea, 443
Rockworm, 319
Rods—see Rhabdites
Rohde, on muscles of Nematoda, 128 f.
Rootlet, in Polyzoa, 485, 517
Rosa, on Oligochaeta, 364, 380, 385, 390
Rosette-plates, 471, 522
Rotifer, 201, 202, 210, 216, 222, 226, 227
Rotifera, 197 f.;
distribution, 200;
parasitic, 204;
digestive organs, 209;
renal organs, 213;
nervous system and sense organs, 215;
reproduction and development, 216;
classification, 220;
habits 226;
preservation, 228;
affinities, 229
Rousselet, on Rotifers, 198, 216, 228
male of, 223 n.
Rhizopoda, as food for Polychaeta, 296
Rhizota, 220 n.
Rhombogen (form of Dicyemid), 93
Rhopalonaria, 521 n.
Rhopalophorus, 73
Rhopalura giardii, occurrence and structure, 94, 95;
R. intoshii, 94
Rhynchelmis, 365, 376
Rhynchobdellae, 396 f., 405
Rhynchodemidae, 35, 42
Rhynchodemus, 34, 35, 42
Rhynchopora, 531
Rhynchozoon, 529 n., 531
Riches, on British Nemertinea, 110;
on Malacobdella, 119
Rietsch, on Gephyrea, 443
Rockworm, 319
Rods—see Rhabdites
Rohde, on muscles of Nematoda, 128 f.
Rootlet, in Polyzoa, 485, 517
Rosa, on Oligochaeta, 364, 380, 385, 390
Rosette-plates, 471, 522
Rotifer, 201, 202, 210, 216, 222, 226, 227
Rotifera, 197 f.;
distribution, 200;
parasitic, 204;
digestive organs, 209;
renal organs, 213;
nervous system and sense organs, 215;
reproduction and development, 216;
classification, 220;
habits 226;
preservation, 228;
affinities, 229
Rousselet, on Rotifers, 198, 216, 228
Page 624
Sabella, 299, 337; parapodium, 265;
habitat, 286;
tube, 287;
tube-building, 288;
colour, 293, 294;
S. saxicava, habits of, 287
Sabellaria, 341;
body, 259;
cirri, 265.;
tube, 287, 290;
S. alveolata, 259, 300;
S. spinulosa, paleae, 267, 300
Sabellidae, 258, 336;
head, 261;
chaetae, 266, 267;
regeneration, 283;
from fresh water, 284;
colour, 292
Sabelliformia, 258, 306, 336;
chlorocruorin in, 252; body, 259;
head, 260, 261;
uncini, 266, 267;
nephridia, 269, 306;
genital organs, 273;
development of gills, 275;
gland shields, 287
Saccobdella, 226
Sacconereis, 275, 276, 280
Saccosoma, 434, 440, 442
Sagitella, 321
Sagitta, 186, 186, 191, 534;
anatomy, 186 f., 188;
development, 189;
habits, 190;
species, 191, 193;
American species, 534
Salensky, on development of Nemertinea, 99;
habitat, 286;
tube, 287;
tube-building, 288;
colour, 293, 294;
S. saxicava, habits of, 287
Sabellaria, 341;
body, 259;
cirri, 265.;
tube, 287, 290;
S. alveolata, 259, 300;
S. spinulosa, paleae, 267, 300
Sabellidae, 258, 336;
head, 261;
chaetae, 266, 267;
regeneration, 283;
from fresh water, 284;
colour, 292
Sabelliformia, 258, 306, 336;
chlorocruorin in, 252; body, 259;
head, 260, 261;
uncini, 266, 267;
nephridia, 269, 306;
genital organs, 273;
development of gills, 275;
gland shields, 287
Saccobdella, 226
Sacconereis, 275, 276, 280
Saccosoma, 434, 440, 442
Sagitella, 321
Sagitta, 186, 186, 191, 534;
anatomy, 186 f., 188;
development, 189;
habits, 190;
species, 191, 193;
American species, 534
Salensky, on development of Nemertinea, 99;
Page 625
of Rotifers, 218
Salinella, 93, 96
Salivary glands, in Polyclads, 10, 24;
in Leeches, 396
Salmacina, 273, 341;
brood-pouch, 276;
fission, 281
Salpina, 200, 225
Salpinidae, 225
Sandmason, 328
Saxicava, Eulalia in borings of, 314
Scales, of Gastrotricha, 233
Scalibregma, 334
Scalibregmidae, 258, 334
Scapha, 259, 330
Scaridium, 201, 207, 225
Schistocephalus, 75, 91;
reproductive organs, 86;
larva, 84;
life-history, 78, 85
Schizocerca, 225
Schizogamy, in Syllidae, 278, 279, 281
Schizonemertea, 109;
characters, 111;
development, 113;
transverse section, 103
Schizoporella, 518, 527, 528, 529, 530, 531;
zooecium and avicularia, 482;
Leptoplana on, 22
Schizotheca, 482, 518, 529
Schmarda, on Oligochaeta, 366, 387
Schmidt, on Rhabdocoels, 6
Schneider, on life-history of certain Mesostoma, 48;
on classification of Nematoda, 129;
on oesophageal glands, 131;
on Strongylidae, 142
Schultze, on Polyclads, 13, 26;
Salinella, 93, 96
Salivary glands, in Polyclads, 10, 24;
in Leeches, 396
Salmacina, 273, 341;
brood-pouch, 276;
fission, 281
Salpina, 200, 225
Salpinidae, 225
Sandmason, 328
Saxicava, Eulalia in borings of, 314
Scales, of Gastrotricha, 233
Scalibregma, 334
Scalibregmidae, 258, 334
Scapha, 259, 330
Scaridium, 201, 207, 225
Schistocephalus, 75, 91;
reproductive organs, 86;
larva, 84;
life-history, 78, 85
Schizocerca, 225
Schizogamy, in Syllidae, 278, 279, 281
Schizonemertea, 109;
characters, 111;
development, 113;
transverse section, 103
Schizoporella, 518, 527, 528, 529, 530, 531;
zooecium and avicularia, 482;
Leptoplana on, 22
Schizotheca, 482, 518, 529
Schmarda, on Oligochaeta, 366, 387
Schmidt, on Rhabdocoels, 6
Schneider, on life-history of certain Mesostoma, 48;
on classification of Nematoda, 129;
on oesophageal glands, 131;
on Strongylidae, 142
Schultze, on Polyclads, 13, 26;
Page 626
on Nemertinea, 108, 109
Schultzia, 50
Schulze, F. E., Stichostemma found by, 118;
Trichoplax found by, 96
Scirtopoda, 200, 201, 203, 206, 207, 223
Sclerocheilus, 334
Sclerostomum, 163
Scoleciformia, 258, 305, 331 f.;
vascular system, 252;
buccal region, 269;
food of, 296
Scolecolepis, 299, 322
Scolex, 5, 74, 75 f., 89;
S. polymorphus, 77;
of Taenia solium, 79
Scolithus, 302
Scoloplos, 299, 321;
parapodium, 265;
habitat, 286
Scruparia, 527
Scrupocellaria, 517, 518, 519, 526;
vibracula, 477, 485, 517;
phosphorescence, 478;
larva, 511
Scutum, 525
Seals, parasites of, 142, 183
Sea-mat, 466, 477
Sea-mouse, 312
Secondary orifice, 522, 524
Sedentaria, 285
Segment, 241;
of Nereis, 246, 247
Seison, 226
Seisonaceae, 204, 216, 220 n., 225, 227
Seisonidae, 226
Selenaria, 518;
vibracula, 487
Schultzia, 50
Schulze, F. E., Stichostemma found by, 118;
Trichoplax found by, 96
Scirtopoda, 200, 201, 203, 206, 207, 223
Sclerocheilus, 334
Sclerostomum, 163
Scoleciformia, 258, 305, 331 f.;
vascular system, 252;
buccal region, 269;
food of, 296
Scolecolepis, 299, 322
Scolex, 5, 74, 75 f., 89;
S. polymorphus, 77;
of Taenia solium, 79
Scolithus, 302
Scoloplos, 299, 321;
parapodium, 265;
habitat, 286
Scruparia, 527
Scrupocellaria, 517, 518, 519, 526;
vibracula, 477, 485, 517;
phosphorescence, 478;
larva, 511
Scutum, 525
Seals, parasites of, 142, 183
Sea-mat, 466, 477
Sea-mouse, 312
Secondary orifice, 522, 524
Sedentaria, 285
Segment, 241;
of Nereis, 246, 247
Seison, 226
Seisonaceae, 204, 216, 220 n., 225, 227
Seisonidae, 226
Selenaria, 518;
vibracula, 487
Page 627
Selenka, on Sipunculids, 424 n., 447
Self-fertilisation, in certain Mesostoma, 48;
in Trematodes, 52, 58;
in Cestodes, 86
Semper, on excretory system of Nemertinea, 108;
on Geonemertes palaensis, 101 n., 117;
on mimicry in Polychaeta, 294
Sense-organs, of Leptoplana, 13;
of Polyclads, 26;
of Triclads, 36;
of Trematodes, 56, 86;
of Cestodes, 86;
of Nemertinea, 106;
of Nematoda, 128;
of Gordius, 166;
of Acanthocephala, 178;
of Chaetognatha, 188;
of Rotifera, etc., 215, 233, 234;
of Polychaeta, 255, 272;
of Oligochaeta, 354;
of Leeches, 395;
of Gephyrea, 417;
of Phoronis, 457
Septum, of Archiannelida, 244;
of Nereis, 249, 251;
of Polychaeta, 269;
of Chlorhaemidae, 334;
of Oligochaeta, 355;
of Gephyrea, 440
Serpula, 300, 339, 340;
fossil, 301;
tubes, 290, 301;
commensal with Polynoid, 298;
colour, 292
Serpulidae, 258, 339;
nerve cords, 255;
gills, 261;
Self-fertilisation, in certain Mesostoma, 48;
in Trematodes, 52, 58;
in Cestodes, 86
Semper, on excretory system of Nemertinea, 108;
on Geonemertes palaensis, 101 n., 117;
on mimicry in Polychaeta, 294
Sense-organs, of Leptoplana, 13;
of Polyclads, 26;
of Triclads, 36;
of Trematodes, 56, 86;
of Cestodes, 86;
of Nemertinea, 106;
of Nematoda, 128;
of Gordius, 166;
of Acanthocephala, 178;
of Chaetognatha, 188;
of Rotifera, etc., 215, 233, 234;
of Polychaeta, 255, 272;
of Oligochaeta, 354;
of Leeches, 395;
of Gephyrea, 417;
of Phoronis, 457
Septum, of Archiannelida, 244;
of Nereis, 249, 251;
of Polychaeta, 269;
of Chlorhaemidae, 334;
of Oligochaeta, 355;
of Gephyrea, 440
Serpula, 300, 339, 340;
fossil, 301;
tubes, 290, 301;
commensal with Polynoid, 298;
colour, 292
Serpulidae, 258, 339;
nerve cords, 255;
gills, 261;
Page 628
operculum, 261;
cirri, 265;
thoracic membrane, 266;
uncinus, 267;
fission, 281;
tube, 290;
colour, 292, 293;
from great depth, 300;
fossil, 301
Serpulite chalk, 301
Seta, of vibraculum, 484, 485, 486, 517, 524
Setosella, 530
Sharks, Trematodes of, 62, 72;
Cestodes of, 78
Sheep, parasites of, 67, 81, 82, 83
Sheldon, Miss, on Nemertinea, 99 f.
Shell-gland, of Leptoplana, 8, 9, 14, 16;
of Polyclads, 28;
of Trematodes, 59;
of Cestodes, 86
Shield, cuticular, of Polychaeta, 259;
of Sternaspis, 335;
glandular—see Gland shields.
Shipley, on Bipalium, 37;
on Nemathelminthes, 123 f.;
on Chaetognatha, 186 f., 534;
on Gephyrea, 411 f.;
on Phoronis, 450 f.
Sialis lutaria, host of Gordius, 171, 172;
host of Acanthocephala, 185
Side organs, of Carinellidae, 107
Siebold, von, on Tape-worms, 76
Sigalion, 313
Silliman, on Nemertinea, 101, 109, 118
Silurian, Polychaeta, 301
Sinus, in Polyzoa, 482, 484, 525
Siphon, of Capitelliformia, 272, 305;
cirri, 265;
thoracic membrane, 266;
uncinus, 267;
fission, 281;
tube, 290;
colour, 292, 293;
from great depth, 300;
fossil, 301
Serpulite chalk, 301
Seta, of vibraculum, 484, 485, 486, 517, 524
Setosella, 530
Sharks, Trematodes of, 62, 72;
Cestodes of, 78
Sheep, parasites of, 67, 81, 82, 83
Sheldon, Miss, on Nemertinea, 99 f.
Shell-gland, of Leptoplana, 8, 9, 14, 16;
of Polyclads, 28;
of Trematodes, 59;
of Cestodes, 86
Shield, cuticular, of Polychaeta, 259;
of Sternaspis, 335;
glandular—see Gland shields.
Shipley, on Bipalium, 37;
on Nemathelminthes, 123 f.;
on Chaetognatha, 186 f., 534;
on Gephyrea, 411 f.;
on Phoronis, 450 f.
Sialis lutaria, host of Gordius, 171, 172;
host of Acanthocephala, 185
Side organs, of Carinellidae, 107
Siebold, von, on Tape-worms, 76
Sigalion, 313
Silliman, on Nemertinea, 101, 109, 118
Silurian, Polychaeta, 301
Sinus, in Polyzoa, 482, 484, 525
Siphon, of Capitelliformia, 272, 305;
Page 629
of Gephyrea, 436
Siphonogaster, 353, 368
Siphonostoma, 334;
commensal, 298
Sipunculoidea, 412, 420, 446;
species, 426
Sipunculus, 425;
history, 411;
species, 426;
anatomy, 412 f., 413, 415;
development, 419, 419;
food, 422;
habits, 426
Size, of Cestodes, 5;
of Polyclads, 20;
of Land Planarians, 33;
of Cestodes, 75;
of Nemertinea, 100
Slavina, 377
Sluiter, on Gephyrea, 429, 447
Smitt, on Polyzoa, 516
Smittia, 518, 527, 529;
zooecium and avicularium, 482
Snakes, parasites of, 142
Solenopharyngidae, 50
Solenopharynx, 50
Solenophorinae, 91
Solenophorus, 91
Sorocelis, 42
Spadella, 186, 189, 192;
anatomy, 186 f.;
eggs, 189;
habits, 190;
species, 192, 194;
American species, 534
Spallanzani, on Oligochaeta, 348
Sparganophilus, 366, 386;
Siphonogaster, 353, 368
Siphonostoma, 334;
commensal, 298
Sipunculoidea, 412, 420, 446;
species, 426
Sipunculus, 425;
history, 411;
species, 426;
anatomy, 412 f., 413, 415;
development, 419, 419;
food, 422;
habits, 426
Size, of Cestodes, 5;
of Polyclads, 20;
of Land Planarians, 33;
of Cestodes, 75;
of Nemertinea, 100
Slavina, 377
Sluiter, on Gephyrea, 429, 447
Smitt, on Polyzoa, 516
Smittia, 518, 527, 529;
zooecium and avicularium, 482
Snakes, parasites of, 142
Solenopharyngidae, 50
Solenopharynx, 50
Solenophorinae, 91
Solenophorus, 91
Sorocelis, 42
Spadella, 186, 189, 192;
anatomy, 186 f.;
eggs, 189;
habits, 190;
species, 192, 194;
American species, 534
Spallanzani, on Oligochaeta, 348
Sparganophilus, 366, 386;
Page 630
anatomy, 355.
Spatangus, as host, 298
Spencer, on Land-Planarians, 34;
on earthworms, 349, 380
Spengel, on Gephyrea, 440
Spermatheca, of Dinophilus, 243;
of Oligochaeta, 362, 363, 364
Spermatophores, 27, 402
Spermiducal gland, 361
Sphaerodoridae, 320
Sphaerodorum, 321
Sphaerosyllis, 308
Sphaerularia, 150, 153, 160, 161
Sphyranura, 73;
setae in, 56
Spine, of Polyzoa, 481, 523 f., 524
Spinther, 318
Spio, 322
Spionidae, 258, 321;
larva, 274, 275
Spioniformia, 258, 304, 321;
peristomial cirri, 263;
gill, 265;
chaetae, 266, 267;
eyes, 272;
food, 296
Spirographin, 290
Spirographis, 338;
substance of tube, 290
Spiroptera, 147, 163;
S. reticulata, 149;
S. obtusa, 161;
S. alata, 163
Spirorbis, 340, 341;
operculum, 261, 341;
genital organs, 273, 274;
brood-pouch, 261, 276;
Spatangus, as host, 298
Spencer, on Land-Planarians, 34;
on earthworms, 349, 380
Spengel, on Gephyrea, 440
Spermatheca, of Dinophilus, 243;
of Oligochaeta, 362, 363, 364
Spermatophores, 27, 402
Spermiducal gland, 361
Sphaerodoridae, 320
Sphaerodorum, 321
Sphaerosyllis, 308
Sphaerularia, 150, 153, 160, 161
Sphyranura, 73;
setae in, 56
Spine, of Polyzoa, 481, 523 f., 524
Spinther, 318
Spio, 322
Spionidae, 258, 321;
larva, 274, 275
Spioniformia, 258, 304, 321;
peristomial cirri, 263;
gill, 265;
chaetae, 266, 267;
eyes, 272;
food, 296
Spirographin, 290
Spirographis, 338;
substance of tube, 290
Spiroptera, 147, 163;
S. reticulata, 149;
S. obtusa, 161;
S. alata, 163
Spirorbis, 340, 341;
operculum, 261, 341;
genital organs, 273, 274;
brood-pouch, 261, 276;
Page 631
fossil, 301; shell, 341
Spirosperma, 378;
chaeta, 350
Spirulaea, 301
Sporocysts, 92;
of Distomum macrostomum, 64, 65;
of D. hepaticum, 67;
hosts of, 71
Staggers, induced by Coenurus, 82
Statoblast, 493, 499, 501 f., 506;
sessile, 502;
germination, 501, 503, 514;
resemblance to ephippian ova, 493
Steenstrup, on Tape-worms, 76
Steganoporella, 530
Stelechopoda, 344
Stelechopus, 342
Stenostoma, 44, 49;
asexual reproduction, 44
Stephanoceros, 202, 205, 210, 213, 220, 221
Stephanops, 225
Stercutus, 376
Sternaspidae, 258, 335;
nephridia of, 305
Sternaspis, 335, 411, 445;
anatomy, 335, 336;
shape, 259;
shield, 259;
head, 264;
chaetae, 265;
gills, 268;
intestine, 271;
compared with Gephyrea, 336, 447, 449
Sthenelais, 299, 300, 309, 313
Stichostemma eilhardii, 118
Stilesia, 91;
generic characters, 90;
Spirosperma, 378;
chaeta, 350
Spirulaea, 301
Sporocysts, 92;
of Distomum macrostomum, 64, 65;
of D. hepaticum, 67;
hosts of, 71
Staggers, induced by Coenurus, 82
Statoblast, 493, 499, 501 f., 506;
sessile, 502;
germination, 501, 503, 514;
resemblance to ephippian ova, 493
Steenstrup, on Tape-worms, 76
Steganoporella, 530
Stelechopoda, 344
Stelechopus, 342
Stenostoma, 44, 49;
asexual reproduction, 44
Stephanoceros, 202, 205, 210, 213, 220, 221
Stephanops, 225
Stercutus, 376
Sternaspidae, 258, 335;
nephridia of, 305
Sternaspis, 335, 411, 445;
anatomy, 335, 336;
shape, 259;
shield, 259;
head, 264;
chaetae, 265;
gills, 268;
intestine, 271;
compared with Gephyrea, 336, 447, 449
Sthenelais, 299, 300, 309, 313
Stichostemma eilhardii, 118
Stilesia, 91;
generic characters, 90;
Page 632
S. centripunctata, 91;
S. globipunctata, 91
Stock, asexual, of Autolytus, 279;
of Myrianida, 281
Stolc, on Oligochaeta, 360
Stolon, 480, 488, 518, 525
Stolonata, 518 n.
Stomatopora, 518, 532
Stork, parasites of, 63, 163
Strobila, 75, 76
Strobilation, 76
Strodtmann, on Chaetognatha, 191
Stromatoporoids, 520
Strongylidae, 131, 142
Strongylus, 129, 142, 143, 160, 163;
S. filaria, 132;
S. tetracanthus, 163
Stuhlmann, on Polyzoa, 493
Stuhlmannia, 359, 386
Stylaria, 348, 377
Stylets of Nemertine proboscis, 104, 110
Stylochoplana, 18, 19, 20
Stylochus, 19;
development, 28
Stylostomum, 19, 22
Sub-cuticle, 125, 175
Submalleate, 210, 211
Succinea putris, infested by larvae of Distomum macrostomum, 64, 66
Sucker, of Leptoplana, 8, 16 n.;
of Triclads, 35, 36;
of Temnocephala, 53, 54;
of Monogenea, 53, 56, 57, 60;
of Digenea, 62, 64, 65, 69;
of Cestodes, 75, 79;
of Dinophilus, 243;
of Chaetopterus, 324;
of Myzostoma, 342;
S. globipunctata, 91
Stock, asexual, of Autolytus, 279;
of Myrianida, 281
Stolc, on Oligochaeta, 360
Stolon, 480, 488, 518, 525
Stolonata, 518 n.
Stomatopora, 518, 532
Stork, parasites of, 63, 163
Strobila, 75, 76
Strobilation, 76
Strodtmann, on Chaetognatha, 191
Stromatoporoids, 520
Strongylidae, 131, 142
Strongylus, 129, 142, 143, 160, 163;
S. filaria, 132;
S. tetracanthus, 163
Stuhlmann, on Polyzoa, 493
Stuhlmannia, 359, 386
Stylaria, 348, 377
Stylets of Nemertine proboscis, 104, 110
Stylochoplana, 18, 19, 20
Stylochus, 19;
development, 28
Stylostomum, 19, 22
Sub-cuticle, 125, 175
Submalleate, 210, 211
Succinea putris, infested by larvae of Distomum macrostomum, 64, 66
Sucker, of Leptoplana, 8, 16 n.;
of Triclads, 35, 36;
of Temnocephala, 53, 54;
of Monogenea, 53, 56, 57, 60;
of Digenea, 62, 64, 65, 69;
of Cestodes, 75, 79;
of Dinophilus, 243;
of Chaetopterus, 324;
of Myzostoma, 342;
Page 633
of larva of Polyzoa, 509, 511
Summer-eggs, of Mesostoma, 48;
of Rotifera, 216
Sutroa, 376, 380
Swim-bladder, of Syllidae, 272
Swimming, of Leptoplana, 9, 10;
of Polyclads, 23;
of Rotifers, etc., 206, 235
Syllidae, 258, 306;
palps, 260;
tentacles, 262;
head, 262;
parapodium, 264;
jaw, 270, 271;
alimentary tract, 271;
swim-bladder, 272;
asexual reproduction, 278 f., 279;
regeneration, 278, 283;
colours, 293;
phosphorescence, 296;
ancestral, 303
Syllis, 274, 307;
development, 278;
S. armillaris, 307;
S. ramosa, 282;
S. vivipara, 276
Synapta, bearing Rotifers, 222, 227
Synchaeta, 200, 204 f., 224, 226
Synchaetidae, 223, 224
Syncoelidium, 33, 42
Syncytium, 125
Syngamus trachealis, 130, 142, 144, 161, 163, 164
Syrinx, 411
Taenia, 74, 78, 79, 91;
life-histories of species of, 83;
table of species, 89;
Summer-eggs, of Mesostoma, 48;
of Rotifera, 216
Sutroa, 376, 380
Swim-bladder, of Syllidae, 272
Swimming, of Leptoplana, 9, 10;
of Polyclads, 23;
of Rotifers, etc., 206, 235
Syllidae, 258, 306;
palps, 260;
tentacles, 262;
head, 262;
parapodium, 264;
jaw, 270, 271;
alimentary tract, 271;
swim-bladder, 272;
asexual reproduction, 278 f., 279;
regeneration, 278, 283;
colours, 293;
phosphorescence, 296;
ancestral, 303
Syllis, 274, 307;
development, 278;
S. armillaris, 307;
S. ramosa, 282;
S. vivipara, 276
Synapta, bearing Rotifers, 222, 227
Synchaeta, 200, 204 f., 224, 226
Synchaetidae, 223, 224
Syncoelidium, 33, 42
Syncytium, 125
Syngamus trachealis, 130, 142, 144, 161, 163, 164
Syrinx, 411
Taenia, 74, 78, 79, 91;
life-histories of species of, 83;
table of species, 89;
Page 634
T. (Cysticercus) acanthotrias, 80;
T. coenurus, 81, 82;
life-history, 83;
specific characters, 90;
T. crassicollis, life-history, 78, 83;
specific characters, 89;
T. echinococcus, 80;
life-history, 83;
specific characters, 90;
T. krabbei, 81;
T. marginata, 81;
life-history, 83;
specific characters, 90;
T. (Hymenolepis) murina, 70, 80 n., 89;
life-history, 80, 83;
specific characters, 91;
T. perfoliata, 163;
T. saginata (= T. mediocanellata), 78, 79;
life-history, 83;
specific characters, 89;
T. serialis, 82;
life-history, 83;
specific characters, 90;
T. serrata, 81;
life-history, 83, 87, 89;
specific characters, 90;
T. solium, 79;
life-history, 79, 83;
specific characters, 89
Taeniasis, 82
Taeniidae, 91
Tail, of Arenicola, 333;
of Nereis, 246, 248;
regeneration of, 283
Tanypus, host of Gordius, 172
Tape-worms, 5, 74
Taphrocampa, 200, 204, 224
T. coenurus, 81, 82;
life-history, 83;
specific characters, 90;
T. crassicollis, life-history, 78, 83;
specific characters, 89;
T. echinococcus, 80;
life-history, 83;
specific characters, 90;
T. krabbei, 81;
T. marginata, 81;
life-history, 83;
specific characters, 90;
T. (Hymenolepis) murina, 70, 80 n., 89;
life-history, 80, 83;
specific characters, 91;
T. perfoliata, 163;
T. saginata (= T. mediocanellata), 78, 79;
life-history, 83;
specific characters, 89;
T. serialis, 82;
life-history, 83;
specific characters, 90;
T. serrata, 81;
life-history, 83, 87, 89;
specific characters, 90;
T. solium, 79;
life-history, 79, 83;
specific characters, 89
Taeniasis, 82
Taeniidae, 91
Tail, of Arenicola, 333;
of Nereis, 246, 248;
regeneration of, 283
Tanypus, host of Gordius, 172
Tape-worms, 5, 74
Taphrocampa, 200, 204, 224
Page 635
Tardigrada, affinities, 344
Telmatodrilus, 378
Temnocephala, 4, 53, 54, 73
Temnocephalidae, 53, 73;
habits and structure, 53 f.;
affinities, 54
Tennent, on land-leeches, 408
Tentacles, in Polyclads, 15, 26;
in Triclads, 30, 36;
in Vorticeros, 45, 46;
in Trematodes, 53;
(peristomial), of Spionidae, 322;
(prostomial), 255, 260, 262 f.;
of Nereis, 248;
of Polycirrus, 294, 295;
of Polygordius, 244;
of Terebellids, use of, 289;
nerves to, 254
Tentacle-sheath, in Polyzoa, 470
Tentacular cirri = Peristomial cirri, q.v.
Tentacular filaments, 304;
of Cirratulids, 326, 327
Terebella, 328;
otocyst, 273;
fossil, 301;
T. conchilega, tube, 286, 287, 288;
building of tube, 289, 290;
gill, 329;
T. nebulosa, colour, 292;
as host, 311;
gill, 329
Terebellidae, 258, 327;
shape, 259;
tentacles, 263;
gill, 265;
chaetae, 266, 267;
gizzard, 271;
Telmatodrilus, 378
Temnocephala, 4, 53, 54, 73
Temnocephalidae, 53, 73;
habits and structure, 53 f.;
affinities, 54
Tennent, on land-leeches, 408
Tentacles, in Polyclads, 15, 26;
in Triclads, 30, 36;
in Vorticeros, 45, 46;
in Trematodes, 53;
(peristomial), of Spionidae, 322;
(prostomial), 255, 260, 262 f.;
of Nereis, 248;
of Polycirrus, 294, 295;
of Polygordius, 244;
of Terebellids, use of, 289;
nerves to, 254
Tentacle-sheath, in Polyzoa, 470
Tentacular cirri = Peristomial cirri, q.v.
Tentacular filaments, 304;
of Cirratulids, 326, 327
Terebella, 328;
otocyst, 273;
fossil, 301;
T. conchilega, tube, 286, 287, 288;
building of tube, 289, 290;
gill, 329;
T. nebulosa, colour, 292;
as host, 311;
gill, 329
Terebellidae, 258, 327;
shape, 259;
tentacles, 263;
gill, 265;
chaetae, 266, 267;
gizzard, 271;
Page 636
tube, 286;
use of tentacles, 289;
colour, 293;
phosphorescence, 296;
food of, 296;
tube containing Polynoid, 298
Terebellides, 299, 330;
gill, 329
Terebelliformia, 258, 325;
definition, 304;
genital organs, 273;
gland shields, 287;
nephridia, 269;
nuchal organs, 273;
uncini, 266, 267;
vascular system, 252
Terebripora, 478
Terricola, 30, 42
Tertiary, Polyzoa, 521
Tessin, on Rotifers, 198, 218
Testes, of Leptoplana, 14, 15;
of Planaria lactea, 38, 39;
of Acoela and Alloeocoela, 47;
of Temnocephala, 54;
of Polystomum, 57;
of Cestodes, 75, 76, 86—see also Reproductive organs
Tetragonurus, 389
Tetraonchus, 73
Tetraphyllidae, 91
Tetrarhynchidae, 91
Tetrarhynchus, 75, 76 n., 85, 91
Tetrastemma, British species, 110;
land forms, 101, 115, 118;
fresh-water forms, 101, 118;
excretory system, 108, 109;
habits, 114;
hermaphrodite species, 109;
use of tentacles, 289;
colour, 293;
phosphorescence, 296;
food of, 296;
tube containing Polynoid, 298
Terebellides, 299, 330;
gill, 329
Terebelliformia, 258, 325;
definition, 304;
genital organs, 273;
gland shields, 287;
nephridia, 269;
nuchal organs, 273;
uncini, 266, 267;
vascular system, 252
Terebripora, 478
Terricola, 30, 42
Tertiary, Polyzoa, 521
Tessin, on Rotifers, 198, 218
Testes, of Leptoplana, 14, 15;
of Planaria lactea, 38, 39;
of Acoela and Alloeocoela, 47;
of Temnocephala, 54;
of Polystomum, 57;
of Cestodes, 75, 76, 86—see also Reproductive organs
Tetragonurus, 389
Tetraonchus, 73
Tetraphyllidae, 91
Tetrarhynchidae, 91
Tetrarhynchus, 75, 76 n., 85, 91
Tetrastemma, British species, 110;
land forms, 101, 115, 118;
fresh-water forms, 101, 118;
excretory system, 108, 109;
habits, 114;
hermaphrodite species, 109;
Page 637
viviparous species, 117
Thalamoporella, 530
Thalassema, 411, 435 f., 441, 443;
development, 439;
habits, 443
Thelepus, 299, 329
Theodisca, 321
Thompson, J. V., on term Polyzoa, 475
Thoracic membrane, 266, 305
Thorax, of Polychaeta, 259, 306, 337
Thysanosoma, 91;
generic characters, 90;
T. fimbriata, life-history, 83;
specific characters, 90;
T. giardii, specific characters, 90
Thysanozoon, 13, 18, 19, 20
Tomopteridae, 258, 291, 315
Tomopteris, 315;
colour, 294;
light-producing organ, 296;
prostomium, 259;
T. rolasi, 315
Tooth, in Polyzoa, 482, 522
Tortoise, Temnocephala associated with, 53
Torus uncinigerus, 268
Tracks, fossil, 302
Travisia, 332
Travisiopsis, 321
Trematoda, 4, 51 f.;
life-histories, 71;
classification, 73
Trembley, on Turbellaria, 6;
on Polyzoa, 496, 497
Trepostomata, 520
Triaenophorus (= Tricuspidaria), 91;
excretory system, 84
Triarthra, 201, 203, 206, 211, 224, 225, 226
Thalamoporella, 530
Thalassema, 411, 435 f., 441, 443;
development, 439;
habits, 443
Thelepus, 299, 329
Theodisca, 321
Thompson, J. V., on term Polyzoa, 475
Thoracic membrane, 266, 305
Thorax, of Polychaeta, 259, 306, 337
Thysanosoma, 91;
generic characters, 90;
T. fimbriata, life-history, 83;
specific characters, 90;
T. giardii, specific characters, 90
Thysanozoon, 13, 18, 19, 20
Tomopteridae, 258, 291, 315
Tomopteris, 315;
colour, 294;
light-producing organ, 296;
prostomium, 259;
T. rolasi, 315
Tooth, in Polyzoa, 482, 522
Tortoise, Temnocephala associated with, 53
Torus uncinigerus, 268
Tracks, fossil, 302
Travisia, 332
Travisiopsis, 321
Trematoda, 4, 51 f.;
life-histories, 71;
classification, 73
Trembley, on Turbellaria, 6;
on Polyzoa, 496, 497
Trepostomata, 520
Triaenophorus (= Tricuspidaria), 91;
excretory system, 84
Triarthra, 201, 203, 206, 211, 224, 225, 226
Page 638
Triarthridae, 200, 201, 202, 206, 207, 224, 226
Trias, Serpulid in, 301
Trichina, 131, 135, 144, 161;
T. spiralis, 146, 163
Trichinosis, 82, 146, 147
Trichocephalus, 131, 135, 136, 144, 160, 163;
species of, 145;
T. dispar, 145
Trichochaeta, chaeta, 351
Trichoderma, 159
Trichoplax, 93, 95
Trichosoma, 144, 163;
species of, 145
Trichotrachelidae, 144
Tricladida, 7, 30 f.;
habits, 35 f.;
sexual reproduction, 38;
asexual reproduction, 40;
classification, 42;
British species, 31, 32, 34, 42
Tricoma cincta, 157
Tricuspidaria, 91
Trigaster, 359, 384
Trigonoporus, 19, 27
Trinephrus, 357, 382 f.
Triophthalmus, 224
Triphylus, 224
Tristicochaeta, 158
Tristomatidae, 53, 55, 73
Tristomatinae, 73
Tristomum, 73
Triticella, 478, 518, 533
Trocheta, 393, 407
Trochophore, 229
Trochopus, 73
Trochosphaera, 200, 201, 221, 229, 230
Trochosphaeridae, 221
Trias, Serpulid in, 301
Trichina, 131, 135, 144, 161;
T. spiralis, 146, 163
Trichinosis, 82, 146, 147
Trichocephalus, 131, 135, 136, 144, 160, 163;
species of, 145;
T. dispar, 145
Trichochaeta, chaeta, 351
Trichoderma, 159
Trichoplax, 93, 95
Trichosoma, 144, 163;
species of, 145
Trichotrachelidae, 144
Tricladida, 7, 30 f.;
habits, 35 f.;
sexual reproduction, 38;
asexual reproduction, 40;
classification, 42;
British species, 31, 32, 34, 42
Tricoma cincta, 157
Tricuspidaria, 91
Trigaster, 359, 384
Trigonoporus, 19, 27
Trinephrus, 357, 382 f.
Triophthalmus, 224
Triphylus, 224
Tristicochaeta, 158
Tristomatidae, 53, 55, 73
Tristomatinae, 73
Tristomum, 73
Triticella, 478, 518, 533
Trocheta, 393, 407
Trochophore, 229
Trochopus, 73
Trochosphaera, 200, 201, 221, 229, 230
Trochosphaeridae, 221
Page 639
Trochosphere, of Archiannelida, 243, 245;
of Polychaeta, 274, 275, 510, 512;
of Echiuroidea, 439, 510;
of Polyzoa, 510
Trochus, in Rotifers, 202, 204
Trophi, of Rotifers, 209, 210
Trophonia, 299, 334;
genital organs, 273;
head, 262;
intestine, 271
Trunk, of Nereis, 246;
of Polychaeta, 259;
of Gephyrea, 412 f.
Tube, of Rotifers, 205;
of Polychaeta, 287 f.; composition of, 290;
fossil, 301, 302;
of Chaetopterus, 323;
of Clymene, 287;
of Dodecaceria, 326;
of Eunice tibiana, 290;
of Eunicidae, 285, 290, 318;
of Haplobranchus, 339;
of Hekaterobranchus, 326;
of Hyalinoecia, 290, 319;
of Maldanidae, 332;
of Myxicola, 285, 338;
of Nereis, 316;
of Nicomache, 287;
of Onuphis, 287, 319;
of Owenia, 325;
of Pectinaria, 285, 288, 330;
of Polydora, 323;
of Polynoids, 285;
of Panthalis, 313;
of Sabella, 287 f.;
of Sabellaria, 287;
of Sabellidae, 337;
of Polychaeta, 274, 275, 510, 512;
of Echiuroidea, 439, 510;
of Polyzoa, 510
Trochus, in Rotifers, 202, 204
Trophi, of Rotifers, 209, 210
Trophonia, 299, 334;
genital organs, 273;
head, 262;
intestine, 271
Trunk, of Nereis, 246;
of Polychaeta, 259;
of Gephyrea, 412 f.
Tube, of Rotifers, 205;
of Polychaeta, 287 f.; composition of, 290;
fossil, 301, 302;
of Chaetopterus, 323;
of Clymene, 287;
of Dodecaceria, 326;
of Eunice tibiana, 290;
of Eunicidae, 285, 290, 318;
of Haplobranchus, 339;
of Hekaterobranchus, 326;
of Hyalinoecia, 290, 319;
of Maldanidae, 332;
of Myxicola, 285, 338;
of Nereis, 316;
of Nicomache, 287;
of Onuphis, 287, 319;
of Owenia, 325;
of Pectinaria, 285, 288, 330;
of Polydora, 323;
of Polynoids, 285;
of Panthalis, 313;
of Sabella, 287 f.;
of Sabellaria, 287;
of Sabellidae, 337;
Page 640
of Serpulidae, 290, 339 f., 340;
of Terebellidae, 286, 287, 288, 289, 327 f.;
of Priapuloidea, 433;
of Echiurus, 444
Tube-forming glands, 304
Tube-making, of Polychaeta, 287 f.
Tubicolous Polychaeta, 285, 300, 304, 306
Tubifex, 351, 367, 369, 378;
chaetae, 350
Tubificidae, 350, 361, 366, 378
Tubulipora, 518, 531, 532
Turbellaria, 3 f.
Turtles, parasites of, 142
Tylenchus, 131, 154, 155, 157, 160, 163
Tylosoma, 422, 423, 426, 430, 447
Typhloscolecidae, 258, 291, 321;
nuchal organ, 273 n.
Typhloscolex, 321
Typosyllis, regeneration of head, 283 n.
Udekem, D', on Oligochaeta, 365
Udonella, 73;
U. caligorum, 55;
U. pollachii, eggs of, 58
Udonellinae, 73
Umbonula, 531
Uncinaria, 143
Uncinate, 210, 211
Uncini, of Polychaeta, 266, 267, 304, 305
Uncus, 210
Urnatella, 490, 493, 518
Urobenus, 388
of Terebellidae, 286, 287, 288, 289, 327 f.;
of Priapuloidea, 433;
of Echiurus, 444
Tube-forming glands, 304
Tube-making, of Polychaeta, 287 f.
Tubicolous Polychaeta, 285, 300, 304, 306
Tubifex, 351, 367, 369, 378;
chaetae, 350
Tubificidae, 350, 361, 366, 378
Tubulipora, 518, 531, 532
Turbellaria, 3 f.
Turtles, parasites of, 142
Tylenchus, 131, 154, 155, 157, 160, 163
Tylosoma, 422, 423, 426, 430, 447
Typhloscolecidae, 258, 291, 321;
nuchal organ, 273 n.
Typhloscolex, 321
Typosyllis, regeneration of head, 283 n.
Udekem, D', on Oligochaeta, 365
Udonella, 73;
U. caligorum, 55;
U. pollachii, eggs of, 58
Udonellinae, 73
Umbonula, 531
Uncinaria, 143
Uncinate, 210, 211
Uncini, of Polychaeta, 266, 267, 304, 305
Uncus, 210
Urnatella, 490, 493, 518
Urobenus, 388
Page 641
Uteriporus, 42
Uterus, of Leptoplana, 8, 14;
of Planaria, 38, 39;
of Triclads, 40;
of Rhabdocoela, 48;
of Temnocephala, 54;
of Polystomum, 57, 59;
of Diplozoon, 60;
of Didymozoon, 71;
of Calliobothrium, 75;
of Taenia, 79;
of Schistocephalus, 86;
in Bothriidae, 87;
of Rotifers, 216
Vagina, of Leptoplana, 16;
in ectoparasitic Trematodes, 57 f.;
in Cestodes, 86, 87
Vaillant, on Hirudinea, 392, 405
Valencinia, 113;
V. lineformis, 112
Valkeria, 533
Vallentin, on Rotifers, 198
Vallisnia, 73
Vanadis, 315
Varme, 297
Vasa deferentia, of Leptoplana, 14, 15;
of Planaria, 38, 39;
of Acoela and Alloeocoela, 47;
of Diplozoon, 60;
of Schistocephalus, 86
Vasa efferentia, of Leptoplana, 14, 15;
of Triclads, 38
Vascular System, of Nemertinea, 106, 107;
of Archiannelida, 244;
of Nereis, 251 f.;
of Polychaeta, 251 f.;
Uterus, of Leptoplana, 8, 14;
of Planaria, 38, 39;
of Triclads, 40;
of Rhabdocoela, 48;
of Temnocephala, 54;
of Polystomum, 57, 59;
of Diplozoon, 60;
of Didymozoon, 71;
of Calliobothrium, 75;
of Taenia, 79;
of Schistocephalus, 86;
in Bothriidae, 87;
of Rotifers, 216
Vagina, of Leptoplana, 16;
in ectoparasitic Trematodes, 57 f.;
in Cestodes, 86, 87
Vaillant, on Hirudinea, 392, 405
Valencinia, 113;
V. lineformis, 112
Valkeria, 533
Vallentin, on Rotifers, 198
Vallisnia, 73
Vanadis, 315
Varme, 297
Vasa deferentia, of Leptoplana, 14, 15;
of Planaria, 38, 39;
of Acoela and Alloeocoela, 47;
of Diplozoon, 60;
of Schistocephalus, 86
Vasa efferentia, of Leptoplana, 14, 15;
of Triclads, 38
Vascular System, of Nemertinea, 106, 107;
of Archiannelida, 244;
of Nereis, 251 f.;
of Polychaeta, 251 f.;
Page 642
of Cryptocephala, 252;
of Scoleciformia, 252;
of Terebelliformia, 252;
absence of, in certain Polychaeta, 253;
of Oligochaeta, 355;
of Leeches, 396;
of Gephyrea, 415, 436, 447;
of Phoronis, 455
Vaucheria, Rotifers in, 227
Vejdovsky, on Rhabdocoels, 46;
on Gordius, 164, 166;
on Oligochaeta, 365, 369, 374, 400
Vermes, 347
Vermiculus, 378
Vermiformia, 461
Verrill, on Chaetognatha, 534
Vertebrates, parasites of, 163, 174, 179, 183
Verworn, on statoblasts, 501
Vesicula seminalis, of Planaria, 39
Vesicularia, 481, 518, 533
Vesicularina, 518, 523
Vestibule, 488, 490;
of larva, 509
Vibracular zooecium, 485, 486, 517, 524
Vibraculum, 477, 484, 485, 517, 524;
movements, 487;
function, 486
Vicarious avicularia, 482
Victorella, 492, 501, 505, 518, 533
Villot, on life-history of Gordius, 172
Vinella, 521 n.
Virgate, 210
Visceral nervous system, of Nereis, 255
Vitellarium = Yolk-gland, q.v.
Vitello-intestinal canal, in Polystomatidae, 57
Viviparous, Nemertinea, 109, 117;
Rotifers, 200, 216 f.;
of Scoleciformia, 252;
of Terebelliformia, 252;
absence of, in certain Polychaeta, 253;
of Oligochaeta, 355;
of Leeches, 396;
of Gephyrea, 415, 436, 447;
of Phoronis, 455
Vaucheria, Rotifers in, 227
Vejdovsky, on Rhabdocoels, 46;
on Gordius, 164, 166;
on Oligochaeta, 365, 369, 374, 400
Vermes, 347
Vermiculus, 378
Vermiformia, 461
Verrill, on Chaetognatha, 534
Vertebrates, parasites of, 163, 174, 179, 183
Verworn, on statoblasts, 501
Vesicula seminalis, of Planaria, 39
Vesicularia, 481, 518, 533
Vesicularina, 518, 523
Vestibule, 488, 490;
of larva, 509
Vibracular zooecium, 485, 486, 517, 524
Vibraculum, 477, 484, 485, 517, 524;
movements, 487;
function, 486
Vicarious avicularia, 482
Victorella, 492, 501, 505, 518, 533
Villot, on life-history of Gordius, 172
Vinella, 521 n.
Virgate, 210
Visceral nervous system, of Nereis, 255
Vitellarium = Yolk-gland, q.v.
Vitello-intestinal canal, in Polystomatidae, 57
Viviparous, Nemertinea, 109, 117;
Rotifers, 200, 216 f.;
Page 643
Polychaeta, 256, 276
Volvox, Rotifers in, 227
Vortex, 44;
British species, 50;
body-cavity, 43
Vorticellids, on Polychaeta, 299
Vorticeros, British species, 45, 46, 50
Vorticidae, 50
Vuillemin (misprinted in text), on Nematodes in deserts, 156
Walford, on Polyzoa, 521
Ward, on Nectonema, 168;
on Sipunculus, 417
Warning colours, in Polychaeta, 294, 314
Waters, on Polyzoa, 517
Wheeler, on Myzostomaria, 344
Whelk, shell occupied by Nereis, 298
White Cat, 317
Whitman, on Dicyemidae, 94;
on Hirudinea, 395 f., 402, 405 f.
Willemoes-Suhm, von, on Tetrastemma agricola, 101, 115, 117, 118
Willey, on affinities of Nemertinea, 120 n.;
on Oligochaeta, 382
Wings, of Chaetopterus, 295, 324
Winter-eggs, of Mesostoma, 48;
of Rotifers, 217;
compared with statoblasts, 493
Woodworth, on yolk-glands, 38 n.
Wreath, in Rotifers, 200
Wright, on Phoronis, 450, 456
Yellow-cells, in Leptoplana, 13
Yolk-gland, in Planaria, 38, 39;
in Rhabdocoelida, 47;
in Temnocephala, 54;
in Polystomatidae, 57;
in Calliobothrium, 75;
Volvox, Rotifers in, 227
Vortex, 44;
British species, 50;
body-cavity, 43
Vorticellids, on Polychaeta, 299
Vorticeros, British species, 45, 46, 50
Vorticidae, 50
Vuillemin (misprinted in text), on Nematodes in deserts, 156
Walford, on Polyzoa, 521
Ward, on Nectonema, 168;
on Sipunculus, 417
Warning colours, in Polychaeta, 294, 314
Waters, on Polyzoa, 517
Wheeler, on Myzostomaria, 344
Whelk, shell occupied by Nereis, 298
White Cat, 317
Whitman, on Dicyemidae, 94;
on Hirudinea, 395 f., 402, 405 f.
Willemoes-Suhm, von, on Tetrastemma agricola, 101, 115, 117, 118
Willey, on affinities of Nemertinea, 120 n.;
on Oligochaeta, 382
Wings, of Chaetopterus, 295, 324
Winter-eggs, of Mesostoma, 48;
of Rotifers, 217;
compared with statoblasts, 493
Woodworth, on yolk-glands, 38 n.
Wreath, in Rotifers, 200
Wright, on Phoronis, 450, 456
Yellow-cells, in Leptoplana, 13
Yolk-gland, in Planaria, 38, 39;
in Rhabdocoelida, 47;
in Temnocephala, 54;
in Polystomatidae, 57;
in Calliobothrium, 75;
Page 644
in Schistocephalus, 86;
in Rotifers, 199, 216
Yoruba Worm, 368, 387
Youatt, on Coenurus, 82
Yungia, 19, 25
Zebra, parasites of, 140
Zelinka, on Rotifers, 198, 215 n., 218, 219, 227, 229;
on Gastrotricha, 232
Zooecium, 466, 469, 474, 488, 523;
of Phylactolaemata, 495;
loss of zooecia, 481, (= calyces), 488;
primary, 506;
alterations with age, 522
Zone of budding, 279, 283
Zooid, sexual and asexual, 278 f.
Zoophytes, 465, 474
in Rotifers, 199, 216
Yoruba Worm, 368, 387
Youatt, on Coenurus, 82
Yungia, 19, 25
Zebra, parasites of, 140
Zelinka, on Rotifers, 198, 215 n., 218, 219, 227, 229;
on Gastrotricha, 232
Zooecium, 466, 469, 474, 488, 523;
of Phylactolaemata, 495;
loss of zooecia, 481, (= calyces), 488;
primary, 506;
alterations with age, 522
Zone of budding, 279, 283
Zooid, sexual and asexual, 278 f.
Zoophytes, 465, 474
Page 645
END OF VOL. II
PREVIOUS VOLUMES OF
THE CAMBRIDGE NATURAL
HISTORY
Edited by S. F. Harmer, M.A., Fellow of King's College, Cambridge,
Superintendent of the University Museum of Zoology; and A. E.
Shipley, M.A., Fellow of Christ's College, Cambridge, University
Lecturer on the Morphology of Invertebrates.
Volume III. Molluscs and Brachiopods. By the Rev. A. H. Cooke, M.A., Fellow and Tutor of
King's College, Cambridge; A. E. Shipley, M.A., Fellow of Christ's College, Cambridge; and
F. R. C. Reed, M.A., Trinity College, Cambridge. Illustrated. Medium 8vo. 17s. net.
TIMES.—"There are very many, not only among educated people who take an interest in science, but
even among specialists, who will welcome a work of reasonable compass and handy form containing
a trustworthy treatment of the various departments of Natural History by men who are familiar with,
and competent to deal with, the latest results of scientific research.... Altogether, to judge from this
first volume, The Cambridge Natural History promises to fulfil all the expectations that its
prospectus holds out."
DAILY CHRONICLE.—"It can be read with profit by the zoologist, and there is a vast amount of
matter which is interesting to those who like the tit-bits of science; but do not care so much for the
more serious aspects of the subject."
NATURE NOTES.—"The work as a whole is thoroughly well got up, and we cordially recommend it
to our readers."
FIELD.—"The work is really an admirable introduction to the study of molluscs, treating of their
position in the animal kingdom, the habits and general economy of land and fresh-water species, their
PREVIOUS VOLUMES OF
THE CAMBRIDGE NATURAL
HISTORY
Edited by S. F. Harmer, M.A., Fellow of King's College, Cambridge,
Superintendent of the University Museum of Zoology; and A. E.
Shipley, M.A., Fellow of Christ's College, Cambridge, University
Lecturer on the Morphology of Invertebrates.
Volume III. Molluscs and Brachiopods. By the Rev. A. H. Cooke, M.A., Fellow and Tutor of
King's College, Cambridge; A. E. Shipley, M.A., Fellow of Christ's College, Cambridge; and
F. R. C. Reed, M.A., Trinity College, Cambridge. Illustrated. Medium 8vo. 17s. net.
TIMES.—"There are very many, not only among educated people who take an interest in science, but
even among specialists, who will welcome a work of reasonable compass and handy form containing
a trustworthy treatment of the various departments of Natural History by men who are familiar with,
and competent to deal with, the latest results of scientific research.... Altogether, to judge from this
first volume, The Cambridge Natural History promises to fulfil all the expectations that its
prospectus holds out."
DAILY CHRONICLE.—"It can be read with profit by the zoologist, and there is a vast amount of
matter which is interesting to those who like the tit-bits of science; but do not care so much for the
more serious aspects of the subject."
NATURE NOTES.—"The work as a whole is thoroughly well got up, and we cordially recommend it
to our readers."
FIELD.—"The work is really an admirable introduction to the study of molluscs, treating of their
position in the animal kingdom, the habits and general economy of land and fresh-water species, their
Page 646
structure, general distribution over the earth's surface (which is illustrated by some very valuable
maps), their growth and development, their uses to man, the cultivation for food of such species as
the oyster, the mussel, and the snail, and the utilisation of their shells for money and ornament.... We
know of no book available to the general reader which affords such a vast fund of information on the
structure and habits of molluscs."
Volume V. Peripatus. By Adam Sedgwick, M.A., F.R.S. Myriapods. By F. G. Sinclair, M.A.
Insects, Part I. By David Sharp, M.A. Cantab., M.B. Edin., F.R.S. Fully Illustrated. Medium
8vo. 17s. net.
Prof. Raphael Meldola, F.R.S., F.C.S., in his Presidential Address to the Entomological Society of
London, said:—"The authors of this volume are certainly to be congratulated upon having furnished
such a valuable contribution to our literature. When its successor appears, and I will venture to
express the hope that this will be at no very distant period, we shall be in possession of a treatise on
the natural history of insects which, from the point of view of the general reader, will compare most
favourably with any similar work that has been published in the English language."
ENTOMOLOGISTS' MONTHLY MAGAZINE.—"We venture to think the work will be found
indispensable to all who seek to extend their general knowledge beyond the narrowing influence of
exclusive attention to certain orders or groups, and that it will take a high position in The Cambridge
Natural History series."
MACMILLAN AND CO., Ltd., LONDON.
BOOKS FOR
STUDENTS OF NATURAL
HISTORY
A HANDBOOK OF BRITISH LEPIDOPTERA. By Edward Meyrick, B.A., F.L.S., F.E.S.
Extra Crown 8vo. 10s. 6d. net.
ENTOMOLOGISTS' MONTHLY MAGAZINE.—"This book cannot fail to afford great assistance to
the student who desires to recognise and identify his specimens without the necessity of comparing
them with named examples. It is without exception the best class-book that has yet appeared for
imparting real sound knowledge of structure, evolution, and classification."
maps), their growth and development, their uses to man, the cultivation for food of such species as
the oyster, the mussel, and the snail, and the utilisation of their shells for money and ornament.... We
know of no book available to the general reader which affords such a vast fund of information on the
structure and habits of molluscs."
Volume V. Peripatus. By Adam Sedgwick, M.A., F.R.S. Myriapods. By F. G. Sinclair, M.A.
Insects, Part I. By David Sharp, M.A. Cantab., M.B. Edin., F.R.S. Fully Illustrated. Medium
8vo. 17s. net.
Prof. Raphael Meldola, F.R.S., F.C.S., in his Presidential Address to the Entomological Society of
London, said:—"The authors of this volume are certainly to be congratulated upon having furnished
such a valuable contribution to our literature. When its successor appears, and I will venture to
express the hope that this will be at no very distant period, we shall be in possession of a treatise on
the natural history of insects which, from the point of view of the general reader, will compare most
favourably with any similar work that has been published in the English language."
ENTOMOLOGISTS' MONTHLY MAGAZINE.—"We venture to think the work will be found
indispensable to all who seek to extend their general knowledge beyond the narrowing influence of
exclusive attention to certain orders or groups, and that it will take a high position in The Cambridge
Natural History series."
MACMILLAN AND CO., Ltd., LONDON.
BOOKS FOR
STUDENTS OF NATURAL
HISTORY
A HANDBOOK OF BRITISH LEPIDOPTERA. By Edward Meyrick, B.A., F.L.S., F.E.S.
Extra Crown 8vo. 10s. 6d. net.
ENTOMOLOGISTS' MONTHLY MAGAZINE.—"This book cannot fail to afford great assistance to
the student who desires to recognise and identify his specimens without the necessity of comparing
them with named examples. It is without exception the best class-book that has yet appeared for
imparting real sound knowledge of structure, evolution, and classification."
Page 647
NATURAL HISTORY AND ANTIQUITIES OF SELBORNE. By Gilbert White. With Notes
by Frank Buckland, a Chapter on Antiquities by Lord Selborne, and New Letters, Illustrated
by P. H. Delamotte. New and Cheaper Edition. Crown 8vo. 6s. Also an Edition in Two Vols.,
with Introduction by John Burroughs, and Illustrations by Clifton Johnson. Crown 8vo. 10s.
6d.
FORTY YEARS IN A MOORLAND PARISH. Reminiscences and Researches in Danby-in-
Cleveland. By Rev. J. C. Atkinson, D.C.L., Canon of York and Incumbent of the Parish,
Author of "A History of Cleveland," "A Glossary of the Cleveland Dialect." With Maps and
Illustrations. Extra Crown 8vo. 5s. net.
THE SCENERY OF SWITZERLAND AND THE CAUSES TO WHICH IT IS DUE. By the
Right Hon. Sir John Lubbock, Bart., M.P., F.R.S., etc. Crown 8vo. 6s.
DAILY TELEGRAPH.—"By his 'Scenery of Switzerland,' he will enhance the pleasure of many a
rambler, and insensibly teach, by practical example, the great lessons that are decipherable on the
face of nature."
AN INTRODUCTION TO THE STUDY OF SEAWEEDS. By George Murray, F.L.S.,
Keeper of Botany in the Natural History Department of the British Museum. Illustrated. Crown
8vo. 7s. 6d.
A SKETCH OF THE NATURAL HISTORY OF AUSTRALIA, WITH SOME NOTES ON
SPORT. By Frederick G. Aflalo, F.R.G.S., F.Z.S., etc. Illustrated by F. Seth. Crown 8vo. 6s.
HANDBOOK OF FIELD AND GENERAL ORNITHOLOGY. A Manual of the Structure and
Classification of Birds. With Instructions for Collecting and Preserving Specimens. By Elliott
Coues. Profusely Illustrated. 8vo. 10s. net.
STRUCTURE AND LIFE OF BIRDS. By F. W. Headley, Assistant Master in Haileybury
College. Illustrated. 8vo. 7s. 6d.
TALES OF THE BIRDS. By W. Warde Fowler, M.A. With Illustrations by Bryan Hook.
Second Edition. Crown 8vo. 8s. 6d.
A YEAR WITH THE BIRDS. By W. Warde Fowler, M.A. With Illustrations by Bryan Hook.
Third Edition, enlarged. Crown 8vo. 3s. 6d.
SUMMER STUDIES OF BIRDS AND BOOKS. By W. Warde Fowler, M.A. Crown 8vo. 6s.
THE NATURAL HISTORY OF AQUATIC INSECTS. By L. C. Miall, F.R.S., Professor of
Biology in the Yorkshire College, Leeds. Illustrated. Crown 8vo. 6s.
ROMANCE OF THE INSECT WORLD. By L. N. Badenoch. With Illustrations by Margaret
J. D. Badenoch and others. Crown 8vo. 6s.
THE DEPTHS OF THE SEA. An Account of the General Results of the Dredging Cruises of
H.M.SS. Porcupine and Lightning during the Summers of 1868, 1869, and 1870, under the
Scientific Direction of Dr. Carpenter, F.R.S.; J. Gwyn Jeffreys, F.R.S. and Dr. Wyville
Thomson, F.R.S. By Sir C. Wyville Thomson, F.R.S. With numerous Illustrations and Maps.
Second Edition. Medium 8vo. 31s. 6d.
THE VOYAGE OF THE CHALLENGER. THE ATLANTIC. A Preliminary Account of the
General Results of the Exploring Voyage of H.M.S. Challenger during the Year 1873 and the
by Frank Buckland, a Chapter on Antiquities by Lord Selborne, and New Letters, Illustrated
by P. H. Delamotte. New and Cheaper Edition. Crown 8vo. 6s. Also an Edition in Two Vols.,
with Introduction by John Burroughs, and Illustrations by Clifton Johnson. Crown 8vo. 10s.
6d.
FORTY YEARS IN A MOORLAND PARISH. Reminiscences and Researches in Danby-in-
Cleveland. By Rev. J. C. Atkinson, D.C.L., Canon of York and Incumbent of the Parish,
Author of "A History of Cleveland," "A Glossary of the Cleveland Dialect." With Maps and
Illustrations. Extra Crown 8vo. 5s. net.
THE SCENERY OF SWITZERLAND AND THE CAUSES TO WHICH IT IS DUE. By the
Right Hon. Sir John Lubbock, Bart., M.P., F.R.S., etc. Crown 8vo. 6s.
DAILY TELEGRAPH.—"By his 'Scenery of Switzerland,' he will enhance the pleasure of many a
rambler, and insensibly teach, by practical example, the great lessons that are decipherable on the
face of nature."
AN INTRODUCTION TO THE STUDY OF SEAWEEDS. By George Murray, F.L.S.,
Keeper of Botany in the Natural History Department of the British Museum. Illustrated. Crown
8vo. 7s. 6d.
A SKETCH OF THE NATURAL HISTORY OF AUSTRALIA, WITH SOME NOTES ON
SPORT. By Frederick G. Aflalo, F.R.G.S., F.Z.S., etc. Illustrated by F. Seth. Crown 8vo. 6s.
HANDBOOK OF FIELD AND GENERAL ORNITHOLOGY. A Manual of the Structure and
Classification of Birds. With Instructions for Collecting and Preserving Specimens. By Elliott
Coues. Profusely Illustrated. 8vo. 10s. net.
STRUCTURE AND LIFE OF BIRDS. By F. W. Headley, Assistant Master in Haileybury
College. Illustrated. 8vo. 7s. 6d.
TALES OF THE BIRDS. By W. Warde Fowler, M.A. With Illustrations by Bryan Hook.
Second Edition. Crown 8vo. 8s. 6d.
A YEAR WITH THE BIRDS. By W. Warde Fowler, M.A. With Illustrations by Bryan Hook.
Third Edition, enlarged. Crown 8vo. 3s. 6d.
SUMMER STUDIES OF BIRDS AND BOOKS. By W. Warde Fowler, M.A. Crown 8vo. 6s.
THE NATURAL HISTORY OF AQUATIC INSECTS. By L. C. Miall, F.R.S., Professor of
Biology in the Yorkshire College, Leeds. Illustrated. Crown 8vo. 6s.
ROMANCE OF THE INSECT WORLD. By L. N. Badenoch. With Illustrations by Margaret
J. D. Badenoch and others. Crown 8vo. 6s.
THE DEPTHS OF THE SEA. An Account of the General Results of the Dredging Cruises of
H.M.SS. Porcupine and Lightning during the Summers of 1868, 1869, and 1870, under the
Scientific Direction of Dr. Carpenter, F.R.S.; J. Gwyn Jeffreys, F.R.S. and Dr. Wyville
Thomson, F.R.S. By Sir C. Wyville Thomson, F.R.S. With numerous Illustrations and Maps.
Second Edition. Medium 8vo. 31s. 6d.
THE VOYAGE OF THE CHALLENGER. THE ATLANTIC. A Preliminary Account of the
General Results of the Exploring Voyage of H.M.S. Challenger during the Year 1873 and the
Page 648
Early Part of the Year 1876. With Portrait, Plates, and Maps. In two Vols. Published by
Authority of the Lords Commissioner of the Admiralty. Medium 8vo. 45s.
OBSERVATIONS ON THE GEOLOGY AND ZOOLOGY OF ABYSSINIA, made during the
Progress of the British Expedition to that Country in 1867-1868. By W. T. Blanford, F.R.S.
With Illustrations and Geological Map. 8vo. 21s.
WORKS BY A. R. WALLACE, F.R.S.
DARWINISM: An Exposition of the Theory of Natural Selection, with Some of its
Applications. With Maps and Illustrations. Extra Crown 8vo. 9s.
NATURAL SELECTION AND TROPICAL NATURE. Essays on Descriptive and Theoretical
Biology. Extra Crown 8vo. 6s.
THE MALAY ARCHIPELAGO: The Land of the Orang Utan and the Bird of Paradise. A
Narrative of Travel. With Studies of Man and Nature. With Maps and Illustrations. Fourth
Edition. Extra Crown 8vo. 6s.
ISLAND LIFE: or the Phenomena and Causes of Insular Faunas and Floras. Including a
Revision and Attempted Solution of the Problem of Geological Climates. With Illustrations and
Maps. Second Edition. Extra Crown 8vo. 6s.
THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS; with a Study of the Relations of
Living and Extinct Faunas as Elucidating the Past Changes of the Earth's Surface. With Maps
and Illustrations. In Two Vols. Medium 8vo. 42s.
* * * * *
AN INTRODUCTION TO THE OSTEOLOGY OF THE MAMMALIA: being the substance
of the course of lectures delivered at the Royal College of Surgeons of England in 1870. By Sir
W. H. Flower, F.R.S., F.R.C.S., Director of the Natural History Museum. Illustrated. Third
Edition. Revised with the assistance of Hans Gadow, Ph.D. Crown 8vo. 10s. 6d.
WILD BEASTS AND THEIR WAYS. Reminiscences of Europe, Asia, Africa, and America,
from 1845-1888. By Sir Samuel W. Baker, Pacha, F.R.S. With Illustrations. New and Cheaper
Edition. Extra Crown 8vo. 12s. 6d.
WANDERINGS IN SOUTH AMERICA, THE NORTH-EAST OF THE UNITED STATES,
AND THE ANTILLES, IN THE YEARS 1812, 1816, 1820, and 1824. With Original
Instructions for the perfect Preservation of Birds, etc., for Cabinets of Natural History. By
Charles Waterton, Esq. Edited by the Rev. J. G. Wood. With 100 Illustrations. Crown 8vo.
6s.
FROM A NEW ENGLAND HILLSIDE. Notes from Underledge. By William Potts. Pott 8vo.
3s.
THE FRIENDSHIP OF NATURE. A New England Chronicle of Birds and Flowers. By Mabel
Osgood Wright. 16mo. 3s.
MACMILLAN AND CO., Ltd., LONDON.
Authority of the Lords Commissioner of the Admiralty. Medium 8vo. 45s.
OBSERVATIONS ON THE GEOLOGY AND ZOOLOGY OF ABYSSINIA, made during the
Progress of the British Expedition to that Country in 1867-1868. By W. T. Blanford, F.R.S.
With Illustrations and Geological Map. 8vo. 21s.
WORKS BY A. R. WALLACE, F.R.S.
DARWINISM: An Exposition of the Theory of Natural Selection, with Some of its
Applications. With Maps and Illustrations. Extra Crown 8vo. 9s.
NATURAL SELECTION AND TROPICAL NATURE. Essays on Descriptive and Theoretical
Biology. Extra Crown 8vo. 6s.
THE MALAY ARCHIPELAGO: The Land of the Orang Utan and the Bird of Paradise. A
Narrative of Travel. With Studies of Man and Nature. With Maps and Illustrations. Fourth
Edition. Extra Crown 8vo. 6s.
ISLAND LIFE: or the Phenomena and Causes of Insular Faunas and Floras. Including a
Revision and Attempted Solution of the Problem of Geological Climates. With Illustrations and
Maps. Second Edition. Extra Crown 8vo. 6s.
THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS; with a Study of the Relations of
Living and Extinct Faunas as Elucidating the Past Changes of the Earth's Surface. With Maps
and Illustrations. In Two Vols. Medium 8vo. 42s.
* * * * *
AN INTRODUCTION TO THE OSTEOLOGY OF THE MAMMALIA: being the substance
of the course of lectures delivered at the Royal College of Surgeons of England in 1870. By Sir
W. H. Flower, F.R.S., F.R.C.S., Director of the Natural History Museum. Illustrated. Third
Edition. Revised with the assistance of Hans Gadow, Ph.D. Crown 8vo. 10s. 6d.
WILD BEASTS AND THEIR WAYS. Reminiscences of Europe, Asia, Africa, and America,
from 1845-1888. By Sir Samuel W. Baker, Pacha, F.R.S. With Illustrations. New and Cheaper
Edition. Extra Crown 8vo. 12s. 6d.
WANDERINGS IN SOUTH AMERICA, THE NORTH-EAST OF THE UNITED STATES,
AND THE ANTILLES, IN THE YEARS 1812, 1816, 1820, and 1824. With Original
Instructions for the perfect Preservation of Birds, etc., for Cabinets of Natural History. By
Charles Waterton, Esq. Edited by the Rev. J. G. Wood. With 100 Illustrations. Crown 8vo.
6s.
FROM A NEW ENGLAND HILLSIDE. Notes from Underledge. By William Potts. Pott 8vo.
3s.
THE FRIENDSHIP OF NATURE. A New England Chronicle of Birds and Flowers. By Mabel
Osgood Wright. 16mo. 3s.
MACMILLAN AND CO., Ltd., LONDON.
Page 649
WORKS ON
BIOLOGY AND ZOOLOGY
A TEXT-BOOK OF COMPARATIVE ANATOMY. By Dr. Arnold Lang, Professor of
Zoology in the University of Zurich, formerly Ritter Professor of Phylogeny in the University
of Jena. With Preface to the English Translation by Professor Dr. Ernst Haeckel. Translated
into English by Henry M. Bernard, M.A., Cantab., and Matilda Bernard. Part I. 8vo. Part II.
(completing the Anatomy of the Invertebrates) 17s. net. each.
AN ATLAS OF PRACTICAL ELEMENTARY BIOLOGY. By G. B. Howes, Assistant
Professor of Zoology. With a preface by Professor Huxley, F.R.S. Med. 4to. 14s.
MATERIALS FOR THE STUDY OF VARIATION. Treated with especial regard to
Discontinuity in the Origin of Species. By William Bateson, M.A., Fellow of St. John's
College, Cambridge. 8vo. 21s. net.
AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES. By Arthur Willey, B.Sc.,
Tutor in Biology, Columbia College; Balfour Student of the University of Cambridge. With a
preface by Henry Fairfield Osborn. 8vo. 10s. 6d. net.
THE MYOLOGY OF THE RAVEN (Corvus corax Sinuatus). A Guide to the Study of the
Muscular System in Birds. By R. W. Shufeldt, of the Smithsonian Institute, Washington,
U.S.A. With Illustrations. 8vo. 13s. net.
ORGANIC EVOLUTION AS THE RESULT OF THE INHERITANCE OF ACQUIRED
CHARACTERS ACCORDING TO THE LAWS OF ORGANIC GROWTH. By Dr. G. H.
Theodor Eimer, Professor of Zoology and Comparative Anatomy in Tübingen. Translated by
J. T. Cunningham, M.A., F.R.S.E., late Fellow of University College, Oxford. 8vo. 12s. 6d.
FROM THE GREEKS TO DARWIN. An Outline of the Development of the Evolution Idea.
By Henry Fairfield Osborn, Sc.D., Da Costa Professor of Biology in Columbia College,
Curator in the American Museum of Natural History. 8vo. 9s. net.
LESSONS IN ELEMENTARY BIOLOGY. By T. Jeffrey Parker, B.Sc., F.R.S., Professor of
Biology in the University of Otago, New Zealand. Illustrated. Second Edition. Crown 8vo. 10s.
6d.
KEY TO NORTH AMERICAN BIRDS. Containing a concise account of every species of
living and fossil bird at present known from the continent north of the Mexican and United
States boundary, inclusive of Greenland. Second Edition, with which are incorporated General
Ornithology—an outline of the structure and classification of birds, and Field Ornithology—a
manual of collecting, preparing, and preserving birds. By Elliott Coues, M.A., M.D., Ph.D.,
Member of the National Academy of Sciences. Profusely illustrated. Super Royal 8vo. 42s.
MONOGRAPH OF THE BRITISH CICADÆ OR TETTIGIIDÆ (Froghoppers and
Grassflies). By George Bowdler Buckton, F.R.S., Corr. Memb. Acad. Nat. Hist, of
Philadelphia, Memb. de la Soc. Ent. de France. Illustrated by more than 400 Coloured
Drawings. Two Vols. Demy 8vo. 33s. 6d. each net. Also in Eight Parts. 8s. each net.
BIOLOGY AND ZOOLOGY
A TEXT-BOOK OF COMPARATIVE ANATOMY. By Dr. Arnold Lang, Professor of
Zoology in the University of Zurich, formerly Ritter Professor of Phylogeny in the University
of Jena. With Preface to the English Translation by Professor Dr. Ernst Haeckel. Translated
into English by Henry M. Bernard, M.A., Cantab., and Matilda Bernard. Part I. 8vo. Part II.
(completing the Anatomy of the Invertebrates) 17s. net. each.
AN ATLAS OF PRACTICAL ELEMENTARY BIOLOGY. By G. B. Howes, Assistant
Professor of Zoology. With a preface by Professor Huxley, F.R.S. Med. 4to. 14s.
MATERIALS FOR THE STUDY OF VARIATION. Treated with especial regard to
Discontinuity in the Origin of Species. By William Bateson, M.A., Fellow of St. John's
College, Cambridge. 8vo. 21s. net.
AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES. By Arthur Willey, B.Sc.,
Tutor in Biology, Columbia College; Balfour Student of the University of Cambridge. With a
preface by Henry Fairfield Osborn. 8vo. 10s. 6d. net.
THE MYOLOGY OF THE RAVEN (Corvus corax Sinuatus). A Guide to the Study of the
Muscular System in Birds. By R. W. Shufeldt, of the Smithsonian Institute, Washington,
U.S.A. With Illustrations. 8vo. 13s. net.
ORGANIC EVOLUTION AS THE RESULT OF THE INHERITANCE OF ACQUIRED
CHARACTERS ACCORDING TO THE LAWS OF ORGANIC GROWTH. By Dr. G. H.
Theodor Eimer, Professor of Zoology and Comparative Anatomy in Tübingen. Translated by
J. T. Cunningham, M.A., F.R.S.E., late Fellow of University College, Oxford. 8vo. 12s. 6d.
FROM THE GREEKS TO DARWIN. An Outline of the Development of the Evolution Idea.
By Henry Fairfield Osborn, Sc.D., Da Costa Professor of Biology in Columbia College,
Curator in the American Museum of Natural History. 8vo. 9s. net.
LESSONS IN ELEMENTARY BIOLOGY. By T. Jeffrey Parker, B.Sc., F.R.S., Professor of
Biology in the University of Otago, New Zealand. Illustrated. Second Edition. Crown 8vo. 10s.
6d.
KEY TO NORTH AMERICAN BIRDS. Containing a concise account of every species of
living and fossil bird at present known from the continent north of the Mexican and United
States boundary, inclusive of Greenland. Second Edition, with which are incorporated General
Ornithology—an outline of the structure and classification of birds, and Field Ornithology—a
manual of collecting, preparing, and preserving birds. By Elliott Coues, M.A., M.D., Ph.D.,
Member of the National Academy of Sciences. Profusely illustrated. Super Royal 8vo. 42s.
MONOGRAPH OF THE BRITISH CICADÆ OR TETTIGIIDÆ (Froghoppers and
Grassflies). By George Bowdler Buckton, F.R.S., Corr. Memb. Acad. Nat. Hist, of
Philadelphia, Memb. de la Soc. Ent. de France. Illustrated by more than 400 Coloured
Drawings. Two Vols. Demy 8vo. 33s. 6d. each net. Also in Eight Parts. 8s. each net.
Page 650
THE FOSSIL INSECTS OF NORTH AMERICA. With Notes on some European Species. By
Samuel H. Scudder. Vol. I. The Pretertiary Insects. With 34 Plates. Vol. II. The Tertiary
Insects. With a Map and 28 Plates. 4to. Paper Boards. 90s. net.
MACMILLAN AND CO., Ltd., LONDON.
NOTES
[1]
Hemprich and Ehrenberg, Symbolae physicae, Berlin, fol. 1831.
[2]
Τρῆμα, a hole; referring to the orifices of the suckers.
[3]
Mémoires pour servir à l'histoire d. Polypes d'eau douce, Leyden, 1744.
[4]
Die Parasiten des Menschen, 1879——. Engl. Transl. by W. E. Hoyle, i.
1886.
[5]
Band 4, by M. Braun. (Mesozoa and Trematoda completed; Cestoda in
progress.)
[6]
Verm. terr. et fluv. ... succincta historia, 1773; Zool. Danica, 1777.
[7]
Observations on Planariae, Edinburgh, 1813.
[8]
M. Faraday, "On the Planariae," Medical Gazette, Feb. 1832; and in
Edinburgh New Philosoph. Journal, vol. xiv. 1833, pp. 183-189.
Samuel H. Scudder. Vol. I. The Pretertiary Insects. With 34 Plates. Vol. II. The Tertiary
Insects. With a Map and 28 Plates. 4to. Paper Boards. 90s. net.
MACMILLAN AND CO., Ltd., LONDON.
NOTES
[1]
Hemprich and Ehrenberg, Symbolae physicae, Berlin, fol. 1831.
[2]
Τρῆμα, a hole; referring to the orifices of the suckers.
[3]
Mémoires pour servir à l'histoire d. Polypes d'eau douce, Leyden, 1744.
[4]
Die Parasiten des Menschen, 1879——. Engl. Transl. by W. E. Hoyle, i.
1886.
[5]
Band 4, by M. Braun. (Mesozoa and Trematoda completed; Cestoda in
progress.)
[6]
Verm. terr. et fluv. ... succincta historia, 1773; Zool. Danica, 1777.
[7]
Observations on Planariae, Edinburgh, 1813.
[8]
M. Faraday, "On the Planariae," Medical Gazette, Feb. 1832; and in
Edinburgh New Philosoph. Journal, vol. xiv. 1833, pp. 183-189.
Page 651
[9]
Nov. Act. Acad. Caes. Leop.-Carol. tom. xiii. 1827.
[10]
Ann. Sci. Nat. (Zool.) I. tom. xv. 1828.; ibid. tom. xxi. 1830.
[11]
Mém. Acad. St. Pétersbourg, 5th ser. tom. ii. 1832.
[12]
Die rhabdocoelen Turbellarien des Süsswassers. Jena 1848.
[13]
Monographie d. Turbellarien. I. Rhabdocoelida, 1882. Die Acoela,
Leipzig, 1892.
[14]
"Die Polycladen," Fauna u. Flora d. Golfes v. Neapel, Monogr. XI. 1884.
[15]
Phil. Trans. 1874, p. 105.
[16]
Since no food, but only the pharynx, passes through this "mouth," the
term is unfortunate. Moreover the true mouth is the aperture placing the
stomach in communication with the pharynx (Fig. 5, gm).
[17]
Ann. Sci. Nat. 1 sér. tom. xv. 1828, p. 146. "La Planaire trémellaire ...
peut parcourir ... en faisant battre rapidement ses parties latérales à la
manière des larges nageoires des Raies."
[18]
Observations on Planariae. Edinburgh, 1813, p. 12.
Nov. Act. Acad. Caes. Leop.-Carol. tom. xiii. 1827.
[10]
Ann. Sci. Nat. (Zool.) I. tom. xv. 1828.; ibid. tom. xxi. 1830.
[11]
Mém. Acad. St. Pétersbourg, 5th ser. tom. ii. 1832.
[12]
Die rhabdocoelen Turbellarien des Süsswassers. Jena 1848.
[13]
Monographie d. Turbellarien. I. Rhabdocoelida, 1882. Die Acoela,
Leipzig, 1892.
[14]
"Die Polycladen," Fauna u. Flora d. Golfes v. Neapel, Monogr. XI. 1884.
[15]
Phil. Trans. 1874, p. 105.
[16]
Since no food, but only the pharynx, passes through this "mouth," the
term is unfortunate. Moreover the true mouth is the aperture placing the
stomach in communication with the pharynx (Fig. 5, gm).
[17]
Ann. Sci. Nat. 1 sér. tom. xv. 1828, p. 146. "La Planaire trémellaire ...
peut parcourir ... en faisant battre rapidement ses parties latérales à la
manière des larges nageoires des Raies."
[18]
Observations on Planariae. Edinburgh, 1813, p. 12.
Page 652
[19]
"Zur Anat. u. Entwickl. einiger Seeplanarien v. St. Malo," Abh. K.
Gesellschaft d. Wiss. Göttingen, 1868.
[20]
The roof of the peripharyngeal chamber is hence known as the
"diaphragm."
[21]
See Brandt, Fauna u. Flora d. Golfes v. Neapel, Monogr. XIII. 1885, p.
65.
[22]
See p. 94.
[23]
Verhandlungen d. med. Gesellschaft zu Würzburg, iv. 1854, p. 223.
[24]
Enantia spinifera Grff. Mittheil. d. Naturwiss. Verein. f. Steiermark, 1889.
[25]
The sucker of Leptoplana tremellaris probably does not correspond with
that of the Cotylea.
[26]
Collingwood, Trans. Linn. Soc. 2 ser. vol. i. pt. 3, 1876, p. 83.
[27]
Von Stummer-Traunfels, Zeitschr. f. wiss. Zool. Bd. lx. 1895, p. 689.
[28]
Planocera pellucida Mertens, P. simrothi v. Grff., P. grubei Grff.,
Stylochoplana sargassicola Mertens, S. californica Woodworth,
Planctoplana challengeri Grff., all belonging to the Planoceridae. See
"Zur Anat. u. Entwickl. einiger Seeplanarien v. St. Malo," Abh. K.
Gesellschaft d. Wiss. Göttingen, 1868.
[20]
The roof of the peripharyngeal chamber is hence known as the
"diaphragm."
[21]
See Brandt, Fauna u. Flora d. Golfes v. Neapel, Monogr. XIII. 1885, p.
65.
[22]
See p. 94.
[23]
Verhandlungen d. med. Gesellschaft zu Würzburg, iv. 1854, p. 223.
[24]
Enantia spinifera Grff. Mittheil. d. Naturwiss. Verein. f. Steiermark, 1889.
[25]
The sucker of Leptoplana tremellaris probably does not correspond with
that of the Cotylea.
[26]
Collingwood, Trans. Linn. Soc. 2 ser. vol. i. pt. 3, 1876, p. 83.
[27]
Von Stummer-Traunfels, Zeitschr. f. wiss. Zool. Bd. lx. 1895, p. 689.
[28]
Planocera pellucida Mertens, P. simrothi v. Grff., P. grubei Grff.,
Stylochoplana sargassicola Mertens, S. californica Woodworth,
Planctoplana challengeri Grff., all belonging to the Planoceridae. See
Page 653
v. Graff, "Pelagische Polycladen," Zeitschrift f. wiss. Zoologie, Bd. lv.
1892, p. 190.
[29]
Cambridge Natural History, vol. iii. p. 74.
[30]
Lang, "Polycladen," p. 629.
[31]
Wheeler, Journal of Morphology, vol. ix. part 2, 1894, p. 195.
[32]
Many Nudibranchiate Mollusca undergo this change of habitat. See
Garstang, Journal of the Marine Biological Assoc. n.s. i. No. 4, 1890, p.
447.
[33]
Chun, "Ctenophoren," Fauna u. Flora G. v. Neapel, Monogr. I. 1880, p.
180.
[34]
See Lang, "Polycladen," p. 607.
[35]
Lang, "Polycladen," Pl. 30, Fig. 8.
[36]
Kongl. Fysiograf. Sällskapets Handlingar, Bd. iv. Lund, 1892-93.
[37]
Whitman, Journal of Morphology, vol. iv. 1890, p. 361.
[38]
A full account of Polyclad development is contained in Lang's
"Polycladen," with references to the literature of the subject. Since the
1892, p. 190.
[29]
Cambridge Natural History, vol. iii. p. 74.
[30]
Lang, "Polycladen," p. 629.
[31]
Wheeler, Journal of Morphology, vol. ix. part 2, 1894, p. 195.
[32]
Many Nudibranchiate Mollusca undergo this change of habitat. See
Garstang, Journal of the Marine Biological Assoc. n.s. i. No. 4, 1890, p.
447.
[33]
Chun, "Ctenophoren," Fauna u. Flora G. v. Neapel, Monogr. I. 1880, p.
180.
[34]
See Lang, "Polycladen," p. 607.
[35]
Lang, "Polycladen," Pl. 30, Fig. 8.
[36]
Kongl. Fysiograf. Sällskapets Handlingar, Bd. iv. Lund, 1892-93.
[37]
Whitman, Journal of Morphology, vol. iv. 1890, p. 361.
[38]
A full account of Polyclad development is contained in Lang's
"Polycladen," with references to the literature of the subject. Since the
Page 654
date of that work (1884) the embryology of Ctenophora has become
better known, but, though the segmentation of the egg and early stages of
development are very similar in both cases, the elaborate investigations
of E. B. Wilson (Journ. Morphology, vol. vi. p. 361) show that the
segmentation of Polychaet worms is again similar. The question of the
affinities of the Polycladida is also discussed by Lang ("Polycladen" p.
642 et seq.). The work of the last decade has neither proved nor disproved
his suggestion that the Ctenophores and Polyclads have been derived
from common ancestors. On this subject the remarks made by Hatschek
(Lehrbuch d. Zoologie, p. 319) are some of the weightiest that have
appeared.
[39]
Hallez, Revue Biologique du Nord de la France, tom. ii. 1889-90.
[40]
Voigt, Zool. Anz. xv. p. 238.
[41]
Grube, Archiv f. Naturgeschichte, 38 Jahrg. Bd. i. 1872, p. 273.
[42]
Vejdovsky, Zeitschr. f. wiss. Zoologie, Bd. lx. 1895, p. 200.
[43]
Woodworth, Bulletin Mus. Comp. Zoology, Harvard, vol. xxi. No. 1,
1891.
[44]
Mitth. Zool. Stat. Neapel, 1882, p. 187.
[45]
Wheeler, Journal of Morphology, vol. ix. 1894, p. 167.
[46]
Dendy, Trans. Roy. Soc. Victoria 1890, p. 65; Id. Austral. Assoc.
Brisbane, 1895, "Presid. Add. to Sect. D," p. 15.
better known, but, though the segmentation of the egg and early stages of
development are very similar in both cases, the elaborate investigations
of E. B. Wilson (Journ. Morphology, vol. vi. p. 361) show that the
segmentation of Polychaet worms is again similar. The question of the
affinities of the Polycladida is also discussed by Lang ("Polycladen" p.
642 et seq.). The work of the last decade has neither proved nor disproved
his suggestion that the Ctenophores and Polyclads have been derived
from common ancestors. On this subject the remarks made by Hatschek
(Lehrbuch d. Zoologie, p. 319) are some of the weightiest that have
appeared.
[39]
Hallez, Revue Biologique du Nord de la France, tom. ii. 1889-90.
[40]
Voigt, Zool. Anz. xv. p. 238.
[41]
Grube, Archiv f. Naturgeschichte, 38 Jahrg. Bd. i. 1872, p. 273.
[42]
Vejdovsky, Zeitschr. f. wiss. Zoologie, Bd. lx. 1895, p. 200.
[43]
Woodworth, Bulletin Mus. Comp. Zoology, Harvard, vol. xxi. No. 1,
1891.
[44]
Mitth. Zool. Stat. Neapel, 1882, p. 187.
[45]
Wheeler, Journal of Morphology, vol. ix. 1894, p. 167.
[46]
Dendy, Trans. Roy. Soc. Victoria 1890, p. 65; Id. Austral. Assoc.
Brisbane, 1895, "Presid. Add. to Sect. D," p. 15.
Page 655
[47]
Darwin, Ann. and Mag. Nat. Hist. vol. xiv. 1844, p. 241.
[48]
Shipley, Proc. Camb. Phil. Soc. vol. vii. pt. 4, 1891 (with literature).
[49]
Trans. Roy. Soc. Victoria from 1889 onwards. Trans. New Zealand
Institute, 1894-95.
[50]
Moseley, Phil. Trans. 1874, p. 105; Id. Quart. Journ. Micr. Sci. vol. xlvii.
1877, p. 273; Loman, Bijdrag tot d. Dierkunde, Aflev. 14, 1887, p. 71; Id.
Zool. Ergeb. ein. Reise in Nieder-Ost-Indien, Hft. 1, p. 131; Beddard,
Zoogeography, 1895, p. 53.
[51]
Beobachtungen ü. Anat. u. Entwickel. an der Küste von Normandie, 1863,
p. 18.
[52]
Archiv f. Naturgeschichte, 57 Jahrg. Bd. i. Hft. 3, 1891, p. 308.
[53]
Dendy, Proc. Roy. Soc. Victoria, vol. iv. n.s. i. 1892.
[54]
Schmarda, Neue wirbellose Thiere, Leipzig, 1859, I. i. p. 30.
[55]
Abhandl. d. Naturf. Gesell. zu Halle, Bd. iv. 1857, p. 33.
[56]
Arb. Zool.-Zoot. Instit. Würzburg, Bd. v. 1882, p. 120.
Darwin, Ann. and Mag. Nat. Hist. vol. xiv. 1844, p. 241.
[48]
Shipley, Proc. Camb. Phil. Soc. vol. vii. pt. 4, 1891 (with literature).
[49]
Trans. Roy. Soc. Victoria from 1889 onwards. Trans. New Zealand
Institute, 1894-95.
[50]
Moseley, Phil. Trans. 1874, p. 105; Id. Quart. Journ. Micr. Sci. vol. xlvii.
1877, p. 273; Loman, Bijdrag tot d. Dierkunde, Aflev. 14, 1887, p. 71; Id.
Zool. Ergeb. ein. Reise in Nieder-Ost-Indien, Hft. 1, p. 131; Beddard,
Zoogeography, 1895, p. 53.
[51]
Beobachtungen ü. Anat. u. Entwickel. an der Küste von Normandie, 1863,
p. 18.
[52]
Archiv f. Naturgeschichte, 57 Jahrg. Bd. i. Hft. 3, 1891, p. 308.
[53]
Dendy, Proc. Roy. Soc. Victoria, vol. iv. n.s. i. 1892.
[54]
Schmarda, Neue wirbellose Thiere, Leipzig, 1859, I. i. p. 30.
[55]
Abhandl. d. Naturf. Gesell. zu Halle, Bd. iv. 1857, p. 33.
[56]
Arb. Zool.-Zoot. Instit. Würzburg, Bd. v. 1882, p. 120.
Page 656
[57]
Woodworth (loc. cit. p. 38) states that in Phagocata the yolk-glands arise
by proliferation from two parovaria, placed just in front of the ordinary
ovaries. Iijima, however (Zeitschr. f. wiss. Zool. Bd. xl. 1883, p. 454),
regarded them as derivatives of the parenchyma.
[58]
The extensive literature on this subject is fairly completely summarised
by Voigt in Biol. Centralblatt, vol. xiv. Nos. 20, 21, 1894. Faraday's
observations (cf. p. 6, note 8) have been generally overlooked.
[59]
Archives d. Biologie, tom. xii. 1892, p. 437.
[60]
Mitth. Zool. Stat. Neapel, Bd. iii. 1882, p. 187.
[61]
Böhmig, Ergebnisse d. Plankton Expedition, Bd. ii. H. g. 1895.
[62]
von Graff, Die Acoela, Leipzig, 1892. Appendix.
[63]
The development of the Acoela has been worked out recently by Mdlle.
Pereyaslawzewa (Zapiski Novoross. Obshch. Odessa, 17 Bd. 1892) and
Gardiner (Journal of Morphology, xi. No. 1, 1895, p. 155) with
conflicting results. The former finds four endoderm cells, which give rise
to a larval intestine. The Acoela are for her, Pseudacoela. Gardiner, on
the other hand, finds no trace of an endoderm at any stage of the
development of Polychoerus caudatus.
[64]
Tijdschr. Nederland. Dierk. Ver. Deel ii. 1875.
Woodworth (loc. cit. p. 38) states that in Phagocata the yolk-glands arise
by proliferation from two parovaria, placed just in front of the ordinary
ovaries. Iijima, however (Zeitschr. f. wiss. Zool. Bd. xl. 1883, p. 454),
regarded them as derivatives of the parenchyma.
[58]
The extensive literature on this subject is fairly completely summarised
by Voigt in Biol. Centralblatt, vol. xiv. Nos. 20, 21, 1894. Faraday's
observations (cf. p. 6, note 8) have been generally overlooked.
[59]
Archives d. Biologie, tom. xii. 1892, p. 437.
[60]
Mitth. Zool. Stat. Neapel, Bd. iii. 1882, p. 187.
[61]
Böhmig, Ergebnisse d. Plankton Expedition, Bd. ii. H. g. 1895.
[62]
von Graff, Die Acoela, Leipzig, 1892. Appendix.
[63]
The development of the Acoela has been worked out recently by Mdlle.
Pereyaslawzewa (Zapiski Novoross. Obshch. Odessa, 17 Bd. 1892) and
Gardiner (Journal of Morphology, xi. No. 1, 1895, p. 155) with
conflicting results. The former finds four endoderm cells, which give rise
to a larval intestine. The Acoela are for her, Pseudacoela. Gardiner, on
the other hand, finds no trace of an endoderm at any stage of the
development of Polychoerus caudatus.
[64]
Tijdschr. Nederland. Dierk. Ver. Deel ii. 1875.
Page 657
[65]
Von Graff, Monographie d. Turbellarien: I. Rhabdocoeliden, 1882.
Gamble, Quart. Journ. Microscop. Science, vol. xxxiv. 1893, p. 433.
[66]
Zeitschr. f. wiss. Zoologie, Bd. lx. 1895, p. 163.
[67]
See von Graffs Monographie, pl. ix.; and Jensen, Turbellaria ad Litora
Norvegiae, Bergen, 1878, pl. iv.
[68]
For the reproductive organs of Rhabdocoelida, consult von Graff,
Monographie, "Die Acoela"; and Böhmig, Zeitschr. f. wiss. Zool. Bd. li.
1891, p. 167.
[69]
Untersuchungen ü. Platyhelminthen, Giessen, 1873, p. 101.
[70]
Compare the remarks on Trematodes, pp. 4-5.
[71]
Haswell, Monograph of the Temnocephaleae. Macleay Memorial
Volume. Mem. iii. 1893.
[72]
Braun, in Bronn's Klassen u. Ordn. d. Thierreichs, vol. iv. p. 407, gives a
valuable summary of our knowledge of this group. For figures, see van
Beneden and Hesse, Mémoires de l'Acad. roy. de Belgique, tom. xxxiv.
1864, pp. 1-169. A valuable paper (with synoptic tables) on Japanese
Monogenea, by Goto, Journ. Coll. Sci. Japan, vol. viii. pt. 1, 1894, has
recently appeared.
[73]
Von Graff, Monographie d. Turbellarien: I. Rhabdocoeliden, 1882.
Gamble, Quart. Journ. Microscop. Science, vol. xxxiv. 1893, p. 433.
[66]
Zeitschr. f. wiss. Zoologie, Bd. lx. 1895, p. 163.
[67]
See von Graffs Monographie, pl. ix.; and Jensen, Turbellaria ad Litora
Norvegiae, Bergen, 1878, pl. iv.
[68]
For the reproductive organs of Rhabdocoelida, consult von Graff,
Monographie, "Die Acoela"; and Böhmig, Zeitschr. f. wiss. Zool. Bd. li.
1891, p. 167.
[69]
Untersuchungen ü. Platyhelminthen, Giessen, 1873, p. 101.
[70]
Compare the remarks on Trematodes, pp. 4-5.
[71]
Haswell, Monograph of the Temnocephaleae. Macleay Memorial
Volume. Mem. iii. 1893.
[72]
Braun, in Bronn's Klassen u. Ordn. d. Thierreichs, vol. iv. p. 407, gives a
valuable summary of our knowledge of this group. For figures, see van
Beneden and Hesse, Mémoires de l'Acad. roy. de Belgique, tom. xxxiv.
1864, pp. 1-169. A valuable paper (with synoptic tables) on Japanese
Monogenea, by Goto, Journ. Coll. Sci. Japan, vol. viii. pt. 1, 1894, has
recently appeared.
[73]
Page 658
See Leuckart, "Parasiten" Bd. ii. p. 238.
[74]
Zeller, Zeitschr. f. wiss. Zool. xxii. 1872, pp. 1, 168; also Bd. xxvii. 1876,
p. 238; xlvi. 1888, p. 233.
[75]
An excellent and beautifully illustrated account, by Looss, of the
Distomatidae of Frogs and Fishes may be found in Leuckart and Chun's
Bibliotheca Zoologica, Heft 16, 1894.
[76]
Leuckart, Parasiten d. Menschen, "Trematoden," 1892-94; R. Blanchard,
Traité d. Zool. médicale, i. 1889; H. B. Ward, Report for 1894 of
Nebraska State Board of Agric. Lincoln, U.S.A. 1895, p. 225.
[77]
Huxley, Anat. of Invert. Animals, 1877, p. 194.
[78]
Braun, Bronn's Thierreichs, Bd. iv. p. 792; Leuckart, Parasiten d.
Menschen, 11 Abth. p. 158; Brandes, in Spengels Zool. Jahrb. Syst.
Abtheil. Bd. v. 1890, p. 849; v. Nordmann, Mikr. Beitr. i. Berlin, 1832.
[79]
Heckert, Bibliotheca Zoologica (Leuckart and Chun), Heft 4, 1889. I am
not aware that Leucochloridium has been noticed in England.
[80]
"Heterogamy" usually means the alternation of bisexual and unisexual
generations (e.g. Rhabdonema nigrovenosum), but is, unfortunately, also
used in the sense of Alloiogenesis, as defined above. See Grobben,
Arbeit. Zool. zoot. Ints. Wien, Bd. iv. 1881, p. 201.
[81]
Parasiten, Bd. i. Abth. II. p. 152.
[74]
Zeller, Zeitschr. f. wiss. Zool. xxii. 1872, pp. 1, 168; also Bd. xxvii. 1876,
p. 238; xlvi. 1888, p. 233.
[75]
An excellent and beautifully illustrated account, by Looss, of the
Distomatidae of Frogs and Fishes may be found in Leuckart and Chun's
Bibliotheca Zoologica, Heft 16, 1894.
[76]
Leuckart, Parasiten d. Menschen, "Trematoden," 1892-94; R. Blanchard,
Traité d. Zool. médicale, i. 1889; H. B. Ward, Report for 1894 of
Nebraska State Board of Agric. Lincoln, U.S.A. 1895, p. 225.
[77]
Huxley, Anat. of Invert. Animals, 1877, p. 194.
[78]
Braun, Bronn's Thierreichs, Bd. iv. p. 792; Leuckart, Parasiten d.
Menschen, 11 Abth. p. 158; Brandes, in Spengels Zool. Jahrb. Syst.
Abtheil. Bd. v. 1890, p. 849; v. Nordmann, Mikr. Beitr. i. Berlin, 1832.
[79]
Heckert, Bibliotheca Zoologica (Leuckart and Chun), Heft 4, 1889. I am
not aware that Leucochloridium has been noticed in England.
[80]
"Heterogamy" usually means the alternation of bisexual and unisexual
generations (e.g. Rhabdonema nigrovenosum), but is, unfortunately, also
used in the sense of Alloiogenesis, as defined above. See Grobben,
Arbeit. Zool. zoot. Ints. Wien, Bd. iv. 1881, p. 201.
[81]
Parasiten, Bd. i. Abth. II. p. 152.
Page 659
[82]
Festschrift f. Leuckart, Leipzig, 1892, p. 167.
[83]
Quart. Journ. Micros. Sci. vol. xxiii. 1883, p. 90.
[84]
The intermediate host in the Sandwich Islands is said to be Limnaea
peregra. See Lutz, Centralbl. f. Bakter. xi. 1892, p. 783.
[85]
The mortality in wet years, however, is said to be largely due to
pulmonary inflammation. This and other causes of death are not always
discriminated in the returns.
[86]
See Thomas, Quart. Journ. Micros. Science, xxiii. 1883. Neumann,
Parasites of Domesticated Animals, translated by Fleming, 1892.
[87]
Leuckart, loc. cit.; Looss, Archiv f. mikroskop. Anatomie, Bd. xlvi. 1895,
p. 1.
[88]
In Leuckart, Die Parasiten d. Menschen, pp. 521-528, 1894.
[89]
Cf. p. 89.
[90]
See Braun. Bronn's Klassen u. Ordnungen d. Thierreichs, vol. iv. p. 572.
[91]
Braun, loc. cit. p. 573.
Festschrift f. Leuckart, Leipzig, 1892, p. 167.
[83]
Quart. Journ. Micros. Sci. vol. xxiii. 1883, p. 90.
[84]
The intermediate host in the Sandwich Islands is said to be Limnaea
peregra. See Lutz, Centralbl. f. Bakter. xi. 1892, p. 783.
[85]
The mortality in wet years, however, is said to be largely due to
pulmonary inflammation. This and other causes of death are not always
discriminated in the returns.
[86]
See Thomas, Quart. Journ. Micros. Science, xxiii. 1883. Neumann,
Parasites of Domesticated Animals, translated by Fleming, 1892.
[87]
Leuckart, loc. cit.; Looss, Archiv f. mikroskop. Anatomie, Bd. xlvi. 1895,
p. 1.
[88]
In Leuckart, Die Parasiten d. Menschen, pp. 521-528, 1894.
[89]
Cf. p. 89.
[90]
See Braun. Bronn's Klassen u. Ordnungen d. Thierreichs, vol. iv. p. 572.
[91]
Braun, loc. cit. p. 573.
Page 660
[92]
Taken largely from Braun, Ibid. pp. 864-866, where the literature of the
subject is referred to fully.
[93]
Festschr. f. Leuckart, 1892, p. 134.
[94]
Cf. p. 5.
[95]
Arbeit. Inst. Wien, iii. 1881, p. 163; see also ibid. ix. 1890, p. 57.
[96]
For figures of various scolices see van Beneden, Mémoire sur les vers
Intestinaux, 1861; Braun in Bronn's Thierreich, Cestoda (in progress),
Bd. iv. Pl. xxxviii.-xlv.
[97]
The mature proglottis of Calliobothrium eschrichti is 8-9 mm. long,
whereas the strobila only measures 4-5 mm. in length. Species of
Phylliobothrium, Anthobothrium, and Tetrarhynchus show a similar but
not an equal contrast between the size of the parent and proglottis (P. J.
van Beneden, "Les Vers Cestoides," Nouv. Mém. de l'Acad. Roy. d.
Belgique, tom. xxv. 1850).
[98]
The difficult question of the nature of the Cestode body and Cestode
larvae is adequately discussed by Braun, loc. cit. p. 1167.
[99]
Leuckart, Die Parasiten d. Menschen [English trans. by W. E. Hoyle];
Blanchard, Traité de Zoologie médicale, 1893.
[100]
Taken largely from Braun, Ibid. pp. 864-866, where the literature of the
subject is referred to fully.
[93]
Festschr. f. Leuckart, 1892, p. 134.
[94]
Cf. p. 5.
[95]
Arbeit. Inst. Wien, iii. 1881, p. 163; see also ibid. ix. 1890, p. 57.
[96]
For figures of various scolices see van Beneden, Mémoire sur les vers
Intestinaux, 1861; Braun in Bronn's Thierreich, Cestoda (in progress),
Bd. iv. Pl. xxxviii.-xlv.
[97]
The mature proglottis of Calliobothrium eschrichti is 8-9 mm. long,
whereas the strobila only measures 4-5 mm. in length. Species of
Phylliobothrium, Anthobothrium, and Tetrarhynchus show a similar but
not an equal contrast between the size of the parent and proglottis (P. J.
van Beneden, "Les Vers Cestoides," Nouv. Mém. de l'Acad. Roy. d.
Belgique, tom. xxv. 1850).
[98]
The difficult question of the nature of the Cestode body and Cestode
larvae is adequately discussed by Braun, loc. cit. p. 1167.
[99]
Leuckart, Die Parasiten d. Menschen [English trans. by W. E. Hoyle];
Blanchard, Traité de Zoologie médicale, 1893.
[100]
Page 661
For a full account of the history of this subject see Leuckart, Parasiten d.
Menschen, p. 28; Braun, loc. cit. Bd. iv. p. 929 et seq.; Huxley, Collected
Essays, vol. viii. p. 229.
[101]
By Grassi this form is considered identical with T. murina. The latter
species is known, from this author's researches, to develop in rats without
migration into an intermediate host. Should Grassi's synonymy prove
correct, the presence of large numbers of this tape-worm in man would
readily receive its explanation.
[102]
Leuckart, loc. cit. p. 752 et seq.
[103]
The distinctive features of these and the foregoing tape-worms are given
on pp. 89-90
[104]
For description of the Cercocystis-larva see Villot, Ann. Sci. Nat. (Zool.)
(6), xv. 1883, Art 4; and compare Leuckart's criticism of this paper,
"Parasiten," p. 979.
[105]
Moniez, "Sur les Cysticerques," Paris, 1880; Id. "Sur les Cestodes," 1881;
Zschokke, "Recherches sur la structure anatomique et histologique d.
Cestodes," Genève, 1888.
[106]
Schmidt, Archiv f. Naturgeschichte, Jahrg. lx. Bd. 1, 1894, p. 65.
[107]
For example, the genitalia in Dipylidium caninum are duplicated in each
proglottis. Other differences are noted in the following table (pp. 89-90).
[108]
Menschen, p. 28; Braun, loc. cit. Bd. iv. p. 929 et seq.; Huxley, Collected
Essays, vol. viii. p. 229.
[101]
By Grassi this form is considered identical with T. murina. The latter
species is known, from this author's researches, to develop in rats without
migration into an intermediate host. Should Grassi's synonymy prove
correct, the presence of large numbers of this tape-worm in man would
readily receive its explanation.
[102]
Leuckart, loc. cit. p. 752 et seq.
[103]
The distinctive features of these and the foregoing tape-worms are given
on pp. 89-90
[104]
For description of the Cercocystis-larva see Villot, Ann. Sci. Nat. (Zool.)
(6), xv. 1883, Art 4; and compare Leuckart's criticism of this paper,
"Parasiten," p. 979.
[105]
Moniez, "Sur les Cysticerques," Paris, 1880; Id. "Sur les Cestodes," 1881;
Zschokke, "Recherches sur la structure anatomique et histologique d.
Cestodes," Genève, 1888.
[106]
Schmidt, Archiv f. Naturgeschichte, Jahrg. lx. Bd. 1, 1894, p. 65.
[107]
For example, the genitalia in Dipylidium caninum are duplicated in each
proglottis. Other differences are noted in the following table (pp. 89-90).
[108]
Page 662
See Stiles, Centralbl. f. Bakt. u. Parasitenkunde, 1893, xiii. p. 457 (conf.
note, p. 90).
[109]
Taken from Neumann, Parasites of Domesticated Animals, 1892, p. 448.
[110]
µ = 1⁄1000 millimetre.
[111]
For a description of these glands, and for further diagnostic details and
literature, see Stiles and Hassall, U. S. Department of Agriculture, Bureau
of Animal Industry, Bulletin 4, 1893.
[112]
Ed. van Beneden, Bull. Acad. Roy. Belgique, 1876, p. 35.
[113]
Whitman, Mittheil. Zool. Stat. Neapel, Bd. iv.; see also Braun, in Bronn's
Thierreich, Bd. iv. p. 253.
[114]
Braun, loc. cit. p. 281 (with literature).
[115]
Giard, "La Castration parasitaire," Bull. Sci. d. France et de Belgique, 3
sér. i. 1888, p. 12.
[116]
Schulze, Abh. Akad. Berlin, 1891, p. 1.
[117]
Arch. Naturg. lviii. 1891, p. 66.
[118]
P. Boston Soc. vol. vi. 1848.
note, p. 90).
[109]
Taken from Neumann, Parasites of Domesticated Animals, 1892, p. 448.
[110]
µ = 1⁄1000 millimetre.
[111]
For a description of these glands, and for further diagnostic details and
literature, see Stiles and Hassall, U. S. Department of Agriculture, Bureau
of Animal Industry, Bulletin 4, 1893.
[112]
Ed. van Beneden, Bull. Acad. Roy. Belgique, 1876, p. 35.
[113]
Whitman, Mittheil. Zool. Stat. Neapel, Bd. iv.; see also Braun, in Bronn's
Thierreich, Bd. iv. p. 253.
[114]
Braun, loc. cit. p. 281 (with literature).
[115]
Giard, "La Castration parasitaire," Bull. Sci. d. France et de Belgique, 3
sér. i. 1888, p. 12.
[116]
Schulze, Abh. Akad. Berlin, 1891, p. 1.
[117]
Arch. Naturg. lviii. 1891, p. 66.
[118]
P. Boston Soc. vol. vi. 1848.
Page 663
[119]
Zeitschr. wiss. Zool. Bd. v. 1854, p. 344.
[120]
Arch. Anat. 1858, p. 289.
[121]
Ibid. 1858, p. 558.
[122]
Mem. Ac. St. Petersb. ser. vii. tom. xiv. 1869.
[123]
Zeitschr. wiss. Zool. Bd. xliii. 1886, p. 481.
[124]
R. von Willemoes-Suhm, Ann. Nat. Hist. ser. iv. xiii. 1874, p. 409.
[125]
Semper, Zeitschr. wiss. Zool. Bd. xiii. 1863, p. 558.
[126]
L. von Graff, Morphol. Jahrb. Bd. v. 1879, p. 430.
[127]
W. A. Silliman, Zeitschr. wiss. Zool. Bd. xli. 1885, p. 48.
[128]
du Plessis, Zool. Anz. vol. xv. 1892, p. 64.
[129]
J. von Kennel, Arb. Inst. Würzburg, Bd. iv. 1877-78, p. 305.
[130]
H. N. Moseley, Ann. Nat. Hist. ser. iv. vol. xv. 1875, p. 165.
Zeitschr. wiss. Zool. Bd. v. 1854, p. 344.
[120]
Arch. Anat. 1858, p. 289.
[121]
Ibid. 1858, p. 558.
[122]
Mem. Ac. St. Petersb. ser. vii. tom. xiv. 1869.
[123]
Zeitschr. wiss. Zool. Bd. xliii. 1886, p. 481.
[124]
R. von Willemoes-Suhm, Ann. Nat. Hist. ser. iv. xiii. 1874, p. 409.
[125]
Semper, Zeitschr. wiss. Zool. Bd. xiii. 1863, p. 558.
[126]
L. von Graff, Morphol. Jahrb. Bd. v. 1879, p. 430.
[127]
W. A. Silliman, Zeitschr. wiss. Zool. Bd. xli. 1885, p. 48.
[128]
du Plessis, Zool. Anz. vol. xv. 1892, p. 64.
[129]
J. von Kennel, Arb. Inst. Würzburg, Bd. iv. 1877-78, p. 305.
[130]
H. N. Moseley, Ann. Nat. Hist. ser. iv. vol. xv. 1875, p. 165.
Page 664
[131]
See Hubrecht, in Verh. Ak. Amsterdam, vol. xx. 1880; and in Quart. J.
Micr. Sci. vol. xx. 1880, p. 431.
[132]
"Nemertinen," Fauna und Flora G. von Neapel, 22 Monogr. 1895.
[133]
Beiträge zur Naturgeschichte der Turbellarien, Griefswald, 1851.
[134]
Arb. Inst. Würzburg, Bd. iii. 1876, p. 115.
[135]
Ibid. Bd. iv. 1877, p. 305.
[136]
Zool. Anz. vol. viii. 1885, p. 51.
[137]
Quart. J. Micr. Sci. vol. xxv. 1885, suppl. p. 1.
[138]
Zeitschr. wiss. Zool. Bd. xli. 1885, p. 48.
[139]
Ibid. Bd. liii. 1892, p. 322, and Fauna und Flora G. von Neapel, 22
Monogr. 1895.
[140]
Ann. Sci. Nat. (5) vol. xvii. 1873.
[141]
Zeitschr. wiss. Zool. Bd. iv. 1853, p. 178.
See Hubrecht, in Verh. Ak. Amsterdam, vol. xx. 1880; and in Quart. J.
Micr. Sci. vol. xx. 1880, p. 431.
[132]
"Nemertinen," Fauna und Flora G. von Neapel, 22 Monogr. 1895.
[133]
Beiträge zur Naturgeschichte der Turbellarien, Griefswald, 1851.
[134]
Arb. Inst. Würzburg, Bd. iii. 1876, p. 115.
[135]
Ibid. Bd. iv. 1877, p. 305.
[136]
Zool. Anz. vol. viii. 1885, p. 51.
[137]
Quart. J. Micr. Sci. vol. xxv. 1885, suppl. p. 1.
[138]
Zeitschr. wiss. Zool. Bd. xli. 1885, p. 48.
[139]
Ibid. Bd. liii. 1892, p. 322, and Fauna und Flora G. von Neapel, 22
Monogr. 1895.
[140]
Ann. Sci. Nat. (5) vol. xvii. 1873.
[141]
Zeitschr. wiss. Zool. Bd. iv. 1853, p. 178.
Page 665
[142]
Our knowledge of British species is mainly due to M‘Intosh (British
Annelids, Ray Society, 4to, 1873) and Riches (Journ. Mar. Biol. Ass. vol.
iii. 1893-1895, p. 1).
[143]
Fauna und Flora G. von Neapel, 22 Monogr. 1895.
[144]
See M‘Intosh, British Annelids, Ray Society, 4to, 1873.
[145]
Loc. cit.
[146]
References to these works are given on p. 101.
[147]
Zitschr. wiss. Zool. Bd. xli. 1885, p. 48.
[148]
Nature, vol. xlvi. 1892, p. 611.
[149]
Zool. Anz. vol. xv. 1892, p. 64.
[150]
Zeitschr. wiss. Zool. Bd. lix. 1895, p. 83.
[151]
Arb. Inst. Würzburg, Bd. iv. 1877-1878, p. 305.
[152]
Journ. Mar. Biol. Ass. vol. iii. 1893-1895, p. 22.
Our knowledge of British species is mainly due to M‘Intosh (British
Annelids, Ray Society, 4to, 1873) and Riches (Journ. Mar. Biol. Ass. vol.
iii. 1893-1895, p. 1).
[143]
Fauna und Flora G. von Neapel, 22 Monogr. 1895.
[144]
See M‘Intosh, British Annelids, Ray Society, 4to, 1873.
[145]
Loc. cit.
[146]
References to these works are given on p. 101.
[147]
Zitschr. wiss. Zool. Bd. xli. 1885, p. 48.
[148]
Nature, vol. xlvi. 1892, p. 611.
[149]
Zool. Anz. vol. xv. 1892, p. 64.
[150]
Zeitschr. wiss. Zool. Bd. lix. 1895, p. 83.
[151]
Arb. Inst. Würzburg, Bd. iv. 1877-1878, p. 305.
[152]
Journ. Mar. Biol. Ass. vol. iii. 1893-1895, p. 22.
Page 666
[153]
Quart. J. Micr. Sci. vol. xxiii. 1883, p. 349; Ibid. vol. xxvii. 1887, p. 605.
[154]
Cf. Willey, Amphioxus and the Ancestry of the Vertebrates, Macmillan,
1894.
[155]
Ann. Sci. nat. 7, sér. vol. xiii. 1892, p. 321.
[156]
E. Rohde, SB. Ak. Berlin, 1892, p. 515.
[157]
R. Hesse, Zeitschr. wiss. Zool. Bd. liv. 1892, p. 548.
[158]
E. Rohde, Zool. Beitr. Bd. i. 1885, p. 11.
[159]
E. Rohde, Zool. Anz. xvii. 1894, p. 38.
[160]
Monographie der Nematoden, 4to, Berlin, 1866.
[161]
Zeit. Physiol. Chem. vol. xiv. 1890, p. 318.
[162]
N. A. Cobb, P. Linn. Soc. N.S. Wales, 2nd ser. vol. vi. 1891, p. 143.
[163]
Monographie der Nematoden, Berlin, 1866, p. 192.
[164]
Quart. J. Micr. Sci. vol. xxiii. 1883, p. 349; Ibid. vol. xxvii. 1887, p. 605.
[154]
Cf. Willey, Amphioxus and the Ancestry of the Vertebrates, Macmillan,
1894.
[155]
Ann. Sci. nat. 7, sér. vol. xiii. 1892, p. 321.
[156]
E. Rohde, SB. Ak. Berlin, 1892, p. 515.
[157]
R. Hesse, Zeitschr. wiss. Zool. Bd. liv. 1892, p. 548.
[158]
E. Rohde, Zool. Beitr. Bd. i. 1885, p. 11.
[159]
E. Rohde, Zool. Anz. xvii. 1894, p. 38.
[160]
Monographie der Nematoden, 4to, Berlin, 1866.
[161]
Zeit. Physiol. Chem. vol. xiv. 1890, p. 318.
[162]
N. A. Cobb, P. Linn. Soc. N.S. Wales, 2nd ser. vol. vi. 1891, p. 143.
[163]
Monographie der Nematoden, Berlin, 1866, p. 192.
[164]
Page 667
Zool. Anz. vol. xvi. 1893, p. 432.
[165]
Arch. Naturg. 60 Jahrg. Bd. i. 1894, p. 255.
[166]
SB. Ak. Berlin, 1891, p. 57.
[167]
[Hamann subsequently withdrew these statements.]
[168]
Leuckart, The Parasites of Man, English Trans. by W. E. Hoyle,
Edinburgh, 1886, p. 56.
[169]
O. Bütschli, Zeitschr. wiss. Zool. Bd. xxvi. 1876, p. 103.
[170]
O. Hamann, Centrlb. Bakter. vol. xi. 1892, p. 501.
[171]
Zeitschr. wiss. Zool. vol. xxiii. 1873, p. 402.
[172]
Ibid. vol. xlii. 1885, p. 708.
[173]
Ann. Nat. Hist. 5th ser. vol. ix. 1882, p. 301.
[174]
Macleay Memorial Volume, Sydney, 1893, p. 252; and Proc. Linn. Soc.
N.S.W. 2nd ser. vol. v. 1890, p. 449.
[175]
4th edition, 1880.
[165]
Arch. Naturg. 60 Jahrg. Bd. i. 1894, p. 255.
[166]
SB. Ak. Berlin, 1891, p. 57.
[167]
[Hamann subsequently withdrew these statements.]
[168]
Leuckart, The Parasites of Man, English Trans. by W. E. Hoyle,
Edinburgh, 1886, p. 56.
[169]
O. Bütschli, Zeitschr. wiss. Zool. Bd. xxvi. 1876, p. 103.
[170]
O. Hamann, Centrlb. Bakter. vol. xi. 1892, p. 501.
[171]
Zeitschr. wiss. Zool. vol. xxiii. 1873, p. 402.
[172]
Ibid. vol. xlii. 1885, p. 708.
[173]
Ann. Nat. Hist. 5th ser. vol. ix. 1882, p. 301.
[174]
Macleay Memorial Volume, Sydney, 1893, p. 252; and Proc. Linn. Soc.
N.S.W. 2nd ser. vol. v. 1890, p. 449.
[175]
4th edition, 1880.
Page 668
[176]
Compendium der Helminthologie, Hannover, 1878, and Nachtrag, 1889.
[177]
A. Heller, "Darmschmarotzen" in v. Liemssen's Handb. d. sp. Path. u.
Ther. vol. vii.
[178]
Cobbold's Parasites, London, 1879, p. 246.
[179]
Arch. Zool. exper. 1 sér. tom. vii. 1878, p. 283.
[180]
Arch. Zool. exper. 1 sér. tom. vii. 1878, p. 283.
[181]
Balbiani, Anat. Physiol. 7th year, 1870-71, p. 180.
[182]
A Treatise on Parasites and Parasitic Diseases. English Trans. by G.
Fleming, London, 1892.
[183]
Journ. Roy. Agric. Soc. 3rd series, vol. iv. 1893.
[184]
Sci. Mem. Medic. Officers, Army of India, vol. vii. 1892, p. 51.
[185]
Shipley, Proc. Phil. Soc. Camb. vol. viii. 1892-95, p. 211.
[186]
"The Distribution, etc., of Filaria sanguinis hominis," Trans. of 7th Inter.
Congress of Hygiene, vol. i. 1892, p. 79.
Compendium der Helminthologie, Hannover, 1878, and Nachtrag, 1889.
[177]
A. Heller, "Darmschmarotzen" in v. Liemssen's Handb. d. sp. Path. u.
Ther. vol. vii.
[178]
Cobbold's Parasites, London, 1879, p. 246.
[179]
Arch. Zool. exper. 1 sér. tom. vii. 1878, p. 283.
[180]
Arch. Zool. exper. 1 sér. tom. vii. 1878, p. 283.
[181]
Balbiani, Anat. Physiol. 7th year, 1870-71, p. 180.
[182]
A Treatise on Parasites and Parasitic Diseases. English Trans. by G.
Fleming, London, 1892.
[183]
Journ. Roy. Agric. Soc. 3rd series, vol. iv. 1893.
[184]
Sci. Mem. Medic. Officers, Army of India, vol. vii. 1892, p. 51.
[185]
Shipley, Proc. Phil. Soc. Camb. vol. viii. 1892-95, p. 211.
[186]
"The Distribution, etc., of Filaria sanguinis hominis," Trans. of 7th Inter.
Congress of Hygiene, vol. i. 1892, p. 79.
Page 669
[187]
v. Linstow, Arch. mikr. Anat. vol. xl. 1892, p. 498.
[188]
zur Strassen, Zeitschr. wiss. Zool. vol. liv. 1892, p. 655.
[189]
Rud. Leuckart, Abh. Sachs. Ges. vol. xiii. 1887, p. 567.
[190]
Macleay Memorial Vol. Sydney, 1893, p. 253.
[191]
Centrbl. Bakter. vol. viii. 1890, p. 489.
[192]
J. Percival, Nat. Sci. vol. vi. 1895, p. 187.
[193]
A. Strubell, Bibl. Zool. Bd. i. Heft 2, 1888, p. 1.
[194]
C. R. Ac. Sci. cxviii. 1894, p. 549.
[195]
Bihang Svenska Ak. Handl. viii. No. 11, 1883.
[196]
Anat. Untersuch. ü. freilebende Nordsee-Nematoden, Leipzig, 1886.
[197]
Cobb, P. Linn. Soc. N. S. Wales, 2nd ser. viii. 1893, p. 389.
[198]
Zeitschr. wiss. Zool. Bd. xvii. 1867, p. 539.
v. Linstow, Arch. mikr. Anat. vol. xl. 1892, p. 498.
[188]
zur Strassen, Zeitschr. wiss. Zool. vol. liv. 1892, p. 655.
[189]
Rud. Leuckart, Abh. Sachs. Ges. vol. xiii. 1887, p. 567.
[190]
Macleay Memorial Vol. Sydney, 1893, p. 253.
[191]
Centrbl. Bakter. vol. viii. 1890, p. 489.
[192]
J. Percival, Nat. Sci. vol. vi. 1895, p. 187.
[193]
A. Strubell, Bibl. Zool. Bd. i. Heft 2, 1888, p. 1.
[194]
C. R. Ac. Sci. cxviii. 1894, p. 549.
[195]
Bihang Svenska Ak. Handl. viii. No. 11, 1883.
[196]
Anat. Untersuch. ü. freilebende Nordsee-Nematoden, Leipzig, 1886.
[197]
Cobb, P. Linn. Soc. N. S. Wales, 2nd ser. viii. 1893, p. 389.
[198]
Zeitschr. wiss. Zool. Bd. xvii. 1867, p. 539.
Page 670
[199]
Panceri, Atti Acc. Napoli, vii. 1878, No. 10.
[200]
Panceri, Atti Acc. Napoli, vii. 1878, No. 10.
[201]
Arch. Naturg. 35 (i.), 1869, p. 112.
[202]
Zeitschr. wiss. Zool. Bd. xlii. 1885, p. 708.
[203]
Arch. Naturg. Jahrg. iii. Bd. i. 1837, p. 52; and van Beneden, Animal
Parasites, p. 91. International Sci. Series.
[204]
F. Vejdovsky, Zeitschr. wiss. Zool. Bd. xliii. 1886, p. 369; Zeitschr. wiss.
Zool. Bd. xlix. 1888, p. 188.
[205]
Arch. mikr. Anat. Bd. xxxvii. 1891, p. 239.
[206]
Arch. mikr. Anat. Bd. xxxiv. 1889, p. 248.
[207]
A. E. Verrill, P. U. S. Mus. vol. ii. 1879, p. 165.
[208]
O. Bürger, Zool. Jahrb. Anat. Bd. iv. 1891, p. 631.
[209]
H. B. Ward, Bull. Mus. Harvard, vol. xxiii. 1892-93, p. 135.
Panceri, Atti Acc. Napoli, vii. 1878, No. 10.
[200]
Panceri, Atti Acc. Napoli, vii. 1878, No. 10.
[201]
Arch. Naturg. 35 (i.), 1869, p. 112.
[202]
Zeitschr. wiss. Zool. Bd. xlii. 1885, p. 708.
[203]
Arch. Naturg. Jahrg. iii. Bd. i. 1837, p. 52; and van Beneden, Animal
Parasites, p. 91. International Sci. Series.
[204]
F. Vejdovsky, Zeitschr. wiss. Zool. Bd. xliii. 1886, p. 369; Zeitschr. wiss.
Zool. Bd. xlix. 1888, p. 188.
[205]
Arch. mikr. Anat. Bd. xxxvii. 1891, p. 239.
[206]
Arch. mikr. Anat. Bd. xxxiv. 1889, p. 248.
[207]
A. E. Verrill, P. U. S. Mus. vol. ii. 1879, p. 165.
[208]
O. Bürger, Zool. Jahrb. Anat. Bd. iv. 1891, p. 631.
[209]
H. B. Ward, Bull. Mus. Harvard, vol. xxiii. 1892-93, p. 135.
Page 671
[210]
Mem. Acc. Torino, 2nd ser. vol. xl. 1890, p. 1.
[211]
Centrlb. Bakter. Bd. ix. 1891, p. 760.
[212]
Zeitschr. wiss. Zool. Bd. vii. 1856, p. 1.
[213]
Zool. Anz. vol. x. 1887, p. 602.
[214]
Von Linstow, Hannover, 1878, and Nachtrag, 1889.
[215]
H. B. Ward, P. Amer. Ac. new ser. vol. xix. 1892, p. 260.
[216]
Jen. Zeitschr. Bd. xxv. 1891, p. 113.
[217]
Bibl. Zool. Bd. ii. Heft 7. 1893.
[218]
Jen. Zeitschr. Bd. xxv. 1891, p. 113.
[219]
Zool. Anz. Bd. xv. 1892, p. 195.
[220]
Zool. Anz. vol. xv. 1892, p. 52.
[221]
Zool. Anz. vol. viii. 1885, p. 19.
Mem. Acc. Torino, 2nd ser. vol. xl. 1890, p. 1.
[211]
Centrlb. Bakter. Bd. ix. 1891, p. 760.
[212]
Zeitschr. wiss. Zool. Bd. vii. 1856, p. 1.
[213]
Zool. Anz. vol. x. 1887, p. 602.
[214]
Von Linstow, Hannover, 1878, and Nachtrag, 1889.
[215]
H. B. Ward, P. Amer. Ac. new ser. vol. xix. 1892, p. 260.
[216]
Jen. Zeitschr. Bd. xxv. 1891, p. 113.
[217]
Bibl. Zool. Bd. ii. Heft 7. 1893.
[218]
Jen. Zeitschr. Bd. xxv. 1891, p. 113.
[219]
Zool. Anz. Bd. xv. 1892, p. 195.
[220]
Zool. Anz. vol. xv. 1892, p. 52.
[221]
Zool. Anz. vol. viii. 1885, p. 19.
Page 672
[222]
Shipley, Quart. J. Micr. Sci. vol. xxxix. 1896.
[223]
O. Hertwig, Jen. Zeitschr. Bd. xiv. 1880, p. 196.
[224]
P. Gourret, Ann. Mus. Marseille, tom. ii. Mem. 2, 1884, p. 103.
[225]
Bibl. Zool. vol. i. 1888-89, p. 1.
[226]
Scott, Annals of Scottish Natural History, 1892 and 1893.
[227]
E. Béraneck, Rev. Zool. Suisse, vol. iii. 1895, p. 137.
[228]
Ann. Mag. Nat. Hist. 6th ser. vol. xiii. 1894, p. 440.
[229]
Archiv Naturg. 58 Jahrg. Bd. i. 1892, p. 333.
[230]
I Chetognati, Flora u. Fauna d. Golfes von Neapel, Mon. v. 1883.
[231]
loc. cit.
[232]
loc. cit.
[233]
The Rotifera, two vols, and supplt. London, 1886-89.
Shipley, Quart. J. Micr. Sci. vol. xxxix. 1896.
[223]
O. Hertwig, Jen. Zeitschr. Bd. xiv. 1880, p. 196.
[224]
P. Gourret, Ann. Mus. Marseille, tom. ii. Mem. 2, 1884, p. 103.
[225]
Bibl. Zool. vol. i. 1888-89, p. 1.
[226]
Scott, Annals of Scottish Natural History, 1892 and 1893.
[227]
E. Béraneck, Rev. Zool. Suisse, vol. iii. 1895, p. 137.
[228]
Ann. Mag. Nat. Hist. 6th ser. vol. xiii. 1894, p. 440.
[229]
Archiv Naturg. 58 Jahrg. Bd. i. 1892, p. 333.
[230]
I Chetognati, Flora u. Fauna d. Golfes von Neapel, Mon. v. 1883.
[231]
loc. cit.
[232]
loc. cit.
[233]
The Rotifera, two vols, and supplt. London, 1886-89.
Page 673
[234]
Phil. Trans. vol. xix. No. 220, p. 254 (abridged ed. vol. iii. 1705, p. 651).
[235]
Ibid. vol. xxiii. No. 283, p. 1304 (abridged ed. vol. v. p. 6).
[236]
Ibid. vol. xxiii. No. 295, p. 1784 (abridged ed. vol. v. p. 175).
[237]
Ibid. No. 337, vol. xxviii. 1714, p. 160.
[238]
Employment for the Microscope. London, 1785.
[239]
Paris, 1841.
[240]
Quart. Journ. Micr. Sci. vol. i. 1853, pp. 3-8, 65-76.
[241]
Trans. Micr. Soc. London, vol. i. (n.s.), 1853, pp. 1-19.
[242]
Verh. Ges. Würzb. vol. iv. 1854; Zeitschr. wiss. Zool. vols. iii. vi. 1851-55.
[243]
Zeitschr. wiss. Zool. vols. vii. ix. xii. 1856-58-63.
[244]
London, 1861.
[245]
Zeitschr. wiss. Zool. vol. xxxix. 1883.
Phil. Trans. vol. xix. No. 220, p. 254 (abridged ed. vol. iii. 1705, p. 651).
[235]
Ibid. vol. xxiii. No. 283, p. 1304 (abridged ed. vol. v. p. 6).
[236]
Ibid. vol. xxiii. No. 295, p. 1784 (abridged ed. vol. v. p. 175).
[237]
Ibid. No. 337, vol. xxviii. 1714, p. 160.
[238]
Employment for the Microscope. London, 1785.
[239]
Paris, 1841.
[240]
Quart. Journ. Micr. Sci. vol. i. 1853, pp. 3-8, 65-76.
[241]
Trans. Micr. Soc. London, vol. i. (n.s.), 1853, pp. 1-19.
[242]
Verh. Ges. Würzb. vol. iv. 1854; Zeitschr. wiss. Zool. vols. iii. vi. 1851-55.
[243]
Zeitschr. wiss. Zool. vols. vii. ix. xii. 1856-58-63.
[244]
London, 1861.
[245]
Zeitschr. wiss. Zool. vol. xxxix. 1883.
Page 674
[246]
Ann. Nat. Hist. ser. 6, vol. v. 1890, p. 1; viii. 1891, p. 34.
[247]
Jen. Zeitschr. Nat. vol. xix. 1886; and Zeitschr. wiss. Zool. vols. xliii. xlix.
1886-90.
[248]
Zeitschr. wiss. Zool. vol. xliv. 1886, p. 273.
[249]
Ibid. vol. xliv. p. 396; xlvii. 1888, p. 353; liii. 1892, p. 1.
[250]
For additions see Rousselet, J. Roy. Micr. Soc. 1893 and 1897.
[251]
See p. 228.
[252]
Quart. Journ. Micr. Soc. (n.s.) vol. xxiv. 1884, p. 352.
[253]
The definition of the Orders and systematic position of the genera and
species referred to under this head will be found in a following section
(pp. 220 f.).
[254]
Reprinted in Baker's Employment for the Microscope, 1785, pp. 267 f.
[255]
"Wheel Animals, though found with most Certainty in Leaden Gutters,
etc. are often discovered in the Waters of some Ditches, and likewise in
Water that has stood a considerable Time even in the House; for I have
often met with them, in sufficient Plenty, in a Sort of slimy Matter that is
Ann. Nat. Hist. ser. 6, vol. v. 1890, p. 1; viii. 1891, p. 34.
[247]
Jen. Zeitschr. Nat. vol. xix. 1886; and Zeitschr. wiss. Zool. vols. xliii. xlix.
1886-90.
[248]
Zeitschr. wiss. Zool. vol. xliv. 1886, p. 273.
[249]
Ibid. vol. xliv. p. 396; xlvii. 1888, p. 353; liii. 1892, p. 1.
[250]
For additions see Rousselet, J. Roy. Micr. Soc. 1893 and 1897.
[251]
See p. 228.
[252]
Quart. Journ. Micr. Soc. (n.s.) vol. xxiv. 1884, p. 352.
[253]
The definition of the Orders and systematic position of the genera and
species referred to under this head will be found in a following section
(pp. 220 f.).
[254]
Reprinted in Baker's Employment for the Microscope, 1785, pp. 267 f.
[255]
"Wheel Animals, though found with most Certainty in Leaden Gutters,
etc. are often discovered in the Waters of some Ditches, and likewise in
Water that has stood a considerable Time even in the House; for I have
often met with them, in sufficient Plenty, in a Sort of slimy Matter that is
Page 675
apt to be produced on the Sides of Glasses and other Vessels, that are kept
long with the Infusions of Hay or other Vegetables; and probably they are
wafted thither by the Air, when in the Condition of little dry Globules."
[256]
Gosse's account of the "Structure, Functions, and Homologies of the
Manducatory Organs in the Class Rotifera" (in Phil. Trans. 1856) remains
as the most complete anatomical account we have, though his attempt to
identify these parts with the modified limbs of the Arthropod mouth has
met with no support from subsequent workers. Gosse rendered these parts
clearly visible by the use of dilute caustic alkali.
[257]
A modification of this type is seen in the parasite Drilophagus, where the
unci and rami are two-pronged at the end, but the trophi are not movable
on one another, but protrusible as a whole to serve as an organ of
attachment to the Oligochaete Lumbriculus, to which this Rotifer attaches
itself. See Vejdovsky, "Ueb. Drilophaga bucephalus," etc., in SB. Böhm.
Ges. Jahrg. 1882 (1883), p. 390.
[258]
"Zur Rotatorien Württemburgs," in Jahresb. Ver. Würt. vol. l. 1894, p. 57.
[259]
Similarly Hudson and Zelinka both regard the dorsal antenna as formed
by the coalescence of two antennae. These retain their distinctness in
Asplanchna; in some Bdelloida the single antenna is supplied by a pair of
nerves.
[260]
C. R. Ac. Sci. cxi. 1890, p. 310; cxiii. 1891, p. 388.
[261]
Acta Univ. Lund. xxviii. 1891-92.
[262]
[See, however, Calman, Natural Science, xiii. 1898, p. 43.]
long with the Infusions of Hay or other Vegetables; and probably they are
wafted thither by the Air, when in the Condition of little dry Globules."
[256]
Gosse's account of the "Structure, Functions, and Homologies of the
Manducatory Organs in the Class Rotifera" (in Phil. Trans. 1856) remains
as the most complete anatomical account we have, though his attempt to
identify these parts with the modified limbs of the Arthropod mouth has
met with no support from subsequent workers. Gosse rendered these parts
clearly visible by the use of dilute caustic alkali.
[257]
A modification of this type is seen in the parasite Drilophagus, where the
unci and rami are two-pronged at the end, but the trophi are not movable
on one another, but protrusible as a whole to serve as an organ of
attachment to the Oligochaete Lumbriculus, to which this Rotifer attaches
itself. See Vejdovsky, "Ueb. Drilophaga bucephalus," etc., in SB. Böhm.
Ges. Jahrg. 1882 (1883), p. 390.
[258]
"Zur Rotatorien Württemburgs," in Jahresb. Ver. Würt. vol. l. 1894, p. 57.
[259]
Similarly Hudson and Zelinka both regard the dorsal antenna as formed
by the coalescence of two antennae. These retain their distinctness in
Asplanchna; in some Bdelloida the single antenna is supplied by a pair of
nerves.
[260]
C. R. Ac. Sci. cxi. 1890, p. 310; cxiii. 1891, p. 388.
[261]
Acta Univ. Lund. xxviii. 1891-92.
[262]
[See, however, Calman, Natural Science, xiii. 1898, p. 43.]
Page 676
[263]
Zeitschr. wiss. Zool. xxii. 1872, p. 455.
[264]
Arch. Zool. Exp. sér. 2, i. 1883, p. 131.
[265]
Zeitschr. wiss. Zool. xliv. 1886, p. 273.
[266]
Ibid. liii. 1892, p. 1.
[267]
[See further Jennings, Bull. Mus. Harvard, xxx. 1896, p. 1; Erlanger and
Lauterborn, Zool. Anz. xx. 1897, p, 452; and Lenssen, Zool. Anz. xxi.
1898, p. 617.]
[268]
It does not appear to us that Zelinka is justified by his account of the
development in regarding this cup as other than a part of the disc.
[269]
The classification we have adopted is a modification of that made by
Hudson and Gosse; we have divided up their first Order Rhizota into two,
and split off from Flosculariidae the family Apsilidae; removed the
Asplanchnaceae from the admittedly heterogeneous Order Ploima, made
distinct families in the Ploima for Microcodonidae and Rhinopidae, and
created a third new Order for the Seisonaceae. Ehrenberg, Gosse, and
Hudson, being the authors of most of the genera, are designated by their
initials only.
[270]
This second species has also been found in the Northern United States.
[271]
Zeitschr. wiss. Zool. xxii. 1872, p. 455.
[264]
Arch. Zool. Exp. sér. 2, i. 1883, p. 131.
[265]
Zeitschr. wiss. Zool. xliv. 1886, p. 273.
[266]
Ibid. liii. 1892, p. 1.
[267]
[See further Jennings, Bull. Mus. Harvard, xxx. 1896, p. 1; Erlanger and
Lauterborn, Zool. Anz. xx. 1897, p, 452; and Lenssen, Zool. Anz. xxi.
1898, p. 617.]
[268]
It does not appear to us that Zelinka is justified by his account of the
development in regarding this cup as other than a part of the disc.
[269]
The classification we have adopted is a modification of that made by
Hudson and Gosse; we have divided up their first Order Rhizota into two,
and split off from Flosculariidae the family Apsilidae; removed the
Asplanchnaceae from the admittedly heterogeneous Order Ploima, made
distinct families in the Ploima for Microcodonidae and Rhinopidae, and
created a third new Order for the Seisonaceae. Ehrenberg, Gosse, and
Hudson, being the authors of most of the genera, are designated by their
initials only.
[270]
This second species has also been found in the Northern United States.
[271]
Page 677
This Order has been monographed recently by Janson in Abh. Ver. Brem.
Bd. xii. Beilage, 1893, p. 1.
[272]
See Hudson in Month. Micr. Journ. vol. vi. 1871, pp. 121, 215, and
Quart. Journ. Micr. Sci. (n.s.) xii. 1872, p. 333; Lankester, ibid. p. 338;
Levander in Act. Soc. Faun. Fenn. xi. 1894.
[273]
In Denk. Ak. Wien, vol. vii. 1854, 2 Abth., p. 15. As has been suggested
by Deby and by Daday, it is not impossible that Hexarthra is identical
with Pedalion (and in this case the latter name, as newer, should be
suppressed in favour of the former); but we must suppose that Schmarda's
figure of the front view is a combination, more or less from memory or
notes, of two sketches or notes taken some time before publication; the
one a side view somewhat obliquely flattened, showing the two eyes as in
Levander's Fig. 3; the other a front view, showing the two pairs of lateral
limbs in their correct positions under pressure.
[274]
The male of Rhinops vitrea is exceptional in possessing a complete,
functional alimentary canal, with mastax, stomach, and intestine
(Rousselet). That of Proales werneckii has a mastax, but no intestine
(Rothert).
[275]
For a full account of this group see Claus in Festschr. Z.-B. Ges. Wien,
1876, p. 75; and Plate in Mt. Stat. Neapel, vol. vii. 1886-87, p. 234; Ann.
Nat. Hist. ser. 6, vol. ii., 1888, p. 86.
[276]
[Eighteen more have since been recorded.]
[277]
I have recently found a large species of this genus dwelling in the shell of
the large Cladoceran Crustacean, Eurycercus lamellatus. It is remarkable
for its power of completely telescoping its extremities within the middle
Bd. xii. Beilage, 1893, p. 1.
[272]
See Hudson in Month. Micr. Journ. vol. vi. 1871, pp. 121, 215, and
Quart. Journ. Micr. Sci. (n.s.) xii. 1872, p. 333; Lankester, ibid. p. 338;
Levander in Act. Soc. Faun. Fenn. xi. 1894.
[273]
In Denk. Ak. Wien, vol. vii. 1854, 2 Abth., p. 15. As has been suggested
by Deby and by Daday, it is not impossible that Hexarthra is identical
with Pedalion (and in this case the latter name, as newer, should be
suppressed in favour of the former); but we must suppose that Schmarda's
figure of the front view is a combination, more or less from memory or
notes, of two sketches or notes taken some time before publication; the
one a side view somewhat obliquely flattened, showing the two eyes as in
Levander's Fig. 3; the other a front view, showing the two pairs of lateral
limbs in their correct positions under pressure.
[274]
The male of Rhinops vitrea is exceptional in possessing a complete,
functional alimentary canal, with mastax, stomach, and intestine
(Rousselet). That of Proales werneckii has a mastax, but no intestine
(Rothert).
[275]
For a full account of this group see Claus in Festschr. Z.-B. Ges. Wien,
1876, p. 75; and Plate in Mt. Stat. Neapel, vol. vii. 1886-87, p. 234; Ann.
Nat. Hist. ser. 6, vol. ii., 1888, p. 86.
[276]
[Eighteen more have since been recorded.]
[277]
I have recently found a large species of this genus dwelling in the shell of
the large Cladoceran Crustacean, Eurycercus lamellatus. It is remarkable
for its power of completely telescoping its extremities within the middle
Page 678
segments, and for its immense foot-glands, both characters being
doubtless correlated with its habitat. Rousselet identifies it with P.
petromyzon.
[278]
Month. Micr. Journ. vol. ix. 1873, p. 287; Journ. Quekett Club, ser. 2,
vol. ii. 1884-86, p. 231.
[279]
See Dr. Hudson's very suggestive presidential addresses to the Royal
Microscopical Society, published in their Journal, vols. ix.-xi. 1889-91.
[280]
Euchlanis lynceus.—This is clearly not an Euchlanis, and of the six
names referred to—Ploesoma, Gomphogaster, Gastropus, Gastroschiza,
Bipalpus, and Dictyoderma—the first has priority, and the other five drop
by the laws of zoological nomenclature.
[281]
Journ. Quekett Club, ser. 2, vol. v. 1892-94, p. 205.
[282]
Trans. Micr. Soc. (n.s.) i. 1853, p. 18 (read Dec. 31, 1851): "We may say,
therefore, that the Rotifera are organized upon the plan of an Annelid
larva.... I do not hesitate to draw the conclusion ... that the Rotifera are
the permanent forms of Echinoderm larvae, and hold the same relation to
the Echinoderms that the Hydriform Polypi hold to the Medusae, or that
Appendicularia holds to the Ascidians."
[283]
Quart. Journ. Micr. Sci. (n.s.) vol. xvii. 1877, p. 399.
[284]
Ibid. (n.s.) vol. xx. 1880, p. 381.
[285]
doubtless correlated with its habitat. Rousselet identifies it with P.
petromyzon.
[278]
Month. Micr. Journ. vol. ix. 1873, p. 287; Journ. Quekett Club, ser. 2,
vol. ii. 1884-86, p. 231.
[279]
See Dr. Hudson's very suggestive presidential addresses to the Royal
Microscopical Society, published in their Journal, vols. ix.-xi. 1889-91.
[280]
Euchlanis lynceus.—This is clearly not an Euchlanis, and of the six
names referred to—Ploesoma, Gomphogaster, Gastropus, Gastroschiza,
Bipalpus, and Dictyoderma—the first has priority, and the other five drop
by the laws of zoological nomenclature.
[281]
Journ. Quekett Club, ser. 2, vol. v. 1892-94, p. 205.
[282]
Trans. Micr. Soc. (n.s.) i. 1853, p. 18 (read Dec. 31, 1851): "We may say,
therefore, that the Rotifera are organized upon the plan of an Annelid
larva.... I do not hesitate to draw the conclusion ... that the Rotifera are
the permanent forms of Echinoderm larvae, and hold the same relation to
the Echinoderms that the Hydriform Polypi hold to the Medusae, or that
Appendicularia holds to the Ascidians."
[283]
Quart. Journ. Micr. Sci. (n.s.) vol. xvii. 1877, p. 399.
[284]
Ibid. (n.s.) vol. xx. 1880, p. 381.
[285]
Page 679
Arb. Z. Inst. Wien, vols. i. iii. v. 1878-84; Lehrbuch der Zoologie, part iii.
1891.
[286]
Zeitschr. wiss. Zool. vol. xliv. 1886, p. 1.
[287]
The Microscope (Detroit), 1887-88.
[288]
Zeitschr. wiss. Zool. xlix. 1890, p. 209.
[289]
Ann. Sci. Nat. ser. 3, vol. xv. 1851, p. 158.
[290]
Zeitschr. wiss. Zool. vol. xlv. 1887, pp. 401-467, t. xx-xxii.
[291]
The breadth of the latter is estimated from Reinhard's figure.
[292]
The Echiuroid Gephyrea (see p. 434) are by some authorities considered
to be a division of the Chaetopoda.
[293]
Another worm, Histriobdella (Histriodrilus) homari, which is parasitic
on the eggs of the lobster, and which occurs on our coast, has been placed
amongst the Archiannelida. It is a minute form, with peculiarities in its
anatomy which render its affinities uncertain.
[294]
Quart. J. Micr. Sci. xxvii. 1887, p. 109.
[295]
J. Mar. Biol. Assoc. vol. i. (n.s.) 1889-90, p. 119.
1891.
[286]
Zeitschr. wiss. Zool. vol. xliv. 1886, p. 1.
[287]
The Microscope (Detroit), 1887-88.
[288]
Zeitschr. wiss. Zool. xlix. 1890, p. 209.
[289]
Ann. Sci. Nat. ser. 3, vol. xv. 1851, p. 158.
[290]
Zeitschr. wiss. Zool. vol. xlv. 1887, pp. 401-467, t. xx-xxii.
[291]
The breadth of the latter is estimated from Reinhard's figure.
[292]
The Echiuroid Gephyrea (see p. 434) are by some authorities considered
to be a division of the Chaetopoda.
[293]
Another worm, Histriobdella (Histriodrilus) homari, which is parasitic
on the eggs of the lobster, and which occurs on our coast, has been placed
amongst the Archiannelida. It is a minute form, with peculiarities in its
anatomy which render its affinities uncertain.
[294]
Quart. J. Micr. Sci. xxvii. 1887, p. 109.
[295]
J. Mar. Biol. Assoc. vol. i. (n.s.) 1889-90, p. 119.
Page 680
[296]
Schimkewitsch, Zeitschr. f. wiss. Zool. lix. 1895, p. 46.
[297]
Hatschek, Arb. Zool. Inst. Wien, iii. 1881, p. 79.
[298]
Fraipont, "Le Genre Polygordius," Fauna u. Flora des Golfes v. Neapel,
Monogr. xiv. 1887.
[299]
T. J. Parker, Lessons in Elementary Biology, London, 1891, p. 267, gives
a full account of the anatomy and development of Polygordius.
[300]
"Die Capitelliden," Fauna u. Flora d. Golfes v. Neapel, Monogr. xvi.
1887, p. 350.
[301]
Encyclopaedia Britannica, 9th ed., Art. "Mollusca," p. 652.
[302]
Benham, "The Post-Larval Stage of Arenicola," J. Mar. Biol. Assoc. iii.
(n.s.) 1893, p. 48.
[303]
The blood is colourless in Syllidae and Nephthydidae.
[304]
Ehlers states that some Eunicidae have green blood.
[305]
Benham, Quart. J. Micr. Sci. xxxix. 1896, p. 1.
[306]
Schimkewitsch, Zeitschr. f. wiss. Zool. lix. 1895, p. 46.
[297]
Hatschek, Arb. Zool. Inst. Wien, iii. 1881, p. 79.
[298]
Fraipont, "Le Genre Polygordius," Fauna u. Flora des Golfes v. Neapel,
Monogr. xiv. 1887.
[299]
T. J. Parker, Lessons in Elementary Biology, London, 1891, p. 267, gives
a full account of the anatomy and development of Polygordius.
[300]
"Die Capitelliden," Fauna u. Flora d. Golfes v. Neapel, Monogr. xvi.
1887, p. 350.
[301]
Encyclopaedia Britannica, 9th ed., Art. "Mollusca," p. 652.
[302]
Benham, "The Post-Larval Stage of Arenicola," J. Mar. Biol. Assoc. iii.
(n.s.) 1893, p. 48.
[303]
The blood is colourless in Syllidae and Nephthydidae.
[304]
Ehlers states that some Eunicidae have green blood.
[305]
Benham, Quart. J. Micr. Sci. xxxix. 1896, p. 1.
[306]
Page 681
Schaeppi, Jena. Zeit. xxviii. 1894, p. 217.
[307]
Goodrich, Quart. J. Micr. Sci. xxxiv. 1893, p. 387.
[308]
Benham, Quart. J. Micr. Sci. xxxii. 1891, p. 325. See also Bourne
(nephridium of Polynoë), Tr. Linn. Soc. (Zool.), ii. 1883, p. 357; Meyer,
for nephridium of Terebellidae, Sabellidae, and Cirratulidae, in Mt. Zool.
Stat. Neapel, vii. 1887, p. 592.
[309]
It is worthy of note that in Aeolosoma alone amongst the Oligochaeta
does the brain lie in the prostomium in the adult.
[310]
Andrews, "The Eyes of Polychaetes," J. Morph. vii. 1892, p. 169.
[311]
Wistinghausen, "Entwick. v. N. dumerilii," Mt. Zool. Stat. Neapel, x.
1891, p. 41.
[312]
This is a modification of the classification proposed by me at the meeting
of the British Association at Oxford, 1894 (see Report, p. 696). For
further characteristics of these Orders and sub-Orders see below Chap.
XII. Ehlers, "Die Borstenwürmer," 1864, gives a historical survey of the
group, and enumerates the earlier classifications.
[313]
In Coabangia (see p. 284) the anus is near the anterior end, on the ventral
surface.
[314]
It is doubtful whether these organs are palps or only lateral lips.
[307]
Goodrich, Quart. J. Micr. Sci. xxxiv. 1893, p. 387.
[308]
Benham, Quart. J. Micr. Sci. xxxii. 1891, p. 325. See also Bourne
(nephridium of Polynoë), Tr. Linn. Soc. (Zool.), ii. 1883, p. 357; Meyer,
for nephridium of Terebellidae, Sabellidae, and Cirratulidae, in Mt. Zool.
Stat. Neapel, vii. 1887, p. 592.
[309]
It is worthy of note that in Aeolosoma alone amongst the Oligochaeta
does the brain lie in the prostomium in the adult.
[310]
Andrews, "The Eyes of Polychaetes," J. Morph. vii. 1892, p. 169.
[311]
Wistinghausen, "Entwick. v. N. dumerilii," Mt. Zool. Stat. Neapel, x.
1891, p. 41.
[312]
This is a modification of the classification proposed by me at the meeting
of the British Association at Oxford, 1894 (see Report, p. 696). For
further characteristics of these Orders and sub-Orders see below Chap.
XII. Ehlers, "Die Borstenwürmer," 1864, gives a historical survey of the
group, and enumerates the earlier classifications.
[313]
In Coabangia (see p. 284) the anus is near the anterior end, on the ventral
surface.
[314]
It is doubtful whether these organs are palps or only lateral lips.
Page 682
[315]
Pruvot traced the nerve supply to these organs, and thus established their
homology. Arch. d. Zool. Expér. (ser. 2) iii. 1885, p. 211.
[316]
Meyer, "Stud. ub. d. Körperbau der Anneliden," Mt. Zool. Stat. Neapel,
vii. 1887, p. 592; viii. 1888, p. 462. In this work a great number of
important and interesting anatomical facts are recorded with respect to
the Terebelliformia and Sabelliformia, as well as certain details as to the
structure and development of the nephridia.
[317]
In some of the members of this family paired lateral tentacles appear to
exist.
[318]
It is possible that some of these may be peristomial.
[319]
Individual cases in which chaetae are present have been recorded.
[320]
Meyer, loc. cit.
[321]
Haswell, P. Linn. Soc. N.S. Wales, vii. 1883, p. 251.
[322]
Eisig, "Die Capitelliden," Fauna u. Flora G. v. Neapel, Monogr. xvi.
1887, p. 331.
[323]
Compare with this the muscular organ of Dinophilus, p. 243, Protodrilus,
and a similar structure which occurs in Terebellids.
Pruvot traced the nerve supply to these organs, and thus established their
homology. Arch. d. Zool. Expér. (ser. 2) iii. 1885, p. 211.
[316]
Meyer, "Stud. ub. d. Körperbau der Anneliden," Mt. Zool. Stat. Neapel,
vii. 1887, p. 592; viii. 1888, p. 462. In this work a great number of
important and interesting anatomical facts are recorded with respect to
the Terebelliformia and Sabelliformia, as well as certain details as to the
structure and development of the nephridia.
[317]
In some of the members of this family paired lateral tentacles appear to
exist.
[318]
It is possible that some of these may be peristomial.
[319]
Individual cases in which chaetae are present have been recorded.
[320]
Meyer, loc. cit.
[321]
Haswell, P. Linn. Soc. N.S. Wales, vii. 1883, p. 251.
[322]
Eisig, "Die Capitelliden," Fauna u. Flora G. v. Neapel, Monogr. xvi.
1887, p. 331.
[323]
Compare with this the muscular organ of Dinophilus, p. 243, Protodrilus,
and a similar structure which occurs in Terebellids.
Page 683
[324]
Korschelt, "Über Ophryotrocha puerilis," Zeitschr. f. wiss. Zool. lv. 1893,
p. 224.
[325]
Eisig, Mt. Zool. Stat. Neapel, ii. 1881, p. 255.
[326]
They are specially large also in the Typhloscolecidae; while Racovitza
(Ann. Mag. N. H. (ser. 6), xv. 1895, p. 279) has recently suggested that
the caruncle of Amphinomidae belongs to the category of nuchal organs,
and compares it with the ciliated lappets of Pterosyllis.
[327]
Ehlers, Zeitschr. f. wiss. Zool. liii. 1892, p. 217.
[328]
See Claparède and Metschnikoff, "Beit. zur Kennt. d. Entwick der
Chaetopoden," Zeitschr. f. wiss. Zool. xix. 1869, p. 163; and Fewkes, "On
the Development of certain Worm Larvae," Bulletin Mus. Harvard, xi.
1883, p. 167.
[329]
For an account of the anatomy and development of a Trochosphere, see
Hatschek, on Eupomatus, in Arbeit. Zool. Inst. Wien, vi. 1885. Also
Meyer, Mt. Zool. Stat. Neapel, viii. 1888, p. 462; and for Polynoid larva
see Häcker, Zool. Jahrb. Abth. Anat. viii. 1895, p. 245.
[330]
See Meyer (ref. on p. 261).
[331]
Many of the Polynoids are sexually dimorphic.
[332]
Korschelt, "Über Ophryotrocha puerilis," Zeitschr. f. wiss. Zool. lv. 1893,
p. 224.
[325]
Eisig, Mt. Zool. Stat. Neapel, ii. 1881, p. 255.
[326]
They are specially large also in the Typhloscolecidae; while Racovitza
(Ann. Mag. N. H. (ser. 6), xv. 1895, p. 279) has recently suggested that
the caruncle of Amphinomidae belongs to the category of nuchal organs,
and compares it with the ciliated lappets of Pterosyllis.
[327]
Ehlers, Zeitschr. f. wiss. Zool. liii. 1892, p. 217.
[328]
See Claparède and Metschnikoff, "Beit. zur Kennt. d. Entwick der
Chaetopoden," Zeitschr. f. wiss. Zool. xix. 1869, p. 163; and Fewkes, "On
the Development of certain Worm Larvae," Bulletin Mus. Harvard, xi.
1883, p. 167.
[329]
For an account of the anatomy and development of a Trochosphere, see
Hatschek, on Eupomatus, in Arbeit. Zool. Inst. Wien, vi. 1885. Also
Meyer, Mt. Zool. Stat. Neapel, viii. 1888, p. 462; and for Polynoid larva
see Häcker, Zool. Jahrb. Abth. Anat. viii. 1895, p. 245.
[330]
See Meyer (ref. on p. 261).
[331]
Many of the Polynoids are sexually dimorphic.
[332]
Page 684
Claparède, "Annélides Chétopodes du Golfe de Naples," Supplement,
1870; and Wistinghausen, Mt. Zool. Stat. Neapel, x. 1891, p. 41.
[333]
Claparède used the term "epigamous" for this phase; Ehlers employed the
term "epitokous," whilst he called the "Nereid" phase "atokous," under
the impression that the worm did not become mature in this condition.
[334]
Malaquin gives a detailed account of the asexual reproduction in Syllidae
in Recherches sur les Syllidiens, Lille, 1893, and in Revue Biol. d. Nord
de la France, iii. 1891. See also St. Joseph, "Les annelides polychétes des
côtes de Dinard," Ann. Sci. Nat. Zool. (7th ser.) i. 1886, p. 134.
[335]
Alex. Agassiz, Boston J. Nat. Hist. vii. 1863, p. 384.
[336]
Huxley, Edinb. New Philosoph. Journ. 1855, i. p. 113.
[337]
"Challenger" Reports, vol. xii. 1885, "Polychaeta," p. 198; and Oka,
Zoolog. Centralbl. ii. 1895, p. 591.
[338]
Two new heads have been observed in Typosyllis variegata by
Langerhans, and two new tails in another Syllis.
[339]
Dalyell, The Powers of the Creator revealed, etc., vol. ii. 1853, p. 225 et
seq.
[340]
von Kennel, Arb. Zool. Instit. Würzburg, vi. 1883, p. 259.
[341]
1870; and Wistinghausen, Mt. Zool. Stat. Neapel, x. 1891, p. 41.
[333]
Claparède used the term "epigamous" for this phase; Ehlers employed the
term "epitokous," whilst he called the "Nereid" phase "atokous," under
the impression that the worm did not become mature in this condition.
[334]
Malaquin gives a detailed account of the asexual reproduction in Syllidae
in Recherches sur les Syllidiens, Lille, 1893, and in Revue Biol. d. Nord
de la France, iii. 1891. See also St. Joseph, "Les annelides polychétes des
côtes de Dinard," Ann. Sci. Nat. Zool. (7th ser.) i. 1886, p. 134.
[335]
Alex. Agassiz, Boston J. Nat. Hist. vii. 1863, p. 384.
[336]
Huxley, Edinb. New Philosoph. Journ. 1855, i. p. 113.
[337]
"Challenger" Reports, vol. xii. 1885, "Polychaeta," p. 198; and Oka,
Zoolog. Centralbl. ii. 1895, p. 591.
[338]
Two new heads have been observed in Typosyllis variegata by
Langerhans, and two new tails in another Syllis.
[339]
Dalyell, The Powers of the Creator revealed, etc., vol. ii. 1853, p. 225 et
seq.
[340]
von Kennel, Arb. Zool. Instit. Würzburg, vi. 1883, p. 259.
[341]
Page 685
Leidy, Proc. Acad. Nat. Hist. Philadelphia, 1883, p. 204.
[342]
Giard, C. R. Soc. Biol. v. 1893, p. 473.
[343]
See M‘Intosh, Ann. Mag. Nat. Hist. (ser. 4) ii. 1868, p. 276.
[344]
Lankester has suggested that a strong acid is secreted for the purpose, see
Ann. Mag. Nat. Hist. (ser. 4) i. 1868, p. 233.
[345]
M‘Intosh, Ann. Mag. Nat. Hist. (ser. 6) xiii. 1894, p. 1.
[346]
Dalyell, The Powers of the Creator revealed, ii. 1853, p. 217.
[347]
Watson, Journ. R. Mic. Soc. 1890, p. 685; see also Dalyell, loc. cit. ii. p.
195.
[348]
Schmiedeberg, Mt. Zool. Stat. Neapel, iii. 1882, p. 373.
[349]
For pelagic forms, see Camille Viguier, Arch. de Zool. Expér. (ser. 2) iv.
1886, p. 347; also Reibisch, Die pelag. Phyllodociden u.
Typhloscoleciden d. Plankton Exped. 1895.
[350]
Lankester, Journ. Anat. and Physiol. 1868, p. 114; and 1870, p. 119; see
also MacMunn, "On the Chromatology of the Blood in some
Invertebrates," Quart. J. Micr. Sci. xxv. 1885, p. 469.
[351]
[342]
Giard, C. R. Soc. Biol. v. 1893, p. 473.
[343]
See M‘Intosh, Ann. Mag. Nat. Hist. (ser. 4) ii. 1868, p. 276.
[344]
Lankester has suggested that a strong acid is secreted for the purpose, see
Ann. Mag. Nat. Hist. (ser. 4) i. 1868, p. 233.
[345]
M‘Intosh, Ann. Mag. Nat. Hist. (ser. 6) xiii. 1894, p. 1.
[346]
Dalyell, The Powers of the Creator revealed, ii. 1853, p. 217.
[347]
Watson, Journ. R. Mic. Soc. 1890, p. 685; see also Dalyell, loc. cit. ii. p.
195.
[348]
Schmiedeberg, Mt. Zool. Stat. Neapel, iii. 1882, p. 373.
[349]
For pelagic forms, see Camille Viguier, Arch. de Zool. Expér. (ser. 2) iv.
1886, p. 347; also Reibisch, Die pelag. Phyllodociden u.
Typhloscoleciden d. Plankton Exped. 1895.
[350]
Lankester, Journ. Anat. and Physiol. 1868, p. 114; and 1870, p. 119; see
also MacMunn, "On the Chromatology of the Blood in some
Invertebrates," Quart. J. Micr. Sci. xxv. 1885, p. 469.
[351]
Page 686
For coloured pictures of worms consult Schmarda, "Neue wirbellose
Thiere," 2nd part, 1861; Milne Edwards in Cuvier's "Règne Animal" (Ed.
Disciples de Cuvier).
[352]
Semper, Animal Life, "Internat. Sci. Series," 1881, p. 401.
[353]
The experiments were made by Mr. Garstang at the Laboratory of the
Marine Biological Association, and are recorded by Poulton in The
Colours of Animals, "Internat. Sci. Series," 1890, p. 201.
[354]
Panceri, Atti Acad. Sci. Napoli, vii. 1875.
[355]
M‘Intosh, H.M.S. "Challenger" Reports, "Polychaeta," vol. xii. p. ix.
[356]
For an account of these worms see M‘Intosh, loc. cit. p. 257.
[357]
For a list of parasitic Polychaetes see St. Joseph, Ann. Sci. Nat. (ser. 7) v.
1888, p. 141.
[358]
Semper, loc. cit. p. 340.
[359]
See "Challenger Reports," and St. Joseph, loc. cit.
[360]
"Challenger" Reports, loc. cit. p. xxx.
[361]
See Hornell, Fauna of Liverpool Bay, Report III. 1892, p. 126.
Thiere," 2nd part, 1861; Milne Edwards in Cuvier's "Règne Animal" (Ed.
Disciples de Cuvier).
[352]
Semper, Animal Life, "Internat. Sci. Series," 1881, p. 401.
[353]
The experiments were made by Mr. Garstang at the Laboratory of the
Marine Biological Association, and are recorded by Poulton in The
Colours of Animals, "Internat. Sci. Series," 1890, p. 201.
[354]
Panceri, Atti Acad. Sci. Napoli, vii. 1875.
[355]
M‘Intosh, H.M.S. "Challenger" Reports, "Polychaeta," vol. xii. p. ix.
[356]
For an account of these worms see M‘Intosh, loc. cit. p. 257.
[357]
For a list of parasitic Polychaetes see St. Joseph, Ann. Sci. Nat. (ser. 7) v.
1888, p. 141.
[358]
Semper, loc. cit. p. 340.
[359]
See "Challenger Reports," and St. Joseph, loc. cit.
[360]
"Challenger" Reports, loc. cit. p. xxx.
[361]
See Hornell, Fauna of Liverpool Bay, Report III. 1892, p. 126.
Page 687
[362]
Zittel, Handbuch d. Palaeontologic (Palaeozoologie), i. 1876-80, p. 562.
[363]
Ehlers, Zeitschr. f. wiss. Zool. xviii. 1868, p. 241.
[364]
The Chaetopteridae may have to be placed elsewhere in the system, as
they are peculiarly modified, and present features recalling the
Cryptocephala, from which it is possible they have descended.
[365]
Meyer (Mt. Zool. Stat. Neapel, vii. 1887, p. 669, note) suggests that the
tentacular filaments of Cirratulids are really prostomial, but have shifted
back on to the peristomium, or even farther.
[366]
It is probable that the genital ducts of Sternaspis and Chlorhaemids are
modified nephridia.
[367]
The character of head and parapodium in each family will be gathered
from the figures accompanying the general description in Chap. X., so
that detailed description is unnecessary. In all cases the chaetae form
valuable specific characters.
The examples of the various families are British, unless the opposite is
expressly stated; but most of them are not confined to our shores, and the
foreign localities are usually given. No attempt is made to enumerate all
the British species.
The following books may be found useful for identifying the worms:—
Claparède, Recherches anat. sur les Annélides observées dans les Hebrides, 1861; Annélides
Chétopodes du golfe de Naples, 1868, and Suppl., 1870.
Zittel, Handbuch d. Palaeontologic (Palaeozoologie), i. 1876-80, p. 562.
[363]
Ehlers, Zeitschr. f. wiss. Zool. xviii. 1868, p. 241.
[364]
The Chaetopteridae may have to be placed elsewhere in the system, as
they are peculiarly modified, and present features recalling the
Cryptocephala, from which it is possible they have descended.
[365]
Meyer (Mt. Zool. Stat. Neapel, vii. 1887, p. 669, note) suggests that the
tentacular filaments of Cirratulids are really prostomial, but have shifted
back on to the peristomium, or even farther.
[366]
It is probable that the genital ducts of Sternaspis and Chlorhaemids are
modified nephridia.
[367]
The character of head and parapodium in each family will be gathered
from the figures accompanying the general description in Chap. X., so
that detailed description is unnecessary. In all cases the chaetae form
valuable specific characters.
The examples of the various families are British, unless the opposite is
expressly stated; but most of them are not confined to our shores, and the
foreign localities are usually given. No attempt is made to enumerate all
the British species.
The following books may be found useful for identifying the worms:—
Claparède, Recherches anat. sur les Annélides observées dans les Hebrides, 1861; Annélides
Chétopodes du golfe de Naples, 1868, and Suppl., 1870.
Page 688
Cunningham and Ramage, "Polychaeta Sedentaria of the Firth of Forth," Trans. Roy. Soc.
Edinburgh, xxxiii. 1888, p. 635.
Ehlers, Die Borstenwürmer, 1868.
Johnston, "British Museum Catalogue of Non-Parasitical Worms," 1865.
M‘Intosh, "British Annelida," Trans. Zool. Soc. ix. 1877, p. 371; "Invert. Marine Fauna of
St. Andrews; Annelida," Ann. Mag. Nat. Hist. (4) xiv. 1874, p. 144.
Malmgren, "Nordiska Hafs-Annulater," Öfversigt af K. Vet.-Akad. Förhandlingar, 1865, pp.
51, 181, 355; and "Annulata Polychaeta," ibid. 1867, p. 127.
St. Joseph, "Les Annélides Polychétes des côtes de Dinard," Ann. Sci. Nat. (Zool.) (7) vol. i.
1886, p. 127; v. 1888, p. 141; xvii. 1894, p. 1; xx. 1895, p. 185.
[368]
Malaquin, Recherches sur les Syllidiens, 1893; for structure of the
gizzard, see also Haswell, Quart. J. Micr. Sci. xxvi. 1886, p. 471; and
xxx. 1889, p. 31.
[369]
See M‘Intosh's Memoirs, loc. cit.
[370]
Herein are included the various genera formed by Kinberg, Malmgren,
and others.
[371]
It appears to be the same as P. grubiana Clap.
[372]
Marenzeller has shown that Johnston's P. scolopendrina is not identical
with that of Savigny, and suggests the above name for it.
[373]
F. Buchanan, "Report on Polychaetes, Part I." Sci. Proc. Roy. Dublin Soc.
vii. (n.s.) 1893, p. 169.
[374]
Polyodontes Ran. deserves mention as being a large, rare form with
peculiar pedal gland; cf. Eisig (ref. on p. 268), p. 324; and Buchanan,
Quart. J. Micr. Sc. xxxv. 1894, p. 433.
Edinburgh, xxxiii. 1888, p. 635.
Ehlers, Die Borstenwürmer, 1868.
Johnston, "British Museum Catalogue of Non-Parasitical Worms," 1865.
M‘Intosh, "British Annelida," Trans. Zool. Soc. ix. 1877, p. 371; "Invert. Marine Fauna of
St. Andrews; Annelida," Ann. Mag. Nat. Hist. (4) xiv. 1874, p. 144.
Malmgren, "Nordiska Hafs-Annulater," Öfversigt af K. Vet.-Akad. Förhandlingar, 1865, pp.
51, 181, 355; and "Annulata Polychaeta," ibid. 1867, p. 127.
St. Joseph, "Les Annélides Polychétes des côtes de Dinard," Ann. Sci. Nat. (Zool.) (7) vol. i.
1886, p. 127; v. 1888, p. 141; xvii. 1894, p. 1; xx. 1895, p. 185.
[368]
Malaquin, Recherches sur les Syllidiens, 1893; for structure of the
gizzard, see also Haswell, Quart. J. Micr. Sci. xxvi. 1886, p. 471; and
xxx. 1889, p. 31.
[369]
See M‘Intosh's Memoirs, loc. cit.
[370]
Herein are included the various genera formed by Kinberg, Malmgren,
and others.
[371]
It appears to be the same as P. grubiana Clap.
[372]
Marenzeller has shown that Johnston's P. scolopendrina is not identical
with that of Savigny, and suggests the above name for it.
[373]
F. Buchanan, "Report on Polychaetes, Part I." Sci. Proc. Roy. Dublin Soc.
vii. (n.s.) 1893, p. 169.
[374]
Polyodontes Ran. deserves mention as being a large, rare form with
peculiar pedal gland; cf. Eisig (ref. on p. 268), p. 324; and Buchanan,
Quart. J. Micr. Sc. xxxv. 1894, p. 433.
Page 689
[375]
Many authorities regard this species as synonymous with Savigny's P.
laminosa.
[376]
According to a verbal communication from Mr. J. Hornell of Jersey, they
belong to P. maculata Müll., while Mr. Garstang believes them to belong
to Eulalia viridis.
[377]
These segmentally-arranged brown spots may perhaps be photogenic.
[378]
Greef, Acta Ac. German., xxxix. 1877.
[379]
Greef, Zeitschr. f. wiss. Zool. xlii. 1885, p. 432.
[380]
Buchanan, Quart. J. Micr. Sci. xxxv. 1894, p. 445.
[381]
Buchanan, Sci. Proc. R. Dublin Soc. viii. (n.s.) 1893, p. 169.
[382]
Reibisch, Phyllodociden u. Typhloscoleciden d. Plankton Exped. 1895.
[383]
The British species is usually referred to as C. insignis Baird, but Joyeux
Laffuie (Arch. Zool. Exp. (ser. 2) viii. 1890, p. 244) has shown that there
is only one European species. It is possible that there is a closer affinity
with the Sabelliformia than is at present supposed.
[384]
Compare Sternaspis, p. 336.
Many authorities regard this species as synonymous with Savigny's P.
laminosa.
[376]
According to a verbal communication from Mr. J. Hornell of Jersey, they
belong to P. maculata Müll., while Mr. Garstang believes them to belong
to Eulalia viridis.
[377]
These segmentally-arranged brown spots may perhaps be photogenic.
[378]
Greef, Acta Ac. German., xxxix. 1877.
[379]
Greef, Zeitschr. f. wiss. Zool. xlii. 1885, p. 432.
[380]
Buchanan, Quart. J. Micr. Sci. xxxv. 1894, p. 445.
[381]
Buchanan, Sci. Proc. R. Dublin Soc. viii. (n.s.) 1893, p. 169.
[382]
Reibisch, Phyllodociden u. Typhloscoleciden d. Plankton Exped. 1895.
[383]
The British species is usually referred to as C. insignis Baird, but Joyeux
Laffuie (Arch. Zool. Exp. (ser. 2) viii. 1890, p. 244) has shown that there
is only one European species. It is possible that there is a closer affinity
with the Sabelliformia than is at present supposed.
[384]
Compare Sternaspis, p. 336.
Page 690
[385]
For literature, see Benham, Quart. J. Micr. Sci. xxxix. part 1, 1896, p. 1.
[386]
F. Buchanan, Quart. J. Micr. Sci. xxxi. 1890, p. 175.
[387]
In some genera there are no gills, e.g. Leaena.
[388]
These characters are not necessarily generic.
[389]
Eisig, "Die Capitelliden," Fauna u. Flora G. v. Neapel, Monogr. xvi.
1887.
[390]
Ed. Meyer., Arch. mikr. Anat. xxi. 1882, p. 769.
[391]
Vejdovsky, Denk. Akad. Wien, xliii. 1882, part 2, p. 33; and Rietsch, Ann.
Sci. Nat. (Zool.) ser. 6, xiii. 1882, art. 5.
[392]
For anatomy see Meyer, Mt. Zool. Stat. Neapel, vii. 1887.
[393]
Andrews, Journ. Morph. v. 1891, p. 271.
[394]
A. G. Bourne, Quart. J. Micr. Sci. xxiii. 1883, p. 168.
[395]
Closely allied is Manayunkia Leidy, which occurs in fresh-water lakes of
America. Another fresh-water genus is Coabangia Giard, which perhaps
For literature, see Benham, Quart. J. Micr. Sci. xxxix. part 1, 1896, p. 1.
[386]
F. Buchanan, Quart. J. Micr. Sci. xxxi. 1890, p. 175.
[387]
In some genera there are no gills, e.g. Leaena.
[388]
These characters are not necessarily generic.
[389]
Eisig, "Die Capitelliden," Fauna u. Flora G. v. Neapel, Monogr. xvi.
1887.
[390]
Ed. Meyer., Arch. mikr. Anat. xxi. 1882, p. 769.
[391]
Vejdovsky, Denk. Akad. Wien, xliii. 1882, part 2, p. 33; and Rietsch, Ann.
Sci. Nat. (Zool.) ser. 6, xiii. 1882, art. 5.
[392]
For anatomy see Meyer, Mt. Zool. Stat. Neapel, vii. 1887.
[393]
Andrews, Journ. Morph. v. 1891, p. 271.
[394]
A. G. Bourne, Quart. J. Micr. Sci. xxiii. 1883, p. 168.
[395]
Closely allied is Manayunkia Leidy, which occurs in fresh-water lakes of
America. Another fresh-water genus is Coabangia Giard, which perhaps
Page 691
deserves the creation of a special family. The anus is ventral and anterior.
The chaetae are peculiarly arranged, dorsal uncini being present only on
four segments. The first body segment carries a ventral bundle of five
great "palmate" chaetae.
[396]
For the anatomy see Meyer, Mt. Stat. Neapel, vii. 1887; see also above, p.
306.
[397]
von Graff, "Myzostomida," "Challenger" Reports, part 27, vol. x. 1884;
and "Supplement," part 61, vol. xx. 1887.
[398]
Marenzeller, Anz. Akad. Wien, xxxii. p. 192.
[399]
Mt. Zool. Stat. Neapel, xii. 1896, p. 227; where, too, see literature.
[400]
Beard, Mt. Zool. St. Neap. v. 1884, p. 544.
[401]
Quart. J. Micr. Sci. (n.s.) vol. iv. 1864, p. 258; and v. pp. 7, 99.
[402]
Zeitschr. wiss. Zool. xix. 1869, p. 563.
[403]
De Lumbrici terrestris Historia naturali, Brussels, 1829.
[404]
Naturg. ein. Wurm-Arten d. süssen u. salzigen Wasser, Copenhagen,
1771.
[405]
The chaetae are peculiarly arranged, dorsal uncini being present only on
four segments. The first body segment carries a ventral bundle of five
great "palmate" chaetae.
[396]
For the anatomy see Meyer, Mt. Stat. Neapel, vii. 1887; see also above, p.
306.
[397]
von Graff, "Myzostomida," "Challenger" Reports, part 27, vol. x. 1884;
and "Supplement," part 61, vol. xx. 1887.
[398]
Marenzeller, Anz. Akad. Wien, xxxii. p. 192.
[399]
Mt. Zool. Stat. Neapel, xii. 1896, p. 227; where, too, see literature.
[400]
Beard, Mt. Zool. St. Neap. v. 1884, p. 544.
[401]
Quart. J. Micr. Sci. (n.s.) vol. iv. 1864, p. 258; and v. pp. 7, 99.
[402]
Zeitschr. wiss. Zool. xix. 1869, p. 563.
[403]
De Lumbrici terrestris Historia naturali, Brussels, 1829.
[404]
Naturg. ein. Wurm-Arten d. süssen u. salzigen Wasser, Copenhagen,
1771.
[405]
Page 692
Trans. Roy. Soc. Victoria, vol. i. 1888, p. 1.
[406]
Phil. Trans. clxxxvi. 1895, A, p. 383.
[407]
Mém. cour. Ac. Belg. lii. 1890-93.
[408]
Quart. J. Micr. Sci. xxxi. 1890, p. 83.
[409]
Beddard, Ibid. xxxiii. 1892, p. 325.
[410]
Beddard, Ann. Mag. Nat. Hist. (6) xiii. 1894, p. 205.
[411]
Mém. Soc. Zool. France, iii. 1890, p. 223.
[412]
Vegetable Mould and Earthworms, London, 1881.
[413]
Zool. Anz. xi. 1888, p. 72.
[414]
See Fletcher, P. Linn. Soc. N.S.W. (2) iii. 1889, p. 1542.
[406]
Phil. Trans. clxxxvi. 1895, A, p. 383.
[407]
Mém. cour. Ac. Belg. lii. 1890-93.
[408]
Quart. J. Micr. Sci. xxxi. 1890, p. 83.
[409]
Beddard, Ibid. xxxiii. 1892, p. 325.
[410]
Beddard, Ann. Mag. Nat. Hist. (6) xiii. 1894, p. 205.
[411]
Mém. Soc. Zool. France, iii. 1890, p. 223.
[412]
Vegetable Mould and Earthworms, London, 1881.
[413]
Zool. Anz. xi. 1888, p. 72.
[414]
See Fletcher, P. Linn. Soc. N.S.W. (2) iii. 1889, p. 1542.
Page 693
[415]
In Sitzungs-Ber. Böhm. Ges. 1889, p. 183.
[416]
See Dr. Rosa in Ann. Hofmus. Wien, vi. 1891, p. 379.
[417]
Entwickelungsgeschichtliche Untersuchungen, Prag, Heft i. 1888, p. 33.
[418]
See Kleinenberg, Quart. J. Micr. Sci. xix., 1879, p. 206.
[419]
Both Col. Feilden and Mr. Trevor-Battye found specimens in Kolguiev.
[420]
Neue wirbellose Thiere, Leipzig, ii. 1861, p. 11.
[421]
Kew Bull. Misc. Information, No. 46, 1890.
[422]
Rev. Biol. Nord France, i. 1889, p. 197.
[423]
SB. Ges. naturf. Berlin, 1893, p. 19.
[424]
System u. Morph. d. Oligochaeten, Prag, 1884.
[425]
See my text-book of Zoogeography (Cambridge, 1895) for fuller
treatment.
[426]
In Sitzungs-Ber. Böhm. Ges. 1889, p. 183.
[416]
See Dr. Rosa in Ann. Hofmus. Wien, vi. 1891, p. 379.
[417]
Entwickelungsgeschichtliche Untersuchungen, Prag, Heft i. 1888, p. 33.
[418]
See Kleinenberg, Quart. J. Micr. Sci. xix., 1879, p. 206.
[419]
Both Col. Feilden and Mr. Trevor-Battye found specimens in Kolguiev.
[420]
Neue wirbellose Thiere, Leipzig, ii. 1861, p. 11.
[421]
Kew Bull. Misc. Information, No. 46, 1890.
[422]
Rev. Biol. Nord France, i. 1889, p. 197.
[423]
SB. Ges. naturf. Berlin, 1893, p. 19.
[424]
System u. Morph. d. Oligochaeten, Prag, 1884.
[425]
See my text-book of Zoogeography (Cambridge, 1895) for fuller
treatment.
[426]
Page 694
Ann. Mag. Nat. Hist. (6) ix. 1892, p. 12.
[427]
Darwin, Vegetable Mould and Earthworms, p. 121.
[428]
"An Attempt to classify Earthworms," Quart. J. Micr. Sci. xxxi. 1890, p.
201.
[429]
Oxford, 1895.
[430]
See especially Vejdovsky, Syst. u. Morph. Olig. Prag, 1884.
[431]
Vejdovsky, Monographie der Enchytraeiden, Prag, 1879. Michaelsen,
"Synopsis der Enchytraiden," Abh. Ver. Hamburg, xi. 1889, p. 1.
[432]
J. P. Moore, "The Anatomy of Bdellodrilus," J. Morphol. x. 1895, p. 497.
[433]
Beddard, Trans. Roy. Soc. Edin. xxxv. 1890, p. 629, and xxxvi. 1892, p.
1.
[434]
A. G. Bourne, "On the Naidiform Oligochaeta," Quart. J. Micr. Sci. xxxii.
1891, p. 335.
[435]
F. E. Beddard, Trans. Roy. Soc. Edin. xxxvi. 1892, p. 273.
[436]
Vejdovsky, System u. Morph. d. Oligochaeten, Prag, 1884.
[427]
Darwin, Vegetable Mould and Earthworms, p. 121.
[428]
"An Attempt to classify Earthworms," Quart. J. Micr. Sci. xxxi. 1890, p.
201.
[429]
Oxford, 1895.
[430]
See especially Vejdovsky, Syst. u. Morph. Olig. Prag, 1884.
[431]
Vejdovsky, Monographie der Enchytraeiden, Prag, 1879. Michaelsen,
"Synopsis der Enchytraiden," Abh. Ver. Hamburg, xi. 1889, p. 1.
[432]
J. P. Moore, "The Anatomy of Bdellodrilus," J. Morphol. x. 1895, p. 497.
[433]
Beddard, Trans. Roy. Soc. Edin. xxxv. 1890, p. 629, and xxxvi. 1892, p.
1.
[434]
A. G. Bourne, "On the Naidiform Oligochaeta," Quart. J. Micr. Sci. xxxii.
1891, p. 335.
[435]
F. E. Beddard, Trans. Roy. Soc. Edin. xxxvi. 1892, p. 273.
[436]
Vejdovsky, System u. Morph. d. Oligochaeten, Prag, 1884.
Page 695
[437]
"Anatomical Notes on Sutroa," Zoe. ii. 1892, p. 321.
[438]
"Pacific Coast Oligochaeta," Mem. California Acad. Sci. vol. ii.
[439]
Quart. J. Micr. Sci. xxxvi. 1894, p. 307.
[440]
See Spencer, Proc. Roy. Soc. Vict. v. 1893, and Fletcher, P. Linn. Soc.
N.S.W. 1886-1888, for Australian forms; Rosa, Ann. Mus. civ. Genova, vi.
1886, x. 1890, and xii. 1892, for Oriental species, etc.
[441]
See Fletcher and Spencer, already quoted, for Australian species.
[442]
Eisen, "Anat. Studies on Ocnerodrilus," Proc. Calif. Acad. (2) iii. 1892,
p. 228.
[443]
Beddard, Ann. Mag. Nat. Hist. (6) x. 1892, p. 74.
[444]
Beddard, P. Z. S. 1885 and 1895, for Antarctic Acanthodrilids;
Michaelsen, in Jahrb. Hamburg. Anst. 1888-95, for Benhamia.
[445]
For a general account of the Eudrilidae, see my Monograph of the Order
Oligochaeta, Oxford, 1895.
[446]
Nouv. Arch. Mus. Paris, viii. 1872, p. 5.
"Anatomical Notes on Sutroa," Zoe. ii. 1892, p. 321.
[438]
"Pacific Coast Oligochaeta," Mem. California Acad. Sci. vol. ii.
[439]
Quart. J. Micr. Sci. xxxvi. 1894, p. 307.
[440]
See Spencer, Proc. Roy. Soc. Vict. v. 1893, and Fletcher, P. Linn. Soc.
N.S.W. 1886-1888, for Australian forms; Rosa, Ann. Mus. civ. Genova, vi.
1886, x. 1890, and xii. 1892, for Oriental species, etc.
[441]
See Fletcher and Spencer, already quoted, for Australian species.
[442]
Eisen, "Anat. Studies on Ocnerodrilus," Proc. Calif. Acad. (2) iii. 1892,
p. 228.
[443]
Beddard, Ann. Mag. Nat. Hist. (6) x. 1892, p. 74.
[444]
Beddard, P. Z. S. 1885 and 1895, for Antarctic Acanthodrilids;
Michaelsen, in Jahrb. Hamburg. Anst. 1888-95, for Benhamia.
[445]
For a general account of the Eudrilidae, see my Monograph of the Order
Oligochaeta, Oxford, 1895.
[446]
Nouv. Arch. Mus. Paris, viii. 1872, p. 5.
Page 696
[447]
The scattered literature of this family is due to Benham, Michaelsen,
Perrier, Rosa, and others.
[448]
Rosa, "Revisione dei Lumbricidae," Mem. Acc. Torino (2), xliii. 1893, p.
399; also the Rev. H. Friend's numerous and useful papers, and especially
"A New Species of Earthworms," Proc. Roy. Irish Ac. (3) ii. 1891-93, p.
402; and "The Earthworms of Ireland," Irish Nat. v. 1896, p. 69, etc.
[449]
In the tables the figures refer to the segments of the body. Opposite the
name of each species are two sets of lines; the upper series indicate the
segments occupied by the clitellum; the lower series those occupied by
the tubercula pubertatis. The dots indicate the occasional extension of the
clitellum or of the tubercula.
[450]
"Annelés," vol. iii. 1889-90, p. 477, in the Suites à Buffon.
[451]
See v. Kennel, Zool. Jahrb. ii. 1887, p. 37.
[452]
Nouvelle Monographie des Sangsues médicinales. Paris, 1857.
[453]
Quart. J. Micr. Sci. xxvi. 1886, p. 317.
[454]
See Grube, "Annulaten" of Middendorff's Sibirische Reise, Zoology,
1851, p. 20; and Kowalevsky, Bull. Ac. St. Petersb. v. June 1896.
[455]
See ref. on p. 395.
The scattered literature of this family is due to Benham, Michaelsen,
Perrier, Rosa, and others.
[448]
Rosa, "Revisione dei Lumbricidae," Mem. Acc. Torino (2), xliii. 1893, p.
399; also the Rev. H. Friend's numerous and useful papers, and especially
"A New Species of Earthworms," Proc. Roy. Irish Ac. (3) ii. 1891-93, p.
402; and "The Earthworms of Ireland," Irish Nat. v. 1896, p. 69, etc.
[449]
In the tables the figures refer to the segments of the body. Opposite the
name of each species are two sets of lines; the upper series indicate the
segments occupied by the clitellum; the lower series those occupied by
the tubercula pubertatis. The dots indicate the occasional extension of the
clitellum or of the tubercula.
[450]
"Annelés," vol. iii. 1889-90, p. 477, in the Suites à Buffon.
[451]
See v. Kennel, Zool. Jahrb. ii. 1887, p. 37.
[452]
Nouvelle Monographie des Sangsues médicinales. Paris, 1857.
[453]
Quart. J. Micr. Sci. xxvi. 1886, p. 317.
[454]
See Grube, "Annulaten" of Middendorff's Sibirische Reise, Zoology,
1851, p. 20; and Kowalevsky, Bull. Ac. St. Petersb. v. June 1896.
[455]
See ref. on p. 395.
Page 697
[456]
Asajiro Oka, Zeitschr. wiss. Zool. lviii. 1894, p. 79.
[457]
See Bürger, quoted on p. 403.
[458]
Loc. cit.
[459]
Quart. J. Micr. Sci. xxiv. 1884, p. 419; see also ibid. xxxiv. 1893, p. 545,
which is mainly a criticism of Bolsius' additions to the very considerable
literature upon the Leech nephridium.
[460]
"Spermatophores as a Means of Hypodermic Impregnation," J. Morphol.
iv. 1891, p. 361.
[461]
Zeitschr. wiss. Zool. lviii. 1894, p. 440; and Zool. Jahrb. Anat. iv. 1891, p.
697.
[462]
"Annelés," vol. iii. 1889-90, p. 493, in the Suites à Buffon.
[463]
Whitman quotes with regretful approval (Proc. Americ. Acad. xx. 1884-
85, p. 76) Sir J. Dalyell's remark, "It does not appear that the history of
the leech has advanced in proportion to the number of literati who have
rendered it the subject of discussion," and adds on his own account the
following severe indictment of his predecessors: "As a considerable share
of the work done in this direction is purely systematic, it is somewhat
surprising that not a single description of any Hirudo has been given with
sufficient accuracy and completeness for a close comparison of even its
more important external characters with those of other species."
Asajiro Oka, Zeitschr. wiss. Zool. lviii. 1894, p. 79.
[457]
See Bürger, quoted on p. 403.
[458]
Loc. cit.
[459]
Quart. J. Micr. Sci. xxiv. 1884, p. 419; see also ibid. xxxiv. 1893, p. 545,
which is mainly a criticism of Bolsius' additions to the very considerable
literature upon the Leech nephridium.
[460]
"Spermatophores as a Means of Hypodermic Impregnation," J. Morphol.
iv. 1891, p. 361.
[461]
Zeitschr. wiss. Zool. lviii. 1894, p. 440; and Zool. Jahrb. Anat. iv. 1891, p.
697.
[462]
"Annelés," vol. iii. 1889-90, p. 493, in the Suites à Buffon.
[463]
Whitman quotes with regretful approval (Proc. Americ. Acad. xx. 1884-
85, p. 76) Sir J. Dalyell's remark, "It does not appear that the history of
the leech has advanced in proportion to the number of literati who have
rendered it the subject of discussion," and adds on his own account the
following severe indictment of his predecessors: "As a considerable share
of the work done in this direction is purely systematic, it is somewhat
surprising that not a single description of any Hirudo has been given with
sufficient accuracy and completeness for a close comparison of even its
more important external characters with those of other species."
Page 698
[464]
"Hirudinées de l'Italie," etc., Boll. Mus. Zool. Torino, vol. ix. 1894, No.
192. See also Apathy, "Süsswasser-Hirudineen," Zool. Jahrb. Syst. iii.
1888, p. 725.
[465]
Zeitschr. f. die gesammt. Naturwiss. vi. 1872, p. 422.
[466]
But Pennant in his British Zoology has referred to a leech which is even
larger. Upon the huge Basking shark (Selache) the fishermen sometimes
observe a leech, which invariably drops off when the fish is brought to
the surface, "of a reddish colour and about 2 feet in length"; this may be a
Pontobdella.
[467]
Ann. Mag. Nat. Hist. (6) xii. 1893, p. 75.
[468]
Memorie sulla Storia e Notomia degli Animali senza Vertebre, 1823.
[469]
Histoire Naturelle des Animaux sans Vertèbres, vol. iii. 1816, p. 76.
[470]
Le Règne Animal, 2nd ed. 1830.
[471]
γέφῦρα = a bridge, Ann. Sci. Nat. (3), vol. vii. 1847, p. 340.
[472]
Fischer, Abh. Ver. Hamburg, Bd. xiii. 1895, p. 1.
[473]
Cuénot, Arch. Zool. exp. (2) ix. 1891, p. 593.
"Hirudinées de l'Italie," etc., Boll. Mus. Zool. Torino, vol. ix. 1894, No.
192. See also Apathy, "Süsswasser-Hirudineen," Zool. Jahrb. Syst. iii.
1888, p. 725.
[465]
Zeitschr. f. die gesammt. Naturwiss. vi. 1872, p. 422.
[466]
But Pennant in his British Zoology has referred to a leech which is even
larger. Upon the huge Basking shark (Selache) the fishermen sometimes
observe a leech, which invariably drops off when the fish is brought to
the surface, "of a reddish colour and about 2 feet in length"; this may be a
Pontobdella.
[467]
Ann. Mag. Nat. Hist. (6) xii. 1893, p. 75.
[468]
Memorie sulla Storia e Notomia degli Animali senza Vertebre, 1823.
[469]
Histoire Naturelle des Animaux sans Vertèbres, vol. iii. 1816, p. 76.
[470]
Le Règne Animal, 2nd ed. 1830.
[471]
γέφῦρα = a bridge, Ann. Sci. Nat. (3), vol. vii. 1847, p. 340.
[472]
Fischer, Abh. Ver. Hamburg, Bd. xiii. 1895, p. 1.
[473]
Cuénot, Arch. Zool. exp. (2) ix. 1891, p. 593.
Page 699
[474]
Bull. Mus. Harvard, vol. xxi. 1891, p. 143.
[475]
Shipley, Quart. J. Micr. Sci. vol. xxxi. 1890, p. 1.
[476]
Stud. Johns Hopkins Univ. vol. iv. 1887-90, p. 389.
[477]
Conn, Stud. Johns Hopkins Univ. vol. iii. 1884-87, p. 351.
[478]
Arb. Instit. Wien, Bd. v. 1884, p. 61.
[479]
Shipley, Quart. J. Micr. Sci. vol. xxxii. 1891, p. 111.
[480]
Proc. Roy. Soc. Edin. xviii. 1892, p. 17.
[481]
Selenka, Die Sipunculiden. Semper's Reisen im Archipel d. Philippinen,
vol. iv. 1883.
[482]
Stud. Johns Hopkins Univ. vol. iv. 1887-90, p. 389.
[483]
Selenka, Challenger Reports, vol. xiii. 1885.
[484]
Ann. Sci. nat. (7) vol. xx. 1895, p. 1.
[485]
Bull. Mus. Harvard, vol. xxi. 1891, p. 143.
[475]
Shipley, Quart. J. Micr. Sci. vol. xxxi. 1890, p. 1.
[476]
Stud. Johns Hopkins Univ. vol. iv. 1887-90, p. 389.
[477]
Conn, Stud. Johns Hopkins Univ. vol. iii. 1884-87, p. 351.
[478]
Arb. Instit. Wien, Bd. v. 1884, p. 61.
[479]
Shipley, Quart. J. Micr. Sci. vol. xxxii. 1891, p. 111.
[480]
Proc. Roy. Soc. Edin. xviii. 1892, p. 17.
[481]
Selenka, Die Sipunculiden. Semper's Reisen im Archipel d. Philippinen,
vol. iv. 1883.
[482]
Stud. Johns Hopkins Univ. vol. iv. 1887-90, p. 389.
[483]
Selenka, Challenger Reports, vol. xiii. 1885.
[484]
Ann. Sci. nat. (7) vol. xx. 1895, p. 1.
[485]
Page 700
Zool. Anz. ix. 1886, p. 574.
[486]
This is not true of all species.
[487]
Acta Ac. German, Halle, xli. Part II. No. 1, 1879.
[488]
Recueil Zool. Suisse, iii. 1886, p. 313.
[489]
Vide p. 335.
[490]
P. Phys. Soc. Edinb. vol. i. 1856, p. 165; and Edinb. New Phil. Journ. vol.
iv. (n.s.) 1856, p. 313; Ann. Sci. Nat. 4th ser. vol. xi. 1859, p. 150; and F.
D. Dyster, Tr. Linn. Soc. London, vol. xxii. 1859, p. 251.
[491]
Ann. Sci. Nat. 4th ser. vol. x. 1858, p. 11.
[492]
"Beiträge zur Anatomie der Phoronis," Inaug. Dissert. Prag. 1889, and
Zeitschr. wiss. Zool. vol. li. 1891, p. 480.
[493]
P. Linn. Soc. N. S. Wales, 1st ser. vol. vii. 1883, p. 606; and 2nd ser. vol.
vii. 1893, p. 340.
[494]
Quart. J. Micr. Sci. vol. xxx. 1890, p. 125.
[495]
Challenger Reports, vol. xxvii. 1888; and Proc. Roy. Soc. Edinb. vol. xi.
1882, p. 211.
[486]
This is not true of all species.
[487]
Acta Ac. German, Halle, xli. Part II. No. 1, 1879.
[488]
Recueil Zool. Suisse, iii. 1886, p. 313.
[489]
Vide p. 335.
[490]
P. Phys. Soc. Edinb. vol. i. 1856, p. 165; and Edinb. New Phil. Journ. vol.
iv. (n.s.) 1856, p. 313; Ann. Sci. Nat. 4th ser. vol. xi. 1859, p. 150; and F.
D. Dyster, Tr. Linn. Soc. London, vol. xxii. 1859, p. 251.
[491]
Ann. Sci. Nat. 4th ser. vol. x. 1858, p. 11.
[492]
"Beiträge zur Anatomie der Phoronis," Inaug. Dissert. Prag. 1889, and
Zeitschr. wiss. Zool. vol. li. 1891, p. 480.
[493]
P. Linn. Soc. N. S. Wales, 1st ser. vol. vii. 1883, p. 606; and 2nd ser. vol.
vii. 1893, p. 340.
[494]
Quart. J. Micr. Sci. vol. xxx. 1890, p. 125.
[495]
Challenger Reports, vol. xxvii. 1888; and Proc. Roy. Soc. Edinb. vol. xi.
1882, p. 211.
Page 701
[496]
Proc. Roy. Soc. London, vol. xxxiv. 1883, p. 371.
[497]
Zapiski Acad. St. Petersb. vol. xi. No. 1, 1867 (Russian). Abstract in
Arch. Naturg. Jahrg. xxxiii. 1867, Bd. ii. p. 235.
[498]
Caldwell, loc. cit. Foettinger, Arch. Biol. vol. iii. 1882, p. 679;
Gegenbaur, Zeitschr. wiss. Zool. vol. v. 1854, p. 345; Krohn, Arch. Anat.
Jahrgang 1858, p. 289; Metschnikoff, Nachricht. k. Ges. Wiss. Göttingen,
No. 12, 1869, p. 227, and Zeitschr. wiss. Zool. vol. xxi. 1871, p. 233; J.
Müller, Arch. Anat. Jahrgang 1846, p. 101; Schneider, Monatsber. Ak.
wiss. Berlin, 1861, p. 934, and Arch. Anat. Jahrgang 1862, p. 47;
Wagener, Arch. Anat. Jahrgang 1847, p. 202; Wilson, Amer. Natural. vol.
xiv. 1880.
[499]
Proc. Roy. Soc. Edinb. vol. xxi. 1896, p. 59; and Zool. Anz. xix. 1896, p.
266.
[500]
The account given in the following pages has been deliberately restricted,
for the most part, to British species. Our own fauna contains an
assemblage of Polyzoa which is so representative that it has seemed
better to do some justice to the British forms than to attempt to cover the
whole ground in the limited number of pages devoted to this group.
Those who desire to make a wider study of the subject should refer, for
marine forms, to Busk's Catalogue of Marine Polyzoa in the Collection of
the British Museum, Parts I.-III. 1852, 1854, 1875; to the Challenger
Reports on Polyzoa, Parts 30 (1884), 50 (1886), and 79 (1888); for
references and lists of species, to Vine's Report on Recent Marine
Polyzoa, Cheilostomata and Cyclostomata (Report, 55th meeting Brit.
Ass. Aberdeen, 1885, pp. 481-680); [and to Nickles and Bassler, Synopsis
Amer. Foss. Bryozoa incl. Bibliography (Bull. U.S. Geol. Survey, No.
Proc. Roy. Soc. London, vol. xxxiv. 1883, p. 371.
[497]
Zapiski Acad. St. Petersb. vol. xi. No. 1, 1867 (Russian). Abstract in
Arch. Naturg. Jahrg. xxxiii. 1867, Bd. ii. p. 235.
[498]
Caldwell, loc. cit. Foettinger, Arch. Biol. vol. iii. 1882, p. 679;
Gegenbaur, Zeitschr. wiss. Zool. vol. v. 1854, p. 345; Krohn, Arch. Anat.
Jahrgang 1858, p. 289; Metschnikoff, Nachricht. k. Ges. Wiss. Göttingen,
No. 12, 1869, p. 227, and Zeitschr. wiss. Zool. vol. xxi. 1871, p. 233; J.
Müller, Arch. Anat. Jahrgang 1846, p. 101; Schneider, Monatsber. Ak.
wiss. Berlin, 1861, p. 934, and Arch. Anat. Jahrgang 1862, p. 47;
Wagener, Arch. Anat. Jahrgang 1847, p. 202; Wilson, Amer. Natural. vol.
xiv. 1880.
[499]
Proc. Roy. Soc. Edinb. vol. xxi. 1896, p. 59; and Zool. Anz. xix. 1896, p.
266.
[500]
The account given in the following pages has been deliberately restricted,
for the most part, to British species. Our own fauna contains an
assemblage of Polyzoa which is so representative that it has seemed
better to do some justice to the British forms than to attempt to cover the
whole ground in the limited number of pages devoted to this group.
Those who desire to make a wider study of the subject should refer, for
marine forms, to Busk's Catalogue of Marine Polyzoa in the Collection of
the British Museum, Parts I.-III. 1852, 1854, 1875; to the Challenger
Reports on Polyzoa, Parts 30 (1884), 50 (1886), and 79 (1888); for
references and lists of species, to Vine's Report on Recent Marine
Polyzoa, Cheilostomata and Cyclostomata (Report, 55th meeting Brit.
Ass. Aberdeen, 1885, pp. 481-680); [and to Nickles and Bassler, Synopsis
Amer. Foss. Bryozoa incl. Bibliography (Bull. U.S. Geol. Survey, No.
Page 702
173, 1900)]. References to the literature of the fresh-water forms will be
found below, in Chap. XVIII.
[501]
Hooker, quoted by Landsborough, Hist. Brit. Zoophytes, 1852, p. 346.
[502]
Rare and Remarkable Animals of Scotland, ii. 1848, p. 15.
[503]
Arch. Zool. Exp. 2 sér. x. 1892.
[504]
Kraepelin, Abh. Ver. Hamburg, x. 1887, No. ix. p. 19; κάμπτειν, to bend;
δέρμα, skin.
[505]
Parts of the ectocyst of some calcareous forms are covered by an external
investment of cells, which give rise to secondary thickenings, ridges, and
other growths.
[506]
From the Quart. J. Micr. Sci. xxxiii. 1892.
[507]
Ibid. p. 123.
[508]
Quart. J. Micr. Sci. xxxiii. 1892, p. 147. The experiment was conducted
in a laboratory, and the results may not be perfectly normal with regard to
the time occupied.
[509]
See also Joliet, Arch. Zool. Exp. vi. 1877, p. 202, and explanation of plate
viii. for another series of observations.
found below, in Chap. XVIII.
[501]
Hooker, quoted by Landsborough, Hist. Brit. Zoophytes, 1852, p. 346.
[502]
Rare and Remarkable Animals of Scotland, ii. 1848, p. 15.
[503]
Arch. Zool. Exp. 2 sér. x. 1892.
[504]
Kraepelin, Abh. Ver. Hamburg, x. 1887, No. ix. p. 19; κάμπτειν, to bend;
δέρμα, skin.
[505]
Parts of the ectocyst of some calcareous forms are covered by an external
investment of cells, which give rise to secondary thickenings, ridges, and
other growths.
[506]
From the Quart. J. Micr. Sci. xxxiii. 1892.
[507]
Ibid. p. 123.
[508]
Quart. J. Micr. Sci. xxxiii. 1892, p. 147. The experiment was conducted
in a laboratory, and the results may not be perfectly normal with regard to
the time occupied.
[509]
See also Joliet, Arch. Zool. Exp. vi. 1877, p. 202, and explanation of plate
viii. for another series of observations.
Page 703
[510]
See especially G. J. Allman, Monograph of the Fresh-water Polyzoa, Ray
Society, 1856, p. 41; and H. Nitsche, Zeitschr. wiss. Zool. xxi. 1871, p.
479.
[511]
Ray Society, 4to, 1856.
[512]
Zoological Researches and Illustrations, v. "On Polyzoa." Cork, 1830.
[513]
"Symbolae Physicae," 1831, and Abh. Ak. Berlin, 1832, i. p. 377, etc.
[514]
T. cit. p. 92.
[515]
Vol. i. 1880, Introduction, p. cxxxi.
[516]
Élémens de Zoologie, 2nd ed. Animaux sans Vertèbres, 1843, pp. 238,
312. Prof. A. Milne-Edwards has kindly written to me, informing me that
he believes this to have been the first occasion on which the term was
thus used.
[517]
Phil. Trans. vol. cxliii, 1853, p. 62.
[518]
Nitsche, Zeitschr. wiss. Zool. xx. 1870, p. 34.
[519]
πρωκτός, anus; ἐντός, within; ἐκτός, without.
See especially G. J. Allman, Monograph of the Fresh-water Polyzoa, Ray
Society, 1856, p. 41; and H. Nitsche, Zeitschr. wiss. Zool. xxi. 1871, p.
479.
[511]
Ray Society, 4to, 1856.
[512]
Zoological Researches and Illustrations, v. "On Polyzoa." Cork, 1830.
[513]
"Symbolae Physicae," 1831, and Abh. Ak. Berlin, 1832, i. p. 377, etc.
[514]
T. cit. p. 92.
[515]
Vol. i. 1880, Introduction, p. cxxxi.
[516]
Élémens de Zoologie, 2nd ed. Animaux sans Vertèbres, 1843, pp. 238,
312. Prof. A. Milne-Edwards has kindly written to me, informing me that
he believes this to have been the first occasion on which the term was
thus used.
[517]
Phil. Trans. vol. cxliii, 1853, p. 62.
[518]
Nitsche, Zeitschr. wiss. Zool. xx. 1870, p. 34.
[519]
πρωκτός, anus; ἐντός, within; ἐκτός, without.
Page 704
[520]
λοφός, crest or tuft.
[521]
γυμνός, naked; λαιμός, throat.
[522]
φυλάσσω, I guard.
[523]
κύκλος, circle; στόμα, mouth.
[524]
χεῖλος, lip.
[525]
κτείς, κτενός, comb.
[526]
Miss E. C. Jelly, Synonymic Cat. Recent Marine Bryozoa, London, 1889.
[527]
Zeitschr. wiss. Zool. xxi. 1871, p. 421.
[528]
Fischer, Nouv. Arch. Mus. Paris, ii. 1866, p. 293.
[529]
Ehlers, Abh. Ges. Göttingen, xxi. 1876, p. 3, and Joyeux-Laffuie, (as
Delagia) Arch. Zool. Exp. 2 sér. vi. 1888, p. 135.
[530]
Busk, "Challenger" Reports, Parts 30 and 50.
[531]
λοφός, crest or tuft.
[521]
γυμνός, naked; λαιμός, throat.
[522]
φυλάσσω, I guard.
[523]
κύκλος, circle; στόμα, mouth.
[524]
χεῖλος, lip.
[525]
κτείς, κτενός, comb.
[526]
Miss E. C. Jelly, Synonymic Cat. Recent Marine Bryozoa, London, 1889.
[527]
Zeitschr. wiss. Zool. xxi. 1871, p. 421.
[528]
Fischer, Nouv. Arch. Mus. Paris, ii. 1866, p. 293.
[529]
Ehlers, Abh. Ges. Göttingen, xxi. 1876, p. 3, and Joyeux-Laffuie, (as
Delagia) Arch. Zool. Exp. 2 sér. vi. 1888, p. 135.
[530]
Busk, "Challenger" Reports, Parts 30 and 50.
[531]
Page 705
Hincks, Brit. Marine Polyzoa, Introduction, p. cxxxv.
[532]
Hincks, Brit. Mar. Polyzoa, i. p. 558.
[533]
See Hincks, Brit. Mar. Polyzoa, i. p. lxiv.; and Busk, Cat. of Marine
Polyzoa in the British Museum, part ii. 1854, p. 103.
[534]
J. Linn. Soc. xv. 1881, p. 359.
[535]
"Challenger" Report, part xxx. 1884, pl. ix.
[536]
Hincks, Brit. Mar. Polyzoa, i. p. 58.
[537]
Brit. Mus. Cat. part ii. 1854, p. 106; Hincks, t. cit. p. 181 n.
[538]
p. 475.
[539]
Barentsia Hincks (= Ascopodaria Busk) differs from Pedicellina in that
each stem has a muscular swelling at its base. The genus is represented
by two British species, B. gracilis Sars and B. nodosa Lomas.
[540]
Arch. Zool. Exp. 2 sér. ix. 1891, p. 91.
[541]
For structure, see Davenport, Bull. Mus. Harvard, xxiv. 1893, p. 1.
[542]
[532]
Hincks, Brit. Mar. Polyzoa, i. p. 558.
[533]
See Hincks, Brit. Mar. Polyzoa, i. p. lxiv.; and Busk, Cat. of Marine
Polyzoa in the British Museum, part ii. 1854, p. 103.
[534]
J. Linn. Soc. xv. 1881, p. 359.
[535]
"Challenger" Report, part xxx. 1884, pl. ix.
[536]
Hincks, Brit. Mar. Polyzoa, i. p. 58.
[537]
Brit. Mus. Cat. part ii. 1854, p. 106; Hincks, t. cit. p. 181 n.
[538]
p. 475.
[539]
Barentsia Hincks (= Ascopodaria Busk) differs from Pedicellina in that
each stem has a muscular swelling at its base. The genus is represented
by two British species, B. gracilis Sars and B. nodosa Lomas.
[540]
Arch. Zool. Exp. 2 sér. ix. 1891, p. 91.
[541]
For structure, see Davenport, Bull. Mus. Harvard, xxiv. 1893, p. 1.
[542]
Page 706
λοξός, oblique; σῶμα, body.
[543]
Quart. J. Micr. Sci. xxvii. 1887, pl. xxi. Fig. 10.
[544]
For a recent account of the Entoprocta, see Ehlers, "Zur Kenntniss d.
Pedicellineen," Abh. Ges. Göttingen, xxxvi. 1890, No. iii.
[An important account of the structure of marine Ectoprocta is given by
Calvet, "Contribution à l'Histoire Naturelle des Bryozoaires Ectoproctes
Marins," Trav. Inst. Zool. Montpellier, N.S., Mém. No. 8, 1900.]
[545]
Kraepelin, K., "Die deutschen Süsswasser-Bryozoen."—Abh. Ver.
Hamburg, x. 1887, No. 9, p. 95.
[546]
Jullien, Bull. Soc. Zool. France, x. 1885, p. 92.
[547]
Hincks, Brit. Marine Polyzoa, i. p. 132.
[548]
T. cit., p. 167.
[549]
Quoted by Kraepelin, t. cit., p. 83.
[550]
Kraepelin, Abh. Ver. Hamburg, xii. 1893, No. 2, p. 65.
[551]
Zool. Anz., xvi. 1893 (1894), p. 385.
[552]
[543]
Quart. J. Micr. Sci. xxvii. 1887, pl. xxi. Fig. 10.
[544]
For a recent account of the Entoprocta, see Ehlers, "Zur Kenntniss d.
Pedicellineen," Abh. Ges. Göttingen, xxxvi. 1890, No. iii.
[An important account of the structure of marine Ectoprocta is given by
Calvet, "Contribution à l'Histoire Naturelle des Bryozoaires Ectoproctes
Marins," Trav. Inst. Zool. Montpellier, N.S., Mém. No. 8, 1900.]
[545]
Kraepelin, K., "Die deutschen Süsswasser-Bryozoen."—Abh. Ver.
Hamburg, x. 1887, No. 9, p. 95.
[546]
Jullien, Bull. Soc. Zool. France, x. 1885, p. 92.
[547]
Hincks, Brit. Marine Polyzoa, i. p. 132.
[548]
T. cit., p. 167.
[549]
Quoted by Kraepelin, t. cit., p. 83.
[550]
Kraepelin, Abh. Ver. Hamburg, xii. 1893, No. 2, p. 65.
[551]
Zool. Anz., xvi. 1893 (1894), p. 385.
[552]
Page 707
Hyatt, Proc. Essex Institute (U.S.A.) (reprint from vols. iv., v. 1866-
1868), p. 9.
[553]
Rare and Remarkable Animals of Scotland, ii. 1848, p. 93.
[554]
Trembley, Mém. Hist. Polypes, 1744; iii. Mém., p. 217. The same
processes are described by Baker, Employment for the Microscope, new
ed. 1785, p. 311.
[555]
Oka, J. Coll. Japan, iv. 1891, p. 90.
[556]
Hyatt, t. cit. p. 99.
[557]
Verworn, Zeitschr. wiss. Zool. xlvi. 1888, p. 119.
[558]
Dalyell, t. cit. p. 94.
[559]
Kraepelin, Abh. Ver. Hamburg, x. 1887, No. 9, p. 141.
[560]
Phil. Trans. 1837, p. 396.
[561]
Zeitschr. wiss. Zool. xxi. 1871, p. 426.
[562]
J. Coll. Japan, iv. 1891, p. 113.
[563]
1868), p. 9.
[553]
Rare and Remarkable Animals of Scotland, ii. 1848, p. 93.
[554]
Trembley, Mém. Hist. Polypes, 1744; iii. Mém., p. 217. The same
processes are described by Baker, Employment for the Microscope, new
ed. 1785, p. 311.
[555]
Oka, J. Coll. Japan, iv. 1891, p. 90.
[556]
Hyatt, t. cit. p. 99.
[557]
Verworn, Zeitschr. wiss. Zool. xlvi. 1888, p. 119.
[558]
Dalyell, t. cit. p. 94.
[559]
Kraepelin, Abh. Ver. Hamburg, x. 1887, No. 9, p. 141.
[560]
Phil. Trans. 1837, p. 396.
[561]
Zeitschr. wiss. Zool. xxi. 1871, p. 426.
[562]
J. Coll. Japan, iv. 1891, p. 113.
[563]
Page 708
Zool. Anz. xii. 1889, p. 508. This paper contains references to M. Jullien's
writings on the mechanism of protrusion.
[564]
[See P. Cambridge Soc. vol. xi. Part 1, 1901.]
[565]
Zeitschr. wiss. Zool. xlvi. 1888, p. 124.
[566]
Kraepelin, Abh. Ver. Hamburg, xii. 1893, No. 2, p. 47; Braem, Bibl. Zool.
(Bd. ii.) Heft 6, 1890, pp. 66 f.
[567]
Cf. Kraepelin, Abh. Ver. Hamburg, x. 1887, No. 9, pp. 154 f.
[568]
T. cit. p. 83.
[569]
Joliet, Arch. Zool. Exp. vi. 1877, p. 262.
[570]
Kraepelin, Abh. Ver. Hamburg, xii. 1893, No. 2, p. 22.
[571]
Harmer, Quart. J. Micr. Sci. xxxiv. 1893, p. 211.
[572]
Arch. Zool. Exp. 2 sér. x. 1892, p. 557.
[573]
Phil. Trans. 1837, p. 408.
[574]
Brit. Marine Polyzoa, Introduction, pp. lxxxvi, xc.
writings on the mechanism of protrusion.
[564]
[See P. Cambridge Soc. vol. xi. Part 1, 1901.]
[565]
Zeitschr. wiss. Zool. xlvi. 1888, p. 124.
[566]
Kraepelin, Abh. Ver. Hamburg, xii. 1893, No. 2, p. 47; Braem, Bibl. Zool.
(Bd. ii.) Heft 6, 1890, pp. 66 f.
[567]
Cf. Kraepelin, Abh. Ver. Hamburg, x. 1887, No. 9, pp. 154 f.
[568]
T. cit. p. 83.
[569]
Joliet, Arch. Zool. Exp. vi. 1877, p. 262.
[570]
Kraepelin, Abh. Ver. Hamburg, xii. 1893, No. 2, p. 22.
[571]
Harmer, Quart. J. Micr. Sci. xxxiv. 1893, p. 211.
[572]
Arch. Zool. Exp. 2 sér. x. 1892, p. 557.
[573]
Phil. Trans. 1837, p. 408.
[574]
Brit. Marine Polyzoa, Introduction, pp. lxxxvi, xc.
Page 709
[575]
Arch. Zool. Exp. vi. 1877, p. 261.
[576]
Recherches sur l'Embryologie des Bryozoaires, 4to Lille, 1877.
[577]
Prouho, loc. cit.
[578]
Arch. Zool. Exp. 2 ser. v. 1887, p. 446.
[579]
Quart. J. Micr. Sci. xxxiv. 1893, p. 199; xxxix. part i. 1896, p. 71.
[580]
Jullien, Mém. Soc. Zool. France, iii. 1890, p. 381.
[581]
Cori, Zeitschr. wiss. Zool. lv. 1893, p. 626.
[582]
Oka, J. Coll. Japan, iv. 1891, p. 109; viii. 1895, p. 339.
[583]
Cf. Seeliger, Zeitschr. wiss. Zool. xlix. 1890, p. 168; and l. 1890, p. 560.
[584]
Cf. Milne-Edwards (H.), Ann. Sci. Nat. 2 ser. vi. 1836, pp. 5, 321.
[585]
See Norman, Ann. Nat. Hist. ser. 6, xiii. 1894, p. 114.
[586]
See Holdsworth, P. Zool. Soc. pt. xxvi. 1858, p. 306.
Arch. Zool. Exp. vi. 1877, p. 261.
[576]
Recherches sur l'Embryologie des Bryozoaires, 4to Lille, 1877.
[577]
Prouho, loc. cit.
[578]
Arch. Zool. Exp. 2 ser. v. 1887, p. 446.
[579]
Quart. J. Micr. Sci. xxxiv. 1893, p. 199; xxxix. part i. 1896, p. 71.
[580]
Jullien, Mém. Soc. Zool. France, iii. 1890, p. 381.
[581]
Cori, Zeitschr. wiss. Zool. lv. 1893, p. 626.
[582]
Oka, J. Coll. Japan, iv. 1891, p. 109; viii. 1895, p. 339.
[583]
Cf. Seeliger, Zeitschr. wiss. Zool. xlix. 1890, p. 168; and l. 1890, p. 560.
[584]
Cf. Milne-Edwards (H.), Ann. Sci. Nat. 2 ser. vi. 1836, pp. 5, 321.
[585]
See Norman, Ann. Nat. Hist. ser. 6, xiii. 1894, p. 114.
[586]
See Holdsworth, P. Zool. Soc. pt. xxvi. 1858, p. 306.
Page 710
[587]
Brit. Mar. Polyzoa, Introduction, p. cxxii.
[588]
Ann. Nat. Hist. ser. 5, xx. 1887, p. 91.
[589]
Aetea, Eucratea, and certain other forms were separated off by Mr. Busk
as a distinct division, the Stolonata.
[590]
Most of the writings of this author are referred to on pp. 277, 278 of Miss
Jelly's Synonymic Catalogue, referred to on p. 523.
[591]
Catalogue of Marine Polyzoa in the Collection of the British Museum,
parts i.-iii. 1852-1875; and Challenger Reports, Parts 30 (1884) and 50
(1886).
[592]
Trans. and Proc. R. Soc. Victoria, xxiii. 1887, p. 187, and Tr. R. Soc.
Victoria, iv. 1895, p. 1.
[593]
Tr. Zool. Soc. xiii. 1895, p. 223.
[594]
Zittel, Text Book of Palaeontology (Eng. Trans.), 1900, p. 257 (Bryozoa,
by E. O. Ulrich).
[595]
Paléontologie Française. Terrains Crétacés, tome v., Bryozoaires, 8vo.
Paris, 1850-1851. This great work refers, however, to recent as well as to
fossil species.
Brit. Mar. Polyzoa, Introduction, p. cxxii.
[588]
Ann. Nat. Hist. ser. 5, xx. 1887, p. 91.
[589]
Aetea, Eucratea, and certain other forms were separated off by Mr. Busk
as a distinct division, the Stolonata.
[590]
Most of the writings of this author are referred to on pp. 277, 278 of Miss
Jelly's Synonymic Catalogue, referred to on p. 523.
[591]
Catalogue of Marine Polyzoa in the Collection of the British Museum,
parts i.-iii. 1852-1875; and Challenger Reports, Parts 30 (1884) and 50
(1886).
[592]
Trans. and Proc. R. Soc. Victoria, xxiii. 1887, p. 187, and Tr. R. Soc.
Victoria, iv. 1895, p. 1.
[593]
Tr. Zool. Soc. xiii. 1895, p. 223.
[594]
Zittel, Text Book of Palaeontology (Eng. Trans.), 1900, p. 257 (Bryozoa,
by E. O. Ulrich).
[595]
Paléontologie Française. Terrains Crétacés, tome v., Bryozoaires, 8vo.
Paris, 1850-1851. This great work refers, however, to recent as well as to
fossil species.
Page 711
[596]
Heteropora, of which recent species exist, is placed by Dr. Gregory in the
Trepostomata.
[597]
Quart. J. Geol. Soc. l. 1894, pp. 72, 79.
[598]
See, however, Vine, Ann. Nat. Hist. ser. 5. xiv. 1884, pp. 87, 88, and P.
Yorksh. Geol. Soc. xii. 1891, p. 74, for possible Palaeozoic Ctenostomes
(Ascodictyon, Rhopalonaria, and Vinella).
[599]
Two vols. 8vo. London (Van Voorst), 1880.
[600]
8vo. London (Dulau), 1889.
[601]
One or two genera of Cheilostomata may be mistaken for Cyclostomata.
In case of doubt, 7 et seq. must be worked through.
[602]
Certain varieties of adherent species occasionally assume an erect form.
[603]
For Celleporella (colony minute: orifice tubular), see 41 et seq.
[604]
Rhynchozoon (see No. 61), in which the primary orifice becomes much
obscured by the development of a large mucro, is placed in this section.
[605]
Hincks, J. Linn. Soc. xxi. 1889, p. 123.
Heteropora, of which recent species exist, is placed by Dr. Gregory in the
Trepostomata.
[597]
Quart. J. Geol. Soc. l. 1894, pp. 72, 79.
[598]
See, however, Vine, Ann. Nat. Hist. ser. 5. xiv. 1884, pp. 87, 88, and P.
Yorksh. Geol. Soc. xii. 1891, p. 74, for possible Palaeozoic Ctenostomes
(Ascodictyon, Rhopalonaria, and Vinella).
[599]
Two vols. 8vo. London (Van Voorst), 1880.
[600]
8vo. London (Dulau), 1889.
[601]
One or two genera of Cheilostomata may be mistaken for Cyclostomata.
In case of doubt, 7 et seq. must be worked through.
[602]
Certain varieties of adherent species occasionally assume an erect form.
[603]
For Celleporella (colony minute: orifice tubular), see 41 et seq.
[604]
Rhynchozoon (see No. 61), in which the primary orifice becomes much
obscured by the development of a large mucro, is placed in this section.
[605]
Hincks, J. Linn. Soc. xxi. 1889, p. 123.
Page 712
[606]
Micropora complanata, Norman, should be placed in the genus Lepralia.
See Hincks, Ann. Nat. Hist. 5 ser. xix. 1887, p. 304.
[607]
See Norman, Ann. Nat. Hist. ser. 6, xiii. 1894, p. 113.
[608]
Hincks, "Marine Polyzoa" (reprints from Ann. Nat. Hist. 1880-91), Index,
p. v. note. (Replacing Rhynchopora, preoccupied for a Brachiopod.)
[609]
A form of Lepralia pallasiana, in which a mucro is developed, may be
mistaken for Umbonula (see characters given for Lepralia under No. 59).
[610]
See Arch. Zool. Exp. 2 ser. vi. 1888, p. 135 (as Delagia), and ibid. x.
1892, p. 594. [See also J. Mar. Biol. Ass. v., 1897-99, p. 51.]
[611]
F. S. Conant, Johns Hopkins Univ. Circ. vol. xv. 1896, p. 82.
[612]
Ibid. vol. xiv. 1896, p. 77.
Micropora complanata, Norman, should be placed in the genus Lepralia.
See Hincks, Ann. Nat. Hist. 5 ser. xix. 1887, p. 304.
[607]
See Norman, Ann. Nat. Hist. ser. 6, xiii. 1894, p. 113.
[608]
Hincks, "Marine Polyzoa" (reprints from Ann. Nat. Hist. 1880-91), Index,
p. v. note. (Replacing Rhynchopora, preoccupied for a Brachiopod.)
[609]
A form of Lepralia pallasiana, in which a mucro is developed, may be
mistaken for Umbonula (see characters given for Lepralia under No. 59).
[610]
See Arch. Zool. Exp. 2 ser. vi. 1888, p. 135 (as Delagia), and ibid. x.
1892, p. 594. [See also J. Mar. Biol. Ass. v., 1897-99, p. 51.]
[611]
F. S. Conant, Johns Hopkins Univ. Circ. vol. xv. 1896, p. 82.
[612]
Ibid. vol. xiv. 1896, p. 77.
Page 713
*** END OF THE PROJECT GUTENBERG EBOOK THE CAMBRIDGE
NATURAL HISTORY, VOL. 02 (OF 10) ***
Updated editions will replace the previous one—the old editions will
be renamed.
Creating the works from print editions not protected by U.S. copyright
law means that no one owns a United States copyright in these works,
so the Foundation (and you!) can copy and distribute it in the United
States without permission and without paying copyright royalties.
Special rules, set forth in the General Terms of Use part of this license,
apply to copying and distributing Project Gutenberg™ electronic
works to protect the PROJECT GUTENBERG™ concept and
trademark. Project Gutenberg is a registered trademark, and may not
be used if you charge for an eBook, except by following the terms of
the trademark license, including paying royalties for use of the Project
Gutenberg trademark. If you do not charge anything for copies of this
eBook, complying with the trademark license is very easy. You may
use this eBook for nearly any purpose such as creation of derivative
works, reports, performances and research. Project Gutenberg eBooks
may be modified and printed and given away—you may do practically
ANYTHING in the United States with eBooks not protected by U.S.
copyright law. Redistribution is subject to the trademark license,
especially commercial redistribution.
START: FULL LICENSE
NATURAL HISTORY, VOL. 02 (OF 10) ***
Updated editions will replace the previous one—the old editions will
be renamed.
Creating the works from print editions not protected by U.S. copyright
law means that no one owns a United States copyright in these works,
so the Foundation (and you!) can copy and distribute it in the United
States without permission and without paying copyright royalties.
Special rules, set forth in the General Terms of Use part of this license,
apply to copying and distributing Project Gutenberg™ electronic
works to protect the PROJECT GUTENBERG™ concept and
trademark. Project Gutenberg is a registered trademark, and may not
be used if you charge for an eBook, except by following the terms of
the trademark license, including paying royalties for use of the Project
Gutenberg trademark. If you do not charge anything for copies of this
eBook, complying with the trademark license is very easy. You may
use this eBook for nearly any purpose such as creation of derivative
works, reports, performances and research. Project Gutenberg eBooks
may be modified and printed and given away—you may do practically
ANYTHING in the United States with eBooks not protected by U.S.
copyright law. Redistribution is subject to the trademark license,
especially commercial redistribution.
START: FULL LICENSE
Page 714
THE FULL PROJECT GUTENBERG™ LICENSE
PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
To protect the Project Gutenberg™ mission of promoting the free
distribution of electronic works, by using or distributing this work (or
any other work associated in any way with the phrase “Project
Gutenberg”), you agree to comply with all the terms of the Full Project
Gutenberg License available with this file or online at
www.gutenberg.org/license.
Section 1. General Terms of Use and Redistributing
Project Gutenberg electronic works
1.A. By reading or using any part of this Project Gutenberg electronic
work, you indicate that you have read, understand, agree to and accept
all the terms of this license and intellectual property
(trademark/copyright) agreement. If you do not agree to abide by all
the terms of this agreement, you must cease using and return or destroy
all copies of Project Gutenberg electronic works in your possession. If
you paid a fee for obtaining a copy of or access to a Project Gutenberg
electronic work and you do not agree to be bound by the terms of this
agreement, you may obtain a refund from the person or entity to whom
you paid the fee as set forth in paragraph 1.E.8.
1.B. “Project Gutenberg” is a registered trademark. It may only be
used on or associated in any way with an electronic work by people
who agree to be bound by the terms of this agreement. There are a few
things that you can do with most Project Gutenberg electronic works
even without complying with the full terms of this agreement. See
paragraph 1.C below. There are a lot of things you can do with Project
Gutenberg electronic works if you follow the terms of this agreement
and help preserve free future access to Project Gutenberg electronic
works. See paragraph 1.E below.
1.C. The Project Gutenberg Literary Archive Foundation (“the
Foundation” or PGLAF), owns a compilation copyright in the
PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
To protect the Project Gutenberg™ mission of promoting the free
distribution of electronic works, by using or distributing this work (or
any other work associated in any way with the phrase “Project
Gutenberg”), you agree to comply with all the terms of the Full Project
Gutenberg License available with this file or online at
www.gutenberg.org/license.
Section 1. General Terms of Use and Redistributing
Project Gutenberg electronic works
1.A. By reading or using any part of this Project Gutenberg electronic
work, you indicate that you have read, understand, agree to and accept
all the terms of this license and intellectual property
(trademark/copyright) agreement. If you do not agree to abide by all
the terms of this agreement, you must cease using and return or destroy
all copies of Project Gutenberg electronic works in your possession. If
you paid a fee for obtaining a copy of or access to a Project Gutenberg
electronic work and you do not agree to be bound by the terms of this
agreement, you may obtain a refund from the person or entity to whom
you paid the fee as set forth in paragraph 1.E.8.
1.B. “Project Gutenberg” is a registered trademark. It may only be
used on or associated in any way with an electronic work by people
who agree to be bound by the terms of this agreement. There are a few
things that you can do with most Project Gutenberg electronic works
even without complying with the full terms of this agreement. See
paragraph 1.C below. There are a lot of things you can do with Project
Gutenberg electronic works if you follow the terms of this agreement
and help preserve free future access to Project Gutenberg electronic
works. See paragraph 1.E below.
1.C. The Project Gutenberg Literary Archive Foundation (“the
Foundation” or PGLAF), owns a compilation copyright in the
Page 715
collection of Project Gutenberg electronic works. Nearly all the
individual works in the collection are in the public domain in the
United States. If an individual work is unprotected by copyright law in
the United States and you are located in the United States, we do not
claim a right to prevent you from copying, distributing, performing,
displaying or creating derivative works based on the work as long as
all references to Project Gutenberg are removed. Of course, we hope
that you will support the Project Gutenberg mission of promoting free
access to electronic works by freely sharing Project Gutenberg works
in compliance with the terms of this agreement for keeping the Project
Gutenberg name associated with the work. You can easily comply with
the terms of this agreement by keeping this work in the same format
with its attached full Project Gutenberg License when you share it
without charge with others.
1.D. The copyright laws of the place where you are located also govern
what you can do with this work. Copyright laws in most countries are
in a constant state of change. If you are outside the United States,
check the laws of your country in addition to the terms of this
agreement before downloading, copying, displaying, performing,
distributing or creating derivative works based on this work or any
other Project Gutenberg work. The Foundation makes no
representations concerning the copyright status of any work in any
country other than the United States.
1.E. Unless you have removed all references to Project Gutenberg:
1.E.1. The following sentence, with active links to, or other immediate
access to, the full Project Gutenberg License must appear prominently
whenever any copy of a Project Gutenberg work (any work on which
the phrase “Project Gutenberg” appears, or with which the phrase
“Project Gutenberg” is associated) is accessed, displayed, performed,
viewed, copied or distributed:
This eBook is for the use of anyone anywhere in the United States
and most other parts of the world at no cost and with almost no
restrictions whatsoever. You may copy it, give it away or re-use it
under the terms of the Project Gutenberg™ License included with
individual works in the collection are in the public domain in the
United States. If an individual work is unprotected by copyright law in
the United States and you are located in the United States, we do not
claim a right to prevent you from copying, distributing, performing,
displaying or creating derivative works based on the work as long as
all references to Project Gutenberg are removed. Of course, we hope
that you will support the Project Gutenberg mission of promoting free
access to electronic works by freely sharing Project Gutenberg works
in compliance with the terms of this agreement for keeping the Project
Gutenberg name associated with the work. You can easily comply with
the terms of this agreement by keeping this work in the same format
with its attached full Project Gutenberg License when you share it
without charge with others.
1.D. The copyright laws of the place where you are located also govern
what you can do with this work. Copyright laws in most countries are
in a constant state of change. If you are outside the United States,
check the laws of your country in addition to the terms of this
agreement before downloading, copying, displaying, performing,
distributing or creating derivative works based on this work or any
other Project Gutenberg work. The Foundation makes no
representations concerning the copyright status of any work in any
country other than the United States.
1.E. Unless you have removed all references to Project Gutenberg:
1.E.1. The following sentence, with active links to, or other immediate
access to, the full Project Gutenberg License must appear prominently
whenever any copy of a Project Gutenberg work (any work on which
the phrase “Project Gutenberg” appears, or with which the phrase
“Project Gutenberg” is associated) is accessed, displayed, performed,
viewed, copied or distributed:
This eBook is for the use of anyone anywhere in the United States
and most other parts of the world at no cost and with almost no
restrictions whatsoever. You may copy it, give it away or re-use it
under the terms of the Project Gutenberg™ License included with
Page 716
this eBook or online at www.gutenberg.org. If you are not located
in the United States, you will have to check the laws of the
country where you are located before using this eBook.
1.E.2. If an individual Project Gutenberg electronic work is derived
from texts not protected by U.S. copyright law (does not contain a
notice indicating that it is posted with permission of the copyright
holder), the work can be copied and distributed to anyone in the United
States without paying any fees or charges. If you are redistributing or
providing access to a work with the phrase “Project Gutenberg”
associated with or appearing on the work, you must comply either with
the requirements of paragraphs 1.E.1 through 1.E.7 or obtain
permission for the use of the work and the Project Gutenberg
trademark as set forth in paragraphs 1.E.8 or 1.E.9.
1.E.3. If an individual Project Gutenberg electronic work is posted
with the permission of the copyright holder, your use and distribution
must comply with both paragraphs 1.E.1 through 1.E.7 and any
additional terms imposed by the copyright holder. Additional terms
will be linked to the Project Gutenberg License for all works posted
with the permission of the copyright holder found at the beginning of
this work.
1.E.4. Do not unlink or detach or remove the full Project Gutenberg
License terms from this work, or any files containing a part of this
work or any other work associated with Project Gutenberg.
1.E.5. Do not copy, display, perform, distribute or redistribute this
electronic work, or any part of this electronic work, without
prominently displaying the sentence set forth in paragraph 1.E.1 with
active links or immediate access to the full terms of the Project
Gutenberg License.
1.E.6. You may convert to and distribute this work in any binary,
compressed, marked up, nonproprietary or proprietary form, including
any word processing or hypertext form. However, if you provide
access to or distribute copies of a Project Gutenberg work in a format
other than “Plain Vanilla ASCII” or other format used in the official
in the United States, you will have to check the laws of the
country where you are located before using this eBook.
1.E.2. If an individual Project Gutenberg electronic work is derived
from texts not protected by U.S. copyright law (does not contain a
notice indicating that it is posted with permission of the copyright
holder), the work can be copied and distributed to anyone in the United
States without paying any fees or charges. If you are redistributing or
providing access to a work with the phrase “Project Gutenberg”
associated with or appearing on the work, you must comply either with
the requirements of paragraphs 1.E.1 through 1.E.7 or obtain
permission for the use of the work and the Project Gutenberg
trademark as set forth in paragraphs 1.E.8 or 1.E.9.
1.E.3. If an individual Project Gutenberg electronic work is posted
with the permission of the copyright holder, your use and distribution
must comply with both paragraphs 1.E.1 through 1.E.7 and any
additional terms imposed by the copyright holder. Additional terms
will be linked to the Project Gutenberg License for all works posted
with the permission of the copyright holder found at the beginning of
this work.
1.E.4. Do not unlink or detach or remove the full Project Gutenberg
License terms from this work, or any files containing a part of this
work or any other work associated with Project Gutenberg.
1.E.5. Do not copy, display, perform, distribute or redistribute this
electronic work, or any part of this electronic work, without
prominently displaying the sentence set forth in paragraph 1.E.1 with
active links or immediate access to the full terms of the Project
Gutenberg License.
1.E.6. You may convert to and distribute this work in any binary,
compressed, marked up, nonproprietary or proprietary form, including
any word processing or hypertext form. However, if you provide
access to or distribute copies of a Project Gutenberg work in a format
other than “Plain Vanilla ASCII” or other format used in the official
Page 717
version posted on the official Project Gutenberg website
(www.gutenberg.org), you must, at no additional cost, fee or expense
to the user, provide a copy, a means of exporting a copy, or a means of
obtaining a copy upon request, of the work in its original “Plain
Vanilla ASCII” or other form. Any alternate format must include the
full Project Gutenberg License as specified in paragraph 1.E.1.
1.E.7. Do not charge a fee for access to, viewing, displaying,
performing, copying or distributing any Project Gutenberg works
unless you comply with paragraph 1.E.8 or 1.E.9.
1.E.8. You may charge a reasonable fee for copies of or providing
access to or distributing Project Gutenberg electronic works provided
that:
• You pay a royalty fee of 20% of the gross profits you derive from the
use of Project Gutenberg works calculated using the method you
already use to calculate your applicable taxes. The fee is owed to the
owner of the Project Gutenberg trademark, but he has agreed to donate
royalties under this paragraph to the Project Gutenberg Literary
Archive Foundation. Royalty payments must be paid within 60 days
following each date on which you prepare (or are legally required to
prepare) your periodic tax returns. Royalty payments should be clearly
marked as such and sent to the Project Gutenberg Literary Archive
Foundation at the address specified in Section 4, “Information about
donations to the Project Gutenberg Literary Archive Foundation.”
• You provide a full refund of any money paid by a user who notifies
you in writing (or by e-mail) within 30 days of receipt that s/he does
not agree to the terms of the full Project Gutenberg™ License. You
must require such a user to return or destroy all copies of the works
possessed in a physical medium and discontinue all use of and all
access to other copies of Project Gutenberg™ works.
• You provide, in accordance with paragraph 1.F.3, a full refund of any
money paid for a work or a replacement copy, if a defect in the
electronic work is discovered and reported to you within 90 days of
receipt of the work.
(www.gutenberg.org), you must, at no additional cost, fee or expense
to the user, provide a copy, a means of exporting a copy, or a means of
obtaining a copy upon request, of the work in its original “Plain
Vanilla ASCII” or other form. Any alternate format must include the
full Project Gutenberg License as specified in paragraph 1.E.1.
1.E.7. Do not charge a fee for access to, viewing, displaying,
performing, copying or distributing any Project Gutenberg works
unless you comply with paragraph 1.E.8 or 1.E.9.
1.E.8. You may charge a reasonable fee for copies of or providing
access to or distributing Project Gutenberg electronic works provided
that:
• You pay a royalty fee of 20% of the gross profits you derive from the
use of Project Gutenberg works calculated using the method you
already use to calculate your applicable taxes. The fee is owed to the
owner of the Project Gutenberg trademark, but he has agreed to donate
royalties under this paragraph to the Project Gutenberg Literary
Archive Foundation. Royalty payments must be paid within 60 days
following each date on which you prepare (or are legally required to
prepare) your periodic tax returns. Royalty payments should be clearly
marked as such and sent to the Project Gutenberg Literary Archive
Foundation at the address specified in Section 4, “Information about
donations to the Project Gutenberg Literary Archive Foundation.”
• You provide a full refund of any money paid by a user who notifies
you in writing (or by e-mail) within 30 days of receipt that s/he does
not agree to the terms of the full Project Gutenberg™ License. You
must require such a user to return or destroy all copies of the works
possessed in a physical medium and discontinue all use of and all
access to other copies of Project Gutenberg™ works.
• You provide, in accordance with paragraph 1.F.3, a full refund of any
money paid for a work or a replacement copy, if a defect in the
electronic work is discovered and reported to you within 90 days of
receipt of the work.
Page 718
• You comply with all other terms of this agreement for free distribution
of Project Gutenberg™ works.
1.E.9. If you wish to charge a fee or distribute a Project Gutenberg™
electronic work or group of works on different terms than are set forth
in this agreement, you must obtain permission in writing from the
Project Gutenberg Literary Archive Foundation, the manager of the
Project Gutenberg™ trademark. Contact the Foundation as set forth in
Section 3 below.
1.F.
1.F.1. Project Gutenberg volunteers and employees expend
considerable effort to identify, do copyright research on, transcribe and
proofread works not protected by U.S. copyright law in creating the
Project Gutenberg™ collection. Despite these efforts, Project
Gutenberg™ electronic works, and the medium on which they may be
stored, may contain “Defects,” such as, but not limited to, incomplete,
inaccurate or corrupt data, transcription errors, a copyright or other
intellectual property infringement, a defective or damaged disk or
other medium, a computer virus, or computer codes that damage or
cannot be read by your equipment.
1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES -
Except for the “Right of Replacement or Refund” described in
paragraph 1.F.3, the Project Gutenberg Literary Archive Foundation,
the owner of the Project Gutenberg™ trademark, and any other party
distributing a Project Gutenberg™ electronic work under this
agreement, disclaim all liability to you for damages, costs and
expenses, including legal fees. YOU AGREE THAT YOU HAVE NO
REMEDIES FOR NEGLIGENCE, STRICT LIABILITY, BREACH
OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE
FOUNDATION, THE TRADEMARK OWNER, AND ANY
DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT,
CONSEQUENTIAL, PUNITIVE OR INCIDENTAL DAMAGES
of Project Gutenberg™ works.
1.E.9. If you wish to charge a fee or distribute a Project Gutenberg™
electronic work or group of works on different terms than are set forth
in this agreement, you must obtain permission in writing from the
Project Gutenberg Literary Archive Foundation, the manager of the
Project Gutenberg™ trademark. Contact the Foundation as set forth in
Section 3 below.
1.F.
1.F.1. Project Gutenberg volunteers and employees expend
considerable effort to identify, do copyright research on, transcribe and
proofread works not protected by U.S. copyright law in creating the
Project Gutenberg™ collection. Despite these efforts, Project
Gutenberg™ electronic works, and the medium on which they may be
stored, may contain “Defects,” such as, but not limited to, incomplete,
inaccurate or corrupt data, transcription errors, a copyright or other
intellectual property infringement, a defective or damaged disk or
other medium, a computer virus, or computer codes that damage or
cannot be read by your equipment.
1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES -
Except for the “Right of Replacement or Refund” described in
paragraph 1.F.3, the Project Gutenberg Literary Archive Foundation,
the owner of the Project Gutenberg™ trademark, and any other party
distributing a Project Gutenberg™ electronic work under this
agreement, disclaim all liability to you for damages, costs and
expenses, including legal fees. YOU AGREE THAT YOU HAVE NO
REMEDIES FOR NEGLIGENCE, STRICT LIABILITY, BREACH
OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE
FOUNDATION, THE TRADEMARK OWNER, AND ANY
DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT,
CONSEQUENTIAL, PUNITIVE OR INCIDENTAL DAMAGES
Page 719
EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
DAMAGE.
1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you
discover a defect in this electronic work within 90 days of receiving it,
you can receive a refund of the money (if any) you paid for it by
sending a written explanation to the person you received the work
from. If you received the work on a physical medium, you must return
the medium with your written explanation. The person or entity that
provided you with the defective work may elect to provide a
replacement copy in lieu of a refund. If you received the work
electronically, the person or entity providing it to you may choose to
give you a second opportunity to receive the work electronically in lieu
of a refund. If the second copy is also defective, you may demand a
refund in writing without further opportunities to fix the problem.
1.F.4. Except for the limited right of replacement or refund set forth in
paragraph 1.F.3, this work is provided to you ‘AS-IS’, WITH NO
OTHER WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR ANY PURPOSE.
1.F.5. Some states do not allow disclaimers of certain implied
warranties or the exclusion or limitation of certain types of damages. If
any disclaimer or limitation set forth in this agreement violates the law
of the state applicable to this agreement, the agreement shall be
interpreted to make the maximum disclaimer or limitation permitted by
the applicable state law. The invalidity or unenforceability of any
provision of this agreement shall not void the remaining provisions.
1.F.6. INDEMNITY - You agree to indemnify and hold the
Foundation, the trademark owner, any agent or employee of the
Foundation, anyone providing copies of Project Gutenberg™
electronic works in accordance with this agreement, and any
volunteers associated with the production, promotion and distribution
of Project Gutenberg™ electronic works, harmless from all liability,
costs and expenses, including legal fees, that arise directly or indirectly
from any of the following which you do or cause to occur: (a)
DAMAGE.
1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you
discover a defect in this electronic work within 90 days of receiving it,
you can receive a refund of the money (if any) you paid for it by
sending a written explanation to the person you received the work
from. If you received the work on a physical medium, you must return
the medium with your written explanation. The person or entity that
provided you with the defective work may elect to provide a
replacement copy in lieu of a refund. If you received the work
electronically, the person or entity providing it to you may choose to
give you a second opportunity to receive the work electronically in lieu
of a refund. If the second copy is also defective, you may demand a
refund in writing without further opportunities to fix the problem.
1.F.4. Except for the limited right of replacement or refund set forth in
paragraph 1.F.3, this work is provided to you ‘AS-IS’, WITH NO
OTHER WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR ANY PURPOSE.
1.F.5. Some states do not allow disclaimers of certain implied
warranties or the exclusion or limitation of certain types of damages. If
any disclaimer or limitation set forth in this agreement violates the law
of the state applicable to this agreement, the agreement shall be
interpreted to make the maximum disclaimer or limitation permitted by
the applicable state law. The invalidity or unenforceability of any
provision of this agreement shall not void the remaining provisions.
1.F.6. INDEMNITY - You agree to indemnify and hold the
Foundation, the trademark owner, any agent or employee of the
Foundation, anyone providing copies of Project Gutenberg™
electronic works in accordance with this agreement, and any
volunteers associated with the production, promotion and distribution
of Project Gutenberg™ electronic works, harmless from all liability,
costs and expenses, including legal fees, that arise directly or indirectly
from any of the following which you do or cause to occur: (a)
Page 720
distribution of this or any Project Gutenberg work, (b) alteration,
modification, or additions or deletions to any Project Gutenberg work,
and (c) any Defect you cause.
Section 2. Information about the Mission of Project
Gutenberg
Project Gutenberg is synonymous with the free distribution of
electronic works in formats readable by the widest variety of
computers including obsolete, old, middle-aged and new computers. It
exists because of the efforts of hundreds of volunteers and donations
from people in all walks of life.
Volunteers and financial support to provide volunteers with the
assistance they need are critical to reaching Project Gutenberg’s goals
and ensuring that the Project Gutenberg collection will remain freely
available for generations to come. In 2001, the Project Gutenberg
Literary Archive Foundation was created to provide a secure and
permanent future for Project Gutenberg and future generations. To
learn more about the Project Gutenberg Literary Archive Foundation
and how your efforts and donations can help, see Sections 3 and 4 and
the Foundation information page at www.gutenberg.org.
Section 3. Information about the Project Gutenberg
Literary Archive Foundation
The Project Gutenberg Literary Archive Foundation is a non-profit
501(c)(3) educational corporation organized under the laws of the state
of Mississippi and granted tax exempt status by the Internal Revenue
Service. The Foundation’s EIN or federal tax identification number is
64-6221541. Contributions to the Project Gutenberg Literary Archive
Foundation are tax deductible to the full extent permitted by U.S.
federal laws and your state’s laws.
The Foundation’s business office is located at 41 Watchung Plaza
#516, Montclair NJ 07042, USA, +1 (862) 621-9288. Email contact
modification, or additions or deletions to any Project Gutenberg work,
and (c) any Defect you cause.
Section 2. Information about the Mission of Project
Gutenberg
Project Gutenberg is synonymous with the free distribution of
electronic works in formats readable by the widest variety of
computers including obsolete, old, middle-aged and new computers. It
exists because of the efforts of hundreds of volunteers and donations
from people in all walks of life.
Volunteers and financial support to provide volunteers with the
assistance they need are critical to reaching Project Gutenberg’s goals
and ensuring that the Project Gutenberg collection will remain freely
available for generations to come. In 2001, the Project Gutenberg
Literary Archive Foundation was created to provide a secure and
permanent future for Project Gutenberg and future generations. To
learn more about the Project Gutenberg Literary Archive Foundation
and how your efforts and donations can help, see Sections 3 and 4 and
the Foundation information page at www.gutenberg.org.
Section 3. Information about the Project Gutenberg
Literary Archive Foundation
The Project Gutenberg Literary Archive Foundation is a non-profit
501(c)(3) educational corporation organized under the laws of the state
of Mississippi and granted tax exempt status by the Internal Revenue
Service. The Foundation’s EIN or federal tax identification number is
64-6221541. Contributions to the Project Gutenberg Literary Archive
Foundation are tax deductible to the full extent permitted by U.S.
federal laws and your state’s laws.
The Foundation’s business office is located at 41 Watchung Plaza
#516, Montclair NJ 07042, USA, +1 (862) 621-9288. Email contact
Page 721
links and up to date contact information can be found at the
Foundation’s website and official page at www.gutenberg.org/contact
Section 4. Information about Donations to the Project
Gutenberg Literary Archive Foundation
Project Gutenberg™ depends upon and cannot survive without
widespread public support and donations to carry out its mission of
increasing the number of public domain and licensed works that can be
freely distributed in machine-readable form accessible by the widest
array of equipment including outdated equipment. Many small
donations ($1 to $5,000) are particularly important to maintaining tax
exempt status with the IRS.
The Foundation is committed to complying with the laws regulating
charities and charitable donations in all 50 states of the United States.
Compliance requirements are not uniform and it takes a considerable
effort, much paperwork and many fees to meet and keep up with these
requirements. We do not solicit donations in locations where we have
not received written confirmation of compliance. To SEND
DONATIONS or determine the status of compliance for any particular
state visit www.gutenberg.org/donate.
While we cannot and do not solicit contributions from states where we
have not met the solicitation requirements, we know of no prohibition
against accepting unsolicited donations from donors in such states who
approach us with offers to donate.
International donations are gratefully accepted, but we cannot make
any statements concerning tax treatment of donations received from
outside the United States. U.S. laws alone swamp our small staff.
Please check the Project Gutenberg web pages for current donation
methods and addresses. Donations are accepted in a number of other
ways including checks, online payments and credit card donations. To
donate, please visit: www.gutenberg.org/donate.
Foundation’s website and official page at www.gutenberg.org/contact
Section 4. Information about Donations to the Project
Gutenberg Literary Archive Foundation
Project Gutenberg™ depends upon and cannot survive without
widespread public support and donations to carry out its mission of
increasing the number of public domain and licensed works that can be
freely distributed in machine-readable form accessible by the widest
array of equipment including outdated equipment. Many small
donations ($1 to $5,000) are particularly important to maintaining tax
exempt status with the IRS.
The Foundation is committed to complying with the laws regulating
charities and charitable donations in all 50 states of the United States.
Compliance requirements are not uniform and it takes a considerable
effort, much paperwork and many fees to meet and keep up with these
requirements. We do not solicit donations in locations where we have
not received written confirmation of compliance. To SEND
DONATIONS or determine the status of compliance for any particular
state visit www.gutenberg.org/donate.
While we cannot and do not solicit contributions from states where we
have not met the solicitation requirements, we know of no prohibition
against accepting unsolicited donations from donors in such states who
approach us with offers to donate.
International donations are gratefully accepted, but we cannot make
any statements concerning tax treatment of donations received from
outside the United States. U.S. laws alone swamp our small staff.
Please check the Project Gutenberg web pages for current donation
methods and addresses. Donations are accepted in a number of other
ways including checks, online payments and credit card donations. To
donate, please visit: www.gutenberg.org/donate.
Page 722
Section 5. General Information About Project Gutenberg
electronic works
Professor Michael S. Hart was the originator of the Project Gutenberg
concept of a library of electronic works that could be freely shared
with anyone. For forty years, he produced and distributed Project
Gutenberg eBooks with only a loose network of volunteer support.
Project Gutenberg eBooks are often created from several printed
editions, all of which are confirmed as not protected by copyright in
the U.S. unless a copyright notice is included. Thus, we do not
necessarily keep eBooks in compliance with any particular paper
edition.
Most people start at our website which has the main PG search facility:
www.gutenberg.org.
This website includes information about Project Gutenberg, including
how to make donations to the Project Gutenberg Literary Archive
Foundation, how to help produce our new eBooks, and how to
subscribe to our email newsletter to hear about new eBooks.
electronic works
Professor Michael S. Hart was the originator of the Project Gutenberg
concept of a library of electronic works that could be freely shared
with anyone. For forty years, he produced and distributed Project
Gutenberg eBooks with only a loose network of volunteer support.
Project Gutenberg eBooks are often created from several printed
editions, all of which are confirmed as not protected by copyright in
the U.S. unless a copyright notice is included. Thus, we do not
necessarily keep eBooks in compliance with any particular paper
edition.
Most people start at our website which has the main PG search facility:
www.gutenberg.org.
This website includes information about Project Gutenberg, including
how to make donations to the Project Gutenberg Literary Archive
Foundation, how to help produce our new eBooks, and how to
subscribe to our email newsletter to hear about new eBooks.
Page 723
back
Page 724
Page 725
back
Page 726
back
Page 727
back
Page 728
back
Page 729
Page 730
back
Page 731
back
Page 732
back
Page 733
Page 734
back
Page 735
back
Page 736
back
Page 737
back
Page 738
back
Page 739
back
Page 740
back
Page 741
Page 742
back
Page 743
back
Page 744
Page 745
back
Page 746
back
Page 747
Page 748
back
Page 749
back
Page 750
Page 751
back
Page 752
Page 753
back
Page 754
Page 755
back
Page 756
back
Page 757
Page 758
back
Page 759
Page 760
back
Page 761
back
Page 762
Page 763
back
Page 764
Page 765
back
Page 766
Page 767
back
Page 768
Page 769
back
Page 770
back
Page 771
Page 772
back
Page 773
back
Page 774
Page 775
back
Page 776
Page 777
back
Page 778
Page 779
back
Page 780
Page 781
back
Page 782
back
Page 783
back
Page 784
back
Page 785
back
Page 786
back
Page 787
Page 788
back
Page 789
Page 790
back
Page 791
Page 792
back
Page 793
Page 794
back
Page 795
Page 796
back
Page 797
Page 798
back
Page 799
Page 800
back
Page 801
back
Page 802
Page 803
back
Page 804
back
Page 805
Page 806
back
Page 807
back
Page 808
back
Page 809
Page 810
back
Page 811
back
Page 812
back
Page 813
back
Page 814
back
Page 815
back
Page 816
Page 817
back
Page 818
Page 819
back
Page 820
Page 821
back
Page 822
Page 823
back
Page 824
back
Page 825
Page 826
back
Page 827
Page 828
back
Page 829
Page 830
back
Page 831
back
Page 832
back
Page 833
Page 834
back
Page 835
back
Page 836
back
Page 837
back
Page 838
back
Page 839
Page 840
back
Page 841
Page 842
back
Page 843
Page 844
back
Page 845
back
Page 846
back
Page 847
back
Page 848
back
Page 849
back
Page 850
back
Page 851
Page 852
back
Page 853
back
Page 854
back
Page 855
Page 856
back
Page 857
back
Page 858
back
Page 859
Page 860
back
Page 861
back
Page 862
Page 863
back
Page 864
Page 865
back
Page 866
back
Page 867
back
Page 868
Page 869
back
Page 870
Page 871
back
Page 872
Page 873
back
Page 874
Page 875
back
Page 876
Page 877
back
Page 878
Page 879
back
Page 880
Page 881
back
Page 882
back
Page 883
back
Page 884
back
Page 885
back
Page 886
back
Page 887
back
Page 888
back
Page 889
back
Page 890
back
Page 891
Page 892
back
Page 893
back
Page 894
Page 895
back
Page 896
back
Page 897
back
Page 898
back
Page 899
Page 900
back
Page 901
Page 902
back
Page 903
back
Page 904
back
Page 905
back
Page 906
Page 907
back
Page 908
back
Page 909
back
Page 910
back
Page 911
Page 912
back
Page 913
back
Page 914
back
Page 915
back
Page 916
Page 917
back
Page 918
back
Page 919
back
Page 920
Page 921
back
Page 922
back
Page 923
back
Page 924
Page 925
back
Page 926
Page 927
back
Page 928
back
Page 929
Page 930
back
Page 931
back
Page 932
Page 933
back
Page 934
back
Page 935
back
Page 936
Page 937
back
Page 938
back
Page 939
Page 940
back
Page 941
Page 942
back
Page 943
Page 944
back
Page 945
Page 946
back
Page 947
Page 948
back
Page 949
Page 950
back
Page 951
back
Page 952
Page 953
back
Page 954
Page 955
back
Page 956
back
Page 957
Page 958
back
Page 959
back
Page 960
back
Page 961
Page 962
back
Page 963
back
Page 964
Page 965
back
Page 966
back
Page 967
back
Page 968
back
Page 969
Page 970
back
Page 971
Page 972
back
Page 973
back
Page 974
Page 975
back
Page 976
Page 977
back
Page 978
Page 979
back
Page 980
back
Page 981
Page 982
back
Page 983
back
Page 984
Page 985
back
Page 986
Page 987
back
Page 988
back
Page 989
back
Page 990
Page 991
back
Page 992
Page 993
back
Page 994
back
Page 995
back
Page 996
back
Page 997
back
Page 998
Page 999
back
Page 1000
Page 1001
back
Page 1002
Page 1003
back
Page 1004
Page 1005
back
Page 1006
Page 1007
back
Page 1008
back
Page 1009
back
Page 1010
Page 1011
back
Page 1012
Page 1013
back
Page 1014
back
Page 1015
Page 1016
back
Page 1017
Page 1018
back
Page 1019
Page 1020
back
Page 1021
back
Page 1022
Page 1023
back
Page 1024
Page 1025
back
Page 1026
Page 1027
back
Page 1028
back
Page 1029
back
Page 1030
Page 1031
back
Page 1032
Page 1033
back
Page 1034
Page 1035
back
Page 1036
Page 1037
back
Page 1038
Page 1039
back
Page 1040
Page 1041
back
Page 1042
Page 1043
back
Page 1044
Page 1045
back
Page 1046
back
Page 1047
Page 1048
back
Page 1049
Page 1050
back
Page 1051
Page 1052
back
Page 1053
Page 1054
back
Page 1055
Page 1056
back
Page 1057
Page 1058
back
Page 1059
Page 1060
back
Page 1061
back
Page 1062
Page 1063
back
Page 1064
back
Page 1065
back
Page 1066
Page 1067
back
Page 1068
back
Page 1069
Page 1070
back
Page 1071
Page 1072
back
Page 1073
back
Page 1074
Page 1075
back
Page 1076
back
Page 1077
back
Page 1078
back
Page 1079
Page 1080
back
Page 1081
back
Page 1082
back
Page 1083
Page 1084
back
Page 1085
back
Page 1086
Page 1087
back
Page 1088
back
Page 1089
Page 1090
back
Page 1091
Page 1092
back
Page 1093
Page 1094
back
Page 1095
back
Page 1096
Page 1097
back
Page 1098
Page 1099
back
Page 1100
Page 1101
back
Page 1102
back
Page 1103
Page 1104
back
Page 1105
back
Page 1106
back
Page 1107
back
Page 1108
back
Page 1109
back