BIOLOGY

A STUDENT'S TEXT-BOOK OF ZOOLOGY.

COREIGENDA.

In the description of Fig. 71 omit "(triods)."'
177. Lines 12 to 16. Professor Hickson has pointed out to me that in some genera the

siphonozooids have generative organs.
17S. 22nd line from the top. For "Stereosoma Hickson, with" read "Stercosoma

Hickson, without."

188. For "Section 2. Paractinia" read "Section 2. Paractiniae."
287. Line 2. For "sarcolemina" read "sarcolemma."

300. Line 8 from bottom. )

[For "Bdclloidea" read "Bdelloida."
306. Line 4 from top. )

323. Line 2 from bottom. For " Pectinobranchiata " read "Pectinibranchiata."

375. Line 4 from bottom. For " Aspidobranchia " read " Aspidobranchiata."

411. For "Section 1. Tritonioidea " read "Tribe 1. Tritonioidea."

413. In description of Fig. 329 for "Eolis" read "Aeolis."

A STUDENT'S TEXT-BOOK

ZOOLOGY.

BY

ADAM SEDGWICK, M.A.. F.R.S.,

FELLOW AND TUTOR OF TRINITY COLLEGE, CAMBRIDGE ;
AND READER OF ANIMAL MORPHOLOGY IN THE UNIVERSITY.

VOL. I.

LONDON:
SWAN SONNENSCHEIN AND CO., LTD.,

NEW YORK: THE MACMILLAN CO.

1898.

BIOLOOI IIBR;

REPUGNS &<*><6& .X .

v. I

S37

V.I

BIOLOGY

PREFACE.

IN preparing the present work I have been actuated
mainly by the desire to place before English students
of Zoology a treatise in which the subject was dealt with
on the lines followed with so much advantage by Glaus
and his predecessors in their works on Zoology. My original
intention was to bring out a new edition of Glaus' Lehrbuch,
revised and brought up to date, and a trace of this intention
may be seen in a few pages of the present volume. But
this plan was, for various reasons, soon given up, and the
present treatise is, with the exception of about twenty pages,
an< entirely new work.

For a successful study of Zoology it is necessary that the
student should begin by making a thorough examination of
individual animals, of their structure, of the functions of
their parts, of their relation to the external world and to
each other. This method of study by types, which was largely
introduced into this country by Huxley, and is admirably
exemplified by that author's book on the Crayfish, is absolutely
necessary as a preliminary to any thorough study of Zoology.
By pursuing it the student acquires, if the animals are
properly selected, a knowledge of the principal forms of
animal life, and a basis from which more extended studies
can be made. It is to assist these more extended studies
that the present work is designed. At the same time it is
hoped that the book will be of value to all interested in
Natural History, whether professedly students of Zoology or
not, if in no other way than as. a handy book of reference in
which, by means of the index, information may be gained of

A 2

MG55S35

VI PREFACE.

the general nature and habits of a large number of animals,
and of the more important and striking of the phenomena of
animal life. To assist in giving the book utility in this
direction, I have endeavoured, in the index, to refer the
reader to the page on which technical terms are used for
the first time and explained. At one time I thought of
adding to each chapter a detailed account of some easily
accessible species belonging to^ the group with which it dealt,
but on reflection it appeared to me that such accounts were
not required; for we possess them in an excellent form in
many useful and well-known books, which are accessible to
everyone. Moreover, to have done so would have either
unduly increased the size of the book or rendered necessary
the omission of much interesting matter concerning the infinite
variation of animal structure and habits not found in works
easily accessible to students.

Small print has been used for those parts of the work
which deal with disputed matters, or with subjects of a more
recondite character. It has also been employed for the
accounts of the families and genera which will be used
mainly for reference. By this means I have been able to
give far more information than would otherwise have been
possible. To further the same object I have used, in the
small print dealing with families and genera, not only
abbreviations, but also what has been called by a friendly
critic the style of the note-book. I very carefully considered
my critic's objection to this "note-book style," but I decided
that so long as I did not become unintelligible, the employ-
ment of it was justified by the object in view. Moreover,
I have been careful to limit its use to those parts of the
work which were apart from the main narrative, and would
be almost entirely used for purposes of reference. Most of the
abbreviations are explained in the index, and it is hoped that
no inconvenience will arise on account of their use. Authors'
names for genera are given throughout. It has been pointed
out to me, too late however for alteration, that the customary
abbreviations for those names are not always used, and that
my abbreviations have varied even on the same page. I am

PREFACE. Vll

afraid that this charge is true. I can only hope that my
carelessness in this respect will not cause my readers serious
annoyance.

To make the book more complete as a work of reference,
I have endeavoured to mention and give an account of as
many families as possible. For the same reason I have
named a large number of genera without giving any account
of them. It may appear to some absurd to name without
describing so many genera. My object in doing it has
been to make the book more useful in enabling students to
track as many unknown names as possible to their place
in the system.

I must ask the indulgence of my readers towards the
many imperfections of this work. It is impossible to have
a specialist's knowledge of every group, and in a book of
this size, dealing with an enormous number of facts and
names, it is beyond human capacity to avoid mistakes. Every
care has been taken, and it is hoped that they will be found
to be neither numerous nor important. The errors would
undoubtedly have been much more numerous had it not
been for the kind assistance given me by my friends. To
Mr. J. J. Lister I am especially indebted. He has looked
through all the proof sheets, and has brought to bear a
critical power and discrimination which have been invalu-
able. I cannot be sufficiently grateful for his assistance.
Mr. Lister has also contributed the account of Coral Eeefs,
and of the reproduction of the Foraminifera. My thanks
are also owing to Mr. Heape and Mr. Graham Kerr. who
looked through the greater part of the proofs, and to Mr.
Shipley, Dr. Benham, Professor Haddon, and Dr. Harmer,
who looked over the proofs of portions of the book, and
gave me the benefit of their special knowledge. I have
thus often been saved from errors into which I should other-
wise have fallen. My principal sources of information are
acknowledged in the foot-notes ; but I must not omit to make
mention here of works from which I have obtained special
help ; these are Biitschli's Protozoa in Bronn's Thierreich,
Chun's introductory account of the Coelenterata also in Bronn,

Vlll PREFACE.

Wasiliewski's Sporozoa, Pelseneer's Mollusca, and Benham's
Polychaeta in the Cambridge Natural History.

Of the illustrations about fifty are new, of the remainder
the majority are from Glaus' Lehrluch ; but some, which I
have been permitted to make use of by the courtesy of the
author and publishers, are from Bronn's Thierreich, Perrier's
Zoologie, Korschelt and Heider's Embryology, and Lang's Text-
book of Comparative Anatomy ^

In the classification the principal departures from precedent
concern the group of Amphineura, which has been given up,
and the Gephyrea, which has been broken up into four inde-
pendent phyla. The reasons for these innovations are given
in the body of the work.

The work will be issued in two volumes. The present
volume deals with the whole of the animal kingdom except
the Arthropoda, the Echinodermata, and the Chordata. The
treatment of these will be included in the second volume, in
the production of which I have been fortunate enough to
gain the co-operation of Mr. Lister. The second volume is
in preparation, and will, we hope, appear without any great
delay. It will, if possible, contain a part dealing generally
with the facts and principles of Zoology, but it may be
necessary, from considerations of size, to reserve this for a
third volume.

TABLE OF CONTENTS.

CHAPTER I.

PAGE

PHYLUM PROTOZOA ... 1

Class I. GYMNOMYXA

(SARCODINA) 3

Sub-class 1. RHIZOPODA . 6

Order 1. Amoeboidea . .11

,, 2. Testacea . .11

Sub-class 2. MYCETOZOA . 15

., 3. HELIOZOA . .18

,, 4. RADIOLARIA . 20

Class II. INFUSORIA . . 24

Sub-class 1. MASTIGOPHOKA . 27

Order 1. Flagellata . . 27

Sub-order 1. Monadina . 30

,, 2. Euglenoidea . 30

,, 3. Heteromastigoda, 31

,, 4. Isomastigoda . 31

,, 5. Phytomastigodn 32

Order 2. Choanoflagellata . 32

„ 3. Dinoflagellata . 33

,, 4. Silicoflagellata . 35

,, 5. Cystoflagellata . 35

Sub-class 2. CILIATA . . 37

Order 1. Gymnostomata . 45

,, 2. Trichostomata . 46

Sub-order 1. Aspirotricha . 46

,, 2. Spirotricha . 48

a. Heterotricha . 48

b. Oligotricha . 49

c. Hypotricha . 49
cl. Peritricha . 50

Sub-class 3. ACINETARIA . 51

Class III. SPOROZOA . . 54

Order 1. Gregarinida . . 56

CHAPTER I. PROTOZOA— contd.

PAGE

Sub- order 1. Monocystidea . 59

,, 2. Polycystidea . 59

Order 2. Coccidiidea . . 59

„ 3. Haemosporidia . 61

Sub-order 1. Drepanidiidia 61

,, 2. Acystosporidia 62

Order 4. Myxosporidia. . 64

., 5. Sarcosporidia . . 68

CHAPTER II.
THE METAZOA .

CHAPTER III.

70

PHYLUM PORIFERA . . . 72

Class I. CALCAREA . . 89

Order 1. Calcarea . . 89

Sub-order 1. Homocoela . 89

,, 2. Heterocoela . 90

Class II. TRIAXONIA . . 90

Order 1. Hexactinellida . 90

Sub-order 1. Lyssacina . 92

,, 2. Dictyonina . 93

Order 2. Hexaceratina . . 93

Class III. DEMOSPONGIAE . 93

Order 1. Tetractinellida . 93

Sub-order 1. Choristida . 93

2. LUMstida . 94

Order 2. Carnosa . . .95

,, 3. Monaxonida . . 95

Sub-order 1. Halichondrina 95

,, '2. Spintharophora 97

Order 4. Ceratina 97

TABLE OF CONTENTS.

CHAPTER IV.

PAGE

PHYLUM COELENTERATA . 99

SUB-PHYLUM I. CNIDARIA . 123

Class I. HYDROMEDUSAE

(CRASPEDOTA) 123

Order 1. Hydrida . .127

,, 2. Hydrocorallinae . 127

„ 3. Tubulariae . .129

Anthomedusae . 130

„ 4. Campanulariae . 132*

Leptomedusae . 133

,, 5. Trachomedusae . 135

„ 6. Narcomedusae . 136

,, 7. Siphonophora. . 137

Sub-order 1. Disconanthae . 141

Section 1. Disconectae

(Velellidae) 141

Sub-order 2. Siphonanthae . 144
Section 1. Calyconectae

(Calycophoridae) 144
,, 2. Physonectae

(Physophoridae) 150

,, 3. Auronectae . 153

,, 4. Cystonectae

(Physalidae) 154

Class II. ACALEPHAE

(ACRASPEDA) 156

Order 1. Scyphomedusae . 162

Sub-order 1. Stauromedusae 163

,, 2. Peromedusae . 165

„ 3. Cubomedusae . 166

Order 2. Ephyroninae . . 166

Sub-order 1. Cannostomae . 167

,, 2. Semostomae . 167

,, 3. Rhizostomae . 167

Class III. ACTINOZOA

(ANTHOZOA) 168
Order 1. Rugosa . . .175
,, 2. Alcyonaria

(Octactinia) 175

Sub-order 1. Protoalcyonaria 17 '8

,, 2. Stolonifera . 178

,, 3. Alcyonacea . 178

,, 4. Pennatulacca . 179

Section 1. Pennatulea . 180

,, 2. Spicata . . 181

,, 3. Renillea . . 181

,, 4. Veretiliea . . 181

Sub -order 5. Gorgonacea . 181

Section 1. Scleraxonia . 182

,, 2. Holaxonia . , 182

CHAPTER IV. COELENTERATA— contd.

PAGE

Order 3. Zoantharia

(Hexactinia) 183

Sub-order 1. Actiniarin . 183

Section 1. Hexactiniae . 186

,, 2. Paractiniae . 188

,, 3. Protactiniae . 189

,, 4. Echvardsiae . 189

,, 5. Zoantheae . . 189

,, 6. Ceriantheae . 190

Sub-order 2. Antipatharia . 190

,, 3. Madreporaria . 191

Section 1. Aporosa . . 194

„ 2. Fungida . . 196

., 3. Perforata . .196

SUB-PHYLUM II. CTENOPHORA 197

Order 1. Tentaculata . . 207

Section 1. Cydippidae . 207

„ 2. Lobatae . . 207

„ 3. Cestidae . . 208

Order 2. Nontentaculata . 208

CHAPTER V.

PHYLUM PLATYHELMINTHES . 209

Class I. TURBELLARIA . 210

Order 1. Acoela . .218

,, 2. Rhabdocoela . .219

,, 3. Alloiocela . . 220

,, 4. Triclada . . 221

,, 5. Polyclada . . 222

Acotylea . . 222

Cotylea . . 223

Class II. TREMATODA . . 223
Order 1. Heterocotylea

(Monogenea) 233

,, 2. Aspidocotylea . 236
„ 3. Malacotylea

(Digenea) 237

Dicyemidae and Orthonectidae 240

Class III. CESTODA . 243

CHAPTER VI.

PHYLUM NEMERTEA . . 263

Order 1. Protonemertini . 270

,, 2. Mesonemertini . 270

,, 3. Metanemertini . 271

„ 4. Heteronemertini . 272

TABLE OF CONTENTS.

XI

CHAPTER VII.

PACK

PHYLUM NEMATHELMINTHES 273
Class I. NEMATODA . . 274

Chaetosomatidae and

Desmoscolecidae 291

Class II. NEMATOMORPHA . 292
,, III. ACANTHOCEPHALA 293

CHAPTER VIII.

PHYLUM ROTIFERA . . 299

Order 1 . Ebizota . . 307

,, 2. Bdelloida . . 308

,, 3. Ploima . . 308

., 4. Scirtopoda . . 310

,, 5. Seisonacea . . 310

Gastrotricha . 310

Eclrinoderidae . 311

CHAPTER IX.
THE COELOMATA . . .313

CHAPTER X.

PHYLUM MOLLUSC A . . .316

Class I. LAMELLI-

BRANCHIATA 324

Order 1. Protobranchiata . 345

,, 2. Filibrancblata . 345

Sub-order 1. Anomiacea, . 345

„ 2. Arcacea . . 345

3. Mytilacea . 349

Order 3. Pseudolamelli-

branchiata 346

„ 4. Eulamellibrancbiata 347

Sub-order 1. Submytilacea . 347

,, 2. Telliiiacea . 347

,, 3. Veneracea . '-'AS

,, 4. Cardiacea . 348

„ 5. Myacca . 348

,, 6. PJioladttcea . 348

,, 7. Anatinacea . 349

Order 5. Septibranchiata . 349

Class II. SCAPHOPODA . 349
, III. SOLENOGASTRES . 352

CHAPTER X. MOLLUSCA— contd.

PAGE

Class IV. GASTROPODA . 356

Sub-class 1. ISOPLEURA . . 387

,, 2. ANISOPLEUJI^ . 392

Order 1. Streptoneura . . 392

Sub-order 1. Aspido-

branckiata 393

Tribe 1. Docoglossa . . 394

,, 2. Rhipidoglossa . . 394

A. Zygobranchiata . 394

B. Azygobranchiata . 395
Sub-order 2. Pectini-

branchiata 395

Tribe 1. Ptenoglossa . . 396

„ 2. Bachiglossa . . 396

,, 3. Toxoglossa . . 397

„ 4. Taenioglossa . . 397

A. Platypoda . . 397

B. Heteropoda . 400
,, 5. Gymnoglossa . . 402

Order 2. Euthyneura . . 402

Sub-order 1. Opistho-

• branchiata 403

Tribe 1. Tectibranchiata

(includes Pteropoda) 403

Section 1. Bulloidea . . 405

,, 2. Aplysioidea . 407

,, 3. Pleurobranchioidea 408

Tribe 2. Nudibranchiata . 409

Tribe 1. Tri tonic-idea . 411

,, 2. Doridioidea . 412

,, 3. Aeolidioidea . 412

„ 4. Elysioidea . . 413

Sub-order 2. Pulmonata . 414

Tribe 1. Basommatophora . 415

,, 2. Stylommatophora . 416

Class V. CEPHALOPODA . 417

Order 1. Tetrabranchiata . 443

,, 2. Dibrancbiata . . 444

Sub-order 1. Decapod 'n, . 444

,, 2. Octopoda . 445

CHAPTER XI.

PHYLUM ANNELIDA. . . 447

Class I. ARCHIAXNELIDA . 451

„ II. CHAETOPODA. . 458

Order 1. Polychaeta . . 458

Phanerocephala . 475

Sub-order 1. Nereidiformia . 475

,, 2. Spioiiiformia . 483

TABLE OF CONTENTS.

CHAPTER XI. ANNELIDA— contd.

PAOE

Sub-order 3. Terebelliformia 484

,, 4. Capitelliformia 486

,, 5. Scoleciformia . 487

Cryptocephala . 490

Sub-order 1. Sdbelliformia . 490
,, 2. Hermelliformia, 491

Myzostoniida

Order 2. Oligochaeta .

Sub -order 1. Limicolae

2. Terricolae

492
49?
508
509

512

Class III. HIRUDINEA

„ IV. ECHIUROIDEA

(GEPHYREA ARMATA) 527

CHAPTER XII.

PHYLUM SIPUNCULOIDEA

(GEPHYREA ACHAETA) 534

CHAPTER XIII.

PAGE

PHYLUM PRIAPULOIDEA . . 540

CHAPTER XIV.

PHYLUM PHORONIDEA . . 542

CHAPTER XV.

PHYLUM POLYZOA . . .549

Class I. ECTOPROCTA . . 564

,, II. ENTOPROCTA. . 568

CHAPTER XVI.

PHYLUM BRACHIOPODA . . 573

Order 1. Ecardines . . 585

,, 2. Testicardines . . 585

CHAPTER XVII.

PHYLUM CHAETOGNATHA . 586

CHAPTER I.

PROTOZOA.*

Animals in ichich there is one nucleus, or, if more than one nucleus,
in which the nuclei are disposed apparently irregularly and without
relation to the functional tissues of the animal. Conjugating cells
of the form of ova and spermatozoa are never formed.

Structurally the Protozoa are so simple that the reproduction of
the species is effected either by division of the body into two or
more parts, or by a separation off of a small portion, which so nearly
resembles the parent in structure that the phenomenon of embryonic
development is almost, if not completely, absent from the life-history.

The body is always composed of a contractile granular substance,
filled with vacuoles; it may also contain a pulsating vacuole, and
present the phenomenon of granule currents. The pulsating vacuole
consists of a space without differentiated walls filled with a clear
fluid. This space apparently diminishes and disappears through the
contraction of the surrounding plasma, and then reappears.

There are, however, differentiations, both in the interior of the
body and in its external boundary, on which a classification may be
founded. In the simplest cases, the entire body consists of a small
lump of protoplasm (or sarcode, as it was at first called), the
contractility of which is confined by no firm external membrane.
This lump of protoplasm is sometimes semi-fluid, and protrudes and
retracts processes. It is sometimes of tougher consistence in parts,
and protrudes thread-like rays (Rhizopoda). Nutrition takes place
through the intussusception of extraneous bodies, which can be
surrounded and enclosed by the protoplasmic substance at any
portion whatsoever of the periphery of the body. In other cases the
body which sends out slender processes (pseudopodia) secretes silicious
or calcareous needles, lattice-work shells, or shells perforated by
holes, to shelter and protect the body (Foraminifera, Radiolaria).

* 0. Biitschli, "Protozoa" in Bronn's Thierreich, 1880-2.
B

PROTOZOA.

In the Infusoria the body is bounded by an external membrane,
and is capable of quick and varied locomotion by means of the
movements of the cilia, hairs, bristles, etc., which it possesses. The
nourishing matter may be solid, in which case it is taken in through
a mouth, and the remainder after digestion cast out through an anal
aperture (holozoic nutrition), or it may be in a fluid form as a
putrescent solution, in which case the name Infusoria is well applied,
and be taken in by simple osmosis through the walls of the body
(sapi'ophytic nutrition).

The conjugation, or fusion, of two or more individuals has been
observed at some period or another of the life-history in most
of the groups of Protozoa ; and in most groups the power of with-
drawing the pseudopodia or cilia and of forming stout membranes
round the body (encystment) to protect the organism against adverse
external influences is generally present.

The Protozoa fall into three main classes. Of these the first
(Gymnomyxa] possess the power of thrusting out processes of their
body as pseudopodia ; the second (Infusoria) are, for the most part,
without pseudopodia, but bear cilia, or flagella; while the third
(Sporozoa) possess neither pseudopodia nor cilia, and are parasitic in
habit.

Table showing the classification of the Protozoa.

CLASS I. GYMNOMYXA

(SARCODINA).
Sub-class 1. RHIZOPODA.
Order 1. Amoeboidea.

,, 2. Testacea.
Sub-class 2. MYCETOZOA.
,, 3. HELIOZOA.
,, 4. RADIOLAUIA.

CLASS II. INFUSORIA.
Sub-class 1. MASTIGOPHOIIA.
Order 1. Flagellata.
Sub-order 1. Monadina.
,, 2. Euglenoidea.
,, 3. Hetcromastigoda.
,, 4. Isomastigoda.
,, 5. Phytomastigoda.
Order 2. Choanoflagellata.
,, 3. Dinoflagellata.
,, 4. Silicoflagellata.
,, 5. Cystoflagellata.

CLASS II. INFUSORIA— Continued.
Sub-class 2. CILIATA.

Order 1. Gynmostomata.
,, 2. Trichostomata.
Sub-order 1. Aspirotricha.
,, 2. Spirotricha.

a. Heterotricha.
I. Oligotricha.

c. Hypotricha.

d. Peritricha.
Sub-class 3. ACINETARIA.

CLASS III. SPOROZOA.
Order 1. Gregarinida.

Sub-order 1. Polycystidea.
, , 2. Monocystidea.
Order 2. Coccidiidea.
,, 3. Haemosporidia.
Sub-order 1. Drepanidiidca.
, , 2. Acystosporidea.
Order 4. Myxosporidia.
,, 5. Sarcosporidia.

GYMNOMYXA. 3

Class 1. GYMNOMYXA (SARCODINA).*

Protozoa possessing the poiver of thrusting out pseudopodia. An
investing membrane is absent, or, if present, is incomplete, and'tyaves
a considerable portion of the protoplasm exposed. A calcareous shell,
or silicious skeleton, is very usually secreted.

The body-substance, which is richly granulated, and may contain
pigment, contracts slowly, and sends out at the same time the
processes called pseudopodia; and these serve not only as a
means of movement, but also for the reception of nourishment.
The pseudopodia may be broad, lobed, or finger-like processes
(Fig. 2), by means of which a quick and flowing motion can
be imparted to the body mass; or they may be filiform radiating
processes (Fig. 1) ; or, lastly, they may anastomose with one
another, and
form networks.
A tougher, clear
homogeneous
external layer
(exoplasm) is
usually to be
distinguished as
the peripheral
boundary from
a more fluid and
more granular
internal mass
(endoplasm).
During motion
the former is

, FIG. 1.— Optical section through portion of the body of Actinosphaerium

projected in Eichhornii (after Hertwig and Lesser). N nuclei in the endoplasm,
processes into from which the vacuolated ectoplasm is clearly distinguishable.
In the centre of the pseudopodia the axial thread is visible.

which the gran-
ules of the latter stream more or less quickly. In the stiffer pseudo-
podia streams of granules are observable, slow but regular, passing
from the base to the extremity and vice versa. The explanation of

* Dujardin, " Observations sur les Rhizopodes." Comptes rendus, 1835.
Ehrenberg, "Uber noch jetzt zahlreich lebeude Thierarten der Kreidebildung
und den Organismus der Polythalamien." Abhandlung der Akad. zu Berlin,
1839. Max Sigm. Schultze, "Uber den Organismus der Polythalamien."
Leipzig, 1854. Joh. Mitller, " Uber die Thalassicolen, Polycystinen und Acan-
thometren." 1858. E. Haeckel, "Die Radiolarien. " Eine Monographic.
Berlin, 1862.

PROTOZOA.

these movements is to be sought in the contractility of the surround-
ing portions of protoplasm (Fig. 1).

A pulsating space, the contractile vacuole, is not unfrequently to
be found in the protoplasm, e.g., Difflugia, Actinpphrys, Arcella
(Fig. 2). Nuclei are usually to be made out, but there are forms
in which no trace of a nucleus has yet been found. In such cases
either our methods of observation are faulty, or the protoplasm
of the nucleus is not yet differentiated as a separate structure

(the Monera of E. Haeckel), or we
have to do with a transient, non-
nucleated stage in the life-history.

The protoplasm usually secretes
silicious or calcareous structures,
either as fine spicula and hollow
spines, which are directed from the
centre to the periphery in regular
T~P<v order and number, or as lattice-
work chambers (Radwlaria), which
often bear points and spines, or
finally as single and many-chambered
shells with, in some cases, finely
perforated walls (Foraminifera) and

one larger opening- Through this

pulsating vacuoie. last (Fig. 4), as well as through the

countless pores of the small shells

(Fig. 3), the slender threads of sarcode pass out to the exterior
as pseudopodia, changing without intermission in form, size, and
number, and often joining themselves together in delicate networks.
(Figs. 3, 4.)

The pseudopodia, by their slow contraction, afford a means of
locomotion, while they also serve for the taking up of nourishment
by surrounding and transporting into the interior of the body small
vegetable organisms as Bacillaria. Among the shell-bearing forms,
the reception and digestion of food takes place outside the shell in
the peripheral threads and networks of sarcode ; for each spot on the
surface can for the time being assume the functions of mouth, and
also of anus, by rejecting the undigested remnants. While the
power of emitting pseudopodia is characteristic of the form in which
the Gymnomyxa are usually met with, it is usual to find a stage in
their life-history in which locomotion is effected by means of flagella.
To such flagellated forms the term mastiyopod has been applied,

GYMNOMYXA. 5

as opposed to myxopod, a word indicating a form with the power of
emitting pseudopodia.

Reproduction is commonly effected by simple division, but in
some cases encystment occurs, and the protoplasm breaks up-lnto
a number of minute portions called spores. The spores may be
either naked or provided with a wall, forming the spore-case.

FIG. 3.— Eotalia veneta (after M. Schultze), with a Diatom taken in the network of
pseudopodia.

The marine shell-bearing forms contribute by the accumulation
of their shells to the formation of the sea sand, and even to the
deposition of thick strata. An innumerable quantity of fossil forms
from various and very ancient formations are known.

6 PROTOZOA.

SUB-CLASS I. KHIZOPODA.*

Gymnomyxa, either naked or with a shell, the shell generally
calcareous and often pierced with fine pores for the exit of the
pseudopodia.

Only in rare cases is the shell substance of a silicious nature ;
in all other forms it is membranous, with or without adhering sand
particles, or consists of a calcareous deposit in a basis of organic

FIG. 4.— Miliola tenera, with network o* pseudopodia (after M. Schultze).

matter. The shell is either a simple chamber, usually provided with
a large opening, or is many- chambered, that is, is composed of
numerous chambers arranged upon one another in a definite order

On

Intro-
Entwurf

1895.

RHIZOPODA. 7

according to definite laws. The spaces of these chambers com-
municate by means of narrow passages and large openings in the
partition walls. In like manner those portions of the protoplasm
which are enclosed in the individual chambers are in direct commu-
nication with one another by means of processes which pass
through the passages and openings in the septa, and connect one
portion with another. In the perforated forms there may be an
additional complication owing to the formation of a secondary
shell by the protoplasm. This secondary shell is placed outside
the primary, and is traversed by canals containing the protoplasm.
The multinucleate condition is very generally found, and probably
constitutes a phase in the life-history. For instance, in Gromia
and Difflugia specimens have been found with a large number of
nuclei, though the usual condition appears to be with one nucleus.
The quality of the body-substance, the mode of movement and
nourishment, agree closely with those which have been depicted as
characteristic of the class. Our knowledge of the mode of repro-
duction is imperfect. Amongst the forms without a shell, fission
has been observed. In Haliphysema one of the nuclei with a small
portion of protoplasm is said to become marked off from the rest
and to form a small body not unlike an ovum imbedded in the
protoplasm. This may be called internal budding.

In several of the families of our order (MilioUdce, Lagenidce,
Rotalidce, and Nummulinidce) we meet with the phenomenon of
dimorphism, that is to say, the species is made of two distinct kinds
of individuals, which appear to alternate with one another in the
life-history. (Fig. 5.) The one of these forms — the microspheric — is
distinguished by the small size of the initial chamber and by the
possession of a large number of small nuclei ; while the other — the
megalospheric — has a large initial chamber and one large nucleus.
In the microspheric form, reproduction is effected by the simple
emergence of the protoplasm from the shell and its division into a
number of spherical bodies; each of these secretes a shell which
constitutes the first chamber of a megalospheric form. In the
megalospheric form, on the other hand, the protoplasm in the
shell breaks up into a number of small masses, each of which
issues as a flagellated zoospore. The further history of these is not
known, but they probably give rise to the microspheric form.

In Polystomclla crispa L., one of the Nummulinidce, whose life-history is better
known than that of other Foranrinifera, the initial chamber, or microsphere,
occupying the centre of the shells of the microspheric form, has a diameter

8

PROTOZOA.

of about 10 p. It is succeeded by a series of chambers of gradually increasing
size, which are added one after another in a spiral manner. Numbers of small
nuclei which increase in number by simple division, are scattered apparently
irregularly through the protoplasm. The existence of the microspheric form,
as an individual, is terminated in the following manner. The animal becomes
firmly attached to some object by its pseudopodia, and the protoplasm emerges
from the shell. After involved streaming movements which continue for some
hours, the protoplasm divides simultaneously into a number of spherical masses,
having generally a diameter of about 70 At., which, after secreting a shell,
rapidly draw apart from one another, and each sets up an independent existence.
These form the initial chambers of tne megalospheric form of the species. The

FIG. 5.—Biloculina depressa d'Orb. Sections of the shell: A, of the megalospheric form
(megalosphere 200-400 /*.) longitudinal. U, of the microspheric form (microsphere 20 /*.)
transverse. The two terminal chambers are omitted in B (from Lister, after Schlumberger).

whole of the protoplasm of the parent is thus divided up to form the brood of
young, its empty shell falling to the bottom. The second chamber of the
megalospheric form of Polystomclla has a peculiar shape, and the other
chambers added in succession build up the spiral shell. In this form a
single large nucleus is present, whose size increases with the growth of the
protoplasm. Prior to the reproduction of the megalospheric form the large
nucleus disappears, and in place of it, though the way in which they are
produced has not been followed, great numbers of minute nuclei are found
scattered through the protoplasm. After a preliminary division of these nuclei
by karyokinesis, the protoplasm breaks up into flagellated zoospores having a

RHIZOPODA. 9

diameter of 5 /x.. The intervening stages between the zoospore, produced by the
megalospheric form, and the microsphere in which the microspheric form takes its
origin, have not been followed ; but there is some, though at present incon-
clusive evidence, in favour of the supposition that the microsphere results
from the conjugation of two zoospores. The relative sizes of the mici^sphere
and zoospore — 10 /*. and 5 p., agrees fairly well with this view. One of the
earliest observations relating to the dimorphism of the Foraminifera was of
the well-established fact that the microspheric form is much less abundant
than the megalospheric, and this admits of easy explanation on the supposition
that the union of two separate organisms is required for its production. Finally,
Schaudinn's observation of the conjugation of the zoospores of Hyalopus,
which is, however, a form not known to be dimorphic, supports the hypothesis.

From the foregoing account of the life-history of Polystomella it appears that
the dimorphism of the Foraminifera is due to the occurrence of alternating or
recurring generations, and there is some, though at present inconclusive
evidence in support of the view that the megalospheric generation arises
asexually, and the microspheric generation as the result of conjugation. In the
genus Orbitolites (Miliolidoe), while the megalospheric form has been found to
be produced from a microspheric form as in Polystomella, it has also been
seen to arise from a megalospheric parent. In this case, then, it must be
supposed that the generations do not regularly alternate, but that the megalo-
spheric form may be repeated before the brood of zoospores is produced.

Besides the difference in the size of the initial chambers, the shells of the
two forms present in some cases marked differences in the mode of growth.
Thus in the genus ^Biloculina* (Miliolidce), while the mode of growth of the
megalospheric form is, as shown by Schlumberger, on the biloculine plan from the
first (Fig. 5), that of the microspheric form is at first on the qiiinqueloculine
plan, and it is not until many chambers have been formed that the biloculine
plan, characteristic of the genus, is assumed.

The application of the term dimorphism to the phenomenon above
described is in accordance with its general use in zoology and
botany. It has, however, been used, together with the terms
trimorphism and polymwpliism, in another and quite different sense,
namely to indicate the occurrence of two (three, or more) different
modes of growth in the building up of the shell of a single
individual. Thus, in the shell of the genus Pener&plis, the chambers

* The mode of growth of the shells of the genera Biloculina, Triloculina,
and Quinqueloculina is a modification of the spiral. The chambers are elongated
and increase in size as they succeed one another, each occupying half a turn of
the spiral. The result is that the mouths of the chambers are directed succes-
sively in opposite directions, and a long axis of the shell is thus established.

In the genus Biloculina, (Fig. 5) the chambers lie in the same plane, and
each overlaps its predecessors at the sides. Hence only two chambers are
exposed in the outer contour of the shell. In the other genera the chambers
are narrower and do not lie in the same plane, the median plane of each being
directed at a definite angle, which is constant for the genus, to that of its
predecessor. The result is that in one case three, and in the other five
chambers are exposed in the contour of the shell, and the triloculine and
quinqueloculine forms of shell are respectively produced. The genei-a Triloculina
and Quinqueloculina (d'O.) were by Williamson included in the genus Miliolina.

10 PROTOZOA.

are at first arranged spirally, but in the later stages of growth in a
rectilinear series. Such forms are called dimorphous.

Conjugation has been observed to take place in a few cases
(Arcella, Difflugia, EuglypJia, etc.), but details concerning it are
unknown. In the Polythalamous forms, it is possible, as hinted
above, that conjugation takes place between the free-swimming
zoospores.

The Foraminifera present four main varieties of shell : (1), the
chitinous, e.g., Gromia, imperforate ; (2), the porcellaneous, e.g.,
Miliola, imperforate, and characterised by their opaque white colour
and abundant organic basis; (3), the hyaline, e.g., Gloligerina,
perforate, and with but little organic basis ; and (4), the arenaceous,
perforate, as in Psammosphcera, but generally imperforate. The
last are formed of small foreign particles united by a cementing
substance. It is the fact that perforate and imperforate arenaceous

forms are found within the limits
of the same family, which has ren-
dered necessary the abandonment
of the old division of the order
into Perforata and Imperforata.
Specimens of Biloculina ringen*
living in the red clay at 3000
fathoms, a depth at which calca-
FIO. 6.— Nummuiitic Limestone, with reous organisms are generally absent,

horizontal section of N. distans (after „ , , .„ ,

Zitteii). were lound by Brady to have a shell

composed of silica.

Analysis of the calcareous shells shows that the mineral con-
stituents consist of carbonate of lime and carbonate of magnesia,
the latter varying from five to ten per cent. There is besides a
trace (generally under 0-5 per cent.) of silica.

In spite of their small size, the shells of our simple organisms
may lay claim to no small consequence, since they not only
accumulate in enormous quantity in the sea sand (M. Schultze
calculated their number for an ounce of sea sand from Molo di
Gaeta at about one and a half millions), but are also found as
fossils in different formations (the cretaceous and tertiary), and
have yielded an essential material to the construction of rocks.
Silicious nodules of Polythalamia are even found in Silurian deposits.
The most remarkable, on account of their considerable size, are the
Nummulites (Fig. 6) in the thick formation of the so-called Num-
mulite limestone (Pyrenees and elsewhere). A coarse chalk of the

RHIZOPODA. 1 1

Paris basin, which makes an excellent building stone, contains the
Triloculina trigonula (Miliolite chalk).

The greater number of Foraminifera are marine, and move by
creeping on the bottom of the sea, but some of them are pefagic and
Globigerina and Orbulina live at the surface. Some of the genera
are found in the brackish water of estuaries, and they may even
extend into fresh water. The bottom of the sea at very consider-
able depths is also covered with a rich abundance of forms,
especially with Globigerina, the remains of the shells of which give
rise to an enduring deposit.

Order I. Amoeboidea.

Naked Amoeba-like Rhizopoda, with lobose or reticulate pseudo-
podia, usually with nucleus and contractile vacuole.

Amceba, nucleated forms, with contractile vacuole and lobose pseudopodia.
Protamasba Haeckel, small forms, with lobose pseudopodia ; nucleus and con-
tractile vacuole not observed. Hyalodiscus Hertwig and Lesser, disc-shaped,
nucleated forms, without pseudopodia ; locomotion by a flowing movement
without change of form. Protomyxa Haeckel, Myxodictyum Haeckel, Protogenes
Haeckel, are forms with anastomosing pseudopodia, and without observed nucleus.
PelomyxaGreef, large amceba-like forms, containing many nuclei, refractile bodies,
and cylindrical crystals. Other genera are Gloidium Sorokin, Chcetoproteus Stein,
Plakopus F. E. Schulze, Dactijlosphcsra Hertw. and Lesser, Podostoma Clap, and
Lachm., Amphizonclla Greef, Gymnophrys Cienk. Baihybius Huxley, found in
the deep sea mud of the Atlantic, if it is indeed a living organism (and not
simply a deposit of gypsum). Coccoliths, Coccospheres, and Rhabdospheres are
found in the gelatinous mud of the bottom of the Atlantic, and were supposed
by Huxley* to be portions of the body of Bathybius. Similar bodies have been
found in the chalk. They are in reality small marine vegetable organisms, with
calcareous walls, and are oceanic in habit. They form with Diatoms and pelagic
Oscillatorice, a large part of the vegetable food of marine animals, f

Order II. Testacea (Foraminifera).

Principally marine Rhizopods, with a shell which is either
membranous, calcareous, or rarely silicious, and may be single-
chambered (Monothalamia) or many-chambered (Polythalamia),
usually with more than one nucleus.

In this order the pseudopodia are generally slender and
anastomosing, but in the fresh water Arcella and Difflugia (Fig. 8)
they are lobed. The protoplasm has the power of exuding through the
openings in the shell and of forming a layer which may be much
vacuolated on the outside of the shell (Fig. 10). In such cases the
shell may be regarded as an internal structure, and appropriately

* Q.J.M.S., vol. 8. f Vide Nature, 1897, p. 510.

12

PROTOZOA.

compared with the internal capsule of the Radiolaria. The shell
also often possesses long, delicate, spiny processes, which are broken
off unless the animal be very carefully handled (Fig. 10).

The Foraminifera are mainly bottom organisms, but a few genera
of the hyaline forms are pelagic. The pelagic genera are important
because of their extraordinary abundance. Whether these pelagic
forms have the power of supporting life on the surface of the bottom-
ooze is unknown.

The definition of species and genera in this order is rendered
difficult by the large number of intermediate varieties, which,
indeed, often constitute a complete series. Carpenter* on this
subject writes as follows: "The ordinary notion of species as
assemblages of individuals marked out from each other by definite

FIG. 7. — Euglyplia glolosa, (after
Hertwig and Lesser).

Fio. 8. — Dijflugia oblonga
(after Stein).

characters that have been genetically transmitted from original
prototypes similarly distinguished, is quite inapplicable to this
group ; since, even if the limits of such assemblages were extended so
as to include what would elsewhere be accounted genera, they would
still be found so intimately connected by gradational links, that
definite lines of demarcation could not be drawn between them."

Fam. 1. Arcellina. Shell watch-glass shape, membranous ; with more than
one nucleus ; with contractile vacuoles ; gas vacuoles with a hydrostatic
function may be secreted by the protoplasm. Fresh water. Cochliopodium
Hertw. and Lesser, Pyxidicula Ehrbg., Arcella Ehrbg., Hyalosphenia Stein,
Quadrula F. E. Schulze, Difflugia Leclerc, shell incrusted by foreign particles,
usually pyriform in shape (fig. 8).

* W. R. Carpenter, " Introduction to the Study of the Foraminifera," preface,

]). X.

RHIZOPODA. 1 3

Fam. 2. Euglyphina. Shell chitinous or silicious, composed of hexagonal or
roundish plates ; pseudopodia pointed, branched. Fresh water. Euglypha Duj.
(Fig. 7), Trinema Duj.

Fam. 3. Gromidae. Test chitinous, smooth or incrusted with foreign bodies,
imperforate, with a pseudopodial aperture at one or both extremitie^ pseudo-
podia long, branching, reticulated. Fresh water and marine. GromiaDuj.,
Lieberkiihnia C. and L., Mikrogromia R. Hertwig, Diaphoropodon Archer,
Shepherdella Siddal.

Fam. 4. Miliolidae. Test imperforate, mono- or polythalamic ; normally
calcareous and porcellaneous, sometimes incrusted with sand ; under starved
conditions (e.g. in brackish water) becoming chitinous or chitino-arenaceous ;
at abyssal depths occasionally consisting of a thin homogeneous, imperforate
silicious film. Marine. Squamulina Schultze, Nubecularia Defrance, Bilo-
culina d'Orb. , Fabularia Defrance, Spiroloculina d'Orb., Miliolina Williamson,
Hauerina d'Orb., Vertebraliiia d'Orb., Orbiculina Lamarck, OrUtolites Lamarck.
Fam. 5.- Astrorhizidae. Test invariably composite, usually of large size and
monothalamic ; often branched or radiate, sometimes segmented by constriction
of the walls, but seldom or never truly septate ; polythalamic forms never
symmetrical.

Sub-fam. 1. Astrorhizince. Walls thick, composed of loose sand or mud
very slightly cemented. Astrorhiza Sandahl, Pdostiia Brady, Syringammina
Brady.

Sub-fam. 2. Piluliiice. Test monothalamic ; walls thick, composed chiefly
of felted sponge-spicules and fine sand, without calcareous or other cement.
Pilulina Carpenter.

Sub-fam. 3. Saccamminince. Chambers nearly spherical; walls thin,
composed of firmly cemented sand grains. Saccammina M. Sars, Psam-
mosphcera Sch., Sorosphcera Brady.

Sub-fam. 4. Rhabdammininaz. Test composed of firmly cemented sand
grains, often with sponge-spicules intermixed ; tubular, straight, radiate,
branched, or irregular ; free or adherent ; with one or more apertures ;
rarely segmented. Rhabdammina M. Sars, Rhizammina Brady, Sagenella
Brady, Botellina, Carp., Haliphysema Bowerbank.

Fam. 6. Lituolidae. Test arenaceous, usually regular in contour ; septation
of the polythalamic forms often imperfect, chambers frequently labyrinthic.
Comprises sandy isomorphs of the simple porcellaneous and hyaline types
(Cornuspira, Miliolina, Lagena, GloUgerina, Rotalia, etc.), together with some
adherent species. Lituola Lamarck, Thurammina Brady, Ammodiscus Reuss,
Trochammina Parker and Jones, WebUna d'Orb., Cijclammina Brady.

Fam. 7. Textularidae. Test of the larger species arenaceous, either with or
without a perforate calcareous basis ; smaller forms hyaline and conspicuously
perforated. Chambers arranged in two or more alternating series, or spiral,
or confused; often dimorphous. Textularia Defrance, Cnneolina d'Orb.,
Verneuilina d'Orb., Tritaxia Reuss, Pavonina d'Orb., Valvulina d'Orb.,
Clavulina d'Orb., Bulimina, d'Orb., Virgulina d'Orb;, Bolimna d'Orb.,
Pleurostomella Reuss.

Fam. 8. Chilostomellidse. Test calcareous, finely perforate, polythalamous.
Segments following each other from the same end of the long axis, or alternately
at the two ends, or in cycles of three ; more or less embracing. Aperture, a
curved slit at the end or margin of the final segment. Ellipsoidina Seguenza,
Chilostomella Reuss, Allomorphina Reuss.

PROTOZOA.

FIG. 9. — Plaruyrbulina (Acervu-
lina)globosa (after M. Schultze).

Fam. 9. Lagenidae. Test calcareous, very finely perforated ; either mono-
thalamous, or consisting of a number of chambers joined in a straight, curved,
spiral, alternating or (rarely) branching series.
Aperture simple or radiate, terminal. No inter-
septal skeleton nor canal system. Lagena, Walker
and Boys, monothalamous ; Nodosaria Lamarck,
chambers in linear series ; Lingulina d'Orb.,
Frondicularia Defrance, Rhabdogonium Reuss,
Marginulina d'Orb., Vaginulina d'Orb., Rimu-
lina d'Orb., Cristellaria Lam., chambers in spiral
series ; Amphicoryne Schlumberger, Lingulinopsis
Reuss, Flabellina d'Orb., Polymoi-phina d'Orb.,
Dimorphina d'Orb., Uvigerina d'Orb.

Fain. 10. Globigerinidee. Test free, calcareous
perforate ; chambers few, inflated, arranged spi-
rally ; aperture single or multiple, conspicuous.

No supplementary skeleton nor canal system. All the larger species pelagic in
habit. Globigerina d'Orb. when taken in a spoon shows very long fine calcareous
spines projecting from the shell (Fig. 10). These are not found in forms taken
in the tow-net or in ooze. Dimorphism has not been observed in this genus.
Orbulina d'Orb., spherical shell, often double, containing Globigerina-like shell ;

it is formed by the external
protoplasm as a kind of
large last chamber. Hasti-
gerina Wy. Thomson, Pul-
lenia P. and J., Sphccroidina
d'Orb., Caiideina d'Orb.

Fam. 11. Rotalidae. Test
calcareous perforate ; free
or adherent. Typically
spiral and " Rotaliform,"
i.e., coiled in such a man-
ner that the whole of the
segments are visible on the
superior surface, those of the
last convolution only on the
inferior or apertural side,
sometimes one face being
more convex, sometimes the
other. Aberrant forms evo-
lute, outspread, acervuline,
or irregular. Some of the
Fig. IQ.—Hastigerina (Globigerina) Murrayi W. Thomson, higher modifications with
a bubbly vacuolated protoplasm, enclosing 6, the per- double chamber walls, sup-
forated Globigerina. like shell. IFrom the peripheral lllpmpntal skeleton and a
protoplasm project not only fine pseudopodia, but pJe °"' .*

hollow calcareous spines, which are set on the shell system of canals. Spinlhna
(from Murray). Ehrbg., Cymbalopora Hage-

now, Discorbina P. and J.,

Planorbulina d'O. (Fig. 9), Truncatulina d'O., Anomalina P. and J., Carpen-
teria Gray, Pulvinulina P. and J., Rotalia Lam., Calcarina d'O., Tinoporus
Carpenter, Gypsina Carter, Thalamopora Roemer, Polytrema Risso, Patellina.

MYCETOZOA. 15

Fam. 12. Nummulinidae. Test calcareous and finely tubulated ; typically
free, polythalamous, and symmetrically spiral. The higher modifications all
possessing a supplemental skeleton and a canal system of greater or less
complexity. Fusulina Fischer and Schwagerina Holier extinct, palaeozoic,
Nonionina d'O., Polystomella Lam., Archcediscus Brady, carboniferous,
Amphistegina d'O., Operculina d'O., Heterostegina d'O., Nummulites Lam.
mostly extinct (Carboniferous and Eocene), Cycloclypeus Carp., Orbitoides
d'O., JEozoon (?) Dawsou.

Testamoebiformia (Carter. An. and Mag, 1880). Adherent testaceous
Rhizopoda with the general form of Amoeba. Systematic position doubtful.
Holocladina test calcareous and branched with pustuliferous surface,
Cysteodidyina test calcareous, sessile, unbranched, uniformly punctate surface,
Ceratestina test chitirious and polythalamous.

SUB-CLASS II. MYCETOZOA.*

Gymnomyxa of large size, formed by the fusion of many small
amoeba-like forms. Fruit-like cysts or sporophore, and coated spores
are always formed.

The Mycetozoa were formerly regarded as Plants, and under the
name Myxomycetes placed amongst the Fungi. After the discovery
that the spores do not produce a mycelium, but hatch out as swarm
cells, de Bary introduced the name Mycetozoa. They have the form
of large masses of a granular protoplasm bounded by a clear proto-
plasm— the ectoplasm — without granules. These masses, which are
called plasmodia and may attain a surface extension of several square
inches, infest the damp surface and interstices of vegetable substances,
such as dead leaves, rotten wood, or even sound wood. They spread
out into a network on their substratum, over which they advance
with a creeping movement due partly to the formation of pseudopodia
at the advancing margin and partly to the flow of the dark granular
endoplasm. The flow of this latter is a rhythmic one, being reversed
at nearly regular intervals. The endoplasm contains numerous
nuclei and vacuoles, and sometimes granules of calcium carbonate.
The vacuoles often contract and expel their contents which is either
watery or of refuse matter. Occasionally the streaming ceases, the
plasmodium breaks up into masses containing ten to twenty nuclei, a
superficial membrane is formed round each of these masses, and they
enter a resting state : this is the stage of the Sclerotium. The
sclerotium can be made to reassume the active condition by the
addition of moisture.

* De Bary, "Die Mycetozoen." 1864. A. Lister, "A Monograph of the
Mycetozoa." London, 1894. W. Zopf, "Die Pilzthiere oder Schleimpilze."
Encyklopcedie der Naturwissenschaften, 1885.

16

PROTOZOA.

The reproduction is always effected by spore-formation. The
spores are either contained within fruit-like cysts — the Sporangia
— (Endosporece), which are either simple (spore fruits) (Fig. 11) or
combined into an cethalium (fruit-cake) of a cushion-like shape
consisting of numerous convoluted sporangia (Fig. 12); or they are
not contained in a cyst, but are produced upon the surface of
upgrowths of the plasmodium — the sporophore — (Exosporece).
In the latter case the spores divide, after issuing as amoeboid
organisms, by three successive bipartitions into eight cells,
which soon obtain flagella and separate ; they are comparable to the
just-hatched spores of the Endosporece. The spores are always
enclosed in a coat of a cellulose-like material and possess a single
nucleus. They are contained as a rule in the meshes of a network of
supporting fibres — the capillitium — which is formed within the

FIG. 11.— Physamm nutans (from Lister),
a, two sporangia magnified nine times ;
?>, capillitium threads, with lime-knots
attached to a fragment of the sporangium-
wall, x 110.

FIG. 12. — Fuligo septica, a, Aethalium, one
third natural size ; b, capillitium threads
with lime-knots and two spores, x 120.

sporangial cyst by the spore-protoplasm. The division into spores is
in the Endosporece preceded by a single division of the nuclei of the
sporeplasm by karyokinesis. * On the germination of the spore
the spore coat bursts and the contents issues as an amoeboid
organism which soon protrudes one flagellum. (Fig. 13.) The
swarm-cells so formed swim by their flagellum, ingest solid food
by their pseudopodia (at the non-flagellate end) and undergo
frequent bipartition. They may also withdraw the flagellum and
encyst (microcysts), but this is only temporary : they emerge and
re-assume the swarm-cell form. After a time the flagellum is
withdrawn and they creep about in an amoeboid manner, and
ultimately several of them fuse together to form the multinucleated
plasmodium. (Fig. 14.)

* The nuclei of the plasmodium sometimes multiply simultaneously by
karyokinesis, though it is highly probable that simple division occurs as well.

MYCETOZOA.

17

Order 1. Exosporeae. Spores produced on the sporophores and not enclosed
in a cyst. Ceratiomyxa Schroeter, plasmodium in rotten wood fruiting on the
outside.

Order 2. Endosporeae. Spores produced in a sporangium. Badhamia
Berkeley, Physarum Persoon, Fuligo Haller, sporangia combined m#b an
jethalium. F. septica Gmelin, flowers of tan. Cienkowslcia Rostafinski,
Physarella Peck, Craterium Trentepohl, Leocarpus Link, Chondrioderma Rost. ,
Trichamphora Junghuhn, Diachcea, Fries, Didymium Schrader, Lepidoderma
de Bary, Stemonitis Gleditsch, Comatricha Preuss, Enerthenema Bowman,
Lamproderma, Rost., Clastoderma Blytt, Amaurochcete Rost., Brefeldia Rost.,
Lindbladia Fries, Cribraria Pers., Dictydium Schrad., Licea Schrad., Orcadella
Wingate, Tubulina Pers., Siphoptychium Rost., Alwisia Berkeley and Broome,
Didydicethalium Rost., Enteridium Ehrenb., Reticularia Bull, Tricliia Haller,
Oligonema Rost., Cornuvia Rost., Arcyria Hill, Lachnobolus Fries, Perichcena
Fries, Margarita Lister, Dianema Rex, Prototrichia Rost., Lycogala Michel i.

FIG. IB.— Didymium di/orme (after Lister),
a, spore ; b, swarm-cell escaping from the
spore-case ; c, newly hatched swarrn-cell
with nucleus and three vacuoles ; d, flagel-
lated swarm-cell ; e, swarm-cell with two
vacuoles containing bacteria, and produced
at the posterior end into pseudopodia ; /,
amoeboid swarm-cell, x 720.

FIG. 14. — Didymium di/orme (after Lister),
young plasmodium with attendant amoe-
boid swarm-cells, some of which have
turned into microcysts (m) ; one micro-
cyst being digested in a vacuole (v). An
empty spore-shell at s. x 470.

In the neighbourhood of Mycetozoa may be placed provisionally the peculiar
marine form Labyrinthula, described by Cienkowsky (Arch.f. M. Anat., III.),
from the harbour of Odessa. This animal consists of aggregations of roundish
to spindle-shaped cells placed in a finely granular substance. From this mass,
hyaline or finely fibrous processes are given off. These processes branch and
anastomose so as to form a labyrinth ic network along which the cells glide.
Chlamydomyxa Archer (Q.J.M.S., XIX.), seems to be a fresh- water organism of
the same nature.

The Sorophora which are classed by some authors with the Mycetozoa, appear
to be more nearly allied to Labyrinthula. In the vegetative phase they live on
the dung of various animals, and are formed by the coming together of numbers
of amcebulfe produced from spores. The amoebulse, however, retain their
distinctness, and do not fuse to form a homogeneous plasmodium as in the
Mycetozoa, nor are there streaming movements throughout the mass. The mode

C

18

PROTOZOA.

of increase of the amcebulse in this stage has not been followed. In the spore
formation of Dictyostelium the mass rises up into club-shaped prominences, in
the axis of which a septate stalk is formed, and the amcebulse become gradually
aggregated at the summit of the stalk, where they encyst. The amcebulse which
escape from the spores divide by fission, but they do not pass through a flagellate

Genera. Copromyxa Zopf., Cynthulina Cienk., Dictyostelium Brefeld, Acrasis
Van Tieghem, Polyspondylium Brefeld.

SUB-CLASS ]JL HELIOZOA.*

For^ the most part fresh-water Gymnomyxa with stiff radiating
pseudopodia, and one or more nuclei ; usually with contractile vacuole.
A radial silicious skeleton sometimes present.

The characteristic pseudo-
podia give the name to the
group. (Fig. 15.)

When a skeleton is secreted,
it consists either of radially
arranged silicious spines ( Acan-
thocystis) or of latticed sili-
cious shells (Clathrulina), and
so closely resembles the skele-
ton of the Radiolaria that the
Heliozoa have been actually
described as fresh-icater Radio-
laria.

They differ from the Radio-
laria in the absence of the
complicated differentiations of
the protoplasm, particularly of
the central capsule. One or
more nuclei may be present
in the central mass. An
important distinguishing mark
is afforded by the presence of
the pulsating vacuoles, which have not been observed in any marine
Radiolarian.

Reproduction is effected by fission. Encystment and subsequent

* L. Cienkowski, ''Ueber Clathrulina." Archiv. fur mikrosk. Anatomic,
Tom III., 1867. R. Greeff, "Ueber Radiolarien und radiolarienahnliche Rhizo-
poden des stissen Wassers." Ibid. Tom V. & XI. R. Hertwig und Lesser,
"Ueber Rhizopoden und denselben nahe stehende Organismen." Ibid. Suppl.
Tom X., 1874. Also Archer and F. E. Schulze, etc.

FIG. 15. — Young Actinosplicerium, still with
a single nucleus (after F. E. Schulze).
N nucleus.

HELIOZOA. 1 9

spore-formation sometimes takes place. This has been observed in
Adinosphcerium, in which form the spores acquire a silicious coat.
In some genera, e.g., Clathrulina the spores are hatched as flagellate*
forms. ^/

Conjugation of two or more individuals has been observed. Ac-
cording to Brauer the nuclei of Actinosphcerium fuse with one
another, so that their number may be much reduced. Whether
this nuclear fusion takes place only in forms which have resulted
from conjugation, is not known.

Schaudinn has recently published a preliminary account of the
encystment and conjugation of Actinophrys sol,] which is of special
interest in view of a similar process described by WoltersJ in the
Gregarines (Monocystis), and the division of nuclei preceding conju-
gation in the Ciliata. He finds that after two individuals have come
together and formed a cyst wall, the nucleus of each divides by
karyokinesis into two daughter nuclei, of which one is extruded
from the protoplasm, while the other unites with its fellow to
form the conjugation nucleus. The subsequent division of this
nucleus, together with the protoplasm, into two or four gives
rise to the resting cysts, from which after some days the young
Actinophrys escapes. The analogy of this process with the forma-
tion of the polar bodies in the maturing ova of higher animals is
striking.

Order 1. Aphrothoraca. Heliozoa without a skeleton (sometimes temporarily
invested by a gelatinous membrane). Nudearia Cienk. body-form changeable,
multinucleate ; (Monobia, Vampyrella, Myxastrum sometimes placed • here).
Actinophrys Ehrb. (the sun animalcule) pseudopodia with axial fibre which
can be traced to the single central nucleus ; may form colonies by in-
complete fission. Actinosphcerium Stein, large, multinucleate ; Actinolophus
F. E. Sch.

Order 2. Chlamydophora. Heliozoa with gelatinous envelope. Hetercphrys
Archer ; Sphcerastrum Greef.

Order 3. Chalarothoraca. Heliozoa with skeleton of loosely arranged
isolated silicious spicules ; Pompholyxophrys Archer ; Eaphidiophrys Archer ;
Pinacocystis H. and L. ; Pinaciophora Greef; Acanthocystis Carter.

Order 4. Desmothoraca. Heliozoa with a stalked or unstalked shell per-
forated by numerous pores ; Clathrulina Cienk. ; Orbulinella Entz.

* Cienkowski, Arch. f. Mic. Anat., 1867, p. 311.

t Fr. Schaudinn. " Uber die Copulation von Actinophrys sol." Sitzungsber.
d. K.pr. Akad. d. Wiss. zu Berlin, 1896, V.

t "Die conjugation und sporenbildung bei Gregarinen." Arch.f. Mikr. Anat.
XXXVII. p. 99.

20

PROTOZOA.

SUB-CLASS IV. KADIOLARIA.*

Marine Gymnomyxa ivitli radiating pseudopodia, central capsule,
and usually a skeleton of silica or acantliin.

The body contains a membranous porous capsule (the central
capsule), in which is contained a slimy protoplasm with vacuoles and
granules (intracapsular sarcode), fat and oil globules, and albuminous
bodies, and more rarely crystals and concretions. The intracapsular
mass contains also a single large* nucleus or several small nuclei. The

\ \

FIG 16, — Tlwlasslcolla pelagica, with central capsule and single large nucleus, also numerous
alveoli in the protoplasm (after E. Haeckel).

extracapsular sarcode which communicates with the intracapsular
through the pores in the capsule, and which emits on all sides simple
or anastomosing pseudopodia, contains numerous yellow cells, some-
times pigment masses ; and in some cases it is much vacuolated like
the external protoplasm of some pelagic Foraminifera (Thalassicolla
pelagica. Fig. 16). The yellow cells are Algse living symbiotically with

* Job. Miiller, "Ueber die Thalassicollen, Polycystinen mid Acanthometren."
Abh. der Berl. AJcad. 1858. E. Haeckel, "Die Radiolarien." Erne Monographic,
Berlin, 1862. R. Hertwig, "Der Organismus der Radiolarien," 'Jena, 1879.
E. Haeckel, "Report on the Radiolaria." Challenger Reports, 1887.

RADIOLARIA.

21

the Radiolarian. They have been named Zooxantliella nutricola, and
contain chlorophyl, a nucleus and a cellulose wall. The central capsule,
which may be either conical or spherical, is either perforated by fine
pores over its whole circumference (Peripylaria), or the p«pes are
limited to a definite part of its surface (Monopylaria\ or there are
only a few, usually three, large pores (Tripylaria).

Many Radiolaria form colonies, and are composed of numerous
individuals. In such colonies the extracapsular protoplasm is united
with that of neighbouring individuals, so that the Avhole colony may
be described as consisting of a common mass of vacuolated protoplasm
containing in itself, not as in the moiiozoic Radiolaria a single central
capsule, but a number of capsules.

The whole animal — in the solitary as well as in the colonial forms — is
embedded in a structureless jelly, called the Calymma. The extracapsular proto-
plasm may be described as consisting of the following parts : (1) the Sarcomatrix,
the layer which surrounds the central capsule ; (2) the Sarcodictyum, the layer
which bounds the outer surface of the calymma ; (3) the Sarcoplegma, or anasto-
mosing threads which traverse the calymma and connect the sarcodictyum and
sarcomatrix. From the extracalymmar sarcodictyum proceed the pseudopodia.

Only a few species remain naked and without firm deposits; as
a rule, the soft body possesses a skeleton, which is composed either
of silica or of an organic
substance called Acanthin,
and either lies entirely
outside the central capsule
(Ectolithia) or is partially
within it (Entolithici). In
the most simple cases
the skeleton consists of
small, simple, or toothed
silicious needles (spicula)
united together, which
sometimes give rise to a
fine sponge -work round
the periphery of the proto-
plasm, e.g., Physematium.
In a higher grade we find
stronger hollow silicious

spicules, which radiate from the middle point of the body to the
periphery in regular number and order, e.g., AcantJwmetra. (Fig. 17.)
A fine peripheral framework of spicules may be added to these.
In other cases simple or compound lattice-works, and perforated

FIG. If.—Acanthoimtra Miilleri (after E. Haeckel).

99

PROTOZOA.

\

shells of various external form (like helmets, bird-cages, shells,
etc.) are found, and on the periphery of these, spicules and needles,
and even external concentric shells of similar shape may be formed,
e.g., Polycystina. (Figs. 18 and 19.)

Up to the present time but little has been made out about the
reproduction of these animals. Besides fission of the central capsule
(Polycyttaria), the formation of spores has been observed. These are
formed from the contents of the central capsule, and, after the burst-
ing of the latter, become free-swimming mastigopods. The spore-
formation is of two kinds : in the one it results in the development

of a mastigopod contain-
ing a crystal — the crys-
talligerous swarmer ; in
the other (dimorphous)
two kinds of swarmers are
formed — the macrospores
and microspores, being
distinguished from one
another by their size.
The further history of
the spores is not known.
Conjugation has not been
observed in the Radio-
laria ; but it has been
suggested that the macro-
spores and microspores
may turn out to be conju-

FIG. 18.— Heliosphcera echinoides (after E. Haeckel).

gating cells. Radiolaria

are inhabitants of the sea, and swim at the surface, but some live
on the bottom, even at great depths.

Fossil remains of Radiolaria have been made known in great
numbers by Ehrenberg, e.g., from the chalky marl and polishing slate
found at certain parts of the coast of the Mediterranean (Caltanisetta
in Sicily, Zante and ^Egina in Greece), and in particular from the
rocks of Barbados and Nikobar, where the Radiolaria have given
rise to widely extended rock formations. Samples of sand also
from very considerable depths have shown themselves rich in
Radiolarian shells.

Order 1. PERIPYLARIA. Central capsule uniformly perforated by numerous
fine pores, with or without silicious skeleton.

Fam. 1. Colloidea without skeleton. —Solitary are ThalassolampeH., Thalasso-

RADIOLARIA. 23

pila H., Thalassicolla Huxl., Thalassopkysa H. ; colonial (Polycyttaria) is
Collozoum H.

Fam. 2. Beloidea, skeleton of loose silicious needles. — Solitary are Thalasso-
sphcera H., Thalassoplancta H., Physematium Meyen ; colonial (Polycyttaria)
are Belonozoum H., Sphcerozoum Meyen. , J >

Fam. 3. Sphaeroidea, with one to numerous concentric spherical shells.
Colonial (Polycyttaria) are Collosphcera Mliller one -shelled, Clathrosphcera H.
two concentric shells ; solitary are Stigmosphcera H. 1 -shelled, Carposphcera H.
2-shelled, Thecosphcera H. 3-shelled, Cromyosphcera H. 4-shelled, Xiphosphcera
H. 1 -shelled with two radial spines, Stylosphcera H. 2-shelled with two radial
spines, Staurosphcera H. 1 -shelled with four radial spines. Hexastylus H. one-
shelled with six spines, Haliomma H. 2-shelled and numerous spines, Helio-
sphcera H. (Fig. 18) with numerous radial spines of two sizes and a fenestrated
shell.

Fam. 4. Prunoidea with ellipsoidal to cylindrical latticed shells and central
capsule. Ellipsis H., Druppula H., Spongurus H., Artiscus H., Cyphinus H.,
Panartus H., Zygartus H.

Fam. 5. Discoidea, shell and central capsule discoidal or lenticular.
Cenodiscus H., Phacodiscus H., Coccodiscus H., Porodiscus H., Polydiscus H.,
Spongodiscus H.

Fam. 6. Larcoidea.

Order 2. ACANTHARIA. Skeleton of acanthin, in the form of spines
radiating from the central point ; central capsule uniformly perforated
(Peripylaria type).

Fam. 7. Actinelida, with a variable number of usually irregularly arranged
spines. Astrolophus H. , Litholophus H. , Chiastolus H.

Fam. 8. Acanthonida, with 20 spines arranged according to Miiller's law.
Acanthometra J. Miiller (Fig. 17), Astrolonche H., Quadrilonche H., Amphi-
lonche H.

Fam. 9. Sphaerophracta, with 20 equal quadrangular spines, and a complete
fenestrated spherical shell. Sphcerocapsa H., Dorataspis H., Phractaspis H.,
Phractopelta H.

Fam. 10. Prunophracta, with ellipsoidal, lenticular, or double-coned shell,
and 20 spines of different size arranged according to Miiller's law. Belonaspis
H., Hexalaspis H., Diploconus H.

Order 3. MONOPYLAKIA. Skeleton silicious, rarely without skeleton;
central capsule monaxonic to bilateral, with simple wall and single polar
perforated area ; extracapsular plasma without pigment.

Fam. 11. Nassoidea, without skeleton. Nassela H.

Fam. 12. Flectoidea. Skeleton of 3 or more spines radiating from one
point (placed beneath the basal pole of the c.c.) or from a central rod; a
complete latticed shell is never formed. Plagoniscus H., Plagonium H.,
Plectanium H.

Fam. 13. Stephoidea. Skeleton of one to several fused rings, which may be
connected by a loose network. Lithocircus H., Zygocircus H., Cortina H.,
Steplianium H., Semantis H., Coronidium H., Tympanidium H.

Fam. 14. Spyroidea. Fam. 15. Botryoidea.

Fam. 16. Cyrtoidea. Eucyrtidium H. (Fig. 19), helmet-shaped latticed
shell outside central capsule, Eucecryplialus H.

Order 4. TEIPYIARIA (PKffiODARIA). Central capsule with double mem-
brane, at one pole with a spout -like main opening on a striped field, and

24

PROTOZOA.

frequently an accessory opening on each side of the main axis of the opposite
pole ; sometimes several central capsules in one individual ; always with extra-
capsular pigment mass (Phceodium H.), which covers the region of the main
opening. Skeleton either purely silicious, or weakly silicated with much
organic suhstance, always extracapsular, rarely absent.

Fam. 17. Phaeocystina. Partly without skeleton, partly with loose skeletal
structures ; central capsule in the centre of the spherical body. Phceodinia H.
Aulacantha H., Auladinium H.

Fam. 18. Phaeosphaeria. Fam. 19. Phaeogromia. Fam. 20. Phaeoconchia.

\ If:

Fict. 19.—Eucyrtidium cranoidcs (after E. Haeckel).

Class II. INFUSORIA.*

Protozoa with a definite form, provided with an external membrane,
and bearing either flagella or cilia. Mouth and anus usually,
contractile vacuole and one or more nuclei always present.

* Ehrenberg, Die Infusionsthierchen als vollkommene Organismen, 1838.
Balbiani, "Etudes sur la Reproduction des Protozoaires. " Journ. de la Phys.,
Tom. III. Balbiani, "Recherches sur les phenomenes sexuels^les Infusoires."
Journ. de la Phys. , Tom. IV. Claparede und Lachmann, Etudes sur les Infu-
soires et Us Rhizopodes, 2 vol. Geneve, 1858-1861. E. Haeckel, "Zur Morphologic

INFUSORIA. 25

Infusoria were discovered towards the end of the 17th century
in a vessel of stagnant water by A. von Leeuwenhoek, who made
use of a magnifying glass for the examination of small organisms.
The name Infusoria, which was at first used to denote all anini^Jculae
which appear in infusions and are only visible with the aid of a
microscope, was first brought into use by Ledermiiller and Wrisberg
in the last century. Later on the Danish naturalist 0. Fr. Miiller
made valuable additions to our knowledge of Infusoria. He observed
their conjugation and their reproduction by fission and gemmation,
and wrote the first systematic work on the subject. 0. Fr. Miiller
included a much larger number of forms than we do nowadays,
for he placed among the Infusoria all invertebrate water animal-
culse without jointed organs of locomotion and of microscopical
size.

The knowledge of Infusoria received a new impulse from the
comprehensive researches of Ehrenberg. The principal work of this
investigator, "Die Infusionsthierchen als vollkommene Organismen,"
discovered a kingdom of organisms hardly thought of. These were
observed and portrayed under the highest microscopic powers. Many
of Ehrenberg's drawings may even yet be taken as patterns, and are
hardly surpassed by later representations, but the significance of the
facts observed has been essentially corrected by more recent investi-
gations. Ehrenberg also conceded too great an extent to the group
of Infusoria, including not only the lowest plants such as Diatomacece,
Desmidiacece, under the name of Polycjastrica anentera, but also the
much more highly organized Rotifera. As he chose the organization
of the last-named for the basis of his explanations, he was led into
numerous errors. Ehrenberg ascribed to the Infusoria mouth and
anus, stomach and intestines, testis and ovary, kidneys, sense-organs,
and a vascular system, without being able to give reliable proofs of
the nature of these organs. There very soon came a reaction in the
way of regarding the Infusorian structure ; for the discoverer of the
Mhizopoda, Dujardin, as well as von Siebold and Kolliker (the latter
taking into consideration the so-called nucleus and nudeolus), referred
the Infusorian body to the simple cell. In the subsequent works of
Stein, Claparede, Lachmann, aird Balbiani numerous differentiations

der Infusorien." Jen. Zeitschrift, Tom. VII., 1873. 0. Biitschli, Studien uber
die ersten Entwickelungsvorgdnge des Eizelle, die Zelltheilung und die Conjuga-
tion des Infusorien, Frankfurt, 1876. Saville Kent, A Manual of the Infusoria,
London, 1880-2. Maupas, "Sur la multiplication des Infusoires Cilies." Arch,
d. Zool. Exp. (2), 6, and " La Rajeunissement Karyogamique chez les Cilies,
ibid. (2), 7.

26

PROTOZOA.

were certainly shown to exist, which, however, can all be referred
to differentiation of the body of the cell. This view is supported
by the more recent work of Biitschli and Maupas, who have
shown that in their reproduction these animals resemble other
Protozoa: that is to say, that the whole body participates in the
reproductive fission, that the parent disappears in the offspring, and

FIG. 21. — a, Cercomonas intestinalis;
b, Tricliomonas vaginalis (after
Leuckart).

FIG. SL—Tridumwas

batraclwrum (after
Stein). Us undu-
lating membrane.

FIG. 23. — Oikomonas termo
(after Biitschli). n nu-
cleus ; Cv contractile
vacuole ; Nv vacuole
which takes up the
food (oral vacuole).

that special conjugating cells of the
nature of ova and spermatozoa are not
formed. Maupas especially, by follow-
ing the history of the individual result-
ing from conjugation, has definitely
established the fundamental distinction
between conjugation and reproduction,
and has thrown a flood of light upon
the meaning of the whole phenomenon
of conjugation.

The outer boundary of the body is
usually formed by a cuticle — a delicate
transparent membrane, the surface of
which is beset with vibratile and
moving appendages of various kinds.

In the smallest Infusoria— i\& Mastigophora, we find only one or
two long whip-like cilia; while the more highly differentiated
Ciliata are usually richly provided with cilia. Finally, in the
Acinetaria the young forms have cilia, and the adults a number
of delicate tentacle-like processes, which either end in suctorial discs
or are pointed.

FIG. 24. — Gonium perforate (after
Stein). The colony a from above,
b from the side.

INFUSORIA. 27

SUB-CLASS I. MASTIGOPHORA.

Infusoria generally of small size provided with flagella.

This sub-class includes forms which live in putrefying infusions,
parasitic forms, and forms which live freely. They all have con-
tractile vacuoles, and some of them have an opening at the base of
the nagellum for the reception of solid substance (holozoic nutrition).
Encystment and spore formation are very commonly found ; and
it has been shown by Dallinger and Drysdale* that the spores are
capable of resisting a temperature above boiling point. Dallinger
has also shown, in the case of some of the infusion forms, that
it is possible by very gradually raising the temperature in which
the animals are living during a number of successive generations to
produce a race for which the optimum temperature is considerably
above the normal killing temperature for the species.

Conjugation is known to occur very generally, and in some cases
the conjugating individuals (or gametes) f are especially differen-
tiated. This is notably the case in Volvox, in which the gametes
are of two kinds, and recall the spermatozoa and ova of the higher
animals. Many members of our sub-class are difficult to distinguish
from the swarm-spores of certain Rhizopoda and of the Mycetozoa,
and even from the zoospores of unicellular Algce. It is necessary,
therefore, to point out that in the Mastigoplwra the flagellated
stage covers the main, if not the entire, period of the life of the
organism.

The nucleus is almost invariably single.

Order 1. — FLAGELLATA.|

Mastigoplwra with flagetta, without collar or cilia.

This order includes holozoic, holophytic, and saprophytic forms.
Many of them are parasitic and many live in infusions. It is not
infrequent to find an amoeboid condition of the body combined with
the possession of the nagellum (Mastigamceba\ or to find these two
conditions alternating in the life -history. Many of them form
colonies, and an outer cuticular skeleton in the form of a cup or
investing membrane may be present ; and in some forms a gelatinous
layer is secreted. In the holozoic forms food may be taken up by

* "Researches on the Life-history of the Monads." Monthly Mic. Journal,
10-13.

t An organism which conjugates, whether specially differentiated or not, is
called a gamete, and the product of the conjugation is a zygote.

I G. Klebs, " Flagellatenstudien." Z. f. w. Z., 55, 1892.

28 PROTOZOA.

means of pseudopodia in an amoeboid fashion, or there is a definite
spot at the base of the main flagellum where the food enters : this
spot is either marked by a mouth- vacuole (Fig. 23 Nv) into which the
food slips, or by the presence of a mouth-opening with or without
a pharyngeal continuation. The expulsion of undigested remains
of food appears to be localised and often to take place by the
bursting of a vacuole ; but the position of the temporary anus,
which seems to be variable in the different forms, has only been
determined in a few cases. Contractile vacuoles close to the body-
surface seem to be always present, and in the Euglenina they appear
to open into a receptacle which is in communication with the hind
end of the pharynx. Chromatophores of the same character and
function as those of plants are present in the holophytic forms,
and vary in colour from a light green to a brown (Chlorophyll and
Diatomin). They contain amylum bodies, which consist of a central
mass of a highly stainable plasma — the pyrenoid— and of an outer
zone of amylum. The pyrenoids may increase by division. Amylum
bodies are also found in colourless saprophytic forms. Paramylum,
a substance more nearly allied to cellulose, is sometimes present in
the protoplasm. Chromatophores may be present or absent in
closely allied forms, and even in the same form at different times ;
their presence is of no systematic importance.

The nucleus is always single except in Trepomonas, which some-
times has two. Stigmata as red pigment spots are often present
in the protoplasm, usually at the base of the flagellum.

Reproduction takes place by fission, which is usually, if not
always, longitudinal, in both the active and resting state, and some-
times by continued fission (spore formation) in the resting state.
In the first case the fission may be into two, or by successive binary
fissions into four, eight, sixteen, or even thirty-two before the young
separate. When the fission is into two, the flagella become doubled
in number before the body divides. The manner in which this
doubling occurs is disputed : very likely a new set of flagella and
of the other organs of the body is formed before the division occurs.
When the first binary fission is succeeded by others, the successive
fissions take place within the cuticle, while the animal continues
to move by the two original flagella which remain attached to one
of the products of fission.

Finally reproduction may take place by continued fission (spore
formation), during the resting state (Bodo, Tetramita). This has
been observed to follow conjugation.

FLAGELLATA. 29

Conjugation* is of very common occurrence. In certain small
Itodoninai it takes place between several individuals in the amoeboid
state, so as to give rise to a plasmodium, which, as in the Mycetozoa,
encysts and ^divides into spores. In Cercomonas the gametes become
amoeboid and conjugate in pairs. Sometimes the gametes, or one
of them, differ in size or history from the ordinary forms. In the
Clilainydomonadina small forms (inicrogametes or microgonidia) often
arise by fission and conjugate with similar inicrogametes or with the
ordinary form, or with forms which have been produced from the
ordinary form by a smaller amount of fission. In Polytoma gametes
are produced by tetrapartite fission, and are all alike.

The differentiation of the gametes is carried furthest in some of
the Volvodna. In Volvox both gametes are specially differentiated
individuals of the colony. The megagamete or macrogonidium is
an ovum-like cell without nagella, while the microgamete or micro-
gonidium is a small flagellated organism produced by fission from the
ordinary form. In some species these two kinds of gametes are not
found in the same individuals, so that there are unisexual colonies.
The zygote resulting from their conjugation secretes a thick membrane,
and remains in the resting state for some time. On the death of the
mother it falls to the bottom, and when conditions are favourable
it develops into a new colony.

Conjugation is, so far as is known, followed by encystment, the
zygote remaining for some time quiescent. While in this condition
it is capable of resisting drought, which indeed seems to be favourable
to it. When placed in suitable conditions the contents of the cyst
divide into two or four parts, which issue as young forms to begin
a new cycle of life. The breaking up of the zygote into minute
spores is only described for a few forms (Dallinger, Bodo, Tetramita).

The Flagellata are allied to the Gymnomyxa by such forms as the Monadina,
in which the amoeboid condition may occur as an important phase in the life-
history, and by those of the Gymnomyxa in which the young leave the spore-case
in the flagellate form (mastigopod). In other words the Flagellata and Gymno-
myxa agree with one another in including forms which pass through both the
myxopod and mastigopod condition in the life-history, the difference between
these forms consisting mainly in the relative duration of the two states.
Paramceba, a form recently described by Schaudinn (Sitzb. K. Preuss. Akad. W.,

* Klebs throws doubt upon the occurrence of conjugation in any true
Flagellate. He admits that it takes place in the Volvodna, which he removes
from the Flagellata, and in certain other forms such as Cilioplirys and Protomonas,
all of which he refers to the Heliozoa; but more recently Dill (Jahrb. wiss.
Bot., 28, 1895) has not only stated that transverse fission occurs, but also that
gametes are formed in Chlamydomonas, which is a member of the Flagellata.

30

PROTOZOA.

1896), seems to be a form exactly intermediate between the two groups. On the
other hand the Flagellata show distinct affinities to the lower plants by such
forms as the Volwcina, which Klebs replaces amongst the Algce, and by the
Chrysomonadina and Cryptomonadina, which he unites into a special group — the
Chromomonadina — of the Flagellata.

Sub-order 1. MONADINA.

Small to very small forms of simple structure, naked and often more or less
amoeboid, sometimes with tests ; usually colourless, rarely with chromatophores ;
with one anterior large flagellum, to which may be added one or two small
flagella ; special mouth-opening sometimes absent, sometimes present, but never
continued into a well -developed pharynx.

Fam. 1. Rhizomastigina. Simple, mouthless forms with one or two flagella,
and in some cases the power of thrusting out pseudopodia ; in other cases the
amoeboid condition may be assumed with or without retraction of the flagella.
Mastigamceba F. E. Sch., fresh-water ; Ciliophrys Cienk., fresh-water, heliozoon-
like ; Dimorpha Gruber ; Actinomonas Kent ; Trypanosoma Gruby, parasitic
forms from blood of Amphibia, Pisces and Chelonia, with undulating membrane.

FIG. 25. — Euglena viridis. a and 6, free-swimming in different stages of contraction ;
c, d, e, encysted and in process of division.

Fam. 2. Cercomonadina. Form oval to elongated, often amoeboid ; one
large, forwardly-directed flagellum with mouth, as a vacuole for taking up
food, at its base. Cercomonas Dujardin (Fig. 21), fresh-water and infusions,
hind end continued into pseudopod-like fibre ; Herpetomonas Kent, parasitic,
gut of Musca; and Trilobus, blood of Mus ; Oikomonas Kent (Fig. 23), fresh-
water, infusions and marine ; Ancyromonas Kent.

Fam. 3. Codonoecina. Monad with attached gelatinous or membranous cup.
Ccdonwca James Clark, salt and fresh-water ; Platytheca Stein.

Fam. 4. Bikoecina. Monads with cup ; hind end fastened to base of cup
with contractile stalk ; cup usually fastened by stalk ; some colonial. Bicoswca
Clark, fresh-water and marine ; Posteriodendron Stein, fresh-water.

Fam. 5. Heteromonadina. Small, colourless monads with an anterior large
flagellum, one or two contiguous smaller accessory flagella ; often colonial and
then stalked. Nonas Ehrb. ; Dendromonas Stein, fresh- water ; Cephalothamnium
Stein, attached to Cyclops ; Anthophysa Bory d. Vine., fresh-water; Dinobryon
Ehrb. ; Uroglena Ehrb.

Sub-order 2. ETJGLENOIDEA.

Monoflagellate forms ; body contractile or stiff ; mouth and well-developed
pharynx at base of flagellum ; contractile vacuole near pharynx, often with

FLAGELLATA. 31

Fam. 6. Coelomonadina. Euglenoids coloured with numerous chlorophyll
bodies, or one to two larger plate-like chromatophores ; usually no true pharynx.
Ccelomonas Stein, ectoplasm with chlorophyll grains ; Gonyostomum Diesing, like
preceding, with trichocysts in ectoplasm ; Microglena Ehrb. ; Chromulina
Cienk.; Cryptoglena Ehrb. ^

Fam. 7. Euglenina. Elongated ; hind end usually pointed ; spirally striped
cuticle ; reservoir with usually several contractile vacuoles and simple stigma
close behind pharynx ; chromatophores, usually green, almost always present.
Euglena Ehrb. (Fig. 25) ; Colacium Ehrb. ; Eutreptia, Perty ; Ascoglena Stein ;
Trachelomonas Ehrb.

Fam. 8. Chloropeltina. Like preceding, but with thicker cuticle. Lepo-
cinclis Perty ; Phacus Nitzsch.

Fam. 9. Menoidina. Like Euglenina, but without chlorophyll and stigma ;
saprophytic. Astasiopsis Biitschli ; Menoidium Perty ; Rhabdomonas Fresenius.

Fam. 10. Peranemina.

Fam. 11. Petalomonadina.

Fam. 12. Astasiina, with small or large second flagellum. Astasia Ehrb.;
Hetcronema Duj. ; Sphenomonas Stein.

Sub-order 3. HETEKOMASTIGODA.

With two flagella of different character and size, the one directed forward and
the other (sometimes two) trailed behind ; with at least a mouth-spot, which
in the larger forms becomes a mouth with pharynx ; colourless, holozoic ; some-
times amoeboid.

Fam. 13. Bodonina. Bodo Ehrb. (ffeteromita), the hooked monad and the
springing monad. Phyllomitus Stein ; Colponema Stein ; Dallingeria Kent.

Fam. 14. Anisonemina.

Sub-order 4. ISOMASTIGODA.

With two, four, rarely five equal flagella at the anterior end ; rarely with
mouth opening and pharynx.

Fam. 15. Amphimonadina.

Fam. 16. Spongomonadina. Biflagellate ; colonial, the individuals living in
a granular jelly, or at the end of branched gelatinous tubes. Spongomonas
Stein ; Cladomonas Stein ; Rhipidodendron Stein ; Diplomita Kent.

Fam. 20. Tetramitina. Naked and sometimes amoeboid Isomastigoda, with
finely pointed hind end ; anterior end with four equal flagella, one of which
may be larger and directed backwards ; the latter may have the form of an
undulating membrane ; distinct mouth only rarely discernible ; holozoic.
Collodictyon Carter ; Tetramitus Perty ; Monocercomonas Grassi ; Trichomonas
Donne (Figs. 21 b and 22) ; Trichomastix Blochmann.

Fam. 21. Polymastigina. Somewhat oval, with broader or pointed hind
end, which is continued into two flagella. At the anterior end of the body
are two or three flagella on each side. Holozoic, and perhaps in part sapro-
phytic. Hexamitus Duj. ; Megastoma Grassi.

Fam. 22. Trepomonadina. The two anterior flagella arise far apart from
one another at the sides of the body. Trepomonas Duj.

Fam. 23. Cryptomonadina. Coloured or colourless ; usually laterally com-
pressed, without true cuticle, with two long anterior flagella ; anterior end
obliquely truncated, and pitted inwards slightly on one side ; the pit may lead
into a pharynx. Cyathomonas Fromentel, possibly having affinities with the
Dinoflagellata ; Chilomona&JSblb,; Cryptomonas Ehrb. ; Oxyrrhis Duj.

32

PROTOZOA.

The following three families of the Isomastigoda are separated as a sub-order
named Phytomastigoda on account of their plant-like features.

Sub-order 5. PHYTOMASTIGODA.

Holophytic, vegetable-like Isomastigoda with chlorophyll, without mouth.
Fam. 17. Chrysomonadina. Solitary or colonial ; rarely with test ; with
two, rarely one, brown to greenish -brown chromatophore ; usually with eye-spot
at the base of flagella ; colonies free-swimming, with spherical grouping of
individuals. Stylochrysalis Stein ; Chrysopyxis Stein ; Nephroselmis Stein ;
Synura Ehrb., colonial, with cuticle often growing
out inltf) fine spines ; Syncrypta Ehrb.

Fam. 18. Chlamydomonadina. Almost always
green on account of considerable, usually single,
chromatophore ; usually delicate membranous shell
without large opening ; one to two contractile
vacuoles at base of flagella ; usually one eye-spot
(stigma). Reproduce by continued division within
the shell-membrane ; usually forming macro- and
microgonidia ; mostly solitary. Hymcnomonas
Stein : Chlorangiuin Stein ; Chlorogonium Ehrb. ;
Polytoma Ehrb., saprophytic, without chromato-
phores, with amylum bodies ; Chlamydomonas
Ehrb. ; Hamatococcus Agardh. ; Spondylomorum
Ehrb., colonial; Coccomonas Stein; Phacotus
Perty.

Fam. 19. Volvocina. Biflagellate colonial
Phytomastigoda, intermediate in structure between
Chlamydomonas and Hcematococcus. Reproduction
by continued division of all, or of certain, indi-
viduals of the colony (parthenogonidia] to form
daughter colonies. In some, probably in all, con-
jugation occurs between definite individuals of the
colony, with or without differentiation of the
colonies and gametes into male and female. The
result of conjugation is a resting zygote, which
develops later into one or into several new colo-
FIG. 26.— Codosiga botrytis (after nies. Gonium 0. F. Mtiller (Fig. 24), colonies of
Butschli). a, colony, b, one four or sixteen individuals united to a quadran-
individual. K collar; nnu- } plate.like group . reproduction by simul-
cleus ; Cv contractile vacuole ; & , J

Nv oral vacuole. taneous division of all the individuals to form

daughter colonies ; Stcphanosph&ra Cohn ; Pan-

dorina Bory de Vincent; Eudorina Ehrb.; Volvox L., spherical colonies with
numerous individuals, which are placed at equal distances within the common
thick colonial membrane, and lie in special membranes which stand off from
the cells and are compressed against one another into the form of hexagons.

Order 2. CHOANOFLAGELLATA.

Mastigopliora with a collar-like process of protoplasm round the
base of the single flagellurn.

Solitary and colonial forms are included in this group. The

DINOFLAGELLATA. 33

individuals may be naked, or may secrete a cup, or may be .embedded
in jelly (Proterospongia). Their nutrition is holozoic. The food-
particles, brought by the currents set up by the flagellum, adhere
to the outer side of the collar, down which they move untif>they
are swallowed by a kind of vacuole-like elevation of the body proto-
plasm at the base of the collar (oral vacuole). Ejection of faecal
matter takes place in the collar area, though there is no distinct
anal spot. The collar is protoplasmic and retractile.

Fam. 1. Phalansterina. Colonial, each individual in a granular gelatinous
tube. Colonies either a lamellar expansion or a dichotomously branching stock ;
collars narrow, conical, and of constant shape. Phalansterium Cienk.

Fam. 2. Craspedomonadina. Solitary or colonial, collars considerable, conical
and of changeable form. Individuals naked or with incomplete cup, or in
gelatinous mass. Monosiga Kent ; Codosiga J. Clark (Fig. 26) ; Codonocladium
Stein ; Hirmidium Perty ; Proterospongia Kent, colonial, the individuals are
embedded in jelly and readily assume the amoeboid condition ; Salpingosca
J. Clark, and Polyceca Kent, with thin-walled cups.

Order 3. DINOFLAGELLATA.*

Bilateral, asymmetrical Mastigophora with a ventral groove and
two flagella. A membrane consisting of cellulose is generally
present.

The Dinoflagellata are most nearly allied to the Cryptomonadina.
Like these they possess two flagella, which
arise from a groove. The flagella are always
distinguishable from one another: the one
as the longitudinal flagellum directed forwards
(Adinida) or backwards (Dinifera), and the
other as the transverse flagellum because it has
a transverse circular course round the base of
the first (Fig. 27). The transverse flagellum
moves by very short waves, and was until lately
taken to be a transverse ring of fine cilia (hence FiG.27-Gien^Uniumcinc-

tum (after Butschli) ven-

Ciliojiagellata). A membrane or shell consisting trai view, g longitudinal
of cellulose and often prolonged into processes gSSlVSS!
(Fig. 28), is nearly always present. They closely OG stigma (eye -spot);
resemble the Flagellata in their internal struc-
ture. Except in one genus (Polykrikoe), there is never more than
a single nucleus. Chromatophores of a green to brown colour are

* R. S. Bergh, "Der Organismus der Cilioflagellaten. " Morph. Jahrb., 7, 1881.
Fr. Schiitt, "Die Peridineen d. Plankton-Expedition," Th. 1. Ergeb. Plankton-
E\p., 4, 1895.

34

PROTOZOA.

generally present, and contain chlorophyll and diatomin*; but there
are colourless forms. Amylum, fat, red pigment, and stigmata may
also be present. There is always a longitudinal groove upon what we
call the ventral surface, and in the Dinifera there is a second groove
— the transverse groove — encircling the body ; the latter generally
has a slightly spiral course (so that the two ventral ends of it are
not quite at the same level, Figs. 27, 28) and in one genus makes
two complete turns. The two flagella arise, as a rule, close together,
where the two grooves cross one another. The transverse flagelluni
lies wrapped round the body in the circular groove. The flagella

project through a hole in the cuticle,
which in some genera at least ex-
tends as a slit along the left side of
the ventral groove, being enlarged
posteriorly where the longitudinal
flagelluni projects. Reproduction
takes place by transverse fission.
Conjugation has been observed in
a few forms, and in a few cases
individuals have been observed to
unite in chains (*? a form of conju-
gation). In PolyfcriJcos, which has
four nuclei, there are eight trans-

FIG. 28.-Shell of Ceratium tripos (after verse ^OWS, each with a flagelluni.

stein), if longitudinal furrow ; qf The presence of a mouth is doubtful.

transverse furrow. ^ ,

± resli- water and marine.

Sub-order 1. ADINIDA.

Longish bilaterally -symmetrical forms with inclination to asymmetry ; the
two flagella arise at the anterior pole, and the transverse furrow is not developed ;
with bivalved porous membrane ; two vacuoles near one another at the anterior
end ; chromatophores.

Fam. 1. Prorocentrina, with characters of sub-order. Exuviaella Cienk. ;
Prorocentrum Ehrb.

Sub-order 2. DINIFERA.

With a more or less distinct transverse furrow containing a flagellum. Longi-
tudinal flagelluni directed backwards.

Fam. 2. Peridinida, with the transverse groove at or near the centre of the
body. Podolampas Stein ; Peridinium Ehrb. ; Goniodoma Stein ; Ceratium
Schrank (Fig. 28) ; Fyrophacus Stein ; Glenodinium Ehrb. (Fig. 27) ; Gymno-
dinium Stein, without cuticle ; Ceratocorys Stein.

* By some naturalists there is supposed to be affinity between the Dino-
flagellata and the silicious Algfe, the Liatomaccce.

CYSTOFLAGELLATA. 35

Fam. 3. Dinophysida. Phalacroma Stein ; Dinophysis Ehrb. ; Amphisolenia
Stein ; Ornithoccrcus Stein ; Histioneis Stein.

Fam. 4. Polydinida, with several transverse grooves and flagella : naked.
Polykrikos Biitschli. x

Order 4. SILICOFLAGELLATA.*

Marine mastigophora with one flagellum and a latticed silicious cap
on one side of the body.

The forms included in this order were formerly regarded by some
naturalists as Radiolaria, on account of their silicious latticed-
skeleton, and by others as parts of the skeleton of Radiolaria (large
species of Phceodaria). Their soft parts were imperfectly known,
owing to the fact that they are small, exceedingly sensitive to adverse
influences, and consequently very difficult to get under observation
in the living state. The body lies within the skeleton, and contains
some small brownish-yellow spherical bodies. There is a nucleus in
the centre of the protoplasm, bounded by a membrane, and con-
taining a nucleolus ; it has been called the central body. There is
one long vibratile flagellum. The body is without a bounding
membrane, and there are no pseudopodia. The reproductive processes
are unknown. The skeleton consists of hollow silicious rods, and
has the form of two circles united by rods; it invests the body in
a cap-like manner.

Fam. Dictyochidae, with the characters of the order. Mesocena Ehrb. ;
Didyoclia Ehrb. ; Distephanus H. ; Cannopilus H.

Order 5. CYSTOFLAGELLATA (RHYNCHOFLAGELLATA).

Mastigophora of large size witli a single nucleus, reticular proto-
plasm, and a stout membrane.

Noctiluca is a nearly spherical form of large size (1 mm. in
diameter), and has on its ventral side a groove, called the peristome,
at the base of which is the elongated slit-like mouth. From the
anterior end of the peristome projects a large transversely striated
flagellum, sometimes called the tentacle, and a little further back
on the right side are two organs, the tooth and the lip. The
flagellum is a contractile organ and varies in form : it moves slowly
from side to side. The tooth is a protoplasmic projection, and
is probably actively movable. From the lip there projects forward
a smaller and vibratile flagellum. The greater part of the protoplasm
with the nucleus is aggregated on the ventral side at the base of

* A. Borgert. " Ueber die Dictyochiden," etc. Z. f. w. Z., 51, 1891, p. 629.

36

PROTOZOA.

the peristomial groove, and from it there radiate in all directions
to the periphery branching strands of protoplasm. At the periphery
there is a thin layer of reticulated phosphorescent protoplasm
immediately underlying the stout cuticle which bounds the body.
The nutrition is holozoic, and food vacuoles are formed. Leptodiscus
has the form of a flattened disc, concave on one side and convex on
the other. On the convex side is the mouth somewhat eccentrically
placed, and from the same side there is a tubular depression from
which projects a flagellum. The protoplasm is much vacuolated as
in Noctiluca, and the principal part of it is aggregated at the centre
of the concave or aboral side of the disc.

FIG. 29.— Noctihica miliaris partly after Cienkowski. N nucleus ;
a, single animal ; ft, conjugation of two individuals ; c and d,
swarm spores.

Noctiluca occasionally draws in its flagella and loses its peristome
and enters the resting state, but has not been observed to encyst.
It reproduces in two ways : by binary fission and by the formation
of small swarmers. If by fission, the division of the nucleus and
central plasma is soon followed by that of the whole body. Before
the latter is completed the development of the peristome and its
organs in the new individuals begins. Individuals with two central
masses and two nuclei are occasionally found. The formation of
spores takes place during the resting state. The central plasma
projects slightly on the surface, and divides by a superficial con-
striction into two prominences. The nucleus karyokinetically
participates in this and future divisions. These two again divide

CILIATA.

37

into four, and so on, until a large number of small prominences
are formed ; these eventually become free, and constitute the spores.
The latter are provided with a flagellum, a pointed process — the
so-called spine — and a nucleus. Their later history has noVbeen
followed, and it is not known whether they conjugate. The process
of division by which these spores arise is incomplete, and resembles
the cleavage of a meroblastic egg. While it is taking place a part
of the protoplasm of the rest of the body seems to pass into the
dividing disc, but the superficial layer beneath the cuticle always
remains. The fate of the maternal body after the separation of
the spores is not known.

Conjugation takes place between two individuals, and results in
complete fusion; but the fate of the zygote
has not been traced.

Noctiluca owes its name to its phospho-
rescent power. The light is emitted from
numerous points in the surface protoplasm,
and principally when the animal is disturbed.
It sometimes appears in enormous numbers
011 the sea surface. It is cosmopolitan, and
is principally confined to the coasts, but it
has been taken in the open ocean.

There are two genera — both marine. Noctiluca
Suriray, with very slight power of change of form ;
cosmopolitan. Leptodiscus R. Hertwig, body con-
tractile and movements energetic ; Mediterranean.

SUB-CLASS II. CILIATA.*

Infusoria provided with cilia ; mouth and
anus, nucleus and paranucleus are generally
present.

This group contains the most highly Flo 30.'_<?¥(m,/cMa mytilus

Organised of the Protozoa. The locomotive (after Stein), seen from ven-
.,. -i-i TO -i • tral side. Wz ad oral zone of

appendages are cilia, which are modified in cilia ; c contractile vacuoie ;
diverse ways, as will be explained below ; N nucleus ; w paranucleus ;
and immovable hairs and stiff bristles, which

may even have the form of bent hooks and be employed in loco-
motion and attachment, are often present. The power of forming

* 0. Biitschli, loc. cit. "W. Saville Kent, A Manual of the Infusoria. London,
1880-82. E. Maupas, " Sur la multiplication des Infusoires Cilies." Arch.
Zool exp. et gin. (2), Vol. VI.; and "La Rajeunissement Karyogamique chez
les Cilies. Ibid., Vol. VII.

38

PROTOZOA.

pseudopodia is almost always absent, and the body is generally
bounded by a thin pellicle or cuticle. Certain fixed Ciliata, as
Stentor (Fig. 31) and Cothurnia, secrete external coverings or shells
into which they can be retracted. Nourishment is in a few cases
taken in by endosmosis through the whole surface of the body ;
but as a general rule there is an oral aperture usually near the
anterior pole of the body, through which solid food is introduced.
A second aperture, which acts as anus, and which can be seen as
a slit durfhg the exit of the excreta, is often
present at a definite part of the body.

The pellicle seems to be part of the living
tissue, and frequently has an alveolated struc-
ture, in which case it forms the alveolar
layer. Beneath it there is generally a layer
of cortical plasma — the ectoplasm — which has
a firmer consistence than the more fluid endo-
plasm. The pharynx, or oesophagus, projects
into the endoplasm as a tubular prolongation of
the ectoplasm and pellicle. Through this the
food-stuff passes into the endoplasm, in which
it gives rise to food-balls. The latter undergo
a slow rotating movement round the body in
the endoplasm, during which the food is
digested; and finally the solid useless remain-
der is ejected through the anal aperture. A
digestive canal, bounded by distinct walls, exists
.. no more than do the numerous stomachs which

riG. ol. — stentor rcesehi

Ehrb., after stein, o Ehrenberg, who was deceived by the food vacu-

oral -P-ture^ith guU ^ ^^ tQ ^ ^^ polygastri^ In

vacuoie ; N nucleus. some cases there is a tube leading in from the
anus towards the oesophagus (Nyctotherus), but
it ends in the digestive endoplasm, and does not join the oasophagus.
In some cases (the EncJielina and Chlamydodonta, Fig. 32), the
oesophagus is surrounded by a layer of stiff rods forming the so-
called rod-apparatus of the oesophagus.

The firmer, more viscid ectoplasm is to be regarded pre-eminently
as the motor and sensory layer of the body. In it we may find
fibrillse resembling muscular fibres (Stentor, stalk of Vorticella). These
fibrillaB are differentiations of the alveolar layer and are sometimes
varicose. When they shift into the cortical layer (ectoplasm), they
form the so-called myophane layer. Small rod-shaped bodies — the

CILIATA. 39

trichocysts — are sometimes present in the cortical plasma. It
appears that on suitable stimulation they have the power of everting
needle-shaped structures which probably have a stunning action
upon other organisms. In one form, Epistylis umbellaria, dcjimte
nematoeysts, like those of the Coclenterata, are present in the
ectoplasm.

The contractile vacuoles are fixed in position and contained in the
ectoplasm, generally near the surface of the body. When more than
one is present they increase in number with the size of the individual.
They open outward through pores in the pellicle, or in some cases
(Vorticellines) into a reservoir, or there may be a long excretory
canal as in Lemladion. The contractile vacuoles are re-formed by
the fusion of formative vacuoles which appear in the neighbouring
plasma during the diastole of the preceding vacuole, or there may
be canals leading even from distant parts of the
body, which collect the fluid for the formation
of the new vacuole (Paramcecidce). The walls
of these canals are, in some cases at any rate,
contractile. These vacuoles and canal -systems
are probably excretory in function, collecting
waste matters in solution from the body gener-
ally and discharging it externally. They have
been compared, probably with some justice, to
the excretory organs of Platyhelmintlies and
Rotifer a.

The vibratile appendages of the body are of FlG- w.-CMiodon cucui-

, , . , j A. *««, after Stein; with

four kinds, and they all seem to be processes rod -apparatus round
of the cuticle or alveolar layer. the oesophagus. N

si\ m .4 -T 1-1 * • • nucleus; excreta are

(1) I he nne cilia which serve for swimming. passing out per anum.

(2) The Cirri : stouter vibratile processes

which taper towards their free ends. They are placed on the ventral
surface of the body, and serve for locomotion in a pediform manner
(hence called legs or styles), or for attachment.

(3) Membranellse : short flattened cilia which, when ending in a
point, are not clearly distinguishable from cirri; they form the
adoral zone of the peristome of the fyrirotricha, in which they create
the whirlpools by which the food is brought to the mouth.

(4) Undulating membranes placed in the neighbourhood of the
mouth, and assisting in the prehension of food.

The fibre which can often be made out running from the base of
the cilium, apparently to the myophane layer, is continuous with the

40

PROTOZOA.

cuticle as well as with the cilium. In a few forms (Actinobolus)
retractile tentacular processes are present.

In the simplest forms the mouth is at the anterior end of the body,
the ciliary covering is uniform, and the cilia are nearly all the same
size (Enchelina). An advance upon this is presented by those forms
in which the mouth is on the ventral surface, and in which there is
a triangular area — the peristome— leading back from the front end of
the body to the mouth (Paramcecium). There may be a special row
of strong cilia, cirri, or menlbranellse — the adored row, or zone —
running along the left side of the peristome (Hypotricha, Fig. 30).
The peristome, when ventral, is very commonly asymmetrical. In
some cases the adoral row has the form of a spiral round the mouth
region, and the peristome may be placed at the front
end of the body (Stentor, Vorticella). In the Hypo-
tricha the following regions may be distinguished on
the ventral surface of the body : a pre-oral and a
post-oral region. The pre-oral region consists of the
peristome on the left side, and the frontal area on
the right (Fig. 41.)

The majority of the Ciliata are multinuclear, and
the nuclei are almost, if not quite, always differ-
entiated into two kinds. One of these — the macro-
nucleus — is larger than the other, the micronucleus.
The macronucleus, which lies in the endoplasm, is
generally single, and presents considerable variation
of form; it may be spheroidal, band-shaped,
moniliform, or even branched. In some cases the
macronucleus is represented by a great number of
small nuclei. It is probable that these small nuclei
are all parts of one nucleus, and connected with one another by
fine fibres; so that the condition is really that of a much-branched
nucleus. Fragmentation of the macronucleus into fine pieces has
been observed, and is probably a stage in its final disappearance ;
but the real significance of the phenomenon is unknown. The
micronucleus is often multiple ; it varies in position, form, and
number, in different species. It is always smaller than the macro-
nucleus, and usually lies close to the latter. It appears only to be
absent in certain Opalines and in some of the so-called multinuclear
Ciliata just referred to. In the normal reproduction of the animal
it appears that, while the micronucleus divides by karyokinesis, the
macronucleus divides directly.

FIG. 33 — Opaliiia
ranarum (after
W. Engelmann).

CILIATA.

41

The most usual method of reproduction is by fission. When the
forms reproduced remain connected together, a colony is formed, e.g.,
the colonies of Epistylis and Carchesium. Fission usually takes place
by a transverse division (at right angles to the long axis), and, the
products may be equal or unequal. In cases of inequality we have
transitions to budding, which is really only a modified fission. Less
frequently ( Vwiicella) the fission takes place through the long axis
(Fig. 36), and still more rarely in a diagonal
direction. The onset of fission does not
appear to depend upon the size of the indi-
vidual, for it may take
place in large or in small
specimens. The nuclei
always participate in the
division, but do not
always lead the way ;
for in many cases un-
doubted new formations
appear in the protoplasm
(rudiments of new cili-
ary structures, of a
mouth and contractile
vacuole), before any
changes are observed in
the macro- and micro-
nuclei. As to the Other FIG- ^5. - Pa^maxium
aurelia in division,

organs they do not par- after R. Hertwig. N

macronucleus ; n micro-
nucleus ; o mouth of

FIG. 34.— Stylonychia mytilus in
C con-

ticipate in the division

division, from Stein.

tractile vacuole ; N macro- -\yhole

nucleus ; n micronuclei.

the anterior portion ;
N', n', o1 the same of
the hinder portion.

(unless they extend the
length of the
body), but one of the
fission products develops them afresh, generally before the fission
is completed. In the Hypotriclia the ciliary structures of both the
products of fission appear to be new formations.

In Opalina the nucleus divides many times, so that a multinucleate
condition is produced (Fig. 33). The gradual division of the whole
animal by a series of binary fissions into a number of small pieces
which encyst, takes place subsequently. From the cyst a small
uninucleate form eventually emerges.

Reproduction is often preceded by envtjutim'ut, which appears to be
of great importance for the preservation of the body from desiccation.

42

PROTOZOA.

The animal retracts its cilia, contracts its body to a globular mass,
and then secretes a transparent cyst which hardens and protects it
and enables it to survive in damp air. In water the contents of
the cyst divide into a number of parts, which attain freedom by the
bursting of the cyst, each one becoming a young animal.

The rapidity of fission depends upon the temperature and upon
the food, and seems to be fairly constant for each species. Thus an
individual of Stylonychia pustulata, if well supplied with food, will
divide once in twenty-four hflurs in a temperature of 5° to 10° C.,

and once in twelve
hours if the tempera-
ture be from 10° to
15° C. Although the
rapidity of fission is
less in senile individ-
uals, there does not
appear to be any special
increase in it after con-
jugation.

The Conjugation of
the Ciliata is generally
of a temporary nature.
Two individuals (rarely
more) apply themselves
together and acquire
protoplasmic continu-
ity. After a few hours

FIG. 36. — Vorticella microstoma, after Stein, a, in process of , , , ,

fission ; N nucleus, the mouth apparatus in each portion is tnev Separate and lead,

formed afresh ; b, fission is completed, one product of it their ordinary life 111

is set free after the formation of a posterior circlet of cilia ; .

w adoral zone of cilia ; ce oesophagus ; c, Vorticella in process the VOrtlCellmeS the

of bud-like conjugation ; fc the bud-like individuals (micro- coni'll^ation is complete
gametes) attached.

and permanent. As a

general rule conjugation takes place between two ordinary individuals
of the species, but in some cases the conjugating individuals, i.e.,
the gametes, are specially produced by division from the ordinary
individuals. Thus Leueophrys patula divides rapidly several times,
and produces dwarfed forms uniformly ciliated and incapable of
taking nourishment. These small forms are the gametes. In the
Vorticellince the gametes differ; one of the conjugating individuals
is the ordinary fixed form, and is called the megagamete, while the
other is a small free-swimming form, produced by two or three

CILIATA. 43

successive fissions (or in some species by budding) of a fixed form
into four or eight. These are the microgainetes ; they become
free-swimming and conjugate with a fixed form (Fig. 36). In
Zoothamnium the megagamete is also modified, being larger Jjjian
the ordinary individual.

The results of conjugation may be considered under two heads-^-
the physiological and the morphological. The physiological results
of, and the conditions favourable to conjugation, have been mainly
elucidated by Maupas. He found that it actually effected, as had
long been suspected, a rejuvenescence of the conjugating individuals ;
that without it senile degeneration, followed by death, ensued, and
that to be effective it must take place at a particular stage in the life-
history. His course of procedure was as follows : he isolated an
exconjugate, i.e., an individual which had just been released from
conjugation, and he kept it and the products of its bipartition under
continuous observation.

He found that after a certain number of bipartitions the vigour
and size of the descendants or products of his initial exconjugate
diminished, and that their nuclear and ciliary apparatus became
imperfect; and that these changes, to which he applies the term
senile, eventually led to the death of the whole stock. He further
found that it was not possible to induce conjugation during the
period of the earlier bipartitions ; this is the period of immaturity ;
but that after a certain number of bipartitions puberty is attained
and conjugation can be induced; this is the period of eugamy.
This stage merges into the last, the period of senescence, during
which the individuals become gradually reduced in size, the ciliary
•apparatus more and more imperfect, the micronuclei absorbed, and
conjugation ineffective. The period of senescence ends in death.
In Stylonychia pustulata puberty occurred at the 130th bipartition,
and senile degeneration began at about the 170th, and death took
place at about the 316th. Conjugation in the period of eugamy con-
ferred the power of again beginning the cycle; but the conjugation of
the period of senescence had no result in retarding the degenerative
changes or in averting death. Maupas further asserts that fertile
conjugation between descendants of the same exconjugate cannot
be effected in the period of eugamy; but this statement requires
confirmation. These facts explain why it is that when conjugating
individuals are met with they generally occur in large numbers
(epidemics of conjugation), for the inclination to conjugation comes
only at a particular stage in the life of the stock ; and the divisions

44

PROTOZOA.

being rapid, there will always be a considerable number of
descendants of the same exconjugate in juxtaposition.

Maupas also found that exhaustion of the food supply, which
usually determines encystrnent, causes conjugation among individuals
of mixed origin and of suitable age.

The morphological changes, our knowledge of which we owe
mainly to Balbiani, Biitschli, and particularly Maupas, appear to
consist of the breaking-up and disappearance of the macronucleus,
the particles of which — in *ome cases, at any rate — are excreted

FIG. 37. — Conjugation of Pammeecium caudatum after R. Hertwig. A" macronucleus ; n micro-
nucleus ; o mouth. In a the micronucleus is forming a spindle ; l> illustrates the second
division of the micronucleus, resulting in the formation of four micronuclei in each animal ;
of these, those marked 2, 3, 4, 6, 7, 8 will atrophy, while 1 and 5 will persist and divide ; c,
the micronuclei 2, 3, 4, 6, 7, 8 are disappearing, while 1 and 5 are dividing into two, one of
which, 1m and 5m, migrate respectively through the protoplasmic connection into the other
conjugating individual, while the other, Iw and 5w, remains in its own individual.

through the anus; and in the increase by successive bipartitions
of the micronucleus. Of the micronuclei so produced, all abort
except two, one of which is migratory and the other stationary ; the
migratory nucleus passes into the other gamete, and fuses with its
stationary nucleus to form the zygote-nucleus. The two gametes,
each with a zygote-nucleus, now separate, and the zygote-nucleus
gives rise by successive bipartitions to the nuclear apparatus of the
exconjugate. The details differ in different species. As an example
of the process we may take the simple case of Colpidium colpoda,
which possesses one macro- and one micronucleus. Soon after the
onset of conjugation, which lasts some hours, the micronucleus of
each gamete undergoes two successive bipartitions, and so gives rise

CILIATA. 45

to four micronuclei ; of these three abort, and one divides again
to form the two prormdei, as we may call them. One of these
migrates into the other gamete, and fuses with its stationary pro-
nucleus to form the zygote-nucleus. This undergoes two bipartitio^is,
during which the gametes separate and the old macronucleus dis-
appears. The exconjugates now possess four nuclei, all derived
from the zygote-nucleus. Of these, two become micronuclei and two
macronuclei of the first bipartition, which takes place at from four to
nine days after the separation. So that the exconjugate has for some
time double the ordinary nuclear apparatus, and the first bipartition
takes place quite independently of the nuclear division. For some
days after conjugation the exconjugates take no food, and appear
to be without a mouth and gullet. They acquire the latter and begin
to feed about twenty-four hours before the first bipartition.

The mode of life of the Ciliata is very various. Most of them lead
an independent life ; some are carnivorous and others herbivorous.
The former are very rapacious, and may take up even Rotifera.
Some, as Ampliile^tus^ select fixed Infusorians, as Carchesium and
Epistylis, for their prey, and swallow them down as far as the origin
of their stalk. They then, while fixed on the stalk, secrete a capsule,
and divide into two or more individuals. Some, as the mouthless
Opalina and many Bursaridce, are parasitic in the intestines and
bladder of Yertebrata. To these belong the Balantidium coli, from
the large intestine of man. (Fig. 40.)

Order 1. GYMNOSTOMATA.

The mouth is usually closed except during inception of food, and
is without undulating membranes. The pharynx when distinctly
developed is without ciliary structures, but is usually provided with
a rod -apparatus or a modification of one. The food is always
swallowed, never taken in by a whirlpool. Ciliation usually
holotrichous, but often more or less reduced.

Fam. 1. Enchelina. The mouth is terminal or sub-terminal, is usually
round, rarely slit-like. Anus usually terminal. Conjugation terminal.

Sub-fam. 1. Holophryina. Without tentacular structures. Holophrya,
Ehrb., m. and f.w.*; Urotricha Clap, and L. with caudal bristle, f.w. ;
Enchelys Hill, m. and f.w.; Spathidium Duj., f.w.; Chocnia Quennerstedt,
m. ; Prorodon Ehrb.; Dinoplirya Biitschli, f.AV. ; Lacrymaria Ehrb.

Sub-fam. 2. Actinobolina. With retractile tentacular organs and cilia.
Actinobolus Stein, t'.w.

* in., f.w., and inftis. are abbreviations for marine, fresh- water, and infusions.

46 PROTOZOA.

Sub-fain. 3. Colepina. Mouth terminal, surrounded by a circle of cirri.
Body sometimes surrounded by armour composed of pieces of the pellicle
arranged in an annular manner. Plagiopogon Stein, f.w. ; Coleps Nitzsch.
f.w. ; Tiarina Berg, m. ; Stephanopogon Entz, m.

Sub-fam. 4. Cyclodinina. Cilia confined to one or several rings. Mouth
on a papilliform projection. JMdinium Stein, f.w.; Mesodinium Stein, a
large oral papilla with one or more cirri arising from its base, m. and f.w.

Sub-fam. 5. Prorotrichina. Bluntly truncated oral end ; ciliation
confined to front end, or there are in addition incomplete rings of cilia.
Butschlia Schuberg, rumen of. Ruminants.

Fam. 2. Trachelina. Mouth is either a long slit which extends from the
front end along the ventral surface backwards, or its hinder part is alone
developed as a short slit-like or roundish opening. The oral end of the body
usually tapers in a proboscis-like manner. Pharynx short or absent.

Sub-fam. 1. Amphileptinae. Mouth on the convex ventral edge of the
dorsalwards-bent proboscis, sometimes as long slit, sometimes as round
opening. Ampliileptus Ehrb., m. and f.w.; Lionotus Wrzesniowski, mouth
along whole ventral edge of long proboscis, f.w. and m.; Loxophyllum
Duj., f.w. and m. ; Trachelius Schrank, mouth as round opening at base of
proboscis, endoplasm vacuolated, f.w.; Dileptus Duj., f.w. and m.

Sub-fam. 2. Loxodina. Proboscis bent ventrally, and mouth on its
concave edge. Ciliatiou confined to the right side. Loxodes Ehrb. , large
size, endoplasm vacuolated, on dorsal side a row of excretion vacuoles, each
with a dark body, f.w.

Fam. 3. Chlamydodonta. Body never elongated ; mouth always at a distance
from the front end. Pharynx always with well-developed rod-apparatus, or a
smooth, sometimes peculiarly-formed CESOphageal tube.

Sub-fam. 1. Nassulina. Ciliation complete; Nassula Ehrb., m. and f.w.

Sub-fam. 2. Chilodontina. Ciliation confined to, or stronger on the

ventral surface than on the back. Orthodon Gruber, m. ; Chilodon Ehrb.

(Fig. 32), f.w. and infus., m. ; Chlamydodon Ehrb., m. ; Opisthodon Stein,

mouth far back, f.w. ; Phascolodon Stein ; Scaphidiodon Stein, m.

Sub-fam. 3. Erviliina. Ciliation confined to ventral surface, or a
small field of it. Caudal end with a well-developed movable style usually
arising a little ventrally of hind end. Aegyria Clap, and L., m. ; Onycho-
dactylus Entz, m. ; Trochilia Stein, f.w. and m. ; Dysteria Huxley, f.w.
and m.

Order 2. TRICHOSTOMATA.

Mouth as a rule always open, rarely closed when not in use ;
pharynx always tubular and open; edges of mouth provided with
undulating membranes which are continued into the pharynx, or the
latter is provided with cilia. Food rarely swallowed, usually brought
by a whirlpool or by special ciliary structures.

Sub-order 1. ASPIEOTRICHA.

The mouth in the most primitive forms extends as a slit from the front end
along the ventral surface ; but is usually removed from the front end as a
reniform or crescent-shaped opening. Pharynx, when present, without rod-
apparatus. At the edges of the mouth or in the pharynx are one or two
undulating membranes.

CILIATA.

47

Fam. 1. Chilifera. Mouth in the anterior half of the body, or close behind
the middle. Pharynx either scarcely developed or short. The undulating
membranes stand either at the edges of the mouth or in the pharynx. A
so-called peristoniial field leading to the mouth absent or little developed.

Leucophrys Ehrb., f.w. ; Glaucoma Ehrb., f.w. and infus. ; Dallasia St6kes,
f.Av. ; Frontonia Clap, and L., f.w. and m. ; Ophryoglena Ehrb., f.w.; Colpidium
Stein, f.w., infus., m. ; Chasmatostoma Engelmann, f.w.; Uronema Duj., f.w.,
m., par. on skin of star-fishes ; Urozona Schewiakoff, f.w.: Loxocephalus Kent,
f.w. and infus.; Colpoda Miiller, f.w. and infus. (hay).

Fam. 2. Microthoracina. Asymmetrical ; mouth in hinder part of body,
placed somewhat laterally at the anterior end of a peristoniial furrow, which
begins behind ; ciliation sometimes complete, sometimes confined to ventral
surface, always sparse. Cinetochilum Perty,
f.w., m. ; Microthorax Engelmann, f. AV. ;
Ptychostomum Stein, paras, in intestine of
Oligochretes ; Ancistrum Maupas, in mantle
cavity of Mytilus, Venus, and probably
Ostrea ; Drepanomonas Fresenius, f. w.

Fam. 3. Paramaecina. Mouth sometimes
in the anterior, sometimes in the hinder half
of the body, with considerable triangular
shallow peristoniial pit passing to it from the
left side of the body. Pharynx tubular, with
long undulating membranes or row of cilia.
Ciliation close and uniform. Paramcecium
Hill (Fig. 37-39), f.w. and m.

Fam. 4. Urocentrina. Mouth in middle
of ventral surface with long tubular pharynx,
like that of Paramcecina. Ciliation reduced
to two broad annular zones, one in front
and one behind. Urocentrum Nitzsch, f.w.
and m.

Fam. 5. Pleuronemina. Ciliation complete
and usually considerable ; mouth at the end
of a peristome placed at varying distances
from the front end on the ventral surface.
The left edge of the peristome with con-
siderable undulating membrane ; the right

edge with a weaker membrane, or with a row of closely-placed cilia. Pharynx
slightly developed or absent. Lembadion Perty, f.w.; Pleuronema Duj., f.w.
and m.; Calyptotricha Phillips ; Lembus Cohn, f.w., infus., m.

Fam. 6. Isotrichina. Pellicle thick ; ciliation total and close. Mouth
posterior. Parasitic in rumen of Ruminants. Isotricha Stein ; Dasytricha
Schuberg.

Fam. 7. Opalinina. Ciliation complete and almost always uniform ; mouth
and pharynx absent. Anoplophrya intest. of Oligochretes, Polychretes, Clepsine,
Paludina ; Hoplitophrya Stein, with two hook-like structures, Oligochfetes and
Planarians ; Discophrya Stein, with anterior sucker, Planarians and Anura ;
Opalinopsis Foettinger, macronucleus in young forms elongated and twisted,
later an irregular, even branched and anastomosing mass breaking up into
pieces ; venous appendages of Sepia, Octopus, or in liver of Sepiola and Octopus ;

FIG. 38. — Paramcecium burso^ria about
one hour after conjugation (after
Biitschli). n micronucleus ; N
macronucleus ; PV contractile
vacuole.

48

PROTOZOA.

Opalina Park, and Val. (Fig. 33), in young state a roundish nucleus. Micro-
nucleus not observed ; no contractile vacuole ; rectum of Anura.

Sub-order 2. SPIROTRICHA.

Always with distinct adoral zone, which usually consists of membranelhe,
and has a more or less spiral course round a peristomial area. The latter is
distinguished by other peculiarities from the rest of the body-surface.

Section 1. Heterotricha.

With well-developed adoral zone or spiral, and a complete ciliary covering
(except Gyrocorys).

Fam. 1. Plagiotomina. Peristome as a narrow furrow, which usually begins
close to the front end and passes along the ventral surface to the mouth, which
is either at the middle of the body or at the hind end. The adoral zone
stretches from the mouth along the left side of the peristome, and is usually
straight. Pharynx tubular. Conchopthirus Stein, ma.n.* single, or multiple,
f.w., ectopar. in slime of different land and f.w. molluscs,
in gastral cavity of Aetmire ; Playiotoma Duj., paras.;

Nydotherns Leidy, with anal tube,

paras, in intestine of Anura, Insects,

and Myriapods ; Blepharisma Perty,

f.w.; Metopus Clap, and L., f.w. and

m. ; Spirostomum Ehrb., ma.n. single,

mi. n. numerous, f.w. and m.

Fam. 2. Bursarina. Peristome as a

more or less triangular (apex oralwards)

field, and not a furrow, as in Plagioto-
mina. Pharynx absent or but slightly

developed. The adoral row extends

along the left peristome-edge only, or

crosses over in front as far as the

right anterior angle of the peristome.

Balantidium Cl. and L., paras, rectum

of man, pig, Amphibia, body cavity

of Polych?etes ; Balantidiopsis Biitschli,

intestine of Rana ; Condylostoma Duj.,

mi. n. numerous, f.w. and m. ; Bursaria,

0. F. Miiller, large size, ma. n. long,

mi. n. numerous, f.w.
Fam. 3. Stentorina. Body elongated. Peristome short and at front end.
Its two edges sometimes prolonged into wings. The adoral spiral passes either
across the front end of the peristome to the right corner of the same, or
completely surrounds the peristomial area. Undulating membrane absent.
The peristomial surface is ciliated and spirally striped. Pharynx tubular.
Climacostomum Stein, f.w.; Stentor Oken (Fig. 31), ma.n. long, mi.n. numerous,
sometimes fixed and with gelatinous tube, f.w.; Folliculina Lam. with peris-
tomial wings, usually inhabits chitinous tubes, f.w. and m.

Fam. 4. Gyrocoryna. Bell-shaped, anterior end rounded, posterior end as
caudal appendage projecting from the bell ; a ventral furrow with cilia, a row of

* ma.n., mi.n. are abbreviations of macro- and micronucleus respectively;
f.w. and m. similarly standing for fresh-water and marine.

FIG. 39. — Paramce-
cium aurelia,after
Ehrenberg. M
mouth ; Cv con-
tractile vacuoles
with canals.

um

coli, with two con-
tractile vacuoles
after Stein. Near
the nucleus lies a
starch grain which
has been eaten ; a
ball of excrement
is passing out per
anum at the hind
end.

CILIATA. 49

cilia at edge of bell leading to mouth at base of appendage. CcenomorpTia
Perty, f.w. and m.

Section 2. Oligotricha.

Never elongated, usually spherical or conical. Peristomial field at front end
and at right angles to the long axis. Adoral row nearly or completely a dosed
circle. Ciliation of body partly well developed, partly much reduced.

Fam. 1. Lieberkuhnina, possibly a young form of Stentor.

Fam. 2. Halterina. Peristomial surface without cilia. Body with few
scattered or no cilia : sometimes with scattered immovable setae. No shell.
Strombidium 01. and L., f.w. and m. ; Halteria Duj., f.w.

Fam. 3. Tintinnoina. Provided with a tubular shell, to the base of which
the body is fastened by a stalk. Adoral row as a circle of large membranellse,
inside which is a row of fine cilia (paroral). Tintinnidium Kent, f.w. and m. ;
Tintinnus Schrank, m. ; Tintinnopsis Stein, m. ; Codonella Hack., f.w. and m.;
Didyocysta Ehrb., m.

Fam. 4. Ophryoscolecina, with thick pellicle, hinder end often with spine-
like processes, deep funnel-shaped peristomial region. Anus terminal, usually
with anal tube. Parasitic in rumen of Ruminants. Entodinium Stein ;
Diplodinium Schuberg ; Ophryoscolex Stein.

Section 3. Hypotricha.

Body dorso-ventrally flattened, ventral surface usually flat, dorsal convex ;
peristomial field usually triangular and in same plane as rest of ventral surface.
Dorsal surface Avithout cilia, but with stiff bristles. The ventral cilia uniform or
in various ways reduced and differentiated. Pharynx little developed or absent.

Fam. 1. Peritromina. Peristome but little marked off from frontal area.
Ciliation of ventral surface close and uniform without differentiation of stronger
cilia or cirri. Peritromus Stein, m. and f.w.

Fam. 2. Oxytrichina. Peristome distinctly marked off from frontal area.
Ventral ciliation in the most primitive forms uniform in oblique longitudinal
rows ; but some stronger cilia are almost always present on the frontal area
(frontal cirri) and at the hind end (anal cirri). Usually the ventral cilia are
cirri. A right and left row are distinguished as marginal cirri from the
imperfect median rows which are called ventral cirri (Fig. 41). These rows of
cirri must not be confused with the adoral row of membranellse (a. ) on the left
side of the peristome. There is an undulating membrane on the right side of
the peristomial area (the preoral membrane, Fig. 41 m.)t and in many forms a
row of cilia on the right side of the adoral row (the paroral row, Fig. 41 &) ;
both these structures are, like the adoral row, continued into the pharynx.
Trichogaster Sterki, f.w.; Urostyla Ehrb., f.w. and m. ; Kerona Ehrb., com-
mensal on Hydra; Epiclintes Stein, m. ; Stichotricha Perty, f.w. and m. ;
Strongylidium Sterki, f.w.; HolostichaWrzesu., m. ; Amphisia Sterki, f.w. and
m. ; Uroleptus Ehrb,., f.w. and m. ; Onychodromus Stein (Fig. 41), f.w.; Pleuro-
tricha Stein, f.w.; Gastrostyla Engelm., f.w.; Gonostomum Sterki, f.w. and m.;
Urosoma Kowalewsky, f.w.; Oxytricha Ehrb., f.w. and m. ; Stylonychia Ehrb.
(Fig. 30), f.w. and m.; Actinotricha Cohn, m.; Balladina Kow., f.w.; Psilotricha
Stein, f.w.

Fam. 3. Euplotina. Ciliation much reduced ; the anal cirri are always
present, but the marginal frontal and ventral cirri may be absent ; encuirassed.
Kuplotes Ehrb., f.w. and m. ; Diophrys Duj., m. ; Uronychia Stein, m. ; Aspidisca
Ehrb. (Fig. 42), f.w. and m.

E

50

PROTOZOA.

Section 4. Peritricha.

Cilia confined to an adoral spiral and a posterior circlet which is not always
present. The adoral spiral with the peristomial area is placed at the front
end of the body (except in one family). The mouth, anus, and reservoir of the
contractile vacuole all open into a depression of the peristome called the vestibule.
The peristome and adoral cilia are generally surrounded by a projecting lip-like
ridge.

Fam. 1. Spirochonina. With a peculiar peristomial funnel rolled into a
spiral at the front end. Reproduction by budding near the peristome. Attached

by an adhesive disc at the hind
end. Total conjugation between
small animals with undeveloped
peristome. No. posterior circlet of
cilia. Parasitic on the legs of
Gammarus, Limnoria, Nebalia.
Spirochona Stein.

771

FIG. 41.— Ciliary apparatus of a Hypotrich Onycho-
dromus grandis (from Perrier after Maupas).
a adoral membranellae ; b paroral cilia ; c mar-
ginal cirri ; d frontal cirri ; e ventral cirri ;
/ anal cirri ; m preoral undulating membrane ;
n nucleus ; v contractile vacuole.

FIG. 42. — a, Aspidisca lyncaster,
and b, Aspidisca polystyla dur-
ing fission (after Stein).

Fam. 2. Lichnophorina. Peris-
tome and adoral spiral ventral.
Hind end as a sucker for attach-
ment, and surrounded by the pos-
terior circlet. Ectoparasitic on the
skin of Medusae, Opisthobranchs,
worms, and Asteroids. Liclmo-
phora Clap.

Fam. 3. Urceolarina. Free-swimming, with posterior circlet of cilia, which
encloses an adhesive disc ; without peristomial lip. Trichodina Ehrb., ecto-
parasitic on the skin of fresh-water and marine animals, e.g., Hydra, Planarians,
etc. — also endoparasitic in bladder of fishes and Amphibia. Cyclochccta, Jackson,
on the surface of sponges, gills of Scorpcena and Trigla, etc.; Trichodinopsis
Clap, and L. , in gut and mantle cavity of Cyclostoma.

Fam. 4. Vorticellina. For the most part attached ; without permanent
posterior circlet ; with peristomial lip, which can be closed over the peristome
in a sphincter-like fashion ; a large undulating membrane continued into the
vestibule. In addition to the adoral zone there is an inner circle of cilia cor-
responding to the paroral row of other types ; it extends into the vestibule.

ACINETAKIA. 51

Scypliidia Lachmann, ectopar. ; Gerda Clap, and L., f.w. ; Astylozoon Engelmann,
f.w. ; Vorticella L., with long contractile fibre for attachment, f.w. and m. ;
Carchesium Ehrb., colonial, f.w.; Zoothamnium Ehrb., colonial, f.w. and m. ;
Glossatella Blitschli, attached, but without stalk; Epistylis Ehrb., colonial,
and Ehabdostyla Kent, solitary, stalk without contractile fibre ; OpcrJularia
Goldf. ; Ophrydium Bory ; Cothurnia Ehrb. ; Vaginicola Lam. ; Lagenophrys
Stein, with lorica.

Forms of uncertain position :

Multicilia Cienk., covered by long flagella-like cilia, m. and f.w.; Grassia
Fisch, covered with long cilia, parasitic in stomach of frog and in blood of
Hyla viridis ; Magosphczra Haeckel, free-swimming ciliated forms occurring
in spherical colonies.

SUB-CLASS III. ACINETARIA.

Infusoria with knobbed tentacle-like processes which serve as sucking
tubes. Ciliated in the young state.

These animals are always sedentary in habit, and either free or
attached; when the latter they may be sessile or stalked. They
prey upon the living tissues of other organisms by means of
their tentacles. The latter
are processes of the cor-
tical protoplasm, and are
of two main kinds, con-
necting which there are
intermediate forms : (1) the
so-called prehensile tenta-
cles which taper distally,
although they do not end
in a sharp point, and (2)
the suctorial, which are
cylindrical in shape and

rounded at the end, which FlG- ^--^cineta femuaMquinum Ehrb., sucking the
. body of a small infusorian (Enchelys), after Lachmann.

may even be swollen into T suctorialtentacle ; V vacuole ; N nucleus.

a distinct knob.

The tentacles of both kinds appear to contain a canal which opens
distally to the exterior, and leads at the other end into the central
protoplasm of the body. The fluid or semi-fluid contents of their
prey pass down these canals in a current, the cause of which is not
quite understood. Maupas has suggested that the transparent ecto-
plasm of the Acinetan first passes in an invisible current by the
tentacle into the body of the prey, there absorbs the protoplasm, and
then returns with its burden to its own body in a current which can
be traced by the granule contents of the protoplasm. All tentacles

52

PROTOZOA.

are retractile, and the prehensile do not seem to differ materially in
function from the suctorial.* In their retraction they often become
marked by a peculiar spiral wrinkling of their surfaces — possibly due
to torsion.

Mouth (other than the tentacular pores) and anus are not present.
Contractile vacuoles are present and vary in number. The macro-
nucleus may be elongated or branched, attaining a great extension
and complexity in such a form as Dendrosoma, which looks like a
colony of Acinetans attached to a creeping stolon. A micronucleus
is certainly present in some forms, and probably in all. The body
has a pellicle which is in some cases thickened to form a shell or
theca. The stalk of attachment, when present, is not contractile.

FIG. 44. — Ephelota (Podoplirya) gemmijxtra, after R. Hertwig. o, with extended tentacles
(both prehensile and suctorial) and two contractile vacuoles ; b, the same, with ripe buds
into which processes of the branched nucleus N enter ; c, free young form.

Keproduction takes place in one of three ways :

1. Equal transverse fission; as a result of this the organism
divides into two equal pieces, one of Avhich — the distal — retracts
its tentacles, acquires cilia, and swims away, while the other, or basal
piece, keeps the old attachment and condition. Such reproduction,
in which the products are more or less equal in size, is found in
Hypocoma, Splicaroplirya^ Podoplirya, Urnula, etc.

2. Simple to multiple budding ; this is characteristic of the genus
Ephelota (Fig. 44). One or more buds, each containing a process of

* The prehensile tentacles when present first seize the prey, bring it within
reach of the knobbed tentacles ; but it is by no means clear that they do not
share in the suction act.

ACINETARIA. 53

the nucleus, are formed, and eventually nipped off as free-swimming
ciliated forms.

3. Internal budding is the most common method of increase. It
takes place in Tokophrya quadripartite, as follows : a funnel-shaped
invagination of the apical surface is formed, the opening of which
narrows to a pore. The bud arises from the base of the pit or
brood-pouch so formed, as a projection containing a part of the
nucleus. Eventually the bud becomes constricted off so as to lie
freely in the brood-pouch, acquires some cilia, and escapes through
the opening as the free-swimming young form. In Dendrocometes
the bud is evaginated through the pore before separation, so that it-
forms a projection of the body of the mother. The young are
always ciliated, and the ciliation may be holotrichous, hypotrichous,
or peritrichous. It occasionally happens (Podophrya fixa, etc.) that
a whole individual retracts its tentacles, acquires cilia, and breaks
away as a free-swimming swarmer.

Conjugation of the temporary kind has been observed, and is
probably a general phenomenon in the group. The changes of the
macro- and micronucleus accompanying it seem to be of the same
nature as in the Ciliata.

Encystment is of common occurrence, but its relation to other
vital phenomena is not known. The cyst wall often possesses
annular thickenings.

Fam. 1. Hypocomina. Freely movable, not attached ; with permanently
ciliated ventral surface and one suctorial tentacle. Hypocoma Gruber, m.,
ectopar. on Zoothamnium.

Fam. 2. Urnulina. With one or two (rarely more) tentacles not distinctly
knobbed. Rhyncheta Zenker, freely motile, without theca, on ventral side of
Cyclops ; Urnula Clap, and L., attached and with theca, on stalk of Epistylis.

Fain. 3. Metacinetina. With stalked funnel-shaped theca, the walls of
which are perforated by slits for the exit of the knobbed tentacles. Metacineta
Biitschli, f.w.

Fam. 4. Podophryina. Tentacles numerous and usually considerable, on the
whole surface or only apical, either all distinctly knobbed, or some of them
without knobs serving as prehensile tentacles. Spcerophrya Clap, and L.,
without stalk, endoparasitic in Ciliata; Endosphcera Engelm., Podophrya Ehrb ,
stalked, with knobbed similar tentacles from all parts of body ; Ephelota
Wright (Fig. 44), tentacles both knobbed and pointed, chiefly from free end,
m. , on Hydroids, Polyzoa, and Crustacea ; Podocyathus Kent, like the last, but
Avith theca.

Fam. 5. Acinetina. Stalked, or with stalked or unstalked theca with
simple opening. Tentacles numerous, all alike, and usually distinctly knobbed.
Tolcophrya Biitschli ; Acineta Ehrb. (Fig. 43). stalk continued as theca ; Soleno-
phrya Clap, and L., theca sessile.

Fam. 6. Dendrosomina. Without stalk or theca. Tentacles numerous, all

PROTOZOA.

alike and knobbed, arranged in tufts, which may be numerous and placed at
the ends of branch-like lobes. Trichophrya Clap, and L., Dendrosoma Ehrb.,
large animal resembling a colony, with branched macronucleus extending
throughout the body.

Fam. 7. Dendrocometina. Sessile, with numerous knobbed tentacles on
branched arms or over the whole free surface. Attached by the whole basal
surface or by a part of it. Dendrocometes Stein, gills of Gammarus pulex ;
Stylocometes Stein, on gill-plates of Asellus aquaticus.

Fam. 8. Ophryodendrina. With short or long stalk, tentacles rarely
distinctly knobbed, and borne by one to several proboscis -like processes of
the body. Ophryodendron Clap. and*L.

Class III. SPOROZOA.*

Parasitic Protozoa
which reproduce by spore-
formation. Nutriment is
taken up in the liquid
state. In most, probably
in all, the young stages at
least are intracellular in
habit.

The Sporozoa are found
in all the great groups of
animals except the Proto-
zoa and Coelenterata. In
the young state at least
they live embedded in the
protoplasm of their host,
into which they make
their way when hatched
out from the minute
spores. They are there-
fore described as intra-
cellular parasites. In
some forms they remain

within the cell throughout life, but more often they outgrow
the cell and come to lie free in the tissues or spaces of the body.
They live entirely on the nutritive juices of their host, and their
power of movement is limited. Some have little or no power of

* Balbiani, Lecons sur Us Sporozoaires, Paris, 1884. Biitschli, "Sporozoa,"
in Bronn's Klassen u. Ord. d. Thierreiches, 1880-82. L. Pfeiffer, Die Protozoan
als Krankheitserreger, ed. 2, Jena, 1891, and Nachtrdge, Jena, 1895. Idem,
Die Zellerkrankungen etc. durch Sporozoen, Jena, 1893. V. Wasielewski,
Sporozoenkunde, Jena, 1896.

FIG. 45.—Gregarines (after Stein and Kolliker). a,
Stylorhynchus oligacanthtis from the intestine of
Calopteryx; b, Gregarina (Clepsidrina) polymorpJia,
from the intestine of the meal-beetle, two forms in
" association " ; c, two forms of the same in conju-
gation ; d, encystment completed ; e, sporulation ;
/, cyst with completely formed spores (pseudo-
navicellse).

SPOROZOA. 55

changing their form, while others are amoeboid. They vary much
in size, some not exceeding ten micromillimetres in length, while
others may attain a length of sixteen mm. The protoplasm
usually exhibits a differentiation into ectoplasm and endeplasm,
and the endoplasm is often highly granular — a feature which
becomes more marked with the age of the individual.

Conjugation occurs in some groups (Gregarinida, Drepanidiidia,
etc.), but has not been observed in all.

Reproduction is effected by the division of the protoplasm into
spores, which may be coated or naked. In most cases encystment
precedes sporulation, but in some of them the spores are produced
gradually during the ordinary life of the individual. In the
Gregarinida and Coccidiidea the spore-protoplasm divides to form
the young forms. In others the whole spore becomes the young
form. There is often a little residual protoplasm — generally non-
nucleated — left over after the sporulation. The young which issue
from the spores are either falciform or amoeboid.

In Gregarinida and Coccidiidea the sporulation usually takes place
after the cyst has left the host (exogeny), but in the other forms
it is effected within the host (endogeny).

A process which may or may not be analogous to the formation of polar
bodies of the metazoan ovum (or speaking more generally, to the reduction-
divisions of the progametes) has been observed by Wolters in Gregarines (Arch.
Mic. Anat. Bd. 37) and by Labbe (loc. cit.) in Coccidia. The nucleus divides ;
one half remains in the animal, while the other passes to the surface and
disappears. This phenomenon precedes the fusion of the nuclei in the con-
jugating gregarine, and sporulation in the Coccidia.

In Gregarinida and Coccidiidea the cysts pass out with the faeces
and enter another host in its food. In the other orders the method
of transference from host to host is not certainly known, but
probably in some cases the spores are not able to leave the host
until its death, after which they may enter a new host in the food ;
while in other cases it is possible that the infection is transmitted
by blood-sucking insects, or through the lungs in dust.

It is possible that there may be — in the exogenous forms at least
— some other mode of reproduction besides that of spore-formation.
Very little is known on this head; but unless there is some other
reproductive process, it is difficult to see how in exogenous forms,
such as Coccidium oviforme of the rabbit, the enormous number
of individuals which characterise acute coccidiosis is produced. It
is also probable that in some cases, e.g., the forms which live in

56 PROTOZOA.

blood, there is an intermediate host, or that the spores have the
power of developing and living outside the body.

As a general rule they do not inflict serious damage on their
hosts; but in some cases they are very injurious, and may cause
death. This is sometimes due to the destruction of large tracts of
cells or of great numbers of blood corpuscles. Whether in such
cases the injury is due to any other cause than merely eating out
the cell, such as the production of an injurious substance as the
result of their vital activity, is not known. In some endogenous
forms, e.g., Myxosporidia, in which the spores cannot escape from
the host, extensive tumours may be formed.

In the classification of the class adopted in this work, the blood -parasites
have been united in the order Hcemosporidia, and the Coccidiidea have been
separated from the Gregarinida. It is very probable that these three orders,
which are more closely allied to each other than to the other two orders, should
be united in one group.

Order 1. GREGARINIDA.*

Parasitic Protozoa which are embedded during the whole or a part
of their lives in the protoplasm of their hosts. They are without
mouth or anus, and they usually reproduce by coated spores. Cilia
and pseudopodia are absent.

The Gregarinida live as parasites in the alimentary canal, and
in the tissues of most animals. They are not found in Protozoa,
Coelenterates, or Vertebrata. In the young state they lie entirely
within the protoplasm of a cell of their host, usually an epithelial
cell of the intestine ; but as they grow older and increase in size
they project from the cell, to which they remain attached for a
time. Eventually they become free, and lie in the cavity of the
intestine or other organ of their host. The body is generally
elongated in a vermiform manner, and consists of a granular semi-
fluid endoplasm containing a nucleus, a thin external layer of clear
ectoplasm, and a thick external cuticle. Hooks for attachment,
and hair-like processes may be present as modifications of the
cuticle. The structure of the body may be complicated by the
presence of a partition wall dividing the endoplasm into an anterior
portion called the protomerite, and a posterior — the deutomerite.
The partition consists of a prolongation of the ectoplasm, and the

* Aime Schneider, " Contributions a 1'histoire des Gregarines des Invertebres
de Paris et de Roscoff." Arch, de Zool. exper. et gen., torn, iv., 1875 ; and in
various succeeding volumes of the same Journal. O. Biitschli, " Protozoa," in
Bronn's Klassen und Ordnungen d. Thierreichs, 1880-2.

GREGARINIDA. 57

nucleus lies in the deutomerite. In such forms there is generally
a small third division of the body in front of the protomerite
called the epimerite. It contains a small quantity of endoplasm,
and is the part of the body by which attachment to the cell-Jiost
is effected. When the animal loses this attachment and lies free
in the alimentary canal the epimerite disappears.

The epimerite varies much in form, and bears appendages of very
different kinds (hooks, spikes, filaments, etc.). It is usually found
only in septate forms (with a proto- and deutomerite), but occasionally
it is present on the front end of a monocystid (non-septate) form.

Occasionally after detachment from their cell-host they penetrate
the gut-wall, and form cysts which project into the body-cavity —
these are known as the body-cavity forms ; but as a rule they lie
freely in the alimentary canal.

Free Gregarines — particularly the Polycystid (septate) forms —
have a peculiar habit of adhering to one another, end to end, in
rows (Fig. 45). These are the so-called associations of Gregarines.
As many as a dozen may be so joined together. The anterior indi-
vidual of an association is called the primite, the rest the satellites.
The phenomenon has nothing to do with conjugation.

Nourishment is effected by endosmosis through the body-walls, and
motion is confined to a slow gliding forward of the body. The body,
however, has sometimes the power of change of form, though such
change is not of an amoeboid character. It consists rather of a
contraction of the ectoplasm which causes movements of the endo-
plasm, and is not unlike the streaming movements seen in the
Myeetozoa.

In many forms there are longitudinal fibrillar thickenings of the
cuticle, and occasionally a special superficial layer of the ectoplasm
immediately beneath the cuticle is distinguished as the sarcocyte.
The sarcocyte, which is sometimes found only on the anterior part
of the body, may contain a layer of transversely-placed fibres, which
are very possibly contractile in function, and form the part of the
ectoplasm called the myocyte.

Reproduction is effected by the division of the body while in an
encysted condition into spores, and seems generally, if not univer-
sally, to be preceded by conjugation of two or more individuals.
The procedure is as follows : two (rarely more) individuals apply
themselves together in various ways, and gradually flatten out against
one another so as to form a rounded syzygium. In some cases,
after remaining in this condition for some little time, it appears

58 PROTOZOA.

that they separate and encyst separately. As a rule, however, they
remain together, and a cyst-wall is secreted round the syzygium ; but
even in this case the fusion of the conjugating individuals does
not appear always to be complete, for the line between them can
frequently be seen until the spore-formation has begun. In Diplo-
cystis and Gamocystis conjugation occurs very early, so that it is
rare to find any but very small forms not united with another in
conjugation. This precocious conjugation may take place some time
before encystment. The internal processes accompanying conjugation
have not been thoroughly made out, but it appears that the nuclei of
the conjugating pair meet in the bridge of protoplasm which connects
the two bodies, and there fuse to form a zygote-nucleus. This divides
and gives rise to a number of nuclei, which travel to the surface and
are budded off with a certain portion of the protoplasm as the small
rounded spores. The protoplasm of the syzygium is more or less
used up in this process, but there generally appears to be a certain
amount (residual protoplasm) left over, unchanged, in the cyst. The
uninucleated spores acquire a chitin-like coat, which has often a
spindle-shaped, oval, or oblong form, and in this condition are called
pseudonavicellce.* The contents of the pseudonavicellse divides longi-
tudinally into a number, generally six to eight, of sickle -shaped
structures called the falciform bodies, and into a small amount of
residual protoplasm, which disappears. The falciform bodies on the
bursting of the cyst and the solution of the spore-case become young
Gregarines. It thus appears that the young Gregarines arise by the
division of the spore -protoplasm. When first liberated from the
case, the young often perform active serpentining movements and
make their wray into a cell of their host (generally a new host,
but in endogenous sporulation it may be the same host, see below),
in which they increase in size, until they grow too large for the
cell and project into the neighbouring space. Eventually they
become detached and lie freely in the organ they infest — alimentary
canal, testis, kidney, or whatever it may be. Some of the forms
are only known in the full-grown free condition, and we cannot
therefore be certain that they are intracellular in habit in the
young stage. The spores escape by the bursting of the cyst, or in
some cases through sporoducts which are formed in the protoplasm
of the syzygium and everted through perforations in the cyst-wall.

As a general rule conjugation precedes the formation of the cyst,
but encystment of solitary forms and subsequent sporulation has been

* In Porospora gigantea of the lobster the spores are naked.

COCCID1IDEA. 59

observed. It is possible, however, that such solitary forms have
escaped from conjugation.* The division of the cyst-contents into
spores in Polycystids usually takes place outside the body of the
host after evacuation with the faeces (exogenous sporulation) ; bttjx in
the Monocystids and body-cavity forms, sporulation is endogenous,
i.e., it takes place in the body of the host. In the latter case the
spores may either be evacuated and produce their germs in a new
host, or the germs may be hatched out in and reinfest the same host.

Endogenous cysts found in organs which do not communicate with the exterior
can only set free their spores for a new host after the death of their host. The
body-cavity cysts are found only in insects, and mainly in females, which often
die after laying their eggs.

Sub-order 1. MONOCYSTIDEA.

Without differentiation of the body into protomerite and deutomerite, etc.
Generally of considerable size ; when full grown lying free in the body-spaces of
their host. The protoplasm after encystment breaks up into spores, each of
which becomes coated and divides into several falciform bodies. Conjugation
appears to be general. Monocystis Stein, elongated, one end with cuticular
hairs, sporulation incomplete ; body-cavity, gut, and testis of earthworm ;
Gamocystis Stein, cyst with gelatinous coat and sporoducts, intestine of Blatta
lapponica and Ephemerid-larvse ; Conorhynchus Greef, almost always in syzygial
condition, gut of Echiurus ; Gonospora Schn., like Monocystis, Annelids,
Urospora Schn., like Monocystis, gut of Nemertines, body-cavity of Sipunculus,
testis of Tubifex.

Sub-order 2. POLYCYSTIDEA (SEPTATA).

With differentiation of the body into protomerite, deutomerite, and sometimes
epimerite. Other characters as in Monocystidea. In alimentary canal of Arthro-
poda. Dufouria Schn., Colymbetes larva ; Bothriopsis Schn., various Dytiscidse ;
Porospora Schn., Homarus ; Stenocephalus Schn., Julus ; Hyalospora Schn.,
Thysanura ; Euspora Schn., Melolontha larva ; Clepsidrina (Gregarina)
Hammersch. (Fig. 45), various insects ; Pileocephalus Schn. ; Eckinocephalus
Schn., Lithobius ; Stylorhynchus Schn. (Fig. 45), Opatrum, Asida, Blaps ;
Actinocephalus Schn., Coleoptera, Locusta, Sciara larva.

Order 2. CoccroiiDEA.f

Minute Gregarine-like forms which mainly infest epithelial cells,
and do not outgrow their cell-host. They produce falciform young.

This is a provisional division to include certain small oval parasites
with' a single nucleus found in the cells of various animals. They
have so far been found in Vertebrates, Arthropods, and Molluscs.
They bring about the destruction of their cell-host, and those which

* According to Leger there is a Gregarine in the body-cavity of Glycera which
produces spores without encystment.

t A. Labbe, "Recherches sur les Coccidies," Arch. Zool. Exp. (3), 4, 1896.

60

PROTOZOA.

infest the epithelium of the alimentary canal may cause the death of
their host. They encyst within the cell which they inhabit, and
their protoplasm gives rise to coated spores. Conjugation is un-
known, and there are no cuticular structures until the cyst-wall is
formed.

The cyst-wall may be thin, in which case sporulation takes place in the same
host, and the germs (falciform bodies) are set free to reinfest the same host
(endogenous sporulation), or it is thick and double-contoured, in which case the
cyst, on the breaking down of iffe cell-host, falls into the alimentary canal and
is ejected with the faeces. In the latter case the sporulation (exogenous) takes
place outside the host, and the germs are set free after the spores have entered ;i
new host.

FIG. 46. — Coccidiwn oviforme from the liver of the rabbit (from Wasielewski, after Balbiani).
a and b, young cocciclia in epithelial cells of the bile duct, the cell-nucleus lies in the upper
process of the cell host ; c, encysted form ; d and e, contraction of the protoplasm to a
sphere ; y, h, i, spore-formation ; k, ripe spore with two falciform young and a residual body.

In some Coccidiidea only one spore* is produced; in such cases the whole
animal becomes the spore, and its cyst-wall the spore case. In the rest the
contents of the cyst divides into two or more spores (leaving as usual a residue)
which acquire cuticular coats. In all cases the contents of the spore gives rise
to the falciform bodies (one or more, leaving a small unused residue) which
are the germs or young.

Tribe 1. Monosporea. The whole contents of the cyst forms only one spore,
and the spore has no spore-case distinct from the cyst- wall. Orthospora A. Schn. ,
spore with four falciform bodies, intesc. epithelium of Triton; Eimeria, Schn.,
numerous falc. bodies, intest. epithelium of mouse, frog, fishes, myriapods, etc.

* The archespore of Labbe seems to be merely the spore before the formation
of the spore-case. The sporozoites are the bodies which proceed from the spore ;
they are called in the text falciform bodies, and are the young forms. In
Labbe's nomenclature a spore which produces one falciform body is called
monozoic ; that which produces two falciform bodies is called dizoic, and so on
to polyzoic.

H.EMOSPORIDIA.

61

Tribe 2. Oligosporea. Cyst produces but few spores. Cyclospora Schn.,
iutest. epithelium of Glomeris, and the cat. Coccidium Leuck., in each of the
four spores only two falciform bodies ; in cells of the intestine and liver of
mammals, birds, reptiles, amphibia, and fishes ; C. oviforme Leuck. (Fig. 46),
epithelium of bile-duct and intestine of rabbit.* J

Tribe 3. Polysporea. With many spores. Klossia Schn. , about sixty spores
each with four to six falc. bodies ; kidney Helix, Succinea, and Neretina ;
Minchinia Labbe, spores with two long filaments, in liver and connective tissue
of Chiton ; Barroussia, Schn., each spore with one falc. body ; Adelea Schn., in
intestinal epithelium of Lithobius forficatus.

Order 3. H^EMOSPORIDIA.

Minute intracellnlar parasites
/('hich mainly infest the corpus-
cles of the blood. The spores
are naked and do not sub-divide.

The Hcemospwidia, like the
Coccidiidea, never become so
large as to outgrow their cell-
host ; but they differ from
them in possessing naked spores.
Moreover the spores do not
sub-divide, but become directly
transformed into the young
forms.f It is not known how
they leave their host or how
they enter new hosts.

Sub-order 1. DEEPANIDIIDIA.

The Drepanidiidia infest the blood-corpuscles and are found in Amphibia,
Reptilia, and Aves. They have not yet been found in fishes and mammals,
or in invertebrates. They were discovered by Ray Lankester £ in the frog.

They are small uninucleated gregarine-like creatures which infest the red
blood-corpuscles (rarely the white blood-corpuscles and cells of spleen, liver,
and kidney) of their host. They cause the destruction of their cell-host, from
which they pass to live for a time freely in the blood. They then enter
another blood-corpuscle, secrete a cyst-wall, and break up into elongated oval

* This forms an exogenous cyst, and it is a question how the rabbit becomes
infested with the innumerable coccidia which are present in acute coccidiosis.
It has been suggested that these coccidia reproduce in two ways — the one by
exogenous sporulation as described in the text, and the other endogenously
in the cell-host by the direct breaking up of the coccidium into numerous
falciform bodies without the formation of spores, or by its simple division.

t This statement perhaps requires qualification, for in some of the Acysto-
sporidia — the so-called two-spored forms — the nucleus of the form about to
sporulate divides into two, and gives rise to two centres of spore-formation.
(See below.)

£ Vide Quart. «7. Mic. Sci., xi., 1871, and ibid., vol. xxii., 1882.

FIG. 47. — Dunilewskya lacazei from the lizard,
a, three free forms with gregarine-like
appearance, fresh ; b, after treatment with
gold - chloride and hsematoxylin, showing
myocyte-fibrillae.

62

PROTOZOA.

bodies which are naked and do not further sub-divide. These constitute the
young form, and may be compared to the spores of the other forms. They are
set free in the blood on the breaking down of the cell-host, and soon enter
another corpuscle, wThere they acquire their full size. They then leave the
corpuscle and enter upon the stage described above, during which they live freely
in the blood. They have been observed to conjugate completely in pairs in this
free stage. In the free state they move either by serpentine bending of the body
or by wave-like contractions of the body substance. It is not known how they
are transported to a new host.

Drepanidium Lankester, Rana^ Aves ; Karyolysus Labbe, Lacerta ; Dani-
lewskya Labbe, Lacerta, Cistudo, Rana.

FIG. 48. — a-c, red blood-corpuscles of the frog infected with Drepanidium princeps; d, free
forms in movement (from Wasielewski after Labbe).

Sub-order 2. ACYSTOSPORIDIA.*

These are amoeboid cell-parasites, found only in vertebrata (except fishes and
reptiles). They do not form a cyst-wall. They mainly infest red blood-
corpuscles, but are also sometimes found in the kidney, liver, and intestinal
epithelium. They cause hypertrophy of the corpuscle and a diminution of its
haemoglobin.

The Acystosporidia are specially interesting, because they include forms
wrhich are associated with some important diseases in certain of the larger
mammals, e.g., malaria in man and Texas-fever in cattle. They are minute
amoeboid organisms, with a nucleus and pigment-grains (Fig. 49). They never
leave their cell-host, and their movements, which are always amreboid, take
place within the cell. They readily undergo degenerative changes in prepara-
tions of the blood of infected animals. These changes consist in the disruption
of their corpuscular host and in the thrusting out of vibratile processes, which
break off from the body (Fig. 50) : this is the so-called Poly mitus- form.
Finally the body itself breaks up.

They reproduce in their cell-host by the formation of minute spores without
encystment. They first assume a rounded form ; the nucleus then breaks up
(so-called one-spored forms) into a number of minute fragments, around which
a portion of the protoplasm becomes segregated (Fig. 51) ; these small nucleated
fragments constitute the naked spores of the animals. In some cases the
nucleus divides (so-called two-spored forms) into two before breaking up, so

* A. Labbe, "Parasites endoglobulaires. " Arch. Zool. exper. (3), 2. Laveran,
L' Hematozoaire du paludisme, Paris, 1891. J. Mannaberg, Die Malariaparasiten,
Vienna, 1893.

ILEMOSPORIDIA.

63

that two groups of spores are formed. The spores are generally ampeboid, but
in Karyophagus they are sickle-shaped. They pass into the blood, and then
enter other blood-corpuscles.

How these organisms are carried from host to host is not known ; but j£ has
been suggested that they may be taken into the lungs in dust, and be carried
by parasitic insects and ticks. It
appears certain that the organism
associated with Texas-fever is carried
by a tick, Boophilus bovis.*

Fam. 1. Acystidae. Epithelial para-
sites which form falciform germs.
Karyophagus Steinhaus, amphibia.

Fam. 2. HaemamcebidEe. Mainly
in blood - corpuscles ; form amoeboid
germs. Halteridium Labbe, with two
spores, birds, health unaffected ; Pro-
teosoma Labbe, with one spore, birds,
produces fever and may cause death ;
Hcemamoeba Grassi, with one spore,
man, occurs in two forms, the one
amoeboid (variety tertiana), and the
other semilunar and immovable (vari-
ety quaterna). H. laverani Labbe

(Figs. 52, 53), discovered in 1880 by Laveran in the blood of malaria patients,
causes destruction of the red corpuscles, period of development of germs 48-72
hours. Golgi showed the connection between the attacks of fever and the
development of this parasite ; Dadylosoma Labbe and Cytamosba Labbe. in
fiana esculenta ; Apiosoma bigeminum Smith, associated with Texas-fever in

FIG. 49. — Cytamceba bacterifera, from the
blood of Rana esculenta (from Wasielewski,
after Labbe). a, amoeboid form with long
movable p.seudopodia ; b, rounded form
with numerous spores.

FIG. 50.— Successive stages or degeneration (Polymitus-form) of Halteridium danilewskyi,
from the blood of the lark ; I, c stages with vibratile flagella ; in d these are being cast
off (after Labbe).

cattle, infection carried by ticks, amoeboid organisms in the red blood-corpuscles,
high fever, anaemia, bloody urine, the number of red blood-corpuscles is dimin-
ished in one week to one-sixth.

Babesia bovis Babes, in blood of the ox, causing hfemoglobinurea ; Aincebo-
sporidium polyphagum Bonone, associated with Icterus -heematuria of the
sheep, are probably allied here.

Th. Smith, Centralbl. Bakt. Parasitk. 13, 1893, p. 511.

64

PROTOZOA.

Order 4. MYXOSPORIDIA.*

Multinucleated, amoeboid sporozoa parasitic in the cells, tissues, or
spaces of animals. The spores possess polar capsules and fibres.
The contents of the spores do not divide, but issue as amosboid young.

These are the so-called fish-psorosperms of J. Miiller. They are
parasitic in worms, arthropods, polyzoa, and vertebrates. They

a b

Fio. 51. — Proteosoma grassii Labbe, from the blood of a finch. Sporulation of the one-spored
parasite, a, showing the parasite in the corpuscle ; b, showing the parasite broken up into
spores (after Labbe).

FIG. 52.—Hcemamceba laverani, variety quaterna, from the blood of a man with malaria
(after Labbe). a, newly-infected blood-corpuscles ; b, c, d, successive stages in the growth
of the parasite in the corpuscle ; e, beginning of sporulation ; /, rosette-shaped group of
spores round a central residual body ; g, spores (young forms) set free in the blood by the
breaking up of the corpuscle.

Fio. 5S.—Ha;mamceba laverani, variety tertiana, from the blood of a man with malaria.
a, young parasites in a corpuscle ; b, amoeboid form ; c, rounded form ; d, sporulation ;
e, free spores (after Labbe).

have attained some notoriety from the fact that the organism (Glugea
bombycis), which causes the Pefrrm-disease of silk-worms, belongs to
the order.

They include two principal varieties, viz., those which lead a free
life, creeping about on the surface of the gall-bladder, urinary
bladder, and kidney tubes (Fig. 54), and those which are embedded

* R. R. Gurley, "The Myxosporidia, or Psorosperms of fishes and the
epidemics produced by them." Hull. U.S. Fish Commission, Part 18, 1894.
P. Thelohan, "Recherches sur les Myxosporidies." Bull. Sci. de la France et
Belgique, 26, 1895.

MYXOSPORIDIA.

65

iii the tissues. The tissue-forms occur either in cysts, which are
often visible to the naked eye, or in an infiltrated form, and they
may infest almost any tissue (bone, cartilage excepted).

It is not quite clear to
what extent they are cell-
parasites. Many of them
are certainly intracellular
in the young state, and it
is possible that all may be
so j but the youngest stages

have not been studied in ?.?

all forms. Sporulation in
the intracellular forms may
begin in the quite young
forms, even before they
have outgrown their cell-
host. The Myxosporidia
differ from other Sporozoa
in their tendency to cause
tumours in their host.
They may cause serious
diseases : the silk - worm
disease has been referred
to, and they have been
known to cause serious
mortality among fishes.

Those which lead a free
life are amoeboid and vary
much in shape (Fig. 54).
The shape of the cysts and
of the infiltration -forms
depends upon the physical
condition of the tissues.

The Myxosporidia, though amoeboid, do not take up solid food,
but resemble other Sporozoa in absorbing the nutritive juices of
their hosts. The body shows a division into ecto- and endoplasm.
The nuclei are numerous and lie in the endoplasm, which contains
granules and fat-drops.

Reproduction takes place by spore-formation. They differ, however, from
other Sporozoa in the fact that the whole body does not break up into spores at
one time, but the spores are formed gradually in the endoplasm while the parent

F

7

5^_Leptotheca ^lis as a type 01 free.living Myxo

sporidia, from the gall-bladder of Trygon vulgaris
ps pseudopodia ; g fat-drops ; r refractile granules ;
S2> spores (after Thelohan).

66

PROTOZOA.

still continues to grow and to move. When a spore is about to be formed, a
small spherical mass of endoplasm containing one nucleus is marked off from
the rest by a delicate membrane ; it thus constitutes an ovum-like body lying
in the endoplasm. It is called a primitive sphere (Fig. 55) ; its nucleus gradually
divides, karyokinetically, into ten nuclei, and it then itself divides into two parts,
each of which contains three of the ten nuclei of the primitive sphere ; the four
remaining nuclei together with a portion of protoplasm forms a small residual
body, which soon disappears (cf. the residual bodies of other Sporozod). The
two trinucleated bodies thus formed are the sporoblasts ; they are enclosed in
the membrane of the original primitive sphere, which soon thickens into a
resistent spore-case. Each sporofxlast divides into three cells (Fig. 55e), of
which one gives rise to one spore, and the other two to the two polar-capsules
(Fig. 55/). The polar- capsules are formed in and at the expense of the protoplasm
of the polar-capsule cells, which wholly disappear in the process. The polar-
capsules are ovoid bodies containing a long spirally-coiled thread (Fig. 56), which
is everted with considerable force when the spore is acted upon by the digestive

FIG. 55.— Spore-formation of Myxdbolus (after Thelohan). a, primitive sphere with nucleus,
a little endoplasm of the parent is shown ; b, stage with six nuclei, and c, with ten nuclei.
d, division of primitive sphere into two sporoblasts a and b, each with three nuclei, and a
residual body with four nuclei n ; e, division of one of the sporoblasts into two smaller
capsule-forming cells op, each with a vacuole, and a larger cell (the spore) g. f, formation
of polar-capsules.

juices of the animal which swallows it. It is probably everted with such force
that it pierces the wall of the alimentary canal, and thus effects the attachment
of the spore to its new host (Fig. 56). The spore-case bursts in the course of
twenty-four hours after this attachment, and the contained germ makes its
way as an amoeboid form through the intestinal wall and migrates to the tissue
in which it is to live.

In the case just described, which is that of the genus Myxobolus, each primitive
sphere gives rise to two spores ; but in some cases only one spore results, and in
others three or more are formed. In the tissue-forms a considerable number of
spores proceed from each primitive sphere.

The species are distributed by the spores, which are carried to the exterior,
or when this is impossible, as in the case of the tissue-forms, are set free on the
death of their host.

MYXOSPORIDIA.

67

Fam. 1. Myxididae. Spores variously formed with two polar-capsules;
includes the forms least degenerated by parasitic life. Principally in gall-
bladder and kidney tubes of fishes and amphibia. Leptotheca Thelohan (Fig.
54), gall-bladder or kidney of various fishes and amphibia; Ceratomyxa, Thel.,
gall-bladder of fishes ; Sphcerospora Thel., kidney-tubes of fishes, S. Regans
Thel., kidney- tubes and ovary of stickleback ; Myxidium Butschli, M. lieberkuhni
Butschli, urinary bladder of pike ; Sphceromyxa Thel. ; Myxosoma Thel.

abed
FIG. 56.— Polar-capsules of Myxobolus
ellipsoides. a, polar -capsule with
spirally-coiled thread ; b, c, d, eversion
of the fibre (after Balbiani).

a b

FIG. 57.— Spores of Myxobolus ellipsoides
(after Balbiani), showing polar-cap-
sules in b the threads are everted.

FIG. 5S.—Glngea bombycis (after Balbiani). a, ripe >pore ; b, c, hatching o. amoeboid young ;
d, e, growth stages ; /, g, h, sporulation ; i, testis-follicle of silk-worm caterpillar, strongly
infested with Glugea ; A;, I, two infected stomach-epithelial cells of the caterpillar of Attacus
(Saturnia) pernyi ; k, beginning of infection ; I, the cell is completely filled with spores.

68

PROTOZOA.

Fam. 2. Chloromyxidae. Spores with four polar-capsules. Chloromyxum
Mingazzini : C. incisum Gurley, gall-bladder Raja batis.

Fam. 3. Myxobolidae. Almost all tissue-parasites, principally gills, spleen,
etc., of fishes ; one or two polar-capsules. Myxobolus Blitschli (Figs. 55-57);
M. piriformis Thel., gills, spleen, kidney of the tench (Tinea vulgar is) ; M.
dispar Thel., gills of Carp (Cyprinus rutilus) ; Henneguya Thel. ; H. psoros-
permica Thel., gills, eye-muscles, ovary of pike; H. media Thel., kidney
and ovary of stickleback.

Fam. 4. Glugeidae. "With very small oviform spores, having at the broad
end a non-colourable vacuole, atf the narrow end a polar-capsule usually
invisible. Glugea Thel., mainly tissue -parasites ; Gl. bombycis Thel. (Micro-
sporidium bombycis Balb.), in all tissues of Bombyx mori, is the cause of the
Pebrine disease of silk-worms (Fig. 58), which between the years 1854-67 caused
the loss of one milliard francs to the French silk-worm industry ; combated

by microscopical examination of eggs
and rejection of those infected (Pasteur
and Balbiani) ; Gl. bryozoides Korot-
neff, sexual organs and body-cavity of
Alcyonella fungosa ; Pleistophora Gur-
ley; Thelohania Henneguy, muscles
of Palfemon, Crangon, Astacus; Th.
contegeani Hen., muscles of Astacus
fluviatilis.

Order 5. SARCOSPORIDIA.*

Cylindrical intracellular para-
sites infestintj the striped mus-
cular fibres of certain vertebrates.
These are the so-called Mi-
scher's tubes, the contents of
which are known as Rainey's
Corpuscles (Fig. 59). They con-
tain a number of more or less
spherical bodies, which divide
up into still smaller bodies — the
germs. These latter become
sickle-shaped and appear to con-
stitute the young. Very little
is known about this group. We
are ignorant of the manner in which the transference from host
to nost is effected, and of the young stages of infection.

* Bertram, "Beitrage z. Kennt. d. Sarcosporidien. " Zool. Jahrb. Abth: f.
Anat., 5. Ai. Schneider, " Ophryocystis biitschlii." Arch. Zool. Exp. (2), 2,
1884.

FIG. 59.— Rainey's Corpuscles from the flesh
of a pig. a, an animal inside a muscle-fibre ;
b, posterior end of same strongly magnified ;
C cuticle ; B spores.

SARCOSPORIDIA. C9

Sarcocystis Lankester, in the muscles of pig, sheep, gecko. Sarcosporidia
have been described in man, cat, dog, mouse, rat, hare, rabbit, ox, deer,
horse, etc.

The Amasbosporidia and Serosporidia may be taken here. The Amcebosporidia
are multinucleated amoeboid forms, which conjugate, encyst, and prodrfce one
coated spore. The spore divides into eight falciform young; they may also
increase by dividing directly ; they live in the Malpighian tubules of some
beetles. Ophryocystis A. Schn. in Blaps, and Akis. The Serosporidia are long
oval parasites which infest the body-cavity of some Crustacea. They increase
~by direct division, and by encysting without conjugation and subsequent
breaking up into numerous amoeboid young. Serosporidium L. Pfeiffer, in
Cypris, Daplmia, and Gammarus.

CHAPTER II.

•

THE METAZOA.

ALL animals above the Protozoa have been classed together as
Metazoa, and possess the following characters in common : —

There is always more than one nucleus, and the nuclei are for
the most part arranged with a definite relation to the functional
tissues.

Conjugation always takes place, but the structure is so complex
that conjugation between the ordinary individuals of the species
is impossible. Consequently special individuals — the gametes — are
produced for the purpose of conjugating. These individuals, which
have a very similar form throughout the group, are simple in
structure and unicellular in character; there are always two kinds
of them in every species, called respectively ova and spermatozoa.
They arise by a process of unequal fission from their parent, and
may both be produced by one individual or by different individuals.
When they are both produced by the same individual, that indi-
vidual is said to be hermaphrodite. When they are produced by
different individuals, that parent which produces the ova is called
the female, while that which produces the spermatozoa is called the
male; and the individuals are said to be unisexual and the species
dioecious. The conjugating individuals, or gametes, produced by
the male never have the power of assuming the ordinary form of
the species, and though they have, as a rule, the power of inde-
pendent locomotion, soon die unless placed in the most favourable
circumstances. The gametes produced by the female, on the other
hand, while they are without the power of locomotion and have a
rather greater power of independent life, are in rare cases capable
of becoming more complex in structure, and of assuming the form
of the adult. To females which produce such ova the term partheno-
genetic is applied. In the vast majority of cases, however, the ovum
has not the power of changing its form and of developing into

METAZOA. 71

the ordinary form of the species unless it first conjugates with the
spermatozoon. The zygote so produced is uninuclear, and has the
property of developing into the ordinary form of the species. This
method of reproduction, in which a new individual arises from the
combination of two independent individualities in the zygote, is
called the sexual method of reproduction, as opposed to the asexual
method, in which a multinucleated mass is separated off from the
parent with the power of assuming more or less directly the ordinary
form of the species. The asexual method, though common in the
vegetable kingdom, is comparatively rarely found amongst animals
(Coelenterata, Polyzoa, Tunicata, Annelida, etc.).

It thus appears that the Metazoa may be defined as —
Animals in which the ordinary (so-called adult) form of the species
has always more than one nucleus, and in which the nuclei are for
the most part arranged regularly and with a definite relation to the
functional tissues of the animal (so-called cellular arrangement).
Special conjugating individuals of the form of ova and spermatozoa
are always formed.

CHAPTEE III.

PORIFERA.*

THE Porifera present a great variety of external form. They
may be cup-shaped, saucer-shaped, tubular, rod-shaped, foliaceous,
trumpet -shaped, fan- shaped, mushroom -shaped, lobed, digitate,
branched, or irregular, etc. (Figs. 60-62.) As a general rule, the
form is extremely variable even in the same species, and is therefore
of little use in identification. They are almost, if not quite, always
attached to foreign objects; this may be effected by a broad basal
surface, or they may be stalked. In some cases they are rooted
in sand or in mud by basal processes or by special rooting spicules.
With the exception of the fresh-water Spongillidai, they are marine,
and are found at all depths. One family — the Clionidce — bore into
shells and stones.

As the name implies, the surface of the body presents a large
number of pores, which are minute in size and inhalent in function.
These pores lead into a system of channels which, after permeating
almost the whole body, open to the exterior by one or more — but
always a few — larger exhalent openings called oscula. This system
of spaces connecting the inhalent pores with the exhalent oscula is
the canal system. Through it there passes — maintained, as we shall
see, by ciliary action — a continual stream of water, which enters by
the inhalent pores and passes out through the oscula. The sponge
is covered by an epithelial layer which we may call ectoderm ; the
canal system is lined by an epithelium, which as we shall see is
usually partly ectoderm and partly endoderm ; but the main mass
of the body is formed of a soft tissue which we shall call mesoderm.
The mesoderm consists of a gelatinous basis (though no gelatine has
been detected in it), containing a protoplasmic network holding

* For principal literature see classes and orders. R. Hanitsch, " Revision of
the generic nomenclature and classification in Bowerbank's 'British Spongiadae.'"
Proceedings and Transactions of the Liverpool Biol. Soc., vol. 8, 1893, p. 173.

PORIPERA.

73

nuclei, and presenting differentiations of various kinds-^— so-called
muscle cells, amoeboid cells, generative cells, scleroblasts {spicule-
forming cells). The mesodermal network is continuous both with
the ectoderm and with the endoderm ; indeed, these layers>may
fairly be regarded as superficial bounding expansions of the meso-
dermal mass. Skeletal structures, the main function of which is

FIG. 61. — Euspongia qfficinalis adriutica, with a number of
oscula, 0 (after F. E. Schulze).

FIG. 60.— Amnella polypvides
(after O. Schmidt).

FIG. 62.— A branched Ascon-colony (after Haeckel).

to support the sponge-body, are contained in the mesoderm. These
may be calcareous or silicious, in which case we get the so-called
sponge-spicules ; or they may consist of a horny material called
spongin (common bath sponge, Fig. 63); or finally, spongin fibres
and silicious spicules may co-exist. The generative cells are budded
off from the mesodermal network, and are eventually dehisced into

74

PORIFERA.

some part of the canal system, whence they are carried to the
exterior.

It is probable that all the protoplasmic tissues of the sponge are
contractile, i.e., both the epithelial layers and the mesodermal net-
work; but special structures in the course of the inhalent and
exhalent parts of the canal system have been described as muscular
sphincters. Ectodermal cells carrying hair-like sensory projections
have been described; these,, like other epithelial structures, are
connected below with the mesodermal network, parts of which
have therefore been interpreted as nerve-fibres and nerve-cells; but

PIG. 63.— Piece of network of
horny fibres from Euspongia
equina.

Mes

Fia. 64. — Section through a calcareous sponge (Sycon
raphanus), after F. E. Sch. Ect ectoderm; En
endoderm of a flagellated chamber; Mes meso-
derm ; N calcareous spicule in the mesoderm ;
Eiz ovum.

there is no reason why one part of the network should be considered
as more especially adapted for nervous conduction and reflection than
another. The ectodermal epithelium consists of flat cells; the
endoderm is partly formed of flat cells and partly of somewhat
cylindrical cells, each with a flagellum and collar. These are the
choanocytes (Fig. 64). They are perhaps the most characteristic
constituents of the sponge-body; the collar is a membranous pro-
longation of the cell at its free end round the base of the flagellum ;
and the whole cell resembles an individual of the Choanoflagellata.
It contains one or more contractile vacuoles, and its base is prolonged

PORIFERA.

75

into processes which join similar processes of neighbouring cells and
the mesodermal network. The collared cells are, as a rule, confined
to special parts of the canal system called the flagellated or ciliated
chambers. Their main function is, no doubt, to cause the curreT>t of
water which is continually flowing through the sponge. Ciliated
epithelium is not found in the Porifera, though in some sponges
(Oscar ella lolularis, Plaldna monoloplia, etc.) the ectoderm cells
carry flagella.

We may now proceed to describe in greater
detail the various parts of the sponge-body.

The simplest form of sponge — we do not say
the most primitive, though it may be so — is
presented by the Ascon type of the order
Calcarea.

The Ascon-person, which is characteristic of
the genus Leucosolenia* consists of a cup- or
vase-shaped animal attached by one end, and
presenting at the other an opening — the oscu-
lum. The walls are thin, and consist of ectoderm
outside, flagellated endoderm inside, lining the
cavity of the cup, and thin mesoderm, containing
triradiate calcareous spicules, between the two.
They are further pierced by numerous pores,
the prosopyles.

In the Sycon-person (Fig. 65), which is
characteristic of the Heterocosla, there is a tube
or cup open by the osculum at one end and
attached at the other. This tube is lined by
flat cells, and gives off all around and through-
out its length numerous short diverticula lined
by flagellated cells. These are the radial flagellated chambers:
they possess, in addition to the one main opening into the cavity of
the central tube, which we may call the gastric cavity, numerous
minute pores — the prosopyles — through which water passes from the
exterior into the flagellated chambers. These radial tubes, in short,
resemble an Ascon in structure, except for the absence of an osculum
at their free end. In the simplest Heteroccela the radial chambers
stand out freely from the central tube, and do not touch at any

* This genus comprises Ascetta primordialis and all Haeckel's Ascons. The
Olynthus is a hypothetical animal imagined by Haeckel, and closely approaching
the Ascon-person in form.

FIG. 65. — Longitudinal
section through Sycon
raphanus, slightly mag-
nified. 0 osculum with
collar of spicules; Rt
radial tubes which open
into the central cavity.

76

PORIFERA.

point (Sycetta). But in the more complex forms the Avails of
adjacent chambers fuse more or less completely where they touch,
and the spaces between them are broken up and called the inlialent
canals or intercanals. These intercanals open by the prosopyles
into the chambers, and outwards on the surface of the sponge
(Sycori). In still more complex forms the outer ends of the
chambers and the openings of the intercanals are covered by a
membrane called the dermal^ membrane or cortex. This cortex is
perforated by numerous pores — the dermal pores — (to be dis-
tinguished from the prosopyles) which lead into the intercanals

FIG. 66. — 1, Diagrammatic section of a Rhagon. H hypophare ; 0 osculum ; G gastral cavity ;

v flagellated chambers ; pi prosopyle (from Perrier, after Sollas).
2, Diagram of a simple form of the Eurypylous type of canal-system. The spongophare is

folded. H hypophare ; G gastral cavity ; o osculum ; i incurrent sinuses ; p dermal pores.

(Grantia, Ute, Sycyssa, Heteropeyma, Amphoriscus, etc.). In this
type the chambers may branch, and the dermal cortex may attain
a considerable thickness, as also may the wall of the central tube
(gastral cortex). A further complication is effected by the retreat
of the flagellated cells towards the distal (outer) ends of the
chambers, their place being taken by pavement epithelium. "We
thus get exhalent canals coming off from the gastral cavity and lined

PORIFERA.

77

by flat cells, together with a reduction in length of the flagellated
chambers (Leucilla uter, Leucandra aspera, etc.). Finally the
chambers are small and spherical and irregularly scattered through
the sponge- wall; the inhalent and exhalent canals being fljuch
developed. This is the Leucon stage of Haeckel and is found in
Leucandra, Leucilla, etc. In the non-calcareous sponges the canal-
system is generally on a somewhat different plan. The simplest
form is the so-called Rhagon type (Fig. 66) found in the embryos of
certain forms (Plakina, Reniera). The Ehagon has the form of a
flattened pyramid, attached by its broad base and opening by the
osculum at its apex. The sac is lined by flat cells, but possesses
on its upper wall a number of small flagellated chambers into which
the prosopyles open. The lower basal wall of the Rhagon, which is

FIG. 67.— Diagram showing the relations of the ectosome. H hypophare; E ectosome ;
I fold of the ectosome roofing over the incurrent sinus ; p-& sieve-plate of dermal ostia
or inhalent pores ; g excurrent sinuses ; v flagellated chambers ; S incurrent sinuses (from
Perrier).

without flagellated chambers, is called the hypophare, and the upper
wall, with the chambers, the spongophare. The openings of the
chambers into the gastric cavity of the Ehagon are called the
apopyles. The Rhagon condition is not found in any adult sponge,
but the nearest approach to it is presented by Plakina monolopha
and Oscarella lobularis, in which the spongophare is folded, so as
to give rise to incurrent sinuses or canals similar to the intercanals
of the Calcarea (Fig. 66, 2).

As a result of this same folding the chambers open, not into the
central or gastral cavity, but into diverticula of it. These diverticula
are the excurrent sinuses. We thus get a modification of the Rhagon
canal-system called the Eurypylous type. As a general rule in the
Eurypylous type, there is concrescence between the folds of the
spongophare, and the openings of the incurrent sinuses are roofed

78 PORIFERA.

over by a membrane (Fig. 67, Z) which is exactly comparable to
the dermal cortex of the Calcarea, and is pierced by inhalent pores
leading into the incurrent sinuses. (Figs. 67, 68.) This membrane
is called the ectosome, as opposed to the rest of the sponge, which
contains the chambers and is called the choanosome ; and the
incurrent sinuses beneath it constitute the subdermal cavities, which,
as is obvious, correspond to the intercanals of the Calcarea. By
further folding of the spongophare and suppression of chambers on
the main excurrent sinuses an increase in complexity is obtained.

In the Eurypylous type the chambers open directly into the
excurrent sinuses ; but in many sponges they are removed from
the surface of the latter, and the apopyle of each of them is pro-
longed into a canaliculus — the aphodus — lined by a prolongation of
the epithelium of the excurrent sinus into which it opens. Further,

FIG. 68.— Diagram of a section ot the outer part 01 Tetilla <pedifera (after Sollas, from Perrier).
C choanosome ; E ectosome ; i incurrent sinus; v flagellated chamber ; g excurrent sinus.

there is only one prosopyle to each chamber. This is the Aphodal
modification of the Khagon type (Stelletidae, Geodinidae, etc.).

Finally there is the Diplodal chamber system (Fig. 69), in which
there is a canaliculus leading to the prosopyle of each chamber —
the prosodus — as well as an aphodus leading from it (Cho?ulrosina,
Corticium candelabrum, etc.).

In Eurypylous sponges the ectosome never attains any special development ;
but in other types it becomes greatly thickened and histologically differentiated,
and is called the cortex. In such cases the tubes leading through the cortex
from the sieve-pores to the subcortical (subdermal) cavities are called chones,
and are provided at some part of their course with a muscular sphincter, the
velum. The inhalent pores may be diffuse or collected into pore-areas forming
the so-called sieve-plates.

Histology. There is but little to add to the statements in the
general account. The most remarkable feature is the flagellated
cells or choanocytes. They are larger in the Calcarea than in most

PORIFERA.

79

other sponges. They present the feature of projecting into the
chambers without contact with their neighbours.

It was supposed that in life their collars were everted so as to touch the
collars of neighbouring cells and form a continuous thin membrane lining the
chamber ; but this has been shown to be a post-mortem phenomenon.

The mesoderm contains many tissue elements which are all con-
nected together, and are embedded in a kind of gelatinous basis.

To revert to the language of the cell theory, those cells of this tissue, to
which no special function can be assigned — such as reproduction, contraction,
skeletal formation— vary somewhat in their arrangement, and so give rise to
different forms of mesoderm ; we may mention Collcnchyme with scattered stellate
cells ; Sarcenchyme gelatinous basis reduced, and granular cells closely packed ;
Cystenchyme with vesicular, vacuolate cells close together or separated by a
matrix ; Chondrenchyme like hyaline cartilage.

There are also pigment cells, fusiform connective tissue cells, muscle cells as
granular fusiform cells round the
openings of the water-canals.

Spicules originate in one cell, or
more than one cell may be asso-
ciated in their production (Lithis-
tida). It has been recently stated
that three cells are concerned in
the formation of the triradiate
spicules of the Calcarea, and that
they are derived from the ectoderm
(Minchin).

The ectoderm is composed
of flattened cells, though the
cell limits are not always dis-
cernible. In some sponges at
least the cells of the ectoderm
seem to be capable of assum-
ing, when contracted, a mush-
room shape.

The ingestion* of food and foreign bodies by sponges is effected by
the collared cells, and probably also by the flat cells of the inhalent
and exhalent canals, and of the surface ectoderm of the body. From
these the solid bodies pass into the subjacent mesoderm cells, this
transit being probably effected by protoplasmic flow along the strands
connecting the surface epithelia with the subjacent tissues, in very
much the same manner as food passes along the pseudopodial network

* Fide E. Metschnikoff, " Spongiologische Studien." Z. f. w. Z., Bd. xxxii.
p. 372. A. Dendy, "Studies on the Comparative Anatomy of Sponges."
Q. J. M. S., vol. xxxv. p. 216.

FIG. 69. — Section of Corticium candelabrum (after
F. E. Sch.). Gk flagellated chamber, with
prosodus leading to it and aphodus from it.

80 PORIFERA.

into the body of a Foraminiferan. But although the choanocytes
may have this ingestive capacity, their main function is probably to
cause currents through the canal system.

The question of the ingestion of solid food by sponges has been much disputed.
There can be no doubt that solid bodies are introduced into the mesoderm cells,
for apart from the fact that foreign bodies such as sand-grains, etc. are found in
the mesoderm cells and spongin fibres of many sponges, Metschnikoff and
other observers have found carmine particles in carmine-fed sponges. It is not,
however, certain that the flat epith^elia co-operate with the choanocytes in this
introduction. Metschnikoff (loc. cit., p. 372) states that Halisarca, when
overfed with carmine, loses its canals and becomes a mass of amoeboid cells
containing swallowed matter and surrounded by a common envelope of ectoderm.
The same fact has been observed by Lieberkiihn* in Spongilla in winter. From
these observations, and others by Haeckel and Carter, it appears that under
certain nutritive conditions the cboanocytes may lose their flagella and collars
(according to Topsent and others these structures are retractile like the pseudo-
pods of an Amoeba) and become amoeboid, and the whole sponge may revert to
the condition of the larva of Aplysitia (F. E. Schulze, Z. f. w. Z. xxx. PI. 24,
Fig. 30), of a protoplasmic network with nuclei at the nodes surrounded by
a cortical layer of ectoderm.

The collared cells are thus inconstant, and appear to be merely parenchyma
cells specially modified and capable, under certain nutritive conditions, of passing
back to their original form. When they vanish the canal system also goes, and
the sponge becomes solid so far as the latter is concerned. Inasmuch as the
parenchyma cells and the ectoderm cells are all connected by their processes
(except in the cases in which they break away and become amoeboid), it is clear
that the sponge in this condition, and in the case of Schulze's larva already
referred to, is but little more than a multinucleated Protozoon, differing from
the latter in the greater development of the vacuoles of the central portions, and
in the presence of a distinct cortical layer of nuclei.

Skeleton. Skeletal structures are found in almost all sponges
(absent in certain Hexaceratina and Carnosa\ and are of considerable
importance in the classification. They may consist of calcareous
spicules, of silicious spicules, or of spongin. Spongin is a horny,
substance, resembling silk in chemical composition. It is usually
found in the form of fibres connecting together the silicious spicules
(many Monaxoriida), or forming the entire skeleton (Ceratosa). In
a few cases it is present as separate horny spicules (Danoinella).
In the Ceratosa, and probably in other sponges, it is secreted in
concentric layers by a number of mesodermal cells, called spongoblasts,
which are found coating the fibres (Fig. 70). In some cases the fibres
enclose foreign bodies, such as sand grains. In the Monaxonida the
amount of spongin present is, roughly speaking, inversely propor-
tional to the number of spicules, and there are all variations between

* "Beitrage zur Entw. d. Spongillen." Mullens, Arch., 1856.

POEIFERA.

81

forms with no spoiigin and forms with no spicules in the spongin
fibres (C&ratosa). Which is the primitive condition — if either is—
it is impossible to say. The Ceratosa are an artificial order, its
families being related to different families of the Halielwndrina.
It may, indeed, be looked upon as an assemblage of halichoriarine
forms, in which the reduction of silica and development of spongin
have reached their extreme limits. The calcareous and silicious
spicules are secreted in the protoplasm of the mesodermal network ;
Sderoblast is the term applied to the special uninucleated part of
the network in which they arise. They consist of an organic axis
which is generally continuous through the points of the spicules
with the adjacent organic structures, and of an organic sheath which
is presumably a remnant of the parent
scleroblast. The silicious spicules are
formed of opal (colloid silica).

The spicules are of two kinds — the
large spicules or megascleres (essential
spicules of Bowerbank, skeletal spic-
ules of Carter), and the small spicules
or microscleres (auxiliary spicules of
Bowerbank, flesh spicules of Carter).
The megascleres (Figs. 71, 72, and
78) are embedded in spongin fibres
which may be either reticulate or
radiating in arrangement ; or if there
is no spongin, they are held together
by strong connective tissue bands.
In addition there is usually a number
of megascleres scattered irregularly

through the tissues. In the Litliistida the spicules which are called
desmas are articulated together so as to form a network. The micro-
scleres (Fig. 73), which are not really sharply distinguishable from the
megascleres — for the two pass into one another — do not, as a rule,
take part in forming the supporting skeleton ; they are embedded in
the mesoderm and sometimes project into the canals. The spicules
near the surface of the body are often differently arranged to those
of the main skeleton. It is well known that some sponges shed
an immense number of spicules; and it appears that in many cases
the spicules are continually being moved towards the surface, where
they are cast off, and replaced by spicules formed in the central
parts of the sponge.

FIG. 70. — Spongin-fibre of Euspongia
irregularis (from Perrier). 11, f axial
medulla of the fibre ; sp spongo-
blasts.

82

PORIFERA.

The spicules of sponges in the diversity, symmetry, and intricacy
of their form, in the perfection and finish of their architecture,
constitute some of the most astonishing objects in natural history.
In view of them it is impossible to regard sponges as low in the
scale of evolution : such finish and such perfection of structure can
only have been reached as the result of a long process of evolutionary
changes. While it is pretty clear that the main function of the
skeletal structures is the support and protection of the sponge body,
it is by no means easy to gfve explanations of the diversity and
complexity of form which they present. The form of the megascleres
is probably connected with the form of the canal system, with which
they are in relation (F. E. Schulze) ; but the form and even the

existence of the micro-
f scleres defies any reason-
able explanation. By some
spongologists the small
spicules are regarded as
functionless, and as having
on that account a greater
value for classificatory pur-
poses. However this may
be, all classes of skeletal
structures are utilised in

classification, and although no single character is by itself of much
use for this purpose, the form of the microscleres is perhaps as
important as the form of the megascleres.

It is therefore necessary to consider in some detail the forms of
sponge spicules.

MEGASCLERES.

There are five principal kinds of megascleres : (1) Monaxons — rod-like megas-
cleres ; (2) Tetraxons — megascleres with four axes, proceeding from a central
point, with four rays ; (3) Triaxons— megascleres with three axes crossing at right
angles, with six rays ; (4) Polyaxons — megascleres with several axes ; (5) Spheres
— megascleres in which growth is concentric about the origin.

Each of these classes contains many varieties, the most important of which
must be dealt with.

I. Monaxons, megascleres in which growth is directed from a single origin in
one or both directions along a single axis. The ray or rays of a monaxon are
called actines.

1. Khabdus, growth proceeds in both directions along the axis — hence
diactine. The principal varieties of Rhabdus are as follows : —

With similar ends :

a. Oxea — needle-shaped, pointed at both ends (Fig. 72, 7).

b. Tornote — abruptly pointed at each end (8).

FIG. 71.— Calcareous spicules (triods) of Sycon.

MEGASCLERES.

83

c. Strongyle — rounded at each end (9).

d. Tylote — knob-like thickening at each end (10).
With dissimilar ends :

e. Strongle-oxea — oxeate externally.

f. Tylotoxea ,, ,, (Fig. 72, 12). ';

g. Oxystrongyle ,, internally.

h. Oxytylote ,, „ (Fig. 72, 11).

i. Oxydad — externally ends in two or more secondary actines or cladi.

k. Strongylodad — ectactine cladose.

1. Tylodad ,, ,,

The two latter have generally three cladi, in which case we have the character-
istic spicule of the Tetractinellida, the Triaene.

The Triaene consists of the rhabdome, or shaft, and the cladome, which consists
of the three cladi, a straight line joining the ends of the tAvo cladi is the chord.
The sagitta is a perpendicular from the origin of the cladome to the chord.

12 rt

9 10

(!)

FIG. 72. — Megascleres of the Monactinellida and of the Tetractinellida. 1, plagiotrisene ;
#, G, protrisene ; 3, 5, anatrisene ; k, dichotrisene ; 7, oxea ; 8, tornote ; 9, strongyle ; 10,
tylote ; 11, oxytylote ; 12, tylotoxea ; 13, style ; Ik, 15, 16, desmas (after Sollas, from Perrier).

Varieties of Trisene :

a. Anatricene (anchor) — cladi directed backwards (Fig. 72, 3, 5).

b. Protricene (Fig. 72, 2, 6),\

c. Plagioiricene (Fig. 72, 1), lcladi dil'ected forwards at different angles with

j the rhabdome.

d. Orthotricene

e. Dichotricene — cladi dichotomous (Fig. 72, Jf).

f. Trichotricene — cladi trifurcate.

g. Phyllotricene — with lamellar cladi, found only in Lithistida.

h. Discotricene — cladome is a disc in which the separate cladi are not dis-
tinguishable ; only in Lithistida.

i. Amphitricene — both ends of rhabdome end in a trisene.
k. Centrotricene — the cladi arise from the centre of the rhabdome.

84

PORIFERA.

2. Stylus, growth proceeds along the axis in one direction only — hence
monactine :

a. Style — strongylote at origin (Fig. 72, 13).

b. Tylostyle — tylote at origin.

Desmas (Fig. 72, 14, 15, 16) are megascleres which form the skeletal network
of the Lithistida. They are usually formed by the deposition of successive
layers of silica upon an ordinary spicule — the crepis — the axial rod of which

is arrested in development.
When the crepis is a mo-
naxon we get a rhabdocrepid
desma, and when a tretraxon
the desma is called tetra-
crepid.

II. Tetraxons are mega-
scleres with four actines
inclined at an angle of
about 110° to one another.
Growth proceeds in one
direction only along each
of the four axes. There are
two kinds : (a) the calthrops,
when all four actines are
present ; and (b) the triod
(Fig. 71), when one actine
is suppressed, the remaining
three lying in one plane.
The triod is characteristic
of the calcareous sponges.

III. The Triaxons (Fig.
78) are megascleres with six
actines, consisting typically
of a system of three equal
axes intersecting at right
angles. They are character-
istic of the Hexadinellida.

IV. Polyaxons are mega-
scleres with several axes
proceeding from a centre.

V. Spheres are mega-
scleres in which growth is
concentric round a central
point.

Firfc 73. — Microscleres (from Perrier, after Solla.s). 1,
globule ; 2, 3, sig.ma spires ; k, 5, 7, sigmas ; 6, micro-
triod ; 8, transition between sigina and microtriocl ; 9,
toxa ; 10, spirula ; 11, microstrongyle ; 12, spiraster ;
13, amphiaster ; K, metaster ; 15, 16, plesiaster ; 77,
chiaster ; 18, spiraster ; 19, samidastcr ; 20, anthaster ;
21, microxea ; 22, oxyaster ; 23. microxea ; 24, micro-
: triod ; 25, orthodragina ; 26, nionolophous microcal-
throps ; 27, dilophous microcalthrops ; 28, simple
niicrocalthrops ; 29, elongated sterraster ; 30, trilo-
phous niicrocalthrops ; 81, tetralophous microcalthrops ;
32, spheraster •; 33, cen-trotylote ; 3k, sterraster ; 35,
candelabrum ; 36, pycnaster ; 37, microstrongyle.

MICROSCLERES.

Microscleres (auxiliary spicules of Bowerbank, flesh spicules of Carter) are of
two chief kinds (Fig. 73).

1. Spires are - microscleres with a spiral twist. There are many varieties, of
which we may mention :

a. Sigmaspire — a C- or S-shaped spicule according to the aspect (#, 3).

b. Sigma — a C-shaped spicule, not spirally twisted (5, 6, 7).

c. Toxa — a> bow-shaped spicule, not spirally twisted (9).

MICROSCLERES.

85

d. Chela — a more or less curved shaft, bearing at each end a variable number
of recurved processes.

2. Asters are multiactinate microscleres. There are two chief kinds ; (A)
asters or euasters, in which the actines proceed from a centre, and (rp strept-
asfcrs/in.which the actines proceed from an axis which is usually spiraiV

A. Euasters are in many varieties ; but of these we need only note the
sterr aster \\i\ which the actines are numerous and soldered together by sub-
sequently deposited silica, which extends almost as far as their extremities (29).
Other varieties are the chiaster (17), the pycnaster (36), the oxyaster (22), and
the spheraster (32).

•Fie. 74.— Development of Sycon raphanus (after F. E. Sch.). a, ripe ovum ; ft, stage with
four segments ; c, stage with sixteen segments ; d, blastosphere with large dark granular
cells at the open pole; e, free-swimming larva, one half of the body (endodermal) being
formed of long ciliated cells, the other (ectodermal) of large granular cells.

B. The Streptasters are also various. There are the spiraster (12), the
metaster (14), the plesiaster (15, 16), the sanidaster (19), and the amphiaster (13).
In the amphiaster the actines form a whorl at each end of the axis, which is
straight.

C. Reduced asters, in which the actines are few and variable. Thus we get
microrhabds, microcalthrops (26-31), microtriods (24). There are several varieties
of the microcalthrops depending on the branching of some of the actines.
Thus there is the monolophous microcalthrops (26) with one cladose (branched)
actine, the dilophous (21), trilophous (30), and telralophous (31) microcalthrops
with two, three, and four cladose actines. The candelabrum (35) is a tetralophous

86

PORIFERA.

microcalthrops, in which one actine differs from the three others, which are
similar to one another. The bacillus of Carter is a microstrongyle.

Bhaphides are long hair-like microscleres not in sheaves.

Dragmas are microscleres, several of which are secreted in a single cell or
scleroblast. They lie in sheaves.

Trichodal is a term applied to any hair -like spicule.

Sexual reproduction was first demonstrated with certainty by
Lieberkiihn for Spongilla, but more recently has been shown to

exist throughout the

V\ !\ / , group. In most cases

A S the ova and sperma-

tozoa seem to reach
maturity at different
times in the same
sponge. The sperma-
tozoa have a small
head, and lie in small
spaces lined with
cells. The ova, like
the mother - cells of
the spermatozoa, are
modified cells of the
mesoderm. They are
naked amoeboid cells,
and are fertilised and
undergo their first
development in the
mesoderm. They

leave the sponge by passing into the canal -system as ciliated
larvae, which after a brief free-swimming life attach themselves and
develop into a young sponge.

An invaginate gastrula is sometimes formed (Sycon, Oscarella, Fig. 76), in
which case it is observed that the Sponge-larva attaches itself by the blastopore
surface, and develops the osculum as a new formation. In other cases a solid
morula is formed. The recent important researches of Delage* have shown that
the mode of development first revealed by the researches of F. E. Schulze in the
Calcarea is found throughout the group. According to the results of these
observers it appears that the locomotive cells of the larva, which are the first
differentiated tissues (Fig. 74e), become internal and transformed into the
flagellated cells of the endoderm, while the other cells, more or less indifferent
in the larva, become transformed into the ectoderm and mesoderm of the adult.

Asexual reproduction is found throughout the Porifera. The presence of

FIG. 75.— Young Sycon (after F. E. Sch.). 0 osculum, or
exhalent aperture ; P pores (inhalent) of the wall.

" Embryogenie des Eponges etc." Arch. Zool. exper. et gen. Tom. x., 1892.

DEVELOPMENT.

87

more than one osculum is often regarded as a case of incomplete budding.
More unequivocal cases are, however, furnished by the external budding found
in Thenea, Tethya, Lophocalyx, Polymastia, Oscarella, etc., and the internal
budding, known as the formation of gemmules, found in fresh- water and ki^ome
marine sponges (Topsent). Gemmules are masses of parenchyma cells containing
yolk grains and surrounded by a shell composed of a thick cuticular layer, to
which silicious structures are often added. The shell possesses an aperture or
micropyle, and the whole structure is to be regarded as a portion of the mesoderm
cut off from the rest of the sponge. In Spongilla the shell contains the
characteristic spicules known as amphidiscs (Fig. 78, 9).

That the power of asexual increase and repair of lost parts is probably a
widespread phenomenon in the group is indicated by the fact that sponges can
be propagated by artificial fission. It has been attempted, with a certain amount
of success, to utilise this property for the purpose of increasing the number of

Fio. 76.— Sections through three stages of the development of Halisarca (Oscarella) lobularis
(after C. Heider). a, gastrula after its fixation ; b, formation of mesoderm ; c, development
of the osculum (Os.), and of the flagellated chambers ; E, inhalent pore.

marketable sponges in the Mediterranean and in other sponge-growing seas.
The marketable sponges belong to the species Euspongia officinalis, the Turkey
or Levant sponge ; Hippospongia equina, the horse sponge ; and Euspongia
zimocca, the zimocca sponge. They occur all along the Mediterranean coast to
a depth of 200 fathoms, and in many other parts of the world. The sand found
in new sponges is an adulteration to increase the weight.

Sponges are found all over the world and at all depths of the
ocean. One family only (Spongillidce) is found in fresh-water. The
Tetractinellida are found in deep and shallow water; but when in
deep water, generally near land. The Monaxonida, which comprise
by far the greatest number of living sponges, also cling to the land ;
while the Hexactinellida, though found in the middle of the great

88 PORIFERA.

oceans, are more numerous near the land. The HexacMnellida are
mainly deep-water forms, the characteristic depth being between
200 and 1000 fathoms. For the Tetractinettida the characteristic
depth is 50 to 200 fathoms, though they are also found in shallow
water. The Calcarea and Ceratosa are mainly shallow-water forms
(to a depth of 200 fathoms). The Monaxonida, though character-
istically inhabitants of shallow water, are found in considerable
numbers at all depths. The deep-sea Monaxonida are distinguished
by their symmetrical and definite shapes.

All spongologists agree as to the immense difficulty of classifying
sponges. Not only are the boundaries of the great groups difficult
to lay down, but the limits of species, and even of genera, often
defy definition. Almost all characters are highly variable, and the
number of intermediate forms and of collateral affinities is immense.
On the whole we may distinguish three main types, which we shall
exalt to the dignity of classes — not because they deserve that rank,
for they do not; but because the term fits in more conveniently
with the terminology generally used for the group. The three
classes are as follows : —

Calcarea. With calcareous spicules and large choanocytes.
Order 1. Calcarea.

Triaxonia. With triaxonic (sex-radiate) spicules and large flagel-
lated chambers.

Order 2. Hexadinellida.

„ 3. Hexaeeratina.

Demospongise. Without triaxonic spicules ; with small choano-
cytes and ciliated chambers ; skeleton of silicious spicules or spongin,
or both combined.

Order 4. Tetradinellida.
„ 5. Carnosa.
„ 6. Monaxonida.
„ 7. Ceratina.

While these groups stand out fairly sharply, their division into
sup-groups, or orders, as we must call them, is fraught with some
difficulty. This is particularly the case with the Demospongice,
which include the great majority of living sponges.

The sub-divisions of the Demospongiae must be regarded as entirely artificial,
and only to be established for the convenience of the student. The four orders
into which we have divided the class are by no means sharply marked off from
one another, nor do they form a single series, but rather three or four series
running parallel to one another, and connected together at several points. In

CALCAREA. 89

fact, if we had to set forth in a pictorial manner the true affinities of the
families of this sub-class, we should be obliged to use a network or, better still,
a sponge work, rather than a tree or a line, because so many of the families
present affinities of apparently equal importance in more than one direction.
And this applies with equal force to genera and species. If this vittf of a
reticular arrangement rather than that of a tree arrangement were generally
held, we feel assured that a good many of the difficulties of sponge classification
would be disposed of. It is the genealogical tree idea which makes the difficulty.

Fossil sponges are found in various formations, e.g., in the chalk,
and these remains appear to differ considerably from those now
living. The Hexadinellida, however, agree so fully with the ancient
forms that they might be direct descendants of them. Finally many
of the principal groups extend back into the palaeozoic age, in which
the Lithistida and Hexactinellida especially are found in the most
ancient Silurian strata.

Class I. CALCAREA.*

Sponges with a calcareous skeleton and large choanocytes.

Order 1. CALCAREA.
With the characters of the class.

Sub-order 1. HOMOC(ELA.

Calcarea without flagellated chambers ; the internal surface entirely lined by
collared cells.

Fam. 1. Asconidae. Gastric cavity a simple sac. Leucosolenia Bow.

Polejaeff and Dendy both unite
all Homoccela in one genus, for
" the spicules of the Calcarea,
being very variable in every direc-
tion, could not serve as a basis
for the distinction of genera."
Haeckel's genera therefore go.
Dendy distinguishes three sections
of the genus: (1) Olynthus types
which do not form colonies, or, if
they do form colonies, in which
the individuality of the members
of the colony (Ascon- persons) is
always recognisable (Fig. 77); (2) FIG. 77.-Section through an Ascon-colony,

colonies the members of which diagrammatic (after Haeckel).

anastomose and form a network ;

(3) colonies consisting of a central Ascon tube from which other tubes are
radially budded off.

* A. Dendy, "A Monograph of the Victorian Sponges," part 1. Transactions
of the Royal Society of Victoria, vol. 3, part 1. A. Dendy, "Observations on
th

e Structure and Classification of the Calcarea Heteroccela." Q. J. M. £., vol.
,
vol.

35, 1893, p. 159. N. Polejaeff, "Report on the Calcarea." Challenger Jieports,
l. 8, 1883.

90 PORIFERA.

Sub-order 2. HETEKOCCELA.

Calcareous sponges in which the collared cells are confined to more or less well-
defined flagellated chambers.

Fam. 1. Leucascidae. Flagellated chambers branched, opening into exhalent
canals which converge towards the oscula ; their outer ends covered over by a
dermal poriferous membrane. Skeleton of irregularly scattered radiate spicules.
Leucascus Bendy.

Fam. 2. Sycettidae. The blind outer ends of the flagellated chambers pro-
jecting freely on the surface and not covered by a dermal cortex. Chamber
skeleton articulate. Sycetta H. ; Sycon Risso ; Sycantha Lendf.

Fam. 3. Grantiidae. With poriferous dermal cortex covering the chamber
layer ; without subdermal sagittal triradiates. Chamber skeleton varies from
regularly articulate to irregularly scattered. Grantia Fleming; Ute O.S.;
Utella Dendy ; Anamixilla Pol. ; Sycyssa H. ; Leucandra H. ; Lelapia Gray ;
Leucyssa H.

Fam. 4. Heteropidae. With poriferous dermal cortex ; with subdermal
sagittal triradiates. An articulate chamber skeleton present or absent.
Grantessa Lendf. ; Heteropia Carter ; Vosmceropsis Dendy.

Fam. 5. Amphoriscidae. With poriferous dermal cortex ; conspicuous sub-
dermal quadriradiate spicules with inwardly directed apical rays are present.
Heteropegma Pol. ; Amphoriscus H. ; Syculmis H. ; Leucilla H.

Class II. TRIAXONIA.

With triaxonic (sex-radiate) spicules and large flagellated chambers.

Order 1. HEXACTINELLIDA.*

Sponges with very loose soft parts, and with silicious spicules which
are either isolated or united into a connected framework, and belong
or are reducible to the triaxial system. Canal system simple, with
syconate chambers.

In the Hexactinellida the ectoderm is a thin layer containing
nuclei, but without discernible cell outlines. The lining cells of
the flagellated chambers project into the cavity of the chamber,
and stand some distance apart from one another. Their bases are
connected by basal strands which are apparently processes of the
cells themselves. No flagella or collars have so far been detected,
but there can be but little doubt that they exist as in other sponges.

The spicules contain a central canal filled with a soft granular
substance which is continuous with adjacent structures through
openings at the end of the rays. These are closed when the spicule
has ceased to grow. The spicules (Fig. 78) typically consist of a
system of three equal axes intersecting at right angles, and variations
in this type are due to the unequal development or branching of

* F. E. Schulze, "Report on the Hexactinellida." Challenger Reports,
vol. 21, 1887.

TRIAXONIA.

91

the rays, or to the suppression of some of them. The variations
in the form of spicule may be classed in six main groups — hexacte
(Fig. 78, 2\ pentacts, tetracts, triacts (7), diacts, and monacts.
The spicules when united are generally bound together by df-fine
laminated silicious substance.

FIG. 78. — Spicules of Hexactinellida. 1, an auto-gastral pinulus of Sympagella nvx; 2, hexact
of Holascus fibulatus to which are applied small diacts ; 3, pinulus of Caulophacus latus ;
t>, pentact pinulus of Hyalonema lusitanicum ; 5, discohexact of Tcegeria pulchra ; 6, disco-
hexacter of Dictyocalyx gracilis ; 7, triact of Hyalonema gracilis ; 8, scopula of Eurete semperi ;
9, amphidisc of Hyalonema Sieboldii. (From Perrier after Schulze.)

Prostalia are the spicules which occur over the outer surface of the sponge.
They are of three kinds : basalia or rooting spicules, pleuralia at the sides,
and marginalia round the osculum.

Dermalia are spicules in relation with the bounding membrane of the sponge,

92 PORIFERA.

and are of two kinds : autodermalia in the dermal membrane, and hypodermalia
beneath the dermal membrane.

Gastralia are spicules on the gastral membrane or membrane lining the
central chamber of the sponge.

Parenchymalia are spicules in the parenchyma.

Dictyonalia are the parenchymalia which become fused to form the con-
tinuous skeletal framework of the Dictyonina.

Synapticula are bridges of silica connecting neighbouring spicules.

Oxyhexacts, hexacts with axes running to a point.

Discohexacts, hexacts with ax§s enlarged at the extremity.

Hexasters, hexacts with axes branching into rays at their extremity.

Pinulus, a pentact or hexact in which one ray bears oblique lateral teeth
or prickles (Fig. 78, 1).

Amphidiscs, a diact at each end of which a convex expansion occurs, which
bears six or more backwardly bent marginal teeth (Fig. 78, 9).

TTncinate, a straight rod, pointed at both ends and beset all over with barbs
pointing in the same direction.

Clavula, a rod which bears at one end a club-shaped or transverse discoidal
expansion.

Scopula, a rod which bears at one end a number of rays.

Sub-order 1. LYSSACINA.

Hexactinellida in which the spicules either remain altogether isolated, or are
in part subsequently and irregularly united by silicious matter or transverse
synapticula.

Tribe 1. HEXASTEROPHORA. Hexasters always present in the parenchyma.
The ciliated chambers are sharply separated from one another, and thimble-
shaped.

Fam. 1. Euplectellidae. Dermal skeleton contains sword-shaped oxyhexacts
with long proximal ray. Euplectella Owen ; Regadrella 0. S. ; Holascus F. E. S. ;
Malacosaccus F. E. S. ; Tccgeria F. E. S. ; Walteria F. E. S. ; Habrodictyum
W. Th.; Eudictyum Marshall; Dictyocalyx F. E. S.; Rhabdodidyum 0. S.;
Rhabdopectella 0. S. ; Hertwigia 0. S. ; Hyalostylus F. E. S.

Fam. 2. Asconematidae. The dermal and gastral skeletons contain pentact
or hexact pinuli. The hypodermalia and hypogastralia are pentacts with
parenchymal discohexasters. Asconema S. Kent ; Aulascus F. E. S. ; Sympagella
0. S.; Polyrhabdus F. E. S.; Balanites F. E. S.; Caulophacus F. E. S.;
Trachycaulus F. E. S.

Fam. 3. Rossellidae. Dermalia always without a distal radial ray. Lanu-
ginella 0. S.; Polylophus F. E. S.; Rossella Carter; Acanthascus F. E. S. ;
Bathydorus F. E. S. ; Rhabdocalyptus F. E. 'S. ; Crateromorpha Gray ; Aulochone
F. E. S. ; Caulocalyx F. E. S. ; Aulocalyx F. E. S. ; Euryplegma F. E. S.

Tribe 2. AMPHIDISCOPHORA. Amphidiscs always present in limiting
membranes. Parenchyma without hexasters. Anchoring basalia always present.
Chambers not thimble-shaped nor sharply marked off from one another, but
forming irregular diverticula of the membrana reticularis.

Fam. 1. Hyalonematidae. Both dermal and gastral membranes contain
numerous pentact pinuli. Hyalonema Gray; Pheronema Leidy; Poliopogon
Wy. Th. ; Semperella Gray.

DEMOSPONGLE. 93

Sub-order 2. DICTYONINA.

Hexactinellida in which the large parenchymal hexacts are from the first more
or less regularly united as dictyonalia in a firmly -connected framework.
Tribe 1. UNCINATAKIA. With uncinates.

A. With clavulce.

Fam. 1. Farreidae. Farrea Bow.

B. With radially disposed scopulce.

Fam. 2. Euretidae. Eurete Carter; Periphragella Marshall; Lefroyella
Wy. Th.

Fam. 3. Melittionidae. Aphrocallistes Gray.

Fam. 4. Coscinoporidae. Chonelasma F. E. S.

Fam. 5. Tetrodictyidae. Hexactinella Carter ; Cyrtaulon F. E. S. ; Fieldingia
S. Kent; Scleroihamnus'W. Marshall.

Tribe 2. INERMIA. Without uncinates or scopulfe.

Fam. 1. Maeandrospongidae. Dactylocalyx Stutchbury; Margaritella 0. S. ;
Scleroplegma 0. S. ; Myliusia Gray ; Aulocystis F. E. S.

Order 2. HEXACERATINA.

Sponges with large and saccular ciliated chambers, with simple
canals. Skeleton composed of soft horny fibres, sometimes accom-
panied by horny spicules. The skeleton may be absent.

Fam. 1. Darwinellidae. Skeleton comprises both horny fibres and horny
spicules. Darwinella Fr. Mliller.

Fam. 2. Aplysillidae. Skeleton is composed of horny fibres only. lanthella
Gray; AplysillaF. E. S. ; Dendrilla Lendf.

Fam. 3. Halisarcidae. Skeletal structures absent ; chambers syconate.
Halisarca Duj. ; Bajulus Lend.

Class III. DEMOSPONGIJE.

Without triaxonic spicules, with small choanocytes and small ciliated
chambers. Skeleton of silicious spicules, or of spongin, or of both
combined.

Order 1. TETRACTINELLIDA.*

Skeleton characterised by tricene or tetraxon megascleres, or lithistid
desmas.

The genus Placospongia, which is without the skeletal characters,
is included here because of the presence of sterrasters which are not
found outside the group.

Sub-order 1. CHORISTIDA.

Tetractinellida in which lithistid desmas are absent, and the megascleres are
never articulated to form a coherent skeleton.

Tribe 1. SIG-MATOPHORA. Microsclere when present a sigmaspire.

* W. J. Sollas, " Report ,on the Tetractinellida." Challenger Reports, vol.
25, 1888. E. Topsent, "Etude Monographique des Spongiaires de France.
I. Tetractinellida." Arch. d. Zool. exper. et gen.^(3) T. 2, 1894.

94 PORIFBRA.

Fam. 1. Tetillidae. The characteristic megasclere a protrisene. Tetilla
0. Schm. ; Chrotella Soil as ; Cinachyra Soil. ; Craniella 0. Schm.

Fam. 2. Samidse. Characteristic megasclere an amphitrisene. Samus Gray.

Tribe 2. ASTROPHORA. One or more of the microscleres is an aster.

Fam. 1. Theneidae. Microscleres are spirasters or amphiasters, and oxyasters
or microxeas. Without cortex. Thenea Gray; Characella Soil.; Pcecillastra
Soil.; Sphinctrella 0. Schm.; Triptolemus Soil.; Stceba Soil.; Nethea Soil.;
Placinastrella F. E. Sch.

Fam. 2. Pachastrellidae. The chief megascleres are calthrops; trisenes
absent. Microscleres may be spirasters, spherasters, or microrabds. Pachastrella
0. Schm.; Derdtus Gray ; Calthrofella Soil.

Fam. 3. Stellettidae. Euasters always present, but never spirasters or
sterrasters. With trirenes; without calthrops. Chamber-system aphodal, and
choanosomal mesoderm sarcenchymatous. Megascleres generally arranged on
the radiate type. Myriastra Soil. ; Pilochrota Soil. ; Astrella Soil. ; Anthastra
Soil. ; Stelletta 0. Schm. ; Dragmastra Soil. ; Aurora Soil. ; Ancorina O. Schm. ;
Tribrachium Weltner; Tethyopsis Stewart; Disyringa Soil.; Stryphnus Soil.;
Ecionema Bow.; Papyrula 0. Schm.; Psammastra Soil.; Algol Soil.

Fam. 4. Geodiidae. The characteristic microsclere is a sterraster. With
trisene megascleres. The sterrasters in the cortex are united together by
fusiform fibrillated cells. Erylus Gray ; Caminus 0. Schm. ; Pachymatisma
Bow. ; Cydonium Fleming ; Geodia Lamarck ; Synops Vos. ; Isops Soil.

Fam. 5. Placospongidae. The characteristic microsclere is a sterraster.
The only megascleres are tylostyles ; triames absent. Often placed with the
Suberitidce (Monaxonid) on account of tylostyles. Placospongia Gray.

Tribe 3. MEGASCLEROPHORA. Without microscleres.

Fam. Tethyopsillidae. Proteleia K. and D.; Tellnjopsilla Lendf.

Sub-order 2. LITHISTIDA.

Tetractinellida provided with a consistent skeleton by the zygosis of modified
spicules or desmas.

Tribe 1. HOPLOPHORA. With special ectosomal spicules, and usually some
form of microsclere.

A. Ectosomal spicules as tricenes. Aphodal.

Fam. 1. Tetracladidae. Desma tetracremd. Theonella Gray ; Discodermia
Bocage ; Racodiscula Zittel ; Kaliapsis Bow Neosiphonia Soil. ; Rimella
0. Schm.; Collinella 0. Schm.; Sulcastrella 0. Schm.

Fam. 2. Corallistidae. Desma monocrepid (i.e., with crepis as monaxon)
and tuberculated. Aphodal. Corallistes 0. Schm. ; Macandrewia Gray ;
Dccdalopelta Soil. ; Heterophymia Pomel ; Callipelta Soil.

Fam. 3. Pleromidae. Desma monocrepid and smooth. Aphodal. Pleroma
Soil.; Lyidium 0. Schm.

B. Ectosomal spicules as microstrongyles or modified microstrongyles (discs}.
Desmas monocrepid.

Fam. 4. Neopeltidae. Ectosomal spicules as monocrepid discs. Neopelta
0. Schm.

Fam. 5. Scleritodermidae. Ectosomal spicules as microstrongyles and the
other microscleres as sigmaspires. Sderitoderma 0. Schm. ; Aciculites 0. Schm.

Fam. 6. Cladopeltidae. Ectosomal spicules as a monocrepid desma highly
branched in a plane parallel to the surface. Microscleres absent. Siphonidium
0. Schm.

CARNOSA. 95

Tribe 2. ANOPLIA. Special ectosomal spicules and microscleres absent.

Fam. 1. Azoricidae. Desmas monocrepid. Azorica Carter ; Tretolophus
Soil.; Gastrophanella 0. S.; Setidium 0. S. ; Poritella 0. S. ; Amphibleptula
0. S. ; Tremaulidium 0. S. ; Leiodcrmatium 0. S.; Sympyla Soil.

Fam. 2. Anomocladidae. Desma acrepid, consisting of a variable number of
smooth cylindrical cladi radiating from a thickened centrum. Zygosis between
the expanded ends of the cladi of one desma and the centrum of another.
Vetulina 0. S.

Order 2. CARNOSA.*

Sponges without megascleres ; microscleres belonging to the tetr axial
type present or absent.

Tribe 1. MICROSCLEROPTERA. Microscleres are variously modified tetrac-
tinose asters, candelabras, or minute triaenes.

Fam. 1. Plakinidae. With tetractinose, triactinose, diactinose asters, and
sometimes mono-, di-, or trilophous candelabra. Chamber-system eurypylous
or aphodal ; mesoderm chiefly collenchymatous. The sponge is divided into a
hypomere and a spongomere. PlaJcina F. E. S. ; Placortis F. E. S.

Fam. 2. Corticidae. Tetractinose asters and candelabras. Aphodal or dip-
lodal. In part sarcenchymatous, in part collenchymatous. Corticium 0. Schm. ;
Calcabrina Soil. ; Corticella Soil. ; Rhacella Soil.

Fam. 3. Thrombidae. Trichotriaenes, and sometimes a peculiar form of
amphiaster. Ectosome thin and not sharply marked off from choanosome.
Diplodal. Mesoderm densely collenchymatous with numerous large granular
cells in addition to collencytes. Thrombus Soil.

Fam. 4. Astropeplidae. With microxeas and asters ; the microxeas are
arranged tangentially to the walls of the canal -system, forming a loose felt ;
eurypylous ; ectosome not a cortex. Astropeplus Soil.

Tribe 2. OLIGOSILICINA. With asters only.

Fam. Chondrillidae. Chondrilla 0. S.

Tribe 3. MYXOSPONGIDA. Without spicules.

Fam. Grumminidae. Chondrosia 0. S. , diplodal rhagon chambers ; Oscarella
Vos. , chambers eurypylous and rhagose.

Order 3. MONAXONIDA.!

Silicious skeleton with uniaxial megascleres.

The Monaxonida are related to the Tetractinellida through the
Astropeplidce on the one]hand, and Plaldna on the other. In fact it
is difficult to see why these forms are placed in separate orders.

Sub-order 1. HALICHONDRINA.

Typically non-corticate ; skeleton usually reticulate ; megascleres usually either
oxea or styli.

Fam. 1. Homorraphidae. Megascleres all diactinal, either oxea or strongyla ;
no microsclera.

* E. Topsent, Arch. Zool. cxper. (3), 3, 1895.

+ Ridley and Dendy, "Report on the Monaxonida." Challenger Reports,
vol. 20, 1887. E. Topsent, " Expose des Principes actuels de la Classification des
Spongiaires. " Revue Biologique du Nord de la France, t. 4. Id., "La classifi-
cation des Halichondrina." Mem. Soc. Zool. France, 1894.

96 PORIFERA.

Sub-fam. 1. Renierinae. Spicules may be enveloped by a small pro-
portion of spongin, but are never completely enveloped in it. Hcdicliondria
Fleming, littoral ; Petrosia Vos. ; Reniera Nardo ; Calyx Vos.

Sub-fam. 2. Chalininae. Spongin plentiful ; spicules enveloped and
united by it. Pachycludina Schm. ; Chalina Grant ; Sipfuniochalina 0.
Schm. ; Cacoclialyna 0. S. ; ChalinorrhapMs Lend. ; Hoploclialina Lend.
Fam. 2. He terorr aphid ae. Megascleres of various forms ; microscleres com-
monly present, but never chelfe.

Sub-fam. 1. Phloeodictyinae. Sponge massive, with tubular processes
(fistulas) projecting from it. With a well-marked external rind. Megasclera
oxea, passing into strongyla in some species. Hhizochalina Schmidt ;
Oceanapia Norman.

Sub-fam. 2. Gelliinae. Megascleres all diactinal, oxea, or strongyla.
Microsclera as sigmata or toxa ; no rind or fistuhe. Gellius Gray ; Gelliodes
Ridley ; Toxochalina Ridley.

Sub-fam. 3. Tedaniinae. Megascleres of two forms — monactinal (styli)
forming the main skeleton, diactinal (tylota or tornota) dermal. Micro-
sclera as rhaphides. Tedania Gray ; Trachytedania Ridley.

Sub-fam. 4. Desmacellinse. Megascleres all monactinal, stylote to
tylostylote. Microscleres sigmata or toxa, or both. Desmacella Schm.;
Biemma Gray.

Sub-fam. 5. Hamacanthinae. Megascleres oxea or styli. Microscleres
large diancistra, and sometimes others. Vomerula Schm.; Hamacantha
Gray.

Fam. 3. Desmacidonidae. Megascleres of various forms, usually monactinal.
Microscleres always present and always including chelae.

Sub-fam. 1. Esperellinae. Skeleton fibre not echinated by laterally
projecting spicules. Esperella Vos. ; Espcriopsis Carter ; Cladorhiza M. Sars,
megascleres long, often projecting radially, like spines, deep-sea; Axoniderma
R. and D. ; Chondrodadia W. Thomson, deep-sea ; Meliiderma R. and D. ;
Desmacidon Bow. ; Artemisina Vos. ; Phelloderma R. and D. ; Sideroderma
R. and D. ; lophon Gray ; Amphilectus Vos. ; Dcndoryx Gray ; Forcepia
Carter ; Yvesia Topsent ; Metonanchora Carter ; Damiria Keller, etc.

Sub-fam. 2. Ectyoninae. Skeleton fibre echinated by laterally projecting
spicules. Myxilla Schmidt ; Pytheas Tops. ; Clathria Schm. ; Rhaphidophlus
Ehlers ; Stylostichon Tops. ; Microciona Bow. ; Uymcraphia Bow. ; Plocamia
O.S. ; Plumohalichondria Carter; Acarnus Gray; Ecliinoclathria, Carter;
Agclas Duch. and Mich. ; Echinodictyum Ridley.

Fam. .4. Axinellidae. Skeleton typically non-reticulate, consisting of ascend-
ing axes of fibres from which arise subsidiary fibres radiating to the cortex.
Megasclera chiefly styli, to which oxea or strongyla may be added. Microsclera
rarely present, never chelate. Hymeniacidon Bow. ; Phakellia Bow. ; Ciocalypta
Bow. ; Acanthella Schm. , Axinella Schm. , generally branched ; Raspailia Nardo,
branched, whip-like ; Dendropsis R. and D. ; Thrinacoplwra Ridley ; Dictyo-
cylindrus Bow.

Fam. 5. Spongillidae. Fresh-water sponges. Asexual reproduction by
gemmules which are often surrounded by a special kind of spicules called
amphidiscs. Spongilla Lamarck ; Ephydatia Lamouroux ; Tubella Carter ;
Parmula Carter ; Heteromeyenia Potts ; Lubomirskia Dybowski ; Lessepsia
Keller ; Uruguay a Carter ; Potamolcpis Marshall.

CERATINA. 97

Sub-order 2. SPINTHAROPHORA.

Usually corticate. Megascleres, as a rule, collected in fibres radially arranged
from the base to the surface. Microscleres, when present, as some form of aster,
never a sigma, sigma spire, or chela. f^

Tribe 1. ACICULINJE. With diactinal megascleres.

Fam. 1. Epallacidae. Megascleres as oxeas, and microscleres as some form
of asters. Epallax Soil.; Scolopes Soil.; Dorypleres Soil.; AmpMus Soil.;
Asteropus Soil.; Coppatias Soil.

Fam. 2. Stylocordylidae. Sponge differentiated into a head and stalk.
Skeleton in head radiately arranged with a cortical layer of smaller spicules set
radiately to the surface. Spicules in stalk set longitudinally in a dense axis.
Oxeas only. Stylocordyla W. Th.

Fam. 3. Tethyidae. Megascleres are strongyloxeas radially arranged.
Microscleres are spherasters, and sometimes other forms of Euasters. Tethya
Lam.; Columnitis 0. S. ; Xcnospongia Gray ; Magog SoU.; Sollasella Lend.
Tribe 2. CLAVULIKffi. With monactinal megascleres.
Fam. 1. Spirastrellidae. Non- boring sponges with numerous microscleres
(asters, spirasters, or discasters), typically forming a more or less continuous
dermal crust. Hymedesmia Bow. ; Spirastrella 0. S. ; Latruncalia Bocage ;
Podospongia Bocage, etc.

Fam. 2. Suberitidae. Without microscleres of the aster type.

Sub-fam. 1. Suberitinae. Skeleton not radially arranged. Suberites
Nardo ; Weberella Vos. ; Poterion Schlegel, etc.

Sub-fam. 2. Polymastinae. Skeleton radially arranged. Polymastia
Bow. ; Quasillina Norman ; Tentorium Vos. ; Ridleia Dendy ; Trichostemma
M. Sars, free-living, deep-sea, symmetrical forms with fringe of hair-like
spicules for attachment in the mud ; Tethyspira Tops., etc.
Fam. 3. Clionidae. Boring sponges, generally with microscleres of the aster
form. Cliona Grant ; Thoosa Carter ; A lectona Carter.

Order 4. CERATINA.*

Sponges with a supporting skeleton formed of spongin fibres which
are without spicules ; ciliated chambers saccular or piriform ; micro-
scleres present or absent.

This is undoubtedly an artificial order, and contains forms which
are more closely allied to various families of the Monaxonida than
to each other. It includes the so-called horny sponges.

Fam. 1. Aulenidae. Vestibular spaces complicated ; ciliated chambers very
small ; skeleton reticulate, formed of more or less areniferous horny fibres which
do not contain proper spicules. Proper echinating spicules may, however, be
attached to the superficial fibres. Allied to the Desmacidonidoe. Aulena Lendf. ;
Hyattella Lendf,

Fam. 2. Spongidae. With small piriform or spherical ciliated chambers ;
without proper spicules ; not clathriform. Allied to the Homorrhaphidce.

Sub-fam. 1. Eusponginae. Skeletal network close-meshed, fibres solid,
generally with foreign bodies in the main fibres. Chalinopsilla Lendf. ;

* R. von Lendenfeld, A Monograph of the Horny Sponges. Royal Society,
London, 1889.

98 PORIFERA.

Phyllospongia Ehlers ; Leiosella Lendf. ; Euspongia Brown ; E. officinalis
L., the fine Turkey or Levant sponge ; Hippospongia F. E. S. ; H. equina.
0. S., the horse sponge or common bath sponge. Coscinoderma Carter ;
Heteronema Keller.

Sub-fam. 2. Aplysinae. Skeletal network loose, the axis of the fibres
is occupied by a kind of pith. Aplysina Nardo; Luff aria Pol.; Thorect-
andra Lendf. ; Thoreeta Lendf. ; Aplysinopsis Lendf.

Sub-fam. 3. Druinellinae. Ciliated chambers with long special efferent
and afferent canals ; fibres thick with irregular lobose surfaces. Druinella
Lendf.

Sub-fam. 4. Halminae. Skeleton as a network of slender fibres containing
at the nodes large sand-grains ; or with a skeleton of loose sand-grains and
dendritically-branched areniferous fibres. Oligoceras F. E. S.; Dysideopsis
Lendf. ; Halme Lendf.

Sub-fam. 5. Stelosponginae. Skeletal network wide-meshed, composed
of solid fibres more or less fasciculated. Stelospongia Schmidt ; Hircinia
Nardo.

Fam. 3. Spongelidae. With large saccular ciliated chambers without efferent
canals, a clear ground substance, and a skeleton of solid fibres without
proper spicules, but containing sand-grains. Sometimes the fibres are replaced
entirely by large scattered sand-grains. More closely allied to the Heteror-
r aphides, than to any family of Ceratina.

Sub-fam. 1. Phoriosponginae. With microscleres. Phoriospongia
Marshall ; Sigmatella Lendf.

Sub-fam. 2. Spongelinae. Without microscleres. Spongelia Nardo;
Psammopemma Marshall ; Haastia Lendf. ; Psammoplysilla Keller.
The deep-sea Ceratosa of Haeckel (Challenger Reports, vol. xxxii., 1889),
belong to this order. He distributes the forms into four families :

Ammoconidae, without spongin skeleton ; Psamminidae, without spongin
skeleton ; the Stannomidae, with spongin skeleton ; and the Spongelidae. Most
of them were taken at a depth of from 2000 to 3000 fathoms.

CHAPTEE IV.

COELENTERATA.*

Radially symmetrical animals with only one cavity in the body —
the gastrovascular space — which serves alike for digestion and circula-
tion. The generative cells are always either ectodermal or endodermal.

The Coelenterata, which include polyps, corals, sea-anemones, jelly-
fishes, etc., are • multinucleate animals, in which the greater number
of the nuclei are arranged in regular layers at the body surfaces, and
constitute, with the protoplasmic layer which contains them, the
external and internal epithelia, commonly called the ectoderm and
endoderm respectively. Between these two layers the protoplasm is
reduced to a sparse reticulum, without or with only a few nuclei, the
spaces between the strands of the reticulum being filled by a gelatinous
matter, the jelly, f When this interposed gelatinous layer is thin and
inconspicuous, as in most polyps, it is called the supporting lamella,
or structureless lamella ; when it is thick and bulky, as in some parts
of the jelly-fishes, it is called simply the jetty. Further, these layers
are always differentiated to a greater or less extent into functional
tissues — contractile tissues and nervous tissues ; and nematocysts are
always present as differentiations of the ectoderm or endoderm, or of
both layers ; the generative cells are always products of one of these
layers ; and finally, the ectoderm or the protoplasm of the jelly very
commonly secretes a skeletal tissue, which may be either cuticular,
horny, or calcareous. On the other hand, the internal surface of the
body is not differentiated into organs of circulation, of digestion, or
of coelom distinct from each other. The vegetative processes are
performed by the internal surface of the enteric cavity, or gastro-
vascular space as we shall call it, of which the central part func-
tions as stomach and intestine, the peripheral as vascular system.

* R. Leuckart, Zoologischc Untersuclmngen, I., Giessen, 1853. C. Chun,
Coelenterata in Bronn's Klassen u. Ordnungen, Bd. 2, Abth. 2.

t Sometimes called the mesoglaea — an unsuitable term, because it suggests an
ectoglaea and entoglaea, which do not exist.

100

COELENTERATA.

R. Leuckart was the first to recognise the importance of these
characters, and made use of them to separate the Polyps and the
Medusae from the Echinoderms, thus resolving Cuvier's type of
Radiata into the types of Coelenterata and Echinodermata.

The Coelenterata are divided into two main sub-phyla, the Cnidaria
and the Ctenopliora^ distinguished from one another by a number of
characters, of which, perhaps, the most compre-
hensive is the presence or absence of iiemato-
cysts. The entire structure of the body is
generally speaking disposed in radial symmetry,
although amongst the Cnidaria transitions
towards bilateral symmetry are sometimes
apparent.

Three distinct types of body -form are met
with amongst the Coelenterata, viz., that of the
Polyp ; of the Medusa; and of the Ctenopliore.
The Polyp type. The Polyp has the form
of a cylinder or sac (Fig. 79), of which the
posterior or lower end is fixed and the opposite
end is free and pierced by an opening — the
mouth — placed on a flat or conical prominence
— the oral cone or liypostome, and leading into
the cavity of the body, or enteric space (coelen-
teron). Around the mouth are placed a number
of regularly or irregularly arranged contractile
processes — the tentacles, which always contain endoderm, either solid
or traversed by a prolongation of the enteric space. The tentacles
may be reduced to knob-like warts or be absent altogether

(siphonozooids of
the Stylasteridae,
etc.). In rare cases
(Arachnactis, Min-
yas) the polyp is
free-swimming.

The ectoderm,
which is the part

FIG. 79. — Diagrammatic
longitudinal section of
a hydroid polyp. 0
mouth ; M enteric
space or coelenteron ;
Ek ectoderm ; En en-
doderm ; T tentacle.

dea. Sz sense cells in the ectoderm ; Gz ganglion cells ; Nf
nerve-fibres ; Stl supporting lamella ; E endoderm cells.

5, — E

FIG. 80.— Longitudinal section through the nerve ring of Charyb-

of the polyp in
closest relation
with the outer world, possesses, to use the ordinary parlance of
histology, sense-cells (Fig; 80) provided with sensory hairs ; nerve or
ganglion-cells with branching processes; epithelio-muscle cells, with

COELENTERATA.

101

FIG. 81. — Ectoderm cells of Hydra with con-
tractile processes (rm). From Chun, after
Kleinenberg.

contractile processes (Fig. 81) arranged along the long axis of the
body; and cnidoblasts, which form the thread-cells, or nematocysts,
and carry sensory processes, the cnidocils or triggers, projecting on the
surface. The thread-cells (Fig.
82) are small capsules consisting
of a highly refractile cuticular
material, and containing some
fluid and a spirally - coiled
thread. Under certain mechan-
ical conditions, e.g., under slight
pressure produced by contact
with a foreign body, these
capsules suddenly protrude the
thread, which either fastens on to the causes of the disturbance, or
pierces it, carrying into it a part of the fluid contents of the capsule.
In many parts of the body, and especially on the tentacles, which
serve for the capture of prey, these microscopic weapons are present
in great numbers, and are often
grouped in a peculiar arrangement
to form batteries of thread-cells.

The endoderm cells are principally
concerned with the processes of
digestion and secretion. They often
bear cilia for the movement of the
contents of the gastrovascular space,
and their deeper ends are sometimes
prolonged into contractile processes
which are transversely arranged.
The endoderm of the tentacles is
sometimes solid, and modified for
a skeletal function by the develop-
ment of vacuoles and cuticular struc-
tures into a form resembling the
vegetable parenchyma of plants, or
the tissue of the vertebrate noto-
chord (Fig. 83). The food is
digested in the Protozoan manner,
being surrounded by protoplasmic processes of the endoderm. The
digestion is therefore intracellular, and the indigestible remains are
cast out into the enteron and ejected through the mouth by the
help of the cilia of the endoderm cells.

FIG. 82. — a, b Nematocysts and cnido-
blasts of Cordilophora, with the cnidocil
of the cell (cnidoblast) ; c adhesive cells
of a ctenophore (from Lang).

102

COELENTERATA.

FIG. 83. —Axial
cells from the
tentacles of
Campanularia.

As a rule there is no localised organ for the excretion of the
nitrogenous waste, but in a few cases deposits of guanin or urea crystals
may be seen in some of the endoderm cells. Some
polyps possess pores at the apices of the tentacles or
through the body wall, which may serve for excretion
(Fig. 84).

Asexual reproduction by budding or fission is very
commonly found. If the individuals so produced
remain united they give rise to the colonies which
are so widely distributed amongst the Cnidama, and
which by the continued multiplication of their mem-
bers may attain a considerable size.

Sexual reproduction is always met with. The
sexual cells arise in the endoderm or ectoderm. They
sometimes remain at their place of origin (Hydra, Anthozoa), but
often they pass through the supporting lamella and wander to
ea>, another place where they

ripen (most Hydromedusae).
There are two kinds of
polyps, characterised by the
structure of the enteric cavity
— the Hydroid polyp and the
Antliozoan or coral polyp.
As types of the former we
may mention Hydra with
^s single row °f hollow
tentacles, and Tubularia
with its double row of solid
tentacles. In such polyps
the gastrovascular space is
simple, and there is no
oesophageal tube.

The Antliozoan Polyps
are usually of a larger size

,-, ,, * TT i • i i

tnan tlie JlydrOldS, and

c.

FIG 84.— Diagrammatic longitudinal section through
an Antliozoan polyp, passing through an enteric

pouch on the left side and through a mesentery possess a more complicated
on the right, e perforation in mesentery ; elc ecto- '
derm; en endoderm (black); ex excretion -pores
(cinclides); ex' excretion pore at the end of a
tentacle ; /pedal disc ; g.t. enteric pouch ; m wall
of body ; mes supporting lamella ; mf mesenterial
filament; o mouth; oes oesophageal tube ; p edge
of penstome ; s supporting lamella of a mesentery ;

t tentacle (from Chun).

., ,^.
gastrovascular Cavity (.big.

§4) In the first place the
mouth leads into a tube
^focll projects into the gas-

trovascular cavity, and opens

COELENTERATA.

103

into the latter at its lower end. This tube is lined with ectoderm
and is called the oesophageal tube, or stomodaeum (Fig. 84 oes).
In the second place there projects inwards from the side walls of
the body a number of vertical partitions formed of folds pf the
endoderm and a prolongation of the supporting lamella. These are
the mesenteries. Internally they are attached to the oesophageal

tube in the region of that structure,
while below it they end in free
edges which are somewhat folded
and thickened and are called the
mesenterial ridges and filaments.
The mesenteries break up the enteric

FIG. 85. — Alcyonarian polyp (Veretillum FIG. 86. — Diagram of a hexactinian polyp (from

cynomorium), from Chun, t pinnate Chun, after Andres). / pedal disc ; m wall of

tentacles ; oes oesophageal tube ; m body ; p peristome ; d edge of peristome ;

mesenterial filaments ; s mesenteries ; t tentacles ; o mouth.
s', s' two adjacent mesenteries with
feebly developed filaments.

cavity into a number of circumferential pouches which, in the lower
part of the polyp, open into the central part of the enteric cavity
or stomach, but in the upper part of the polyp where the mesenteries
are attached to the oesophagus form separate chambers (Figs. 88 and
89). Each of these communicates above with the cavity of a tentacle
(Fig. 84). The gastral pouches then are the peripheral parts of the
enteric cavity (coelenteron) between the mesenteries. An opening
may be present in each mesentery just below the oral disc putting

104

COELENTERATA.

the adjacent chambers in communication (Fig. 84, c). Between
these mesenteries, which join the oesophageal tube and are called
primary mesenteries, there may be intercalated mesenteries which,
as a rule, do not reach the oesophagus and are called accessory
mesenteries. There are secondary, tertiary, etc., accessory mesenteries.

All the mesenteries
decrease in breadth
towards the base of
the polyp (Fig. 89).
The mouth open-
ing is rarely round,
but usually has the
form of a slit, at the
two ends of which
(or sometimes at
one end) there is a
groove lined with
long cilia. These
grooves are the
oesophageal grooves
or yonidial grooves
(siphonoglypJies).
They remain open
when the walls of
the rest of the
oesophagus are ap-
plied to one another
(Figs. 88 and 89).

The tentacles are
hollow, and may be
smooth (Zoantharia,
Fig. 86) or pinnate
(Alcyonaria, Fig.
85), and are placed
in one or in several

rows. Pores may be present at the tips of the hollow tentacles,
and on the side walls of the body, in which case they are called
cinclides (Fig. 84). In the genus Cerianthus and its allies there
is a large aboral pore. The mesenterial thickenings or filaments
are specially characteristic of the Anthozoa. They consist of thick-
enings of the endoderm containing gland -cells and thread -cells.

FIG. 87. — Longitudinal section through a Hexactinian (Phellia
limicola), from Chun, after Andres, a acontia ; c, c' septal
ostia ; g gonad ; m.f mesenterial filament; m.l longitudinal
muscles ; o mouth ; o' internal opening of oesophageal tube ;
oes oesophageal tube : s primary mesentery ; s' secondary
mesentery; s" tertiary mesentery; t tentacle.

COELENTERATA.

105

In some sea-anemones contractile fibres — the acontia — arise from
the edges of the lower ends of the mesenteries : they are closely
set with thread -cells and can be protruded from the lateral pores
(cinclides) in the contraction of the polyp and serve as weapons
of defence (Fig. 87).

The muscular system is much more complicated than in Hydroids.
The muscles are both ectodermal and endodermal. The ectodermal
muscles of the body- wall (longitudinal) are generally feebly developed,
while those of the peristomial disc (radial) and of the tentacles
(longitudinal) are powerfully developed. The endodermal circular
muscles of the pedal disc, the side body-wall, and of the oesophageal

FIG. 88. — Transverse section through
an Alcyonarian (after R. Hertwig).
11 gonidial groove ; 1, 2, 3, 4 the
four pairs of mesenteries with their
muscles.

FIG. 89. — Section through an Actinian (Adamsia),
after R. Hertwig. Hf the unpaired (dorsal and
ventral) chambers ; R, R gonidial grooves.

tube are well developed. To this system there is added a character-
istic and well-developed set of endodermal muscles on the mesenteries.
Each septum is provided on one face with transverse (radial) fibres,
and on the other with longitudinal (Fig. 90). The lowest section of
the transverse muscles are often independent of the rest, and pass
from the side body-wall to the pedal disc (m.t). The longitudinal
muscles are well developed and cause a projection on the face of the
mesentery (Figs. 88, 89). While a nucleus is generally associated
with each of the ectodermal muscular fibres, the endodermal muscles
are in close connection with the base of a cylindrical epithelial cell.

In correspondence with the powerful formation of the musculature,
the nervous system reaches a considerable development. It has the

106

COELENTERATA.

form of a diffuse plexus of much-branched glanglion cells, which are
contained in both ectoderm and endoderm between the lower ends of
the epithelial cells, and are especially developed in the peristome,

tentacles, and oesophagus.

The AntJiozoa are almost
always dioecious, rarely her-
maphrodite ( Cerianthus) . 0 va
and spermatozoa arise from
the endoderm al cells of the
mesenteries, and lie in follicles
in the jelly of the same struc-
tures. They cause swellings on
the faces of the mesenteries,
a short distance from their
free ends (Fig. 91). Asexual
reproduction by budding and
fission is very generally present,
and often leads to the forma-
tion of colonies. The Antho-
zoan polyps are much inclined
to the formation of skeletal
structures, which consist of
slimy (Cerianthus), horny, or
calcareous substances.

The symmetry of the Antho-

zoan polyps is almost always radial. The Octactinia (Alcyonarid)
indicate their 8-radiate structure by their eight feathered tentacles,

m.p.

FIG. 90.— Primary mesentery of a Hexactinian
(Sagartia parasitica), and the parts of the body
to which it is attached, ac Acontia ; c Septal
ostium ; / pedal disc ; m.l longitudinal mus-
cular fibres; m.t transverse muscular fibres;
m.p parietal muscles ; p peristome, t tentacle.

FIG. 91.— Section through the mesentery of an Actinian (Edwardsia tulcrculata), after O. and
R. Hertwig. ck ectoderm ; en endoderm ; m./mesenterial filament; m.l section of the pro-
jection caused by the folding of the muscular lamella of the longitudinal muscles, the fibres
appear as dots ; ov ovary.

COELENTERATA.

107

FIG. 92. — Eight-armed Scyphistoma-polyp with
wide mouth. M longitudinal muscles of the
gastral ridges; Csk chitinous tube.

a strictly radiate and
a bilateral structure.
The tentacles rarely
show a tendency to
the bilateral arrange-
ment, but the mesen-
teries, as shown
by the arrange-
ment of the lon-
gitudinal muscu-
lar bands, are
generally grouped
in a bilateral
manner (Figs. 88
and 89).

The Scypho-
polyp or Scy-
phistoma is a
transitional form
between the
Hydro- and An-
thozoan- polyp.
It resembles the
hydroid in the

and the horny corals (Anti-
patliarioi) their 6-radiate sym-
metry by their six tentacles;
multiradiate — usually in ^ mul-
tiple of six — are the Actiniaria
and stone-corals. Nevertheless,
hardly a single anthozoan-polyp
can be found in which all the
organs are strictly arranged
according to one and the same
number. The fact that the
mouth-opening is not usually
round, but slit-like, indicates
an inclination to a biradiate or
bilateral symmetry, and there
are transitional forms between

FIG. 93. — Sixteen-armed Scy-

; phistoma (slightly |magni-

fied). GttTgastralJridges.

108

COELENTERATA.

absence of the oesopliageal tube* and mesenteries, but it recalls the
Anthozoan-polyp in the fact that the structureless lamella is developed
into a gelatinous layer, and in the presence of gastral ridges (taenioles)
or folds of endoderm resembling rudimentary mesenteries, into which
the jelly is continued. It is somewhat cup-shaped (Fig. 92), and
is attached by the aboral end which is elongated and narrow, and often
secretes a chitinous tube for fixation. There are eight or sixteen
tentacles (Fig. 93) round the^mouth supported by a central axis
of stiff endoderm cells. There are four gastral ridges or taenioles
(Fig. 94), each of which is accompanied by a longitudinal muscle
derived from the endoderm.

The Medusa is a free-swimming animal, and consists of a flattened

disc or arched
bell of gelatinous
consistence, from
the under or sub-
umbrella surface
of which hangs
a central stalk —
the luanulrium —
bearing at its free
end the mouth.
The greater part
of the umbrella
consists of the
jelly or enlarged
structureless la-
mella ; this is
often traversed
by protoplasmic
strands which

may contain nuclei. In the normal position the medusa swims —
by the contraction of the bell — with its convex or ex-umbrella surface
upwards. The manubrium is frequently prolonged in the region of
the mouth into lobes and tentacle-like structures, while the edge of
the umbrella is beset with a variable number of true tentacles,

In a few cases the medusae are attached by the ex-umbrella surface ; in the
Lucernaridae (Fig. 134) by a styliform prolongation of the aboral pole ; in some
Rhizostomas by a sucker-like plate of the ex-umbrella. Some of them can creep

m.L-

FIG. 94.— Transverse section through the middle part of a Scy-
phistoma. ek ectoderm ; en endoderm ; s jelly (structureless
lamella) ; ml longitudinal muscle ; gw gastral ridge; gv enteron
(from Chun, after Claus).

* Gotte asserts that there is an oesopliageal depression of ectoderm in the
Scyphopolyp.

COELENTERATA.

109

COC..V.

by means of small suckers on their tentacles (Clavatella prolifera, Pectanthus
asteroides), or can adhere by the suctorial action of their mouth openings
(Pelagia), and even in rare cases are able to lead a parasitic life (Mnestra
-//arasitica on a pelagic snail Phyllirhoe bucephala}.

v

The contraction of the bell is effected by the circular muscles of
the sub-umbrella surface. The ejection of water caused by this
contraction drives
the medusa along.
The velum is a mus-
cular membrane at
the edge of the bell.
It consists of a fold
of ectoderm, and
assists in the move-
ment of the medusa
by elongating the
umbrella cavity and
narrowing its aper-
ture. When the
velum is absent the
margin of the bell
is lobed (Acraspe-
dote Medusae, as
opposed to Craspe-
dote Medusae in
which a velum is
present).

The marginal ten-
tacles are rarely absent
(tihizostoma) ; occasion-
ally there is only one
(Steenstrupia) or two
(Aeginopsis, Gemella-
rici) ; more frequently
there are four or some
multiple of four. Occa-
sionally there are six
or a multiple of six
(Carmarina, Fig. 101); or the tentacles may be numerous, in which case they
are either uniformly distributed round the edge of the bell ( Tiaropsis, Aurelia,
Fig. 100), or grouped in bundles (four bundles in £ougainvillea, eight in
Lucernaridae, Fig. 134, and in Cyanea}. Occasionally the tentacles are removed
from the edge of the umbrella, and inserted either on the ex-umbrella (Narco-
medusae, Fig. 96), or on the sub-umbrella (Cyaneidac). The tentacles are

FIG. 95. — Sarsia mirabilis (from Chun, after Agassiz). A cras-
pedote ocellate medusa budded from Cory tie mirabilis. c.r
radial canal ; c.c circular canal ; ex.u ex-umbrella ; g inanu-
brium containing the elongated stomach and surrounded by
the gonads (manubrial gonads) ; o mouth ; t tentacles ; v
velum ; s.u sub- umbrella.

110

COELENTERATA.

usually hollow and
unbranched, more
rarely they have a
solid endodermal axis
(Narcomedusae, Fig.
96, Tesseridae, Ephy-
ridae), or are dicho-
tomously branched
(Cladonemidae). Be-
sides the larger main
tentacles there are
often smaller inter-
mediate tentacles at
the umbrella edge
(Tessera, Fig. 133).
Occasionally the ac-
cessory tentacles are
confined to the young
stages and drop off
in later life, or they
may become trans-
formed into the mar-
ginal bodies.

In the gastrovascular apparatus a central stomach for digestion,
and a carrying or circulating system of peripheral canals and pouches

•tb.

FIG. 96. — Portion of the edge of the umbrella of a Narcomedusan
(Cunina lativentris) from Chun, after O. and K. Hertwig. v
velum ; t tentacles with stiff endodermal axes ; t.b roots of
tentacles ; n.r nerve ring ; n.s radial nerve which passes to the
base "of the tentacles ; ot marginal bodies ; x otoporpa ; g.t
gastral pouches ; c.p, c.p the two peronial vessels ; they form
originally a part of the circular canal, which in the shifting
of the tentacles dorsalwards on to the ex-umbrella is festooned
and opens into the gastral pouches (after Hertwig, from Chun).

Z

FIG. 97. — Diagrammatic longitudinal section through a Rhizostoma. U umbrella ; M gastric
cavity ; S sub-umbrella ; G gonad ; Sh sub-genital pit ; F gastral filament ; SM muscular
system of the sub-umbrella; ligf radial canal; Blc marginal body; Eg olfactory pit; Al ocular
lobe ; Sk shoulder tufts, Dk dorsal tufts, Vk ventral tufts of the eight arms ; Z terminal
parts of the arms.

COELENTERATA.

Ill

can always be distinguished. The mouth leads directly. (Fig. 101,
Carmarina), or by a tube into the stomach, and its lips are often
drawn out into four grooved processes— the oral arms (Fig. 100).
The edges of the grooves are often frilled, and carry small tentacular
filaments.

In Rhizostoma the four arms bifurcate (Fig. 97), giving rise to eight, the frilled
edges of which fuse and bring about the closure of the mouth. The fusion is
not, however, complete, but numerous small openings are left — the suctorial
mouthlets, in which digestion
of the food takes place. From
these openings arise small ves-
sels, which gradually uniting
with each other form a system
of canals passing up the oral
arms to open into the stomach
(Fig. 97).

The stomach is generally
flattened, rarely elongated
(Lucernaria, PeriphyUa, Tes-
sera) in its main axis. Occa-
sionally it is divided by a
constriction into two sections,
an aboral basal section and
a central stomach (Tessera,
Pericolpa, PeriphyUa (Fig. 99),
the stalk tube of Lucernaria).
Gastral filaments (phacellae)
are highly characteristic of
the acraspedote medusae, and
recall the same structures in
the Anthozoa, as do the gas-
tral ridges or taenioles, which
to the number of four are
placed interradially in the
basal and central stomach in
the Lucernaridae and Tesseri-
clae (Figs. 98, 99).

ml

c!t

TO .re.

FIG. 98. — Section through the peripheral part of the
umbrella of a young Lucernarian (Craterolophu*
thetys). e/c ectoderm ; mes jelly ; en endoderm ; g
central stomach ; g' radial diverticula of the stomach
between the funnels (stibgenital pits); g.t radial
pouches ; se septa ; inf funnels lined by ectoderm ;
m.se septal muscles ; m.i longitudinal muscles of the
funnels ; gen gonads (after Glaus).

The peripheral part of
the gastrovascular system
may appear in the young

form as a continuous dorso-ventrally flattened space extending
almost to the edge of the umbrella. Later the dorsal and ventral
walls of this space come together along certain radially directed lines
and fuse with one another, so that the originally continuous space is
broken up into a number of pouches or vessels, all leading outwards
from the central stomach. At the places where the concrescence of

112

COELENTERATA.

the two walls occurs the endoderm epithelium is retained in the
form of a layer of cells called the vascular or endoderm lamella
(Fig. 107).

In many medusae these concrescent places appear as four small septal unions
(Cathammata, Fig. 98 se). They delimitate four wide radial pouches of the
stomach, which however communicate with one another peripherally beyond the
unions by a kind of circular canal.

In the Lucernaridae and Charybdeidae the septal unions are extended into
elongated partitions (Fig. 98, se), 4;he septa, which delimitate the four radial
pouches in nearly their whole extent. But the septa never quite reach

the umbrella edge, so

Gift.-

canals are connected
by a narrow circular
canal. The gastric
pouches open into the
stomach by the gastral
ostia (Fig. 99 g.o).

When the four
places of fusion of
the dorsal and ven-
tral stomach walls
are of considerable
extent, the gastral
pouches have the
form of four narrow
radial vessels : this
is characteristic of
the tetra-radiate

craspedote medusae. A circular canal connecting them peripherally

is however retained.

In many acraspedote medusae there are, beyond and independent of the four
septal unions, sixteen lines of adhesion between the dorsal and ventral walls of
the gastric pouches. In some cases the four septal unions are not formed, and
only the peripheral lines of adhesion appear : in this way the more or less com-
plicated form of the peripheral gastrovascular apparatus of the Semostomae and
Jihizostomae is introduced. Sometimes the adhesion-lines are narrow and extend
up to the edge of the disc (Pelagidae, Cyaneidae), sometimes they are broad and
leave a circular canal at the periphery. In the first case broad, blindly-ending
gastric pouches are formed ; in the latter the*" pouches are reduced to narrow
vessels which frequently branch peripherally, or even anastomose (Aurelia,
Fig. 100, Rhizostoma}.

A similar branching of the radial vessels occurs also in the Craspedota. The
endoderm lamella may become secondarily excavated, and thereby new radial
vessels may arise, vessels dichotomously branching in a peripheral direction, or

FIG. 99.— Section through the central stomach of an acraspedote
medusa (Periphyllct mirabilis). v.g umbrella-jelly ; in/ the
four funnels ; g.c basal stomach ; /gastral filaments ; g.o gas-
tral ostia ; sin circular sinus ; kn septal unions ; s gonads.

COELENTERATA.

113

centripetal vessels arising at the umbrella edge and ending blindly (Carmarina,
Fig. 101).

Excretion pores may be present at the umbrella-edge in both craspedote and
acraspedote medusae. In the Craspedota (most frequently in the Leptomedusae)
they are placed on warts on the circular canal and open on the sub-umbrella
surface. The endoderm cells near the openings are of a glandular nature, and
contain concretions which are emptied through the pore. In the Acraspeda
there are eight excretion pores at the distal end of the eight adradial canals.

The ectoderm which is composed of a flat epithelium on the dorsal surface,
and of a muscular epithelium on the sub-umbrella surface and velum, is
thickened and stiffened along certain lines and contains a large number of

RK

FIG. 100. — Aurelia aurita from the oral surface. MA the four oral tentacles with the mouth
in the centre ; GK gonads ; GH aperture of sub-genital pit ; RK marginal body ; RG radial
vessel ; T marginal tentacles.

nematocysts. An annular thickening of this kind is found round the umbrella
margin in some forms (Fig. 101), and similar thickenings ascend for a short
distance on the ex-umbrella surface from the roots of the tentacles — the
peroniums (Fig. 101, pe)— and from the roots of the auditory tentacles—
the otoporpas (Fig. 96, x). The peroniums and otoporpas are continuations of
the first-mentioned circular thickening.

The gastro vascular apparatus is lined by endoderm, which in places carries cilia
for the movement of the contained matter. The digestion seems to be, partly
at least, intracellular. The endoderm is without muscular structures and nema-
tocysts, except on the gastral filaments, which are actively moveable and contain
both. Possibly the four longitudinal muscular bands, found beneath the four
taenioles and septa in some acraspedote medusae, are of endodermal origin.

I

114

COELENTERATA.

The nervous system has the form of a plexus of multipolar
ganglion cells placed between the muscle-fibres and the ectoderm
cells. In addition to this peripheral plexus there are special

FIG. 101.— Carmarina (Geryonia) Jiastata (from Chun, after Haeckel)— a sex-radiate Tracho-
medusan. s.u sub-umbrella; a manubrium ; v velum; n nerve-ring; rv circular vessel;
en thickened tract of ectoderm at edge of bell ; t marginal tentacle ; mu interradial longitu-
dinal muscular bands of the manubrium ; o mouth ; g stomach ; cr one of the six radial
canals ; ov ovaries on the sub-umbrella-wall of the radial vessels ; c.cp centripetal, blindly
ending radial vessel ; pe peronium. The tentaculocysts are shown near the base of and
between the tentacles.

COELENTERATA.

115

aggregations of nervous tissue in certain regions. In the. craspedote
medusae there are two annular nervous tracts in the ectoderm at
the base of the velum, one on each side of the supporting lamella
(Fig. 102 ri, n"). They consist of ganglion-cells, nerve-fibres,>some
of which perforate the supporting lamella to put the two rings in
communication, and of sensory epithelial cells bearing stiff projecting
sensory hairs, and ending internally in fibres which pass into the
nerve-rings.

In the Acraspeda there is a special aggregation (Fig. 103 F) of the nervous
tissue, of the same structure as the nerve-rings of the Craspedota, round the
base of each of the sense tentacles (marginal bodies, or rhopalia) ; and in the
Charybdeidae there is a sub -um-
brella marginal nerve with a zigzag
course connecting together these
rudimentary ganglia, which in the
other forms are apparently inde-
pendent of one another. In the
Acraspedota, pits — the so-called
olfactory pits — lined by a sensory
epithelium are found on the edge
of the umbrella above the marginal
bodies (Fig. 103 K).

At the edge of the um-
brella are always placed special
sense organs — the marginal
bodies. They are of two
kinds — those which by their
structure indicate an auditory
function, and those which
indicate a visual purpose. In
the craspedote medusae they
are mutually exclusive, so that
we find ocellate medusae with
sense organs of the visual
type and vesiculate medusae with sense organs of the auditory type.
In the Acraspeda the marginal bodies may carry organs of both
types.

The sense organs of the auditory type always contain concretions — the
otoliths — of an organic or inorganic material, which concretions are contained
inside cells ; and two types of auditory organ are distinguished according as
these concrements are contained in cells of the ectoderm (Fig. 104) or in cells
of the endoderm (Fig. 105). In the Craspedota we find auditory organs of both
types. In the Leptomcdusae they consist of ectodermal pits, which may be
closed into vesicles, on the under side of the base of the velum ; some of the

71.0C.

St.

FIG. 102. — Diagrammatic transverse section
through the edge of the umbrella of Carmarina
hastata (from Chun), v velum ; $ t supporting
lamella of velum ; mu circular muscles of velum
in section ; n1 lower, n" upper nerve ring; n.iv
thickening of the ectoderm of the edge of the
umbrella ; c.r radial vessel ; r.k circular vessel ;
en solid cord of endoderm beneath the peronium
pe ; ot tentaculocyst ; n.ac auditory nerve ; ga
umbrella jelly.

116 COELENTERATA.

ectoderm cells of the pit or vesicle contain otoliths, while others bear sensory
hairs (Fig. 104). In the other type, found in the Trachomedusae and Narco-
medusae, the auditory organs have the form of short reduced tentacles of the edge
of the disc, containing a solid endodermal axis and surrounded at their base by cells
bearing long auditory sense hairs. The otoliths are contained in the endoderm
cells of the tentacles. These sense tentacles may project freely on the surface
(Aeginidae, Fig. 96), or they may be sunk in pits, or the pits may be closed
and they may lie in vesicles embedded in the jelly of the umbrella (Fig. 102), in
which case they may be fitly termed tentaculocysts. In both types the hair-
bearing sensory cells are prolonged into fine fibres which join the nerve rings
(Fig. 105).

FIG. 103. — Section through the olfactory pit (R), the sense tentacle (marginal body), and its
nerve centre of Aiirelia aitrita. L lobe of umbrella covering the sense tentacle ; P eye-spot ;
Ot otoliths in the endoderm of the sense tentacle ; Z endoderm cells after solution of the
otoliths ; En endoderm ; EC ectoderm with the underlying tissue of the nerve centre F.

The eye-spots of the Craspedota (ocellate medusae or Anthomedusae] consist of
a pigmented patch of ectoderm cells just dorsal to the insertion of the velum ;
a lens-like cuticular thickening over them is sometimes developed (Lizzia).
The ectoderm patches contain two kinds ^>f cells, namely peripheral cells with
pigment surrounding some colourless cells, the bases of which are prolonged into
nerve fibres.

The marginal bodies of the Acraspeda or the rhopalia are absent in the
Tesseridae, and in most Lucernaridae. When they are present they have the form
of short marginal tentacles and are distinguished from those of the Craspedota,
by the fact that they contain a hollow prolongation of the gastrovascular system,
and are covered on the dorsal side by a hood-like prolongation of the umbrella

COELENTERATA.

117

(hence Steganophthalmata, Fig. 103). In some Lucernaridae the marginal bodies
are present as the so-called marginal anchors (Halidystus, Fig. 134). There are
eight of them, four being called radial in position, and the other four interradial ;
they are placed respectively between the -eight marginal lobes. They end in a
small swelling with thread cells ; their middle portion is surrounded by a kind
of collar formed of sticky glandular ectoderm cells, and on the sub-umbrella side
of their basal part is an eye -spot.

In other Acraspcda the eudoderm at the end of the sense tentacle is thickened
and loaded with concretions, and the ectoderm round its base is columnar and
provided with cilia and sense hairs (Fig. 103). The fibrillar continuations of
these cells form a nervous network, with ganglion cells, round the base of the
tentacle (Fig. 103, F).

Visual organs are sometimes present in
this sensory epithelium. They are most
complicated in Charybdca, where there
are two large terminal eyes with a retina,
vitreous humour, lens, and cornea.

FIG. 104.— Sense organ on the
nerve-ring and circular vessel
of Octorchis (after the Hert-
\vigs). Rb Sense organ; 0, 0
two otoliths ; Hh auditory
hairs ; Hz auditory cells ; Nv
upper nerve-ring ; Rg circular
vessel (type of Vesiculata).

Jff

FIG. 105.— Tentaculocyst of Geryo-
nia (after O. and R. Hertwig).
N, N' the auditory nerves ; Ot
otolith; Hz auditory cells; Hh
auditory hairs (type of the Tracho-
niediisae).

Beproductive organs. The medusae are almost always dioecious,
only in rare cases are they hermaphrodite (Chrysaord).

The sexual cells of the Craspedota appear always to arise in ectoderm,
and those of the Acraspeda in endoderm. In the Antliomedusae they
are developed in the ectoderm of the manubrium (Fig. 95) in four
radial streaks, each of which later splits into two. In the other
Craspedota (Leptomedusae) they are placed in the ectoderm of the
sub-umbrella beneath the radial canals (Fig. 106). It appears, how-
ever, that in many medusae (Obelia) the generative cells arise in the
ectoderm of the manubrium, and then later migrate to the ecto-
derm below the radial canals, where they occasionally wander into
the endoderm and ripen partly in the ectoderm and partly in the
endoderm.

In the Acraspeda the sexual cells arise in the endodermal walls of

118

COELENTERATA.

the central stomach or gastral pouches. They are interradially*
placed, and have the form of four horseshoe-shaped glands, which
may secondarily divide into eight adradial halves. In all cases the
sexual cells are dehisced into the enteron and pass out by the
mouth.

In connection with the genital glands there are very generally
present ectodermal invaginations in the form of pits of the sub-
umbrella surface. These pit* are for respiratory purposes, and
constitute the so-called sub-genital pits (Discomedusae, Fig. 100),
and funnels (Lucernaridae and Periphyllidae, Fig. 98). They occur

interradially beneath the
genital glands.

Asexual reproduction by
budding is of very general
occurrence in the craspe-
dote medusae. The buds
are formed, usually in
groups, rarely singly, on
the wall of the manubrium,
more rarely at the base of
the tentacles, on the cir-
cular canal, or on other
places. In the Narco-
medusae the budding is
confined to larval life,
when a bud-nurse is formed
which attaches itself para-
sitically to other Medusae.
As hinted often in the above description the medusae fall into two
well-marked divisions, viz., into the Craspedota and Acraspedota
(Acraspeda) or Acalepliae. Since the celebrated discovery of the
alternation of generations in the medusae by Sars we have known
that the former are budded off by Hydroid-polyps, the latter by the
Scypho-polyp or Scyphistoma.

The Craspedote Medusae are distinguished by the following
characters : a smooth umbrella edge ; a muscular velum, without
endoderm; a double nerve-ring; gastral filaments and taenioles are

* In describing a Scyphomedusa it is usual to speak of eight primary radii.
These are the radii of the marginal bodies. These eight primary radii are further
distinguished into four perradii and four interradii. The oral arms lie in the four
perradii, and the gastral ridges and gonads in the four interradii. The adradii
are the eight radii between the eight primary radii.

Ov ""^ Ob

FIG. 106. — Phialidium variabile represented from the
under side of the umbrella. V velum ; 0 mouth ;
Ov ovary ; Ob auditory vesicle ; Rf marginal ten-
tacles.

COELENTERATA. 119

absent ; sexual cells arise in the ectoderm of the mamibrium, or along
the radial canals ; they are rarely developed directly from the egg.

The Acraspeda, on the other hand, have a lobed umbrella edge and
no double nerve ring; the marginal sense bodies are always tentacular
in form, and contain a prolongation of the gastrovascular system;
gastral filaments are always developed on the stomach wall, and
taenioles are generally present ; the sexual cells are endodermal, and
the development is either direct or by fission from a Scypho-polyp.

Connection between the Polyp and the Medusa. The medusa
is very generally produced by budding from a polyp, although in
certain orders it does rise directly from the egg. For a long time
it was considered a remarkable circumstance, hardly admitting of
a satisfactory explanation, that organisms which differed so widely
as polyps and medusae — they had indeed been systematically separated
in different classes — should only form different stages in the life-
history of a single cycle of development. The theory of "Alternation
of Generations" contained only a description of the matter, and
offered no explanation. The discovery of the mode of origin of
the medusa as a bud on the body of the polyp first clearly demon-
strated the direct relation of the two forms; for it proved that the
medusa is a flattened disc-shaped polyp with a shallow, but wide
gastric cavity, the peripheral part of which has, by the fusion (Fig.
107, c) of its upper and lower walls along four, six, or more radiating
areas, become divided into the vascular pouches, or as they are often
called, radial canals. The differences consist mainly in the presence
of the oral cone or hypostome of the polyp as a well-marked external
appendage, the manubrium; in the enlargement of the oral disc to
form the muscular sub -umbrella surface (Fig. 107, c, S) ; in the
collapse of the coelenteron (leaving the endoderm lamella) above
referred to ; and in the greater development of the nervous and
muscular systems in connection with the free -swimming habit of
life. To these may be added the thickening of the structureless
lamella between the dorsal endoderm and ectoderm, to form the jelly-
like tissue which is so characteristic of medusae.

As stated above the medusa is generally produced by budding from a polyp-
colony, but however produced it always develops the generative cells. For this
reason it is frequently called a gonophore. This name, though not employed when
the polyp stage is unimportant (Acalephae) or absent (some Acalephae, Tracho-
medusae, etc.), is applied to all medusae or medusa-like organisms which are
produced by budding from a polyp. Typically a gonophore becomes detached
from its origin, and as a free -swimming medusa distributes the generative
products far and wide ; but in some colonies the gonophore does not become

120

COELENTERATA.

detached. In such cases it may acquire the full development of a medusa, but
more often its development is not complete, and a degenerate medusa — or as it
is often called, a gonophore with concealed medusiform structure — is produced.
These degenerate medusae (hedrioblasts, adelocodonic gonophores, medusoids, as
they are variously called) vary considerably in structure from the stage of an
almost perfect medusa, to a stage in which they consist of little more than
a bud containing the generative cells (sporosacs).

The Ctenophore. The description of the fundamental form of the
Ctenophora will be more conveniently dealt with under the descrip-
tion of the class (see below, p. 197).

Rdc

Eli

FIG. 107.— Diagrammatic longitudinal sections of a, a hydroid polyp, and 5, c, a medusa.
Section b passes through two radial canals, section c between two radial canals. 0 mouth ;
T tentacle ; M enteron ; Ek ectoderm ; En endoderm ; Rdc radial canals ; Re circular canal ;
vel velum ; Gp vascular or endoderm lamella ; S sub-umbrella ; U umbrella.

Asexual reproduction by budding and fission is very widely spread.
It is found in all groups with the exception of the Ctenophora, and
it frequently leads to the formation of colonies, the component
members of which are in bodily continuity. In most cases both
layers of the body wall participate in this mode of reproduction,
but it has recently been asserted that the ectoderm alone participates
in the gemmation of the buds of Hydra; and in the so-called
sporogony, which is found in some Narcomedusae, a single ovum-like
cell of the body has the power of reproducing the whole organism.
The latter should perhaps be regarded as a case of parthenogenesis
which otherwise has not been observed in the Coelenterata. With
this phenomenon of asexual reproduction must be connected the

COELENTERATA.

121

power of regenerating lost parts — a property which is probably widely
diffused in the Coelenterata, and reaches, perhaps, its highest expression
in Hydra. The smallest pieces into which the body of Hydra can be
cut are able to reproduce the whole polyp.

In the asexual reproduction budding and fission may achieve
results varying from the complete formation of a new individual
which separates from the parent, to the mere repetition of a portion
of the growing organism, which remains attached to the parent.
As an instance of the one extreme we may mention Hydra ; of the
other, the Siplionophora ; and between these two extremes we have
the colonial Hydroinedusae and Anthozoa.

In Hydra the whole organism is reproduced; in the Hydromedusan
colonies the whole
parent except the
rooting portion or
hydrorliiza ; in the
Maeandrine Corals
the reproduction is
confined to the oral
disc and stomodaeum,
and perhaps a few
tentacles and mesen-
teries: finally, in the
Siphonophora the
manubrium of the
parent Medusa (or
polyp, according to
the view taken) may
produce almost any
portion of an entire
organism from an um-
brella to a tentacle.

Connected Avith this asexual reproduction are two important
phenomena which must shortly be referred to here. The one is
polymorphism, and the other alternation of generations. In the
colonial Coelenterata the individuals associated in the colony are
rarely all alike in structure. A certain number have one form, others
another form, and with this difference in form is often associated a
difference in the part which they respectively play in the life of
the colony. As an instance we may take the Tubularian colony
called Podocoryne (Fig. 108). Here from a creeping coenosark or

FIG. 108. — Podocoryne carnea (after C. Grobben). P pol^p ;
M medusa bud on the blastostyle ; Sk skeleton polyp ;
S spiral zooid.

122 COELENTERATA.

hydrorhiza arise several individuals, some of which are ordinary
polyps, with a mouth and tentacles; others are polyps lacking the
mouth and tentacles, and acting as defensive organs for the colony
(the dactylozooids) ; others again, while lacking the mouth and
possessing only vestiges of tentacles, have the property of budding
off the gonophores or sexual members of the colony — these are the
blastostyles, and the sexual individuals they produce are imperfectly
developed medusae, which characterize this particular species. In
some species the medusa acquires a complete development, and
breaking away from the colony swims in the sea and distributes
its products far and wide.

The phenomenon of alternation of generations depends upon the
fact that in many Hydromedusae and Acdlephae the fertilized ovum
gives rise to an organism (the polyp) which can produce buds,
but not ova and spermatozoa. Some of the buds become Medusae
or medusa-like individuals in which the sexual elements are formed.
This kind of alternation of generations in which a sexually repro-
ducing generation succeeds one or more generations of asexual forms
is called metagenesis.

The ovum is generally fertilized outside the parent, but in some
Anthozoa the fertilization and the early stages of development take
place in the enteric cavity. In many forms, particularly amongst
the Medusae, all the individuals of the same species discharge their
eggs at the same time of day, but this time may alter slightly
according to the time of year. It is remarkable that in the most
nearly allied species the eggs are discharged at the most different
times. It has been suggested that this is an arrangement to prevent
the crossing of closely allied species.

Almost all Coelenterates are marine. Hydra, Microhydra, Cordy-
lophora amongst polyp forms; and Limnocodium, found in the
Victoria Regia tank of the Royal Botanical Society, London, and
Limnocnida from Lake Tanganyika, amongst Medusae, are the
most striking of the few fresh-water members of the group. The
polyps and polyp colonies are for the most part attached to foreign
bodies and lead sedentary lives, w,hile the Medusae, Siplionophora,
and CtenopJwra are free-swimming pelagic organisms, striking
for their beauty and for the extreme fragility and transparency
of their tissues. Many of them are phosphorescent. The greater
number are littoral or pelagic in habit, but a few forms, often
characterized by important peculiarities of structure, are from the
deep sea.

CNIDARIA.

123

A few are parasitic, e.g., Polypodium hydriforme parasitic in the young stage
in the ova of the Sterlet (Acipenser ruthenus), (Ussow, Ann. and Mag. N". Hist.
(5), 18, 1886); and Mnestra, a medusa parasitic on Phyllirhoe.

The few fossil forms known belong for the most part to the corals,
the hard tissues of which have left traces in the rocks of most periods.
There are traces of Medusa remains in the Solenhofen slates, and the
Graptolites of the Cambrian formation may possibly have been
hydroid colonies, resembling the Sertularidae.

The following table shows the classification of the Coelenterata
adopted in this work : —

Sub-phylum I. CNIDARIA.

CLASS I. HYDROMEDUSAE

(CRASPEDOTA).
Order 1. HYDRIDA.
„ 2. HYDROOOKALLINAE.
,, 3. TUBULARIAE.

ANTHOMEDUSAE.
,, 4. CAMPANTJLARIAE.

LEPTOMEDUSAE.
,, 5. TRACHOMEDUSAE.
,, 6. NARCOMEDUSAE.
„ 7. SIPHONOPHORA.

CLASS II. ACALEPHAE

(ACRASPEDOTA).
Order 1. SCYPHOMEDUSAE

(TETRAMERALIA).

CLASS II. ACALEPHAE— Continued.

Order 2. EPHYRONIAE

(OCTOMERALIA).

CLASS III. ANTHOZOA.

Order 1. RUGOSA

(TETRACORALLA).
,, 2. ALCYONARIA

(OCTACTINIA).
,, 3. ZOANTHARIA

(HEXACTINIA).

Sub-phylum II. CTENOPHOBA.

CLASS CTENOPHORA.

Order 1. TENTACULATA.
2. NUDA.

Sub-phylum I. CNIDARIA.

Coelenterata with thread-cells.

It is on the whole convenient to use the characteristic thread-cells
to divide the Coelenterata into two sub-phyla — the Cnidaria and
Ctenopliora — although it must not be forgotten that these structures
have been observed in one Ctenophore, and are found outside the
limits of the Coelenterata altogether (Platyhelminthes, Mollusca,
Protozoa).

Class I. HYDROMEDUSAE (CRASPEDOTA).*

Cnidaria in which the medusa has a velum and the polyp is
without gastral ridges or filaments.

This class includes polyps; colonies of polyps, which produce

* The Hydroniedusae coincides with the old group Hydrozoa, excluding the
Acalephae. It appears convenient to place the latter in a separate class to mark
their intermediate position between the Hydromedusae and Actinozoa.

124

COELENTERATA.

medusae or modified medusae by budding; and medusae which
arise directly from the egg. The polyps are generally attached
permanently to foreign bodies, and are of small size ; but in the
SipTionophora the whole colony is free-swimming. The medusae
are also of small size and possess a velum. When skeletal structures
are present they consist, as a rule, of a more or less horny secretion
of the ectoderm (perisark). In one order, however, the secretion
is calcareous (Hydrocorallinae).

The colonies very often pfesent, in a well-marked manner, the
phenomenon of polymorphism, and in describing the various

FIG. 109.— Development of hydroid polyps (from Chun, I and II
after Metschnikoff, III after Allnian). I. Young larva of Clytia
flavidula six hours after attachment, ek ectoderm ; en radially
pouched endoderm (rudiment of hydrorhiza) ; g enteric space ;
hy cylindrical projection which constitutes the hydrocaulus.
II. Larva of Clytia one day after fixation ; the hydrorhiza forms
a chambered disc from which the cylindrical hydrocaulus pro-
jects ; nematocysts are present in the ectoderm. III. Older
larva of Eudendrium ramosum; the hydrocaulus invested by the
chitinous perisark (ch) projects from the discoidal hydrorhiza ; a hydrocephalis with a
tentacular circlet (t) has been developed at the free end of the hydrocaulus ; the mouth
is not yet formed.

modifications which may be present it will be convenient to explain
some of the more common terms which are used in the cumbrous
and complicated nomenclature of the group.

The fertilized ovum very generally giVes rise to an oviform free-swimming
larva — the planula (Daly ell*), consisting of an outer layer of ciliated ectoderm
and an inner hollow mass of endoderm. After a short time it loses its cilia and
secretes a thin cuticular covering — the perisark — and becomes attached by one
end (Fig. 109). The free end elongates and develops a terminal mouth and

1847.

Sir J. Graham Dalyell, Rare and Remarkable Animals of Scotland, London,

HYDROMEDUSAE.

125

mec-

tentacles, while the attached end often spreads itself into a discoidal root
(Fig. 109), the hydrorhiza.* This is the first polyp. The free upstanding
portion is correctly
termed the hy-
dranth, though the
word polyp is some-
times loosely ap-
plied to it. The
hydranth elongates
and begins to bud,
and two parts be-
come distinguish-
able in it — a ter-
minal part called
the polyp-head or
hydrocephalis with
the mouth and ten-
tacles, and a lower part with
the buds, the stem or coeno-
sark. The buds lengthen,
remain attached to the parent,
and themselves become differ-
entiated into hydrocephalis and
coenosark. The whole colony
of hydranths thus formed is
called the hydrosoma. The
term hydropJiyton seems to be
applied to the coenosark plus
hydrorhiza, while hydrocaulus^
appears to be synonymous with
coenosark. In some forms the
perisark does not extend on to
the polyp-head but stops short
at its base ; in others it is con-
tinued round the polyp- head
as a cup — the hydrotheca (Fig.
114), which, however, stands
off from the polyp, being only
connected with it by pseudo-
podial prolongations of the
ectoderm. The polyp-head can
shrink into the hydrotheca for
protection. Some of the buds
formed by the colony develop

gth-

FIG. 110. — Gonangium with hedrioblasts of Gono-
thyraea loveni (from Chun, after Allman). U
blastostyle ; gth gonangium (gonotheca) ; c oper-
culum of gonangium ; go1-^ budding gonophores
(hedrioblasts) ; mec1 hedrioblast with planulae
pi; mec2 hedrioblast with ova in manubrium.

* The hydrorhiza has some-
times the form of a branching
and anastomosing tube, from
which the hydranths arise by
budding.

f The coenosark or hydrocaulus is said to be fascicled or polysiphonic when it
is composed of several adherent tubes, monosiphonic when consisting of a single
tube.

126

COELENTERATA.

into medusae which become free-swimming, or medusoids which are imperfectly
developed medusae and do not become free. These medusae and medusoids are
called the gonophores because the gonads are contained in them. A phanero-

codonic gonophore is a free - swimming
medusa, and is sometimes termed a
planoblast ; an adelocodonic gonophore is
a medusoid, and is sometimes called a
hedrioblast. Sometimes the gonophores
are budded only from special hydranths,
which are then modified by the absence
or diminution of size of the tentacles
and mouth. Such a proliferous hydranth
is a blastostyle. In the forms with
hydrothecae, the hydrotheca of the
blastostyle forms a chitinous capsule
enclosing the blastostyle and gonophores ;
it is called the gonangium or gonotheca
(Figs. 110, 114). Colonies with gonangia
are called calyptoUastic ; those without
gymnoblastic. The word zooid or person
is sometimes applied to any individual
of a colony, whether hydranth, gono-
phore, or blastostyle, etc. Trophosome
means the entire assemblage of zooids
which are concerned with the nutrition
of the colony, i.e., all the hydranths;
gonosomc the entire assemblage of zooids
which are concerned with the sexual
reproduction of the colony, i.e., all the
gonophores. A dactylozooid or spiral
zooid is a hydranth without or with
reduced mouth and tentacles, specially
developed in some genera (Hydractinia
and Podocoryne, Fig. 108) for defensive
purposes. A nematophore (macho-polyp,
guard -polyp, sarcostyle) is a special
stalked projection of the coenosark found
in the Plumularidae (Fig. 111). It con-
sists of ectoderm, which contains thread-
cells and is highly amoeboid, and of a
solid axis of endoderm ; the whole is en-
closed in a theca (sarcotheca) of perisark.
Nematophores are probably nutritive,
catching food as an Amoeba does, by
th'e pseudopodia of their ectoderm.

Hydrocladium is a special term applied
to the hydrotheca - bearing branches
(ramuli) of the coenosark of Plumula-
ridae. Phyladocarps are specially modified hydrocladia bearing gonangia as
well as nematophores and sometimes hydrothecae ; they often develop protective
branches — the costae — which form the walls of an open basket-work and enclose

FIG. 1 1 1 . —A ntennularia ante nnina. Bran ch
(hydrocladium) of colony with hydranths
and nematophores (from Chun, after All-
man), p extended, p* retracted hydranth ;
n, ng nematophores ; r coenosark (hydro-
cladium).

HYDRIDA HYDROCORALLINAE. 127

the gonangia. When the costae are well developed and the hydrothecae are
suppressed, the phylactocarp is called a corbula (Aglaophenia).

The generative cells, though nearly always ripening in and discharg-
ing from the ectoderm of gonophores, make their first appearanpe in
a great variety of places : in the ectoderm of the free Medusa, in the
endoderm or ectoderm of the fixed gonophore, in the ectoderm of the
coenosark, near or remote from the budding gonophore, or even in
the endoderm. But wherever they arise they eventually migrate —
passing, if necessary, through the structureless lamella — to the gono-
phore, in the ectoderm of which they are generally, though not
always, contained.

The Hydromedusae feed chiefly on animal substances, and Hydra
possesses chlorophyll bodies in its endoderm. Whether these are
chlorophyll bodies like those of plants or symbiotic Algae, like those
of Radiolaria, seems uncertain. The free-swimming Medusae and
Siphonophora are phosphorescent. With a few exceptions they are
marine organisms.

Order 1. HYDRIDA.

Solitary polyps without medusoid buds. Both generative products
are developed in the ectoderm of the polyp.

In this order colonies are not formed, and there are no medusoid
individuals. The generative cells are produced by the ectoderm of
the polyp itself. There is only one genus, Hydra L., the fresh-
water polyp.

The genera Protohydra Greeff, and Microhydra Potts, are possibly allied here.
Protohydra is marine, and reproduces by transverse fission. Microhydra is fresh-
water, and invested by a coat of mud. Both genera are without tentacles, and
the sexual reproduction is unknown.

Order 2. HYDROCORALLINAE.*

Colonial Hydromedusae consisting of a meshwork of coenosarcal
canals, the ectoderm of which secretes a hard calcareous matter filling
up the spaces of the meshwork. Polyps of two forms, gastrozooids
and dactylozooids. Gonophores of the form of rudimentary medusae
are generally present.

For a long time the position of the Hydrocorallinae was uncertain.
L. Agassis first suggested that Millepora was not an Anthozoon but
a Hydroid, but it was not until Moseley had worked out the anatomy

* H. N. Moseley, "Report on Corals," Challenger Reports, vol. 2. S. J.
Hickson, "The Medusae of Millepora Murrayi, etc," Q.J.M.S., vol. 32. 1891.

128

COELENTERATA.

FIG. 112. — Group of polyps of Millepora
nodosa. A gastrozooid surrounded
by five dactylozooids B ; o mouth ;
c tentacles ; d tubes (after Moseley).

of the soft parts of this genus and
of the Stylasteridae, that the Hydro-
medusan affinities of these animals
were clearly proved, and that the order
Hiidrocorallinae was definitely estab-
lished.

The colonies have the form of
encrusting or arborescent masses con-
sisting of a network of coenosarcal
canals (Fig. 113) permeating a hard
calcareous support called the coeno-
steum. The canals consist of ectoderm
and endoderm, and the coenosteum is
calcareous matter secreted by the
ectoderm and comparable to the peri-

sark of other Hydroid colonies. From the surface of the colony
which is covered by a layer of ectoderm the polyps project. They
are of two kinds — gastro-
zooid s with a mouth and
tentacles, and more nu-
merous dactylozooids (Fig.
112) with or without
tentacles, but always
without a mouth. They
are lodged in pits or caly-
cles excavated in the sur-
face of the coenosteum,
and lined by a continuation
of the surface ectoderm.
The relation of the surface
ectoderm to the ectoderm
of the polyps and of the
canals is not known. The
polyps of the two kinds
are either scattered irregu-
larly over the surface of
the colony, or gathered
into groups more or less
regular, in each of which
a centrally placed gastro-
zooid is surrounded by a

DZ--

G2-

--DZ

FIG. 113. — Vertical section through a group of retracted
zooids of Allopora profunda (after Moseley). DZ dac-
tylozooids ; P calycles of dactylozooids separated by
pseudosepta ; Z gastrozooid giving off canals which
join the coenosarcal network ; GZ calycle of gastro-
zooid ; DZ' dactylozooids of an adjacent group; G
gonozooid (gonophore).

TUBULARIAE. 129

ring of dactylozooids. The cavities of the zooids communicate with
the coenosarcal meshwork by large canal offsets. Gonophores having
the form of rudimentary medusae are developed on the coenosarcal
tubes, and are often lodged in special ampullae of the coenoat^um.
The tentacles generally possess knobbed extremities armed with
thread cells. From coral reefs and warm seas.

Fam. 1. Milleporidae. Coenosteum arborescent or encrusting, composed of
a thin superficial living layer, lying upon dead layers of former growth. Pores
without styles, but divided by tabulae marking the successive layers of growth.
Dactylozooids with knobbed tentacles. Millepora L.

Fain. 2. Stylasteridae. Coenosteum arborescent, with a strong tendency to
assume a fan-like form, and to the development of the pores on one face only
or on the lateral margins of its branches. In some genera a superficial layer
only of the coenosteum is living, in others nearly the entire mass retains its
vitality. Pores with tabulae in two genera only. Gastropores provided with
a conical calcareous projection — the style — at their bases. Pseudosepta, arising
from the partial confluence of the dactylopores and gastropores, sometimes
present. Dactylozooids without tentacles. Colonies dioecious. Found in all
seas in shallow and deep waters.

Sporadopora Moseley ; Pliobothrus Pourtales ; Errina Cray ; Distichopora
Lamarck ; Labiopora Moseley ; Spinipora Moseley ; Allopora Ehrenberg ;
Stylaster Gray ; Stenohelia S. Kent ; Conopora Moseley ; Astylus Moseley ;
Cryptohelia M. Edw. and Haime.

Order 3. TUBULARIAE* (GYMNOBLASTEA).

Without hydrothecae and gonangia. Polyps, ivhen more than one,
forming permanent colonies. Generative individuals, ivhen set free,
are Anthomedusae.

The Tubulariae are almost all colonial (the Corymorphinae, Myrio-
thela, etc., are solitary), and they all produce medusoid gonophores
by budding. The gonophores are either set free as Medusae, or
only become partially developed as medusoids, with rudiments of the
medusan organs, e.g., manubrium, gastro vascular canals, and marginal
tentacles. The Medusae have ocelli, and their gonads are in the

manubrium.

Section 1. Tubularinae.

Colonial forms with a perisark destitute of investing layer of coenosark.

Fam. 1. Clavidae. Polyps with scattered filiform tentacles. Clava Gmelin ;
Cordylophora Allm., fresh and brackish water; Tubidava Allrn. ; Merona
Norman ; Rhizogeton Ag. ; Clavula Wright ; Dendrodava "Weissman ; Campani-
dava Allm. ; Corydendrium v. Ben.

* G. J. Alhnan, A Monograph of the Gymnoblastic or Tubularian Hydroids,
Ray Society, 1871. G. J. Allman, "Report on the Hydroidea," Pts. 1 and 2
Challenger Reports, 1883 and 1888. T. Hincks, A Monograph of the British
Hydroid Zoophytes, London, 1868. E. Haeckel, Monographic der Medusen,
Jena, 1879.

130 COELENTERATA.

Fam. 2. Corynidae. Polyps with scattered, more or less spirally disposed,
capitate tentacles. Coryne Gartner ; Actinogonium Allm. ; Syncoryne Ehrb. ;
Gfymnocoryne Hincks ; Gemmaria McCrady.

Fam. 3. Bougainvillidae. Hypostome not abruptly differentiated (conical).
Tentacles filiform in a single circle round the base of the hypostome. Bougain-
villia Lesson; Perigonimus Sars ; Bimeria S. Wright; Dicoryne Allm. ; Stylactis
Allm.; Atractylis S. Wright; Diplura Green; Hydranthea Hincks; Cionistes
S. Wright ; Heterocordyle Allm. ; Wrightia Allm. ; Garveia S. Wright.

Fam. 4. Eudendridae. Hypostome abruptly differentiated from the body
(everted). Tentacles filiform in a ^ngle row. Eudendrium Ehrb.

Fam. 5. Pennaridae. Polyps with filiform and capitate tentacles. Pennaria
Goldfuss ; Halocordyle Allm. ; Stauridium Duj. ; Vorticlava Alder ; Heteroste-
phanus Allm. ; Acharadria S. Wright ; Acaulis Stimpson ; Cladonema Duj.

Fam. 6. Cladocorynidae. Polyps with simple and ramified capitate tentacles.
Cladocoryne Rotch.

Fam. 7. Clavatellidae. With simple capitate tentacles in a single row.
Clavatella Hincks.

Fam. 8. Tubularidae. Polyp with a proximal and distal row of simple
filiform tentacles. Tubularia L. ; Hybocodon Ag. ; Ectopleura Ag.

Fam. 9. Myriothelidae. Polyp solitary. Tentacles scattered, capitate.
Myriothela Sars.

Section 2. Hydractininae.

Colonial. Perisark invested by a superficial covering of naked coenosark ;
with spiral zooids. Very frequently found coating the gastropod shell of a
Hermit Crab.

Fam. 10. Hydractinidae. With sessile gonophores. Hydradinia v. Ben.

Fam. 11. Podocorynidae. Gonophores as free medusae. Podocoryne Sars
(Fig. 108) ; Corynopsis Allm.

Section 3. Corymorphinae.
Polyps solitary, without perisark.

Fam. 12. Corymorphidae. Gonophores as free medusae. Corymorplia Sars ;
Halatraclus Allm. ; Amalthaea 0. Schmidt.

Fam. 13. Monocaulidae. Gonophores as fixed sporosacs. Monocaulus Allm.

Section 4. Hydrolarinae.

Polyps unsymrnetrical, with the tentacles, one or two in number, springing
from one side of the body.

Fam. 14. Hydrolaridae. Lar Gosse.

The Medusae of this order are arranged by Haeckel as follows : —
ANTHOMEDUSAE.

Craspedota without otocysts, wifii ocelli at the base of the tentacles,
and ititli manulrial gonads ; radial canals usually 4, rarely 6 or 8 ;
budded from Polyps of the Tubular iae.

Fam. 1. Codonidae. Mouth-opening simple; gonads not radially divided;
4 narrow radial canals ; imbranched tentacles. The polyps of most Sarsiadae
belong to the genus Syncoryne, of Ectopleura to Tubularia, of Euphysidae to
Corymorpha, of Globiceps to Pennaria.

ANTHOMEDUSAE. 131

Sub-fara. 1. Sarsiadae. With 4 radial tentacles. Codonium H. * ; Sarsia
Lesson ; Syndictyon A. Ag. ; Ectopleura L. Ag. ; Dipurena McCrady ;
Bathycodon H.

Sub-fam. 2. Dinemidae. With 2 radial tentacles. Dicodonipm H. ;
Dinema v. Ben.

Sub-fam. 3. Euphysidae. With 3 rudimentary tentacles, and one
strongly developed. Sieenstrupia Forbes ; Euphysa Forbes ; Hybocodon
L. Ag. ; Amplncodon H.

Sub-fam. 4. Amalthaeidae. All four tentacles rudimentary, Amalthaea
0. Schmidt ; Globiccps Ayres.

Fam. 2. Tiaridae. With 4 frilled buccal lobes ; with 4 manubrial gonads,
which may be split into 8 ; with 4 wide radial canals ; and unbranched tentacles.
Ontogeny only known in two species. The polyp of Turris neglecta is Clavula
Gossei, that of Corynetes Agassizii is Halocharis spiralis.

Sub-fam. 1. Protiaridae. With 4 perradial tentacles. Protiara H.;
Modceria Forbes ; Corynetes McCrady.

Sub-fam. 2. Amphinemidae. With 2 opposite radial tentacles. AmpTii-
nema H. ; Codonorchis H. ; Stomotoca L. Ag.

Sub-fam. 3. Pandaeidae. With numerous tentacles. Pandaea Lesson ;
Conis Brandt ; Tiara Lesson ; Turris Lesson ; Catablema H. ; Turritopsis
McCrady ; Callitiara H.

Fam. 3. Margelidae. With 4 or more simple or branched oral tentacles,
with 4 or 8 separate manubrial gonads ; with simple unbranched tentacles, which
may be uniformly distributed or grouped in 4 or 8 bundles. Development
known in a few species ; pol}7p usually belongs to Bougainvillea (Lizusa, Margelis,
Hippocrene, Rathkca), polyp of Dysomorpha to Podocoryne, of Cytaeandra to
llhizocline. The polyp of Lizzia (blondina ?} is said by Allman to be a Campanu-
larian, Laomedia (Leptoscyphus) tennis.

Sub-fam. 1. Cytaeidae. With unbranched oral, and uniformly distributed
marginal tentacles. Cytaeis Eschsch ; Cubogaster H. ; Dysmorphosa Phillipi ;
Cytaeandra H.

Sub-fam. 2. Lizusidae. With unbranched oral, and 4 or 8 bundles of
marginal tentacles. Lizusa H. ; Lizzia Forbes ; Lizzella H.

Sub-fam. 3. Thamnostomidae. With 4 branched oral, and uniformly
distributed marginal tentacles. Thamnitis H., Thamnostylus H. ; Tham-
nostoma H. ; Limnorea Peron.

Sub-fam. 4. Hippocrenidae. Oral tentacles branched, marginal tentacles
in 4 or 8 groups. Margelis Steenstrup ; Hippocrene Mertens ; Nemopsis
L. Ag. ; Margellium H. ; Rathkea Brandt.

Fam. 4. Cladonemidae. With dichotomously branched or feathered tentacles,
with 4 to 8 narrow, simple or bifurcated radial canals, with 4 or 8 separate
manubrial gonads. Oral arms 4, numerous, or absent. Polyp form known
inl 3 genera, viz. , Gemmaria is the medusa of Gemellaria, Eleutheria of Clava-
tclla, Cladonema of Stauridium.

Sub-fam. 1. Pteronemidae. Radial canals simple. PteronemaH. ; Zanclea
Gegenb. ; Gemmaria McCrady ; Eleutheria Quatref.

Sub-fam. 2. Dendronemidae. Radial canals bifurcated. Ctenaria H.
resembles the Ctenophora, ex-umbrella with 8 adradial ribs of thread cells ;
Cladonema Duj. ; Dendronema H.

* Throughout the Cnidaria H. stands for Haeckel. •

132

COELEXTERATA.

Order 4. CAMPANULARIAE* (CALYPTOBLASTEA).

With hydrothecae and gonangia. Colonial. Generative individuals,
when set free, are Leptomedusae.

The Campanulariae are colonial Hydromedusae, and they all
produce gonophores by budding. The zooids are provided with
hydrothecae (Fig. 114), which, in the case of the blastostyles, form
gonangia. The gonophores are either set free as Medusae, or are

only partially developed
as Medusoids (hedrio-
blastic), with rudiments
of the medusan organs.
The Medusae generally
have marginal auditory
organs of the vesiculate
type, and their gonads
lie beneath the radial
canals (Fig. 106).

Section 1. Campanularinae.

Hydrothecae at least in
the proximal part of the
colony never adnate by their
sides to the hydrocaulus.

Fam. 1. Haleciidae. Hy-
drothecae reduced to shallow
saucer-shaped pedunculate
appendages (hydrophores).
Hydranths with conical
hypostome. Gonophores
hedrioblastic. Halecium
Oken ; Diplocyatlms Allm.;
Ophioides Hincks.

Fam. 2. Campanularidae.
Hydrothecae borne by pe-
duncles, campanulate or
tubular. Hydrocaulus not
enveloped by peripheral
tubes. Gonophores free-
swimming or sessile. Campanularia Lamarck ; Obelia Peron and Lesueur ;
Thyroscyphus Allm. ; Hypanthea Allm. ; Calamphora Allm. ; Hebella Allm. ;
Halisiphonia Allm. ; Coppinia Hassall ; Calycella Hincks ; Clytia Lamouroux ;
Campanopsis Glaus ; Melicertaria Haeckel ; Lovtnella Hincks ; Cuspidella
Hincks ; Thaumantias Esch. ; Campanulina v. Ben. ; Leptoscyphus Allm.

* T. Hincks, A Monograph of the British Hydroid Zoophytes, London, 1868.
G. 3. Allman, "Report on the Hydroidea," Pts. 1 and 2, Challenger Reports,
Ife83 and 1888. E. Haeckel, Monographie der Medusen, Jena, 1879.

Fio. 114. — Branch of an Obelia colony (0. gelatinosa).
0 mouth of a nutritive polyp with extended tentacles ;
M medusa-buds on a blastostyle in a gonatheca ; Th
hydrotheca.

LBPTOMEDUSAE.

133

Fam. 3. Perisiphonidae. Hydrocaulus enveloped by peripheral tubes ; the
hydrothecae are never adnate and are carried by the axial tube only. Lafoea
Lamouroux ; Lictorella Allm. ; Cryptolaria Busk ; Perisiphonia Allm.

Section 2. Sertularinae. ^

Hydrothecae developed from more than one side of the hydrocaulus, to which
they are all adnate for a greater or less extent by their sides.

Fam. 4. Grammaridae. Hydrocaulus consisting of an axial tube which carries
the hydrothecae and is sur-
rounded by and inseparably
coalesced with peripheral tubes
without hydrothecae. Hydro-
thecae adnate to axial tube.
Grammaria Stimpson.

Fam. 5. Sertularidae. Hy-
drothecae in two or more
series, adnate to hydrocaulus.
Gonophores sessile. Sertularia
L. ; Diphasia Agassiz ; Thui-
aria Fleming ; Desmoscyphus
Allm. ; Hypopyxis Allm. ;
Staurotkeca Allm. ; Dictyo-
cladium Allm. ; Synthecium
Allm. ; Thecocladium Allm. ;
Hydrallmania Hincks.

FIG. 115.— Free Medusa of Obelia gelatinosa as yet
without gonads ; g otocysts.

Section 3. Idiinae.

Hydrothecae adnate to hy-
drocaulus. Coenosark divided
into segments which form two longitudinal series of intercommunicating cham-
bers, each of which communicates with the gastral cavity of a hydranth.

Fam. 6. Idiidae. Idia Lamouroux.

Section 4. Plunmlarinae.

Hydrothecae developed from one side only of the hydrocaulus, to which they
are adnate by their sides. Sarcostyles (nematophores) are always present.

Fam. 7. Plumularidae. Antennularia Lamarck; Sciurella Allm. ; Acanthella
Allm. ; Plumularia Lamk. ; Schizotricha Allm. ; Polyplumaria Sars ; Heteroplon
Allm. ; Halicornaria Busk ; Azygoplon Allm. ; Streptocaulus Allm. ; Diplochcilus
Allm.; Lytocarpus Kirchenpauer ; Acanthocladium Allm.; Cladocarpus Allm.;
Aglaophenia Lamouroux.

The Medusae of this order are arranged by Haeckel as follows : —
LEPTOMEDUSAE.

Craspedota partly icifh, partly without, otocysts ; ocelli ywesent or
absent ; gonads on radial canals ; budded from polyps of the
Campanulariae.

Fam. 1. Thaumantidae. Radial canals simple, unbranched, without otocysts.
Polyp form known only in Laodice (Thaumantaria) calcarata as Thaumantias
inconspicua, and in Melicertum campanula as Melicertum campanula.

134 COELENTERATA.

Sub-fam. 1. Laodicidae. With 4 radial canals and 4 gonads. Tetranema
H. ; Dissonema H. ; Octonema H. ; Thaumantias Eschsch. ; Staurostoma H. ;
Laodice Lesson.

Sub-fam. 2. Melicertidae. With 8 radial canals and 8 gonads. Meli-
certella H. ; Mclicertissa H. ; Melicertum A. Ag. ; Melicertidium H.

Sub-fam. 3. Orchistomidae. With numerous radial canals. Orchis-
toma H.

Fam. 2. Cannotidae. Without marginal vesicles, with 4 or 6 radial canals
which are branched, bifurcated, or pinnate. Development unknown.

Sub-fam. 1. Polyorchidae. •With 4 or 8 pinnate radial canals, the side
branches ending blindly. Staurodiscus H. ; Gonynema A. Ag. ; Ptychogena
A. Ag. ; Staurophora Brandt ; PolyorcMs A. Ag.

Sub-fam. 2. Berenicidae. With 4 or 6 branched radial canals, branches
and main canals open into circular canal. Cannota H. ; Dyscannota H. ;
Berenice Peron and Lesueur ; Dipleurosoma Axel Boeck.

Sub-fam. 3. Williadae. With 4 or 6 bifurcated radial canals, the
branches only open into circular canals. Dicranocanna H.; Toxorchis H. ;
Willetta H. ; Willla Forbes ; Proboscidactyla Brandt ; Cladocanna H.
Fam. 3. Eucopidae. With marginal vesicles and 4 simple unbranched radial
canals, in whose course 4 or 8 gonads lie. The polyps when known belong to
the genera Campanularia, Obelaria, Clytia, Campanulina, etc.

Sub-fam. 1. Obelidae. 8 adradial marginal vesicles, stomach without
stalk. Eucopium H. ; Saphenella H. ; Eucope Gegenbaur ; Obelia Peron and
Les. (Fig. 115) ; Tiaropsis L. Ag. ; Eucliilota McCrady.

Sub-fam. 2. Phialidae. Numerous marginal vesicles, stomach without
stalk. Phialium H. ; Phialis H. ; Mitrocomium H. ; Epenthcsis McCrady ;
Mitrocomella H. ; Phialidium Leuckart ; Mitrocoma H.

Sub-fam. 3. Eutimidae. 8 adradial marginal vesicles, a distinct, often
long, stomach-stalk. Eutimium H. ; Eutima McCrady ; Sapiienia Eschsch. ;
Eutirneta H. ; Eutimalphcs H. ; Octorchidium H.; Octorchis H.; Octor-
chandra H.

Sub-fam. 4. Irenidae. Numerous marginal vesicles, a distinct stomach-
stalk. IreniumH. ; Irene TLsch. ; Tima Esch.

Fam. 4. Aequoridae. With marginal vesicles and with numerous (often
over 100) simple or branched radial canals. Polyp of Polycanna (Zyyodactyla)
mtrina only known as a very small Campanaria.

Sub-fam. 1. Octocannidae. With 8 simple radial canals. Odocanna H.
Sub-fam. 2. Zygocannidae. With 8 or more radial canals bifurcated at
their base. Zygocanna H. ; Zygocannota H.; Zygocannula H. ; Halopsis
A. Ag.

Sub-fam. 3. Polycannidae. With numerous simple radial canals which
arise separately from the stomach (12 or more to over 100). Aequorea
Peron and Les. ; fihcgmatocfcs A. Ag. ; Stomobrachium Brandt ; Stauro-
brachium H. ; Mesonema Esch. ; Polycanna H.

Limnocodium,* a fresh-water medusa from the Victoria Regia tanks of the
Royal Botanic Society, London, and of unknown habitat, is probably allied
here.

* G. H. Fowler, Quart. J. Mic. Sci., vol. 30, 1889, p. 507.

TRACHOMEDUSAE. 135

Order 5. TRACHOMEDUSAE.*

Hydromedusae without hydrosome (polyp stage); with marginal
sense-tentacles in pits or vesicles, ivith endodermal otoliths. Ocelli
usually absent. Gonads radial. Radial canals 4, 6, or 8, oft&jrwith
centripetal canals. With .thread-cell thickening of ectoderm round the
edge of the umbrella.

The medusae of this order (Fig. 101) develop directly from the
egg, and no polyps are known.

Fam. 1. Petasidae. With 4 radial canals and 4 gonads, stomach without
stalk, with sense-tentacles sometimes free, sometimes in vesicles.

Sub-fam. 1. Petachnidae. Without centripetal canals. Petasus H-.,
Dipetasus H. ; Petasata H. ; Petachnum H. ; Aglauropsis F. Miiller ; Gossea
L. Ag.

Sub-fam. 2. Olindiadae. With blind centripetal canals. Olindias
F. Miiller.

Fam. 2. Trachynemidae. 8 radial canals and 8 gonads, without stomach-
stalk, sense-tentacles rarely free, usually in vesicles.

Sub-fam. 1. Marmanemidae. Tentacles without suckers, mesogonionsf
absent. Trachynema Gegenbaur ; Marmanema H. ; Hhopalonema Gegenbaur.
Sub-fam. 2. Pectyllidae. Tentacles with suckers, with 8 radial meso-
gonions.t Pectyllis H. ; Pectis H. ; Pectanthis H.

Fam. 3. Aglauridae. With 8 radial canals, stomach with stalk, sense
tentacles free.

Sub-fam. 1. Aglanthidae. With 8 radial gonads (sometimes 011 the
stomach-stalk, sometimes on the sub-umbrella). Aglantha H. ; Aglaura
Peron and Les. ; Agliscra H.

Sub-fam. 2. Persidae. 4 or only 2 opposite gonads. Stauraglaura H. ;
Persa McCrady.

Fam. 4. Geryonidae. With 4 or 6 radial canals and flattened gonads ; with
long stomach-stalk ; with 8 or 12 marginal umbrella-clasps or peroniums ; and
with 8 or 12 closed tentaculocysts (sense tentacles enclosed in vesicles), which are
embedded in the jelly on the axial side of the peroniums (Fig. 102).

The tentacles are in three different groups which appear at three different
periods of the development. (1) The primary tentacles are transitory larval
organs, and filled with solid endoderm. They are perradial and 4 or 6 in
number. They pass on to the ex-umbrella, and remain connected with the
edge by a peronium. (2) The secondary tentacles are interradial and also solid,
and 4 or 6 in number. They pass on to the ex-umbrella, and remain connected
with the edge by peroniums. They may fall off or persist. (3) The tertiary
tentacles develop last and persist. .They arise beneath the perradial primary
tentacles just to one side of the peroniums of these latter. They are hollow
and long, and their cavity opens into the circular canal. There is a solid

* E. Haeckel, Monographic der Medusen. Jena, 1879.

f Mesogonions are thin vertical radial folds of the sub-umbrella, which underlie
the radial canals and divide the gonads into two separate halves. They incom-

g'etely divide the umbrella cavity into spaces recalling the funnel-cavities of the
eriphyllidac.

136 COELENTERATA.

cartilaginous strip of endoderm beneath each of the 8 or 12 peroniums, close
to which are the tentaculocysts.

Sub-fam. 1. Liriopidae. 4 gonads and 4 radial canals ; 8 tentaculocysts
(4 primary perradial and 4 secondary iuterradial). Permanent tentacles,
4 or 8. Liriantha H. ; Lirwpe Lesson ; Glossoconus H. ; Glossocodon H.

Sub-farn. 2. Carmarinidae. 6 gonads in the course of the 6 radial canals,
12 tentaculocysts (6 primary interradial, and 6 primary perradial). Tentacles
6 or 12. Geryones H. ; Geryonia, Per. and Les., without centripetal canals ;
Carmaris H.; Carmarina H. (Fig. 101), with centripetal canals.

Order 6. "^ARCOMEDUSAE.*

Craspedota with free auditory tentacles. Tentacles inserted dorsally
on the ex-umbrella, and connected ivith its edge by peroniums. Radial
canals when present in the form of flat radial gastric pouches.

So far as is known the Narcomedusae are without the hydroid
phase. There is a thickened ectodermal ring at the umbrella edge
which is prolonged on to the ex-umbrella to the insertion of the
tentacles as the peroniums (Fig. 96). The peripheral part of the
umbrella is lobed. The gonads are primitively in the ventral or
lateral wall of the stomach, whence they are often spread out on
the radial gastral pouches. The circular canal is either obliterated,
or else in festoons (Fig. 96), following the edge of the lobes to
open into the gastral pouches. The radial structures (tentacles,
lobes, and pouches) vary in number — they may be rarely 4, usually
8 or more to 32. Otoporpae or peronial streaks of ectoderm passing
from the auditory tentacles may be present (Fig. 96).

Fam. 1. Cunanthidae. With wide, pouch-like radial canals, which are
connected with the circular canal by double peronial canals (festoon canals,
Fig. 96). With otoporpae. Ounantha H. ; Cunarcha H. ; Cunoctantha H. ;
Cunina Esch. ; Cunissa H.

Fam. 2. Peganthidae. Without radial canals and gastral pouches, but
with a festoon canal, with otoporpae. Polycolpa H. ; Polyxcnia Esch. ; Pegasia
Per. and Les. ; Pegantha H.

Fam. 3. Aeginidae. With a circular canal which communicates with the
stomach by double peronial canals ; with internemalf gastral pouches ; without
otoporpae. Aegina Esch. ; Aeginella H. ; Aegineta Gegenbaur ; Aeginopsis
Brandt; Aeginura H. ; Aeginodiscus H. ; Aeginodorus H. ; Aeginorhodtisld.

Fam. 4. Solmaridae. Without circular canal and peronial canals ; sometimes
without radial canals, sometimes with modified radial canals (pernemal or inter -

* E. Haeckel, Monographic d. Medusen. Jena, 1879.

t Internemal gastral pouches are really interradial pouches projecting from
a radial (pernemal) pouch (suppressed in the Acginidae] into the lobes of the
peripheral part of the umbrella. Each original radial pouch gives off two of
these internemal pouches, one into one lobe and the other into the adjacent
lobe. The two internemal pouches of one radial gastric pouch are therefore
separated by the double peronial canal, or festoon-like loop of the circular
canal, which runs into the central stomach radially.

SIPHONOPHOR A. 137

nenial gastral pouches) ; without otoporpae. Solmissus H. ; Solmundus H. ;
Solmundella H. ; Solmoncta H. ; Solmaris H.

Limnocnida,* a fresh- water Medusa from Lake Tanganyika, is probably allied
here.

Order 7. SIPHONOPHORA.!

Free-swimming polymorphic colonies of Hydromedusae produced by
budding from an original, probably medusoid, individual. Gonads in
gonophores which, as a rule, are not set free.

The colonies of the Siphonophora are characterised by the extreme
specialization of the individuals composing them. So great indeed
is this specialization that some zoologists (Eschscholtz, Huxley,
Metscknikoff) have held the view that their component parts are
really organs of a single medusoid individual, which is distinguished
from an ordinary medusa by the fact that its various parts — manu-
brium, tentacles, umbrella — have multiplied independently of one
another, and have become differentiated and in part dislocated from
their primitive positions ; in short, that a siphonophore, in possessing
in a marked degree the power of vegetative increase of its parts,
resembles a plant more than an animal.

This multiplication of the parts of an organism, often independently of one
another, is not however by any means exclusively a vegetable characteristic.
It must have happened largely in the animal kingdom, and have been a potent
factor in determining the forms of animal life.

Another view, and the one more generally held, is that they are
free-swimming polymorphic colonies of highly specialized polyps,
with the power of producing medusae (Yogt, Leuckart, Gegenbaur,
Glaus, Chun).

According to it, all the parts of a siphonophore are either modified
polyps or medusae, and the primitive zooid of the colony is of the
polyp type. Just as the first theory errs too much in denying the
colonial origin of our group, so the second theory probably goes too
far in affirming it. It is probable that the truth lies between the
two views. We hold, with Haeckel and Balfour, that the colonial
theory is the true one, but that the primitive zooid of the colony
was probably a medusa which has produced other medusae by
budding, and that the parts of these medusae possess the power
of becoming discrete and removed from the bud to which they
belong, and of becoming in some cases secondarily multiplied. So

* R. T. Giinther, Quart. J. Mic. Sci., vol. 36, p. 284.

t E. Haeckel, "Report on the Siphonophorae," Challenger Reports, vol. 28,
1888. C. Chun, "Die Canarischen Siphonophoren," I. and II., Abhandlungcn d.
Senckenbergischen naturf. Gesellsch. 1891-2.

138

COELENTERATA.

that many organs of the colony — which on the old colonial theory
are modified polyps — are on this view nothing more than parts of

medusiform indi-
viduals which
have shifted their
attachment, and
are therefore really
organs. For in-
stance, the struc-
tures called pal-
pons (hydrocysts,
dactylozooids) are
to be looked upon
as mouthless ma-
nubria of medu-
soids, the um-
brellas of which
have become modi-
fied as bracts, or
are entirely degen-
erate. The siphons
(trumpet - shaped
polyps, nutritive
polyps) are the
manubria of medu-
soids, of which the
umbrella is a bract,
or a nectocalyx or
degenerate. The
tentacle, on the
other hand, is to
be looked upon
as the only sur-
viving marginal
tentacle of the
medusoid of the
siphon, which has
shifted so as to be
attached to the base of its manubrium. This theory then agrees
with the second theory in asserting the colonial nature of the
Siphonophora, but admits that there has been that vegetative

FIG. 116. — Diagram of a colony of Siphonanthae. St coenosome
or stem ; Ek ectoderm ; En endoderm ; Pn pi*eumatophore ; Sk
budding nectocalyx ; S nectocalyx ; T palpon (hydrocyst, dacty-
lozooid); Sf tentacle and pal pacle ; P siphon (polyp) ; 0 mouth
of siphon ; Nk battery of nematocysts ; D hydrophyllium ; G
gonophore.

SIPHONOPHORA. 139

repetition and specialization of certain organs which is demanded
by the first view.

The diagram (Fig. 116) shows nearly all the possible parts found
in colonies of Siphonanthae, the largest of the two sub-orders <& the
Siphonophora. We may briefly enumerate these and consider their
relation to the colony on this " medusome " theory of Haeckel. The
stem (St) or trunk is the coenosark or coenosome of the colony ; it
is the elongated manubrium of the original larval medusoid, and
produces by budding all the parts of the colony. Two parts may be
distinguished in it — an upper part, the nectosome, to which the
swimming organs (nectocalyces and pneumatophores) are attached,
and a lower part, the siphosome, bearing the nutritive and repro-
ductive organs (siphons, palpons, gonophores). All parts are budded
off from the same surface of the stem (the so-called ventral median
line), their apparent radial disposition in some forms being due to
a spiral twisting of the stem.*

The swimming organs. The nectocalyx (S) is a medusa with
canal system and velum but without a manubrium. The pneumato-
phore (Pn) is more difficult of interpretation; it may either be
regarded as a medusa, in which the umbrella cavity is the air-
chamber or pneumatocyst, or it may be simply regarded — and this
is Haeckel's view — as a part of the ex-umbrella region of the original
medusoid larva, the ectoderm of which has become invaginated upon
the contained enteric system to form the pneumatocyst (Haeckel
distinguishes the ectodermal imagination as the pneumatosac, the
secreted chitinous lining as the pneumatocyst). The space round
the pneumatocyst lined by endoderm is the pericystic space.

The siphons (P) may be regarded as polyps, or as the manubria
of medusoids. The palpons (tasters, hydrocysts, dactylozooids) are
mouthless manubria. The tentacles (Sf) are organs of the siphons
(see above). The palpacles (Sf) are similar organs of the palpons
found in one order. The hydrophyllia (bracts) are the umbrellas
of medusae which are cleft on one side, or which have simply
lost their umbrella cavity and of which the manubria are either
degenerate or slightly shifted as siphons and palpons. In many
forms bracts have undergone a large secondary increase.

Gfonophores (G) are either budded from the stem or from processes
of the latter called gonostyles, which may, or may not be, mouthless
polyps.

* The twisting when present takes place in opposite directions in the necto-
some and siphosome.

140 COELENTERATA.

The zooids are generally attached to the stem in groups called
cormidia (Fig. 119). The points of attachment of the cormidia
are called nodes, the part of the stem between being internodes ;
in such cases the cormidia are said to be ordinate. Sometimes this
regular grouping does not occur, and the various zooids bud off
separately from the stem ; the cormidia are then said to be irregular
or dissolved.

The nectocalyces by their contractions move the colony through
the water; they have a deeply concave muscular sub-umbrella sur-
face. The pneumatophore is a hydrostatic apparatus, and, in those
forms which have a long spiral stem, serves to keep the body in
an upright condition. The gaseous contents is secreted by some
of the cells lining the pneumatocyst and can, in some cases, be
expelled freely by contraction of the walls of the pneumatophore
through one or more openings — the stigmata.

The enteric or gastro vascular system is continuous throughout the
colony. The gastral zooids are without oral tentacles, but possess
a tentacle arising at their base. This tentacle can be extended to
a considerable length and be retracted into a spiral coil. It rarely
has a simple form, but, as a rule, it bears a number of unbranched
lateral twigs — the tentilla, which are also very contractile. These
tentacles are invariably beset with a great number of nematocysts,
which in many places are closely packed and have a regular arrange-
ment. These aggregations of thread-cells are especially found upon
the tentilla, where they give rise to large brightly-coloured swellings,
the cnidosacs or batteries.

The gonophores have a velum, a complete gastrovascular system,
and a manubrium; but the mouth is nearly always absent. The
generative cells are ectodermal, and arise in the manubrium ; they are
without radial divisions (as in the Codonidae of the AntJwmedusae).
The colonies are generally hermaphrodite, but the gonophores are-
male and female. The sexual medusoids frequently become separate
from the colony when ripe, but are only rarely liberated as small
medusae ( Velellidae), which produce the generative cells during their
free life. »

The hydrophyllia are leaf-shaped, and composed of a stiff gelatinous
substance ; they are protective in function. All the appendages are
developed as buds formed of ectoderm and endoderm, and containing
an endoderm-lined cavity which communicates with the cavity of
the stem.

The Siplwnophora are extremely beautiful transparent, marine

DISCONANTHAE. 141

organisms, with here and there spots of colour (the hepatic cells of
the siphon — the apex of the pneumatophore, the cnidosacs of the
tentacles, etc.). They are mostly pelagic in habit, but some come
from the deep sea.

The ova are large, generally without vitelline membrane, and
undergo a complete and regular segmentation. A free-swimming,
solid planula is formed.

There are two main sub-orders*— the Disconanthae, in which the primary
form is an 8-radiate medusa, the Disconula, which produces buds on the ventral
side of its umbrella ; and the Siphonanthae, in which the promorph is a bilateral
medusa which produces buds on the ventral side of the base of its manubrium.

Sub-order 1. Disconanthae.

TJie body (coenosome) formed by the umbrella of the original octo-
radial medusa, which includes a polythalamous pneumatocyst ; the
huds arise in concentric rings from the sub-umbrella. Larva octoradial
(Disconula).

This sub-class includes one order.

Section 1. DISCONECTAE. YELELLIDAE.

Siphonophora with a permanent primary umbrella, without necto-
calyces and bracts.

The Disconectae are medusae with a large manubrium (Fig. 117,
7ns), hollow marginal tentacles, and radial canals opening into a
circular canal. There is no velum, and the ex-umbrella surface is
pitted inwards in the centre to form an ectodermal sac, the pneumato-
cyst (Hi}. From the under side there hangs downwards a number of
accessory manubria (giii) which bud the gonophores and are called
gonostyles (gm). The gonostyles open into the radial canals at their
basal ends, while distally they may be closed or open. Beneath the
pneumatocyst there is a large cellular mass, the centradenia (cd\ or
so-called liver. The pneumatocyst opens on the upper surface by

* Chun, who objects to Haeckel's separation of the Disconanthae from the rest
of the class, arranges the Siphonophora as follows :

Order 1. CALYCOPHOEIDAE. With nectocatyces without pneumatophore.
Order 2. PHYSOPHORIDAE. With pneumatophore.

Sub-order 1. Haplophysae. Physophoridae with unchambered pneumato-
cyst, which is partly lined by gas -secret ing ectoderm and is without tracheae.
Tribe 1. Physonectae. With pneumatophore and nectocalyces.
Tribe 2. Pneumatophoridae (Physalidae}. Without nectocalyces.
Sub-order 2. Tracheophysae (Haeckel's Disconectae}. With chambered,
chitin -lined pneumatocj^st, which gives off tracheae to the polyps. Gono-
phores set free as medusae (Chrysomitra}.

142

COELEXTERATA.

Ik

small apertures — the stigmata — and communicates with the centra-
denia and adjacent tissues by a number of fine tubes — the tracheae —
which project from its base. The tracheae are lined by a prolongation
of the chitinous lining of the pneumatocyst.

The centradenia is separated from the dorsal endoderm of the
stomach by a gelatinous plate — the gastrobasal plate (sp) — which is
pierced by the gastral ostia (primitively 8) for the passage dorsalwards
of the radial canals (?•&), whicl^ arise from the fundus of the stomach.
It is a composite organ, partly consisting of a dense network of

endodermal gastral
canals, and partly of
a parenchyma of
ectoderm cells with
many cnidoblasts.
The function of the
former is probably
, partly digestive and
p^s^% partly renal, of the
latter gas-producing.
In the simpler Dis-
conectae, i.e., in the
Discalidae the cen-
tradenia is composed
solely of a compact
mass of ectoderm
cells and cnidoblasts
without canals. The
only canals of the
centradenia of such
forms are eight sim-
ple radial canals

which arise from the eight ostia of the stomacli and run on its
upper face — between it and the pneumatosac — uniting in its centre
to form a typical octoradial liver star. They are to be looked upon
as ascending branches of the eight' primary radial canals of -the sub-
umbrella. The canals which perforate the centradenia of the more
complex forms are branches of these (Fig. 117).

The canal system is primitively octoradiate; it consists of the
radial canals above mentioned, which branch as they pass outwards
to be united at the margin of the umbrella by a circular canal (not
marked in the figure). This system gives off, in addition to the

FIG. 117. — Porpalia prunella (after Haeckel from Lang), cd
centradenia (central gland); Ik pneumatocyst; cp central
stigma of pneumatocyst ; rlc radial canal ; sp gastrobasal
plate; eii ex-umbrella; su sub - umbrella ; t tentacles; g
gonophores ; o mouth ; ms chief siphon ; gm accessory
siphons, in this case gonostyles.

DISCONECTAE. 143

centradenial canals, a set of canals — the pallia! canals— on the ex-
umbrella or upper surface of the pneumatocyst, which unite over the
centre of the pneumatophore (round cp). This pallial system is
the result of the invagination of ectoderm to form the pneumato^feore.

The constitution and function of the centradenia, tracheae, and pneumatocyst
of the Disconectae is disputed. Haeckel's account has been followed in the text.
He regards the supposed ectodermal portion of the centradenia or liver as gas-
secreting in function, and corresponding to the gas-secreting portion of the
pneumatocyst of the Siphonanthae (see below), the tracheae being for the purpose
of carrying the gas, so secreted, into the pneumatocyst, which is entirely hydro-
static. Chun, on the other hand, holds that in the Disconanthae, which
habitually float on the surface, the pneumatocyst has no gas-gland, and that the
cell mass of the centradenia, which Haeckel calls ectoderm,, is endoderm with a
rich development of thread cells ; further, that the tracheae often end in places
where this tissue is absent. He considers that these tubes are really tracheae
for the conveyance of oxygen to the thick glandular endoderm, and that the
pneumatocyst in this group is a breathing organ. In confirmation of this view
he states that the living Velella does periodically contract its body as though it
were expelling air from the air-sac. The elastic chitinous lining receives its
explanation also on this view, as it would by its elasticity tend, in regaining its
original form, to suck air in through the stigmata.

The gas-secreting ectoderm of the pneumatocyst is present in the young forms,
which apparently live below the surface, and probably in the deep sea forms ;
and no doubt the function of the air-sac is, in these cases, purely hydrostatic,
as in other Siphonophora in which there is a gas-gland and no tracheae.

Chun C. , Bericht ub. cine nach d. Canarischen Inseln ausgef. lieise. Sitzb. Acad.
Wiss. Berlin, 1888.

The gonophores which are produced on the gonostyles are small
4-radiate medusae, which do not produce sexual cells until after
detachment, when they are known as CJirysomitra.

It is probable that the young of the Disconectae pass through a larval stage
resembling in structure Discalia. This would be the so-called Disconula, a form
actually met with in Discalia and presenting an 8-radiate medusiform structure
with eight radial canals, eight marginal tentacles, and a dorsal 8-radiate in-
vagination of ectoderm — the pneumatocyst.

Fam. 1. Discalidae. From the deep sea. Ex-umbrella without crest,
gonostyles without mouth, pneumatocyst divided into a central chamber sur-
rounded by 8 radial chambers, to which may be added a still more circumferential
arrangement of 5 to 10 concentric ring-chambers. These chambers communicate
with each other by the apertures called pneumothyrae, and some of them with
the exterior by stigmata. The tentacles have terminal cnidospheres.f Discalia
H. ; Disconalia H.

Fam. 2. Porpitidae. Circular umbrella without crest ; pneumatocyst divided
into an octoradiate central part and numerous concentric rings. The gonostyles
have mouths. Pneumothyrae* are present. With many stalked cnidospheresf
on the tentacles.

* Pneumothyrae are communications between the concentric chambers of the
pneumatocyst. f Cnidospheres are spherical knobs composed of cnidobjasts.

144

COELENTERATA.

Sub-fam. 1. Porpalidae. Umbrella highly vaulted. Pneumatocyst
campanulate, with a radially lobate margin. Porpalia H. (Fig. 117) ;
Porpema H.

Sub-fam. 2. Porpitellidae. Umbrella flat, slightly vaulted. Pneu-
matocyst discoidal, without prominent radial marginal lobes. Porpitella
H.; Porpita Lamarck.

Fam. 3. Velellidae. With an elliptical, often nearly quadrangular, umbrella
including a polythalamous pneumatocyst of the same form, composed of numerous
concentric rings, and usually bearing in its diagonal a vertical crest. Marginal
tentacles simple, without cnidospheres ; gonostyles with mouths. A chitinous
prolongation of the pneumatocyst -fining into the crest is generally present.
The 8-radiate character of the canal system exists but is much hidden and
has become in part bilateral. The pneumatocyst consists of a central chamber
sometimes markedly 8-radiate and of many concentric elliptical rings, with
stigmata and pneumothyrae. Rataria Esch., pneumatocyst without crest.
Velella Lamarck ; Armenista H.

nata magnified about 8

times, sb somatocyst.

Sub-order 2. Siphonanthae.

Stem (eoenosome) formed by the manubrium of
the original bilateral medusa. The buds arise in
the ventral line of this manubrium. Larva bilateral
(Siphonula).

Section 1. CALYCONECTAE. CALYCOPHORIDAE.

Siphonanthae with one or
more nectocalyces, without
p?ieumatocyst and palpons.
Cormidia ordinate.

A typical member of this
group such as Diphyes (Fig.
118) consists of a long con-
tractile hollow stem bearing
at its upper end two opposed
nectocalyces or swimming
bells without manubria, but
with four radial canals, a
circular canal, and velum ;
and at regular intervals along
its course groups of indi-
viduals called cormidia (Figs.
119, 120).

At the point where the
stem joins the nectocalyx
(Fig. 121), or between the

FIG. 119. — Three cor-
midia attached to the
stem (eoenosome) of a
Diphyid (after Leuck-
art). D hydrophyl-
lium ; GS gonophore ;
P polyp (siphon), with
tentacle. The cormidia
separate from the stem
to form eudoxids.

CALYCONECTAE.

145

nectocalyces if two are present (Fig. 118), there is a deep groove or
pit in the jelly called the hydroecium, into which the contractile
stem with its cormidia can be retracted. In the jelly of the upper-
most nectocalyx is a
space lined by large
vacuolated cells, and

br-

an oil-drop. This is a
dilatation of the upper
end of the central
canal of the stem and
is called the somato-
cyst.

Each cormidium
consists of two medu-
soid individuals — the
one of these is a
sterile and the other
a fertile medusoid.
The sterile medusoid
consists of a bract or
liydropliy Ilium, a
siphon (trump-et-
shaped polyp), and a
tentacle, while the
fertile one is a gono-
phore. The hydro-
phyllium is the bell
of the sterile medu-
soid; it possesses
rudiments of the
radial canals which
radiate from an api-
cal dilatation — the
phyllocyst (Fig. 120)
— which corresponds
to the somatocyst of
the nectocalyx and is
connected with the central canal of the stem. The siphon is the
manubrium of the sterile medusoid, which is displaced from its
umbrella and has a trumpet-shaped mouth at its free end. The

L

FIG. 120.— Eiidoxia Eschscholtzii—a, female eudoxid of Mug-
gioea Kochii (after Chun), with helmet-shaped hydrophyl-
lium, br containing phyllocyst, siphon p, tentacle t, and
three gonophores of different ages, go1, go2, go3, with eggs
in the manubrium.

146

COELENTERATA.

-col

tentacle is the single marginal tentacle of the medusoid which has
shifted on to the base of the manubrium. In some forms the gono-
phores become sexually mature while still attached to the stem, but
in the greater number the cormidia are detached before maturity
and become free-swimming. Such free-swimming groups are called
Eudoxia (Fig. 120), and are distinguished as monogastric forms
(there being only one mouth and stomach) from the polygastric
colonies from which they arise, and when found free are classified

separately from the
polygastric forms, just
as the medusae of the
Anthomedusae are classi-
fied separately from the
polyp colonies. The
nutritive canals of all
the parts of a cormidium
unite in the bract (Fig.
120), from which point
a bracteal canal passes
to join the canal of the

I stem. The phyllocyst

I (Fig. 120), which corre-
sponds to the somatocyst
(Fig. 122), arises from
the same point. The
tentacle is tubular and
is beset with a series of
lateral tentilla, also tubu-
lar. Each tentillum is
composed of three parts
— (1) a thin pedicle or
proximal part, (2) a

dilated middle part the cnidosac, and (3) a slender terminal filament.
The swelling of the cnidosac is due to a rich development of nemato-
cysts of various kinds, forming the battery.

The gonophore has a 4-radiate canal system and a velum, but is
without tentacles or mouth (Fig. 120). The sexual cells originate
in the ectoderm of its manubrium. It forms the swimming organ
of the cormidium. In some forms it becomes detached, and
then a secondary gonophore is formed. In some species (of Alyla)
a cluster of small gonophores is developed in a single cormidium,

FIG. 121.— Sphaeronectes gracilis (from Chun), seen from
the side, ny hydroecium : c.ol somatocyst ; c.v ventral
radial canal, c.d dorsal radial canal, c.c circular canal
of nectocalyx ; tr coenosome with connidia.

CALYCONECTAE.

147

in which case a special nectocalyx is developed as a swimming organ.
The gonophores are of separate sexes, but the same stem is usually
hermaphrodite, bear-
ing male and female A
cormidia.

7?

The variations in
structure of the order
depend principally
upon the number of
the nectocalyces. In
the MonopTiyidae
there is one necto-
calyx, in the Diphyi-
dae two, and in the
Polyphyidae several
pairs of nectocalyces.

The first formed
mouthless siphon is
supposed by Haeckel to
elongate and form the
stem of the future colony.
The oldest cormidium is
that . which is placed
furthest from the necto-
calyces (Fig. 122). Chun
states that the first nec-
tocalyx (cap-shaped) is
retained only in Mono-
phyes and Sphaeronectes
(Fig. 121) ; in the other
Calyconectae it is thrown
off and replaced by a
differently shaped (pyra-
midal) secondary necto-
calyx (Fig. 122), to
which more secondary
nectocalyces are added
later. All Calyconectae
pass therefore through a
monophyid stage.

As stated above the
buds of the cormidia are
always formed at the
upper end of the stem,
so that the oldest cor-

FIG. 122. — Young colony of Muggiaea Tcochii with the primary
cap -shaped nectocalyx (A) which is soon cast off, and
the secondary pyramidal nectocalyx (£). c.ol somatocyst
with oil-drop ; hy hydroecium ; tr coenosome (stem) with
two cormidia, the upper one being the younger ; ~br bud
of hydrophyllium ; go bud of gonophore ; p siphon ; t
tentacle, su sub-umbrella.

midium is the lowest (Fig. 122). The law as to the formation of the necto-
calyces is not clear in the Calyconectae, but in the Physonectae the pneumatophore

148

COELENTERATA.

is at the top of the stem, the youngest nectocalyx bud next to it, while the
oldest nectocalyx is at the lowest end of the siphosome, i.e., next the youngest
cormidium bud.

The development of the egg leads to the formation of a variety of the
Siphonula larva (Fig. 123). It is a medusoid composed of a nectocalyx (A)—
the umbrella, of a cylindrical mouthless process — the manubrium, and of a
tentacle. The mouthless process is attached to the ex-umbrella surface of
the nectocalyx (to what is called in Siphonophoran parlance its ventral side),

and is regarded by
Haeckel as the original
siphon. It is supposed
to have protruded
through a fissure in the
ventral wall of the nec-
tocalyx. This disloca-
tion* of the siphon (if
it really exists) from its
proper position in the
nectocalyx is an example
of a Avidespread phenom-
enon in the Siphono-
Pnora> which accounts
for a good many of the
peculiar features of the
group.

The alternation of
generations in this
order is between the
polygastric colony and
the monogastric cormi-
dium, produced by bud-
ding from the former
and when detached
known as a eudoxid. f
The gonophore of the
eudoxid after shedding
its genital cells is cast
off and a new gonophore
is formed.

Fam. 1 . Eudoxidae.
Monogastric, cormidium
composed of two medu-
soid s, a sterile and a

FIG. 123.— Developing Siptionula larva of Muggiaea Kochii
with buds on the ventral surface. A, rudiment of primary
nectocalyx, with somatocyst ol, and commencing jelly ga
between ectoderm ek and endoderm en; su sub-umbrella;
t budding tentacle ; p siphon ; en' yolky endoderm cells
which are absorbed later (after Chun).

* This attachment of the primary siphon to the ex-umbrella surface of the

Srimary nectocalyx is a serious difficulty to the medusome theory. The
ifliculty may be got over by supposing that the primary siphon is the
manubrium of an umbrella which has disappeared, and that the primary
nectocalyx is the first bud from the persistent manubrium.

f In some forms the primary gonophore loses its sexual manubrium, and
is developed into a special nectocalyx, and a secondary gonophore is formed.
In this case the cormidium is composed of three medusoids, and is called an
Ersaeid.

CALYCONECTAE.

149

fertile ; without special nectocalyx. Diplophysa Gegenbaur ; Eudoxella H. ;
Cucubalus Q. and G. ; Cucullus Q. and G. ; Cuboides Q. and G. ; Amphiroa
Blainville ; Sphenoides Huxley ; Aglaisma Esch.

Fam. 2. Ersaeidae. Monogastric, cormidium composed of three medusoids,
a sterile, a fertile, and a special nectocalyx. Ersaea Esch. ; Lilaea H. ^

Fam. 3. Monophyidae. Calyconedae Polygastricae with a single nectophore
at the apex of the long tubular stem. Cormidia eudoxiform, separated by equal
free intern odes ; each siphon with a bract. Monophyes* Glaus ; Sphaeronectes*
Huxley (Fig. 121); Mitropliyes H.; Cymbonectes^ H.; Muggiaea^ Busch. (Fig.
122); Cymba Esch. ; Doramasia^
Chun ; Halopyramis^ Chun.

Fam. 4. Diphyidae.iJ: Poly-
gastric Calyconectae with two
nectocalyces at the apex of the
long tubular trunk. Cormidia
eudoxiform separated by free
equal internodes ; each siphon
with a bract. Pray a Blainville ;
Galeolaria (confounded with
Epibulia a Cystonect) Lesueur ;
Diphyes Cuvier (Fig. 118) ;
Diphyopsis H. ; Abyla Q. and G. ;
Bassia Q. and G.; Calpe Q.
and G.

Fam. 5. Stephanophyidae.
Polygastric, with several apical
nectocalyces and a special necto-
calyx on each cormidium. With
small palpons with long tentacles
on the intemodes. Cormidia not
set free as ersaeids. Stephana-
phyes Chun.

Fam. 6. Desmophyidae. Poly-
gastric Calyconectae with four or
more nectocalyces, opposite, in
pairs. Cormidia eudoxiform or
ersaeiform, separated by equal
internodes ; each siphon with a
bract. Dcsmalia H. ; Desmophyes
H.; umbrella edge of special
nectocalyx with 8 ocelli and 8
short tentacles.

Fam. 7. Polyphyidae. Poly-
gastric Calyconectae with four or

FIG. 124. — An advanced Siphonula larva of Epi-
bulia aurantiaca with one large nectocalyx (after
Metschnikoff, from Balfour). So somatocyst;
?ic second imperfectly developed nectocalyx ;
Tipli hydrophyllium ; po siphon ; t tentacle.

* According to Chun the primary nectocalyx of the larva persists in these
genera, and there are no secondary or replacement nectocalyces.

t Chun states that in these genera the primary cap-like nectocalyx is thrown
off and replaced by a pyramidal secondary nectocalyx.

J In this family the primary nectocalyx is replaced by two secondary bells,
which are themselves replaced by a succession of similar bells formed from
similar buds.

150

COELENTERATA.

more nectocalyces opposite in pairs. Cormidia without bracts. Gonophores
reach maturity while attached to the stem ; no free eudoxids or ersaeids.
Hippopodius Q. and G.; Polyphyes H. ; Vogtia, Kolliker.

Section 2. PHYSONECTAE. PHYSOPHORA.

Siphonanthae with a pneumatocyst and several nectocalyces (or

bracts instead), and pal-
pons. Cormidia ordinate
or irregular.

The Physonectae include
monogastric and polygastric
forms.

The stem carrying the
cormidia is either short,
sometimes spread out in
the form of a sac (Fig.
125), or elongated and
spirally twisted (Fig. 126).

The small, often brightly
coloured apical pneumato-
phore is without a terminal
opening of the pneumato-
cyst, though sometimes an
opening near its base may
be made out. The endo-
dermal space of the pneu-
matophore itself is usually
divided by a number of
radial septa into pouches,
while the invaginated pneu-
matocyst is divided into
two communicating parts
— an upper part with a
chitinous lining, and a
lower part with a thick
glandular lining. The latter

FIG. 125.—Physophora Jiydrostatica. Pn pneumato- is Called the air funnel. It

phore ; S nectocalyces arranged in a double row • .-* o-lqnrl nnrl its
on the stem ; T palpon ; P siphon with tentacles

Sf; NJc groups of nematocysts (cnidosacs) ; G lining secretes the gas of

clusters of gonophores. , rpi

the pneumatocyst. 1 he nec-
tocalyces (except when replaced by paddling bracts with rudimentary

PHYSONECTAE.

nectocalyces at their ends)
are usually numerous.
They have four radial
canals, a circular canal, a
velum, and sometimes
ocelli. The cormidia are
rarely dissolved : i.e., the
parts are rarely scattered
along the stem, but gener-
ally ordinate, i.e., in groups
(Fig. 126). Each cormi-
dium consists of one siphon
(sometimes two or four)
with tentacle ; several pal-
pons each with a tentacle
called a palpacle ; several
bracts which may even in
the forms with ordinate
cormidia occur in the in-
ternodes of the stem (Fig.
126); two gonostyles, one
bearing male gonophores
and the other female, and
very often a cyston. A
cyston is a structure like
a palpon but with a ter- /
minal opening : it acts as
an anus to the colony, ex-
pelling fluid and crystalline
excretions through its aper-
ture.

The batteries of the
tentilla of the tentacles
are enveloped in an invo-
lucrum or fold of ectoderm
arising at their proximal
end. The female gono-
phore produces only one
egg-

FIG. 126.— HoMstemma tergestinum. Pn pneumatophore ; S nectocalyx ;
P siphon ; D hydrophyllium ; Nk group of neraatocysts on tentacles.

152

COELENTERATA.

The planula develops at one pole a pneumatocyst as a thickening and involu-
tion of ectoderm (like the entocodon of a medusa bud), and at the other a siphon
(Fig. 127 d). The pneumatocyst is supposed by Chun to be homologous with
the primary nectocalyx of the Calyconectae. In some forms the upper part of
the body gives rise to a cap-shaped hydrophyllium as well as to a pneumatophore
(Fig. 127). The crown of hydrophyllia which is sometimes formed persists only
in Athorybia, Avhere nectocalyces are not formed. In Agalmopsis and Physo-
phora the primary hydrophyllia of the larva (Fig. 128) fall off as the stem
becomes larger, and are replaced by nectocalyces.

FIG. 127. — Development of Agalmopsis Sarsii (after Metschnikoff). a, planula ; b, stage with
developing hydrophyllium D; c, stage with cap-shaped hydrophyllium (D)and developing
pneumatocyst Lf; d, stage with three hydrophyllia (D, D', D"), siphon P and tentacle;
Lf pneumatocyst.

Fam. 1. Circalidae. Monogastric Physonectae with a corona of nectocalyces,
without bracts. Circalia H.

Fam. 2. Athoridae. Monogastric Physonectae with a corona of bracts, without
nectocalyces. Athoria H. ; Athoralia H.

Fam. 3. Apolemidae. Polygastric Physonectae with a long tubular stem
bearing numerous siphons, palpons, and bracts ; each siphon with unbranched
tentacle. Nectocalyces biserial ; either two opposite nectocalyces, or two alter-
nate series of opposite nectocalyces. Pneumatophore without radial pouches.
Nectocalyces with tentacles arising from the stem.

Sub-fam. 1. Dicymbidae. Two opposite nectocalyces only. Cormidia
monogastric ; each with a single cyston. Dicymba H.

Sub-fam. 2. Apolemopsidae. Two opposite rows of nectocalyces. Cor-
midia polygastric ; each with several cystons. Apolemia Esch. ; Apolemopsis
Brandt.

AURONECTAE.

153

Fam. 4. Agalmidae. Polygastric Physonectae with a long tubular stem,
bearing numerous siphons, palpons, and bracts. Nectocalyces numerous,
biserial. Pneumatophore Avith radial pouches. All the genera except four,
viz., Stephanomia Per. and Les., Crystallodes H., Anthemodes H., Curjfolaria
Eysenhardt, have dissolved cormidia. Phyllophysa L. Ag. ; Agalma "Esch. ;
Halistemma Huxley (Fig. 126) ; Cupulita Q. and G. ; Agalmopsis Sars (Fig. 128) ;
Lychnagalma H.

Fam. 5. Forskalidae. Polygastric, with a long tubular stem bearing
numerous siphons, palpons, bracts ;
each siphon with a branched ten-
tacle. Nectocalyces numerous ;
multiserial, strobiliform in several
spiral rows. Pneumatophore with
radial pouches. The largest and
most splendid of all Physonectae.
Cormidia dissolved in all except
Strobalia H. Forskaliopsis H. has
palpacles among the nematocalyces.
Forskalia Kolliker ; Bathyphysa
Studer.

Fam. 6. Nectalidae. Polygas-
tric, with a short vesicular stem,
bearing numerous siphons, palpons,
and bracts ; tentacles branched. 2
or 4 rows of nectocalyces. Pneu-
matophore with radial pouches.
Nectalia H.; Sphyrophysa L. Ag.

Fam. 7. Discolabidae. Like
the preceding but with a corona
of palpons instead of bracts ; with-
out bracts. Physophom Forskal,
biserial nectocalyces (Fig. 125) ;
Discolabe Esch., quadriserial necto-
calyces ; Stcphanospira Gegenbaur,
multiserial nectocalyces.

Fam. 8. Anthophysidae. Poly-
gastric, with short vesicular stem
bearing numerous siphons and pal-
pons ; each siphon with a branched
tentacle. Nectocalyces replaced by
corona of bracts (as in Fig. 128).
Pneumatophore with radial pouches.
Ehodophysa Blainville ; Melophysa H.
Ploeophysa Fewkes.

NK

FIG. 128. — Small larval colony of Agalmopsis after
the type of Athorybia. Lf pneumatophore ; D
the crown of hydrophyllia ; Nk groups of nema-
tocysts ; P siphon.

; Athorybia Esch.; Anthophysa Mertens ;

Section 3. AURONECTAE.

Siphonanthae icith a large pneumatophore, a corona of nectocalyces,
a peculiar aurophore, and a network of canals in the jelly of the
thickened trunk. Siphosome spheroidal, ovate, or turnip-shaped.

Deep sea forms. The aurophore (Fig. 129) is an appendage of

154

COELENTERATA.

the pneumatocyst, and contains a central tube putting the cavity
of the pneumatocyst in communication with the exterior. It is
placed on one side of the pneumatophore, and its central tube
(pistillum) is surrounded by a number of radial chambers, which
are separated by septa and communicate with the pericystic (endo-
dermal) space of the pneumatophore. Very possibly the aurophore
is a gas-secreting gland.

Fam. 1.
Fam. 2.

Stephalidae.
Khodalidae.

Stephalit
Auralia

. ; Stephonalia H.
; Ehodalia H.

Aph

FIG. 129. — Stephalia corona (after Haeckel). a, side view ; fc, section. Aph Aurophore ;
Sg corona of nectocalyces ; P siphons with their tentacles ; CP the large central siphon,
the enteron of which forms the central tube of the siphosome (coenosome or stem).

Section 4. CYSTONECTAE. PHYSALIDAE.

Siphonanthae ivith a large apical pneumatophore without necto-
calyces and ivithout bracts. Pneumatocyst with an apical stigma.

This order includes Physalia, the well-known Portuguese Man
of War, which we may take as type.

Physalia possesses a large pneumatophore lying nearly horizontally
and bearing posteriorly and ventrally the numerous siphons, palpons,
and branched gonostyles. The stigma is at the front end of the
pneumatophore, and leads into a large pneumatocyst. The pericystic
cavity is simple and not divided. The air-secreting cells or pneu-

CYSTONECTAE. 155

madenia are confined to the under part of the pneumatocyst. The
float bears on its dorsal side a crest formed by a fold of the trunk,
i.e., of the part of the body which projects behind the sac (as well
as ventral to it), and which carries the cormidia. The pneumatpcyst
extends into the crest, and becomes divided up by a number
of transverse septa into air-chambers. The cormidia are very
numerous; they appear to be dissolved in the old individuals, but
in the younger stages they are ordinate. When they can be made
out they may be seen to consist of palpons, siphons, and branched
gonostyles arising from a common stem. The tentacles arise from
the palpons. The gonostyles are hermaphrodite, and the female
gonophores break away and develop their ova as free -swimming
Antliomedusae.

The youngest larva of the Physalidae is known as a Cystonula. It has a
float and one siphon with tentacle hanging below it. Later it elongates
horizontally and produces on the ventral side, anterior to the first siphon
(i.e., nearer the morphological apex), the cormidia. The primary siphon or
cormidium persists at the hinder end of the float, i.e., at the end opposite to the
stigma, and is in some forms always marked off from the numerous secondary
cormidia.

There are monogastric and polygastric forms in the order. The pneumatocyst
has generally a gas-secreting thick epithelium or pneumadenia in its basal part.
This may be partly constricted off as a hypocystic air-funnel. The epithelium
of the pneumadenia in many forms sends out branching villi of its ectoderm
which project into the pericystic space, and are covered towards the latter
by its ciliated endodermal lining. These hypocystic villi are composed of
large cells and are solid. They are probably mechanical in function helping
to support the air-vessel.

In many forms the gonostyles bear palpons (gono-palpons) ; and in the
Physalidae the palpons have a tentacle. The tentacles are often branched,
but without a cnidosac (battery). The sting of Physalia is particularly
poisonous.

Fam. 1. Cystalidae. Monogastric, with one large siphon bearing a tentacle
and surrounded by a corona of siphons. Pneumatophore without radial septa
or hypocystic villi. Cystalia H.

Fam. 2. Rhizophysidae. Polygastric, with a long stem bearing in its
ventral median line numerous monogastric cormidia with single palpon and
tentacle. Pneumatophore large with radial pericystic pouches, but with hypo-
cystic villi.

Sub-fam. 1. Cannophysidae. Cormidia ordinate. Gonostyles attached
to the stem at the base of the siphons. Aurophysa H. ; Cannophysa H.

Sub-fam. 2. Linophysidae. Cormidia dissolved. Gonostyles attached
to stem between the siphons. Linophysa H. ; Nedophysa H. ; Pneumophysa
H. ; RMzophysa Per. and Les.

Fam. 3. Salacidae. Polygastric with long stem bearing in its ventral
median line numerous polygastric cormidia. Pneumatophore large, without
radial pericystic pouches, but with hypocystic villi. Salacia H.

156

COELENTERATA.

Fam. 4. Epibulidae. Polygastric with a short inflated spirally convoluted
stem. Cormidia ordinate in a spiral ring protected by a corona of palpons.
Pneumatophore without pericystic radial pouches, but with hypocystic villi.
Epibulia Esch. ; Angela Lesson.

Fam. 5. Physalidae. Polygastric, with a short inflated stem horizontally
expanded along the ventral side of the large horizontal pneumatophore. Cor-
midia in a multiple series along the ventral side of the trunk, usually dissolved.
Pneumatophore large, with a chambered dorsal crest, without radial septa
or hypocystic villi. Alophota Brandt; Arethusa H. ; Physalia Lamarck;

Caravella H.

•

Class II. ACALEPHAE.* ACKASPEDA.

Medusae of considerable size with gastral filaments (pliacellae) ;
with endodermal gonads ; with lobed umbrella-edge; without true
velum.

The medusae of this class are distinguished from those of the

RK

FIG. 130. — Aurelia aurita, from the oral surface. MA the four oral tentacles with the mouth
in the centre ; Gk generative organs ; GH aperture of subgenital pit ; Rk sense organ
(marginal body) ; RG radial vessel ; T, tentacle at edge of the disc.

* E. Haeckel, Monographic der Medusen, Jena, 1879. L. Agassiz, Contributions
to the Natural History of the United States, Acalephae, vol. 3, 1860, vol. 4,
1862. C. Glaus, " Studien tiber Polypen u. Quallen der Adria," Denks. d. k.
Akad. Wiss. Wien, 1877... Id., Unters. ub. d. Organisation u. Entw. Acalephcn,
Prag, 1883. A. Gotte, Ub. d. Entwickelung v. Aurelia aurita u. Cotylorhiza
tuberculata, 1887. C. Glaus, "Ub. dieEntwick. desScyphostoma, etc," I. and II.
Arb. a. d. Zool. Inst. Wien, 9 and 10, 1S91 and 1893.

ACALEPHAE. 157

Hydromedusae by their larger size and the greater thickness and
stiffness of their umbrella, the gelatinous tissue of which contains
a quantity of strong fibrillae, and a network of elastic fibres.

Another characteristic of the group is derived from the stkrfcture
of the edge of the umbrella. This is divided by a regular number
of indentations usually into eight groups of lobes between which the
sense organs are contained in special pits (Fig. 130).

The marginal lobes of the Acalepliae, like the continuous velum
of the Hydromedusae, appear to be secondary formations at the edge
of the disc. In the young stage known as Epliyra (Fig. 131), which
is common to most of the Ephyroninae, they are present as eight
pairs of relatively long tongue-like processes, and grow out from the
disc-like segments of the Strolila as marginal processes. An un-
divided marginal membrane (the vela-
rium), differing from the velum of the
Craspedota in containing prolongations
of the canals of the gastrovascular
system, is present in the Charyldeidae
alone.

The Acalepliae differ from the Hy-
dromedusae in possessing, as a rule,
large oral tentacles at the free end of
the wide manubrium. These may be
regarded as being derived from an FlG 131 _An Ephym seen from the

unequal growth of the edges of the oral side. Ek marginal body ; Gf

,1 r™ £ TI gastral filament; Re radial pouch

mouth. They grow as four arm-like Of enteron ; o mouth,
processes of the manubrium from the

angles of the mouth, and are placed perradially (see p. 118, note),
i.e., they alternate with the genital organs and gastric filaments.
In some cases the arms become forked at an early period, and four
pairs of arms are formed, the lobed tufted edges of which may again
divide and sub-divide into many branches. In this case, the margins
of the mouth and the opposed surfaces of each pair of arms fuse
in early life as described above, p. Ill (Rhizostomidae, Fig. 97).

Further, there is to be observed in the Acalepliae two types of
structure, which we may term the type of the Scyphistoma and
the type of the Epliyra, respectively. To the former type, which
is called the Scyphomedusae, belong the sessile forms (Lucernaridae,
Fig. 134), and swimming forms which perhaps possess a direct
development (Tesseridae, Fig. 133, Charyldeidae, Fig. 136). The
edge of the umbrella is only incompletely divided into lobes ; marginal

158 COELENTERATA.

bodies are absent in the Lueernaridae and Tesseridae, their place
being taken by tentacles or marginal anchors, which are homologous
with marginal bodies. The stomach is surrounded by four wide
gastric pouches separated from one another by septa (Fig. 99).
The sexual organs are placed in the sub-umbrella wall of the
gastric pouches. The umbrella is usually much arched and fre-
quently prolonged into a stalk.

The second type, which is called the Ephyroninae, is a modifica-
tion of that of the Ephyra itself. The Ephyra (Fig. 131) possesses
eight marginal lobes, which are forked distally and carry in the
clefts of the forks eight rhopalia. Each marginal lobe has a radial
prolongation of the stomach The Ephyra therefore shows while
it is still on the Strobila, a predominance of the 8-racliate structure
in opposition to the 4-radiate build of the Scyphistoma type. At
the same time it should be noted that the more centrally placed
organs (buccal arms, gonads, gastral filaments) are 4-radiate. Between
the eight lobes of the Ephyra there grow out later eight additional
lobes (sometimes more), also bifurcated distally and carrying tentacles
in place of the marginal bodies.

The Ephyroninae then are distinguished from Scyphomedusae by
the lobed structure of the umbrella edge, by the presence of eight
or more rhopalia, and by the division of the peripheral part of the
coelenteron into eight or more radial vessels, which are seldom
widened in a pouch-like manner. The gonads are interradial and
placed in the ventral wall of the central stomach. The umbrella
is flattened, usually discoidal. The Periphyllidae (Fig. 135) and
Pericolpidae are intermediate between these two groups in that
the central part of the umbrella presents the characters of the Scypho-
medusae, while the peripheral parts recall the structure of the Ephyra.
They possess four knot-like septa which bound the four gastric
pouches, and at the edge of the umbrella there are sixteen places
of adhesion between the dorsal and ventral endoderm. Moreover,
the Periphyllidae have four taenioles (gastral ridges); their gonads
are in the circular sinus; the umbrella is bell-shaped or flat, and
marked on its dorsal surface by an annular constriction which
indicates the junction between the ventral Scyphistoma-like and the
distal Ephyra-like parts.

The Scyphistoma, which may be regarded as the promorph of
the Scyphomedusae, is the larval form of the JEphyroninae.

The gastric filaments which are worm-like and movable, and are
not found in Hydromedusae, afford a distinctive mark. They cor-

ACALEPHAE. 159

respond to the mesenteric filament of the Anthozoa, and lend the
same aid to digestion by the secretion of their glandular endodermal
covering. They are always attached to the sub-umbrella wall of the
stomach, and fall in the four interradii, i.e., the radii of the generative
organs which alternate with the radii of the angles of theVmouth
(radii of the first order). They usually follow the inner edge of the
generative frill in a simple or curved line.

The nervous system and rhopalia have already been described
(p. 115).

The four generative organs of the Acalephae can be easily dis-
tinguished in consequence of their size and their bright colouring.
In some cases, at any rate in the Discomedusae, they protrude as folded
bands into special cavities in the umbrella, the so-called sub-genital
pits (hence the term Phanerocarpae Esch.). In all cases these bands
lie on the lower (sub-umbrella) wall of the digestive cavity, from
which they originate as leaf-like prominences. Their upper surface
is covered with gastric epithelium; their under, which is turned
towards the sub-umbrella, with germinal epithelium, the elements
of which in the process of development, pass into the gelatinous
substance of the band. The subgenital pits have already been
described (p. 118): they may be completely absent (Ephyra,
Nausithoe) : their lining consists of sub-umbrella ectoderm and is
quite distinct from the generative epithelium, which is of endodermal
origin. The mature generative products are dehisced into the
gastric cavity, and pass out through the mouth; but in many cases
the ova undergo their embryonic development either in the ovary
(CJirysaora) or in the oral tentacles (Aurelia). Separate sexes are
the rule. Male and female individuals, however, apart from the
colour of their generative organs, have only slight sexual differences ;
as, for instance, the form and length of the tentacles (Aurelia).
CJirysaora is hermaphrodite.

In the Ephyroninae the development is generally accompanied by
an alternation of generations; the asexual generations being repre-
sented by the Scyphistoma (Hydra tula) and StroUla ; but in
exceptional cases it is direct (Pelagia). In all cases a complete
segmentation leads to the formation of a ciliated larva (Fig. 132 a),
the so-called planula, which attaches itself by the pole which is
directed forwards in swimming. This pole is, however, opposite to
the gastrula mouth, which in the meantime becomes closed, while
round the mouth, which is formed as a perforation at the free end,
the tentacles appear (Fig. 132 b, c). As in the embryo Actinia, two

160

COELENTERATA.

opposite tentacles first make their appearance ; not, however, simul-
taneously, the one appearing after the other, so that the young larva
about to develop into the Scyphistoma presents a bilaterally sym-
metrical structure. Subsequently the second pair appears in a plane
at right angles to the plane of the first tentacles. These four tentacles
mark the radii of the first order. Then alternating with these, but
in a less regular succession, the third and fourth pairs appear; and
soon after, in the plane of these latter, four longitudinal folds
(Fig. 132 d) of the gastric cavity are developed (radii of the second
order or of the gastric filaments and genital organs; often called
the interradii, see above, p. 118, note).

d

FIG. 132 a-li.— Larval development of Chrysaora ; a, plauula with narrow enteron ; b, the same
after attachment and formation of mouth 0 and commencing tentacles ; c, young scyphistoma
with 4 tentacles ; Csk periderm ; d, eight-armed scyphistoma with wide mouth ; M longi-
tudinal muscles of gastral ridges.

The eight-armed Scyphistoma soon produces eight fresh tentacles
(Fig. 132 e\ which succeed one another in irregular succession, and
alternate with the tentacles already present. Their position deter-
mines the intermediate radii, or adradii, of the future young Discophor
or Ephyra. After the formation of the circle of tentacles and the
secretion of a clear basal periderm (Chrysaora), the Scyphistoma is
capable of reproduction by gemmation and fission. At first the
Scyphistoma appears to multiply only by budding ; the second mode
of reproduction, the process of strobilization, begins later. This
consists essentially in the fission and division of the anterior half
of the body into a number of segments, thus changing the Scyphistoma

ACALEPHAE.

161

into a Strobila (Fig. 132 /). The separation of the segments progresses
continuously from the anterior end to the base of the Strobila, so
that after the disappearance of the tentacles (Fig. 132 g), first the
terminal segment, then the second, and so forth, attain independent
existence (Fig. 132 h). Each segment becomes an Ephyra (Fig. 131),
developing eight pairs of elongated marginal lobes, with a marginal

FIG. 132.— e, scyphistoma with sixteen arms (slightly magnified) ; Gw gastral ridges ;
/, commencing strobilisation.

body in the notch which separates the two lobes of the same pair.
It is these marginal lobes which give to the edge of the umbrella of
the Ephyra its characteristic appearance. The young Ephyra gradually
acquires the special peculiarities of form and organization of the
sexually mature animal.

The number of nematocysts accumulated on the upper surface of

162

COELENTERATA.

the disc and on the tentacles of many Medusae enables them to cause
a perceptible stinging sensation on contact. Many, e.g. Pelagia, are
phosphorescent. According to Panceri, this phenomenon originates in
the fat-like contents of certain epithelial cells on the surface. The
Acalephae may attain a large size, the bell in some Rliizostomae
and Cyaneidae reaching a diameter of from two to six feet.

In spite of the delicacy of their tissues, certain large Medusae have

left impressions in the litho-
graphic slate of Sohlenhofen
(Medusites circularis, etc.).

Order 1.

SCYPHOMEDUSAE.

TETRAMERALIA. TESSERONAE.

Acalephae with or without
four rliopalia (sense-tentacles) ;
stomach with four gastral
pouches separated by short or
long septal-unions. Gonads in
sub-umbrella wall of the gas-
tral pouches. Umbrella highly
vaulted.

The Scyphomedusae are best
considered in their relation to
the Scyphistoma. They may
be looked upon as Scyphistomas
deprived of their tentacles,
which indeed are only transi-
tory structures, and elongated
so as to assume the form of a
cup, and changed in several par-
ticulars which are characteristic
of the medusa stage. The four septa (Fig. 98) arise by the fusion
of the four gastric folds with the wide oral disc, which becomes
drawn in and concave like a sub-umbrella. These four septa separate
the same number of gastrovascular 'pouches ; while the margin of
the cup may be drawn out into eight arm-like processes from which
groups of short, knobbed tentacles arise (Fig. 134).

The genital organs extend on the oral wall of the umbrella into
the arms as eight band-shaped, plicated ridges (Fig. 134, /.). They
run along in pairs at the lower part of each septum in the gastric

FIG. F132.— g, fully formed strobila with sepa-
rating ephyrae; h, free ephyra (1-5 to 2 mm.
in diameter).

STAUROMEDUSAE.

163

cavity (Fig. 98). The ovum, according to Fol, undergoes a complete
segmentation, which results in a single-layered blastosphere. This
becomes an oval, two-layered larva, which becomes ciliated, swims
freely about, and finally attaches itself. The further development
probably takes place directly without alternation of generations.

The Scyphomedusae are without exception marine animals, and are remarkable
for their great reproductive power. According to A. Meyer, if the stalk of
Lucertiaria be cut off, the cup reproduces a new one, and injured individuals,
and even excised pieces, can become perfect animals.

Fio. 133.— Tessera princeps (after Haeckel). o, external view magnified about 20 times;
6, longitudinal section through two perradii ; c, view of sub-umbrella. Gf gastral filaments ;
G gonads ; Rm circular muscle ; Sk septal unions.

Sub-order 1. STAUROMEDUSAE.

Without rhopalia, but in their place 8 simple principal tentacles (Fig. 133)
or marginal anchors (Fig. 134). Stomach with 4 wide perradial pouches con-
nected peripherally by a ring-canal. Gonads as 4 interradial horse-shoe shaped
thickenings (Fig. 133), or 4 pairs of adradial ridges in the ventral walls of the
gastric pouches (Fig. 134).

164 COELBNTERATA.

Fam. 1. Tesseridae. Umbrella edge without lobes ; 8 principal tentacles
(4 perradial and 4 interradial) ; marginal anchors absent. Apex of the ex-
umbrella surface prolonged into a hollow process or stalk for attachment.
Tessera H. (Fig. 133) and Tesserantha H., with hollow, ex-umbrella process not
used for attachment ; Depastrella H., Depastrum H., with ex-umbrella stalk for
attachment.

FIG. l34.—Haliclystus auricula (from Chun, after Clark). I. From the side. II. From the oral
face. III. From the side with evaginated umbrella and protruded mouth. IV. Marginal
anchor from the axial side, p stalk ; su sub-umbrella ; t one of the eight tufts of knobbed
tentacles on the eight hollow triangular marginal lobes ; ra one of the eight marginal
anchors ; t1 anchor tentacle ; U collar of adhesive glandular ectoderm ; oc eye-spot ; en vessel
of marginal anchor ; o mouth ; se interradial septal ridge passing into the taenioles (ft) of
the stalk ; gen one of the eight adradial gonads on the sub-umbrella wall of the four radial
gastric pouches, representing four interradial horse-shoe gonads connected at the oral end of
the septal ridge.

Fam. 2. Lucernaridae. With 8 adradial umbrella lobes, and tufts of short
knobbed tentacles at end of each lobe. With 8 principal tentacles (4 per-
and 4 interradial) as marginal anchors (Fig. 134), or absent. An ex-umbrella
stalk for attachment. Halidystus Clark, Halicyathus Clark, with marginal
anchors ; Lucernaria 0. F. Miiller, Craterolophus Clark, without marginal
anchors.

PEROMEDUSAE.

165

Sub-order 2. PEROMEDUSAE.

With 4 interradial rhopalia (with otoliths and eyes) ; with 4 perradial tentacles,
or with 12 tentacles (4 per- and 8 adradial, Fig. 135); with 8 or IG-T^arginal
lobes. The 4 radial gastral pouches are separated from one another by very
short septal-unions or septa, so that the
stomach may be said to be surrounded by
a wide circular sinus, communicating with
it by 4 ostia (Fig. 99). The circular sinus
gives off towards the periphery of the
umbrella 8 or 16 flat pockets, each of
which gives off two lobe -pockets, and
between these one pocket to a tentacle
or sense - body. 4 horse - shoe shaped
gonads in the ventral wall of the circular
sinus.

FIG. 135. — Periphylla hyacinthina (after Haeckel). FIG. 136. — Charybdea marmpialis, natural

Rf annular groove dividing the umbrella into size. T tentacles ; Ilk marginal bodies 5

a proximal conical part, and a ventral lobed Ov gonads.
region.

Fam. 3. Pericolpidae. With 4 perradial tentacles, 4 interradial rhopalia,
and 8 adradial marginal lobes. Pericolpa H. ; 'Pericrypta H.

Fam. 4. Periphyllidae. 12 tentacles, 4 rhopalia, 16 marginal lobes.

Peripalma H.; Periphylla H. (Fig. 135).

166

COELENTERATA.

Sub-order 3. CUBOMEDUSAE (Marsupialida).

FIG. 1 37. — The apical half of a Charybdea
divided transversely, seen from the
sub-umbrella side. The four oral
arms are visible. Ov ovaries on the
four septa; Ost ostia of the gastric
pouches; Gf gastric filaments; S
septa.

With quadrangular umbrella (Fig. 136),
4 perradial rhopalia (with otoliths and
eyes), 4 interradial marginal tentacles,
4 perradial gastric pouches, separated by
long and narrow interradial septa. Gonads
as 4 pairs of broad plates fastened by one
«dge to the radial septa (Fig. 137), and
projecting into the pouches. "With a
smooth - edged velarium containing pro-
longations of the gastro vascular system.
With a nerve ring on the sub -umbrella
side of the edge of the bell, having a zig-
zag course.

Fam. 5. Charybdeidae. Procharagma
H.; Procharybdis H. ; Charybdea Per. and
Les.; Tamoya F. Miiller.

Fam. 6. Chirodropidae. Chiropscdmus
L. Ag. ; Chirodropus H.

Order 2. EPHYRONINAE. OCTOMERALIA. DISCOMEDUSAE.

Acalepliae with 8 or more rJiopalia (sense tentacles) (4 per- and
4 interradial, and often several accessory}. Stomach with 8, 16, 32,
or more radial pockets or canals. Gonads sub-gastral (in ventral wall
of central stomach}. Umbrella flat, generally discoidal. Larval form
Ephyra.

The Ephyroninae can at once be distinguished from the Scypho-
medusae by the discoidal lobed umbrella, and usually by the large
size of the oral tentacles. The lobes of the umbrella, however much
they may differ in detail, can always be reduced to the eight pairs of
lobes of the Ephyra (Fig. 131), which, as the promorph of the
Ephyroninae, presents most clearly the 8-rayed symmetry character-
istic of the group.

The gonads have the form of horse-shoe shaped frills (Fig. 130),
and project into the widely open subgenital pits. The germinal
epithelium, which is always embedded in the gelatinous substance
of the umbrella, is covered with an endodermal layer. Development
takes place by alternation of generations. In rare cases (Pelagia)
the development is simplified, and the larva passes directly into the
Ephyra, missing out the attached Scyphistoma and StroUla stage.

The gastrovascular system may be pouch-like or canalicular. In
Aurelia (Fig. 130), in which it is canalicular, the eight primary radial
canals (i.e., the four perradial and four interradial) are branched, while

CANNOSTOMAE SEMOSTOMAE — KHIZOSTOMAE. 167

the eight secondary radial canals (adradial) are unbranched. The
parts of the stomach from which the eight adradial and the four
interradial canals arise are pouched outwards.

Sub-order 1. CANNOSTOMAE.

With simple quadrangular manubrium without oral arms ; with short solid
marginal tentacles.

Fam. 7. Ephyridae. Usually 16 wide gastric pouches, rarely 32-64, without
terminal branches ; usually 8 rhopalia, rarely 16-32 ; usually 16, rarely 32-64
marginal lobes. This family may be described as consisting of sexually mature
Ephyrae. Ephyra Per. and Les. ; Palephyra H. ; Zonephyra H.; Nausicaa H. ;
Nausithoe Kolliker ; Nauphanta H. ; Atolla H. ; Collaspis H.

Fam. 8. Linergidae. With wide radial gastric pouches, and branched, blind
lobe-canals ; without circular canal. Linantha H. ; Linerges H. ; Liniscus H. ;
Linuche Esch.

Sub-order 2. SEMOSTOMAE.

With 4 large perradial oral arms, and with long hollow tentacles.

Fam. 9. Pelagidae. Semostomae with 16 simple wide gastric pouches,
without branched distal canals, without circular canal. PelagiaPer. and Les.,
with 8 adradial tentacles, 8 rhopalia, and 16 marginal lobes ; Chrysaora Per.
and Les. , with 24 tentacles (and 8 rhopalia), and 32 marginal lobes ; Dacty-
lometra L. Ag.

Fam. 10. Cyaneidae. Semostomae with 16 or 32 wide gastral pouches, and
branched, blind lobe-canals, without circular canal. 16-32 or more marginal
lobes ; 8 or 16 rhopalia (4 per-, 4 inter-, and 8 adradial) ; 8 or more long hollow
tentacles. Procyanea H.; Medora Couthouy; Stenoptycha L. Ag.; Desmonema
L. Ag. ; Cyanea Per. and Les. ; Patera Lesson ; Melusina H.

Fam. 11. Flosculidae. Semostomae with 16 or more simple unbranched
narrow radial canals and with a circular canal. 8 rhopalia ; 8-24 or more
long hollow tentacles. Floscula H. ; Floresca H.

Fam. 12. Ulmaridae. Semostomae with 16 or more narrow radial canals,
which branch and often anastomose, and are connected by a circular canal.
8 or 16 rhopalia; 8-24 or more hollow tentacles. Ulmaris H.; Umbrosa H. ;
Undosa H. ; Sthenonia Esch. ; Phacellophora Brandt ; Aurelia Per. and Les. ;
Aurosa H.

Sub-order 3. KHIZOSTOMAE.*

With 8 large adradial, root-like, simple or branched, oral arms, with numerous
suctorial mouths, without central mouth opening, and without marginal
tentacles.

Fam. 13. Toreumidae. Rhizostomae with 4 separated subgenital pits, and
with ventral suctorial frills on the 8 oral arms (no dorsal frills). 8, 12, or 16
rhopalia ; 8-16 or more narrow radial canals, branched and anastomosing.
Archirhiza H. ; Toreuma H. ; Polydonia L. Ag. ; Cassiopea Per. and Les.;
Cephea Per. and Les. ; Polyrhiza L. Ag.

Fam. 14. Pilemidae. Rhizostomae with 4 separated subgenital pits, and
with dorsal as well as ventral sucking frills on the 8 oral arms. 8 rhopalia ;
8-16 or more branched and anastomosing radial canals, with circular canal.

* The forms commonly called by the generic name Rhizostoma belong to the
genus Pilema. The term Rhizostomae is kept for the sub-order.

168

COELENTERATA.

Toxoclytus L. Ag. ; Lychnorhiza H. ; Phyllorhiza L. Ag. ; Eupilema H. ; Pilema
H. ; PJiopilema H. ; Brachiolophus H. ; Stomolophus L. Ag.

Fam. 15. Versuridae. Rhizostomae with a single central subgenital porticus
(i.e., subgenital pits united), with ventral suctorial oral frills only. 8 rhopalia;
8-16 or more narrow, branched, anastomosing, radial canals. Haplorhiza H. ;
Cannorhiza H. ; Versura H. ; Crossostoma L. Ag.; Cotylorhiza L. Ag. ; Stylo-
rhiza H.

Fam. 16. Crambessidae. Rhizostomae with a single central subgenital
porticus, oral amis with dorsal an*d ventral frills. 8 rhopalia ; 8-16 or more
anastomosing radial canals ; usually a circular canal. Crambessa H. ; Mastigias
L. Ag. ; Eucranibessa H. ; Thysanostoma L. Ag. ; Himantostoma L. Ag. ; Lepto-
brachia Brandt ; Leonura H.

Class III. ACTINOZOA* (ANTHOZOA).

Polyps colonial or solitary, with oesophageal tube, mesenteric folds,

and endodermal gonads. A medu-
soid sexual generation is unknown.

The polyp of the Actinozoa has
already been described (p. 102). It
differs from that of the Hydro-
medusae in being larger, in having
a greater muscular development, a
.better developed structureless la-
mella or jelly which often contains
muscular and skeletal elements. The
development of this jelly, which has
a tough, dense character, is, in the
colonial forms, greater in the lower
parts of the polyps than in the
upper, the result of which is the
formation of the branched or massive
coenenchyme (Fig. 138), from the
surface of which the free ends of "the polyps project. A calcareous
skeleton is very generally present, but its form and method of
formation vary in the different groups.

The mesenteries and tentacles vary much in number. In the
Alcyonaria there are always eight; in the Zoantharia, in which there
are primary and secondary mesenteries, the number is sometimes six

* Ehrenberg, "Beitrage zur physiologischen Kenntniss der Korallenthiere im
Allgemeinen u. besonders des rothen Meeres, etc," Abhand. d. Berliner Akad.,
1832. Ch. Darwin, The Structure and Distribution of Coral Reefs, London,
1842. J. D. Dana, United States Expl. Expedition, Zoophytes, Philadelphia,
1846. M. Edwards and J. Haime, Histoire Naturelle des Coraillaires, 3 vols.,
Paris, 1857-60. Lacaze Duthiers, Histoire Naturelle du Corail, Paris, 1864.

FIG. 138.— Branch of a polyparium of
Corallium rubrum (after Lacaze Du-
thiers). P polyp.

ACTINOZOA.

169

or some multiple of six ; but it may be different : indeed, the greatest
variety is found in this character in the order Zoantharia.

The gonads are produced on the mesenteries (Fig. 91), aVd the
embryos sometimes undergo the early stages of development within
the parent.

Asexual reproduction by budding and fission is of great importance.
Buds can be formed in various positions, even at the oral end, in
which case a strobila-like form appears. In Blastotrochus the buds
appear at right angles to the axis of the parent (Fig. 139).

In Gonadinia prolifera the polyp divides transversely, a new set
of tentacles arising on the lower half (Fig. 139a). In some cases
a portion of the basal expansion is separated off by contraction of the
body, and develops into a new polyp. This is called laceration.

FIG. 139. —Blastotrochus
nutrix (after C. Sem-
per). LK lateral bud.

FIG. 139a. — Two stages of transverse fission of Gonactinia
prolifera, Sars (after Blochman and Hilger).

If the individuals so produced remain connected with one another,
a polyp-colony is formed, which may attain very various forms and
great size. As a rule the individuals are embedded in a common
body mass, the coenenchyme* and their gastric cavities communicate
more or less directly, so that the juices acquired by the individual
polyps penetrate through the whole stock. This stock affords us
an excellent example of an animal community built up out of similar
members. The formation of the generative products alone is some-
times confined to special polyps, which, however, discharge all
other functions of polyp life.

The skeletal formations of the polyps are specially noteworthy.
In almost every case, with the exception of Actinia, there is a deposit
of solid calcareous matter, and according to the density of this deposit,
there is produced a leathery, chalky, or even stony framework.

* This word is used in a different sense in the Madreporaria, which see.

170

COELENTERATA.

If the skeleton has the form of isolated needles or toothed rods
(Fig. 140) of calcareous substance deposited in the jelly of the

coenenchyma (or polyp), the
polyp-stock has a fleshy, leathery
nature (Alcyonaria) ; but if, on
the contrary, the calcareous
structures are fused or cemented
together, a solid, more or less
firm calcareous skeleton is de-
veloped (Corattium, Tubipora).
Finally, the skeleton may be of
a stony character and secreted
by the ectoderm of the lower
part of the polyp (Madre-
poraria).

The important diversities of
form in the polyp-stocks are
not only occasioned by the
differences of structure of the
skeleton of the polyp, but are
also the resultant of varying

FIG. 140.— Calcareous bodies (Sderodermites) of methods of growth by gem-
Alcyonaria (after Kolliker). a, of Plexaurella ; mati0n and imperfect fission.
0, ofGorgoma; c, of Alcyonium.

According to the method, nu-
merous modifications of branched stocks are
distinguished, e.g., Madrepores (Fig. 141), Ocu-
linidae (Fig. 142), and the lamellar and massive

stocks as Astraea (Fig.

143) and the Maeandri-

nidae (Fig.- 144).

The Anthozoa are all

inhabitants of the sea, and

live mostly in the warmer

zones, but certain types of

the fleshy Octactinia and

Actinia are distributed in

all latitudes. Some genera

of the Madreporaria are

found in the deep sea,

FlG.l4l.-MadrePoraVerru
co*. (after Ed. H.).

Ed. H.).

mulations of considerable extent, but the polyps which take the

ACTINOZOA. 171

principal share in the formation of coral reefs live near the surface,
being rarely found alive at a greater depth than 40 fathoms. They
are confined to a zone extending about 28 degrees on either' side
of the equator, and only here and there extend beyond these
bounds. Their calcareous skeletons, together with those of mille-

Fio. 143. — Astraea (Goniastraea) pectinata FIG. 144. — Maeandrina (Coeloria) arabica Klz.
Ehrbg. (after Klunzinger). (after Klunzinger).

pores, the shells of molluscs, echinoderms, annelids, foraminifera,
cemented together into a compact rock by encrusting organisms and
by deposited lime, build up in the course of time masses of colossal
extent.

Coral reefs are generally met with in one of three forms, fringing reefs, barrier
reefs, and atolls.

A fringing or shore reef is a platform of rock skirting the shore and ending,
seawards, in an abrupt edge from which there is a steep slope down to the sea
bottom. To a depth of 20 or 30 fathoms the slope is covered with growing
coral, the upper part being bathed in the surf of the breaking rollers. The
upper surface of the outer edge of the reef, which is generally uncovered at low
water, is higher than the part nearer the shore, and, in exposed reefs, is largely
formed by encrusting calcareous algae (Nullipores), which thrive in the freshly
aerated water.

In reefs in protected situations some corals, especially the Madrepores, grow
on the edge of the reef wh ere they are laid bare at low tide. The reef is frequently
broken here and there by channels which have a depth of a few fathoms and
run in towards the land in branching and tortuous courses, often expanding
into irregular pools floored by coral sand. These protected pools and channels,
whose vertical sides are formed by a luxuriant growth of hard corals, millepores,
and the leathery colonies of Alcyonaria, are tenanted by an abundant reef fauna
often displaying the most brilliant and varied colours. Between the channels
the surface of the reef is formed of beds of corals which have nearly reached
the surface, or of tracts of dead coral-rock, or sand often consisting largely of
Foraminifera.

Nearer the land the growth of coral becomes less abundant and the water-
deepens, forming a shallow channel which at high water may be practicable for

172

COELENTERATA.

vessels of small draft.* The width of the reef is largely dependent on the slope
of the sea bottom, becoming narrowed in proportion as this is steep ; and also,
as Semper has shown, on the set of the currents, which, when they are strong,
hinder the extension of the reef past which they flow.

The edge of a fringing reef is often seen to be strewn with large masses of
dead coral, which have been torn from the outer slopes by the breakers and

FIG. 144a.— A barrier reef (from Darwin), seen from within, from one of the high peaks 01
Bolabola, one of the Society Islands.

thrown upon the reef. Many such masses must, on the other hand, fall down
the slope, and here, by their gradual accumulation, together with the shells of
Pteropods, Foraminifera, and other pelagic organisms borne by ocean currents,
form a basis on which the living margin of the reef may extend outward.

The structure and growth of a fringing reef do not appear to offer problems
which are very difficult to solve, but the case is different when we come to the
other two classes of reef, the barrier reef and atoll.

FIG. 144b.— A small atoll (from Darwin), being a sketch of Whitsunday Island in the S. Pacific,
taken from Captain Beechey's Voyage. The whole circle has been converted into land, which
is a comparatively rare occurrence.

A barrier reef resembles a fringing reef except in one important particular,
namely, that it is separated from the shore by a channel, which is often of great
width and which may attain a depth of 50-60 fathoms.

The great barrier reef of Australia which runs along the east coast of Queensland
is over 1100 miles in length, and encloses a channel which is in many places

* Opposite the mouths of streams there are wide openings in the reef where
the coral does not grow, by which the fresh waters reach the sea.

ACTINOZOA.

173

more than 30 miles wide, and 10-25 fathoms deep. A similar reef, though of
less extent, borders the western shore of New Caledonia. In many cases, as
in the Society Islands and elsewhere, a similar barrier or, as it is here called, an
encircling reef surrounds an island or group of islands, having at intervals Dreaks
in it, which lead into the deep lagoon channels and are often situated opposite
the valleys on the land. Low islands (coral islands] formed of coral rock and
sand thrown up by the sea, and supporting- a littoral vegetation, are often
situated on the reef.

A' *

FIG. 144 d.— Diagram illustrating Darwin's view of the formation of a barrier reef from a
fringing reef (from Darwin). AA outer edge of the fringing reef at the level of the sea ;
BB shores of the island ; A' A' outer edge of reef (now a barrier reef) after its upward growth
during a period of subsidence ; CO the lagoon channel between the reef and the island ;
B'B' the shore of the island.

The lagoon islands or atolls consist of a similar ring-shaped reef, enclosing
an open lagoon in which there is no island (Fig. 1446). There may be gaps
leading into the lagoon, or the ring may be so complete, that, as in the case of
Fakaofu in the Union Islands, it is left at low tide brim full of water standing
some feet above sea level. The floor of the lagoon is generally nearly flat,
shelving slightly towards the reef, and is often from 20 to 35 fathoms below

0'

FIG. 144e. — Diagram illustrating Darwin's view of the formation of an atoll from a barrier reef
by subsidence. A' A' outer edges of the barrier reef at the level of the sea. The cocoanut
trees represent coral islets formed on the reef. CO the lagoon channel ; B'B' the shores of
the island generally formed of low alluvial land and of coral detritus from the lagoon channel ;
A" A" the lagoon of the newly formed atoll. According to the scale the depth of the lagoon
and of the lagoon channel is exaggerated.

the surface — whereas the sea outside the reef rapidly deepens, so that it is not
uncommon to find a depth of more than 1000 fathoms within a mile of the
reef. The slope of the Seaward side of the reef below the region of growing
coral in many cases exceeds an angle of 45°. Low islands (coral islands) with
glittering white sand and characteristic vegetation are often situated on the
reef, scattered or united into a continuous belt of land.

The mode of the formation of the atoll has been much discussed. Whatever
the foundation of an atoll may be, it is requisite (1) that it should at one time,

174 COELENTBRATA.

at any rate, have readied so near the surface that coral polyps could form a
settlement on it, and (2), as whole groups of islands have the atoll form, that
it should in the great majority of cases not rise above that level.

Formerly the view was held that atolls were formed on submarine moun-
tains (volcanic) which reached to within the limit of growing coral distance
(40 fathoms), but this was objected to on the ground that it was exceedingly
unlikely that there should have been so many mountains reaching to just within
the right distance from the surface. But it has recently been pointed out* that
a large number of banks exist in»the ocean, springing from deep water and
rising to a wide level top at a depth of about 30 fathoms from the surface.
On many of these banks a rim of growing coral has been found raised a few
fathoms above the general level. Such banks have probably been produced by
a submarine volcanic eruption which has formed a mound, sometimes reaching
to the surface, sometimes reaching above it, but composed of loose scoriae in a
more or less finely divided state. Within the last few years the formation of
such mounds has been observed in different parts of the sea, and they have since
been, or are now in process of being reduced, by the action of the waves on the
loose material, to the condition of submarine banks such as are known to exist,
and such as are required for the foundation of atolls.

Darwin, to whom the existence of these banks was unknown, pronmlgated
his well-known theory of coral reefs, which was as follows : fringing reefs are
formed within the coral-reef zone on the shores of places where the conditions
are favourable for coral growth. Barrier reefs and atolls are derived from fring-
ing reefs by the subsidence of the land on which the reef is placed.

If we suppose an island bordered by a fringing reef to begin to subside (Fig.
144^), the corals, which as we have seen, are in the most vigorous condition on
the edge of the reef, no longer limited in their growth by the level of low water,
will grow upward ; the width of the lagoon will be increased by the extent to
which the sea now encroaches on the shore, and its depth by the amount of the
subsidence. Continue the subsidence and the reef will rise like a wall round the
land from which it is separated by the deepening lagoon, and the land itself,
lessened in area, will be reduced to the higher parts of the original mass, forming
an island or a group of islands in the centre of the wide lagoon (Fig. 144^).
The breaks in the fringing reef at the mouths of rivers still remain in the
barrier corresponding to the valleys, these parts of the shore line having been
originally free from coral growth. Although the lagoon deepens as the island
subsides, its depth will not be increased by the whole amount of that subsidence,
being partially filled up by detrital matter carried down by streams on the one
hand, and on the other by the material broken off by the wear and tear of the
breakers on the outside of the reef.

Continue the subsidence further till the highest mountain peak disappears
below the waters of the lagoon and an atoll remains, "like a monument, marking
the place of the burial," of the island (Fig. 144e).

In confirmation of his view as to the conditions under which fringing reefs
are formed, Darwin pointed out that their distribution is in many cases
coincident with lines of recent volcanic activity, with which elevation of the
earth's crust is often associated ; as well as with raised shore lines giving direct
evidence of elevation. Although not ignoring the possibility of atoll-shaped
islands being formed without the aid of subsidence, Darwin regarded this as

* See "Foundations of Coral Atolls," by Admiral W. J. L. Wharton, F.R.S.
Nature 1426, Feb. 25, 1897, p. 390.

RUGOSA ALCYONARIA. 175

exceptional, and, on the whole, the areas in which barrier reefs, encircling reefs,
and atolls occur were considered by him to be areas of subsidence. To this view
lie was led in part by the difficulty of finding any other foundation for atolls
than an island which had subsided. Direct indications of subsidence arerf from
the nature of the case, difficult to obtain, but such evidence as we have is
not altogether in harmony with Darwin's theory. Thus Dana, although an
adherent of the view, was of the opinion that the movement now going on in
many of the Paumotu Islands is one of elevation ; and similar evidence is forth-
coming from elsewhere (Solomon Islands, Tonga Islands, etc.). Such evidence
is, on the other hand, in keeping with the view that atolls rest, at any rate in
some cases, on such banks as those described by Admiral Wharton, and referred
to above (p. 174). It has been urged by Murray that an atoll on such a basis
would increase in size by the extension of the reef to seaward on its own talus,
while the lagoon would be widened by the solution of the dead portions of the
reef. A fringing reef would be converted into a barrier reef by the same process.

The part which the Anthozoa take in the alteration of the earth's
surface is considerable. In the present time they protect the coast
from the consequences of the breaking of the waves, and assist in the
formation of islands and rocks by producing immense masses of
calcareous matter. In earlier geological epochs they have played
a still more important part, judging from the great thickness of the
coral formations of the Palaeozoic period and of the Jurassic formation.

Order 1. RUGOSA = TETRACORALLA.

Palaeozoic Corals with numerous symmetrically arranged septa
grouped in multiples of four.

To these belong the families of the CyathophyHidae, Stauridae, etc.

Order 2. ALCYONARIA.*

Polyps and polyp colonies with eight pinnate tentacles and eight
mesenteric folds.

The Alcyonaria are all marine and, with the exception of the
Haimeidae, colonial. The buds are formed as a rule, not from the
bodies of the polyps themselves, but from stolons which originate as
tubular processes of the body-wall of the polyps at the base of the
colony (Fig. 145, A), or from the small canals which ramify in the
common jelly or coenenchyma and connect together the polyps
(Fig. 145, D). In the simplest colonies the polyps arise directly
from the basal stolon (Cornularia) ; an advance upon this occurs
when the basal part of the polyp acquires a greatly developed jelly,

* Wright and Studer, "Report on the Alcyonaria," Challenger Reports, 1889.
S. J. Hickson, "A Revision of the genera of the Alcyonaria Stolonifera, " Trans.
ZooL Soc.t vol. 13, 1894. A. Kolliker, Anat.-syst. Beschreibuwg d. Alcyonarien,
1872.

176

COELENTERATA.

and spreads out so as to form a plate-like expansion of coenenchyma
containing endodermal canals from which the new polyps bud
(Clavularia rosed). By the increase of this basal coenenchyme we
get the massive colonies of Alcyonium, with long polyp tubes and
canal system (Fig. 145, D). Another variation in the colonial
form may be deduced by supposing the plate-like expansion to be
invaginated so as to bring its lower surface to the inside, and the
polyps to the outside. Such a process would lead to the production
of colonies with an ectodermal axial rod (Gorgonia, Fig. 145, B,
? Pennatula). Calcareous spicules are very generally present. They
may occur either in the coenenchyma, or in the walls and tentacles
of the polyps, and they may either be loose or coalesced to form a

B

FIG. 145. — Diagrams to show the budding and mode of formation of the colonies of various
Alcyonaria. A, general diagram. B, Gorgonia. C, Tubipora. D, Alcyonium. The enteric
space and canals are black. S oesophagus ; se mesenteries ; mf mesenterial filaments ; dh
enteron ; sk axial skeletal rods with lines to show the mode of growth.

continuous corallum. When this coalescence occurs in the polyp-
walls we get the thecal tubes of Tubipora; when it occurs in the
coenenchyma, the axial rod of the Scleraxonia (Corallium rubrum).
Sometimes the spicules are embedded in a horny material, sometimes
in a calcareous cement. In the Pennatulacea and the Holaxonia
(Gorgonia} there is an axial rod secreted by an epithelial layer
contained in the stem or axis of the colony. This epithelial
layer is of ectodermal origin in the Holaxonia (Fig. 145, B\ but
its origin in the Pennatulacea is doubtful (? endodermal). In all
other cases the spicules arise in the jelly of the coenenchyma.

ALCYONARIA.

177

The polyps (autozooids) have eight pinnate tentacles and eight
mesenteries (Fig. 146). The gonidial groove (siphonoglyphe) when
present is single, and the side on which it is placed is called ventral. *
The longitudinal muscles are placed on the ventral faces of the
mesenteries (Fig. 146). The dorsal mesenteries are often longer
than the others, and are developed earlier in the bud, though later
in the egg. The polyps vary considerably in their power of con-
tractility. In the genera, with a good development of spicules in
the body-wall, there is hardly any retractility, but the tentacles are
simply folded over the mouth on irritation. In Stereosoma, which
has a horny layer beneath the ectoderm, the polyps are non-retractile.
The polyps are often dimorphic. There are the autozooids with
tentacles and generative organs, and
the siplwnozooids without these struc- R

tures, and with filaments only on
the dorsal mesenteries. A gonidial
groove (siphonoglyphe) is present
in the Alcyonidae and in Scircophy-
ton ; it is absent in the autozooids of
Pennatulacea, Heteroxenia, and Para-
f/oryia, but present in the siphono-
zooids, in which it is always specially
developed. The Pennatulacea are
phosphorescent.

The enteric cavities of the polyps
are connected with the fine canal-
system of the coenenchyma, when
such exists, and are continued as

main canals for a longer or shorter distance towards the base of
the colony. In the Stolonifera they all, of course, open into the
basal stolon.

Development. The ova develop inside (as far as the planula) and
outside the parent. They have yolk, and the segmentation is on the
centro-lecithal type, and is often delayed until the nucleus has under-
gone many divisions. There is usually a free-swimming planula-larva.

Extinct forms.! The genera Heliolites (palaeozoic) and Poly-
tremacis (chalk, greensand, eocene) were probably Helioporidae, and

FIG. 146.— Transverse section through
Alcyonium (after Hertwig). R goni-
dial groove ; 1, 2, 3, k, the four pairs
of septa with their muscles.

* This is a special use of the term ventral, and does not imply any homology
with the ventral surface of bilateral animals.

t K. A. Zittel, Handbuch der Palaeontologic, Bd. 1, p. 208. Munich and
Leipzig, 1876-80.

1 78 COELENTERATA.

Heliopora itself is found in the cretaceous formation. Syringopora
(Silurian, Devonian, Carboniferous) was probably allied to Tubipora.
The Favositidae were probably Alcyonarian.

Sub-order 1. PROTOALCYONAKIA.

Polyps solitary ; with or without spicules.

Fam. 1. Haimeidae. Haimea M. Edw. ; Hartea P. Wright ; Monoxenia H.

Sub-order 2. STOLONIFEEA.

Colonial Alcyonaria with a membranous or ribbon-like stolon. Jelly poorly
developed. Polyps either entirely free from one another except at their bases, or
connected by horizontal platforms (Tubipora) or connecting tubes (Clavularia
viridis}. Skeleton absent, or composed of calcareous spicules which may be joined
together or be isolated. In some cases the body-wall is supported by a horny
secretion.

Fam. 2. Cornularidae. Polyps are not united in bundles, but either spring
from a plate-like expansion or a creeping stolon ; or are branched and bear
lateral buds. Gornularia Lam. , no spicules, horny secretion on polyp-walls and
stolon ; Ehizoxenia Ehrb. ; Clavularia Q. and G. ; Sarcodictyon Forbes ; Anthelia
Savigny ; Gymnosarca S. Kent ; Cornulariella Verrill ; Telesto Lamouroux,
polyps rise from a flat base, or from stolons, and bear buds ; Coelogorgia
M. Edwards, colony arborescent, an axial polyp with buds ; Cyathopodium
Verrill, stolons calcined connecting the short cup-shaped polyps ; Scleranthelia
Studer ; Anthopodium Verrill ; Sympodium Ehrb. ; Stereosoma Hickson, with
spicules, with non-contractile polyps and tentacles, with a horny layer between
the ectoderm and supporting lamella ; Erythropodium Roll. ; Callipodium Verr. ;
Pseudogorgia Koll., axial polyp with lateral polyps budded from the upper part.

Fam. 3. Tubiporidae. Colonies consist of tubular polyps parallel to one
another, and united by horizontal platforms containing endodermal canals
(Fig. 145, C}. The platforms are formed as outgrowths of the lips of the polyps,
into which prolongations of the enteric cavity pass to form the endodermal
canals ; they are, at first without or with only a few spicules. The platforms
and the greater part of the walls of the polyp-tubes contain a skeleton formed
of coalesced spicules, so that the dry corallum has the form of parallel tubes
united by lamellae. The first layer of platforms constitutes the plate-like stolon
of origin. The tubes are divided at intervals by partitions called tabulae which
may be funnel-shaped. Tubipora L., the organ-pipe coral.

Sub-order 3. ALCYONACEA.

Colonial Alcyonaria with a well-developed canaliferous coenenchyma and loose
spicules. Without axial skeletal rod. The buds are formed from the coenenchymal
canals (Fig. 145, D}.

Fam. 4. Xeniidae. Colonies of long polyps, united in their lower portion by
a canal system, ramifying in a connecting coenenchyma with feebly calcareous
spicules. Xenia (Heteroxenia Koll.) Savigny.

Fam. 5. Organidae. Elongated polyps united together so as to form a short
upright stem. Polyps and tentacles provided with spicules. Organidus
Danielssen.

Fam. 6. Alcyonidae. Massive coenenchyma containing the polyp tubes,
which are united by endodermal canals from which the buds are formed.
Isolated spicules in the jelly of the coenenchyma. Crystallophanes Dan.;

PENNATULACEA.

179

Bellonella Gray; Nidalia Gray; Paralcyoniutn M. Edw. ; Sarakka Dan.;
Alcyonium L., A. digitatum, dead men's fingers; Lobularia Savigny ; Sarco-
phyton Lesson, with dimorphic polyps ; Lubophytum Marenzeller, with dimorphic
polyps ; Anthomastus Verr., dimor-
phic polyps ; Nannodendron Dan.,
dimorphic polyps.

Fam. 7. Nephthyidae. A branched
coenenchyma with sterile base and
terminal polyps. The latter do not
exhibit separate calycine and ten-
tacular regions, and there is no in-
vagination of the latter ; when at
rest tentacles folded over oral disc.
Buds arise from fine endodermal
canals between the polyps. Voerin-
gia Dan.; Fulla Dan.; Barathrobius
Dan. ; Gersemia Marenzeller ; Ger-
semiopsis Dan.; Drifa Dan.; Duva
Kor. and Dan. ; Eunephthya Verr. ;
Ammothea Sav. ; Nephthya Sav. ;
Spongodes Lesson ; Paranephthya
Wright and Studer ; Sderonephthya
Wr. and St. ; Chironephthya Wr.
and St.; Siphonogorgia Kbll.

Fam. 8. Helioporidae.* Compact
corallum formed in the jelly of the
coenenchyma. The corallum is tra-
versed by tubes closed above, called
coenenchymal tubes (possibly modi-
fied siphonozooids), and by tubes
continued from the polyp calycles.
Both systems of tubes are divided
by tabulae and are united by endo-
dermal canals in the superficial
coenenchyma. False septa formed
by denticulations of the margins of
the calycles. Heliopora Blainville.

Sub-order 4. PENNATTJLACEA.f

Unattached polyp colonies with a
stalk embedded in mud or sand, and
a rachis bearing polyps. The stalk
generally has an axial rod.

The stalk is without polyps and
is embedded in mud or sand. The

FIG. 147. — Kophobdemnon Leiickartii.

rachis is a continuation of the stalk and carries the polyps, which are arranged

* H. N. Moseley, "The Structure and Relations of the Alcyonarian Heliopora
Coerulea," Phil. Trans., 1876.

t A. Kolliker, Anat.-syst. Beschreib. d. Alcyonarien Abt. 1. Die Pennati diden,
Frankfurt-a-M.; 1872. A. Kolliker, "Report on the Pennatulidae," Challenger
Reports, 1880.

180

COELENTBRATA.

upon it in different ways. In Veretillum they are distributed all round the
rachis ; in Kophobelemnon (Fig. 147) they are absent on a streak of one side —
the so-called ventral side ; in most genera they are arranged bilaterally, there
being a dorsal as well as a ventral streak free from them. Further, in some
genera they are sessile on the rachis, but in the Pennatulea, or Sea-Feathers
proper, the polyps are borne only on lateral processes of the coenenchyma, called
the pinnules. The pinnules are broad triangular leaf-shaped structures attached
by their base to the rachis and carrying the polyps on their dorsal edges (Fig.
148). The polyp-tubes project in fome cases to form the so-called cells; the
cells may have spines or tufts of spicules.

The polyps are dimorphic ; the autozooids have tentacles and generative organs,
and are without a gonidial groove ; the siphonozooids possess a gonidial groove
but are without tentacles and gonads, also they have filaments on the two dorsal

mesenteries only. The siphon o-
zooids are distributed over the
whole rachis in Renilla and Vere-
tillum ; and in the Pennatulea
they are on the rachis or on the
pinnules.

The stalk generally contains an
axial calcareous or horny rod sur-
rounded by a sheath of epithelial
cells ; and the coenenchyma and
bodies of the polyps may contain

FIG. 148.— Pennatula Sulcata Roll, (after Kolliker).
A, from the dorsal ; B, from the ventral side.

isolated spicules. The polyps are
continued into tubes which join
the canal system of the coenen-
chyma. This canal-system con-
sists of large canals continued
down from the polyps and open-
ing after a longer or shorter
course into a few "main canals,"
which run in the stalk. There
are generally four of the latter
(two in Renilla}, of which two
are lateral, one dorsal, and one
ventral. At the lower end of

the stalk the lateral canals cease, leaving only the dorsal and ventral. They
fuse at the end of the stalk and are said to open there. In addition to the
large canals there are minute canals uniting them. Some of the polyps are
closed below, and open at their base by narrow openings into the general canal
system of the colony.

The Pennatulacea are not distributed uniformly over all seas. They are
mainly littoral, but deep water forms are known, and these, it is important to
notice, belong principally to the simpler families, e.g., the Protoptilidae and
Umbellulidae. They appear to be absent, or nearly so, in the deeper parts of
the Pacific and Atlantic Oceans and the South Polar Sea at a certain distance
from the shore.

Section 1. Pennatulea.

The Sea-feathers. With pinnules ; rachis with a bilateral arrangement of the
polyps, elongated, cylindrical.

GORGONACEA. 181

Fain. 1. Pteroeididae. Pinnules well developed, with siphonozooids on the
pinnules. Pteroeides Herklot ; Godcfroyia Kbll. ; Sarcophyllum Kbll.

Fara. 2. Pennatulidae. Pinnules well developed ; siphonozooid^ on the
ventral and lateral sides of the rachis. Pennatula Lam. ; Leioptilum Verr. ;
Ptilosarcus Gray ; Halisceptrum Herklot.

Fam. 3. Virgularidae. Pinnules small, without a calcareous plate. Virgu-
laria Lam. ; Scytalium Herkl. ; Pavonaria Kbll.

Fam. 4. Stylatulidae. Pinnules small, with a calcareous plate. Stylatula
Yerr. ; Dubenia Kor. and Dan. ; Acanthoptilum Kbll.

Section 2. Spicata.

Rachis elongated, cylindrical, with a bilateral arrangement of the polyps ;
without pinnules ; polyps sessile.

Fam. 5. Funiculinidae. Polyps on both sides of the rachis in distinct rows,
with cells ; ventral siphonozooids absent. Funiculina Lamarck ; Ualipteris
Kbll.

Fam. 6. Stachyptilidae. Polyps (with cells) on both sides of the rachis in
distinct rows. Ventral siphonozooids present. Stachyptilum Koll.

Fam. 7. Anthoptilidae. Polyps on both sides of the rachis in distinct rows,
without cells. Anthoptilum Kbll.

Fam. 8. Kophobelemnonidae (Fig. 147). Polyps on both sides of the rachis
in a single series, or in indistinct rows, large and without cells; rachis elongated,
cylindrical ; ventral streak of rachis without polyps. Kophobelemnon Asbjbrnsen,
Sclerobelemnon Kbll. ; Bathyptilum Kbll.

Fam. 9. Umbellulidae. Polyps on both sides of the rachis in a single series,
or in indistinct rows, large and without cells ; rachis short (i.e.) the polyps are
placed at the end of the central stem). Umbellula Lam.

Fam. 10. Protocaulidae. Polyps on both sides of the rachis in a single
series, or in indistinct rows, small and without cells. Protocaulon Kbll. ;
Cladiscus Kor. and Dan.

Fam. 11. Protoptilidae. Polyps on both sides of the rachis in a single series
or in indistinct rows, with cells. Protoptilum Kbll. ; Lygomorpha Kor. and
Dan. ; Microptilum Kbll. ; Leptoptilum Kbll. ; Trichoptilum Kbll. ; Scleroptilum
Kbll.

Section 3. Kenillea.

Rachis expanded in the form of a leaf, with bilateral arrangement of the
polyps on one side of the expansion ; without pinnules. A single large siphono-
zooid (exhalent zooid) terminates the end of the central stem.

Fam. 12. Renillidae. Renilla Lam.

Section 4. Veretillea.

Club-shaped colonies, without pinnules. Polyps arranged all round the
rachis.

Fam. 13. Cavernularidae. Spicules long. Cavernularia Valenciennes;
Stylobelemnon Kbll.

Fam. 14. Lituaridae. Spicules short. Lituaria Val. ; Veretillum Cuv.;
Policella Gray ; Clavella Gray.

Sub-order 5. GORGONACEA.

Fixed colonial Alcyonaria with a horny or calcareous axial rod, which is
covered by a coenenchyma from which the polyps arise.

182 COELENTEEATA.

Section 1. Scleraxonia (Pseudaxonia).

Fixed upright branched colonies. The coenenchyma consists of a canaliferous
cortical layer (with spicules) in which the polyps are placed, and of a medullary
substance. The latter contains spicules (different in form from the cortical
spicules) which are generally tightly packed, and sometimes fastened together
by a horny substance, or cemented into a strong axis by calcareous matter.'
Without epithelial layer round the central rod.

Fam. 1. Briareidae. Coenenchyma consists of a polyp-bearing cortex and
a medullary substance of closely packed spicules. These are either developed on
the surface of an upright shrubby colony, or the medullary substance is relegated
to the interior of a cylindrical stem, over which is spread the cortex. In the
latter case there is a more or less well-defined axis, which may be permeated by
nutritive canals. Leucoella Gray ; Solenocaulon Gray ; Semperina Koll. ; Suberia
Studer ; AnthothelaVen\', Paragorgia M.-Edw. ; Briareum Blainville ; Titani-
deum Ag. ; Iciligorgia Ridley ; Spongioderma Koll.

Fam. 2. Sclerogorgldae. An axis consisting of closely intercalated elongated
spicules with dense horny sheaths. The axis is surrounded by longitudinal
canals, into which there open the reticulated coenenchymatous canals, uniting
the polyps. Suberogorgia Gray ; Keroeides Wr. and St.

Fam. 3. Melitodidae. Axis jointed, consisting of alternate portions of cal-
careous and soft horny substance. Melitodes Verr. ; Mopsella Gray ; Acabaria
Gray ; Psilacdbaria Ridley ; Wrightdla Gray ; Clathraria Gray ; Parisis Verr.

Fam. 4. Corallidae. Axis of a dense calcareous mass of fused spicules ;
polyps dimorphic ; the siphonozooids are said to grow into autozooids. Corallium
Lam.; C. rubrum, the red coral (Fig. 138) ; Pleurocorallium Gray.

Section 2. Holaxonia (Axifera)

Coenenchyma branched or simple, with cortical canaliferous layer and axial
rod, which is either horny, or of calcified horn, or of alternating joints of
calcareous matter and horn. Axial rod derived from a layer of ectoderm cells
invaginated at the base of the colony, and surrounding it as an epithelium
(Fig. 145).

Fam. 5. Dasygorgidae. Simple or branched, coenenchyma thin, potyps
large ; both polyps and coenenchyma contain spicules. When at rest the
tentacles are folded over the oral disc. Strophogorgia Wright ; Chrysogorgia
Duch. and Mich. ; Herophila Steenstrup ; Dasygorgia Verr. ; Iridogwgia Verr.

Fam. 6. Isidae. Axis consists of alternating horny and calcareous portions.
Bathygorgia Wright ; Ceratoisis Wright ; Callisis Verr. ; Acanella Gray ; Isidella
Gray ; Sclerisis Studer ; Primnoisis Wr. and St. ; Mopsea Lamouroux ; Acan-
thoisis Wr. and St. ; Isis L.

Fam. 7. Primnoidae. Axis calcareous and horny, basal attachment calcareous.
Polyps with club-shaped calycine portion. Operculum calycine formed by some of
the scale-like spicules of the calycine region, which shut over the tentacular region.
Callozostron Wright ; Calyptrophora Gray ; Primnoa Lamouroux ; Stachyodes
Wr. and St. ; Calypterinus Wr. and St. ; Stenella Gray ; ThouareUa Gray ;
AmphilaphisWr. and St. ; Plumarella Gray; Primnoella Gray; Caligorgia Gray.

Fam. 8. Muriceidae. Axis horny ; spicules project beyond the surface of
coenenchyma ; operculum tentacular, formed by the spicules at the base of the
tentacles which close over the calyx when the oral region is retracted. Acan-
thogorgia Gray ; Paramuricea Koll. ; Hypnogorgia Duch. and Mich. : Muriceides
Wr. and St. ; Clematissa Wr. and St. ; Villogorgia Duch. and Mich. ; Anthogorgia

ZOANTHARIA. 183

Verr. ; Menella Gray ; Ads Duch. and Mich.; Thesea Duch. and Mich.; Bebryce
Philippi.

Fam. 9. Plexauridae. Colony branched, axis horny ; polyps occur fty. over
the thick coenerichyma ; spicules large ; cortical club-shaped and deeper spindle-
shaped spicules. Eunicea Lamouroux ; Plexaura Lamotiroux ; Psammogorgia
Verr. ; Platygorgia Studer.

Fam. 10. Gorgonidae. Colonies upright and branched usually in one plane ;
axis horny, rarely horny and calcareous ; polyps arise from stem and twigs in a
bilateral and biradiate manner. Coenenchyma smooth, spicules small. Platy-
caulos "Wr. and St.; Loplwgorgia M.-Edw. ; Leptogorgia- M. -Edw. ; Stenogorgia
Verr.; Callistephanus Wr. and St.; Swiftia Duch. and Mich.; Gorgonia L. ;
Eugorgia Verr.

Fam. 11. Gorgonellidae.

Order 3. ZOANTHARIA = HEXACTINIA.

Polyps and polyp-colonies, usually with simple unbranched tentacles.
There are usually incomplete as tcell as complete mesenteries, and the
tentacles usually alternate in several circles.

This order includes the Sea-Anemones and Corals. The order
owes its name Hexactinia to the fact that in some of the best-
known forms the mesenteries and tentacles are arranged in some
multiple of the number six. There is, however, the greatest variation
in this respect, and with the progress of research it has become clear
that the number six is by no means universally characteristic; indeed
we may go further, and say that it is not even typical; and it appears
probable that, when this matter has been more fully looked into, the
hexactinian arrangement will be found tq be only one of many
mesenterial arrangements found in the group. In some cases the
number of mesenteries increases with the growth of the animal.

Development. Our knowledge is not very complete. An in-
vaginate gastrula has been observed, with a blastopore persisting as
mouth. A ciliated, free-swimming larva is usually formed.

There are three sub-orders.

Sub-order 1. ACTINIARIA.* MALACODERMATA.

Solitary, rarely colonial polyps with mesenteries, the number of which is
usually a multiple of six ; without skeleton. Body moving freely, or adherent
by means of the pedal disc ; rarely firmly fixed.

* P. H. Gosse, A History of the British Sea-Anemones and Corals, London,
1860. R. Hertwig, "Report on the Actiniaria," Challenger Reports, Pt. 15,
1882. R. Hertwig, Supplement to the above, Challenger Reports, Pt. 73, 1888.
A. Andres, " Le Attinie," Fauna and Flora des Golfes von Neapel, 1884. A. C.
Haddon, "A Revision of the British Actiniae," Pts. 1 and 2, Sci. Trans. Roy.
Dublin Soc. (2), 4, 1889-91. J. Playfair McMurrich, "Report on the Actiniae
collected by the United States Fish Commission Steamer Albatross," Proc. U. S.
National Museum, vol. xvi. p. 119, 1893.

184

COELENTERATA.

The Zoantheae alone are colonial. As a rule there is a single corona of
tentacles at the edge of the oral disc ; these are the primary (marginal)
tentacles. When they are in several rows the inner are the oldest. They arise
both from intra- and intermesenterial spaces (see below, p. 184). In addition to
these there are in some forms (Corallimorphidae) secondary or accessory tentacles
arising from the disc midway between the inouth and margin, and these are
always intramesenterial. There is nearly always a sphincter muscle at the
peristomial margin, which may be endodermal or mesodermal (i.e. in the jelly).
It closes the peristomial margin ove*r the mouth and tentacles during retraction.
The mouth is usually slit-like, and the oesophagus has two gonidial grooves
(Gosse). Sometimes there is only one gonidial groove (Peachia, Zoantheae,
Cerianthus). The thickened walls of these grooves are prolonged beyond the
lip at the two ends of the long axis of the mouth as two tubercles (called in
the Siphonactinidae the conchula).

The oesophageal lappets are processes of the oesophageal wall at each end of

the long axis which hang down
into the coelenteron beyond the
rest of the oesophagus ; the gonidial
grooves are continued on to them.
The gonidial grooves are, in this
work, denned as dorsal and ven-
tral. The ventral groove is the
most conspicuous, and the only
one present in Peachia and the
Zoantheae. When there is only
one groove, it is not always pos-
sible to determine whether it is
dorsal or ventral. In the termi-
nology which has more recently
been introduced by Haddon the
ventral groove is termed the sulcus,
and the dorsal the sulculus. It
will, of course, be understood that
the above use of the words dorsal
and ventral is special to the group,
and implies no homologies with
the dorsal and ventral surfaces of
other animals.

The mesenterial arrangement
presents the greatest variation.

The arrangement* generally described as typical is that of the Hexactiniae, in
which the mesenteries are arranged in pairs (Fig. 149), and in the simplest cases
in six pairs. These are the primary mesenteries, and they all reach and are
inserted into the oesophagus. The mesenteries of each pair are usually provided
with longitudinal muscles on those faces which are turned towards one another,
except on the two pairs of directive mesenteries ; these carry the longitudinal
muscles on the faces turned from one another. The portion of coelenteron enclosed
in each pair of mesenteries is called an intramesenterial space or endocoele, the
portion between the pairs being intermesenterial (exocoele). There are, there-
fore, six of the former and six of the latter. There are in many cases secondary

* For variations see descriptions of the different sections.

FIG. 149.— Transverse section through Adamsia
(Sagartidae) (after R. Hertwig). Hf the cham-
bers between the directive mesenteries ; R
gonidial grooves.

ACTINIARIA. 185

mesenteries (formed later than the primary) in addition to the primary; these are
complete in most Hexadiniae (incomplete in some Sagartidae, Peachia, etc.) ;
there are six pairs of them, and they are placed in the intermesenterialfspaces,
the longitudinal muscular faces of each mesentery being turned towards the
corresponding face of its fellow of a pair, as in the case of the lateral primaries.
There may be, in addition, twelve pairs of tertiary mesenteries and twenty-four
quaternaries, and so on ; the mesenteries of each order being always in pairs and
placed in intermesenterial spaces. The mesenteries of each order are smaller
than those of the preceding order, and except in the case of the primaries and
secondaries do not, as a rule, reach the oesophagus. The space between the
mesenteries of a primary pair is a primary intramesenterial space, that between
the mesenteries of the next cycle a secondary intramesenterial space, and so on.

The tentacles, like the mesenteries, are in cycles of different age, so that we
can distinguish tentacles of the first, second, etc. order. There is often a
corresponding distinction in size (Corallimorphidae), and the arrangement of
the mesenteries is reflected in that of the tentacles. In such cases the six
largest tentacles are over the primary mesenterial spaces ; the next six, which
are a little smaller, belong to the secondary intramesenterial chambers ; then
follow the twelve tentacles, still smaller, of the tertiary intramesenterial spaces ;
while the twenty-four last tentacles communicate with the intermesenterial
spaces.

Acontia are present in the Sagartidae. The epithelial cells always carry
flagella or cilia.

The sexes are usually separate, but a few are hermaphrodite. The generative
cells in some cases, if not all, escape through the gonidial grooves.

Budding takes place in the colonial Zoantheae, and both budding and fission
are occasionally observed in some solitary forms (Anthea cereus = Anemonia
sulcata, Actinoloba, Actinia, and other genera).

The development of mesenteries in some larval Actiniae is interesting in
view of permanent arrangements in the various tribes of the Actiniaria. It
is as follows : —

Stage 1. — The two first mesenteries are at right angles to the long axis of the
oesophagus, and divide the coelenteron into two, generally unequal, chambers.

Stage 2. — The mesenteries of the second pair are in the larger of the two
chambers so formed.

Stage 3. — The mesenteries of the third pair develop in the smaller of the two
primitive chambers.

Stage 4.— The mesenteries of the fourth pair are within the unpaired chamber
enclosed by the mesenteries No. 2 (Fig. 149«).

Stage 5. — Two pairs now arise simultaneously, and for some time remain
incomplete ; they are respectively between the first and second, and the first and
third ; their longitudinal muscles face the longitudinal muscles of the first and
second respectively. When these are completed we get the typical Hexactinian
arrangement of the above mesenterial pairs ; the third and second are directive.
Moreover, it is to be noted that Stage 4 exists permanently in the Edwardsiae,
while Stage 5 is found in Gonactinia and in a modified form in the ZoantJieae.

Stage 6. — A pair of small mesenteries with their muscles facing each other
appears in each intermesenterial chamber (exocoele), and so with subsequent
cycles. In Peachia only four pairs of secondaries are formed, those of the
dorsal intermesenterial chamber (opposite to the gonidial groove) being absent.

The deep-sea forms are very commonly distinguished by the reduction of their

186

COELENTERATA.

tentacles even to vanishing point and by the enlargement of their terminal
openings to large slit-like stomidia* ; also by variations from the type of
mesenterial arrangement.

The Actiniaria comprise the Sea- Anemones ; they live in the sea, attached to
rocks or other bodies, or embedded in sand, or sessile, as commensals, on hermit
crab shells.

Section 1. Hexactiniae.

With paired mesenteries. The mesenteries of each pair are usually provided
with longitudinal muscular fibres on those faces which are turned towards one
another, except on the two pairs of directive mesenteries, which carry the
longitudinal muscles on the faces turned from one another (Fig. 149). Six or
more pairs of mesenteries, increasing in multiples of six.t Mouth slit-like,
oesophagus usually with two gonidial grooves.

FIG. 149 a.— Diagram of the growth of the mesenteries in Hexactinians (from Korschelt and
Heider). A , stage of Manicina areolata, with eight primary mesenteries, in transverse section
(after H. V. Wilson) ; 7>, stage of Aulactinia stelloides with twelve primary mesenteries (after
McMurrich). The mesenteries are numbered in the order of their appearance, ec ectoderm ;
en endoderm ; s supporting lamella ; / mesenterial filaments.

Sub-tribe 1. STICHODACTYLINAE. Tentacles arranged radially, some or
all of the iutramesenterial chambers communicating with more than one
tentacle.

Fam. 1. Corallimorphidae. With a double or multiple corona of tentacles
(marginal, principal, and intermediate accessory), more than one tentacle com-
municating with each intramesenterial chamber. Tentacles various ; pedal disc
present ; gonads on all the septa ; muscular system weak ; sphincter muscle
various ; acontia absent. Corallimorphus Moseley, from the deep-sea ; Corynactis
Allman ; Capnea Forbes ; Discosoma Leuck. ; Aureliana Gosse ; Rhodactis

* Recent researches render it probable that in these cases the tentacles have
dropped off.

t There is, however, variation in this character, even within the section
Hexactiniae.

ACTINIARIA. 187

M.-Ed. and H.; Phymanthus M.-Ed. and H.; Crambactis Haeckel ; Cryptoden-
drum Klunzinger ; Actinothrix D. and M. ; Heterodactyla Ehr.

Fam. 2. Minyadidae. Pedal disc transformed into an apparatus for floating.
Tentacles in some as in the Corallimorphidae. Minyas Cuv. ; Dactylommyas
And. ; Acerominyas And. ; Phyllominyas And.

Sub-tribe 2. ACTININAE. Tentacles arranged in cycles, only a single
tentacle communicating with each intramesenterial chamber.

Fam. 3. Antheomorphidae. Tentacles digitate ; pedal disc present ; accessory
tentacles absent; gonads on all the mesenteries ; numerous complete mesenteries ;
muscular system weak ; without sphincter muscle or acontia. Antheomorphe
R. Hertwig, deep-sea form.

Fam. 4. Actiniidae. Tentacles digitate, in a single corona ; pedal disc
present ; acontia absent, sphincter muscle endodermal, weak ; with numerous
mesenteries. Actinia Browne ; Anemonia Eisso ; Cotidylactis D. and M. ;
Actinioides Hadd. and Shack. ; Bolocera Gosse.

Fam. 5. Aliciidae. With large flat base. Lateral body-wall with simple
or compound hollow processes or vesicles, mostly in vertical rows. No cinclides.
Sphincter variable, diffuse, endodermal. Acontia absent. A licia Johnson ; Cysti-
actis M.-Edw. ; Thaumactis Fowler ; Bunodeopsis And. ; Phyllactis M.-Ed. and H.
Fam. 6. Bunodidae. Tentacles digitate ; pedal disc present ; acontia absent ;
sphincter well developed, circumscribed, endodermal ; with numerous perfect
mesenteries. Tealia Gosse ; Leiotealia R. Hertwig. ; Bunodes Gosse ; Phymactis
M.-Edw. and H.; AulactiniaVei'r.; Anthopleura Duch. ; Evactis Verr. ; Thelactis
Klunzinger ; Cereactis Andres.

Fam. 7. Paractidae. Tentacles digitate ; pedal disc present ; acontia
absent ; sphincter strong, mesodermal ; with numerous perfect mesenteries.
Paractis M.-Edw.; Dysactis M.-Edw.; Tealidium Hertwig ; Antholoba Hertwig;
OpModiscus Hertwig; Paranthus Andres; Paractinia And.; Actinerus Verr.;
Actinostola Verr. ; Pycnanthus McM. ; Cymbactis McM. ; Stomphia Gosse.

Fam. 8. AmpManthidae. Tentacles digitate ; pedal disc present ; acontia
absent ; mesodermal sphincter present ; transverse axis of body and mouth
elongated, so that the two gonidial grooves almost touch ; principal mesenteries
sterile ; secondary mesenteries incomplete. Attached to the axial skeletons of
Gorgonidae. Stephanactis Hertw.; Amphianthus Hertw.

Fam. 9. Sagartidae. With mesodermal sphincter muscle, usually with
only a few complete mesenteries, with acontia.

Sub-fam. 1. Sagartinae. WTith naked ectoderm, the acontia emitted
through the mouth and through cinclides. The mesenteries of the second
and subsequent cycles may, in a more irregular manner, reach the oeso-
phagus. Sagartia Gosse ; Cereus Oken ; Actinoloba Blainv. ; Adamsia
Forbes, sessile upon Gastropod shells containing a Hermit crab; Cylista
Gosse ; Mitactis Haddon and Duerden ; Aiptasia Gosse ; Gephyra V. Koch
(Morph. Jahrb. 4) solitary or colonial, sessile on zoophytes, to which it
is glued by a cuticular matter secreted by the ectoderm, with more than
24 tentacles.

Sub-fam. 2. Chondractininae. With thick body-wall, upper portion
different in character from the lower, which is provided with a cuticle.
The 12 primary mesenteries alone are complete and without gonads.
Acontia emitted by the mouth, cinclides absent. Actinauge Verrill ;
Chitonanthus McM. ; Hormathia Gosse ; Ckitonactis Fischer ; Chondradinia
Littken ; Paraphellia Haddon.

188 COELENTERATA.

Sub-fam. 3. Phellinae. Sagartidae with a cuticular covering ; primary
mesenteries alone fertile. Phellia Gosse ; Octophellia And.; Ilyactis And.;
Ammonactis Verr.

Fam. 10. Heteractidae. Tentacles clavate, knobbed. Eloactis And. ; Rhopo-
lactis And.; Ragactis And.; Heteractis M.-Edw. and H. ; Stauractis And.

Fam. 11. Sideractidae. "With sixteen pairs of perfect mesenteries, and
three series of non-retractile tentacles, of which the innermost contains eight.
Sideractis Dan.

Fam. 12. Madoniactidae. With a few principal mesenteries, acontia, and
a prominent endodernial circular muscular system. Intermediate between
Bunodidae and Sagartidae. Madoniactis Dan.

Fam. 13. Andvakiadae. Elongated, without any real pedal disc, seated
loose in the sand, the greater part of the body encrusted. The uppermost bare
part of the body, the oral disc, and the tentacles completely retractile. Few
mesenteries. Endodermal circular muscular system. Near Sagartidae.

Fam. 14. Liponemidae.* Tentacles reduced to short tubes or stomidia ;
with numerous perfect mesenteries. Deep-sea forms. Polysiphonia R. Hert.,
tentacles short tubes with large terminal opening, allied to Paractidae ; Poly-
stomidium, R. Hert., with stomidia, allied to Actinidae ; Liponema R. Hertwig,
stomidia very numerous ; Aulorchis R. Hert., with gonads modified into a tube
opening through the mouth.

Fam. 15. SarcophiantMdae. Sarcophianthus Lesson.

Fam. 16. Thalassianthidae. Tentacles replaced by bushy excrescences of the
disc. Thalassianthus Leuck. ; Actineria Blain.; Megalactis Ehrb. ; Actinodendron
Blain.

Fam. 17. Ilyanthidae. With single corona of tentacles ; pedal disc absent,
gonidial grooves and sphincter obscure. Ilyanthus Forbes ; Mesacmaea And. ;
Halcampa Gosse ; Halcampella And.

Fam. 18. Siphonactinidae. Like the last, but with a gonidial groove, the
lips of which project beyond the mouth (conchula). Peachia Gosse ; Siphon-
actinia K. and D. ; Philomedusa Miiller ; Adinopsis K. and D.

Danielssen's genera Aegir and Fenja^ do not exist. They were founded upon
mutilated specimens.

Section 2. Paractinia.

With paired mesenteries. There are two pairs of directives, and the longi-
tudinal muscles are arranged as in Hexactinia. Number of mesenteries has no
relation to the number 6. With two gonidial grooves and two oesophageal
lappets.

Fam. 1. Sicyonidae. Sessile, with tetramerous arrangement of the mesenteries,
sphincter muscle mesodermal, tentacles as short knob-like stumps. Possibly
related to the Tetracorallia. Sicyonis R. Hert. Deep-sea form.

Fam. 2. Polyopidae. Without pedal disc, tentacles transformed into
stomidia. J Polyopis R. Hert. Deep-sea form, probably tetramerous.

* Vide note on p. 186.

t D. E. Danielssen, "Actinida," The Norwegian North Atlantic Expedition
1876-8. 1890.
J See note on p. 186.

ACTINIARIA.

189

Section 3. Protactiniae (Protantheae).

With 12 primary and 1 or 2 pairs of secondary mesenteries, which are dorsal
rather than ventral. Body-wall and oesophagus with ectodermal ganglionic
and muscular layers.

Fam. Gonactinidae. Scytophorus R. H. ; Gonactinia Sars, with the power of
transverse fission ; Oractis McM. ; Protanthea Calg.

Section 4. Edwardsiae.

Without pedal disc, with 8 mesenteries, including two pairs of directive
mesenteries and 4 unpaired mesenteries (Fig. 150). All mesenteries with gonads.
Tentacles usually more numerous than the mesenteries. The muscular (longi-
tudinal) faces of the 4 unpaired mesenteries are all turned the same way. Live
in sand. Edwardsia Quatrefages.

S

FIG. 150. — Diagram of the arrangement of FIG. 151. — Diagram of a transverse section

the muscles and mesenteries of Edwardsia through a young Zoanthus. The section is

(from Chun after Boveri). S, S sagittal a little oblique. D dorsal, V ventral side ;

plane ; a, a gonidial grooves. x gonidial groove ; c inesenteric filaments ;

s1 macro-, s2 micro-mesenteries (from

Perrier).

Section 5. Zoantheae.

With numerous mesenteries of two kinds, (a) imperfect sterile micro-mesenteries,
(b) larger perfect macro-mesenteries with gonads and filaments : the two kinds
(Fig. 151) usually placed alternately, so that each pair is composed of a larger
and a smaller mesentery ; two pairs of directive mesenteries, one pair consisting
of macro-, the other pair (dorsal) of micro-mesenteries ; one gonidial groove
ventral (near large directives). Usually colonial ; wall of body usually traversed
by ectodermal canals, and encrusted with foreign bodies which may even be
embedded in the wall. The longitudinal muscular faces of the mesenteries of
each pair are arranged as in Hexactiniae. New mesenteries are formed in the
inter-mesenterial space on either side of the ventral directives. The colonial
forms arise either from a branched stolon, or from a broad basal plate containing
anastomosing endodermal canals.

Fam. ZoantMdae. Zoanthus Cuvier ; Gemmaria D. and M. ; Isaurus Gray ;
Palythoa Lamx. ; Splienopus Stenstr. , with rounded aboral end, embedded in
sand ; Epizoanthus Gray, often on hermit-crab gastropod shells ; Parazoanthus
Haddon and Shack.

190

COELENTERATA.

Section 6. Ceriantheae.

With numerous unpaired mesenteries (Fig. 152), and a single gonidial groove
e (ventral). The two mesenteries attached

to the gonidial groove (directive) are
very small ; the mesentery on either
side of these is large, and reaches to
the aboral end ; the remaining mesen-
teries diminish in size towards the dorsal
region where new mesenteries are added
(not ventrally as in Zoantlieae).

Fam. Cerianthidae. With a double
corona of tentacles, marginal principal
and circumoral accessory ; aboral end
rounded ; without sphincter. With an
aboral pore and a sheath of mud, sand
grains, and nematocysts, in which the
aboral end of the body lies as in a
case. Cerianthus D. Chiaje ; Bathyan-
thus Moseley ; Arachnactis Sars, pelagic
(possibly a larval form).

FIG. 152. — Diagram of the arrangement of
the mesenteries of Cerianthus. a goni-
dial groove.

Sub-order 2. ANTIPATHARIA.*

Colonial Zoaniharia with a tendency to Jiexamery ; with a usually branched,
axial, hollow, horny skeletal rod contained in an epithelial sheath.

The coenenchyma consists of the fused bases of the polyps ; it is always thin
and without spicules. Except in one genus there is a central horny rod, round
which the coenenchyma is disposed. The origin of the epithelial sheath which
surrounds the rod is unknown. The polyps have generally six tentacles and six
primary mesenteries, four of which are directives, and the other two transverse.
The transverse mesenteries bear the gonads. The 4 or 6 secondary mesenteries
fade away in the lower part of the polyp. The polyps are always much elongated
in the transverse axis (i.e. at right angles to the elongation of the mouth), and
in the Schizopathinae the body is actually constricted into three divisions, two
lateral containing the gonads and one central with the mouth. Each division
has two of the tentacles. To this phenomenon the name pseudo-dimorphism
rather than dimorphism (gonozooids and gastrozooids) should be applied.

Fam. 1. Savagliidae. With 24 mesenteries and tentacles. The colonies are
without an axial rod, but form a sheath round Gorgonid skeletons. Polyps
with typical Actinian structure. Probably Actiniarians. Savaglia Nardo
(Gerardia L. Dnth.).

Fam. 2. Antipathidae. With 6 tentacles, 6 primary mesenteries, and with
or without 4 or 6 secondary mesenteries. The two lateral primary mesenteries
bear the gonads. The axial skeleton is spiny and has a central canal.

Sub-fam. 1. Antipathinae. Polyps not pseudo- dimorphic, each with
6 tentacles; transverse axis of the polyp more elongated than the axis
(sagittal) which is marked by the long axis of the mouth. Cirripathes
Blainv. ; Stichopathes Brook; Leiopathes Gray; Antipathes Pall.; Anti-
pathella Brook ; Aphanipathcs Brook ; Tylopathes Brook ; Pteropathcs
Brook ; Parantipathes Brook.

* G. Brook, "Report on Antipatharia," Challenger Heports, Pt. 80, 1889.

MADREPORARIA. 19.1

Sub-fam. 2. Schizopathinae, Polyps exhibit pseudo-dimorphism ; each
with two tentacles (i.e. 6 to each polyp). Schizopathes Brook ; Bathypathes
Brook ; Taxipathes Brook ; Cladopathes Brook.

Fain. 3. Dendrobrachiidae. With branched retractile tentacles. Axial rod
without central canal. Anatomy not known, possibly Alcyonarian. Dendro-
brachia Brook.

Sub -order 3. MADREPORARIA.*

Colonial, rarely solitary, zoantharian polyps, which secrete by the ectoderm a
continuous and complicated calcareous corallum.

This old and apparently well-established division of the Zoantharia is still,
from a structural point of view, very imperfectly known. The less important
features of structure, viz. the arrangement of the hard parts — the corallum — has
been minutely examined, but the soft parts have been neglected, and had it not
been for the investigations of the Oxford School, and of v. Koch, we should still
know very little more about them than we do of the soft parts of extinct forms.
These investigations which will, we may hope, soon lead to the possibility of a
satisfactory classification of the sub-order, have established the following im-
portant points: (1) the complete disestablishment of the Tabulate division,
which, on examination of the soft parts, has been found to comprise forms
belonging to Hydromedusae, Alcyonaria, as well as to Madreporaria ; (2) that the
corallum is entirely a product of the epithelial ectoderm, and lies wholly outside
the animal ; (3) that the structure of the polyps varies in the different groups,
though the Hexactinian type seems on the whole to prevail. The most important
deviations from that type, so far known, are presented by those forms, in which
the directive mesenteries (if indeed they can be called so) present the same
arrangement of their muscles as do the other pairs (Lophohelia, Mussa, Euphyllia,
Heteropsammia], and the number of mesenteries and tentacles is not a multiple
of six.

Acontia appear to be absent ; but peristomial cinclides are said to be present,
allowing of the emission of the much convoluted mesenteric filaments. The
colonies are generally dioecious ; and the gonads are borne upon all or certain
of the mesenteries. Pores at the apex of the tentacles seem to be absent.

Asexual reproduction by budding, or by fission, is always present. In Fungia
and its allies there is formed from the egg a fixed nurse-stock, which has the
property of nipping off its disc-shaped apical portion, and of forming in its
place a new disc. The fixed nurse-stock is a typical polyp with theca and septa,
and at first it does not terminate in an expanded disc. When the walls of the
theca, which are at first vertical, have widened out into a disc, the lower
part of it forms a stalk. It is this stalk which is left after the fission, and
which produces a new disc. The new disc is not a bud, but is a product of
the growth of the structures already existing in the base of its predecessor
(Lister, Q. J. M. S. , 29). It is not certain whether the Fungia stock increases
by budding.

* Martin Duncan, "A Revision of the Families and Genera of the Sclero-
dermic Zoantharia," Journal of ike Linnean Society, vol. 18, 1885. H. N.
Moseley, "Report on the Corals," Challenger Reports, 7, 1881. G. C. Bourne,
"Anatomy of Mussa and Euphyllia," etc., Q. J. M. S., 27, 1887, p. 21.
G. H. Fowler, "Anatomy of the Madreporaria," I.-V., Q. J. M. S., vol. 25
to vol. 28. V. Koch, " Ub. d. Verhaltniss v. Skelet u. Weichtheile b. d.
Madreporen," Morph. Jahrb., 12, 1886. M. M. Ogilvie, "Microscopic and
systematic study of Madreporarian types of Corals," Phil. Trans., 187, 1896.

192

COELENTERATA.

In the colonial forms, fission by division of the polyps into two may occur
(Oculinae, Astraea), or the division may be confined to the oral disc, so that
a complex polyp is formed, with several mouths and oesophaguses opening into
a common coelenteron (Maeandrina, Fig. 144). In many cases, perhaps the
majority, the colony is increased by budding from the extra-thecal coenosark.

The hard structures or corallum follows more or less closely the shape of
the polyp, and were at one time thought to be actually contained in the
tissue of the polyp. They consist of a cup or theca, from which the polyp
projects and into which it can shrink, and in some forms of a connecting
substance, which may or may not be porous, connecting the cups — this is the
coenenchyma. The cup has, projecting inwards from its walls, a number of
radiately and vertically arranged calcareous plates, which suggest calcified
mesenteries. These are the septa;
they are not mesenteries, but occur
between mesenteries. The cup
presents a basal plate below, from
which rise the walls.

FIG. 153. — Basal plate of a larva of
Astroides ccdycularis, soon after at-
tachment. With 12 radial ridges
(after Lacaze Duthiers, from Bal-
four).

FIG. 154. — Diagram to exhibit the relations of
the polyp to the corallum. T tentacles ; ec
ectoderm ; ed endoderm ; st oesophagus ; mf
mesenterial filaments; r extra-thecal coelen-
teron ; m mesentery ; TO' extra-thecal portion
of inesentery ; Ep basal plate ; ep epitheca ;
Th theca ; cy calicoblasts (after G. C. Bourne).

The hard structures or corallum are secreted by, and on the outer side of,
the ectoderm.

The first part of the skeleton to appear (Astroides calycularis) is an annular
basal plate (Fig. 153), incomplete at first in its central part, between the basal
ectoderm and the surface to which the young polyp is attached. Next twelve
radially arranged folds of the basal body-wall rise up and project into the
enteron. The ectoderm of these folds secrete calcareous deposits, which
constitute the first trace of the septa (Fig. 153). The folds of the septa
differ from those of the mesenteries (between which they are placed) in being
folds of the whole body-wall, and not of the endoderm alone.

The septa, therefore, arise as rod-shaped structures in continuity with the
basal plate. They increase in thickness and height as the polyp grows, and
their outer ends, which do not reach to the body-wall of the polyp, become

MADREPORARIA.

193

forked. The theca is formed by the junction (complete in the Aporosa, incom-
plete in the Porosa) of these forked extremities of the septa.

From this account it is obvious that the theca must not only projet> into
the cavity of the polyp in exactly the same way as do the septa, and divide
it into an extra- and intra-thecal portion (Fig. 154), but also must divide
the mesenteries in a similar manner. This is actually found to occur in adult
polyps, in which the body- wall projects over the lip of the calycle and lies
on the outer side of the theca (Fig. 154, r).

It appears that when the polyps of a colony are connected by soft tissues
(coenosark), the connection is effected by this extra-thecal portion of the polyp,
and that the so-called coenenchyme or hard matter filling up the valleys between
adjacent polyps is secreted
by the ectoderm on the
lower side of this connecting
coenosark. The coenosark
is generally broken up into
canals which, in the Porosa,
communicate with the coel-
enteron of the polyps by
apertures left in the theca,
and may in some cases, at
any rate, be embedded in
the superficial layer of the
hard coenenchyma. The
extra-thecal coelenteron is
confined to the upper part
of the thecae, and the
coenosarkal continuation of
it over the coenenchyme
(when present) may or may
not be broken up by con-
tinuations of the mesen-
teries. When there is no
coenenchyme, and the thecae
are isolated from one another
except at their base, the
living tissues appear to have
died away round the basal
parts of the thecae.

As may be gathered from
the last statement, the
polyps ascend as the thecae grow and forsake the lower older parts of the cup.
In their ascent the ectoderm of their basal walls secretes calcareous laminae,
which may either completely occlude the cup — as the tabulae of Serialopora
and Podllopora, or merely stretch as imperfect plates between the septa as the
so-called dissepiments.

Synapticula are more rod-like calcareous structures passing from septum to
septum through the mesenteries. The columella (Fig. 155) is a central calcareous
projection into the theca rising up from the basal plate, and pali (Fig. 156) are
accessory columellae arranged in a circle round the central columella, and
sometimes joined to the edges of the septa : they are sometimes looked upon as

FIG. 155. — Vertical section through a polyp of Astraides
calycularis (after Lacaze-Duthiers). The mouth-opening,
oesophageal tube and mesenteries are seen ; also the
calcareous septa between the mesenteries, and the
columella Sk (the line from Sk should be produced to
the middle of the cup).

194

COELENTERATA.

FIG. 156. — Vertical section
through the cup of Cyathina
cyathus E. and H. = Caryo-
phyllia cyathus Lamk. (after
M. Edwards). S septa; P
pali ; C columella.

Fam. 1. Turbinolidae.

projections of the septa. The costae are vertical ridges along the outside of the
theca : they are extra-thecal projections of the septa.

The septa may be confined to the intramesenterial
spaces, or they may occur in the intermesenterial
as well. They are generally present in cycles of
different sizes like the mesenteries, but the number
is not always a multiple of six.

The epitheca when present is outside the theca :
it is attached to the edge of the basal plate (Fig.
154).

Section 1. Aporosa.

Solitary or colonial forms. Hard parts usually
solid and imperforate. Theca or wall solid, may
be epithecate. Septa solid near the wall, and
usually, but not invariably, solid at the further
part. Interseptal loculi (i.e., the chambers between
the septa) open throughout, or closed more or less
by endotheca in the form of dissepiments and
tabulae.

One or more rows of tentacles in relation to the
septa and interseptal loculi. The disc with one or
more mouths ; a mesentery usually in each inter-
septal loculus. Mesenteries usually in multiples
of six.

Corallum simple (solitary), or in colonies. Gemma-
tion from the wall or from an expansion of the basal structures. Wall solid.
Septal loculi open to the base. Endotheca rarely present.

(a) Corallum simple, rarely producing deciduous buds. Smilotrochus Ed. and
H. ; Onchotroehus Duncan ; Desinophyllum Ehrb. ; Schizocyathus Pourtales ;
Fldbellum Lesson ; Rhizotrochus Ed. and H. ; Thysanus Dune. ; Placotrochus
Ed. and H. ; Sphenotrochus Ed. and H. ; Nototrochus Dune. ; Placocyathus Ed.
and H. ; Platytrochus Ed. and H. ; Turbinolia Ed. and H. ; Stylocyathus d'Orb. ;
Conocyathus d'Orb. ; Bistylia T. Woods ; Trematoirochus T. Woods ; Trocho-
cyathus Ed. and H. ; Dcltocyathus Ed. and H. ; Odontocyathus Moseley ;
Caryophyllia Lmk. (Fig. 156) ; Ceratotrochus Ed. and H. ; Discocyathus Ed.
and H.; Brachytrochus Duncan ; Sabinotrochus Dune.; Stephanotrochus Moseley;
Anthemiphyllia Pourt. : Fungiacyathus Sars ; Guynia Dune. ; Duncania Pourt. ;
Haplophyllia Pourt.

(b) Colonial ; buds free above their origin ; no exotheca uniting the corallites.
Coenocyathus Ed. and H. ; Gemmulatroclms Dune.

(c) Colony growing from basal expansions; exotheca absent. Pohjcyathus
Dune.

Fam. 2. Oculinidae. Colonial, in the form of branches, espaliers, irregular
ramifications on a thick stem ; or massive, or incrusting. Interseptal loculi
usually open to the base, but dissepiments or tabulae sometimes occur. Walls
of corallites often increasing in thickness exogenously with age, and becoming
a solid mass by union with others. Solid intercalicular coenenchyma usually
present. Polyps when expanded rising above the wall, or long and exsert, the
mouth protruding ; the tentacles 10 to 48 or more, elongated, tips usually
swollen or capitate.

(a) Massive or incrusting colonies. Columella and pali absent, or a false

MADREPORARI A. 195

columella may be present. Coenenchyma well developed between the calices.
Barylielia, Ed. and H. ; Neohelia Moseley ; Diblasus Lonsdale.

(b) Dendroid or bunch-shaped colonies. Corallites often coalescing ; gfemma-
tion alternate. Columella absent or rudimentary. Tabulae or dissepiments
present or not. Lopholielia^A. and H. ; Amphihelia Ed. and H.; Acrohelia
Ed. and H.

(c) Arborescent or tufted colonies. Gemmation rarely from one side only.
Columella various. Oculina Ed. and H. ; Cyathohelia Ed. and H. ; Trymohelia
Ed. and H. ; Sclerohelia Ed. and H. ; Bathelia Moseley.

(d) Branched espalier-like colonies. Corallites projecting or twisted. Colu-
mella styliform. No pali. Coenenchyma well developed. Prohelia E. de Fro.
Jurassic and cretaceous.

(e) Arborescent, palmate, or incrusting colonies. Septa few, unequal. Colu-
mella styliform. Costae short or absent. Stylophora, Ed. and H. ; Madracis
From.

Fam. 3. Pocilloporidae. Colonial, with tabulae ; septa small ; columella
well or ill developed. Inter-corallite structure coenenchymal and solid. Polyps
with disc, tentacles, and one pair of long mesenterial filaments. Pocillopora
Lamarck ; Seriatopora Lamk.

Fam. 4. Astraeidae. Solitary or colonial, rarely reproducing by deciduous
buds. Colonies increase by gemmation and fissiparous division. Interseptal
loculi with dissepimental endotheca, rarely tabulae. Soft parts resembling
those of Turbinolidae ; the long serial calices have several mouths in the limited
disc which is surrounded by tentacles. Corallites may unite by their walls,
but true intermural solid Coenenchyma is rarely seen. Includes the so-called
brain corals.

Sub-fam. 1. Astraeidae simplices. Simple solitary torms. Propagation
rarely by deciduous buds. Pali present or absent. Endotheca always
present, but variable in amount. Lophosmilia Ed. and H. ; Spheno-
phyllia Moseley; Parasmilia Ed. and H.; Dasmosmilia P.; Lithophyllia
Ed. and H.; Asterosmilia Duncan.

Sub-fdm. 2. Astraeidae reptantes. Colonies composed of short coral -
lites, which arise by gemmation from stolons or basal expansions. Cylicia
Ed. and H. ; Astrangia Ed. and H. ; Ulangia Ed. and H. ; Colangia Pourt.
Sub-fam. 3. Astraeidae gemmantes. Colonies increasing by gemmation
from the wall below the calicular margin. Endotheca dissepimental.
Cladocora Ed. and H. ; Pourtalosmilia Duncan.

Sub-fam. 4. Astraeidae caespitosae. Corallites isolated terminally,
being free at their sides, springing from a common parent ; increasing
by fissiparity, separation occurring rapidly or serial growth persisting.
Gemmation rare. Eusmilia Ed. and H. ; Solenosmilict Dune. ; Dasyphyllia
Ed. and H. ; Dendrocora Dune ; Trachyphyllia Ed. and H. ; Mussa Oken.
Sub-fam. 5. Astraeidae confluentes. Increase by fissiparity, with
excess of serial growth. Gemmation may occur. Corallites united by
their walls, costae, or by intermediate tissue, or free. Euphyllia Ed.
and H. ; Dendrogyra Ehrbg. ; Pectinia Oken ; Diploria Ed. and H. ;
Manicina Ehrb. ; Maeandrina Ed. and H. ; Coeloria Ed. and H. ; Leptoria
Ed. and H.; Symphyllia Ed. and H. ; Mycetophyllia Ed. and H. ; Ulophyllia
Ed. and H. ; Tridacophyllia Blainv. ; Colpophyllia Ed. and H. ; Scapo-
phyllia Ed. and H. ; Plerogyra Ed. and H. ; Physogyra Quelch ; Hydnophora
Ed. and H.

196 COELENTERATA.

Sub-fam. 6. Astraeidae agglomeratae fissiparantes. Colonies massive
or incrusting. Corallites increasing by fissiparity, and sometimes also by
gemmation ; united by costae or coenenchynia ; not forming long series.
Dichocoenia Ed. and H.; Favia Oken ; Goniastraea Ed. and H.

Sub-fam. 7. Astraeidae agglomeratae gemmantes. Massive and foliaceous
colonies. Colonies increasing by gemmation from the wall from within the
calice, or from intercorallite tissue. Corallites joined by costae, exotheca,
or peritheca, or fused by their walls. Endotheca vesicular, rarely tabulate.
Heliastraect Ed. and H.; Phymastraea Ed. and H.; Solenastraea, Ed. and
H. ; Plesiastraca Ed. and H.; Echinopora Dana; Galaxea Oken; Acan-
thopora Verrill ; Leptastraea Ed. and H. ; Acanthastraea Ed. and H. ;
Astrocoenia Ed. and H. ; Prionastraea Ed. and H. ; Merulina Ehrbg. ;
Moseley a Quelch.

Section 2. Fungida.

Solitary or colonial forms. Septa and septo-costae with synapticula, which
cross the interseptal and intercostal loculi. An endotheca is present or absent.
Basal structures perforate or imperforate. Soft structures with short, lobe-like,
scattered, sometimes obsolete tentacles, not covered when contracted ; discs not
circumscribed, and in colonial forms confluent.

Fam. 1. Plesiofungidae. Transitional between the Aporosa and Fungida.
Simple or colonial, with synapticula in the interseptal loculi, besides endothecal
dissepiments. Septa solid and imperforate, occasionally perforate and trabeculate.
Epistreptophyllum Milaschewitsch ; Siderastraea Blainv. ; Polyaraect Fritsch.

Fam. 2. Fungidae. Simple or colonial, usually depressed ; septa solid or
porous. With synapticula, without dissepimental endotheca ; tentacles short ;
scattered, sometimes absent. Wall perforated and echinulate. Fungia Dana ;
Diafungia Duncan, both solitary. The following are colonial : Halomitra Dana ;
Sandalolitha Quelch ; Cryptabacia Ed. and H. ; Herpolitha Esch. ; Polyphyllia,
Q. and G. ; Lithactinia Lesson ; Zoopilus Dana.

Fam. 3. Lophoseridae. Wall neither perforated nor echinulated. Simple
forms. Trochoseris Ed. and H. ; Cycloseris Ed. and H. ; Diaseris Ed. and H. ;
Bathyadis Moseley; Psammoseris Ed. and H. ; Stephanoseris Ed. and H.
Colonial forms : Cyathoseris Ed. and H. ; Lophoseris Ed. and H. ; Haloseris
Ed. and H. ; Tichoseris Quelch ; Mycedium Oken. ; Phyllastraea Dana ; Trachy-
pora Verrill ; Leptoseris Ed. and H. ; Stephanaria Verrill ; Agaricia Lamck. ;
Plesioseris Duncan ; Psammocora Dana ; Pachyscris Ed. and H. ; Coscinaraca
Ed. and H.

Fam. 4. Anabaciadae. Simple or colonial, septa trabeculate and fenestrated.
Synapticula small. Dissepiments absent. Wall indistinct. Anabacia d'Orb.

Fam. 5. Plesioporitidae. Transitional group with regularly perforate septa.
Menndroseris Rouss.

Section 3. Perforata.

Corallum entirely or almost entirely composed of porous or reticulate coenen-
chynia. Dissepiments and tabulae may be present or absent. Septa solid or
much perforated, or represented by trabeculae only.

Fam. 1. Eupsammidae. Simple or colonial. Walls with costae and apertures
in the intercostal spaces. Calices well developed. Increase by geihmation and
fission. Stephanophyllia Michelin. ; Leptopenus Moseley, deep-water, southern
hemisphere ; Balanophyllia S. Wood ; Thecopsammia Pourt. ; Eupsammia Ed.
and H. ; Heteropsammia Ed. and H.; Dendrophyllia Ed. and H. ; Pachypsammia

CTENOPHORA.

197

Verrill ; Leptopsammia Ed. and H. ; Endopsammia Ed. and H. ; Astroides Blainv.
(Fig. 155) ; Lobopsammia Ed. and H. ; PJiodopsammia Semper ; Rhizopsammia, Verr.

Fam. 2. Madreporidae. Colonial, arising by gemmation from the j^des of
the parent polyp : coenenchyma more or less abundant, spongy and reticulate,
slightly or not distinct from the porous corallite-walls. Madrepora L. ; Turbi-
naria Oken ; Astraeopora Blainv. ;. Montipora Q. and G. ; Anacropora Ridley.

Fam. 3. Poritidae. Sclerenchyma reticulate and perforate. Septa never
completely lamellary. Walls very porose. Corallites increasing by gemmation,
and united directly or by intervening porous sclerenchyma. Forties Ed. and
H. ; Synaraea Verr.; Napopora Quelch ; Ehodaraea Ed. and H. ; Alveopora
Q. and G. ; Dichoraea T. Woods.

Sub-phylum II. CTENOPHORA.*

Free-swimming, transparent pelagic coelen-
terata, with eight meridional rows of vibratile
plates formed of fused cilia. They possess
an oesopliageal tube — called the stomach — -
lined by ectoderm, and a gastrovascular
canal system. Nematocysts are almost
always absent.

The fundamental form of the Ctenophora
is a gelatinous, spherical, or ovoid body,
which swims in the sea by the activity of
its ciliated plates. It has two poles — the
oral pole marked by the mouth, and the
aboral pole marked by the sense organ.
The line connecting these two poles is the
main axis, and in describing the structure
of the body it is important to recognise two
planes which pass through this axis at right
angles to one another. The mouth leads
into a tube called the stomach (sometimes
called oesophagus or stomodaeum, because
it is lined by ectoderm), and the stomach
opens into the central part of the gastro-
vascular apparatus called the funnel (infuii-
dibulum). The stomach is furnished with
two hepatic bands. Both stomach and
funnel are flattened sacs, and both lie in
the main axis — the funnel of course above
the stomach — but with their long diameters

FIG. 157. — Hormiphora (Cy-
dippe) phtmosa (after Chun).
0 mouth.

* C. Chun, "Die Ctenophoren des Golfes von Neapel," Fauna und Flora des
Golfes von Neapel. 1880.

198 COELENTERATA.

in different planes. The long diameter of the stomach lies in one
of the two planes mentioned above, while that of the funnel lies
in the other plane, which is at right angles to the first. These
two planes are called the stomach-plane* (Fig. 158, Mt M.) and
funnel-plane (T, T.) respectively.

The stomach-plane divides the body into a right and left half;
but it is impossible to speak of the two parts of the body marked off
by the funnel-plane as dorsal and ventral, or as anterior and posterior,
as is done by some authors, because these two parts are identical and

FIG. 158. — Diagram of a Cydippe seen from the aboral pole (after Chun). M-M stomach
(sagittal) plane ; T-T funnel (transverse) plane ; ri to r« the eight rows of vibratile plates ;
p polar plates ; n^ to %» the eight ciliated grooves ; t.b base of tentacle ; t.st stalk of tentacle ;
tt branch of tentacle ; scJi sheath of tentacle ; sch.o opening of tentacle-sheath ; c.pr per-
raclial vessel; c.ir interradial vessel; c.adr adradial vessel ; sp1 to sp8 the sperm producing,
oiA to ov8 the ova-producing sides of the eight meridional vessels ; t.g tentacle vessel ;
ex1 and ea;2 the two aboral openings of the gastrovascular system.

not distinguishable from one another by any differential character.
The tentacles when present are two in number : they arise from the
sides of the body in the funnel-plane (Fig. 158, T, T). Further, we
may speak of two transverse axes — a stomachal axis passing through
the long diameter of the stomach, and a funnel axis passing through
the long diameter of the funnel.

The body (Fig. 157) carries eight meridional rows of vibratile

* The plane of the stomach is sometimes called the sagittal plane, and that of
the funnel the transverse plane.

CTENOPHORA. 199

plates — the ribs. These rows begin close to the aboral pole, and
pass in the meridians of the animal towards the oral pole. Four
of these rows lie in one half of the body, and four in the '<>ther.
Further it is to be noted, that of these eight rows we may distinguish
those which lie on each side of the tentacle (or funnel-plane) — these
are the sub-tentacular rows*' — and those which lie on each side of
the stomach-plane, which we may call the sub-stomachal f rows
(Fig. 158). There are therefore four sub-tentacular rows and four
sub-stomachal rows of meridional plates.

The central nervous system and sense organ are placed at the aboral
pole. (Fig. 159). It has the form of a flat depression formed of
ciliated sensory ectoderm, and covered over by a bell-shaped structure
(the bell) formed of fused cilia (gl). Some of the cilia of the sensory
area are very long and fused together to form four large triangular
plates. These are the springs (/). Their tips are attached to, and
carry a small mass of otoliths (ot), which is placed over the centre
of the sensory area. The sensory plate is drawn out in the stomach
plane into two lobes — the polar plates (Fig. 158, j»). Beginning at
the base of each of the four springs, or otolith-bearers, is a ciliated
groove (pi), which, passing outward through a hole in the bell-like
cover, divides into two grooves (ft1"8). These are continuous with the
aboral ends of two rows of vibratile plates, and are sometimes called
nerves because they seem to transmit any movement of the otolith-
bearer to the row of vibratile plates, and so set the latter in motion.
The movement of the vibratile plates begins at the aboral pole and
passes oralwards, each plate successively bending energetically
towards the aboral pole, and then slowly regaining its original posi-
tion. The movement of the animal is thus with the oral end
forwards.

The vibratile plates have the appearance of consisting of long cilia
fused together at their bases. They arise from specially long ectoderm
cells.

The gastro vascular apparatus (Fig. 158) consists of a central space,
the funnel, which gives off two vessels — the perracUal vessels (c.pr);
these pass outwards in the funnel-plane in opposite directions and
divide dichotomously into the interradial vessels (c.ir), of which
there are four. These again divide, and give rise to eight adradial
vessels (c.adr\ which enter the meridional vessels. The meridional
vessels underlie the rows of vibratile plates and end blindly above

* Sometimes called sub-transversal.

t Sometimes called sub-sagittal and sub-ventral.

200

COBLENTBRATA.

ex —

FIG. 159. — Sense organs and adjacent organs, I of Cestus veneris in side view (from the stomach
plane) x 100, II of Eucharis multicornis from above x 120 (after Chun), a sense organ ;
gl bell ; / the four springs ; ri1 to %8 the eight ciliated grooves with their cilia ci, and their
plate-like expansions at the base of the springs pi and pi' ; k granules ; ot otoliths ; otl otoliths
in process of formation ; p edge of polar plate ; pf middle part of polar plate (polar field) ;
mu (in II) muscular fibres running beneath the ciliated grooves ; me circular muscular fibres ;
mu (in I) longitudinal muscles of the funnel-vessels ; v funnel-vessel ; gg branching of a
funnel-vessel into the ampullae ; ex aboral excretion pores.

CTENOPHOBA. . 201

and below. The perradial vessels give rise, close to their origin,
to the paragastric canals, which run oralwards on each side of the
stomach (Fig. 157). They end blindly, and are absent only jrn one
genus (Euchlora). The tentacular vessels are direct continuations
of the perradial vessels (Fig. 158, tg). The funnel is continued
upwards as the funnel-vessel, which divides beneath the sense-
organ into two limbs, each of which again divides into two ampullae,
one situated in each quadrant of the body. Two of these ampullae
(and two which lie in diagonally opposite quadrants) open to the
exterior by small pores placed just outside the sensory plate
(Fig. 159 I, ex).

There are two extensile tentacles (Fig. 157) in the funnel-plane.
They consist of a stout base contained in a depression of the body-
wall, which constitutes the tentacular sheath and into which the
tentacle can be withdrawn. The tentacle vessel is not prolonged
along the tentacle, but ends in two ampullae at its base. The tentacles
carry a row of branches which are provided with the peculiar adhesive
cells (Fig. 161).

The muscular tissue is feebly developed. It has the form of fibres,
lying in the jelly and branched at both ends.

There is a sub-epithelial nervous plexus with scattered ganglion
cells. It extends on to the stomach, but no connection has been
observed between it and the sense-organ and ciliated grooves and
ribs.

The description given above applies to one group of the Ctenophora,
the Cydippidae, the structure of which may be taken as typical.
There are, besides, the Cestidae, the Lolatae, and the Bervidae.

The Cydippidae include, besides the spherical form just described,
forms in which the main axis is elongated (cylindrical Pleuro-
Irachiadae), and forms in which the body is compressed in the stomach-
plane, i.e., the stomach-axis is much reduced (Euchlora, Callianira).
In Callianira (Fig. 165) tnere are two wing-like processes of the
aboral end of the body; they lie in the funnel-plane, and the
meridional vessels are prolonged into them. In Euchlora the sub-
tentacular ribs are longer than the sub-stomachal.

The larvae of the Cestidae and Lobatae closely resemble the above
described typical form (particularly the Mertensid variety of it) and
acquire the adult condition by a complicated metamorphosis (see
below).

The Cestidae are ribbon-shaped (Fig. 160), and the body is
enormously elongated in the stomach-plane and much compressed

202

COELENTERATA.

in the funnel-plane (cf. Fig. 158); i.e., the stomach-axis of the body
is very long, and the funnel-axis very short. Further, the sub-
tentacular ribs (r\ ?A, r5, r8) are very short, and reduced to a few
plates at the aboral pole, while the sub-stomachal ribs (r2, r3, r6, r7)
extend close together along the whole length of each side of the
aboral surface of the body.

The perradial vessels are absent, as the four interradial vessels
arise directly from the funnel (in correspondence with the compression
of the body). The sub-stomachal meridional vessels run horizontally
beneath the long ribs to the ends of the body, while the sub-tentacular
(fflt #45 /75j y8) Pass along the middle of each side of the body, also
to the extremity, where they are connected with the sub-stomachal
vessels (#2), and with the paragastric vessels which are continued
along the flattened oral surface of the body. In the Cestidae generative
cells are only produced in the sub-stomachal meridional vessels.

The tentacular apparatus is hidden in a sheath. There is no
projecting tentacle, but a very large tentacle base which is in
the sheath. Each tentacle-sheath is continued right and left as
a furrow, which extends along its own side of the oral edge of
the body to the extremity. The numerous lateral fibres which arise
from the tentacle base lie in these tentacular furrows and hang down
from them all along like a fringe (Fig. 160), being held in the
tentacular furrows by hooks.

In the Lobatae the body is compressed in the same way, but not
to the same extent as in the Cestidae, i.e. the funnel axis is shortened.
There are two large buccal lobes, one on each side of the mouth in
the stomach-plane. The sub-tentacular ribs are shorter than the sub-
stomachal, and at their oral ends arise the four auricles. The auricles
are processes of the body, and each carries one row of vibratile plates.
The sense-organ lies in a deep pit at the aboral pole, and the ciliated
furrows (the so-called nerves), which pass from it, extend all along
the ribs. The interradial vessels arise directly from the funnel, and
the sub-tentacular vessels anastomose with the paragastric vessels at
the base of the auricle. From the point of junction there arises a
vessel which forms a loop in the lobes and anastomoses with its fellow
of the neighbouring quadrant. The sub-stomachal vessels also form
loops and anastomose in the oral lobes.

The Beroidae are without any tentacular apparatus in both larvae
and adults. The body is compressed in the funnel-plane, and the
main axis is elongated. The mouth and stomach are enormous, and
the lower third of the stomach-wall is closely beset with sabre-like

203

204

COELENTERATA.

hooks for the retention of food. The hepatic bands are absent.

The edges of the polar plates of the sense-organ are dendritically
branched. The interradial vessels and the
ampullae spring directly from the funnel.
The musculature is well developed, and the
meridional and paragastric vessels give nu-
merous branches which anastomose.

Thread-cells are almost universally absent ;
but the ectoderm of the tentacles contains
peculiar "adhesive cells," the base of which
is prolonged into a spirally coiled thread
(Fig. 161), while the convex free end is soft
and glutinous and becomes readily attached
to any object which touches it. Thread-cells
are found in the ectoderm of Euclilora alone,
the tentacles of which are characterized by
the absence of adhesive cells and the presence
of amoeboid ectodermal prominences.

The nervous system and sense-organs have
already been described (p. 199).

The Ctenoplwra are hermaphrodite, and

sexual reproduction alone is known. The generative cells arise on

the walls of the meridional vessel, or of diverticula of the same.

Sometimes they are localized

(Cestus) ; sometimes they arise

along the whole length of the

canals, one side being beset by

egg-follicles, the other by sperm-
sacs. Ova and spermatozoa

when ripe pass into the gastro-

vascular space, and are ejected

through the apertures of the

same.

FIG. 161.— Muscle-fibres, ad-
hesive cells (fc/) and tactile
cells (6) from the lateral
filaments of the tentacle of
Euplocamis stationis (after
R. Hertwig). ltf> prolon-
gation of the contractile
thread of a prehensile cell.

The early development takes place
within the egg -membranes. The
segmentation is complete. A cap of
small ectoderm cells is soon formed
(Fig. 163), which grow round the
larger endoderm cells ; but before
this overgrowth is completed a number of cells are separated from the lower
ends of the large endoderm cells, and constitute an embryonic mesoderm (Fig.
163, 5, Ms) (Metschnikoff). The mesoderm gives rise to the protoplasmic

FIG. 162.— Meridional vessel (Gc) of Beroe ovata
with ova (Ov) and spermatozoa (Sp) in their
walls (after Will).

CTENOPHORA.

205

network (wandering cells) of the jelly. The mouth is a new formation, and
the stomodaeum (stomach) arises as an invagination of ectoderm at the lower
pole (Fig. 163, 7, 8, 9}. y

The larva when hatched differs more or less from the sexually mature arfiimal
in the simpler and usually more spherical form of the body, in the small size of

FIG. 163.— Development of Callianira Ualata (after Metschnikoff). 1, stage with eight ; 3, stage
with sixteen blastomeres ; 3, the eight upper cells of the previous stage have divided into 48
micromeres (ectoderm), which form a cap on the 8 macromeres (endoderm) ; &, side view of an
older stage ; 5, embryo in the stage of formation and invagination of mesoderm (Ms) ; 6, more
advanced stage in sagittal section ; 7, stage with developing stomodaeum ; 8, later stage with
commencing formation of tentacles ; 9, ripe embryo ; T tentacles ; Ot sense-organ ; 0 mouth ;
Me mesoderm (jelly).

the tentacles and swimming plates, and in the difference in the relative size of the
oesophageal tube, infundibulum, and vascular canals. The differences, putting
Cestus on one side, are most striking in the lobed Ctenopliora, the embryos of
which have a great similarity to the young of Cydippe. It is only after a longer

206

COELENTERATA.

period of larval life that the completely mature form is attained by the unequal
growth of the swimming plates and their canals, the outgrowth of the tentacle-
like processes, and the formation of two lobe-like projections round the mouth
from those halves of the body which correspond to the longer rows of swimming
plates. The Lobatae present a peculiar phenomenon, which has been called by
Chun, dissogony. The Cydippe-like larva develops sexual cells on its four sub-
stomach vessels, and becomes sexually mature during the hot period of the year.
The eggs are fertilised and develop normally into larvae smaller than those
produced from adults. After the sexual activity has continued for some days,
the larva loses its generative organs, undergoes a complicated metamorphosis, and
develops into the adult, with generative* organs in all of its eight meridional
vessels. The phenomenon of dissogony is therefore characterised by the fact
that sexual maturity occurs twice in the same individual, and that the two
sexual periods are separated by a sterile period in which there are no generative
cells, and in which a complicated metamorphosis occurs.

Ot

FIG. 164.— Bcroe ovatus. Ot
sense-organ, at its sides are
the small tentacles of the
polar areas ; Tr funnel.

FIG. 165.—Callianira Ualata (after Chun).
0 mouth.

The Ctenophora live in the warmer seas, and, under favourable
conditions, often appear in great quantities at the surface. They
feed on marine animals of various size, which they capture with their
tentacles. Many, as the Beroidae, which do not possess tentacles,
are compensated for this deficiency by the possession of an unusually
large mouth (Fig. 164), by means of which they are able to receive
relatively large bodies, even fishes, into the wide oesophageal tube,

TENTACULATA. 207

and to digest them. Although the average size is small, some of
them, as Cestus, Eucharis, reach the length of a foot."

Order 1. TENTACULATA.
Ctenophora witli tentacles. -/

Section 1. Cydippidae.

Spherical or cylindrical Ctenophora, with two simple or pinnate tentacles,
retractile into a sheath. The meridional and paragastric vessels end blindly.

Fam. 1. Mertensidae. Body compressed in the stomachal-plane ; sub-
tentacular ribs longer than the sub-stomachal. No wing-like appendages at
the sensory pole. Euchlora Chun (Haeckelia Car. and Gerst., Owenia Koll.,
Mertensia Geg.) ; Charistephane Chun.

Fam. 2. Callianiridae. Body compressed in the stomach-plane ; sub-
tentacular ribs longer than the sub-stomachal. Wing-like appendages at the
sensory pole. Callianira Peron (Fig. 165).

Fam. 3. Pleurobrachiadae. Body round in section. Sub-tentacular and
sub-stomachal ribs equal in length. Hormiphora L. Ag. (Cydippe Geg.);
Pleurobrachia Fleming ; Lampetia Chun ; Euplokamis Chun.

Section 2. Lobatae.

Body laterally compressed ; stomach-axis longer than the funnel-axis. With
two lateral lobes in the oral region, and four auricles. Lateral tentacles lie in
a tentacular furrow ; tentacle-sheath absent.

The auricles are provided with swimming plates, and are placed at the end
of the sub-tentacular ribs. The central nervous system is sunk in a pit. The
stomachal ribs are longer than the sub-tentacular. Mouth-opening wide, and
extending into a buccal furrow reaching to the base of the lobes. The four
interradial vessels arise direct from the funnel. The meridional vessels are con-
tinued on to the lobes in a sinuous course, and anastomose. The larvae are
Mertensia-\\k& forms which, in Eucharis, become sexually mature, and reproduce
themselves.

Fam. 1. Lesueuridae. Lobes and lobe-windings of vessels rudimentary.
Auricles long and ribbon-shaped. Lesueuria M.-Edw.

Fam. 2. Bolinidae. Lobes of medium size. Lobe-windings of vessels simple.
Adradial vessels pass directly into the aboral ends of the meridional vessels.
Auricles short. Bolina Mertens ; Bolinopsis L. Ag. ; Hapalia Esch.

Fam. 3. Deiopeidae. Body strongly compressed. Lobes of medium size.
Windings of lobe-vessels more complicated than in the Bolinidae. Auricle short.
Ribs consist of few but enormous plates. Sub-tentacular vessels possess short
aboral blind processes. Dewpea Chun.

Fam. 4. Eurhamphaeidae. Two aliform processes in the tentacular-plane at
the aboral pole, on which the sub-tentacular ribs are continued. Eurhamphaea
Gegenb.

Fam. 5. Eucharidae. Lobes of considerable size, Avith complicated vessel-
windings. Auricles vermiform. Body beset with papillae. Aboral blind ends
of sub-tentacular vessels long. A long main tentacular fibre as well as the
lateral tentacular fibres. Eucharis Esch.

Fam. 6. Mnemiidae. Lobes very large. Origin of auricles and lobes placed
almost at the same height as the funnel. Auricles long and ribbon-shaped.
Mnemia Esch. ; Alcinoe Rang ; Mnemiopsis L. Ag.

208 COELENTBRATA.

Fam. 7. Calymmidae. Body strongly compressed. The great lobes arise
almost at the height of the funnel. Ribs nearly horizontal. Calymma Esch.

Fam. 8. Ocyroidae. Lobes enormous, almost independent of the body.
Ocyroe Rang.

Section 3. Cestidae.

Body much compressed in the funnel-plane, i.e.y with the broad faces parallel to
the stomach-plane.

The sub-tentacular ribs much shorter than the sub-stomachal, which extend
all along the aboral edges of the body. The interred ial vessels arise direct from
the funnel. The sub-tentacular vessels run along the middle of the band to
unite at the ends of the body with the* long sub-stomachal and paragastric
vessels. Gonads in the sub-stomachal vessels only. The larvae are Mertensia-
like forms.

Fam. Cestidae. CestusLes. ; Vexillum Fol.

Order 2. NONTENTACULATA.
Without tentacles.

Fam. Berdidae. With large mouth and stomach. Body conical or oviform,
compressed in the funnel-plane. The vessels give off branches which anastomose
in the jelly. Beroe Brown.

Ctenoplana* Korotneff (Z.f.w.Z., 43, 1886) and Goeloplana Kowalewsky
(Nachrichten der Liebhaber der Natunviss., 1882, Russian) should probably be
included amongst the Ctenophora.

Pemmatodiscus Monticelli,t a gastrula-like form living in the jelly
of Rhizostoma,) may be mentioned amongst the Coelenterates.

* A. Willey, "On Ctenoplana," Q. J. M. 8., vol. 39, p. 323.
t Monticelli, Naples Mitth., 12, 1897.

CHAPTER V.

PHYLUM PLATYHELMINTHES.

Vermiform, bilateral, more or less elongated, and usually dorso-
ventrally flattened animals, wifh an anteriorly-placed central nervous
mass (cerebral ganglion), and an excretory system of ramified canals
containing flame-cells. Enteron ivhen present aproctous.

The forms included in this phylum are mostly parasitic Entozoa,
but some live freely in water or on land. Suckers and hooks for
attachment are often present, especially in the parasitic forms. The
enteron is absent in one class (Cestoda), and when present is without
an anus. Vascular system and body cavity are not found in the
group, and the organs are embedded in a plasmatic mass — the
parenchyma — in which muscular and connective tissue elements are
differentiated. This is the so-called mesoderm. The excretory
system is distributed as a system of branching and often anasto-
mosing canaliculi throughout the parenchyma, and in the absence
of a vascular system collects the excretory products in all parts of
the body. Projecting from the walls of the canals at intervals are
thick flame-shaped cilia, and sometimes finer cilia. The canaliculi
are supposed to end blindly in hollow cells of the parenchyma, from
which cells there often projects into the blind end of the canal a
flame-shaped cilium. Such terminal cells are called flame-cells.

In the terms of the cell-theory this system may be described as consisting of
a number of branched and hollow anastomosing cells, the spaces or vacuoles
within which form a continuous system opening externally, and constituting the
cavities of the excretory canaliculi. Such canals are often distinguished as
intracellular, and contrasted with intercellular canals, in the walls of which cell
limits can be made out. It is extremely doubtful if this distinction has the
reality or morphological importance which is often attributed to it.

The external openings of the excretory canals vary much, both in
number and position.

The animals are usually hermaphrodite, and the reproductive
organs are complex. A vitellarium or yolk-gland is very generally

p

210 PLATYHELMINTHES.

present, and may be part of the ovary or distinct from it. Such
glands are to be regarded as parts of the ovary, the cells of which
are without the capacity of becoming ova, but store up yolk matter
and are deposited round the ovuin in the cocoon or egg-shell, and
consumed by the embryo during its development. Asexual repro-
duction is very often found, and may take place at different stages of
the development. The life history is in such cases very complicated.
So far as is known parthenogenesis is not met with in the group,
unless the germ-cells of the sporocysts and rediae of the Trematoda
be regarded as parthenogenetic ova.

Class I. TURBELLARIA.*

Free-living Platyhelminthes with delicate, soft, and often leaf-shaped
bodies, and with a ciliated ectoderm containing rhabdites and sometimes
thread-cells, and with muscular protrusible pharynx.

The Turbellaria include fresh-water, marine, and terrestrial forms.
They are distinguished by the possession of a ciliated ectoderm and
soft delicate tissues. They usually have an oval, flattened body, and
they reach only a small size. It is exceptional to find organs for
adhering, viz., small hooks and suckers. The anterior end of the
body is especially sensitive, and generally bears eyes and sometimes
a pair of tentacl'es, which in a few cases (Euryleptidae and Pseudo-
ceridae) contain prolongations of the enteron. In some forms the
dorsal surface is covered with papillae, and these also sometimes
contain prolongations of the enteron. A pair of ciliated pits, not
unlike those of Nemertines, are occasionally present on the front
of the body, around which there may be present a ciliated marginal
groove. A sucker is found in some Polyclada on the ventral surface.

The mouth is on the front, middle, or hinder part of the ventral
surface. In the American Triclad Phagocata there are eight or nine
pairs of mouths and pharynges in addition to the main one, and the
same peculiarity has been observed as an exception in the genera
Planaria and Polycelis. The generative openings are on the ventral
surface behind the mouth.

The skin consists of a single layer of cells, or of a finely granular

*L. v. Graff, Monographic der Turbellarien, Leipzig, 1882. L. v. Graff, Die
Organisation der Turbellaria Acoela, Leipzig, 1891. P. Hallez, "Catalogue des
Turbellarie's du Nord de la France, ".etc., Revue Biologique dn Nord de la France,
Ts. ii., iv., and v., 1892, 3. A. Lang, "Die Polycladen," Fauna and Flora des
Golfes von Neapel, 1884. F. W. Gamble, "British Marine Turbellaria,"
Q. J. M. S., 34, 1893, p. 433; and Article on Turbellaria, in the Cambridge
Natural History, vol. 2, 1896.

TURBELLARIA.

211

nucleated material, which bears cilia and rests upon a stratified
basement membrane (Fig. 166). It is covered externally by a
homogeneous membrane bearing tactile hairs and comparable to
a cuticle. Peculiar rod-like structures, called rhabdites^ are found
in the ectoderm cells and in cells lying deeper in the parenchyma,
but connected with the ectoderm layer by processes. The rhabdites
are homogeneous, highly refractile structures of unknown function,
and can be extruded from the ectoderm.
Other structures probably of a similar $

character, but differing slightly, are also
found in the ectoderm — these are the
pseudorJudxlites and sayittocysts. Nema-
tocysts are found in some members of
the class (Microstoma, Anonymus, Stylo-
choplana). Various pigments are often
present in the epidermis or in the
parenchyma; and green vesicles con-
taining chlorophyll and starch grains
(Vortex), or yellow cells (Convolute),
are found in the parenchyma in some
forms C? symbiotic Algae). The dermis,
or outer layer of the parenchyma, lies
beneath the basement membrane, and
contains well-developed muscular layers
(usually outer circular and inner longi-
tudinal).

The structure of the parenchyma is
difficult to make out. In the Acoela
the whole of the tissues within the
basement membrane may be described
as consisting of a plasmatic mass con-
taining nuclei, vacuoles, and fibres,
both muscular and connective. The

centre of this mass is of a softer consistency than the outer
parts, and constitutes the solid digestive endoderm into which
the food passes to be digested. The outer part of the paren-
chyma, which is not at all marked off from the central, contains
dermal muscles externally, networks of connective tissue fibres, and
muscular fibres running dorso-ventrally through the body. Further,
the central nervous mass and the nerves and the gonads are all parts
of this parenchyma, differentiated from it indeed, but not in any

FIG. 166.— Portion of a longitudinal
section of Planaria polychroa,
showing the ectoderm and outer
part of the parenchyma. R rhab-
dites in ectoderm ; K~L nuclei of
ectoderm ; Bm basement mem-
brane ; Pg pigmented connective
tissue cell ; K2 nucleus of paren-
chyma cell ; Rz deep rhabdite-
forming cell (after Leuckarfc and
Nitsche).

212 PLATYHBLMINTHES.

sense marked off from it (except in the case of the ripe generative
cells), and passing perfectly gradually into it. Cell limits, save for
the ripening generative cells, and possibly here and there a wandering
cell, are entirely absent from it. It should also be mentioned that
spaces or vacuoles filled with fluid are present in all parts of the
parenchyma. The parenchyma of the other Turbellaria, generally
speaking, resembles that of the Acoela in structure, but differs in
the fact that the organs — enteron, cerebral ganglion, gonads— are
more completely delimited from it-
It cannot be said that there is a perivisceral cavity in the Turbettaria.
There are vacuoles in the parenchyma, and these, in some Rhabdococlida, are
so much developed round the enteron as to suggest a body cavity. According
to v. Graff indeed, there is in such cases a lining of endothelium.

As to the homologies of the parenchyma tissue, it appears probable, from
its condition in the Acoela, that it is a part of the endodemi in which the
enteric cavity is either not developed or lias collapsed, or become filled with
plasmodial extensions of its protoplasmic walls, of a nature similar to the filling
up of the enteron described by Bourne in a ooral polyp (Q. J. M. S., 28, p. 29).

In the Acoela this absence of enteron extends to the whole of the endoderm.
The close relation of the parenchyma to the endoderm is not only suggested by
the condition in the Acoela, in which they are actually continuous, but is
indicated by an observation of Lang's that the endodermal lining of the enteron
contains extensions of the excretory system. This suggests that possibly the
continuity between the parenchyma and the endoderm in the Triclada, at any
rate, is closer than is supposed. The origin of the generative cells in the
parenchyma, and their passage through the vacuolatecl spongy mass to the
genital opening is exactly what must happen in Bourne's coral polyp with
a spongy enteron. At the same time I do not wish to suggest that the paren-
chyma ever had a continuous digestive space. I would rather suggest that the
Acoela are connecting forms between large Infusoria and the higher animals, in
which the endodermal protoplasm, though without a continuous cavity, is
partly differentiated into a number of important organs.

FIG. 167 — Planaria polychroa creeping with outstretched pharynx.

The mouth leads into a muscular pharynx, which is contained
in a sheath, and can usually be protruded like a proboscis (Fig. 167).
The enteron, into which the pharynx opens, consists only of a simple
chamber (Fig. 168), or of a central chamber prolonged into branches,
which may themselves branch and even anastomose. In some cases

TURBELLARIA.

213

(Yungia, Cydoporus) the enteric diverticula open to the exterior.
The internal wall of the enteron is some-
times ciliated.

In the Acoela the pharynx leads into
the central parenchyma, in the vacuoles
of which digestion takes place.

The excretory organs are the draining
system of the parenchyma. They also
sometimes extend into the endoderm,
which is really the central part of the
parenchyma. A general account of what
is known of these organs has already been
given. To that may now be added that
there is generally a main trunk opening
externally by one or several openings
(Fig. 172) on the dorsal, or on the ventral
surface, or even into the pharynx-sheath;
that this main canal gives off secondary
canals which may branch and even anas-
tomose ; that the secondary canals receive
the finest canaliculi, which come direct
from the terminal cells — the flame-cells
as they are called. Flame-like cilia and
smaller cilia may project into these canals
at different parts of their course.

The whole system is said to be intra-
cellular, and without well-marked walls.
It can only be made out in the living

FIG. 168.— Alimentary canal and
nervous system of Mesostomum
Ehrenbergii (after Graff). G the
two cerebral ganglia with two
eye-spots; St the two lateral
nerve - trunks ; D alimentary
canal with mouth and pharynx.

Phg

Dst

Sch

Qm

Dvm

FIG. 169. — Transverse section of Planaria polychroa, passing through the pharynx (after
Leuckart and Nitsche). D intestine ; Ph pharynx ; Phg cavity of pharynx ; Pht sheath of
pharynx ; Ln lateral nerve-trunks with commissures Co connecting them, and lateral
branches Sn ; T testes ; Od oviduct ; Dst yolk-glands ; Dvm dorsoventrally running muscular
fibres ; Qm transverse muscular fibres ; Sch mucous glands opening externally at the edge of
the ventral surface ; Vd vas deferens.

214 PLATYHELMINTHES.

animals. No doubt what we really have to do with here is a con-
tinuous system of tubular vacuoles in the plasmatic parenchyma —
similar in nature to the tubes leading from the contractile vacuole
of an Infusorian.

The excretory system has not yet been observed in the Acoela.

The nervous system (Fig. 168) consists of a bilobed ganglion at
the anterior end of the body. It is embedded in the parenchyma,
and gives off nerve trunks in all directions ; of these, two especially
large lateral trunks run backwards, one on either side (Fig. 168).
The latter are sometimes connected at regular intervals by delicate
transverse cords, and in the Polydada and Tridada all the peripheral
nerve-trunks anastomose. In a number of the two last-named groups
a diverticulum of the enteron runs forward above the transverse
commissure in a groove between the two cerebral lobes ; and in some
genera this enteric prolongation is encircled by a nervous commissure.

Sense-organs. Eye-spots are very generally present. In the lower
forms (Acoela) they are simply pigment-spots in the ectoderm. As
a rule, however, they are placed in the parenchyma or in the brain,
and consist of many retinal rods contained in a pigmented sheath.
The outer ends of these rods, i.e., the ends turned towards the
external surface, are continuous with the nerves passing to the brain.

In the Polydada the eyes have been observed to increase by
division, and in the Tridada they have been seen to fuse, so as
to give rise to more complex eyes. The eyes, which may be present
in any number, from one to a hundred or more, are placed over the
brain, or on the tentacles, or on the margin of the body.

Auditory organs, as otocysts, are sometimes found. In Acoela
and in some Rhaldocoela (Monotus), and more rarely in Polydada,
a single otocyst is found in the neighbourhood of the brain.

The integument is endowed with a highly developed tactile sense ;
the large hairs and stiff bristles which project between the cilia have
probably this function. Lateral ciliated pits, which may also be
explained as sense-organs, are in rare cases present at the anterior
end of the body. In the Proloscidae the anterior end of the body
is retractile into a sheath, and probably highly sensitive.

Reproductive organs. With the exception of Microstomum and
Stenostomum, and possibly Plagiostomum dioicum, the Turbellaria are
hermaphrodite ; but steps between the hermaphrodite and dioecious
condition are not wanting, for according to Metschnikoff in Gyrator
Jiermapliroditus (Prostomum Uneare), the male generative organs are
sometimes developed, while the female organs remain rudimentary,

TURBELLARIA.

215

or vice versa. This is probably only a case of successive hermaphro-
ditism common amongst the Turlellaria, a condition in which the
male organs attain maturity before the female.

The generative organs are always complex, and the gonads are
either compact, or follicular and scattered. As a type of the first
condition we may .take Mesostomum Ehrenbergii (Fig. 170). Here
there is a single external opening leading into an atrium genitale,
into which opens the vas deferens (Vd) through the penis (P), the

FIG. 170. — Generative apparatus of Meso-
stomum Ehrenbergii (combined from Graff
and Schneider). S pharynx ; Go sexual
opening ; Ov ovary ; Ut uterus with winter
eggs; Do yolk -gland; Dg duct of yolk-
gland : T testes ; Vd vas deferens ; P
penis ; Rs receptaculum seminis.

FIG. 171. — Generative organs of
Vortex viridis (after M. Schultze).
T testes; Vd vas deferens; Vs
vesicula seminalis ; P penis ; Or
ovary ; Va vagina ; M uterus ; 1)
yolk-gland ; Rs receptaculum

oviduct, the two uteruses (Ut), the receptaculum seminis (Rs\ and
the ducts of the yolk-glands (Dg). The testes (T) are paired and
tubular, their ducts join in the penis, which projects into the atrium.
The ovary (Ov) is single, and its duct opens directly into the atrium
yenitale. The receptaculum seminis stores up the sperm received in
copulation, and the eggs remain in the uterus for a shorter or longer
time. As a type of the second condition we may take the fresh-water
Triclad Planaria lactea. Here (Fig. 172) also there is a single external
opening (Go) leading into an atrium genitale, into which open the

216

PLATYHELMINTHES.

vasa deferentia through the penis, the oviduct (Od), the uterus
(Ut), and a muscular sac of unknown function (X}. There are
two ovaries (Ov) placed between the third and fourth pairs of
intestinal caeca or thereabouts. The two
oviducts (Od) pass backwards, receiving
as they go the yolk -glands which are
placed between the caeca of the intes-
tine; they join to open by a single tube
into the genital atrium. The testes are
numerous vesicles placed irregularly be-
tween the gut caeca, and communicating
with a longitudinal tube on each side —

FIG. 172. — Diagrammatic representa-
tion of the anatomy of Planaria
Icwtea (after Leuckartand Nitsche).
D intestine ; Ph pharynx ; M open-
ing of sheath of pharynx ; E exter-
nal openings of excretory vessels ;
To tactile organs ; Gl cerebral gan-
glion ; Ln origin of lateral nerve ;
Ov ovary : Od oviduct (anterior
and posterior part only shown) ;
Ut uterus ; X muscular piriform
organ ; Go external genital opening ;
Vd vesiculae seminales opening
into the base of the penis. The
yolk-gland and testes are omitted,
and the vasa deferentia are not
shown.

w.a**

FIG. 173. — Anatomy of Leptoplana pallida (after
Quatrefages). G cerebral ganglion with the nerves
given off from it : 0 mouth ; D branches of intes-
tine; Od oviduct; V vagina; W. Goe female genera-
tive opening ; M. Goe male generative opening ;
T vas deferens ; Ov ova.

TURBELLARIA. 217

the vasa def erentia : * these open into glandular sacs — the vesiculae
seminales (Vd\ which themselves open into the penis. The penis
is an eversible organ, which can be protruded through the genital
pore.

In the Polydada the ovaries as well as the testes are follicular
and scattered, and there are no yolk-glands. Moreover, the, external
openings are separate, the male being in front of the female. In
some Rhabdocoela also the generative openings are separate. In the
Acoela the ovaries are compact, but the testes are follicular, and there
are no generative ducts, so that the generative cells have to make
their way through the parenchyma to the external generative
opening or openings.

The penis is protrusible and very commonly armed with hooks,
which are said to assist the animal in retaining hold in copulation,
and also to serve as weapons of offence. In Prorhynchus and
Stylostomum the penis opens into the mouth.

A curious instance of vegetative repetition is presented by some
Polydada, in which there may be (Anonymus) several pairs of penes
and of male openings placed in two rows on the ventral surface.

In some cases it is said that true copulation takes place ; but in
many forms (e.g., Polydada) the sperm masses are deposited on the
body of another worm, or even in a wound in the body-wall made by
the impact of the penis. In such cases of sperm injection the
spermatozoa must make their way to the receptaculum or uterus
by travelling through the tissues of their host. These creatures
do not always confine their attentions to individuals of their own
species, for Lang observed a Pseudoceros crawl over a Thysanozoon
and make several wounds, in each of which a sperm mass was
deposited.

Some Rhabdocoela form two kinds of eggs — summer eggs, which
have thin shells, and are retained in the uterus till hatching; and
winter eggs, which have thick brown shells, are laid, and last through
the winter to be hatched out in the spring. The eggs are either
enclosed singly in egg-shells, or several of them are included with
a number of yolk -cells in one shell or cocoon. The Polydada
agglutinate a number of eggs together in an albuminous mass.

The fresh-water Turlellaria as well as many marine forms undergo
a simple direct development, and in the young state are often difficult
to distinguish from Infusoria. Some of the Polydada undergo a

* It is possible that there are no vasa deferentia, but that the spermatozoa
make their way through the parenchyma to the vesiculae seminales.

218

PLATYHELMIXTHES.

metamorphosis, the larvae, known as Miiller's larva, possessing finger-
shaped ciliated lobes (Fig. 174).

Asexual reproduction by transverse fission takes place in the
Microstomidae (Fig. 175). The posterior third of the body becomes
separated from the rest by a septum, and develops its own mouth
and organs. This process may continue both in the offspring and
parent before separation
takes place, so that a com-
plex chain of individuals
arises (Fig. 175).

Planaria alpina is also
known to undergo fission.
The power of regenerating
lost parts is great.

Order 1. ACOELA.*

FIG. 174. — Larva of Eurylepta
auricnlata (after Hallez).

Small marine Turbellaria
without digestive cavity, but
with a spongy digestive paren-
chyma not differentiated into

endoderm and mesoderm. Dejinite excretory organs
have not been Observed. A single otocyst is alirai/*
present. Mouth ventral, leading into a short pharynx.

The central nervous system, generative organs, and
digestive organs, are not sharply separated from the
parenchyma, but appear rather to be a part of it.
Generative ducts are not specially developed, though
in the male organs there appear to be fairly -well
specialized tracts along which the sperm passes. The
genital opening is double or single ; a penis is always,
and a bursa seminalis sometimes present. There are
no yolk-glands, and the excretory system has not been
made out. There is always a pharynx, which ends
in the central mass. At the front end of the body
there is an organ of a glandular or sensory nature, which was
formerly mistaken for the mouth. It is the "frontal organ."

The Acoela are marine. Most are carnivorous, but it is said that
some species of Convoluta can live like a green plant by means of the
green cells (1 symbiotic algae}, which live symbiotically in their tissues.

* Y. Delage, "Etudes histologiques sur les Planaires Rhabdocoeles Acoeles,"
Arch. zool. exp. et gin. (2) T. iv. 1886.

FIG. 175.— Micro-
stomuin lineare
(after Graff). A
chain produced
by fission ; 0, 0'
mouth open-
ings.

RHABDOCOELA. 219

Fam. 1. Proporidae. With one generative opening, without accessory female
apparatus ; with soft penis. Proporus v. Graff, Proporus venenosus 0. Schm.,
Plymouth; Monoporus v. Graff, M. rubropunctalus 0. Schm., Plymouth.
Haplodiscus Weldon.

Fam. 2. Aphanostomidae. With two sexual openings, the female being
anterior to the male. With bursa seminalis and soft penis. Apkdnostomum
Oersted, A. diversicolor Oe. , A. elegans Jen., Plymouth ; .Nadina Uljanin ;
Cyrtomorpha v. Graff; Convoluta Oersted, C. paradoxa Oerst., English coast,
etc.; Amphickoerus v. Gr. ; Polychoerus.

Order 2. RHABDOCOELA.

With straight, rod-shaped enteron, and protrusille pharynx.

This order includes the smallest forms in the class, but not the
most simply organised. On the contrary, the structure of the
parenchyma lends support to the view that they are the most
highly organised of the class. The enteron is unbranched, and lies
in a space simulating a body-cavity. The vitellarium is sometimes
not separated from the ovary. They live on the juices of small
worms and of the larvae of Entomostraca and Insecta, which they
envelop with a cutaneous secretion containing rhabdites, and after-
wards suck. They are mostly fresh-water, but a few of them are
to be met with in the sea, and some upon land (Prorhynchus sphyro-
ceplialus). Parasitic forms are also known (Grafilla muricicola in
the kidney of Murex Irandaris, Fecampia erytlirocepliala in gut of
Carcinus maenas, etc.).

Fam. 1. Macrostomidae. With two generative openings, the female being in
front of the male. Without accessory female apparatus ; with simple pharynx.
Mecynostomum E. v. Ben., marine ; Mctcrostomum E. v. Ben., f.w. and mar.,
M. hystrix Oe., f.w.; Omalostomum E. v. Ben., marine.

Fam. 2. Microstomidae. With sexual and asexual reproduction ; with
simple ovary, without accessory female apparatus ; with simple pharynx.
Microstomum 0. Schmidt, dioecious, f.w. and mar., M. lineare Oe., f.w.;
Stenostomum 0. Schm., dioecious, f.w. and mar., S. lemnae Dug., S. leucops
0. Schm., f.w.; Alaurina Busch, hermaphrodite with follicular. testes, A
Claparedii v. Graff, coast of Skye.

Fam. 3. Prorhynchidae. With separate generative openings, the female
being ventral, the male combined with the mouth. With simple ovary divided
into germarium and vitellarium ; with variable pharynx. The so-called pro-
boscis is the copulatory organ. Damp earth or fresh water. Prorhynchus
M. Schultze, P. stagnalis M. Sch.

Fam. 4. Mesostomidae. With one or two generative openings ; vitellarium
and germarium either distinct organs or separate parts of the same organ.
Usually with accessory female apparatus, and always with compact paired testes.
With a ventrally-placed rosette-shaped pharynx. F.w. and mar. Otomesostomum
v. Graff; Mesostomum Duges (Fig. 168); Bothromesostomum'bL Braun ; Castrada
O. Schm.; Promesostomum v. Gr., P. marmoratmn Schultze, coasts of Britain;

220 TLATYHELMINTHES.

P. solea 0. Sell. Plymouth, P. lenticulatum 0. Sclim. Isle of Man ; Byrsophlebs
Jen., B. Graffi, Jen. Plymouth, Millport, B. intermedia v. Gr. Isle of Man, Mill-
port; Proxenetes Jen., P. cochlear v. Gr., Millport.

Fam. 5. Proboscidae. With a tactile proboscis, one or two generative
openings, separate germarium and vitellarium, bursa seminalis and compact
testes. Mouth ventral ; pharynx rosette-shaped. The continuity of the enteron
is interrupted at the period of sexual maturity. All marine except Gyrator
Ehbg. Pseudorhynchus v. Gr., Irish Channel; Acrorhynchus v. Gr., Brit, coast;
Macrorhynchus v. Gr., Brit, coast; Hyporhynchus v. Gr., Brit, coast; Gyrator
Ehrb., St. Andrews.

Fam. 6. Vorticidae. With one generative opening ; germarium and vitellarium
combined or separate ; with accessory female apparatus, always simple uterus,
and compact paired testes. Mouth ventral, and usually near the anterior end ;
pharynx with a single exception cask-shaped. The chitinous penis very various.
Schultzia v. Gr. ; Provortex v. Gr., Brit, coast; Vortex Ehbg.; Jensenia v. Gr. ;
Opistomum 0. Schm. ; Derostomum Oers. ; Graffilla v. Jhering, parasitic ; Anoplo-
dium Schneider ; Fecampia crythrocepliala Giard, in gut of Carcinus maenas.

Fam. 7. Solenopharyngidae. With one gen. opening, one germarium (ovary),
paired compact elongated testes. The pharynx elongated, tubular, directed
backwards. Solenophitrynx v. Gr.

Order 3. ALLOIOCOELA.

Enteron lobed or an irregularly widened sac. Testes follicular.
Paired ovaries and vitellaria, combined or separate ; vitellaria irregu-
larly lobed or partially branched.

The parenchyma is less differentiated than in the Rliabdocoela, and
more in the condition it has in the Acoela. The generative openings
are separate or united, as in the latter group. With few exceptions
they are marine (Plagiostomum leinani. Lake of Geneva, Bothrioplana}.

Fam. 1. Plagiostomidae. With one gen. opening, and without accessory female
apparatus (except Cylindrostomum} ; with testicular follicles in front of, alongside,
and behind the brain. Pharynx varying in position and size. Otocyst absent.
Usually small, cylindrical, or plano-convex forms with narrow hind end.
Acmostomum v. Gr. ; Plagiostomum 0. Schm. ; Vorticeros 0. Schm. ; Enteros-
tomum Clap.; AllostomumP. J. v. Ben.; Cylindrostomum Oers. All recorded
from British coast except Acmostomum.

Fam. 2. Monotidae. With two gen. openings, and with bursa seminalis ;
testicular follicles closely aggregated between brain and pharynx. Pharynx
always elongated with opening directed backwards. With one otocyst.
Elongated forms with narrow front end and broad hind end. Monotus
Diesing ; Automolos v. Gr. Both recorded from British coast.

Fam. 3. Bothrioplanidae.* Intestine with three branches, of which the
two posterior unite behind the pharynx. With one genital opening. Allied to
the Triclada. Genital glands with tunica propria. Bothrioplana Braun. , fresh
water.

* F. Vejdovsky, Z. f. w. Z., 60, 1895, p. 198.

TRICLADA.

221

Order 4. TRICLADA.

Enteron with three branches, one forward and two backward ;
pharynx cylindrical, inserted at the junction of the three branches.
Genital pore single, behind the mouth. ^

The Triclada comprises marine, fresh-water, and terrestrial forms.
A description of a typical member of the order has already been
given. The testes are numerous and
follicular; the vitellarium consists of
scattered follicles, and is only exception-
ally compact (Otopland); the ovaries are
two in number, placed anteriorly. The
mouth is usually behind the middle of
the body, and the body is more or less
flattened. The skin is often provided
with glands, the secretion of which in
certain land forms (Bipalium, Rhyncho-
demus) hardens to a fibrous web. The
Triclada have great power of repairing
lost parts; fission occurs in Planaria
alpina and cornuta.

a

FIG. 176. — Planaria polychroa (a),
P. lugiibris (b), P. torva (c),
about twice natural size (after
O. Schmidt).

Marine forms. Enteric branches but little ramified, sometimes simply lobed.
Mouth placed in the posterior half of the body (except Bdellura). Body flattened.
Uterus placed behind the genital opening.

Fam. 1. Otoplanidae. "With otocyst and ciliated pits, without eyes. Otoplana
Du Plessis.

Fain. 2. Procerodidae. Without otocyst and ciliated pits. Cercyra 0. Schm. ;
Procerodes Girard (including Gunda, Fovia, Haga) ; Uteriporus Bergendal.
Gundct and Fovia recorded from British coast.

Fam. 3. Bdelluridae. Ectoparasitic on Limulus, provided with a caudal
apparatus for fixation. Bdellura Leidy.

Fresh-water forms. Enteric branches much ramified. Mouth placed in the
posterior half of the body. Body flattened. Uterus placed between the
pharynx and the penis.

Fam. 1. Planaridae. Head without differentiated organ of fixation.
Planaria 0. F. Miill. (including Dugesid), with two eyes ; P. lactea 0. F. M. ;
P. punctata Pall. ; P. polychroa Schm. ; P. torva M. Sch. ; P. alpina Dana are
British. Phagocata Leidy, witli 8 or 9 pairs of pharynges additional to the main
one, Pennsylvania; Anocdis Stimpson, no eyes; Polycelis Hemprick and Ehrenb.,
many marginal eyes ; P. nigra Ehr., P. cornuta are British.

Fam. 2. Dendrocoelidae. Head with several differentiated organs of fixation.
Dendrocoelum Oerst. (incl. Bdellocephala and Galeocephala), two eyes ; Oligocelis
Stimpson, six eyes ; Procotyla Leidy ; Sorocelis Grube, and Dicotylus Grube,
from Lake Baikal.

Terrestrial forms. Enteric branches generally simply lobed. Position of

999

PLATYHELMINTHES.

mouth and form of body variable. Uterus slightly developed and behind
the genital pore. Ventral muscular system much developed.

Fam. 1 . Leimacopsidae. Dorsal face very convex ; mouth in the anterior
part of body. Leimacopsis Diesiug, 2 frontal tentacles with eyes at base,
tropical America.

Fam. 2. Geoplanidae. Body sub-cylindrical ; mouth almost median (except
Microplana and Dolichoplana). Geoplana Stimpson (with Geobia and Coeno-
plana) S. America, Australia, K". Zealand, etc.; Sphyrocephalus Kuhl and
v. Hasselt (with Bipalium}, Ceylon, India, N. Zealand, etc.; Geodesmus
Metschnikoff ; Rhynchodcmus Leidy, world-wide, mouth a little behind the
middle of body. Dolichoplana Moseley ^Philippines ; Microplana Vejdovsky.

Fam. 3. Polycladidae. Body flattened ; mouth in posterior part of body.
Polycladus Blanchard.

Order 5. POLYCLADA.

Enteron with many branches, which ramify or anastomose. Male
and female openings distinct (exceptionally united in Stylochoplana,
Discocelis). Ovaries follicular, without vitelline glands.

The Polyclada are marine animals. Both testes and ovaries
are numerous and follicular. A vitellarium is absent. The female
genital opening is behind the male. In some forms the young are
hatched out as larvae, called after their discoverer, Mliller's larvae
(Fig. 174).

ACOTYLEA.

Without suckers. Mouth in the middle of the body or behind it. Copulating
apparatus in the posterior half of body. Without tentacles, or Avith nuchal
tentacles.

Fam. 1. Planoceridae. With nuchal tentacles ; mouth about median ; male
copulating apparatus directed backwards. Planocera de Blainville ; P. folium
Grube, Berwick Bay. Imagine Girard ; Conoceros Lang ; Styloclms Ehrb. :
Stylochoplana Stimps., body widened in front, attenuated behind, male and
female openings united, with two tentacles and eyes at their base ; St. maculata
Quatr. , Brit, coast. Diplonchus Stimps.

Fam. 2. Leptoplanidae. Without tentacles ; mouth about median ; male
copulating apparatus directed backwards. Cryptocelis Lang, with oval,
consistent body, mouth median, genital openings separate, eyes small in
indistinct groups between the brain and front body end, and round the whole
edge of the body; Discocelis Ehrb., broadly oval, tolerably consistent body,
mouth median or in front of middle, a single genital opening, eyes in two
groups, one on each side of brain, and on the anterior edge of the body ;
Leptoplana Ehrb. (Fig. 173), body elongated, genital openings more or less re-
moved from hind end of body, eyes in two sometimes indistinct tentacular
groups, and in the brain area, small eyes on the anterior edge of body ; L. tre-
mellaris 0. F. M., Brit, coast. Trigonoporus Lang.

Fam. 3. Cestoplanidae. Without tentacles, body ribbon-like. Mouth not
far from hind end of body. Copulating apparatus directed forwards ; eyes
scattered over the whole head. Cestoplana Lang.

TREMATODA. 223

COTYLEA.

With central or sub-central ventral sucker always placed behind the openings
of the body. Mouth in middle of body, or in front of it. Copulating apparatus
(except Anonymus) in the anterior half of the body. Without tentacles, or with
marginal tentacles. .

Fam. 1. Anonymidae. Body broad, oval, without tentacles. Numerous
penes in two lateral rows. Single female opening between mouth and sucker.
Eyes in brain area and on whole edge of body. Anonymus Lang.

Fam. 2. Pseudoceridae. Body oval or elliptical, with fold-like marginal
tentacles. Mouth in middle of anterior half of body. Eyes on brain areas, and
on the tentacles. Thysanozoon Grube, with dorsal villi and double penis.
Pseudoceros Lang, and Yungia Lang, without villi. In Yungia the gut diverti-
cula open by numerous pores on the dorsal surface of the body.

Fam. 3. Euryleptidae. Body oval or elliptical, with or without pointed
frontal tentacles. Mouth near the front end of the body. Pharynx tubular.
Eyes in the brain area and on the tentacles (or at the two sides of front edge
of body). Prostheceraeus Schmarda, Brit, coast ; Cydoporus Lang, gut branches
open along the whole of the edge of the body, C. papillosus Lang, Plymouth,
Port Erin; Eurylepta Ehrb. ; Eu. cornuta 0. F. M., Brit, coast. Oligodadus
Lang, Brit, coast ; Stylostomum Lang, Brit, coast ; Aceros Lang.

Fam. 4. Prosthiostomidae. Body elongated, without tentacles. Mouth
immediately behind brain. Pharynx long and tubular. Prosthiostomum
Quatrefages.

Class II. TBEMATODA.*

Parasitic Platyhelminthes with unsegmented, usually flattened,
rarely cylindrical, body. They possess a mouth and ventr ally-placed
organ for attachment. The intestine is forked and without an
anus.

The Trematodes, in the main features of their organisation, are
most nearly related to the Turbellaria. They differ from them in
their parasitic habit, and in the absence in the adult of a ciliated
ectoderm, though the Temnocephalidae, in possessing a partially
ciliated ectoderm and in other respects, are intermediate between
the two classes. In connection with their parasitic habit they
possess special organs for adhering, such as suckers and hooks,
which are stronger and better developed in those which are external
parasites than in those which infest the internal organs of animals.

The mouth is invariably placed at the anterior end of the animal,
usually in the middle of a small sucker. It usually leads into a

* M. Braun, "Trematoda" in Bronn's Klassen u. Ordnungen, Bd. iv.,
1887-93. A. v. Nordmann, " Mikrographische Beitrdge z. Kenntniss der wir-
bellosen Thiere, Berlin, 1832. P. J. v. Beneden and Hesse, Mem. de VAcad.
Roy. Belgique, 34, 1864, p. 60. P. J. v. Beneden, Mem. s. Us Vers intestinaux,
Paris, 1858-61. v. Linstow, Compendium der Helminthologie, Hanover, 1878.
A. P. Thomas, "The Life-History of the Liver-Fluke," Q. J. M. S., 23, liiSS,
p. 99. R. Leuckart, "Die Parasiten des Menschen,"Ed. 2, Leipzig, 1879-1894.
S. Goto, " Ectopar. Trematodes of Japan, " Journ. Coll. Sci. Imp. Univ. Japan, 8.

224

PLATYHELMINTHES.

muscular pharynx with a more or less elongated oesophagus (Fig.
177), which is prolonged into a forked intestine, ending blindly
and often beset with coeca. The organs are embedded in a paren-
chyma of muscle and connective tissue.

The excretory apparatus consists of two large lateral trunks,
and of a network of fine vessels permeating the tissues and ending
in small ciliated lobules (flame-cells). The two large trunks usually
open into a common contractile vesicle, which opens to the exterior

at th$ hind end

of the body.
The nervous

system consists of

a bilobed ganglion

lying above the

oesophagus. From

it there pass out,

in addition to

some small nerves,

two strong back-

wardly directed

ventral nerve-
trunks. These

are connected by

transverse anasto-
with each
and with

two weaker lateral

longitudinal cords,
which are themselves connected with two dorsal FlG- ire. -Nervous system

.of Distomum isostomum

trunks (Fig. 178). Eye -spots with refractive (after E. Gam-on). MS
bodies are sometimes present on the larvae
during their migration, and in many of the
ectoparasitic forms.

Locomotion is effected by the dermo-muscular system, with the
co-operation of the organs of adhesion (suckers and hooks) which
present numerous modifications in number, form, and arrangement.

The organs of adhesion, in size and development, are related to
the endoparasitic or ectoparasitic mode of life. In the endo-
parasitic Trematodes they are less developed, and usually consist
of the oral sucker and of a second larger sucker on the ventral
surface, either near the mouth as in Distomum, or at the opposite

FIG. 177. — Young Distomum (after la
Valette). Ex trunk of the excretory
system ; Ep excretory pore ; 0 mouth other,
with sucker ; S ventral sucker ; P
pharynx ; D forked intestine.

oral sucker; Bs ventral
sucker ; Sn lateral nerve ;
En dorsal nerve; Bn
ventral nerve.

TREMATODA.

225

end of the body (Amphistomum). The large sucker may however
be absent (Monostomum). The ectoparasitic forms are, on the other
hand, distinguished by a much more powerful adhesive armature ;
for, besides two small suckers at the sides of the mouth, they possess
one or more large suckers at the posterior end of the body \ Fig. 185),
which, moreover, may be supported by a chitinous framework.
There are often in addition chitinous
hooks, and very frequently two
larger hooks among the posterior
suckers in the middle line (Fig.
185). In the . Temnoceplialidae the
anterior suckers are replaced by a
group of tentacles, and in the Aspi-
docotylea the adhesive apparatus is
a kind of large ventral foot bearing
numerous suckers.

Reproductive organs. The
Trematoda are mostly hermaphro-
dite. * As a rule, the male generative
opening and the uterine opening of
the female are side by side or one
behind the other, not far from the
middle line of the ventral surface,
near the anterior end of the body
(Fig. 179). The openings may be
separate, or they may lead into a
genital cloaca which opens by the
single genital pore. The male open-
ing leads into § sac, the cirrus sac,
which encloses the protrusible ter-
minal part (penis or cirrus) of the
vas deferens. The vas deferens soon
divides into two, which lead back
to the two large simple or multi-
lobed — in Distoinum liepaticuin

much branched — testes. Both testes and ovaries are, as a rule,
placed between the two limbs of the intestine.

The female organs consist of a convoluted uterus and of an ovary
and paired yolk-glands, to which may be added a special shell-gland.

* Bilharzia, Distomum Okenii, and perhaps one or two other Digenca are
dioecious.

Do

FIG. 179. — Distoinum hepaticum (after
Sommer). 0 mouth ; D caecum of in-
testine (hinder part of intestine not
shown) ; S sucker ; T testes ; Do yolk-
glands ; Dr ovary ; Ov uterus.

226 PLATYHBLMINTHES.

The ovary may be rounded (Fig. 185) or branched (Fig. 179); the
yolk-glands, which secrete vitelline matter, are much branched
tubular glands occupying the sides of the body (Fig. 179). The
oviduct, after receiving the ducts from the yolk-gland, is continued
as the convoluted, somewhat dilated, uterus which opens near the
male opening. The shell-gland is placed round the junction of the
oviduct and vitelline ducts, or round the first part of the uterus.
Here the egg is fertilised, and the vitelline particles come into
contact with the ova. In the Hetyrocotylea (Polystomeae) the part
of the uterus into which the oviduct opens is dilated and called the
ootype. Here, or in the beginning of the uterus if there is no
ootype, each ovum acquires its investment of yolk, and is surrounded
by a strong shell; it is then ready to be passed out through the
opening of the uterus.

In a great many Trematodes, if not in all, there is a special paired
or unpaired canal, called the canal of Laurer,* which opens externally
in the dorsal middle line (Distomum), or laterally through two warts
on the sides of the body (Polystomum, Fig. 185), and internally into
the oviduct where it joins the yolk-ducts, or into the yolk-ducts near
this point. This canal, certainly in some cases, probably in all, is
functionally a vagina, and serves for the entrance of the spermatozoa re-
ceived in copulation, or otherwise, from another individual. In some
genera (Polystomum, Diplozoon, Octobothrium) there is a duct (vitello-
intestinal) connecting the oviduct with the intestine. It appears to
serve the purpose of carrying the superfluous yolk into the intestine.

The so-called third vas deferens, as a tube connecting the vas deferens with the
oviduct, appears not to exist. It is probable that the vitello-intestinal canal
(and possibly the canal of Laurer) have been mistaken for a tube connecting the
oviduct with the male-duct in such a way as to permit of self-fertilization.

The function of Laurer's canal is in some doubt. It has very generally been
interpreted as a vagina, but, excepting in Polystomum integerrimum, in which
two worms have been detected in reciprocal copulation, with their male generative
openings applied to one of its openings in the other worm, the apposition of the
penis to it has never been observed. On the other hand, in the Diatomic (dige-
netic) division reciprocal copulation with the penis of one worm inserted into
the uterine opening of the other has been observed in some forms, t and in one
casej the penis of one individual Avas found to be inserted into the adjacent
opening of its own uterus. These latter cases point to the view that the uterus
functions as vagina. Then the question arises, what is the function of the canal
of Laurer ? It has been suggested that its function is to carry off the superfluous

* J. Fr. Laurer, Disquisitiones anatomicae de Amphistomo conico, 1830, 4°.
f Holostomum serpens, Monostomum faba, Distomum clavigerum, D. cylin-
draceum.

J Distomum cirrigerum.

TREMATODA. 227

yolk. This view is not, however, borne out by an examination of its contents,
which are often spermatozoa, though sometimes yolk, and even ova. Some
observers hold that the single canal of the digenetic forms is not homologous
with the two canals of many monogenetic forms, but with the vitelio -intestinal
canal, which is not present in the Digenea.

On the whole we incline to the view that the canal of Laurer, whether
double or single, is in all cases homologous, and serves for the entrance of
spermatozoa to the female ducts, when, as is often the case, the uterus is full
of ova. It may be that in some cases the penis is used, like that of the
Turbellaria, for hypodermic injection of spermatozoa ; but as a general rule the
thickness of the cuticle and the isolation of the individuals will prevent this ;
again, sometimes the penis may, more or less accidentally, find its Avay into the
opening of its own uterus, or into that of another worm ; but, as a general rule,
the parasites being not contiguous, and having but little power of locomotion,
the spermatozoa are discharged into the cavity in which the parasite is lodged.
The testis being very large, the number of spermatozoa so discharged is probably
very great, so that they spread over the whole surface of the infected organ, to
which other parasites of the same species are affixed. Some of them, therefore,
are sure to reach the body of other individuals, and to pass, by their own move-
ments, into the opening of the canal in question.

That some kind of haphazard impregnation of this kind is the rule in Trematoda
is rendered almost certain by the relatively enormous size of the testis. On
this view the penis must be regarded as a vestigial organ, with little or no
function under the present conditions of life.

Although the so-called internal or third vas deferens does not exist, self-
impregnation* seems in some cases to occur. For in some species solitary
specimens have been found with spermatozoa in the female passages (e.g.,
Polystomum integerrimum, Distomum agamos encysted in Gammarus pulex).
This self-fertilization may have been effected by the insertion of the penis into
the opening of the uterus, but probably it has more often been effected in the
manner above suggested.

The egg-shell is usually in two parts, a small piece being
separated by a suture from a larger, and constituting the oper-
culum. In the ectoparasitic forms it is often prolonged into a
filament at one or both poles of the egg, which filament serves for
the attachment of the egg (Fig. 188). Filaments are only rarely
found in the endoparasitic forms.

The eggs of the endoparasitic forms are smaller and more
numerous than those of the ectoparasitic division. The early
stages of development are sometimes passed through in the uterus,
but in some cases the segmentation does not begin till after ovi-
position. Most Trematodes lay their eggs, but a few are viviparous
(Gyrodadylus).

The just hatched young either possess (in most ectoparasitic forms,
Heterocotylea) the form and organisation of the parent (Fig. 186),

* A. Looss, "Beitrage z. Kenntniss der Trematoden," Z. f. w. Z., 41, 18§5,
p. 420-427.

228

PLATYHELMINTHES.

in which case there is no intermediate host and no alternation of
generations : such forms are monogenetic, and are mostly ecto-
parasites; or they have the form of ciliated larvae (Mimcidium)
which pass into an intermediate host, and eventually become
transformed into the adult without alternation of generations :
such forms are monogenetic and metastatic, and are endoparasites ;
or they undergo a change of host and present the phenomenon of a
complicated alternation of generations, in which the miracidium larva
develops into an asexual form whicfc reproduces itself : such forms are
called digenetic, and are all endoparasites. In the monogenetic forms
the relatively large eggs become, in most cases, attached on the place

FIG. 180. — Embryonic development of Distomum tereticollc (after H. Schauinsland). a, egg
after hardening in picric acid ; Es shell ; E ovum ; D yolk-cells, b, the yolk has been largely
used up by the embryonic cells ; // the first-formed cells of the cellular membrane of the
shell ; S operculum. c, later stage, the shell membrane H surrounds the embryo, the yolk
D almost gone, d, later stage showing ectoblast EC, the internal mass being endoblast.
e, later stage. /, a ripe embryo just before the hatching ; B setigerous plates with their nuclei.

where the mother lives, and the young are hatched out as non-ciliated
or partially ciliated forms (Polystomum integerrimum has transverse
rows of cilia at hatching, Fig. 186). In the case of the metastatic
and digenetic forms the eggs (relatively small in the Digened} are
deposited in a damp place, usually in the water.

In the Digenea* the ovum is placed next the operculum — the
pole of the egg where the anterior end of the future embryo will
be formed (Fig. 180, E). It undergoes a total cleavage and gives
rise to a solid cell-mass, from the surface of which is differentiated
a cellular membrane (Fig. 180, H), which lines the shell and is

* H. Schauinsland, "Beitrag z. k. d. embryonalen Entwicklung der Trema-
toden," Jena, Zeitschrift, 16, 1883.

TREMATODA. 229

left behind at hatching. Beneath this there is formed a second
membrane (Ec)t which gives rise to the ectoderm of the just-hatched
larva; this is ciliated in some forms (D. hepaticum, Fig. 182), but
in others it develops a stout cuticular layer (D. tereticolle, Fig
180, e, EC).

The peripheral cells of the contained cell-mass now differentiate
a third membrane of 'flattened epithelial cells, while of the remaining
cells those at the head end give rise to the rudiment of the alimentary
canal— the others becoming the germ cells of the larva. The embryo
is now hatched, and becomes a small free larva — the Miracidium.
This, which may be ciliated (Fig. 182) or non-ciliated, or even pro-
vided with stiff bristles (D. tereticolle, D. ovocaudatum), has a
contractile body and often an x-shaped eye-spot; it is also provided
with excretory canals in its walls, and in cases in which the structure
has been fully examined, a sucker with a
mouth opening, intestine, and a ganglion
can be made out (Fig. 181). Further,
between the intestine and the body-wall
there are some ova-like cells — the germ
cells.

This larva leaves the egg and, if ciliated,
wanders about independently in search of FlG- isi.— Anterior pole of an

, ,, egg of the liver-fluke with

a host, through the body-wall of Which it fully developed embryo, in

bores its way ; if non-ciliated it is taken °Ptical section- The Probos-

cis, with mouth, oesophagus,
Up by the new host in its food. and intestine, the ganglion

Sometimes the unhatched egg is swal- *nd w» are visible (after

Leuckart).

lowed (D. lanceolatum) and the larva is

set free in the alimentary canal. In any case the larva makes
its way into the tissues of its host, which is a mollusc, usually
a water-snail, and, casting its cuticularized or ciliated skin, becomes
a sporocyst or a redia* The sporocyst (Fig. 182, I) is a hollow sac
with excretory canals in its wall, and containing in its cavity a
number of germ-cells ; a redia (Fig. 182, c) is like a sporocyst except
that it contains a mouth at one end and an intestine, and two lateral
processes near its hind end ; it likewise contains a cavity with germ-
cells. The germ-cells of these organisms develop into more sporocysts
or rediae, or into Cercariae* The Cercariae are young Trematodes,
which eventually reach (often only after two migrations, an active

* The miracidium generally becomes a sporocyst, rarely a redia (Monostomtnn
flavmn and mutabile). The sporocyst may produce other sporocysts (D. cygnoides),
or Cercariae direct, but generally gives rise to rediae (D. hepaticum, Diplodiscus
subclavatus), which produce the Cercariae.

230

PLATYHELMINTHES.

and a passive one) the final host, where they become sexually mature.
They are furnished (Fig. 182, d) with an exceedingly motile caudal
appendage, frequently with a buccal spine, and occasionally with eyes,
and they present in the rest of their organization great resemblances
to the adult, excepting that the generative organs are not developed.
In this form they make their way out of the body of the redia
or sporocyst, and of their host, and move about in the water,
partly creeping and partly swimming. Here they either perish
or find a new host (snail, worm* insect larva, crustacean, fish,

FIG. 182.— Stages in the life-history of Distomwm liepaticum. a, Miracidium (ciliated embryo),
fc, Sporocyst with rediae R (after Leuckart). c, redia (after Thomas); D gut, C Cercaria,
R redia, K germ-cells, rf, Cercaria (after Thomas).

batrachian), into which they penetrate aided by the powerful vibra-
tions of their tails ; they then lose the tail and encyst.

The Cercariae thus become distributed amongst a number of hosts,
and in each case give rise to an encysted form, which only differs
from the adult in being without generative organs. This young
Trematode migrates passively with the flesh of its host into the
stomach of another animal, and thence, freed from its cyst, into
the organ (intestine, liver, etc.) in which it becomes sexually
mature.

There are then, as a rule, three different hosts, in the organs of

TREMATODA.

231

which the different stages (miracidium, sporocyst, redia, encysted form,
sexually mature animal) of the digenetic Trematoda are buried.

The transitions from one host to another are effected partly by
independent migration (Miracidium, Cercaria), partly ]>y passive
migration (encysted sexless adult). Modifications of the ordinary
course of development may, however, take place; these may be
either complications or simplifications. The embryo at hatching
may contain a single redia (as in Monostomum flavum and mutabile),
which it carries about till it enters the first host (Fig. 184, I). In
some cases the course of development is simplified by the omission
of the second intermediate host, viz., that which contains the

encysted immature

Trematode (Cercaria

macrocerca of Dis-

tomum cygnoides;

also Leucochloridium,

the sporocyst of Dis-

tomum macrostomum,

in the tentacles of

Succinea ampJiilia ;

D. hepaticum, in

which the Cercaria

encysts upon a blade

Of grass). In other FlG. 184._a, Miracidium (ciUated

cases the sporocysts

FIG. 183.-A sporocyst produce rediae, which

with contained Cerca-

riae c, B boring spine produce Cercariae or

of Cercariae.

embryo) of Diplodiscus (Amphi-
stomum) subclavatus (after G.
Wagener). D intestine ; Ex ex-
cretory vessels. 5, Miracidiun-
of Monostomum, mutabile (after
v. Siebold). p eye-spot ; R redia.

more rediae (D. he-
paticum).

Further, there are unencysted young Distoma which never be-
come sexually mature in their host (e.g. in the lens and vitreous
humour of the vertebrate eye, in the jelly of Coelenterates). On
the other hand encysted forms are known (Distomum agamos of
Gammarids) which are sexually ripe and produce eggs within the
cyst (? self -impregnation). The sporocyst may increase by division
(e.g. the sporocyst of Cercaria minuta). The tail of the Cercaria
may become transformed into a sporocyst, and after detachment
produce a brood.

Many forms possess great adaptability to changed conditions of
life, e.g. D. echinatum, which proceeds from Cercaria echinata of
Paludina vivipara and normally infests the intestine of the Duck

232 PLATYHELMINTHES.

and of water birds ; it can, however, attain maturity in the intestine
of the Dog, Mouse, and Rat.

If we summarise the development of the endoparasitic Trematodes
we get the following results :

(1) Development with a non-ciliated larva, which changes direct
into the sexual animal. No intermediate host, but transference to
another individual. Aspidogaster and its allies.

(2) Development with ciliated larva, which enters other animals
(Molluscs, Hirudinea, Fishes, Amphibians, Mammals), there encysts, and
takes on a second larval form (metastatic Trematodes). Holostomidae.

(3) Development with ciliated or non-ciliated larva (Miracidium),
which passes actively or passively into another animal (Mollusc),
in which it becomes transformed into an asexual form (sporocyst
or redia), which produces Cercariae either directly, or after the
formation by internal budding and rarely by fission of more asexual
forms. These are the larvae of the adult sexual animal, and they
usually migrate into another host (Mollusc, or Crustacean, Insect,
Fish, Amphibian* and even Mammal), where they lose their larval
organs and encyst. Here they remain until they are passively
transferred into the alimentary canal of their permanent host
(almost always a Vertebrate), in which they become sexually mature
(digenetic Trematodes). Most Malacotylea.

The life-cycle of the digenetic Trematoda must he looked upon as an alterna-
tion of generations of the variety called heterogamy. That is to say, the
alternation is hetween a sexual generation (the so-called adult) and one or more
parthenogenetically producing generations (sporocyst, redia). The Miracidium
is a larva which, becoming parasitic, loses its gut, nervous system, etc., and
degenerates into a sporocyst, or more rarely a redia. The sporocyst or redia
possesses a kind of diffuse ovary in the germ-cells, which develop either into
rediae or Cercariae (see above, p. 229). The redia is very similar to the sporocyst,
but is not so degenerate. The Cercaria is simply the larva of the final stage ;
it possesses special larval organs, e.g. tail and spine, which however may be
absent in cases in which they are not required ; e.g. Macrostomum, in which the
migration of the Cercaria into its final host is a passive one.

On this view the germ-cells of the sporocysts and rediae are ova, and from
what is known of the development (see p. 229), they seem to be set apart at an
early stage (the end of cleavage). Some observers hold the view that we have
to do here with a kind of embryonic fission at a very early stage, the divided off
cells remaining latent for some time, and only developing later into sporocysts or
rediae. But whatever view be taken of the reproduction of the sporocysts and
rediae, there are two facts to be noted with regard to it ; (1) it starts, as does
sexual reproduction, from a one-celled stage, and (2) the phases of the develop-
ment of the so-called germ-cells, whether into rediae or Cercariae, seem closely
to resemble what is known of the development of the fertilised ovum into the
Miracidium.

HETEROCOTYLEA.

233

Order 1. HETEROCOTYLEA = MONOGENEA.

Body variously shaped. Anterior end with or without suckers;
hind end always with a suctorial organ. The ectodermal epithelium
is transformed into a cuticular layer except in the Temn6cepJialidae
and in the lateral suckers of the Tristomidae. Eyes are present.
The openings of the excretory organs are usually paired, dorsal and
anterior ; rarely single and posterior. Always hermaphrodite ; male
and female openings separate or united,
ventral and usually anterior. A paired or
unpaired vagina is generally present, opening
ventrally or laterally, or more rarely dorsally.
Eeproduction sexual; development direct,
without metagenesis or heterogamy. For the
most part external parasites, on the integu-
ment, or in the mouth, nasal passages,
branchial cavity, in some cases in the urinary
bladder, of Fishes, Amphibia, Reptiles, and
Crustacea. They are usually hatched in the
locality inhabited by the mother. Some-
times the development is a metamorphosis,
and the young live in another place.

The development of Polystomum integcrrimum,
parasitic in the bladder of the frog, is the Lest
known, owing to the researches of E. Zeller* (Fig.
186). The production of eggs begins in the spring,
when the frog awakens from its winter sleep and
proceeds to pair. It lasts from three to four weeks.
It is easy then to observe the Polystoma in the
process of reciprocal copulation. When the eggs
are being laid, the parasite forces the anterior end
of the body with the genital opening through the
mouth of the bladder nearly as far as the anus.
The development of the embryo takes place in
water, and occupies a period of some weeks, so
that the young larvae are not hatched until the
tadpoles have acquired internal gills. The larvae
(Fig. 186) are Gyrodactylus-like, and possess four
eyes, a pharynx and alimentary canal, as well as
a posterior disc for attachment, which is surrounded by sixteen hooks. They
possess five transverse rows of cilia, three are ventral and anterior, two dorsal
and posterior. There is also a ciliated cell upon the anterior extremity. The
larvae now migrate into the branchial cavity of the tadpole, lose their cilia,
and are transformed into young Polystoma by the formation of the two median

* Z.f. w. Z., 22, 1872.

FIG. 185.— Polystomum inte-
gerrimum (after E. Zeller).
0 mouth ; Go genital open-
ing ; D intestine ; W lateral
papillae bearing openings
of vaginae (Laurer's canal) ;
Dg yolk - gland duct ; S
sucker; Ov o vary ;H hooks.

234

PLATYHELMINTHES.

FIG. 186. — a, egg with embryo of Polystomum
integerrimum ; &, larva of same. Dk oper-
culum (after Zeller).

hooks, and of the three pairs of suckers upon the posterior disc. The young
Polystomum, eight weeks after the migration into the branchial cavity, at the
time when the latter begins to abort, passes through the stomach and intestine
into the bladder, and there only becomes sexually mature after three or more
years. In some exceptional cases, and always when the larva has passed on to
the gills of a very young tadpole, it becomes sexually mature in the branchial

cavity of the latter. The forms then
remain very small, are without the
vaginae and uterus, and die after the
production of a single egg, without
e*er getting to the bladder.

Fam. 1. Temnocephalidae. With
4 to 12 tentacles at the anterior end,
and a posterior sucker without hooks
or marginal membrane. The integu-
ment consists of a cuticle, epidermis,
and basement membrane ; in some
cases it is, in part, ciliated. There
are rhabdites in the tentacles. Mouth
subterminal, a muscular pharynx (ab-
sent in Craspedella),a,nd an unbranched
intestine. A pair of contractile ex-
cretory sacs opening anteriorly and
dorsally. Genital pore single, ventral,
and posterior ; it leads into an atrium,
which receives the opening of the uterus and the penis. Eggs with stalk-like
appendages, by means of which they are sometimes attached. They live as
external parasites on Crustacea, Chelonia, and Mollusca of fresh waters, and
feed on Infusoria, small insect-larvae, Rotifers, and Crustacea. They have been
found in Australia, New Zealand, Malay Archipelago, S. America, India, and
may be regarded as connecting links between the Turbellaria and Trematoda.
Temnocephala Blanchard ; Craspedella Haswell.

Fam. 2. Tristomatidae. With flattened, discoidal, or elongated body ; with
two lateral anteriorly-placed suckers, and one large posterior sucker, often pro-
vided with radiations and hooks. Parasitic on the skin or the gills of marine
fishes, or on the bodies of parasitic marine Crustacea.

Sub-fam. 1. Tristomidae. With flat body, two suckers, and a large
ventral sucker ; genital opening and opening of vagina usually on the left.
On the skin and gills of marine fishes. Nitzschia v. Baer ; Epibdella
Blainv. ; Phyllonella v. Ben. and Hesse ; Trochopus Dies. ; Placundla
v. Ben. and Hesse ; Tristomum Cuv. ; Acanthocotyle Montic. ; Encotyllcibe
Dies.

Sub-fam. 2. Monocotylidae. With flat body. Without lateral suckers,
with small ventral sucker. Genital opening median, vagina paired. On
skin, gills, or in cloaca of marine fishes. Pseudocotyle Ben. and Hesse ;
Calicotyle Dies. ; Monocotyle Tschbg.

Sub-fam. 3. TTdonellidae. With cylindrical body, with lateral suckers,
and large simple ventral sucker. On parasitic Crustacea. Udonella Johnst. ;
Echinella v. Ben. and Hesse ; Pteronella Ben. and Hesse.
Fam. 3. Polystomatidae. With a more or less distinctly marked-off adhesive

HETEROCOTYLEA.

235

organ at the hind end, bearing suckers and hooks ; usually with two oral suckers.

On the gills of fishes, in Amphibia and Reptiles on the skin, nasal passages, or

bladder.

Sub-fam. 1. Octocotylidae. With two oral suckers and genital hooks ;
adhesive organ Avith 4, usually 8 small suckers. On the gills of marine and
f.w. fish. Octobothrium Leuck. ; Pleurocotyle Gerv. and Ben.; Diplozoon
v. Nordrn. (Fig. 187). The animal is double, two individuals being fused
to form an x-shaped double animal, the posterior ends of which are provided

FIG. 187. — Young Diplozoon (after Zeller). a, two young Diporpae beginning to attach them-
selves together ; b, after complete attachment. 0 mouth ; H posterior suckers ; Z dorsal
papilla ; G ventral sucker.

with two large suckers divided into four pits. In the young state they
live solitarily as Diporpa ; they then possess a ventral sucker and a dorsal
papilla (Fig. 187, a). The Diporpa is without generative organs ; these are
not formed until after it has fused with another Diporpa to form the
x-shaped Diplozoon (Fig. 187, b). The production of ova is confined to
a definite period of the year,
usually the spring. The eggs
are laid singly after the forma-
tion of the thread by which
they are attached, and two
weeks later the embryo (Fig.
188), which only differs from
Diporpa in the possession of
two eye - spots and a ciliated
apparatus upon the sides and
on the posterior extremity of
the body, is hatched. When
an opportunity of fixing itself
on the gills of a fresh -water
fish occurs, the young animal
loses its cilia and becomes a Diporpa, which possesses the characteristic
apparatus for attachment, and sucks the branchial blood. The junc-
tion of two Diporpae can now take place ; this is not effected as was
formerly believed, by the fusion of the two ventral suckers, but in such
a manner that the ventral sucker of each animal affixes itself to the dorsal
papilla of the other, and fuses with it (Fig. 187, b). In this fusion the
vas deferens of the one animal is directly connected with the opening of
the vagina of the other. D. paradoxum v. Nord. , on the gills of many
fresh-water fish. AnthocotyU Ben. and Hesse; Vallisia Perugia - Par'ona ;

FIG. 188. — Egg (a) and larva (6) of Diplozoon
(after Zeller).

236 PLATYHELMINTHES.

Phyllocotyle Ben. and Hesse ; Hexacotyle Blainv. ; Platycotyle Ben. and
Hesse ; Pledanocotyle Dies.

Sub-fam. 2. Polystomidae. Without oral suckers and larger genital
hooks. Adhesive disc usually with 6 suckers, and with hooks. On
the gills of m. fishes, on the skin, gills, or in the bladder of Amphibia or
Reptiles. Polystomum (Fig. 185) Zeder ; Onchocotyle Dies. ; Erpocotylc
Ben. and Hesse ; Diplobothrium Leuck.; Sphyranura R. Wright.

Sub-fam. 3. Microcotylidae. With two oral suckers, and with genital
hooks. Adhesive disc with numerous suckers. On gills of in. fishes.
Microcotyle Ben. and Hesse ; Gastrocotyle Ben. and Hesse ; Axine Abildgaard ;
Pseudaxine Par. and Per.

Sub-fam. 4. Gyrodactylidae. Usually without oral suckers. Anterior
end with 2 or 4 cephalic lappets, or with sucker-like membrane ; excretory
organs opening at the hind end ; adhesive disc usually with small radially
arranged hooks, and 2 or 4 larger central hooks, without suckers. Repro-
duction by eggs which are either laid, or develop within the mother into
a young form which may itself produce a second generation while still in
the parent, v. Siebold believed that he had observed a young animal
developing from a germ-cell of Gyrodadylus, and that this became pregnant
during its development. He regarded the Gyrodadylus as an asexual form
since he failed to find organs for the production of sperm. G. Wagener,
however, showed that the reproduction is sexual, and conceived the idea
that the germs from which the second and third generations are formed are
derived from the remains of the fertilized ovum, from which the first
generation is formed. Metschnikoff too is of the opinion that the individuals
of the first and second generations are formed at the same time from a
common mass of similar embryonic cells. On gills or integument of fishes.
Calceostoma Ben. and Hesse ; Gyrodadylus v. Nordm., G. elegans v. Nordm.,
from the gills of Cyprinoids and f. w. fishes ; Dadylogyrus Dies. ; Tdraonchus
Dies. ; Amphibdella Chatin ; Dipledanum Dies.

Order 2. ASPIDOCOTYLEA.

Body very variously shaped. Adhesive apparatus ventral, large,
round, oval, or elongated, more or less distinctly marked off from the
body, and possessing numerous suckers arranged in one or several
rows, without armature. Mouth terminal or sub-terminal without
oral sucker; oesophagus short, with a more or less developed pharynx;
intestine saccular. Genital pore median, ventral, anterior to adhesive
organ; penis sheath opens into widened end of uterus, which is
much coiled; usually one testis; Laurer's canal absent; yolk-gland
paired. Eggs without filaments. Excretory organs open posteriorly
by one, somewhat dorsally placed, pore. Development direct with
simple metamorphosis. A ciliated covering is not developed during
the embryonic development. Parasitic in the alimentary canal
and gall bladder in Chelonia and fishes, and in different organs
in Molluscs.

MALACOTYLEA. 237

Fam. Aspidobothridae. With the characters of the order. Aspidogaster
v. Baer ; A. conchicola v. Baer, from the pericardial cavity of Anodonta and Unio.
Platyaspis Mont. ; Cotylogaster Montic ; Macraspis Olss.

Order 3. MALACOTYLEA = DIGENEA. ^

Body variously shaped. Being internal parasites the adhesive
apparatus is, as a rule, feebly developed, consisting of two suckers,
one — the oral sucker — at the anterior end, and the other (less
frequently present) on the ventral surface, or at the hind end. An
armature of chitinous hooks is never present on the posterior sucker,
and only exceptionally on the anterior sucker. Additional adhesive
organs are occasionally present (Holostomatidae, Amphistomatidae).
Mouth terminal or sub-terminal, exceptionally on the middle of the
ventral surface (Gasterostomum), almost always surrounded by a
sucker; eyes exceptionally present. Excretory organs open posteriorly
by a terminal or dorsal pore. Hermaphrodite, except Bilharzia and
possibly one or two other forms.* Genital organs open close to one
another, or into an atrium. Genital pores usually on the ventral
surface anteriorly, rarely placed posteriorly, or laterally, or at the
front end. One ovary and usually two testes; yolk-gland paired,
rarely unpaired. Laurer's canal usually present. Eggs usually
without filaments, with operculum. Life-history with alternation
of generations (digenetic, except Holostomidae) and more than one
host. The sexual form is parasitic in the alimentary canal, and its
appendages, of Vertebrates f ; the asexual generations in Mollusca,
and the encapsuled larva in Invertebrata and lower Vertebrata.
Insectivorous birds are particularly infested by them. It may be
of interest to gourmets to know that the trail of a woodcock
largely consists of distomic Trematodes.

Fam. 1. Holostomatidae (Metastatica). With two suckers, and a peculiar
adhesive apparatus behind the ventral sucker on the anterior region of the hody.
Body divided into an anterior flattened and a posterior cylindrical region (Fig.
189). Genital organs in the posterior region, and genital opening at the hind
end. In the alimentary canal of birds, reptiles, and mammals, rarely in am-
phibia and fishes. The eggs are large and not very numerous, and hatch out

* Dimorphic forms are found in certain species of Monostomum and Distomum
in connection with the division of labour of the sexual functions ; one individual
develops only male organs, and the other only female, the former producing
spermatozoa, and the latter ova. The vestige of the functionless generative
gland undergoes in these cases a more or less complete degeneration. Such forms
are morphologically hermaphrodite, but practically of separate sexes.

t There are a few exceptions to this rule, e.g., Distomum Echiuri in the
nephridia of Echiurus pallasii, and D. rhizophysae in the gastrovascular
apparatus of the siphonophore Rhizophysa conifera.

238

PLATYHELMINTHES.

as ciliated larvae (of the miracidium type), which probably make their way into
an intermediate host (fish, amphibian, mollusc, mammal), in which they develop
into a larva known as Tetracotyle (usually with four suckers). The Tetracotyle
probably becomes directly transformed into the adult when the intermediate host
is eaten by the permanent host. This kind of development, in which there is

a change of host but no alternation of genera-

Dra Ms tions, is called metastatic. Diplostomum

Brds. ; Polycotyle Will, and Schm. ; Hemi-
stomum Brds. (Fig. 189) ; Holostomum
Nitzsch.

Fam. 2. Amphistomatidae. Digenetic
forms with two suckers ; the posterior (ven-
tral) sucker is terminal, and on it or just in
front of it there are sometimes numerous
papillae or pits for attachment. Genital
opening median, ventral, in anterior third of
body. Eggs with operculum, without fila-
ment. In alimentary canal of Vertebrata.
Amphistommn Rud.; Diplodiscus'Die.s.', Gas-
trodiscus Cobb.; Homalogaster Poir.; Gastro-
thylax Poir. ; Aspidocotyle Dies.

Fam. 3. Distomatidae. Digenetic forms
with two suckers ; the posterior sucker is on
ventral surface. Genital opening median, in
anterior third of body, anterior to ventral
sucker, rarely behind the latter or lateral.
Eggs usually with operculum, without fila-
ment. Laurer's canal usually present. In
alimentary canal and its appendages of Verte-
brates. Distomum Retz., D. hepaticum L.
liver-fluke (Fig. 179) ; with conical anterior
end and numerous spine-like prominences on
the surface of the broad, leaf-shaped body,
which is about 33 mm. long. In the bile-
ducts of sheep and of other domestic animals,
causing sheep-rot. It is occasionally found
in man, and bores its way into the portal
vein and into the system of the vena cava.
The embryo is hatched after the egg has been
some time in water as a ciliated larva (Fig.
182), with an x-shaped eye-spot ; this passes
into the water-snail Limnaea truncatula, and
there casts its ciliated skin and emerges
as a sporocyst. The sporocyst produces
rcdiae, which produce more rediae or Cer-

cariae. The Cercariae, which are provided with long tails, leave the host,
swim about for a short time in water, and then encyst upon foreign objects,
e.g., blades of grass. In this condition they are eaten by the sheep.
D. crassum Busk, perhaps identical with D. rathouisi Poir. (Fig. 190) in the
intestine of Chinese. D. lanceolatum Mehlis, body lancet-shaped, 8- 9 mm. long,
lives in same place as D. hepaticum; the miracidium is pear-shaped, ciliated on

FIG. 189. — Hemistotmim clathratum
Dies., from the gut of Lutra bra-
siliensis, ventral view (from Bronn,
after Brandes). M.s oral sucker;
K.st. ovary ; Ut. uterus, the open-
ing of the uterus is rather indis-
tinctly rendered, just below the
lower Ut. ; H testis ; V.s. vesicula
seminalis ; Dr.a openings of glands
Dr. ; z ventral adhesive apparatus,
the ventral sucker is just in front
of this ; Sch shell-glands.

MALACOTYLBA.

239

anterior half of body only, and bears a styliform spine on the projecting apex.
D. conjunct-urn Cobb., lancet-shaped, 12 mm. long, in the liver of dog, rarely on
man, East Indies. D. spathulatum R. Leuck.
= D. sinense Cobb., in liver of man and cat in
Japan and China ; D. pulmonale Bolz, in the
lungs of man in Japan and China. D. ophthal-
mobium Dies., a doubtful species, 4 specimens
only found, in the lens-capsule of a nine-months
child. D. heterophyes in the intestine of jnan in
Egypt. D. macrostomum End. (Fig. 191), in
the intestine of insectivorous birds, with genital
pore at hind end. The eggs are consumed by
the snail, Sttccinea amphibia, in the gut of which
the miracidium is set free ; this makes its way
through the gut -wall into the tissues, and
becomes a branched sporocyst, known as Leu-
cochloridium paradoxum. Some of the branches
extend into the tentacles, to which they give a
peculiar appearance by their colouring of green
and white bands and red tip. A bird, attracted
by this, pecks off the tentacle, and so swallows

a branch of the sporocyst, in which have been formed tailless Cercariae. The
latter are thus transferred to the intestine of the final host. The remarkable
feature about this life-history is that the Cercaria is never free, and is without a

Fio. 190. — Distomum rathouisi
Poir., after Leuckart.

FIG. 191.— Life-history of Distomum macrostomum, after Heckert. a, Sucdnea amphibia contain-
ing a ripe sporocyst of a Leucochloridium in its right tentacle. b, Leucochloridium paradoxum
isolated, c, Cercaria (tailless) ready for transference in a double membrane, d, sexual
Distomum macrostomum; D yolk-glands ; T testis ; Ov ovary ; LK canal of Laurer. The open-
ings of the vas deferens and uterus are at the hind end.

240

PLATYHELMIXTHES.

tail. Rhopalophorus Dies.; Koellik.eria Cobb., dioecious, living in pairs con-
tained in cysts in the mucous membrane of the mouth and branchial cavity
of fishes ; the one individual is cylindrical and narrow, and produces sperma-
tozoa ; the other is swollen in the middle and posterior region of the body,
and is rilled with eggs. The dissimilar condition of the two individuals is
probably due to the fact that copulation only leads to the fertilization of one
of them, which alone is able to perform the female sexual functions. K. filicolle
Rud. (D. Okenii Roll.) in Brama Raji. Bilharzia* Cobb. (Fig. 192), dioecious ;
body elongated, nematode-like ; the female is slender and cylindrical ; the male
has powerful suckers and the margins of its body are bent round so as to form a
groove — the canalis gynaecophorus — for the reception of the female ; they live in
pairs in the blood-vessels of mammals. B. haematobia Cobb., portal veins and
veins of bladder of man in most parts of Africa. The
embryos, which are ciliated, escape by the urethra.
By the deposition of masses of eggs in the vessels of
the mucous membrane of the ureter, bladder, and
great intestine, inflammation is set up which may
cause haematuria and stone. B. crassa Sons., in Bos
taurus domesticus ; B. magnet, Cobb., in Cercopithecus
fuliginosus.

Fam. 4. Gasterostomatidae. With the anterior
sucker only ; mouth on the ventral surface, not in
the sucker ; eggs with operculum, without filament.
Genital opening terminal, at hind end. The Cercaria
is known as Bucephalus, and has a bifid tail. In
alimentary canal of fishes. Gasterostomum v. Sieb.

Fam. 5. Didymozoonidae. With the anterior sucker
only ; mouth in the sucker ; gut present or absent.
Hermaphrodite, but live in pairs in cysts. Eggs with
operculum without filament. Genital pore in front of
the oral sucker, terminal. On the integument, or in
the mouth and branchial cavity of marine fishes.
Didymozoon Tschbg. ; Nematobothrium v. Ben.

Fam. 6. Monostomatidae. With only one anterior
sucker. Mouth in the sucker. Genital pore usually
in front, median, ventral. Eggs often with two fila-
ments. Laurer's canal usually absent. In alimentary
canal of most vertebrate classes. Monostomum, Zed.; M. lentis v. Nord. , the
young form without generative organs is found in the lens of the human eye ;
M. bipartitum Wedl., living in pairs enclosed in a common cyst, the one
individual surrounded by the posterior lobe of the other, branchiae of Tunny-
fish ; Notocotyle Dies. ; Ogmogaster Jaegerskiold ; Opisthotrema Leuck.

THE DICYEMIDAE AND ORTHONECTIDAE.t

The systematic position of these forms is obscure : it will, hoAvever, be con-
venient to place them provisionally near the Trematoda. They all consist of an

* G. Fritsch, " Zur Anat. d. Bilharzia haematobia Cobb.," Arch. f. Mic.
AnaL, 31, 1888.

t C. 0. Whitman, "A contribution to the embryology, life^history, and
classification of the Dicyemids," Naples Mittheilungen, Bd. 4. 1882. Julin C.,
"Contribution a 1'histoire cles Mesozoaires," Arch, de Biologic, Bd. 3, 1882.

FIG. 192. — Bilharzia haema-
tobia. Male and female,
the latter being in the
catialis gynaecophorus of
the former. S sucker.

DICYEMIDAE ORTHONECTIDAE.

241

outer layer of ciliated cells surrounding an inner mass, which in the Dicyemidae
consists of a protoplasmic mass with many nuclei, and in the Orthonectidae
(single genus Rhopalura) of a mass of cells compacted together. None of them
have a digestive cavity. The Dicyemidae are parasitic in the kidneys of
Cephalopoda, the Orthonectidae in the gut of Turbellarians, in the, body- wall
and tissue-spaces of Nemertines, and in the body-cavity and broocT pouches of
Ophiurids.

h-Cy

iS

FIG. 193.— Rhopalura Giardii. a, male; 5, cylindrical
female of the same (after E. v. Beneden).

FIG. 194. — Dicyemopsis
macrocephalus (after
v. Beneden).

In the Dicyemidae egg-like germs are found in the central plasmic mass which
give rise to embryos : no spermatozoa have been found (Fig. 194). In Ortho-
nectidae both spermatozoa and ova are found in the central mass, and in different
individuals. No light is thrown upon their affinities by their development.
The Orthonectidae possess a layer of fibres, presumably muscular, between the
outer cells and the inner mass. The males are smaller than the females
(Fig. 193); and there are two kinds of females — the cylindrical forms
(Fig. 193, b) and the flattened forms. The history of these forms is obscure.
Both forms produce eggs, and are supposed to leave the host to wander into a

R

242

PLATYHELMINTHES.

new host, where the cylindrical female ends her existence in the act of expelling
her eggs, while the flat female breaks up into a number of sacs, each enclosing a
number of ova. The eggs of the cylindrical female are probably fertilised, while

those of the flattened form are supposed to
develop parthenogenetically.

The Dicyemidae have two kinds of embryos
(hence the name of the group) — the infusori-
form (Fig. 196) and the vermiform (Fig. 195)
— which arise from the egg-like germs in the
central plasmic mass. They arise in indi-
viduate of slightly different form — the indi-
viduals producing vermiform embryo are
called nematogens and are longer and thinner
than those producing infusoriform embryos,
which are called rhombogens. The rhom-
bogens, however, after producing a certain
number of infusoriform embryos become
nematogens and produce vermiform embryos.
The vermiform embryo changes directly into
the parent form. The infusoriform embryo
is very different from the parent, and its fate
is unknown. Very possibly it has the power
of making its way out of its host, and so
distributing the species. No males or sperma-
tozoa have been observed in the Dicyemidae,
and it has been suggested that the infusori-
form embryos are immature males, or that
they contain the male elements. Whitmtin
indeed states that he has found them in a
modified form within nematogenic adults.
The origin of the egg-like germs within the
central plasmic mass has been described as
a case of endogenous cell-formation; i.e. a
nucleus gathers round itself a certain amount
of protoplasm, Avhich becomes delimited, to

FIG. 195. — A-D, stages in the develop-
ment of the vermiform embryos of
Dicyema; A, of Dicyemennea eledones
(after Whitman) ; B-D, of Dicyema
typus (after E. van Beneden). Ax
axial cell ; K nucleus of the axial
cell ; Kz germ cells (from Korschelt
and Heider).

FIG. 196.— Infusoriform embryos and their development. A-D, of Dicyema typus ; E-G, of
Dicyemella Wagnerii (after van Beneden from Balfour). A-C, developing embryos ; D, embryo
from the ventral side, E from the right side, F from the front ; G side view of the urn
isolated, gr granular bodies in the urn ; I bed of urn ; u floor of the urn ; r refractive bodies.

CESTODA. 243

an extent and in a manner which has not been ascertained, from the" surrounding
plasma.

By some naturalists the Dicyemidae and the Orthonectidae have been regarded
as survivals of a most primitive Metazoan group— of a group possibly inter-
mediate between the Protozoa and the Metazoa, and they have b^en grouped
together as Mesozoa. There does not, however, appear to us to be any sufficient
reason for this view, especially when we remember their parasitic habit. We
are inclined to regard them as allied to the Trematoda, to the miracidium larva
of which they do present some considerable resemblance.

Trichoplax, which may be mentioned here, has been found in salt-water
aquaria (F. E. Schulze, Zool. Anzeiger 6). It is a small, flattened organism
(1-3 mm. in diameter), and consists of a sponge-work of protoplasm, with
nuclei at the nodes, and continuous with processes of the surface epithelial cells.
The latter are ciliated on the lower surface of the animal. Nothing is known of
the reproduction.

Salinella is another form which may be mentioned here (Frenzel, Arch, f
Naturg., 58, 1891). It has only been found in aquaria.

Order 3. CESTODA.*

Elongated and usually segmented Platyhelminthes without mouth
or alimentary canal, with organs for attachment at the anterioi'
extremity.

The tape-worms (Fig. 196), which may easily be recognised by
their band-shaped, usually segmented bodies, are parasitic in the
alimentary canal of Vertebrata, and were formerly taken for single
animals. Steenstrup was the first to introduce a different view,
according to which the tape-worm is a colonial animal (Strobild),
a chain of single animals, each segment or proglottis being an
individual. There are, however, Cestoda, like Caryophyllaeus (Fig.
212), which are destitute both of external segmentation and of

* Besides the older works and papers of Pallas, Zeder, Bremser, Rudolphi,
Diesing, and others, compare van Beneden, "Les vers cestoides ou acotyles,"
Brussels, ]850. Kiichenmeister, Ueber Cestoden im Allgemeinen und die des
Menschen insbesondere, Dresden, 1853. V. Siebold, Ueber die Band- und Blasen-
wiirmer, Leipzig, 1854. G. Wagener, "Die Entwickelung, der Cestoden," Nov.
Act. Leop.-Car., torn. 24, Suppl., 1854. G. Wagener, Beitrag zur Entwicke-
lungsgeschichte der Eingeweidewiirmer, Haarlem, 1857. R. Leuckart, Die
Blasenbandwurmer und ihre Entwickelung, Giessen, 1856. R. Leuckart, The
Parasites of Man, vol. 1, 1886, London. F. Sommer and L. Landois, "Ueber
den Bau der geschlechtsreifen Glieder von Bothriocephalus latus," Zeitschr.
f. wiss. Zool., 1872. F. Sommer, "Ueber den Bau und die Entwickelungs-
geschichte der Geschlechtsorgane von Taenia mediocanellata und Taenia solium,"
Ibid., torn. 24, 1874. M. Braun, Zur Entwick. gesch. des breiten Bandivurines
( Bothriocephal i
Entwick.
Nervensystei

La Structure anat. et hist, des Cesto'ides, Geneva, 1888. B. Grassi u. G. Rovelli,
"Embryol. Forsch. an Cestoden," Centralbl. f. BaJcteriol., 5, 1889. M. Braun,
"Vermes" in Bronn's Thierreich, 4, 1895. 0. v. Linstow, Compendium der
Helminthologie, Hannover, 1878 ; and Nachtrag to the same, 1889.

244 PLATYHELMINTHES.

segmentation of the generative organs ; while in other cases the
segments of the body are clearly differentiated, and each is provided
with a set of generative organs, but they do not attain individual
independence (Ligula). The proglottides, however, usually become
separated off, and after their separation from the body of the
tape-worm continue to live for some time independently, and in
some cases even increase considerably in size, if they remain within
the intestine of their host (Echeneibotliriuin, Calliobothrium, etc.).
The proglottis after separation rrfHy remain for a certain time in
the intestine, but eventually makes its way either passively in the
faeces (e.g. T. solium), or actively by its own movement ( T. saginata)
to the exterior per anum. Here it retains its vital power for a
short time, and crawling away from the faeces ascends the stalks
of plants. It soon dies, and the body decomposes and the eggs
are scattered; or in some cases the eggs escape through a rupture
in the body-wall, and are left as a trail on the objects over which
the proglottis crawls. The eggs soon lose their vitality in a dry
atmosphere. The proglottides of T. saginata, which have consider-
able powers of movement, have been found on the wall a yard above
the bed of their quondam host, and they frequently creep over his
warm body.

These facts seem to be sufficient to justify the view that the
tape-worm is a colonial or polyzoic animal, the individual members
of which have the power of separate and independent life. At
the same time the existence of monozoic forms like Archigetes
(Fig. 211) and Caryopliyllaeus (Fig. 212) must not be forgotten:
in these — the Cestodariidae — there is only one set of generative
organs, and the body is unsegmented ; the head and body not being
sharply distinguished. It would appear that these monozoic forms
of Cestoda have the same relation to the proglottis that Lucernaria
has to Aurelia in the Acalephae. Just as the Lucernaria may be
compared to a Scyphistoma, which develops generative organs and
does not strobilate, so an Archigetes may be looked upon as a scolex,
which becomes sexual but does not bud off proglottides (i.e. does
not develop into a strobila).

This is the only satisfactory mode of regarding the Cestoda;
especially as the entire tape-worm, and not the proglottis alone,
corresponds to the Trematode, and is to be regarded as being
derived from the latter by a simplification of organization and loss
of the alimentary canal.

The anterior part of the tape-worm is narrow, and presents a

CESTODA.

245

FIG. 196«. — Head of Taenia solium,
viewed from the front (apical surface),
with rostellum and double circle of
hooks. The four suckers are visible
(from Clans).

rostellum, which is armed with a
circle of hooks, while the lateral
surfaces of the head are furnished
with four suckers (Taenia, Fig.
196a). In other cases only two
suckers are present (Bottiriocepk-
alus) ; or we find suckers of more
complicated structure and beset with
hooks (Acanthobothmum), or four
protrusible proboscises beset with
recurved hooks (Tetrarhynchus, Fig.
198) ; while in other genera the
head armature presents various
special forms.

That portion of the animal, which
follows the head and is distin-
guished as the neck, shows, as a
rule, the first traces of commencing
segmentation. The rings, which are
at first faintly marked and very
narrow, become more and more
distinct and gradually larger the
further they are removed from the
head. At the posterior extremity
the segments or proglottides are
largest, and have the power of
becoming detached.

terminal swelling by which it at-
taches itself. This anterior swollen
part is distinguished as the head of
the tape-worm, but it is mainly its
external form which entitles it to
this name. In Caryophyllcteus the
head armature is very weak, and
consists of a lobed fringed expan-
sion. The apex of the head often
ends in a conical projection, the

FIG. 197. — Taenia saginata (mediocanel-
lata), natural size (after R. Leuckart).

246

PLATYHELMINTHES.

The simplicity of the internal organization corre
spends with the simple appearance of the external
structure. Like the Trematoda, the Cestoda are
said to possess no epithelial ectoderm. Beneath
the cuticle -like outer membrane is a layer of
spindle-shaped cells lying at right angles to the
surface ; their external ends abut upon the cuticle,
and their inner ends are prolonged as fibres into
the parenchyina. Beneath this layer there is a
delicate superficial layer of longitudinal muscular
fibres, and next a parenchyma of connective tissue,
in which strongly-developed bundles of longitudinal
muscular fibres, as well as an inner layer of circular
muscles, are embedded ; both these muscular layers
are traversed, principally at the sides of the body,
by groups of dorso-ventral muscular fibres. The
power which the proglottis possesses of altering
its form is due to the interaction of all these
FIG. 198. — Young muscles. By means of them it is able to shorten
Tetrarhynchus with itself considerably, at the same time becoming

beginning segment- J ' . °

ation. The four ex- much broader and thicker, or to elongate to double
the^o^recting its normal length, becoming much thinner. In the
loops in the head, connective tissue parenchyma of the body, not only
velif^ar^visiWe the muscles, but all the other organs are embedded,
(from ciaus). In its peripheral portion, especially in the neigh-

bourhood of the head, we find small densely packed
calcareous concretions, which are prob-
ably contained in connective tissue cells.

The nervous system consists of two
lateral longitudinal cords passing exter-
nally to the main trunks of the excretory
system. They are somewhat swollen in
the head, where they are connected by a
transverse commissure ; these anterior
swellings and the commissure may repre-
sent a cephalic ganglion. In Moniezia
the lateral nerves are connected by two
transverse commissures at the hind end
of each proglottis. Distinct sense-organs FlG> i99._Head of a Taenia with
are wanting, but the tactile sense may be the four suckers, and the con-

. necting loops of the excretory

ascribed to the Skin, especially to that Of canal (after Pintner).

CESTODA.

247

the head and the suckers. An alimentary canal is also wanting.
The nutritive fluid, already prepared for absorption by the host,
passes endosmotically through the body-wall into the parenchyma.

The excretory apparatus, on the contrary, attains a considerable
development as a system of much ramified canals which are distributed
throughout the whole body.* It consists primarily of two longi-
tudinal canals (a dorsal and a ventral f), running along each side of
the body and connected in the head and in each segment by trans-
verse trunks (Figs. 198, 199). According to the state of contraction
of the muscular system these longitudinal trunks and cross branches
appear sometimes straight and some-
times bent in a wavy or zigzag
manner : their breadth also presents
considerable variation, so that the
power of contraction has been
ascribed to their walls. The longi-
tudinal trunks only serve as the
efferent ducts of a system of very
fine vessels which ramify through-
out the whole parenchyma and
receive numerous long tubes : the
latter begin in the parenchyma with
closed funnels, which contain a
vibratile ciliated lappet (Fig. 200).
The larger vessels are said to con-
tain valves. In many cases, as in
Ligula and Caryophyllaeus, these
longitudinal trunks are broken up
into numerous longitudinal vessels,
which are connected by transverse
anastomoses. In other cases, on the
other hand, the two ventral vessels are enlarged at the cost of the
two dorsal, which may entirely atrophy. The external opening of
the excretory system is, as a rule, placed at the posterior end of the
body, i.e., at the hind end of the last segment, in which a small
vesicle with an external opening receives the longitudinal trunks.
According to the observations of Leuckart on Taenia cucumerina,
the posterior transverse canals in the segments immediately preceding

* Compare Th. Pintner, " Untersuchungen iiber den Bau des Bandwurm-
korpers," Wien, 1880.

t These surfaces are distinguished by the generative apparatus (see below).

FIG. 200.— A portion of the excretory
system of Caryophyllaeus mutabilis
(after Pintner). Wb ciliated funnels
with the nucleus of the cell belonging
to them.

248

PLATYHELMINTHES.

the last become, by their gradual shortening and the approach of
the longitudinal trunks, transformed into the vesicle, which acquires
an external opening when the segment behind it is detached. In
rare cases the excretory system possesses additional openings in the
anterior part of the body behind the suckers, and elsewhere.

The generative apparatus is repeated in each proglottis. The
male apparatus consists of numerous small vesicles, the testes (Fig.
201, T), which are situated nearer one surface of the proglottis than
the other ; this surface is distinguished as the dorsal surface.
Delicate ducts proceed from the testes to open into a common efferent

FIG. 201. — Proglottis of Taenia saginata, with male and female organs (after Sommer).
Ov ovary ; Ds yolk-gland (vitellarium) ; Sd shell-gland ; Ut uterus ; T testes ; Vd vas
deferens ; Cb pouch of the cirrus ; K generative cloaca ; Va vagina.

duct (vas deferens). The coiled end of this duct lies in a muscular
pouch (cirrus sheath), whence it can be protruded through the
genital opening as the so-called cirrus. This cirrus is frequently
beset with spines which are directed backwards, and serves as a
copulatory organ. The female generative organs consist of ovary,
yolk-gland, shell-gland, uterus, receptaculum, and vagina. The vagina
and vas deferens usually open into a common genital cloaca, which
lies either on the ventral surface of the segment (Bothriocephalus),
or on the lateral margin (Taenia) (Fig. 201). In the last case it may
be placed alternately on the right and on the left side. Sometimes
the two genital openings are widely separate, the male opening being

CESTODA. 249

placed at the side, the female on the surface of the segment. In
other cases there are two sets of generative organs in each segment,
opening on the right and left margins (Dipylidium). In the Bothrio-
cephalidae and other forms (possibly in all Cestodes except the
Taeniadae) the uterus has a special opening of its own to the exterior
in addition to the vagina, which opens close to the vas def erens
(Fig. 216). This opening is comparable to the uterine opening in
Trematoda, differing from the latter in being remote from the
male opening. The vagina of Cestodes, which is not used for the
exit of eggs, even when there is no uterine opening (see above,
p. 244), must be compared to the canal of Laurer in the Trematoda.
In forms with a special uterine opening, eggs are deposited through
it while the proglottis is part of the chain in the intestine. When
there is no uterine opening, the eggs are only set free by the
rupture of the proglottis after it has broken away from the chain
and reached the exterior.

As the segments increase in size and become further removed from
the head, the contained generative organs gradually reach maturity
in such a way that the male generative organs arrive at maturity
rather earlier than the female. As soon as the male elements are
mature, copulation is said to take place, and the receptaculum seminis
is filled with sperm, and then only do the female generative organs
reach maturity.

The method of sperm -transference is not fully understood. The penis is
sometimes found projecting from the genital opening (Fig. 207), and Leuckart
states that he has seen it inserted into the vagina of the same proglottis, thus
being in a position to effect self-fertilization. In other cases it has been found
(Pagenstecher) inserted into the vagina of another proglottis of the same chain.
There is also the possibility of copulation between the proglottides of different
chains in the same host, though this has not been observed ; and it may be that
in some cases the penis is used, like that of the Turbellaria, for hypodermic
injection of spermatozoa. Finally we must admit the possibility of the sperm
passing out into the fluids of the intestine in which the body of the tape-worm
is bathed, and of the spermatozoa so set free migrating in sufficient numbers
into the vagina of other proglottides.

The ova are fertilized and pass into the uterus, which then assumes
its characteristic form and size. As the uterus becomes distended,
the testes and then the ovaries and vitellaria are more or less com-
pletely absorbed (Fig. 202). The posterior proglottides, viz., those
which are ready for separation, have alone undergone full develop-
ment, and the eggs in their uterus often contain completely developed
embryos. Accordingly we can recognize in a continuous series of the

250

PLATYHELMINTHES.

segments the course of development passed through hy the sexual
organs and products in their origin and gradual progress towards
maturity. An examination of the segments between that with the
first trace of the generative organs and the first proglottis with fully
developed organs will give us an idea of the stages of structure
through which each segment has to pass. The tape-worms are ovi-
parous ; either the embryo develops within the egg-shell in the body
of the mother, or the development takes place outside the proglottis,
for example, in water (Bothriocephal'm).

FIG. 202— Ripe proglottides ready to sepa-
rate, a, of Taenia soliiim; b, of Taenia
saginata. We water - vascular (excretory)
canal (from Glaus).

FIG. 203.— Egg with embryo : a, of Taenia
solium ; b, of Microtaenia; c, larva of
Bothmocepliahis latiis (after R. Leuckart).

The eggs are round or oval and of small size (Fig. 203) : they
consist of the minute ovum embedded in yolk-cells and surrounded
by a membrane, which is thin when the development takes place in
the uterus, and thick and provided with an operculum when it occurs
only after oviposition (Bothriocepholidae, etc.). The early develop-
ment appears to be closely similar to that of Trematodes; the
segmentation is complete, and is followed by the epibolic formation
of two membranes, of which the outer, lining the inner surface of
the shell in the BothriocepTialidae (Fig. 204), is called the shell or
enveloping membrane, the inner being the so-called ectoderm or outer
layer. These two membranes surround the rest of the embryo,
which we shall call the inner mass. The enveloping membrane is

CESTODA.

251

left in the shell at hatching, and the outer layer either becomes thick
and ciliated, as in some Bothriocephalidae (Fig. 203, c), or thin and
not ciliated as in other Bothriocephalidae and Taenias which inhabit
aquatic animals, or finally it becomes cuticularised as a thick, radially
striated layer (Fig. 203, a), as in the Taenias which infest land
animals (protection against desiccation). Meanwhile, either while
the embryo is free (Bofhrioceplialidae), or while it is within the
uterus of the mother, the inner mass develops six hooks, and
becomes the six-hooked embryo or Onchosphere (Fig. 205, 6). In
the Bothriocephalidae the further history of the embryo is unknown;
it loses its ciliated coat and probably soon dies, unless it migrates into
its next host, which is unknown. In
other cases, in which the life-history has
been followed, the development of the
embryo into the asexual scolex rarely
takes place in the intestine of the original
host. It is said to do so in Taenia
(Hymenolepis) nana (see p. 261), and it
has been suggested that it might occur
in the stomach of the same animal, if by
reversed peristalsis a ripe proglottis was
passed back into the stomach, and there
digested (T. saginata).

As a rule the Scolex, i.e. the head and
neck of the tape-worm, is developed from
the six-hooked embryo in another host,
and in some cases (Coenurus, Echino-
coccus) more than one scolex arises from
a single embryo (Fig. 206).

The eggs usually leave the intestine of

the host in the proglottis, either by active migration or in the faeces.
The proglottides are deposited on the ground or in water. Here they
crawl about and deposit their eggs as described on page 244, but they
soon die, especially if the temperature is unfavourable and the air dry.
The embryo, which in the case of the land forms is protected against
desiccation by the thick cuticle described above, retains its vitality
for a time, which depends on the external conditions. Eventually
it dies, unless it passes into the stomach of a suitable host. As a
rule this host is an herbivorous or omnivorous animal, but it may
be a carnivorous animal. The embryos are usually taken up in the
food, or in drinking water, but occasionally they enter accidentally

FIG. 204.— Embryo of Bothrio-
cephalus latus pressed out of
the egg. EG outer layer (so-
called ectoderm) ; Hm the shell
(enveloping) membrane.

252

PLATYHELMINTHES.

in consequence of dirty habits. * As soon as the egg membranes are
digested or burst by the action of the juices of the stomach of the
new host, the embryos, or onchospheres as they are called, which
have been thus set free, bore their way into the gastric or intestinal
vessels by means of their six (rarely four) hooks, the points of which
can be approached and removed from one another over the periphery
of the small globular embryonic body (Fig. 205, I). When they are
once within the vascular system, they are no doubt carried along
passively by the current of blood, g,nd transported by a longer or
shorter route into the capillaries of the different organs, as the liver,
lungs, muscles, brain, etc. After losing their hooks, they usually
become enveloped by a cyst of the connective tissue of their host,

d

Fi'> 205. — Stages in the development of Taenia solium to the Cysticercus stage (partly after R.
Leuckart). a, egg with embryo ; 6, free embryo ; c, rudiment of the head as a hollow papilla
on the wall of the vesicle ; d, bladder- worm with retracted head ; e, the same with protruded
head, magnified about four times.

and grow into large vesicles with liquid contents and a contractile
wall. The vesicle gradually becomes a cystic or bladder worm by
the formation of one (Cysticercus^ Fig. 205, e) or several (Coenurus)
hollow buds, which are developed from the walls and project into the
interior of the vesicle (Fig. 205, c). The armature of the tape-worm
head (suckers and double circle of hooks) is formed on the inside
and at the bottom of this invagination of the wall of the vesicle
(Fig. 205, d). When these hollow buds are evaginated so as to form
external appendages of the vesicle, they present the form and
armature of the Cestode head, as well as a more or less developed

* The habit of allowing dogs to lick the face and to feed off plates which
their owners use is, to say the least of it, an unclean one, and should be
avoided.

t Exceptionally two or more heads are found in some Cysticercus forms.

CESTODA.

253

neck, which presents even at this stage traces of segments (Fig.
205, e). The head and neck together constitute the scolex. In some
cases (Echinococcus) the irregularly shaped maternal vesicle produces
from its internal walls one or two generations * of secondary vesicles
which project into it ; and the Cestode heads originate' in special
small brood-capsules on these secondary vesicles (Fig. 206, a). In
such cases the number of tape-worms which arise from one embryo

FIG. 206.— a, brood-capsule of Echinococcus with developing heads (after R. Leuckart). fo, brood-
capsule of Echinococcus (after G. Wagener). c, heads of Echinococcusstill connected with the
wall of the brood-capsule— one is evaginated ; Vc excretory canals.

is naturally enormous, and the parent vesicle may reach a very
considerable size, being sometimes as large as a man's head. In
consequence of this enormous growth the vesicles frequently obtain
an irregular shape ; while on the other hand, the tape-worms which
are developed from them remain very small, and carry, as a rule,
only one ripe proglottis (Fig. 207). The cyst in which the bladder-
worm lies, and which is caused by it, is called an hydatid cyst.

* In Cysticerci (C. longicollis, tenuicollis) also, sterile daughter vesicles are
sometimes budded off.

254

PLATYHELMINTHES.

So long as the tape-worm head (scolex) remains attached to the
body of the bladder-worm and in the host of the latter, it never
develops into a sexually mature tape-worm ; although in many cases
it grows to a considerable length (Cysticercus fasciolaris of the
house-mouse). The bladder-worm must enter the alimentary canal
of another animal before the head (scolex) can, after separation from
the body of the bladder-worm, develop into the sexually mature
tape-worm. This transportation is effected passively, the new host
eating the flesh or organs of the Animal infected with Cysticerci.
The tape-worms, therefore, are principally found in the Carnivora,

the Insectivora, and the Omnivora, which receive the

bladder-worms in the flesh of the animals on which

they feed. The vesicles are digested in the stomach,

and the cestode head becomes free as a scolex. The

latter is, perhaps, protected from the too intense

action of the gastric juice by its

calcareous concretions, and at

once enters the small intestine,

fastens itself to the intestinal

wall, and grows by gradual seg-

mentation into a tape -worm.

From the scolex the chain of

proglottides proceeds as the re-

sult of a growth in length

accompanied by segmentation, a

Fig. 2Q7.-Taenia process which is to be looked FIG 208.-C^fcem>id of

°f aS6XUal

Sr T °Le7c-

kart), magnified duction (budding in the direction

12 to 15 times. Qf

Taenia cucumerina, mag-
nified 60 times (after R.
Leuckart).

ment of the scolex is then to be explained as a metamorphosis,
characterized by the individualization of certain stages of the
development. But the whole life-history is a case of metagenesis,
inasmuch as the sexual proglottides alternate with the asexual scolex.
The development of some tape-worms (Microtaeniinae) presents
considerable simplifications. In the cysticercus stage the vesicle is
represented by a small appendage (Fig. 209, b), in which the cavity
is much reduced or absent. Such cysticercus forms are called
Oysticercoids, in which an appendage bearing the embryonic hooks
is distinct from a larger part which represents the scolex (Fig. 210).
Cysticercoids are found principally in Invertebrates (Gammarids,
Cyclops, Insects, Slugs, Oligochaetes).

CESTODA.

255

The tape-worms found in herbivorous animals are probably
derived from the Cysticercoids of Invertebrates,- but the inter-
mediate host is generally unknown. The same may be said of
the tape-worms of birds, only in this case the intermediate host
is more often known.

In some cases the caudal appendage, which is the homologue of
the vesicle of the Cysticerci, is elongated (Fig. 210), and the
Cysticercoids then present a considerable resemblance to the Cercaria
of a Trematode. If this comparison is a just one, as it probably is,
the Cysticercoid must be regarded as a more primitive larval form
than the Cysticercus. Moreover Caryophyllaeus (Fig. 212) with its
single set of generative organs and unsegmented body is probably
the most primitive member of the group, and may be compared to
the ordinary sexual Trematode.

a

FIG. 209. — a, Echinococcus-like Cyst from
the body -cavity of the earth-worm
(after *E. Metschnikoff), containing
three Cysticercoids ; b, Cysticercoid
with evaginated head.

FIG. 210. — Cysticercoid of
Taenia sinuosa from Gam-
marus pulex (after Ha-
mann).

Amphilina (Fig. 213) and Amphiptyches are forms intermediate
between the Trematodes and Cestodes, while Archigetes (Fig. 211)
is either the most primitive Cestode, or a larval form which has
become sexually mature. All the other Cestodes differ from the
primitive Caryophyllaeus in the fissive reproduction which the body
undergoes in the process of strobilization. The only part of the
body which is not reproduced in this asexual increase is the organ
of attachment; just as in the Scyphistoma (Fig. 132, g) all the
organs of the body participate in the fission by which the epliyrae
arise except the stalk of attachment. Finally it must be pointed
out, that on this view Ligula is not a primitive, but a highly

* Verh. d. Peter sburger Naturforsch. , 1868, Zool., p. 263.

256

PLATYHELMINTHES.

specialized form, in which the sexual persons produced by division
have lost their distinctness and do not separate from the colony.
In other words, Ligula bears the same relation to a sharply seg-
mented tape-worm that a hydroid colony with medusoids bears to
a colony which buds off free-swimming medusae. Bothriocephalus,
in which the segments separate off in groups (Fig. 214), may be
regarded as a stage on the road to the condition found in Ligula.

Fam. 1. Cestodariidae. The body is unsegmented and the generative organs
are not repeated. Archigetes Lkt. A. Sieboldii Lkt. (Fig. 211), in the body-
cavity of the generative segments of Tubifex rivulorum, about 3 mm. long, with
caudal appendage (? Onchosphere) which carries three pairs of small hooks at its
free end. The anterior end of the body has two weak suckers.
Life-history unknown. The only Cestode which attains sexual
maturity outside the Vertebrata. It is to be regarded as a
Cestode retaining the Onchosphere, and still fixed by the
embryonic hooks. Caryophyllaeus Mill!., elongated, no ex-
ternal distinction between head and body, without suckers ;
excretory opening at hind end ; genital pore on ventral surface
of hind end, receives the vas deferens, uterus, and vagina.
C. mutabilis Rud. (Fig. 212), intestine of Cyprinoids, asexual
form probably in Tubifex rivulorum. Amphilina Wagoner,
body-cavity of sturgeons, A. foliacca Rud. (Fig. 213). Body
flattened, Trematode-like, 60 mm. long, pointed at one end
which carries a sucker near by the opening of the uterus
(TJt.ni) ; the vagina (Vg) and vas deferens (C) open at the
other end; body -cavity of sturgeon; produces a partially
ciliated hooked embryo, life -history unknown. Gyrocotyle
Dies. (Amphiptyches Wagener), alimentary canal of Holo-
cephali, a sucker at the anterior end, edge of body folded.
Uterus, vagina, vas deferens open separately ; G. urna W. ,
alimentary canal of Chimaera. The Onchosphere probably
passes into bivalves. Wageneria Monticelli, in Scymnus
nicaeensis.

Fam. 2. Bothriocephalidae. With only two suckers, which
are weak and flat. Generative organs usually open on the flat
surface of the proglottis. Proglottides are often detached in groups. Hydatid
stage represented by an encysted scolex (Fig. 215), which is usually found
in fishes. Bothridinm Blainv. (Solenophorus Creplin) intestine of pythons and
boas ; Diplocotyle Krabbe, intestine of fishes ; Diphyllobothrium Cobbold,
intestine of dolphin ; Ptychdbothrium Lonnberg ; Duthiersia Perrier, from
Varanus.

Bothriocephalus Brems. Segmented body. Head with two pits, without
hooks. The genital openings are on the middle of the ventral surface. The
young stage usually in fishes. B. latus Brems. (Fig. 214), the largest of the
tape-worms parasitic in man, twenty-four to thirty feet in length, principally
found in Russia, Poland, Switzerland, and South France. The sexually mature
segments are broader than they are long (about 10-12 mm. broad and 3-5 mm.
long). They do not become detached singly, but in groups (Fig. 214). The
segments of the hindermost portion of the body are, however, narrower and

Fio.211.— Archi-
getes Sieboldii
Lkt. (after
Leuckart).

CESTODA.

257

longer. The head is club-shaped, and is provided with two slit-like pits. The
cortical parts of the lateral regions of the body contain a number of round
masses of granules, the yolk-glands (Fig. 216, Dst), the contents of which are
poured into the shell glands (coiled glands) through the so-called yellow ducts.

The genital openings lie close together, one behind the other, in the midst of
the segment (Fig. 216, a). The anterior and larger belongs to the mal/generative
apparatus, and leads into the muscular terminal portion of the vas deferens,
which is enclosed in the cirrus sheath (Fig. 216, Ob), and can be evaginated
as the cirrus. The vas deferens just before its entrance into the cirrus pouch

D.st,

FIG. 212.—Caryoi)hyllaeus muta-
Ulis (after V. Carus). W ex-
cretory canal ; H testes ; Vd
vas deferens ; Vs vesicula
seminalis ; P penis ; Ov ovary ;
D yolk - gland ; Dg duct of
yolk gland ; Ut uterus ; Rs
receptaculum seminis.

~JC.se

FIG. 213. — AmpMlina foliacea, showing
the generative ducts. S.g sucker; Ut.m
opening of uterus; D.st yolk-gland;
K.st ovary"; Vg opening of vagina ; C
opening of vas deferens (after Wagener).

is dilated (Fig. 216, b) to form a large muscular swelling (the vesicula seminalis?).
It then becomes coiled, and passes in the direction of the long axis of the
segment on the dorsal surface and divides into two side branches. These
receive the efferent canals of the delicate testicular sacs, which occupy the
lateral parts of the middle layer (T). The female genital opening (Fig. 216)
leads into a vagina ( Va] situated behind the pouch of the cirrus, and frequently
filled with semen. This vagina runs as a tolerably straight median canal on the
ventral surface, and opens by a short, narrow tube into the oviduct. The
vagina also functions as a receptaculum seminis. There is yet a third opening

s

258

PLATYHELMINTHES.

FIG. 214,—BothriocepMlus latus (after
Leuckart).

FIG. 215. — Encysted larva of Bothrio-
cephalus from the Smelt (after
Leuckart).

(Fig. 216, a), situated at some distance behind
the other two ; this is the opening of the
tubular uterus (Ut), the convolutions of
which give rise to a peculiar rosette-shaped
figure in the midst of the segment. Close
to the hind end of the segment the ducts of
the yolk-glands (Dst] and of the ovaries (Ov)
unite with each other and open into the
uterus ; the cells of the shell -gland (Sd)
surround and open into the point of junction
of these»structures.

The ova are for the most part developed
in water, and escape from the upper pole of
the egg-shell through a lid-like valve (Fig.
204). The escaped embryo is covered with
cilia (Fig. 203), by means of which it swims
about for a long time. The encysted larval
form (scolex without a bladder) is found
between the muscles or in the viscera of the
pike, turbot (Lota vulgaris), and possibly of
other fresh-water fish (Fig. 215). How they
become infected is not known, as experiment
tends to show that the ciliated larva does not
enter them directly, and no intermediate host
is known. The scolex enters the body of its
final host in the flesh of the fish. B. cordatus
Lkt. With large, heart-shaped head, without
a filiform neck ; with deposits of numerous
calcareous bodies in the parenchyma. It
attains a length of about three feet, and
lives in the intestines of man and of the
dog in Greenland. B. liguloides Lkt. Young
form about 20 cm. in the subperitoneal tissue
of man in China and Japan.

ScMstocephalus Crepl. Head split, with a
sucker on each side. The body of the cestoid
form is segmented. S. solidus Crepl. Lives
in the body cavity of the stickleback, escapes
into the water, and becomes sexually adult
in the intestine of water-birds. Triaeno-
phorus Rud. Head not distinct, with two
weak suckers and with two pairs of triden-
tate hooks. The body has no external seg-
mentation. The generative openings are
marginal. T. nodulosus Rud. In the intes-
tine of the pike. Asexual encysted form in
the liver of Cyprinus. Bothrimonus Duver-
noy, intestine of sturgeon.

Ligula Bloch. Body band-shaped and un-
segmented. Without real suckers. Hooks
may be present or absent. The Cestoid has

CESTODA.

259

no segmentation, but the generative organs are repeated. They live in the
body cavity of Teleosteans and become sexually mature in the intestine of
birds. L. simplicissima Rud., in the body cavity of fishes and in the intestine
of aquatic birds. L. tuba v. Sieb., in the intestine of the tench.

Fam. 3. Tetrarhynchidae. Head with two or four suckers, and with four
protractile proboscises armed with hooks (Fig. 217) ; genital openings marginal.
The scolices live encysted in bony fishes, and the sexual worms in the intestine
of skates and rays. Tetrarhynchus Cuv., with four suckers ; Rhynchobothrium
Blainv., with two suckers.

Fam. 4. Echinobothridae. With two suckers and two armed proboscises ;
genital openings marginal. Echinobothrium v. Ben.

Fam. 5. Tetraphyllidae. Head with four very mobile suckers often armed
with hooks. Proglottides detached singly. Genital pores marginal. In the
intestines of Selachians.

FIG. 216.— Generative organs of a sexually mature proglottis of Bothriocephahis latus (after
Sommer and Landois) ; a, from the ventral surface ; 6, from the dorsal surface. Ov and v
ovary ; Ut uterus opening to the exterior independently of the vagina ; Sd shell-gland ;
Dst vitellarium (yolk -gland) ; Va vagina with opening; T testes ; Cb pouch of the cirrus;
Vd vas deferens.

Sub-fam. 1. Phyllobothrinae. Suckers without hooks, more or less
stalked. Echeneibothrium v. Ben.; Phyllobothrium v. Ben., suckers sessile;
Anthobothrium v. Ben.

Sub-fam. 2. Phyllacanthinae. Suckers armed, each with 2 or 4 hooks.
Acanthobothrium v. Ben. ; Calliobothrium v. Ben. ; Onchobothrium Blainv.
Fam. 6. Taeniadae. The armature of the head consists of four muscular
suckers, to which is frequently added a single or double circle of hooks on
the rostellum. The proglottides have a marginal sexual opening. The vagina
is usually long, and enlarged at the internal end to form a receptaculum seminis
(Fig. 201). The uterus is without a special opening to the exterior. The young
stages are Cysticerci or Cysticercoids, rarely quite without caudal vesicle.
Parasitic in warm and cold-blooded animals.

Sub-fam. 1. Cystotaeniinae. Rostellum usually with double row of

260

PLATYHELMINTHES.

hooks. Development by means of Cysticerci (bladder -worms). Both
bladder-worm and tape-worm stage in mammals. Taenia L. (Cystotaenia
R. Lkt). The vesicles of the Cysticerci are large. The heads arise from
the bladder of the Cysticercus.

T. solium. L. 2-3 metres long. A double circle of 26 hooks. The ripe
proglottides are 8-10 mm. long and 6-7 mm. broad ; the uterus has 7-10
dendritic branches (Fig. 202). It lives in the human intestine. The
bladder-worms belonging to it (Cysticercus cellulosae) live principally in
the dermal cellular tissue and in the muscles
of pigs, but also in the human body (muscles,
eyes, brainj, in which self-infection with them
is possible if a Taenia is present in the digestive
canal ; more rarely in the muscles of the roe-
deer, the dog, and the cat. In the human brain
the Cysticercus acquires an elongated form, and
sometimes does not produce a head.

T. saginata Goeze = mediocanellata Kiichenm.,
in the intestine of man, distinguished by the
older helminthologists as a variety of T. solium.
Head without circle of
hooks or rostellum, but
with four more power-
ful suckers. The tape-
worm reaches a length
of four metres, and
becomes much stronger
and thicker. The ma-
ture proglottides are
about 18 mm. long
and 7-9 mm. broad.
The uterus forms 20-35
dichotomous side
branches (Fig. 202).
The Cysticercus lives
in the muscles of the
ox (Fig. 218). It ap-
pears to be principally
distributed in the
warmer parts of the
Old World, but is
often found in great numbers in many places in the north. It is the
common tape-worm of the Abyssinians.

T. serrata Goeze, in the intestinal canal of the dog. The Cysticercus
is known as Cysticercus pisiformis in the liver of the hare and rabbit.
T. crassicollis Hud. in the cat, with Cysticercus fasciolaris of the common
mouse. T. marginata Batsch. of the dog (butcher's dog) and wolf with
Cysticercus tenuicollis from ruminants and pigs, and occasionally in man
(Cyst, visceralis}. T. crassiceps Rud. in the fox with Cysticercus longicollis
from the thoracic cavity of the field-mouse. T. coenurus v. Sieb. in the
intestine of the sheep-dog with Coenurus cerebralis in the brain of one-year-
old sheep causing staggers. The presence of Coenurus in other places has

FIG. 217.— Scolex of Tetrarltyn-
chus ruficollis, showing the four
hooked proboscises protruded
and two of the suckers (after
van Beneden).

Fio. 218. — Cysticercus of
Taenia sngi nata (medioca-
ncllata), magnified about
eight times. The head is
protruded (from Glaus).

CESTODA. 261

been stated, as for instance, in the body cavity of the rabbit. T. tenui-
collis Rud. in the intestine of the weasel and the pole-cat, with a Cysticercus
which, according to Kiichenmeister, lives in the hepatic ducts of the field-
mouse.

Echinococcifer "Weinl. The heads bud on special brood-capsules in such
a way that their imagination is turned towards the lumen of the vesicle
(Fig. 206). T. echinococcus v. Sieb. (Fig. 207) in the intestine of the dog,
3-4 mm. long, forming but few proglottides. The hooks on the head are
numerous but small. Its bladder-worm is distinguished by the great thick-
ness of the stratified cuticula. It lives as Echinococcus principally in the
liver and the lungs of man (E. hominis), and of domestic animals (E. veteri-
norum). The first form is also distinguished as E. altricipariens on account
of the frequent production of primary and secondary vesicles ; it usually
reaches a very considerable size, and has a very irregular shape ; while that
form which inhabits domestic animals, E. scolicipariens, more frequently
retains the form of the simple vesicle. Finally these echinococcus cysts
frequently remain sterile, in which case they are called Acephalocysts.
Another, and indeed pathological form is the so-called multilocular Echino-
coccus, which was for a long time taken for a colloid cancer. It is also
found in mammalia (in cattle), and here presents a confusing resemblance
to a mass of tubercles. The echinococcus disease (hydatid plague] was
widely spread in Iceland. This disease likewise seems endemic in many
places in Australia.

Sub-fam. 2. Microtaeniinae. The rostellum is frequently absent, or
unarmed, or beset with small hooks. Development by means of Cysticercoids,
the vesicle having but little fluid, or being absent. The Cysticercoid lives
principally in invertebrates (slugs, insects, &c.), more rarely in cold-blooded
vertebrates (the tench).

Sub-genus Dipylidium Leuck. With two sets of generative organs in
each segment. T. cucumerina, Bloch, in the intestine of dogs (house dogs).
The Cysticercoid is entirely without the caudal vesicle, and lives (according
to Melnikoff' and R. Leuckart) in the body cavity of the dog-louse (Tricho-
dectes canis). The infection with the Cysticercoids takes place when the
dog swallows the parasites which are annoying him, while the parasites
swallow the eggs contained in faeces adherent to the hair of the dog.
Nearly allied is T. clliptica, Batsch. in the intestine of the cat, occasionally
in that of man .

Sub-genus Hymcnolepis Weinland. One set of generative organs in each
segment, opening on one side ; eggs with two smooth shells. T. nana
Bilh.-v. Sieb., in the intestine of the Abyssinians and in Sicily, hardly an
inch long ; probably identical with T. murina of the rat, the Cysticercoid
of which, according to Grassi and Rovelli, is able to develop in the
intestinal villi of its host, and then emerge to form a tape-worm in
the intestine (self-infection). T. flavopunctata Weinl., in the human in-
testine (North America). Also found by Grassi in Italy, and regarded as
identical with T. diminuta Rud. = leptocephala Crepl., of the rat. The
Cysticercoids of the meal-worm are probably developed into tape-worms
in the intestines of mice and rats.

In other partially unarmed Taenias* the generative organs and develop-
ment are as yet not accurately known ; such are— T. (Anoplocephala

* See note on following page.

262 PLATYHELMINTHES.

R. Bl.) perfoliata Goeze, and T. plicata Rud., in the horse ; T. (Moniczia
R. Bl.) pectinata Goeze, in the hare; T. dispar Rud., in the frog; T.
(Ctenotaenia R.) expansa Im., in the ox.

There is a special section of Taenias,* in which the genital opening is on the
broad surface of the segment : such are T. litterata Batsch. ; T. lineata Goeze,
in the intestine of the dog. To another group belong Taenias from the gut of
birds, e.g. T. simiosa Zed., in the goose and duck; T. tenuirostris from
Merganser and Anas, both with tailed Cysticercoids in Gammarus.

* A number of new genera have been recently created for the reception of
species formerly united under Taenia: mde A. Railliet, "Notices parasitolo-
giques," Bull. Soc. Zool. France, 1892 ; and R. Blanchard, Mem. de la Soc. Zool.
de France, 4, 1891, p. 420.

CHAPTER VI.

PHYLUM ISTEMERTEA.*

Elongated, vermiform animals ivith a ciliated ectoderm, and an
eversible proboscis lying in a sheath on the dorsal side of the enteron.
With mouth and anus, simple gonads, and a vascular system. Dioecious.

The position of the Nemertea is difficult to settle. Formerly they were united
with the Platyhelminthes, but the presence of an anus, and of a vascular system,
and the higher organization of the organs and tissues in general, renders it
advisable, for the present at any rate, to place them in a separate phylum,
allied to the Platyhelminth phylum but not part of it. It has been suggested
that the proboscis of Nemertines is homologous with the retractile anterior part
of the body found in some Turbellaria, particularly Prorhynchus. The general
structure of the Nemertine tissues strongly recalls that of

The Nemertea are elongated worms, some of them attaining an
immense length, and are found in the sea, in fresh water, and on
land. The marine forms are, however, by far the most numerous.
They are often brilliantly coloured, and many of them have the
power of forming a tube around their bodies by the mucous
secretion of the skin. The body is excessively contractile, so much
so that a worm which is measured by yards when extended may
shrink to a length of as many inches. The mouth is large and
placed on the ventral surface of the anterior end of the body. It
leads into a straight alimentary canal consisting of oesophagus and
intestine. The latter opens posteriorly by a terminal anus, and
possesses lateral caeca which are generally, but not always, regularly
arranged in pairs ; it also gives off from its front end an anteriorly-
directed caecum.

The most characteristic organ of the group is the proboscis. This

* W. C. Mclntosh, A Monograph of British Annelida, Ft. 1, "Nemerteans,"
Ray Society, 1873-4. A. A. W. Hubrecht, "Unters. lib. Nemertinen a. d.
Golf v. Neapel," Niederl. Arch. f. Zoologie, 2, 1874. Id., "The Genera of
European Nemertines critically revised," Notes from the Leiden Museum,
1879-80. Id., "Report on the Nemertea," Challenger Reports, vol. 19, 1887.
0. Burger, "Die Enden des exkretorischen Apparates bei den Nemertinen,"
Zeit.f. w. Zoologie, 53, 1891. 0. Burger, "Die Nemertinen," Fauna u. Flora
des Golfes von Neapel, 22, 1895.

264

NEMERTEA.

lies in a sheath (Fig. 219 bis) which is placed on the dorsal side
of the gut, and extends in most forms along the whole length of
the body. It is a hollow tubular organ, opening nearly always at the
front end* of the body, but closed behind. In the retracted state

rsh.

FIG. 219 bis. — Diagram showing the proboscis of
an armed Nemertine in its relation to its sheath
(from Lang). A, in the retracted condition ;
B, in the protruded state, r proboscis ; rs pro-
boscis sheath ; rsh rhyncocoelom ; st spine ;
gd cavity of the posterior non-eversible part 01
the proboscis ; rm retractor muscle.

FIG. 219.— Tetrastemma obscurum
(after M. Schulze). Young
specimen about 3 lines in
length ; 0 mouth ; D intestine ;
A anus ; Bg blood-vessels ; R
proboscis armed with stylet;
Ex lateral trunks of the excre-
tory system ; P excretory pore ;
G lateral organ ; Nc nerve
centre ; Ss lateral nerve cords ;
Oc eyes.

the proboscis lies in its sheath, to the hind end of which its blind
end is fastened by a muscular band (Fig. 219 bis, A}; its walls
contain both transverse and longitudinal muscles, the latter of
which are continued into the band. The proboscis sheath also

* In Akrostomum, Malacobdella, etc., the opening of the proboscis is within
the mouth.

NEMERTEA.

265

has muscular walls, and contains a corpusculated fluid; it contains
a closed cavity (rhynchocoelom), and its epithelioid lining is
continuous anteriorly with that covering the outer side (in the
retracted state) of the proboscis, i.e. with the epithelium on that
surface of the retracted proboscis which is in contact with the
proboscis-sheath fluid. The proboscis and its sheath may therefore

N

FIG. 220.— A young Pelagowmcrtes Rollestoni, dorsal view (after Hubrecht, from Perrier). P pro-
boscis ; G sheath of proboscis ; I intestine ; D diverticula of intestine ; C cerebral ganglia ;
N lateral nerve cords ; V lateral vessels ; 0 ovaries : A anus ; m longitudinal muscles ;
t transverse muscles.

be compared to the finger of a glove, of which the free end is
pulled in upon the portion next the hand, the pulling in being
effected by a string attached to the inner side of the tip of the
glove, and lying inside the finger. From the above description it
will also be clear that the epithelium lining the inner surface of the
retracted proboscis is*continuous with the surface ectoderm of the

266 NEMBRTEA.

body at the anterior opening, and becomes external when the proboscis
is projected by eversion (Fig. 219 Us, B). The eversion is no doubt
caused by the contraction of the muscular wall of the sheath bringing
pressure to bear upon the contained fluid, and, when completed, the
middle portion of the retracted proboscis is at the front end of the
protruded organ. That is to say, the hinder part of the proboscis is
not eversible : it lies within the protruded part of the proboscis in
the projected state, and in the hinder part of the sheath in the
retracted state. This non-eversible portion has glandular walls and
contains a fluid. In the armed forms (Hoplonemertini) it is separated
from the eversible part by a contraction of its cavity, which almost
closes up the eversible part, and a stylet, to which may be added two
groups of small accessory reserve stylets, is placed at this point.
The posterior part of the proboscis opens by a narrow aperture at
the base of this stylet, and allows the contents of the glandular
non-eversible part, which is very possibly poisonous, to exude.
When the proboscis is completely everted the stylet projects freely
at its apex.

In the unarmed forms (Anopla) the stylet is absent, but the
surface of the proboscis which becomes external on eversion possesses
numerous nematocysts. The proboscis is therefore clearly offensive,
but very possibly it also possesses a tactile function.

The body-wall varies in structure in the different orders. It
always possesses an external layer of ciliated ectoderm cells con-
taining mucus -secreting gland-cells. Within this there is in the
Heteronemertini (1) a thin basement membrane, (2) a cutis con-
taining connective tissue and some longitudinal muscular fibres, (3)
a layer of longitudinal muscular fibres, (4) a thin layer of a plexiform
nervous matter containing at two points the lateral nerve-cords, (5)
a layer of circular muscular fibres, and (6) of longitudinal muscles;
this is followed by a compact mass of reticular connective tissue
which passes into the muscular coats of the intestine and proboscis
sheath. In other Nemertini there are only an external circular and
internal longitudinal muscular layer. All the layers above mentioned
are embedded in a gelatinous albuminoid material, which is especially
developed in the transparent pelagic form, Pelagonemertes, and is of
the same nature as the jelly of Medusae. There is therefore no
body cavity in ISTemertines, though, as in Rhabdocoeles, spaces in
the connective tissue may in some cases be so large as to simulate
one.

The nervous system consists of two cerebral ganglia connected

NEMERTEA.

267

above and below the proboscis sheath and each divided into two
lobes, a dorsal and ventral. The ventral lobes are continued back-
wards as the lateral nerve-cords (Fig. 221), which in some, cases
unite posteriorly above the intestine by a supra -anal commissure.
The dorsal lobe (Fig. 221, O) is partly or completely divided into an
anterior and posterior lobe. In the armed forms (Fig. 221, L) this
third lobe is com-
pletely separated off
and united with the
anterior only by
nerves. This pos-
terior part of the
dorsal lobe contains
in nearly all forms
an epithelium - lined
cavity which com-
municates with the
exterior by a fine
ciliated tube. The
latter opens, in the
forms with head-slits,
into the slits, in the
other forms on the
side of the head.
The whole apparatus
including the brain
lobe constitutes the
lateral organs, or as
it is sometimes called,
the cerebral organs.
The central nervous
system lies in Cari-
nella outside the
muscular layers ; in
the Heteronemertini
between the external

longitudinal and the circular layer; and in the Metanemertini com-
pletely within the muscles. In all, except the Metanemertini^ in
which the central nervous system gives off nerve-cords, there is a
complete nerve-sheath of a reticulate nervous substance, occupying
the same position with regard to the muscles as do the central

FIG. 221.— Diagram of the nervous system of Drepanophorus
Lankesteri (from Perrier after Hubrecht). C dorsal lobes of
the cerebral ganglia ; t nerves of the proboscis ; s sensory
nerves of head ; ce stomatogastric nerves ; L posterior part
of the dorsal lobes of the brain in which are the lateral
organs ; 0 opening of lateral organ ; n peripheral nerves ;
T lateral nerve-cords ; v, k transverse commissures.

268

NEMERTEA.

-ecs.

organs. The lateral nerve-cords are thickenings of this sheath, and
there is a median dorsal thickening constituting the proboscis nerve.

In Heteronemertini the central organs are impregnated with
haemoglobin. As sense organs there are the lateral organs above
mentioned, the tactile hairs of the ectoderm cells, cephalic eyes
more or less numerous, and sometimes provided with refractive

bodies. Exceptionally, as in
Oerstedia pallida, two oto-
lithic vesicles are found on the
brain.

The vascular system consists
of three longitudinal vessels
with contractile walls placed
just outside the intestinal wall ;
one of them is straight and
dorso- median, and the other
two are sinuous and lateral.
They communicate in front and
behind ; and anteriorly the
lateral vessels often dissolve
themselves in a network of
vascular spaces on the oeso-
phagus. The longitudinal
vessels give off lateral branches,
which no doubt open into a
system of lacunae in the tissues.
The blood is usually colourless,
but in some species it is red.
In Amphiporus splendens and
Borlasia splendida, the red colour (haemoglobin) is contained in
the blood corpuscles.

The excretory organs consist of two lateral tubes, which lie close
to the lateral vessel, and open externally by one, or rarely by several
openings on each side. They are confined to the anterior region
of the body, usually not extending further back than the oesophagus
(fore-gut). These tubes have a glandular ciliated lining, and in some
forms, possibly in all, give off branches which themselves branch
and finally end in small swellings, containing a long flame-shaped
cilium. These flame-cell ends are said to differ from the corre-
sponding structure in Turbellaria by consisting of many cells. As
already pointed out, this distinction is probably unimportant,

PIG. 222.— Lateral organ of Drepanophorus
cerinus (after Burger, from Perrier). e ecto-
derm ; b basement membrane ; v canal of the
organ ; dg dorsal lobe of cerebral ganglion ;
n nerve connecting dg to its posterior lobe ;
c point of division of the canal into a glan-
dular tube dc, which projects back behind
the [brain and into a canal cs which passes
into the dilatation s in the posterior lobe ;
ecs epithelium of the sac ; pi pigment.

NEMERTEA.

depending merely on the size of the organ. The flame-cell knobs-
of JNemertines sometimes project into the blood-vessels, but do not
open into them. In the forms in which flame-cells have not been
observed, the excretory canals are said to open into the lateral blood-
vessels. This will probably turn out to be an error. The^ animals-
are generally dioecious, and the gonads quite simple, consisting of
paired sacs regularly placed between the gut caeca, or in some cases
more numerous than the caeca and irregularly arranged. They open
by simple openings on the dorso-lateral surface of the body.

Some genera are viviparous (Prosorochmus Claparedii, Tetrastemma
obscurum), but most of them lay eggs in albuminous strings. The
development is usually direct, but in many Heteronemertini the young
are hatched as helmet-shaped, free-swimming larvae (Fig. 223),,
known as Pilidium.

FIG. 223. — Pilidium (after E. Metschnikoff). a, free-swimming larva. 6, later stage, helmet-
shaped. E, E1 the two pairs of ectodermal invaginations ; D alimentary canal.

The Pilidium was formerly described as a species of a supposed
independent genus. The enteron is formed by the invagination of
the wall of a hollow blastosphere ; the blastopore forms the larval
mouth ; at the aboral pole a long flagellum is developed, and a
broad lobe grows out on each side of the mouth, on to the edges
of which the circumoral ciliated band extends. By an elaborate
metamorphosis this larva turns into the young worm.

Asexual reproduction is unknown, but the power of repair is great.
In some cases the body readily breaks up into pieces when touched,
and the pieces have the power of developing the whole.

The ISTemertines live principally in the sea, under stones in the

270

NEMERTEA.

R

mud, but the smaller species swim freely. There are also forms
which live on land (Geonemertes), fresh-water forms (species of
Tetrastemma), and a pelagic form (Pelagonemertes). Certain species
form tubes and passages which are lined by a slimy secretion. The
food of the larger species principally consists of tubicolous worms,

which they extract by
their proboscis. There are,
however, parasitic (or com-
mensal) Nemertines, which
infest Crustacea, or live on
the mantle and gills of
Mollusca. In this case
they are, like the Hiru-
dinea, furnished with a
posterior sucker (Malacob-
della).

Order 1.
PROTONEMERTINI.

Am

FIG. 224.— Later stage of Pilidium, with tuft of cilia
and enclosed Nemertine (after O. Biitschli); Oe
oesophagus ; D alimentary canal ; Am amnion ;
R rudimentary proboscis of the Nemertine ; So
lateral pit.

The cerebral ganglia and
lateral nerves are outside the
dermal muscles, either in the
ectoderm or beneath the dermis.
The body-wall consists of the
ectoderm, a dermis, an external
circular and an internal longi-
tudinal layer of muscles, between which is usually interposed a diagonal layer.
The mouth is behind the brain. There is no caecum. The proboscis is without
stylets.

Fam. 1. Carinellidae. The lateral organs have the form of epithelial pits
or canals, which only exceptionally perforate the dermis and penetrate into
the brain ; they have no relation to the lateral vessels. There is no dorsal
vessel. The brain and lateral nerves lie in the epithelium or beneath the
dermis. The dermis is homogeneous and has a gelatinous appearance. Carinella
Mclntosh.

Fam. 2. Hubrechtidae. The lateral organs are spherical structures which
lie deep within the body-wall and project into the lateral vessels. Brain and
lateral nerve-cords lie beneath the dermis, which is reticular. There is a dorsal
vessel. The excretory organs constitute a richly-branched canal - system.
Hubrechtia Burger.

Order 2. MESONEMERTINI.

The lateral nerves lie in the dermal muscular layer. Body- wall as in Order 1.
Mouth behind the brain. No caecum. The proboscis is without stylets.

Fam. 1. Cephalothricidae. The lateral nerves are in the longitudinal
muscles. Lateral organs, and cephalic slits absent. Carinoma Oudemans ;
Cephalothrix Oersted.

METANEMERTINI. 271

Order 3. METANEMERTINI.

Brain and lateral nerves lie within the dermal muscles in the body-
parenchyma. The body-wall is as in previous orders. Mouth in front of the
ganglion. The mouth and the proboscis usually open together. The proboscis
as a rule has stylets, and there is almost always a caecum given off from the
anterior end of the intestine, and projecting forwards.

A. PKORHYNCHOCOELOMIA. With long and thin body, which coils itself
in complicated windings. They do not swim. The proboscis is much shorter
than the body.

Fam. 1. Eunemertidae. Usually several small eyes. No otocysts. Only
one stylet. Slow in movement. Eunemertes Vaillant ; Nemertopsis Burger.

Fam. 2. Otptyphlonemertidae. Eyes absent. One, rarely two pairs of
otocysts, ventral to brain. The body is more cylindrical than flat. The worms
belonging to this family are small (1-3 cm.). Ototyphlonemertes Diesing.

B. HOLORHYNCHOCOELOMIA. Usually with short body. Some of them
swim. The proboscis is at least as long as the body. The proboscis sheath
always reaches into the hinder third of the body.

Fam. 3. Prosorhochmidae. With four eyes. Gut-pouches and gonads
alternate with one another. The lateral organs are very small, in front of
the brain. Usually hermaphrodite. Prosorlwchmus Keferstein ; Prosadenoporus
Burger ; Geonemertes Semper, terrestrial form.

Fam. 4. Amphiporidae. Body when extended comparatively short and wide.
Extensile part of proboscis thick and covered with adhesive papillae. The gonads
and gut-pouches do not, as a rule, strictly alternate. The gut-pouches are
branched. There are almost always numerous eyes. Amphiporus Ehrbg. ; A.
lactifloreus Johnst. Lives under stones and is distributed from the North Sea
to the Mediterranean. Drepanophorus Hubrecht.

Fam. 5. Tetrastemmidae. The body is, as a rule, short (1-3 cm.). There
are almost always four eyes. The gut-pouches are not branched, and the gonads
alternate with them. The lateral organs are in front of the brain. For the
most part dioecious. Tetrastemma Ehrbg. ; T. obscurum M. Sch. , viviparous ;
Baltic ; T. agricola Will. Suhm. , terrestrial ; T. clepsinoides Duges, fresh-water,
North America, probably Europe, e.g., Cherwell at Oxford, T. lacustre Du
Plessis, Lake of Geneva. Oerstedia, Quatref.

Fam. 6. Neetonemertidae. Deep-sea forms, with short, broad bodies and
hind end flattened into a fin. They can swim. The mouth and proboscis
openings are separate. The presence of stylets has not been certainly shown.
Without eyes. Nectonemertcs Verrill ; Hyalonemertes Verrill.

Fam. 7. Pelagonemertidae. Body leaf-shaped, gelatinous, hyaline. Anterior
extremity broad and abrupt, posterior narrowed to a point. Digestive canal
with 13 pairs of lateral ramifications. Integument thin and hyaline, with a
thin muscular tunic immediately beneath it consisting of external circular and
internal longitudinal fibres. The viscera and tissues are embedded in the
hyaline gelatinous matter. Gonads open on the ventral surface. Nerve-cords
internal to the muscular coats. Free-swimming, pelagic. Pelagonemertes
Moseley (Fig. 220).

Fam. 8. Malacobdellidae. Parasitic forms. The body is short and provided
with a sucker at the hind end. Intestine coiled, without pouches. The

272 NEMERTEA.

proboscis is unarmed and opens with the mouth. There is a dorsal vessel, and
two lateral. The proboscis-sheath reaches to the anus. Malacobdella Blainv. ,
in the mantle-cavity of various marine Lamellibranchs.

Order 4. HETERONEMEKTINI.

The lateral nerves are in the dermal muscles ; they lie outside the circular
muscles. The body-wall consists of ectoderm, dermis, an outer longitudinal
layer of muscles (which is not present in the other orders), a circular and an
internal longitudinal muscular layer. The diagonal muscles, if present, lie
between the circular and outer longitudinal. The mouth is behind the brain.
There is no caecum. The proboscis is unarmed.

Fam. 1. Eupoliidae. There are usually no lateral cephalic slits. The canal
of the lateral organ opens either directly to the exterior, or into a shallow
ventral slit. Eapolia Hubrecht ; Poliopsis Joubin. ; Valencinia Quatrefages.

Fam. 2. Lineidae. The body is more or less flattened. There is a deep
longitudinal lateral fissure on each side of the head. A ciliated groove leads
from the bottom of the fissure into the posterior lobe of the ganglion. The
nervous tissue is tinged with haemaglobin. Development often by ciliated
larvae. Linens Sow. (Fig. 225) ; L. marinus Mont.; L. longissimus Sim., sea-
long-worm ; Borlasia Oken ; Euborlasia Vaill. ; Micrura, Ehrbg. ; Cerebratulus
Renier ; Langia Hubrecht, the margins of the body slightly frilled.

Fio. 2-25.—Lineus sanguineus (after Me Intosh).

CHAPTER VII.

PHYLUM NBMATHELMINTHES.

THE Nemathelminthes include three orders — the Nematoda, the
Nematomorpha, and the Acanthocephala — which have little else in
common than the round form of body and the parasitic habit.

The body is unsegmented, rounded, more or less elongated, tubular
or filiform, and both ends are, as a rule, tapered off. Appendages
are always wanting, as are, with few exceptions, movable bristles.
On the other hand, special organs for attack and attachment, such as
teeth and hooks, are not unfrequently present on the anterior end of
the body : and in some cases small suckers, which serve for attach-
ment during copulation, may be developed near the hind end. As
a rule the integument possesses a cuticular layer of relatively
considerable thickness, and the ectoderm is very generally reduced
to a nucleated granular layer, in which cell outlines are absent.
These features of the skin are probably correlated with the endo-
parasitic habit, for we find them in the Trematoda, and the ectoderm
of the Cestoda is, to say the least of it, much modified. In these
latter groups the ectoderm is even less conspicuous than in the
Nematlielminthes. There is a well-developed muscular layer, which
generally consists of longitudinal fibres only, but circular fibres are
also present in the Acanthocephala. A body -cavity is always present,
but it appears generally to be without an epithelial lining, and in
Nematoda, at least, is bounded on one side by the endodermal wall
of the alimentary canal. As to the nature of this body-cavity we
have little evidence except in the Acanthocephala, in which, from
its relation to the generative organs and duct in the female we may
infer it to be a coelom. It contains a vascular fluid, and in the
other orders it is probably a haemocoele. Blood vessels and
special respiratory organs are wanting. A nervous system is always
present, but it presents very different features in the three- orders.
Of sense organs there are often sensory papillae in the neighbourhood
of the mouth and genital openings, and eye spots are often present

274 NEMATHELMINTHES.

in the free-living forms. While in the Acanthocephala mouth and
alimentary canal are completely absent, the Nematoda and Nemato-
morpha possess a mouth at the anterior end of the body, an
oesophagus, and a straight digestive canal, which usually opens by
the anus on the ventral surface near the hind end of the body.
The excretory organs have various forms, and their nature is not
understood : there are no flame-cells. In the Nematoda they consist
of paired canals in the ectoderm, which open by a common pore on
the same surface (ventral) as the anus. In the Acanthocephala there
is a pair of organs which appear to be of the nature of nephridia.
The absence of cilia may be stated as a general characteristic of the
group ; but they are said to be present in the supposed nephridia of
the Acanthocephala.

With a few exceptions the Nemathelminthes have separated sexes,
and the male organs often open into the rectum and are provided
with copulatory spicula. The larvae and sexual animals are not
unfrequently distributed in two different hosts.

The majority of the Nemathelminthes are parasites either during
the whole period of their life or at certain stages. There are,
however, also free -living forms which often show the closest
relationship to the parasitic members of the group.

Class I. NEMATODA (THREAD-WORMS).*

Nemathelminthes, with mouth and alimentary canal. With longi-
tudinal muscles only, with lateral lines, without cilia. The vas deferens
opens into the rectum. They are principally parasites. Dioecious.

The Nematodes possess an extremely elongated thread-like body,
which may be provided with papillae at the anterior pole in the
region of the mouth, or with hooks and spines within the oral
cavity. The mouth leads into a narrow oesophagus, which usually
has thick muscular walls, a chitinous lining, and a triangular lumen,

* Besides the older writings of Rudolphi, Bremser, Cloquet, Dujardin,
compare Diesing, " Sy sterna helminthum," 2 Bde. Wien, 1850-51. Diesing,
"Revision der Nematoden," Wiener Sitzungsberichte, 42, 1860. Claparede,"Zte
la formation et de la fecondation des ceitfs chez les vers Nematodes," Geneve, 1856.
A. Schneider, "Monographic der Nematoden," Berlin, 1866. R. Leuckart.
"Untersuchungen uber Trichina spiralis," Leipzig and Heidelberg, 1866, 2nd
edition; also "Die menschlichen Parasiten," etc., torn. 2., Leipzig and
Heidelberg, 1876. C. Glaus, " Ueber Leptodera appendiculata," Marburg, 1868.
0. Biitschli, " Untersuchungen liber die beiden Nematoden der Periplaneta
orientalis," Zeitzschr. fur Wiss. ZooL, torn. 21., 1871. And "Beitrage zur
Kenntniss des Nervensystems der Nematoden," Archiv. fur MiTcr. Anatomic,
torn. 10. A. Goette, "Unters. z. Entwick. d. Wurmer" Leipzig, 1882. R.
Leuckart, "Neue Beitrage z. Kent. d. Ban u. d. Lebensgeschichte d. Nematoden,"
Leipzig, 1887. A. E. Shipley, "Nemathelminthes," Cambridge Natural History,
vol. 2, May, 1896.

NEMATODA.

275

a 0

and is frequently dilated behind to a muscular bulb (pharynx). In
certain genera (Rhabditis, Oxyuris\ the
chitinous lining of the pharynx is raised
into ridges or tooth-like prominences, to
which the radial muscles converge in the
form of conical bundles. According to
its function, the oesophagus is essentially
a suctorial tube, which pumps in fluids,
and by peristaltic action passes them on
to the intestine. The intestine follows
the pharynx, and opens by the anus not
far from the hind end of the body on
the ventral surface (Fig. 226). Its walls
are formed of cells and are non-muscular,
and are coated with cuticle both inside
and outside ; it may be reduced to a row
of perforated cells (Filaria). The ter-
minal portion, or rectum, has a special
investment of muscular fibres which
render it contractile. Muscular fibres
passing from the body-wall to the wall
of the rectum are also frequently present.
In certain Nematodes the anus may be
wanting (Mermis) ; and in some genera
(see p. 290) even the alimentary canal
undergoes degeneration.

Beneath the stiff cuticle, which is often
transversely ringed and is composed of
several layers, lies a soft granular nu-
cleated sub-cuticular layer (hypodermis),
which is without cell limits and is to be

. . P , i /. FIG. 226. — Oxyurls vermlcularis

regarded as the matrix of the former. (after R. Leuckart). a, female;
Beneath this lies the highly -developed o mouth; A anus; v genital

opening. 6, male with curved
muscular layer, which consists of band- posterior end. c, the latter en-

shaped or fusiform longitudinal muscles, larged ; sp spicnium. d.eggwith

A ° enclosed embryo.

The surface of the body may present

markings, as for instance polyhedric spaces and longitudinal ribs,

also processes in the form of tubercles, spines,* and hairs. Ecdyses,

* There may also be prominences of various kinds, and even in some cases a
complete covering of spines (Cheir acanthus Dies. = Gnathostoma Ow., Ch.
hispiduin Fedsch. ).

276

NEMATH ELMINTHES.

i.e., sheddings of the cuticular layer, seem only to occur in the young
forms. The muscles are each composed of a single cell, in which
two parts are distinguishable, — a clear, sometimes a granular proto-
plasmic portion (medullary substance), which projects into the
body-cavity and is often prolonged into processes; and an external
fibrillated layer (Fig. 227).

The ISTematodes may be distinguished as Meromyaria or Polij-
myaria, according to the arrangement of their muscular system.
In the Meromyaria the number of muscle-cells (which are arranged
according to definite laws) in the cross section is
small (eight), while in the Polymyaria their number
is considerable. In the latter the muscle-cells arc;
often connected together by transverse processes of
the medullary substance, which unite on the so-called
median lines to form a longitudinal cord.

In almost every case two lateral regions remain
free from muscles, and form the so-called lateral
lines or regions, which may equal in breadth the
neighbouring muscular regions. These lateral regions
are internal projections of the hypodermis, and are
formed of a finely granular nucleated substance, and
enclose a clear vessel containing granules. This
vessel is connected with that of the opposite side
in the anterior part of the body, and the two open
by a common transverse slit, the excretory pore, on
the ventral surface in the median line. The lateral
lines are regarded as the excretory organs* Median
lines (dorsal and ventral), accessory median lines
(sub-median lines), the latter being placed between
the principal median line and the lateral line, are
also to be distinguished. Cutaneous glands, in the form of uni-
cellular glands, have been observed principally in the region of the
oesophagus and in the tail.

The nervous system, owing to the difficulty which its investigation
offers, has only been satisfactorily recognized in a few forms. It
consists of a nerve ring (Fig. 228) surrounding the oesophagus, near
the anterior end of the body, in Asc. megalocephala just in front of

FIG. 227. -Muscle-
cell of a Nema-
tode.

* Hamann (Sitz. Ber. Akad. Berlin, 1891, p. 57) asserts that in Lecanocephalus,
in which the right canal only is present, the excretory canal is coiled, and ends
posteriorly in a small opening into the body-cavity. This statement needs
confirmation.

NEMATODA.

277

Sn-

.Rn.

the excretory pore, and sending off posteriorly six and anteriorly six
nerve trunks (Ascaris megalocepTiala). The two largest posterior
trunks run in the dorsal and ventral lines (N. dorsalis, ventralis),
the four smaller, two in each lateral line, to the extremity of the
tail ; while of the six anterior nerves, two run in the "lateral lines
(N. laterales), and four in the interspaces between the lateral and
median lines (N. submediani) ; they supply
the papillae around the mouth. The gan-
glion cells lie partly near, in front of and
behind the nerve ring, partly on the fibrous
cords themselves, and are arranged in groups
which can be distinguished as ventral, dorsal,
and lateral ganglia. There are in addition
groups of ganglion cells in the median lines
and in the lateral lines in the caudal region.

As sense organs we must mention the
eyes found in the free-living Nematoda, and
the papillae and tactile hairs found princi-
pally in the neighbourhood of the mouth.
Each papilla is supplied by one nerve fibre,
which is swollen to a knob and forms the
axis of the papilla.

The body -cavity is a continuous space
between the longitudinal muscles of the
body-wall and the outer cuticle of the gut-
wall ; it contains a corpusculated and colour-
less fluid. The homology of the cavity is
doubtful ; it occurs between the muscles and
the endoderm, and it has no relation to the
gonads or excretory organs. There is no vas-
cular system.

Generative organs. The Nematodes are
dioecious (with exception of the hermaphro-
dite Pelodytes, and of RJiabdonema (Ascaris)
nigrovenosum and Allantonema mirabile,
which produce first spermatozoa and later

ova). The males are characterised by their smaller size, and by
the posterior end of the body being generally curved. Both kinds
of generative organs consist of a single tube or of paired and
often much coiled tubes, at the upper end of which the generative
products are developed, the lower ends representing the efferent ducts

FIG. 228. — Nervous system of
Nematodes, diagrammatic
after Butschli. C lateral
ganglion on the nerve ring ;
S anterior lateral nerve ;
Sm submedian nerve ; SI
sublateral nerve ; Bn ven-
tral nerve ; Rn dorsal
nerve ; Ag anal ganglion ;
A anus.

278 NBMATHBLMINTHES.

and receptacula of the generative products. The usually paired
ovarian tubes are distinguishable into the following regions : the
ovary where the eggs are developed; the oviduct along which they
pass to reach the uterus, a more dilated region where they are
fertilised and often pass through a part or the whole (viviparous
forms) of their development; the two uteruses lead into the single
vagina, which opens to the exterior on the ventral surface somewhat
in the anterior region of the body or near the middle, rarely near
the hind end. The male generati^ apparatus, which contains
amoeboid spermatozoa without flagellum or vibratile appendage, is
almost invariably represented by an unpaired tube, and usually
opens on the ventral surface near the posterior end of the body in
a common opening with the intestine. As a rule, the common
cloacal portion contains two pointed chitinous rods, the so-called
spicula, in a pouch-like invagination. These spicula can be pro-
truded and retracted by a special muscular apparatus, and serve to
fasten the male body to the female during copulation. In many
cases (Strong ylidae) an umbrella-like bursa is added, or the terminal
portion of the cloaca can be protruded like a penis (Trichina):, in
such cases the cloacal aperture lies almost at the extreme end but is
still ventral (Acrophalli). In the male, papillae are almost always
present in the region of the posterior end of the body, and their
number and arrangement afford important specific characters. The
upper ends of the generative organs in both sexes (ovary and testis)
consist of a multinucleated cord in which cell limits are not dis-
cernible; lower down cell limits become discernible, but all the
cells are attached by a stalk to a central protoplasmic cord — the
rachis. In the oviduct and vas deferens the germ cells (progametes)
become entirely free and lie loose in the cavity of the duct, and
divide into the definite genital cells or gametes (ova or spermatozoa).
Development. The Nematoda for the most part lay eggs; it is
only in rare cases that they bear living young. The eggs usually
possess a hard shell and may be laid at different stages of the
embryonic development or before it has begun. In the viviparous
Nematodes the eggs lose their delicate membranes in the uterus of
the mother (Trichina, Filaria). Fertilization takes place by the
entry of a spermatozoon into the ovum, which is still without a
membrane. The segmentation is equal, and leads to the formation
of a kind of invaginate gastrula, from the two cell-layers of which
are developed the body-wall and the alimentary canal. The embryo
gradually assumes an elongated cylindrical form, and comes to lie

NEMATODA. 279

rolled up in several coils within the shell. The excretory pore and
the rudiments of generative organs, as well as a nerve ring, are
present in the embryo, which is also provided with mouth and
anus. The free development is a metamorphosis, usualjy compli-
cated by the circumstance that it is not undergone in the habitat
of the mother. The young stages or larvae, probably of most
Nematodes, have a different habitat to that of the sexually adult
animal, being contained in different organs of the same or even
of different hosts. The larvae live for the most part in parenchy-
matous organs, either free or encysted in a connective tissue capsule;
the adults, on the contrary, live principally in the alimentary canal.

The embryo is almost invariably characterised by the special form
of the oral and caudal extremities, but sometimes also by the
possession of a boring tooth. Sooner or later the skin is shed, and
the animal enters its second
stage, which may often still be
considered as a larval stage;
repeated ecdyses precede the
sexually adult stage.

The post -embryonic develop-
ment of the Nematodes presents
numerous modifications. In the
simplest cases the embryo, while
still enveloped in the egg mem-
branes, is transported passively Fia 2^_sderostomum tetracanthum>

in the food (OxyuriS vermicularis encysted (after R. Leuckart).

and Trichocephalus). In many

Ascaridae the embryos, which are provided with a boring tooth,

first make their way into an intermediate host, by which they are

transported into the intestine of the second host with the food or

water.

More frequently the young forms encyst within the intermediate
host, and, enclosed in the cyst, are transferred into the stomach
and intestine of the permanent host (Fig. 229). For example, the
embryos of Spiroptera obtusa of the mouse, while still in the egg
membranes, are taken with the food by the meal-worm, in the body
cavity of which they encyst. In the viviparous Trichina spiralis
there is a modification of this mode of development, inasmuch as
the migration of the embryos and their development, to the stage
found encysted in the muscles (muscle-trichina), takes place in the
same animal which contains the sexually mature intestinal Trichinas.

280 NEMATHELMINTHES.

The development of the Nematode larvae often makes a consider-
able advance within the intermediate host into which they have
migrated. Thus, for instance, in Cucullanus elegans, the embryos
migrate into the Cyclops, and in the body cavity of these small
Crustacea undergo two ecdyses and essential alterations of form,
obtaining at this early stage the characteristic oral capsule of the
sexually adult stage, to which they only develop in the intestine
of the perch. According to Fedschenko,* a similar mode of develop-
ment occurs in Filaria medinensis. The embryos pass into puddles
of water, and migrate thence into the body cavity of the Cyclopidae ;
and after casting their skin assume a form which, except for the
absence of the oral capsule, resembles that of the larva of Cucullanus.
After the expiration of two weeks there is another ecdysis, with
which is connected the loss of the long tail. The later history is
unknown. It has not yet been discovered whether the migration
of the Filarian larva into the permanent host (man, see p. 289) takes
place within the body of the Cyclops, or independently after copulat-
ing in the free state.

The embryos of some Nematoda develop in damp muddy earth,
after casting their skin, to small so-called Rhabditis forms with a
double enlargement of the oesophagus, and with a pharyngeal arm-
ature. They lead an independent life in this habitat, and finally
migrate to lead a parasitic life within the permanent host, where,
after several ecdyses and alterations of form, they attain the sexually
mature condition. This mode of development occurs in Dochmius
trigonocephalus from the intestine of the dog, and very probably
in the nearly allied D. (Ancylostomwii) duodenalis of man, and also
in Sclerostomum.

The offspring of parasitic Nematodes may, however, attain sexual
maturity in damp earth, as free Rhabditis forms, and represent a
special generation of forms whose offspring again migrate and become
parasites. Such a life -history is a case of heterogamy. It occurs
in Rhaldonema mgrovenosum, a parasite in the lungs of Batrachians.
These parasites, which are about half to three-quarters of an inch
long, all have the structure of females, but contain spermatozoa,
which are produced (as in the viviparous Pelodytes) in the same tubes
as, but earlier than the ova. They are viviparous. The embryos
make their way into the intestine of their host, and accumulate in

* Compare Fedschenko, " Ueber den Ban und Entwieklung der Filaria
medinensis," in the Berichtcn der Freunde der Naturwissenschaften in Moskau,
torn. 8 and 10.

NEMATODA.

281

the rectum, but finally pass to the exterior in the faeces, and so
reach the damp earth or muddy water, where they develop in a short
time into the Rhabditis-like forms, which have separate sexes and
are barely 1 mm. in length (Fig. 230, a and b). The impregnated
females of the latter produce only from two to four embryos, which
become free inside the body of the mother, pass into her body cavity,
and there feed on her organs, which disintegrate to form a granular
detritus. They finally migrate as slender, already tolerably large

FIG. 230. — a, Rhdbdonema (Ascaris) nigrovenosum, about 3'5 mm. in length, in the stage of
maturity of the male products ; G genital glands ; 0 mouth ; D intestine ; A anus ; N nerve-
ring ; Drz glandular cells ; Z isolated spermatozoa, b, male and female Khdbditis forms from
about 1'5 mm. to 2 mm. long ; Ov ovary ; T testis ; V female genital opening ; Sp spicula.

Nematodes into the lungs of the Batrachia, passing through the
buccal cavity and glottis. A similar alternation of parasitic forms
with free-living Rhabditis generations is presented by Rliabdonema
strongyloides (Anguillula stercoralis), parasitic in man (p. 290), and
by Bradynema mirabile (this is probably the real explanation of
Zur Strasse's observation, see p. 290). Khabdonema (Leptodera)
appendiculata, which lives in the slug Arion empiricorum, also
presents in its development a like alternation of heteromorphic
generations, which, however, are not strictly alternating, inasmuch

282 NEMATHELMINTHES.

as numerous generations of the free Rhdbditis form may succeed
one another, before there is a return to the parasitic condition. The
Ehabdonema appendiculata is also peculiar, in that the form parasitic
in the slug is a larva characterized by the absence of a mouth
and by the possession of two long band-shaped caudal appendages ;
it quickly attains maturity, but only after a migration into damp
earth and after losing the caudal appendages and casting the skin.

The Nematoda feed on organic juices, some of them also on blood,
and are enabled by their armed moutk to inflict wounds and to gnaw
tissues. They move by bending their body with a rapid undulatory
movement towards the ventral and dorsal surfaces. Although most
Nematoda are parasitic, they usually lead an independent life in
certain stages of their life-history. Numerous small Nematoda
(Anguillulidae, Enoplidae), however, are never parasitic, but live
freely in fresh and salt water, and in the earth. Some Nematodes
are parasitic in plants, 6.17., Anguillula tritici, dipsaci, etc., and may
even produce gall-like deformities (Tylenchus), others live in decaying
vegetable matter, e.g., the vinegar worm in fermenting vinegar and
paste. In many cases the migration of the parasite is a condition
necessary to the attainment of sexual maturity, e.g., in Mermis, where
sexual organs are not developed till the worm leaves its host and
becomes free in damp earth, in which copulation of the sexes is
effected. Finally there are certain small Nematodes the females of
which alone are parasitic. These, after copulation in the free state
with the small males, migrate into insects, and under the favourable
conditions of parasitism not only increase enormously in size, but also
undergo structural modifications favourable for the production of a
large number of embryos. In Attractonema gibbosum and in Spliae-
rularia bombi, the remarkable parasite of the humble-bee, the females,
after copulating in the free state, migrate, the former into the larva
of the gall-fly Cecidomyia pini, the latter into the queen-bees, which
live through the winter. Here the gut degenerates, and a kind of
hernia of the body-wall, containing the generative organs, is formed,
while the body of the worm shrinks to a small appendage (Fig. 231).
The eggs develop in the body of the insect into larvae, which pass
out of the body, become free, and, either after a few days (Attract-
onema) or after some months (Spliaerularia), become sexually
mature.

The power possessed by small Nematodes of resisting the effects
of prolonged desiccation and of coming to life again (so to speak)
on being moistened is remarkable.

NEMATODA.

283

Farn. 1 . Ascaridae. Body tolerably stout. Mouth with three lips furnished
with papillae, one of which is dorsal, while the other two meet- together in the
ventral line. Buccal cavity rarely furnished with pieces of chitin. Posterior
portion of oesophagus often forming a distinct pharyngeal bulb. Posterior
end of male ventrally curved, and usually furnished with two horny spicula.
Parasitic in the alimentary canal of animals.

FIG. 231.— a, male SpJiaerularia in its larval skin (Lc) x about 75. 6, female with partially
protruded vagina S. c, the same with still more developed uterine outgrowth S. d, uterine
outgrowth fully formed, containing ovary, oviduct, and uterus x 10 ; W the relatively minute
body of the worm.

Ascaris L. Polymyarian, edges of lips dentated in the larger species.
Pharyngeal bulb not distinct ; hind end usually short and conical, and in the
male always provided with two spicula (Fig. 232) ; in Vertebrata. A. lumbricoides,

'284

NEMATHELMINTHES.

Cloquet, the human round worm, 4 to 14 in. in length, a smaller variety in the
pig (A. suilla, Duj.). The eggs pass out into water or damp earth, and remain
there for some months, until the embryonic development is completed. They
are probably introduced direct into the alimentary canal of their host (Grassi
and Ebstein). The smallest worm found in the human intestine is 3 mm.
in length. A. megalocephala Cloq., horse and ox, may attain a length of
17 inches. A. mystax Zed., dog and cat, sometimes man. There is a large
number of species found in all classes of Vertebrates.

Heterakis Duj. Polymyarian, hind end of male with a preanal sucker and
two lateral thickenings, spicules unequal, intestine of Vertebrates.

Oxyuris Rud. Meromyarian ; pharyngeal bulb with teeth, hind end of female
thin and pointed, male with one spiculum, in Vertebrates and Insects (cockroach
and beetles) ; 0. vermicularis L., large intestine of man, introduced directly as
eggs- 0. curvula, caecum of horse; Nematoxys Sclm., in Amphibia; Oxysoma
Schn. ; Isakis Lespes, Arthropods and terrestrial Molluscs ; Labidurus Sclm. ;
Asiridocephalus'Dies.; Heterocheilus Dies.; Peritrachelius Dies.

Fin. 232. — Ascaris lumbricoides (after Leuckart). a, hind end of male with the two spicula ;
b, anterior end from the dorsal side, showing the dorsal lip with its two papillae ; c, the
same from the ventral side with the two lateral ventral lips and the excretory pore (P) ;
d, egg with the external membrane formed of small clear spherules.

Fam. 2. Strongylidae. The male genital opening is at the posterior end of
the body, at the bottom of a bell-shaped bursa, the margin of which carries a
variable number of papillae; no pharyngeal bulb. Eustrongyhis Dies., poly-
myarian, with six oral papillae and a row of papillae on either lateral line.
The bursa is bell-shaped and completely closed, with regular muscular walls and
numerous marginal papillae. There is only one spiculum. The female genital
opening is far forward. The larvae live encysted in fishes (Filaria cystica
from Symbranchus). E. gigas Rud., the body of the female is three feet in
length, and only twelve mm. thick. It lives singly in the pelvis of the kidney
of the seal and otter, etc., and very rarely in man ; got by eating raw fish.

Strongylus Rud. With six oral papillae and small mouth. Two conical
cervical papillae upon the lateral lines. The posterior end of the male has
an umbrella-like incompletely closed bursa. Two equal spicula, usually with
unpaired supporting organ. The female sexual opening is sometimes approached
to the posterior end of the body. They live for the most part in the lungs
and bronchial tubes. The larvae live in damp earth, and probably pass into
the host directly in the food. St. lonyevaginatus Dies. Body 26 mm. long,
5 to 7 mm. thick. The female sexual opening lies directly in front of the
anus, and leads into a simple ovarian tube. Only once found in the lung
of a six-year old boy, in Klausenburg. St. paradoxtis Mehlis, in the bronchial

NEMATODA.

285

tubes of the pig. St. filaria Rud., in the bronchial tubes of the sheep. St.
commutatus Dies., in the trachea and bronchial tubes of the hare and rabbit.
St. auricularis Rud., in the small intestine of Batrachia. St. micrurus in.
aneurisms on the arteries of the ox.

Dochmius Duj. With wide mouth and horny oral capsule, the edge of which
is strongly toothed. Two ventrally placed teeth project at the bottom of the
oral capsule, while on the dorsal wall a conical spine projects obliquely forwards.
D. duodenalis Dub. (Ancylostomum duodenale Dub.), 10 to 18 mm. long, in the
small intestine of man, discovered in Italy (Fig. 233) ; very widely distributed
in the countries of the Nile (Bilharz and Griesinger).
By aid of its strongly armed mouth it wounds the
intestinal mucous membrane, and sucks the blood
from the vessels. The frequent haemorrhages occa-
sioned by these Dochmii are the cause of the illness
known by the name of Egyptian chlorosis. It has
lately been established that this worm occurs in
Brazil, and that, like D. trigonocephalus, it develops
in puddles of water ( Wucherer). D. trigonocephalus
Rud., in the dog. Sclerostomum Rud. With char-
acters of Dochmius, but with a different oral
capsule, into which two long glanular sacs open.
Sc. equinum Duj. = armatum Dies. In the intes-
tine and the mesenteric arteries of the horse.
Lives freely in Ehabditis form. Bellinger* has
shown that the phenomena of colic in the horse
may be referred to embolic processes proceeding
from aneurism of the intestinal artery. Each
aneurism contains about nine worms. Sc. tetra-
canthum Mehlis, also in the intestine of the horse.
The embryos, after migrating into the intestine,
become encysted in the walls of the rectum and
caecum, assume within the cyst their definite form,
break out from the cyst, and escape again into the
intestine. Pseudalius Duj. ; Physaloptera Rud. ;
Cucullanus Miill.; C. elegans Zed., in the perch,
buccal capsule well developed ; viviparous, the
young pass into water and enter Cyclops.

Olullanus Lkt. ; 0. tricuspis Lkt., in the cat,
sexless young encysted in the mouse. Syngamus
Siebold ; S. trachealis Sieb. , in trachea and bronchi
of poultry— cause of gapes, the male is permanently

attached to the female by the application of the bursa to the female opening.
The eggs hatch on the ground or in water. No second host, though the
embryos may be eaten by earthworms and remain alive in their alimentary
canal.

Fam. 3. Trichotrachelidae, with long, thin anterior portion of the body.
Mouth small, without papillae. Oesophagus very long, traversing a peculiar
cord of cells.

Trichoceplialus Goeze. Anterior part (Fig. 234) of the body elongated and

* Bellinger, "Die Kolik der Pferde und das Wurmaneurysma der Einge-
weidearterien," Miinchen, 1870.

FIG. 233. — Dochmiits duodenalis
(after R. Leuckart). a, male ;
0 mouth ; B bursa. b, female ;.
0 mouth ; A anus ; V vulva.

286

NEMATHELMINTHBS.

whip-shaped : posterior part cylindrical and sharply distinct, enclosing the
generative organs, curved in the male. Lateral lines absent. Main median
lines present. The penis is slender and furnished with a sheath, which is turned
inside out when the former is protruded. The hard-shelled, lemon-shaped eggs
undergo the first part of their development in water, without intermediate host.
Tr. dispar Rud. In the human colon : these worms do not live free in the
intestine, but bury their filiform anterior extremity in the mucous membrane
(Fig. 234). The eggs pass out of the host with the faeces, as yet without a sign
of beginning development, which only takes place after a prolonged sojourn in
the water or in a damp place. According to the experiments of Leuckart,
performed with Tr. affinis of the sheep and Tr. crenatus of the pig, embryos
with the egg membranes, if introduced into the intestine, develop into the adult
Trichocephalus ; and we may therefore conclude that the human Tr. dispar is

introduced directly, and with-
out an intermediate host, either
in the drinking water or in
uncleaned food. The young
Tr. dispar is at first hair-like,
and resembles a Trichina, and
only gradually acquires the
considerable thickness of the
hind end of the body.

Trichosomum Rud. Body
thin, hair-like, but the pos-
terior end of the body in the
female is swollen. Lateral
lines and the principal median
lines are present. The male
caudal extremity has a cuta-
neous fold and a simple penis
(spiculum) and sheath. Tr.
muris Creplin., in the large
intestine of the house-mouse.
Tr. crassicauda Bellingh., in
the bladder of the rat.
According to Leuckart, the
dwarfed male lives in the

uterus of the female, and there are usually two or three, more rarely four or
five males in a single female. There is also a second species of Trichosomum
found in the bladder of the rat, Tr. Schmidtii v. Linst., the larger male of
which was formerly taken for that of Tr. crassicauda.

Trichina Owen. * Body thin, hair-like. Principal median lines and lateral
lines are present. The female generative opening well forward. The hind end
of the body without spicule ; with two small conical papillae, between which
the cloaca projects.

Tr. spiralis Owen, in the alimentary canal of man and numerous, principally
carnivorous, mammalia ; hardly two lines in length. The viviparous females
begin to bring forth embryos about eight days after their entrance into the
alimentary canal. These embryos traverse the intestinal walls and body cavity
•of the host, and migrate, partly by their own movements in the bundles of

* Compare the writings of R. Leuckart, Zenker, R. Virchow, Pagenstecher, etc.

FIG. 234.— -Trichocephalus dispar (after R. Leuckart).
a, egg. b, female, c, male with the anterior part of the
body buried in the mucous membrane ; Sp spiculum.

NEMATODA.

287

connective tissue, partly with the aid of the currents of blood, into the striped
muscles of the body. They pierce the sarcolemima and penetrate into the

FIG. 235. — Trich'na spiraHs. a, mature female Trichina from the alimentary canal ; G genital
opening; E embryos ; GJ ovary, b, male ; T testis. c, embryo, d, embryo which has migrated
into a muscle fibre, already considerably enlarged, e, the same developed into a coiled Muscle
Trichina, and encysted.

288

NEMATHELMINTHES.

primitive bundles, the substance of which degenerates, the degeneration being
accompanied by an active multiplication of the nuclei. In a space of fourteen
days they develop, within a sac-like swelling of the muscle fibres, into spirally
coiled worms, around which and within the sarcolemma and its connective
tissue investment a clear lemon-shaped capsule is excreted from the degenerated
muscle substance. The young Muscle -Trichina can remain, living for years
within this capsule, which at first very delicate, gradually becomes thickened

and hard by the formation of
other layers and by the gradual
deposition of calcareous matter.
If the encysted animal is trans-
ferred into the intestine of some
warm-blooded animal in the flesh
of its first host, it is freed from
its cyst by the action of the gas-
tric juice, and the rudimentary
generative organs, which are
already tolerably far developed,
quickly attain maturity. In from
three to four days after their
introduction the asexual Muscle-
Trichinas become sexual Trichinas
These copulate and produce a
brood of embryos which migrate
into the tissues of the host (one
female may produce as many as
1000 embryos) (Fig. 235). The
house rat is especially to be men-
tioned as the natural host of the
Trichina. This animal does not
hesitate to eat the carcase of its
own species, and so the Trichina
infection is passed on from genera-
tion to generation. Carcases in-
fected with Trichinas are sometimes
eaten by the omnivorous pig, in
whose flesh the encysted Trichinas
are introduced into the intestine
of man, and occasion the well-
known disease, Trichinosis, which
when the migration takes place
in numbers, often has a fatal

FIG. 236. — Filaria medinensis (after Bastian and
Leuckart). a, anterior end seen from the oral
surface ; 0 mouth ; P papilla. &, pregnant
female (size reduced more than half), c,

embryos strongly magnified.

result.

Fam. 4. Filariidae. Body filiform, elongated, often with six oral papillae,
sometimes with a horny oral capsule, with four praeanal pairs of papillae, to
which an unpaired papilla may be added, with two unequal spicula or with
simple spiculum.

Filaria 0. Fr. Mtill. (Fig. 236). With small mouth and narrow oesophagus.
This genus, which is sometimes destitute of papillae, lives outside the viscera,
usually in connective tissue, frequently beneath the skin, and is divided by

NEMATODA. 289

Diesing into numerous genera. F. (Dracunculus) medinensis* Gmel. the Guinea
worm, in the subcutaneous cellular tissue of man in the Tropics.of the Old World,
reaches a length of two feet or more. The head is provided with two small
and two larger papillae. Alimentary canal degenerate. The female is vivipa-
rous, and without sexual opening. The male form is unknown. The worm
lives in the connective tissue between the muscles and beneath ttte skin, and
after reaching sexual maturity, occasions the formation of an abscess, with the
contents of which the embryos escape to the exterior (Fig. 236). It has lately
been proved (Fedschenko) that the embryos of Filaria migrate into a Cyclops
and there undergo an ecdysis. Whether they are then (in the body of the
Cyclops) introduced into man in his drinking water, or whether they first escape
and copulate in a free state, is not known. F. immitis lives in the right
ventricle of the dog, and is very abundant in East Asia. It is viviparous.
The embryos pass directly into the blood, where, however, they do not undergo
their further development. Similar immature Filariae are also found in the
blood of man in the Tropics of the New and Old Worlds, and havB been
described as F. sanguinis hominis nocturna, the sexual form living in the
lymphatic glands as F. Bancrofti Cobb. The intermediate host is probably the
mosquito, on the death of which the larvae make their way into the water in
which they, presumably, enter the alimentary canal of man. It is supposed
that they make their way from the alimentary canal, by active migration, to
the lymphatics where they mature and pair, f The larvae enter the blood and
probably escape by means of abscesses, etc., and by the kidneys, since they are
also found in the urine ; their appearance seems to have an aetiological con-
nection with chyluria and elephantiasis. F. sanguinis hominis nocturna is
periodic, appearing only in the blood at night. Two other varieties of Filaria
are also found in the human blood, viz. diurna which appears in the day, and
perstans. Filaria perstans is supposed to have a connection with the sleeping
sickness of negroes. The sexual forms of F. diurna and perstans are unknown.
In the East Indies, young Filaria also live in the blood of the street dog, and
would seem to be related to the brood of Filaria sanguinolenta, since, according
to Lewis, knotty swellings on the aorta and oesophagus are invariably found
with these Filaria. F. papillosa Hud. in the peritoneum of the horse. F. loa
Guyot., in the conjunctiva of negroes on the Congo. F. labialis Pane, only
once observed at Naples. An immature Filaria described as Filaria lentis (oculi
humani) has been found in the human capsula lentis. Ichthyonema Dies. , anus and
vulva absent, male minute, in fishes. Spiroptera Rud., S. obtusa Rud., stomach
of mouse, asexual larva in meal-worm. Spiroxys Schn., Hystrichis Molin ; Tetra-
meres Crepl. ( Tropidocera Dies. ) ; Hedruris Crepl. ; Ancyracanthus Dies.

Fam. 5. Mermithidae. Aproctous Nematodes, with very long filiform body,
and six oral papillae. The male caudal region is broad, and is provided with
two spicula and three rows of numerous papillae. They live in the body-cavity
of insects, and escape into the damp earrtli, where they attain sexual maturity
and copulate. Mermis nigrescens Duj. was the occasion of the fable of the
rain-worm. M. albicans v. Sieb. v. Siebold established by experiment the
migration of the embryos into the caterpillars of Tinea evonymella.

* Compare H. C. Bastian, " On the Structure and Nature of the Dracunculus,"
Trans. Linn. Society, vol. xxiv., 1863. Fedschenko I.e.

t P. Hanson, China Customs Report, No. xiv., 1878. T. Lewis, Q.J.M.S.,
19. 1879. See also Hanson, in Davidson's "Hygiene and Diseases in Warm
Climates" London, 1893.

U

290 NEMATHELMINTHES.

Fam. 6. Anguillulidae. * Free-living Nematodes of small size, usually with a
double swelling on oesophagus. Caudal glands are sometimes present. The
lateral canals are often replaced by the so-called ventral glands ; males with two
equal spicules. Some species either live on or are parasitic in plants ; others
live in fermenting or decaying matter. The greater number, however, live free
in earth or water. Tylenchus Bast. Buccal cavity small, and containing a
small spine. The female genital opening lies far back. T. scandens Schn. =
tritici Needham, in mildewed wheat grains. When the grains of wheat fall the
dried embryos grow in the damp earth, bore through the softened membranes,
and make their way on to the growing wheat plant. Here they remain some
time, perhaps a whole winter without alteration, until the ears begin to be
formed. They then pass into the latter, grow, and become sexually mature,
while the ear is ripening. They copulate and deposit their eggs, from which
the embryos creep out, and at length constitute the sole contents of the wheat
grains (ear-cockles). T. dipsaci Kulm, in heads of thistles (Carduus) ; T. Davainii
Bast., on roots of moss and grass. Heterodcra Schachtii Schmidt., roots of the
beet-root, also of the cabbage, of wheat, barley, etc.

Rhabditis Duj. (divided by Schneider into Leptodera Duj. and Pelodcra Schn.),
with two strongly-developed oesophageal swellings, of which the hinder has a
dental armature. Rh. flexilis Duj., head very sharply pointed, mouth with two
lips ; in the salivary glands of Limax cinereus. Eh. angiostoma Duj.

Rhabditis nigrovenosa, the free dioecious generation of Rhabdonema (Ascaris)
nigrovenosum, which is hermaphrodite, and infests the lungs of frogs.
Rhabdonema strongyloides Lkt. (Anguillula intestinalis) in intestine of man in
Lombardy and Cochin China, causing diarrhoea ; Anguillula stercoralis is the
free Rhabditis generation of this.f Rhabdonema (Leptodera) appcndiculata
Schn., in damp earth, 3mm. long. The parasitic form, which is without a
mouth and has two caudal bands, lives in Arion empiricorum, and does not
attain sexual maturity until after its escape from its host. It is dioecious,
and gives rise to free-living, also dioecious, Rhabditis forms, many generations
of which may succeed one another.

Bradynema Zur Strasse, Br. regidum v. Sieb. in the body-cavity of the beetle
Aphodius fimentarius, without mouth, intestine, anus, excretory and nervous
systems. Mainly consisting of uterus full of embryos ; viviparous ; larvae, male
and female, set free in body-cavity, bore through into intestine, and pass out by
anus of host. According to Zur Strasse £ the female larvae die without pro-
ducing eggs, while the male larvae become protandrous hermaphrodites, and
enter in an unknown way the body -cavity of their host. This account requires
confirmation.

Allantonema mirabile Lkt. in the beetle Hylobius pini, 3 mm. long, sausage-
shaped, surrounded by a membrane, and attached to tracheae in the body-cavity ;
without mouth, intestine, anus; are protandrous hermaphrodites, with a free-
living dioecious Rhabditis generation.

* Davaine, " Recherches sur 1'Anguillule du ble nielle," Paris, 1857. Kiihn,
"Ueber das Vorkommen von Anguillulen in erkrankten Bliithenkb'pfen von
Dipsacus fullonum," Zeitschr. fur wiss Zool., torn 9., 1859. Bastian, "Mono-
graph of the Anguillulidae or free Nematoids, marine, land, and fresh water,"
London, 1864. 0. Biitschli, " Beitrage zur Kentniss der freilebenden Nema-
toden," Nov. Ada, torn. 36, 1873. J. G. de Man, "Diefrei in der reinen Erde
und im sussen Wasser lebenden Nematoden der Nied. Fauna," Leiden, 1884.

t Leuckart, Ber. d. k. Sachs. Gesel. d. Wiss, 1882.

£ Z.f. w. Z.,54, 1892, p. 700.

NEMATODA.

291

Attractonema gibbosum Lkt. in body-cavity of Cecidomyia pini, without
mouth and anus ; with alimentary canal reduced to a cell-cord ; with prolapsed
uterus and vagina, full of eggs, projecting from the body. Males and females
are found in the free state; they copulate; the female alone enters the host.

Sphaerularia bombi* Leon. Duf., in the body-cavity of the humhie bees which
have survived the winter (Fig. 231) ; the life-history is similar to that of At.
gibbosum. The form in the body-cavity of the bee is the female, and consists
of a 15 mm. vermiform body carrying a small Nematode-like worm. The former
is the enormously grown protruded female generative apparatus, and the latter is
the body of the female worm, which alone enters the host. The larvae become
free in the bee, and leave it by the anus.
When free and 1 mm. long they become sexual
as males and females, and copulate. After
copulation the female enters the bee.

Anguilhila Ehrbg. Small buccal cavity,
oesophagus with a posterior bulb and a
valvular apparatus. Male without bursa.
Usually two circular lateral organs. No
anal gland. A. aceti = glutinis 0. Fr. M.,
the vinegar- and paste-worm 1-2 mm. long.
Chromadora Bast. ; Spilophora Bast. ; Odonto-
phora Bast.

Fam. 7. Enoplidae.f Small, usually free-
living, marine forms, without the posterior
pharyngeal bulb, often with eyes and a buccal
armature, often with fine hairs and bristles
round the mouth. Dorylaimus Duj. ( Urolabes
Carter) ; D. palustris Cart., supposed by
Carter to be a non- parasitic stage in the
development of Filaria medinensis ; D. stag-
nalis found in mud everywhere in Europe.
Trilobus Bast.; Monhystera Bast.; Comesoma
Bast.; Enchdidium Ehrbg., a large eye on
the oesophagus, in the sea. Enoplus Duj.,
marine ; Symplocostoma Bast. ; Oncholaimus
Duj.; Odontobius Roussel.

The Chaetosomatidae and the Desmoscole-
cidae may be mentioned here. They are
minute non-parasitic, marine organisms, pre-
senting in the arrangement of their generative
organs resemblances to the Nematoda. Their
anatomy, however, is imperfectly known.

FIG. 237.— Desmoscolex minutus x 200.
a eye ; b ventral surface ; c long
dorsal bristles, which exist only
in the female ; d anus ; « ventral
bristles (after Greef, from Perrier).

* A. Schneider, Zool. Beitrage, Breslau, vol. i. R. Leuckart, "Zool. Anzeiger,"
1885. Id., Neue Beitrage 2. Kennt. d. Nematoden, Leipzig, 1887.

f Eberth, Unters. ub. Nematoden, Leipzig, 1863. Marion, "Rech. anat. et
physiol. sur les Nematoides non-parasites marins," Ann. Sc. Nat., XIII., 1870.
O. Biitsclili, "Ub. freileb. Nematoden, insb. d. Kieler Hafens," Abh. Senk. Nat.
Oesel. Frankfurt, 9, 1874. De Man, "Onderz. o. v. in der Aarde lev. Nematoden,"
Tyds. d. Nederland. Tierkund. Vereenig, 1875. Id. " Contributions d la con-
naissance des Nematodcs du golfe de Naples," Leiden, 1876.

292 NEMATHELMINTHES.

Chaetosomatidae. * The anterior end of the body is swollen into a head, with
a semicircle of moveable hooks. The body is covered with fine hair. There is
a terminal mouth, an oesophagus, intestine and ventral anus. Two rows of
knobbed processes on the ventral surface of hind end of body. Dioecious.
Testis single, vas deferens opens with the anus, and is provided with two
spicules. Two ovaries, single vagina, opening ventrally about middle of body.
Minute. Marine. Chaetosoma Clap., Rhabdogaster Metschnikoff.

Desmoscolecidae.f Minute, vermiform marine animals. Body marked with
transverse ridges, which carry bristles. Mouth anterior and terminal, anus
dorsal. Dioecious. Testis and ovary as impaired tubes. Male with two
spicula, vas deferens opens with the anusf ovary opens on ventral surface.
They move by looping. Nervous system unknown. Desmoscolex Clap.
(Fig. 237), Trichoderma Greef.

Class II. NEMATOMORPHA. +

Elongated, unsegmented round worms without lateral lines, witli
ventral nerve-cord and circumoesophageal ring.

The position of these worms in the system is obscure. The name
chosen for the order expresses the fact that in general form of body
they resemble the Nematoda. Their anatomy, however, is very
different from that of the latter group. The body is elongated and
filiform, but is without oral papillae and lateral lines. There is a
marked cuticle, beneath which is a cellular epidermis. The body-
muscles are in one layer of longitudinal fibres. The nervous system
consists of three cords closely approximated in the middle ventral
line, within the muscular layer. This ventral cord divides in front
into the two cords which embrace, and unite with one another dorsal
to, the oesophagus. The mouth (which is anterior) and oesophagus
are occluded in the adult state, and the anus is at the hind end of
the body.

Between the body-wall and the gut there lie polygonal cells,
which in the adult seem to differentiate into various organs, e.g.
genital glands, genital ducts ; and a space, which may or may not be
a coelomic space, appears among them.

* E. Metschnikoff, Z. f. w. Z., 17, 1867. Panceri, Atti Accad. delle Scienze,
Naples 7, 1878, p. 7.

f Greef. Unters. lib. einige merkwiirdige Thiergruppen der Arthropoden u,
Wurmtypus, Arch. Naturg. 35 (1) 1869. Panceri, Op. cit.

I F. Vejdovsky, " Zur Morphologic der Gordiiden," Z. /. w. Z., 43, 1886,
p. 369, and Ibid., 46, 1888, p. 188. v. Linstow, "Ueb. d. Entwick. und
d. Anat. v. Gordius," Arch. f. Mic. Anat., 34, 1889, p. 248. Id., " Weitere
Beobachtungen an Gordius," Arch. f. Mic. Anat., 37, 1891, p. 239. Id., "Uber
d. Entwick. v. Gordius," Cenlralbl. Bctct. ParasitJc., 11, p. 475. 0. Biirger,
"Zur Kenntniss v. Nectonema agile Verr.," Zool. Jahrb. Morph. Abth., 4, 1891,
p. 631. H. B. Ward, "On Nectonema agile," Bull Mus. Harvard Coll., 23,
1892, p. 135.

NEMATOMORPHA. 293

The sexes are separate, and the generative organs are paired ; they
open to the exterior, with the anus near the hind end of the body.
The ovaries are metamerically repeated masses of cells on each side.
The ova are collected into two tubes — the egg-sacs, which behind
become the oviducts. The oviducts open into a median atrium,
which also receives the opening of the single receptaculum seminis.
The male organs are much the same,
except that the two vasa deferentia
open separately into the rectum
(cloaca). The male caudal region is
forked, and is devoid of spicula.

In the adult stage these animals are
free and sexually mature, but the

-,. , FIG. 238.— Larvae of Gordius subbi-

alimentary canal is generally degen- furcm (after Meissner). a, in the

erate, being occluded in front, and egg-membrane with protruded pro-

, , „ , „, boscis; 6, out of the egg-membrane;

presumably functionless. They are c> with invaginated proboscis,
found in fresh -water ponds and

streams, and move in an undulating manner. The eggs give rise
in the water to an embryo, with a circle of boring-spines, which
leaves the egg and migrates into insect larvae (Ephemerid larvae,
etc., they have been found even in fishes, molluscs, and oligochaetes)
and there encysts. Water beetles and other aquatic predatory insects
eat with the flesh of their prey the encysted young forms, which
then develop in the body-cavity of their new and larger host to
young Gordiidae, which make their way into the water. Gordius L. ;
Nectonema Verr., a marine form, life-history unknown.

Class III. ACANTHOCEPHALA.*

Elongated round ivorms, with protrusible proboscis furnished with
hooks ; without mouth, and alimentary canal ; icith a body-cavity, into
which the ova are dehisced and the oviducts open ; parasitic.

The saccular, often transversely wrinkled body begins with a
proboscis, which is furnished with recurved hooks, and can be
retracted into a tube projecting into the body-cavity (sheath of the

* Besides Dujardin, Diesing, 1. c., compare: R. Leuckart, " Parasiten des
Menschen," torn 2, 1876. Greeff, " Untersuchungen liber Echinorhynchus
miliaris," Arch, fur Naturgesch, 1864. A. Schneider, "Ueber den Bau der
Acanthocephalen," Mutter's Archiv., 1868. Also the Sitzungsbcrichte der
Oberhessischen Gesellschaft fur Natur- und fleilkunde, 1871. B. Grassi and S.
Calandmccio, " Ueb. einen Echinorhynchus, welcher auch in Menschen parasitirt
u. dessen Zwischemvirth ein Blaps ist," Centralbl. fur Bakt. u. Parasitekund.
3, 1888. 0. Hamann, Die Nemathelminthen, Heft 1, Monographic der Acantho-
cephalen, Jena 1891 ; Heft 2, 1895.

294

NEMATHELMINTHES.

3,

proboscis) (Fig. 239, R and Ms). The posterior end of this sheath
is fastened to the body-wall by a ligament, and by retractor muscles
(retinacula).

The nervous system (Fig. 239, G) is placed at the base of the
proboscis, and consists of a simple ganglion formed of large cells.
Nerves are given off from the ganglion anteriorly
to the proboscis, and through the lateral retrac-
tors to the body-wall (Fig. 239, R). The latter
supply partly the muscular system of *he body,
and partly the genital apparatus, in which there
are, principally in the male animal, special
nerve-centres, consisting of ganglionic enlarge-
ments. Sense organs are entirely wanting, as
also are mouth, alimentary canal, and anus.
The nutritive juices are taken in through
the whole outer surface of
the body. In the soft
granular subcuticular layer
of the integument (epider-
mis}) in which, as in
Nematodes, cell -limits are
not discernible, lies a com-
plicated system of canals,
filled with a clear fluid
containing granules. Be-
neath the subcuticular layer
of the integument, which
layer is often very extensive
and of a yellow colour, is FIG. 240.— Male of ECU
placed the powerful mus-
cular tunic; it is composed
of external transverse arid
internal longitudinal fibres,
which latter bound the body-cavity. The struc-
ture of the muscular fibres is not unlike that of
Nematodes. The complicated ramified system of
the epidermal canals, of which two principal longitudinal trunks may
be recognized, is filled with juices, and probably functions as a nutri-
tive apparatus. The epidermis and canal system of the proboscis is
entirely cut off from the epidermis and vessels of the trunk by a
thin ingrowth of cuticle. The lemnisci are two bodies which

R

FIG. 239.— Anterior part
of an Echinorhynchus.
R Proboscis ; Rs
sheath of proboscis ;
G ganglion ; Le lem-
nisci : R retinacula.

rhyncus nngnstatus (after
R. Leuckart). 11 pro-
boscis ; Rs sheath of the
proboscis ; Li ligament ;
(; ganglion ; Le lemnisci :
T testes ; Vd vasa defer-
entia ; Pr prostatic sacs ;
De ductus ejaculatorius ;
P penis; B retracted
bursa.

ACANTHOCEPHALA.

295

project through the muscular tunic into the body-cavity at the base
of the proboscis (Fig. 240, Le). They consist of epidermis,
continuous with that of the proboscis, and a thin muscular coat,
and they contain a great number of anastomosing canals, It has
been suggested that the epidermal spaces of the lemnisci and
proboscis are organs for the protrusion of the
proboscis ; the fluid which in the retraction of
the proboscis enters the epidermal spaces of
the lemnisci being by the contraction of these
latter organs forced back into the walls of the
proboscis, so bringing about its protrusion.
According to Schneider, the vessels of the
lemnisci open into a circular vessel in the
integument, and only communicate with the net-
work of canals in the proboscis, while the other
dermal vessels (nutritive apparatus), the con-
tents of which differs from that of the vessels
of the lemnisci, are, as above stated, completely
shut off from the latter.

It has recently* been asserted that there is in Echino-
rhynchus gigas a pair of nephridia. They consist of a
bunch of tine tubes, which terminate in a sieve-plate,
the pores of which open into the body -cavity. The
sieve-plate carries on its inner side a bunch of flagella.
The fine tubes unite to form a duct, which joins its
fellow. The single duct so formed opens into the
generative duct.

Generative organs. The body-cavity through
which fluids circulate encloses the greatly-
developed generative organs, which are attached
to the end of the sheath of the proboscis by the
ligament (Figs. 240£* and 241 1). The sexes are
separate. The male (Fig. 240) has two testes
(T\ and the same number of efferent ducts
( Vd). The latter unite behind to form a ductus
ejaculatorius (De), which is often furnished
with six or eight glandular sacs (Pr), and a conical penis (P), at the
bottom of a bell-shaped protrusible bursa (B), situated at the posterior
end of the body (Fig. 240). The generative organs of the larger
females (Fig. 241) consist of the ovary developed in the ligament; of

* J. E. Kaiser "Die Acanthocephalen u. ilire Entwick." Bill. Zool. Bd. 2,
Heft 7, 2 Theile, 1892.

FIG. 241. — Generative
ducts of a female
Echinorhynchus tricho-
cephahis from the so-
called dorsal side, i.e.,
the side of the pos-
terior opening of the
bell. The opening of
the uterine bell b
looking forward and
its relation to the liga-
ment I. c posterior
opening of the bell, by
which the unripe eggs
pass back into the
body-cavity; d uterus;
e vagina (after Kaiser).

296 NEMATHELMINTHES.

a complicated " uterine bell," which opens into the body-cavity (ft),
and to the base of which the ligament is attached; of two short
oviducts connecting the bell with the uterus, which leads into the
vagina ; the vagina opens at the hind end. There is at the hind
end of the bell a second opening into the body-cavity on the so-
called dorsal side (c). The female generative ducts consist of a few
very large cells, like the cells constituting the skin of the embryo,
and the muscles of the ducts are fibrous differentiations of the outer
parts of these cells.

It is only in the young stage that the ovary is a simple body
enclosed by the membrane of the above-mentioned ligament. As
the animal increases in size, the ovary grows, and becomes divided
into numerous spherical masses of eggs, the pressure of which bursts
the membrane of the ligament; the masses of ova, as well as the
ripe elliptical eggs, which gradually become free from them, fall into
the body -cavity. The egg membranes are not
formed till after segmentation, and ought perhaps
to be interpreted as embryonic membranes. The
eggs, which already contain embryos, pass out of
the body-cavity into the uterine bell, which is
continually dilating and contracting, thence into
the oviduct, and through the genital opening to
the exterior; while the round still unripe eggs
pass from the uterine bell through the dorsal

FIG. 242. — Embryo

of EcMnorhynchus posterior opening back into the body-cavity.
gigas enclosed in Development. Segmentation is irregular and

the egg membranes ° °

(after Leuckart). complete, and results in the formation of an em-
bryo, which is enclosed in three egg-membranes.
The embryo has a small, somewhat long body, armed with small
spines at the anterior pole, and consists of a central mass of small
cells and a peripheral layer containing a few large nuclei and
without cell-limits (Fig. 242). The peripheral layer gives rise to
the ectoderm and the lemnisci ; the central cells to the other organs.
The large nuclei are said to break up into the small nuclei of the
ectoderm of the adult except in Neorhynclms and Arhynclms. The
body cavity arises in the central mass, and the cells on the outside
of it form the muscles of the body-wall. In this development there
can be no talk of layers in the ordinary sense. The embryo passes
into the intestine of Amphipods (Ech. proteus, polymorphus), or of
Isopods (Ech. angustatus), and there becomes free, bores through
the wall of the intestine, and after losing the embryonic spines,

ACANTHOCBPHALA.

297

develops to a small elongated larva, which, like a pupa, lies in the
body-cavity of the small Crustacean, with its proboscis retracted and
surrounded by its firm external skin as by a cyst (Fig. 243, I). As
stated above, the skin of the larva gives rise only to the integu-
ment, the vessels and the lemnisci of the adult ; while all the other
organs enclosed within the dermal muscular envelope, viz., the nervous
system, the sheath of the proboscis, and the generative organs, are de-
veloped from the so-called embryonic nucleus. It is only after their
introduction into the intestine of fishes (Ech. proteus) or of aquatic
birds (Ech. polymorphus), which feed on these Crustacea, that the
larvae attain to sexual maturity, copulate, and reach their full size.
T c s3± d

FIG. 243.— Larvae of EcMnorhynclius proteus from Gammarus (after Leuckart). a, free embryo ;
Ek embryonic nucleus. 6, older stage, with more differentiated embryonic nucleus,
c, young female worm ; Ov ovary, d, a young male worm ; T testes ; Le lemnisci.

The numerous species of the genus Echinorhynchus 0. F. M tiller, live in the
alimentary canal of different Vertebrates, principally fishes, the gut wall of
which may be as it were sown with these animals ; the asexual larvae are
found in small Crustacea (Amphipods, Isopods). Lambl found a small sexually
immature Echinorhynchus in the small intestine of a child which died of
leukhaemia. Ech. polymorphus Brems, in the intestine of the duck and other
birds, larva in the crayfish ; E. proteus Westrumb., larval form in Gammarus
and in the body -cavity and liver of Phoxinus, sexual form in the trout.
Gigantorhynchus Hamann, with ringed and flattened body, intestine of ant-
eaters, birds, swine ; larval form in grubs of insects ; G. gigcts Goeze, as large
as an Ascaris lumbricoides, in the small intestine of the pig, larval form in
grubs of beetles. Neorhynchus Hamann, the nuclei of the epidermis and
lemnisci are large and few in number, as in the larvae of other forms ; in the
carp, larval form in larvae of Neuroptera, etc. Arhynchus Shipley, without
eversible proboscis and hooks ; epidermis and lemnisci with giant nuclei ; in-
side the skin of a bird Hemignathus procerus.

298 NEMATHELMINTHES.

Following the usual custom, the Acanthocephala are placed in
the phylum Nemathelminthes ; but it must be borne in mind that
the relationship to the Nematoda thus expressed is more than
doubtful. Indeed, there is nothing in common between the two
groups, and there are many remarkable differences. The absence
of an alimentary canal, the presence of a coelorn with relations to
the generative organs and ducts, the form of the nervous system,
the presence of cilia in the so-called nephridia, are all characters
of great importance and quite different from anything in the
Nematoda. Further, the canals in the skin, though they may
be compared to the lateral excretory organs of Nematodes, are, in
reality, totally different, inasmuch as they form anastomosing net-
works, and are found throughout the whole of the epidermis.
Finally, the development cannot be brought into relation with
anything else in the animal kingdom. It is peculiar in the fact
of the giant nuclei of the outer layer and in their behaviour, and
in the absence of a third layer or group of cells in the early stages.

Our inclination is to create a separate phylum — the Acantho-
cephala— for this strange group of parasites.

CHAPTER VIII.

PHYLUM ROTIFERA.*

Minute animals with a ciliated trochal disc, an anterior mouth,
and a dorsal posterior anus. Perivisceral cavity ivell developed ;
excretory system ivith flame-cells; vascular system absent.

The Rotifera are small aquatic organisms which swim in the
water by means of a ciliary apparatus at the front end of the
body, called the trochal disc. This consists of the anterior end
which generally has a somewhat discoidal form, and of the cilia
which are disposed in one or two rows round its margin. The
name "Wheel-animalcules," sometimes applied to this group, is due
to the co-ordinated movement of these cilia, which produces the
appearance of a rotating wheel, or in some cases, when the ciliary
band is indented or interrupted at its median dorsal point and
its median ventral, of two wheels (Philodina, Limnias). It will
be useful to use the word corona for the discoidal anterior end
of the body, and velum for the ciliary apparatus of its margin—
the whole being the trochal disc. The posterior end of the body
tapers, and is called the foot or pseudopodium ; it may be jointed,
and the joints are often telescopically retractile. It terminates
either in a sucker-like surface for adhesion, on which the secretion
of a cement-gland may be poured, or in two (or more) styles, which
can be used as pincers for anchoring the animal (Fig. 244). It
is used both for locomotion and attachment.

The trochal disc is generally retractile, and the foot is, in rare
cases, absent.

The mouth is 011 the ventral side of the trochal disc, and the
anus is on the dorsal surface, usually near the foot.

* Ehrenberg, "Die InfusionsthiercTien als vollkommene Organismen," Leipzig,
1838. C. T. Hudson and P. H. Gosse, ".The Rotifera or Wheel- animalcules,'"
2 vols., London, 1886. L. H. Plate, "Ub. d. Rotatorienfauna d. bottnisclien
Meerbusens," etc., Z. f. w. Z., 49, 1890. C. Zelinka, " Studien lib. Rotatorien,"
Z. /. w. Z., 44, 1886 ; 47, 1888 ; 53, 1892.

300

ROTIFERA.

There is often a spur-like process, carrying a tuft of setae and
projecting from the dorsal middle line close to the trochal disc :
this is the calcar or antenna. There may be, in addition, a pair
of ventral setigerous processes or antennae of a similar character.
The single nerve-ganglion is placed on the dorsal side of the body,
close to the trochal disc.

The velum varies in its arrangement. It may consist of a simple
circle of cilia at the margin of the trochal disc (Microcodon) : in
this case it surrounds the mouth, and is a circum-oral ring. In the

Floscularidae (Fig.

a 245, 3\ this ring is

reduced to a half-ring
on? the ventral side of
the mouth, and the
edges of the disc may
be produced into long
processes (Stephano-
ceros). In other forms
the ring encircles the
disc twice by bending
on itself (Fig. 245, 7,
2) ; thus enclosing the
mouth, and having a
dorsal gap between the
points of flexure (Rhi-
zota). In this form of
velum a fusion of the
two points of flexure
would result in the
formation of two rings,
one pre-oral (above the
mouth), and one post-
oral (circum-oral)

below the mouth. In the Bdelloidea the ring is doubled on itself,
but there are two gaps, one dorsal, at the point of flexure, and the
other ventral in the upper ring just above the mouth (Fig. 245, 4)-
Very frequently, especially in the parasitic forms, the trochal disc is
reduced, and in certain cases entirely aborted (Apsilus). In Notoin-
mata tardigrada the trochal disc is reduced to a ciliated disc round
the mouth. In some cases the ciliated edge of the disc projects over
the head and forms the double wheel above referred to (Philodina,

FIG. 244,—Hydatina senta (after F. Cohn). a, female, b,
male. Wpr ciliated ring (velum) ; CBl contractile vesicle
of the excretory system; Wtr ciliated lobule of the
excretory organs (Ex) ; K mastax ; Dr salivary glands ;
Md stomach ; Ov ovary ; T testis ; P penis.

ROTIFERA.

301

Brachionus), or becomes a ciliated cephalic shield (Megalotrocha,
Tubicolaria). Finally it may be produced into ciliated processes
of various form (Floscularia, Stephanoceros). The cilia are con-

FIG. 245. — Vela of various Rotifera (after Hudson and Gosse). 1, Rhizotic velum, front view
(Melicerta ringens). 2, Rhizotic velum, side view (M. ringens). 3, Velum of Floscularia
campanulata. k, Bdelloidic velum (Rotifer citrinus). 5, The same, side view. 6, Bdelloidic
velum of Adineta vaga. bf the buccal funnel ; pw the principal ring of cilia ; sw the
secondary ring ; lp the lips ; cw the velum.

cerned with locomotion, but in addition they play an important
part in procuring food.

Locomotive organs. In addition to the foot and trochal disc,
there are often styliform processes of the body, into the bases of

302

ROTIFERA.

which special muscles are inserted. Such are found in Triarthra,
Polyarthra, etc. In one family — the Pedalionidae — the body pos-
sesses hollow appendages containing muscles, and recalling very
closely the limbs of Arthropoda (Fig. 246).

The body-wall consists of a cuticle with a subjacent protoplasmic
layer with scattered nuclei, but without cell-limits. This doubtless
represents the ectoderm. There does not appear to be any con-

FIG. 246. — Pedalion mirum, side view (from Perrier,
after Gosse). g eyes ; c velum ; m, m', m" mus-
cular bands ; v ventral appendage ; d dorsal appen-
dage ; 1,1' lateral appendages.

FIG. 247.— Melicerta ringens (after
Leuckart and Nitsch, modified
from Ehrenberg and Joliet).
showing the tube formed of
pellets cemented together. 0
mouth ; Ph pharynx ; L ciliated
lobe overhanging W the cili-
ated cup ; Dr cement gland ;
M stomach ; T tentacle ; B
trochal disc.

tinuous muscular layer in the body-wall, but there may be a small
amount of connective tissue, inasmuch as connective tissue fibres
can be seen passing between the various organs across the body-
cavity.

The cuticle is sometimes soft and thin, sometimes hardened into
a kind of shell, called the lorica (the Ploima) ; there are sometimes
joints in it, which give the body a segmented appearance. The

ROTIFERA. 303

skin is not ciliated except in certain spots, of which the trochal
disc is the chief. The principal integumentary glands are the
cement glands of the foot, which open at the extremity of the
pincers and secrete the substance by which the animal is fixed.
The tube or urceolus, in which some Rotifera live, is pfobably a
secretion of the skin; it is often gelatinous, but in Melicerta it
consists of pellets. These pellets are formed of foreign or faecal
particles which are worked up and cemented together by a ciliated
cup on the ventral side close to the trochal disc, the cementing
substance being a secretion of a gland (Dr) near the ciliated cup
(Fig. 247).

The body-cavity is a well-marked space, traversed as stated above
by a few fine connective tissue strands and filled with a clear
vascular fluid. As to its nature we know nothing. The generative
and, apparently, the renal organs are in no way connected with
it, so that presumably it is not coelomic. It may be a haemocoele;
if it is, it is the only representative of the vascular system, for
nothing in the shape of heart or blood-vessels are known.

The alimentary canal (Fig. 244) is ciliated throughout. It consists
of a mouth leading into a muscular pharynx called the mastax, and
provided with a special armature — the troplii. The parts of the
armature (see below) are in continual movement, and serve for
mastication. In the more predaceous forms they can be protruded
so as to act as jaws. Following the pharynx is a short oesophageal
tube ; this leads into the digestive sac or stomach. The stomach is
lined with large ciliated cells, which often contain green or yellow
pigment grains. The anterior or gastric part of this cavity is wide
and receives two large glandular tubes, which may be explained as
salivary or pancreatic glands. The posterior narrow intestinal part
leads into a cloacal chamber, which opens on the dorsal surface at
the point where the foot-like posterior region joins the anterior part
of the body. In some cases, e.g. Asplanchna, the intestine ends
blindly, and the faeces are rejected through the mouth.

Respiration is carried on by the general surface of the body;
special organs are wanting.

The muscular system is complex, being composed mainly of
muscular bands passing between definite points. The muscular
tissue is in part, at any rate, cross-striped.

Excretory organs. The so-called respiratory canals are excretory.
They consist of two sinuous longitudinal canals, with fluid contents ;
they open into the cloaca either directly or by means of a contractile

304 ROTIFERA.

vesicle, and are beset by short appendages called the vibratile tags
(Fig. 244). The latter appear to be simply flame-cells, which open
into the main trunks : whether they open into the perivisceral cavity
or not is disputed.

The nervous system consists of a simple or bilobed cerebral
ganglion placed dorsal to the oesophagus, and giving off nerves
to peculiar cutaneous sense organs and to the muscles. In Calli-
dina and Discopus there is in addition a small ventral ganglion
connected with the dorsal ganglion rotund the oesophagus. Eyes are
often present, and lie upon the brain either as an x-shaped, unpaired
pigment body, or as paired pigment spots provided with refractile
spheres. There is often a small mass* of calcareous granules in
connection with the ganglion : its function is unknown. The
above-mentioned cutaneous sense-organs, which have the form of
prominences beset with hairs and setae, e.g. calcar, so-called
antennae, etc., are probably tactile.

Generative organs. The sexes are separate, and are distinguished,
except in Seison, by a strongly marked dimorphism. The males
(Fig. 244, b) are much smaller than the females, and often have a
very different form ; they possess excretory tubes and ganglion, etc.,
but are without either oesophagus or intestinal canal — these organs
being reduced to a cord of cells : they leave the egg completely
developed. Their generative organs are reduced to a testicular sac,
the muscular duct of which opens at the hind end of the body,
sometimes on a papilliform protuberance. This is the penis, which
either introduces sperm into the female's cloaca in true copulation,
or perforates her body-wall and deposits the spermatozoa in the
body-cavity.

The males of many species are unknown, and when they are
known they often appear only in the autumn, when the winter-
eggs are formed; but they are also found in summer. The generative
organs of the female consist of a roundish ovary, with which a
yolk-gland is associated, and of a short oviduct which usually opens
into the cloaca. The oviduct is sometimes absent (Rotifer), and
in the Pldlodinidae and Seisonidae the ovaries are double. Almost
all Rotifera are oviparous, and their eggs are distinguishable into
thin-shelled summer eggs, which develop immediately without being-
fertilized, and thick-shelled winter eggs, which last through the
winter and are probably fertilized. They carry both kinds of eggs
about on their body in their tube, but the summer eggs not un-
frequently develop in the oviduct. The summer eggs are of two

HOTIFERA. 305

kinds, large and small. The large develop into females, and the
small into males; they are produced by different individuals. Asexual
reproduction is unknown.

It has been established by Maupas* that in certain Rotifera
(Hydatina senta) the same animal produces only eggs of^bne sex;
thus, a female which has once laid the small male egg never produces
a female egg, and vice versa. He has further shown that while
the general rule is that female eggs should be produced — a rise
in temperature, if applied at the earliest stages of their short life,
will ensure the production of the small male eggs. Further, he has
shown that the layers of female eggs are devoted to parthenogenesis,
and only produce the thin-shelled immediate eggs. Copulation of
such with a male has no effect. On the other hand copulation
between a young female, which would, if left alone, lay only male
eggs, and a male brings about a complete change in the character
of the eggs ; in this case the egg acquires a thick, hard, often orna-
mented shell, and develops immediately to a certain stage ; but the
development soon ceases and the egg becomes a resting — so-called
winter — egg. Such eggs may be produced at any season of the
year, and their peculiar property is to be able to resist drought
and other adverse influences ; they give rise only to parthenogenetic
females, which lay thin-shelled immediate eggs. Finally, copulation
between a male-producing female, in which the eggs have been
formed, and a male has no effect; in such a case the female lays
small immediate eggs, which develop at once into males.

It thus appears that, as in the bees, an egg which would, if
fertilized, produce a female, will, if not fertilized, produce a male.
Should these most important and interesting observations be con-
firmed— and here it may be observed is a subject of the most
fascinating and far-reaching character for research — it would appear
that in the Rotifera the problem of how to control the production
of the sexes has been solved.

The development has been studied in the parthenogenetic imme-
diate eggs. It throws no light upon the affinities of the group.
The young are hatched with practically the form of the adult.
There is said to be no mesoderm in the ordinary sense of the
word, but the rudiments of the organs are laid down independently.

The Rotifera principally inhabit fresh water, but marine forms
are known. Some species live in gelatinous tubes which they
secrete, or in a case consisting of pellets manufactured by the animal

* Ccmiptes rendus Acad. Sci., 109, 1889, 90, 91.
X

306

ROTIFERA.

(Melicerta, Fig. 247). A small number are parasitic. Many of
them possess to a remarkable degree the property of resisting the
effects of drought and a high temperature (200° F.). This power
is particularly developed in the Bdelloidea. On the approach of the
adverse influence they protect themselves by a gelatinous secretion

FIG. 248.— Jaws of RoUfera.—l, Malleate ; 3, Sub-malleate ; 3, Forcipate ; 4, Incudate ;
5, Malleo-ramate ; 6, Uncinate ; 7, Ramate (from Hudson and Gosse). ms malleus ;
is incus ; rs rami ; fin fulcrum ; mm manubrium ; us uncus.

which protects them against evaporation. The duration of life is
often very short. The female of Hydatina senta attains maturity
in three days and lives only fourteen days; and the males live
only three days.

The position of the Rotifera in the system is obscure. Apparently

RHIZOTA. 307

they form an isolated phylum with affinities through Pedalion (Fig.
246) to the Arthropoda ; and through the Trochosphere larva to
Annelids and Molluscs. As in the Trochosphere, it is impossible
to say whether the perivisceral space is a coelom or a haemocoele;
probably it is a haemocoele. There is a further important feature
of resemblance to the Trochosphere in the form of the excretory
organs, which also recall those of Platyhelminthes and Nemertines.
The Rotifera are highly specialized animals, and perhaps the most
remarkable general fact to note about them is the rarity of marine
forms. World-wide in distribution, and extremely rich in species,
still they are mainly confined to fresh waters. One cannot help
feeling that there must be an equally important marine branch of
the phylum which has so far been overlooked, and which when
discovered will throw light upon the affinities of the group.

The jaws or troplii are three in number ; two mallei and one incus (Fig.
248, 1). The malleus ms consists of a head or uncus (us), and of a handle or
manubrium (mm). The incus (is) consists of two rami (rs), against which the
mallei work, and of a basal piece — the fulcrum (fm). The modifications (Fig.
248, 1-7) of their jaws are as follows : — 1. Malleate. Mallei stout, manubria
and unci of equal length. 2. Sub-malleate. Mallei slender ; manubria about
twice as long as unci. 3. Fordpate. Mallei rod-like ; manubria and fulcrum
long ; unci pointed or absent ; rami used as forceps. 4. Incudate. Mallei
absent ; rami as curved forceps. 5. Malleo-ramate. Mallei fastened by unci
to rami. Unci 3-toothed ; rami large, fulcrum slender. 6. Uncinate. Unci
2-toothed ; incus slender. 7. Hamate. Rami, crossed by two or three teeth,
fulcrum rudimentary ; manubria absent.

Order 1. EHIZOTA.

Fixed when adult, usually inhabiting a gelatinous tube excreted from the skin;
foot transversely wrinkled, not retractile within the body, ending in an adhesive
disc or cup.

The foot of the RMzota is unlike the foot of all other Rotifera, in that it
is a prolongation of the dorsal, and not of the ventral, region of the body.

Fam. 1. Floscularidae. Corona* produced into setigerous lobes ; mouth
central; velum* a single half circle ventral to the buccal orifice (i.e., the
gap in velum is dorsal, Fig. 245, 3) ; trophi uncinate. Floscularia Oken ;
Acyclus Leidy, without setae ; Apsilus Metschnikoft', without setae, velum, and
foot ; Stephanoceros Ehrbg. , lobes long, convergent ; St. eichhornii Ehbg.

Fam. 2. Melicertidae.f Corona without setigerous lobes ; mouth lateral ;
velum a marginal continuous band, bent on itself at the dorsal surface, so as to
encircle the corona twice ; with the mouth between its upper and lower curves,
and having also a dorsal gap between its points of flexure (Fig. 245, 1) ; trophi
malleo-ramate. Social, the tubes are often adherent to each other. Melicerta
Schrank, corona of four lobes, dorsal antenna minute, ventral antennae

* Corona is used for trochal disc, and velum for ciliary ring or rings,
f This family must not be confused with the Leptomedusan sub-family of the
same name (p. 134).

308

EOTIFERA.

obvious, Melicerta ringens L. (Fig. 247) ; Limnias Schrank, tube without
pellets ; Cephalosiphon Ehrb., vent, antennae absent ; Oecistes Ehrb., dors.

ant. absent ; Lacinularia
Schweigger, adherent gela-
tinous tubes in clusters,
antennae absent ; Megalo-
trocha Ehrb. , clustered,
without tubes, ant. ab-
sent ; Trochosphaera Sem-
per (Fig. 249), solitary,
free -swimming, spherical,
velum as preoral ring
broken dorsally, ventral
antennae minute, trophi
malleo-ramate, lateral
canals end in cloaca, nerve
ganglion close to mastax,
male unknown, ovary
opens into cloaca. Fresh
water of Philippine
Islands. Interesting from
its resemblance in form,
gut, velum, and appear-
ance to a trochosphere
larva ; Conochilus Ehrb. ,
gap in velum ventral.

FIG. 249. — Trochosphaera aequatorialis (after Semper, from
Korschelt and Heider). Ce cloaca ; Dr glands of the
foregut ; Ex duct of the excretory organs ; G brain ; Ge
ovary and oviduct ; M mouth ; Mu muscles ; N nerve ;
S mastax; Si sense-organ; W, preoral, Wn postoral
ciliated band ; A cloacal orifice.

Order 2. BDELLOIDA.

Swimming with their velum, and creeping like a leech. Foot telescopic, wholly
retractile within the body, usually ending in three toes.

Fam. 3. PMlodinidae. Corona a pair of circular lobes, transversely placed.
Velum a continuous marginal curve, bent on itself at the dorsal surface so
as to encircle the corona twice, with the mouth between its upper and lower
curves, and having also two gaps, the one dorsal between its points of flexure,
and the other ventral in the upper curve opposite to the mouth (Fig. 245, 4) 5
trophi ramate. Philodina Ehrb., eyes two, cervical ; Rotifer Schrank, eyes two,
within the frontal column ; in both these genera no oviduct has been seen, but
the eggs develop in the body-cavity, and both eggs and young have been seen
to leave the cloaca ; males not known. Actinurus Ehrb. ; Callidina Ehrb.

Fam. 4. Adinetidae. Corona a flat prone surface ; velum as the furred
(with cilia) ventral surface of the corona ; trophi ramate ; frontal column
soldered to dorsal surface, and ending in two hooks. Adineta Hudson.

Order 3. PLOIMA.

Swimming with their velum, and (in some cases) creeping with their toes.
The mastax can be protruded so as to seize the prey ; the ganglion is well
developed and the eyes often have lenses.

Sub-order 1. ILLOEICATA.

Integument flexible, not stiffened to an enclosing shell ; foot when present
almost always furcate, but not transversely wrinkled, rarely more than feebly
telescopic, and partially retractile.

LORICATA. 309

Fam. 5. Microcodidae. Corona obliquely transverse, flat, circular ; buccal
orifice central ; velum a marginal continuous band encircling the corona and
two curves of larger cilia, one on each side of the mouth ; trophi forcipate ; foot
stylate. Microcodmi Ehrb.

Fam. 6. Asplanchnidae. Corona sub-conical with one or two apices ; velum
single, edging the corona; with large stomach which ends blindly, intestine
and cloaca being absent. Asplanchna Gosse ; Sacculus Gosse.

Fam. 7. Synchaetidae. Corona a transverse spheroidal segment, sometimes
much flattened, with styligerous prominences ; velum a single interrupted or
continuous marginal band ; mastax large, piriform ; trophi forcipate ; foot
minute, furcate. Synchaeta.

Fam. 8. Triarthridae. Body furnished with skipping appendages ; corona
transverse ; velum single, marginal ; foot absent. Polyarthra Ehrb. ; Pteroessa
Gosse ; Triarthra Ehrb. ; Pedetes Gosse.

Fam. 9. Hydatinidae. Corona truncate with styligerous prominences ;
velum two parallel bands, the one marginal fringing the corona and mouth,
the other lying within the first, the styligerous prominences being between the
two ; trophi malleate ; foot furcate. Both rings are continued into the mouth.
Eydatina Ehrb., eye absent, H. senta 0. F. M. (Fig. 244) ; Rhinops Hudson,
eyes two ; Notops Hudson, eye single. In Hydatina senta, there is a small
styliferous pit on the dorsal surface with a strong nerve from the ganglion.

Fam. 10. Notommatidae. Corona obliquely transverse ; velum of interrupted
curves and clusters, usually with a marginal band surrounding the mouth ;
trophi forcipate ; foot furcate. Albertia, Duj., vermiform, eiitozoically parasitic
in Annelida; Taphrocampa Gosse, Pleurotrocha Ehrb., without eyes; Nolom-
mata Gosse, not annulose, cylindrical, with projecting tail : auricles on head ;
brain contains opaque chalk masses, trophi virgate ; Copeus Gosse ; Proales
Gosse ; Furcularia Ehrb. ; Eosphora Ehrb. ; Diglena Ehrb. ; Distemma Ehrb.

Sub-order 2. LORICATA.

With a stiffened, wholly or partially enclosing shell ; foot various.

Fam. 11. Eattulidae. Body cylindric or fusiform, smooth without plicae or
angles ; contained in a lorica closed all round, but open at each end, often
ridged ; trophi long asymmetric ; eye single, cervical. Generally subject to
abnormal conditions. With tendency to asymmetry, in mastax, antennae, toes.
Mastigocerca Ehrb. , toe as single style with accessory stylets ; Rattulus Ehrb. ,
toes two ; Coelopus Gosse, body curved, toes one broad plate with another laid
upon it in a different plane.

Fam. 12. Dinocharidae. Lorica entire, vase-shaped or depressed ; sometimes
facetted, often spinous ; foot and toes often greatly developed ; trophi sym-
metrical. Dinocharis Ehrb., foot and toes long, foot with spurs; Scaridium
Ehrb. , foot without spurs, toes long ; Stephanops Ehrb. , head with a wide
circular shield.

Fam. 13. Salpinidae. Body more or less completely enclosed in a firm
lorica which is open at each end and divided down the back by a fissure whose
sides are united by membrane ; two furcate toes always exposed. DiascMza
Gosse, Diplax Gosse, Salpina Ehrb., lorica with spines, trophi sub-malleate,
eye single, cervical ; Diplois Gosse.

Fam. 14. Euchlanidae. Lorica of two dissimilar plates, one dorsal and
one ventral, united so as to form two confluent cavities of which the upper

310

ROTIFERA.

is much the larger ; foot jointed, furcate. Euchlanis Ehrb. ; Cathypna Gosse ;
Distyla Eckstein ; Monostyla Ehbg.

Fam. 16. Coluridae. Body enclosed in a lorica, open at both ends, closed
dorsally, usually open or wanting ventrally ; head surmounted by a chitinous
hood ; toes two, rarely one, always exposed. Colurus Ehbg. ; Metopidia Ehbg. ;
Monura Ehbg. ; Mytilia Gosse ; Cochleare Gosse.

Fain. 17. Pterodinidae. Lorica entire, various ; corona and velum those
of the Philodinidae ; trophi malleo-ramate ; foot wholly retractile, transversely
wrinkled, jointless, toeless, ending in a ciliated cup ; or foot absent ; (foot and
trophi Rhi/otic, corona Bdelloidic). Pterodina Ehbg. ; Pompholyx Gosse.

Fam. 18. Brachionidae. Lorica box-lifte, open at each end, and generally

armed with anterior and posterior
spmes ; foot long, very flexible, wholly
retractile, wrinkled, ending in two
toes. Brachionus Ehrb., lacustrine
and marine ; Noteus, Notholca Gosse ;
Eretmia Gosse.

Order 4. SCIRTOPODA.

Swimming with velum, and skipping
with arthropodo^ls limbs ; foot absent.

Fam. 20. Pedalionidae. Six hollow
limbs ; head truncate, corona of two
concave lobes, and velum as in Philo-
dinidae; trophi malleo-ramate. Peda-
lion Hudson (Fig. 246), one limb (the
longest) Centre-median, another dorso-
median, and two pairs of lateral limbs ;
and two stylate ciliated appendages on
its posterior dorsal surface ; Hexarthra
Schmarda, with three pairs of limbs
attached to the ventral surface.

Order 5. SEISONACEA.*
Marine forms parasitic on Nebalia.
The cloaca opens at base of neck in

male, at hind end of body in female ;

male otherwise like female. Intestine

complete or blind.

Fam. 21. Seisonidae. Seison Griibe ;

Paraseison Plate ; Saccobdella v. Ben.

and Hesse.

GASTROTRICHA.f

Small aquatic organisms with a
double ventral row of cilia, a cuticle

* C. Claus, "Ueb. die Organisation, etc., der Gattung Seison," Festschrift
z. F. d. 25 j. Best. d. K. k. z. b. Gesellschaft, Wien, 1876. L. Plate, "Ectopar.
Rotatorien d. Golfes v. Neapel," Naples Mit., 7, 1886.

f C. Zelinka, "Die Gastrotrichen," Z. f. w. Z., 49, 1890.

FIG. 250.—Chaetonotus maxlmus (after Biit-
schli), ventral view. Cb row of cilia ; Oe
oesophagus.

ECHINODERIDAE. 311

often prolonged into spines and hairs, a cerebral ganglion connected with the
ectoderm and with mouth and anus.

The Gastrotricha (Fig. 250) are small fresh-water organisms of unknown
affinities. They have a ventral mouth in front, a dorsal anus behind, and an
alimentary canal presenting a muscular pharynx, stomach lined withj^ few large
cells, and a rectum. The body cavity is indistinct, and if present is without
epithelioid lining. There is no vascular system, and the excretory organs
consist of two coiled tubes opening on the ventral surface, and internally ending
in a ciliated portion. The ovaries are paired, and no oviducts have been observed.
It is doubtful if they are hermaphrodite, and if a small median organ behind the
ovaries is a testis. No male is known. There is only one kind of egg, found in
summer as well as winter. The muscular system is highly developed, and
in part in specialized muscular bands. There are no transversely arranged
muscular fibres. The cilia are in two ventral rows, and a patch is found on
the head in the neighbourhood of the mouth. There is a dorsal ganglion in
front which extends a little distance backwards on each side.

The marine forms, Hemidasys Clap, and Turbanella M. Sch., appear not to
be Gastrotricha. The former has a parenchyma, a well-developed testis, vas
deferens, and chitinous penis, and two small ciliated pits in front like Nemer-
tines and some Turbellarians ; the ovary, nervous system, and excretory organs
are unknown. In Turbanella the whole ventral surface is ciliated, and there is
no chitinous cuticle ; and there are two ciliated pits.

Section 1. Euichthydina.

With forked tail, and adhesive glandular apparatus.

Fam. 1. Ichthydiidae. Skin either naked or beset with scales or papillae,
never with spines. Ichthydium Ehbg. ; Lepidoderma Zelinka.

Fam. 2. Chaetonotidae. Skin either with spines or with spines placed on
scales. Chaetonotus Ehbg. ; Chaetura Metschn.

Section 2. Apodina.

Without caudal fork ; hind end either simply rounded, or lobed and provided
with tufts of hairs. Dasydytes Gosse ; Gossecc Zelinka.

ECHINODERIDAE.*

These are minute marine animals with an elongated body, covered with a strong
cuticle which is divided into segments, and an anterior protrusible spiniferous
proboscis, at the apex of which the mouth opens. The anus opens at the hind
end of the body. The cuticle is produced into bristles and spines. The central
nervous system, which lies in the ectoderm, consists of a nerve-ring surrounding
the pharynx and clothed with nerve-cells, and of a ventral cord with segmentally
arranged groups of ganglia. The alimentary canal consists of a muscular pharynx,
a non-muscular intestine, and a rectum. The excretory organs are represented
by blind ciliated tubes, which open separately on the dorsal surface. The
animals are dioecious ; the testes and ovaries are paired tubes opening ventrally
on either side of the anus. They occur in mud on the sea-bottom, and on marine
Algae.

* W. Reinhard, " Kinorhyncha (Echinoderes), anat. Bau u. Stellung ini
System," Z. f. w. Z., 45, 1887. C. Zelinka, " Ub. Echinoderes," Verh. d.
deutschen Zool. GcseL, 1894.

312 ROTIFERA.

The systematic position of these animals is very uncertain ; indeed, our know-
ledge of their anatomy hardly justifies us in coming to a decision on the matter.
In the published accounts of their anatomy there is no description of the
vascular system, nor is the arrangement of the body-cavity made clear. It
would appear, however, that the kidneys and generative organs are not connected
with any other space, and it is possible that they are to be regarded as coelomic,
as the products of two pairs of coelomic chambers (mesoblastic somites). If this
should turn out to be a correct supposition, it would support the view that they
are related to Annelids — a view which is prompted by the relations and segmenta-
tion of the central nervous system. Ecliinodercs Duj.

CHAPTER IX.

THE COELOMATA.

THE coelom, the possession of which characterizes all the remaining
groups of the animal kingdom, is an organ of the greatest importance,
and one the real nature of which has only recently been appreciated
by anatomists.

Formerly the word coelom was used as synonymous with body-
cavity or perivisceral cavity, and no distinction was recognized
between the body-cavity of the Arthropoda and the same structure
in such forms as the Vertebrata. In fact, there are works on
Zoology now in use in which the term coelom is applied alike to
the blood-containing space of the Arthropods, and to the body-cavity
of Annelids and Vertebrates, which is free of blood, and into which
the generative ducts and kidney tubes open and the generative cells
are dehisced. We now know that the organ called coelom, so far
from being necessarily or primarily a body-cavity, may in some cases
have nothing of that mechanical relation to the viscera which is
implied in the conception of a perivisceral space. It is true that
in the majority of cases a portion of the coelom does enlarge, acquire
a thin smooth wall, and enter into a relation with some of the more
important viscera, a relation the purpose of which is apparently to
enable the functional movements of the internal organs to take place
with the least amount of friction and of resistance from surrounding
structures. But there is one group, the Arthropoda, in which the
coelom, though present and discharging important functions, develops
no such perivisceral portion, and another, the Mollusca, in which the
perivisceral portion is sometimes much limited, not extending to any
other viscus than the heart.

The functions which the coelom discharges in such cases, and the
real nature and relations of the organ will be dealt with more fully
in the general part of this work ; here we shall only consider the
subject in its main outlines, and not being in a position to place all

314 COELOMATA.

the facts before the reader, our treatment of it must be more or less
dogmatic.

The coelom presents the fullest and, what we may call most
typical development in the dibranchiate Cephalopoda. Here it is
divided into three parts, all of which communicate. These parts are,
(1) the genital sac or gonadial coelom, from the epithelial walls of
which the reproductive cells arise ; (2) the viscero-pericardial sac or
perivisceral coelom, which has the functions of a typical body-cavity
for the heart and certain other viscera* (3) the renal sacs or nephridial
coelom, the epithelial walls of which' secrete the nitrogenous waste,
thus performing the functions of kidneys.

As stated above all these sections of the coelom are in communi-
cation, the gonadial with the viscero-pericardial, and the viscero-
pericardial with the nephridial. Moreover, the gonadial and nephridial
open directly to the exterior, the former through the generative ducts,
and the latter through the nephridiopores. From this it would
appear that the coelom, in addition to its mechanical relations, has
two most important functions : the one of these is to bud out the
reproductive cells, and the other to secrete the nitrogenous waste.
These functions are always discharged by the coelom in the Coelomata.
In certain forms, e.g., Peripatus, elasmobranch fishes, Cephalopoda,
some Gastropoda and the Annelida, this is perfectly obvious ; but in
most Arthropods, and in some Vertebrates and Molluscs it is a
matter of inference, and might possibly be disputed by those zoologists
who have not followed recent morphological research. We, however,
have no hesitation in laying it down as a general law that in all
Coelomata the functions of producing the reproductive cells and
secreting the nitrogenous waste are discharged by this organ which
we now call Coelom.

With regard to the origin of the coelom and its relation to other
organs, we have here only the following statements to make.

The coelom is derived from the enteron ; it is a part of the enteric
cavity, which has, in all Coelomata, lost its connection with that
portion which constitutes the alimentary canal in the adult, though
it has retained its connection with the enteron, thus showing its
enteric origin, in the young stages of certain groups, e.g., the
Echinodermata, Chaetognatha, Brachiopoda, Enteropneusta, and in
Amphioxus. In the one division of the Coelenterata, viz., the
Actinozoa, there is an incipient coelom in the enteric pouches, on
the walls of which the reproductive cells are formed. The Coelen-
terata, however, are not Coelomata; they have no organ distinct from

COELOMATA. 315

the enteron concerned with the renal and with the reproductive
functions.

The Platyhelminthes, Nemathelminthes, and Motif era are also not

Coelomata ; or perhaps it would be better to say that they cannot
be ranked as Coelomata in the present state of our knowledge. It
may be that in these phyla also, or in some of them, the progress
of research will show that the renal and reproductive organs are
enteric in origin, and are to be regarded as homologous with the
coelom.

It has already (p. 312) been pointed out that in the lower Tur-
bellaria there is reason to believe, from a study of the adult structure,
that the whole of the mesodermal parenchyma, of which the genital
and renal organs are part, is in reality a portion of the enteric wall.

Finally, before leaving this subject, there is one more point to
notice with regard to the coelom. In all metamerically segmented
animals the coelom is the first organ to show segmentation in the
embryo : it is the first organ to show that repetition along the long
axis which constitutes metameric segmentation. In fact, we may lay
it down as a general law that in metamerically segmented animals
the coelom. is not only the first organ to present segmentation, but
is segmented from its very first appearance, and that the subsequent
segmentation or repetition of other organs is evolved out of this
primal segmentation.

There are a few apparent exceptions to this law amongst certain groups in
which the number of segments is very small, being, in fact, limited to three.
These exceptions are the Brachiopoda, Chaetog-natha, and the Echinodermata.
In the first two of these groups the coelom is said to be separated off as a single
sac on each side, which, presumably, subsequently becomes divided into the three
sacs characteristic of the adult (for qualification with regard to Brachiopods see
chapter on Brachiopoda). In the Echinoderms there is some variation with
regard to this point.

CHAPTER X.

PHYLUM MOLLUSCA.*

Bilaterally symmetrical unsegmented animals, with a ventral foot,
and usually with a radula, a mantle fold, and a univalve or bivalve
calcareous shell. The central nervous system consists of a circum-
oesophageal ring with various ganglionic developments, and both the
haemoeoel and coelom contribute to the formation of the perivisceral
cavities.

The group Mollusca^ with somewhat of its present limits was
established by Cuvier (1798). Linnaeus had used the word before,
but his group Mollusca bore very little resemblance to that of Cuvier,
and even Cuvier himself included in the " embranchement " a number
of forms which are now known to have nothing to do with it.
Cuvier's Mollusca included the Cephalopoda, the Gastropoda, the
Pteropoda, the Acephala, and the following groups now removed
from them : the Brachiopoda, the Tunicata, and the Cirripedia.

In many points the Mollusca resemble the Annelida, with which
phylum they are clearly closely allied. The arrangement of the

* J. Poll, "Testacea utriusque Siciliae, eorumque Instoria et anatome," 3 vols.,
Parma, 1791-1795. G. Cuvier, Memoires pour servir a I'histoire et a I1 anatomic
des Mollusques, Paris, 1817. G. B. Deshayes, "Histoire naturelle des Mollusques
(Exploration de I'Algerie)," Paris, 1844-48. R. Leuckart, " Ueb. d. Morphologic
u. d. Vcrwand. Verhalt. der Wirbellosen Thierc," Braunschweig, 1848. Eydoux
and Souleyet, " Voyage autour du monde sur la corvette la Bonite. Histoire naturelle
Zoologie" Paris, 1852. T. H. Huxley, "On the Morphology of the Cephalous
Mollusca as illustrated by the Anatomy of certain Heteropoda and Pteropoda, etc.,"
Phil. Trans., 1853. Bronn and Keferstein, "Die Klassen u. Ordnungcn der Weidi-
thiere," Leipzig and Heidelberg, 1862-66. E. Ray Lankester, "Contributions
to the developmental history of the Mollusca," Phil. Trans. , 1875. P. Fischer,
" Manual de Conchy liologie et de Paleontologie conchy liologique, Histoire nat. des
Mollusques vivants etfossiles," 2 vols., Paris, 1887. P. Pelseneer, "Introduction
a 1' etude des Mollusques," Bruxelles, 1894. K. A. Zittel, Handbuch der Palaeon-
tologie, Abth. 1, Palaeozoologie, Bd. 2, Mollusca and Arthropoda, Munich and
Leipzig, 1881-85. S. P. Woodward, A Manual of the Mollusca, 3rd Ed., London,
1875.

t For a short literary history of the Mollusca, vide E. Ray Lankester's Article
on Mollusca in the last edition of the Encyclopaedia Britannica, and republished
in " Zoological Articles," London, 1891.

MOLLUSCA. 317

central nervous system as a circum-oesophageal ring, of which the
sub-oesophageal portion may be pulled out into ventral cords; the
presence of a more or less developed perivisceral portion of the
coelom ; the dorsal position of the main vascular trunk ; an/1, finally,
the very general presence of a trochosphere larva, are all important
characters, which point to a connection more close than that which
ordinarily exists between groups of phyletic rank.

On the other hand, the differences, which are also of great
importance, must be noted. The Mollusca are almost entirely
without the phenomenon of metamerism, which is so generally
characteristic of Annelida. It is true that signs of this phenomenon
are not altogether absent, for we find in Nautilus a twofold repe-
tition of the gills, kidneys, and auricles, and in Chiton multifold
repetition of the shell-plates and gills. But these are isolated
instances, and not generally characteristic of the group. Moreover,
so far as is known there is nothing in the embryo comparable to
the repetition of the mesoblastic somites of the Annelids — the
phenomenon by which the adult metamerism is preceded, and on
which it is based. Finally, whereas in Annelids the perivisceral
cavity is entirely furnished by coelom, and the haemocoel is almost
completely canalicular; in Molluscs vascular sinuses are well developed,
and in some parts of the body so large that they constitute perivisceral
cavities to the organs in relation with them. Thus in Molluscs part
of the body-cavity is coelomic — the portion called pericardial or viscero-
pericardial — and part is haemocoelic ; but it must be carefully borne
in mind that the coelomic portion of the body-cavity is entirely
separate from the haemocoelic, and that, however much they may
appear to resemble each other in the adult, their relations and de-
velopment are totally different.

The asymmetry and distortion found in the class Gastropoda is
a very interesting phenomenon, and in some respects comparable to
the still more remarkable distortion from the original symmetry
found in the Echinodermata. But the two phenomena differ in
their mode of occurrence in certain important respects, which it
may be desirable to point out. In Echinodermata not only is the
distortion completely carried out in every living member of the
group, but a new symmetry has in all cases been obtained, and
sometimes (certain Echinoidea) a second time lost. Therefore, in
order to arrive at an understanding of the course which the dis-
tortion has taken, we are entirely dependent upon embryology;
indeed, were it not for the knowledge gained by a study of the

318 MOLLUSCA.

development, we should not know that any departure from the
original symmetry had occurred. In the Gastropoda, on the other
hand, not only is there one form in which there is no asymmetry
at all, but the other members of the group present the distortion
in various degrees, and in no living Gastropod has a new symmetry
been completely attained. It is possible, therefore, by a comparison
of adult forms to arrive at an understanding of the course by which
the distortion in the most extreme members has been brought about.

The Mollusca are unsegmented Eftiimals without jointed append-
ages. The body is covered by a soft, slimy integument, bounded
externally by an epithelium frequently ciliated and containing a
considerable number of gland-cells. They lack both an internal
and external locomotory skeleton, and are therefore especially suited
for life in water. But few of them are terrestrial, and when
this is the case the movements are always limited and slow ; while
the aquatic forms may be endowed with the power of rapid
swimming.

Beneath the epithelium is the dermal connective tissue, which
consists of cells of various forms, branched cells, elongated fibre-
cells, and especially characteristic are the vesicular cells, which
sometimes secrete and contain calcareous concretions or spicules
(Pleurobranchs, and some Nudibranchs). This tissue contains
blood-spaces, the filling of which with blood may cause a turgescent
swollen condition of that part of the integument. Sometimes it is
condensed, and forms the cartilage of the Cephalopoda, the skeletal
tissue of the branchial filaments of Lamellibranchs, the shell of the
Cymbuliidae.

The muscular fibres are generally non-striped. There is often
an appearance of striation in consequence of the arrangement of
the granules, e.g., muscles of buccal mass, of heart, columellar
muscles of the larvae of some Nudibranchs, etc., and in some cases
the fibres are more distinctly cross-striped, e.g., portion of adductor
muscles of Pecten.

The dermal muscular system plays an important part in the loco-
motion of these animals, especially that part of it which is placed
on the ventral surface of the body. In this region it is greatly
developed, and gives rise to a more or less projecting locomotory
organ of very various shape, the foot (Fig. 254).

The foot always consists of an unpaired median structure, which
is sometimes divided into several parts, and may possess, in addi-
tion, paired lateral lobes — the epipodia.

MOLLUSC A. 319

In most Mollusca — the Cephalophora as opposed to the AcepTiala
or Lamellibranchiata — the anterior part of the body is marked off
as a distinct head, and bears the mouth, tentacles, and special
organs of sense. The dorsal part of the body behind, the head
constitutes the main mass of the animal, and is called the visceral
sac. The integument of the visceral sac constitutes the mantle or
pallium, and is nearly always folded near the junction of the
visceral sac with the head and foot. This fold is the mantle-fold^
or pallial-fold, and the groove enclosed by it is the mantle-groove,
or pallial-groove. The mantle-groove contains the gills, anus, and
renal openings, and is nearly always deeper in the neighbourhood
of these structures than elsewhere, thus constituting the mantle- or
pallial-cavity proper. The outer surface of the mantle generally
secretes a calcareous shell — though this structure may, by secondary
modification, be absent in the adult. The head and foot are
attached to the shell by paired and symmetrical muscles in the
Placophora, Scaphopoda, Lamellibranchiata (retractors of the foot),
and Cephalopoda (retractors of the head and funnel) ; and in Gastro-
poda by a single muscle — the columellar or spindle-muscle.

The central nervous system consists of a circum-oesophageal ring
with a uniform coating of nerve-cells, or the latter may be specially
aggregated into ganglia — the cerebral or supra-oesophageal, and the
pedal or sub-oesophageal. In some forms the pedal or ventral
portion of this nerve-ring may extend as a pair of long cords into
the foot (Chiton, Haliotis, etc.). Sometimes there is a second circum-
oesophageal commissure connecting the cerebral and pedal, and pro-
vided with a ganglion — the pleural. These various ganglia give
off nerves — the cerebral to the head, cephalic sense organs and
lips, the pedal to the foot, and the pleural to the mantle and
gills.

In addition to this somatic system, as we may call it, there is
the visceral system, which generally consists of two commissures
with ganglia in their course. Of these there is (1) the stomato-
gastric commissure, which starts on each side from the cerebral,
and is completed ventrally to the oesophagus; the ganglia upon
it are called the buccal, and supply the buccal mass and stomach;,
and (2) the visceral commissure, which starts on each side from
the pleural, and is completed posteriorly ventral to the intestine.
The ganglia upon this commissure vary in number in different
forms, and are called the visceral. They innervate the intestine,
vascular, renal, and reproductive organs. The stomatogastric and

320 MOLLUSCA.

visceral commissures very frequently anastomose (Cephalopoda,
Gastropoda).

Tactile organs. In addition to the general sensibility of the
skin there are tentacles on the head, or in the Acephala on the
mantle-edge. The olfactory sense is partly discharged by the ten-
tacles, and partly by the osphradia, which are sensory patches of
the mantle epithelium near the base of the gills, and are innervated
by nerves from the visceral commissure. The eyes have generally a
complicated structure; there are usually two on the head, and in
rare cases they are found on the mantle-edge (Acephala), and even
on the dorsal surface (Chiton, Onchidium).

Auditory organs, or organs which, from their structure, are
supposed to have that function are very generally present. They
have the form of otocysts, provided with sense-hairs on their
internal walls, and containing one or more otoliths. They are
usually paired, and lie either on the cerebral or pedal ganglia.
They are, however, said to be always innervated from the former.

The alimentary canal (absent in two parasitic forms, Entoconclia
.and Entocolax) is always provided with a mouth and anus. The
mouth is always at the front end of the body, on the head in
the Cephalophora, and the anus opens into the mantle-cavity
behind, excepting in Gastropods, in which the mantle-cavity is on
the front side in consequence of the torsion of the visceral sac.
Three parts can be distinguished^ — (1) the stomodaeum, consisting
of buccal cavity and oesophagus; (2) the mesenteron, consisting of
stomach and intestine; and (3) the proctodaeum, which is very
.short in most forms, even if it can be distinguished at all.

The buccal cavity is absent in Acephala (Lamellibranchs) ; but
in the other forms, which may be called Odontophora, it forms
a chamber with muscular and cartilaginous walls, which receives
the salivary ducts, and has on its floor an apparatus called the
odontophore. This consists of a toothed chitinous ribbon — the
radula, a pair of cartilaginous pieces beneath the buccal floor,
and a sheath in which the ribbon is formed (for detailed descrip-
tion see under Gastropoda, p. 356). There is usually an extensive
liver opening into some part of the mesenteron.

The relations of the perivisceral or body-cavity, in the formation
of which the coelom and haemocoele take varying parts, have already
been described, and will be dealt with again in detail under the
various classes.

The vascular system forms a completely closed system. Even

MOLLUSC A. 321

in cases when some of the vessels open out into large spaces, which
surround some of the viscera and form a true perivisceral cavity,
there is no communication with the coelom, or with any other
organ, or with the exterior. The so-called aquiferous canals, when
present, do not lead into the blood system, but merely"mto spaces
in the integument.

The heart consists of a median ventricle, and of two lateral
auricles (four in Nautilus, one in most Gastropoda) • it is placed
on the dorsal surface in. the pericardium (except in Anomia and the
Oetopoda). As already hinted the ventricle is merely a portion
of a longitudinal dorsal vessel (the rest being formed by the aortae)
comparable to the dorsal vessel of Annelids.

The arteries branch, but, except in Cephalopoda, in which capil-
laries are found, they end in sinuses amongst the organs, from
which the blood passes into the large veins ; these conduct the
blood to the gills, part or all of it passing through the kidney on
the way. In many cases the blood in the mantle passes directly
to the heart without traversing the gills.

The blood is either colourless or of a slightly blue tinge, due to
the presence of haemocyanin (an albuminoid pigment containing
copper). In rare cases it is red owing to the presence of haemo-
globin in the plasma (Planorbis), or in the corpuscles (Solenogastres,
some Lamellibranchs).

A lymphatic gland consisting of a framework of connective
tissue, in which blood corpuscles are formed, is often present on
the course of the aorta.

Respiration is in all cases carried on through the general outer
surface of the body, but in addition special respiratory organs in
the form of branchiae or of lungs are generally present.

The branchiae are projections (often ciliated) of the body surface
and are usually placed in the mantle-cavity. Very generally they
have a certain form designated by the term Ctenidium. A ctenidium
is a branchia consisting of an axis attached to the body and bearing
two rows of projecting lamellae. Although not always found, the
ctenidium is the typical Molluscan gill, and is always contained
to the number of one, two, or four (Nautilus) in the mantle-cavity.
In the Ghitonidae only are the ctenidia more numerous than four.
The gills may have other forms (Nudibranchiata\ and in the
terrestrial forms are absent altogether, the mantle-cavity having
assumed a form and structure suitable for aerial respiration.

The excretory organs, often called the organs of Bojanus, are

Y

322 MOLLUSC A.

special portions of the coelom, and as such are nearly always in
free communication with other parts of the coelom. In Nautilus
alone are they isolated. The glandular tissue of the excretory
organs is arranged in various ways in different forms (for which
see accounts of separate groups). The forms in which the nitro-
genous waste is got rid of is said to be guanin in Cephalopods,
uric acid in many Opisthobranchs, and urea in Lamellibranchs.

The pericardial or viscero-pericardial division of the coelom also
often contains glandular tissue, wlych constitutes the pericardial
gland.

Reproduction is always sexual, and no cases of parthenogenesis
are known in the phylum. The power of reproducing lost parts,
whether cast off voluntarily or lost accidentally, is considerable —
parts of the foot and its appendages, siphons of some bivalves, dorsal
papillae, etc., of some Nudihranchs, cephalic tentacles, arms of
Cephalopoda; and very often the part reproduced may bear organs
of a complicated kind, e.g., eyes, suckers, etc. But this power of
reproducing lost parts is never so great — so far as is known — as to
lead to the complete formation of a new individual from the part
removed from the body, i.e., asexual reproduction is unknown in
the group. The hermaphrodite condition is fairly common.

The genital glands, however much they may be modified, are
always to be regarded as portions of the coelom. This fact is
perfectly obvious in the Scaphopoda, and in some Lamellibranchs
and Gastropoda, in which they open into the renal division of the
coelom; and in the Solenogastres and Cephalopoda, in which they
open into the peri visceral part of the coelom. But in the majority
of Lamellibranchs and Gastropods it is not so obvious ; but there
can be no doubt of this being the real, if modified and concealed,
relation, when such forms are compared with others in the same class
in which the two organs communicate ; and further, it must not be
forgotten that in some Lamellibranchs, and in Paludina amongst
Gastropods, the genital cells can, in their origin in the embryo, be
directly related to the coelom.

Development. We cannot here enter into details of the develop-
ment ; the greatest variety prevails from the large meroblastic eggs
of Cephalopoda, through viviparous forms such as Paludina, to
the immense majority of forms in which the eggs are small, and
the young hatched at an early stage as a larva. The larva always
has the trochosphere form, and soon acquires a shell-gland on its
dorsal, and a rudiment of the foot on its ventral surface (Fig. 268).

MOLLUSCA.

323

The velum at the same time becomes drawn out into lobes, and
we get the well-known veliger larva. A point to notice about the
development is that the blastopore often assumes the form of a slit
which may completely close, or close behind and remajn open in
front as the mouth, or less often close in front and remain open
behind as the anus.

The Mollusca are essentially aquatic animals, and especially
marine; only a few live on land, and these seek damp situations.
They are one of the largest and most diversified of animal groups,
and apparently have always been so since the earliest fossiliferous
periods, for all of the great groups are represented in the Palaeozoic
period, and a Helix, or a form allied to Helix and belonging to the
most specialized of Mollusca is now known even from the Car-
boniferous.

At the present day about 25,000 species are known; they are
distributed over the whole surface of the earth, and are found in
the sea to a depth of nearly 3000 fathoms. Their habits of life
are most various; there are parasitic forms, JEntoconcha, Eulima,
Entocolax, Entovalva, Stilifer, Thyca (all on Echinoderms) ; com-
mensals (e.g., Montacuta) ; fixed forms ( Vermetus, Ostrea) ; pelagic
forms; and creeping forms, the latter constituting the majority.

Their duration of life, where known, varies from one to thirty
years ; the Pulmonates generally live two years, but the garden-snail
has been known to live five years. The oyster is adult at about five
years, and lives to ten years. The Anodonta do not arrive at sexual
maturity till five years, and live for twenty or thirty years.

The following is the classification of the Mollusca adopted in
this work : —

CLASS I. LAMELLIBRANCHIATA.

„ II. SCAPHOPODA.

,, III. SOLENOGASTRES.

„ IV. GASTROPODA,

Sub-class 1. ISOPLEURA.
,, 2. ANISOPLEURA.
Order 1. Streptoneura.
Sub-order 1. Aspidobranchiata.
Tribe 1. DOCOGLOSSA.
,, 2. RHIPIDOGLOSSA.
Section A. Zygobranchiata.

„ B. Azygobranchiata.
Sub-order 2. Pectinobranchiata.
Tribe 1. PTENOGLOSSA.
„ 2. RACHIGLOSSA.

CLASS IV. GASTROPODA— Contimwd.
Tribe 3. TOXOGLOSSA.
,, 4. TAENIOGLOSSA.
Section A. Platypoda.

,, B. Heteropoda.
Order 2. Euthyneura.
Sub- order 1. Opisthobranchiata.
Tribe 1. TECTIBRANCHIATA

(includes Pteropoda).

,, 2. NUDIBRANCHIATA.

Sub-order 2. Pulmonata.
Tribe 1. BASOMMATOPHORA.
,, 2. STYLOMMATOPHORA.

CLASS V. CEPHALOPODA.
Order 1. Dibranchiata.

2. Tetrabranckiata.

324 MOLLUSCA.

Class I.
LAMELLIBRANCHIATA* (PELECYPODA. LIPOCEPHALA).

Symmetrical Mollusca without head or odontophore; with bilobed
mantle, bivalve shell, and usually lamellate gills.

The name of this class f is taken from the form which the gills
present in most members of the group. The fresh-water mussel
Anodonta cygnea is a typical member of the class.

The mantle-fold is in reality a Continuous annular fold of the
dorsal integument, but in connection with the lateral compression
of the body it is especially developed on the two sides of the
animal into a right and left lobe. It is, therefore, usually described
as being bilobed. The mantle secretes over the whole of its outer
surface a cuticular covering, which becomes calcified everywhere
except in the dorsal middle line, forming the two pieces, or valves,
of which the shell is composed. In the dorsal middle line it
remains as an uncalcified elastic membrane — the hinge-ligament —
which connects together the two valves of the shell. The latter
are rarely exactly alike ; nevertheless, the term unequivalve is
only applied to those shells in which the asymmetry is very
marked and the valves can be distinguished as an upper and
lower. In such forms (Ostreidae) the lower valve is the larger
and more arched, while the upper is smaller and flatter, closing
up the concavity of the lower after the manner of an operculum.
The two valves of the shell are in contact dorsally, where they
are also connected by the ligament. This line of contact may be
complicated by the presence of interlocking hinge-teeth. The hinge-
edge with the ligament is, therefore, to be distinguished from the
free edge of the shell, which is divided into an anterior, ventral,
and posterior (siphonal) edge. The anterior and posterior edge

* G. Cuvier, " L'histoire et V anatomic des Mollusques" Paris, 1817. Bojanus,
" Ueber die Athem — und Kreislaufswerkzeuge der ZAveischaligen Muscheln," Isis,
1817, 1820, 1827. Deshayes, "Histoire Naturelle des Mollusques" (Exploration
. de I'Algtrie), 1844-1848. S. Loven, K. Vet. Akad. Hanlgr. Stockholm, 1848.
Translated in the Arch. f. Naturgesch., 1849. Lacaze Duthiers, Ann. des Sc.
Nat. 1854-1861. H. and A. Adams, " The Genera of recent Mollusca" London,
1853-1858. L. Reeve, " Conchologica iconica," London, 1846-1858. R. H. Peck
"The Minute Structure of the Gills of Lamellibranch Mollusca," Quart. J. Mic.
Sci., vol. xvii., 1877. K. Mitsukuri, "Structure and Significance of some aber-
rant forms of Lamellibranchiate Gill," Quart. J. Mic. Sci., xxi., 1881. P.
Pelseneer, "Contribution a 1' etude des Lamellibranches," Arch. d. Biologic, xi.,
1891. P. Pelseneer, "Introduction a V etude des Mollusques," Bmxelles, 1894.

t There does not appear to us to be any sufficient reason for altering this well-
established name in favour of the less suitable, but perhaps more symmetrical
term, Pelecypoda (TreXe/cus, an axe).

LAMELLIBRANCHIATA.

325

may generally be determined by the fact that the hinge-ligament
is posterior to the two umbones (nates), which have the form of
two beak-like prominences projecting over the dorsal edge of the
shell (Fig. 250 bis, u), and indicate the point (o^ea^where the
development of the valves began. The area (c) is behind the apex,
and includes the dorsal posterior side of the shell. The part of the
dorsal edge in front of the apex is usually shorter, and contains,
at least in the equivalve species, an excavation, the lunula (Fig.
250 Us, Z), by means of which the anterior edge can at once be
recognized. The apex in some forms (Isocardia, Diceras) is spirally
twisted.

KIS

M.

VM

M.I

FIG. 250 Ins. — Dorsal view of shell of Lucina
pennsylvanica. AB anteroposterior axis;
CD transverse (right and left) axis ; I
lunula ; u umbo ; d ligament ; c area (from
Perrier, after Fischer).

FIG. 251.— a, Mactra dliptica in its shell;
b, inner surface of left valve of Mactra
solida. KIS dorsal siphon (cloacal or
exhalent) ; KS ventral siphon (branchial
or inhalent) ; P foot ; VM impression of
anterior adductor muscle ; HM impres-
sion of posterior adductor muscle; Ml
pallial line ; Mb pallial indentation.

The hinge-teeth are placed ventral to the umbo. They generally
consist of cardinal teeth placed below the umbo, and of anterior
lateral teeth in front of, and posterior lateral behind, the umbo.
Hinge-teeth are entirely absent in some genera (e.g., Anodonta,
Ostrea).

The ligament is an elastic structure, and is so arranged that it
is either stretched or compressed when the shell is closed by the
action of the adductor muscles. In the former case it connects
the two valves on the dorsal side of the hinge-line (Fig. 250 bis),
and is said to be external; in the latter it is on the ventral side
of the hinge, and is called internal.

326

MOLLUSCA.

While the outer surface of the shell presents various sculpture
markings, the inner surface is smooth and shines with the lustre
of mother-of-pearl. On a closer examination impressions and pits
become visible on the inner surface. A narrow line, the so-called
mantle or pallial line (the line of attachment of the pallial
muscle of the mantle-edge to the shell), is placed near and
fairly parallel to the ventral edgef of the shell (Fig. 251). In
the siphoned forms this presents posteriorly a bend directed
forwards and upwards (Mb) — the p&llial bay or indentation (Sinu-
palliatae).

This curve in the attachment of the mantle-edge permits of the
siphons being contained within the shell when retracted. Impres-
sions are usually caused by the insertion of an anterior and
posterior adductor muscle which pass through the body transversely

from one side to the
other, and are attached
to the inner surface of
the shell (Fig. 251).

While in the equi-
valve mussels (Ortho-
concha) the two im-
pressions are usually
of equal size, in the
unequivalve forms(JD/ew-
roconcha) the anterior
adductor may be re-
duced, and even com-
pletely vanish, in which
case the posterior

adductor has a much larger size and shifts forwards to the middle of
the shell. Hence the names Dimyaria and Monomyaria.

Chemically the shell consists of carbonate of lime and an organic
matrix (conchyolin), which usually has a laminated texture. In
addition to this laminated layer there is also a thick external
calcareous layer composed of large, pallisade-like prisms, which are
placed side by side and may be compared to the enamel of teeth
(Fig. 253). Finally, on the outer surface of the shell there is a
horny cuticle, the so-called epidermis or periostracum.

The internal laminated layer is called the nacreous or mother-of-
pearl layer; it has an iridescent lustre, and is secreted by the
whole surface of the mantle. The middle layer is called the

FIG. 252. — Avicula semisagitta, the valves are shifted over
one another. M impression of the single adductor
muscle.

LAMELLIBRANCHIATA.

327

prismatic layer. It and the periostracum are secreted only by the
free edge of the mantle.

The whole of the shell is a cuticular formation of the epi-
dermis, and its growth is effected in two ways : (1) by additions
to the nacreous layer whereby the shell increases in thickness; (2) by
additions to the prismatic and horny layers, whereby it increases
in superficial extent. Accordingly the outer coloured part of
the shell, which is com-
posed of vertical prisms
and the horny cuticle,
when once formed does
not increase in thickness ;
while new concentric layers
are continually being added
to the colourless nacreous
layer during the whole life
of the animal. It is this
nacreous secretion of the
mantle surface which, when
thrown down round foreign
objects which have worked
their way in between the
mantle and the shell, in
the so-called pearl oysters
(Meleagrind) and to a less
extent in other forms
(Unio, Margaritana), gives
rise to pearls.

In some cases the valves do not meet ventrally, but always gape (Pholadidae,
Gastrochaenidae, etc. ). In exceptional cases the valves are fused dorsally (Pinna}.
The edges of the mantle are folded back over the shell in the Galeommidae
and in Entovalva. In some gaping forms the parts of the body projecting
beyond the shell secrete accessory pieces. Such pieces may be independent
of the shell, as in the case of the dorsal pieces of Pholas (Fig. 270), and the
calcareous tube with which Teredo lines its burrow (Fig. 271), or fused to
the shell, as the calcareous tube of Aspergillum (Fig. 272).

The skin consists of a slimy, one-layered epidermis, beneath
which lies a highly vascular connective tissue traversed by
abundant muscular fibres. The epidermis on the outer surface
of the mantle consists of columnar cells; while on the inner sur-
face the cells composing it are ciliated (Fig. 253). Pigments are
present principally upon the edges of the mantle, which are

FIG. 253. — Vertical section through the shell and
mantle of Anodonta (after Leydig). Cu cuticle or
horny layer (periostracum) ; S prismatic layer ; Bl
laminated nacreous layer (mother-of-pearl); Ep'
external epithelium of mantle ; Bd connective
tissue of mantle; Ep" internal epithelium of
mantle, ciliated.

328 MOLLUSCA.

thickened and frequently folded and beset with tentacles, papillae,
and eyes.

A head, properly so-called, is absent in this class, the parts of
the body in the neighbourhood of the mouth being devoid of
sense-organs. These are placed mainly on the mantle edges, which
are the parts of the body in closest relation with the external
medium.

The edges of the mantle may be entirely free from each other
(those forms in which the gill-filaments are not connected to the
mantle, and in which there is no concrescence of the mantle-lobes,
e.y., Nucula, the Anomiidae, Arcidae, Trigoniidae, Pectinidae); or
they may be united to one another indirectly by the attachment
of the branchiae, e.g., Unionidae, Ostreidae; or they may be fused
with one another in one, two, or three places. When there is
only one fusion it separates off the opening of the cloacal or supra-
branchial chamber from the general mantle-opening (Mytilidae,
Fig. 256, Carditidae, Astartidae, Crassatellidae, most of the Luci-
nidae, etc.). When there are two fusions — as there are in Yoldia
and Leda, and in most of the Eulamellibranchs, and in Septibranchs
— the one separates off the cloacal opening as in the forms with
one fusion, while the second is near the first, and with it bounds
an opening adjacent to the cloacal opening. This second opening
is the branchial opening; it leads into the general mantle-chamber
(Cardlum, Fig. 255). In such forms there is a third opening — the
pedal opening — in front of the second fusion, through which the foot
can be protruded. The size of the foot-opening is in inverse pro-
portion to the extent of the second fusion. When the second fusion
is much elongated, there may be a fourth opening between the
pedal and branchial orifices (Solen, Lutraria, and some Anatinacea).
In some cases, at any rate, this fourth opening is in relation to
the byssus, for in Lyonsia the byssus filaments project through it.
The further forwards the fusion of the two mantle-lobes extends,
the more marked becomes a peculiar elongation of the posterior
mantle region round the inhalent (branchial) and exhalent (cloacal)
openings — an elongation of such a nature that two contractile
tubes or siphons (Fig. 251) become formed (especially in boring
and burrowing bivalves). These may be so large that they cannot
be drawn between the posterior edges of the gaping valves of
the shell. The two siphons are often fused with one another,
but the two canals, with their openings surrounded by tentacles,
remain separate. In the most extreme cases the siphons are

LAMELLIBRANCHIATA.

329

enormously enlarged and the posterior region of the body is
peculiarly elongated and uncovered by the rudimentary shell ; so
that the whole animal acquires a vermiform appearance, the shell-
bearing anterior part of the body constituting the heajl (Teredo,
Fig. 271).

In cases in which there is no fusion the hind end of the edges of
the mantle lobes often presents two slight contiguous excavations
(Anodonta, Fig. 254), the ventral of which is bordered by numerous
papillae, When the two halves of the mantle are applied together
these excavations form, with the corresponding structures of the
opposite side, two slit-like openings placed one above the other.

VA

KrS

RS

V

FIG. 254.— Anatomy of Unio pictorum (after C. Grobben). A region of mantle lobes bounding
the cloacal or exhalent orifice ; Af anus ; Cg cerebral ganglion ; D intestine ; E region of
mantle lobes bounding the inhalent or branchial orifice ; F foot ; G generative organs ;
HA posterior aorta ; Hk ventricle ; HS posterior adductor muscle ; K branchiae ; KrS crys-
talline style ; L liver ; M stomach ; Mg splanchnic ganglion ; MS labial palp ; Mt mantle ;
N kidney ; 0 mouth ; P pericardial gland ; Pg pedal ganglion ; Va anterior aorta ; Vh auricle ;
VS anterior adductor muscle.

The dorsal of these two openings functions as the cloacal (exhalent)
opening, the ventral as the branchial (inhalent). So that in such
cases, though there is no actual fusion, functionally two siphons are
present as in the siphoned forms.

The most important of the muscles attached to the shell are
(1) those of the edge of the mantle : these are attached to the
pallial line of the shell, and serve to retract the edges of the mantle;
the siphonal muscles which serve for the retraction of the siphons
are a specialized portion of this system, and arise from the pallial
indentation. (2) The adductors which pass from valve to valve of

330

MOLLUSCA.

ES

the shell. These are typically two in number (Dimyaria), but in
some forms the anterior adductor is smaller than the posterior
(Mytilus), and may be absent altogether (Monomyaria), as in Ostrea,
Pecten, etc. (Fig. 252). The adductors sometimes consist of two
parts of a different aspect : the fibres of one of these parts are said
to be transversely striated, and capable of rapid contraction, those
of the other being smooth, but this has been denied. (3) The
anterior and posterior retractors, which are specialized portions of

the adductors, serve
for the retraction of
the animal into the
shell; and the pro-
tractor which passes
from its attachment
just behind the ven-
tral portion of the
anterior adductor.

The foot, which
often contains some
of the viscera (intes-
tine, liver, and gon-
ad), is completely
absent in compara-
tively few forms, and
only in those which
have lost the power
of locomotion (Os-
trea, Anomia, Teredo,
etc.). In many
forms, principally in
the larva, less fre-
quently in the adult
(Mytilus, Fig. 256), the foot possesses a byssus gland, which secretes
silk -like fibres, by which a temporary or permanent attachment
of the animal is effected. The form and size of the foot vary
very considerably, in accordance with particular kinds of locomotion.
The foot is most frequently used for creeping in sand, and is then
hatchet - shaped ; in other cases it is spread out laterally, and its
creeping surface has the form of a disc. More rarely it is of a
large size and bent, in which case it is used for springing movements
in the water (Cardium, Fig. 255). Some Lamellibranchs possess a

M

FIG. 255.— Anatomy of Cardium tuberculatum (after C. Grob-
ben). A exhalent siphon ; A auricle of heart ; Af anus ;
D intestine ; E inhalent siphon ; F foot ; G generative
organ ; Goe generative opening ; HS posterior adductor ;
K gill of right side ; L liver ; M right lobe of mantle ; Mg
stomach ; N kidney ; 0 mouth ; S right valve of shell ;
V ventricle ; VS anterior adductor muscle.

LAMELLIBRANCHIA TA.

331

FIG. 256. — Mytilus edulis attached by its byssus to a piece
of wood (after Meyer and Moebius).

linear club-shaped or cylindrical foot (Solen, Solenomya\ and move
by rapidly retracting it and ejecting water through the siphons.
Many use the foot for burying themselves in mud ; others bore into
wood (Teredo}, or hard rock (Pholas, Lithodomus, Saxicfiva, etc.),
for which purpose
they push them-
selves against the
rock with their
short blunt foot,
and use the hard
and often serrated
edge of their shell
as a ' grater, giving
it a rotatory move-
ment. According to
Hancock, the foot
and edge of the
mantle at the an-
terior edge of the gaping shell are beset with silicious crystals, and
effect the excavation of the rock after the manner of a file.

The protraction of the foot is due to its turgescence by blood ; its retraction
to the retractor muscles. An aquiferous pore by which the vascular system
communicates with the exterior does not exist.

The byssus-gland opens by a pore in the middle line of the foot. It is
well-developed in the adult in Anomia, Area, Mytilus, Avicula, Pecten,
Saxicava, Lyonsia, Tridacna, Dreissena, etc. In Anomia the byssus passes
through a hole in the right valve, and is calcified.

The nervous system presents three pairs of ganglia, the cerebral
(supra-oesophageal), pedal (sub-oesophageal), and visceral ganglia
(Fig. 257). In Nucula (Fig. 258) there is, in addition, close to
the cerebral a pair of pleural ganglia; these are connected with
the pedal by a pleuro-pedal connective which, however, joins the
cerebro-pedal connective before it reaches the pedal. In Solenomya,
in which there is also a pleural ganglion, the pleuro-pedal con-
nective is fused with the cerebro-pedal throughout almost its whole
extent. In all other Lamellibranchs a pleural ganglion is not
present as a distinct ganglion, but is in all probability fused with
the cerebral, which must, therefore, be regarded as a cerebro-pleural
ganglion. The visceral ganglia are on the hinder part of the
visceral loop ; they are usually placed on the ventral side of the
posterior adductor muscle.

332

MOLLUSCA.

Since there is never a distinct head and sense-organs are not present upon
the anterior part of the body, the cerebral ganglia are but slightly developed
They supply mainly the regions round the mouth and the anterior part of
the mantle, to the margins of which two large nerves pass. They also send
fibres along the cerebro-pedal connective to the otocysts. The two ganglia
are frequently (Unio) far removed from one another laterally, and are some-
times approximated to the anteriorly
placed pedal ganglia (Pecten\ the nerves
of which supply the ventral region of
the body. The pedal ganglia are reduced
when the foot is atrophied.

The visceral ganglia innervate the
viscera, the gills, the heart, and the

FIG. 257.— Nervous system of the pond mussel
Anodonta (after Keber). 0 mouth ; A anus ;
K gills ; P foot ; Se labial palps ; Gg cerebral
ganglion ; Pg pedal ganglion ; Vg splanchnic
(visceral) ganglion; G generative gland ; Oe'
external opening of generative gland ; Oe"
opening of kidney.

Fio. 258. — Dorsal view of nervous
system of Numla, the middle part
of the foot is represented by dotted
shading (after Pelseneer). / pleural
ganglion ; II pleuro-pedal connective ;
///combined pleuro-pedal and cerebro-
pedal connective; IV nerve to the
otocyst ; V pedal ganglion ; VI visceral
ganglion ; VII posterior pallial nerve ;
VIII osphradiurn ; IX visceral commis-
sure ; X otocyst ; XI canal from otocyst
to exterior, and XII its external open-
ing; XIII cerebro-pedal connective;
XIV anterior pallial nerve ; XV nerve
to palps; XVI cerebral ganglion.

posterior part of the mantle. The nerves supplying the latter are two large
trunks which run in the edge of the mantle, and anastomose with the mantle
nerves from the cerebral ganglia. Large nerves also pass from the visceral
ganglia to the siphons, at the base of which they form a pair of accessory
ganglia.

LAMELLIBRANCHIATA. 333

Sense organs. Auditory, visual, tactile, and probably olfactory
organs are present. The auditory organs have the form of paired
otocysts placed in the foot. They are apparently innervated from
the pedal ganglia, or from the cerebro-pedal connective je^ose to the
pedal ganglion, but the nerve fibres really arise in the cerebral ganglia.
They contain one or more otoliths, and are lined by hair-cells and by
ciliated cells. In the Protobranchiata (Fig. 258) they open to the
exterior by a fine canal, and contain foreign bodies (fine grains of
sand).

Eyes, when present, are placed on the edge of the mantle : they
may either be simple pigment spots at the end of the respiratory
tube (Solen, Venus), or they may be more highly developed and
placed along the edges of the mantle in Area, Pectunculus, Tellina,
and especially in Peden and Spondylus. In the two latter genera

FIG. 259.— Openings of the siphons of Cardium edule (from Perrier after Mb'bius).

they are placed on stalks between the marginal tentacles, and have
an emerald-green or brown-red colour : they consist (Fig. 260) of an
eye-bulb with a corneal lens, choroid, iris, and a well-developed layer
of rods, into the external ends of which the optic nerve (from the
circumpallial nerve) passes. The sense of touch is specially localized
on the exposed parts of the body, i.e. on the edges of the mantle
and round the openings of the siphons. In these regions there are
very generally present papillae, cirri, or even tentacles (Fig. 259).

The olfactory sense is supposed to reside in the so-called osphra-
dium, which is a pigmented patch of epithelium placed one on each
side close behind the gills (in the roof of the supra-branchial chamber
near the visceral ganglia) ; it is innervated from a small ganglion
placed close to the visceral on the visceral commissure, in which its
nerve-fibres run from their origin in the cerebral ganglion.

334

MOLLUSCA.

Many bivalves, especially littoral forms, are highly sensitive to light. This
is due to the presence of pigmented cells with a refractile cuticle on the edge of
the mantle ; these may be aggregated, as in Area, into groups, and so assume
the form of a compound eye. In Area some of the eyes have the form of pits

FIG. 260. — Axjal section through the eye of Pecten (from Lang after Patten), c cornea;
I lens ; ep pigmented ectoderm ; g layer of ganglion cells ; r retina ; st layer of rods of
retina ; d tapetum ; e pigment ; /sclerotic; n optic nerve, nl and nz its two branches.

of the skin, while in others the sensitive surface is convex towards the light,
and the eye forms a slight projection on the surface : the latter are on the type
of compound eyes. In Pecten and Spondylus the eyes are much more complex
(Fig. 260). They are placed at the end of short tentacles at the edge of the

LAMBLLIBRANCHIATA. 335

mantle, and the sensitive surface is concave ; the light being refracted on to it
by a cellular lens. Further, these eyes are constructed on the so-called verte-
brate type, the optic nerve entering the retina on the side turned towards the
light and running back to the rods, which are on the inner side of the retina.

Alimentary canal. The mouth is at the front end of the body,
and ventral to the anterior adductor when that is present. It is
placed on the median bridge, which connects the two labial palps
(Fig. 263). These latter structures are extensions, so to speak, of
the margins of the mouth. They are usually bilobed at the end
remote from the mouth, and marked by a median groove running
from the cleft between the peripheral lobes to the mouth. Their
surface on each side of the median groove is marked by transversely
directed grooves leading into the median groove. The whole sur-
face is richly ciliated, and they are to be looked upon as food-
procuring organs which create currents of water, carrying the
floating particles of which the food of these animals consists to the
mouth. Jaws and tongue are always absent. The mouth leads by
a short oesophagus into the stomach, at the pyloric end of which
there is sometimes a blind sac. A rod-like transparent structure
(crystalline style) is often present in this diverticulum of the
stomach, or in the alimentary canal itself. The significance of
this structure is doubtful, but it is a secretion of the alimentary
epithelium, and is probably to be regarded as a reserve of nutri-
ment, for it is periodically renewed. The liver or hepato-pancreas
surrounds the stomach, and opens into it by a duct on either side ; it
also extends into the foot. The intestine is of considerable length,
is much coiled, and is surrounded by the liver and gonads; it
projects into the foot, and then ascends again behind the stomach
to the dorsal surface, where it enters the pericardium and passes
through the ventricle. After leaving the ventricle it passes dorsal
to the posterior adductor muscle to open at the end of a short
papilla into the cloacal chamber.

Vascular System. The heart, which is contained in the pericar-
dium and lies in the dorsal region slightly in front of the posterior
adductor, consists of a median ventricle and two lateral symmetri-
cally placed auricles. The ventricle is continued as an anterior
aorta dorsal to the intestine, and a posterior aorta ventral to it.
The ramifications of the aortae lead the blood into a complicated
system of lacunae in the mantle and in the interspaces between
the viscera. These represent the capillaries and finer venous vessels.
From them the blood passes into the large venous sinuses, the

336

MOLLUSCA.

TS

VR

chief of which are two lateral sinuses placed at the bases of the
gills and a pedal sinus leading into the large median sinus or
vena cava in the floor of the pericardium. The course of the
circulation, though it cannot be certainly determined, seems to be
somewhat as follows : the blood from the mantle, which acts as
a respiratory organ, returns directly to the heart; of the rest of
the systemic blood, part is supposed to go direct to the gills, and
thence to the auricles ; the bulk of it, however, is probably collected
into the vena cava, whence it pastes through blood spaces in the

adjacent kidneys to the gills, and
thence to the heart. There is a valve
at the junction of the main pedal
sinus with the vena cava, which closes
during the turgescence of the foot.

The blood is generally colourless, though
in some forms it has a bluish tint owing
to the presence of haemocyanin. It contains
amoeboid cells, and in Solen legumen and
Area none discoidal corpuscles charged with
haemoglobin, which gives the blood a red
colour.

The relation of the ventricle to the rectum
varies in different forms. As a rule the
rectum perforates the ventricle, but it passes
dorsal to it in Area, Nucula, and Anomia,
ventral to it in Teredo and most species of
Ostrea, and has a tendency to the latter
arrangement in Pinna, Perna, and Avicula.

The vascular system does not communicate
either with the exterior or with the peri-
cardium.

In Area (Fig. 261) there are two ven-
tricles, and each gives off a single artery,
which divides at once into an anterior and
posterior vessel ; the two anterior arteries
fuse to form a single anterior aorta, and
the two posterior unite into a posterior
aorta.

In Ostreidae (Fig. 262) the auricles have partly coalesced, though their outer
portions have remained distinct.

Organs of respiration. The Lamellibranchs possess two ctenidia
attached to the ventral surface of the body, one on either side of the
foot. In the simplest cases (Protobranchiatd) the ctenidium has the
typical Molluscan form (Figs. 263, 264 A) ; that is to say, it consists
of a vascular axis bearing two rows of hollow lamellate processes or

•Ad

FIG. 261. — Dorsal view of Area noae
removed from the shell (after
Grobben). The double pericardial
cavities P are opened, and the
rectum D turned forward. VS
anterior, HS posterior adductor
mnscle ; VR anterior, HR posterior
retractor ; V ventricle ; A auricle ;
Ao anterior, Ao' posterior aorta;
N kidney.

LAMELLIBRANCHIATA.

337

filaments. The axis projects freely posteriorly, and the filaments are
directed transversely in Nucula and Leda, while in Solenomya one is
directed dorsally and the other ventrally. In the Filibranchiata the

ft

IV

FIG. 262.— Heart of Ostrea
magnified (after Poli,
from Pelseneer). 7 fused
auricles ; II afferent
veins ; III ventricle ; IV
aorta.

FIG. 263.— Ventral view ofNitcula (after
Deshayes, from Perrier). a anterior
adductor muscle ; b ctenidium ; d
posterior adductor; I labial palps;
m internal surface of mantle ; o pos-
terior appendage of palps ; p foot.

branchial processes of the ctenidial axis have the form of filaments
(Fig. 264 B), which project ventrally into the mantle cavity ; more-
over, they are bent upon themselves in such a manner that the reflected
portion, or ascending limb, is external in the case of the filaments^of

FIG. 264. — Series of diagrams of transverse sections, illustrating the different arrangement of
the gills in Lamellibranchs. A, Protobranchiata. B, Filibranchiata. C, Eulamellibranchiata.
D, Septibranchiata. 1 mantle ; # body ; 3 foot ; £ suprabranchial cavity ; 5 branchial
(mantle) cavity ; e outer plate or filament of ctenidium— descending limb ; ex ascending
limb of e ; i, il the corresponding parts of the inner filaments of ctenidium; o pores in s the
branchial membrane of the Septibranchiata (from Lang).

338

MOLLUSC A.

V\

\j

the outer row, and internal in the case of the inner filaments. The
adjacent filaments of the same row, both in their descending and
ascending limbs, are held together by the inter-
locking of some especially long cilia (Fig. 265, cj) ;
and the ascending and descending limbs of the
same filament are in some cases united by fusion

of tissue at
certain points,
'giving rise to
the so - called
interlamellar
concrescences
(Fig. 266, ilj).
Further, the
ends of the as-
cending or re-
flected limb of
the outer fila-
ments may be
united to the
mantle, or may
be free (Fig.
264 B, C), and
similarly the
ends of the as-
cending limbs
of the inner
filaments may
be free, or
those behind
the foot may
be united with
their fellows a-
cross the middle

line, thus forming a septum, which cuts off a supra-
branchial chamber from the general mantle cavity.

In all the Eulamellibranchiata and in a few of
the Pseudolamellibranchs (Ostreidae, Lima, Pinna,
etc.), the neighbouring filaments of the same row,
in both their limbs, are united at certain points by interfilamentar
vascular concrescences (Fig. 267). The filamentous character is still

FIG. 265. — Transverse section through the as-
cending and descending limbs of two adjacent
gill-filaments in Mytilus (after Peck). The
two filaments are connected by a ciliary
junction in the upper part of the figure.
be blood-corpuscle ; ch chitinous layer ; cj
ciliary junction ; ep epithelial prominence
which carries the cilia of a ciliary junction ;
fe frontal epithelium ; lac lacunar (vascular)
tissue ; Ife1 latero-frontal epithelium with
long cilia ; Ife" second row of the same.

FIG. 206. — One fila-
ment of the gill of
Mytilus (after Peck).
fil descending limb,
fol ascending limb of
the filament ; ilj in-
terlamellar concres-
cence ; ep position
of interfilamentar
ciliary junctions.
The ascending limb
ends freely in a hook-
like manner. The
apex or angle of the
filament is grooved.

LAMELLIBRANCHIATA.

339

obvious, but both the descending and ascending limbs of adjacent
filaments are connected so as to form a kind of trellis-like mem-
brane, the ascending limbs into one membrane and the descending
limbs into another. Between the porous membranes ^o formed
is contained a space, which communicates with the general mantle-
chamber by the
pores left be- P

tween the fila-
ments where the
latter have not
undergone these
interfilamentar
concrescences.

In this way
the Eulamelli-
branch condi-
tion, in which
there appear to
be on each side
two gills, each
composed of two
lamellae, is ar-
rived at. A very
similar condition
is presented by
the Filibranchs
and some Pseudo-
lamellibranchs,
the difference
being that in
these groups the
lamellae of the
gill break up at
the slightest
touch into their
constituent fila-
ments, because the filaments are only held together by the inter-
locking of cilia; whereas in the former the lamellae are coherent,
because the filaments (which are still perfectly obvious) are held
together by continuity of tissue. Further, in the Eulamellibranchs
the outer lamella of the outer gill has undergone concrescence with

FIG. 267. — Pieces of transverse sections through the branchiae of
Anodonta (from Lang, after Peck). A outer, B inner gill. In
each section the two lamellae are shown as connected together
by the interlamellar concrescences, which are formed by the
sub-filamentar vascular tissues of, in B. The interfilamentar
concrescences are effected by the same tissue. In C, which is
a part of B more magnified, this tissue is marked il, lac, and ol ;
and the filaments with their frontal epithelium and their chit;-
nous tissue ch, and rods chr. ol outer lamella ; il inner lamella ;
v blood vessel ; of subfllamentar tissue ; /filaments ; ch chitinous
tissue of filaments ; chr specially condensed chitinous rod in ch ;
lac subfilamentar tissue.

340 MOLLUSCA.

the mantle (Fig. 264), and the inner lamella of the inner gill with
its fellow across the middle line behind the foot. In this way a
septum is formed which divides the mantle cavity into a dorsal part
— the suprabranchial cavity, and a ventral — the general mantle cavity.
These two cavities communicate by the pores in the gill lamellae, and
in many forms along the sides of the foot where the inner lamella
of the inner gill may end freely, not having undergone concrescence
with the foot. In some forms the inner lamella of the inner
gill is joined to the base of the foot in front, but not behind
The part of the suprabranchial cavity within the gill lamellae is
broken up by vascular strands which connect the lamellae, and
which result from the interlamellar concrescences already referred
to. In the siphoned forms the median septum resulting from
the . fusion of the inner lamellae of the inner gills across the
middle line is continued into the siphon, and causes the division
of that tube into a dorsal or exhalent channel, which communicates
with the suprabranchial chamber, and a ventral or inhalent which
communicates with the general mantle-cavity.

In the Septibranchiata (Fig. 264 D) the gills are represented by
a muscular septum which is perforated by a certain number of pores,
and which, being fused with the mantle and foot and being con-
tinuous across the middle line behind the foot, completely divides
the mantle-cavity into a dorsal and ventral part.

The filaments of the gills are always clothed with an epithelium,
which is in part at any rate ciliated. The cilia are specially long on
the so-called latero-frontal cells (Fig. 265), and in the Filibranchs and
Pseudo-lamellibranchs on the ciliated discs of the ciliary junctions.
The filaments are moreover stiffened by a dense chitin-like connective
tissue, which in the Filibranchs forms a tube (Fig. 265) lying just
beneath the epithelium and surrounding the central blood space
(which is often divided by a septum) ; and in the Eulamellibranchs,
on the other hand, this chitinous supporting substance has the form
of two stout rods lying side by side in the filament part of the gill
(Fig. 267 (7), the vascular tissue being mainly contained in the
internal outgrowths of the filaments, which have brought about
the interfilamentous and interlamellar concrescences (Fig. 267, of,
il, lac, and ol).

Amongst the Eulamellibranchs we find some peculiar modifications of the
outer gill. In Tellina it is directed dorsally ; in the Anatinacea it is directed
dorsal ly and the outer lamella is absent ; in Lucina it is absent altogether.

In Pseudolamellibranchs and some Eulamellibranchs the gills are folded along

LAMELLIBRANCHIATA. 341

dorso-ventral lines, each fold including a certain number of filaments. The
filament at the re-entering angle of each fold is stronger than the others.

Summary and additional details of gill-structure. The successive filaments
of the same row are united (a) by the cilia of the lateral cells (Nuculidae,
Solenomyidae, Anomiidae} ; (V) by the cilia of the ciliated disks <>£ the ciliary
junctions (Arcidae, Trigoniidae, Mytilidae, Avicula, Pecten, and Meleagrina] ;
by vascular interfilamentar concrescences (Lima, Ostrea, Pinna, and all Eula-
mellibranchs). Interlamellar concrescences, i.e. fusions between the ascending
and descending limbs of the same filament, or between the lamellae of the same
gill, are absent in Anomiidae, Arcidae, Trigoniidae ; they are present in a non-
vascular form (i.e. consist only of epithelium and connective tissue) in Mytilidae,
Pectinidae, and in a vascular form in Pseudolamellibranchs except Pectinidae,
and in Eulamellibranchs. Finally there are forms like Lima with non-vascular
interlamellar concrescences and vascular interfilamentar junctions.

Concrescence of the gills with the mantle and with those of the opposite side,
is absent in Nuculidae, Solenomyidae, Arcidae, Trigoniidae, Pectinidae. In
Anomia there is concrescence between the two branchiae, but none with the
mantle. In all other Lamellibranchs they are fused to the mantle by the
ascending limb of the outer filaments, and to their fellows across the middle
line by the ascending limb of their inner filaments behind the foot.

Excretory system and pericardium. The pericardium is a dorsal
median chamber enclosing the heart (except in Anomia). There are
two nephridia — the so-called Organs of Bojanus. These usually have
the form of twisted tubes, more or less dilated in certain parts, and
opening at one end into the pericardium and at the other to the
exterior on the ventral surface of the body on each side of the foot.
The part of the tube which opens into the pericardium is generally
lined with yellow or dark-coloured glandular tissue, which secretes
concrements containing calcareous matter, uric acid, and guanin. The
kidneys of the two sides communicate in some forms. In Ostrea the
glandular part of the kidneys is a branched gland ramifying on the
surface of the visceral mass.

The pericardial glands are differentiations of the epithelial lining
of the pericardium. They may be placed on the auricles, to which
they impart a yellow colour, or near the auricles at the anterior end
of the pericardium.

Generative organs. The sexes are, with a few exceptions (some
species of Pecten, Ostrea, Cardium, and the genera Cydas, Pisidium,
Poromya, JEntovalva), separate, and except in some species of Unio
do not present external differences. The generative glands lie
amongst the viscera, and have the form of lobed or racemose glands,
which are placed near the liver, surround the windings of the
intestine, and extend into the base of the foot, and in some forms
into the mantle lobes (Mytilus). The testis and ovary can often be

342 MOLLUSCA.

distinguished from one another by their colour ; the ovary being red,
and the testis milk white or yellow. In the Protobranclis the
generative glands open into the kidney near the pericardial opening ;
in the Anomiidae and Pectinidae also into the kidney, but nearer
the external opening. In Ostrea, Cyclas, and some Lucinidae
they open with the renal duct by a common opening. As a rule,
however, the two organs (renal and genital) open separately,
but close together, on the external side of the visceral commissure
(Fig. 257).

In the hermaphrodite forms the whole gland may be herma-
phrodite even to the ultimate acini, which produce ova and
spermatozoa simultaneously or alternately (Ostrea edulis and plicata) ;
or the male and female follicles may be separate, and open together
by a common duct (species of Pecten and Cyclas), or by separate
ducts leading to separate openings (Poromya, Anatinaced). Herma-
phrodite individuals are sometimes met with in the fresh-water
mussels — Unio and Anodonta.

Development. The fertilization of the eggs is sometimes effected in the
branchial cavity, and the first part of the development often takes place in
the mantle cavity, or between the lamellae of the inner (Cyclas} or outer gill
( Unio, Anodonta) as in a brood-pouch ; sometimes it takes place outside the
mother (Pecten, dioecious Ostreae, Mytilas, in all of which artificial fertilization
is possible). In Ostrea edulis it is effected in the oviduct. The egg is surrounded
by a vitelline membrane with a micropylar aperture at one point.

The segmentation is unequal (Fig. 268), the formative pole being opposite to
the micropyle. The gastrula is generally formed by epibole, rarely by imagina-
tion. The blastopore sometimes remains open, e.g. Ostrea, or closes, e g. Cyclas,
Teredo, but the mouth is formed almost immediately by an ectodermal invagina-
tion at the same point. The stomach, liver, and intestine are formed from the
endoderm, and the proctodaeum is established later as an ectodermal invagination
after the shell has been formed.

The embryo, which is partially ciliated and often rotates within the egg-
membranes, soon acquires a preoral ring of cilia and a shell-gland (Fig. 268).
The latter is on the side opposite to the blastopore, and gives rise to a pellicle
which is calcified from two symmetrical points, thus forming the rudiments of
the two valves (Fig. 268 c). The cuticular shell remains uncalcified in the middle
dorsal line, where it gives rise to the ligament. An ectodermal invagination,
giving rise to the byssus gland, is almost always formed at the hind end of the
foot, even in forms which are without a byssus in the adult. The anterior ad-
ductor appears before the posterior. Among the provisional arrangements the
velum, as the preoral ciliated ring is called, is very generally present, and in
the free-swimming larvae has the form of a large ciliated ring or collar ; a pair
of larval eyes provided with a lens may also exist within the velar area.

The gills appear as filaments, one by one from behind forwards in the posterior
part of the larva between the mantle and the visceral mass. A pair of larval
kidneys has been observed in some groups (Fig. 268 d, N). They consist of an

LAMELLIBRANCHIATA.

343

internal part, having the form of a ciliated canal, and of a superficial part which
opens externally on the posterior and ventral side of the cephalic region (Cyclas,
Teredo).

The development of the fresh-water forms (Cyclas, Unio, Anodonta), in which
the eggs and embryos are contained in well protected brood-pojjches, may he

En

Mz

FIG. 268. — Stages in the development of the larva of Teredo (after Hatschek). EG ectoderm ;
En endoderm ; Ms mesoderm. a, median optical section of an embryo with two mesoderm
cells Ms and two endoderm cells En. b, ciliated embryo with mouth 0, stomach, intestine,
shell-gland Sdr and shell S. c, later stage with anal imagination A, apical plate Sp, and
more extensive shell S. d, Trochosphere larva of Teredo. 0 mouth ; A anus ; Prw preoral
ciliated ring or velum ; Pow postoral ciliated ring ; N larval kidney or pronephros (head-
kidney) ; Ot otocyst ; Pg pedal ganglion ; Mz mesoderm.

called direct. The marine Lamellihranchs on the other hand are set free at an
early stage and swim about for a long time as larvae with large umbrella-like
vela, from which the labial palps are developed.

The Unionidae have a somewhat complicated development.* The eggs are

* Schierholz, C. "Ueber die Entw. d. Unioniden," Denkschr. k. Akad. Wiss.
zu Wien, Math.-Naturw. Bd. 45, 1889.

344 MOLLUSCA.

laid in spring or summer, and pass into the space between the lamellae of the
inner gill, and thence into that between the lamellae of the outer gill at the
posterior end of the gill, where these spaces communicate. In this space they
remain as in a brood-pouch, and undergo the first stages of their development.
These take two months. They then cease to develop, and pass the winter in the
brood-pouch. In the following spring they pass out by the exhalent orifice
under the larval form, known as Glochidiiim (Fig. 269). This possesses a bivalve
shell with hooks in the middle of the ventral edge of the valves, a single
adductor (the anterior), and a byssus thread which appears to arise just behind
the adductor. They swim by snapping their valves, and attach themselves to
the skin (gills or fin) of a fish, in which 4hey become embedded. Here they
remain as parasites from two to five weeks, and undergo further development ;
but they are not fully formed for some time after leaving their host. The gills
grow, and the external lamina is not developed till the third year. Sexual
maturity is not attained till the fifth year, and growth continues later.

FIG. 269.— Ventral view of the Glochidium of Anodonta (from Pelseneer after Schierholtz).
a bunch of setae ; b visceral ganglia ; c stoinodeal invagination ; d ciliated patch ;
e enteron ; / lateral pits ; g hooks on the edge of the valves ; h byssus filament ;
i the single adductor.

The Lamellibranchs are all aquatic animals, for the most part
marine, but a few are fresh-water. They feed on microscopic,
mainly vegetable organisms (Diatoms, etc.), which float in the water,
and are conveyed to them by currents set up by the cilia of the
mantle-chamber. The Septibranchs alone are carnivorous. A great
many forms live partly or wholly embedded in sand or mud, procuring
food and water and getting rid of waste by their siphons which
project at the surface. Many are sedentary, being attached to
foreign objects by their byssus, or by one of the valves of their
shell (Ostrea, Spondylus). Some are borers into wood (Teredo) or
into stone (Lithodomus, Pliolas, Clavagella). Some build nests by
means of their byssus (Lima) ; while some are commensals — Modio-

PROTOBRANCHIATA FILIBRANCHIATA. 345

laria marmorata in the test of Ascidians; Vulsella in sponges;
Montacuta on Spatangids ; Entovalva is parasitic in the oesophagus of
Synapta. Some species are very active, leaping by aid of their foot
(Cardium, Tellina, etc.); some are crawlers (Cyclas, Lasaea\ and some
swimmers, by napping the valves of their shells (Pecten, Lima).

The Lamellibranchs are found in all parts of the world to the
number of more than 5000 species. They have been found to a
depth of 2900 fathoms. They have a wide distribution in the
earlier periods of the earth's history, being known since the Silurian.
Their fossil shells are most excellently preserved, and they are of the
greatest importance as characteristic fossils for the determination of
the age of formations.

Order 1. PKOTOBRANCHIATA.

The gill-filaments are plate-like and not reflected, and the mantle-cavity is not
divided into two parts.

The mantle has an hypo-branchial gland external to each gill ; the foot has a
ventral plantar surface, and the byssus gland is but slightly developed. The
nervous system has a distinct pleural ganglion ; the otocysts are connected with
the surface by a tube. The sexes are separate, and the genital glands open into
the inner end of the kidney-tube.

Fam. 1. Nuculidae. Palps large, with posterior appendage (Fig. 263).
Nucula Lam., heart dorsal to rectum; Leda Schumacher, heart traversed by
rectum, mantle with two siphons; Yoldia Moll.

Fam. 2. Solenomyidae. The palps are not bilobed ; in each gill one ro\v
of filaments is directed dorsally, the other ventrally. Mantle lobes fused,
having a single posterior opening, and one anteriorly for the foot, tiolenomya
Lam.

Order 2. FILIBRANCHIATA.

The gill-filaments are reflected, and united by ciliary junctions. The foot
usually with a well-developed byssus apparatus.

Sub-order 1. ANOMIACEA.

Asymmetrical; posterior adductor large ; heart dorsal to rectum, and causing
projection into mantle-cavity; the reflected limbs of the inner filaments are
fused across the middle line with their fellows ; genital glands open into kidney,
and that of right side extends into mantle.

Fam. 1. Anomiidae. Anomia L., byssus calcified, passing through a hole in
the right valve. Placuna Bruguiere.

Sub -order 2. ARC ACE A.

Symmetrical ; mantle open ; both adductors well developed ; gills without
interlamellar junctions ; renal and generative openings separate.

Fam. 2. Arcidae. Edges of mantle with compound pal Hal eyes. Pectunculus
Lam., Limopsis Sassi ; Area L., heart dorsal to rectum (Fig. 261).

Fam. 3. Trigoniidae. Trigonia Bruguiere.

346 MOLLUSCA.

Sub-order 3. MYTILACEA.

Symmetrical; mantle-lobes fused posteriorly; anterior adductor smaller than
posterior; a single aorta; gill-filaments with interlamellar junctions; genital
glands extending into the mantle, and opening by the side of the kidney
openings.

Fam. 4. Mytilidae. Mussels. Attached by the byssus fibres of the tongue-
shaped foot. Mytilus L. ; M. edulis L. (Fig. 256), edible mussel of North Sea
and Baltic ; Modiolaria Loven ; Modiola Lam. ; Lithodomus Cuv. ; L. dadylus
Sow., Mediterranean (Temple of Serapis at Pozzuoli).

-
Order 3. PSEUDOLAMELLIBRANCHIATA.

Mantle entirely open; gills folded and filament at reentrant angle of fold
modified; inter filamentar junctions effected by ciliated: discs or vascular con-
crescence.

Foot feebly developed ; anterior adductor usually absent ; the auricles
communicate with one another ; the branchial filaments have interlamellar
concrescences ; genital glands open into or near the kidneys.

Fam. 1. Aviculidae. Byssus -apparatus well developed ; shell usually un-
equivalve, dorsal margin straight and often long ; ascending limbs of outer
gill-filaments fused to mantle. Avicula Klein (Fig. 252) ; Pinna L. ; Perna
Bruguiere; Meleagrina Lam. ; M. margaritifera L., pearl-oysters, Indian Ocean,
Persian Gulf, and Gulf of Mexico ; Malleus Lam. : Vulsclla Lam.

Fam. 2. Ostreidae. Byssus absent ; fixed by shell ; outer gill-filaments fused
to mantle ; shell unequi valve, fixed by left valve. Ostrea L. Oysters. Shell valves
unequal, laminated, with weak hinge usually without teeth, single somewhat
ventrally placed adductor muscle. In the true oysters the more arched left
valve is firmly attached, while the right and upper valve, which is fastened
by an internal ligament, lies as an operculum on the lower valve. Edges of
mantle fringed, not fused ; gill lamellae fused with mantle and across the
middle line. Foot absent or rudimentary. They usually live together, and
form banks of considerable extent. Found in the Jura and the Chalk.
Ostrea edulis L., on the coasts of Europe on rocky ground ; probably
includes a number of different species according to the locality. According
to Davaine, the oysters are said to produce only male sexual products towards
the end of the first year, and it is not until later, from the third year
onwards, that they become females and produce ova. Moebius, on the con-
trary, asserts that the sperm is the later formed, and not until after the
pregnant beast has got rid of her eggs. The reproduction takes place especially
in the months of June and July, at which time in spite of their extraordinary
fertility the oysters should not be gathered. In the American oyster (0.
mrginiana] and the Portuguese oyster (0. angulata] the sexes are separate.
The green oyster owes its colour to its food — a diatom Namcula ostrearia*
The colour is confined to its gills and labial palps, and is said to be due
to selective absorption of the pigment from the blood. It is, however, possible
that the diatoms may adhere to the surface of the gills and palps, and be
consumed by phagocytes or other cells. This suggestion requires testing.

Fam. 3. Pectinidae. Byssus absent or feebly developed; shell ribbed;
mantle-edge tentaculiferous ; a duplication of mantle-edge folded internally ;

* Ray Lankester, Q. J. M. S., 26, p. 71.

EULAMELLIBRANCHIATA. 347

generally with emerald -green pallial eyes; outer gill-filaments free. Some are
fixed by one valve, and some can swim by opening and shutting their valves.
Pecten Lam. ; Pedum Drug. ; Hinnites Defr. ; Spondylus L. ; Lima Bruguiere.
Pectens, the Scollops are edible ; they swim by flapping their shells ; Spondylus
is attached by one valve. ^/

The Dimyidae are allied here.

Order 4. EULAMELLIBRANCHIATA.

Interftlamentar and interlamellar (vascular) concrescences always present.
The mantle-lobes are connected together either by direct fusion or by the
gills ; the genital glands have independent external openings.

Sub-order 1. SUBMYTILACEA.

Mantle generally widely open, usually with one fusion ; usually without
siphons.

Fam. 1. Carditidae. A single mantle-fusion ; foot keeled, often byssiferous.
Cardita Bruguiere. The families Astartidae and Crassatellidae are allied here.

Fam. 2. Cyprinidae. Foot long and bent ; two mantle-fusions ; papillose
orifices ; umbones often spiral. Cyprina Lam. ; Isocardia Lam.

Fam. 3. Lucinidae. The external gill sometimes absent ; foot vermiform
without byssus. Lucina Bruguiere (Fig. 250 bis) ; Axinus Sowerby ; Montacuta
Turton ; Corbis Cuv. ; Diplodonta Br. ; Ungulina Daudet.

Fam. 4. Erycinidae. Foot byssiferous or with ventral surface enlarged.
Kellya Turton ; Lepton Turton ; Lasaea Leach.

Fam. 5. Galeommidae. Foot with furrow, mantle edges reflected over the
shell. Galeomma Turton ; Ephipodonta Tate. Chlamydoconcha Dall without
adductor muscles, and Scioberetia Bernard with only one gill on each side, have
an internal shell and are allied here.

Fam. 6. Cyrenidae. Foot non-byssiferous ; two siphons usually not united ;
hermaphrodite, viviparous, fluviatile. Cyclas Bruguiere ; Pisidium PfeifFer,
siphons united ; Galatea Brug. ; Corbicula Mlilhf.

Fam. 7. Unionidae. Fresh-water mussels. Foot long, compressed, without
byssus. Anodonta Lamarck (Fig. 257) ; A. cygnea Lam., in ponds ; A. anatina
L., in rivers and brooks; Unio Philipsson (Fig. 254); Margaritana Schum.,
river pearl-mussels ; Mycetopus d' Orb. , America. Mutela Scop. , and Pliodon
Conrad, Africa, are allied here.

Fam. 8. Aetheriidae. Fluviatile forms without foot, usually fixed by one
valve. Aetheria Lamck., Africa.

Fam. 9. Dreissenidae. Foot cylindrical, byssiferous, two siphons. Dreis-
sena v. Ben., fresh-water.

Sub-order 2. TELLINACEA.

Mantle well open ; gills smooth ; siphons well developed, separate ; foot
compressed, elongated ; palps large.

Fam. 10. Tellinidae. External gill directed dorsally; siphons much elongated.
Tellina L. ; Scrobicularia Schumacher ; Semele Schum. ; Gastrana Schum.

Fam. 11. Donacidae. External gill directed ventrally ; siphons separated.
Donax L.

Fam. 12. Mactridae. External gill directed ventrally; siphons united.
Maclra L., clams (Fig. 251).

348

MOLLUSCA.

Sub-order 3. VENERACEA.

Gills slightly folded ; foot compressed ; siphons generally short.

Fam. 13. Veneridae. Foot tongue-shaped ; siphons more or less united.
Venus L. ; Tapes Megerle ; Dosinia Scop. ; Cytherea Lam. ; Lucinopsis Forb. ;
Veiwrupis Lam. The Petricolidae (rock-borers) are allied here.

Sub-order 4. CARDIACEA.

Gills much folded ; foot cylindrical, more or less elongated ; generally without
siphons.

Fam. 14. Cardiidae. Cockles. Foot long, bent, without byssus; pallial
orifices contiguous, with short siphons surrounded by papillae. Cardium L.
(Figs. 255, 259) ; Hemicardium Cuv.

Fam. 15. Tridacnidae. Foot short, byssiferous ; pallial
orifices apart ; posterior adductor only. Hippopus Lam. ;
Tridacna Bruguiere.

Fam. 16. Chamidae. Foot short, without byssus ; two
adductors ; shell fixed, asymmetrical ; pallial orifices sepa-
rated. Chama Bruguiere.

Sub-order 5. MYACEA.

Branchiae much folded ; foot compressed, more or less
reduced ; pedal orifice generally small ; siphons well de-
veloped.

Fam. 17. Psammobiidae. Siphons separated, elongated ;
foot large, tongue-shaped. Psammobia
Lamarck ; Sanguinolaria Lam.

Fam. 18. Myidae. Siphons united ;
foot reduced, without byssus. Mya
L. ; Lutraria Lamarck ; Corbula Brug.
Fam. 19. Solenidae. Foot strong,
elongated, often cylindrical, without
byssus ; siphons more or less short.
Solenocurtus Blain. ; Solen L. (razor
shell).

Fam. 20. Saxicavidae. Rock-borers.
Foot small, byssiferous ; pedal orifice
very short. Saxicava Fleuriau.

Fam. 21. Gastroehaenidae. Foot
cylindrical, very small, without bys-

FIG. 270. -Shell of SUS ; gllls narrOW' ^ tWn she11 ls

Pholas dactylus (after sometimes contained in a calcareous

Quatrefages). [7um- tube secreted by the mantle. Gastro-

bonal plates ; D dor- chaena Spengler.
sal plate.

Sub-order 6. PHOLADACEA (Boring Mussels).

Foot very short, truncated ; siphons long, united ; without shell-ligament.

Fam. 22. Pholadidae. Organs contained in the shell ; with one or several
accessory shell-pieces. Gills prolonged into branchial siphon. Pholas L.
(Fig. 270), P. dactylus L., mantle and siphons phosphorescent ; Pholadidea
Goodall ; Jouannetia des Moulins.

FIG. 271. — Teredo
namlis removed
from its calca-
reous tube, with
elongated si-
phons (after
Quatrefages).

SCAPHOPODA.

349

Fam. 23. Teredinidae. The branchiae are to a large extent contained in
the branchial siphon. Siphonal region vermiform, provided behind with two
accessory shell-pieces. Shell very small, covering only anterior part of animal.
Teredo L., T. navalis L. (Fig. 271), shipworm, was the cause of the famous
dam-break in Holland at the beginning of last century. ^^/

Sub-order 7. ANATINACEA.

Hermaphrodite ; ovary and testis with separate orifices ; external gill directed
dorsally, and without the reflected (outer) lamella.

Fam. 24. Pandoridae. Foot tongue - shaped, without
byssus. Siphons very short. Pandora Bruguiere ; Myo-
chama Stutchbury.

Fam. 25. Lyonsiidae. Foot cylindrical, byssiferous ;
siphons short. Lyonsia Sturton ; Lyonsiella Sars.

Fam. 26. Anatinidae. Foot slender, without byssws ;
siphons long ; a fourth pallial orifice. Anatina Lam. ;
Thracia Blainville ; Pholadomya Sowerby.

Fam 27. Clavagellidae. Foot reduced, without byssus ;
siphons long, united ; valves continued by a calcareous
tube secreted by the siphons. Clavagella Lam. ; Asper-
gillum Lam. (Fig. 272).

Order 5. SEPTIBRANCHIATA.

With branchial septum.

There are three pallial fusions, two siphons more or
less elongated, and two adductors. The gills (Fig. 264 D)
have the form of a muscular septum, extending from the
anterior adductor to the junction of the two siphons and
surrounding the foot, with which it is continuous. This
septum presents symmetrical orifices.

Fam. 1. Poromyidae. Siphons short ; foot elongated.
On each half of the septum there are several groups of lamellae separated by
orifices. Palps well developed. Hermaphrodite. Poromya Forbes ; Silenia
Smith.

Fam. 2. Cuspidariidae. Siphons elongated, united; foot reduced; palps
reduced or absent; branchial septum pierced by isolated symmetrical orifices;
sexes separate. Cuspidaria Nardo.

The genus Entovalva Voeltzkow, is not well enough known for its affinities to be-
determined. The mantle has a posterior orifice ; the foot is large, with a posterior
sucker. There is an hermaphrodite gland. It inhabits the oesophagus of a
Holothurian from Madagascar.

FIG. 272. —Shell of

Aspergillutn javanum
(after Adams).

Class II. SCAPHOPODA* (SOLENOCONCHAE).

Dioecious Molhisca without eyes or heart. The edges of the mantle
are fused to form a tube which is open before and behind, and secretes-
a tubular calcareous shell.

* Lacaze Duthiers, "Histoire de 1'organisation et du developpement du
Dentale," Ann. Sc. Nat. 1856-58. Plate, "Ueb. d. Ban u. d. Verwandt. d.
Solenoconchen," Zool. Jahrb. f. Morph. Bd. 5, 1892. Kowalewsky, "Etudes sur
1'Embryogenie du Dentale," Ann. du Mus. de Marseille, t. 1, 1883.

350

MOLLUSCA.

S

The body is elongated, slightly curved, with a dorsal concavity.
The shell is shaped like an elephant's tusk, and is open at both ends.
The animal, which is entirely contained within ' the shell, has a
similar shape, and is enclosed by a tubular mantle also open at
the two ends. It is attached to the shell by a muscle at the
hind end. The mantle is to be regarded as paired folds of the
dorso- lateral integument which have undergone concrescence ven-
trally.

A distinct head is not present, but tnere is an egg-shaped projection
into the mantle-cavity at the front end, at the apex of which is the

mouth, surrounded by leaf -like
labial appendages. Springing
from two lobes at the base of
the cephalic prominence are a
number of ciliated contractile
filaments (captacula) which
are swollen at their ends.
These have been supposed to
~Mh represent the ctenidia, which
are otherwise not represented.
The foot is cylindrical and
directed forwards; it can be
protruded through the ante-
rior (larger) opening of the
mantle. Its front end is tri-
lobed (Dentalium\ or carries
a retractile disc with papillose
margins (Siphonodentalium),
from the centre of which a
filiform tentacle arises in Pul-
sellum.

The nervous system con-
sists of four groups of ganglia :
a pair of cerebral with closely
adjacent pleural, a pair of
pedal, and a pair of visceral
ganglia just in front of the anus. The visceral commissure arises
from the pleural, and the pleuro- pedal commissure is completely
fused with the cerebro-pedal. There is a system of labial ganglia
(stomatogastric) in connection writh the buccal mass : it is connected
with the cerebral.

Mt

FIG. 273. — Dentalium as seen in longitudinal
section (except the foot) after Grobben. S
shell ; Mt mantle ; Sm shell muscle ; M h
mantle-cavity ; F foot ; Mk cephalic prominence
or oral cone ; T captacula ; R radula ; D intes-
tine ; L liver ; Af anus ; G cerebral ganglion ;
N kidney ; Ge generative gland.

SCAPHOPODA.

351

Sense organs. Eyes are absent. A pair of otocysts are placed on
the pedal ganglia. The tentacles serve as tactile organs.

The alimentary canal is divided into a buccal cavity, oesophagus
with two lateral pockets, stomach with large liver, and aji intestine,
which after several coils closely pressed together, opens behind the
foot and the visceral commissure into the
middle of the mantle cavity. The buccal
cavity is placed in the body at the base
of the cephalic projection, and contains a
dorsal jaw and a ventral radula, which
has a short sac and powerful muscles.

The vascular system is reduced to two
mantle vessels and a complicated system
of wall-less spaces throughout the body.
There are no specialized respiratory
organs.

The excretory organs are paired and
lie in the middle region of the body.
They open on either side of the anus.

The Scapliopoda are dioecious. The
ovaries and testes are unpaired organs
occupying the posterior part of the body
behind the liver and intestine. They
open into the right kidney.

The animals live buried in mud, and
creep about slowly by means of their
foot. There are about 100 species scat-
tered in all seas, from the littoral to a
depth of about 2000 fathoms. They are
known since the Devonian. a

Development. The eggs are laid singly. There
is an invaginate gastrula with a large blastopore,
which is at first at the hind end. The embryo
elongates and the hinder part of the body grows
out behind the blastopore, which becomes the
mouth. The free-swimming larva has a preoral
region with a ciliated tuft and several circles
of cilia, which eventually consolidate into the
velum. The mantle arises as two dorso-lateral folds which eventually coalesce
ventrally. The shell also is at first bivalve, but subsequently becomes tubular.

The Scaphopoda are allied to the Lamellibranchs by their mantle
and nervous system, but they possess an odontophore which approxi-

FIG. 274.— Larva of Dentalium
(after Lacaze Duthiers). a,
young larva with first rudi-
ment of shell, b, older larva
seen from the dorsal surface.
T tentacle-collar ; MT circular
muscle of mantle ; P foot ; Gg
cerebral ganglion ; Oes oeso-
phagus ; L liver ; BM buccal
mass ; S rudiment of shell.

352 MOLLUSC A.

mates them to the Cephalophora. It is, however, impossible to say
that they are more nearly allied to one than to the other.

There are three genera : Dentalium L. ; Siphonodentalium Sars ; Pulsellum
Stoliczka.

In the preceding account the thin end of the animal has been spoken of as
posterior ; it is, however, possible to regard it as dorsal and as corresponding
roughly to the visceral sac of a Gastropod.

Class III. SOLENOGA&TRES* (APLACOPHORA).

Symmetrical vermiform animals without mantle-fold, distinct foot,
or shell. The integument is provided with a cuticle and calcareous
spicules or scales.

It appears that the Class Amphineura, which is established by many authors
to include the Solenogastres and Chitonidcte is quite unjustifiable ; for, whereas
the Chitons are clearly Gastropods, it is by no means certain that the Soleno-
gastres are really Mollusca at all. Certainly they are not Gastropoda, for
they differ from that class in numerous features, of which we may call special
attention to the fact, of great morphological importance, that in them the
gonad opens directly into the pericardium, a feature found in no Gastropod.

The Solenogastres comprise two families, the Neomeniidae and
the Chaetodermidae. They are elongated, vermiform animals with
a skin stiffened by the cuticle and spicules; and although in
the Neomeniidae there is a ventral ciliated furrow, which is sup-
posed to be homologous with the Molluscan foot, it may generally
be said of them that they are without a foot. Further, there is
neither mantle-fold nor shell; the respiratory structures, when present,
cannot be certainly homologised with ctenidia; the alimentary canal
is perfectly straight, passing between the anterior mouth and the
posterior anus; the blood is red; and finally, the head is but ill
marked off from the body, and entirely unprovided with special
organs of sense. There is a haemocOelic body-cavity, a coelom
consisting of a pericardium, gonad, and two nephridia; the gonad
communicates with the pericardium. The reasons for regarding
them as allied to the Gastropoda are to be found in the presence
on the floor of the mouth of a chitinous structure, more or less
closely resembling in its relations and appearance the radula; in
the arrangement of the central nervous system; in the fact that

* A. A. W. Hubrecht, " Proneomenia Sluiteri" Niederl. Arch. f. Zoologie,
Sup^. Bd. 2, 1881. Kowalewsky and Marion, "Contributions a 1'histoire des
Solenogastres," Ann. Mus. Marseille (Zoologie}, 3, 1889. Pruvot, "Sur 1' organi-
sation de quelques Neomeniens des cotes de France," Arch. Zool. Exp. (2), 9,
1891. Wiren, "Studien iib. die Solenogastres," I. and II., Svenska Vet. Akad.
Handl, 24 and 25, 1892-3.

SOLENOGASTRES.

353

the body-cavity is a haemocoele and contains blood; and in the
presence of a pericardium which communicates with the exterior
by a pair of nephridia. With regard to the latter point, however,
it is not quite certain that the structure called pericardiuin is of
that nature (it may be merely a conjoined portion of the gener-
ative ducts, of which the structures called nephridia constitute
the remainder), and it has been maintained that in the Neomeniidae
at least the organs called nephridia show no signs of being renal
in function. And even if the cavity in question is pericardial it
differs entirely from the pericardium of Gastropoda in the fact
that it communicates with the gonad, and the generative cells
pass through it on their way to the nephridia,
through which they are ejected.

The Solenogastres are marine, but not littoral
animals. Hitherto they have been found only at
considerable depths — from 15 fathoms downwards
as far as the abyss, often in association with
colonies of Hydrozoa and Actinozoa on which
they appear to feed.

Fam. 1. Neomeniidae. Hermaphrodite Solenogastres
with ventral pedal groove, without differentiated liver, with
paired nephridial tubes with a common opening. The
body is covered with spicules, which are embedded in
the cuticle and in relation internally with epithelial
papillae. There is a ventral furrow which is free from
spicules ; this structure begins in a rather marked ciliated
pit, which is placed just behind the mouth and Contains
the openings of a large mucous gland, and ends behind
by passing into the cloacal depression ; further, it contains
along its floor a ciliated projection, which is supposed to
be homologous with the Molluscan foot.

The mouth is anterior and ventral, and leads into a
buccal cavity which has muscular walls, and is sometimes
protractile ; it is lined by a thick cuticle, and the ducts
of the salivary glands and the sheath of the radula open
into it. The latter is absent in Neomenia and in certain
species of Proneomenia and Dondersia; elsewhere it bears

several transverse rows of chitinous teeth. The oesophagus is short, the stomach
tubular and often provided with an anterior dorsal caecum ; the intestine is
straight, and opens into the cloaca, which also receives the openings of the
nephridia and of a mucous gland. The liver is represented by several pairs
of short lateral diverticula of the stomach.

The nervous system (Fig. 276) consists of a large cerebral ganglion in front of
the buccal mass, giving origin to a stomatogastric commissure with two small
ganglia and to two cords on each side — the pallial and pedal — passing backwards.
The pedal cords are swollen into a ganglion below the oesophagus, and into smaller

2 A

FIG. 275. — Proneomenia
sluiteri (after Hu-
brecht). 0 mouth ;
F ventral furrow.

354

MOLLUSCA.

ganglia at intervals along their course. The swellings are united by commissures.
The pallial cords have a ganglion near their origin from the cerebral, and are
connected with the pedal by commissures ; they unite in a supra-rectal ganglion
behind. In Neomenia (Fig. 276) these cords are united for a short distance in
front, and sometimes they join behind.

There are no special organs of sense.

The blood corpuscles contain haemoglobin, which gives the blood a red colour.
There are no definite vessels, but there are two more or less marked sinuses— a

- Gpv

FIG. 276 — Diagram of the central ner-
vous system of Neomenia carinata
(after Wireri). Ce cerebral ganglion ;
SI stomatogastric ganglia ; Tlv pedal
cord ; Gpi posterior ganglion on the
pedal cords ; Tld pallial cords ; Gps
supra-rectal ganglion (from Bronn).

FIG. 2Y7.— Diagram of the renal and generative
organs and pericardium ; A, of Chaetoderina
nitidulum; B, of Neomenia carinata (after
Wiren). Ps generative gland ; Pg opening of
generative gland into pericardium P ; Cg neph-
ridium ; Rs receptaculum seminis ; Co copu-
latory organ ; C cloaca ; S, D accessory glands.

ventral between the intestine and the ventral surface, and a dorsal sinus, the
hinder part of which is contractile and supposed to represent the heart. These
presumably communicate with the peri visceral cavity, which contains blood.
Respiratory organs are supposed to be represented by some epithelial folds of
he cloacal wall.

SOLENOGASTRES. 355

The cavity called pericardial (Fig. 277 B) is dorsal to the rectum. The heart
projects into it dorsally ; it communicates with the exterior by two tubes — the
so-called nephridia — which are bent on themselves like those of so many Mol-
lusca, and open by a common median opening into the cloaca ventral to the anus.

The animals are hermaphrodite, and the genital glands are paired and
tubular ; they open posteriorly into the pericardium.

It is extremely doubtful whether we ought to regard the nephridia as
anything else than generative ducts, as they bear accessory organs on their
course, and no signs of renal excretory products have been seen in them.

The development has been partly followed in Dondersia. There is an
invaginate gastrula and a trochosphere with a velum, but no veliger stage
nor shell -gland, nor foot.

The Neomeniidae have been taken in the North Atlantic and in the
Mediterranean. There are 6 genera and about 20 species.

Neomenia Tullberg, with branchiae, without radula ; Paramenia Pruvot,
with branchiae and radula ; Pronemnenia Hubrecht, without branchiae, thick
cuticle enclosing epithelial papillae ; Ismenia Pruvot, cuticle thin, a pre-
cloacal ventral prominence; Lepidomenia Kow. and Mar., cuticle thin, radula
large ; Dondersia Hubrecht, cuticle thin, radula rudimentary or absent.

Fam. 2. Chaetodermidae. Dioecious Solenogastres without pedal groove,
with radula as single horny tooth; nephridia with separate openings; branchiae
paired and projecting ; gonad median. Body with uniform covering of short
spicules embedded in the cuticle. Hind end of body bell -like, consisting
of widely open cloaca, which contains two foliaceous branchiae, the anus and
the two openings of the nephridia.

The nervous system consists of two closely apposed cerebral ganglia, from
which arises a stomatogastric commissure with two ganglia, and on each side
two lateral cords, the pallial and pedal, which are
joined at intervals by commissures. Posteriorly the
pedal joins the pallial, and the single cord thus formed
joins its fellow dorsal to the rectum in the supra-rectal
ganglion. There are no special organs of sense.

The mouth is anterior and terminal, the radula is
represented by a single horny spine in a pit in the
floor of the mouth, the alimentary canal is straight,
and the liver is a single ventral caecum directed
forwards and opening into the middle region of the
alimentary canal.

The vascular system is much as in the Neomeniidae
except that the haemoglobin is in the plasma.

The nephridia (Fig. 277) resemble those of Neomenia, FIQ 27g< _ chaetoderriul
but they are without accessory genital structures, are nitidulum (from Per-
more obviously renal in function, and they open rier). a anterior end ;
separately. b posterior end.

The sexes are separate. The gonad is a single

median tube opening into the pericardium, and the genital products pass out
by the kidneys (Fig. 277^4).

The development is unknown.

There is one genus with three species ; from the North Atlantic, the Arctic,
and the Pacific Oceans.

Chaetoderma Loven.

356 MOLLUSC A.

Class IV. GASTROPODA.*

Mollusca with a distinct head yenerally bearing tentacles, with a
ventral muscular foot usually used for creeping, and typically with a
continuous mantle-fold. The shell 'when present is composed of one or
of more than two pieces.

The organization of the Gastropoda is with one exception asym-
metrical, but the asymmetry is confined to the organs of the visceral
mass, and rarely, if ever, affects thfc head. The head has the mouth
at its anterior extremity, and usually bears one (Streptoneura, Theco-
somata, Phyllirhoe, . Elysiids, and some Pulmonates) or two (most
Opisthobranchs and some Pulmonates) pairs of tentacles, and two
eyes, which are placed at the base, sometimes at the apex of a pair
of tentacles. The tentacles are contractile, and in the stylommato-
phorous Pulmonates they are invaginable.

Their form varies and they are often modified, and may even be absent
(Olivella, Homalogyra, Pterotrachea, etc.); in most of the Bulloids both pairs
are Avidened out and transformed into a quadrangular cephalic shield, the four
corners of which correspond to the apices of the four tentacles. The single pair
of the Amphibolidae, Otinidae, Siphonariidae, and Gadiniidae are reduced, and
give to the head the aspect of a flattened disc. The anterior pair of Pleuro-
branchidae, Tritoniidae, etc., is transformed into a frontal velum. They may
also be bind, flattened or branched. The labial palps, which are processes of
the lips, found in some forms, are not to be regarded as tentacles ; nor are the
small lobe-like processes (palniettes) sometimes found between the tentacles.
The pseudopallium is a process of the cephalic integument which projects back
over the shell.

The foot is a muscular organ, and projects from the ventral surface
of the body. Typically it has a flat sole, and is used for creeping.

* Martini and Chemnitz, Conchylien Cabinet, 12 Bde., Niirnberg, 1837-1865.
Sowerby, " Thesaurus conchyliorum, or Figures and Descriptions of Shells,"
London, 1832-62. Reeve, " ConcJiologica iconica, etc.," London, 1842-62.
H. and A. Adams, " The Genera of the recent Mollusca," 3 vols , London, 1858.
H. Troschel, "Das Gebiss der Schnecken," Berlin, 1856-78. S. P. Woodward,

"Manual of the Mollusca," ed. 3, London, 1875. V. Hensen, "Ueb. das Auge
einiger Cephalophoren," Z. f. w. Z., 15, 1865. J. W. Spengel, "Die Geruchs-
organe u. d. Nervensystem der Mollusken," Z. f. w. Z., 35. Souleyet, " Voyage

de la Bonite" Zoologie, T. 2., 1852. Hilger, "Beitriige zur Kenntniss des
Gastropodenauges," Morph. Jahrb., 10, 1885. Willem, "Observations sur la
vision et les organes visuels de quelques Mollusques, etc.," Arch. £ioL, 12,
1892. Leydig, "Ueb. d. Gehororgan der Gastropoden," Arch. f. Mic. Anat.,
7, 1871. Lacaze Duthiers, " Otocysts ou capsules auditives des Mollusques,"
Arch. Zool. Exp. et Gen. (1), 1, 1872. Houssay, " Recherches sur 1'opercule
et les glandes du pied des Gasteropodes," ^rcA. Zool. Exp. (2), 2, 1884. Grobben,
" Die Pericardialdriise der Gastropoden," Arb. Zool. Inst. Wien, 9, 1890.
Baudelot, "Recherches sur 1'appareil generateur des Mollusques Gast.," Ann.
Sci. Nat. (Zoologie) (4), 19, 1863. P. Pelseneer, "Introduction a V Etude des
Mollusques," Paris, 1897. A. H. Cooke, "Molluscs," Cambridge Natural
History, London, 1895.

GASTROPODA. 357

It very generally bears on its hind end a horny or calcareous
operculum for closing the shell-aperture when the animal is retracted.
The form and size of the foot present various modifications according
to the condition of life. ^

In the sedentary Gastropods it is reduced — in Vermetus and Magilus, which
are fixed, to a small discoidal projection ; and in Thyca and Stilifer, which are
parasitic, to a small appendage. In the pelagic forms it is flattened laterally
us a fin (Heteropoda)
or may even be absent

(Pkyllirhoe). In the ^•••^ O

leaping forms (Strom-
bidae) it is also flat-
tened.

The creeping surface
is sometimes divided
by a longitudinal fur-
row, and the two halves
may move alternately
(Cyclostoma). The two
anterior corners of the Fio. 27P.— Helix pomatia. 0 eyes at the extremities of the long
foot may be prolonged
as tentacles.

The anterior part of the foot may project beneath the head, forming the
propodium (burrowing forms); in Natica the propodium projects back on to
the cephalic region.

The epipodia (sometimes called parapodia) are fin-like, produced lateral
portions of the foot (in many Opisthobranchs) ; in Notarchus the epipodia
fuse over the dorsal surface. In the Rhipidoglossa the epipodia are present,
and carry papillae. The posterior part of the foot is often marked off from the
r^est as metapodium ; in such cases when a propodium is present as well, the
middle part is called mesopodium.

The pedal glands secrete a mucous substance, which lubricates the
surface on which the animal moves, or hardens on contact with air or
water into a thread by which the animal suspends itself (Limax,
Litiopa, Cerithidea, etc.), or, as in lanthina, becomes entangled with
bubbles of air and forms a float to which, in the female, the eggs are
attached. The secreting cells are distributed as unicellular glands in
the epithelium of the foot, and are often aggregated in special invagi-
nations of the skin. Such are .the supra-pedal gland which opens at
the front edge of the foot (Pulmo?iata, etc.); the labial glands
which open into a furrow at the anterior end of the foot (creeping
Streptoneura and Opisthobranchs) ; and the median pedal gland
which opens on the ventral surface, and is comparable to the byssus
gland of Lamellibranchs (Cyclostoma, Cypraea, etc.) ; it was formerly
mistaken for an "aquiferous pore." Finally, in some forms there
are glands at the hind end of the foot, either dorsal or ventral.

358 MOLLUSCA.

The integument consists of a superficial layer of cylindrical cells
which are frequently ciliated; and of a connective-tissue dermis
which is inseparably connected with the dermal muscles. Calcareous
and pigment glands are placed in the integument ; they are specially
numerous at the edge of the mantle-fold, where they contribute to
the growth and peculiar colouring of the shell.

The mantle (pallium) or integument of the visceral sac is thrown
into a continuous fold, which completely encircles the body at the
junction of the visceral sac with ihe head and foot. This fold is
the mantle-fold; it encloses between itself and the body a space
called the mantle- or pallial-groove. The mantle-groove is quite
shallow, and groove-like over the greater part of its extent, and in
the Placophora (Fig. 305 B) over its whole extent ; but in all other
forms it is especially deepened at one point. This specially deep
part of the mantle-groove is the mantle-cavity proper. The mantle-
cavity contains the ctenidium (in the Zygobranchiata the two ctenidia)
when there is a ctenidium, and generally the anus, renal orifice, and
generative opening.

The free edge of the mantle-fold is thickened and may be provided with short
tentacles, pigment spots, and glands. In the Zygobrancliiatay and in one or
two other forms, there is a slit along the roof of the mantle-cavity in the
mantle-fold. This slit, the edges of which may be fused at one or more points,
allows of the exit of the spent water from the mantle-cavity.

The siphon (Fig. 280, 22) is a kind of spout-like continuation of the mantle-
edge on the left side of the mantle-cavity. It occurs in many, principally
carnivorous, Streptoneura, and it conducts water into the mantle- cavity.

The hypobranchial gland (Fig. 280, 17) is a highly glandular and generally
folded portion of the mantle-lining between the two gills and the rectum (Zygo-
branchs), or between the single gill and the rectum (most other Gastropods).

In the typical Gastropoda, such as the whelk (Buccinum) or the
garden-snail (Helix), the visceral sac is covered by a univalve shell.
This shell has, to a certain extent, the same shape as the visceral sac
(Fig. 312), and can usually completely receive and protect the head
and foot when the animal is retracted. As a rule it is hard and
calcareous, consisting of the three layers, an outer periostracum,
a middle prismatic or porcellanous, and an internal nacreous layer :
the nacreous layer is not, however, always present in Gastropods, and
the porcellanous is of complex structure, consisting often of three
layers of laminae, which are themselves composed of prisms. Some-
times it is a delicate structure, horny and flexible, or it may have a
gelatinous or cartilaginous consistence, as in the Cymbuliidae, where,
however, it is not a mantle-shell, but a subepidermic dermal product.

GASTROPODA.

359

The shell is secreted by the epidermis of the mantle; the^epi-
dermic (periostracum) and porcellanous layers by the edge, and
the nacreous layer by the whole surface. In cases in which the
nacreous layer is absent, the mantle surface still has a shell-forming

FIG. 28Q.—Pymla tula, male, removed from the shell. The mantle has been cut through along
the right side of the mantle-cavity and turned over to the left. The pallial organs are accord-
ingly reversed (after Souleyet from Lang). 1 proboscis ; 2 head ; 3 foot ; 4 penis ; 5 vas
deferens cut and continued in the roof of mantle-cavity at 15; 6 floor of the mantle-cavity ;
7 spindle muscle ; 8 intestine ; 9 heart in the opened pericardium ; 10 liver ; 11 testis ; 12 and
13 kidney ; Ik kidney opening ; 15 vas deferens ; 16 rectum ; 17 hypobranchial gland ; 18 anus ;
19 ctenidium ; 20 roof of mantle-cavity ; 21 osphradium ; 22 siphon.

360

MOLLUSCA.

power, for lesions are repaired by a cement-like substance secreted

by the mantle.

The shell consists of one piece, except in the Chitonidae (Fig.

305) in which there are eight pieces, and it usually has the same

shape as the visceral sac. When that is flat or conical, the shell

is also flat and conical (Patella,
Fissurella) ; when the visceral sac
is spirally coiled, the shell also is
spirafty coiled ; and when the mantle-
fold has a slit extending along the
roof of the mantle-cavity, the shell
has a corresponding slit or perforation
(Fissurella, Haliotis}. Finally, pro-
longations of the edge of the mantle,
such as the siphon, leave their mark
upon the lip of the shell -aperture
(Sipli onostomata).

The visceral sac of Chiton is not
prominent and never coiled. The
shell-pieces of this animal are par-
tially covered by upgrowths of the
mantle, and may be entirely covered
by them (Cryptochiton). The shell-
beds so formed have been compared
by Lankester to the persisting shell-
sac (in this case multiple) of the larva.

The visceral sac and shell are almost
always coiled to a certain extent in the
young or larva, even if not in the adult.
The coils may be lost by decollation, as
in Coecam, in which the spiral part drops
off; or by modification during growth as
in Fissurella (Fig. 281, F, Gf, H), or by
subsequent addition during growth (by
secretion from two reflected lobes of the
mantle) of calcareous matter, which over-
lies the spiral shell and hides it, as in
the cowries (Cypraea).

The spiral is generally dextral (leiotropic), i.e., if the shell is placed with
its spire uppermost and the aperture towards the observer, the aperture is to
the right ; or it may be sinistral. When it is sinistral the organization is
sometimes affected, and the organs and apertures usually placed to the right
are on the left side. This is always the case with sinistral monstrosities,
but not always when, the species is normally sinistral. In Spirialis, Limacina,

FIG. 281.— Shells of A Pleurotomaria,
B Polytremaria, C and E Emarginula,
D Haliotis, F Fissurella, G and H
stages in the growth of the shell of
Fissurella (from Lang).

GASTROPODA. 361

Lanistcs, and a few other forms the shell is sinistral, but the organization is
dextral ; such shells are said to be ultra-dextral (Pelseneer). In some cases
both sinistral and dextral species are known in the same genus.

As a general rule the whorls of the spire are closely applied together, the line
or groove of apposition being called the suture. Sometimes, however, the whorls
are more or less separate (Scalaria, Cyclostoma, Valvata, Vermetus). The shell
is never multilocular, , but sometimes the animal ceases to occupy, the upper
whorls, which drop oft' (decollation). The axis round which the whorls are coiled
is called the columella ; it may be hollow, in which case the shell is said to be
perforated or umbilicated (Solarium) and the axial tube is called the umbilicus;
the umbilicus may be shallow or deep. In Natica the umbilicus is filled up
with calcareous matter. In other shells the whorls are closely coiled, and
the columella is a central pillar ; such shells are imperforate. In addition to
the above the following terms are applied to the shell : the apex is the top
of the spire — the first formed part of the shell ; the aperture is the opening
of the shell at the end of the last, or body-whorl. The aperture is entire,
as in most vegetable feeders (holostomatous), or produced at its anterior
end into a spout (canal), as in many carnivorous families (siphonostomatous).
Sometimes there is a posterior canal as well ; this is anal in function, and in
some forms is represented by the so-called slit (Emarginula, Pleurotomaria,
Scissurella). The slit lies over a slit in the mantle (see above). In Fissurella
(Fig. 281) it becomes in the adult an apical pore, and in Haliotis a number
•of pores.

The margin of the aperture is called the peristome, the right side of which is
the outer lip or labrum, the inner or columellar lip being the labium. The
outer lip is sometimes thin, more often thickened, or reflected or inflected
(Cypraea), or expanded (Pteroceras) or fringed with spines (Murex). When the
fringes or expansions of the outer lip are formed periodically during the growth
of the shell they are called varices.

Shells which are always covered by the mantle are colourless (Limax,
Parmophorus). Those which are covered by the mantle when the animal
expands acquire a glazed or enamelled surface like the cowries. When the
shell is deeply immersed in the foot of the animal it becomes partly glazed
(Cymba). In all other cases there is an epidermis or periostracum, though it is
often thin and transparent.

In some cases the parts of the shell separating the successive whorls and the
columella are absorbed in the adult, e.g., Nerita, Olivella, Cypraea, Auriculidae;
in such cases the visceral sac loses its spiral form.

The operculum is attached to the dorsal hind end of the foot. It consists of
a horny basis which may be calcified. It grows with the shell, and the oldest
part of it is called the nucleus. It is marked by lines of growth, which may be
concentric or spiral (siuistral in dextral shells). Sometimes it is claw-shaped
or unguiculate, in which case the nucleus is apical. It generally fits the mouth
of the shell ; but is sometimes too small, or even ridiculously inadequate for this
purpose, as in Bullia, Conus, etc.; it also persists in some limpet-like forms
which adhere by their flat foot, and in which it is not used (Navicella, Conclio-
lepas, Sigaretus). In such cases the operculum affords a good instance of an
organ persisting after it has entirely lost its original function. The operculum
is present in most adult Streptoneura, and in their larvae, if absent in the adult
(except Stilifer) ; it is absent in the adults of most Euthyneura (except Actaeon,
Limacina, Amphibola), but is present in their development except in some of

362 MOLLUSC A.

the more specialized, e.g. Pulmonata (except Auriculidae, Siphonaria, Gadinia}
and Cavoliniidae. It may be present or absent in the same genus (Stomatella,
Vermetus, Conus). and may even be caducous in adults (Limacina helicina).

The edges of the mantle are often folded over the shell, so as to
cover a part of it (many Fissurellidae, Marsenina, many Cypraeidae
and Marginellidae, Aplysia, and some Bullidae, various Pulmonates),
or the whole of it. In the latter case the edges fuse, and the shell
is enclosed in a sac. Such an internal shell is found in Cryptochiton,
Pupilia, most Lamellariidae, Pustule/via, Notarchus, Doridium, Gas-
tropteron, Philine, Pleurobranchus, and some species of Limax, and is
very generally much reduced in size, and quite incapable of receiving
the head and foot in retraction. Finally the shell and its sac may be
absent, and the visceral sac become secondarily symmetrical (Titis-
caniidae, Pterotrachea, Runcina, Gymnosomatous Pteropods and
Cymbuliidae, Pleurobranchaea, Nudibranchiata, Philomycidae, On-
chidiidae, Vaginulidae). In such cases the shell exists only in the
larva (in some Pulmonates it is never formed at all), and disappears
at the end of larval life. In most cases in which there is no shell
the pallial chamber (and groove) and ctenidium are reduced or absent;
e.g. in Nudibranchs where the ctenidium is said to be replaced by the
papillae of the mantle (i.e. of the dorsal integument) called cerata
(Fig. 328). In certain cases in which the larval shell is shed,
another persistent and internal shell is formed (Lamellaria, the first
spiny shell of which is called Echinospira). The attachment to the
shell is effected by the columellar or spindle muscle (Fig. 296), which
arises from the foot and is inserted into the columella in the spiral
forms, or when there is no columella to the internal surface of the
shell in a horse-shoe-shaped line (Patella), or over an oval area
(HaUotis, Fig. 296 S).

The central nervous system consists typically of the three pairs
of ganglia in the head (Fig. 282) — the cerebral supplying the
head and sense-organs, the pedal supplying the foot, and the
pleural which innervate the mantle and spindle muscle ; and of
two commissures which are completed ventrally to the gut and
contain ganglia in their course; these are the anterior or stomato-
gastric commissure, on which are developed the buccal ganglia, and
the posterior or visceral, on which may be developed the supra-
and sub -intestinal ganglia and one or more abdominal ganglia.
The stomatogastric commissure is connected with the cerebral
ganglia, and supplies the buccal mass and alimentary canal, while
the visceral commissure is connected with the pleural ganglia, and

GASTROPODA,

363

innervates the vascular, excretory, and reproductive organs, and
also gives off from the supra- and sub-intestinal ganglia nerves to
the mantle, gills and osphradium. In all Gastropoda except the

•Ag

FIG. 282.— Nervous system of Paludina (after
v. Jhering). Cg cerebral, Pig pleural, Pg
pedal, Sp supra-intestinal, Sb sub-intestinal,
Ag abdominal ganglion ; o otocyst ; Eg sto-
matogastric (buccal) ganglion.

CMtonidae the visceral com-
missure is asymmetrical, in
connection with the asymmetry
of the organs which it supplies.
In the arrangement which is
usually described as primitive
the cerebral ganglia are placed
at the sides of the oesophagus,
and are connected by a long
commissure ; the pedal ganglia
are drawn out into long gan-
glionic cords (Fig. 283, 15, Fig.
284, pe) extending along the
ventral surface (Aspidobranchs,
Paludina, Cydophorus, Cypraea),
and connected in a ladder-like

manner by numerous commissures; the pleural ganglia are approxi-
mated to the pedal; and the visceral commissure is of considerable

FIG. 283.— Nervous system of Patella (from
Lang, combined after Pelseneer and Bou-
vier). 1 cerebral ganglion ; # cerebral
commissure ; 3 labial ganglion ; k buccal
ganglion ; 5 cerebro-pleural commissure ;
6 cerebro-pedal commissure ; 7 nerve to
otocyst 8; 9 pleural ganglion; 10 pedal
commissure ; 11 right, 12 left osphradium :
13 visceral ganglion ; lit supra-intestinal
ganglion ; 15 pedal cord ; 16 indication
of a sub-intestinal ganglion.

364

MOLLUSCA.

length, and its ganglia are
widely separate (Strepto-
neura and the less special-
ized Euthyneura).

The principal variations
in this arrangement are as
folloAvs : the cerebral gan-
glia are close together, and
the pleural are approxi-
mated to them or may
even fuse with them (most
Pectinibranchs, Pteropoda
Thecosomata, Adaeon); the
pedal ganglia are concen-
trated and not drawn out
into cords ; the visceral
commissure is short, and
its ganglia approximated
both to each other and to
the pleural (Fig. 285, most
Euthyneura) ; finally, all
the ganglia (cerebral, pedal,
pleural, and ganglia of vis-
ceral commissure) may be
closely approximated on the dorsal side of the oesophagus (many
Nudibranchs).

The visceral commis-
sure is in the Strepto-
neura twisted into a figure
of 8 in the following
manner (Figs. 282, 283);
the commissure from the
right pleural ganglion
passes dorsal to the ali-
mentary canal to the left
side, and there forms a
ganglion — the supra-intes-
tinal ganglion (sp, 14) —
which supplies the left
osphradium and ctenidium
and left side of the mantle,

FIG. 284.— Nervous system of Haliotis (diagrammatic
after Spengel). Cg cerebral ganglion; Pg fused
pleural and pedal ganglia; Ag abdominal gan-
glion ; 0 and 0' osphradia ; Pe pedal cord ; S and S'
pallial nerves ; Br gills.

FIG. 285. — Nervous system of Limnaea (after L. Du-
thiers). Cg cerebral, Pg pedal, Pig pleural, Ag ab-
dominal ganglion ; 0 osphradium.

GASTROPODA.

365

or without forming a ganglion gives off a strong branchial nerve,
which passes to a ganglion
— the branchial ganglion,
close under the osphra-
dium; while the commis-
sure from the left pleural
ganglion passes ventral to
the alimentary canal to the
right side, and there gives
rise to the sub -intestinal
ganglion (sb, 16), which
supplies the right side, or
gives off a nerve to the
right branchial ganglion.
The part of the commissure
connecting these two gan-
glia generally contains one
or more purely visceral
ganglia. The supra -intes-
tinal ganglion supplies the
left osphradium, which is
generally present, while
the sub -intestinal supplies
the right osphradium,
which is absent in all
except the Zygobranchiate
forms.

The nervous system has
not been seen in the adult
of Entoconcha and Ento-
colax.

In the Streptoneura each side
of the mantle is usually inner-
vated by a mantle-nerve from the
pleural of the same side, and by
a mantle-nerve from the supra-
(left side of mantle) or sub-
intestinal (right side of mantle)
ganglia, or, if they are absent,
from the corresponding parts of
the visceral commissure. The
nerves from these two sources
generally anastomose in the

FIG. 28G.— Nervous system of Cassidaria (after Haller),
illustrating dialyneury on the left side, and zygo-
neury on the right. The pallial nerves from the
left pleural ganglion Pig anastomose with the pallial
nerves from the supra - intestinal ganglion Gsp
(dialyneury), whereas the pallial nerve from the
right pleural (not lettered) runs to the subin-
testinal ganglion Gsb (zygoneury), from which all
the mantle-nerves of the right side arise. Cg
cerebral ; Pig left pleural ; Pg right pedal ; Gsp
supra-intestinal ; Gsb subintestinal ; Vg abdominal
ganglion ; Ot otocyst.

366

MOLLUSCA.

mantle (dialyneury). This arrangement is sometimes modified (more often on
the right side), in that the mantle-nerve of the pleural passes direct to the
ganglion of the visceral commissure of its own side (supra- or subintestinal),
from which ganglion all the mantle-nerves of that side appear to be given off
(zygoneury, right side of Fig. 286).

In some Streptoneura, there is, in addition to the stomatogastric commissure,
a labial commissure (Fig. 283, 3} given off from the cerebral ganglia and
passing ventrally to the oesophagus.

Sense organs. Tactile organs are represented by the tentacles, the
edges of the lips, which are often folded (labial palps), and tentacular

and lobe-like prolongations which are found here

and there on the head, mantle, and foot (see

these organs).

The rhinophores are the organs which subserve

the olfactory sense; they are placed upon the

cephalic tentacles, and on the posterior tentacles

when there are two pairs. They are epithelial

structures, and may be localised in a patch of

high epithelium at the end of

the tentacles, or in a pit, the

walls of which may be even

folded (some Opisthobranchs).

The olfactory nerve arises from

the cerebral ganglion, some-
times in common with the

optic, and may have a ganglion

on its course. The olfactory

sense is well developed in

most Gastropods.

The osphradium (Fig. 280)

is also supposed to be an

It lies in the mantle-cavity close to the ctenidium
and consists of a special patch of epithelium generally columnar and
ciliated, and frequently placed upon a special ganglion (Fig. 284,
branchial ganglion, see above). It is innervated by a nerve from the
visceral commissure (supra-intestinal ganglion — if it is present). In
some forms its surface is much folded, and it has the appearance of a
bipectinate ctenidium (Fig. 280), for which it was formerly mistaken
(e.g., Natica, Bmcinum, Cypraea, Strombidae, etc.) ; in some
Euthyneura it is invaginated into the ganglion, and has the form
of a pit. In the Zygobranchiate forms there are two osphradia —
the right one supplied by the sub-intestinal, and the left by the

V

FIG. 287. — Lamellar
rhinophore of Eolis
coronata (from Per-
rier, after Alder
and Hancock).

olfactory organ.

FIG. 288.— Rhinophore of
Hermaea Hfida (from
Perrier, after Alder
and Hancock).

GASTROPODA.

367

supra-intestinal ganglion, or from the part of the visceral commissure
where these ganglia would be if present. In the Chitonidae there
is an osphradium at the base of each ctenidium. In Fissurella it
is only present in a diffuse and indistinct form. It is aljp found in
some forms in which the ctenidium is absent (Patella, Clione, etc.,
Basommatophora).

Otocysts which are supposed to be auditory in function exist in
most gastropods (absent in lanthina, Vermetus) as a pair of closed
sacs, which are lined by an epithelium bearing cilia and sensory
hairs, and contain concretions and a fluid. They are usually placed
in the foot near the pedal ganglia (though innervated from the
cerebral by way of the cerebro-pedal commissure, Fig. 283), but in the
pelagic forms (Heteropoda) and in most Nudibranchs they are near
the cerebral ganglia (Fig. 315). They contain a fluid, and one large
concretion — the otolith (as in the Ctenobranchiate Streptoneura, and a
few Opisthobranchs), or
numerous small ones —
the otoconia (Aspido-
branchs, most Euthy-
neura and dialyneuric
Taenioglossa). It has
riot been proved by
actual observation that
any gastropod possesses
the sense of hearing.

Eyes. There is a pair
of cephalic eyes in almost
all gastropods. They are
placed at the base of the
tentacles (of the second
pair in Opisthobranchs)
or at the apex of the
posterior tentacles (Sty-
lommatophord), or half-
way along the tentacles
(some Streptoneurd).
They consist in their
simplest form of a widely open pit of the skin (Fig. 290 A), the
epithelium of which is pigmented and carries on its free surface
a layer of rods (Docoglossd) ; in some of the Rhipidoglossa, e.g.,
Haliotis, Trochus, the lips of this pit are approximated and its

JT— .5

FIG. 289.— Otocyst of Pterotrachea (after Glaus). 1 auditory
nerve ; 3 structureless membrane ; 3 and k ciliated
cells ; 5 otolith ; 6 hair cells ; 8 central cell (from
Lang).

368

MOLLUSCA.

cavity filled with a cuticular lens (Fig. 290 B) ; finally, the pit may
be closed and the retinal epithelium continued in front of the lens
as a kind of internal cornea, thus lining a complete vesicle, while
the outer epithelium, together with some connective tissue, is con-
tinued over the eyes as a cornea proper (Fig. 290 C). The optic
nerve enters the retina on its internal side, and the percipient
elements are on the side of the retina next the light.

The cephalic eyes are vestigial, being buried in the skin or absent,
in most burrowing forms ; absent iif most abyssal and subterranean
species, and in the Chitonidae ; and, curiously enough, absent in
A

FIG. 290.— Eyes of Gastropoda. A, of Patella; B,
of Trochus; C, of Helix. No and N optic nerve;
R and r retina ; L and (11 lens ; Ep cornea (A and
C after Carriere, U after Hilger).

N

some pelagic forms, e.g. lanthina, many Pteropods; though the
Heteropoda possess the best developed eyes of the class.

Eyes are found in considerable numbers on the dorsal surface in
the Onchidiidae* in addition to the cephalic eyes. These pallial
eyes are constructed upon the so-called Vertebrate type, i.e. the optic
nerve perforates the retina, spreads out on the surface turned towards
the lens, and then passes inwards to the percipient elements which
are on the side of the retina turned inwards. Moreover, they possess

Semper C., "Forms of Animal Life.'

GASTROPODA.

369

a cellular lens. Pallial eyes* are also found in certain genera of the
Chitonidae on the shell pieces ; they possess a calcareous cornea.

The alimentary canal is usually coiled, and, as a rule, bends
forward to open in front on the right side, into the mantle-cavity
if that is present. In Chitonidae it opens into the mantle-cavity
in the middle line behind, and in
some Nudibranchs the anus is median,
dorsal, and posterior.

Most of the more specialized forms
possess an invaginable proboscis (Fig.
280), the invagination generally begin-
ning at the base ; but some possess one
which is retractile from the point.

ill

FIG. 291. — Axial section of the eye
of Onchidium (from Pelseneer after
Semper). / retina ; II optic nerve ;
III pigment; 7F"lens; V cornea.

In the Natiddae there is a glandular disc
on the ventral face of the proboscis, the
function of which is to assist the animal in
perforating the shells of bivalves. In the
Pneumodermatidae the proboscis bears some
suckers, which are either isolated or placed
upon two retractile lobes (Fig. 321).

The buccal cavity is provided in its
anterior part with a pair of horny
jaws, which may be closely approxi-
mated dorsally (Natica), or even fused.
In Patella, Aegirus, and all Pulmo-
nates there is only a single dorsal jaw, and in many forms the
jaws are absent entirely.

The walls of the buccal-cavity are much thickened owing to
the muscles of the jaws and odontophore, and to the cartilages
of the latter, and give rise to the structure called the buccal mass.

There is no lower jaw, but on the floor of the buccal-cavity
there is a ridge, partly muscular, partly cartilaginous, which has
received the same name, though it should rather be regarded
as a tongue : this is the odontophore (Fig. 292). The surface
of this tongue is covered by a chitinous or horny membrane,
called the lingual ribbon, or radula, on which are carried horny
teeth of various forms. Behind, the radula passes into a cylin-
drical pocket, the so-called sheath of the radula, which projects
as a small, generally papilla -like prominence from the ventral
and posterior end of the buccal .mass. The radula and its teeth

* Moseley, H. K, Q. J. M. S., 1884.

2 B

370

MOLLUSCA.

Mh,

are secreted by the epithelium of the radula sheath, which may be
compared to the bed of a nail, or to the persistent pulp of a tooth ;

for as the front part of the radula
is continually being worn away by
use, it is replaced from behind by
the new growth in the sheath.

The odontophore can be pro-
truded and retracted as a whole
bjp its muscles, and there is pos-
sibly a small power of movement

Fig. 292.-Longitudinal section through the Qf faQ ribbon itself Oil the Sub-
buccal mass of Helix (after Keferstein).

o mouth ; Mh buccai cavity ; M muscles ; radular membrane.

Rd radula ; Kn lingual cartilage ; Oe oeso- The teeth are arranged in tems-
phagus ; A/jaw ; Z sheath of radula. °

verse rows on the surface of the

radula; their form, size, and number vary in different species, and
afford important systematic characters of species, genera, and families.

The middle tooth of each row is called the central or rachidian tooth; the
teeth on each side of this are called laterals, while the outermost of all are
the marginals or uncini. The laterals and marginals sometimes merge into
one another, so that the distinction between them is lost. The varying
arrangement in number of these different teeth is expressed by formulae :
thus the typical formula of the Toxoglossa is 1.0.0.0.1., which means that one

FIG. 293. — One row of teeth of the radula of A, Helicina tropica, Rhipidoglossa ; B, Bythinia
tentaculata, Taenioglossa ; C, two rows of Fasciolaria tarentina, Rachiglossa (from Perrier).

GASTROPODA.

371

marginal tooth alone is present, and that central and laterals are absent alto-
gether; in the Rachiglossa (Fig. 293 C] it is 1.1.1., which means that a central
and one lateral on each side are present ; the teeth are strongly cusped in this
group. In the Taenioglossa (ribbon-tongned) the typical formula is 2.1.1.1.2.
(Fig. 293 B). In the Ptenoglossa there are an indefinite number'oJP outer teeth,
not distinguishable into marginals and laterals, and the formula is written

oo. 1. oo. The Rhipidoglossa (fan-tongued) are characterized by an indefinite
number of marginals, arranged like the ribs of a fan; typical formula

00.5.1.5. oo. (Fig. 293 A}. The Docoglossa have a few, but strong columnar
teeth, and the special feature is the multiplication of the central ; thus Patella
has 3.1.4.1.3., or, as it may be written, 3.1. (2 + 0 + 2) 1.3.

In the Euthyneura there is generally no distinction into marginals and
laterals. The length of the radula, and the number of rows of teeth, varies
much in different species. In Patella it is very long, in the Pulmonata it is
short and broad. The radula is entirely absent in the Eulimidae, Pyrami-
dellidae, Thyca, Entoconcha, Entocolax, Coral-
liophilidae, certain species of Terebra, Torna-
tinidae, Cymbuliopsis, Gleba, Doridiidae,
Doridopsis, Corambe, Phyllidia, Tethyidae
(i.e., in parasitic and suctorial forms).

The subradular organ is a papilla in front
of the radula on the floor of the mouth.

In addition to buccal glands, some-
times found round the buccal opening,
there is always a pair of salivary
glands opening into the buccal-cavity.
The buccal-cavity leads into the oeso-
phagus, which is followed by a dilated
stomach, usually provided with a caecal
appendage. The stomach opens into
an intestine, which is usually long and
coiled, and surrounded by a large multi-
lobed liver. The liver occupies nearly
all the upper coils of the visceral sac,
and pours its secretion into the intes-
tine and into the stomach (Fig. 295).

FIG. 294.— Alimentary canal of Aeolis
papillosa (after Hancock). Bm
buccal mass ; Oe oesophagus ; M
stomach ; L liver caeca which enter
the dorsal appendages (cerata) : A
anus.

The arrangement of the alimentary canal and of the liver presents in detail
many essential modifications ; one of the most remarkable being that offered by
the stomach with its diffuse hepatic caeca (often extending into the cerata) in so
many of the Nudibranchiata (Fig. 294). The terminal part of the intestine is
distinguished by its size, and may be called the rectum.

The oesophagus may have a crop-like swelling in its course, and sometimes
there is a gland on about the middle of its length (gland of Leiblein, Fig.
295). The stomach may contain in its middle region masticatory plates
(some Opisthobranchs), or be divided by constrictions into three regions
(Aplysia).

372

MOLLUSCA.

The vascular system presents numerous and important modifica-
tions. The heart is enclosed in a special pericardium, and is usually
placed on one side of the middle line, more or less anteriorly, near
the respiratory organs. It usually consists of a conical ventricle

(Fig. 280) which gives off the
aorta, and of an auricle which is
turned towards the respiratory
organs, and into which the blood
passes by the respiratory veins.
In some Gastropods (Rhipidoglossa,
except Helicina) there are two
auricles (the right one being usually
the smaller), and the ventricle is
pierced by the rectum (Fig. 297 b, c}.
In the Chitonidae alone is the heart
not only symmetrical (with two
symmetrical auricles), but placed
at the hind end of the animal.

When there is only one auricle it
is the left, though in the majority
of the Streptoneura and of the
Pulmonata, and in Actaeon, Lima-
cina, Clio virgula and C. adcula
it lies in front of the ventricle,
and in most Opisthobranchs, in
Testacellidae, Onchidiidae, Firo-
lidae, and some Calyptraeidae it
is behind the ventricle.

The aorta, which is given off
from the end of the ventricle
opposite to the auricle, or from
the hind end in the Rhipidoglossa
with two auricles, usually divides
into two arteries, of which one
passes forward and branches to the
head and foot, while the other
passes dorsalwards to the viscera.
There is a bulb, extra- or intra-
pericardial, on the root of the
aorta in some forms (Patella, etc.).
The arteries terminate by opening

FIG. 295. — Enlarged dorsal view of the
alimentary canal of Murex (from Pel-
seneer, after Haller). I duct of gland
of Leiblein ; II oesophagus ; /// duct of
liver; IV liver; V stomach; VI anal
gland ; VII anus ; VIII gland of Leib-
lein ; IX crop or proventriculus ; X
salivary gland ; XI radula ; XII mouth.

GASTROPODA.

373

M

into irregular spaces in the tissues and amongst the organs, some
of which spaces have coalesced or dilated to give rise to the
perivisceral cavity (exclusive of the pericardium) of these animals.
From these systemic spaces the blood passes through -tjje branchial
(pulmonary) vessels to the respiratory organs. In some cases there
is, in addition to the ctenidial blood, a certain amount of blood
returning to the auricle from other parts of the mantle, e.g.,
Acmaeidae, Heteropoda, Pleurobranchidae, Pneumodermatidae. Of
these the Pleurobranchidae, Hetero-
poda, and some Acmaeidae do
not possess secondary branchial
structures on the mantle; but in
other Acmaeidae and in the Pneu-
modermatidae there are secondary
branchiae in addition to the cteni-
dium.

The blood is generally colourless ; it is
red in Planorbis (haemoglobin in the
plasma), and in certain forms has a blue
tinge (haemocyanin). There is a blood-
gland on the aorta in some Opistho-
branchs (Bn\]oids,Pleurobranchus, Dorids) ;
and in certain streptoneurous Platypoda
there is a corresponding organ near the
kidney, communicating with the auricle.

Respiratory organs. In only a
small number of Gastropods is respi-
ration effected exclusively through
the general integument (some Nudi-
branchs). By far the greater number
breathe through gills, and many
through lungs ; a few combine
branchial and pulmonary respiration.

The gills are either typical cte-
nidia contained in the mantle-cavity, or freely-exposed branched
processes of the dorsal integument (some Nudibranchs).

Excluding the Chitonidae (Fig. 305), which are unlike other
Gastropods in having a number of pairs of ctenidia bearing two
rows of lamellae (i.e., bipennate) and placed in the hinder part
of the mantle-groove, there are never more than two ctenidia (Zygo-
branchs, Fig. 296) ; but usually an asymmetrical development takes
place, and only one gill (the left) remains (Fig. 280).

TIG. 296.— Dorsal view of Haliotis tuber-
culata after removal from its shell.
The roof of the mantle-cavity has been
cut through so as to expose the two
ctenidia, and the rectum D. The peri-
cardium also has been opened. K the
left ctenidium ; Dr the hypobranchial
gland; S the spindle - muscle ; F the
margin of the foot ; T tentacle ; 0 eye ;
V ventricle ; A, A the two auricles
(from Glaus).

374 MOLLUSCA.

The Gastropod ctenidium is (except in Chitonidae) attached by the
whole or greater part of its length to the mantle-wall, and carries
typically (in the Aspidobranchs and Tectibranchs) two rows of
plates arranged perpendicularly to the axis (Fig. 296), but in the
more specialized Streptoneura (Fig. 280) one row of plates is absent
(it is reduced in the monobranchiate Aspidobranchs). In the former
case the gill is said to be bipectinate, in the latter monopectinate.

The respiration of air is confined to some Prosobranchs and to the
Pulmonata. In this case the mantle^avity serves as the respiratory
cavity, but it differs from the branchial mantle-cavity by containing
air, and by possessing instead of a gill a rich network of blood-vessels
on the inner surface of its roof. The mantle-cavity communicates
by a long slit with the external medium, but in some forms it is very
widely open (Tectibranchs), and in others the opening is reduced
to a small, round aperture capable of being closed (Pulmonata}.
Frequently the edge of the mantle is prolonged into a siphon (see
above, p. 358).

The arrangement of the respiratory organs is of importance for
the classification of the larger groups. According to their position
with regard to the heart two great divisions can, as Milne-Edwards
has pointed out, be established: (1) the Opisthobranchiata, in which
the auricle and gill are behind the ventricle; (2) the Prosobranchiata,
in which the auricle and gill are in front of the ventricle (Fig. 280).
So far as this character is concerned, most Pulmonata are Proso-
branchiate; but the Pulmonata in many features of their organiza-
tion, particularly in their hermaphroditism, stand closer to the
Opisthobrancliiata.

In some aquatic forms the ctenidium is entirely absent, and respiration is
carried on either by the mantle and integument generally, without any secondary
branchiae (Lepetidae, Dermatobranchus, Heterodoris, many Elysiids, Phyllirhoe,
Clionidae, Halopsychidae), or by secondary branchiae ; these may be in the
mantle-groove as the branchial plates of Patella, or on the external surface
of the mantle, as in Clionopsis, Notobranchaea, and most Nudibranchs.

Some littoral forms (Littorina, etc.) are able to live for a long time out
of water and habitually do so when the tide recedes ; in such cases the internal
surface of the mantle may be modified, and in Cerithidea obtusa the ctenidium
even completely disappears. In Ampullaria one part of the mantle-chamber
is modified as a lung, and is partly separated from the other, which contains
the ctenidium ; such forms are truly amphibious. Finally, there are the
so-called land Operculates ; these are streptoneurous forms in which the ctenidium
has disappeared and the mantle-cavity is completely transformed into a lung.
Of such forms we have the rhipidoglossate family — the Helicinidae, and three
families of the Taenioglossa, viz., the Cyclophoridae, Cyclostomatidae, Aciculidae.

In the Pulmonata proper the ctenidium is entirely absent and the opening

GASTROPODA 375

of the mantle-cavity (pulmonary cavity) much restricted : in the Onchidiidae
the lung sac is said to be absent, but this is doubtful (Bergh. Morph. Jahrb. 10).
A few of the Pulmonata have partly or wholly reverted to an aquatic life
(the so-called fresh-water Pulmonata} ; some of these forms (Limnaeidae) are
really air-breathers, and make periodic visits to the surface fcj/procure air,
while others (Amphibola, Siphonaria, Gadinia, Ancylus, Limnaeidae of deep
lakes) are truly aquatic, as the lung sac is always filled with water.

Body-cavity. In Gastropoda there is usually a well-developed
peri visceral cavity in relation with the alimentary canal or with
the anterior part of it. It is the cavity which is opened up in
dissecting the alimentary canal of Chitonidae^ and the anterior part
at least of the alimentary canal of most other Gastropoda. We
may call this cavity the perivisceral. There is also another cavity,
which has no connection with the perivisceral, and is called the
pericardial because it is related to the heart. Whereas it is quite
certain that the pericardial cavity is a part of the coelom, the
nature , of the perivisceral cavity is doubtful. By most anatomists
it is regarded as haemocoelic in nature, and this is probably the
correct view, but recently it has been interpreted as a part of the
coelom at least in the Chitonidae. This view is not, however,
supported by any evidence anatomical or embryological, for the
space in question has no connection with the nephridia or gener-
ative organs, and has not been traced from the paired cavity,
which appears at an early stage in the development of Chiton
and is probably coelomic. We may, therefore, safely say that so
far as our knowledge at present goes the perivisceral cavity of
Gastropoda is a part of the vascular system, and therefore
haemocoelic.

It has been recently asserted* that in some of the Docoglossa the pericardium
has a considerable visceral extension.

The coelom of the Gastropoda is in three sections : (1) the
pericardium; (2) the nephridia; (3) the gonad.

(1) The pericardium is in relation with the heart; it normally
communicates with the nephridial system, and part of its lining is
generally glandular and forms the pericardial gland. It has no
connection with the blood system.

(2) The nephridial part of the coelom will be described below
under the head of excretory organs.

(3) The gonad retains its connection with the rest of the coelom
only in the Aspidobranchia, in which it communicates with the right
kidney. In Chitonidae it is separated both from the nephridia and

* B. Haller, " Studien ilb. Docoglosse u. Rhipidoglosse Prosobranchier," Leipzig,
1894.

376 MOLLUSCA.

pericardium, and in other Gastropods it has its own special duct,
which has been interpreted as, and probably is, a persistent portion
of the otherwise absent right (primitive left) nephridium. The
developmental evidence in favour of this view is not very strong,
but we may hold it at present as a provisional view. In no
Gastropod is the gonadial section of the coelom in direct connection
with the pericardial.

Excretory organs. The kidneys, or organs of Bojanus, of the
Gastropoda are typically paired and •symmetrical, somewhat dorsally
placed near the pericardium, and open externally on each side
into the mantle - cavity, generally not far from the anus, and
internally into the pericardium by the reno-pericardial openings.
This typical condition is found in the Chitonidae (Fig. 308) alone.
In all other Gastropods the kidneys are of unequal size, and in all
but the Aspidobranchiata there is only a single kidney, the right
one (primitive left) being absent (Fig. 297).

In the Aspidobranchs there are two kidneys (except the Neritidae) ;
of these the right is always larger than the left, and in addition to
its proper function discharges that of generative duct, inasmuch as
the genital gland opens into it (in Haliotis by a large slit, and in
Fissurella on a papilla not far from the external opening, Fig. 297
5»and c). They both open into the mantle-cavity, one on each side
of the anus; but with regard to their pericardial opening there is
some variation. In Trochus, Turbo, and Haliotis the small left sac
opens into the pericardium, while the right kidney is without the peri-
cardial opening. In Fissurella^ Emarginula, Patella, etc., it is said
by some authors that neither of the kidneys have the reno-pericardial
opening; whereas in Lottia, and according to other authors Patella
and Fissurella, the right kidney sac alone has a pericardial opening*
(Fig. 297 b). In other Gastropods there is only one kidney, the left
(primitive right) ; it opens externally near the anus, generally into
the mantle-cavity, but sometimes it opens with the anus, with or
without a long ureter, and there is a common cloaca (some Pulmo-
nates, Pteropoda Gymnosomata) ; internally it opens by a ciliated
orifice into the pericardium (Fig. 297 e). In Paludina there are
two kidneys in the embryo, but the one on the right side disappears
in the course of development.

In the simplest cases the kidney is a sac with glandular walls, but
it may acquire a spongy texture, or it may consist of a non-glandular

* R. v. Erlanger, "On the paired nephridia of Prosobranchs," Q.J.M.S. 33,

p. 587.

GASTROPODA.

377

sac giving off branching glandular tubes (Chitonidae, some Nudi-
branchs).

Pericardial glands are present as differentiations of the lining of
the pericardium. -^

Generative organs. The Streptoneura are dioecious, with the
exception of Valvata, Marsenina, Onchidiopsis, Odostomia, and Ento-
conclia ; the Euthyneura and these five genera are hermaphrodite.

In the dioecious forms there is usually but little to mark the
sexes externally, unless a penis be present. The generative gland
a d

n'

FIG. 297.— Diagrams illustrating the arrange-
ment of the kidneys arid pericardium in
Prosobranchiate Gastropods (from E. Per-
rier, after R. Perrier). a, Lamellibranchs.
&, Fismrella. c, Haliotis. d, Patella, e, Pec-
tinibranchs. g gonad ; i rectum ; k reno-
pericardial opening; n duct of right kidney
(of left in e), n1 duct of left; o right, o'
left auricle (except in d and e, in which o is
the left auricle) ; p pericardium ; r right,
r1 left kidney (except in e, where r is the left
kidney, and r' a blood gland) ; v ventricle.

378 MOLLUSCA.

is a racemose body placed at the dorsal summit of the visceral
mass in the liver. In the Aspidobranchs as already mentioned it
opens into the right kidney, and there is no penis. In the Neri-
tidae and Pectinibranchs it has its own duct, which passes along
the right side of the rectum (Figs. 280 and 297 e) and opens into
the mantle-cavity not far from the anus.

The penis, which is very generally present, is a muscular, non-
invaginable process of the neck of the animal (Fig. 280) on the
right side ; and there is a ciliate<? groove, for the conduct of the
sperm, leading from the male opening in the mantle-cavity to the
penis, and along the penis to its end (Ampullaria, Littorinidae,
Naticidae, Cypmeidae, Heteropoda, Murex, Dolium, Strombus).
In many forms, however, this groove is closed into a canal so
that the vas deferens is continued as a tube to the end of the
penis (Fig. 280).

There are not usually accessory glands in the dioecious Gastro-
pods, but in some forms there is a glandular region in the oviduct,
which secretes albumen, and there is a receptaculum seminis in
Neritidae, Paludinidae, Heteropoda, etc.

In the hermaphrodite Streptoneura there may be an herma-
phrodite duct leading to the external opening, or dividing into
male and female portions, which open separately; and the accessory
glands are more developed than in the dioecious forms.

In the Euthyneura the organs are more complicated. The
generative gland, which has the same relations as in the Strepto-
neura, may be itself hermaphrodite to its ultimate follicles; or the
male and female follicles may be separate, several female follicles
being grouped round and opening into a central male follicle
(Pleurobranchs, most Nudibranchs). In the streptoneurous form
Entoconcha alone are the male and female parts quite separate.

There is always a single hermaphrodite duct leaving the ovo-testis.
In the simplest cases it is undivided (monaulic) and passes to its
opening on the right side ; from the latter passes a seminal groove
along the side of the body to the penis, which is placed in front
(Bullids, Aplysids). In Valvata, Pleurobranchidae, most Nudi-
branchs and Pulmonates the duct is diaulic, i.e., at a certain point
in its course it divides into the male part — the vas deferens,
which passes to the penis, and into a female part — the oviduct,
which passes to the female opening. In the diaulic arrangement
the male and female openings are either remote from each other
(Valvata, most Basommatophora, Onchidium, Vaginulus), or close

GASTROPODA.

379

together (most ISTudibranchs), or the two ducts join again to open
into a common cloaca (Stylommatophora, SipJionaria) (Fig. 298).

There is a receptaculum seminis, which opens into the herma-
phrodite duct in the monaulic forms, and into the ovidu(?^/( vaginal
part) in the diaulic forms ; in the Dorids and Elysids this structure
not only opens into the oviduct but communicates directly with
the surface of the body by a tube which may be called the vagina.
The vagina opens close to the oviduct. This is the triaulic arrange-
ment, and recalls that of the Trematoda.

The penis, which is always invaginable, is cephalic in Pulmonates,
pedal in most Opisthobranchs.

The accessory glands are numerous in the hermaphrodite forms
(Fig. 298). In addition to the receptaculum seminis already men-
tioned, there is generally an albuminous gland in connection with the
hermaphrodite duct, and a
mucous gland (multifid
vesicles of Helix) opening
into the vaginal part of the
oviduct. In some Helicidae
a peculiar sac — the dart-sac
— which produces in its in-
terior a dart-like calcareous
rod, opens into the vagina
between the two groups of
multifid vesicles. This rod
— the so-called love-dart — is
attached to a papilla at the
base of the sac ; it is pro-
truded during copulation,
and seems to play the part
of a stimulating organ. It
is usually broken off during
use, and often remains in the
body of the other snail.

The vas deferens often
presents a prostatic gland,
which in some forms is in
close connection with the
evaginable penial part, and is called the flagellum.

The hermaphrodite forms appear as a rule to be protandrous, and
rarely, if ever, self -fertilizing. It is stated that specimens of Avion

FIG. 298.— Sexual organs of the Roman Snail (Helix
pomatia), illustrating the diaulic arrangement.
Zd hermaphrodite gland ; Zg its duct ; Ed albumen
gland ; Od oviduct and seminal groove ; Vd
vas deferens ; P penis ; Fl flagellum ; Rs recep-
taculum seminis ; D mucous glands ; L love-dart
in dart-sac ; Go genital opening (after Baasen).

380 MOLLUSCA.

and Limnaea, which had been kept isolated all their lives, have
been known to lay eggs, from which young were hatched ; but these
may have been cases of parthenogenesis, a phenomenon which has
of late been observed in quite unexpected quarters.

In some Gastropods (Paludina, Ampullaria, and some species of
Murex) two kinds of spermatozoa are produced in the same gonad.
One of these is hair-like and the other vermiform. The meaning
of the phenomenon is unknown, but it appears that the former
alone conjugate with the ovum. •

Fertilization is nearly always internal, and brought about by copulation, which
in hermaphrodite forms with contiguous openings for male and female may be
reciprocal ; but in Chitonidae, Patella, Haliotis, and other forms without a penis,
it is probable that it takes place externally in the sea (it certainly does so in
Chiton). In such forms also the eggs are often laid singly and without any
accessory protective capsule (Patella, Haliotis, Chiton), though in Fissurella they
are embedded in jelly. In aquatic forms the eggs are generally united in masses
of gelatinous matter, which may be rounded, elongated, or ribbon -shaped, and
are attached to plants or other bodies (fresh-water Pulmonates, Opisthobranchs,
Bithynia, Valvata, Heteropoda, etc.). In Streptoneura several eggs floating in
albumen are generally enclosed in hard and coriaceous capsules or cocoons, and
it often happens that all the eggs in a cocoon do not develop, some serving as
food for the others. The eggs of Natica are embedded in albumen mixed with
sand, and have the appearance of a sandy ribbon. In some Streptoneura the
eggs are attached to a part of the body or shell, e.g. Vermetus on the inside
of the shell, Nerita on the outside. In lanthina they are attached to the float.

In Stylommatophora the eggs are laid singly, and are often remarkable for
their size ; in Bulimus, Aehatina, and some species of Helix they are as large as
the eggs of small birds, and provided with calcareous shells. In such cases,
however, the ovum itself is small, the mass of the egg consisting of albumen.
The young of Helix Waltoni when first hatched is about the size of a full-grown
Helix hortensis. In Helix hortensis and aspersa the eggs are laid in hollows in
the ground and covered with earth. In some species of Paludina, Melania,
Littorina, Cymba, lanthina, Clausilia, Helix, Pupa, and Vitrina the eggs
develop in the uterus, and the young are born fully developed.

The development begins with an unequal segmentation leading to
the formation of a blastula and gastrula. The blastopore varies in
its fate : it often has a slit-like form, and as a rule it closes up from
behind forwards either entirely or persists as the mouth-opening.
In Paludina, however, it persists as the anus. There is a
well -developed stomodaeum, giving rise to the buccal cavity and
a short proctodaeum. The mesoderm is derived from the endoderm
near the blastopore (or according to Tonniges from the ectoderm
along the site of the blastopore in Paludina), and often gives
rise to two mesoblastic bands, which in Chiton and some other
forms early exhibit a cavity. In Chiton, however, the fate of

GASTROPODA.

381

this cavity is unknown; it appears to break up, at any rate it
has not been traced. In some other forms (Paludina, Bithynia)
v. Erlanger* has shown that it gives rise to the pericardium,
kidney, and gonad.

Ms

The same observer also asserts that in*I}aludina

FIG. 299.— Some stages in the embryonic development of PlanorUs (after C. Rabl). a, optical
section through a segmenting ovum, with 24 segments, b, stage with four mesoderm cells,
viewed from the lower pole, c, oblique optical section through b. d, older embryo, with
shell gland (trochosphere stage). D alimentary canal ; EG ectoderm ; En endoderm ; FJi
segmentation cavity ; Ms mesoderm ; N primitive kidney (pronephros) ; 0 mouth ; Oc eyes ;
Ot otocyst ; R rudiment of radula ; Rk polar bodies ; S shell ; Stir shell-gland : Sp apical
plate (thickening of ectoderm of preoral lobe) ; Ve velum.

it is developed as a bilobed outgrowth of the primitive gut of the
embryo in the neighbourhood of the blastopore.f In the land
Pulmonates the young are born with the adult form, and there are
but very slight traces of a velum in the development, but in most
Gastropoda the young leave the egg-membranes as a trochosphere
larva (Fig. 299 d), which very soon
acquires, if it does not already
possess them, a shell-gland as an
ectodermal invagination of the
extra-velar dorsal surface, and a
rudiment of the foot as a pro-
jection of the ventral surface
(Fig. 299 d). The shell-gland may
or may not secrete a chitinous
plug, but in the veliger stage
(Fig. 300), which follows the tro-

Vel

FIG. 300. — Young veliger larva 01 a Gas-
tropod (after Gegenbaur). S shell ;
P foot ; Op operculum ; Vel velum ;
T tentacles.

* R. v. Erlanger, "Zur Entwick. d. Falndina vivipara," Pt. 1 and 2. Morph.
Jahrb., Bd. 17, 1891, and "Zur. Ent. v. Bithynia tentaculata," Mith. ZooL Stat.
NeapeL, Bd. 10, 1892.

f This is denied by Tormiges, who asserts that the mesoderm in Paludina
is derived from the ventral ectoderm along the line of the blastopore. Vide
Z.f. w. Z.,G1, 1896.

382 MOLLUSCA.

chosphere, it flattens out and secretes a plate-like shell, which
with the development of the visceral sac acquires a cap-like form.
At the same time the dorsal integument at the edge of the shell is
formed into an annular fold, encircling the visceral sac. This
is the mantle-fold; it becomes especially deepened on the right
side, and gives rise to the rudiment of the mantle-cavity. The
preoral part of the body along the line of the ciliated ring is pro-
longed into 2, 4, or 6 processes, and forms the definite velum
or sail of the veliger larva. Th» foot also becomes much more
prominent, and develops in most cases an operculum on its hind
end (Fig. 300).

While these changes are going on, the visceral sac and shell
become coiled in a nautiloid fashion, and at the same time more

developed on the left
side than on the right;
the beginning of this
asymmetry has already
been indicated by the
development of the
mantle-cavity somewhat
on the right side of the
visceral sac. It soon
becomes more marked
and results in the

FIG. 301.— Larva of Vermetus (after L. Duthiers). Older mantle-Cavitv COminff to
veliger. S velum ; Br gill ; F tentacle ; P foot ; Oc eye.

lie on the anterior side

of the visceral sac, and in the commencement of that dextral spiral
twist of the visceral sac and shell which is characteristic of so many
Gastropods.

The vascular system arises as a set of spaces in the mesoderm ; it
is customary to state that these spaces are persistent remnants of the
segmentation-cavity, but it is very doubtful if there is any meaning
in this statement.

The larva often possesses some other special organs which deserve
mention : these are the contractile sinuses and the larval kidneys.
The former are blister-like projections of the integument, with
muscular walls ; they are supposed to assist in the larval circulation,
and are found in various parts of the body, e.g., foot. The latter
(Fig. 299 d) are a pair of glandular tubes which open externally just
outside the velar area on each side. It has been stated that they
have internal openings into the blastocoel, but the opposite has also

GASTROPODA. 383

been stated, and the balance of evidence is against the existence of
such openings.

Metamorphosis of the larva into the adult. However sym-
metrical the adult may appear to be, the larva (except in the
Ghitonidae) always presents, after the trochosphere stage, an
asymmetrical development of its visceral sac, and there is, in
almost all, a shell more or less nautiloid in character, and generally,
though less invariably, an operculum. In the great majority of
EutJiyneura the shell is lost in the adult, and the operculum, with
a very few exceptions, also disappears in the same group. In some
cases the larval shell is replaced by a permanent shell.

The asymmetry sometimes appears before the anus and mantle-cavity
are formed, in which case the visceral sac becomes more developed on
the left side, and the anus and mantle-cavity appear on the right side
and then, by the relative growth of parts, shift forwards along the
right side until they are placed on the anterior face of the visceral
sac. In cases in which the anus appears before the asymmetry,
e.g., Paludina, it and the mantle-cavity are at first posterior and
median ; they then gradually pass round to the right side, and
so to the anterior face of the visceral sac, this shifting being accom-
panied by a greater growth of the visceral sac towards the left.
This movement of the anus and mantle-cavity, if viewed from the
dorsal surface, has been in a direction opposite to that of the hands
of a watch, and has consisted of a twisting of the visceral sac
about an axis, which may roughly be described as dorso -ventral,
through an angle of 180°, so that the original posterior face of the
visceral sac becomes the actual anterior face, and the visceral organs
of the original right side become placed on the left, and vice versa.
But in all Gastropods, except the Aspidobranchiata, the organs of the
original left side of the visceral sac are either not developed, or,
if they are developed, disappear; consequently the anus, instead of
opening into the middle of the mantle-cavity, is on its right side, and
the actual right gill, osphradium, kidney, and auricle are not present.
This torsion of the visceral sac round a dorso -ventral axis in a
direction opposite to that of the hands of the watch when viewed
from the dorsal pole, is not the only twisting the visceral sac under-
goes. It also twists round a horizontal axis passing from right to
left in such a manner as to form a spiral. If this twisting be
supposed to have taken place before the torsion first described, the
visceral sac must have fallen forwards, and so formed a coil like that
of the shell of Nautilus on the anterior side: such a coil is called

384

MOLLUSCA.

exogastric (Fig. 303). But when the visceral sac has undergone
the torsion just described, which resulted in its anterior face becoming
posterior, this coil would naturally be on the hinder face of the
visceral sac (Fig. 303). Such a coil is secondarily endogastric and
is the permanent condition in the ordinary dextral visceral sac of
most Gastropoda.

.v.s

l.v.

l.ct

••ret.

I aur

let

I au,r

let

U

f

FIG. 302.— Diagrams illustrating the torsion of the visceral sac, which is supposed to have
taken place in most Gastropoda (after Lang). A represents the hypothetical primitive form in
which no torsion has taken place. In B the visceral sac has rotated through an angle of 45°
in a direction opposite to that of the hands of a watch ; the mantle-cavity with the gills and
anus, etc. is now placed on the right side of the body. C, Intermediate stage. D, final
stage, in which the visceral sac has rotated through an angle of 180° in a direction opposite
to that of the hands of a watch, and about a dorso- ventral axis ; the mantle-cavity with
gills, anus, etc. are now on the anterior side of the visceral sac, and the primitive right gills,
kidney, auricle, have become placed on the left side. The visceral commissure has become
twisted into a figure of 8 loop. The outline of the visceral sac is indicated by the dotted
line, a anus ; l.aur left auricle ; in C, l.aur points to the right auricle ; / foot ; l.ct primitive
left gill ; l.v primitive left visceral ganglion (sub-intestinal); m mouth ; man edge of mantle-
fold ; r.ct primitive right gill ; r.v primitive right visceral ganglion (supra-intestinal) ;
t tentacle ; v ventricle ; v.c visceral commissure ; v.s outline of visceral sac.

GASTROPODA.

385

FIG. 303. — Ampullaria cornu arietis (regne
animal), illustrating the spiral torsion of
the visceral sac about a right and left
horizontal axis, in which the visceral sac
has apparently fallen backwards (endo-
gastric). It is, however, really an exogastric
coil, because the visceral sac has been
twisted so that its hinder surface is in
front.

A glance at the accompanying diagram will explain the effect of
the first-described torsion about the dorso- ventral axis upon the
organs of the visceral sac, and
the course of the peculiar figure-
of-8 loop of the visceral com-
missure. Why the organs of
the primitive left side disappear
in so many Gastropods is not
clear, but their disappearance is
doubtless connected in some way
with the torsion, and consequent
asymmetry produced in the parts
affected by the torsion.

In some groups there is a
tendency for the visceral sac to
flatten out into a conical form, and
for the nautiloid shell to become
conical (Patella, Fissurella, Aplysia, Pleurobranchus, Doris, etc.).
This is, however, a purely secondary feature, for the young possess
the typical nautiloid shell, and in some cases the stages of the loss
of the spire can be completely followed.

This acquisition of a secondary symmetry, which is found very
commonly in the Euthyneura, must not, however, be confused with
a tendency to detorsion of the visceral sac which is found in most
Euthyneura. It shows itself in the shifting back of the anus well
on to the right side and even to the hind end, and in the untwisted
condition or only partially twisted condition of the visceral loop (see
account of Adaeon and allies). Formerly this condition was looked
upon as an arrested stage in the torsion, but having regard to the
arrangement of the visceral commissure in Actaeon and its allies, and
to the fact that in the suppression of the organs of the right
(primitive left) side the Euthyneura are as specialized as the most
specialized Streptoneura, it is more probable that the condition
referred to is due to detorsion. Forms in which the anus is
secondarily shifted backwards almost always present a reduction
or disappearance of the mantle and shell (Pterotrachea, Aplysia,
Dorids, Janus, Alderia, Limapontia, Testacella, Onchidium, Vaginulus).

By far the majority of the Gastropoda are marine. Almost the
whole of one group of the Pulmonata (Basommatophora) and the
following Streptoneura live in fresh water — some Neritidae, the
Ampullariidae, Paludinidae, Valvatidae, Bithyniidae, Hydrobiidae,

2 c

386

MOLLUSCA.

some Cerithiidae, the Melaniidae, Cremnoconchus, Canidia. The
Pulmonata Stylommatophora and certain Streptoneura (Helicinidae,
Cydophoridae, Cydostomatidae, Aciculidae) are terrestrial. Many
Littorina, Cerithium, Melania, etc., live in brackish water. Many
branchiate Gastropods are able to live for some time out of water

in dry places; in such circumstances
they are withdrawn into their shells,
the opening of which is closed by
tli» operculum. Almost all move by
creeping; some, however, as Strom-
bus, jump ; others, as Oliva and
Ancillaria swim excellently by the
aid of the lobes of their foot. Some
marine forms, e.g., Magilus, Vermetus,
etc., are fixed by their shells; a few
only are parasitic, as Stilifer on Sea-
urchins and Starfishes, Entocondia in
Synapta. The method of nutrition
differs as much as does the habitat.
Many, especially the siphonostomate
forms, are voracious predatory animals,
and prey on living animals; some, as
Murex and Natica, with this object
bore into the shells of Molluscs ;
several (Strombus, Buccinum) prefer
dead animals. An equally large num-
ber, viz. almost all Pulmonates and
holostomatous branchiate Gastropods,
feed on plants. More than 17,000
species are known : they are found
on all parts of the earth ; in the deep
sea to a depth of 2650 fathoms, and
from the Himalayas above the snow
line. Geologically they are found
at the very commencement of the

palaeozoic epoch in the Cambrian, and the genus Helix (Zonites
Montf.) is known in the Carboniferous.

FIG. 304.— Shells of A Pleiirotomaria,
B Pojfstremaria, C and E Emarginula,
D Haliotis, F Fissurella, G and H
stages in the growth of the shell of

Fissurella.

ISOPLEURA.

387

SUB-CLASS 1. ISOPLEURA* (PLACOPHORA).

Symmetrical Gastropoda, with metameric repetition of the ctenidia
and shell-plates.

In this sub-class the head is without tentacles and sense-organs.
The foot occupies the greater part of the ventral surface, and has
a broad flat sole (in Cryptoplax the foot is narrow). The mantle
occupies the whole dorsal surface, and completely hides the head.
The visceral sac is flattened and not drawn out into a dome. The
mantle-fold encloses a shallow groove which completely surrounds
the body, and is roughly of uniform depth throughout. The
ctenidia, which are bipectinate and projecting, are attached to the

FIG. 305.— A, Plaxipliora carpenteri from
above (4:1). B, a Chiton from below,
after Cuvier. C, Leptochiton Belknapi
from the left (4:1), after Haddon
(from Simroth).

floor of this groove, generally in the hinder part, but in some
forms they extend forwards nearly to the head; they vary in
number from six to eighty pairs.

The shell-plates, of which there are eight, are partly, and in
Cryptochiton wholly, embedded in the mantle; each plate is over-
lapped by the plate in front, except in Cryptoplax (Chitonellus), in
which the plates do not touch (Fig. 306). The parts of the mantle

* A. Th. Middendorf, " Beitrage zu einer Malacozoologica rossica," Mem.
Acad. Imp. Petersburg, 1848. A. Sedgwick, "On certain points in the anatomy
of Chiton," Proc. Roy. Soc., 1881. H. Simroth, " Mollusca" in Bronn's
Klassen u. Ordnungcn, 1893-94. I. Bhimrich, "Das Integument der Chitonen,"
Z. /. w. Z., 52, 1891. A. C. Haddon, "Report on the Polyplacophora,"
Challenger Reports, Ft. 43, 1886.

388

MOLLUSCA.

not covered by the plates bear spicules, which are inserted in
ectodermal pits.

The mantle-groove contains, in addition to the gills, the anus on
a short papilla in the middle line behind, and on each side the
opening of the kidney, and in front of that the opening of the
generative duct (Fig. 308).

In the nervous system (Fig. 307) the nerve-cells are not con-
centrated into ganglia, but are diffused along the main nerve
trunks. There are two pairs Bf main longitudinal trunks — the
pedal in the foot, and the pallial along the mantle-groove. The
former are connected by a number of commissures throughout
their extent. The latter supply the mantle, gills, aaid osphradia,

B

FIG. 306. — A, Acanlhochiton fascicularis ? (after Blumrich). I), Cryptochiton stelleri var. violacea
$ (after A. v. Norclinann). C, Cryptoplax oculatus f (after Haddon). From Siniroth.

and to a certain extent the viscera, and end behind by running
into one another dorsal to the rectum : they are to be regarded
as . corresponding to the • -mantle-nerves,, and partly as the much
extended pleura! ganglia of other.. forms, These two cords on each
side join in front, and the single gan^lionic cord passes round the
oesophagus to unite Math its fellow Across the middle line dorsal
to the oesophagus* ^ Wiis broaogangltonic Dand corresponds generally
to-4ke-jeerebral ganglia of other forms.

The visceral commissure (Fig. 307, VII) is given off from the
pallial nerves close to where these join the pedal cords, and passes
only a short distance backwards ventral to the alimentary canal.

ISOPLEURA.

389

VIII

--VI

It has a pair of small ganglia posteriorly near the anterior part
of the stomach.

The stomatogastric commissure, with its contained buccal ganglia,
arises from the point of division of the cerebral into pallial and
pedal trunks, and passes between the buccal mass and oesophagus.
Finally, there is another suboeso-
phageal commissure with a pair of
small ganglia arising from the
labial commissure and supplyir
the subradular organ. -^^*t- L

Sense organs. The edges of the
snout or head are extended into
short labial palps. On the floor
of the mouth just in front of the
radula is a small epithelial projec-
tion, which is supposed to be a
sense-organ — the subradular organ.
The shell -pieces are traversed by
fine nerve-cords, which end in the
megalaesthetes and the micraes-
thetes. These are sensory epithelial
papillae, and in some forms the
megalaesthetes are modified into
eyes (Moseley), with a calcareous
cornea, a lens, and a pigmented
envelope. It has been asserted that
the ospliradia are multiple — one at
the base of each ctenidium — but it
is doubtful whether there are any
structures corresponding to the
ospliradia of other Gastropods.
Eidges of high epithelium contain-
ing sense-cells have been described
in the mantle-groove.

The alimentary canal begins
with the mouth, which is placed on
a projection in front of the foot, the head or snout; it passes back
to the anus, which is median and posterior. The radula is well
developed, and its formula is (3 + 1) • (2 + 1) • 3 • (1 + 2) (1 + 3). There
are two salivary glands with very short ducts. The oesophagus is
short, and is extended into a glandular pocket on each side. The

FIG. 307.— Central nervous system of
Chiton seen from the dorsal side. The
anterior and posterior ends of the
alimentary canal are represented dia-
grammatically in their relation to the
nervous system (modified from Pel-
seneer). I stomatogastric commissure
(buccal) ; II, labial commissure ; III
pedal cord ; IV anus ; V supra-rectal
pallial commissure ; VI pallial cord ;
VII visceral commissure; VIII sub-
radular commissure ; IX cerebral com-
missure ; X mouth.

390

MOLLUSCA.

.yon

stomach is large and surrounded by the large liver, the ducts of
which it receives. The intestine is long and coiled.

Body-cavity. There is a well-marked perivisceral-cavity in rela-
tion with the alimentary canal. Its nature is not certain, for its

development is not
known, and it is not
connected with the
pericardium. Provi-
sionally it may be re-
garded as haemocoele.
^ Coelom. The peri-
cardial cavity placed
at the hind end on
the dorsal surface is
undoubtedly coelo-
mic, for although it
has no connection
with the gonad, it
opens into the
nephridia.

The heart (Fig.
308) consists of a
median ventricle
giving off an anterior
-f>c aorta, and of two

symmetrical auricles,
each of which has
two openings into
the ventricle (in
Chiton maynificus it
has recently been
stated that there are
four openings on each
side*). The blood
flows to the auricles
from the gills.

Excretory organs. There are two kidneys (Fig. 308), each con-
sisting of bent tubes of the typical Molluscan type with glandular
diverticula. They open into the pericardium on each side, and to the
exterior in the mantle-groove between two of the posterior ctenidia.

* B. Haller. Beitrage zur Kenntniss der Placophoren, MorpJi. Jahrb. 21.

FIG. 308. — Dorsal view of the kidneys, generative organs, and
heart of Chiton discrepans (modified after Sedgwick). a
anus ; ct ctenidia ; g.d generative duct ; g.o opening of
generative duct into the mantle-groove ; gon generative
organ ; h head ; k kidney with its glandular diverticula ;
m mouth ; man mantle-fold ; pc wall of pericardium ; p.o
opening of kidney into the pericardium; r.o external
opening of kidney into the mantle-groove ; v ventricle of
heart, the auricles are cut away, but their openings into
the ventricle are shown.

ISOPLEURA.

391

Generative organs. The sexes are separate, and the generative
gland is single and median, and occupies the dorsal part of the body
just in front of the pericardium, with which, however, it has no
connection. The generative ducts are paired, and arise Jfrom the
hinder end of its ventral surface; they are curved on themselves
near their origin, and in the female have a glandular enlargement on
their course. They open into the mantle-groove a little in front of
the renal openings (Fig. 308).

st:--

FIG. 309.— J. larva of CUton marginatus (after Loven). B embryo, and C larva of Chiton polii
(after Kowalevsky) from Korschelt and Heider. a eye ; k rudiment of shell-plates ; m
mouth ; st spines ; w velum ; ws apical tuft of cilia.

The eggs when laid have a spiny shell, and may be kept in
the mantle-groove or expelled freely into the sea. Fertilization is
external.

In the development the young are hatched as larvae and pass
through a trochosphere stage. There is no veliger stage or nautiloid
shell. The blastopore becomes the mouth.

The Chitons are marine animals which live like limpets attached
to stones by the foot. They inhabit the littoral zone, and have

392 MOLLUSCA.

been found to a depth of 2000 fathoms. They are known fossil
since the Silurian.

There is only one family, the Chitonidae, but there is considerable variation
in the group, both specific and individual, and consequently a large number
of species has been described. These have been arranged in genera, of which
there are a considerable number ; but the attempt which has been made by some
authors to arrange these genera in several families, and these again in sub-orders,
seems to be going further than the facts warrant, for the uniformity in structure
in the group is remarkable, and the differences, though numerous, are trivial
and unimportant.

Fam. Chitonidae. With characters of sub-class. Chiton L. plates of shell
much exposed; Leptochiton Gray, edge of mantle uniformly covered with scale-
like spicules ; Callochiton Gray, with branchiae only in the hinder part of the
mantle-groove; Acanthochiton Leach, edges of mantle with spicules united in
bundles corresponding to the plates of the shell ; Plaxiphora Gray ; Cryptoplax
Blainville (Chitonellus Lam.), shell-plates largely concealed and not articulated
together, foot narrow ; Cryptochiton Middendorf, shell-plates completely em-
bedded in the mantle.

SUB-CLASS 2. ANISOPLEUKA.

Asymmetrical Gastropoda with shell of one piece, never more
than two ctenidia, and with a well-marked visceral commissure.
Generally with a veliger larva.

The above definition contains the main points in which the rest
of the Gastropoda differ from the Isopleura. The Anisopleura are
divided into two orders, the Streptoneura and the Euthyneura.

Order 1. STREPTONEURA.*

Dioecious Anisopleura with shell and generally with operculum;
with gills in front of the heart. Visceral commissure twisted into
a Jigure-of-8.

Behind the head, which is usually distinct and bears a single pair
of tentacles, lies the mantle-cavity, into which the rectum, kidney,
and oviduct open. In rare cases two gills are present, but as a
rule the right gill is absent. The branchial veins enter the heart
from the front. The visceral commissure is twisted into a figure-
of-8, of which the right half passes dorsal to the alimentary canal,

* E. Claparede, "Anatomie u. Entwick. d. Neritina fluv.," Z.f. w. Z., 2, 1850.
H. Lacaze Duthiers, "Sur le systeme nerv. de 1'Haliotide et sur la Poupre," Ann.
Sci. Nat. (4), 12, 1859. Id., "Sur I'anat. et 1'embryog. des Vermets," Ann.
Sci. Nat. (4), 13, 1860. E. L. Bouvier, " Systeme nerv., inorph. gen. et classi-

Zool. Exp. (2), 2, 1884. Boutan, "Sur I'anat. et le devel. de la Fissurella," Arch.
Zool. Exp. (2), 3 bis, 1886.

ASPIDOBRANCHIATA.

393

the left half ventral to it. The pleural ganglia are sometimes
joined to the opposite half of the visceral commissure by an anas-
tomotic branch of the pallial nerve (dialyneury, e.g., Cassidaria, on
left side), or the pallial nerve directly joins the ganglion on the
opposite half of the visceral commissure, i.e., the pamal nerve
from the right pleural joins
the sub-intestinal ganglion,
and that from the left
pleural joins the supra-
intestinal (zygoneury, more
common on the right side,
e.g., Cassidaria, where the
right pleural is directly
joined to the sub-intestinal,
see above, p. 365, Fig. 286).
The males are often pro-
vided with a large penis
placed on the right anterior
side of the body. In the
generative organs accessory
glands are usually absent.
The eggs are surrounded
by albumen and laid in
capsules, which are fre-
quently fixed to foreign
objects; sometimes they
are attached to a raft of
mucous bubbles, to which
the animal itself adheres
(lantliina).

FIG. 310.^-Nervous system of Haliotis (diagrammatic
after Spengel). Cg cerebral ganglion ; Pg fused
pleural and pedal ganglia ; 0 right and 0' left
osphradium ; Ag abdominal ganglion ; Pe pedal
cord ; S and S' pallial nerves ; Br gills.

Sub-order 1. Aspidobranchiata (Diotocardia, Scutibranchia).

Ctenidium Itipedinate or absent, labial commissure present.

The pleural ganglia are approximated to the pedal, which are
prolonged posteriorly into long ganglionic cords (Figs. 283, 310).
The cerebral ganglia are widely separate from each other, and the
commissure connecting them passes in front of the buccal mass and
salivary glands. There is a sub-oesophageal labial commissure with
buccal ganglia (Fig. 283). The osphradium is small, and placed on
the branchial nerve. The otocyst has numerous small concretions
(otoconia). The eye is open (Fig. 290 A), or closed with a very

394 MOLLUSC A.

small cornea. The radula lias multiple centrals. The ctenidia are
bipectinate and free anteriorly. Traces of bilateral symmetry are
usually present. There are generally two auricles and two kidneys,
which open on short papillae. The gonad (Fig. 297 b) opens into
the right kidney (except in the Neritidae).

Tribe 1. DOCOGLOSSA.

Nervous system without dialyneury ; eyes open without lens. Two osphradia.
Operculum and hypobranchial glands absent. Jaw unpaired and dorsal. Radula
has strong, pillar-shaped teeth, and never more than three marginals on each
side. A single auricle; the rectum does not traverse the ventricle or the
pericardium. The visceral sac is conical in the adult, and not twisted.

Fam. 1. Acmaeidae. Left ctenidium only ; it is to a great extent free.
Acmaea Esch. ; Scurria Gray; Addisonia Dall.

Fam. 2. Patellidae. Limpets. Ctenidia absent, replaced by a circlet of
plate-like structures in the mantle-groove. Patella L. ; Helcion Gray.

Fam. 3. Lepetidae. Ctenidia, pallial branchiae, and eyes absent. Lepeta
Gray.

Tribe 2. RHIPIDOBLOSSA.

Nervous system with dialyneury ; eyes with lens ; a single osphradium (the
left), except when there are two ctenidia; one or two hypobranchial glands.
Jaws paired ; marginal teeth of radula numerous, and crowded together like
the ribs of a fan (Fig. 293 A}. A crop, oesophageal gland, and a stomach
caecum (often spiral) present. Two auricles, ventricle traversed by rectum
(except in Helicinidae). Often with an epipodial projection, which is frequently
tentaculiferous, on each side of foot.

Section A. With two ctenidia (Zygobranchiate). Shell with marginal slit or
holes corresponding to an anal opening in mantle.

Fam. 1. Pleurotomaridae. Visceral mass and shell twisted. Mantle slit in
front in the middle line. Operculate. Cambrian onwards. Pleurotomaria

Defrance (Fig. 304 A] ; P. quo-
yana, Gulf of Mexico ; Scissur-
ella d'Orb. ; Trochotoma Desh.

Fam. 2. Haliotidae. Spire
of the visceral sac and shell
much reduced. Shell flat, with
wide aperture, with internal
mother-of-pearl lustre and a
row of holes on the left side
FIG. 311.— Fissurdla maxima (from Eroiiii). over the mantle slit. The

mantle - cavity is displaced to

the left side by the enormous spindle -muscle. Epipodium tentaculiferous.
Without operculum. Haliotis L., ear shell, ormer (Figs. 296 and 304 D),
adherent to rocks like a limpet ; found in large numbers in the Channel Islands.
Fam. 3. Fissurellidae. Visceral sac and shell conical, with an apical
aperture or an anterior marginal excavation. Limpet-like. Without oper-
culum. Fissurella Brug., key-hole limpet (Figs. 304 F, and 311) ; Puncturella
Lowe ; Pupillia Gray ; Emarginula Lam., with anterior marginal excavation ;

PECTINIBRANCHIATA. 395

Scutum (Scutus) Montfort (Parmophorus~B\a,inv.), Australia, shell partly covered
by mantle ; Cemoria Leech, Rimula Defrance. Propilidium.Forbes and H., and
Gocculina Ball, allied here.

Section B. With one (left) ctenidium (Azyg abranchiate}.

Fain. 4. Trochidae. Visceral sac and shell coiled in a spiral j eyes open ;
operculum horny ; with head-lobes between the tentacles. Trochus L. ; Marga-
rita Leach (Fig. 312) ; .Monodonta Lam.

Fam. 5. Stomatiidae. Spire of visceral sac and shell reduced. Stomatella
Lam. ; Gfena Gray ; Broderipia Gray ; Stomatia Lam. , without operculum ;
Phaneta Ad., fluviatile.

Fam. 6. Delphiuulidae. Visceral mass and shell spiral ; no cephalic lobes.
Delphinula Lam. ; Cyclostrema
Marryat.

Fam. 7. Liotiidae. Liotia
Gray.

Fam. 8. Turbinidae. Visceral
sac and shell spirally coiled ;
epipodial tentacles ; calcareous
operculum. Turbo L., top-shell.
Phasianella Lam., pheasant-shell ;
Mdlleria Jeffreys.

Fam. 9. Neritopsidae. Neri-
topsis Grateloup.

Fam. 10. Macluritidae. Ma-
clurea Lesueur.

Fam 11 Neritidae. Epipo- FlG- *&•— Margarita greenlandica (after Pelseneer,
dium little developed, without JT,^ ^;eacl ; ^ anterior epipoclal lobes ;

3 foot ; k pigmented eminences at the base of the

tentacles ; a cephalic penis ; cal- epipodial tentacles 5; 6 visceral sac.

careous operculum ; eyes stalked.

Nerita L. ; Neritina Lam. , chiefly brackish water and fluviatile ; land species
are known ; N. fluviatilis Miiller, British rivers. Theodoxia Mont. ; Sinaragdia
Issel ; Septaria Fer.

Fam. 12. Titiscanidae. Shell and operculum absent. Titiscania Bergh ;
T. limacina Bergh., Pacific Ocean.

Fam. 13. Helicinidae. Epipodium without tentacles ; branchia absent,
mantle cavity transformed into a pulmonary chamber ; heart with a single
auricle, not traversed by the rectum. Operculum without apophysis. Terrestrial.
Helicina Lam. , Central America and Bahamas ; Hydrocena Parreys ; Georissa
Blanford.

Fam. 14. Proserpinidae. Branchia replaced by pulmonary cavity; mantle
partly reflected over shell; operculum absent. Terrestrial. Proserpina Gray,
Cuba, Jamaica, Venezuela ; Ceres Gray, Mexico.

Sub-order 2. Pectinibranchiata (Ctenobranchia, Monotocardia).

Ctenidium monopectinate, generally without labial commissure.

The nerve-collar is behind the buccal mass, and there is no labial
commissure (except in Paludina and Ampullaria). The single
osphradium is often pectinate, and well differentiated. The eye is
always closed. Otocysts with otolith (except Paludina, Valvata,

396 MOLLUSCA.

Amputtaria, CyclopJiorus, Acicula, some Cerithiidae, etc.). Radula
with central tooth single or absent.

The ctenidium, auricle, and kidney of one (right) side are absent,
and the ventricle is not traversed by the rectum. The ctenidium is
monopectinate (Fig. 280), and attached to the mantle by its whole
length. The kidney opens by a slit, exceptionally by a ureter
(Paludina, Cyclophorus, Valvata), and never receives the generative
products. A penis is generally present, and the gonad has its own
duct and opening.

Tribe 1. PTENOGLOSSA.

Without siphon. Peristome entire. Mouth with proboscis or snout. Penis
absent. Radula without median tooth, with numerous lateral hooks (co . 0. oo ).

Fam. 1. lanthinidae. Snout prominent, blunt ; tentacles bifid ; no eyes ;
shell thin, spiral, without operculum. Foot small, secreting a float, to which
the eggs are attached. Pelagic, carnivorous. lanthina Lam. ; /. fragilis L. ,
Atlantic and Med.; Rediizia Pet.

Fam. 2. Solariidae. Shell flattened, with a large umbilicus which extends
to summit of spire. Head short, proboscis long; foot small. Tentacles slit
along their whole length. Solarium Lam. Stair-case shell.

Fam. 3. Scalariidae. Shell turriculated ; a small siphon ; foot and proboscis
short. The animal secretes a purple liquid when molested. Carnivorous.
Scalaria Lam., wentle-trap.

Tribe 2. RACHIGLOSSA.

With long proboscis, evaginable from the base. Radula with at most three
teeth in each row, a cusped median tooth, and a cusped lateral on each side,
which may be absent ; marginals absent (Fig. 293 C). All possess a siphon and
are predatory.

Fam. 1. Muricidae. Eyes at the base of the tentacles; foot truncated; an
anal gland. Murex L. The Ancients obtained their purple from species of
Murex; it is secreted by the anal gland. M. erinaceus, sting- winkle, English
Channel ; M. trunculus L. Heaps of shells of this species still to be seen on
the Tyrian shore. Purpura Brug. ; P. lapillus L., destructive to mussel beds;
Trophon Montf. ; Urosalpinx Stimpson.

Fam. 2. Coralliophilidae. Radula absent. Inhabits coral reefs. Magilus
Montf. ; Leptoconchus Riipp. ; Coralliophila H. and A. Adams.

Fam. 3. Columbellidae. Columbella, Lam.

Fam. 4. Nassidae. Foot long, broad, often with terminal appendage;
siphon long; eyes on outer base of tentacles; central tooth of radula arched,
multicusped, laterals bicuspid with small denticles between the cusps; shell
buccinoid. Na-ssa Lam.; N. reticulata L., dog- whelk, common on English
coasts at low water ; Canidia Adams ; Cyclonassa Swainson ; Bullia Gray.

Fam. 5. Buccinidae. Eyes at base of tentacles; foot large; proboscis long.
Central tooth of radula with 5-7 cusps, laterals bi- or tri-cnsped. Shell thick,
covered with periostracum ; canal of varying length ; operculum corneous.
Buccinum L., whelk; Chrysodomus Swainson.

The Haliidae (Halia Risso) are allied here.

TOXOGLOSSA TAENIOGLOSSA. 397

Fam. 6. Fasciolaridae. Shell fusiform ; spire long ; operculum corneous ;
head small ; short tentacles, with eyes at base ; siphon moderate. Fasciolaria
Lam. ; Fusus Lam.

The Turbinellidae (Hemifusus Swainson; Fidgur Montf. ; Latirus Montf. ;
Lagena Schum.) are allied here. f,

Fam. 7. Mitridae. Tentacles carrying eyes laterally; proboscis long; shell
fusiform, spire pointed; operculum absent. Mitra Lam., mitre-shell; Thala
Ad. ; Turricula Ad.

Fam. 8. Volutidae. Head flattened, and prolonged laterally into lobes, on
which are the eyes. Proboscis short ; siphon with interior appendages ; operculum
generally absent. Valuta L. ; Guivillea Watson ; Cymba Brod. and Sow. , boat-
shell; Cyinbium Montf.

Fam. 9. Olividae. Anterior part of foot separated by a transverse furrow,
rnesopodium reflected laterally over the shell; eyes placed half-way up the
tentacles ; shell olive-shaped ; operculum present or absent. Oliva Brug. , olive-
shell ; Olivella Swainson ; Ancillaria Lam. ; Olivancillaria d'Orb.

The Harpidae (Harpa Lam., harp-shell) and Marginellidae (Marginella Lam.)
are allied here.

Tribe 3. TOXOGLOSSA.

Radula without median and lateral teeth (except Spirotropis), 1.0.0.0.1.
Oesophagus with a large poison gland ; siphon and proboscis well developed ;
carnivorous.

Fam. 1. Terebridae.
Eyes at end of tentacles ; Si
foot small; shell turricu-
lated. Terebra Adanson,
auger- shell.

Fam. 2. Conidae. Eyes
on outer side of tentacles;
siphon prominent ; shell
conical. Oonus L., cone- ~J*

shell (Fig. 313); Bda Leach; FIG. 313.— Conus textilis (regne animal). R proboscis; ,s
Clavatula Lam. ; Drillia siPhon 5 F tentacle ; 0 eye ; P foot.
Gray ; Conorbis Sow.

Fam. 3. Cancellariidae. Proboscis short, usually no radula; no operculum ;
vegetable feeders. Cancellaria Lam.

Tribe 4. TAENIOGLOSSA.

Radula with normal formula 2.1.1.1.2. (Fig. 293 B). Marginals sometimes
numerous.

There are two sections, the Platypoda and Heteropoda.

Section 1. Platypoda.

Normal creeping Pectinibranchs, little modified. Foot more or less flattened
ventrally. Rarely with accessory glands on the generative ducts (Paludina,
Cyclostoma, Naticidae, etc. ). Generally with jaws.

Fam. 1. Naticidae. Foot very large, partly covers shell ; propodium reflected
on the head ; shell semi-globular, spire small ; operculum. Eyes often absent,
carnivorous, feeding on bivalves. Natica Lam. ; Sigaretus Lam.

398 MOLLUSCA.

Fam. 2. Lamellariidae. Mantle more or less completely covering the shell.
Without operculum. Jaws fused dorsally. Lamellaria Montagu ; Onchidiopsis
Beck ; Velutina Blainv. ; Marsenina Gray.

Fam. 3. Trichotropidae. Radula allied to that of Velutina. Trichotropis
Broderip.

Fam. 4. Naricidae. Foot circular, carrying an epipodial lobe on each side ;
tentacles flattened ; shell naticoid, with a velvety periostracum. Narica Recluz.

Fam. 5. Xenophoridae. Mineralogists, conchologists. Snout elongated ;
foot divided transversely into two parts, of which the posterior carries the
operculum. Shell trochiform, attaching foreign bodies (stones, shells) externally.
Xenophora Fischer.

Fam. 6. Capulidae. Visceral sac and shell conical (patelliform), slightly
curved behind, usually with an internal plate ; without operculum ; columellar
muscle horseshoe-shaped. Capulus Montf. (Pileopsis Lam.), bonnet limpet ;
Grepidula Lam. ; Calyptraea Lam. , cup and saucer limpet ; Thy COL Adams.

Fam. 7. Hipponycidae. Visceral mass and shell conical ; foot reduced,
may secrete a calcareous base. Hipponyx Defrance.

Fam. 8. Littorinidae. Proboscis short, broad ; tentacles long, eyes at their
outer bases ; penis behind the right tentacle ; oviparous or viviparous ; radula
long ; shell turbinate, solid, operculum corneous. Marine or brackish water ;
mostly littoral. Littorina Ferussac, periwinkle ; Lacuna Turton ; Cremno-
conchus Blanford. Fossarus Philippi is allied here.

Fam. 9. Cyclophoridae. Mantle-cavity without ctenidium, transformed into
a pulmonary sac. Tentacles long, filiform. Pedal ganglia elongated into cords.
Otocysts with otoconia. Operculum circular. Terrestrial. Pomatias Hartmann ;
P. obscurum S. Europe ; Cydophorus Montf. ; Cyclosurus Morelet ; Pupina
Vign. ; Cataulus Pfr. ; Cyclotus Guilding ; Pterocydus Benson ; Leptopoma Pfr. ;
Mcgalomastoma Guild. ; Craspedopoma Pfr. ; Diplommatina Bens.

Fam. 10. Cyclostomatidae. Mantle-cavity pulmonary. Ctenidium absent.
Otocysts with otolith ; jaws absent ; deep median longitudinal groove in foot.
Operculum generally calcareous. Terrestrial. Cydostoma Drap. ; C. elegans
Miiller, Britain and temp. Europe.

The Aciculidae (Acicula Hartm.), also terrestrial and found in Britain, are
allied here.

Fam. 11. Truncatellidae. Looping snails. A monopectinate gill ; snout
long, bilobed ; foot very short. They walk by contracting the space between
the lips and foot. Found between tide-marks, survive many weeks out of water,
Truncatella Risso.

Fam. 12. Eissoidae. Epipodial filaments ; operculigerous lobe with appen-
dages ; shell small, acuminate ; marine and brackish water. Rissoa Freminville ;
Litiopa Rang.

Fam. 13. Hydrobiidae. Operculigerous lobe without filaments ; shell small,
acuminate. Brackish or fresh - water. HydroUa Hartm. ; Bithynia Gray ;
Lithoglyphus Miihlfeldt ; Pomatiopsis Tyron ; Bithynella Moquin ; Assiminea
Leach.

The Skeneidae (Skenea Fleming) and Jeffreysiidae (Jeffrey sia Alder) are
allied here ; as also are probably the Homalogyridae (Homalogyra Jeffreys) and
the Choristidae (Choristes Carpentier).

Fam. 14. Adeorbidae. Adeorbis S. Wood.

TAENIOGLOSSA.

399

Fam. 15. Paludinidae. Shell conical or globular, with thick olive-green
periostracum ; operculum horny, normally concentric. Snout blunt, tentacles
long, eyes on short pedicels outside tentacles. Pedal ganglia elongated into
cords ; kidney with ureter. Viviparous. Fresh-water. Paludina Lam. , river-
snail.

Fam. 16. Valvatidae. A bipectinate ctenidium projecting freer^on the left
side ; a filiform appendage on the right side ; eyes sessile behind the tentacles.
Hermaphrodite. Fresh-water. Valvata Mliller.

Fam. 17. Ampullariidae. Mantle-cavity divided into a right branchial
division containing a monopectinate ctenidium, and into a left half functioning
as a pulmonary chamber. Oesophageal nerve-collar in front of buccal mass.
Fresh water. Ampullaria Lam. (Fig. 303). Apple-snail or idol-shell. Inhabit
lakes and rivers in warmer parts of world, retiring into the mud in the dry
season.

Fam. 18. Cerithiidae. Spire elongated; siphon short; operculum horny.
Marine or brackish water. Cerithium Adanson ; Cerithidea Swainson ; Triforis
Deshayes ; Laeocochlis Dunker and Metzger ; Potamides Brongniart.

The Planaxidae (Planaxis Lam.) and the Modulidae (Modulus Gray) are
allied here.

FIG. 314.— Cassis sukosa (after Poli, from Lang), a shell ; b anterior canal or spout for the
siphon ; c siphon ; d head ; g proboscis ; e eye ; / tentacle ; h foot ; i operculum.

Fam. 19. Nerinaeidae. Nerinaea Defrance.

Fam. 20. Melaniidae. Spire elongated; thick, dark periostracum; edge of
mantle fringed. Viviparous. Fresh-water in warmer parts of world. Melania
Lam. ; Melanopsis Lam. ; Paludomus Swainson.

Pleuroceridae (fresh- water), Pseudomelaniidae (marine) are allied here.

Fam. 21. Turritelidae. Shell multispiral or tubular; operculum horny-;
head large and projecting; edge of mantle fringed; foot broad. Turritella
Lam.; Mathilda Semper; Coecum Fleming.

Fam. 22. Vermetidae. Shell tubular, attached, irregularly coiled, last coils
not in contact; operculum circular. Vermetus Adans., worm-shell; Siliquaria
Brug.

Fam. 23. Strombidae. Wing -shells. Foot narrow, arched, compressed
laterally, without ventral sole; snout long; large and elaborate eyes placed on
thick pedicels with slender tentacles arising from the middle of the pedicels.
Very active, progressing by a sort of leaping movement. Strombus L. ;
Ptcroceras Lam., scorpion-shell; Terebcllum Klein ; Rostellaria Lam.

400

MOLLUSCA.

Fam. 24. Chenopodidae (Aporrhaidae). Foot elongated, narrow; proboscis
short, tentacles long; siphon short. Shell like that of S trombus. Chenopus
Philippi (Aporrhais Aldrovandus) .

Fam. 25. Struthiolariidae. Shell buccinoid ; operculum claw-shaped,
notched; foot broad and short. Struthiolaria Lara.

Fam. 26. Cypraeidae. Cowries. Mantle reflected over the shell, and
provided with appendages ; shell convolute, enamelled ; spire concealed ; outer
lip thickened, inflected; operculum absent. The young shell has a prominent
spire. Cypraea L. , Cowry ; Erato Risso ; OvulalSmg. ; Pustularia Swainson.

Fam. 27. Doliidae. Shell ventricose, spirally furrowed; no operculum;
eyes stalked; foot large and expanded ; ^iphon long. Dolium Lam., the Tun;
Pyrula (Pirula) Lam., fig-shell.

Fam. 28. Cassididae. Shell ventricose with varices, spire short, outer lip
reflected or thickened, operculum semilunar ; eyes sessile ; foot large, rounded in
front; proboscis and siphon long. Cassis Lam., helmet -shell (Fig. 314);
Cassidaria Lam.

Fam. 29. Tritonidae. A proboscis; siphon well developed but short; foot
short; shell thick, varicose, outer lip inflected and thickened, operculum
corneous ; periostracum often thick and hairy. Triton Lam. ; Raiulla Lam.
frog-shell. The genus Oocorys Fischer, is allied here.

TV "

FIG. 315. — Male of Carinaria mediterranea (after Souleyet, Gegenbaur, and Keferstein). A anus ;
Ar anterior aorta ; At auricle ; EG buccal ganglion; Bm buccal mass; Br gills ; CG cerebral
ganglion ; F flagellum ; L liver ; M crop ; Mg mantle ganglion ; N kidney ; 0 mouth ; Oc
eye ; Ot otocyst ; p pro- and mesopodium ; Pe penis ; Pg pedal ganglion ; S sucker ; Sp
salivary gland ; T testis ; Te tentacles ; Vd vas deferens ; Ve ventricle ; Wp ciliated furrow ;
Z posterior branch of anterior aorta.

Section 2. Heteropoda.*

The Heteropoda, are free-swimming, pelagic Pectinibranchiates, with laterally-
compressed foot, taenioglossate radula, and otocysts near the cerebral ganglia.
They are without jaws.

* C. Gegenbaur, " Untersucli. ub. Pteropoden u. Heteropoden," Leipzig, 1854.
T. H. Huxley, "On the Morphology of the Cephalous Mollusca," etc., Phil.
Travis. 1853.

TAENIOGLOSSA. 401

The main peculiarity of the body consists in the large size of the head
and foot, and the small size of the visceral sac. The foot is divided into an
anterior part — the so-called pro- and mesopodium (Fig. 315 p) — and a posterior
part— the metapodium. The former is foliaceous, and often carries a sucker on
its posterior part ; while the latter, considerably elongated and extended far
backwards, forms the caudal continuation of the body.

The visceral sac is either spirally twisted and enclosed by a mantle and spiral
shell (Atlanta), or has the form of a projecting mass, which is placed over the
hinder part of the foot, and is likewise covered by the mantle and a reduced
hat-shaped shell (Carinaria) ; or finally, the visceral sac is reduced to a small,
scarcely-projecting nucleus, which is covered on the front side by a membrane
with a metallic lustre, and is completely without a shell.

The nervous system is well-developed. The cerebral ganglia are conjoined,
and the pleural are fused with them (visibly in Atlanta and Pterotrachea).
There are two pedal connectives on each side, which are partially free proximally
in Atlanta. The pedal ganglia are situated at the base of the fin (pro-meso-
podium). The visceral commissure is long, streptoneurous, and provided with
several ganglia, but without dialyneury or zygoneury (p. 365). In the Carinariidae
there are secondary viscero-pedal anastomoses which are not twisted. In the
Firolidae the pedal connectives are fused with the anterior part of the visceral
commissure ; and behind the pedal ganglion the two branches of the visceral
commissure are fused together for the greater part of their extent.

The osphradium has the form of a more or less elongated ciliated organ in
the pallial cavity to the left of the ctenidium. The otocysts are close to
the cerebral ganglia. The eyes are very large, contained in capsules, and
moved by special muscles ; they are highly elaborate and are placed at the
base of the tentacles, which are entirely absent in Pterotrachea.

The alimentary canal has a protractile pharynx with radula, a long oeso-
phagus slightly swollen towards its middle, and a stomach and liver placed
behind. The intestine is short and is not curved forward in Pterotrachea.

The heart is near the stomach ; it is in front of the gill in Pterotrachea, but
is disposed as in the Platypoda in the less specialized forms. The arteries
terminate abruptly in the blood-sinuses. The ctenidium is monopectinate, not
covered by mantle-fold in Pterotrachea, and absent in Firoloida. The kidney
is a transparent sac with contractile walls ; it has the same relations as in
other Gastropods, and opens not far from the anus.

The males are distinguished by the possession of a large penis, which projects
freely on the right side of the foot. The males of Pterotrachea possess a sucker
on the hinder part of the anterior division of the foot ; in Atlanta and Carinaria
the sucker is present in both sexes. The ovaries and testes fill the posterior
part of the visceral sac, and are partially embedded in the liver. The ducts
open on the right side of the body near the anus. There is a ciliated groove
to conduct the sperm from the generative opening to the penis. The penis
is provided with a glandular appendage or flagellum. The oviduct possesses
a large albumen gland and a receptaculum seminis opening into it.

The Heteropoda are exclusively pelagic animals, and are often found in great
numbers in the warmer seas. Their tissues and shell are transparent. They
are somewhat clumsy in their movements, which are effected with the ventral
surface uppermost, by oscillations of the whole body and fin. They are all
carnivorous. When the tongue is protruded, the lateral teeth fly apart from
one another like the limbs of a pair of forceps, and when retracted they again

2 D

402 MOLLUSCA.

fall together ; in this way small marine animals are seized and drawn into
the mouth.

Fam. 1. Atlantidae. Visceral sac and shell coiled in a spiral. The
metapodium carries an operculum. Atlanta Lesueur.

Fam. 2. Carinariidae. Visceral sac and shell conical, and small in relation
to rest of body; foot elongated, without operculum. Carinaria Lam.

Fam. 3. Pterotracheidae. Visceral sac reduced ; without mantle and shell ;
a sucker on foot in male only. Pterotrdchea Forskal. No tentacles ; a filiform
appendage at posterior part of foot. Firoloida Lesueur. Tentacles present ;
gill and posterior pedal appendage absent.

Tribe 5. GYftNOGLOSSA.

Radula and jaws absent.

Fam. 1. Eulhnidae. Proboscis elongated; tentacles without furrow; often
parasitic on Echinoderms. Shell small, long, subulate, polished. Eulima
Risso; Stilifer (Stylifer) Brod., a cephalic pseudopallium extending over shell,
in body-wall of male star-fish.

It is convenient to place here the two genera Entocolax and Entoconcha, both
parasitic on Echinoderms. In these genera there is only a vestige of the
alimentary canal with a single opening. The visceral mass is surrounded by
the pseudopallium, and the cavity so formed receives the generative duct and
opens to the exterior by a small orifice. Entocolax Voigt. Fixed by the
aboral extremity ; sexes separate. E. Ludwigi, fixed to the body-wall in body-
cavity of a Holothurian. Entoconcha Miiller, vermiform, fixed by the oral end ;
hermaphrodite. Larva with a shell (resembling that of Natica), operculum and
velum. E. mirabilis Miiller, in body-cavity of Synapta digitata attached to
intestinal wall.

Order 2. EUTHYNEUKA.*

Hermaphrodite Anisopleura, in wliicli the visceral commissure is
not twisted (save in the Actaeonidae). The primitive left c/ill,
nephridium, and auricle are always aborted, and the operculum is
generally absent.

There are typically two pairs of tentacles on the head. The vis-
ceral commissure is generally very short, and its ganglia (Fig. 316)

* Alder and Hancock, "A Monograph of the British Nudibranchiate Mollusca"
London, 1845-55. Hancock, "On the Anatomy of Doridopsis," Trans. Linn.
Soc. London, 25, 1865. H. Lacaze Duthiers, "Anat. et Phys. du Pleurobranche
orange," Ann. Sci. Nat. (4), 11, 1859. Id.,"Du systeme nerveux des Mollusques

rteropodes pulmones aquatiques," Arch. Zool. Exp. (1), 1, 1872. Id., "Histoire
la Testacelle," ib. (2), 5, 1887. Vayssiere, "Recherches zoologiques et
anatomiques sur les mollusques Opisthobrancb.es du Golfe de Marseille," Ann.
Mus. Marseille (Zool.), 2 and 3, 1885-88. P. Pelseneer, "Report on the
Pteropoda," Challenger Reports, pt. 66, 1888. Bergh, "Die kladohepatischen
Nudibranchier," Zool. Jahrb. (Abth. f. System.}, 5, 1890. Leidy, "Special
Anatomy of the terrestrial Gastropoda of the U.S." in Binney, The terrestrial
air-breathing Molluscs of the U.S., vol. i., Boston, 1851. P. Pelseneer,
" Recherches , sur divers Opisthobranches," Mtinoires Couronnes et Mtmoires
des Savants Strangers, Acad. Bruxelles, 53, 1894. L. Pfeiffer, "Monographia Heli-
ceorum Viventium," Leipzig, 1848-69 ; and Monographia Auriculaceorum
Viventium, Cassel, 1856. A. Rossmassler, " Iconographie der Land-u. Silssivasser
Mollusken Europas, Leipzig, 1835-59. Ferussac et Deshayes, Hist. nat. gen.
et partic. des Mollusques terrestres et fluviatiles, Paris, 1829-51.

OP1STHOBRANCHIATA.

403

all approximated to the oesophagus (except in the Bulloids and
in Aplysia). In the Bulloids it shows traces of the characteristic
torsion of the Streptoneura ; and in one form, Actaeon, it is actually
streptoneurous (Fig. 318). Hermaphroditism is universal and the
generative system is complicated by the presence of a number of
accessory structures (albu-
men and mucous glands,
spermathecae, etc.).

The otocysts generally
contain otoconia. Fur-
ther, there is in this order
a tendency to the reduc-
tion of the pallial cavity,
the shell, and the oper-
culum. The operculum
is absent in almost all
forms; the shell is com-
pletely absent in Kudi-
branchs, and it tends to
disappear in Pulmonates
and Tectibranchs. The
mantle-cavity is absent in
Nudibranchs, and is but slightly marked off in most Tectibranchs;
and in cases in which it is present its reduction is indicated by
the fact that the genital ducts generally open outside it.

As explained on p. 385, the Euthyneura may be looked upon as streptoneurous
forms which have undergone partial detorsion, the result of which is that the
visceral commissure is generally untwisted, and the mantle-cavity and external
'openings are, as a rule, shifted off the anterior face of the visceral sac to the
right side, and often displaced far backwards.

Sub-order 1. Opisthobranchiata.

Marine Euthyneura with aquatic respiration. The gills are
generally behind the heart. The pallial-cavity when it exists is
widely open.

The mantle-cavity never contains more than one ctenidium, placed
on the right side of the body. Often there is no ctenidium
(Nudibranchs).

Tribe 1. TECTIBEANCHIATA,

Opisthobranchs provided with a mantle, and a shell (except in JKuncina,
Pleurobranchaea, the Pneumatodermatidae, Clionopsidae, and Clionidae), with
a ctenidium (except in the three above-named families), and with an osphradium.

FIG. 316.— Nervous system of Limnaea (after L. Du-
thiers). Cg cerebral, Pg pedal, Pig pleural, Ag
abdominal ganglion ; 0 osphradium.

404

MOLLUSCA.

The tribe includes three sections — the Bulloidea, the Aplysioidea, and the
Pleurobranchioidea. All the families formerly united as Gymnosomatous
Pteropoda are included with the Aplysioidea, while the thecosomatous Ptero-
pods are placed with the Bulloidea. All are marine.

The leading features of the group are as follows : —

1. The displacement backwards of the pallial opening, the anus and the
circumanal complex.

2. The disappearance of the visceral twist and of the operculum ; the reduc-
tion of the mantle and shell ; the exposure of the genital opening, and of
the ctenidium.

3. The acquisition of external symmetry.

4. The absence of the spermatic groove, which is transformed into a vas
deferens.

5. The reduction in the number of teeth in the transverse rows of the radula.

6. The concentration of the central nervous system, and the shortening of
the visceral commissure.

7. The displacement of the oesophageal nerve collar towards the posterior
part of the buccal mass.

In the following table the distribution of these characters amongst the families
is shown : —

Pleurobranchidae

Umbrellidae

Gymnosomata

Aplysiidae .

Lobiger

Pelta .

Thecosomata

Philinidae .

Bullidae

Actaeonidae

2

6

* In some members of the type only.

From this table it is apparent that Actaeon most resembles the Streptoneura,
inasmuch as it has its visceral commissure twisted, auricle anterior to ventricle,
an operculum, genital opening (female) in mantle-cavity, anus forward ; but
it differs from that group in being hermaphrodite. With all these strepto-
neurous affinities one might expect the genital apparatus to be of the most
unspecialized construction, i.e., with an hermaphrodite opening and perhaps
without even a spermatic groove, but this is not the case : in its ducts Actaeon
is as specialized as any Tectibranch. If we attempt to draw up a genealogical
scheme for the group, we cannot place Actaeon at the root because in this
particular it is as highly specialized as any form. Aplysia on the other hand,.

TECTIBRANCHIATA.

405

while most highly specialized in many of its organs, presents the unspecialized
features of having an open spermatic groove and a much elongated visceral
commissure.

Section 1. Bulloidea.

Shell well developed, external or internal (absent only in Runcwia). Head
usually without tentacles, with a broad
cephalic disc. Epipodia continuous with
ventral face of foot. Stomach generally
provided with masticatory plates. In Actaeon
and the Limacinidae the foot carries a semi-
lunar operculum. The pleural ganglia are
close to or fused with the cerebral. Visceral
commissure long except in the Limacinidae,
Cymbuliidae, Cavoliniidae. The visceral com-
missure is twisted in Actaeon in the strepto-

FIG. 317. — Actaeon tornatilis (after Pelseneer) x 5.
I inferior lobe of mantle ; II pallial gland ; III
hypobranchial gland ; I V pallial aperture ; V eye
and cephalic shield ; VI penis.

neurons fashion, and shows indications of the
same feature in many other Bulloidea. For
instance, in ScapJiander the left half of the
commissure passes, ventral to the oesophagus,
to the subintestinal ganglion ; while the
right half is placed mainly dorsal to the
alimentary canal and passes to the supra-
intestinal ganglion which supplies the gill
and the osphradium. The nerve collar is
anterior to the buccal mass in Actaeon,
Bulla striata, Philine, Doridium, while in
others (Bulla hydatis, B. cornea, Accra, etc.)
it is behind. The male and female generative
openings may be in common or separate. In
the latter case the male opening is at the
end of the penis on the right side in front
of the mantle opening, while the female is
within the mantle cavity (Actaeon}. When
there is a common opening (e.g., Cymbuliidae,
etc. ) there is a seminal groove to the penis.

"-XI

FIG. 318.— Nervous system of Actaeon,
dorsal view, x 20 (after Pelseneer).
I cerebropleural ganglion ; II eye ;
III cerebropedal connective, IV
nerve from pleuropedal connective,
Fpenial nerve ; VI right accessory
pallial, VII stomatogastric, VIII
supraintestinal, IX sub-intestinal,
and XI abdominal ganglion ; X
sub-intestinal part of the visceral
commissure, XIII supraintestinal
part of same ; XII genital nerve ;
XI V osphradial and XV left acces-
sory pallial ganglion ; X VI para-
pedal commissure ; XVII otocyst ;
XVIII pedal ganglion ; XIX pleuro-
pedal connective.

Limacinidae, Cavoliniidae, Pelta,

406 MOLLUSCA.

Fam. 1. Actaeonidae. Cephalic disc bifid behind. Shell external with
prominent spire, entirely covering animal ; operculum horny ; visceral loop
streptoneurous ; epipodia absent. Actaeon Montf. (Fig. 317).

Fam. 2. Eingiculidae. Cephalic disc forms behind an open tube. Shell
external with prominent spire, without operculum. Ringicula Deshayes.

Fam. 3. Tornatinidae. Shell as before, but spire concealed. Radula absent.
Tornatina Adams ; Volvula Adams.

Fam. 4. Scaphandridae. Shell external, without projecting spire ; cephalic
disc short, truncated behind ; radula with first lateral very large ; epipodia well
developed ; stomach with three well-developed calcareous plates. Scaphander
Montf. ; Cylichna Loven ; Amphisphyra I*) veil ; Atys Montf. ; Smaragdinella Ad.
.Fam. 5. Bullidae. Shell external without projecting spire; cephalic disc
bifurcated behind ; epipodia large ; radula usually multiserial. Bulla L.,
bubble-shell; Accra Mliller.

The Aplustridae (Aplustrum Schumacher) are allied here.

Fam. 6. Philinidae. Shell internal; epipodia large; cephalic disc simple.
Philine Ascanius, three calcareous stomach - plates ; Doridium Meckel, no
stomach-plates, two posterior pallial appendages; Gastropteron Meckel, mantle
and shell much reduced, epipodia large, united behind.

Fam. 7. Enncinidae. Cephalic shield and mantle continuous ; shell absent ;
four stomach-plates. Runcina Forbes (Pclta Quatrefages).

The following three families were formerly united as Pteropoda Thecosomata,
characterized by their foot extending round the dorsal side of the head and
being entirely transformed into two anterior lateral fins, by the existence of a
mantle-fold, by the absence, in the adult, of a ctenidium (except in certain
Cavolinia] and of eyes, by the presence of one pair of tentacles of which the
right is often the larger, by the position of the cerebral ganglia at the sides of
the oesophagus, by the radula having three teeth in each row (1:1:1), by the
stomach containing horny plates, and by being pelagic in habit. By the
operculum of Limacina they are allied to Actaeon, and by the approximation of
the pleural to the cerebral ganglia and by the stomach-plates, they are allied to
the Bulloidca generally. The heart has one auricle and one ventricle ; the
kidney is on the right side, and opens into the pericardium and into the mantle-
cavity. The genital glands open on the right side, and there is a ciliated
groove for the sperm leading from the opening to the penis, which is anterior
and cephalo-dorsal.

Fam. 8. Limacinidae. Fins large, mantle-cavity dorsal ; shell spiral,
sinistral (ultradextral), operculate. Anus, etc., on right side. Peraclis Forbes ;
Limacina Cuvier.

Fam. 9. Cymbuliidae. Adult without shell ; a cartilaginoid pseudo-shell,
subepithelial and formed by the connective tissue ; mantle -cavity ventral.
Larva with a calcareous, spiral operculate shell. Cymbulia Per. et Les. : Tied-
mannia D. Chiaje ; Cymbuliopsis Pelseneer ; Gleba Forskal ; Desmopterus Chun.

Fam. 10. Cavoliniidae. Visceral mass and shell not coiled, symmetrical ;
pallia] -cavity ventral. Cavolinia Abildgaard (Hyalea Lam., Fig. 319) ; Cuvierina
Boas ; Clio L., with subgenera Crcseis Rang (Fig. 320), Hyalocylix Fol, and
Styliola Les.

The Lophocercidae are allied to the Bulloidea. They have an external shell,
a long foot, epipodia separated from the ventral face of foot, and a short visceral
commissure, and a ctenidium and branchial chamber on right side. Lobiger
Krohn ; Lophocercus Krohn.

TECTIBRANCHIATA.

407

Section 2. Aplysioidea.

The shell is reduced or absent. The head is without cephalic disc and has
two pairs of tentacles. The epipodia arise from the sides of the body, and
are not direct continuations of the ventral surface of the foot. The visceral
commissure is much shortened (except in Aplysia), and the nervc^ganglia are
closely aggregated. There is a „,

second commissure connecting the

pedal ganglia called the parapedal I ~~==^S^v 0
commissure, in addition to the
ordinary one ; the aorta passes
between the two. The osphradium
and its ganglion (supplied by a

Md

M

FIG. 319.— Larva of Cavolinia (Hyaleu)
tridentata (after Fol). Ms velum; P
foot; P' the two lateral (epipodial)
lobes of the foot ; A anus ; M retractor
muscle; Md stomach.

R

FIG. 320. — Creseis acicula, dorsal view, after
Gegenbaur (hind end omitted). A anus ; At
auricle ; SI blind sac of stomach ; F tentacle ;
Fl fins ; G gonad ; Gg cerebral ganglion ; M
stomach ; Mn mantle-nerve ; N kidney ; U
mouth; Oe opening of kidney into mantle-
cavity ; Oes oesophagus ; P median lobe of
foot; R retractor; Ve ventricle; Ws ciliated
shield. The terminal part of intestine passes
ventral to anterior, not! dorsal as here repre-
sented.

nerve from the supraintestinal) is
placed at the base of the gill,
between the openings of the genital
organ and the kidney. There is
a seminal groove leading from the
former to the penis, which is on
the right side of the head.

The Aplysiidae and the Pteropoda Gymnosomata are included in this section.
The Aplysiidae have a widely open mantle-cavity, ctenidium, and an internal
shell, all of which are absent in the other families. Pneumoderma, however, is
said to retain the ctenidium in the lateral gill.

Fam. 1. Aplysiidae. Shell internal, but the sac in which it lies opens by
a pore in the centre of the dorsal surface. With a mantle-cavity and ctenidium.
Aplysia L., Sea-hare; Aplysiella Fischer; Phyllaplysia Fischer, shell absent;
Notarchus Cuvier, epipodia fused, dorsally to the visceral sac ; Dolabella, Lmk.

The following families, formerly included under Pteropoda Gymnosomata, are
without mantle or shell. The head is well developed and bears two pairs of

408

MOLLUSCA.

tentacles, the posterior pair with eyes. The median part of the foot consists
of a posterior lobe and two antero-lateral lobes joined in front (horse-shoe-
shaped) ; the epipodia or fins are quite separate from this median part of the
foot and from the head. The penis is latero-ventral on the right side of
the foot ; a groove leads to it from the genital opening. There is an evaginable
proboscis generally bearing suckers or appendages with suckers. These have
nothing to do with the foot. The buccal cavity contains evaginable hook-sacs
opening on each side of the radula. The jaws are united ventrally in the middle
line. The stomach is without plates. The anus is on the right side. The
cerebral ganglia are closely approximated on the dorsal side of the oesophagus,
and the pleural are near the pedal ; iy. this they differ from the so-called
thecosomatous Pteropods, and resemble the Aplysiidae, There may be
branchial processes of the integument — a lateral one on the right side — and
a posterior gill.

Te

Fl

FIG. 321. — a, Pneumoderma violaceum (from Bronn) from
the ventral surface, b, Clione australis (regne animal)
from the side. Fl fins (epipodia); Te appendages of
the proboscis, with suckers in o.

FIG. 322 — Larva of Pneumoderma
(after Gegenbaur).

Fam. 2. Pneumodermatidae. With suckers on the proboscis. Dexiobranchaea
Boas ; Pneumoderma Cuvier (Fig. 321) ; Spongiobranchaea d'Orb.

Fam. 3. Clionopsidae. Without suckers and buccal appendages. Proboscis
very long. Posterior gill tetraradiate. Clionopsis Troschel.

Fam. 4. Clionidae. With conical glandular buccal appendages (cephalocones).
No gill. Clione Pallas (Fig. 321).

Fam. 5. Notobranchaeidae. With conical buccal appendages, without
lateral gill. Notobranchaea Pelseneer.

Fam. 6. Halopsychidae. Body ovate, rounded behind ; without gills or
proboscis ; fins broadened at the ends. Halopsyche Bronn.

Section 3. Pleurobranchioidea.

The head has two pairs of tentacles, of which the posterior are the rhino-
phores ; the foot is without epipodia ; the mantle-cavity is shallow and contains
a large ctenidium on the right side. The male and female generative openings
are near but separate, and there is no seminal groove. The pleural ganglia are

NUDIBRANCHIATA.

409

close to, or fused with, the cerebral, which are themselves closely approximated.
The visceral commissure is short and possesses but few ganglia. In Tylodina
alone is there an osphradium and osphradial ganglion.

Fam. 1. Umbrellidae. Visceral sac and external shell in the form of a flat
cone ; foot very thick. Umbrella Lam. ; Tylodina Rafinesque.

Fam. 2. Pleurobranchidae. Shell internal or absent ; anterior tentacles
forming a frontal velum ; spicules in the mantle ; foot flat. Pleurobranchus
Cuv., internal shell ; Pleurobranchaea Meckel (Fig. 323), no shell ; Neda Adams.

Tribe 2. NUDIBRANCHIATA.

Opisthobranchs without shell in
the adult state.

There is no ctenidium or os-
phradium ; the nervous system is

Br

FIG. 323. — Pleurobranchaea Meckdii (regne
animal). ' Br ctenidium ; F posterior
tentacle (rhinophore) ; R proboscis ; P
penis.

xi---

Fio. 324. — Nervous system of Tritonia hombergi
(after Pelseneer), dorsal view x 15. I cerebral
ganglion; II tentacular, III optic nerve; IV
pleuropedal commissure ; V penial nerve ; VI
parapedal commissure ; VI' visceral commis-
sure ; VII abdominal ganglion and genital
nerve; VIII stomatogastric commissure; IX
buccal, Xgastro-oesophageal ganglion ; XT pedal,
XII sub-cerebral commissure ; XIII pedal gan-
glion ; XTFcerebro-pedal commissure ; XVoto-
cyst ; XVI pleural ganglion.

much concentrated, and the gan-
glia are generally aggregated, and
more or less fused together, on the
dorsal side of the oesophagus ; but
the different commissures — visceral,
pedal, and buccal — are distinct.

There are four suboesophageal commissures — the visceral, the pedal, the para-
pedal (a second thin commissure between the pedal ganglia), and the subcerebral
(Fig. 324). In addition to these there is the stomatogastric system, which
constitutes another commissure completed ventral to the oesophagus. The
nerves springing from the visceral commissure are always unsymmetrical and
are exclusively genital and reno-pericardial.

The pedal commissure is generally long, but it is short in Fiona, Ancula,

410

MOLLUSCA.

and most Elysioidea, in which the pedal ganglia are approximated ventral to
the oesophagus.

The parapedal commissure is homologous with the same structure in Tecti-
branchs, but it gives off no nerves. The relation of the aorta to these
commissures varies, as it does in the Tectibranchs. The dorsal appendages
or cerata are innervated from the pleural ganglia, showing that these structures
are homologous and of a pallial nature. The penis is of a pedal nature, being
innervated from the pedal ganglion as in the majority of Streptoneura.

The hermaphrodite gland has male and female acini, which however
communicate. The animals are protandrous.

The characters of specialization of th%N"udibranchs are as follows :

(1) Return to external symmetry. This was indicated in Tectibranchs, but
it is carried further in Nudibranchs, where there may be complete external
symmetry as in the Doridioidea with median anus, and even internal symmetry
in many of the organs (heart, kidney, liver), but never in the generative
apparatus. In the Tritonioidea this internal symmetry is not found.

(2) Displacement of the nervous system behind the buccal mass.

(3) Concentration of the central nervous system dorsal to the oesophagus.
The pedal ganglia are approximated to the cerebral, and the pleural are fused
with the cerebral except in Tritoniidae. But as already mentioned in Fiona,
Ancula, and in most Elysioidea, we find the pedal more or less approximated
ventrally to oesophagus, and distinct ganglia on the short visceral commissure.
In the presence of distinct ganglia on the visceral commissure, often three in
number, the Elysioidea are more primitive than other Nudibranchs.

(4) Reduction of the number of teeth of the radula (even to a single tooth
for each transverse row).

(5) Diffusion of the liver.

(6) Triaulic condition of genital ducts.

The Tritoniidae, which are Nudibranchs because they are without ctenidium,
osphradium, mantle-fold, shell, and because they have cerata, are without any
of these features of specialization ; except the dorsal grouping of the cerebral,
pedal, and pleural ganglia, which are, however, distinct. But even in the

EOUD

'ELYSID

If we had another dimension we could connect the Elysid group and Janus to show the
common presence of cerata.

NUDIBRANCHIATA.

411

nervous system they show the specialized feature of the reduction of ganglia
on the visceral commissure.

The Dorids are the most specialized of all in possessing the median anus
and the triaulic generative ducts ; but they lack the
diffusion of the liver.

The Eolids are highly specialized in their nervous
system and cerata, but have the diaulic ducts. Janus,
however, goes further in having a median anus, though
the kidney is still lateral ; but if we should be tempted
to put Janus at the top of our genealogical tree we should
be prevented by the fact that in its nervous system it
approaches Tritonia, and that it has diaulic generative
ducts .

The Elysiids retain primitive features of the nervous
system, but in other respects are the most specialized of
the group. But the nervous system drags them down,
and would prevent us from putting them at the top of
our genealogical tree. Indeed, by it we might feel inclined
with Bergh to place them in a separate Tribe between the
Tecti- and Nudi-branchiata.

Section 1. Tritonioidea.

The liver is contained entirely or principally in the
visceral mass. The anus is on the right side. There are
generally two rows of branched dorsal appendages. Male
and female openings contiguous ; genital ducts diaulic.
The heart is asymmetrical, being on the right side.

Fam. 1. Tritoniidae. Anterior tentacles forming a
frontal velum, foot large. Pleural ganglion distinct from
cerebral. Kidney a simple sac opening externally on right
side above the anus. Two rows of branched cerata without
liver continuations. Tritonia Cuv. (Fig. 325), Marionia
Vayssiere.

FIG. 325. — Tritonia
lineata, dorsal view,
X 7 (after Hancock,
from Pelseneer). /
posterior tentacle ;
II dorsal appendages
(qerata) ; III eye ;
I V frontal velum ; o
genital opening.

FIG. ZZ&.—PhyllirUoe bucephalum, from the right side, x 3 (after Sonleyet). The genital ducts
are supposed to be a little unrolled. I genital gland ; II sperm oviduct ; III hepatic duct ;
IF female genital orifice; V pedal ganglion ; VI salivary gland ; VII mouth ; F/TTstomato-
gastric ganglion ; IX buccal mass ; X tentacle ; XI cerebral and pleural ganglion ; XII lobe
of liver; XIII heart in pericardium; XIV reno-pericardial opening; XV external opening
of kidney ; XVI anus ; XVII liver.

412

MOLLUSCA.

Fam. 2. Scyllaeidae. Anterior tentacles absent ; two pairs of large folia-
ceous cerata ; foot narrow. Scyllaea L., on floating seaweed.

Fam. 3. Phyllirhoidae. Anterior tentacles and cerata absent. Body com-
pressed laterally, without foot. Stomach with caeca. Orifices on the right
side. With fin -like tail. Transparent. Pelagic. Phyllirhoe Per. et Les.
(Fig. 326).

Fam. 4. Tethyidae. Anterior tentacles absent ; rhinophores conical ; head
surrounded by a funnel -like velum ; cerata foliaceous ; foot large ; radula
absent. Tethys L. Melibe Rang. Cerata of Tethys are capable of independent
movement after separation.

Fam. 5. Dendronotidae. Tentacles forming a fringed frontal velum ; cerata
branched ; rhinophores arborescent ; radula 10 : 1 : 10 ; liver extending into the
cerata. Dendronotus A. and H. ; Hero Loven ; Lomanotus Verany.

Tribe 2. DORIDIOIDEA.

Liver not branched ; anus median posterior, generally dorsal and surrounded
by ramified appendages — the cerata or branchiae. Genital ducts triaulic.
Spicules in the mantle.

Fam. 1. Polyceridae. A frontal velum more or less projecting. Branchiae
non-retractile. Ehinophores foliate. Euplocamus Philippi ; Triopct Johnston ;
Polycera Cuv. ; Ancula Loven ; Goniodoris Forbes ; Idalia Leuckart ; Hetero-
doris Verril and Emerton ; Aegirus Loven ; Acanthodoris Grube.

Fam. 2. Dorididae. Mantle covering the head ; anterior tentacles small ;
rhinophores foliate ; branchiae retractile into a perianal pocket. Doris L. ;
Chromodoris A. and H. ; Hcxabranchus Elirbg.

Fam. 3. Doridopsidae. Doris-like, but mouth
suctorial, without radula. Doridopsis A. and H.

Fam. 4. Corambidae. Doris-like, but anus and
branchiae behind, below the edge of the mantle.
Corambe Bergh.

Fam. 5. Phyllidiidae. Mouth suctorial ; no
radula ; branchiae all round the body between the
mantle and the foot. Phyllidia Cuvier.

Tribe 3. AEOLIDIOIDEA.

The liver caeca extend into the cerata, which often
contain nematocysts. Genital duct diaulic, with
contiguous male and female openings. Jaws are
present.

Fam. 1. Aeolididae. Cerata terminating in open
sacs (Fig. 329), which communicate with the hepatic
caeca and give origin by their lining epithelium to
nematocysts (Fig. 330). Aeolis Cuvier (Fig. 323).

Fam. 2. Glaucidae. With three pairs of lateral
lobes (cerata) carrying tegumentary papillae. Foot
narrow. Glaucus Forster.

Fam. 3. Pleurophyllidiidae. Anterior tentacles constitute a burrowing shield.
Branchiae beneath the edge of the mantle ; radula 30 : 1 : 30. Pleurophyllidia
Meckel (Fig. 331) ; Dermatobranchus Van Hasselt.

Fam. 4. Dotonidae. Cerata tuberculated, without nematocysts, and in one
row on each side. Doto Oken.

FIG. 327. — Doris pilosa
(after Alder and Han-
cock). Br gills ; A anus ;
F tentacle.

ELYSIOIDEA.

413

Fam. 5. Proctonotidae. Anus posterior in the middle dorsal line. Anterior
tentacles atrophied. Janus Verany ; Proctonotus A. and H.

Fam. 6. Fionidae. Liver as two longitudinal canals, into which open the
caeca of the cerata. Fiona Hancock and Embleton.

Tribe 4. ELYSIOIDEA (SACCOGLOSSA).

Liver branched, the branches generally extending into cerata. Genital ducts
usually triaulic, with widely separated genital openings. The vaginal orifice
is, in some cases at any rate, developed later than the other two openings.
Without jaws. Radula with one series of strong teeth, the worn-out teeth at
the front end not dropping off, but preserved in a special sac (Ascoglossa Bergh).
The pedal ganglia are near together, and the visceral commissure has three
ganglia almost in contact.

FIG. 328. — Aeolis pnpillosa
(after Alder and Hancock).
Rp dorsal papillae (cerata).

FIG. 329.— Section of a dorsal
papilla of Eolis x,40. a ter-
minal sac which produces
nematocysts; b ectoderm; c
hepatic caecum; d tube con-
necting the caecum with the
terminal sac ; e opening of th«
sac (after Pelseneer).

FIG. 330. — A neinato-
cyst wi.th pro-
truded thread of
Aeolis punctata]x
500 (from Pelse-
neer, after Vays-
siere).

Fam. 1. Hermaeidae. Cerata in several rows ; anus dorsal. Hermaea
Loven, Stiliger Ehrb., Phyllobranchus A. and H., Cyerce Bergh, hepatic caeca
do not extend into cerata ; Alderia Allmaii.

Fam. 2. Elysiidae. Cerata absent ; dorsal integument forms two lateral
expansions containing hepatic caeca. Anus lateral. Reno-pericardial openings,
numerous. Elysia Risso,

414

MOLLUSCA.

...-5

3-

Fam. 3. Limapontiidae. Without lateral expansions or cerata. Anus
median postero- dorsal. Liver but little branched. Limapontia Johnston ;
Actaeonia Quatref.

The position of the Bhodopidae is uncertain : they are planarian-like naked

forms, without branchiae, ten-
tacles, buccal mass, or radula.
Recently it has been shown*
that the larva of this form is
6 without a shell ; thus destroying

the main reason for regarding it
as a nudibranch mollusc.

Sub:order 2. Pulmonata.

Euthyneura in which the
pallial-cavity is modified as
a lung, and is without a
ctenidium. Tlie opening of
the pallial-cavity is small.

The pallial-cavity is often
reduced, as well as the shell.
Sometimes the shell is in-
ternal or absent. There is
never an operculum in the
adult except in Amphibola
(it is present in the young
stages of Auricula, Siphon-
aria, Gadinid). The roof
of the mantle-cavity is pro-
vided with a network of
vessels for aerial respiration,

and the mantle-cavity constitutes a lung. In Vaginulus, Peronia, and
Onchidium the lung is absent in consequence of the almost complete
disappearance of the mantle-cavity. In some cases the lung may
be filled with water and serve for aquatic respiration (Siphonaria,
some Limnaea and Planorbis). The auricle is usually in front of
the ventricle. The kidney has usually a more or less elongated
duct (ureter).

The opening of the pallial-cavity is reduced to a pore placed on
the right side. The anus and renal openings are placed near the
opening of the lung (in Auricula alone does the anus open in the

FIG. 331. — PleuropJiyllidia lineata, ventral view
(from Lang, after Souleyet). 1 genital opening;
2 branchial processes ; 3 anus ; k pedal gland ;
5 mouth 6 tentacle shield ; 7 foot.

* S. Trichinese, "Nuove osservationi s. Rhodope Veranii" Rend. Accad.
Napoli (2), vol. 1., p. 131. See also L. Bohmig in Z. f. w. Z., 56.

BASOMMATOPHORA. 415

lung sac). The generative organs open some way in front, on
the right side.

The Pulmonata are generally terrestrial, sometimes fresh-water,
rarely marine. They are cosmopolitan and include about 6000
species. They generally become torpid during part of tlt^ year —
in warm countries in .the dry season (aestivation), in cold in .winter
(hibernation). Hibernation in this country lasts about one quarter
of the year, and during it the heart beats no more than twice
a minute.

The mouth armature consists of an unpaired, horny upper jaw
(which may be absent), and of a radula with a great number of teeth
in the transverse row.

All are hermaphrodite. A few, e.g. species of Clausilia and
Pupa, are viviparous. Most lay eggs, either, as in the fresh-water
forms on water plants, united in tubular or flat masses, or as in the
terrestrial forms in damp places, each one being surrounded by a
protecting shell which may be calcareous. The ovum is always
embedded in a large mass of albumen, which serves as nourishment
for the developing embryo.

Tribe 1. BASOMMATOPHORA.

Shell always present and external. There is one pair of non-invaginable
tentacles, at the base of which are the eyes. The penis is remote from the
female orifice (except in Amphibola and Siphonaria). In Auricula alone among
Pulmonates is the hermaphrodite duct not divided ; and, passing from its opening
which is anterior to the mantle-opening, there is a groove which is closed in front
and leads to the penis. The closed part of this groove lies close beneath a
superficial groove in the skin. In Amphibola, Chilina, and the Siphonariidae
the duct splits, but the penial and vaginal openings are joined. There is
generally a circular osphradium near the opening of the pulmonary cavity,
between it and the renal opening. Radula multiserial. Fresh-water or quasi-
marine.

Fam. 1. Auriculidae. Terrestrial, usually maritime. Respiratory aperture
behind. Shell spiral. Auricula Lam., found in brackish- water swamps of
tropical islands, on roots of mangroves, and by small streams within the
influence of the tide ; traces of small anterior tentacles ; Carychium Miiller ;
Alexia Lam.; Pedipes Adanson ; Melampus Montf. ; Otina Gray.

Fam 2. Amphibolidae. Visceral mass and shell spiral ; operculum present.
Aquatic, marine. Amphibola Schumacher, shores of New Zealand and Pacific
Islands.

Fam. 3. Siphonariidae. Visceral mass and shell patellifonn ; tentacles
atrophied; marine with aquatic respiration. Siphonaria Sow., secondary
branchial lamellae on roof of mantle-cavity ; Gadinia Gray, no branchia.

Fam. 4. Limnaeidae. Fresh-water animals with aerial respiration. Shell
variable. Limnaea L. ; L. stagnalis L., pond-sn#il ; Amphipeplea Nillsson ;

416 MOLLUSC A.

Physa Draparnaud ; Planorbis Guettard, spire in same plane; Ancylus Geoffrey,
river-limpet, visceral mass conical.

Fam. 5. Chilinidae. Pulmonary aperture larger than in any other pulmonate.
Visceral commissure longer than usual. Chilina Gray, Chilian-snail.

Tribe 2. STYLOMMATOPHORA.

Two pairs of invaginable tentacles (except A thoracophorus), the posterior being
oculiferous ; male and female openings united (except in Vaginulus, Onchidium,
and Peronia) ; no osphradium.

Fam. 1. Succineidae. Anterior tentacles reduced ; male and female openings
distinct, but contiguous. Succinea Draf>arnaud, amber-snail.

The Athoracophoridae (Athoracophorus Gould) are allied here.

Fam. 2. Helicidae. Land-snails. Shell external, spire short ; genital organs
generally with a dart and multifid vesicles ; genital orifice under right tentacle.
Helix L., over 1600 species; H. aspersa Miiller, hedge-snail; H. pomatia L. ,
Roman snail; Vitrina Drap., glass-snail; Bulimus Scopoli (1200 species);
HempMllia Binney and Bland.

The Philomycidae (Philomycus), without shell, allied here.

Fam. 3. Arionidae. Shell absent, or represented by calcareous granules in
mantle. Slug-like. Genital opening just below pulmonary. Arion Fer., land-
sole ; eggs of A. hortensis phosphoresce for 15 days after deposition.

FIG. 332. — Arion empirico-rwm (regne animal). Al respiratory aperture.

Fam. 4. Pupidae. Shell external, spire long ; male duct without multifid
vesicles. Pupa Lam. , chrysalis shell ; Clausilia Drap. ; Vertigo Miiller ; Zospeum
Bourguignat ; Balea Prideaux ; Ferussacia Risso ; Caecilianella Fer.

Fam. 5. Limacidae. Slugs. Shell small or absent, generally internal, may
be spiral ; tail often with mucous pore. Genital ducts without multifid vesicles ;
genital opening under right tentacle. Limax L., slug, mantle reduced, shell
internal, 51 species; Vitrina Drap., glass-snail (here or with Helix}; Parma-
cella Cuvier ; Zonites Montf. ; Urocyclus Gray ; Orpiella Gould.

Fam. 6. Testacellidae. Pharynx protractile ; jaw absent ; cervical region
elongated. Slug-like, or with visceral sac spirally coiled ; carnivorous. Glan-
dina Schumacher ; Daudebardia, Hartm. ; Testacella Cuv. , slug-like, subterranean,
feeds on earthworms, S. Europe, Canaries, introduced into Britain.

Fain. 7. Vaginulidae. Without shell; male opening beneath the right
tentacle, female midway beneath the mantle ; respiratory and excretory orifices
at hind end. Vaginulus Fer.; Atopos Simroth.

Fam. 8. Onchidiidae. Marine, without shell, mantle often warty, some-
times with eyes ; genital openings widely separate ; female opening posterior,
near anus ; anus and pulmonary opening as in Vaginulus. Onchidium
Buchanan ; Peronia Blainv,

CEPHALOPODA. 417

Class V. CEPHALOPODA.*

With well-marked head, a circle of processes bearing suckers or
tentacles round the mouth, and a funnel composed of two separate
or fused halves. The genital coelom is continuous ivitfcjhe peri-
cardial. Dioecious.

The Cephalopoda are symmetrical animals with a much-shortened
antero-posterior axis, and with a strongly -developed visceral sac,
which has undergone neither torsion nor asymmetrical development,
and which is, except in Nautilus, unprotected by an external shell.
The mantle-fold is circular and the mantle -cavity is especially
developed on the posterior side of the visceral sac; in it are placed
the ctenidia, either two (Dibranchiata) or four (Tetrabranchiata),
and into it open the median anus, the ink-sac, the paired kidneys,
and the genital duct. There are always processes round the
mouth, which are either lobe-like and carry tentacles as in the
Tetrabranchiates, or are arm -like and carry suckers as in the
Dibranchiates. They are active, voracious animals, with a complex
organization, highly developed sense-organs, and often possessed of
considerable intelligence. The Cephalopods are marine animals,
some frequenting the coast, others the high seas, and some the
floor of the ocean to a depth of nearly 2000 fathoms. About 400
species are known. They feed on the flesh of animals, especially
Crustacea, and some of them attain a great size.f The flesh is
eaten, and the colouring matter of the ink-sac (sepia) and the dorsal
shell (os sepiae or cuttle-bone) are used by man. The remains of
Cephalopods occur in all formations from the Cambrian, and con-
stitute important characteristic fossils (Belemnites, Ammonites).

* Ferussac et d'Orbigny, " Histoire naturelle generate et particuliere des
Cephalopodes acttabuliferes vivants et fossiles," Paris, 1835-45. J. B. Verany,
" Mollusques mediterranes observes, etc., d'apres le vivant," le Partie, Genes,
1847-51. H. Milller, " Ueber das Mannchen von Argonauta argo u. die Hec-
tocotylen," Z. f. w. Z., 1855. Jap. Steenstrup, " Hectocotylus dannelsen hos
Octopodsl., etc.," K. Danks. Vidensk. Selskabs Skrifter, 1856; translated in
Archiv. f. Naturgesch., 1856. C. Grobben, " Morphologische Studien lib. den
Harn-u. Geschlechtsapparat, etc., der Cephalopoden," Arb. a. d. Zool. Inst.
Wien, 5, 1884. W. E. Hoyle, "Report on the Cephalopoda," Challenger
Reports, vol. 16, 1886. J. Brock, "Zur Anat. n. Syst. d. Cephalopoden,"
Z. f. w. Z., 36, 1882. P. Pelseneer, " Sur la value morphologique des bras et la
composition du syst. nerv. cent. d. Cephalopodes," Arch. Biol. 8, 1888.
Milne-Edwards et Valenciennes, " Obs. sur la circulation chez les Mollusques,"
Mem. Acad. Sci. Paris, 20, 1840. Vigelius, " Ueb. d. excretionssystem der
Cephalopoden," Niederl. Arch. f. Zool., 5, 1880. Milne -Ed wards, "Sur les
spermatophores des Cephalopodes," Ann. Sci. Nat. Zool. (2), 18, 1842.

f Specimens of Architeuthis have been taken measuring from apex of visceral
sac to end of extended arms more than 50 feet, and with eyes 15 inches
across.

2 E

418

MOLLUSCA.

The normal swimming position for a Cephalopod (Fig. 333) is
horizontal, with the anterior surface of the visceral sac upward,
and the posterior, i.e., the surface on which lies the mantle-cavity
and the mantle -opening, downward. When creeping the animals
apply their arms to the substratum and the hump projects backward.

"'"f-r

FIG. 333.— Octopus vulgaris (after Merculiano, from Lang), in swimming and sitting positions.

Bearing in mind these facts and the fact already mentioned that
the antero-posterior axis is much shortened, the ordinary terminology,
which is often confusing, used in describing Cephalopoda will be
readily understood. The ventral surface is the region including the
mouth and the 'anus. The funnel is therefore a purely ventral

CEPHALOPODA.

419

structure. The dorsal surface includes the visceral sac; roughly
the apex of the visceral sac may be regarded as the middle of
the dorsal surface. The anterior end is that surface of the head on
the sides of which the eyes are placed; while the posterior end
may be said to be marked by the anus. Inasmuch as the vis-
ceral sac is normally carried horizontally, the words " upper " and

FIG. 334.— Loligo vulgaris (from Lang, after D'Orbigny). A, from the posterior side, showing
the funnel just in front of the free edge of the mantle. H, from the front side showing the
eyes on the head. There are also shown the ten arms, the fins, and the chromatophores in
the skin.

"lower" are sometimes used in the sense of "anterior-dorsal" and
"posterior-ventral" respectively; further, inasmuch as the visceral
hump is sometimes shown in figures in its proper morphological
position, as standing straight up above the head, the words upper
and lower are sometimes used in the sense of dorsal and ventral.

420 MOLLUSCA.

In our descriptions the words upper and lower will be discarded,
and we shall use only anterior and posterior, dorsal and ventral,
in the sense described above.

The head is sometimes described as being placed in the centre
of the foot, and the arms are looked upon as the frayed-out margins
of the foot ; on this view the name Cephalopoda is justified anatomi-
cally as well as functionally. On the other hand, this view is not
taken by all anatomists, many of whom regard the funnel as the
sole representative of the foot»of other Gastropods. We shall
consider this question further on.

The head is well-developed, and carries on its anterior sides a pair
of conspicuous and generally elaborate eyes. Immediately behind
(ventral to) the eyes there is often on each side a pit supposed to be
olfactory. In certain Oeyopsida the eyes are stalked; in Nautilus
they are also stalked, and there are on each side two cephalic
tentacles in relation with the eye, the preocular and the postocular
tentacles (Fig. 338, Pr.o, Pt.o).

The margins of the head are produced into exceedingly muscular
sucker-bearing arms in the Dibranchiates, and into tentacle-bearing
lobes in Nautilus. Of the former there are always four pairs (Odo-
2Joda), and sometimes five (Decapoda) ; they are arranged in a circle
round the head, and the anterior arm of each side is called the first,
while the posterior arm, viz., that nearest the funnel, is called the
fourth. The arms of the fifth pair, which are found in the Decapoda,
are longer than, and attached somewhat internally to, the others
between the third and fourth ; they are often inserted into pits, into
which they may be retractile (Sepia, Sepiola, Rossid), and are called
the prehensile or tentacular arms. The tentacular arms have suckers
only near their free, club-shaped end, but the other arms are suckered
all along their internal (oral) surface.

The basal parts of some or all of the eight arms of the Octopoda
may be united by a membrane ; in Tremoctopus the four anterior,
in Histioteutliis the six anterior, in Alloposus and CirroteutMs all the
arms are so united along their whole length. The umbrella so formed
assists in locomotion by its alternate contraction and expansion.

In the female Argonauta (Fig. 335) the terminal parts of the two
anterior (dorsal) arms are expanded into thin membranes (vela), which
secrete the unilocular spiral shell.

Finally, in the males one of the arms is more or less modified for
the purposes of sperm-transference in reproduction. The arm so
modified is said to be Jiectocotylized, because in some species (Argo-

CEPHALOPODA. 421

nauta, Tremoctopus, Philonexis) it is entirely detached from the
male and left in the mantle-cavity of the female, where it was found
by Cuvier, who mistook it for a parasitic worm and called it
Hectocotylus. ,

The suckers are stalked in Decapoda, sessile in Octopoda. Further, in Deca-
poda, they have a horny ring, which may be smooth or denticulated in some cases ;
on certain parts of the arms the suckers may be replaced by hooks, and on the
tentacular arms of Onychoteuthis a large retractile hook arises from the centre
of each sucker. The suckers consist of a disc-like surface, in the centre of which
is a pit ; the depth of this pit can be increased by the retraction of its bottom,
to which muscle-fibres are attached.

FIG. 335. — Argonauta argo (female), the paper Nautilus, swimming.

In the Tetrabranchiates (Nautilus) there are no arms, but in their place we
find lobe-like prolongations of the margin of the head, which bear tentacles.
The tentacles are retractile into sheaths, which are possibly comparable to the
suckers of the Dibranchiates. The lobes are as follows (Fig. 336) : an external
annular lobe (J), the anterior part of which forms the hood, into which the coil
of the shell fits, while the posterior part is much reduced ; this lobe carries
19 tentacles on each side ; within the annular lobe are in the female three tenta-
culiferous lobes, a posterior (ventral) and two lateral (d, c) ; in the male the
posterior lobe (d) is reduced to a paired group of lamellae and bears no tentacles,
and the right and left inner lobes are divided into two parts, a larger and a
smaller. On the posterior inner lobe of the female there is a lamellated organ (?i),
and behind it, on the inner side of the annular lobe, another lamellated
organ (m) to which the spermatophores of the male appear to be affixed (Kerr).
In the male the smaller of the two parts into which the left inner lobe
is divided ends in imbricated modified foliaceous tentacles (p) ; it is the
spadix, and has been regarded as the lobe used in sperm transference and

422

MOLLUSCA.

corresponding to the hectocotylized arm of Dibranchs. The corresponding part
of the right inner lobe carries four tentacles, and is called the antispadix (q).

In addition to these tentacles
of the lobes, there are the
four ocular tentacles already
referred to.

The funnel is a tube
with muscular walls lead-
ing into the mantle-cavity,
and often containing (in
Nautilus and most Deca-
pods) a valve which admits
of passage outwards only.
It is placed on the ven-
tral surface behind the
head, and is to be regarded
either as the entire foot
of the animal, or as the
epipodia, the rest of the
foot having been wrapped
round the head and frayed
out peripherally into the
arms or lobes.* The view
that the funnel represents
the whole foot is strongly
suggested by the arrange-
ment in Nautilus. In
this animal it consists of
two muscular lateral lobes
of the ventral surface just
behind the head, which
are rolled round one
another without fusion.
When these lobes, which
are of considerable size,

FIG. 336.— Oral surface of a male (A) and female
(E) specimen of Nautilus pompilius in the expanded
condition, one-third the natural size linear (from
Lankester, after Bourne), a the shell ; b the external
annular lobe carrying 19 tentacles on each side, and
anteriorly enlarged to form the hood (Fig. 337) ; c the
right and left inner lobes, each carrying 12 tentacles
in the female, and divided in the male into two parts ;
d the posterior inner lobe ; e the oral cone ; / the ten-
tacles of the outer annular lobe projecting from their
sheaths ; g the two anterior tentacles of this lobe
belonging to the hood ; i superior, k inferior ophthal-
mic tentacle ; I eye ; n lamellated organ on the pos-
terior inner lobe of the female ; m paired laminated
organ on each side of the posterior inner lobe of the
female ; o the funnel ; p spadix ; q antispadix.

* The view that the arms represent a portion of the foot is not in our
opinion satisfactorily established. It rests largely upon the fact that the
nervous supply is derived from that portion of the central nervous system
which is supposed to represent the pedal ganglion of other Mollusca. But
this, as Graham Kerr has pointed out, is not a strong argument, for a main
reason for regarding that part of the central nervous system, from which the
brachial nerves arise, as pedal, is that the nerves to the arms arise from it.
As pointed out below, separate and distinct ganglia are not distinguishable
in the central nervous system of Cephalopoda.

CEPHALOPODA. 423

are unrolled and flattened out, their resemblance to the foot of a
Gastropod is considerable, and Graham Kerr has suggested the
possibility of the animal being able actually to unroll them in life
and to use them as a foot (Fig. 337). In the Dibranchs ,, the edges
of these folds are fused, so that the funnel is a complete tube
(Fig. 334), and in both Dibranchs and Nautilus the broad hinder
part of it is covered by the mantle-folds.

On each side of the funnel there is in Decapods a peculiar sucker-
like arrangement by which the mantle-fold can be attached to the
funnel so as to close the general mantle-opening; it consists of a
smooth cartilaginous projection on the mantle, and a corresponding

FIG. 337. — Side view of Nautilus pompilius extracted from the shell, the funnel has been opened
out, and the mantle-flap partly cut away (after Graham Kerr). /funnel ; e eye ; g gill ; h hood ;
TO cut edge of mantle ; s siphuncle ; t tentaculiferous lobes.

depression on the funnel. In the Octopoda the mantle-fold is fused
to the head anteriorly and laterally, so that the mantle opening is
much restricted.

The deep part of the mantle-cavity is placed on the posterior
surface of the visceral sac, which in the natural position is the under
surface. It has in Dibranchs thick, muscular walls, and it contains
one or two pairs of bipectinate ctenidia, the median anus, the paired
renal openings, and the generative opening, which is sometimes single
and sometimes paired. The regularly repeated contraction of the
mantle-muscles causes the expulsion through the funnel of the re-
spiratory water, which has been taken in through the mantle-opening,
and with it of the excrementitious (renal and anal) and generative
products. When the contraction is rapid and violent the jet from
the funnel causes the animal to shoot rapidly backwards; on any

424 MOLLUSCA.

alarm the ink -gland, which opens with the anus, pours out its
black secretion into the water in the mantle-cavity, so that on the
retreat of the animal backwards in the rapid manner just explained,
the ejected water is black and produces a murky cloud which
completely obscures its movements, and under cover of which it
escapes.

Nautilus alone has an external shell secreted by the mantle. It
is spirally coiled, the coil being directed on to the anterior face of
the animal, i.e., being of the kincf called exogastric ; moreover, it is
divided by transverse septa into chambers. The bulk of the animal

___ _ Ma

EK "

FIG. 338. — Nautilus pompilius (original drawing made under direction of Graham Kerr). EK
penultimate chamber of the shell, which is in some specimens larger than the ante-
penultimate ; H hood ; G groove in the hood ; M shell-muscle ; Ma edge of mantle-fold
passing at Ma' on to the anterior face of the visceral sac, where it is in relation with
the anterior convexity of the shell-coil ; P eye partly covered by the mantle-fold ; Pr.o
preocular tentacle; Pt.o postocular tentacle; 0 part of the outer wall of shell which has
not been cut away ; On initial coil of the shell ; S siphon ; S/ postseptal neck ; T tentacu-
liferous lobes ; Tr funnel.

occupies only the last of these chambers, but it is incorrect to say
that all the chambers except the last are untenanted by the animal,
for there is a delicate process of the dorsal end of the hump — the
siphon or siphuncle, which is coated with a thin layer of calcareous
matter, and passes through all the septa right up to the first chamber.
The chambers of the shell contain a gas which is said to have
approximately the composition of atmospheric air.

The retractor muscles of the head and foot are inserted on to the
internal wall of the shell, and a small anterior flap of the mantle-fold

CEPHALOPODA.

425

extends on to the convexity of the coil just dorsal to the hood
(Fig. 338, Ma).

In the Dibranchs there is a spiral, chambered, mantle-shell in the
Decapod Spirula, but it is coiled in the
opposite way to that of Nautilus (endo-
gastric), and does not enclose the vis-
ceral sac. It is in fact partly internal,
being largely covered by lobes of the
mantle. The septa are, however, per-
forated by a siphon, which contains a
prolongation of the visceral sac.

In certain extinct Dibranchs there
was a similar internal, chambered shell

— either coiled (Spiruli-

rostra) or straight (Belem-

nitidae). That these were

internal or partly internal

is shown by the fact that

the chambered part of

the shell or phragmocone

is covered by a calcareous

layer, often laminated,

which forms the rostrum

or guard. In the Belem-

nites the wall of the

phragmocone (conatheca)

is continued forwards into
ii proostracum, which must have been
somewhere in the neighbourhood of the
animal's body and head.

In all living Dibranchs except Spirilla
the shell is quite internal, being con-
tained in a sac in the anterior wall of
the visceral sac, and much reduced.
In the Sepiidae, or cuttle-fishes, it is
called the cuttle-lone or sepiostaire, and
consists of a broad plate composed of
laminated tissue containing air spaces and ending behind in a
pointed rostrum. In the Squids it is a lamellar body composed
•of conchyolin, without calcareous matter, and is called the pen.
In the Odopoda both the shell and its sac are absent. The shell of

Fio. 339.— Spirula
peronii (Bronn).

FIG. 340.— Belemnites . with the re-
mains of the body of the animal
(after Huxley), a arms with
hooks ; 6 head ; c ink-bag ; d
phragmocone ; e guard.

426

MOLLUSCA.

the female Argonaut, which has already been referred to, is not
a mantle-shell. Fins of various forms are often present as lateral
expansions of the mantle.

The dermis contains the remarkable chromatophores which cause
the well-known play of colours. These consist of large cells filled
with pigment (red, blue, yellow, or dark colours) ; to their walls,
which are formed of a cellular membrane, numerous radiating
muscular fibres (by some observers said to be connective tissue
fibres) are attached. When the latter contract the cells are dilated
and the pigment spreads over a larger area, and so gives colour to the

skin. When the contrac-
tion ceases the cell returns,
in virtue of the elasticity
of its walls, to its original
shape, and the pigment is
again concentrated in a
small space, arid the skin
becomes uncoloured ; thus
the animal changes its
colour. The chromato-
phores are probably under
the control of the will, and
are connected with a special
centre in the stalk of the
optic ganglion. The eye
seems to be the organ most
intimately connected with

as to show the chambered shell and the laminated them, for if the Optic nerve
guard deposited upon its surface. D, shell of Spirilla .

iaevis. be cut the power of volun-

tarily changing colour on

that side is said to be lost. Nevertheless there seem to be peripheral
centres through which these organs* can be brought into action,
and the animals seem to have the power of changing their colour
involuntarily according to the colour of their environment. In
addition to the chromatophores there is a deeper layer of small
shining spangles, which produce interference colours and thus give
rise to the peculiar lustre and iridescence of the skin.

In certain abyssal Cephalopods there are cutaneous phosphorescent organs,
consisting of a superficial refractile structure and a deep photogenic layer ; they

* Krukenberg, Vergl. physiol. Studien an den Kusten der Adria, Heidelberg,.
1880.

FIG. 341.— Internal shells of Cephalopoda (from Lan-
kester). A , shell of Conoteuthis dupininna from the
Neocomian of France. />, shell of Sepia Orbigniana,
Mediterranean. C, shell of Spiritlirostra Bellardii,
from the Miocene of Turin ; the specimen is cut so

CEPHALOPODA. 427

are all directed towards the oral extremity (Histioteuthis). Aquiferous pores
leading into spaces in the integument, but not communicating with the vascular
system, are found in many Dibranchs.

There is an internal cartilaginous skeleton which serves for the
protection of nerve-centres and sense-organs, and for the attachment
of muscles. The cartilaginous tissue itself closely resembles the
hyaline cartilage of vertebrates, differing in the fact that the cells
are connected by their branching processes which traverse the matrix
in all directions. In the head there is in Dibranchs a complete
cartilaginous investment for the great ganglionic masses and otocysts,
which furnishes lateral cup-like expansions for the eyes. In Nautilus
there is a corresponding cephalic cartilage on the ventral side only of
the nerve-centres, extending also into the tissue of the funnel.
Cartilage is present also in other parts of the body, e.g. the branchial
cartilage, fin cartilages, nuchal cartilage, dorsal cartilage.

Nervous system. There is a great concentration of ganglionic
matter round the oesophagus, and it is difficult to trace exact
homologies with the nerve-centres of other Molluscs.

In Nautilus there are two ganglionic rings round the oesophagus
behind the buccal mass (Fig. 342). They are connected dorsally,
above the oesophagus, in a common mass (Jf), which may be called
the cerebral mass and compared to
the cerebral ganglion of other Mol-
luscs. The anterior ring innervates
the funnel and cephalic lobes, and
may be compared to the cerebro-
pedal commissure and pedal ganglia

of other types; the posterior ring , ^ -, / -,

innervates the mantle and viscera, ** «< »v v

and may be compared to the cerebro- FIG. 342.— Central nervous system of a

, , ,. female Nautilus from the left side (from

pleiiral commissure, pleura! ganglia, Pelseneer after Valenciennes). I ac-

and visceral commissure of other cessory Pedal ganglion; n nerve to

. funnel; /// pedal; IV visceral gan-

MollllSCS j it gives Off a pair of StOUt giion ; V visceral nerve ; 71 pallial

nerves (V} which pass backward nerves ; Til tentacular nerves ; FT//

olfactory, IX optic nerve ; X cerebral

(dorsalwards), on either side of the ganglion ; xi otocyst ; xn stomato-
vena cava; these supply the gills, ""

osphradia, and viscera, but do not

form dorsalwards in the visceral sac, visceral ganglia. The cerebral
portion supplies the eyes, otocysts, ocular tentacles, lips, etc., and
gives off on each side two nerves to form stomatogastric commis-
sures (XII)) which surround the oesophagus immediately behind

428

MOLLUSCA.

the buccal mass. This stomatogastric system (Fig. 343) consists of
the two above-mentioned nerves (c.c) on each side, which pass forward
from the cerebral ganglion to end in the two pharyngeal ganglia
(ph. g). These are connected by a long anterior commissure (ant.

com} which passes ventral
to the mouth, and by a
shorter posterior commis-
sure, the buccal commis-
sure— (buc. phar. com. and
b. com.) — which is also
ventral to the oesophagus,
and contains in its course
two buccal ganglia (buc.g.).
The ganglia and commis-
sures of the stomatogastric
system supply the buccal
mass. In the female there
is an accessory ganglion
supplying the inner ven-
tral cephalic lobe, and
connected with what has
been called above the
pedal ganglion (Fig.
342, /).

bvc.phw con

FIG. 343. — Buccal nervous system of Nautilus pompilius
(after Graham Kerr). ph.g pharyngeal ganglion ;
Zmc.gr buccal ganglion (buc.g ought to point to the
swelling from which the nerves ph. n come off) ;
c.c cerebro - pharyngeal connective; buc.phar.con
bucco - pharyngeal connective ; ph.n pharyngeal
nerves ; b.com buccal commissure (stomatogastric) ;
ant.com anterior pharyngeal commissure.

It should be noted that the nerves to the cephalic arms come off rather high
up on the anterior ring, and that the nerve to the funnel arises quite ventrally.

In the Dibranchs
the great nerve
centres are com-
pletely enclosed in
the skull. As in
Nautilus it is difficult
to speak of special
ganglia, for the whole
mass is ganglionic.
The part dorsal to
the oesophagus we
may call the cerebral
ganglion (Fig. 344, 1);
this gives off later-

FIG. 344. — Central nervous system of Ommatostrephes from
the left side, magnified (after Pelseneer). a buccal mass ;
6 brachial ganglion ; c oesophagus ; d pedal ganglion ; e
nerve of the funnel ; / position of the otocyst ; g pleuro-
visceral ganglion ; h visceral nerve ; i posterior salivary
gland ; j pallial nerve ; k optic nerve, cut ; I cerebral gan-
glion ; m stomatogastric (buccaJ) ganglion ; n anterior part
of the cerebral ganglion (suprabuccal) ; o anterior salivary
Bland.

CEPHALOPODA.

429

ally the great optic nerves (A;), and
is continued at the sides of the
oesophagus as a broad commissure,
which leads to the sub-oesophageal
mass. The sub-oesophageal mass is
indistinctly divided into a posterior
part, which is supposed to consist
of the pleural and visceral ganglia
(i.e., ganglia of the visceral com-
missure) fused (g\ and an anterior
comparable to the pedal of other
types (d\ the anterior aorta passing
ventralwards between the two. The
pedal portion is generally divided
into two parts, a portion behind —
the pedal proper — supplying the
funnel, and a brachial part (b) in
front, supplying the arms.

The cerebral ganglion is connected
by two thin cords, or by one soon
dividing into two, with a ganglion
on the buccal mass called the supra-
Imccal ganglion (Fig. 344, n; Fig.
345, b). This is to be regarded as
a detached portion of the cerebral;
it gives off the stomatogastric com-
missure, which is completed ven-
trally to the oesophagus in the
infra-buccal ganglion (Fig. 344, m;
Fig. 345, a), or buccal ganglion
proper. The cerebral and the supra-
buccal are both connected with the
brachial or anterior part of the pedal
by separate commissures (Figs. 344
and 345). In Octopus the supra-
buccal ganglion is not separated
from the cerebral.

The pleuro-visceral portion of the
sub-oesophageal gives off from the
pleural portion two large pallial
nerves (Fig. 344, j; Fig. 345, m)

FIG. 345. — Central nervous system of
Ommatostrephes, dorsal view (after
Hancock, from Pelseneer). o stomato-
gastric (buccal) ganglion ; b anterior
part of cerebral ganglion (suprabuccal) ;
c optic ganglion ; d visceral ganglion ;
e rectal nerve; / stellate ganglion
(mantle ganglion) ; g commissural gan-
glion of the visceral nerves ; h brachial
ganglion ; i viscero - stomatogastric
anastomosis; j stomach ganglion; k
oesophageal stomatogastric nerves ; I
commissure of the mantle ganglia ; m
pallial nerve ; n visceral nerve ; o cere-
bral ganglion, beneath which a probe
indicates the passage of the oesophagus,
and of the stomatogastric nerve from
q to k; p brachial ganglion; q oeso-
phageal stomatogastric nerve.

430 MOLLUSCA.

to the mantle ganglion (ganglion stellatum), which are in some
forms connected by a commissure (Fig. 345, Z) dorsal to the oeso-
phagus, and from the visceral portion two visceral nerves, fused
at their origin, to the viscera (Fig. 345, n). The visceral nerves
join behind in a ganglion (g), which gives off a right and left
nerve to the two brachial ganglia (p). The infra-buccal ganglion
gives off a nerve backwards (Fig. 345, k, and Fig. 342, XI), which
runs along the oesophagus and ends in a large ganglion on the
stomach (j). This ganglion givts off a nerve which anastomoses
with the visceral nerves (i).

Organs of sense. Tactile sensibility is specially localized in the
arms of Dibranchs and tentacles of Nautilus. There is an organ
which is supposed to be olfactory, just ventral to the eye; it generally
has the form of a pit (Sepia), but it may be tubercular. It is
innervated from the cerebral ganglion. Osphradia are absent in
Dibranchs, but are supposed to be present in Nautilus (see below).
The otocysts in Nautilus are placed high up on the anterior ring close
to the cerebral ganglion (Fig. 342, XI), and are sometimes described as
being adjacent to the pedal centres ; they contain numerous otoconia.
In Dibranchs they are embedded in the floor of the skull, and they
form a kind of labyrinth, their walls being drawn out into short
diverticula; they each contain one large otolith, and are innervated
from the pedal ganglion by a nerve which arises from the cerebral.
The tube which connects them with the exterior in the embryo
persists as a caecal process from the otocyst. Damage to the otocysts
of Cephalopoda has been found to interfere with their power of
maintaining equilibrium.

The eyes in most forms are extremely complicated in structure.
In Nautilus, however, they are very simple, being altogether without
refractive media, and consisting merely of a vesicle with an extremely
narrow opening to the exterior. The lining of the vesicle constitutes
the retina, and is continuous through the aperture with the external
ectoderm ; it consists of two layers separated by a layer of pigment.
The eye of Nautilus is therefore constructed on the principle of the
pin-hole camera, there being a dark chamber lined by the sensitive
membrane, and a minute hole for the entrance of light.

In the Dibranchs (Fig. 346) the optic vesicle is closed, and its
front wall secretes a cuticular biconvex lens (L) ; part of this lens is
thrown down by the lining epithelium of the outer wall of the vesicle,
and part of it by the outer ectoderm. The lens is therefore theoreti-
cally in two parts, and is traversed by the front wall of the vesicle.

CEPHALOPODA. 431

The front wall of the vesicle at the point where it runs into the lens
is thickened, and constitutes the ciliary body (Ci). The outside skin
is • thrown into folds over the eye : internally there is a fold which
covers over the ciliary body, and extends as far as the periphery of
the lens; it is highly pigmented and constitutes the ifris (Jk).
Outside this is another fold of much greater extent, which meets
over the front of the lens ((7), and bounds a space — the anterior
optic chamber — the inner wall of which is formed by the lens,
iridean folds, and choroid. This fold constitutes the sclerotic and
cornea; it is in the Oegopsida perforated by a small pore over the
lens. Outside the skin may be again folded to form an eyelid.

___^ L
At

"Opt

FIG. 346.— Section through the eye of Sepia, diagrammatic after Hensen. Ae argentea externa ;
C cornea ; Ci ciliary body ; Go optic ganglion ; Jk iris cartilage ; K cartilage of optic bulb ;
KK cephalic cartilage ; L lens ; Opt optic nerve ; P pigment layer of retina ; Re outer layer of
retina ; Ri inner layer of retina ; W white body.

The \retina consists of two layers (Re and Ri), as in Nautilus,
divided -.by a layer of pigment (P), and the sensitive layer is that
which lines the optic vesicle or posterior optic chamber (vitreous
humour). The optic nerve comes from the large optic ganglion (Go),
which is 'protected by the orbital expansion of the cephalic cartilage
(KK). The clioroid is the internal continuation of the iris, and forms
the inner wall of the deeper parts of the anterior optic chamber ; it

432

MOLLUSCA.

Mxi

is pigmented and contains from without inwards (1) a layer of
epithelium,* (2) a layer of obliquely-placed plates called the argentea
externa, (3) a layer of muscles, (4) the argentea interna, (5) a carti-
laginous capsule (K), which lies next (6) the spreading out fibres of
the optic nerve.

At the side of the optic ganglion within the orbit is a glandular
body called the white body ( W).

Alimentary canal. The mouth, which is placed within the circlet
of arms, is surrounded by a circular fold forming a kind of lip (Fig.

347, L\ and, in addition, in the
Dibranchs by a membrane called
the buccal membrane. The buccal
membrane is in some Decapods
divided into lobes alternating with
the arms and bearing suckers. The
entrance to the mouth is armed
with two powerful horny jaws, an
upper and a lower (Mxi, Mxs), which
resemble in form a reversed parrot's
beak, the lower jaw being the larger
and overlapping the upper. The
radula (Ha), which arises in a
sheath, usually has in each row a
median tooth and three teeth on
each side, and there may be in
addition, outside these, some flat,
non-toothed 'plates (the radula is
absent in Cirroteuthis). There is
a sub-radular organ in front of the
radula. The salivary glands (Spd)
open into the buccal cavity; in
Octopoda there are two pairs, of
which the ventral is applied against
the buccal mass, while the dorsal is
dorsal to the skull. The ducts of
the latter unite, and pass forwards
with the oesophagus. In the Deca-
pods the dorsal glands are alone
present.

* Not very distinct in the figure ; it is the inner lining of the space enclosed
by the great cornea] sclerotic folds.

M

FIG. 347.— Digestive apparatus of Sepia
(after W. Keferstein). L lip ; Mxi, Mxs
lower and upper jaws ; Ra radula ; Eg
supra-buccal ganglion ; Spd salivary
gland ; Oe oesophagus ; L liver ; Gg bile
duct;(7spsplanchnic(stomach)ganglion;
M stomach ; M1 caecum of stomach ; A
anus ; Tb ink sac.

CEPHALOPODA.

433

The oesophagus (Oe), with or without a crop-like dilatation, is
long and ends behind in the stomach (M), which is provided with
a large, often spiral, caecum (M'). The intestine leaves the stomach
close to the oesophageal entrance, and passes as a straight or^slightly
coiled tube (Nautilus, Octopus) to the anus (A).

FIG. 348. — Male Nautilus, ventral view ; the mantle is draAvn back ; reduced, after Keferstein
(from Pelseneer). a eye ; ft genital opening ; c opening of the anterior kidney ; d inter-
branchial papilla ; e opening of the posterior kidney; /edge of mantle ; g postanal papilla ;
h external opening of the pericardium ; i posterior gill ; j anus ; k anterior gill ; I funnel ;
m tentaculiferous appendages.

The liver (L) is a compact gland, and consists of two lobes, more
or less united, one on each side of the oesophagus. The bile ducts
(G-g) are two in number and covered by a glandular tissue called
pancreatic, but really renal (see below) ; they open into the caecum
of the stomach.

2 F

434

MOLLUSCA.

In Nautilus the dorsal salivary glands are not present and the liver is less
compact and in four lobes, each with its own bile duct.

The ink sac (Tb), which is absent in Nautilus and Cirroteuthis,
is a rectal gland. It is placed on the posterior side of the visceral
sac close to the mantle-lining, and opens into the rectum.

The perivisceral cavity is, as in Gastropods, partly coelomic and
partly haemocoelic, but the coelomic portion has a much greater
extension than in other Molluscs.

The haemocoelic part of the0 body-cavity is best developed in

Nautilus, where it forms a
cavity, in relation with the
crop, vena cava and one loop
of the intestine ; it occupies
the anterior side of the vis-
ceral sac, and does not extend
to the apex (which is occu-
pied by genital coelom). It
is traversed by connective-
tissue strands, and commu-
nicates with the vena cava
by numerous foramina in the
wall of the latter. In Di-
branchs the haemocoele is
less developed; in Octopods
it has the form of a large
sinus surrounding the oeso-
phagus, dorsal salivary
glands, bile ducts, and ante-
rior aorta ; and communicates
with the great vena cava.
Also the cavity round the
buccal mass is a blood space.

The perivisceral part of the coelom is divided into two parts, which
however communicate — the so-called viscero-pericardial sac, corre-
sponding to the pericardium of other types, and the genital portion.
In Nautilus the viscero-pericardial cavity is in relation with the heart
and pericardial gland, while the genital portion contains the gonad
and has relations with the stomach and intestine. Both open to the
exterior, the pericardium by two openings placed respectively just
internally to the openings of the posterior nephridia (Fig. 348, Ji),
while the genital opens by the single genital duct into the posterior

FIG. 349. — Diagram of the renal and circulatory
apparatus of a Decapod, ventral view (after
Pelseneer). I ctenidium; II renal sac; III
afferent branchial vessel; IV branchial heart;
V abdominal vein ; VI ventricle ; VII coelom ;
VIII genital gland projecting into the genital
part of the coelom, which in front is in relation
with the heart as the viscero-pericardial coelom,
and opens into the renal sac at XVII; IX
posterior aorta ; X auricle ; XI appendage of
branchial heart (pericardial gland) ; XII glan-
dular tissue of the kidney ; XIII external opening
of kidney ; ^7 V vena cava ; XV anterior aorta ;
XVI branch of vena cava ; XVII reno-pericardial
opening.

CEPHALOPODA.

435

region of the mantle-cavity (Fig. 348, b). In Dibranchs (Fig. 349)
the perivisceral part of the coelom is also in two communicating
parts : (1) the genital division, which opens to the exterior by the
genital duct, and is related only to the gonad; and (2) th^ viscero-
pericardial which has relations to the heart, stomach, intestine,
branchial hearts, and pericardial glands (Decapoda), and does not
open to the exterior. In Octopoda (Fig. 350) the viscero-pericardial
coelom is prac-
tically absent,
being reduced to
a small space
( VI) on each
side round the
glandular appen-
dages of the
branchial heart
( pericardial
glands), which
opens ( VII) into

the nephridiuill ^IG' ^^. — Diagram of the coelom of a female Octopus, ventral

. (posterior) view (from Pelseneer, after Brock). / branchial heart ;

and COm muni- JI canal connecting the genital and visceral parts of the coelom;

Cates bv a narrow ^^ oyiducts 5 J^oviducal gland ; V appendage of branchial heart;

VI perivisceral (pericardial) coelom ; VII reno-pericardial opening ;

Canal (//) with VIII ovary ; IX genital coelom.

the apically-

placed genital division of the coelom. In Dibranchs the perivisceral
(viscero-pericardial) part of the coelom also communicates with the
kidneys, and not directly with the exterior (Fig. 349, XVII), whereas
in Nautilus it has no opening into the kidney.

The branchiae have the form of two (Dibranchiata) or four
(TetrabrancJiiata) bilamellate ctenidia, which are placed on the
visceral sac in the mantle-cavity, and are not ciliated. In Nautilus
they project freely and the posterior are a little larger than the
anterior; in Dibranchs they are attached to the body along one
side of the axis.

Osphradia are absent in Dibranchs, but in Nautilus there are two
pairs of papillae in the mantle-cavity, which are supposed to repre-
sent them. The anterior pair is between the two pairs of gills
(Fig. 348, d), while the posterior osphradia* are the so-called post-
anal papillae placed near together on the mantle between the renal
sacs and the nidamental glands in the female, and in the same

* Vide A. Willey, Q. J. M. S., 40, 1897.

436

MOLLUSCA.

position in the male (Willey). They are innervated by branches
of the visceral nerves.

Vascular system. The heart lies in the viscero-pericardial cavity
(except in the Octopoda), and is placed at about the middle of the vis-
ceral sac. It consists of a median ventricle and of as many lateral
auricles as there are gills (Fig. 351). A large anterior (ventral)
aorta passes off from the ventricle, and gives in its course strong
branches to the mantle, alimentary canal and funnel, and breaks
up in the head into vessels to the cephalic organs. A posteriorly
(dorsally) directed visceral artery also leaves the ventricle, supplying
the viscera and gonad. The capillary network, which is richly
developed in all the organs, passes partly into sinuses, partly into

veins which are col-
lected through lateral
veins into a large
anterior and a pos-
terior vena cava.
Each of these bi-
furcates into two or
four trunks (accord-
ing to the number
of the gills) which
carry the blood
through the kidneys
to the gills. Im-
mediately before
their entrance into
the gills, the walls
of these afferent
branchial vessels are
(except in Nautilus)
especially muscular
and rhythmically
contractile, and con-
stitute the branchial hearts. The glandular appendages of the
branchial hearts are the pericardia! glands.

In Nautilus the vascular system is largely lacunar, but in Dibranchs capillaries
are developed, though these may end in sinuses which open into the veins ; in
Octopoda especially there is a large sinus already described, which opens into the
anterior vena cava.

FIG. 351. — Circulatory and renal organs of Sepia officinalis
from the dorsal (anterior) side (after Hunter), Ad and Ao"
anterior and posterior aorta ; Ap appendage of the branchial
heart : At, At' auricles ; Br gills ; C ventricle ; Kh branchial
heart; N renal appendages of the veins; V lateral vein;
Vbr afferent branchial vessels ; Vc', Vc" anterior and
posterior vena cava.

CEPHALOPODA. 437

The excretory organs lie on the posterior side of the visceral sac
close to the mantle-cavity, into which they open. In Dibranchs they
are two in number and are either completely separate (Octopoda),
or they are connected together, generally through an anfyBriorly and
dorsally-placed portion which is of considerable extent and lies close
under the shell. This unpaired portion contains the so-called pan-
creatic tissue of the bile ducts, and is in relation with these
structures. The anterior and posterior afferent branchial vessels
run in the walls of these kidney sacs on their way to the gills,
and give off blind diverticula which project into the cavities of the
kidneys. The kidney epithelium, which is flattened over the rest
of the sac, is especially glandular on these vascular diverticula
(Fig. 349, XII) and secretes the waste matter in the form of
concretions which largely consist of guanin.

Each kidney opens into the mantle-cavity through a papilla placed
not far from the anus, and into the pericardial coelom by a pore not
far from the external opening.

In Nautilus there are four kidneys which open to the exterior;
one pair opens just anterior (i.e., ventral) to the anterior gills, and
the other pair just anterior to the posterior gills and close to the
openings of the pericardium ; they are without any internal opening
into the coelom. The four afferent branchial vessels run in the wall
separating the four kidneys from the pericardium, and give off
diverticula, which are covered with glandular tissue, into the peri-
cardium as well as into the renal sacs. The four tufts of glandular
processes thus projecting into the pericardium constitute the peri-
cardial gland, and are larger than the corresponding processes on the
opposite side of the septa projecting into the renal sacs.

The kidneys and gills of Nautilus have been spoken of in the text as anterior
and posterior, but it must be borne in mind that, oAving to the fact that the
part of the body in which they lie has been prolonged ventrally in the mantle-
fold, the posterior kidney and gill are really ventral, i.e., nearer to the mouth
than the anterior, which are placed just at the point where the mantle-fold
is given off from the body. The pericardium, which is also in the mantle-
fold, is actually posterior to the kidneys, and the posterior walls of the
kidney -sacs form the anterior wall of the pericardium ; but it must be
remembered that morphologically the pericardium is dorsal to, i.e., nearer the
apex of the visceral sac than, the kidneys.

The Cephalopoda are dioecious. The sexes present external differ-
ences, which are sometimes very marked. In many cases the males
are much smaller than the females, as in Argonauta, in which genus

438

MOLLUSCA.

the female is further distinguished from the male by possessing a
shell. In Nautilus there are considerable differences in the number
and arrangement of the cephalic tentacles (see above p. 421) ; and in
all Dibranchs one of the arms of the male is different from the rest
and said to be hectocotylized (see p. 420).

The sexual gland is single, and at the apex of the visceral sac.
It is in both sexes a special development of a portion of the
epithelium lining the genital division of the coelom. The sexual
cells are dehisced into the coefcmi and pass out by the genital
ducts, which open into the coelom and possess accessory glands on
their course.

The generative duct of one side is usually suppressed or vestigial.
In Nautilus in both sexes the right duct persists, and the left is
vestigial, having lost its internal opening but retained the external.
In all male Dibranchs the left duct is alone present ; this is also

the case in all females
excepting the Oegopsida
and Octopoda (except
Cirroteuthis), in which
both oviducts are present
in functional develop-
ment.

In Nautilus the genital
coelom communicates with
the pericardial by three
openings in the septum
which separates them, and
the stomach and intestine
project into it. The genital
gland is a hollow structure,
and is to be regarded as a
folded -off portion of the
genital coelom, to the ante-
rior wall of which it is
attached ; it opens into the
genital coelom close to the
openings of this latter struc-
ture into the pericardium.
The reproductive cells are
produced from the lining
of the genital gland, and

in the female the ripening ova, covered with their follicle cells and the flat
cells of the peritoneum, project into its cavity. In the male the walls of the
genital gland are folded so as to give rise to a number of branched tubes,
which open into the central cavity of the organ. The genital duct in both

FIG. 352.— Male sexual organs of Sepia officinalis (after
Duvernoy, modified from Grobben). T testis with a
piece of peritoneum ; To opening of the testicular tubes
into the coelom ; Vd vas deferens ; 0 opening of the
vas deferens into the body-cavity ; Vs vesictila seminalis ;
Pr prostate ; Sp Needhain's sac ; Oe generative opening.

CEPHALOPODA.

439

sexes opens into the coelom close to the opening of the genital gland, and into
the mantle-cavity to the right side of the middle line on the oral side of the
anus ; while the vestigial left duct opens to the left as the so-called pyriform
organ. The vas deferens has an accessory gland and a spermatophore sac, and
opens at the end of a papilla — the so-called penis.

In Dibranchs the genital glands and genital coelom are much as hi Nautilus,
except that the latter has no relation to the alimentary canal. The oviduct
possesses an oviducal gland in its course, and opens into the mantle-cavity
on the left side, or when two are present symmetrically on both sides.

FIG. 353. — Sper-
matophore of
Sepia (after M.
Edwards).

Oe

McL

FIG. 354. — Posterior view of visceral sac of a female Sepia
partly dissected (after Grobben). Ad accessory nida--
mental gland ; .4/anus ; Gst stellate ganglion ; K gills ;
Kh branchial heart ; Kha pericardial gland (appendage
of branchial heart); Lk tube from peri visceral coelom
to the kidney (renal coelom), often called the aquiferous
canal ; N kidney ; Nd nidamental gland ; Od oviduct ;
Od. D oviducal gland ; Oe external opening of oviduct ;
Ov ovary in the genital coelom which has been opened ;
U ureter.

The vas deferens opens at the same place as the oviduct, but has a much more
complicated structure. In Sepia we get the following parts (Fig. 352) : (1) a
coiled narrow tube ( Vd) which opens into the genital coelom, (2) a long dilated
vesicula seminalis (Vs) with two prostatic glands opening into its terminal
portion (Pr}, (3) a spacious sac, known as Needham's sac, in which the sperma-
tophores are stored, and which opens into the mantle-cavity at the apex of a
papilla placed on the left side.

440

MOLLUSCA.

The nidamental glands are accessory glands of the female, which secrete the
egg envelopes and open into the mantle-cavity. In Nautilus there is a single
gland in the mantle-wall dorsally. In Decapoda they are in the anterior wall
of the mantle-cavity superficial to the kidneys, and there are generally two pairs
—the ventral being the smaller (Fig. 354, Ad, Nd).

The eggs are surrounded (Argonauta, Octopus, Sepia) by capsules
with long stalks, which are united together in racemose masses (so-
called sea-grapes), and fastened to foreign objects in the sea. In
other cases the eggs are aggregate^ in gelatinous tubes which may be
attached together in great numbers (Loligo). In Argonauta they are
placed in the shell.

The spermatopliores (Fig. 353) are manufactured in the male
generative ducts. They are elongated, vermiform bodies containing
spermatozoa, and often presenting a most elaborate structure. In
Dibranchs they may be described as tubes containing spermatozoa
at one end, and a piston and spiral elastic spring at the other.
We may presume that under proper conditions the spiral spring
elongates and drives down the piston, which then expels the
spermatozoa.

The spermatophore are sometimes very long : in Eledone 8 centi-
metres, in Octopoda with autotomous hectocotylus they may attain
a length of 50 centimetres; and in Nautilus, in which they are coiled
on themselves, they may be more than 30 centimetres long.

In the Dibranchs one of the
arms of the male is always modi-
fied, or hedocotylized as it is called,
for purposes of copulation. In
the Decapoda it is usually the
fourth left arm ; but in Enoplo-
teuthis it is the fourth right,
and it may vary from the fourth
right to the fourth left in the same
species ; in Idiosepius and Spirula
both right and left fourth arms
are modified, and in Spirula en-
closed in a common envelope ; in
Octopoda it is usually the third
right, but in Scaeurgus and Argo-
nauta it is the third left, and the
second right in Cirroteuthis. In
most cases the modification con-
sists mainly in a reduction of the
suckers, and the arm is not de-
tached ; it affects the extremity of
the arm in Enoploteuthis, Eledone,

FIG. 355. — Male of Argonauta argo (after H.
Miiller). He hectocotylized arm.

CEPHALOPODA. 441

Octopus; its base in Sepia, its whole length in Idiosepius and Rossia, and Loliolus.
But in three genera, Philonexis, Tremoctopus, and Argonauta,. the modification
is much more extensive, and the arm affected is charged with spermatozoa,
cast off, and deposited in the mantle-cavity of the female (see above). This
is called an autotomous hectocotylus. The modification is as follows : before
sexual congress the arm in question is represented by a somewhat globular
sac, which consists of flaps of the basal part of the arm wrapped round the distal
part. Soon this sac bursts and allows the distal part and the suckers of the
basal part to appear (Fig. 355). The distal part thus set free has at its end
a small sac, which in its turn bursts and allows a long terminal filament to
issue. The folds which formed the first-named sac, give rise to a receptacle on
the aboral side of the arm, which becomes charged with spermatophores. This
spermatophore receptacle communicates with a small vesicle in the base of the
arm, which leads into a long canal extending along the arm and filament, and
opening at the end of the latter. How this arm, which is deposited in the
mantle-cavity of the female, is used in fertilization, and how it becomes charged
with spermatophores is not known. After the arm is detached a new encysted
arm is said to be formed on the scar.

Those Cephalopoda which are without this autotomous hectocotylus are said to
copulate mouth to mouth, the modified arm being used to affix the spermato-
phores to the buccal membrane, or to transfer them to the mantle-cavity of the
female. In Sepia and Loligo spermatophores are found in the pockets in the
buccal membrane, and in Nautilus within the annular lobe of the head (v. p. 421).

Development. The egg of all Cephalopoda is large and heavily
charged with yolk. This is the case even with Nautilus, as may
be gathered from the ovarian egg, for the laid egg"* of Nautilus
has never been found. There is no larval stage, not even a trace
of the velum, and the young are hatched with the form of the
adult. The development is therefore very different from that of
other molluscs.

In Dibranchs the cleavage is partial, and confined to one pole of the egg ; as
in the bird's egg it gives rise to a blastoderm or germinal disc, which in the
subsequent development is raised more and more from the subjacent yolk. Soon
several projections appear on the embryonic rudiment (Fig. 356). First in the
centre of the germ a flattened circular ridge is formed round a central depression ;
the ridge is the mantle, and the depression is the shell-gland. In Octopoda
(Argonauta] the shell -gland seems to shallow out and disappear, but in
Decapods it becomes closed over and persists as a sac in which the shell is
deposited.

On each side of the mantle the two parts of the funnel (Tr), which even in
Dibranchs are separate in the embryo, appear; and between these and the
mantle the gills (£r). Also laterally, but external to the folds of the funnel,
the first traces of the head appear as two pairs of elongated lobes, of which the

* Since this was written, the eggs of Nautilus have been found by Dr. Arthur
Willey, the Balfour student of the University of Cambridge (Proc. Roy. Soc.,
vol. 60, 1897, p. 467). The eggs, which are laid singly, are enclosed in a double
capsule of cartilaginous consistency. The ovum is very large (17 mm. in its
longest diameter) and is surrounded by albumen.

442

MOLLUSCA

FIG. 356. — Embryonic development of Sepia
officinalis (after Kolliker). a, view of germinal
disc from above ; the commencing embryo lying
on the yolk ; Br gills ; Tr folds of the funnel ;
Oc eye; M mantle, b, somewhat later stage,
from the front ; D yolk ; Kl' anterior, Kl" pos-
terior cephalic lobe ; 0 mouth, c, later stage,
from the side ; 1-k first rudiments of arms, d,
older stage from the front ; 5 fifth pair of arms.
e, still later stage in lateral view ; the halves of
the funnel have united.

anterior external pair bear the eyes
(Oc). On the outer edge of the disc
papilliform structures are formed,
the first rudiments of the arms.
In the later growth of this abso-
lutely symmetrical embryo, the
Cephalopod form becomes gradu-
ally more and more apparent : the
mantle projects considerably, and
grows over the gills and two parts
of the funnel, which fuse to form
the definite funnel. The cephalic

FIG. 357. — Almost
ripe embryo of
Sepia officinalis
from the dorsal
(anterior) face
(after Kolliker).
Ds yolk sac.

lobes grow together between the
mouth and funnel, and on their
oral sides become more sharply
constricted off from the yolk,
which, with a few exceptions,
persists for some time as a yolk
sac. The yolk sac is attached
between the mouth and anus, and
may be regarded in the later
stages as a swollen up portion of
the foot. It should be noted that
the embryo is formed on the dorsal
side of the yolk sac, and never
completely surrounds it.

TETRABRANCHIATA. 443

Order 1. TETRABRANCHIATA.*

Cephalopoda with four gills in the mantle-cavity.

The appendages of the head are peculiar, consisting of a number
of lobes carrying sheathed tentacles ; they are described on p. 421.

The cephalic cartilage, instead of forming a complete ring, consists
of two horse-shoe-shaped limbs, on which the central parts of the
nervous system lie. The eyes are without a lens or other refractive
media. The funnel is formed of two lobes which are not fused.
There is no ink sac. The ctenidia are four in number, as also are
the branchial vessels, auricles, and kidneys, and probably the
osphradia. The pericardium has a pair of external openings, and
does not communicate with the kidneys. There is a multilocular
external shell, in the last chamber of which the animal lies. It is
secreted by the mantle and covers the visceral sac. Its chambers
are filled with air and are traversed by a siphon. The shell consists
of an external, frequently coloured, calcareous, porcellanous layer,
and an internal mother-of -pearl layer.

The position and structure of the siphon, as well as the form of
the septa, and the lines of fusion of the latter with the shell, afford
important characters for the classification of the fossil Tetrabran-
chiates.

There is only one living genus confined to the Indian and Pacific
Oceans, but the extinct members of the order are numerous and
important.

The siphon (or siphuncle) in Nautilus may have a complete but thin nacreous
investment, or only a partial one next one face of the septa, in which case it is
called a septal neck (Fig. 338, Sf). In most Nautilidae the septal necks project
from the sides of the septa which look towards the apex of the shell, while in
the Ammonitidae they are, as a rule, on the other sides of the septa. The
siphuncle varies in position ; it may perforate the centre of the septa, in which
case it is central or sub-central (Nautilidae}, or it may be marginal, on the
outer side of the septa (Ammonitidae). The suture is the name given to the
line of union of the edge of the septum with the shell- wall. In the Nautilidae
the sutures are uniformly curved or straight ; in Ammonitidae they are exceed-
ingly complex, being folded into a number of lobes with the concavity towards
the aperture ; the parts of the suture between the lobes are called the saddles,

* R. Owen, " Memoir on the Pearly Nautilus" London, 1832. J. Van der
Hoeven, "Bydraagen tot de ontleedkundige Kennis aangaande Nautilus
pompilius," Verhandel. k. Akad. Amsterdam, diel 3, 1856. T. H. Huxley,
''On some points in the Anatomy of Nautilus pompilius," Journ. Proc.
Linn. Soc., London, 3, 1859. Keferstein, "Beitr. z. Anat. d. Nautilus pomp.,"
Nachrichtsbl. k. Ges, wiss. Qottingen, 1865. Lankester and Bourne, "On the
existence of Spengel's olfactory organ and of paired genital ducts in the Pearly
Nautilus," Q. J. M. S., vol. 23, 1883. J. Graham Kerr, "On some points in the
Anatomy of Nautilus pompilius,"' Proc. Zool. Soc. London, 1895. A. AVilley,
Q. J. M. S., 39, 40.

444 MOLLUSCA.

and are convex towards the aperture. The lobes and saddles may be themselves
secondarily folded or denticulated (Ammonites'), or the lobes alone, the saddles
being round (Ceratites}.

The Aptychus of the Ammonitidae is a calcareous or horny plate, which was
probably secreted by the hood and served as an operculum ; it may be a single
plate, or divided by a suture into two (Synaptychus).

Fam. 1. Nautilidae. Shell straight, or coiled ; aperture simple. Septa
concave towards aperture ; suture simple ; siphon usually central, or internal.
From Cambrian to present day; attained their highest development in Devonian
and Silurian. Orthoceras and Nautilus alone persist beyond the Palaeozoic epoch.
Nautilus L., sole living genus, N. fompilius L. ; Orthoceras Breynius, shell
straight, lower Silurian to Lias.

Fam. 2. Ammonitidae. Shell of various forms, straight to spiral or turretted.
Septa much folded, suture complex ; siphon external. Extinct ; Silurian to
Eocene. Goniatites De Haan ; Ceratites De Haan ; Ammonites Bruguiere.

Order 2. DIBRANCHIATA.*

Cephalopoda with two gills in the mantle-cavity.

The appendages are four pairs of arms with suckers on their oral
faces; in the Decapoda there are, in addition, two long, prehensile,
tentacle-like arms with suckers at their extremities only, placed
between the third and fourth arms.

The cephalic cartilage constitutes a complete investment for the
-central nerve-organs. The eyes are elaborate, and have refractive
media. The lobes of the funnel are fused. An ink-sac is generally
present. The ctenidia are two in number, as are the branchial
vessels, auricles, and kidneys. There are no osphradia. The kidneys
open internally into the pericardium, and the latter has no external
opening. The shell is in many forms completely absent; in the
rest it is internal, or partly internal, and never protective to the
visceral sac.

Sub-order 1. DECAPODA.

In addition to the eight arms there are two long tentacles between the third
and fourth pairs of arms (ventral). The suckers are stalked and provided with
a horny rim. The eyes are without a sphincter-like lid. The mantle bears two
lateral fins, and there is a well-developed apparatus for closing the mantle-
opening. An internal shell is present. The heart is contained in the coelom.
Nidamental glands are generally present.

Fam. 1. Ommatostrephidae. Tentacular arms short and broad; suckers
with toothed ring. Ommatostrcphes Gray, sagittated calamary, is able to

* Hancock, "On certain points in the Anatomy and Physiology of the
Dibranchiate Cephalopoda," Nat. Hist. Jteview, 1861. R. Owen, "Supple-
mentary Observations on the Anatomy of Spirilla Australis," Ann. Mag. Nat.
Hist. (3), 3, 1879. T. H. Huxley and P. Pelseneer, "Report on Spirilla,"
Challenger Reports, Pt. 83 (bound in at the end of the second volume of the
"Summary of Results").

OCTOPODA. 445

project itself for long distances from the water and is not unfrequently found
on the decks of ships ; Ctenopteryx Appellof ; Chaunoteuthis Appellof ; Arclii-
teuthis Steenstrup, includes the largest Cephalopoda known.

The Thysanoteuthidae are allied here.

Fam. 2. Onychoteuthidae. Tentacular arms long ; suckers with, hooks.
Onychoteuthis Lichtenstein, the uncinated calamary, with hooks on the tentacular
arms, and a small group of suckers at the base of each club, enabling them to
act like forceps. Enoploteuthis d'Orb., armed calamary, with hooks on all the
arms (as well as suckers). Verania Krohn, tentacular arms atrophied in the
adult.

The Gonatidae (Gonatus Gray) are allied here.

Fam. 3. Chiroteuthidae. Tentacular arms very long, pen expanded at each
end. Chiroteuthis d'Orb. ; Histioteuthis d'Orb. ; Histiopsis Hoyle ; Calliteuthis
Verr.; Doratopsis Rochebrune.

Fam. 4. Cranchiidae. Arms very short ; fins terminal, small ; eyes pro-
jecting. Loligopsis Lam. ; Histioteuthis d'Orb. ; Cranchia Leach ; Leachia Les. ;.
Taonius Steenstrup.

The above-named four families constitute the Oegopsida, which are character-
ized by their pelagic habit, by the possession of a perforated cornea, and by the
presence of two oviducts.

Fam. 5. Spirulidae. Female with a single oviduct (right) and two nida-
mental glands. Shell spiral, coils not touching, multilocular, with internal
siphon, partly internal, enclosed in two lobes of the mantle ; it is coiled
ventrally (Fig. 339), i.e. in the opposite way to that of Nautilus. Without
rostrum and proostracum. Spirula Lam.; &'. Peronii Lam., Pacific Ocean,
probably abyssal.

Fam. 6. Belemnitidae. Arms with hooks, shell multilocular, straight,
probably internal, with rostrum and proostracum. Extinct. Lias to Cretaceous.
Belemnites Breyn.

Fam. 7. Sepiolidae. Body short, rounded dorsally ; fins rounded, inserted
somewhat on anterior surface of visceral sac, midway. Sepiola Leach ; JKossia
Owen ; Stoloteuthis Verrill ; Inioteuthis Verrill.

The Idiosepiidae (Idiosepius Steenstrup smallest cephalopod known) and
Sepiadariidae are allied here.

Fam. 8. Loliginidae. Body elongated, conical ; fins terminal, rhombic ;
pen lanceolate. Loligo Lam. , calamary ; the pens increase in number with age ;.
several are found in old specimens (Owen, in Todd's Cyclopaedia of Anatomy and
Physiology, vol. i. p. 546). Sepiotcuthis Blainville ; Loliolus Steenstrup.

Fam. 9. Sepiidae. Body flattened, broad ; fins narrow, elongated, shell
internal calcareous. Sepia L., cuttle-fish.

The families Sepiolidae, Loliginidae, Sepiidae constitute the group Myopsida
characterized by their unperforated cornea and single oviduct (left).

Sub-order 2. OCTOPODA.

With eight arms, without tentacular arms. The suckers are sessile. Eyes
relatively small, with sphincter-like lid. Shell absent. The heart does not
project into coelom. Oviduct paired. Nidamental glands absent. Funnel
without valve. Mantle without sucker-like apparatus for closing mantle-
opening.

446 MOLLUSC A.

Fara. 1. Cirrhoteuthidae. Arms united by a membrane and carrying on each
side of the suckers filamentous appendages ; radula absent ; deep water. Cirrho-
teuthis Eschricht.

Fam. 2. Amphitretidae. Mantle fused with funnel in median line, leaving
two openings into mantle-cavity. Amphitretus Hoyle.

Fam. 3. Octopodidae. Arms alike, more or less webbed ; often without fins.
Octopus Cuv. poulpe ; Scaeurgus Trosch. ; Eledone Leach; Pinnoclopus d'Orb.,
with fins ; Alloposus Verrill.

Fam. 4. Argonautidae. Female with a null ocular spiral shell (Fig. 335);
males very small ; hectocotylized arm autotomous (Fig. 355). Argonauta L.,
the paper-nautilus.

Fam. 5. Philonexidae. Hectocotylized arm autotomous ; other arms all
alike in the two sexes ; large aquiferous pores near the head and funnel.
Philonexis d'Orb.; Tremoctopus Delle Chiaje.

CHAPTER XI.

ANNELIDA.

Segmented worms in which the perivisceral cavity is a part of the
coelom. They almost all possess chitinous setae embedded in and
secreted by pits of the skin.

The Annelida include the segmented worms. They differ from
the Arthropoda, which in many respects they resemble, by the
possession of a perivisceral division of the coelom. In other words
the body-cavity is a part of the coelom. In this respect and in the
arrangement of the central nervous system, and in the wide-spread
occurrence of the trochosphere larva, they approach the Mollusca.
They differ, however, from the Mollusca in the fact that the body is
segmented. This segmentation, which is exhibited by a considerable
number of organs, proceeds from and is based upon the mesoblastic
somites in the embryo. The Annelida possess a dermo-muscular
body-wall; that is to say, muscular tissue enters largely into the
composition of the integument. In consequence of this fact the
body-wall is always extremely contractile, and the body shrinks
considerably when the animals are placed in spirit.

They all possess chitinous spines — the setae, which are secreted
by the ectoderm and are embedded in pits of the skin. These
setae are very conspicuous in the class Chaetopoda, less so in the
classes Hirudinea, Echiuroidea, and Archiannelida.

The alimentary canal is tubular, and generally straight : it opens
by a mouth which is placed on the ventral surface of the front end,
and by an anus which is terminal, or subterminal and dorsal.

The head consists of the anterior -part of the body, on the ventral
side of which the mouth is placed. It is divided, very often by a
mark, into a preoral portion — the prestomium — and a postoral portion,
which is called the peristomium. The prestomium is sometimes
called the first segment, but in the enumeration of segments the
peristomium is counted as the first (Fig. 358).

448

ANNELIDA.

"Whether the prestomium should be regarded as a segment or not is a disputed
question, and one which can only be settled by a study of development. Un-
fortunately Embryology speaks with an uncertain voice on this point in the
Annelida ; but from our knowledge of the Arthropoda
we are inclined to the view that the preoral part of the
body does contain at least one pair of mesoblastic somites
(or their equivalent) — the only real test of a segment —
which are serially homologous with the other somites.
This is clearly shown in the embryo of Peripatus, in
which the somites of the preoral region possess the rudi-
ments of a nephtidium, and send extensions into the
Z.— -6 preoral appendages called antennae ; just as the posterior
somites are prolonged into the legs.

The prestomium is sometimes quite small and
inconspicuous ; it may however be large and
much elongated into a proboscis-like organ, as in
Nais lacustris and the Echiuroidea. In some
cases it bears special sensory appendages called
tentacles and palps. It sometimes happens in
the Polychaeta that a certain number of body
segments are fused with the peristomium, forming
a secondary composite head.

The central nervous system consists of two
nervous tracts, mainly ventral and called the
nerve cords. These are generally closely approxi-
mated in the middle ventral line over the greater
part of their course, but sometimes they are

FIG. 358. — Anterior end
of Polygordius nea-

pciitanus, seen in widely separated (some Polychaeta sedentaria),

tinction between the
prestomium and
peristomium, and be-
tween the peristo-
mium and the next
segment is clearly

fhe difr and in the Echiuroidea the ventral parts of them
are fused to form a single ventral cord. But in
all forms, even in those in which there is com-
plete union between them behind, they separate
from one another in front, and embracing the
anterior Part of the alimentary canal become con-
tinuous with one another on the dorsal side at
the front end of the body. The ventral portions of these cords are
almost always swollen at segmental intervals into the so-called
ganglia, from which the nerves generally proceed, and there is
universally a single or bilobed swelling at the point where they
are continuous with one another dorsal to the alimentary canal. This
dorsal swelling (or swellings) is called the cerebral ganglion (or ganglia),
or brain : the nerves which pass out from it (or rather which enter
it) are the sensory nerves of the anterior end of the body, and of

ANNELIDA. 449

the important sense organs there located. The first swelling on the
ventral cord is called the sub-oesophageal ganglion, and the sub-
sequent swellings the ventral ganglia. The ganglionated condition
is not due to the exclusive presence of nerve cells at certain points,
for, as in the Vertebrata, nerve cells are found along the whole length
of the central organ; but is rather due to the fact that there are
more nerve cells and more nerve fibres in the ganglia than elsewhere,
in consequence of the fact that the nerve fibres do not as a rule
pass out all along the cords, but are gathered up into bundles, and
leave the ventral cords at any rate at segmental intervals. The
central nervous system is generally separated from the ectoderm
and placed within the muscular layer, but in the Archiannelida
and in one or two Chaetopoda it lies in and forms part of the
ectoderm.

A vascular system is nearly always, probably always, present. It
has a canalicular character, and the principal vessels are the dorsal
and subintestinal longitudinal vessels.

The perivisceral cavity is a portion of the coelom. It is derived
from the paired cavities of the mesoblastic somites of the embryo,
which swell up and surround the intestine. Primitively therefore
the body-cavity is divided into a series of paired cavities, the walls
of which are in contact with the walls of the somites anterior and
posterior to them in the series, and with the walls of their fellows of
the opposite side dorsal and ventral to the alimentary canal. Two
kinds of septa are thus formed, the one separating the cavities of
somites adjacent to each other in the series : these are the transverse
septa found running between the body-wall and the gut-wall in many
Chaetopoda ; and the other separating the cavities of the two somites
of a pair on the dorsal and ventral side of the alimentary canal :
these are the dorsal and ventral longitudinal mesenteries, which also
run between the body-wall and the gut-wall, but in a longitudinal
direction. These two kinds of coelomic septa are found coexisting
in the Archiannelida^ and possibly in one or two Chaetopods, but as
a general rule the dorsal and ventral mesenteries break down in the
adult, so that the two sides of the body-cavity become continuous
with each other on the dorsal and ventral sides of the alimentary
canal; while the transverse septa, though more often found in the
adult (Oligocliaeta and some Polychaeta), also generally break down
either partially or completely, so that the perivisceral cavity becomes
a continuous space from end to end of the animal (Echiuroidea, some
Polychaeta). In the Hirudinea the coelom generally (Acantliobdella

2 G

450 ANNELIDA.

excepted) becomes more or less broken up into a system of com-
municating spaces.

The renal organs, called nephridia, are portions of the coelom,
though this is not so obviously the case as in certain other groups
(e.g., Vertebrata, Peripatus, Mollusca). Still they almost always
retain a communication with the rest of the coelom in the ne-
phrostome or ciliated coelomic funnel (Cliaetogaster and one or
two other forms excepted). They almost always have a tubular
form, and open externally on 4he ventro- lateral surface of the
body. As might be surmised from the condition of the coelom
in the. embryo, they share in the segmentation of the body ; and,
moreover, with regard to them it should be noted that they very
rarely (Echiuroidea, Sternaspis, Chlorliaemidae) lose their relation to
the segmentation of the body. As a general rule there is a single
pair of nephridia in each segment, but this rule is sometimes departed
from in the Chaetopoda, where there may be more than one pair in a
segment (Perichaetidae, Acanthodrilidae, Capitettidae.)

In a few cases some of the anterior and posterior nephridia
shift their external openings from the outer surface of the body
into the anterior and posterior end of the alimentary canal. This
is seen in some Oligockaeta (so-called pepto-nephridia), and in the
case of one posterior pair in the Echiuroidea (anal vesicles).

The generative organs are always products of the coelomic walls,
being thickened patches of the coelomic epithelium. Occasionally,
in the male more often than in the female, the generative section
of the coelom is cut off from the rest by special membranes. This
is seen in the sperm-reservoirs of some Oligocliaeta.

The generative ducts open into the coelom, and have, of course,
a tubular character with ciliated internal openings. Sometimes
they are distinct from the nephridia (Oligochaeta), but, as a rule,
some or all of the nephridia are used for the exit of the generative
products, thus combining a renal and generative function. This
association of the generative and excretory functions in the carrying
apparatus is, of course, to be connected with the fact that these two
functions are discharged by the same organ, viz., the coelom ; it is
a feature characteristic on the whole of all coelomate animals (cf.
Vertebrata).

The Annelida are for the most part aquatic animals, but terrestrial
forms are known (earth worms).

Their eggs are sometimes laid, several together, in a cocoon
(Hirudinea and Oligochaeta), but, as a general rule they are

ARCHIANNELIDA. 451

deposited in the water, with but little more protection than is
afforded by the vitelline membrane.

In the former case the development is direct and there is no
larval stage, the development taking place at the expense of
albuminous matter, which is included in the cocoon. But in the
latter case the young undergo only a small part of their develop-
ment in the egg-membranes, and are hatched out as larvae at
an early stage, to undergo the rest of their development in
the free-swimming state. The larval form, most commonly, one
may almost say invariably, found, is that called the trochosphere,
This larval form, which we have already met with in Mollusca,
is fully described further on. The larva of Polygordius, which
is known as the larva of Loven, is a typical trochosphere (Fig. 360),
and the larvae of many Chaetopoda, and of Echiuroidea (Fig. 431),
are typical trochospheres.

The Annelida are classified as follows : —

CLASS 1. ARCHIANNELIDA.
„ 2. CHAETOPODA.

Order 1. Polychaeta.
„ 2. Oligochaeta.
CLASS 3. HIRUDINEA.
„ 4. ECHIUROIDEA (GEPHYREA ARMATA).

For reasons fully stated in the sequel, we have thought it
necessary to break up the old group Gephyrea, and to exclude
some of its divisions (Sipunculoidea, Priapuloidea, Phoronis) from
the Annelida. The Echiuroidea, however, we retain as being
obviously true Annelids.

Class I. ARCHIANNELIDA.*

Marine Chaetopoda ivithout setae or parapodia.

There are two genera in this order, Polygordius Schn. and Proto-
drilus Hatschek, the former found in sand of European seas, and
the latter in the sand of an inland sea-lake at Faro near Messina.
They are elongated and thread-like, and are entirely without setae
or parapodia. The head has two tentacles and two ciliated pits (Fig.
358). The segmentation is but faintly marked externally, by slight

* Fraipont, " Le Genre Polygordius," Fauna and Flora d. Golfes v. Neapel
xiv., 1887. Hatschek, " Protodrilus," Arb. Zool. InsL Wien, 3, 1881. Weldon,
"Dinophilus Gigas," Q. J. M. S., 1886, 27. Harmer, " Dinophilus," Journ.
Mar. Biol. Ass., New Series, 1, 1889. For a description of Polygordius see
T. J. Parker, Lessons in Elementary Biology, London, 1891.

452

ANNELIDA.

grooves in Polygordius, and by ciliated rings in Protodrilus. There
is a median ciliated groove extending along the ventral surface of
Protodrilus. The segmentation is homonomous and is marked by
the coelomic septa (Fig. 361, d). There are no circular muscles in
the body-wall.

The cerebral ganglion is in the preoral lobe, and the ventral
cords lie in the epidermis (Fig. 359), and are without ganglionic
swellings ; in Protodrilus they are separated, one being placed on each

FIG. 359. — Polygordius neapolitamts. b, dorsal view of head and anterior part of body,
showing the ciliated pits, c, hind end showing the last three segments, and the anal
segment with a circle of papillae, and the anus (after Fraipont).

side of the ventral groove; while in Polygwdius* they are fused.
There is in Polygordius a very short eversible buccal region followed
by an oesophagus, which does not extend beyond the head (peri-
stomial part). In Protodrilus there is a U-shaped muscular tube
placed ventral to, and opening into the oesophagus.

There is a dorsal and ventral mesentery, and oblique longitudinal
septa passing across the body-cavity on each side from the region

>,

* In Polygordius there is a fine canal in the ventral cord, which is said to be
a remnant of the ventral ciliated groove of the larva.

ARCHIANNBLIDA.

453

FIG. 360. — Transverse section through
the body of Protodrilus (after Hat-
schek). S, S the two ventral nerve
cords ; G ganglionic layer of the
same ; D alimentary canal ; N ne-
phridium ; M oblique muscular
sheets (transverse muscles); Ov
ova. The dorsal and ventral mesen-
teries are shown.

of the nerve cord to the lateral body-walls (Fig. 359), and in
Protodrilus the body-cavity is traversed by a sparse reticulum.

There is a pair of simple nephridia
in each segment, opening internally
into the preceding segment; the first
pair opens into the body-cavity of the
hinder part of the head in Protodrilus.

The vascular system consists of a
dorsal vessel in the dorsal mesentery, and
a ventral in the ventral mesentery, and
of connecting vessels. The blood is
red, yellow, or green, or colourless.

The generative organs are developed
from the coelomic epithelium, and are
discharged into the body-cavity. In
Polygordius* the ova probably escape
by rupture of the body-wall, and the
spermatozoa by the nephridia. Proto-
drilus is hermaphrodite.

The larva of Polygordius is known as Loven's larva. It is a
typical trochosphere (Fig. 361, a), and possesses a preoral ciliated
ring (Prw\ a weaker postoral ring (Pow), a thickening of ectoderm on
the preoral lobe — the apical plate, a ventral mouth, and a terminal
anus. There is a pair of mesoblastic bands at the hind end (Ms),
terminating in front in the larval kidney. This posterior part of the
body elongates, its mesoderm becomes segmented into somites; and
it gives rise to the body of the worm (Fig. 361, b, c). Later the
anterior end diminishes relatively in size, and becomes the head of
the adult (Fig. 361, d).

Saccocirrus Bobr. , f should probably be placed here. It is found in the Black
Sea and Mediterranean in shallow water on gravel, has a long (20 to 80 mm.)
and narrow body with a groove on its ventral surface. The segments are
numerous, and each of them, except the first, carries two dorso-lateral bundles
of simple setae. The preoral lobe has two long tentacles and two eyes ; between
the preoral and postoral part (buccal segment) of the head are two ciliated pits.
There are no parapodia, but the lower parts of the bundles of setae are enveloped
in a cutaneous sheath, which can be protruded or retracted into the body. The
setae are enlarged and grooved at their free ends. There are two characteris-
tically marked appendages at the hind end, on each side of the anus, by which

* In Protodrilus it is said that the eggs pass backwards through the meshes
of the body-cavity reticulum to a pore on the ventral side of the last segment
(Repiachoff).

t Marion and Bobretzky, Ann. Sci. Nat. (6), 2, 1875, p. 69.

454

ANNELIDA.

the animal fixes itself to the stones on which it creeps. The circular muscles
of the body-wall are less developed than the longitudinal. There are also
obliquely -placed muscular sheets passing from the ventral body -wall to the
lateral, and dividing the body-cavity into two lateral and one median chamber.
The insertion of these oblique muscles is associated with the division of the
longitudinal muscle into four bands — one dorsal, two lateral, and one ventral.

FIG. 361.— Development of Polygordius (after Hatschek). a, young trochosphere larva ; Sp
apical plate with pigment spots ; Prw preoral, Pow postoral ring of cilia ; 0 mouth ; A anus ;
Ms mesoderm ; Kn larval kidney (pronephros or head-kidney), b, older larva with commenc-
ing segmentation of the body, c, older stage ; the body is elongated and vermiform, and
segmented; HWk posterior circle of cilia; Af eye spot; F tentacle.

The ventral nerve cords are widely separate, and are placed, as is also the
cerebral ganglion, in contact with the ectoderm immediately beneath the ventral
insertions of these oblique septa. They are without ganglionic swellings.
There are two contractile vesicles at the base of the tentacles, which drive
a colourless fluid into the hollow tentacles and so distend them.

The oesophagus extends for thirteen or fourteen segments, and is followed

ARCHIANNELIDA.

455

-ff

by the intestine, which is dilated segmentally. Coelomic septa and dorsal and
ventral mesenteries are present. Of the vascular system a dorsal vessel in the
dorsal mesentery has been detected.

The sexes are separate, and the gonads are found in
all segments behind the fourteenth. The germ -cells
are developed from paired patches of the coelomic
epithelium on the posterior faces of the septa, and are
dehisced into the body-cavity, where they ripen. They
escape by the nephridia of the part of the body in
which they are contained.

The nephridia are simple tubes opening externally
close to the bundles of setae, and internally into the
preceding segment. In the male the nephridia of the
testicular segments are swollen near their openings,
and their terminal parts pass into small papillae which
project on the surface as small penes. These penes can
be retracted into penial sheaths. In the female there
are, in the ovarian segments, receptacula seminis ; they
are yellowish vesicles lying in the central chamber of
the body-cavity, and passing into a duct which traverses
the oblique muscles and the lateral chamber to open
on the ventral surface.

Histriodrilus* (Histrio'bdella van Ben.) formerly
classified with the leeches, is said to belong to the
Archiannelida. It is a small worm (1'4 mm.) parasitic
on the lobster, the eggs of which it devours. It has a
distinct cephalic region, and an externally segmented
body without setae. There is a pair of limbs on the
head, and another on the last segment. There are
cerebral ganglia and two ventral nerve cords which
are continuous with the epidermis and united in each
segment to form a ganglion ; there are about eight
segments. There is a muscular sub-oesophageal sac
armed with three chitinous teeth, and the alimentary
canal is ciliated. There are four or five pairs of
nephridia, the internal openings of which have not
been satisfactorily made out. The sexes are separate,
and the generative organs complicated. The ovaries
and testes are coelomic. A vascular system has not
been observed. The body-cavity is present, and there
are dorsal and ventral mesenteries. There are four
longitudinal bands of muscular fibres in the body-wall.

Aeolosoma\ Elirb., often included amongst the Oligo-
chaeta as the sole member of the sub-order Aphaneura,
must be placed wyith the forms of uncertain position.
It is a small (1-10 mm.), fresh-water transparent worm with a loose and
uncertain outline. The prestomium is ciliated ventrally, and bears a pair of
ciliated pits. The segmentation is ill-marked. There are four bundles of hair-
like setae on each segment behind the peristomium. The ectoderm contains

FIG. 361. — d, The young
Polygordius ; G cerebral
ganglion ; Wg ciliated
pit; Dalimentary canal.

* Foettinger, Arch. JBioL, 5, 1884, p. 435.

t Beddard, Monograph of Oligochaeta, Oxford, 1895.

456

ANNELIDA.

coloured gland-cells. The circular and longitudinal muscular layers are both
thin. Segmental coelomic septa are not present, except the septum between
the peristomium and the next segment. Dorsal pores and head pores are not
present. One pair of nephridia is present in each of the setigerous segments.
The alimentary canal consists of pharynx, oesophagus, and intestine ; and the
anus is at the hind end of the body. The central nervous system consists of
the cerebral ganglion, which is continuous with the ectoderm of the prestomium.
It is said that there is no ventral nerve cord. Generative organs are only
occasionally developed, reproduction generally taking place by fission. The
testis is median and unpaired, and lies in the fifth segment (the peristomium
being the first) ; the ovary is similarly placed in the sixth segment. There
are no generative ducts. The sperm escapes by nephridia, the ova by a
pore on the ventral side of the sixth segment. Spermathecae are small oval
sacs in segments 3-5. At sexual maturity there is a feeble clitellum on the
ventral surface of segments 5-7. The oviposition is unknown. One species
has the habit of encysting in a chitinous capsule. There are several English
species.

Aeolosoma differs from Oligochaets in the folloAving characters, some of which
point to Archiannelidan affinities ; the continuity of the cerebral ganglion with
the ectoderm, the absence of a ventral nerve
cord, the absence of generative ducts, the
cephalic ciliated pits, the absence of transverse
coelomic septa ; it resembles them in being
hermaphrodite and in having spermathecae
(which, however, are found in Saccocirrus).

It is possible that the marine genus Ctenodrilus
(Scharff. Q. J. M. S., 27) should be placed with
Aeolosoma. It has one row of comb-like setae
on each segment, the prestomium is ciliated on
its ventral surface, and bears two ciliated pits.
There is only a single pair of nephridia in the
peristomium, and only a single layer of muscles
— longitudinal — in the body- wall. The nervous
system, which consists of a cerebral ganglion and
ventral cord, lies in the ectoderm. The sexual
worm is unknown.

Dinophilus is a small marine worm found in
the Channel in the spring on sea- weeds. There
is a head consisting of preoral and postoral
portions, and a body consisting of five or six
segments, each marked externally by one or
two ciliated rings. The ventral surface is-
ciliated. The anus is posterior, and projecting
on the ventral side of it is a kind of tail-append-
age. The preoral lobe either possesses two ciliated
rings, or is uniformly ciliated : it also bears a pair
of eyes and some groups of stiff sensory hairs,
and a pair of ciliated pits.

The alimentary canal is straight and ciliated ; there is a ventral muscular
organ opening into the oesophagus like that of Protodrilus.

The nervous system consists of a ganglion in the preoral lobe, and a pair of

Fro 362.— Dinophilus gigas (after
Weldon). an anus; cp cephalic
pits; ci transverse ciliated
bands ; M mouth ; St stomach ;
sh cephalic sense hairs ; sh'
post- cephalic rings of sense
hairs placed close behind the
ciliary rings.

ARCHIANNEL1DA. 457

separated lateral nerve cords placed close to, though not in, the ectoderm. The
ventral cords are sometimes ganglionated segmentally.

The body-cavity is occupied (or traversed) by a network of connective tissue,
in which the genital cells appear to arise. The spaces of this network are
specially enlarged round the internal ends of the nephridia. There are no
septa, no dorsal and ventral mesentery, and no vascular system.

The nephridia are in five pairs, of which the posterior in the male communicate
by a ciliated funnel with the cavity of the testis. With the exception of this
fifth pair, the nephridia open on the sides of the ventral surface : they are
simple tubes which internally possess a large flame-shaped cilium, or a row of
small cilia which give the appearance of a flame ; it is uncertain whether they
open internally or not ; indeed it is uncertain whether we ought to speak of a
body-cavity at all in these animals. The part of the nephridia next the external
opening is ciliated, and no nuclei are distinguishable in connection with their
walls.

The animals are dioecious. The nephridia of the fifth pair are connected with
the testis internally and join together to open at the hind end of the body into
a vestibule, which opens externally in the middle ventral line ; they are dilated
near the opening, and constitute a pair of vesiculae seminales. There is a median
penis projecting into the vestibule. Spermatozoa are introduced into the female
by means of the penis which perforates the skin at any point of the surface, and
so introduces spermatozoa into the body- cavity. The ovaries like the testes
appear to arise from cords of the parenchyma, and the eggs when ripe probably
pass into a special median ventral passage in this parenchyma, which opens to
the exterior by a median pore at the base of the caudal appendage.

There appears to be a thin layer of circular muscles, and a pair of longitudinal
muscular bands just external to the lateral nerve cords.

Saccocirrus in many points of its anatomy closely resembles Polygordius and
Protodrilus, near which it may be provisionally placed. The principal point of
difference is the presence of setae — while the resemblances are numerous : the
ciliated pits, the uniformly segmented body, the oblique septa, the dorsal and
ventral muscles, the position of the ventral cords in the ectoderm. It clearly
resembles the two Archiannelidan genera far more closely than does Dinophilus
(see below), which is without coelomic septa, oblique septa, or vascular system,
and has a body-cavity extensively occupied by a reticulum, and nephridia of
doubtful relations. Moreover, the structure of the male and female generative
organs of Dinophilus is quite different from that of Archiannelids, with the
doubtful exception of the female Protodrilus, which needs reinvestigation on
this point.

It must be remembered that the sub-oesophageal muscular organ, upon which
so much stress has been laid as indicating affinity between Dinophilus and
Archiannelida, though present in Protodrilus, is altogether absent from
Polygordius.

The union of Histriodrilus with the Archiannelids is more fully justified,
but before finally deciding the matter AVC require more knowledge of the
generative organs and nephridia, and a re-examination of the vascular system.

In the present state of our knowledge the Archiannelida must
be regarded as having very much the same relation to the Chaeto-
poda as Chiton has to the other Gastropoda ; while, carrying on the
same comparison, Dinophilus and Histriodrilus occupy, relatively to

458 ANNELIDA.

the main group, a similar position to that assigned above to Neomenia
and Chaetoderma in the Molluscan phylum. They are isolated forms
with Annelidan affinities. As to Saccocirrus it seems clear that it
connects Archiannelids with such Polychaets as the Oplieliidae, in
which, though coelomic septa are absent, the oblique septa, predomin-
ance of the longitudinal muscles and in PolyoplitJialmus at least, if
not in other genera, the cephalic ciliated pits, and contiguity of the
ventral nerve cords to the ectoderm are noticeable characters.

•

Class 2. CHAETOPODA.

Annelids with conspicuous setae. The perivisceral cavity is in
many cases divided by septa.

The Chaetopoda include Polychaeta, in which the setae are
generally borne on parapodial processes of the body, which may be
fairly compared to the appendages of Arthropods, and the Oligochaeta,
in which there are no parapodia, the setae simply projecting from
the body-wall.

Order 1. POLYCHAETA.*

Marine Chaetopoda with numerous setae embedded in parapodia;
usually witli distinct head, tentacles, cirri and branchiae. They are
for the most part dioecious, and develop with a metamorphosis.

The Polychaeta are, with a few exceptions, marine Chaetopods,
in which the setae are numerous and borne upon special processes of
the body-wall called parapodia. The head, which is called the
prestomium, very generally bears tentacular appendages, while the
next segment, called the peristomium, is usually modified and may
be fused with one or two of the following segments. The alimentary
canal generally possesses an eversible buccal region, and a muscular
protrusible (not eversible) pharynx. The coelomic septa may persist,

* Audouin et Milne -Edwards, Ann. Sci. Nat., t. 27-30, 1832-38. Delle
Chiaje, " Descrizione e notomia degli animali sensa vertebre d. Sicilia citeriore,"
Napoli, 1841. Quatrefages, " Histoire Nat. d. Anneles," 1 and 2, 1865. Ed.
Claparede, " Annelides Chetopodes du Golf de Naples," 1868, and Supplement,
1870. Ehlers, "Die. Borstenwurmer" 1868. Johnston, "frit. Mus. Catalogue
of non-parasitical worms," 1865. Mclntosh, "British Annelida," Trans. Zool.
Soc., ix., 1877. Malmgren, "Nordiska Hafs-Annulater, " Ofversigt k. Vet. Akad.
Fb'rdhandlingar, 1865 and 1867. St. Joseph, "Ann. Polychetes des cotes de
Dinard," Ann. Sci. Nat. (7), 1, 5, 17, 20, 1886-94. Malaquin, Recherches sur
Us Syllidiens, 1893. Bobretzky et Marion, " Et. s. les Annelides du Golf de
Marseille, Ann. Sci. Nat. (6), 2, 1875. Mclntosh, "Report on the Annelida
Polychaeta," Challenger Reports, 1885, and numerous papers by E. Grube.
W. B. Benham, "Polychaeta," Cambridge Natural History, 1896. Meyer,
"Stud. lib. d. Korperbau der Anneliden," Naples Mitth., 7 and 8, 1887-8.
Pruvot, Arch. Zool. Exper. (2), 3, 1885.

POLYCHAETA. 459

but in a large number of cases partly or entirely break down and
disappear. As a rule there are no special generative ducts, and the
generative products, which are dehisced into the coelom, pass out by
any or some of the nephridia. A vascular system is present, except
in a few cases, in which its absence, though stated on good authority,
must be regarded as doubtful until renewed investigations of the
matter have been made. Some are free, but a large number inhabit
tubes which they manufacture or construct for themselves.

The body is generally elongated, and the internal segmentation
shown externally. The number of segments is usually considerable,
and in some cases is variable, increasing with age. The segments
may be all alike, or the body may be divided into two regions, often
called thorax and abdomen, which differ from one another in the
form of the parapodia, of the setae, and in other respects (Sabellidae,
Capitellidae, etc.). In some forms the hind end of the body is much
reduced, and may be without setae.

The head consists of the anterior part of the body, on the
ventral side of which the mouth is placed. It is almost always
divided by a mark into a preoral portion — the prestomium, and
a postoral portion, which is miscalled the peristomium. The pres-
tomium is often called the first segment, and the peristomium the
second; but in this work the peristomium is reckoned as the first.

The prestomium may be a well-marked structure, or it may be
much reduced, and hardly distinguishable from the peristomium
(Arenicola). In the Cryptocephala the prestomium is hidden by
the forward extension of the peristomium. The prestomium may
be without appendages, but it usually bears two kinds of sensory
appendages — the tentacles, which are attached dorsally and vary in
number from two to five, and the palps which are two in number
and ventrally placed (Fig. 363). It often bears one or two pairs
of eyes. The peristomium is, in rare cases, provided with parapodia
and setae, like the other segments (Aphrodite, Hermione, Nephthys) ;
usually it is without setae and parapodia, though the cirri are often
present as long, tentacle-like structures called tentacular cirri (Fig.
363, Fc). When there is more than one pair of tentacular cirri it
is supposed that one or more of the hinder segments have become
merged in the peristomium, and have lost their parapodia; in such
cases the head is a compound or secondary head, one or two body
segments having fused with the peristomeal.

The parapodia are segmental, hollow, lateral projections of the
body. They carry the setae and are either biramous or uniramous.

460

ANNELIDA.

When they are biramous the dorsal branch is called the notopodium,

and the ventral the neuropodium.

The acicula are especially strong, dark-
coloured setae, hardly projecting at all, and
deeply embedded in the parapodia (Fig. 364).
Typically there is one in the noto- and one
in the neuropodium; they serve for the
attachment of the muscles of the setae.
The setae are chitinous, and project in
groups from sacs on the parapodia; each
seta is formed by a single large cell at

PIG. 363.— Nereis inargaritacea the bottom of the Sac.

(after M Edwards). Head The form of the getae yaries extremely,

with everted mouth and pro- *

traded jaws (K). The small and affords a good character for the classifi-
^^±£X* <»*<* of families and genera. According
shown. The prestomium to the strength, form, and mode of ending

carries at its front end two ,-, f -,-, . f -i -,- • • • i a

tentacles F, and ventraiiy the following forms may be distinguished :
two palps p. The peristo- simple setae, which may be hair-like or

mium carries four tentacular

cirri FC on each side. flattened (paleae), or lance-shaped, or curved

at the end (crotchets), etc.; jointed setae

(composite), which carry a terminal articulated appendix (Fig. 365, g)
— found in the Nereidiformia ; uncini (a, b), setae with a sharply-

FIG. 364. — Section through a segment of a Polychaet, diagrammatic (from Lang), oc aciculum ;
1) setae ; bm ventral nerve cord ; dc dorsal cirrus ; dp notopodium ; k gill ; Im longitudinal
muscles ; md intestine ; np nephridium ; ov ovary; rm circular muscles ; tm transverse muscle ;
tr funnel of nephridium ; vc ventral cirrus ; vd dorsal, vo ventral vessel ; vp neuropodium.
There are ova in the body-cavity.

POLYCHAETA.

461

curved hook (Terebelliformia, Sabelliformia). When the parapodia
are completely wanting, the setae project from the body -wall
(Capitella).

K

a. c d f / m3

FIG. 365. — Setae of different Polychaeta (after Malmgren and Claparede). o, hooked setae of
Sabella crassicornis ; b, of Terebella Danielsseni; c, seta with spiral ridge from Sthenelais;
d, lance-shaped seta of Phyllochaetopterus ; e, of Sabella crassicornis ; f, of Sabella pavonis ;
g, composite, sickle-shaped seta of Nereis oultrifera.

The appendages of the parapodia present a great variety of form,
and not unfrequently vary in the different parts of the body. Most
important are the cirri, which are attached to the dorsal and. ventral
surfaces of the parapodia. The cirri are for the most part filiform,
and sometimes pointed ;

they may also be ringed. 1 , ft

In some cases the dorsal
cirri are flattened out as
broad scale-like structures
—the elytra (Fig. 366)—
which constitute a protec-
tive covering to the back
(Apliroditidae). In other
cases the dorsal cirri* are
modified as branchiae, which
may be filiform, branched
and antler - like, comb -
shaped, or in tufts ; some-
times they are confined to
the middle region of the
body (Arenicola, Fig. 397),

FIG. 366.— Anterior end of Polynoe extunuata, the first
elytron on the left hand being removed (after
Claparede). The two setae of the oral segment aie
visible. El elytron.

* It sometimes happens that cirri are found on branchiferous segments, in
which case the gills must be regarded as additional to cirri.

462

ANNELIDA.

or are extended almost across the whole dorsal surface (Euphrosyne) •-.
sometimes they are confined to the anterior segments immediately
following the oral segment (Terebelld)* Both cirri, or one of them,
may be altogether absent.

The last or anal segment is always modified : the parapodia and
setae are absent, but one or two pairs of cirri — the anal cirri — are
present. The anus is usually terminal; in Notopygos it is dorsal,
and in Caobangia it is anterior and ventral.

The alimentary canal is usually straight (coiled in Pectinaria,
Sternaspis, SipTionostoma, etc.) ; it is divided into buccal cavity,
pharynx, oesophagus, and intestine. The buccal cavity has muscular
walls, and is often eversible, while the pharynx which also has
muscular walls is often protrusible (Figs. 363 and 367). The buccal
cavity has a chitinous lining, which may be thickened at certain

m,

FIG. 367.— Diagrammatic representation of the pharyngeal apparatus of a predatory Chaetopod.
g brain; fc jaw; m mouth ; ph pharynx; pt protractor muscles ; rt, ct retractors ; vt wall of
buccal cavity (eversible) with papillae or denticles p. In A the apparatus is retracted, in B
protruded. (After Lang.)

spots into denticles, and the pharynx is often armed with powerful
and movable chitinous jaws or plates. These structures, however,
are not always present (e.g. Terebellids and Sabellids) ; they are well
developed in the Nereidiformia. The oesophagus is often provided
with a pair of diverticula, which in some Syllidae and Hesionidae
contain air. The intestine reaches to the anus, and is constricted
segmentally. In the Apliroditidae the sacculations are elongated
into caeca (Fig. 368). In Syllids and some Terebellids there is a
muscular gizzard with a hard chitinous lining. In the Capitellidae
there is a siphonal tube leaving the intestine in front, and entering it
again behind.

The nervous system is constructed on the typical Annelidan plan.
It is sometimes in contact with the epidermis, though more often
separated from the skin. The cerebral ganglion is contained in

* The cephalic branchiae of the Sabelliformia are palps not cirri.

POLYCHAETA.

463

Ph

the prestomium, and the eyes, when present, are often sessile upon

it. The ventral cord is double, and the two halves are usually

closely approximated, though in some Sabelliformia (Serpulidae)

they are widely separated (Fig. 369),

especially in front, and connected together

by transverse commissures which pass

between the ganglionic swellings. These

latter are segmental, the first or sub-

pharyngeal being often contained in the

third segment, and the nerves are given

off from them. In some forms, e.g.

Arenicola, the ganglionic enlargements

are very inconspicuous. A stomatogastric

or visceral system is given off from the

cerebral ganglion, or from the circum-

pharyngeal commissures, or from both.

Giant fibres are often present on the

dorsal side of the ventral cords. The

nerves to the palps arise from a special

section of the cerebral ganglion ; the

nerves to the tentacular cirri come off

from the subpharyngeal ganglion, and

sometimes from the circum-pharyngeal

commissures as well. The subpharyngeal

ganglion, which also supplies the first-

parapodium, seems, as a rule, to consist

of the ganglia of two or more segments

fused.

Sense organs. The tentacles, palps,
and tentacular cirri must be regarded as
tactile organs ; and the ciliated pits which
are often present on the prestomium and abut upon a special lobe of
the brain (Capitellidae, Oplieliidae, Arenicola, etc.) as olfactory. In
addition to these we sometimes find otocysts in the prestomium
(Arenicola and Polyophthalmus), or in some other segment of the
body (Fabrida, Myxicola, Terebella), or even segmentally repeated
in the dorsal regions of a certain number of segments (Aricia).
In some species of Arenicola they retain the opening to the
exterior.*

In the Capitellidae groups of sensory cells bearing sense-hairs are

* Ehlers, Z.f. w. Z., Sup. Bd. 53, 1892.

FIG. 368.— Alimentary canal of
Aphrodite aculeata (after M.
Edwards). Ph pharynx; D
intestine ; L intestinal (hepatic)
caeca.

464

ANNELIDA.

found on the lateral portions of the segments, and are called the
lateral line organs.

The pigmented bodies, called eyes, and occurring in pairs on some
of the segments of PolyopTithalinus, are probably photogenic organs.

Eyes.* Paired eyes are often present on the prestomium, especially
in the free-living forms; but they are also found in other places,
e.g., the anal segment (Myxicola, Fdbricia), the gills of some
Sabellids (Branchiomma, Dasychone). The cephalic eyes attain a
large size and complex development in the pelagic Alciopidae^

a

FIG. 369. — Brain and anterior portion of the ganglionic chain of a, Serpula ; b, Nereis (after
Quatrefages). 0 eyes; G cerebral ganglion (brain); c oesophageal (or pharyngeal) com-
missures ; Ug suboesophageal ganglion ; e, e' nerves to the tentacular cirri and peristomium.

where they have a large lens and a complex retina (Fig. 389). In
most forms the prestomial eyes are simple cups of the epidermal
layer, which may be open or filled by a substance continuous with
the outer cuticle and constituting a lens, as in the eye of some
Gastropoda (vide Fig. 290, B).

The vascular system is constructed on the usual type ; there are
dorsal and ventral contractile vessels giving off vessels to the skin
and internal organs. In some forms there is a continuous blood
sinus round the intestine instead of the usual capillary plexus

* E. Andrews, " Eyes of Polychaetous Annelids," Journ. Morph. 7, 1892,
p. 169.

t Greef. " Ub. d. Auge d, Alciopiden," etc., Marburg, 1876.

POLYCHAETA. 465

(Terebellids, Cryptocephala, etc.). The blood is usually red, owing
to the presence of haemoglobin in solution; but in some forms
(ClilorJiaemidae, and some SabelUformia) it is green, owing to the
presence of a green pigment called chlorocruorin. In Aphrodite
the blood fluid is yellow, and in Magelona it is pink, owing to
the presence of a pigment called liaemerytTirin. The vascular system
is said to be absent in the Glyceridae, Capitellidae, Polycirrus, and
Tomopteris.

The respiratory function is discharged by the gills (see above),
and probably by the whole surface of the skin.

The perivisceral cavity (coelom) is well developed, and is
frequently divided by transverse segmental septa into chambers,
but in some of the tubicolous forms the septa are deficient, many of
them being absent. Muscular bands pass from the median ventral
line, where they are inserted on each side of the nerve cord obliquely
dorsally and outwards, where they spread out in a fan-like manner to
be inserted into the dorso-lateral body-wall. They divide the body-
cavity more or less completely into three regions, two lateral, and a
median containing the alimentary canal (Fig. 364). The coelomic
fluid contains amoeboid corpuscles, and is usually colourless ; but in
the Glyceridae, Capitellidae, Polycirrus, the coelomic corpuscles are
coloured with haemoglobin.

Median dorsal and ventral mesenteries passing from the body-wall
to the gut- wall, and dividing the body-cavity into a right and left
half, are present in some forms (Capitellidae, Sabella, etc.).

Excretory organs. In many Polychaets the nephridia occur in all
the segments except a few of the anterior and posterior ; but in some
they are reduced in number, e.g., to six pairs in Arenicola, one pair
in Sternaspis, and one or two pairs in Chlorhaemidae. In the
Capitellidae there may be more than one pair in a segment, and a
single nepliridium may have more than one internal opening ; more-
over, adjacent nephridia may be connected together.

The nephridia of Polychaets are either long convoluted tubes
(e.a., Nereis, Fig. 370) with a small internal funnel, or short and
wide tubes (e.g., Arenicola, Fig. 371) with a wide funnel. The
nephridia of the former kind cannot serve as escape-ducts for the
ova, and it becomes a question, in animals which possess them alone,
how the eggs pass outwards.* In some tube-dwellers one or more

It is possible that the dorsal ciliated organs of Nereis, which occur in pairs

atche
Dodri<

2 H

in most of the segments as ciliated patches of coelomic epithelium, may really
have undetected external apertures (Goodrich, Q.J.M.S., 34, 1893.)

466

ANNELIDA.

pairs of the anterior nephridia become much enlarged as renal organs,
while the nephridia of the posterior part of the body become much
reduced, and serve as genital ducts.

Reproductive organs. The Polychaets are mostly dioecious, but
a few are hermaphrodite (some Sabelliformia, e.g., AuipMglena,

nepti.p.

FIG. 370. — Nephridium of Nereis (after Goodrich, diagrammatic). The nephridial tube opens
internally at neph.fun., externally at nepli.p., and is divided into four regions; p. s. can.
postseptal canal.

Salmacina, Protula, Spirorbis, and some Hesionidae). The gonads,
which are differentiations of the coelomic epithelium, are not so
narrowly localized as in OUgochaeta, but are more diffused over the
body — on the walls of blood vessels, on the intestinal wall, or even
on the body-wall.* The products, when ripe, are dehisced into the

k.

FIG. 371.— Nephridium of Arenicola marina (after Vogt and Yung). « vesicle ; b glandular
appendage ; c funnel ; d lower, e upper lip of funnel ; / opening of funnel into the vesicle ;
g nerve cord ; h longitudinal muscles ; i line of insertion of setae ; k setigerous sacs ;
I aggregation of reproductive cells.

* Cosmovici, Arch. Zool. Expcr., 8, 1879-80.

POLYCHAETA.

467

body-cavity, where they ma-
ture; they eventually escape
either by rupture of the body-
wall, or through the nephridia.
There are no special generative
ducts. Only a few Polychaets
are viviparous (e.g., Syllis
vivipara Kr., Marphysa san-
guinea Mont., etc.) ; all the
rest are oviparous; many lay
their eggs in a jelly (Aricia,

FIG. 372. — A parapodium of Tomopteris with a
mass of ova Ov, and one free ovum (after
Gegenbaur).

FIG. 373.— Different forms of Nereis
dumerilii (after Claparede, from Per-
rier). 1, young form ; 2, heteronereid
female ; 8 heteronereid male.

Ophelia, Phyllodoce), others attach
them to their own body, e.g., to the
back beneath the elytra (Polynoe
cirrata), to the dorsal or ventral
cirri (Exogone), in a ventral brood-
sac (Autolytus), in the operculum
(Spirorbis), or in various tubicolous
forms to the tube.

Polymorphism. The forms for-
merly placed in the genus Hetero-
nereis have been shown by Malmgren
to be merely the sexually mature in-
dividuals of certain species of Nereis.
The genus has consequently been
given up, but the name has been
retained to denote the sexual phase
in the life-history of these Nereids.

The changes which the worms
undergo in passing from the imma-
ture condition to the mature Hetero-
nereid condition chiefly affect the
posterior part of the body in which
the generative organs are contained;
in this part (Fig. 373) the parapodia
become larger and acquire flattened
foliaceous outgrowths, while the setae
are thrown off and replaced by new
setae of a flattened form and a fan-
like arrangement. Moreover, the eyes
become enlarged, the dorsal cirri

468 ANNELIDA.

altered, and the animal passes from a creeping to a free-swimming
existence. Further, there is a sexual dimorphism, inasmuch as the
sexually mature male is more altered from the immature form than
the female, having fewer unaltered anterior segments.

In Nereis dumerilii Claparede has shown that there is a still
more remarkable phenomenon of the same kind. In this species
it appears that there are four distinct sexual forms, differing from
one another in size, form, mode of life, etc.; they are (1) a sexual,
dioecious Nereis form, distinguished by its small size; (2) a sexual
hermaphrodite Nereis form; (3) a dioecious Heteronereis which is
small, and swims on the surface ; (4) a dioecious Heteronereis which
is larger, and creeps on the bottom. It is not known how these
forms are related to each other.

In the Syllidae phenomena of a very similar kind have been
observed, and there is a Heterosyllid sexual condition in which
the posterior sexual segments acquire a dorsal bundle of specially
long setae; but in this family the phenomenon is often accom-
panied by asexual reproduction, which we will now proceed to
consider.

Asexual reproduction. The power of asexual reproduction is
closely associated with the power of reproducing lost parts, and with
the power of indefinite growth, i.e. of growth after the adult
condition has been attained. In many Polychaetes the number of
segments continues to increase throughout the life of the animal by
the addition of new segments between the penultimate and anal
segments ; and in most, if not in all of them, the power of repro-
ducing lost parts is very extensive. For instance, in many of them
it has been observed that if the body be cut into two parts, the
anterior part will produce a new hind end, and the posterior part
a new head.

These two phenomena — the reproduction of lost parts and the
protracted formation of new segments — are both instances of the
phenomenon of budding, and it is not surprising to find reproductive
gemmation normally occurring in the group.

The simplest cases are those in which a zone of fission is formed
between two segments, which becomes differentiated into an anal
region for the part of the worm in front, and a cephalic region
for the part of the worm behind. This results in the division of
the worm into two (Salmacina dysteri, Filigrana implexa). Sexual
reproduction does not appear to take place in a worm undergoing
fission.

POLYCHAETA.

469

In some genera of the Syllidae the process is more complicated.*
The Heterosyllid condition is assumed (Fig. 375, /), and the worm
divides into an anterior non-sexual portion, and into a posterior
sexual portion (Fig. 375, //), which after separation acquires a new
head, and becomes an independent male or female worm. The
anterior non-sexual portion develops after separation new anal

FIG. 374. — Autolytus
cornutus, with the
male animal Polybos-
trichus (after A.
Agassiz). .Ftentacles;
CT tentacular cirri
of the asexual worm;
/ tentacles ; ct tenta-
cular cirri of the male
Polybostrichus.

FIG. 375.— Diagrams illustrating the asexual
reproduction of different Chaetopods. I,
the heteronereid or heterosyllid stage ; A
non-sexual anterior part ; B posterior sexual
part. //, the posterior sexual part is
separating from the anterior non-sexual
(Syllis hyalina). Ill, the same in Autolytvs,
the hinder zooid develops a head before
separation. IFand V budding in Autolytus,
Myrianida, etc. , in which the zone of fission,
after producing the head of the sexual worm,
persists (Z), and gives rise to a chain of
sexual zooids (C, D). Altered from Benhain.

segments, which eventually acquire generative organs and Hetero-
syllid setae, and in their turn separate from the anterior portion to
form an independent sexual worm, male or female ; in this case the
two sexes are similar. In some cases the sexual form may never

* Schizogamy is the name given to that method of reproduction in which a
sexual worm is produced by fission (fissiparous) or by gemmation (gemmiparous)
from a sexless worm ; in other words, schizogamy is synonymous with meta-
genesis.

470

ANNELIDA.

develop a head, but as a rule it develops a head, and is then known,
according to the characters of the head, as the Tetraglena, Chaeto-
syllis, Syllis arnica, or loda.

In Autolytus (Fig. 375, ///) the process is still more complicated,

ci

cs

S.66

FIG. yi&.—Myrianida fasciata. 1, sexless budding form with a chain of 29 budded sexual
forms. #, male form produced by budding, and called Polybostrichus. 3, a female form,
called Sacconereis. am unpaired antenna ; al lateral antennae ; ap posterior lateral antennae ;
ci,'cs, ct tentacular cirri ; cp terminal cirri ; cd dorsal cirri ; Se sexless zooid ; so ovigerous
sac ; y, y' eyes"(after Malaquin, from Perrier).

POLYCHAETA. 47 1

for the formation of the new segments begins before the two parts of
the worm separate, so that the posterior sexual worm acquires its
head while still attached to its sexless nurse. In other words a zone
of fission is formed, and this zone may produce not only the^head of
the hinder worm, but a number of segments which become marked
out into a series of zooids in which genital organs eventually appear.
In this way a chain of sexual zooids, attached to the asexual "scolex"
in front, is formed; the zooids are all of the same sex, and the
posterior of them is the oldest and most developed (Fig. 375, IV, V).
The male zooids differ very remarkably from the female, and were
formerly relegated to a distinct genus called Polybostrichus (Fig. 374),
the female being known as Sacconereis and characterized by the
possession of a ventral brood-sac. In this case we have a combina-
tion of fission, by which the first -formed zooid is formed, and
gemmation, by which the succeeding worms are formed from the
segments successively budded off at the zone of fission.

In Myrianida a very similar process takes place, and a chain of
sexual zooids attached to an anterior sexless zooid is formed ; in this
case, however, there is no fission, but gemmation only from a zone of
fission, for none of the segments of the original worm, except the
anal, enter into the constitution of the first formed sexual zooid;
the process starts with the formation, in the gemmiparous zone
between the penultimate and anal segment, of new segments, which
give rise successively to the first formed and all subsequent zooids
of the chain. In this case, as in Autolytus, the males and females
are never formed on the same stock, and are distinguished as
Polybostrichus and Sacconereis forms (Fig. 376). Moreover, in each
zooid there is a region in which new segments are formed, so that
the posterior and oldest zooid of the chain is also the largest.

Syllis ramosa — a form obtained by the " Challenger " in the canal-
system of an Hexactinellid sponge — possesses the peculiar property
of forming lateral buds, which may themselves produce buds before
separation : in this manner a branched colony arises, some of the
individuals of which develop genital organs, and probably become
free.

Almost all Polychaets are marine, but a few fresh-water forms
are known, e.g., a Nereis and Lumbriconereis from Trinidad (Kennel),
Manayunkia in N". America (Leidy). A few are parasitic, e.g.,
Olic/ognatlius bonelliae (one of the Eunicidae) in the 'body-cavity
of Bonellia ; Labrorostratus parasiticus, another Eunicid, in the
body-cavity of Odontosyllis ctenostomatus ; larvae of the Alciopinae

472

ANNELIDA.

in the Cydippidae. Many are commensals, living in the tubes
of other worms, and in the ambulacral grooves of starfishes; this
is especially common with the Polynoids. A few are pelagic, e.g.,

Alciopidae, some
Pliyllodocidae,
Tomopteris, Typh-
loscolex, and some
sexual Nereids
and Syllids (He-
teronereids and
Heterosyllids). A
few are borers,
e.g., Polydora
ciliata in chalk,
limestone, shells,
etc., Sdbella saxi-
cava, etc.

The majority
are littoral, but
they are found at
all depths to 3000
fathoms. They
either live freely,
creeping on the
bottom, or inhabit
tubes. The tube
is formed of
mucus which is
secreted by the
ventral gland-
shield, or other
glands. The mu-
cus hardens to

form the tube, which may be strengthened by the incorporation of
mud, sand-grains, or pieces of shell, which are actively collected for
the purpose by the animal itself. In the Serpulids the tube is
fortified by the presence of calcareous matter secreted by the animal.
Some worms are phosphorescent, e.g., Chaetopterus, many Poly-
noids, Syllids, Terelellids, etc., and probably Tomopteris by special
organs on the parapodia, and PolyophtTialmus by the so-called
segmental eyes.

FJG. 877.— Part of a stock of Syllis ramosa (somewhat diagram-
matic, after Mclntosh, from Korschelt and Heider). d intestine
which branches through the entire stock. The stock is injured
in some places.

POLYCHAETA.

473

The Polycliaeta are found fossil from the Silurian onwards.

Development. There are two main types of embryonic develop-
ment met with in this group. In one of them the ovum is small
and has little food-yolk, the gastrula arises by invagination^ and the
blastopore remains open as the mouth (Eupomatus tirficinatus,
Pomatoceros triqueter) -, in the other the ovum is larger and has
more food-yolk, the gastrula arises by epibole, and the blastopore
closes (Psyymobranclius protensus, Nereis cultrifera, etc.). In all
cases hatching takes place at ah early stage, and there is a prolonged
period of larval life. The larva has the trochosphere form, which
has already been described in the case of Polygordius (p. 453), or
a form which can be readily reduced to that of the trochosphere.

The trochosphere of the marine Chaetopods presents two distinct
types: (1) larvae in which there is an extremely large blastocoele,
i.e., space between the ectoderm and endoderm, derived from the

FIG. 378.— Atrochal larvae. A, of Lumbrico-
nereis (after Claparede and Metsclmikoff) ;
B, of Sternaspis scutata (after Ve.jdovsky).
cu cuticle ; d intestine ; ent endoderm.

FIG 379.— Mesotrochal larva
of Chaetopterus pergamen-
taceus (after Wilson), m
mouth.

segmentation cavity of the embryo; (2) larvae in which there is no
blastocoele, the ectoderm and endoderm being in contact except
where separated by the larval mesoderm.

Larvae of the first type, in all cases in which their embryonic
development is known, proceed from embryos with an invaginate
gastrula, i.e., from embryos which develop on the type first
described. The best known instances of this larval type are
afforded by Eupomatus, Pomatoceros, and Polygordius (Fig. 454).

In like manner larvae of the second type, in all cases in which
the embryonic development is known, proceed from embryos with
an epibolic gastrula. As instances of this larval type, the larvae
of Psygmobranchus, Nereis, etc., described by Salensky, may be

474

ANNELIDA.

mentioned. The larva of Lopadorhynchus (Kleinenberg) is of this

type, but its embry-
onic development is
unfortunately not
known.

In the larvae
cilia are rarely dis-
tributed over the
whole surface of
the body (Atrocha,*
Fig. 378). They
are usually confined
to special rings.
Sometimes, as in
Loven's larva, there
is one row placed
in front of the

FIG. 380. —Larvae of PolycJiaeta (after Busch.). a, larva of berets. mouth at some dis-
F tentacle ; Oc eyes ; PrW preoral ring ; 0 mouth ; A anus. tance from the an-
b, mesotrochal larva of Chaetopterus ; Wp circles of cilia.

terior end of the
body (e.g., larva of Polynoe, etc.). Sometimes there are two rows,

FIG. 381. — Lateral view of Mitraria larvae (after Metschnikoff, from Balfour). an anus ;
b and br the processes carrying the provisional setae ; m mouth ; pr.b preoral ring ; sg apical
plate.

* Cf. E. Claparede and E. Metschnikoff, " Beitrage zur Entwickelungsgesch.
der Chaetopoden," Z.f. w. Z., 19, 1869.

PHANEROCEPHALA.

475

one at each end of the body, constituting a
preoral and perianal ring (Telotrocha, e.g.,
Spio, Nephthys larva). In addition to these
two rings of cilia, incomplete rings jnay also
be present on the ventral surface (Gastro-
trocha), or both ventrally and dorsally
(Amphitrocha). In other cases one or more
rows of cilia surround the middle of the
body (Mesotrochd), while the terminal rings
(preoral and perianal) are absent, e.g., Chae-
topterus larvae (Fig. 379). Many larvae are
provided with long pro-
visional setae, which are
later replaced by permanent
structures, e.g. , the Mitra-
ria larva (Fig. 381), and
the larva of Nerine, etc.
In some cases the larvae
have true mesoderm seg-
ments, each of which is
provided with a ring of
cilia (Polytrocha, Fig. 383).
In spite of their great
diversity of form the Chae-
topod larvae can in their
later development also be

reduced to the type of the larva of Loven (larva of Polygordius,

Fig. 454).

Branch A.* PHANEROCEPHALA.
Prestomium free and exposed, generally with eyes, tentacles, and

palps. The body segments are more or less alike.

Sub-order 1. NEREIDIFORMIA.

With well-developed tentacles and palps ; the peristomium generally
possesses cirri. The parapodia are well-marked locomotor organs,
supported by acicula ; they carry dorsal and ventral cirri. The
setae are usually jointed ; uncini are never present. There is an
•eversible buccal region and a muscular pharynx, which is usually

* The classification here adopted is that of Dr. W. B. Benhara in his
admirable account of the Polychaeta in the Cambridge Natural History,
Worms, Rotifers, and Polyzoa, Macmilkn & Co., London, 1896.

FIG. 382.— Annelid larva
with provisional setae
(after Agassiz, from Bal-
four) .

FIG. 383. — Polytro-
chal larva of Oph-
ryotrocha puerilis
(after Clap, and
Metsch.). d intes-
tine; /ojaws.

476

ANNELIDA.

armed with chitinous jaws (Fig. 367). The septa and nephridia are
regularly repeated throughout the body. For the most part preda-
ceous; a few form tubes.

Fam. 1. Syllidae. Small worms with elongated, flattened body ; head
usually with three tentacles, palps, and two to four tentacular cirri. The palps
are often fused with each other, or with the prestomium. Parapodia with a
single setigerous branch (neuropodium), often with a dorsal and ventral cirrus ;
the dorsal cirrus always appears with sexual maturity. Following the pharynx,
which has one or more teeth, is a special gizzard with thick muscular walls.
The oesophagus receives in many gener% a pair of T-shaped diverticula. Sexual
and asexual forms are sometimes found in the same species. Many carry their
eggs about till the young are hatched. Syllis Sav., tentacles and cirri monili-
form, three tentacles ; Odontosyllis Clap. ; Trypanosyllis Clap. ; Sphaerosyllis
Clap. ; Grubea Clap. ; Syllides Oersted ; Paedophylax Clp. ; Anoplosyllis Clp. ;

Eusyllis Mlg. ;
Pionosyllis Mlg. ;
Pterosyllis Clp. ;
Exogone Oerst.
Autolytus Gr. ,
palps small, and
fused with pre-
stomium, no ven-
tral cirri ; A.
prolifer 0. F. M.,
asexual form, the
male has been
described as Poly-
bostrichus Miilleri
Kef., the female as
Sacconereis helgo-
landicaM.\i\].(Fig.
384) ; Proceraea
Ehlers. Myrian-
ida M. Edw. ; M.
fasciata M. Edw.,
with foliaceous
cirri (Fig. 376).
The position of Ne-
rillaO.Sclim.(2)u-
jardinia Clap.) is
uncertain.

Fam. 2. Sphae-
rodoridae. Dorsal
and ventral cirri
spherical. Sphae-
rodorum Oerst.

FIG. 384.— The two sexes of Autolytus prolifer. 1, female carrying its (Pollicita Johnst. )
sac of eggs (Sacconereis helgolandica Miiller). 2, male (PolylostricMs Efihesia Rathke
Miilleri Kef.), a antennae ; b first pair of dorsal cirri ; c bifurcated ^— .'

palps of the male ; d normal dorsal cirri ; e median antenna of male ;
/ tentacular cirri. (From Perrier.) nidae. Body

NEREIDIFORMIA.

477

FIG. 385.— Hesione splendida Sav. (Regne Animal).

short, with only a few segments ; prestomium with 4 eyes, 2 or 3 tentacles,

and generally with jointed palps ; peristomium and 2 or 3 following segments
'•achaetous, with long tentacular cirri. Parapodium usually uniramous, or, if

biramous, notopodium small, dorsal cirri long and multi-articulate. Eversible

region short, pharynx long, unarmed ; two diverticula behind pharynx often

containing air (air-bladders*).
Anal segment with two cirri,
and often with reduced para-
podia. Hesione Sav. (Fig.
385); H. sicula, D. Ch.,
Med. ; Psamathe Johnst. :
Tyrrliena, Clp. ; Telamone
Clp. ; Stephania Clp. (Ophio-
dromus Sars) ; Dalhousia
M'Int. ; Salvatoria M'Int. ;

Magalia Mar. and Bob.; Oxydromus Gr. ; Kefersteinia Qtf.

Fam. 4. Aphroditidae. With broad scales (elytra, i.e., flattened dorsal

cirri) on the notopodia ; these are usually placed on alternate segments, often

only on the anterior part of the

body. Prestomium with eyes, with

one unpaired and usually two lateral

tentacles, to which may be added

two palps. Facial tubercle in front

of mouth. Pharynx thick-walled,

with two upper and two lower jaws.

The intestine is provided with a

number of paired caeca. Very com-
monly as epiparasites on other

animals, e.g., Malmgrenia castanea

M'Int, in the mouth of Spatangus

purpureus ; Hermadion assimile

M'Int., round the peristome of

Echinus esculentus, Halosydna

Bairdi between the mantle and foot

of Fissurella craiitia ; Acholoe asteri-

cola Clp. in the amubulacra of Astro-

pecten, Polynoe cirrata in those of

Spatangus spinosissimus, Hermadion

echini in those of Echinus sphaera;

.Evarne pentactes Giard on the body

of Cucumaria pentactes ; or as com-
mensals with other Annelids, e.g.,

Lagisca extenuata in the tube of

Serpula vermicularis, Harmothoe

macleodi in the tube of Terebella

conchilega, Polynoe scolopendrina in

the tubes of Terebellids, Harmothoe

Malmgreni, and Nychia cirrosa in

the tubes of Ghaetopterus insignis

( 1 variopedatus).

FIG. 386. — Aphrodite aculeata Baster (Regne
Animal).

* H. Eisig, Mit. a. d. Zool. Stat. Neapel, 2, p. 255.

478

ANNELIDA.

Sub-fam. 1. Hermioninae. Body short, oval; notopodial setae directed
upwards and backwards to protect the elytra. Prestomium with median
tentacle and two long palps, without lateral tentacles. Peristomium
setigerous with long cirri. Elytra on segments 2, 4, 5, 7, 9, etc., up to 23,
then on every third segment. Jaws not hardened. Aphrodite L. (Fig. 386),
the back and elytra are covered by a feltwork of
chitinous threads arising from the notopodium. A.
aculeata L., the sea-mouse (Hystrix marina Redi), the
strong notopodial setae are iridescent, Atlantic and
Med. ; Hermione Blainv. (Laetmonice Kinb.), dorsal
feltwork abs»nt ; Pontogenia Clp.

Sub-fam. 2. Polynoinae. Elytra as in Hermio-
ninae ; two lateral frontal tentacles, with or without
facial tubercle ; peristomium with long dorsal and
ventral cirri, and the ventral cirri of the next segment
elongated. Large teeth on the pharynx. Polynoe Sav.
(Fig. 387), with three tentacles, posterior region often
without elytra ; P. scolopendrina Sav. ; P. (Harmothoe]
areolata Gr., in the tubes of Chaetopterus and Terebella
nebulosa ; Iphione Kinb. , two tentacles ; Lepidonotus
Leach ; Halosydna Sars ; Lepidasthenia Mgr. ; Lepi-
dametria Webs. ; Nychia Mgr. ; Dasylepis Mgr. ; Har-
mothoe Kbg. ; Leucia Mgr. ; Lagisca Mgr. ; Hermadiou
Kbg. ; Enipo Mgr. ; Melaenis Mgr. ; Bylgia Theel ;
Acholoe Clp. ; Malmgrenia Mclnt. ; Eupolynoe Mclnt. ;
Polyeunoa Mclnt.; Allmaniella Mclnt.

Sub-fam. 3. Acoetinae. Long vermiform body. The elytriferous segments
alternate regularly with segments bearing dorsal cirri throughout the body.
With two pedunculated eyes, without facial tubercle. Three tentacles.
AcoetaM.-~Ed\v.; EupompeKinb.; Polyodontes Renier ; Panthalis Kinb.

FIG. 387.— Polynoe setosis-
simaSav.(RegneAnhnal).

FIG. 388.— Phyllodoce Paretti Blv. (Regne Animal).

Sub-fam. 4. Sigalioninae. Long vermiform body. Elytra anteriorly
on alternate segments, posteriorly on all the segments with or without
gills. Without facial tubercle. Sigalion Aud. and Edw. ; Sthenelais Kinb. ;
Psammolyce Kinb . ; Thalenessa Baird ; Leanira Kinb. ; Pholoe Johnst.

Sub-fam. 5. Polylepinae. Elytra on all segments, no dorsal cirri.
Lepidopleurus Clap. ; Pelogenia Schm.

Fam. 5. Palmyridae. No elytra ; strong setae disposed in a fan-like manner
arise from all the parapodia dorsal to the dorsal cirrus. Chrysopetalum Ehl. ;
Palmyra Sav.

XEREIDIFORMIA.

479

Fam. 6. Phyllodocidae. Body elongated, with numerous segments ; presto-
mium rounded with 4 or 5 tentacles ; peristomium with 4 tentacular cirri ; the
cirri of the parapodia are foliaceous.

Sub-fam. 1. Phyllodocinae. With small eyes. Phyllodoce Sav. (Fig.

388), with 4 tentacles; Eulalia Sav., with 5 tentacles; Eteone Say.- Anaitis

Mgr. ; Genethyllis Mgr. ; My slides Theel ; Notophyllum Oerst. ; "Lacydonia

Mar. and Bob.

Sub-fam. 2. Lopadorhynchinae. Small transparent pelagic forms with

small eyes ; intermediate between Phyllodocinae and Alciopinae. Lopado-

rhynchus Gr. ; Hydrophanes Clp. ; Pelagobia Grf.

Sub-fam. 3. Alciopinae.* Transparent, pelagic worms with one pair of

large hemispherical projecting eyes (Fig. 389). There are long peristomial

cirri and 5 prestomial tentacles. Found

in most oceans, but rare in the North

Sea. The larvae are in part parasitic

in Cydippidae. Alciopa And. and Edw.;

Alciopina Clp. and Pane.; Asterope Clp.;

Vanadis Clp. (Fig. 389) ; Halodora Grf. ;

Greefia (Nauphanta) M'Int. ; Callizona

Grf. ; Rhynchonereella A. Costa.
Fam. 7. Tomopteridae.f Transparent,
pelagic forms, with two eyes, bifid presto-
miuin (the lobes of the prestomiuin may
be tentacles ; their cavity is continuous with
the body-cavity), and four tentacular cirri,
of which the posterior are much the longest
and contain one seta, while the anterior
contain two setae. The mouth is with-
out proboscis and jaws. The parapodia are
large, biramous, and without setae ; each
branch contains a yellow rosette-shaped organ, probably photogenic. Tomopteris
Eschsch. (Fig. 390).

Fam. 8. Nereidae (Lycoridae). Body elongated, with many segments. Pre-
stomium with two tentacles, two palps and four eyes ; peristomium with four
pairs of tentacular cirri. Parapodia uni- or biramous with dorsal and ventral cirri
and composite setae. Proboscis usually with spines, and always with two jaws.
Nereis L. ; N. diversicolor Mull. , burrows in mud and sand, fleshy red colour ;
N. cultrifera Gr., greenish grey, with small rectangular light spots along the
dorsal surface ; 6 inches. N. dumerilii Aud. and Edw. (Figs. 391, 392), reddish
violet with darker transverse lines in each segment ; peristomial cirri very long.
N. pelagica L., bronze, large, widest in middle of body, back arched, on rocky
ground. N. (Nereilepas) fucata Sav., lives on whelk shells. N. (Alitta) virens
Sars — the creeper — may reach length of 18 inches, burrows in clay, etc., para-
podia with large foliaceous lobes. Lycastis Sav. ; Dendronereis Peters.

Fam. 9. Nephthydidae. Body elongated, quadrangular in section with flat
dorsal and ventral surfaces. Prestomium inconspicuous, with 2 or 4 small
tentacles. Peristomium with reduced parapodia bearing setae and two tentacular
cirri. Parapodia biramous ; the two branches are widely separated, and each
is fringed with a membrane. The notopodium has a curved gill on its under

* R. Greeff, Nova Acta Acad. Car. Leop., 29, 1876, p. 35.
f R. Greeff, Zeit. f. wiss. Zool., 42, 1885, p. 432.

and anterior end of
Vanadis melanophthalmus Greeff
(after Greeff). Showing the large
eyes.

480

ANNELIDA.

side, and a small cirrus. The neuropodium has a ventral cirrus. Pharynx
large, with papillae and two small jaws. Nephthys Guv. ; N. hombergii Aud.
and Edw., burrows in the sand near the shore to 20 fathoms ; Portellia Qtg.

Fam. 10. Amphinomidae. Body vermiform or oval and flattened, with a
small number of segments. The mouth is shifted backwards and surrounded
by several similarly-built segments. The prestomium is indistinct, or repre-
sented dorsally by a sense-organ — the caruncle — which extends over several
segments. Usually three tentacles, two palps, and one or two pairs of eyes.
Proboscis well-developed, without teeth. Parapodia biramous, with dorsal and
ventral cirri, and dorsal branchiae. Most of the species are tropical. Euphrosyne
foliosa Aud. and Edw., and Eurythoe borealis Oerst., are found in the British area.
Sub-fam. 1. Amphinominae. With caruncle ; with 2 branchiae on each
segment. Amphinoma Brug. (Pleione Sav.) ; Hermodice Kinb. ; Eurythoe
Kinb. ; Notopygos Gr. ; Chloeia Sav.

Sub-fam. 2. Euphrosyninae. With caruncle ; with numerous branchiae
on each segment. Euphrosyne Sav.

Sub-fam. 3. Hipponinae. Without caruncle. Hipponoa Aud. and Edw. ;
Spinther Johnst. ; Aristenia Sav.

FIG. 390.— Tomopteris rolasi Greeff (after Greeff).

Fam. 11. Staurocephalidae. Prestomium with two dorsal jointed tentacles,
and two inferior lateral tentacles (? palps). The two first segments without
appendages. Parapodia biramous, with two kinds of setae. Without branchiae.
Staurocephalus Gr. (Anisoceras Gr. ; Prionognathus Kef. ) ; Paractius Lev.

Fam. 12. Lysaretidae. Prestomium with three tentacles and four eyes.
The two first segments without appendages. Parapodia uniramous with one
kind of seta. Dorsal cirri foliaceous, branchial. Halla Costa ; Lysarete Kinb. ;
Danymene Kinb.

Fam. 13. Lumbriconereidae. Without branchiae, without or with reduced
cirri, and without tentacles. The two first segments without appendages.

NEREIDIFORMIA.

481

Arabella Gr. ; Lumbriconereis Gr. prestomium conical without tentacles and
palps ; Drilonereis Clp. ; Notocirrus Schm. ; Laranda Kinb. ; Ophryotrocha
Clp. and Meczn., with segmental ciliated rings.

Fam. 14. Eunicidae. Elongated body, with numerous segments. Prestomium
distinct and projecting, with 3 or 5 tentacles, or with 5 tentacles and 2 palps,
or without appendages ; usually with eyes. The first (peristomium) or the
two first segments without parapodia, but they may have cirri. In Eunice
and Diopatra the second segment has a dorsal cirrus — the nuchal cirrus.
Parapodia uniramous, rarely biramous, with ventral cirri and branchiae (the
so-called dorsal cirrus contains an aciculum, and is the reduced notopodium).
Usually 4 cirri below the anus. An upper jaw formed of several pieces,
and a lower jaw of 2 lamellae are placed in a pocket attached below the oeso-
phagus (Fig. 393). In most genera there are parchment-like tubes. Diopatra

FIG. 391.— Head and anterior body segments of Nereis dumerilii (after Claparede). 0 eyes ;
P palps ; Ct tentacular cirri ; K pharyngeal jaws.

And. and Edw. ; Eunice Cuv. , 5 tentacles, 2 palps, and 2 nuchal cirri ;
Marphysa Qtf., like Eunice, but without nuchal cirri ; Hyalinoecia Malmg.,
5 tentacles, 2 palps, 2 frontal palps, no nuchal cirri ; Onuphis Aud. and Edw. ;
Nicidion Kinb.; Macduffia Mclnt. ; Lysidice Sav., 3 tentacles, 2 palps, no
gills ; Nematonereis Schmarda, one tentacle ; Palola Gray, 3 tentacles. A
species of this worm lives in fissures in the coral-reefs of certain parts of
the Pacific (Samoa, Fiji). Twice in every year — once in October and once
in November — these worms swarm out to the surface of the sea in enormous
numbers to spawn, and are caught by the natives for food. In each of
these months the worms appear on two successive days, viz., at dawn on
the day on which the moon is in her last quarter and at dawn on the day
before (vide S. J. Whitmee, "On the habits of Palola viridis," Proc. Zool. Soc.,

9 T

482

ANNELIDA.

1875, p. 496, and A. Collin, " Bemerk. lib. d. essbaren Palolowurm," in
Appendix to Kramer's work on the Coral-reefs of Samoa, Kiel and Leipzig, 1897,
Lipsius and Fischer).

Fam. 15. Glyceridae. Body elongated, with numerous segments. Pre-
stomium is long, 'conical, annulated, and carries at its apex four small tentacles,
at its base two palps. The pharynx can be protruded to a great length, and is
provided with four, or several, strong teeth. Parapodia of first two segments

FIG. 392. — Parapodium of Nereis (after Quatre-
fages). DP notopodiurn; VP neuropodium,
with bundles of setae ; Ac aciculum ; EC, dorsal
cirrus ; Be ventral cirrus.

FIG. 393. — Pharyngeal apparatus of
Eunice in a retracted condition.
g brain; vd oesophagus; ph
pharynx ; pht pharyngeal pocket ;
7c jaws ; mh buccal cavity ; m
mouth ; r dorsal, b ventral surface.
(After Lang.)

incomplete, without tentacular cirri, uni- or biramous. Two anal cirri. Special
retractile gills are present. The corpuscles of the coelomic fluid are coloured
red with haemoglobin, and there are said to be no blood-vessels. Glycera Sav.,
parapodia all alike ; G. gigantea Qfg. , and G. capitata, Oerst. , under stones and
in sand, English Channel ; Hemipodus Qfg. ; Goniada And. and Edw., anterior
and posterior parapodia not alike.

FIG. 394.— Glycera Meckelii Aud. and Edw. (Regne Animal), with everted pharynx.

Fam. 16. Ariciidae. Numerous segments. Prestomium without tentacles,
or with small tentacles, or with tentacular cirri. Peristomium with setigerous
tubercles. Pharynx short, unarmed, slightly or non -retractile. Parapodia
short, biramous. In all but the first few segments the parapodia are somewhat
dorsally placed. Burrow in sand. Aricia Sav. ; Theodisca F. Mull. ; Scoloplos
Blainv. ; Sc. armiger Mill]., is common on our coast, length one inch, red gills ;
Aricidea Webs.

Fam. 17. Typhloscolecidae.* Pelagic forms of uncertain affinities. Typhlo-
scolex Busch ; Sagitella Wag. ; Travisiopsis Lev.

Reibisch, Phyllodociden u. Typhloscoleciden d. Plankton Expedition, 1895.

SPIONIFORMIA. 483

Sub-order 2. SPIONIFORMIA.

"Without tentacles or palps ; the peristomium usually carries a pair
of long tentacular cirri, and extends forwards at the sides of the
prestomium. The parapodia project but slightly; the dorsal cirri
may attain a considerable size, and act as gills throughout the greater
part of the body. The setae are unjointed ; uncini are present only
in Cliaetopterus.

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 burrow or are
tubiculous.

Fig. 395. — Chaetopterus pergamentaceus Cuv. = variopedatus Ren.
(Regne Animal), in its tube, which is partly laid open.

Fam. 1. Spionidae. Prestomium small, without tentacles or palps, though
sometimes with tentaculiform projections, usually with small eyes. Peristomium
extends forward on each side of the prestomium, and bears two long tentacular
cirri. Parapodia generally biramous, with simple setae. The notopodial cirri
are long, finger-shaped, and ciliated, and function as gills. There are no ventral
cirri. The buccal region is eversible. They burrow in mud and sand. The
females lay their eggs in the tubes. Polydora Bosc. (Leucodore Johnst.). Pre-
stomium with two tentaculiform projections. The 5th setigerous segment is
enlarged, and bears specially strong setae arranged in a comb-like manner.
P. ciliata Johnst., in soft mud tubes in U-shaped galleries in stones and
shells ; length ^-inch ; 40 segments ; anus surrounded by incomplete funnel ;
world-wide; P. coeca Oerst. Spio Fabr., S. seticornis Fabr., Greenland and
Scandinavia ; Prionospio Mlg. ; Scolecolepis Blainv. ; Nerine Johnst. ; N. vulgaris
Johnst., under stones and on seaweed, 3 or 4 inches long, N". Atlantic.

Fam. 2. Chaetopteridae.* Body divided into two or three unequal regions.
Prestomium small, often with eye-spots. Peristomium prolonged round the
mouth in a funnel-like manner, and bearing two or four tentacular cirri. The
fourth segment behind the peristomium with specially strong setae as in Poly-
dora. Neuropodia bifid in the posterior region, and sometimes in the middle

* Joyeux-Laffuie, Arch. Zool. Exp., (2), 8, 1890, p. 244.

484 ANNELIDA.

region. Notopodia of the middle region in the form of fins, often lobed. They
inhabit U-shaped parchment-like tubes, the two ends of which arc placed at
some distance from each other, and project above the sand. The skin of the
worm is soft and delicate. The larvae are mesotrochal. Telcpsavus G. Costa,
two long tentacular cirri ; body divided into two regions ; Spiochae.toptcrus fSars ;
Phyllochaetopterus Gr., two pairs of tentacular cirri; body divided into three
regions. Chactoptfirus Cuv. (Fig. 395), two tentacular cirri. Hody divided into
three regions. Phosphorescent. Ch. vario/tn/K/nn Ren., Channel Islands, English
coast, etc., anterior region with 9 pairs* of setigerous conical parapodia ; middle
region of 5 segments, of which the first carries two large wing-like processes
directed forwards (notopodia), the second carries a dorsal and ventral sticker
(modified parapodia), the third, fourth, and fifth a membranous fin-like noto-
podium — the fans, and a ventral bilobed neuropodium ; the posterior region
consists of from 25 to 35 less modified, similar segments, with notopodinm and
bilobed neuropodinm.

Fam. 3. Magelonidae.f Body divisible into two regions by differences in the
setae. Prestomium large and flat, two long peristomial cirri. Large evcrsible.
buccal region, blood of maclder-]>iiik colour when oxygenated, and colourless
when deoxidized (haemerythrin, found also in Sipnncn.lus) ; the colouring mallei-
being contained in globules which float in the colourless plasma ; isolated nuclei
are also found in the plasma. Live buried in sand. Sole genus, M<i<jcl<»nt
F. Miill.

Fam. 4. The Ammocharidae may be placed here. They live in sandy tubes,
and the mouth is surrounded, except ventrally, by a membrane, which is frayed
out marginally into filaments, and is probably an appendage of the pcristominm.
The anterior segments longer than the hinder ones. Sole genus Owenia D. (Mi.

Sub-order 3. TEREBELLIFORMIA.

The prestomium is a more or less prominent lobe (upper lip) with
or without tentacles, but without palps. The pcristomium may
carry cirri or tentacular filaments. The parapodia arc feebly de-
veloped; there are no ventral cirri; the dorsal cirri may exist and
function as gills on some of the segments. The setae are un jointed,
and uncini are usually present. The buccal region is not eversiblc,
and there are no jaws. The septa are usually incomplete, with tlie
exception of one strongly-developed diaphragm anteriorly. The
nephridia arc dimorphic, those of the prediaphragmatic segments
being of large size and excretory, while the posterior nephridia are
mere funnels which servo as generative ducts. They are hurn>wers
or tube-formers, and in the majority the tube-forming glands are
grouped on the ventral surface of the anterior segments, where
they form gland-shields.

* The number is variable ; specimens have been found with 12, or with 9 on
one side and 8 on the oilier.

f W. B. Benham, Q. J. M. S., 39, 1896, p. 1.

TKKKKKI.I.ll OKM1A.

48f>

T

Fain. 1. Cirratulidae. Cylindrical body pointed at both ends. Prestomiuni
elongated, conical, without tentacles, or with two tentacles, (tentacular cirri,
Grube). Parapodia small, with simple setae. On some of the segments the
dorsal cirri are long and lilaiut'iilous, and function as gills. A single pair of
anterior nephridia ; tin- septa and genital ducts are repeated through the hinder
part oft lie body. Inhabit bin rows. Cirratuhis Lain. ; Audouinia QfgT; Chaeto-
BMM Mulmg.; ])od<\'accnu-<i (Dodccaccritt) Oerst. ; Hekaterobranchias V. Buchanan.
Fain. 2. Terebellidae. Body vermiform and thicker anteriorly. The
thinner posterior por-
tion is sometimes dis-
tinctly marked off as
an appendage devoid of
setae. The prestouiium,
\\liich is indistinctly
separated from the
peristominm, forms an
upper lip and carries
numerous filiform ten-
tacles arranged in a
transverse ro\v ; it may
have four eye spots.
There are pectinate or
1'ianclied, rarely fila-
mentous, gills on one
to three of the an-
terior segments ; they
contain a prolonga-
tion of the eoelom.
Dorsal prominences
(notopodia) with. simple
setae, and ventral
transverse ridges (neil-
ro podia) with hooked
setae. One to three
pairs of large nephridia.
From three to twelve
pairs of small nephridia.
(gen. ducts) behind the
diaphragm. Tubi-

rolous, tube formed of
foreign bodies.

Sub-tarn. 1. Amphitritinae. Almost always with gills ; cephalic lobe
short, with numerous tentacles. AmphitrUe 0. F. Midi., simple setae in
anterior region only, 3 pairs of gills of nearly the same size, no eyes ;
A. Johnston i Mlmg. TcrelcUn L. (Fig. ;W(>), distinguished by the small
si/e of the posterior of the three pairs of branchiae ; '/'. (Lt nice) conchilega
Pall., Knglish coast; A'iculea Mlmg., two pairs of equal gills; Hclcro-
tcrebrtlu (.){(.; Thelcfnin Lei-ick. (ind. JIrt,'roj>h<'>itn'ia Qt.f., Phenacia Qtf.,
Ncottis Mlmg., etc.), liliforin gills in two segments; Entli<-t<in(x Mclnt. ;
Leacna Mlmg.; Lanassa Mlmg.; Loiinia Mlmg.; J'tstti Mlmg.; Nicolea
-Mlmg.

Fio. 390.— Terebdla ncbvlosa opened from tho dorsal side (aftor
M. Edwards). T tentacles ; A" Kills ; Dg dorsal vessel or heart.

486 ANNELIDA.

Sub-fam. 2. Polycirrinae. "Without branchiae. The prestomium forms
a large upper lip, and gives origin to many long tentacles. Polycirrus Gr.
(including Leucariste Mlmg. ; Ereutho Mling.); P. aurantiacus, bright
red, with orange tentacles.

Malmgren distinguishes 3 other sub-families, Artamaceae, TrichobrancMdae,
Canephoridae (Terebellides, Sars.).

Fam. 3. Ampharetidae. Body formed of two regions, of which the anterior
is broad and bears simple setae and hooks, while the posterior part is narrow
and has only hooks. Numerous filiform tentacles spring from the prestomium.
The peristomium forms a kind of lower lip. Four filiform branchiae are placed
on each side of the anterior segment!, and in front of them are some strong
setae. Inhabit tubes in mud. Ampharete Mlmg. ; Amphicteis Gr. (Lysippe,
Sosane Mlmg. ) ; Sabellides Gr. ; Melinna Mlmg. ; Melinnopsis, Mclnt. ; Phyllo-
comus Gr. ; Grubianella Mclnt. ; Samythopsis Mclnt. ; Eusamytha Mclnt.

Fam. 4. Amphictenidae. Distinguished from Terebellidae mainly by the
presence of tentacles disposed in two bundles on the buccal ring, of two pairs
of tentacular cirri and of pectinated branchiae on the second and third
segments. The anterior end bears two rows of golden setae, which act as an
operculum to the tube. The tubes are straight or slightly curved, and composed
of small grains of sand. Pectinaria Lam. ; Amphictene Sav. ; Petta Mlmg.

Sub-order 4. CAPITELLIFORMIA.

Blood-red worms, with a conical prestomium. Without prestomial
processes, but with a pair of large retractile ciliated organs. The
segment next the prestomium is without setae or cirri. The parapodia
do not project ; the setae are unjointed, and are hair-like in the
anterior segments, and hooked posteriorly. This external division
of the body does not correspond with internal differences. There are
no cirri, though special, sometimes retractile, gills are frequently
present. The buccal region is eversible ; there is no armed pharynx.
A pair of prominences with sensory hairs, placed one on each side,
in most segments. 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 are no
blood-vessels; the coelomic corpuscles are red. The larvae are
telotrochous, and are ciliated on the ventral surface. They are
burrowers.

Fam. Capitellidae,* with characters of sub-order. Capitella Blainv. ; C.
capitata v. Ben., North Sea, etc. ; Notomastus Sars ; Dasybranchus Grube ;
Mastobranchus Eisig ; Capitomastus Eisig.

* H. Eisig, "Die Capitelliden," Fauna and Flora d. G. v. Neapel, xvi., 1887.

SCOLECIFORMIA.

Sub-order 5. SCOLECIFORMIA.

With a prestomium which rarely
(Chlorhaemid ae) carries sensory pro-
cesses; the peristomium is without
cirri (except perhaps in the Chlor-
kaemidae). The parapodia are re-
duced, and may be absent; dorsal
cirri (acting as gills) are rarely
present ; ventral cirri are absent.
Setae unjointed ; uncini are not
present. Buccal region eversible —
without armed pharynx. The septa
are not developed regularly; the
nephridia, which are all alike, are
considerably reduced in number, it
may be to a single pair (Sternaspidae
and some Chlorliaemidae). Mostly
burrowers.

This is the most unsatisfactory of
Benham's sub-orders. Its merit is that
it comprises a number of families which
cannot be placed with any of the other
sub-orders.

Fam. 1. Opheliidae. Short worms ;
prestomium conical, without appendages,
but with two ciliated pits. Parapodia
reduced, with simple setae in two groups.
Dorsal cirri acting as gills, or reduced,
usually present. They live in the sand.
Ophelia Sav. ; Ammotrypane Rathke ;
Travisia Johnst. ; Armandia Fil. ; Poly-
ophthalmus Qtf., without gills, eye -like
pigment spots on the sides of some of the
segments ; circular muscles absent ; oeso-
phageal commissures and ventral cords in
contact with the ectoderm ; septa absent,
except three in front.

Fam. 2. Maldanidae* (Clymenidae).
Body cylindrical, divided into two or
three regions. The segments towards
the middle of the body may be longer
than the rest. Prestomium small, fused
with peristomium ; often with eye spots.

* St. Joseph, Ann. Sci. Nat. (7), 17,
1894, p. 130.

487

a5

FIG. 397. — Arenicpla piscatorum, dorsal
view. A anterior region, comprising
six segments; B middle or branchial
region, with thirteen segments ; C tail
region of variable length a eversible
buccal region ; 6, c notopodia with
bundles of setae ; d gills. (From Vogt
and Yung.)

488

ANNELIDA.

A horny plate may be developed on upper side of head. Anus usually
surrounded by a papillated funnel. Tentacles and branchiae absent. Noto-
podium small with simple or pinnate setae, absent posteriorly ; neuropodium
as transverse ridge with hooked setae, absent in anterior region. Inhabit long,
sandy tubes. Mitraria is a clymenid larva. Clymene Sav., head with plate ;
C. lumbricoides Qtf.; Pr axilla Mlmg.; Leiocephalus Qtf.; Maldane Gr., head
without plate ; Nicomache Mlmg. ; Axiothea Mlmg. ; Leiochone Gr. ; Petalo-
proctus Qtf.

Fam. 3. Arenicolidae (Telethusidae). Prestomium small, without tentacles,
fused with peristomium. Peristomium without setae ; eversible buccal region

covered with papillae,
without jaws. Notopodia
small, with a bundle of
simple setae ; neuropodia
with hooks in rows.
Branched gills on middle
segments. Posterior seg-
ments without parapodia
and gills. Burrow in
sand. Arenicola Leach ;
A. marina* L. (A. pis-
catorum Lam.). North
Sea and Mediterranean.
Lob- or lug-worm. Length,
5-6 inches (Naples speci-
mens smaller), colour,
brownish green. The bur-
rows are U-shaped, one
opening being marked by
a heap of vermicular,
sandy ejecta. Body
divided into three regions ;
an anterior thicker than
the rest, consisting of the
peristomium and 6 chaeti-
ferous segments ; a middle,
not so thick, of 13 chaeti-
ferous and branchiferous ;
a posterior much thinner
and devoid of setae and
branchiae, with segments
less clearly marked and
variable in number. In
the anterior and middle
region of the body there

are 3 coelomic septa, the 1st behind the peristomium, the 2nd between the
2nd and 3rd setigerous segments, and the 3rd between the 3rd and 4th
setigerous segments. In the caudal regions the coelomic septa are segmental.
There are 6 pairs of nephridia in segments 4-9.

FIG. 398. — Anterior end of Arenicola opened from the dorsal
side, a anterior small chamber of the coelom ; 6, d, and /
first, second, and third septa ; c and e second and third
chambers ; g papillae of proboscis ; h oesophagus : i gut ;
fc gland ; I nerve cord ; TO setigerous sacs ; n nephridia ;
o anterior glands ; p heart ; q dorsal vessel ; r vesicles of
nephridia. (From Vogt and Yung.)

* Vogt and Yung, PraUische Vcrgl. Anat., Bd. 1, 1888, p. 487.

SCOLECIFORMIA.

489

vb

Fam. 4. Scalibregmidae.* Scalibregma Rathke ; Eumenia Oerst.; Sclero-
cheilus Gr.; Lipobranchius Cunn. and Ram.

Fam. 5. Chlorhaemidaef (Pherusidae). Elongated cylindrical body with green
blood (due to chlorocruorin). Prestomium with a pair of long processes (? palps)
and several green tentacles arranged in a transverse row and acting as gills.
Peristomium achaetous. The head can be withdrawn into the body. The setae
of the anterior segments are long and directed forwards. Skin papillated. Only
one or two coelomic septa, and two or four nephridia. Flabelligera, Sars (Siphon-
ostoma Voigt ; Chlorhaema Duj.); F. affinis Sars, transparent body- wall, skin
with long papillae, which traverse a thick jelly-like envelope secreted by it,
under stones at low tide ; Trophonia M. -Edw.
(Pkerusa Blv.) ; Brada Stimp.; Buskiella Mclnt.;
Stylarioides D. Ch.

Fam. 6. Sternaspidae. J Body short, ante-
rior region thickened and carrying on each
side 3 rows of setae ; on the ventral surface
of the hind end there is a bilobed horny plate,
round the edges of which are placed a number
of bundles of long setae. Mouth overhung by
a small knob -like prestomium ; anus on a
papilla dorsal to the horny shield. Two
bundles of filamentous branchiae just anterior
to, and on each side of the anus on the dorsal
surface. About 30 segments ; segments 2, 3, 4
have a row of strong setae on each side, seg-
ments 5, 6, 7 are without setae, segments 8-15
have setae which do not pierce the cuticle ;
the remaining segments are marked by the
bundles of long setae round the horny plate.
Coelomic septa absent ; alimentary canal coiled ;
one pair of nephridia attached to the skin between
segments 6 and 7, and opening internally. Pro-
jecting externally between segments 8 and 9 on
the ventral surface are two processes which con-
tain the terminal parts of the generative ducts.
The generative organ is a sac which communicates
with the visceral coelom by a narrow canal ; the
walls of the sac are continued into the two gener-
ative ducts. Sternaspis Otto, S. scutata Ranzani,
Mediterranean.

FIG. 399. — Sternaspis scutata, ven-
tral view x 2 (after Vejdov-
sky). The segments in front
of the shield are numbered
I-XV. K branchial filaments ;
Ir processes containing the
generative ducts; m mouth;
rb, sb, eb, setae of horny shield ;
vb rows of setae on segments
1 1, III, I F.

* Levinsen, Syst. geog. Overs, over, de Nord. Annul {Vidensk. Meddelser) for
1883, Copenhague, 1884, p. 130.

t E. Grube, " Mitth. iiber d. Fam. Chlorhaemiden," Sitz. ber. d. Schlesischen
Gesellschaft, Breslau, 1876.

J Vejdovsky, " Vk. Akad. Wien, 43, 1882. Rietsch, Ann. Sci. Nat. (6),
13, 1882. Goodrich, Q. J. M. S., 40, p. 233.

490 ANNELIDA.

Branch B. CKYPTOCEPHALA.

Prestomium more or less hidden by the peristomium which grows
forward. The tentacles are reduced, but the palps are greatly developed
and subdivided, forming the crown of gills. The body is distinguish-
able into two regions — the thorax and abdomen characterized by the
form and arrangement of the setae, and by cei^tain internal differences..

Sub-order 1. SABELLIFORMIA.

Prestomium entirely hidden by the forward extension of the
peristomium ; tentacles very small, being often represented by small
knobs of sense-cells; palps large and vascular, acting as respiratory
and sensory organs. Peristomium without cirri or setae; it is
usually raised into a projecting collar used in fashioning the lip of
the tube. The parapodia are small; cirri are absent except in the
Serpulidae. The setae are of two kinds — hair-like and uncini; by
their arrangement the body is divided into a thorax, typically of
nine segments, and into an abdomen; in the thorax the hair setae
are dorsal, in the abdomen ventral. The buccal region is not
eversible; there is no pharynx. Septa absent in thorax, present
in abdomen. There are two large nephridia in the thorax, opening
by a median dorsal pore just above the brain ; while the nephridia
of the abdomen are small funnels which act as generative ducts.
Tubicolous; gland-shields are present on the thoracic segments.
Some genera are hermaphrodite.

Fam. 1. Sabellidae * (including Eriographidae and Amphicorinidae). Tube
formed of mucin of variable consistence and more or less transparent, covered or
not with mud, sand, or pieces of shells. Without thoracic membrane and
operculum. Branchial filaments usually arise from a semicircular base. The
ventral gland-shields are continued on to the abdomen. A median ciliated
groove, usually situated on the ventral surface (it sometimes bends to one side
on reaching the thorax, and may extend forwards on the dorsal surface to the
head), starts from the anus and conducts the faecal matters to the opening of
the tube. The species are highly variable : the individuals of the same species
often vary in the following features ; colour, number of branchiae, form of
collar, number of thoracic segments, number and position of eyes and otocysts.

Spirographis Viv., the basal lamella of the gill filaments describes several
turns in spiral. The branchiae of the two sides are of unequal size ; Sp.
spallanzanii Viv., Naples ; Bispira Kr. Like preceding, except the two
branchiae are equal. Sabdla L., gill-filaments arise from a semicircular base, gills
equal, two filamentous dorsally-placed lip-processes (found in other Sabellids :
they are not tentacles) ; S. pavonina Sav. ; Potamilla Mgr. ; Hypsieomus Gr. ;.
Potamis Ehlers ; Branchiomma Roll., with a compound eye close to the tip

* St. Joseph, Ann. Sci. Nat. (7), 17, 1894, p. 248.

HERMELLIFORMIA.

491

of each gill-filament ; Protulides Webst. ; Dasychone Sars, gill -filaments with
dorsal appendices, D. bombyx Dal., with compound eyes at the base of the dorsal
appendices of the gills ; Laonome Mgr. ; Notaulax Tauber ; Sabellastarte Kr. :
Eurato St. Jos. ; Haplobranchus A. G. Bourne, estuarine ; Manayunkia Leidy,
fresh- water ; Cadbangia Giard, fresh-water, anus ventral and anterior ; Fdbricia,
Blv. ; Othonia Johnst. ; Amphicora Ehr., with two eyes on the last segment;
Oria Qtf. ; Jasmineira Lang ; Myxicola Koch (Eriographis Gr. ; Arippasa Johnst),
gill-filaments connected by a membrane which reaches nearly to their tips ;
Chone Kroyer ; Euchone Mgr. ; Dialychone Clp.

Fam. 2. Serpulidae.* Tube formed of mucine indurated with calcareous
matter. Almost always with thoracic membrane and operculum. Without a
ciliated groove, but the ventral surface (and sometimes the dorsal) is in part
ciliated. The thoracic membrane is formed by the fusion of the dorsal and
ventral cirri of the thoracic segments. The operculum consist of a terminal
dilatation of one of the branchial filaments. Serpula L. ; sub-genera Hydroides
Gunn. (Eupomatus Phil.; Eucarphus Morch.; Polyphragma Qtf.), and Crucigera
Benedict. ; Protis Ehl. ; Chitinopoma Lev. ; Filograna Oken, two or several oper-
cula ; Salmacina Clp., no operculum ; Spirorbis Daudin (Fig. 400), operculum
grooved on one side, serving as
brood pouch ; Pileolaria Clp. ;
Janua St. Joseph ; Ompha-
lopoma Morch ; Circeis, Ompha-
lopomopsis, Janita, Leodora,
Mera, Hyalopomatopsis, all St.
Jos. ; Vermilia, Lmk., etc. ;
Pomatoceros Phil. ; Spiro-
branchus Blv. ; Pomatostegus
Schm.; Placostegus Phil.;
Protu la Risso ; (Psygmobranchus
Phil. ), no operculum ; Apomatus
Phil.

Sub-order 2.
HERMELLIFORMIA.

The peristomium 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
setae, which act as a protec-
tion when the worm is
withdrawn into its tube.
The prestomium is small,
but possesses a pair of well-

FIG. 400.— Spirorbis laevis (after Claparede). a, the
animal removed from its tube, strongly magnified ;
b, its tube. T tentacles; Bs brood pouch, with
operculum ; Dr glands ; Ov ova ; Oe oesophagus ;
M stomach ; D intestine.

* St. Joseph, Ann. ScL Nat. (7), 17, p. 259.

492

ANNELIDA.

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
setae; dorsal cirri are present along the greater part of the body,
and act as gills. The worms form tubes of sand.

Fam. Hermellidae. Sabellaria Lam. (Henrietta Sav.).

B

FIG. 401. — Diagrammatic figure representing the organisation of Myzostoma (after v. Graff,
from Perrier). B mouth ; cl, clO marginal cirri ; d cloaca ; E stomach ; i branches of the
intestine ; N ventral nervous system ; o coelom filled with ova ; pi, p5 parapodia ; ph
pharynx ; R rectum ; t testis ; u female generative opening ; v suckers ; $ male opening.

MYZOSTOMIDA.*

The Myzoetomida, though, differing in many respects from the Polychaeta,
may most conveniently be treated in an appendix to that group. There are
two genera, Myzostoma Leuckart, and Stelechopus (parasitic on Hyocrinus)
von Graff. They are all parasitic on Crinoids, external for the most part

* v. Graff., "Myzostomida," Challenger Reports, vol. x., 1884, and Supplement,
vol. 20, 1887. Wheeler,- Naples Mitth., 12, 1896, p. 227.

OLIGOCHAETA.

493

(M. pulvinar v. Gr., lives in the intestine). They infest the disc and arms,
and may be free or enclosed in globular cysts.

They possess a soft and ciliated skin ; five pairs of ventrally placed parapodia
(Fig. 401), each of which bears a hooked seta and an aciculum ; four pairs of
laterally placed suckers ; and ten or more pairs of cirri placed on the niargin of
the body.

The alimentary canal consists of a protrusible pharynx, a stomach which
gives off the radially arranged caeca, and a rectum. The mouth is anterior
and ventral, and the anus posterior and ven-
tral (except in a few species in which one or
both openings may be dorsal).

The nervous system consists of a nerve ring
surrounding the pharynx, slightly enlarged
dorsally, and ventrally continued into a large
ganglionic mass (Fig. 401), which represents
the ventral cords.

The animals are hermaphrodite and protan-
drous, the testes maturing before the ovaries.
The testes are branched glands on each side,
and lead into two ducts which open laterally,
one on each side, just external to the third
parapodium.

The ovaries are two small patches of coelomic
epithelium, and the eggs are dehisced into the
coelom, which they fill. From the coelom a
tube — the oviduct — passes dorsal to the rectum,
and opens either into the latter, or by a median
pore just dorsal to the anus.

There are two nephridia, opening with cili-
ated funnels into the coelom and into the
rectum behind.

Order 2. OLIGOCHAETA.*

Hermaphrodite Ghaetopoda without
pharyngeal armature and parapodia.
Without tentacles and cirri, rarely with
branchiae. Gonads limited in number,
and restricted in position. The develop-
ment is direct.

The Olicjochaeta comprise certain small,
and for the most part fresh-water worms,
and all the worms known as earthworms,

FIG. 402. — Lumbricus rubellus (after
G. Eisen). a, the whole worm ;
Cl clitellum. b, the anterior end
from the ventral 4side. c, isolated

* E. Claparede, " Recherchcs A natomiques sur les Oligochaetes," Geneva, 1862.
F. Yejdovsky, System u. Morphologic der Oligochaeten, Prag, 1884. W. B.
Benham, "An attempt to classify Earthworms," Q. J. M. S., vol. 31, 1890.
F. E. Beddard, "A Monograph of the Oligochaeta," Oxford, 1895, which see for
literature.

494

ANNELIDA.

which are sometimes of considerable size, even reaching a length
of from four to six feet (Microchaeta rappi ; Megascolides australis).
The setae are, as a rule, few in number, and are not set in parapodia.
The head consists of a prestomium, which is sometimes much elon-
gated (Nais lacustris), and is generally marked off from the oral
segment (peristomium), or first segment of the body, by a groove.
The oral segment is always without setae, and is never reinforced
by the fusion with it of posterior body segments. There are no
cephalic appendages either on*the pre- or peristomium. The seg-
mentation of the body is always well marked externally by circular
grooves,* and the coelomic septa are always present. The segments
are all alike, and are not divided into regions, though some of the

FIG. 403.— Setae of Oligochaeta (after Vejdovsky, Stole, and Michaelsen, from Beddard). 1,
^ Onychochaeta windlei, posterior seta. 2, ornamented seta of Geoscolecid. 3, Trichochaeta
hesperidum; Sb, end of same more highly magnified.

segments behind the peristomium are occasionally devoid of setae.
The gonads are localized thickenings of the coelomic epithelium,
and special generative ducts are present to convey their products to
the exterior. There is always present a glandular development of
the ectoderm, generally having a marked annular form and called
the ditellum or girdle : it secretes the cocoon in which the eggs
.are laid.

Considering the great constancy presented by the Oligochaeta
in the arrangement and structure of many important organs, e.g.

* In some species of Lumbricus a curious modification of the metamerism,
called spiral metamerism, has been observed as a variation. The grooves between
the segments in such cases have a spiral course (Vide Bates on " Materials for
the Stitdy of Variation" p. 157, London, 1894).

OLIGOCHAETA.

495

the body -form, the ventral nervous system, etc., the variations
in structure in the excretory and generative organs are most
remarkable.

The setae are small chitinous rods projecting from the body- wall.
Their lower ends are embedded in small ectodermal pits, tne cells
of which secrete them. They are absent in the Discodrilidae and
in the genus Anachaeta, otherwise they are present to the number of
•eight or a larger number on most of the segments. When there
are eight they are usually arranged in four groups of two on the
ventral side, but the number and arrangement presents great variety,
and in some forms (Perichaetidae) there is a continuous circle of
them round each segment (Fig. 411). The usual form of seta is
that of anyj but they vary somewhat, as is shown by the accompanying

FIG. 404. — 1, 2, Penial setae of Acanthodrilus georgianus. 3, Spirosperma ferox. It, Hyodrilus
coccineus. 5, Lophochaeta ignota. 6, Tubifex rivnlorum. 7, 8, Nais. 9, Bohemilla comata.
(From Beddard.)

diagrams. The setae are retractile and protractile by special muscles
attached to the walls of the setigerous sacs (Fig. 405). They are
organs which assist in locomotion.

Branchiae are found in a few forms, e.g. Chaetobranchus semperi,
Branchiura Soicerbyi, and Hesperodrilus branchiatus.

The body-wall consists of a cuticle, a layer of ectoderm, an outer
circular and an inner longitudinal muscular layer. The ectoderm
consists of cells, many of which are glandular. It also contains
tactile sense organs in the form of papillae, and organs which resemble
taste-buds; and in the aquatic forms many of the ectoderm cells
carry sensory hairs. The gland-cells are especially well-developed in
the clitellum.

496

ANNELIDA.

The muscles are constructed upon the nematode type (i.e., the contractile

substance partially surrounds
the unmodified nucleated pro-
toplasm (Fig. 406, A, £, C).
In the earthworms, however,
the longitudinal muscular layer
presents an appearance, which
it is difficult to interpret.
In transverse section they
appear to consist of a num-
ber of lamellae placed like

the barbs of a feather upon a

central axis, the whole structure

, . 1

being placed in a connective
substance with nuclei (Fig.
406, D). The explanation
appears to be that we have to
do in such cases with a folded
layer of longitudinal muscles ;
each lamella consisting of a
FIG. 405.— Section of the body-wall of Alloloboptwra muscle - cell, from which the
(Dendrobaena) rubida in the neighbourhood of a seta. granular unmodified protoplasm

with pigment p; b seta; bf setigerous sac; m its
muscles. (From Perrier, after Vejdovsky.)

(m"e Hesse, Z. f. w. Z., 58,

1894, p. 394).

The central nervous system is on

consisting of two ventral cords closely
in a common sheath. They are swollen
in each segment where the main nerves
are given off, and in front they separate
from one another and embrace the
anterior end of the alimentary canal,
to be continuous with one another
dorsally. At this dorsal point there is
generally a bilobed swelling which con-
stitutes the cerebral or suprapharyngeal
ganglia, from which the nerves to the
prestomium are given off. The first
ventral swelling is where the circum-
pharyngeal commissures join to form
the ventral cord, and constitutes the
sub-pharyngeal ganglion. It gives off
a large number of nerves to the
peristomium. In some forms a few
large, longitudinal fibres resembling

the usual Annelidan type,
approximated and enclosed

FIG. 406. — A-C, sections through the
circular muscle-cells of Allolobo-
pliora chlorotica ; D, section through
the longitudinal muscular layer of
a young earthworm ; p coelomic
epithelium. (After Hesse.)

OLIGOCHAETA. 497

tubes, run along the dorsal side of the conjoined nerve cords in the
neurilemma. They are called the giant fibres, and are probably large
medullated nerve fibres. A number of visceral nerves are given off
})j the circumpharyngeal commissures to the pharynx and constitute
the visceral system.

Eye-spots are present in a few of the aquatic forms, but they are
absent in the terrestrial forms ; in spite of this fact the earthworms
appear to be able to distinguish light from darkness. There appears
to be no auditory sense.

The alimentary canal is often divided into several regions, the rela-
tions of which are most complicated in the Terricolae. In Lumbricus
the buccal cavity leads into a muscular pharynx, which is probably
used for sucking. This is followed by a long oesophagus extending
into about the fourteenth segment, and furnished with a thick layer of
glandular cells, and several dilated glandular appendages, the calcareous
ijlands. The oesophagus is dilated behind into a crop which leads into
a muscular gizzard. The gizzard (double in Moniligastridae and Ben-
hamia) has muscular walls and a chitinous lining, and it often contains
small stones; it leads into the straight intestine, the dorsal wall of
which is pushed inwards so as to form a longitudinal fold, the
typlilosole (comparable to a spiral valve). The intestine is dilated in
each segment and opens at the hind end by a terminal anus. In
the Limicolae the alimentary canal is simpler by the absence of a
gizzard ; a pharynx and oesophagus however are always present.

The vascular system is a closed system of tubes containing a red
fluid, in which colourless corpuscles float. The red (yellow in thin
layers) colour is due to haemoglobin in solution in the plasma.
Although in solution, the haemoglobin does not appear to diffuse
through into the tissues or body spaces, the fluids of which are
colourless. The principal blood vessels are (1) a longitudinal dorsal
vessel, contractile from behind forwards ; (2) a ventral subintestinal
vessel also longitudinal, but noncontractile, and sometimes (3) a
subneural longitudinal vessel beneath the nerve-cord. These longi-
tudinal vessels give off lateral branches all along their course, which
themselves branch in the skin, nephridia, and other organs. In
some of the anterior segments there is a single pair of dilated lateral
vessels, which pass round the gut and open into the subintestinal
vessel : these are the so-called hearts, and are contractile from above
downwards. The dorsal vessel is sometimes double, either wholly or
in part. In some forms there appears to be a perienteric blood-sinus
in the intestinal wall, from which the dorsal vessel arises.

2 K

498 ANNELIDA.

In the lower Oligochaeta the walls of even the large vessels
consist merely of a thin, apparently structureless, membrane, with
here and there a nucleus. In the contractile vessels the contractility
would appear to reside in this membrane. In the higher forms the
large vessels possess muscular fibres in their walls, and an epitheloid
lining.

The coelom is spacious, and is always divided by transverse
segmental septa into chambers, which communicate usually above
the nerve-cord. It contains a colourless fluid with amoeboid cells,
and communicates with the exterior through three sets of aper-
tures— the nephridia, the generative ducts, and the dorsal pores.
The dorsal pores are present, one in each segment, in many Terricolae,
but in the Limicolae are confined to one, in the prestomium. They
are usually placed intersegmentally over the septa. Their function
is unknown, but in some worms fluid has been seen to exude
from them.

The lining of the coelom consists mainly of a flat epithelium, but
on some parts of the alimentary canal it has the form of large, yellow
cells— the so-called yellow or chloragogen cells — which are loaded
with pigment grains. These cells are probably excretory in function,
and allow their contents to escape into the body-cavity, and to pass
thence to the exterior through the nephridia. The coelom is sub-
divided, as stated above, by the transverse septa, and in certain forms
(Libyodrilus, Bmnchiura) there are obliquely placed sheets shutting
off a lateral, parapodial-like section of it, as in some Polychaets.
Further, portions of the coelom are sometimes shut off from the
rest in connection with the generative organs (see below). There
is no longitudinal dorso-ventral mesentery (except in Criodrilus), but
traces of the ventral mesentery are sometimes left.

Sometimes certain of the larger blood vessels are enclosed in
perihaemal spaces. Whether or not these are coelomic is unknown.

Nephridia are absent from a certain number of the anterior
segments ; and in the Limicolae the generative segments are without
them in the breeding season. They are of two kinds: (1) the
meganephric, or ordinary kind, such as is found in the Limicolae
and in many of the Terricolae, and (2) the pledonepliric or diffuse
variety, found in some members of the families Perichaetidae,
Cryptodrilidae, and Acanthodrilidae. The two kinds may co-exist
in the same animal, and even in the same segment (Megascolides).

In Lumbricus we find the meganephric condition. The nephridia,
of which there is a single pair in each segment, consist of a long

OLIGOCHAETA.

499

winding tube, in which the following regions can be distinguished
(Fig. 407): (1) the preseptal
portion consisting of the coelomic
funnel and a short tube (a), lead-
ing back to the septum which it
perforates, to become continuous
with (2) the rest of the nephrid-
ium, which lies in the segment
behind. This postseptal part
presents the following regions :
(b) the narrow tube of consider-
able length and thin wall; parts
of it are ciliated : (c) the middle
tube which is short and confined
to the length of one loop only;
the middle tube is ciliated : (d)
the wide tube, which is long,
non-ciliated, and opens into a
short, dilated, muscular - walled
portion — the muscular duct which
opens to the exterior through the
ventral body-wall. The whole
nephridium, except the muscular
duct and the funnel, consists of
the so-called perforated or drain-
pipe cells.

In the Limicolae the nephrid-
ium is generally simpler, consisting

FIG. 407. — Nephridinm of Lumbricus (from
Vogt and Yung, after Gegenbaur). a funnel
and preseptal portion ; b the narrow tube ;
c the middle tube ; d the wide tube ; e the
muscular duct.

FIG. 408.— Section through a loop of the nephridium of
Lumbricus (after Claparede, from Vogt and Yung), showing
the perforated cellular character ; a nuclei ; b lumen ; c
blood vessel ; d connective tissue.

of the funnel (pre-
septal) and a long
coiled duct, passing
through a protoplas-
mic tube or mass in
which cell limits are
not always discernible
(Fig. 409), and lead-
ing to the wider ter-
minal part.

As a rule there
is only one pair of
nephridia in each

500

ANNELIDA.

FIG. 409.— Nephridiurn of Pontodrilus (after
E. Perrier). pv nephrostome; o dilated
part (vesicle) near the external opening;
tv the tube of the nephridium passing
through the nucleated protoplasmic mass u.

different places. This
difference in position
of the opening may
be accompanied by a
difference in struc-
ture, e.g. in Acantlio-
drilus novae-zealan-
diae the nephridia
which open in front
of the ventral setae
have a caecal appen-
dage, while those
which open in front
of the dorsal setae
are without this
appendage.

The pledonepliric
or diffuse nephridia
are networks of fine
tubes lying on the
body-wall and septa
in each segment
(Figs. 410, 411).
They have several
openings to the ex-
terior, and they some-

segment, but in Brachydrilus
there are two pairs, and in
Trinephrus three. The neph-
ridia always extend over two
segments, the internal opening
being in the segment anterior to
that in which the main part of
the nephridium lies.

The external opening is usually
near the setae of the ventral row,
but sometimes it is near the setae
of the dorsal row, and even dorsal
to these; and nephridia in suc-
cessive segments may open in

FIG. 410.— The diffuse or plectonephric nephridia of Oligcchaeta.
1, portion of a transverse section at the level of the setae of
Octochaetus multiporvs. S setae ; a, a1 nephridial pores ; n
nerve cord ; p peritoneum. 2, section across a nephridial tube
of Perichaeta aspergillum passing through the wall of the body.
ep epidermis ; m layer of circular, m' of longitudinal muscles
(the lines mark the inner limits of these layers) ; a nephridial
tube with its vesicle in the layer of circular muscles ; b blood
vessel. (From Perrier, after Beddard.)

OLIGOCHAETA.

501

17

times open into the coelom (Perichaeta, and in Octochaetus in the
case of the nephridia which open into the rectum), and sometimes
they do not (Odo-
ehaetus, Megasco-
hdes). I he coelomic
openings when pre-
sent are numerous,
but whether they
have any numerical
relation to the ex-
ternal openings is
not clear from the
published accounts.
Nor is it clear
whether we are to
look upon the plec-
tonephric condition
as being due to

the presence of FIG. 411.— Diagram showing the disposition of the nephridia of a

m P r mi «* «? rn 1 1 1 segment of Perichaeta aspergillum (from Perrier, after Beddard).

p dorsal pore; o external openings of nephridia: i intestine ; s

nephridia in a Seg- setae ; vv ventral blood vessel ; n nerve cord ; r nephridial net-

ment which have work ; vd dorsal blood vesse1'

become connected together, or whether they are derived from the
modification of a single pair of nephridia. However this may be, it
appears certain that the plectonephric condition is preceded in the
embryo by a stage in which there is only one pair of ordinary
nephridia in each segment. It is supposed that the adult condition
in such forms has arisen by the multiplication of the original simple
tubes. The diffuse nephridia may be the only kind of nephridia
present; or they may coexist in the same segment with meganephridia
(Perichaeta armata, etc.) ; or meganephridia may be present in one
part of the body, and plectonephric nephridia in another part, the
two conditions gradually passing into one another; e.g. in Megas-
colides australis there are plectonephridia without internal funnels
in the anterior segments, an intermediate condition in the middle
segments, while in the posterior segments the nephridia are mega-
nephric and possess coelomic funnels. It appears that in some cases
the nephridial network is continuous from segment to segment.

In some Oligochaeta the external opening of a certain number of
nephridia is into the alimentary canal. This is the case in the
Enchytraeidae, Octochaetus multiporus, species of Rhinodrilus,Acantlw-

502

ANNELIDA.

drilus, Megascolides, etc., in which the salivary glands are supposed
to be modified nephridia, and in Octochaetus multiporus there are
nephridia in the posterior segments, which open both to the exterior
and into the rectal part of the gut, as well as internally into the
coelom (recalling the respiratory trees of Gephyrea), see p. 530.

In the Eudrilidae, which have paired meganephridia, the ducts
of the nephridia branch in the body-wall, and form a network which
has several openings to the exterior.

The nephridia are developed from certain structures in the embryo called
pronephridia. These are small cellular aggregations attached to the septa, one
pair in each segment, except in front. The first pair constitutes the head-kidney :
they open on the head, sometimes on the dorsal surface by the head pore
(Lumbricus), and occupy two or three segments. They may persist or disappear.
In the hinder segments they are at first straight rows of cells ending anteriorly
on the septum in a flame-cell with a vacuole containing a flame-shaped flagellum
(Rhynchelmis). This large terminal cell eventually divides up, loses its flagellum,
and forms the ciliated coelomic opening.

As stated above, the plectonephric condition is preceded by a stage with one
pair of pronephridia in the segment.

In Megascolides anstralis the pronephridia in the anterior part of the body
give off loops, which become disconnected, so as to form several separate nephridia,
of which one retains the coelomic opening, and forms the large nephridium of
the segment.

Generative organs.

FIG. 412. — Generative organs of Lumbricus (after Bering).
T testes in X and XI; St the two sperm-rosettes (funnels of
vas deferens); Vd vas deferens; Ov ovary; Od oviduct;
Re receptacula seminis. One half of the sperm-reservoir and
the sperm sacs of one side have been removed.

The Oligochaeta are all hermaphrodite. The
position of the
gonads varies in the
Limicolae ; but it
is fairly constant in
the Terricolae, there
being in this group
usually (Fig. 412)
two pairs of testes
placed in segments
10 and 11 respec-
tively, and one pair
of ovaries in seg-
ment 13 (except
in the Moniligas-
tridae).

When there is only
one pair of testes, it
is in 10 in Typhaeus,
in 11 in Diachaeta
and Eudriloides, and

OLIGOCHAETA.

503

in 12 in Pontoscolex and Geoscolex. In Brachydrilus the ovaries are said to be in
12, but this is doubtful.

The reproductive glands are definitely localised thickenings of the
coelomic epithelium, and are placed upon the posterior faces o£ Certain
septa. The part of the body-cavity in which the testes lie may, in
some Terricolae, be cut off from the rest by a development of the
septa which forms the median part of the vesicula seminalis or
sperm reservoir (Figs. 412, 413).

The vesiculae seminales or sperm sacs are developments of the
septa of the testes segments. They are paired structures in Terri-
colae, and unpaired in most Limicolae. They communicate with the
coelom, but in many Terricolae the part of the coelom into which they
open is, as stated above, cut off from the rest by a membrane which

IX

FIG. 413. — Diagram of a longitudinal 'section through the generative segments of Lutnbricus
herculeus to show the relation of the generative ducts and sperm sacs, etc. The segments
are numbered in roman numerals, eh ovisac ; ep ectoderm ; ct internal opening of oviduct ;
/i testes ; Im longitudinal muscles ; ov ovary ; rm circular muscles ; rs spermathecae ; s?) sperm
sacs ; sk sperm reservoir ; st sperm rosette (internal opening of vas deferens) in the sperm
reservoir. (After Hesse.)

encloses a space containing the testes and the sperm rosette. This
is the sperm reservoir (Fig. 413). A sperm reservoir is not developed
in Allolobophora, Acanthodrilus, and some other forms (Fig. 414).
Sperm sacs are absent in the Encliytraeidae (except Mesencliytraeus).

The vesiculae seminales or sperm sacs do not necessarily correspond
in number with the testes ; they vary in number from one pair to
four (Fig. 414). They may attain a great size, extending back
through a great number of segments (60 in a species of Geoscolex). In
the Limicolae the sperm sac is, as stated above, generally unpaired.

A similar sac is formed in connection with the ovary in some
forms. This ovisac in the Limicolae is unpaired, and may be very

504

ANNELIDA.

large (RJiyncJielmis). In the Terricolae the ovisacs, when present, are

usually small and paired
(Fig. 413, etc.). They are
diverticula of the septum
at the hind end of the
ovarian segment, and in
some Liinicolae the
sperm-sac projects into
them.

The generative ducts
correspond in number to
the generative glands.
They usually open into
the general body-cavity

— Tls

ing the gonads, but in
some Terricolae (Lum-
bricus, etc.) the vasa
deferentia open into the
median part of the
sperm-sacs (sperm-
reservoir). In the Ter-
ricolae there are two
oviducts and two pairs

of vasa deferentia. The oviducts, as in the Limicolae, are short, and
open externally on the segment behind that containing the ovaries,
usually on the 14th; and internally into the coelomic chamber of the
ovarian segment, usually the 13th. The two vasa deferentia of the
same side join behind to form a single duct, except in Phreoryctes,
where they open on two consecutive segments, and in Pelodrilus, in
which they open on the same segment. The opening of the vas
deferens is variable in position*; in Lumbricus it opens on segment
15. The internal openings of the vasa deferentia — or sperm rosettes
as they are called — are in the coelom of the segments of the testis
(generally 10 and 11), and if there is a sperm reservoir they open
into it. There is in many forms attached to and opening into the
vas deferens near its external opening a glandular appendage called
the prostate, or spermiducal gland (Fig. 414). In some genera the
spermiducal gland opens to the exterior independently of the sperm
ducts.

* From segment 11 in Moniligaster to 22 in Diachaeta.

FIG. 414.— Diagram of the organisation of Megascolides
(from Perrier, after Benham). 1, generative apparatus ;
2, renal organs. Segments numbered in roman numerals.
In VIII and IX are the spermathecae ; in X and XI the
testes ; in XI to XIV the four sperm-sacs S ; in XIII
the ovaries and funnels of the oviducts ; in XVIII the
male generative opening and spermiducal glands pr.
ip the pepto-nephridia ; p dilatations of the intestine.
The nephridial network is shown in 2.

OLIGOCHAETA. 505

In the Limicolae the atrium, which is a dilatation on the vas
deferens close to its opening, seems to correspond to the spermiducal
gland.

In the Limicolae there is usually one pair of ovaries ^(except
Phreoryctes) and one pair of testes (except Lumbriculidae), and
their position varies somewhat in the different families. They are
placed further forward than in the Terricolae (for position see account
of families), and their ducts are short, opening on the segment
following that containing the gland. The nephridia of the segments
of the ovaries and testes disappear as soon as these organs begin
to develop.

The ova of the Limicolae are much larger, and have more yolk
than the ova of the Terricolae.

According to Beddard a trace of a second pair of ovaries can be made out in
the young of some earthworms (Lumbricus and Octochaetus) in the 12th segment.
In this case the number of ovaries will equal the number of testes, and the
series of gonads becomes a continuous one.

The spermatozoa, which are filiform, develop in the sperm sacs,
into which the cells of the testis (progametes) are dehisced. When
ripe they are drawn into the vasa deferentia by the cilia of the sperm
rosettes, and passed down these tubes, which their presence renders
of an opaque white colour and so visible to the naked eye in
earthworms, to the exterior. Here they are taken up, in the manner
described below, by the spermathecae (receptacula seminis) of
another worm, where they are stored until they are required for use.
The sperm athecae are small vascular sacs, which open externally
near one end of the segment which contains them (usually the
anterior); the number of them varies considerably. In the Tei~ricolae
there are usually several pairs (4 or 5). Generally there is only one
pair in a segment. In the Limicolae they are generally contained in
the testicular segment. In Enchytraeus, and possibly other genera,
the spermathecae open into the gut as well as to the exterior.

The capsulogenous glands, or as they are now called from their
supposed function, the albumen glands, are glandular developments
in the ventral body-wall in the generative segments of some earth-
worms. They probably secrete the albuminous matter found in
the cocoon.

Spermatoplwres have been observed in some forms, both aquatic
and terrestrial (e.g. Tubifex, some Lumbricidae). They have a
somewhat elongated shape, and often have a certain complexity of
structure. They consist essentially of spermatozoa cemented together

506 ANNELIDA.

into a packet. They are found on the segments which during
copulation are placed opposite to the male genital pores. The
tubercula pubertatis are papillae on the ventral side of the clitellar
segments.

The clitellum or girdle is a glandular thickening of the integument
of one or more segments of the body. In the Limicolae it is on the
generative segments themselves. In the Terricolae it varies in
position, but is never in front of the 12th segment, except in the
Moniligastridae.

The male and female openings are on the clitellum in Typhaeus, Megascolides,
Evdrilus, Pontoscolex, Criodrilus, Moniligaster, etc. (in Moniligaster the male
openings are between 10 and 11, the female openings between 11 and 12) ; in
Hormogaster, Diachacta, Rhinodrilus, Brachydrilus, etc., the male openings are
on it, the female being in front of it ; the female openings are on it, and the
male behind it in Cryptodrilus, Perichaeta, Deinodrilus, etc. ; finally in the
Lumbricidae both orifices are in front of it.

As a rule the clitellum is saddle-shaped, the glandular development
being confined to the dorsal and lateral regions, but in some forms it
is a complete girdle. Its secretion serves to make the cocoon, and in
some earthworms at any rate to bind the worms together in copulation.
Long modified setae are found in some forms in the neighbourhood
of the male pores, and protruding through them; and in a few
species bundles of similar setae are found near the spermathecae.
They are termed genital setae, those near the male pore being male
penial setae, and those near the spermatheca pore female copulatory
setae. When these modified setae are present, the ordinary setae of
the segment are absent. The cocoons in which the eggs are enclosed
may be spheroidal; more usually they are ellipsoidal, the two poles
being prolonged into short projections. They are formed by the
secretion of the clitellum which the worm slips over its head. As
the cocoon passes over the openings of the generative organs, it
receives the ova, spermatozoa, and albumen which form its ultimate
contents. Being elastic it shrinks when free of the worm and forms
a compact case, traces of its origin being generally retained in the
two projections from its poles. The cocoons are attached to aquatic
plants (Limicolae), or deposited in damp earth (Terricolae). It is
common, though not universal, to find that only one embryo in each
cocoon attains full development. There is no free larval stage : the
young leave the egg as minute fully formed worms.

Earthworms copulate. In the common earthworm of this country the process
may be observed as follows : two worms in neighbouring burrows apply the
anterior ends of their bodies together (the posterior ends remaining in the

OLIGOCHAETA. 507

furrows) in such a way that the openings of the spermathecae are opposite
the clitellum of the other worm. The bodies become adherent, probably by
suction of the ventral surface of the clitella, with the assistance of a secretion
of the clitellum, and sperm is poured out of the openings of the vasa deferentia.
This is passed back along the ventral body of the worm in grooves which, can be
faintly discerned in sexually mature worms, leading back from the male genital
opening. These grooves end at the clitellum, and the transmission of the sperm
backwards is probably effected by the coordinated contraction of their sides.
However that may be, the sperm is transported backwards until it comes to
the ventral surface of the clitellar region ; here it is opposite the openings
of the spermathecae of the adherent worm. These appear to take it up by
a suctorial action, and so to become filled with the sperm of the other worm.
The use of spermatophores in such cases is unknown.*

Asexual reproduction is found in some of the aquatic forms, and
the earthworms seem to have considerable power of reproducing
lost parts.

The asexual reproduction consists of a process of fission combined
with gemmation. It takes place at certain periods of the year under
certain climatic conditions, and is exhibited by worms which are
immature in the fact that the generative organs are not developed.
In the Naididae (Nais, Cliaetog aster, etc.) a zone of fission is formed,
i.e. one of the somites enlarges and becomes divided into two parts :
the anterior part forms the anal segment of the anterior worm, and
the posterior gives rise to the head and anterior segments of the
posterior portion. A chain of zooids may be formed in this way,
the individuals of which eventually separate. In the earthworms
the anterior end, including the pharynx and cerebral ganglia, can
be reproduced after excision, and the same remark applies to the
hind end.f

The Oligochaeta are distributed all over the world in fresh-water
and on the land. Some are amphibious, and a few species are
marine; but the majority are terrestrial, and are earthworms in the
-ordinary sense of the word.

Earthworms are found in the surface soil of the earth, in which
they form burrows, coming to the surface to get rid of their faeces
(worm casts), and to procure food, and to copulate. Their food
consists of decaying vegetable substances, which they find in the
form of leaves and twigs on the surface and in the dark vegetable
surface soil, large quantities of which they swallow. The part which
earthworms play in modifying the surface soil is well known, and
has been fully treated by Darwin in his celebrated work on the
subject. Briefly their action may be summed up as follows : they

* Andrews, American Naturalist, 1895. t Billow, Z. f. w. Z., 1883.

508 ANNELIDA.

are continually bringing up to the surface some of the deeper soil,
and depositing it in the form of casts ; they thus assist in turning
over the soil, and in mixing together the different parts of it, and
the soil of the deeper layers is thus exposed to the atmosphere.
Phosphorescent earthworms have been observed, but they are not
common.

Sub-order 1. Limicolae.

Oligocliaeta with a clitellum commencing not later than the tenth
or eleventh segment, and consisting only of a single layer of cells ;
the sperm-ducts only occupy two segments, the external pore being
on the segment following that into which the funnel opens; the
male pore is situated in front of the female pore ; eggs generally
large, always provided with abundant yolk ; egg-sacs large ; spermi-
ducal glands, when present, possess a muscular layer interposed
between the inner epithelium and the glandular layer; sexual
maturity at a fixed period. For the most part fresh-water forms.

Fam. 1. Phreoryctidae. Aquatic or terrestrial, of slender form, often very
long. Setae in four rows of single setae or of couples, sigmoid. Testes in 10
and 11. Ovaries in 12 and 13, or in 13 only. Sperm-ducts, two pairs opening
separately, without spermiducal glands. Spermathecae in front of testes,
without diverticula. No genital setae. Phreoryctes Hoffmeister, Eur. , N. Am. ,
N. Z., clitellum 11-14, 4 ovaries ; Pelodrilus Beddard, New Zealand, clitellum
11-13.

Fam. 2. Lumbriculidae. Aquatic worms of moderate size. Setae paired and
/-shaped, sometimes with the free extremity bifid. The dorsal blood vessel or
the transverse vessels with blind contractile appendages (except Stylodrilus and
(?) Alluroides}. Testes in 9 and 10; ovaries in 11. Two pairs of sperm-ducts
(exc. Alluroides) uniting to open by a single spermiducal gland on each side,
which lies in front of the oviducal pores usually in 10. Lumbriculus Gr.,
male pore in 8 ; Ehynchelmis Hoffmeister ; Trichodrilus Clap. ; Phreatothrix
Vejd. ; Claparedilla Vejd. ; Stylodrilus Clap. ; Sutroa Eisen ; Alluroides Bed.,
this genus presents certain characteristics of Terricolae. Edipidrilus Eisen.

Fam. 3. Tubificidae. Aquatic, fresh-water or marine, of small size and
slender build. Setae of three kinds — capilliform, pectinate, and uncinate — of
which the first two (when present) are only found in the dorsal bundles. Dorsal
and ventral blood vessels connected in every segment. Testes in 10, ovaries in
11, sperm-ducts always ending in spermiducal gland opening on 11. Oviducts
open between 11 and 12. Spermathecae one pair in 10. Tubifex Lam., dorsal
bundles with capilliform, pectinate, and uncinate setae ; Clitellio Sav. ; CL
arenarius Sav. , coasts of Europe ; Limnodrilus Clap. , with uncinate setae
only, Eur. and California; Hesperodrilus Bedd., Falkland Isl. and S. Am.;
Heterochaeta Clap., marine, coasts Engl. and Belg. ; Peloscolex Leidy, N.
Am. ; Psammoryctes Vejd., setae capillif., unc., palmate, and pectinate, Eur. ;
Hemitubifex Eis. ; Telmatodrilus Eis. ; Spirosperma Eis. ; Ilyodrilus Eis.;
Bothrioneuron Stole; Lophochaeta Stole; Branchiura Bedd., with median
dorsal and ventral gills, Victoria regia tank in Regent's Park, London ;

TERRICOLAE. 509

Vermiculus Goodrich, marine, Weymouth ; Embolocephalus Randolph, Lakes of
•Geneva and Zurich ; Phreodrilus Bedd., subterranean water, N. Zeal.

Fam. 4. Naididae. Small aquatic worms. Setae usually in four groups
upon each segment — sigmoid, bifurcate, hastiform, and capilliform. In most
genera the dorsal setae are absent from a variable number of the anterior
segments. Sexual reproduction at fixed intervals, between which asexual
reproduction by fission occurs. Sexual organs (only known in a few types)
far forward, commencing even in the 5th segment. Testes in 5, ovaries in 6.
There is sometimes only one ncphridium in a segment, and in Uncinais littoralis
they are said to be absent altogether. Nais 0. F. Mliller (including Slavina
Vejd. ; Stylaria Lamk., etc.), the first 5 segments lack dorsal setae ; N. lacustris
L. ; Pristina Ehrbg. (incl. Naidium Schm.); Eipistes Duj. ; Uncinais Lev.;
Bohemilla Vejd. ; Dero Oken, gills as processes surrounding the anus ; D.
Mulleri, Gt. Brit. ; Chaetobranchus Bourne, gills as hollow processes of body-
wall enclosing the dorsal setae, Madras ; Amphichaeta Tauber, several segments
without setae ; Chaetogasler v. Baer, ventral setae only present, uncinate, some
segments without setae, ventral ganglia more numerous than apparent segments,
as also in Vetrovermis Imhof., which is probably allied here.

Fam. 5. Enchytraeidae. Small worms ; setae (absent in Anachaeta) short,
straight or curved, not bifid. A single pair of calciferous glands sometimes
present. Dorsal vessel present only anteriorly, sometimes with cardiac body.
Testes in 11, male pores in 12 ; a reduced spermiducal gland present ; oviducts
represented by pores. Spermathecae one pair, in 5, generally opening into gut.*
In most there is a single pore on the prestomium. Dorsal pores occasionally
present. Fresh-water, marine, damp earth, littoral. In the presence of calciferous
glands and in the distance between the spermathecae and the male pores this
family approaches the Terricolae. The presence of dorsal pores in some genera
(Fridericia) points in same direction. Distichopus Verrill; Chirodrilus Verrill ;
Mesenchytraeus Eisen ; Stercutus Michaels., in manure, lumen of al. canal
sometimes obliterated; Pachydrilus Clap.; Marionia Michaels.; Buchhohia
Michaels. ; Enchytraeus Henle, setae hooked at free extremity ; Fridericia
Michaels. ; Henlea Michaels. ; Anachaeta Vejd. (Achaeta Vejd. ), setae absent,
represented by large cells ; Bryodrilus Ude ; Parenchytraeus Hesse.

The Discodrilidaef are allied here ; they are small parasitic forms, without
setae, with a small number of segments ; cephalic lobe divided into two ; a
sucker at the hind end. Pharynx with two jaws, one above the other, formerly
mistaken for Leeches. Branchiobdella Odier (Astacobdella Villot), parasitic on
gills of the Crayfish ; Bdellodrilus Moore ; Myzobdella Leidy.

Sub-order 2. Terricolae.

Earthworms. Oligochaeta with a clitellum which never commences
before the twelfth segment (except in Moniligastridae), and always
consists of two layers of cells. The sperm-ducts traverse two or
more segments on their way to the exterior. Ova small and with
little yolk ; egg-sacs small. Spermiducal glands, when present, have
not a muscular layer interposed between the inner epithelium and

* Found also in Ehynchelmis and Sutroa.

t J. P. Moore, Journ. Morph., 10, 1895, p. 497.

510 ANNELIDA.

the glandular layer. Sexual maturity seems to be more or less
continuous. Oviducal pores always on segment 14, and ovaries in
segment 13.

Fam. 1. Moniligastridae. Large or small earthworms with paired setae,
8 per segment; clitellum 10-13, inconspicuous, one cell thick. One pair of male
pores in Moniligaster, between 10 and 11, testes in 10 ; two pairs in Desmo-
gaster, on 11 and 12, testes in 10 and 11. Spermiducal gland showing the same
structure as in the Lumbriculidae, with sometimes a protrusible penis. Ovaries
in 13 in Desmogaster and some specjes of Moniligaster, in 11 in other species of
M. Egg-sacs large ; eggs smallish, larger than those of .other Earthworms,
smaller than those of aquatic forms. India, Ceylon, Sumatra, Borneo, Burmah,
Bahamas. Moniligaster Per.; Desmogaster Rosa. This family of earthworms
is placed by some zoologists amongst the Limicolae, because of the position and
structure of the clitellum, the length of the vas deferens, and the position
of the ovaries in some species. Terricolous.

Fam. 2. Perichaetidae. With numerous setae in each segment arranged in a
continuous circle, or with dorsal and ventral gaps ; male pore nearly always on
18. Gizzard always present ; intestine frequently with two (sometimes more)
caeca and a rudimentary typhlosole. Nephridia diffused or paired. Spermiducal
glands generally lobate ; penial setae present or absent ; spermathecae with one
or two diverticula.

Perichaeta Schmarda, very active, setae usually in a continuous row, nephridia
diffuse, mainly tropical. Oriental, also in Australia, Europe and America ;
Megascolex Templeton, setae interrupted dorsally and ventral ly, nephridia diffuse
and paired, Australian and Oriental ; Pleionogaster Michaels. , Philippines ;
Perionyx Perr., tropics Old World ; Diporochaeta Bedd., N. Z. and Australia.

Fam. 3. Cryptodrilidae. Terrestrial, sometimes aquatic, with 8 setae per
segment. Clitellum variable in extent, occupying some or all of segments
12 to 23, usually complete anteriorly. Spermathecae one to five pairs, placed
anteriorly, nearly always with one or two diverticula. Male pores on segment
17 or 18, opening independently of or into the distal non-glandular part of the
spermiducal gland, which is either tubular or lobate. Penial setae generally
present. Nephridia paired or diffuse. The large number of new forms which
have been described make it a difficult matter to separate the genera. In most
parts of the world, but mainly tropical, specially Australian. This family inter-
digitates with the Acanthodrilidae and with the Perichaetidae, from which the
only difference is the character of 8 setae per segment, which, indeed, is shared
by the anterior (though not the posterior part of the body) of Megascolex.
Microscolex Rosa, mainly S. America ; Pontodrilus Perr. ; Typhaeus Bedd. ;
Dichogaster Bedd. ; Deodrilus Bedd. ; Millsonia Bedd. ; Fletcherodrilus Michaels;
Trinephrus Bedd., 3 pairs of nephridia in each segment; Digaster Perr.;
Megascolides McCoy ; M. australis Spencer, the giant earthworm of Gippsland,
1 '23 m. ; Cryptodrilus Fletcher ; the last five genera are mainly confined to
Australia; Microdrilus Bedd., Java, very active; Gordiodrilus Bedd., mainly
trop. Africa; Ocnerodrilus Eisen, America and Africa; Nannodrilus Bedd.,
West Africa, aquatic.

Fam. 4. Acanthodrilidae. Large or small, usually terrestrial, rarely aquatic.
Setae 8, 12, or numerous. Male pore on 18 ; pores of spermiducal glands,
which are tubular structures generally with penial setae, on 17 and 19.

TERRICOLAE. 511

Spermathecae generally 2 pairs in 8 and 9, with diverticulum or diverticula.
This family is closely connected with the last. Acanthodrilus.PerT., paired
nephridia, entirely from the Southern hemisphere ; Diplocardia Gannan ;
Octochaetus Bedd., nephridia diffuse, N. Z. ; Kerria Bedd., American ; Deinodrilus
Bedd., with pericardium, N. Z. ; Plagiochaeta Benh., N. Z. ; Trigastey Benh.,
St. Thomas ; Benhamia Michaels, diffuse nephridia, mainly tropical Africa.

Fam. 5. Eudrilidae. Size variable, with paired nephridia ; in some genera
nephridial ducts as networks in body-wall, with numerous external openings ;
setae in couples, sigmoid ; spermiducal glands always present ; sperm-ducts
open into these glands at some distance from external orifice. Spermathecae
(if present) unpaired, and opening outwards near the female genital pores,
generally replaced by, or, if present, enclosed in coelomic sacs, which are
frequently connected with the other parts of the female reproductive system.
In some genera the male and female generative openings are unpaired. With
the exception of Eudrilus the family is restricted to Africa.

Sub-fam. 1. Pareudrilini. Integumental sense organs rarely present.
Sperm-ducts without dilatation ; ducts of nephridia branching in body-
walls ; calciferous glands modified or absent. Eudriloides Michaels, ;
Reithrodrilus Mich. ; Megachaeta Mich. ; Metadrilus Mich. ; Notykus Mich. ;
Parendrilus Bedd. ; Unyoria Mich. ; Platydrilus Mich. ; Nemertodrilus.
Mich. ; Libyodrilus Bedd. ; Stuhlmannia Mich.

Sub-fam. 2. Eudrilini. Integumental sense organs present. Calciferous
glands, paired and unpaired, of the usual structure. No integumental
nephridial network ; sperm-ducts with dilatation immediately following
funnel. Eudrilus Perr. ; Eminoscolex Mich. ; Polytoreutus Mich. ; Preussia
Mich. ; Paradrilus Mich. ; Hyperiodrilus Bedd. ; Heliodrilus Bedd. ;.
Alvania Bedd. ; Teleudrilus Rosa.

Fam. 6. Geoscolicidae. Size various, sometimes aquatic. Setae 8 in a segment,
paired or irregular in arrangement. Clitellum saddle-shaped except in Diachaetct
and Ilyogenia, usually rather extensive, often furnished with modified setae.
Nephridia always paired, rarely more than one pair in a segment. Gizzard
anterior. Male pores generally within the clitellum, with or without spermiducal
glands. Spermathecae without diverticula.

Sub-fam. 1. Geoscolicinae. Spermathecae one to four pairs in the
neighbourhood of the gizzard. All tropical American except Ilyogenia
from Natal. Prestomium absent in Pontoscolex, Diachaeta, and Onycho-
chacta (as in Deodrilus). Rhinodrilus Perr. ; Geoscolex Leuck. ; Spargano-
philus Benham ; Sp. tamesis Benham, England ; Trichochaeta Bedd. ;
Onychochaeta Bedd. ; Ilyogenia Bedd. ; Tylconus Mich. ; Anteus Perr. ;
Pontoscolex Schm. ; Urobenus Benh. ; Diachaeta Benh.

Sub-fam. 2. Microchaetinae. Spermathecae, if present, usually near
female apertures, nearly always minute, and generally numerous in each
segment. Copulatory papillae furnished with special glands, and usually
with modified setae. Old world. Criodrilus Hoffmeister ; Microchaeta
Perr ; Callidrilus Mich. ; Kynotus Mich. ; Glyphidrilus Horst ; Annadrilus
Horst ; Hormogaster Rosa, Italy ; Alma Gr. (Siphon ogaster Levinsen), with
long paired penial processes ; Bilimba Rosa ; Brachydrilus Benh. , ovaries
said to be in 12.

Fam. Lumbricidae. Terrestrial (rarely aquatic), of moderate size. Setae
8 in a segment. Male pores usually on 15, rarely on 12 or 13. Clitellum

512 ANNELIDA.

saddle-shaped, begins some way behind the segment of the male pores. Dorsal
pores present. Gizzard single, at end of oesophagus. Nephridia paired and
similar. No spermidncal glands or penial setae. Tubercula pubertatis nearly
always present. Cosmopolitan, but most characteristic of Palaearctic and
Nearctic regions. Allurus Eisen, male pores on 13 ; Tetragonus Eisen, male
pores on 12 ; Allolobophora Eisen, prestomium incompletely divides buccal lobe,
male pores on 15, no median seminal reservoirs ; A. terrestris Sav., spermathecae
in 9 and 10 resp. ; Lumbricus Eisen, prestomium completely divides buccal
segment, male pores on 15, two median seminal reservoirs occupying segments
10 and 11 into which open three pairs of sperm -sacs, spermathecae two
pairs, in 9 and 10 resp.; L. rubellm Hoffm., clitell. 27-32, tubercula puber-
tatis 28-31, 1st dorsal pore 7/8. Male pores almost invisible ; L. herculeus Sav.;
the common earthworm of this country, number of segments 180, cli tell um
:32-37, tubercula pubertatis 33-36, 1st dorsal pore 7/8, male pores conspicuous.

Class III. HIKUDINEA.*

Elongated, vermiform Annelida with anterior and posterior suckers,
without setae (except Acanthobdella) or parapodia, and with median
genital openings. Coelom usually broken up into numerous inter-
communicating spaces. Hermaphrodite.

The Hirudinea have, owing to certain superficial resemblances,
often been associated with the Trematoda, with which group they
have however nothing in common. They are in reality segmented,
coelomate animals with distinct affinities to the Oligochaetous
Chaetopoda. These affinities are specially obvious in the genus
Acantholxlella, in which there are setae in the anterior segments
embedded in pits in the body-wall, and a spacious body-cavity
divided by transverse septa into chambers. In the typical Leeches
the coelom is difficult to trace completely in the adult, but it is
undoubtedly present in the embryo in the usual Annelidan form of
a series of paired cavities in the mesoblastic somites ; and these
cavities give rise in the adult to the sinus system, and indirectly to
the tubes of the botryoidal tissue ; likewise, though in a modified and
veiled form, to the gonads and nephridia. A vascular system is
present, and by many anatomists is regarded as being continuous
with the sinus system; but this continuity is doubtful, and in the

* S. Apathy, " Siiss-wasser Hirudineen," Zool. Jahrb., 3, 1888, p. 725. Id.,
"Analyse der ausseren Kbrperforni der Hirudineen," Naples Mittheilungen, 8,
1888, p. 153. A.. Oka, " Beitrage z. Anat. d. Clepsine," Z. f. w. Z., 58, 1894,
p. 79. Fr. Leydig, " Circulations— u. Respirationssystem v. JSTephelis u. Clep-
sine," Ber. d. K. Zoot. Anst. zu Wiirzburg, 1849. Id., " Zur Anat. v. Piscicola
geometrica, etc.," Z.f. w. Z., 1. E. Ray Lankester, "On the connective and
vasifactive tissue of the medicinal leech," Q.J.M. S., 20, 1880, p. 307. A. G.
Bourne, "Contributions to the Anatomy of the Hirudinea," Q. J. M. S., 24,
1884, p. 419. C. 0. Whitman, "The Leeches of Japan," Q. J. M. S., 26, 1886,
p. 317. A. Moquin-Tandon, Monographic des Hirudindes, Paris, 1846.

HIRUDINEA.

present state of our knowledge cannot
be admitted. Externally the body is
marked by a number of transverse
rings — the annuli — which are short,
and may be more or less indistinct.
These rings do not correspond with
the internal segments, which may be
indicated by incomplete partitions; but
they constitute much shorter portions
of the body, three (Branchellion,
Clepsine), six (lehthyobdella, Callio-
l>della, Pontobdetta), five (Hirudo),
twelve (Piscicola) of them corre-
sponding to one internal segment.
Towards the two ends of the body the
segments are reduced in the number
of rings, and in other respects.

There is always a posterior sucker,
into the constitution of which a num-
ber of true segments (six or seven)
enter, and generally an anterior sucker
at the anterior end of the body ; both
are ventral. The anus opens dorsal to
the posterior sucker, and the mouth is
on the ventral surface in the anterior
sucker. The animal moves in a looping
manner by means of its suckers. There
are no parapodia, or setae (except in
Acanthobdetta), or head appendages,
but in one genus (Branchellion) there
are leaf-like branchial processes on the
middle part of the body.

On the annuli in transverse rows
are arranged the so-called segmental
sense-organs or sensory papillae. The
arrangement of these differs on the
different annuli of a segment, but is
the same for corresponding annuli of
different segments. On the head some
of these organs are modified into eyes
and into the cup-shaped organs. The

2 L

513

FIG. 415. — Hirudo medicinalis show-
ing the segments according to
Whitman, and illustrating the
enumeration adopted in the text
(after Whitman, from Lang)., The
5 pairs of eyes are marked by the
larger, the segmental sense-organs
by the smaller black dots ; the
openings of the nephridia by ob-
long marks (lp-17p). The rings are
counted on the right, the segments
on the left. 30/3 1 marks the position
of the male, 35J36 of the female
genital opening, an anus ; 6s pos-
terior sucker which is supposed to
consist of 7 segments fused together.

514 ANNELIDA.

skin is also often highly coloured, owing to the presence of
pigment, not only in the cutis, but to a certain extent also in the
epidermis.

The clitellum consists of a glandular development of the skin of
the 9th, 10th, and llth segments (UOth, llth, and 12th). Amongst
the Gnatholtdellidae it is most developed in Neplielis; in Hirudo it
is inconspicuous. The genital openings are on the 10th and llth
segments* (Whitman, Oka) the male opening being in front of the
female (Fig. 415).

According to the most recent statements the Hirudinea possess, without ex-
ception, 33 segments, some of which are however always reduced. A true
segment is determined by the presence of a ganglion, so that 33 ventral ganglia
can be made out. It must, however, be admitted that these ganglia are not
easy to see. The number is arrived at in this way : the suboesophageal ganglion
consists of 5 ganglia (Whitman, Oka) ; then follow 21 single free ganglia, and
then one composite one consisting of 7 fused ganglia.

Apathy also makes 33 segments, but according to him the suboesophageal
ganglion consists of 6, and the last ganglion also of 6. His enumeration is as
follows. The body is divisible into six regions, viz. the region of (1) the head,
(2) the clitellum and preclitellum, (3) the stomach, (4) the intestine, (5) the anus,
and (6) the posterior sucker ; of these the anal region contains three segments, the
rest six each. The head region consists of six more or less reduced and shortened
segments, four or five of which may enter into the formation of the sucker. Segment
1 is always eyeless, and segment 6 possesses eyes only in the ten-eyed Gnathobdell-
idae. The mouth is on the ventral surface, and its anterior limit is at least two
segments from the front end of the body. The preclitellar segments are 7, 8, 9,
and the clitellar segments are 10, 11, 12. Of the 12 segments of the middle-
body, i.e., of the stomach and intestine, the first and last are usually reduced,
but the 2nd to the llth are complete, and each contains the number of rings
characteristic of the genus. The anal region contains three segments much
reduced ; the anus is in the dorsal middle line at most two segments in front of
the sucker. The post-anal segments are all incorporated in the sucker — some of
them being invaginated into it ; they are six in number, as is shown by the
constitution of the last ganglion.

The body-wall consists of a single layer of epidermis cells with a
cuticle; a cutis containing pigment cells and blood vessels, both of
"which intrude into the epidermis ; an outer circular and an inner
longitudinal layer of muscles. The muscular fibres are tubular, i.e.,
they consist of an outer cortex of striated, presumably differentiated,
contractile substance, and an inner core of granular matter, in which
lies the nucleus. Unicellular glands, opening on the surface and
secreting a mucous fluid, are found in great numbers in the epidermis

* Apathy makes the genital openings in segments 11 and 12, and the clitellum
to include 10, 11, and 12. Bourne agrees with the position in the text, if we
allow, as Oka does, that the suboesophageal ganglion consists of 5 fused ganglia.

HIRUDINEA.

515

Sb

or sunk in the cutis, or even amongst the muscles. The clitellar
glands are specially enlarged modifications of the ordinary skin gland,
and are found deeply situated in the clitellar region ; they secrete a
clear viscid substance which quickly hardens outside the bojiy and
is used to form the cocoons when the eggs are laid. Within the
muscles there is a connective tissue, in which the various organs are
embedded. These organs we may now proceed to consider.

The central nervous system has the typical Annelidan character
of two ventral cords closely approximated, but diverging from one
another in front to pass round the oesophagus. There is a bilobed
swelling dorsal to the alimentary canal constituting the supra-
oesophageal ganglion, and supplying the
cephalic sense-organs; and a series of
swellings on the ventral cords, each
of which gives off two pairs of nerves.
These ventral ganglia are segmental in
their arrangement, but are partly fused
anteriorly and posteriorly. Thus in the
suboesophageal ganglion and circum-
oesophageal commissures five (or six)
ganglia can be made .out (Fig. 416);
these belong to the first five (or six)
segments of the head region. The last
ganglion, which supplies the sucker,
consists of seven (or six) ganglia
fused, and between these two composite
ganglia there are twenty-one separate
ventral ganglia* (Fig. 424). There is
an unpaired median longitudinal nerve
passing from ganglion to ganglion be-
tween the two halves of the ventral
cord and a system of visceral nerves
which was discovered by Brandt. The
latter consists of an intestinal nerve,
which arises from the brain and runs
close to and above the ganglionic chain;
it sends branches to supply the caeca
of the stomach. Three ganglia, which

FIG. 416. — Anterior end of Hirudo
(after Leydig). G cerebral ganglion,
with suboesophageal ganglionic
mass ; Sp visceral nerves ; A eyes ;
Sb sense-organs.

* According to Bourne's enumeration there are 23 ventral ganglia, but he
counts the suboesophageal and posterior ganglion as single ganglia ; if the
former be allowed at 5 and the latter at 7, it makes the total number 33.

516

ANNELIDA.

in the common leech lie in front of the brain, and send their nerve-
plexuses to the jaws and pharynx, are considered
by Leydig to be enlargements of cerebral nerves,
and very likely control the movements which
occur in swallowing.

The alimentary canal. The mouth leads into
a muscular pharynx provided with salivary glands.
In the Rliyncobdellidae the anterior part of the
pharynx is protractile and highly muscular; it
forms the so-called proboscis. In the Gnatlio-
bdellidae the anterior part of the pharynx projects
as three prominent ridges, over which lie the
three serrated chitinous plates or jaws (Fig. 417).
Occasionally the jaws are reduced in number
(Greobdella), or
they may be vesti-
gial (Trochetia),
or entirely ab-
sent (Leptostoma
edentuluni). The
pharynx (Fig.
418) is followed
by a tubular
oesophagus (in-
conspicuous in
Hirudo), which
leads into a thin-
walled stomach

(sometimes called the crop or proventriculus) pro-
vided with paired, segmentally arranged lateral
caeca. These vary in number in different forms,
and the last pair are much the largest, and extend
backwards on each side of the intestine. The
blood swallowed by the animal is stored up in
these caeca, consequently they are best developed
in forms which feed most rarely ; in Aulastoma,
which does not suck blood at all, but feeds on
small worms, etc., the last pair alone are present.
From the stomach a short intestine, the anterior
part of which is often provided with two dorsal
caeca (Hirudo), leads back to the anus. The

a 1)

FIG. 417.— ft, cephalic region of the
Medicinal Leech ; the three jaws are
shown, b, one of the jaws isolated
with the finely serrated free edge.

FIG. 418. — Diagram of a
longitudinal section
through the Medi-
cinal Leech (after
Leuckart). D stom-
ach with 11 lateral
caeca ; G cerebral
ganglion ; Gk ventral
nerve-cord; Ex
nephridia. The in-
testinal caeca are
not shown.

HIRUDINEA.

517

anterior part of the intestine is sometimes called the stomach, and
the hinder part may be distinguished as the rectum.

The perivisceral or body-cavity is a coelom, as is shown by its
development and its relations to the renal organs ; but in Ayantho-
bdella alone is it a spacious cavity divided by septa into chambers, as
in the Oligochaetes. In all other leeches it is much broken up, and
though retaining its relations with some of the organs, e.g. ventral
nerve cords, principal blood vessels, etc., it is largely without a peri-
visceral character, and has the form of longitudinal canals or sinuses
connected by a complicated system of intercommunicating spaces.
This system of canals and spaces is commonly called in leech
morphology the sinus system; the arrangement of it varies some-
what in the different genera.

hi

dl

Owing to the fact that the sinus system contains a fluid closely resembling the
fluid in the blood-vessels, it has often been held to be a part of the vascular system.
Ley dig was the first to recognize the distinction between the two, and in this he
was followed by subsequent workers. But although it is now recognized by the
majority of workers that
the two systems are dis-
tinct, it is still generally
held that they are con-
tinuous through their finer
branches. This view is,
as we shall see, based on
insufficient evidence, and
having regard to the state-
ments of Oka and Burger,
it seems safe to assert as
a fact that the two sys-
tems are separate, as has
been shown to be the case
for all other groups in
which the matter has been
closely investigated.

In Clepsine (Fig. 419)
there are five longitudinal
canals : (1) a median sinus,

si

FIG. 419.— Diagram illustrating the arrangement of the
coelom or sinus system in the middle part of the body of
Clepsine complanata (after Oka), dc, mlr, vc, sc, he trans-
verse sinuses connecting the main longitudinal sinuses ;
dg dorsal blood vessel ; dl dorsal sinus ; vg ventral blood
vessel ; vt ventral sinus ; n nerve cord ; zl intermediate
sinus as a network of canals in this part of the body ;
si lateral sinus ; 111 hypodermal sinuses.

which in the region of the
gut diverticula, i.e., in the

middle part of the body, is divided into a dorsal sinus enclosing the dorsal blood
vessel, and a ventral having relation to the ventral blood vessel, nerve cord, and
some of the reproductive organs (ovaries and vas deferens) ; (2 and 3) a pair of
lateral sinuses placed at the two margins of the body ; and (4 and 5) a pair of
intermediate sinuses, which, in the region of the nephridia, are broken up into
a network of canals. The median sinus is divided up by a few incomplete, but
where they occur segmental, septa. These five sinuses communicate Avith one
another by numerous transverse sinuses, and there is a system of hypodermal

518

ANNELIDA.

sinuses communicating with the others. The fluid in the sinuses contains two
kinds of corpuscles, the smaller are exactly similar to the corpuscles of the
blood, the larger are apparently detached from the epithelium lining the sinuses,
and are not found in the blood. That these sinuses are coelornic is shown by
the fact that the nephridia open into them, and that they do not communicate
with the vascular system. The latter fact, though long unrecognized on account
of the difficulty of distinguishing between blood-vessels and the finer ramifi-
cations of the sinus system, can hardly be disputed if Oka is correct in his
statements that the two can easily be distinguished in stained preparations,
and that the corpuscles of the sinus fluid differ as above explained from those
of the blood. Moreover, developrffentally the two systems are absolutely
distinct.

l o n vs

FIG. 420.— Diagrams of transverse sections through various leeches to show the relation of the
sinus system (coelom) to the other organs. 1, Clepsine. 2, Nephelis. 3, Pontdbdclla.
h, Hirudo. (After Bourne, from Perrier). a alimentary canal ; ds dorsal sinus ; dv dorsal
vessel ; /nephridial funnel ; c, Is lateral sinus ; Iv lateral vessel ; n nerve cord ; na nephridio-
pore ; o ovary ; t testis ; vs ventral sinus ; v ventral vessel.

In other leeches the coelom is very similar (Fig. 420). In Pontoldella it is
even more complete than in Clepsine. In Hirudo the lateral sinuses are absent,
and in Nephelis the dorsal.

Vascular system. The blood is colourless in the Wiynchobdellidae,
and coloured red with haemoglobin in the Gnathobdellidae. In all
cases it has approximately the same colour as the coelomic fluid.*
Since Leydig's work the main blood vessels have been distinguished

* In the young Nephelis the blood is red and the coelomic fluid yellow
(Burger).

HIRUDINEA. 519

from the longitudinal canals of the sinus system by having thicker,
often more muscular walls. The main longitudinal trunks vary
considerably in different genera (Fig. 420), but however many there
are they all communicate with one another and form a continuous
system, and are often contained in one or more of the canals of the
coelomic system.

In Pontobdella there are four main trunks, a dorsal and ventral and two lateral,
all contained in sinuses ; in Clepsine there is a dorsal and a ventral, both con-
tained in sinuses ; in Hirudo and Nephelis there are no dorsal and ventral vessels,
but only two lateral, which are not contained in sinuses.

In Clepsine the dorsal vessel is dilated into fifteen small chambers, each of
which possesses a cellular projection of its wall, which is called a valve and
probably buds off blood corpuscles. Moreover, the hinder part of the dorsal
vessel in this animal spreads out into a sinus, which completely surrounds the
intestine and opens into the ventral vessel.

The botryoidal tissue is found in the GnathoMelUdae. It is a
brown pigmented tissue which embraces the alimentary canal, the
blood vessels, the main lacunae of the coelom, etc., "in a word, it is
a pigmented tissue, which in the absence of a proper perivisceral
cavity fills up all the interstices situated between the organs it
invests " (Leydig quoted by Lankester). It consists of swollen cells
joined together in anastomosing rows, and containing tubular cavities
continuous along the cells of a row. These botryoidal vessels contain
a red fluid, and constitute a tubular network lying between the
alimentary canal and body-wall, and extending into the muscles of
the latter. In places they are swollen into the botryoidal sinuses,
which are vesicles lined by botryoidal cells. These are conspicuously
developed in Nephelis and Trochetia (forms without the dorsal
sinus), and some of them contain and receive the opening of the
funnels of the nephridia. They are comparable to the so-called
perinephrostomial sinuses, or parts of the sinus system which contain
the nephridial funnels in other Gnathobdellidae.

In Hirudo a similar, but less conspicuous structure, formed of botryoidal
tissue and containing the funnel of the nephridium, is present on the dorsal side
of the testis.

The botryoidal vessels undoubtedly communicate with the dorsal and ventral
sinuses, or with extensions of these. From their development (see below) there
can be no doubt of their coelomic nature, and they clearly correspond to the
network of tubes which connect together the main sinuses of the Rhyncho-
bdellidae, in which group botryoidal tissue is absent. As in this group they
contain a fluid similar in colour and character to the blood (red in the Gnatho-
bdellidae), and this similarity has led to the view that the sinus system and
vascular system are continuous in both divisions of the Hirudinea. As we have
already seen (p. 517), no observations have been brought in support of this for the

520

ANNELIDA.

Ehynchobdellidae ; on the contrary, Oka has shown that in Clepsine no such
continuity exists ; but for the Gnathobdellidae we have the statements of Bourne
and Lankester that they have seen botryoidal tubes and small blood vessels in
direct continuity, and the statement of Burger, in direct opposition to the above,
that in the young Nephelis the two systems are separate, and contain differently
coloured fluids.

In weighing these statements, we must not forget (1) that it is extremely
unlikely that animals so closely similar in other respects as the Gnathobdellidae
and Hhynchobdellidae should differ in such an important point of structure ; (2)
that the sinus network and the small blood vessels are intermingled in the
greatest complexity of arrangement, and that the walls of both have a very
similar structure, and that they contain a very similar fluid, and therefore might
very easily be mistaken for one another, and (3) that a continuity between the
vascular system and the undoubted coelom of the sinuses would be a unique
phenomenon in the structure of the animal kingdom. The bearing of these
considerations is obvious, their weight indubitable ; and it is clear that until
more detailed and elaborate observations in support of the view of continuity
are forthcoming, we are bound to hold, provisionally at any rate, that in the
Leeches, as in other animals, the blood system and coelom are separate from one
another. This position is still further strengthened when we remember that
developmentally the two systems are separate, and if continuity exists it is only
established comparatively late in life, after the larval and embryonic period.

vl

/3 nphg dr

FIG. 421. — Diagrammatic representation of a nephriclium of Clepsine (after Oka), a the
anterior division ; /3 the posterior division ; 7 the median division ; bl the invagination of
skin ; caps capsule ; dr glandular cells of the nephridium ; lab labyrinthic coil of nephridial
tube ; n nerve cord ; nphg duct of nephridium ; si lateral sinus ; tr funnel ; vl ventral sinus.

The nephridia vary in number in 'the different genera, and even in
species of the same genus. They are absent from the anterior and
posterior part (Fig. 424), and are best developed in the middle
region of the body. They consist (Fig. 421) of a long convoluted
canal, which opens at one end to the exterior on the ventral surface
of the body, and at the other internally into some part of the sinus
system (see above, p. 518). The part of the organ next the external
opening (sometimes as in Hirudo dilated into a vesicle) is probably
derived from an invagination of the skin, and is intercellular; the

HIRUDINEA.

521

remainder is intracellular, and is described as consisting of a row
of tubular cells fitted end to end like drain-pipes. On account of
the long convoluted character of the nephridium, different parts of the
cell-rows are in contact, and where this happens the cells,, of the
different rows are not distinguishable save by their nuclei. At
some parts of its course the main tube of the nephridium gives off
branching ductules in the protoplasm of the nephridial cells. Just
before the internal opening is reached, the nephridium often becomes
dilated into the cap-
sule (Oka), which con- iaHfc — a
sists of a protoplasmic
wall with embedded
nuclei and an internal
mass of cells, which
are partially, sometimes
completely, fused with
one another (Fig. 421).
On reaching the cap-
sule the intracellular
tube of the nephridium
branches out into a
number of branching
and anastomosing fine
ductules, which open
into a space between
the wall and central
mass; this space leads
into the funnel, and
is most developed near
the point, where that
structure is connected
to the capsule. The
funnel itself and its
stalk consist of protoplasm without cell-limits, but containing a few
nuclei ; it is ciliated, and the cilia are directed towards the capsule.

In Pontobdella (Fig. 423) and Brancliellion the nephridial system consists of
a network of hollow cells extending from segment to segment, and across the
middle line. In each of the segments in which the nephridial network is
found there are connected to the network two internal openings (of the usual
structure, a syncytial ciliated funnel and neck, and a 'capsule), and two ventral
external openings.

In Clepsine (Fig. 423 C] and Hirudo (Fig. 423 B) the nephridial tube is much

Fia 422._Diagram of a nephridium of Hirudo (from Perrier)

after Bourne), a capsule and funnel ; b-c testis lobe ; c-d
main lobe ; e-g recurrent lobe ; f-g apical lobe ; h-j the
duct ; j-fc the vesicle ; I the external opening.

522

ANNELIDA.

twisted, and gives off branching ductules just before reaching the capsule
(Fig. 422).

In Hirudo the internal opening is a
large structure, and is sessile upon the
capsule (Fig. 422) ; it is divided up into
several ciliated spoon -shaped openings,
and has the usual syncytial character.

In Hirudo medicinalis there are 17 pairs
of nephridia ; the first one is in the seg-
ment of the 2nd free ganglion, the last
one in that of the 18th ganglion. *The
first six are without internal funnels ;
the remainder, the first nine of which
are in the segments of the testes, and
the last two in the segments behind the
testes, possess internal openings at the
end of the testis-lobe. The testis-lobe is
a process of the nephridium which pro-
jects towards the middle line, and in the
testis segments abuts upon the testis.

A B C

FIG. 423. — Diagrams of the nephridia. A, of
Pontobdella (two contiguous nephridia are
shown) ; B, of Hirudo • C, of Clepsine. a, a
capsules and funnels ; b-c canal in testis lobe ;
c-e canal in main lobe ; d in Hirudo, canals in
caecal end of the "main lobe"; e-g in Hirudo
ducts in the apical lobe; g the apex; e-l, in
Clepsine, and g-l, in Himdo, unbranched canal
passing to the external aperture; j-k, in
Hirudo, the vesicle ; x, x caecal ductules in
Pontobdella. (After Bourne.)

ff-"-

FIG. 424. — Diagram illustrating the
arrangement of the renal, generative,
vascular, and nervous organs of
Hirudo medicinalis (from Perrier, after
Bourne), cer.gr. passage of the oeso-
phagus through the nerve-collar ; ep
epididymis ; g. l-%3 the ventral gan-
glia ; gl. glandular dilation of oviduct :
l.v. lateral blood vessel ; l.L, Lab., l.d.
branches of the same ; neph., or n. 1-17
the 17 pairs of nephridia ; oe circuni-
oesophageal commissure of the left
side ; ov ovary ; pe penis ; te 1-9 the
9 pairs of testes.

HIRUDINEA.

523

Generative organs. The Hirudinea are hermaphrodite. As in
many marine Planaria, the openings of the male and female organs
are placed one behind the other, the male being anterior, in the
middle ventral line of the anterior region of the body. In ^irudo
medicinalis the male opening, which in the Gnathobdellidae is pro-
vided with a protrusible penis, is in the segment
of the 6th distinct postoral ganglion (llth segment
counting the suboesophageal ganglion as consisting
of 6 fused ganglia), and the female opening in the
segment behind (Fig. 424).

The reproductive glands are hollow structures, and
are continuous with their ducts.

There are usually several pairs of testes arranged
segmentally, but in Nepkelis they are arranged irre-
gularly. In Hirudo (Fig. 424) there are nine or
ten pairs of testicular vesicles, which are connected
by short ducts with a sinuous vas deferens on either
side. Each vas deferens is coiled in front to form
a kind of epididymis (Fig. 425), and is then prolonged
into a muscular portion, the ductus ejaculatorius,
which unites with that of the other side to form
an unpaired eversible organ called the penis, with
the internal end of which is connected a well-
developed gland — the prostate. The female apparatus
(Fig. 426) consists either of two long tubular ovaries
-extending over several segments (Clepsine, Nephelis),
or of two short saccular structures. The ovaries may
either join together at the genital opening (Clepsine),
or their walls may be continued as the two oviducts,
which soon join. The single oviduct so formed becomes convoluted,
and passes through the albumin gland, after which it becomes dilated
and constitutes the vagina which opens to the exterior (Fig. 426).

The reproductive cells are produced by the cells lining the re-
productive glands, which must be regarded as special parts of the
coelom (sinus system) which have become shut off from the rest in
continuity with their ducts. This separation of the generative part
of the coelom from the rest takes place as we have seen in some
Oligochaeta.

The spermatozoa are united together in packets — the spermato-
phores. There does not appear to be any true copulation, but the
;spermatophores are deposited on the body of another leech, whence

FIG. 425. -Genera-
tive organs of the
Medicinal Leech.
T testis ; Vd vas
deferens; Nh
epididymis ; Pr
prostate; C
penis; Ov ovaries
with vagina and
female genital
opening.

524

ANNELIDA.

FIG. 426. — a, cocoon ; ft, female organs
of Hirudo medicinalis (after
Leuckart).

the spermatozoa appear to make their way through the skin and
tissues to the ovarian tubes, where it is probable that fertilization

occurs.* This process of cutaneous
injection of spermatozoa is found in
other groups, amongst which may be
mentioned Turbellaria and Peripatus.

The eggs are usually laid in cocoons
(Fig. 426 a) either on stones or plants
(Nephelis, Clepsine), or in damp earth,
the animal, if aquatic, leaving the
water for the purpose. The cocoon is
formed by the clitellar glands. When
the eggs are about to be laid the
leech attaches itself firmly by its
ventral sucker, and, twisting itself
about, envelops the anterior part of
the body with a viscid mass, which
covers especially the genital rings like a girdle and gradually
hardens to form a firm membrane. A number of small eggs 'and
a considerable quantity of albuminous matter in the case of the
Gnathobdellidae, then pass out, and the animal withdraws its
anterior end from the barrel-shaped membrane, which now contains
eggs, etc., and which, after the animal has left it, becomes in
consequence of the narrowing of the external openings a tolerably
completely closed cocoon.

The number of eggs contained in a cocoon varies, but is never
large. The eggs of the Gnathobdellidae are small, and the young
are hatched early and float as larvae in the albumen which they
swallow. In the Rliynchobdellidae the eggs are larger and contain
more yolk ; they are hatched at a later stage. Clepsine (see p. 526)
attaches its cocoon to stones and broods over it till the young are
hatched, which takes place at an early stage ; the young then attach
themselves to the ventral side of the mother, and are carried about
by her, living on albumen secreted by her.

The development is characterized by the early specialization of the so-called
pole-cells (neuro-nephroblasts, mesoblasts), and by the formation from them of
cords of cells with a definite destination. This characteristic is not confined to
the embryo, but is found also in the adult, where the rows of cells of which the
nephridia and botryoidal tissue are botli formed, not to speak of the egg-strings,

* Vide Whitman, " Spermatophores as a means of hypodermic impregnation,"
Journ. Morph.j 4, 1891.

HIRUDINEA. 525

are striking features. The segmentation is unequal. The mouth is formed
early, and through it, after the formation of the pharynx and rudiments of the
alimentary canal, the albumen contained in the cocoon is taken into the intestine
of the growing embryo by means of swallowing movements of the pharynx.

In the Gnathobdellidae it appears that a considerable part of the la*^a is cast
off in the attainment of the adult stage, e.g. the ectoderm, muscles, pharynx,
and provisional kidneys. The development* resembles in many respects that of
the Oligochaetes. This particularly applies to the origin and fate. of the meso-
blastic bands. They arise from two pole-mesoblasts and become segmented into
somites, each of which soon acquires a cavity — the coelom. The somites spread
ventrally, and unite with one another across the middle line. In this ventral
part the walls between successive somites break down, and a continuous tube is
formed — the ventral sinus — while in the lateral parts they give rise to the septa,
which in an incomplete manner persists throughout life. In this way arise the
ventral sinus and the lateral sinuses, while partial obliteration of the connection
between these (intermediate sinus of Clepsine) and diverticula of them give rise
to the complicated sinuses of the adult.

The ncphridia arise from a single large cell of the somite-wall, which pro-
liferates and produces the characteristic cord, which becomes the nephridium —
the strings of botryoidal tissue appear to arise in a very similar manner from
large cells of the somite wall which produce strings of cells by proliferation.
In both cases the cell-cords become hollow, the lumen communicating with the
coelom. The botryoidal sinus in Nephelis, which contains the nephridial funnel,
is directly derived from the lateral part of the primitive somites, the segmenta-
tion of which is retained. If this account of the origin of the botryoidal cords
is correct, it would appear that they resemble the nephridia closely in their
development, structure, and relations to the coelom, and we must regard them,
like the nephridia, as special organs of the coelom.

The ovaries arise as thickened patches of the coelomic epithelium in parts of
the coelom which become constricted off from the rest ; the ducts arise by
prolongation of the sac so formed to the skin of the ventral surface. The testes
arise on each side from a continuous ridge of cells, which separates from the
peritoneum and becomes hollowed out into the testes and vas deferens.

The terminal parts of the nephridia and generative ducts are developed from
ectodermal ingrowths.

Asexual reproduction is unknown in the group. The leeches live
for the most part in water, or temporarily in damp earth. A few of
the Gnathobdellidae are true land forms, and have lost the power of
swimming. Comparatively few are marine, and they belong to the
IchtJiyoMellidae. They move partly by "looping," with the help of
their suckers, and partly by swimming with active undulations of the
body. Many of them are parasitic on the skin or gills of aquatic
animals ; most, however, are only occasionally parasites of the outer
skin of warm-blooded animals. They do not feed exclusively on any
special genus of animals, and their diet is not always the same in the
different periods of their existence. The caeca of the stomach

* 0. Burger, Zoologische Jahrbucher, 4, 1891, and Z.f. w. Z., 58, 1894.

526 ANNELIDA.

enable them to store up a large quantity of food, and many of
them are able to go without food for a long period.

Fam. 1. Khynchobdellidae. With colourless blood, with a protrusible pro-
boscis, without jaws. Each typical segment consists of 3, 6, or 12 rings. The
6 -ringed forms are all marine except Haementaria. Organs concerned in the
formation of blood corpuscles (so-called valves) are often present in the dorsal
vessel. Without botryoidal tissues.

Sub-fam. 1. Ichthyobdellidae. Marine and fresh-water leeches, parasitic
for the most part on fishes. With cylindrical body. The proboscis is not
longer than the preclitellum. Ic^thyobdella Blainv. , on marine fish ; Pis-
cicala Blainv., on fresh- water fish ; Pontobdella Leach, marine, on sharks
and rays; Branchellion Sav., with foliaceous lateral appendages; B. tor-
pedinis Sav.; Calliobdella v. Ben. and Hesse; Ozobranchus Qfg., with
branchiae, in the mouth of tortoises, crocodiles, pelicans.

Sub-fam. 2. Clepsinidae. Fresh-water leeches, generally parasitic on

snails, but also on fish. With dorsoventrally compressed, never cylindrical

body. The proboscis is longer than the preclitellum. Clepsine* Sav.,

common fresh-water form. They brood over their eggs, which are attached

to some foreign body. In two species bioculata and heterodita the eggs

are attached to the ventral surface of the body. After hatching the young

attach themselves to the ventral surface of the mother. Batrachdbdella

Viguier, on Batrachians, Algeria ; Haementaria de Fil. ; H. mexicana de Fil. ,

H. officinalis de Fil, both in the lagunes of Mexico, the latter used for

medicinal purposes ; H. Ghilanii de Fil., in the Amazon.

Fam. 2. Gnathobdellidae. Fresh-water and land leeches with jaws, without

protrusible proboscis, with red blood ; the complete segments have five rings.

With botryoidal tissue.

Sub-fam. 1. Nephelidae. With 19 complete segments ; the sexual
openings are separated from one another by two rings. Eyes are never
present on the 6th segment, 4 pairs only. Nephclis Sav. (Herpobdella
Blainv.), without hard jaws, feeds on snails and planarians ; Liostomum
Wagler ; L. lumbricoides, lives in the earth after the fashion of earthworms,
which it resembles, Brazil. Macrobdella Phil.; Trochetia Dutroch., jaws
vestigial, without teeth, 4 pairs of eyes ; it is a water-leech, but leaves the
water to feed on earthworms, continent of Europe, has been introduced into
England ; Archaeobdella 0. Grimm, A. esmonti 0. Grimm, from the mud
at the bottom of the Caspian.

Sub-fam. 2. Hirudinidae. With 16 complete segments ; sexual openings
separated by 5 rings ; 5 pairs of eyes. Hirudo Ray and Linnaeus, with
102 rings ; eyes on the three anterior rings, and on the fifth and eighth ;
male opening between rings 30 and 31, female opening between rings 35 and
36. The three jaws are finely serrated, and can be moved like a circular
saw in a manner well-adapted to make a wound, which readily heals, in
the external skin of man ; aquatic, but deposits its cocoons in damp earth.
H. medicinalis Ray, with the variety distinguished as officinalis, possesses
80-90 fine teeth on the free edge of the jaws, and attains a length of about
6 inches. They were formerly common in Germany, and are still frequently

* The genus Glossiphonia Johnson has priority over Clepsine, but whether it
is advisable to give up a name so well-known as Clepsine is a doubtful question.

ECHIUROIDEA. 527

to be found in Hungary and France. They are cultivated in special ponds,
and take three years to attain sexual maturity. In the young stage they
live on the blood of insects, then on that of frogs, and only when they have
attained sexual maturity is a diet of warm blood necessary to them. Aulas-
toma Moq. Tand. , often called the horse-leech, feeds on worms and^olluscs,
last pair of gut- caeca alone present ; A. gulo M. T. Haemopis Sav. ; H.
vorax M. T., the horse-leech, indigenous in Europe and N. Africa, attaches
itself to the interior of the pharynx of horses, cattle, and men ; jaws with
30 denticles. Haemadipsa Tennent, the land-leech, in forests or damp
districts in or near the tropics ; Geobdella Whitman, Australian land-leech ;
Leptostoma Whitman, jaws vestigial ; Limnatis M. T., 4 pairs of eyes, jaws
without denticles, fresh-water ; L. nilotica M. T.

Fain. 3. Acanthobdellidae.* Fish parasites from Siberia, on caudal and anal
tins of Salmo salvelinus, with two
double rows of setae on each side on
the first 5 segments of the body (Fig.
427). The setae are embedded in
setigerous sacs which are provided
with retractor muscles. Body com-
posed of 20 segments ; male opening
on segment 7, female on segment 8.
Anus dorsal to sucker (Kowalevsky).
4 or 5 rings to one segment. Body-
cavity spacious and incompletely
divided by 20 segmental transverse
septa. The nephridia are in the dis-
sepiments, and open between the seg-
ments ; internal openings not observed.
The visceral peritoneum consists of Fm 427>_Ventral view of anterior end of
chloragogen cells. The vascular system Acanthobdella, showing the setae S, and
consists of a dorsal and ventral vessel. reserve setae Sr (after Kowalevsky).

The nervous system consists of 20

ventral ganglia, of which the first and last are composite. Testes as two
continuous tubes in segments 6-15. Ovaries as two tubes in segments 8-13.
The genital ducts are presumably continuous with the glands. Acanthobdella
Grube.

Class IV. ECHIUROIDEAf (GEPHYREA ARMATA).

Annelida ivith variable traces of segmentation in the adult ; with a
well-marked preoral lobe and a pair of ventral hooked setae.

The Echiuroidea were formerly united with the Sipunculoidea in
the class Gephyrea. In the present work, however, it has heeii

* A. Kowalevsky, Bull. Acad. Imp. des Sciences St. Petersbourg, June and
Nov., 1896, T. v.

f R. Greef, "Die Echiuren," Nov. Act. Leop. Car., 41, 1879. J. Spengel,
" Die Organisation des Echiurus Pallasii," Z.f. w. Z., 34, 1880. D. C. Danielssen
and J. Koren, "Gephyrea," Norwegian North Atlantic Expedition, 1881. B.
Hatschek, " TJeb. Entwick. von Echiurus," Arb. Zool. Inst. Wien, 3, 1881.
E. Selenka,," Report on the Gephyrea," Challenger Reports, vol. 13, 1885. M.
Rietsch, "Etude sur les Gephyriens armes," Recueil z. Suisse, 3, 1886. A. E.
Shipley, "Gephyrea" in Cambridge Natural History, 2, 1896.

528

ANNELIDA,

deemed advisable, for reasons set forth on another page (p. 533),
to break up this class, and to establish the Sipunculoidea as an
independent phylum of the animal kingdom, with affinities to
Phoi'onis and perhaps to the Annelida, and the Ecliiuroidea as an
aberrant class of the phylum Annelida.

The Ecliiuroidea have a somewhat cylindrical body, which is
prolonged anteriorly into a long, highly contractile preoral proboscis
(Figs. 428, 429). They are exclusively marine, and for the most
part live in holes and fissures in f ocks and between stones ; Echiurus,
however, frequents sand or mud, in which it forms tubes with two

openings. Many members of
the class appear to have the
habit of frequently changing
their residence. The proboscis
has a ciliated groove on its
ventral surface, which leads
behind into the mouth situated
at its base. The animals appear
to subsist on organisms and
organic particles, which are
brought to the mouth by the
currents of water driven along
the groove of the proboscis by
the cilia. The anus is posterior
and terminal.

There are almost always two
hooked setae on the ventral
surface not far from the front
end (Fig. 428 H) ; they are
embedded in pits of the skin,
by the lining of Avhich they

are secreted in the typical annelidan manner. In Echiurus there
is in addition a single or double row of setae round the hind end;
these are the anal setae. A short distance behind the hooked setae
are the openings of the anterior nephridia ; these vary in number
from four pairs to a single one.

The skin is covered with small papillae, which are often arranged
in rings. The body-wall is highly muscular, and consists of the
usual layers.

The central nervous system consists, as in the Sipunculoidea,
of a single ventral cord, lying entirely within the body-wall. In

FIG. 428. — Young Echiurus, ventral view (after
Hatschek). 0 mouth at the base of the
proboscis; SC circumoesophageal commis-
sures ; BS ventral cord ; A anus ; H ventral
hooks.

ECHIUROIDEA.

529

front this cord divides into two, which pass round the oesophagus
and extend quite to the anterior end of the proboscis, where they
join one another (Fig. 428). There are no ganglionic swellings, hut
the whole system has a uniform coating of nerve-cells. Th^ ventral
portion, moreover, contains a fine canal, which extends into the
commissures, hut is absent from the hind end of the cord, and from
the supra-oesophageal portion. The central organ gives off nerves
to the adjacent parts of the body.
There are no special sense-organs.

FIG. 429. — Female of Bonellia viridis; a, the whole animal; 6, anatomy; c, integument and
generative organs after removal of the intestine (after L. Duthiers). Ab anal vesicles ; Ad
rectum ; D alimentary canal ; Hd cutaneous glands ; M mesentery ; Ov ovary ; R proboscis
(preoral lobe) ; Tr ciliated funnel of the single brown tube or anterior nephridium (uterus) ;
U uterus (anterior nephridium).

The alimentary canal, in which various divisions can be made
out, consists of a long, thin-walled, much convoluted tube, along the
ventral wall of part of which is a ciliated groove. There is also a
siphon, or accessory intestine, like that found in Echinids and some
Chaetopods; this is a tube given off ventrally from the anterior
part of the long and coiled intestine; it lies ventral to the ciliated
groove, and opens posteriorly into the hind part of the intestine.
There is no special mesentery, but strands of tissue run from all
parts of the body-wall across the body-cavity, to be inserted into the
walls of the alimentary canal.

2 M

530

ANNELIDA.

The rectum resembles the skin in its lining epithelium, having
many unicellular glands. It receives the openings of the two anal
vesicles (Fig. 429, Ab) — one on each side; these are elongated
tubular, sometimes branched, contractile structures which open into
the body-cavity by many ciliated openings. They are supposed to
be a pair of modified nephridia, the openings of which, as in some
Oligochaetes (p. 502), have got shifted into the rectum.

The perivisceral cavity is spacious and entirely coelomic, and
contains a corpusculated fluid, tfie corpuscles of which are said, in
some forms, to contain haemoglobin.

The vascular system consists of a dorsal vessel, lying on the
anterior part of the alimentary canal and continued along the
proboscis, and of a ventral supra-neural vessel. These two vessels
communicate in front and behind, and doubtless give off branches to
the organs, though such have not been described.

The renal organs are constituted by the so-
called brown tubes or anterior nephridia, and
the anal vesicles or posterior nephridia. The
anterior nephridia closely resemble in form and
relations the brown tubes of Sipunculus ; they
are attached to the ventral body-wall at their
external openings, and project back into the
body-cavity as long blind tubes; the internal
opening, as in Sipunculus, is close to the ex-
ternal. They function also as generative ducts,
and the generative cells are collected in them
before extrusion, for which reason they are
sometimes called uteri. They vary in number
from one to four pairs. In Ecliiurus there are
two pairs, but in Thalassema the number varies
in the different species from one to four pairs.
In Bonellia there is only one brown tube (Fig.
429), sometimes on the right side and some-
times on the left. The posterior nephridia or
anal vesicles have already been described.

The sexes are separate, and the generative
FIG. 430.— Pianarian-iike ce^s are derived from that portion of the
male of Bonellia (after coelomic epithelium which overlies the ventral

Spengel). D intestine ; , , ,

WT ciliated funnel of (supra- neural) vessel (Fig. 429 b). They are
the vas deferens (Vd), dehisced into the bod v- cavity, where they

which is filled with J J'

sperm. mature and escape by the anterior nephridia.

ECHIUROIDEA.

531

The males and females are not distinguishable externally except
in Bonellia and Hamingia, in which there is a very pronounced
sexual dimorphism. In these genera the female has the ordinary
form of the species; but the male (Fig. 430) is a minute (in
Bonellia 1-5 mm. long) planarian-like organism which lives in
considerable numbers as a parasite, principally in the uterus and
pharynx of the female. It possesses an alimentary canal which is
without any opening to the exterior; the skin is ciliated, and
contains muscular fibres; there is a body-cavity, the lining cells of
which give rise to spermatozoa; there is also a single anterior

SP

FIG. 431. -a, Larva of Echiurus from the ventral side (after Hatschek). SP apical plate ; Prw
preoral ; Pow postoral ring of cilia ; KN head-kidney ; VG ventral nerve cord connected
with the apical plate by the long oesophageal commissures ; AS anal vesicles, fe, ventral
region of the Echiurus larva with segmented mesodermal bands ; SC oesophageal com-
missures ; Dsp dissepiments of the anterior body segments ; MS mesodermal bands ; A anus
(after Hatschek).

nephridium which opens to the exterior at the front end of the
body, and internally into the body-cavity at its hind end. Small
vestiges of the anal vesicles, which open directly on the surface of
the body, can be made out, and in both the genera the hooked
setae are present.

Development. In the Echiuroidea a typical trochosphere larva
(Fig. 431) has been observed in Echiurus and TJialassema, with a
strong preoral circle of cilia (Pnv), in addition to which there is also

532

ANNELIDA.

a delicate postoral circle (Poiv). In Eehiurus early in larval life an
excretory organ, the head-kidney or pronephros (KN) is developed,
one on either side ; and behind it a pair of mesoblastic bands make
their appearance, and become divided up in subsequent development
into the rudiments of 15 pairs of mesoblastic somites (Fig. 431, b).
In the terminal segment, which is surrounded by a circle of cilia,
there appear in the somatic mesoderm the rudiments of the anal
vesicles (Fig. 431, .4$). The rudiments of both the cerebral ganglion
and of the ventral cord are derived from growths of the ectoderm —
the former from the apical plate, and the latter from paired thicken-
ings of the ventral ectoderm. The two are connected by the
oesophageal ring, which is also provided with ganglion cells. In
later stages the segments disappear, and the ciliary apparatus
degenerates and vanishes; after which two strong hooked setae
appear at the side of the nerve cord, not
far from the mouth, and two circles of
shorter setae are formed at the hind end
of the body (Fig. 432). The preoral lobe
of the larva becomes the proboscis of the
young fichiurus. In Thalassema the
development is very similar, and the meso-
blastic bands are segmented. In Bonellia,
on the other hand, no traces of segmentation
have as yet been observed, and the larva is
not so obviously built on the trochosphere
type.

In view of the development of Eehiurus and
Thalassema, it is difficult to resist the conclusion
that the EcMuroidea are Annelida, a conclusion
which is further emphasized by the presence in all
genera of typical Annelidan setae embedded in and
secreted by pits of the skin. It is curious that in
Bonellia the trochosphere stage is so much modified,
and especially that no traces of segmented meso-
blastic bands should be seen. With regard to the
latter point, however, it must not be forgotten
that a renewed investigation may yet bring to
light some traces of larval segments. We may
therefore regard the Echiuroidea as Annelids in
which the segmentation is feeble, showing faintly
in the young, but except in the repetition of the
nephridia (e.g. Thalassema with three pairs of
anterior and one pair of posterior nephridia),
being absent from the adult.

sc

FIG. 432. — Older Eehiurus larva
from the side(after Hatschek).
The head-kidney is atrophied.
A anus ; AS anal vesicles ;
BK circles of setae ; G cere-
bral ganglion developed from
the apical plate ; H ventral
hooks ; M stomach ; 0 mouth ;
SC oesophageal commissures;
VG ventral nerve cord.

ECHIUROIDEA. 533

The resemblances between the Sipunculoidea and Echiuroidea have been
referred to above. They formerly led to the union of the two groups in the
class Gephyrea, and they consist mainly in the resemblance between the brown
tubes of the former and the anterior nephridia of the latter, in the spacious
character of the coelom in the two groups, and in the singleness of Jthe ventral
nerve cord. As to these we may remark that nephridia tend to resemble each
other in groups much more remote from each other than those under discussion,
that a spacious coelom is found in many widely divergent forms, and that the
singleness of the ventral cord, though an important feature, is not of itself
sufficient to outweigh the following most important differences: (1) the difference
in the position of the anus ; (2) the absence of a preoral lobe in the Sipuncu-
loidea ; (3) the absence of anal vesicles in the same group ; (4) the absence of
any traces of Annelidan setae ; and (5) the total absence of any trace of
segmentation in the larva and in the adult.

Echiurus Cuv. (Fig. 428). Proboscis not bifurcated ; anal setae in one or two
rows ; two pairs of anterior nephridia ; males and females alike. E. pallasii
Guerin, N. Sea, English Channel, etc.

Thalassema Gaert. Proboscis not bifurcated ; no anal setae ; one to four pairs
of anterior nephridia ; sexes alike. Th. neptuni Gaert., English Channel, etc.

Bonellia Rolando (Fig. 429). The animals are of a green colour, owing to the
presence of a pigment distinct from chlorophyll, and called bonellein. Proboscis
bifurcated ; no anal setae ; a single anterior nephridium ; sexual dimorphism
pronounced. B. viridis Rolando, North Sea, etc.

Eamingia Dan. and Kor. Proboscis not bifurcated ; no ventral hooks and
no anal setae ; one or two anterior nephridia ; sexual dimorphism pronounced ;
males provided with ventral hooks. H. arctica D. and K.

Saccosoma Dan. and Kor. Proboscis absent ; no hooks or setae ; one anterior
nephridium ; male unknown. S. vitreum D. and K.

Epithetosoma Dan. and Kor. , may be placed here, though it differs considerably
from other Echiuroidea. The proboscis is long and whip-like, and contains a
cavity continuous with the body-cavity. Posterior to this tubular proboscis,
on either side of the anterior extremity of the trunk, is a fissure, the bottom of
which is pierced with apertures leading into the body-cavity. There are no
hooks or setae, and no anal vesicles. The mouth is at the base of the proboscis,
and the anus is posterior ; the alimentary canal is straight. The nerve-cord
contains a tube. Vascular system not observed.

CHAPTER XII.

SIPUNCULOIDEA* (GEPHYREA ACHAETA).

Unsegmented vermiform animals with a spacious coelom, antero-
dorsal anus, and one pair of nephridia. The anterior part of the
body is invagindble.

As stated before on p. 451, we have thought it necessary, in the
present state of our knowledge, to break up the old group Gephyrea
into (1) the Echiuroidea (Gephyrea armata) which remains with
the Annelida, (2) the Sipunculoidea (Gephyrea Achaeta), (3), the
Priapuloidea, and (4) Phoronidea (Gephyrea tubicola}. The three
last of these we advance provisionally to phyletic rank, not being
able to subordinate them to any other group. The Sipunculoidea
and Phoronidea are undoubtedly Coelomata; but of the Priapuloidea
we cannot say this, and the fact that we deal with them in the
part of the work devoted to coelomate animals must be regarded
as a concession to the older view of their relationship to the
Sipunculoidea, rather than as an expression of opinion on our part
that they have a coelom.

The Sipunculoidea are elongated, vermiform animals and live in
sand and ooze in the sea; they also bore in coral rock. The
anterior part of the body is of a different appearance to the
posterior or main portion; it is called the introvert, because it
can be invaginated into the larger posterior portion by means
of special retractor muscles. The mouth is placed at the anterior
end of the introvert and is in relation with a row of ciliated,
hollow tentacles, which may be arranged in a circle or in the
form of a double horseshoe, the concavity of which is dorsal.

* Keferstein, "Beitragez. Anat. u. syst. Kenntnissd. Sipunculiden,"^./. w. Z.,
xv., 1865. E. Seleuka, "Die Sipunculiden," Semper 's Reisen, 1883. D. C.
Danielssen and J. Koren, " Gephyrea," The Norwegian N. Atlantic Expedition,
1876-78, 1881. B. Hatschek, "Ub. Entwick. v. Sipunculus midus," Arb. Zool.
List. Wien, 5, 1884. A. E. Shipley, " On Phymosoma varians," Q. J. M. S., 31.

SIPUNCULOIDEA.

535

Te

A

D

There is no trace of a preoral lobe. The anus is approximated to
the mouth, being placed on the dorsal surface about one-third of
the length of the body from the anterior end. The body is devoid
of setae, but the introvert is often covered by rows of hornj hooks
or by small, scale-like papillae which are directed backwards and
overlap one another. There is no trace of segmentation, but the
skin is often thrown
into ridges, both
transverse and lon-
gitudinal. There
are no special
organs of sense.
The body -wall is
highly muscular,
and consists of an
external cuticle, a
single - layered epi-
dermis, a cutis, a
layer of circular
muscles, a thin
layer of oblique
muscles, and a thick
layer of longitudinal
muscles which are
often arranged in
bundles ; lastly
there is a layer of
flat coelomic epi-
thelial cells bearing-
isolated cilia. The
cutis contains nu-
merous unicellular
or multicellular
glandular organs
which open to the
exterior by pores ;
these structures have often a marked nervous supply and have
been mistaken for sense-organs.

The alimentary canal is a thin-walled tube in which three regions
may be distinguished — the anterior portion (oesophagus) straight and
uncoiled, the middle portion (intestine) coiled and bent on itself, and

FIG. 433.— Sipunculus nudus, laid open from the side (after
W. Keferstein). Te tentacles; G cerebral ganglion; VG
ventral nerve cord ; D intestine ; A anus ; BD brown tubes
(nephridia).

536 SIPUNCULOIDEA.

the terminal portion (rectum) short and straight, leading to the anus.
The intestine passes back to the hind end of the hody and then turns
forwards, the two limbs being coiled spirally round one another.
Delicate muscular bands pass from the body-wall to the intestine,
and there is often a muscle — the spindle muscle — which extends
along the axis of the intestinal spiral from the hind end of the
body to the rectum. There are no special glands, but a caecal
diverticulum, which varies much in size in different individuals
and opens into the rectum, is T>ften present. Two tufts of tissue
are also attached to the rectum; they were formerly supposed to
be vestiges of the anal vesicles of the EcMuroidea. The alimentary
canal — particularly the intestinal portion — is generally full of sand,
excepting along a ciliated groove, which extends along its whole
length.

The retractor muscles are usually four in number; they are
inserted into the alimentary canal just behind the mouth, and arise
from the body-wall a little behind the anus (Fig. 433).

The nervous system consists of a single ventral cord without
ganglionic swellings, and showing no sign of being formed of two
halves; it divides below the oesophagus into two cords which embrace
the oesophagus and unite in a single supra-oesophageal ganglion on
the dorsal side just behind the attachment of the retractor muscles.
The cord and ganglion give off numerous nerves to adjacent parts.
In the dorsal middle line, outside the tentacular circlet, there is
an ectodermal pit which reaches as far as the supra-oesophageal
ganglion ; it is called the cerebral organ, and is lined by ciliated cells.
In Physcosoma (Pliymosoma) the inner end of this pit is bilobed and
lined with cells containing a black pigment; it is embedded in the
substance of the supra-oesophageal ganglion.

The body-cavity is entirely coelomic and very spacious ; it contains
a richly corpusculated fluid, which often has a pink colour. The cor-
puscles are of two kinds — biconcave discs, which contain the red
pigment called haemerythrin, and amoeboid cells. In addition there
are found floating in the coelomic fluid the reproductive cells, and in
Sipunculus and Phascolosoma some peculiar ciliated structures called
"urns"; these are apparently budded off from the coelomic epithelium
overlying the dorsal blood-vessel.

The vascular system is closed, and contains a corpusculated fluid ;
it consists of a contractile vessel lying on the dorsal side of the
oesophagus, and of an annular vessel surrounding the mouth. The
dorsal vessel ends blindly behind, and in front opens into the circum-

SIPUNCULOIDEA.

537

oral vessel, which sends prolongations into the tentacles ; it gives off
no branches. There is often present in addition a vessel on the
ventral side of the oesophagus, which also opens into the circumoral
vessel. Inasmuch as this system gives no branches to the viscera,
it cannot be regarded as a nutritive or respiratory organ; it is probably
mainly concerned with expanding the tentacles. A vascular system
is absent in Onchnesoma and in Tylosoma. There are no special
organs of respiration, unless the tentacles are such.

The nephridia are two in number ; they are often called the broivn
tubes, and open externally on the ventral surface in the anterior
region. They project backwards in the body-cavity from their attach-
ment to the skin, and they possess an internal opening into the
perivisceral coelom at their anterior end close to the internal opening.
They have glandular walls, and serve to transmit the reproductive
cells to the exterior.

FIG. 434. — Stage of Sipunculus embryos, in which the cephalic and ventral plates are beginning
to fuse with one another. The vitelline membrane and the cilia of the serosa which perforate
it are omitted (after Hatschek). a, In transverse section ; Kp cephalic, Rp ventral plate ;
E endoderm ; Ms mesoderm ; S serosa. &, In median longitudinal section ; Oe oesophagus ;
Mz pole cells of the mesoderm.

The sexes are generally separate, and the reproductive glands are
simply proliferations of the coelomic epithelium. In Sipunculus
these proliferations form an annular thickening of the peritoneal
lining at the point of attachment of the retractor muscle to the
body-wall. The reproductive cells are dehisced from the generative
ridge before they are ripe, and mature in the body-cavity.

Fertilization is probably external. In Sipunculus, the development
of which was observed by Hatschek on larvae taken in the Pantano,
near the lighthouse at the north end of the Straits of Messina, there
is an invaginate gastrula. The blastopore closes; the mouth and
anus being new formations. There are two primary mesoblast cells

538

SIPUNCULOIDEA.

which give rise to two mesoblastic bands, which do not undergo
segmentation. Invaginations of the ectoderm of the animal pole
and ventral surface of the embryo give rise to cephalic and ventral
plates respectively (Fig. 434), while the remainder of the ectoderm
cells grow round these, and form an external envelope for the embryo
of the nature of a serous membrane (serosa). Cilia project from the
latter through the pores of the vitelline membrane, and are employed

FIG. 435.— Larva of Sipunculus (after Hat-
schek). 0 mouth ; Sp apical plate ; A anus;
PoW postoral circle of cilia ; N kidney.

Fio.436.— Quite young Sipunculus
still without tentacles (after
Hatschek). 0 mouth ; A anus;
Bs ventral nerve cord ; N neph-
ridium (brown tube); G cerebral
ganglion ; Bg blood vessel.

by the embryo in swimming. The cephalic and ventral plates soon
grow together. The mesodermal bands soon split into somatic and
splanchnic layers, between which is the coelom, and give rise to
the rudiments of the two nephridia ; while the oesophagus arises
as an invagination of the ectoderm of the antero-ventral region,
and a postoral circlet of cilia is formed behind it (Fig. 435). The
serous membrane is cast off with the vitelline membrane, and the

SIPUNCULOIDEA. 539

larva then contains all the essential organs of the young Sipunculus,
except the ventral cord and the blood vessels. At a later stage,
during the growth of the larva, the ventral nerve cord is developed
from the ectoderm, the circle of cilia disappears, the first teprtacles
sprout out at the edge of the mouth, and the metamorphosis of the
free-swimming larva into the creeping young Sipunculus (Fig. 436)
is completed. The anus is never posterior, but is dorsal at its first
appearance. There is a small preoral lobe with an apical plate in the
larva, which disappears in the adult, the mouth becoming terminal.
It is important to notice that the anus is on the same side of the
body as the preoral lobe, and is therefore truly dorsal. Whether it
marks the morphological hind end of the body, as it does in Phoronis,
or whether it is, as described in the text, on the anterior part of the
true dorsal surface, cannot be certainly determined, though from its
position at its first appearance it is reasonable to conclude that it is
at least dorsal in position.

Fam. Sipunculidae. With the characters of the order.

(a) Longitudinal muscles of the body-wall divided into bands. Physcosoma
• Sel. (Phymosoma Sel.), with papillae ; Sipunculus L., without papillae ; S. nudus
L., English Channel, North Sea.

(&) Longitudinal muscles continuous. Phascolosoma Leuckart, two nephridia,
numerous tentacles; P. vulgare Blainv., English Channel and N. Sea; P.
elongatum Kef. ; P. papillosum Thompson, E. Channel ; Dendrostoma Grube,
two nephridia, 4-6 tentacles ; Phascolion Theel, right nephridium only ; P.
stronibi Mont., E. Channel.

(c) A distinct shield at the anus and at the hind end, or a calcareous ring
round the anus. Aspidosiphon Grube, with both shields ; Cloeosiphon Grube,
a calcareous ring in front of the anus ; Golfingia Lankester, a preanal horny
ring, and a posterior horny spike.

(d) Two foliaceous tentacles. Petalostoma Keferstein ; P. minutum Kef., E.
Channel.

(e) No tentacles or vascular system; one retractor muscle and nephridium.
-Onchnesoma Kor. and Dan. ; Tylosoma Kor. and Dan.

CHAPTER XIII.

PRIAPULOIDEA.*

Unsegmented vermiform animals with an anterior terminal mouth
and a posterior terminal anus. The central nervous system is not
separated from the ectoderm, and the renal and reproductive organs
are entirely separate from the body-cavity.

These are vermiform animals which live in sand and mud in the
sea. They have a short introvert, and the mouth, which is terminal
and anterior, is surrounded by chitinous teeth. The anus is terminal
and posterior, and in Priapulus there is a hollow caudal appendage
attached ventral to the anus, and covered with a number of hollow
papillae. There are no tentacles. The body-wall is muscular, and
the skin is transversely ridged.

The alimentary canal is straight, or but slightly looped, and is
divided into a muscular pharynx lined with chitinous teeth, an
intestine, and a rectum.

The central nervous system consists of a circumpharyngeal ring
and a ventral cord, and is throughout in continuity with the surface
ectoderm.

There are no special sense-organs.

There is a spacious body-cavity, which is probably a haemocoele,
inasmuch as it has no connection with the renal or generative organs.
There is no canalicular vascular system, and if the body-cavity be
not a haemocoele it must be admitted that the vascular system
is absent.

The renal and reproductive organs are paired, and have common
ducts, which open posteriorly, one on either side of the anus. These
ducts are beset with two kinds of caecal diverticula — the one
generative and the other renal. The generative caeca produce the

* W. Apel, "Zur Anat. d. Priapulus caudatus u. d. Halicryptus spinulosus,"
Z. f. w. Z., 42, 1885. E. Ehlers, "Ueb. d. Gattung Priapulus," Z. f. w. Z.,
11, 1861. H. Schauinsland, " Die Excret. u. Geschlechtsorgane d. Priapuliden,"
Zool. Anz., 9, 1886.

PRIAPULOIDBA. 541

generative cells from their lining epithelium, and the renal caeca
are branched and ciliated, and terminate in pear-shaped cells, which
contain a long, flame-shaped cilium projecting into the lumen of the
canal. It therefore appears that in the Priapuloidea the generative
glands are continuous with their ducts, and not connected in any way
with the body-cavity ; while the renal organs resemble those of the
Platyhelminthes.

The sexes are separate, and the development is unknown.

Fam. Priapulidae. With the characters of the group. Priapulus Lam.,
Halicryptus v. Sieb., both found in the North Sea.

CHAPTER XIV.

PHORONIDEA.*

Tubicolous, hermaphrodite Coelomata, with a tentaculated, horseshoe-
shaped lophophore, a dorsal anus, and one pair of nephridia.

It is convenient in the present state of our knowledge to give
Phoronis the rank of an independent phylum of the animal kingdom.
It has been relegated by various naturalists to the Gephyrea, the
Polyzoa, the Brachiopoda, and even to the Enteropneusta, but to not
one of these groups are its affinities close enough to justify a phyletic
association.

Phoronis is a coelomate animal with a vascular system, and an ecto-
dermal nervous system. In the adult state it is sedentary, and inhabits
leathery tubes, to which particles of foreign matter, such as sand

grains and sponge spicules, are
often found adhering (Fig. 437).
The animal can protrude the
anterior part of its body from
the opening of the tube, to
which it appears to be but
loosely attached.

A number of individuals are
™™™*y •»«*** together,
their tubes being twisted round
one another; but their bodies are not connected in any way. We
are ignorant of the cause of this association of individuals; it is
not known that they possess the power of budding at any stage of
their existence. The tube is secreted by the animal, very possibly

* W. H. Caldwell, "On the Structure, Development, and Affinities of
Phoronis," Proc. Roy. Soc., 1882. Id., "Blastopore, Mesoderm, and Metameric
Segmentation," Q. J. M. S., 25, 1885. W. C. Mclntosh, "Phoronis Buskii,"
Challenger Reports, 28, 1888. W. B. Benham, "The Anatomy of Phoronis
australis," Q. J. M. S., 30, 1889. E. Metschnikoff, "Ueb. d. Metamorphose
einiger Seethiere," Z.f. w. Z., 21, 1871. Id., " Vergl. Emb. Studien," Ibid., 37,
1882.

PHORONIDEA.

543

by cutaneous glands in the ante-
rior region.

At the anterior or oral end of
the animal there is a horseshoe-
shaped lophophore entirely at-
tached to the oral surface (Fig.
438), no part of it projecting as
in fresh-water Polyzoa (see Fig.
441). The concavity of the
horseshoe is dorsal. In some
forms, e.g. Ph. australis, the two
ends of the horseshoe are curved
inwards into a spiral. The lopho-
phore carries two rows of hollow
ciliated tentacles, between which
is a groove leading into the
median mouth. Overhanging the
mouth on its dorsal side, i.e.
between it and the inner ten-
tacles of the lophophore, is a
laterally extended flap of the
body-wall — the epistome (Fig.
438, ep.). The anus (an) is
dorsal and outside the lopho-
phore, at the summit of a median
longitudinal ridge (Rr\ on each
side of which there is a lateral
ridge (nr), each bearing at its
oral end a pore, the aperture of
a nephridium (neo). The row
of tentacles on the inner, i.e.
concave side of the lophophore,
is incomplete in the middle line.

The body is elongated aborally,
and may attain a length of
6 inches. Development shows
us that the dorsal surface* is
the area between the mouth and

FIG. 438.— Diagram showing the anatomy of
Phoronis ; the left side of the body-wall and
the left half of the lophophore is supposed
to be cut away (after Benham) a oesopha-
geal mesentery ; af afferent blood vessel ; an
anus ; b right lateral mesentery ; ~bw body-
wall ; c rectal mesentery ; ef efferent blood
vessel; ep epistome; gl glandular ridge
and pit; int intestine; it inner series of
tentacles ; m mouth ; N nerve band ; 71.7-.
right nephridial ridge ; ne.d left nephridial
duct ; ne.f large funnel of the left nephri-
. diuni; ne.f small funnel of the left
nephridium ; ne.o right nephridiopore ; o
ovary ; oe oesophagus ; ot outer tentacles ;
R rectum ; R.r rectal ridge ; s transverse
septum ; st stomach ; tv tentacular vessel ;
T testis.

* Caldwell states that the epistome is derived from the preoral lobe of the
larva, but this is inconsistent with the statement he also makes that the preoral
lobe is swallowed and digested at the metamorphosis.

544 PHORONIDEA.

the anus, the whole of the aboral extension of the body being
ventral. The tentacles possess within the epidermis a ring of skeletal
tissue of mesoblastic origin, and contain a blood vessel and an
extension of the oral coelom. The body-wall consists of an ecto-
dermal epithelium, a basement membrane, the usual two layers of
muscle, and internally the coelomic epithelium.

The nervous system lies in the skin immediately within the
epidermis, and outside the basement membrane. There is a special
concentration of it round the mouth in the form of a circumoral
ring (N), which is enlarged on the dorsal side between the mouth
and the anus into what may be called a dorsal or supra-oesophageal
ganglion. This ring follows the curve of the lophophore near the
base of the outer tentacles, and gives off nerves to the tentacles
and kidneys. There are also two tubes lying in the skin, and
extending aboralwards from the nerve ring along the insertion of
the lateral mesenteries. These are probably large nerve-fibres com-
parable to the giant-fibres of earthworms, etc. Some punctated
nervous tissue lies internally to the tube of the left side.

There are no organs of special sense.

On the dorsal side of the base of the inner series of tentacles are
two ciliated pits, which have been interpreted by some observers as
glandular structures, by others as sense-organs (gl).

The alimentary canal is a U-shaped structure occupying the aboral
extension of the body. It presents four regions — the oesophagus ;
the stomach (st\ at the base of the proximal limb of the U ; the
intestine, or second stomach (int) ; and the rectum, which leads to
the anus. The walls of the stomach are glandular.

The perivisceral cavity is entirely coelomic; it is divided at
the level of the lophophore by a transverse septum (s) into a
small oral section, which is continued into the epistome and
tentacles, and a larger posterior (aboral) part in relation with
the alimentary and other viscera. This septum is perforated by
the oesophagus, but not by the rectum, the anus being placed
aborally to it.

The posterior (aboral) section is further subdivided by longitudinal
mesenteries, which run from the gut-wall to the body-wall. One of
these is a median ventral mesentery (a and c) attaching the outside
of both descending and ascending limbs of the alimentary canal to
the body-wall. Besides this there are two lateral mesenteries passing
from the oesophagus and stomach to the body-wall (Fig. 438, b). The
body-cavity is thus divided into three chambers — a rectal chamber

PHORONIDEA. 545

lying between the right and left lateral mesenteries and containing
the rectum, and a right and left chamber between the oesophageal
and stomach part of the median mesentery and the right and left
lateral mesenteries. As the lateral mesenteries end before the>aboral
apex of the body is reached, all three chambers are in communication.
In addition to the mesenteries, bridles of connective tissue pass
across the body-cavity from the body- to the gut-wall. The coelom
contains a corpusculated fluid, in which the reproductive cells are
often found floating.

The vascular system consists of two main longitudinal trunks,
one lying in the rectal chamber between the two limbs of the
alimentary canal (of), and the other on the left side of the oeso-
phagus (ef). These vessels are contractile, and are continuous
aborally; they both give branches to the gut-wall and gonads.
Anteriorly they pass through the septum, and are both connected
with the single vessel found in each tentacle. The blood consists
of a colourless plasma, containing nucleated red (haemoglobin)
corpuscles in suspension.

The renal organs consist of two nephridia, which also act as
generative ducts and open externally on each side of the anus.
Each nephridium, after passing aboral wards through the septum,
opens into the body-cavity by two openings. One of these — the
smaller (ne.f) — is into the lateral chamber of the body-cavity, the
other — and larger (ne.f) — into the rectal chamber.

Phoronis is hermaphrodite, and the gonads lie on the left side of
the stomach in the aboral region of the body-cavity — the ovaries (o)
on one side of the oesophageal blood vessel, and the testes (T) on
the other. They consist of special developments of the coelomic
epithelium overlying certain caecal branches of -the oesophageal
vessel. The reproductive cells are dehisced into the coelom, and
pass out by the nephridia.

Development. The eggs are small, and are probably fertilized
externally. They undergo the first part of their development
entangled in the arms of the mother. They are then hatched out
as free-swimming larvae, which after a certain period of free life
undergo a remarkable metamorphosis, and acquire the adult form
and habit. The larva is called Adinotrocha.

There is an invaginate gastrula, and the blastopore, which assumes
a slit-like form, closes up behind, but remains open in front as the
mouth. The anus is formed as a pit at the hind end of the closed-
up portion. The mesoderm arises partly as cells budded off from

2 N

546

PHORONIDBA.

the endoderm on each side, and partly as a pair of diverticula from
the anal pit.

The fully-formed larva has a preoral lobe covered with cilia, a
ventral mouth, and a posterior anus, and, like so many larvae, has
a gelatinous, transparent appearance. The preoral lobe possesses an
apical thickening of ectoderm — the larval ganglion — and in some
species eye-spots.

Behind the mouth there i§ a circlet of ciliated larval tentacles
(Fig. 439, Lt), and behind these again the rudiments of the adult
tentacles may be discerned. On the ventral surface behind the
tentacles an invagination of skin is formed which projects into the
body of the larva. There is a circlet of long cilia round the anus,
and the cilia on the margin of the preoral lobe are longer than the
rest, constituting a velar or preoral ring. It is this ring, combined
with the preoral lobe and apical plate, which has led naturalists to

regard Actinotro-
clia as a modified
trochosphere larva.
But this type of
larva is found in
so many widely
divergent groups
(e.g. Mollusca,
Annelida, Echino-
dermata, Entero-
pneusta), that too
much attention
must not be paid
to it as a sign of
phyletic affinity.
In this connec-
tion it should be
noted that Ac-
tinotroclia differs
from the trocho-
sphere of Molluscs
and Annelids in
possessing a coelom
in the form of two
pairs of mesoblastic
sacs which not only

FIG. 439.— a, Metamorphosing Actinotrocha with ventral invagi-
nation evaginated at S (after Schneider), a, anus with circle of
cilia ; D intestine ; Lt larval tentacles. The preoral lobe is the
part of the larva above Lt (in the position of the drawing). It
overhangs the mouth, which is on the right hand side of it in
the drawing. 6, Young Phoronis (after Metschnikoff). D intes-
tine ; A anus ; T adult tentacles ; Vc circular blood vessel ; VI
longitudinal blood vessels.

PHORONIDEA. 547

constitute a body-cavity for the larva, but also give rise to the body-
cavity of the adult Phoronis.

After a certain period of free life the larva sinks to the bottom,
and undergoes a sudden change of form and character ./which
constitutes the metamorphosis. The ventral invagination becomes
evaginated, and forms a tubular projection standing out from the
ventral surface almost at right angles to the long axis of the larva
(Fig. 439, a). Into this projection, which will constitute the
body of the adult, and which soon becomes larger than the larval
body, the alimentary canal passes and forms the U-shaped loop
characteristic of the adult. At the same time the hind part of
the larval body, or, as we may now call it, the anal papilla,
becomes less and less conspicuous, and eventually reduced to the
anal projection of the adult. While these changes are going on,
the preoral lobe with its ganglion and sense-organs passes into the
stomach by the oesophagus and is digested. The larval tentacles
likewise pass into the stomach. Meanwhile the adult tentacles have
become fully formed, attachment effected by the aboral apex of the
new body and the adult form acquired.

Phoronis is exclusively a marine animal, and about 6 species are
known.

Phoronis S. Wright ; Ph. hippocrepia S. Wright, embedded in coral or lime-
stone, Devonshire Coast, Firth of Forth ; Ph. Jcowalevskii Caldwell, tubes coated
with sand, Mediterranean.

It has been suggested by Caldwell and others that Phoronis has affinities to
the Polyzoa and to the Brachiopoda. According to this view in all these
animals the dorsal surface of the body is reduced to the space between the
mouth and the anus, and the preoral lobe of the larva almost or entirely
disappears in the adult. There is much to be said for this view, which is
fully discussed under the two groups concerned (pp. 571 and 584).

A. T. Masterman has quite recently (Q. J. M. S., 40, 1897, p. 281) endeavoured
to show that Actinotrocha has Enteropneust features. The principal data upon
which he bases his view are partly new and partly old. The old are the presence
of two glandular pockets opening into the anterior end of the stomach, which
he identifies as a double notochord ; on what substantial grounds it is difficult
to see. The new data are (1) the presence of three sections of the body-cavity:
(a) one, unpaired, situated in the preoral lobe and opening to the exterior by
two pores placed on each side of the preoral ganglion, (b) a second chamber —
which he calls collar body-cavity—divided by a dorsal mesentery but not by a
ventral, and opening to the exterior ventrally by a pair of nephridial tubes;
and (c) a posterior chamber divided by a ventral mesentery and possessing paired
nephridia or the rudiments of them. (2) The presence of an ectodermal pit in
front of the preoral ganglion, which he calls the neuropore ; and (3) the presence
of an ectodermal pit on the ventral side of the preoral lobe, the opening of
which shifts into the stomodaeum, and which he calls the subneural gland.

548 PHORONIDEA.

Of these new facts the second and third derive any importance they may have
in the discussion from the names which Masterman has given them. The state-
ments under (1) are more important, but they are supported by evidence which
is very insufficient when one remembers the size of the edifice which he erects
upon them ; e.g., the external openings of his proboscis pores are not shown in
section, nor is either of the openings of the collar nephridium. Further, one
sees no reason for speaking of a collar region of the body ; and lastly, the
development of these most important spaces has not been examined. All we
know on this subject is based on Caldwell's observations that there are two pairs
of coelomic cavities in the embryo. 9 The method of development of these spaces
in Adinotrocha is a highly important one from Masterman's point of view, and
should, in our opinion, have been examined by him. For, in the Balanoglossus
larva, the collar coelom and the trunk coelom are paired, whereas the spaces in
Adinotrocha with which he compares them are not paired, but, however they
may arise in the embryo, are continuous in one case dorsally and in the other
ventrally to the alimentary canal.

CHAPTER XV.

PHYLUM POLYZOA.*

Small animals usually united together in colonies. With ciliated
tentacular crown^ \J-shaped alimentary canal, and simple ganglion.
With coelom, but without vascular system. Asexual reproduction by
budding always found.

The Polyzoa (J. V. Thompson) or Bryozoa (moss-like animals) as
they are sometimes called (Ehrenberg), are with rare exceptions
(Loxosoma) colonial in habit. The colonies, which may present a
superficial resemblance to colonies of Hydroids, may have a foliaceous
or dendritic appearance, or they may form crusts on the surface of
foreign objects. The erect forms may have a calcareous ectocyst,
and be rigid, in which case owing to their brittle character they
are not found between tide-marks ; or they are flexible. Flexibility
may coexist with a calcified ectocyst, but in this case there are
horny joints at intervals. In such jointed colonies the part between
any two joints is an inter node.

The individual zooids of the colony (Fig. 440) are small polyp-
like organisms, and usually possess a horny, or coriaceous,^ frequently
calcareous, rarely gelatinous exoskeleton, which is really the cuticle
of the zooids, and is secreted by the ectoderm. This cuticular layer
is called the ectocyst, and the case formed by it is the cell.

The soft part of the body-wall, which consists of ectoderm and
mesoderm, lies close beneath the ectocyst, and is called the endocyst.
The ectocyst and endocyst together constitute the zooecium ; while

* T. Hincks, "A History of the British Marine Polyzoa," London, 1880,
2 vols. G. J. Allman, Monograph of Fresh-water Polyzoa, Kay Society, 1856.
G. Busk, "Report on the Polyzoa," Challenger Reports, vols. 10 and 17, 1884
and 1886. K. Kraepelin, "Die Deutschen Siisswasser-Bryozoen," Abh. Natur-
wiss. Ver. Hamburg, Bd. x., 1887, and Bd. xii., 1892. E. C. Jelly, Synonymic
Catalogue of the Recent Marine Polyzoa, London, 1889. S. F. Harmer, " On the
Nature of the Excretory Processes of Marine Polyzoa," Quart. J. Mic. Sci.,
vol. 33 ; and ' ' On the Occurrence of Embryonic Fission in Cyclostomatous
Polyzoa," Ibid., vols. 34 and 39, 1893 and 1896. S. F. Harmer, "Polyzoa," in
the Cambridge Natural History, -London, 1896. *

550

POLYZOA.

the alimentary canal and tentacles are called the polypide (for
origin of this absurd nomenclature see below, p. 555). The cell
at, or near, its anterior end has an opening called the orifice,
through which the anterior part of the zooid can be protruded and
retracted. This anterior invaginable part of the body, which carries
a crown of tentacles, is also covered by cuticle, which is continuous
with the stiffer ectocyst at the orifice, but distinguished from the
latter by its softness and flexibility. At the orifice the body-wall
(with its soft cuticle) is invagfhated inwards, and passes thence on
to the anterior and extrusible part of the body. In many Polyzoa

this reduplication of the body-
wall is present even when the
zooid is protruded (Fig. 440).
The greater part of the anterior
region of the body, with its
crown of tentacles, can however
be protruded from the cell and
retracted into it again by special
muscles — the parieto-vaginal and
the retractor muscles — which tra-
verse the body-cavity (Fig. 440).
That part of the body-wall which
encloses the space in which the
tentacles lie when completely
retracted is called the tentacle-
sheath.

In the Cheilostomata there is
a movable chitinous lid, the
operculum, which can shut down
over the orifice. Sometimes the
ectocyst is raised into a ridge —
the peristome — round the orifice :

the tube thus formed is the secondary orifice. ' Zoarium is the term
applied to the whole colony. The term ooecium or ovicell is
applied to the receptacles in which the ova undergo their develop-
ment. The ooecia are of very different kinds : in the Cheilo-
stomata they are merely pouches of the zooecia into which the eggs
pass. In some — if not all — Cyclostomata (Crisia) they are special
zooecia in which the polypide is rudimentary or degenerates. This
is probably the case with all ovicells in the Cyclostomata, but it has
not been proved In all cases. In Phylactolaemata, in which the

FIG. HQ.—Plumatella repens (after Allman).
T tentacles ; L lophophore ; Oe oeso-
phagus ; A anus ; Mg stomach ; F funi-
culus ; St statoblasts ; Ts tentacle
sheath; Ek ectocyst; En endocyst;
Gg ganglion ; Pvm parieto-vaginal mus-
cles ; Rm retractor muscle.

POLYZOA.

551

body-cavities of the zooecia are in wide communication, a rudimentary
polypide bud is formed near the ovum. This passes round the egg
and invests it, but remains rudimentary. In the Ctenostomata the
eggs develop in the tentacular sheath or in the sea. ^

The body -wall consists of cuticle, ectoderm, and a delicate
layer of cells which line the body- cavity. The peritoneal cells
are ciliated in the Phylactolaemata, in which group there is also
a thin muscular layer in the body-wall.

The mouth is placed at the anterior end of the body in the
midst of the circlet of ciliated tentacles, and the disc bearing it and
the tentacles is called the lophophore (Fig. 440). The lophophore
is either circular (Gymnolaemata), or is drawn out into two lobes
(horseshoe-shaped lophophore, Fig. 441, Phylactolaemata), and the
tentacles are set along its
edge. The latter are simply
hollow processes of the body-
wall; they are provided with
longitudinal muscles, and
their cavity communicates
with a circular canal which
surrounds the body at their
base. This canal communi-
cates with the body-cavity
in the Phylactolaemata, but
is separate from it in the
Gymnolaemata. The tenta-
cles serve both for procuring
food (setting up by means
of their cilia whirlpools in
the water) and for respira-
tion.

The digestive organs lie
freely in the body-cavity,
and are attached to the body- wall by a mesodermal reticulum which
traverses the body-cavity. The term funiculus is applied to one
or two special strands (Fig. 440, F) of this tissue. The mouth is
placed in the centre of the circular or horseshoe-shaped lophophore,
and a movable epiglottis-like process, called the epistome, is in the
fresh-water forms placed on the dorsal side of it, and projects
over it.

The alimentary canal is bent on itself, and consists of (1) an

FIG. 441. — Anterior part of the body of Lophopus
(from Lang, after Allman) from the right side.
t tentacles cut off near the base ; o mouth ; ep
epistome ; si pharynx ; ga ganglion ; an anus ;
pr rectum.

552 POLYZOA.

elongated ciliated oesophagus, often dilated at its upper end into
a muscular pharynx ; (2) a spacious stomach with a blind backward
prolongation, the hind end of which is attached to the body-wall
by the funiculus ; and (3) a narrow intestine which is bent nearly
parallel with the pharynx, and is directed upwards. The intestine
opens by the anus, which is placed either within the tentacular
circlet (Entoprocta), or near but outside it on the body-wall (Edo-
procta, Fig. 440). The anal side of the body is called the dorsal
side. In the Phyladolaematd* the epistome and concavity of the
horseshoe lophophore are dorsal.

The nervous system consists of a ganglion placed on the oeso-
phagus between the mouth and the anus (Fig. 441, go). It lies
in the space (ring-canal of lophophore) already described (p. 551),
which surrounds the oesophagus and is developed as a part of the
body-cavity. In the Phyladolaemata the ganglion is placed in
the concavity of the lophophore, and is attached to the oesophagus
by a delicate circumoesophageal ring: it contains a cavity which
arises as an ectodermal pit in the bud, and it sends off numerous
nerves to the tentacles and oesophagus. According to Fr. Miiller
there is in Serialaria (Zoobotryon) a so-called colonial nervous system
which connects the individual zooids of a colony, and enables them
to coordinate their activities. Claparede describes the same in some
forms. Special organs of sense have not been recognized.

Heart and vascular system are absent. The body-cavity is
absent in the Entoproda. In the Edoproda it is spacious and
filled with fluid, and its lining gives rise to the generative cells;
it is therefore to be regarded as coelomic, which view of it is justified
by the intertentacular organ of the Edoproda. This is a fine
ciliated tube leading outwards from the body-cavity, and opening
externally between two of the tentacles on the anal side of the
lophophore. It is not found in all specimens, and, according to
Prouho, only in individuals containing an ovary. It functions as
an oviduct, and probably also as an outlet for the sperm.

The body-cavity is divided, as stated above, into two parts, (1) the general
body-cavity and (2) the ring-canal of the lophophore which is prolonged into
the tentacles. The ring-canal is completely shut off from the general body-
cavity in the Gymnolaemata, but in the Phyladolaemata the two are in
communication on the dorsal (anal) side of the lophophore except in the middle
line, where the ring-canal is cut off from the general body-cavity by the
prolongation of the latter into the epistome. For the epistome of the Phylac-
tolaemata is hollow and contains a prolongation from the general body-cavity
which is continued upwards into it as a tube which passes on the anal side

POLYZOA.

553

of the ganglion, between the ganglion and the median dorsal part of the
ring-canal. In the Phylactolaemata this median dorsal part of the ring-canal
communicates with the exterior by a pore which together with some columnar
ciliated epithelium of the adjacent parts of the ring-canal constitutes the
so-called nephridium.* In some Gymnolaemata the intertentacular organ
opens externally in a corresponding position, and internally into the body-cavity.
Into what part of the body -cavity the intertentacular organ opens is not clear
from the accounts available, but presumably into the general body-cavity, for
it is said to form an escape-duct for the ova.

The zooids are usually hermaphrodite. The testes are developed
either on the upper part of the funiculus, or near the point of
attachment of the latter to the body-wall. The ovaries are placed
on the body- wall near the anterior end of the zooecium. Both kinds
of generative cells are dehisced into the body-cavity. There do not
appear to be any special renal organs,
unless the intertentacular organ be such,
and the fine ciliated canal of the Entoproda.

Many forms of Polyzoa present examples
of a well-marked polymorphism. In Zoobo-
tryon and its allies the joints of the stalk
represent a special form of individual ; they
have a considerable size and a simplified
organization, and serve as the ramified sub-
stratum on which the nutritive zooids are
placed. In addition there are here and
there joints of the roots, which, under the
form of tendril and stolon -like processes,
serve to attach the colony. The stalk of
KinetosMas is a modified stalk -zooid. In
addition to these stem- and root -forming
zooids, there are the peculiar avicularia
(Fig. 442) and vibracula (Fig. 443). These
are only found in the Cheilostomata. They
are both modifications of an ordinary zooe-
cium, with the operculum as the mandible
in the one case, and as the lashing filament
in the other. A fully-developed avicularium
resembles a bird's head ; the upper beak is hooked, and the lower
one, or mandible, is spiked. There is a strong adductor muscle
arising in the "head" of the avicularium, and inserted into the

* Verworn, Z. f. w. Z., 46. Braem, Bibliotheca, Zoologica, Heft 6. Cori,
Z. f. w. Z., 55. Oka, Journal Coll. Sri. Japan, 8.

Ovz

Fio. 442. — Biigula avicularia
(after v. Nordmann). Te
tentacular crown; £ retractor
muscle ; D alimentary canal;
F funiculus; Av avicularia;
Oes oesophagus ; Ovz ovicells.

554 POLYZOA.

middle of the mandible; the contraction of this muscle causes
the lower jaw to close upon the upper, and there are two small
muscles which bring about the opening.

There are all stages between such an avicularium as that just
described, and a small zooecium with a movable operculum. From
Flustra foliacea, Cellaria, etc., in which the avicularium occupies
the place of an ordinary zooecium (vicarious avicularia), we pass
through stages in which the avicularium, though still a recognizable
zooecium, has lost the place of a zooecium in the colony, and is
attached to some part of an ordinary zooecium (adventitious) until
we reach the highly specialized form just described.

Vibracula (Fig. 443) are merely avicularia with the beak much
elongated, as a long whip-like seta, which has the power of sweeping

through the water. The function of
avicularia is obscure. They have been
observed to seize small organisms, e.g.
worms, and to hold them until they
are dead; the decomposing organic
remains may possibly be swept into
the mouth by the currents caused by
the cilia of the tentacles.

Finally there are the ovicells of
some Cyclostomata (see above, p. 550),
which are zooecia with a vestigial
polypide.*

FIG. 443.— Sempocellaria ferox (after ^.

Busk), vi vibracuia. ihe torm ot the cells, and the

manner in which they are connected

together, are very different in the different groups, and give rise to a
great variety in the form of the colonies. The zooecia are usually
completely cut off from one another, though the soft parts are
continuous through pores in the ectocysts of adjacent zooecia (rosette
plates, communication plates). In the Pliylactolaemata the body-
cavities of neighbouring zooecia are in open communication. These
two conditions result from the manner of budding : in the first case
the bud, which arises as an outgrowth of the body-wall, becomes
completely cut off by an ingrowth of body-wall ; while in the second
no such partition is formed, so that the body-cavity of the whole
colony is a single, continuous space.

The brown bodies, which are present in most colonies of the Polyzoa,

* In some Cyclostomes (Lichenopora, etc.) the polypide is fully formed and
functional in the young ovicells.

POLYZOA.

555

consist of brown pigment masses contained in the zooecia, and are
derived from the breaking down of the tentacles, alimentary canal,
and nervous system of the polypides. A new set of these organs
may be formed from the persistent body-wall of such partially
degenerated polypides, as an internal bud. The brown body finally
breaks up, and its pigments may pass into the new stomach and so
out by the anus. It is this degeneration of the tentacles, digestive
organs, etc., and the subsequent acquisition of a new set by growth
from the body-wall, which gave rise to the idea that the zooid of a
Polyzoan colony really consists of two individuals — one the poly-
pide, and the other the zooecium or house of the polypide, which
has the power of budding new polypides (tentacles, alimentary
canal, etc.).

The funicular tissue contains numerous transparent cells with processes, by
means of which they are suspended in the funicular network. They may be
faintly yellow in colour, and are regarded as excretory* in function. As there
is no organ for the ejection of such excreted matters to the exterior, it is
supposed that the disruption of the internal organs resulting in the formation
of the brown bodies, and the subsequent ejection of the latter through the
alimentary canal of the new polypide, are the means by which excretory products
are removed from the colony, f

Reproduction is partly sexual and partly asexual; in the latter
case it may be effected by the so-called statoblasts or by budding.
The generative cells are products of the coelomic lining (vide p. 553),
and are dehisced into the coelom.

The name statoblast (Fig. 444) was given by Allman to certain
peculiar reproductive bodies which were formerly regarded as hard-
shelled winter eggs, but by him
were recognized to be multi-
nuclear and of the nature of
internal buds. These statoblasts
are found only in the Phylacto-
laemata : they arise from masses
of cells which appear, mainly
towards the end of summer, on
the funiculus (Fig. 440). They
usually possess a lens-like, bicon-
vex form, and are enclosed by

FIG. 444.— Statoblasts of Cristatella vmcedo
(from Allman). a, from the surface &,
from the side.

* S. F. Harmer, "On the Nature of the Excretory Processes of Marine
Polyzoa," Q. J. M. S., 33, p. 123.

t Cf. Tunicates, in which there is no apparatus for voiding the excretory
concretions which are stored in various parts of the body.

556

POLYZOA.

two watchglass-shaped, hard chitinous shells, the edges of which are
usually enclosed by a flat ring formed of cells containing air (float),
and sometimes provided with a crown of projecting spines (Fig. 444).
The Phylactolaemata generally die down in the winter, and the
statoblasts, which germinate in spring and give rise to new colonies,
serve the purpose of perpetuating the species. In the fresh-water
Ctenostomes, Paludicella and Victorella, the colonies also die down in
winter, and the species is continued by means of certain external
buds, which are arrested in development and last through the winter:
they are called hibernacula. In some cases (Cristatella, Lophopus)
parts separated off from the colony are able to develop into new
colonies, and in Lophopus the colonies divide spontaneously.
* The Polyzoa are for the most part marine organisms. They are
found between tide-marks, and on the floor of the ocean to a depth
of 3000 fathoms. Cheilostomata only are recorded from depths of

FIG. 445. — a, Larva of Scrupocellaria reptans. b, Larva of Schizoporella (after Barrois). Cb

ciliated disc.

over 3000 fathoms; Cydostomata are found in depths of 1400'
fathoms and less. Ctenostomes are mostly found in depths of less
than 40 fathoms.

One order — the Phyladolaemata — is exclusively fresh-water, and a
few fresh-water forms are known in the Gymnolaemata. A few forms
are phosphorescent. Some forms (Terebripora) excavate passages in
the shells of Mollusca ; and Hypophorella is found in passages in the
tubes of Lanice and Chaetopterus.

The eggs of the Ectoprocta are sometimes laid and develop freely
in the sea (HypopJiorella expansa, Alcyonidium albidum, Membrani-
pora pilosa, Farrella repens). But more often the early stages of
development take place under the protection of the parent ; either in
the tentacle-sheath (some Ctenostomatd), or, in many Cheilostomata,
in a pouch of the zooecium ; or in special zooecia (ooecia), of which
the polypide is rudimentary or degenerate (Cydostomata); or in a

POLYZOA.

557

rudimentary polypide bud (Phylactolaemata, see p. 551). It is not
certain where fertilization is effected, but it is generally described
as taking place in the body-cavity, and the eggs or larvae escape
•either by the intertentacular canal, or by the rupture of tf\# body-
wall of the parent, or by the degeneration of its polypide. In
Ahyonidium duplex the sexual zooecia possess two polypides; the
first of these produces spermatozoa and then undergoes disruption
into a brown body, whereupon a second polypide is formed which
produces ova.

In the oviparous forms, to whatever sub-order they belong, in
which the early

development takes r fa

i \ a. I \
place in the sea, a

free-swimming larva c
with a functional
alimentary canal is
rapidly produced.
This larva has, gener-
ally speaking, always
the same form, and
is called Cyphonautes.
On the other hand,
in all forms in which
the early stages are
passed through under
the protection of the
parent, the larva is
without a functional
alimentary canal, and
the other larval organs
present varying de-
grees of development
in different cases.

Cyphonautes (Fig. 446) has the form of a laterally compressed
bell with a circle of cilia round the base. The base of the bell is
the ventral surface ; it has two openings both enclosed by a special
lobe of the ciliated ring. The larger and posterior of these leads
into a depression called the vestibule ; the smaller and anterior into
an ectodermal depression called the pyriform organ (pi). The vesti-
bule is divided into two parts, the anterior chamber (va), at the
bottom of which is the mouth, and a posterior chamber (vp)t into

FIG. 446. — Optical section of a Cyphonautes (larva of Mem-
branipora or of Alcyonidium albidum). (From Perrier, after
Prouho.) ad adhesive organ ; coa anterior, cop posterior part
of the ciliary ring (velum) ; coq chitinous valves of the shell ;
ex ectoderm ; es stomach ; fa anterior pit ; fc cavity of pyri-
form organ ; ma adductor muscle of the shell-valves ; mn
musculo-nervous tract ; ob aboral disc ; or entry into oeso-
phagus ; ph pharynx ; pi pyriform organ ; pi vibratile tuft
of pyriform organ ; q horns of the adhesive organ ; r rec-
tum ; va anterior, vp posterior chamber of vestibule.

558

POLYZOA.

FIG. 447. — A, larva of Alcyonidium mytili (after Barrois). B, diagram
of longitudinal section through the larva of Alcyonidinm (after
Banner), both from Korschelt and Heider. c cells of the velum ;
g ganglion (! cerebral) in connection with the ciliated disc and
pyriform organ o; m mouth; p mantle-groove; r ciliated disc;
s adhesive organ (sucker). In these figures the oral surface is
directed downwards, whereas in Figs. 445 and 446 it is upwards.

which the rec-
tum (r) opens.
The alimentary
canal consists of
the pharynx (ph\
oesophagus, sto-
mach (es) and
rectum (r). Just
in front of the
anus on the floor
of the vestibule
there is an in-
vagination of
thickened ecto-
derm ; this is the
adhesive organ
(ad), by which
the larva attach-
es itself. There
are two shell-
plates placed
right and left
on the aboral
surface. They

FIG. 448. — A, larva of Bugula plumosa (after Barrois). B, diagram of median section through
a larva of Bugula (after Vigelius), both from Korschelt and Heider. c cells of velum ;
e groove of pyriform organ ; / internal tissue of the larva ; o pyriform organ ; p mantle-
groove ; r ciliated disc ; s adhesive organ or sucker.

POLYZOA.

559

meet in front and behind, but gape ventrally. At the aboral apex
there is an opening between the two valves, through which a ciliated
disc (ob) projects.

In the larva of Alcyonidium mytili (Fig. 447) we find all tl>e parts
present in Cyphonautes, except the bivalve shell. But it must be
noted that the alimentary canal is partly aborted, there being no
rectum or anus.
Also the aboral
structure (r) which
corresponds to the
ciliated disc is
larger, and sur-
rounded by a
groove called the
mantle-groove (^>).

The larva of
Flustrella is inter-
mediate between
the above forms;
it has the shell
plates but not the
complete alimen-
tary canal.

Finally, in some
Cheilostomata the
specialisation of
the larva is carried
still further in the
great development
of the ciliary circle,
and in the absence
of an alimentary
canal. In these
larvae (Fig. 448)
there is a pyri-
form organ (o)

FIG. 449. — Metamorphosis of the larva of Schizoporella (?) uni-
cornis (after Barrois, from Korschelt and Heider). A, first
stage of the metamorphosis, showing the evagination of the
adhesive organ s. B, next or so-called umbrella stage ; the
velum has spread out and become bent towards the sucker,
giving the umbrella shape, c cells of velum ; o pyriform organ ;
p mantle-groove ; r ciliated disc ; s evaginated sucker ; v vesti-
bule or concavity of umbrella— the edge of the umbrella
eventually applies itself to the sucker, and the inner walls of
the umbrella fuse and disappear ; x unknown organ.

with its tuft of

cilia; an adhesive organ (s), an aboral, ciliated disc (r) surrounded
by a mantle-groove (p\ but there is no trace of alimentary canal,
mouth, or anus.

After a certain duration of free life, the object of which is to

560

POLYZOA.

distribute the species, the larva comes to rest and attaches itself to
some foreign object. The attachment is effected by the ventral
adhesive organ, which is evaginated and applied to the substratum
(Fig. 449). At the same time the larval organs are in process of
disappearance. The alimentary canal, if present in the larva, totally
disappears, and is in no way concerned in the formation of the
digestive tube of the adult. The pyriform organ and the velum
share in the general fate, and the larva becomes reduced to a layer
of epithelium surrounding a central mass of cells and broken-down
larval organs.

The attached organism is now called the primary zooecium, and
the degenerated larval organs in its interior constitute the first brown

FIG. 450.— Two stages of the primary zooecium, showing the development of the first polypide
otBugula calathus (after Vigelius, from Korschelt and Heider). A, imagination of ectoderm
for the formation of the vesicular rudiment of the first polypide ; & cells of the mesoderm
of the future polypide ; e ectoderm. J3, somewhat older stage, showing the two-layered
vesicular rudiment of the first polypide ; a ectoderm lining the vesicle ; b mesoderm.
In A the internal mass resulting from the degenerated larval organs is omitted.

body. The next stage consists in the invagination inward of the
aboral ciliated disc* (Fig. 450 A, a); the pit so formed becomes
converted into a vesicle (Fig. 450 B), round the walls of which
some of the internal cells arrange themselves. These latter give
rise to the mesoderm of the future polypide, while from the lining
cells of the vesicle, which are ectoderm al in origin, are developed

* According to Prouho the aboral disc, after invagination, shares the fate of
the other larval organs, and the polypide rudiment is derived from an invagina-
tion of ectoderm of the primary zooecium, or it may be a new formation possibly
from the internal tissue.

POLYZOA.

561

the lining of the alimentary canal, the ganglion, and the covering
of the tentacles and the tentacle-sheath (Fig. 451).

The muscles, funiculus, and somatic mesoderm of the animal are
derived from other cells of the internal mass, while the body-cavity
comes from the space in the same mass.

In the Phylactolaemata the embryo develops in the brood pouch
into a vesicle, the outer wall of which is ectoderm, the inner
mesoderm, and the cavity coelom. The larva which issues,
either by the degeneration
of the polypide or the open-
ing out of the zooecium, is
•covered with cilia by means
of which it swims. It is the
primary zooecium: during its
free-swimming life it develops
a complete polypide, or it may
be two polypides (Plumatella),
or even a greater number
(Cristatetta), before fixation
takes place ; thus differing
from the primary zooecium
of the Gymnolaemata, which
does not develop the polypide
until after fixation. As in other
forms, an invagination occurs,
from the walls of which the polypide is developed, i.e. the lining of
the alimentary canal,* the covering of the tentacles and tentacle-sheath,
and the nerve ganglion are alike derived from so-called ectoderm.

From the foregoing account a certain number of conclusions may
be drawn. (1) The free-swimming larva of the Edoprocta is a
trochosphere with a preoral ciliated ring, and an apical sense-organ —
the aboral disc, f (2) The larva attaches itself by its oral face, and
becomes the primary zooecium. (3) The larval organs disappear in
the primary zooecium. (4) The formation of the adult organs
(except the body-wall) is either to be looked upon as a case of

* In a recent work on the development of Plumatella (Leuckart and Chun's
Bibliothcca Zoologica, heft 23, 1897) Braem states that endoderm tissue can
he made out in the embryo.

t It is not quite certain that the aboral disc is the apical plate, but if
Farmer's observation that it is connected with nerve tissue (Fig. 447) is correct,
and further, if Prouho is right in describing its degeneration in the primary
.zooecium (Note, p. 560), this conclusion may reasonably be drawn.

2 o

FIG. 451.— Diagram showing the developing first
polypide in connection with the wall of the
primary zooecium. a anus ; d rudiment of
stomach ; ee wall of primary zooecium (endo-
cyst) ; in mouth ; n rudiment of ganglion ;
r retractor muscle ; t tentacles ; ts tentacle-
sheath. (From Korschelt and Heider.)

562 POLYZOA.

budding from the primary zooecium, or as a process of meta-
morphosis in which the larval organs undergo degeneration and
new formation in consequence of the extensive changes compressed
into the metamorphosis. Until this point is settled it is impossible
to relate with certainty the adult organs and surfaces to those of
the larva, because of the extensive degenerative changes and new
formations which take place at the metamorphosis.

If the formation of the first polypide is a case of budding,
we ought, in determining the* homologous surfaces of the primary
zooecium and first polypide, to attach no more importance to the
fact that apparently the oro-anal surface of the first polypide is
derived from the aboral surface of the larva, because it is formed
from it, than we should to the fact that in a bud developed from the
dorsal surface of the adult, the oro-anal surface of the budded form is
derived from the dorsal (aboral) surface of the parent. Consequently
the argument of Korschelt and Heider, which is based upon this
consideration, and from which they deduce most far-reaching con-
sequences, that the oro-anal line of CypTionautes and other Ectoproct
larvae is really dorsal — has no value. Moreover, on the same
hypothesis, the fact that in the formation of the first polypide the
ectoderm of the primary zooecium apparently gives rise to the
alimentary canal — has 110 more importance than a similar phenomenon
would have in ordinary gemmation, in which the value of the layers
is not the same as in embryonic development.

It must be noted here that in the embryonic origin (not described in this work)
of the larvae of the Ectoprocta without alimentary canal, the endoderm is, in
some cases, not formed at all ; the internal tissue being, to judge by its fate,
entirely mesodermal, and any cavity in it entirely coelomic (vide especially the
larva of Phylactolaemata). The endoderm appears only in the first bud, and is
in that derived from ectoderm.

Finally, to sum up the matter, if the larva is a trochosphere and
the ciliated disc an apical plate, and if we regard the formation of
the first polypide as a case of budding from the primary zooecium,
which is the metamorphosed larva ; and if moreover there is in the
Polyzoa, as there is in other animals, an homology between the
mouth and anus and ventral surface of an organism produced by
budding and the corresponding structures in the parent organism;
then it follows that the oro-anal line of the Ectoprocta is ventral, and
the ganglion a suboesophageal ganglion, and to be compared to the
suboesophageal ganglion of other types : that is to say, it is not
dorsal as might be surmised from the terminology applied to the

POLYZOA. 563

parts in the adult (see p. 552). On the other hand, it may be
argued with equal force that the oro-anal surface of the adult is
equivalent to the dorsal surface of the larva, for the larva attaches
itself by a sucker on the ventral surface between the rtfbjith and
anus. In this case we should have to regard the formation of the
first polypide as a case of larval metamorphosis, comparable to that
of a holometabolous insect, in which the changes are so extensive
that many of the larval organs degenerate completely, and are re-
formed in the imago. If this view is correct the reduction of the
dorsal surface and the approximation of the mouth and anus in
the adult as compared with the larva, would be comparable to the
phenomena which take place in Actinotroclia at the metamorphosis
into the adult Phoronis. On the whole we are inclined to the view
that the first polypide is formed by budding from the primary
zooecium, which is the metamorphosed larva, and that consequently
the ganglion of the Polyzoa is really a ventral, suboesophageal
ganglion, and that the surface between the mouth and anus of the
adult is the ventral surface, and comparable to the surface on which
the mouth and anus of the larva are placed. In coming to this con-
clusion we attach great importance to the fact that the formation of
the first polypide from the primary zooecium is closely similar to the
budding which takes place in the formation of the adult colonies.

Before leaving the subject of the development of the Ectoprocta,
attention must be called to a most important process of embryonic
fission discovered by Harmer in the Cydostomata. In this sub-order
the ovicell is a zooecium with a rudimentary polypide (Crisia), in
the funicular tissue of which the ovum arises. Fertilisation has
not been observed, but the alimentary canal of the polypide grows
round the egg and forms a multinucleated follicle for it. The
ovum segments and becomes a multinucleated mass, in which cell
limits cannot be seen. This buds off small pieces, which become
ciliated, escape from the zooecium in a manner not clearly ascer-
tained, and swim away as ciliated larvae.

Asexual reproduction by budding is of course a most important
process in the Edoprocta. As shown above, it begins even in the
larva, and is a marked feature of the metamorphosis ; and the forma-
tion of the colonies is entirely due to it. Indeed, we may say that
the Edoprocta resemble the Siphonophora and other Coelenterates in
possessing that power of multiplication and of differentiation of parts
(e.g., avicularia, etc.) which is so preeminently a characteristic of the
vegetable kingdom.

564 POLYZOA.

The actual process of budding appears to be similar to the process
by which the first polypide arises from the primary zooecium, that is
to say the budding polypide is derived from a two-layered vesicle
attached to the inner side of the body-wall of the parent zooecium.
The inner wall of this vesicle is formed from the ectoderm, and
gives rise to the alimentary canal, ganglion, and covering of the
tentacles and tentacle-sheath of the new form, while the outer wall
constitutes the mesodermal structures of the new polypide. The
endoderm does not take part in tRe gemmation of the Ectoprocta.

Class I. ECTOPROCTA.

Anus outside the tentacular circlet.

This group includes by far the greater number of the Polyzoa,
and their structure has been specially referred to in the precedent
description of the class. The anus always opens outside the ring
of tentacles, which are either arranged in a circle (Gymnolaemata)
or on a two-armed horseshoe-shaped lophophore The coelom is
well developed, and the reproductive cells are developed from its
lining.

Order 1. GYMNOLAEMATA.

Ectoprocta with circular lophophore, without epistome.

The Gymnolaemata are, with a few exceptions, marine forms. Alcyonidium
and Bowerbankia are found in estuaries, and Victordla and Paludicella are only
known in fresh or brackish water. Statoblasts are never found ; but in the
fresh-water forms the whole colony dies down in the winter with the exception
of certain external buds, which are called hibernacula and give rise in the spring
to new colonies.

The cuticle is sometimes horny, and sometimes encrusted with calcareous
matters, over which a layer of cells may even extend. The zooecia present
a great variety of form.

Sub-order 1. CHEILOSTOMATA.

The orifice of the zooecium can be closed by an operculum. Avicularia, vibra-
cula, and ovicells are often present.

Tribe A. CELLTJLARINA. With corneous or corneo-calcareous infundibuli-
form cells, the inferior part of which below the aperture is tubular or obconic.

Fam. 1. Aeteidae. Zooecia tubular, with a lateral membranous area;
orifice terminal. Tentacle-sheath terminating above in a circle of setae, which
are everted during the expansion of the polypide. Aetea Lamouroux.

Fam. 2. Eucrateidae. Zooecia uniserial, or in two series placed back to
back, with a terminal or subterminal and usually oblique aperture. Avicularia
and vibracula absent. Zoaria as slender, branching, phytoid tufts. Eucratea
Lamx. ; Gemellaria Sav. ; Scruparia Hincks ; Huxleya Dyster ; Brettia Dyster ;
Pasythea Lamx.

CHEILOSTOMATA. 565

Fam. 3. Chlidoniidae. Zooecium composed of upright, free, segmented stems
springing from a stolonate network. Zooecia bicamerate ; unarmed. Chlidonia
Sav.

Fam. 4. Catenariidae. Zooecium radicate, segmented ; internodes except
at a bifurcation formed of a single zooecium. Catenicella Blainv. ; Catcdaria Sav.

Fam. 5. Cellulariidae. Zooecia in two or more series, closely united and
ranged in the same plane ; avic. and vibrac., or avic. only, almost always present
and sessile. Zoarium erect, dichotomously branched. Cellularia Pall. ; Menipea
Lamx. (Emma Gray) ; Scrupocellaria v. Ben. ; Caberea Lamx. ; Canda Lamx. ;
Nellia Busk.

Fam. 6. Bicellariidae. Zooecia rather loosely united in two or more series,
or disjunct ; obconic or boat-shaped ; the aperture usually occupying a large
proportion of the front. Avic. when present, capitate, pedunculate, and jointed.
Zoarium not articulated, erect and phytoid, or composed of a number of cells
connected by tubular processes. Bicellaria Blainv. ; Bugula, Oken. ; Beania,
Johnston (Diachoris Busk) ; Kinetoskias Kor. and Dan. ; Ichthyaria Busk.

Fam. 7. Farciminariidae. Fardminaria Busk.

Fam. 8. Notamiidae. Zooecia in pairs, each pair arising by tubular pro-
longations from the pair next but one below it ; at each bifurcation a new series
of cells intercalated into the branches. Notamia Fleming.

Tribe B. FLUSTRINA. With quadrate cells, the front surface of which is
flat and equals the area of the primitive aperture.

Fam. 9. Cellariidae. Zooecia usually rhomboidal or hexangular, disposed in
series round an imaginary axis, so as to form cylindrical shoots. Zoarium erect,
calcareous, dichotomously branched. Cellaria Lamx. (Salicornaria Cuv.) ;
Melicerita M.-Edw.

Fam. 10. Flustridae. Zoarium corneous and flexible, expanded, foliaceous,
erect. Zooecia contiguous, nmltiserial. Avicularia usually of a very simple
type. Flustra L. , F. foliacea L. ; Carbasea Gray.

Fam. 11. Membraniporidae. Zoarium calcareous or membrane-calcareous.
Zooecia forming an irregular continuous expansion, or in linear series, with raised
margins, and more or less membranous in front. Membranipora Blainv.;
Electra Lamx. ; Megapora Hincks ; Amphiblestrum Gray ; Biflustra d'Orb. ;
Foveolaria Busk.

Fam. 12. Microporidae. Zooecia with the front wall wholly calcareous ;
margins elevated. Micropora Gray ; Steganoporella Smith ; Setosella Hincks ;
Vincularia Defrance ; Caleschara MacGillivray.

Tribe C. ESCHAEINA. With calcareous cells, the aperture of which about
equals the operculum in size, no membranous area being left.

Fam. 13. Bifaxariidae. Bifaxaria Busk ; Calymmophora Busk.

Fam. 14. Tubucellariidae. Tubucellaria d'Orb. ; Siplionicytara Busk.

Fam. 15. Onchoporidae. Onchopora Busk ; Onchoporella Busk.

Fam. 16. Beteporidae. Zoarium calcareous, erect, fixed ; foliaceous and
fenestrate, unilaminar ; or reticulately or freely ramose in one plane. Zooecia
secund. Retepora Imperato ; Reteporella Busk ; Turritigera Busk.

Fam. 17. Cribrilinidae. Zoarium adnate, forming an indefinite crust, or
erect. Zooecia with the front wall more or less fissured or traversed by radiating
furrows. Cribrilina Gray ; Membraniporella Smitt.

Fam. 18. Microporellidae. Zoarium incrusting. Zooecia with a semi-

566 POLYZOA.

circular aperture, the lower margin entire, and a semilunate or circular pore
below it. Microporella H. ; Dipomla H. ; Cliorizopora H. ; Flustramorpha Gray.

Fam. 19. Porinidae. Zoarium encrusting, or erect and ramified. Zooecia
with a raised tubular or subtubular orifice, and frequently a special pore on the
front wall. Porina d'Orb. (Tessaradoma Norman) ; Anarthropora Smitt ;
Lagcnipora Hincks ; Celleporella Gray.

Fam. 20. Myriozoidae. Zoarium encrusting, or rising into foliaceous
expansions, or dendroid. Zooecia calcareous, destitute of membranous area
and of raised margins ; orifice with a sinus on the lower lip. Schizoporella H. ;
Mastigophora H. ; Rhynchozoon H. ; •Hippothoa Lamx. ; Myriozoum Donati ;
(Gephyrophora B. ; Haswellia B. ; Gemellipora Smitt).

Fam. 21. Escharidae. Zoarium calcareous, encrusting, or erect and lamellate,
or ramose. Zooecia without a membranous area or raised margins. "Without
special pores and orifice without a true sinus. Lepralia Johnston ; Umbonula
H. ; Porella Gray ; Escliaroides Smitt ; Smittia H. ; Phyladella H. ; Mucronella
H. ; Palmicellaria Alder ; Eschara Pallas ; Aspidostoma H.

Fam. 22. Adeonidae. Adeona Lamx. ; Adeonella, B. ; Reptadeonella B.

Fam. 23. Celleporidae. Zooecia calcareous, more or less vertical to the
plane of the colony, irregularly heaped together, with a terminal orifice.
Cellepora Fabricius.

Fam. 24. Selenariidae. Cupularia and Lunularia Lamx. ; Selenaria Busk.

Sub-order 2. CYCLOSTOMATA.

Zooecia tubular, with a plain terminal orifice without operculum. Without
movable appendages. The ovicells are modified zooecia. Many fossil species.

Tribe A. ARTICULATA. With erect branches divided at intervals by
chitinous joints.

Fam. 1. Crisiidae. Zoarium dendroid, calcareous, composed of segments
united by corneous joints. Crisia Lamx.

Tribe B. INARTICULATA. With unjointed zoarium.

Fam. 2. Tubuliporidae. Zoarium entirely adherent, or more or less free and
erect, multiform, often linear, or flabellate or lobate, sometimes cylindrical.
Zooecia tubular, disposed in contiguous series, or in single lines. Ooecium formed
by the inflation of the branch. Aledo Lamx. ; Tubulipora Lamx. ; Stomatopora
Bronn ; Jdmonea Lamx. ; Entalopliora Lamx. ; Diastopora Lamx. ; Pustulopora
Blainv.

Fam. 3. Horneridae. Zooecia opening on one side only of a ramose zoarium,
never adnate and repent. Horncra Lamx.

Fam. 4. Lichenoporidae. Zoarium discoid, simple or composite, adnate, or
partially free and stipitate. Zooecia tubular, erect or suberect, disposed in more
or less distinct series, which radiate from a free central area ; the intermediate
surface cancellated or porous. Lichenopora Defrance ; Domopora d'Orb.

Fam. 5. Frondiporidae. Frondipora Imperato ; Fasdculipora d'Orb. ; Super-
cytis d'Orb.

Sub-order 3. CTENOSTOMATA.

When the tentacle-sheath is retracted, the orifice of the zooecium is closed
by a folded membrane as by an operculum. Zoarium never calcareous. Ovicells
and appendages absent.

PHYLACTOLAEMATA. 567

Tribe 1. HALCYONELLEA. Zoariura fleshy or membranous. Zooecia
developed by budding from other zooecia, and not from the internodes of a
stolon.

Fam. 1. Alcyonidiidae. Zooecia more or less closely united, immersed in
an expanded and adherent gelatinous crust, or forming an erect cylindrical or
compressed zoarium ; orifice closed by the mere invagination of the tentacular
sheath ; not protected by external labia. Alcyonidium Lamx.

Fam. 2. Flustrellidae. Zooecia immersed in a gelatinous crust ; orifice
bilabiate. Larvae with a bivalve shell. Flustrella Gray ; F. hispidct Fabr. ,
on Fuci between tide-marks.

Fam. 3. Arachnidiidae. Zooecia usually more or less distant, membranous.
Arachnidium Hincks.

Tribe 2. STOLONIFERA. Zoarium horny or membranous. Zooecia de-
veloped by budding from the internodes of a distinct stolon or stem.

A. All the tentacles erect.

Fam. 4. Vesiculariidae. Zooecia contracted below, not closely united to the
stem at the base, deciduous, destitute of a membranous area. Zoarium repent
or erect. All with gizzard except Farrella. Vesicularia J. V. Thompson ;
Amathia Lamx. ; Zoobotryon Ehr. ; Bowerbankia Farre ; Avenella Dalyell ;
Farrella Ehrenb.

Fam. 5. Buskiidae. Zooecia contracted below, not continuous with the
creeping stolon, with an aperture on the ventral surface. BusTcia Alder.

Fam. 6. Cylindroeciidae. Zooecia not contracted below, closely united to
the stem at the base, not deciduous ; destitute of a membranous area. Cylin-
droecium Hincks ; Angidnella v. Ben.

Fam. 7. Triticellidae. Zooecia horny, with an aperture and membranous
area on the ventral aspect ; borne on a rigid peduncle, to which they are attached
by a movable joint, deciduous. Triticella Dalyell ; Hippuraria Busk.

B. Two of the tentacles everted.

Fam. 8. Valkeriidae. Zooecia contracted below, deciduous, destitute of
a membranous area. Valkeria Fleming.

Fam. 9. Mimosellidae. Zooecia contracted below, movable, deciduous, with
an aperture on the ventral side. Mimosella Hincks.

Fam. 10. Victorellidae. Zooecia originating in an enlargement of the creep-
ing tubular stem, with which they are continuous at the base; above free
and cylindrical ; not deciduous. Fictorella S. Kent, fresh-water form, with
hibernacula. Paludicella Gerv. is allied here.

Order 2. PHYLACTOLAEMATA.

Fresh-water Polyzoa with horseshoe-shaped lophophore and epistome.

The Phylactolaemata are mainly distinguished by the bilateral arrangement
of the numerous tentacles on the two-armed lophophore. There is always present
above the mouth a movable tongue-shaped process — the epistome, whence the
name given by Allman to this sub-order. The zooids are usually of considerable
size, and are all alike (i.e. there is no polymorphism). The body-cavities of the
zooids of a colony are in wide communication, and the colonies are ramified or
massive, often transparent, and of a horny, or leathery, or gelatinous con-
sistency. Statoblasts are present. The cerebral ganglion contains a cavity
which is developed as a pit in the. ectoderm of the bud.

568

POLYZOA.

Fam. 1. Cristatellidae. Free-moving colonies, on the upper surface of which

the zooids are arranged in concen-
tric ellipses. Cristatella Cuvier.

Lp fltofefc. Fam 2 Plumatellidae. At-

tached, massive or ramified colo-
nies of fleshy or coriaceous con-
sistency. Pectinatella Leidy ;
Lophopus Dumortier, discovered
lay Trembley in 1741, and is the
first Polyzoon of which we have
any notice ; L. crystallinus Pall. ;
Plumatella Lamk., including Al-
cyonella Lamk., A. fungosa Pall.;
P. repens L. (Fig. 452) ; Frederi-
cella Gervais, differs from the other
members of the family in having
a nearly circular lophophore ; the
statoblasts are without a ring of
air-cells.

Fia. 452. — Plumatella repens slightly magnified
(after Allman). Lp lophophore ; D alimentary
canal.

Class II. ENTOPROCTA.

Anus within the tentacular circlet.

The Entoproda are more simply organised than the Ectoprocta.
The tentacular circlet surrounds a kind of vestibule into which the
mouth and anus, the gener-
arid excretory organs
The alimentary canal

ative
open.

is a simple U-shaped tube,
differentiated into oesophagus,
stomach, and rectum (Fig.
453). There is a ganglion
in the floor of the vestibule
between the mouth and anus.
There is no body-cavity, but
only a slight amount of con-
nective tissue between the
body- wall and gut-wall. There
is a pair of fine, ciliated canals,
which are described by some
observers as intracellular, by
others as intercellular, which
lie on the ventral face of the
stomach and open into the
vestibule on the oral side of
the ganglion.

t

FIG. 453. —Diagrammatic longitudinal section
through Pedicellina (after Ehlers, from Kor-
schelt and Heider). a anus ; ep epistome ; ex
excretory canal : g gonad ; TO mouth ; ms fibres
of the circular muscle ; n ganglion ; t tentacles.

ENTOPROCTA.

569

The generative organs are continuous with their ducts, and open
on the ventral surface between the mouth and arms ; in Pedicellina
they open into a kind of brood-pouch in the ventral wall of the
vestibule on the anal side of the ganglion. They are paired glands,
and the ducts of the testes open into a vesicula seminalis. Pedi-
cellina is hermaphrodite, but the organs of the two sexes do not
appear usually to mature at the same time. Loxosoma is dioecious.

The early stages of development take place in the brood-pouch.
The ovum undergoes total cleavage, and an invaginate gastrula with
two pole cells is formed. The blastopore remains open in the

Fm. 454.— Development of Pedicellina ecUnata (after Hatschek). a, blastosphere. 6 and c,.
later stages in optical section, d, young larva in median optical section, e, free-swimming
larva extended. A vestibule ; Af rudiment of the rectum ; Dr apical thickening ; EC
ectoderm ; En endoderm ; Fh segmentation cavity ; Hd rectum ; Kn dorsal organ ; L liver
cells ; Ms mesoderm ; N excretory canal ; Oe oesophagus.

position of the anus, and the pole cells give rise to two short
mesoblastic bands. The embryo leaves the brood -pouch as a
trochosphere larva (Fig. 454), with a well-marked velar ring of
cilia having the same relation to the mouth and anus that the
tentacles have in the adult, an apical thickening of ectoderm (Z>r),
which carries a tuft of cilia and consists of large glandular cells,
and a pit of thickened ectoderm on the anterior side of the dorsal
surface (Jm) called the dorsal organ. The apical thickening is
variously interpreted as a sense organ and an organ for adhering;,
the dorsal organ is provided with two pigmented eye -spots in

570

POLYZOA.

Loxosoma, and is interpreted by Harmer as the rudiment of the
supraoesophageal ganglion; it is connected by two nervous tracts
round the oesophagus with the persistent ganglion, which probably
develops from the floor of the vestibule between the mouth and
anus as a thickening of ectoderm, and on the same view may be
interpreted as the suboesophageal ganglion.

As was first made known by the independent researches of Barrois
and Harmer, the larva fixes itself by the oral surface and then

R

~

PIG. 455.— Three stages in the metamorphosis of Pedicdlina (after Harmer, from Korschelt
and Heider). A, just fixed larva. B, beginning of the rotation of the alimentary canal,
and disappearance of larval organs. C, formation of new opening of vestibule and of
tentacles, a anus ; d dorsal organ ; m mouth ; p gland of attaching surface ; * rudiments
of tentacles ; w ciliated disc.

proceeds to undergo the following metamorphosis (Fig. 455). The
opening of the vestibule closes, the dorsal organ and apical plate
disappear, and the alimentary canal apparently undergoes a process
of rotation of such a kind that the atrium conies to lie on the
.surface opposite to that by which the animal is attached. Mean-
while a stalk is formed by the elongation of the new aboral region,

ENTOPROCTA. 571

and the tentacles and a new opening for the vestibule are established.
During the whole of this process the alimentary tube, with its
mouth and anus, persist.

Here then is a metamorphosis very similar in its results to^the
process which takes place in the Ectoprocta, viz., an entire shifting of
the oral surface round to the opposite side of the larva ; but differing
from that, in the fact (1) that the attachment is effected by the edge
of the ventral* surface, and not by an adhesive organ between the
mouth and anus, and (2) that the larval organs do not undergo
disruption, but allow us to perceive that the alteration is due to the
relative growth of the parts rather than to the formation of a new
mouth and anus on the aboral side of the larva.

As to the actual relations between this larva and the Cyphonautes,
they appear to resemble one another very nearly, but on a critical
examination certain points of difference become obvious. These are
(1) the absence in the Entoproct larva of an adhesive organ ; (2) the
presence of a rudiment of the cerebral ganglion (dorsal organ), and
(3) the absence of the pyriform organ in the Entoproct larva. The
pyriform organ, which has been supposed to have something to do
with the cerebral ganglion, t cannot be homologous with the dorsal
organ of Entoprocta, because it is within the velar circlet. So that,
on the whole, we are inclined to think that the resemblances between
these larvae are superficial ones, and cannot be used as important
arguments in favour of the view that the Polyzoa constitute a
monophyletic group. On the other hand, it is held by many
zoologists that the Ectoprocta and Entoprocta should not be
associated in the same group, and that there is really no close
relationship between them. The principal argument used in favour
of this contention is that the Entoprocta are without a coelom,
and should be removed altogether from the Coelomata. This view
of the matter is further borne out by the relations of the gonads
and the presence of the two ciliated excretory canals. We, however,
while admitting that there is much to be said for it, do not regard
it as proven, and cannot give it expression in this work.

The comparison which Caldwell has instituted between Phoronis and the
Polyzoa is based upon the supposed resemblance between Phoronis and the

* This attachment must have been confined to the anterior side of the ventral
edge, otherwise it is impossible to conceive how the process of relative shifting
of the mouth and anus above described in its abbreviated embryonic form
•could have happened in the ancestral history,

t The cerebral ganglion on the view here adopted of the Ectoprocta is not, of
•course, present in the adult, for as pointed out above, the ganglion of the
Ectoprocta, though sometimes called dorsal, must be really suboesophageal.

572

POLYZOA.

Te

Phylactolaemata. In both there is a horseshoe-shaped lophophore, an epistomer
a division of the body-cavity by a septum into a small part at the oral end, and
the main part around the alimentary canal, and the presence of a pair of very
similar nephridia. Of these resemblances the first two
are not important, while the third and fourth concern
doubtful points of anatomy. Against this comparison
is to be set the development. In Phoronis the line
between the mouth and anus is dorsal, and would
contain, if it still existed, the preoral lobe of the larva.
In the Ectoprocta, on the other hand, the line between
the mouth and anus is ventral, though this would
possibly be disputed by some zoologists (see p. 563) ;
while in the Entoprocta the oro-anal surface is unques-
tionably ventral, the preoral lobe and its sense organ
belonging demonstrably to the surface between the anus,
and the attachment of the adult (Fig. 455).

The Entoprocta are, with the exception of
Urnatella, marine animals. Pedicellina is
stalked and colonial. Loxosoma is solitary;
the buds, which are formed, separating from
their parent. Loxosoma is generally a com-
mensal.

Fam. 1. Loxosomatidae. Solitary forms budding
from the body ; the buds separate from the parent.
Loxosoma Kef., L. phascolosomatum at the end of the
body of Phascolosoma, L. (Cyclatella) annelidicola, on
the Maldanidae, etc.

Fam. 2. Pedicellinidae. Stalked, colonial forms,
attached to a creeping stolon ; budding at the growing
point of the stolon. Pedicellina M. Sars.

Fam. 3. Urnatellidae. Stalked colonial, fresh-water
forms, N. America. Urnatella Leidy.

FIG. 456. — Pedicellina,
echinata. Te tentacular
crown ; 0 mouth ; Md
alimentary canal ; A
anus ; Or ovary; G gan-
glion. (From Glaus.)

X

CHAPTER XVI.

PHYLUM BRACHIOPODA.*

Fixed, solitary, apparently unsegmented Coelomata, with a ten-
taculated ljuccal groove often prolonged into arms, and a bivalve
shell.

The Brachiopoda constitute an isolated phylum of the animal
kingdom. They were formerly placed with the Mollusca, with
which they have clearly no affinities. Later they were associated
with the Polyzoa under the heading Molluscoidea ; but this grouping
must also be regarded as unsatisfactory, for they differ from the
Polyzoa in several important points, amongst which may be men-
tioned the presence of a vascular system, of paired nephridia, of
setae embedded in pits of the skin, of a shell composed of two
pieces, and in not forming colonies.

On the whole, the increased knowledge of their anatomy and
development which has been acquired of late years, though still
far from satisfactory, points to the view that we must assign to
the group the position of an independent phylum of the animal
kingdom with affinities, by the form of their central nervous system,
and by their setae, by the presence of a well-developed perivisceral
coelom and a canalicular haemocoel, and by the traces of an
imperfect segmentation, to the Annelida; though at the same time
it must be pointed out that by the presence of longitudinal dorsal

* K. Owen, "On the Anatomy of the Brachiopoda," Trans. Zool. Soc. London
1835. A. Hancock, "On the Organisation of the Brachiopoda," Phil. Trans.
148, London, 1858. T. Davidson, "A Monograph of the British Fossil Brachio-
poda," I. -VI., Palaeontographical Society, London, 1851-84. Id., "A Mon.
of recent Brachiopoda," Pts. 1, 2, Trans. Lin. Soc. London, 1885-8. T. H.
Huxley, "Contributions to the Anatomy of the Brachiopoda," Proc. Roy. Soc.,
7, 1854 (2), 14, 1854. H. Lacaze-Duthiers, " Histoire Nat. d. Brachiopodes de
la Mediterranee," Ann. Sci. Nat. (4), 15, 1861. J. F. van Bemmelen, " Unters.
lib. d. Anat. u. hist. Bau d. Brachiopoda Testicardinia," Jen. Zeits., 16, 1883.
A. E. Shipley, "On the Structure and Devel. of Argiope," Mil. Zool. Stat.
Neapel, 4, 1883. A. E. Shipley and F. R. C. Reed, "Brachiopoda Recent and
Extinct," in Cambridge Natural History, vol. 3, 1895.

574

BRACHIOPODA.

and ventral mesenteries, and by the development of the coelom as-
enteric outgrowths, they recall the Chaetognatlia. The possible
affinities of the group with Phoronis, in favour of which there is
much to be said, are discussed at the end of the chapter.

The mouth is placed in a buccal groove, one side of which (the
dorsal) is provided with a lip, and the other with a row of tentacles.
The groove is either continued as a circle on the dorsal lobe of the
mantle or is drawn out on each side into the characteristic arms
which project into the mgfiitle- cavity. The anus is absent, or
present usually on the right side of the front surface of the body,
in a position which is described as ventral to the mouth (in Crania
it is median, slightly dorsal and posterior). The two valves of the
shell are commonly described as being dorsal and ventral, though it
must be borne in mind that there are embryological reasons for
regarding the surface between the mouth and anus as dorsal, and
the whole of the surface on which the shell-valves lie as ventral.
There is a circumoesophageal nerve-collar, not separated from the
ectoderm and bearing supra-oesophageal and suboesophageal gangli-
onic swellings. There are no organs of special sense in the adult,
though the larva possesses eye spots. The edges of the mantle-
lobes, which are folds of the body-wall, contain setae embedded in
ectodermal pits. There is a heart on the so-called dorsal side of
the stomach giving off vessels. The perivisceral cavity is coelomic,
and extends into the mantle-folds ; it communicates with the exterior
by one pair (in Rliynclwnella two pairs) of nephridia ; the generative
cells are developed on its walls and dehisced into it, and carried
outwards by the
nephridia. Asexual
reproduction and par-
thenogenesis are un-
known in the group.

It is commonly said
of the Brachiopoda
that they are pre-
eminently an ancient
group, and some im-
portance is attached
to this fact. It is
true that they are

an ancient group, representatives of it being known in the Cambrian,
and the number of fossil forms is vastly greater than that of the

FIG. 457.—Rhynchonella psittacea. A, from above ; B from the
left side (after Lang).

BRACHIOPODA. 575

living ; but no special distinctive importance can be attached to these
facts, for similar statements may be made of almost all the great
groups, representatives of which are known from the earliest
formations. ,

The body is enclosed in a bivalve shell, of which one valve i&
called dorsal, and the other ventral (Fig. 457). Both valves lie upon
corresponding folds of the integument called the mantle lobes, and
are often connected posteriorly by a kind of hinge, beyond which the
usually more arched ventral valve projects like a beak (Fig. 458, St).
The ventral valve is usually larger than the dorsal, and is either

Fia. 458. — Anatomy of Waldheimia australis, side view of partly dissected specimen (after
Hancock). Ar arms (the proximal loop of the left arm has been cut away); Do dorsal
valve ; L liver ; Ma adductor, Md divaricator muscles ; 0 the liver ducts of the left side cut
short; Oe oesophagus; St peduncle; Tr folded margins of the funnel of the right nephridium
(oviduct) ; Ve ventral valve ; Vw anterior wall of body.

directly fused with foreign bodies, or the animal is attached by a
peduncle projecting through the opening in the beak. The peduncle
may however pass out between the two valves (Lingula). In Crania,
which is attached by its ventral valve, the peduncle is absent. It is
doubtful which surface of the body the stalk belongs to ; according
to the view stated below, which is admittedly highly speculative,
it is a projection of the ventral surface of the body. The valves
of the shell are cuticular structures secreted by the skin and
impregnated with calcareous salts; they are not opened by a
ligament, but by special groups of muscles (Fig. 458, Md) ; they
are also closed by muscles, which are placed near the hinge and pass

576 BRACHIOPODA.

transversely from the dorsal to the ventral surface through the
body-cavity (Ma).

In many forms the shell is perforated by minute pores, which
however are closed externally by the outer uncalcified layer of the
shell. They transmit tubular prolongations of the mantle. The body
is bilaterally symmetrical, excepting for the anus which in some forms
is on the right side, and is enclosed by the shell, of which it only
occupies the posterior part ; it possesses the two large reduplications
of the integument, the two mantle lobes already mentioned, which are
applied to the inner surface of the shell. The edges of the mantle
are thickened and carry setae, which are regularly arranged and
secreted by the lining of pits of the skin. The mantle may also
produce within its own substance calcareous spicules, or a continuous
calcareous framework.

FIG. 459. — Diagram of a view of the left half of Cistdla (Argiope) neapolitana, showing the
alimentary canal, the left nephridium, and the buccal groove. The animal is supposed
to have been removed from its shell, and to be cut in two by a median longitudinal incision.
c.o external, i.o internal opening of nephridium n ; d.m dorsal, v.m ventral lobe of the
mantle; I and c lip ; t tentacles ; m mouth ; st stalk. (Modified from Shipley.)

The mouth is placed in a transversely directed groove, bounded
dorsally by a lip, and ventrally by a row of tentacles. In the
simplest cases (Argiope, Cistella) this groove has a somewhat circular
course (Figs. 459, 460 a), and lies along the dorsal part of the anterior
wall of the body which is spread out on the dorsal valve. The
mouth is in the posterior part of it, and the anterior part of it is
bent backwards. In other forms the buccal groove does not form
a complete circle, but is incomplete anteriorly, and the two ends
so formed are coiled into a spiral, which is variously disposed in
different forms. Moreover, in these forms it is not united to the
dorsal wall, but projects into the mantle-cavity.

In Waldheimia (Figs. 460, 462) the buccal groove with its dorsal
lip and ventral row of tentacles passes outwards (j) on each side
of the mouth, and forwards towards the opening of the shell ; it then
bends on itself and passes backwards (t, h) on the ventral side of the

BRACHIOPODA.

577

FIG. 460.— Diagrams showing course of buccal groove in a,
Argiope; b, WaJdheimia • and c, Rhynchonella. m mouth;
Hip ; t tentacles.

proximal part, extending almost as far as the mouth. This may be

called the proximal loop of the buccal groove; its two limbs are

united by a mem-
brane. The groove

now turns ventral-
wards, and again

passes forwards into

a vertically placed

spiral, which is coiled

on to the dorsal valve

and at the apex of

which it terminates.

The spiral part is

united with the spiral

part of the opposite

side by a membrane.

The course of the

buccal groove in

Waldheimia is shown

in the diagram (Fig.

460). The proximal

loop of the apparatus is supported in Waldheimia and Terebratula

by a calcareous process of the dorsal valve (Fig. 461). In Rhyn-
chonella there is no calcareous
support for the arms, but the
buccal groove is prolonged into a
long, horizontally placed spiral on
each side, the apex of the spiral
being directed to the dorsal side
(Figs. 460 c, 463). In Lingula the
arms are very much as they are
in Rhynchonella, the spiral being
horizontally placed with its apex
towards the dorsal valve.

In Lingula and Rhynchonella it
appears that the animal has the
power of protruding its arms from
the shell. The epithelium of the
buccal groove and the tentacles is

ciliated, and the whole apparatus is to be regarded as a food-
procuring organ.

2 p

FIG. 461.— Dorsal valve of the shell of
Waldheimia atistralis, with the brachial
skeleton (after Hancock).

578

BRACHIOPODA.

The mouth leads into an oesophagus which, passing dorsalwards,
opens into the stomach. The stomach receives the ducts of a paired
gland called the liver (Fig. 458, o\ and passes into the intestine which
is directed ventralwards. The intestine is short, and ends blindly
in the Testicardines ; while in the JEcardines it is long and coiled,
and opens by an anus into the mantle-cavity. The anus opens on
the right side in Lingula and Discina ; in Lingula it is placed
between the margins of the mantle. In Crania* the rectum is in
the middle line and opens at tne hind end in the middle line into a
space between the two valves where the hinge would be. Sometimes
the end of the intestine is continued as a cord (Thecidium).

FIG. 462. — Waldheimia australis removed from ijs shell, and with the mantle lobes turned back
so as to expose the arms and anterior wall of the body, a ventral, b dorsal lobe of mantle ;
c, c gonads ; / peduncle ; g spiral part of the left arm ; h distal limb of the proximal loop ;
i tentacles ; j lip, a few tentacles cut away to show it : k position of mouth, which is
concealed by the lip ; I occlusor muscles seen through the anterior wall of body ; m left
nephridium opening at n. (After Hancock.) .

The alimentary canal is supported by a median dorsal and ventral
mesentery, which partially divides the body-cavity into a right and
left half; and by two incomplete transverse septa which pass, as
does the dorsal mesentery, from the body-wall to the gut-wall.
Of the two latter the anterior is called the gastroparietdl, and the
posterior the ilioparietal band, from their relations to the stomach
and intestine respectively.

The nervous system consists of a circumoesophageal ring, upon

* Joubin, Arch. Zool. Exp. (2) 4.

BRACHIOPODA.

579

which are developed a variable number of ganglia. The most
general arrangement appears to be one small supra-oesophageal and
one larger suboesophageal swelling. The suboesophageal gives off
nerves to the dorsal mantle-lobe, the arms, and adductor muscles,
and to two small ganglia which supply the ventral mantle-lobe and
the peduncular muscles. The ganglia and commissure are in
immediate contact with

fj

the ectoderm. Special
organs of sense have
not been described.

The vascular sys-
tem has a canalicular
character. There is a
heart placed on the
dorsal side of the
stomach in the dorsal
mesentery. It gives
off a vessel which
passes forwards along
the oesophagus in the
dorsal mesentery ; this
divides into two, which
are continued into the
arms as the tentacular
vessels, and are con-
nected with a vessel
which surrounds the
oesophagus. In addi-
tion to the above there

are two pairs of lateral FlG 463>_view of mail tie-chamber of Rhync^nella psittacea,

vessels running from the ventral mantle lobe turned back (after Hancock).

, -, •, a dorsal, b ventral mantle lobe ; c, c mantle sinuses ; d, d
genital glands ; g circumpallial vessel; j occlusor muscles;

erative organs. k ventral nephridia opening at I ; m arms ; n lip of brachial

rri , , , . , groove ; o position of mouth concealed by lip ; p tentacles

I he blood IS Colour- contracted; q oesophagus.

less.

Our knowledge of the vascular system and its ramifications is
very small, as may be gathered from the statement made by some
observers that the blood vessels communicate with the coelom. This
is a statement which has been made of other groups, and has
always been disproved with the progress of knowledge; and in the
present instance, having regard to the difficulties of the observations

580 BRACHIOPODA.

required, and to the fact that the vascular system is essentially an
organ separate from the coelom and from other organs derived from
the primitive enteron, it cannot be accepted (it should not have been
made at the present day by any well-informed Zoologist) without a
good deal more evidence than has yet been adduced in its favour.

The body-cavity is well developed, and is a coelom. As already
stated it is divided, incompletely it is true, into two lateral halves by
a longitudinal mesentery, and into three successive chambers by two
imperfect transverse septa, the 'gastroparietal and ilioparietal bands.
The latter structures are, however, merely bands, there being three
(or two) gastroparietal and two ilioparietal. They are important,
because they may turn out to be remains of transverse septa
dividing up the coelom in the embryo (see account of development).
The body-cavity contains a corpusculated fluid, and possesses a
ciliated epithelial lining. It is prolonged into the mantle lobes as
i\\Q pallial sinuses, which may be much branched (Lingula). With
regard to other extensions of the body-cavity we know very little.
For instance, there are two channels running along each arm, the one
small and in relation with the row of tentacles, into each of which it
sends a prolongation, and the other larger and in relation with the lip
(1 epistome). It is disputed whether these canals communicate with
each other or with the body-cavity. It is said, however (see above),
that the tentacular channel is a blood vessel, and is a continuation of
the vessel which leaves the anterior end of the heart.

As in coelomate animals the renal organs are nephridia. There
is usually one pair, but in Rhynclionella there are two. They open
externally on each side of the mouth, near the base of the arms, and
internally by funnel-shaped apertures into the body-cavity. When
there is one pair, the internal opening is on the ilioparietal band, into
the posterior chamber of the body-cavity ; when there are two pairs
the openings of the second pair is supported by the gastroparietal
bands, and is into the middle chamber of the body-cavity. The
external openings of the posterior pair, i.e. the pair usually present,
are a little on the ventral side of the mouth, while those of the
anterior pair are a little nearer the dorsal valve. The nephridia
function also as generative ducts, and were called oviducts by
Hancock.

Generative organs. In all probability most Brachiopoda are
dioecious, but possibly a few of them may be hermaphrodite. The
generative organs are developments of the coelomic epithelium.
They are thick yellow bands or ridges which project into the body-

BRACHIOPODA.

581

cavity, and extend into the lacunae of the mantle where they may
be considerably ramified. The ripe sexual cells are dehisced into
the coelom, whence they pass to the exterior through the nephridia.
In some genera (Tliecidium, Cistella, Argiope) the eggs undergo the

St'

FIG. 464. — Development of Argiope (after Kowalewsky). a, embryo in which the enteron D
still communicates in front with the coelomic sacs Lh. b, embryo with three segments, and
commencing mantle fold with setae, c, older embryo showing the same features ; M mantle
fold, d, free larva with eye spots, cephalic umbrella, ciliated ring, and large mantle lobes,
e, attached larva with mantle lobes bent anteriorly. /, later stage with tentacles T, and
commencing peduncle St.

first stages of their development in brood-pouches placed near the
openings of the nephridia. In Thecidium the brood-pouch is median
and ventral. In Argiope and Cistella it is paired.

Our knowledge of the development is very incomplete, and what
we do know relates almost entirely to the Testicardines. The egg

582

BKACHIOPODA.

is small and the segmentation is complete, the gastmla is formed
usually by invagination, and the blastopore closes at the anterior
end of the ventral surface. The archenteron gives off two lateral
diverticula, which are gradually constricted off from it as the coelomic
sacs (Fig. 464, a, b).

The coelomic sacs extend posteriorly behind the enteron, but the
last remnant of the communication between the two is at the front
end of the body. The embryo now becomes constricted by an
annular furrow into two parts, the anterior of which soon divides
in a similar manner, so that three segments are formed (Fig. 464, b).
It does not appear, however, that the coelomic sacs participate in
this segmentation. The enteron is confined to the two anterior
segments, and does not extend into the caudal segment.

K

FIG. 465.— Three diagrams illustrating the hypothetical metamorphosis of a Brachiopod in
relation to that of Actinotrocha (after Korschelt and Heider). A, free-swimming larva show-
ing the mouth-opening and commencing tentacles of the lophophore, neither of which are
present at this stage. B, a transitional stage showing reduction of supposed preoral lobe. C,
young Brachiopod after the turning forward of the mantle lobes. The preoral lobe (cephalic
umbrella) has shrunk to the epistome. d dorsal mantle lobe ; ep epistome ; k preoral lobe
(cephalic umbrella) with its ring of cilia (trochosphere ring) ; m mouth ; st stalk ; t rudi-
mentary tentacles ; v ventral mantle lobe.

On the first segment (head) there is developed an umbrella-like
disc, the edge of which becomes ciliated, and four eye spots. On the
second segment (thorax) there is an annular fold (Fig. 464, c), which
soon grows out into a dorsal and ventral lobe — the mantle-lobes. On
the ventral part of this are developed four bundles of provisional
setae.

The mantle-lobes project back over the caudal region (Fig. 464, d).
The embryo now leaves the brood-pouch and enters upon its free-
swimming life.

The larval stage is of short duration, and during it the enteron

BRACHIOPODA. 583

remains an entirely closed sac. Attachment is effected by the hind
(caudal) end (Fig. 464, e, /), and as soon as it has occurred the mantle-
lobes turn forward and envelop the first segment.

The larva now assumes the adult condition ; the shell valves are
developed on the mantle-folds, the provisional setae are replaced by
the permanent ones, and a mouth is formed at the front end. The
exact relation of the mouth to the umbrella-like head segment is
obscure. It has been suggested that the mouth is formed upon
the ventral side of it, and that the head segment (Fig. 465) is really
a preoral lobe, like that of Phoronis — which soon disappears or is
reduced to the epistome (lip of the buccal groove). The tentacles of
the arms appear on the inner side of the dorsal mantle lobe (Fig.
465, C).

Nothing is known of the embryonic development of the Ecardines.
Their larvae differ from those of the Testicardines in possessing a
shell while free-swimming. A larva of Discina radiata with a large
process overhanging the mouth has been described by F. Miiller
(Mutter's Arch., 1860), and we owe an account of the larva of Lingula
to Brooks (Chesapeake Zool. Lab. Kesults, 1878).

A consideration of the above facts does not lead us very far in deciding the
question of the affinities of the Brachiopoda. If we adopt the suggestion
made above, that the mouth is formed on
the ventral surface — which, it must be
remembered, is opposed to Kowalevsky's /.

statement that it is at the anterior end —
we may regard the larva as a trochosphere
with a preoral ring of cilia and preoral sense-
organs.

The presence of setae secreted in cutaneou
sacs, the indications of segmentation, and
the relations of the coelom in the adult,
further suggest Annelidan affinities. Finally,
the form of the central nervous system is
not opposed to this view of the relationship
of the group. If we adopt this view we
should regard the BncMvfa as Annelids
with three segments, marked in the embryo D alimentary canal ; Af anus ; L
by the annular constrictions of the integu- liver ; St rudiment of peduncle,
ment, and in the adult by the imperfect

septa represented by the gastro- and ilioparietal bands, and by the two pairs
of nephridia in Rhynchonella, which have relations to these bands.

But it must be remembered that according to present accounts there are no
traces of mesoblastic segments in the embryo, the coelomic sacs being con-
tinuous and not divided up by septa. This, however, may be due to imperfect
observation, a possibility which becomes the more likely when we remember
that the larvae are extremely minute, the observations very difficult to make,

584

BRACHIOPODA.

and that there is no account of the formation of the structures which are
supposed to be transverse septa in the adult, or of the nephridia.

But this Annelid view of the group is not the only one which has been put
forward. It has been suggested that the arms, with their tentacles, are com-
parable to the lophophore, and the lip to the epistome
of Phoronis (Fig. 465). There is much to be said for the
affinities with Phoronis which this view suggests, but it
must be remembered that the view is one which itself
rests upon a basis of hypothesis (see p. 583), for in neither
group has the development of the lip been satisfactorily
followed.

The most important objection to it is that the flexure
of the intestine, and the position of the anus nearer the
ventral valve, is different to the arrangement in Phoronis,
in which the intestine has the opposite flexure, and the
anus is on the epistome side (dorsal) of the mouth. It
may fairly be urged, however, that, in our present state
of ignorance of the development of the Brachiopods with
an anus, and consequently of the real position of that
organ, too much weight must not be attached to this
objection. The possible presence of three mesoblastic
segments, and the relations of the nephridia and coelom,
are not opposed to it, nor is the mode of attachment by
the caudal region ; for it is argued the caudal region
might fairly be regarded as equivalent to the evaginated
foot of Phoronis. We think the suggestion that the
Brachiopods are allied to Phoronis an attractive, but at
the same time a highly speculative one. For the principal
arguments in its favour, viz., that in both the preoral
lobe shrivels up or disappears, leaving at most the epis-
tome as an indication of its presence, and that in both
the dorsal surface between the mouth and anus is extra-
ordinarily shortened, are open to the serious reply, that
although these statements may fairly be made of Phoronis,
they can only be put forward in a hypothetical form with
regard to Brachiopods.

FIG. 467.— Longitudi-
nal section of an
older larva of Lin-
gula (after Brooks).
Do dorsal ; Ve ventral
valve of shell ; Mr
thickened edge of
mantle; T tentacles;
0 mouth ; Md stom-
ach ; Ad intestine ;
M posterior muscle ;
G ganglion.

The Brachiopoda are found in all seas at different depths. The
larger number live at moderate depths, down to 500 or 600 fathoms.
Beyond this depth they are rare, though species of Discina and
Terebratula have been taken at a depth of over 2000 fathoms.
Lingula and Glottidia are found between tide-marks. For the most
part they live on rocky ground, and are found in great numbers
together. Lingula burrows in the sand.

The number of living Brachiopods is small, as compared with the
much larger number found in the earlier geological formations,
certain species of which have great importance as characteristic
fossils. The oldest known fossils are Brachiopods, and certain

ECARDINES — TESTICARDINES. 585

genera which first appeared in the Camhrian have persisted to the
present day.

Order 1. ECARDINES (INARTICULATA).*

Shell without hinge and brachial skeleton. Alimentary canal
with anus either ventral and to the right of the middle line, or
posterior and median (Crania}.

Fam. 1. Lingulidae. Shell thin, horny, almost equivalve, a long peduncle
passing between the two valves. Live in tubes in sand. Lingula Brug. ;
L. anatina Lara. ; Glottidia Dall.

Farn. 2. Discinidae. Shell fixed by a peduncle passing through a hole in the
ventral valve. Discina Lam.; D. atlantica King, 1330 fathoms, off West of
Ireland ; Discinisca Dall.

Fam. 3. Craniidae. Shell orbicular, calcareous ; ventral valve adherent ;
without peduncle. Crania Retz. ; C. anomala Mitller, Loch Fyne.

Order 2. TESTICARDINES (ARTICULATA).*

The shell is calcareous, with hinge and brachial skeleton. The
intestine ends blindly.

The exclusively fossil family Productidae, the edge of the shells of which
have no hinge, form the transition between the two orders.

Fam. 1. Terebratulidae. Shell usually biconvex ; punctate, with complete
hinge ; beak of ventral valve perforated for short peduncle ; calcareous loop
bent back on itself. Waldheimia King (Figs. 461, 462), W. cranium Milll.,
North British seas; Terebratula Brug., T. capsula Jeff., English Channel;
Terebratulina d'Orb., T. caput serpentis L. Oban ; Terebratella d'Orb., T.
Spitzbergensis Dav., N. British seas ; Argiope Deslongchamps, A. decollate,
Chemnitz, English Channel ; Cistella Gray (Fig. 459), C. cistellula S. Wood,
N. British seas, English Channel ; Megerlia King ; Kraussina Dav.

Fam. 2. Thecidiidae. Shell plano-convex, usually fixed by beak of ventral
valve. Thecidium Defr.

Fam. 3. Rhynchonellidae. Shell biconvex, hinge usually curved ; beak of
ventral valve incurved with foramen ; calcareous brachial supports as a pair of
short curved crura ; arms coiled in spiral. Rhynchonella Fisch. (Fig. 463),
R. psittacea Gmelin, N. British seas; Atretia Jeff., A. gnomon J., west of
Donegal Bay in 1400 fathoms.

* The localities mentioned in this list refer only to the places in the British
•area, where the species have been obtained. They are taken from Shipley's
•article in the Camb. Nat. Hist.

CHAPTER XVII.

CHAETOGNATHA.*

Hermaphrodite Coelomata, in which the body is divided into three
regions or segments. The head carries two groups of sickle-shaped
setae, and the central nervous system consists of cerebral and sub-
oesophageal ganglia connected by circumoesophageal commissures.

The Chaetognatha are a very small group of transparent pelagic
organisms. Though small in numbers and presenting but little
variety of organisation, the group is one which, both in its adult
structure and embryonic development, is of the greatest interest
to naturalists. It is impossible to relate it to any of the great
phyla of the animal kingdoms, and, like so many of the groups
which we have recently considered, it must have assigned to it
the dignity of phyletic rank.

In certain features of structure, e.g., in the form of the nervous
system, and in the relations and character of the coelom, it resembles
the Annelida, but it differs from them in the small number and in
the character of the segments of which the body is composed, in the
absence of distinct nephridia and a vascular system, and in the
structure of the embryo. For though the egg is small, and the whole
development takes place in the sea, there is no larval stage which
in any way recalls the trochosphere, and the coelom is developed
from archenteric diverticula, a feature which is found in no Annelid.

As in the JBrachiopoda the coelom consists of three pairs of
chambers separated by transverse septa, and as in that group the
division of the coelom is effected subsequently to its establish-
ment as a single enteric diverticulum on each side.

* A. Krohn, " Anat.-physiol. Beobachtungen ub. die Sagitta bipunctata,"
Hamburg, 1844. R. Wilms, " De Sagitta mare germanicum circa insulam
Helgoland incolente" Beroliui, 1846. A. Kowalewski, "Embryologische Studien
au Wurmern u. Arthropoden," Mem. de I'Acad. Petersbourg, 16. 0. Hertwig,
" Die Chaetognathen, eine Monographic," Jena, 1880. B. Grassi, "I. Chetognathi,"
Flora und Fauna d. Golfes von Neapel, 1883. S. Strodtmann, " Die Systematik
der Chaetognathen etc.," Arch. Naturg., 58, 1892.

CHAETOGNATHA.

587

The body is elongated and divided into
the trunk, and the tail (Fig. 468). The
surface of the head, and has the form
of an elongated slit (Fig. 469). The
anus is on the ventral surface, at the
junction of the trunk and the tail.

The head is slightly swollen, and is
partly covered by a prepuce-like fold of
the skin (Fig. 469), which arises from the
dorsal side of the head and forms a kind
of hood more developed laterally than
ventrally. It carries two laterally placed
groups of sickle - shaped setae and a
number of short spines. Moreover, there
are two eyes in close connection with
the cerebral ganglion. Close behind the
head on the dorsal surface there is an
annular modification of the ectoderm (Fig.
468 jR), the cells of which bear cilia;
this is supposed to be an olfactory organ.
The body possesses one or two pairs of
flat cutaneous fin -like folds — the lateral
fins — and the tail is surrounded by a
caudal fin. The fins consist of a fold
of the ectoderm containing a gelatinous
substance, on each surface of which lie
some chitinous rod-like rays beneath the
ectoderm.

The skin consist.s of an epithelium, the
cells of which may be arranged in one
or in more than one layer, of a basement
membrane, and of a layer of longitudinally
disposed muscular fibres ; the latter are
disposed in the trunk and tail in four
bundles — two dorsal and two ventral
(Fig. 470), and the fibres are cross-striped ;
these muscles, both in their arrangement
and appearance in transverse section, are
very like those of the Nematodes. In
the head the muscles are broken up into
bundles which work upon the jaws.

three regions — the head,
mouth is on the ventral

R,

FIG. 468. — Spadella cephaloptera
(after O. Hertwig), dorsal view.
F lateral fin (in caudal region
only, in this genus) ; G cerebral
ganglion ; Te tentacles ; Ov
ovary ; Od oviduct ; T testis J
Vd vas deferens ; Sb vesicula
seminalis ; R olfactory organ.

588

CHAETOGNATHA.

The alimentary canal is a straight tube, and is divided into

oesophagus and intestine. There
are no special glands opening
into it.

The nervous system consists of
a cerebral ganglion in the head,
and a large elongated ventral gan-
glion— the suboesophageal ganglion
— placed in about the middle of
the body length. These two gan-
glia are connected by long circum-
oesophageal commissures, and the
whole of this part of the nervous
system lies in the ectoderm (Fig.
470). There is in addition a pair
of ganglia connected with the cere-
bral, and with each other below the
oesophagus ; these are placed in the
mesoderm and supply the muscles
of the head.

The sense-organs consist of a
pair of eyes on the dorsal surface
of the head, innervated from the
cerebral ganglion ; the annular tract
of ciliated ectoderm on the dorsal

surface already mentioned — it is supposed to be olfactory in function,

and varies in shape in different

species ; and tactile papillae consisting

of ectoderm cells, and distributed all

over the surface.

There is no vascular system.
The body-cavity is well developed,

and, as is shown by its development

and its relation to the male generative

organs, is a coelom. It is lined by

a layer of flat epithelium, and is

divided into two lateral halves by a

longitudinal septum, in which the

alimentary canal is placed (Fig. 470) ;

this Constitutes the dorsal and ventral Hertwig). lh coelom ; mes mesentery;
, . -, , -I i W'd intestine ; hn longitudinal mus-

mesentery, and in the tail the septum. cies ; bg suboesophageai ganglion.

FIG. 469.— Head ofSagitta Upunctata. A
dorsal, B ventral view. 02 cerebral
ganglion ; kk cephalic hood ; ?i,l circuin-
oesophageal commissures ; 710 optic
nerve ; nr olfactory nerve ; o mouth ;
r olfactory organ ; v hooks ; z spines.
(After Hertwig.)

CHAETOGNATHA.

589

It is further divided by two transverse septa into three successive
chambers : one in the head, another in the trunk, and the third
in the tail (Fig. 468). These chambers are indications of segmenta-
tion, though the exact mode of their origin from the original
continuous coelom has not been made out. Of these three coelomic
chambers or segments, the posterior alone has, so far as is known,
a communication with the exterior through the male generative
ducts.

Generative organs. The animals are hermaphrodite. The female
organs are contained in the middle segment of the body, and the
oviduct opens on each side of the anus at the junction of the middle
and caudal regions. The ovaries are placed one on each side
(Fig. 468) ; they are solid and are attached to the wall of the
body, projecting into the body-cavity. The oviducts are narrow

FIG. 471.— Three embryos of Sagitta (from Lang, after Hertwig). U blastopore ; ud arch-
enteron ; g primitive generative cells ; vm splanchnic, pm somatic (parietal) layer of
mesoderm ; d rudiment of intestine ; cs coelomic sacs ; st stomodaeum (ectodermal ingrowth
which forms the anterior part of the alimentary canal).

tubes extending along the outer sides of the ovaries and lined by
an epithelium. They end blindly in front, and open to the exterior
behind; they sometimes contain spermatozoa. The ova are not
dehisced into the coelom, and it is not known how they get into
the oviducts, which appear to be much too narrow to contain
them.

The testes are thickenings of the parietal coelomic epithelium in
the anterior part of the caudal chambers of the body-cavity. Cells
break off from them and fall into the body-cavity, where they develop
into spermatozoa. The male generative ducts (Fig. 468) are paired
tubes opening on the side of the body in the caudal region, and
internally by a ciliated opening into the caudal region of the coelom.
The vesicula seminalis is a dilatation on the course of the short
vas deferens.

590

CHAETOGNATHA.

No separate renal organs are known.

Development. The ova are transparent structures which float on
the surface of the sea, except in Spadella cepJialoptera, which attaches
them to seaweeds. The mode of oviposition and the place of fertili-
zation is not known. The whole development takes place in the sea,
and there is no larval stage. The segmentation is complete, and leads
to the formation of a hollow blastophere, and an invaginate gastrula.
The blastopore closes at the posterior end of the embryo, and the
mouth is a new formation ft the anterior end. The archenteron
gives off two pouches from its posterior end (Fig. 471), and thus
becomes trilobed. The middle lobe acquires an opening to the exterior
at the front end, while posteriorly it opens into the part of the

archenteron which
opens into the lateral
pouches (Fig. 471).
This hind opening
becomes closed, so
that the middle lobe
forms a tube opening
in front by the mouth,
and behind ending
blindly, and thus
gives rise to the en-
teron. The anus is
formed later. The
portion of the arch-
enteron thus sepa-
rated off is the coel-
om; it consists of two

lateral sacs opening into an unpaired portion (Fig. 471) behind.
From the anterior end of the two lateral sacs a portion is cut off,
which apparently becomes the cephalic sections of the adult coelom
(Fig. 472). The further changes of the hinder part of the coelom
into the adult condition have not been followed.

One of the most remarkable features of the development of Sagitta
is the early appearance of the generative cells, if indeed they be such.
These appear in the gastrula stage as a prominence of six cells
projecting from the hypoblast at the anterior end of the archenteron.
This mass, on the folding of the archenteric wall, is placed at the
hind end of the median lobe (Fig. 471), and when the division of the
archenteron takes place it remains in the coelomic portion (Fig. 472),

FIG. 472.— A, dorsal ; B, lateral views of an advanced embryo
of Sagitta (from Balfour, after Biitschli). m mouth; al
alimentary canal ; vg ventral ganglion ; ep ectoderm ; cpv
cephalic section of the body- cavity; so somatic; sp
splanchnic layer of mesoderm ; gc generative organs.

CHAETOGNATHA. 591

and divides into an anterior and posterior part on each side. The
former is said to constitute the ovary, and the latter the testis.

As stated above the Cliaetognatlia are essentially pelagic organisms.
They swim by flexion of the body, and have been taken at
considerable depths (600 fathoms). One species is littoral (Spadella
cephalopterd).

The Chaetognatha^ in possessing three divisions of the coelom, resemble the
Brachiopoda, on the assumption that the Castro -> and ilioparietal bands of the
latter group are the remains of transverse coelomic septa (p. 580). In the
same feature they also resemble Balanoglossus. The resemblance to the latter
is, however, diminished by the fact that the division of the coelom into three
chambers is not an original one, but occurs subsequently to the separation from
the archenteron. There is this further difference, viz., in Balanoglossus it is the
anterior portion of the embryonic coelom which is unpaired and median, while
in Chaetognatha it is the posterior part. With regard to the latter point it is
possible that further investigations of the embryos of the Chaetognatha with
modern methods may disclose some errors in the old accounts, and with regard
to the first, it must not be forgotten that even in the same group the coelomic
sacs may differ as to when they divide up transversely; e.g., in the Echiiw-
dermata — in which group it is probable that the typical arrangement of coelomic
sacs is one unpaired and two paired — the sacs may in some forms arise separately
from the archenteron, and in others arise by the division of one archenteric
diverticulum on each side.

Three genera of Chaetognatha are known.

Sagitta Slabber, with two pairs of lateral fins.

Krohnia Langerhans, with one lateral fin on each side extending on to the
caudal region.

Spadella Langerhans, with one pair of lateral fins on the tail, and a thicken-
ing of epidermis on each side of the body from the head to the fin.

END OF VOL. I.

INDKX.

Abyla, 149.
Acaharia, 182
Acalepbae. 156.
Acanella, 182.
Acantliaria, 23.
Acanthascus. 92.
Acantbastraea, 196.
Acanthella, 96, 133.
Acantliiri. 21.
Acanthobdella, 449, 512,

513, .117, 527.
Acantliobotlmum, 245,

259.

Acanthocepliala, 293.
Acanthochiton, 392.
Acanthocladium 133.
Acanthocotyle, 234.
Acantbocystis, 18 19.
Acauthodoris, 412.
Acanthodrilos 450, 500,

501, 503, 511.
Acanthogorgia, 182.
Acanthoisis, 182.
Acan thorn etra 21, 23.
Acanthonida, 23.
Acanthopora 196.
Acanthoptilum, 181.
Acarnus, 96.
Acaulis, 130.
Acephala. 320.
Acephalocyst. 261.
Acera, 405, 406.
Acerominyas, 187.
Aceros, 223.
Achaeta. 509.
Acharadria, 130.
Achatina, 380.
Acholoe, 478.
Acicula, 396. 398.
Aciculiriae, 97.
Acicidites, 94.
Aciculum, 460.
Acineta. 53.
Acinetaria, 26, 51.
Acis, 183.

Acmaea, 394.
Acmostomum, 220.
Acoela, 211, 218.
Acoeta, 478.
Acontia, 105.
Acotylea, 222.
Acrasis, 18.
Acraspeda. 156.
Acraspedote, 109.
Acrohelia. 195.
Acrophalli, 278.
Acrorhynchus, 220.
Actaeon, 361, 364, 372,

385, 404, 405, 406.
Actaeoni'i, 414.
Actinauge, 187.
Actine, 82.
Actinelida, 23.
Actineria, 188.
Actinerus. 187.
Actinia, 187.
Actiniaria, 183.
Actinidae. 188.
Actininae, 187.
Actinioides, 187.
Actinobolus. 45.
Actinocephalus, 59.
Actinodendron 188.
Actinogonium 130.
Actinoloba, 187.
Actinoloplius, 19.
Actinomonas, 30.
Actinophrys, 19.
Actinopsis, 188.
Actinosphaerium, 19.
Acystosporidia, 62.
Actinostola, 187.
Actinothrix, 187.
Actinotricha. 49.
Aotinotrocha, 545.
Actinozoa, 168.
Actimmis 308.
Acyclus, 307.
Adanisia, 187.
Addisonia, 394.

2 Q

Adelea, 61.
Adelocodonic, 126.
Adelocodonic gonopbore,

120.

Adeona, 566.
Adeonella, 566.
Adeorbis. 398.
Adineta, 308.
Adinida, 34.
Adoral row, 40.
Adradial, 118.
Aegina, 136.
Aeginella, 136.
Aetea, 564.
Aegineta, 136.
Aeginodiscus, 136.
Aeginodorus, 136.
Aeginopsis, 109.
Aeginorhodus, 136.
Aeginura, 136
Aegir, 188.
Aegirus, 369, 412.
Aegyria, 46.
Aeolidioidea, 412.
Aeolis, 412.
Aeolosonia, 455.
Aequorea, 134.
Aequoridae, 134.
Aethalium, 16.
Aetheria, 347.
Agalma, 153.
Agalmopsis, 153.
Agaricia, 196.
Agelas, 96.
Aglaisma, 149.
Aglantba, 135.
Aglaophenia, 133.
Aglaura, 135.
Aglauropsis, 135.
Agliscra, 135.
Aiptasia, 187.
Air-funnel, 150.
Al = alimentary.
Alaurina, 219.
Albertia, 309.

594

INDEX.

Albumen glands of Oli-
gochaeta, 505.

Alcinoe, 208.

Aloiopa, 479.

Alciopina, 479.

Alcyonacea, 178.

Alcyonaria, 175.

Alcyonella, 568.

Alcyonidium, 556, 567.

Alcyonium, 179.

Alderia, 385, 413.

Alecto, 566.

Alectona, 97.

Alexia, 415.

Algol, 94.

Alicia, 187.

Alitta, 479.

Allantonema, 277, 290.

Allmaniella, 478.

Alloiocela, 220.

Allolobophora, 503, 512.

Allomorphina, 13.

Allopora, 129.

Alloposus, 420, 446.

Allostomura, 220.

Alluroides, 508.

Alhirus, 512.

Alma, 511.

Alophota, 156.

Alternation of genera-
tions, 121.

Alvania, 511.

Alveopora, 197.

Alwisia, 17.

Amalthaea, 130, 131.

Amathia, 567.

Amaurochaete, 17.

Amber-snail, 416.

Ammocharidae, 484.

Ammodiscus, 13.

Ammoconidae, 98.

Ammonactis, 188.

Ammonites, 417, 444.

Ammothea, 179.

Ammotrypane, 487.

Amoeba, 11.

Amoeboidea, 11.

Amoebosporidia, 69.

Amoebosporidium, 63.

Amoebulae, 17.

Ampharete, 486.

Amphianthus, 187.

Amphibdella, 236.

Amphibleptula, 95.

Amphiblestrum, 565.

Ampbibola, 361, 375,
414, 415.

AmpMchaeta, 509.

Amphichoerus, 219.

Amphicodon, 131.

Amphicora, 491.

Amphicorinidae, 490.
Ampbicoryne, 14.
Amphicteis, 486.
Amphictene, 486.
Ampliidisc, 92.
Ampliidiscophora, 92.
Amphiglena, 466.
Amphihelia, 195.
Amphil aphis, 182.
Amphilectus, 96.
Amphileptus, 45, 46.
Amphiliua, 255, 256.
Amphinema, 131.
Amphilonche, 23.
Amphimonadina, 31.
Ampbineura, 352.
Amphinoma, 480.
Amphipeplea, 415.
Amphiporns, 271.
Amphiporus splendens,

268.

Amplnptyches, 255, 256.
Amphiroa, 149.
Amphisia, 49.
Amphisolenia, 35.
Amphisphyra, 406.
Amphistegina, 15.
Amphistomum, 225, 238.
Amphitretus, 446.
Amphitrite, 485.
Amphitrocha, 475.
Ampliius, 97.
Amphi/oneila, 11.
Amphoriscus, 90.
Ampullaria, 374, 37S,

380, 395, 396, 399.
Anabacia, 196.
Anachaeta, 495, 509.
Anacropora, 197.
Anaitis, 479.
Anal cirri, 49.
Anamixilla, 90.
Anarthropora, 566.
Anatina, 349.
Anatmacea, 340, 342,

349.

Anatmacea, 328.
Ancillaria, 386, 397.
Ancistrum, 47.
Ancorina. 94.
Ancula, 410, 412.
Ancylus, 375, 416.
Ancyracantlms, 289.
Ancyromonas, 30.
Andvakiadae. 188.
Anemonia, 187.
Angela, 156.
Anguillula, 281, 291.
Anguillnlidae, 282.
Anguinella, 567.
Anisoceras, 480.

Anisonemina, 31.

Anisopleura, 392.

Annadrilus, 511.
! Annelida, 447.
j Anocelis, 221.

Anodonta, 329, 342, 343,
347.

Anomalina, 14.

Anomia, 321, 330, 331,
336, 345.

Anomiacea, 345.

Anomiidae, 328, 341.

Anomocladidae, 95.

Anonymus,211, 217, 223.

Anoplia, 95.
• Anoplocephala, 261.
! Anoplodium, 220.
| Anoplosyllis, 476.

Anoplophrya, 47.

Antenna Rotifera, 300.

Antennularia, 133.

Anteus, 511.

Anthastra, 94.

Anthelia, 178.

Anthemiphyllia, 194.

Anthemodes, 153.

Antheomorphe, 187.

Anthobothrium, 259.

Anthocotyle, 235.

Anthogorgia, 182.

Antholoba, 187.

Anthomastus, 179.

Anthomedusae, 130.

Anthophysa, 30, 153.

Anthopleura, 187.

Anthopodium, 178.

Anthoptilum, 181.

Aiithothela, 182.

Anthozoa, 168.

Antipatliaria, 190.

Antipathella, 190.

Antipatbes, 190.

Antispadix of Nautilus,
422.

Aperture of shell, 361.

Apex of shell, 325, 361.

Aphanipathes, 190.

Aphanostomuin, 219.

Aphodus, 78.

Aphrocallistes, 93.

Aphrodite, 459, 465, 478.

Aphrothoraca, 19.

Apiosoma, 63.

Aplacopliora, 352.

Aplustrum, 406.

Aplysia, 362, 371, 385,
404, 407.

Aplysiella, 407.

Aplysilla, 93.

Aplysina, 98.

Aplysinopsis, 98.

INDEX.

595

Aplysioidea, 407.
Apodina, 311.

Aspergillum, 327, 349.
Aspidisca, 49.

Apolemia, 152.
Apolemopsis, 152.

Aspidobranchiata, 393.
Aspidocephalus, 284.

Apomatus, 491.

Aspidocotyle, 238.

Apopyle, 77.

Aspidocotylea, 236.

Aporosa, 193, 194.

Aspidogaster, 232, 237.

Aporrhais, 400.

Aspidosiphon, 539.

Apple-snail, 399.

Aspidostoma, 566.

Apsilus. 300, 307.

Aspirotricha, 46.

Aptychus, 444. Asplanchna, 303, 309.

Aquiferous canals, 321 ; Assiminea, 398.

pore, 357. Astacobdella, 509.

Arabella, 481.

Astartidae, 328, 347.

Arachnactis, 100, 190.

Aster ope, 479.

Area. 331, 333, 334, 336,

Asteropus, 97.

345.

Asterosmilia, 195.

Arcacea, 345.

Astraeopora, 197.

Araclmidium, 567.

Astrangia, 195.

Arcella, 11, 12.

Astrella, 94.

Archaediscus, 15.

Astasia, 31.

Archaeobdella, 526.

Astasiopsis, 31.

Archespore, 60.

Aster, 85.

Archiannelida, 451.

Astrocoenia, 196.

Archigetes, 244, 256.

Astroides, 197.

Archirhiza, 167.

Astrolonche, 23.

Areliiteutliis, 417, 445.

Astrolophus, 23.

Arcidae, 328, 341.

Astropeplus, 95.

Arcyria, 17.

Astrophora, 94.

Area, 325.

Astrorliiza, 13.

Arenicola, 459, 461, 463,

Astylozoon, 51.

465, 488. Astylus, 129.

Aretlmsa, 156. Asymmetry of Gastro-

Argiope, 576, 581, 585. poda, 383, 385.

Argonauta, 420, 437, Athoracophorus, 416.

440, 441, 446. Athoralia, 152.

Arhynchus, 296, 297.

Athoria, 152.

Aricia, 463, 467, 482.

Athorybia, 153.

Aricidea, 482.

Atlanta, 401, 402.

Avion, 379, 416.

Atoll, 173.

Arippasa, 491.

Atolla, 167.

Aristenia, 480.

Atopos, 416.

Armandia, 487. Atractylis, 130.

Armed calamary, 445. Atretia, 585

Armenista, 144.

Atrium genitale, 215 ; of

Arnula, 52, 53.

Oligochaeta, 505.

Artamaceae, 486.

Atrocha, 474.

Artemisina, 96.

Attractonema, 282, 291.

Articulata, 566.

Atys, 406.

Artiscus, 23. > Auditory organs, Medu-

Ascaris, 276, 277, 283. sae, 115.

Ascoglena, 31.

Audouinia, 485.

Ascoglossa, 413.

Auger-shell, 397.

Ascon, 75.

Aulacantha, 24.

Asconema, 92.

Aulactinia, 187.

Asconidac, 89,

Aulactinium, 24.

Asexual reproduction, 71,

Aulascus, 92

218, 221 ; medusae,

Aulastoma, 516, 527.

118;coelenterata, 120;

Aulena. 97.

polychaeta, 468 ; oligo-

Aulocalyx, 92.

chaeta, 507.

Aulochone, 92.

Aulocystis, 93.
Aulorchis, 188.
Auralia, 154.
Atirelia, 109, 167.
Aureliana, 186. J
Auricle of Ctenophora,

202.

Auricula, 414, 415.
Auronectae, 153.
Aurophore, 153.
Aurophysa, 155.
Aurora, 94.
Aurosa, 167.
Autolytus, 467, 470,

476.

Automolos, 220.
Autozooids, 177.
Avenella, 567.
Avic. = avicularia.
Avicula, 331, 336, 341,

346.

Avicularia, 553.
Axifera, 182.
Axine, 236.
Axinella, 96.
Axinus, 347.
Axiothea, 488.
Axoniderma, 96.
Azorica, 95.
Azygobranchiate, 395.
Azygoplon, 133.

Babesia, 63.
Bacillus, 86.
Badhamia, 17.
Bajulus, 93.
Ba'lanites, 92.
Balanophyllia, 196.
Balantidiopsis, 48.
Balantidium, 48.
Balea, 416.
Balladiua, 49.
Barathrobius, 179.
Barrier reef, 172.
Barroussia, 61.
Baryhelia, 195.
Basal plate, coral, 192.
Basommatophora, 415.
Bassia. 149
Bathelia, 195.
Bath sponge, 98.
Bathyactis, 196.
Bathyanthus, 190.
Bathybius, 11.
Bathycodon, 131.
Bathydorus, 92.
Bathygorgia, 182.
Bathypathes, 191.
Bathyphysa, 153.
Bathy})tilum, 181.
Batrachobdella, 526.

596

INDEX.

Bdellodrilus, 509.

Bdelloida, 308.

Bdelloidea, 300.

Bdellura. 221.

Beania. 565

Bebryce, 183.

Bela, 397.

Belemnites, 417, 445.

Beloidea, 23.

Belonaspis, 23.

Belonozoum, 23.

Bellonella, 179.

Beiihamia, 497, 511.

Berenice, 134.

Beroe. 208.

Bicellaria, 565.

Bicosoeca, 30.

Biemma, 96.

Bifaxaria, 565.

Biflustra, 565.

Bikoecina, 30.

Bilharzia, 240.

Bilimba, 511.

Biloculina, 13.

Biloculine, 9.

Bimeria, 130.

Bipectinate, 394.

Bipennate (bipectinate)
ctenidimn, 373, 374.

Bispira, 490.

Bistylia, 194.

Bithynella, 398.

Bithynia, 380, 381 , 398.

Bladder- worm, 252.

Blastopore of Gastro-
poda, 380.

Blastopore is the mouth
of the Gastrula.

Blastostyle, 1'26.

Blepharisma, 48.

Blood-gland of Gastro-
poda, 373.

Boat-shell, 397.

Bodo, 28, 29.

Bodonina, 31.

Bodoninae, 29.

Bohemilla, 509.

Bojanus, organ of, 321,
341.

Bolina, 207.

Bolinopsis, 207.

Bolivina, 13.

Bolocera, 187.

Bonellia, 530, 533.

Bonnet limpet, 398.

Boring Mussels, 348.

Borlasia, 272.

Borlasia splendida, 268.

Botellina, 13.

Bothridinm, 256.

Bothrimonus, 258.

Bothrioeephalus, 245,
250, 256.

Bothrionenron, 508.

Bothrioplana, 220.

Bothriopsis, 59.

Bothromesostoinurn,219.

Botryoidal tissue, 519.

Botryoidea, 23.

Bougainvillea, 109, 130.

Bowerbankia, 567.
j Brachiolophus, 168.
J Brachionas, 301, 310.
i Brachiopoda, 573.

Brachydrilus, 500, 503,
506, 511.

Brachytrochus, 194.

Bract, 139.

Brada, 489.

Bradynema, 281, 290.

Branchellion, 526, 513,
521.

Branchial heart, 436.

Branchiobdella, 509.

Branchionima, 464, 490.

Branchiura, 495, 498,
508.

Brefeldia, 17.

Brettia, 564.

Briareuni, 182.

Broderipia, 395.

Bryodrilus, 509.

Bryo/oa, 549.

Bubble-shell, 406.

Buccal ganglia, 319 ;
mass, 369.

Buccinum, 358, 386, 396.

Buchholzia, 509.

Bugula, 565.

Bulimina, 13.

Bulimus, 380, 416.

Bui la, 405, 406.

Bui Ha, 361. 396.

Bulloidea, 405.

Bunodeopsis, 187.

Bunodes, 187.

Bursaria. 48.

Buskia, 567.

Buskiella, 489.

Butschlia, 46.

Bylgia, 478.

Byrsophlebs, 220.

Byssus, 330.

Caberea, 565.
Cacochalyna, 96.
Caecilianella, 416.
Caenomorpha. 49.
Calamary, 445.
Calamphora, 132.
Calcabrina, 95.
Calcar, 300.

Calcarea, 89.
Calcareous glands, 497.
Calcarina, 14.
Caleschara, 565.
Calices, 195.
Calicotyle, 234.
Caligorgia, 182.
Callianira. 207.
Callidina, 304. 308.
Callidrilus, 511.
Calliobdella, 513, 526.
Calliobothriura, 244 259.
Callipelta, 94.
Callipodium, 178.
Callisis, 182.
Callistephanus, 183.
Calliteuthis, 445.
Callitiara, 131.
Callizona, 479.
Callochiton, 392.
Callozostron, 182.
Calpe, 149.
Calthropella, 94.
Calthrops, 84.
Calycella, 132.
Calyclo, 128.

,, (theca), in:!.
Calyconectae, 144.
Calycophoridae, 144.
Calyniina, 21, 208.
Calymmophora, 565.
Calypterinus, 182.
Calyptoblastca, 126,132,

132.

Calyptotricha, 47.
Calyptraea, 398.
Calyptrophora, 182.
Calyx, 96.
Caminus, 94.
Cam pan aria, 134.
Campaniclava, 129.
Campanopsis, 132.
Campaiiularia, 132, 134.
Campanulina, 132, 134.
Canal .system of Aeras-

poda. 112 ; of Craspe-

dota, 112.
Canalis gynaeoophorus,

240.

Cancellaria, 397.
Canda, 565.
Candeina, 14.
Caneplioridae, 486.
Canidia, 386, 396.
Cannophysa, 155.
Caimopilus, 35.
Cannorhiza, 168.
Cannostomae, 167.
Cannota, 134.
Caobangia, 462, 491.
Capillitium, 16.

INDEX.

597

Capitella, 461, 486.
Capitelliforrnia, 486.
Capitomastus, 486.
'Capnea, 186.
Capsulogenous glands,

505.

Captacula, 350.
Capulus, 398.
Caravella, 156.
Carbasea, 565.
Carchesium, 41, 51.
Cardiaeea, 348.
Cardinal teeth, 325.
Cardita, 347.
Cardium, 328, 330, 341,

345, 348.
Carpenteria, 14.
Carposphaera, 23.
Garinaria, 401, 402.
Carinella, 270.
Carinoma, 270.
Carmarina, 109, 111,

136.

Carmaris, 136.
Carnosa, 95.
Cartilage of cephalopoda,

427.

Caruncle, 480.
Carychimn, 415.
Caryophyllaeus, 245, 247,

256.

Caryophyllia, 194.
Cassidaria, 393, 400.
Cassiopea, 167.
Cassis, 400.
Castrada, 219.
Catablema, 131.
Cataulus, 398.
Catenaria, 565.
Catenicella, 565.
Gathammata, 112.
Cathypna, 310.
Caulocalyx, 92.
Caulophacus, 92.
Cavernularia, 181.
Cavolinia, 406.
Cellaria, 554, 565.
Cellepora, 566.
Celleporella, 566.
Cell of polyzoa, 549.
Cellularia, "565.
Cellularina. 564.
Cemoria, 395.
Cenodiscus, 23.
Centradenia, 141.
Central capsule, 20.
Cephalopoda, 417.
Cephalosiphon, 308.
Cephalothrix, 270.
Cephea, 167.
Cerata, 362.

Ceratina, 97.
Ceratites, 444.
Ceratoisis, 182.
Ceratosa, 98.
Ceratotrochus, 194.
Cercaria, 229 ; echinata,

231 ; macrocerca, 231 :

minuta, 231.
Cercyra, 221.
Cereactis, 187.
Cerebratulus, 272.
Cephalotharnnium, 30.
Cerastestina, 15.
Ceratiomyxa, 17.
Ceratium, 34.
Ceratocorys, 34.
Ceratomyxa, 67.
Cercomonas, 29, 30.
Ceres, 395.
Cereus, 187.
Ceriantheae, 190.
Cerianthus, 104, 106,

190.
Cerithidea, 357, 374,

399.

Cerithium, 386, 399.
Cestoda, 243.
Cestodariidae, 256.
Cestoplana, 222.
Cestus, 208.
Chaenia, 45.
Chaetobranchus, 495,

509.

Chaetoderma, 355.
Chaetogaster, 450, 507,

509.

Chaetognatha, 586.
Ohaetonotus, 311.
Chaetopoda, 458.
Chaetoproteus, 11.
Chaetopterus, 472, 475.
Chaetosoma, 292, 484.
Chaetozone, 485.
Chaetura, 311.
Chalarothoraca, 19.
Chalina, 96.
Chalinopsilla, 97.
Chalinorrhaphis, 96.
Chalk, 10
Chama, 348.
Characella, 94.
Charistephane, 207.
Charybdea, 166.
Chary bdea eye, 117.
Chasmatostoma, 47.
Chaunoteuthis, 445.
Cheilostomata, 564.
Cheiracanthus, 275.
Chela, 85.
Chenopus, 400.
Chiastolus, 23.

Chilian snail, 416.
Chilifera, 47.
Chiliua, 416.
Chilodon, 46.
Chilonionas. 31.
Chilostomella, 13y
Chirodrilus, 509.
Chirodropus, 166.
Chironephthya, 179.
Chiropsalmus. 166.
Chiroteuthis, 445.
Chitinopoma, 491.
Chiton, 380, 392.
Chitonactis, 187.
Chiton an thus, 187.
Chitonellus, 387, 392.
Chlamydoconcha, 347.
Chlamydodon, 46.
Chlamydodonta, 38.
Chlamydomonadina, 29
Chlamydomonas, 29, 32.
Chlamydoniyxa, 17.
Chlamydophora, 19.
Chlidonia, 565.
Chloeia, 480.
Chloragogen cells, 498.
Chlorangiuni, 32.
Chlorhaema, 489.
Chlorocruorin, 465.
Chlorogonium, 32.
Chloroinyxum, 68.
Chloropeltina, 31.
Chlorophyll, 28.
Chlorosis, 285.
Choanocytes, 74.
Choanoflagellata, 32.
Choanosome, 78.
Chondractinia, 187.
Chondrenchynie, 79.
Chondrilla, 95.
Chondrioderma, 17.
Chondrocladia, 96.
Chondrosia, 95.
Chone, 491.
Chonelasma, 93.
Chord, 83.
Choristes, 398.
Choristida, 93.
Ghorizopora, 566.
Chromadora, 291.
Chromatophores, 28.
Chromatophores of Ceph-

alopods, 426.
Chroniodoris, 412.
Chromulina, 31.
Chrotella, 94.
Chrysaora, 117, 167.
Chrysodonius, 396.
Chrysogorgia, 182.
Chrysoniitra, 143.
Chrysomonadina, 32.

598

INDEX.

Chrysopetalum, 478.
Chrysopyxis, 32.
Chyluria, 289.
Cienkowskia, 17.
Ciliata, 26, 37.
Cilioflagellata, 33.
Ciliophrys, 29, 30.
Cinachyra, 94.
Cinclides, 104.
Cinetochilum, 47.
Ciocalypta, 96.
Cionistes, 130.
Circalia, 152.
Circeis, 491.
Cirratulus, 485.
Cirrhoteuthis. See Cirro-

teuthis.
Cirri, 461.
Cirripathes, 190.
Cirroteuthis, 420, 434,

438, 440, 446.
Cirrus, 39, 225.
Cistella, 576. 581, 585.
Cladiscus, 181.
Cladocanna, 134.
Cladocarpus, 133.
Cladocora, 195
Oladocoryne, 130.
Cladome, 83.
Cladomonas, 31.
Cladonema, 130, 131.
Cladopathes, 191.
Cladopcltidae, 94.
Cladorhiza, 96.
Cladus, 83.
Clam, 347.
Claparedilla, 508.
Olastoderma, 17.
Clathraria, 182.
Clathria, 96.
Clathrosphaera, 23.
Clathrtilina, 18, 19.
Clausilia, 380, 415, 416.
Clava, 129.
Clavagella, 344, 349.
Clavatella, 130, 131;

prolifera, 109.
Clavatula. 397.
Clavella, 181.
Clavula, 92, 129.
Clavularia, 178.
Clavulina, 13.
Clavulinae, 97.
Clematissa, 182.
Clepsidrina, 59.
Clepsine, 513, 519, 523,

524, 526.

Climacostonium, 48.
Clio, 372, 406.
Cliona, 97.
Clione, 367, 408.

Clionidae, 72.

Clionopsis, 374, 408.

Clitellio, 508.

Clitellum, 494, 506 ; of
Hirudinea, 514.

Cloeosiplion, 539.

Clymene, 488.

Clytia, 132, 134.

Cnidaria, 123.

Cnidoblast, 101.

Cnidocil, 101.

Cnidosac, 140, 146.

Cnidosphtre, 143.

Coccidiidea, 59.

Coccidium, 61.

Coccodiscns, 23.

Coccoliths, 11.

Coccomonas, 32.

Coccospheres, 11.

Cocculina, 395.

Cochleare, 310.

Cochliopodium, 12.

Cockles, 348.

Cocoon of earthworms,
506 ; Hirudinea, 524.

Codonella, 49.

Codonidae, 130.

Codouium, 131.

Codonoeca, 30.

Codonocladium, 33.

Codonorchis, 131.

Codosiga, 33.

Coecum, 360, 399.

Coelenteron, 100.

Coelogorgia, 178.

Coelom, 313 ; of Gastro-
poda, 375.

Coeloniata, 313.

Coelomonas, 31.

Coeloplana, 208.

Coelopus, 309.

Coeloria, 195.

Coenenchyma of corals,
192, 193.

Coenenchyme, 168, 169.

Coenocyathus, 194.

Coenosark, 125 ; corals,
193.

Coenosome, 139.

Coenosteum, 128.

Coenurus, 251, 252.

Colacium, 31.

Colangia. 195.

Coleps, 46.

Colic in horse, 285.

Collar, 32.

Collaspis, 167.

Collenchyme, 79.

Collinella, 94.

Collodictyon, 31.

Colloidea, 22.

Collosphaera, 23.

Collozoum, 23.

Colpidium, 44, 47.

Colpoda, 47.

Colponema, 31.

Colpophyllia, 195.

Columbella, 396.

Columella, 193, 361.

Columellar muscle, 319,
362.

Columnitis, 97.

Colurus, 310.

Comatricha, 17.

Comesoma, 291.

Conatheca, 425.

Concholepas, 361.

Conchologists, 398.

Conchophthirus, 48.

Conchula, 184.

Conchyolin, 326.

Condylactis, 187.

Condylostoma, 48.

Cone-shell, 397.

Conis, 131.

Conjugation, 2.

Conoceros, 222.

Conochilus, 308.

Conocyathus, 194.

Conopora, 129.

Conorbis, 397.

Conorhynchus, 59.

Conns, 361, 362, 397.

Convoluta, 211, 219.

Copeus, 309.

Coppatias, 97.

Coppinia, 132.

Copromyxa, 18.

Copulation of Cestoda,
249 ; of earthworms,
506 ; of Gastropoda,
380 ; of Trematoda,
226; of Turbellaria,
217.

Coral island, 173.

Coral-reefs, 171.

Corallimorphus, 186.

Coralliopbila, 396.

Corallistes, 94.

Coral lite (theca), 195.

Corallium, 182.

Corallum, 191.

Corals, 183.

Corambe, 371, 412.

Corbicula, 347.

Corbis, 347.

Corbula, 127, 348.

Cordylophora, 129.

Cormidium, 140.

Cornularia, 175, 178.

Cornulariella, 178.

Cornuvia, 17.

INDEX.

599

Corona, 299.
Coronidium, 23.
Cortex, 76, 78.
Corticella, 95.
Corticinm, 95.
Cortina, 23.
Corydendrium, 129.
Corymorpha, 130.
Corynactis, 186.
Coryne, 130.
Corynetes, 131.
Corynopsis, 130.
Coscinaraea, 196.
Coscinodernia, 98.
Coscinoporidae, 93.
Costa, 126.
Costae, 194.
Cothurnia, 38, 51.
Cotylea, 223.
Cotylogaster, 237.
Cotylorhiza, 168.
Cowries, 400.
Crambactis, 187.
Crambessa, 168.
Cranchia, 445.
Crania, 574, 575, 578,

585

Craniella, 94.
Craspedella, 234.
Craspedopoma, 398.
Craspedomonadina, 33.
Craspedota 123.
Craspedote, 109.
Crassatellidae, 328, 347.
Craterium, 17.
Crateroloplms, 164.
Crateromorpha. 92.
Cremnoconchus,386,398.
Crepidula, 398.
Crepis, 84.
Creseis, 406.
Cribraria, 17.
Cribrilina, 565.
Criodrilus, 498, 506, 511.
Crisia, 550, 563, 566.
Cristatella, 556, 561,

568.

Cristellaria, 14.
Cromyosphaera, 23.
Crossostoma, 168.
Crucigera, 491.
Cryptabacia, 196.
Cryptocelis, 222.
Cryptocephala, 490.
Cryptochiton, 360, 362,

387, 392.

Cryptodendrum, 187.
Cryptodrilus, 506, 510.
Cryptoglena, 31.
Cryptohelia, 129.
Cryptolaria, 133.

Cryptomouas, 31.
Cryptoplax, 387, 392.
Crystalline style, 335.
Crystallades, 153.
Crystallophanes, 178.
Ctenaria, 131.
Ctenidium, 321.
Ctenidium bipennate

(bipectinate), 373, 374;

monopectinate, 374.
Ctenobranchia, 395.
Ctenodrilus, 456.
Ctenophora, 197.
Ctenophore, 120.
Ctenoplana, 208.
Ctenopteryx, 445.
Ctenostomata, 566.
Ctenotaenia, 262.
Cubogaster, 131.
Cuboides, 149.
Cubomedusae, 166.
Cucubalus, 149.
Cncullanus, 235, 280.
Cucullus, 149.
Cunantha, 136.
Cunarcha, 136.
Cuneolaria, 153.
Cuneolina, 13.
Cunina, 136.
Cunissa, 136.
Cunoctantha, 136.
Cnp and saucer limpet,

398.

Cupularia, 566.
Cupulita, 153.
Cuspidaria, 349.
Cuspidella, 132.
Cuttle-bone, 417, 425.
Cuttle-fish, 445.
Cuvierina, 406.
Cyanea, 167.
Cyathohelia, 195.
Cyathomonas, 31.
Cyathophyllidae, 175.
Cyathopodium, 178.
Cyathoseris, 196.
Cyclammina, 13.
Cyclas, 341, 342, 343,

347.

Cyclochaeta, 50.
Cycloclypeus, 15.
Cyclodinina, 46.
Cyclonassa, 396.
Cyclophorus, 363, 396,

398.

Cycloporus, 213, 223.
Cycloseris, 196.
Cyclospora, 61.
Cyclostoma, 357, 361,

398
Cyclostomata, 566.

Cyclostrema, 395.
Cyclosurus, 398.
Cyclotus, 398.
Cydippe, 207.
Cydippidae, 207.
Cydonium, 94. >
Cyerce, 413.
Cylichna, 406.
Cylicia, 195.
Cylindroecium, 567.
Cylindrostoinuni, 220.
Cylista, 187.
Cymba, 149, 361, 380,

397.

Cymbactis, 187.
Cymbalopora, 14.
Cymbiuin, 397.
Cymbonectes, 149.
Cymbulia, 406.
Cymbuliopsis, 371, 406.
Cyntlmlina, 18.
Cyphinus, 23.
Cyphonautes, 557.
Cypraea, 357, 360, 361,

363, 400.
Cyprina, 347.
Cyrenidae, 347.
Cyrtauloii, 93.
Cyrtoidea, 23.
Cyrtomorpha, 219.
Cystalia, 155.
Cystenchyme, 79.
Cysteodictyina, 15.
Cystiactis, 187.
Cysticercoid, 254.
Cysticercus, 252; tenui-

collis, 253 ; longicollis,

253 ; fasciolaris, 254.
Cystic -worm, 252.
Cystoflagellata, 35.
Cyston, 151.
Cystonectae, 154.
Cystonula, 155.
Cystotaenia, 260.
Cytaeandra, 131.
Cytaeis, 131.
Cytamoeba, 63.
Cytherea, 348.

Dactylocalyx, 93.
Dactylogyrus, 236.
Dactylometra, 167.
Dactylominyas, 187.
Dactylosoma, 63.
Dactylosphaera, 11.
Dactylozooid, 122, 126,

128.

Daedalopelta, 94.
Dalhousia, 477.
Dallasia, 47.
Dallingeria, 31.

600

INDEX.

Damiria, 96.
Danilewskya, 62.
Danymene, 480.
Dart-sac, 379.
Danvinella, 93.
Dasmosmilia, 195.
Dasybranchus, 486.
Dasychone, 464, 491.
Dasydytes, 311.
Dasygorgia, 182.
Dasylepis, 478.
Dasyphyllia, 195.
Dasytricha, 47.
Daudebardia. 416.
Dead men's fingers, 179.
Decapoda, 444.
Decollation, 360, 361.
Deinodrilus, 506, 511.
Deiopea, 207.
Delphinula, 395.
Deltocyatlms, 194.
Demospongiae, 93.
Dendoryx, 96.
Dendrilla, 93.
Dendrobrachia, 191.
Dendroclava, 129.
Dendrocoelum, 221.
Dendroconietes, 52, 54.
Dendrocora, 195.
Dendrogyra, 195.
Deiidromonas, 30.
Dendronema, 131.
Dendronereis, 479.
Dendronotus, 412.
Dendrophyllia, 196.
Dendropsis, 96.
Dendrosoma, 52, 54.
Dendrostoma, 539.
Dental him, 352.
Deodrilus, 510.
Depastrella, 164.
Depastrum, 164.
Dercitns, 94.
Dermal ia, 91.
Dermal membrane, 76.
Dermal pore, 76.
Dermatobranchus, 374,

412.

Dero, 509.
Derostomum, 220.
Desma, 84.
Desmacella, 96.
Desmacidon, 96.
Desmacidonidae, 96.
Desmalia, 149.
Desmogaster, 510.
Desmoscolex, 292.
Desmonema, 167.
Desmophyes, 149.
Desmophyllum, 194.
Desmopterus, 406.

Desmosoyplms, 133.
Desmothoraca, 19.
Detorsion, 385.
Deutomerite, 56.
Dexiobranchaea, 408.
Dextral shell, 360.
Diachaea, 17.
Diachaeta. 502, 506, 511.
Diachoris, 565.
Diactine, 82.
Diafungia, 196.
Dialycli^ie, 491.
Dialyneury, 365, 393.
Dianema, 17.
Diaphoropodon, 13.
Diaschiza. 309.
Diaseris. 196.
Diastopora, 566.
Diatomin, 28.
Dianlic, 378.
Diblasus, 195.
Dibranchiata, 444.
Diceras, 325,
Dichocoetiia, 196.
Dichogaster, 510.
Dichoraea, 197.
Dicodonium, 131.
Dicoryne, 130.
Dicotylns. 221.
Dicranocanna, 134.
Dictydiacthaliimi, 17.
Dictydium, 17.
Dictyocalyx, 92.
Dictyocha, 35.
Dictyocladium, 133.
Dictyocylindrus, 96.
Dictyocysta, 49.
Dictyonalia, 92.
Dictyonina 93.
Dictyostelinm, 18.
Dicyemidae, 240.
Dicymba, 152.
Didinium, 46
Didymiurn, 17.
Didymozoon, 240.
Difflugia, 11, 12.
Digaster, 510.
Digenea, 237.
Digenetic, 228.
Diglena, 309.
Dileptns, 46.
Dimorpha, 30.
Dimorphina, 14.
Dimoriihism, 7, 9.
Dimorphous, 10.
Dimyaria, 326, 330.
Dimyidae, 347.
Dinema, 131.
Dinifera, 34.
Dinobryon, 30.
Dinocharis, 309.

Dinoflagellata, 33.
Dinophilus. 456, 457.
Dinophrya, 45.
Dinophysis, 35.
Dioecious, 70.
Diopatra, 481.
Diophrys, 49.
Diotocardia, 393.
Dipetasus, 135.
Diphasia, 133.
Diphyes, 149.
Diphyllobothrium, 256.
Diphyo]»sis, 149.
Diplax, 309.
Diplectanum, 236.
Dipleurosoma, 134.
Diplobothrium, 236.
Diplocardia, 511.
Diplocheilus, 133.
Diploconus, 23.
Diplocotyle 256.
Diplocyatlms, 132.
Dij)locystis, 58.
Diplodal, 78.
Diplodinium, 49.
Diplodiscus, 2-29, 238.
Diplodonta, 347.
Diplois, 309.
Diplomita, 31.
Diplommatina, 398.
Diplonchus, 222.
Diplophysa, 149.
Diploria, 195.
Diplostomum, 238.
! Diplozoon, 226, 235.
Diplura, 130.
Diporcchaeta, 510.
Diporpa, 235.
Diporula, 566.
Di[mrena, 131.
Dipylidium, 248, 261.
Discalia, 143.
Disconalia, 143.
Discina, 578, 583, 584,

585

Discinisca. 585
Discocelis. 222.
Discocyathus, 194.
Discodermia, 94.
Discohexact, 92.
Discoidea, 23
Discomedusae, 166.
Disconanthae, 141.
Disconectae, 141.
Disconula, 141, 143.
Discophrya, 47.
Discopus, 304.
Discorbina. 14.
Discosorna, 186.
Dislocabe, 153.
Dissepiments, 193.

INDEX.

601

Dissogony, 206.

Dufouria, 59.

Dissonema, 134.

Dujardinia, 476.

Distemraa, 309.

Duncania, 194.

Distephanus, 35.

Duthiersia, 256.

Distichopora, 129.

Duva, 179.

Distichopus, 509.

Dysactis, 187.

Distomum, 238 ; agamos,

Dyscannota, 134.

227, 231 ; cirrigerum

Dysideopsis, 98.

226 ; clavigerum, 226

Dysmorphosa, 131.

cygnoides, 229, 231

Dysomorpha, 131.

cylindraceum, 226

Dysteria, 46.

ecliinatum, 231 ; hep

aticum, 229, 231

Ear-shell, 394.

laiieeolatum, 229

Earthworm, common,

macrostomum, 231

512 ; habits, 507.

ovocaudatum, 229

Ecardines, 585.

tereticolle, 229.

Ecdysis, 275.

Distyla, 310.

Echeneibothrium, 244,

Disyringa, 94.

259.

Dizoic, 60.

Echinella, 234.

Doch mius, 280, 285.

Echinobotlirium, 259.

Docoglossa, 394.

Eehinocephalus, 59.

Dodecaceraea, 485.

Echinoclathria, 96.

Dodecaceria, 485.

Echinococcifer, 261.

Dog-whelk, 396.

Echinococcus, 251, 253.

Dolabella, 407.

Echinoderes, 312.

Dolichoplana, 222.

Echinodictyuni, 96.

Doliuni, 378, 400.

Echiuopora, 196.

Doniopora, 566.

Echinorhynchus, 297.

Donax. 347.

Echinospira, 362.

Dondersia, 355.

Echiuroidea, 527.

Uoramasia, 149.

Echiurus 528, 530, 533.

Dorataspis, 23.

Ecionema, 94.

Doratopsis, 445.

Eclipidrilus, 508.

Doridioidea. 412.

Ectocyst, 549.

Doridium, 362, 405,406.

Ectoderm, 99.

Doridopsis, 371, 412.

Ectolithia, 21.

Doris, 385, 412.

Ectopleura, 130, 131.

Dorsal in cestoda, 247,

Ectoprocta, 564.

248.

Ectosome, 78.

Dorsal in polyzoa, 552 ;

Ectyoninae, 96.

nematoda, 276 ; pen-

Edwardsia, 189.

natulacea, 180; actini-

Eimeria, 60.

aria, 184.

Electra, 565.

Dorylaimus, 291.

Eledone, 440, 446.

Dorypleres, 97.
Dosinia, 348.

Elephantiasis, 289.
Eleutheria, 131.

Doto, 412.

Ellipsis, 23.

Dragma, 86.

Ellipsoidina, 13.

Dragmastra, 94.

Eloactis, 188.

Dreissena, 347.

Elysia, 413.

Drepanidiidia, 61.

Elysioidea, 413.

Drepauidinni, 62.

Elytra, 461.

Drepanomonas, 47.

Emarginula, 361, 376,

Drepanophorus, 271.

394.

Drifa. 179.

Embolocephalus, 509.

Drillia, 397.

Eminoscolex, 511.

Drilonereis, 481.

Emma, 565.

Druinella, 98.

Enchelidium, 291.

Druppula, 23.

Enchelina, 38, 40, 45.

Dubenia, 181.

Enchelys, 45.

Enchytraeus, 505, 509.
Encotyllabe, 234.
Encystment, 2.
Endocoele, 184.
Endocyst, 549.
Endoderm, 99. ^
Endoderm lamella, 112.
Endogastric, 425 ; coil,

384.

Endogeny, 55.
Endoplasm, 3.
Endopsanmiia, 197.
Endosphaera, 53.
Endosporeae, 16, 17.
Enerthenema, 17.
Enipo, 478.
Enoplidae, 282.
Enoploteuthis, 440, 445.
Enoplus, 291.
Entalophora, 566.
Enteric cavity, 99.
Enteridium. 17.
Enterostomum, 220.
Entocolax, 320, 365,371,

402.
Entoconcha, 320, 365,

371, 377, 378, 386,

402.

Entodinium, 49.
Entolithia, 21.
Entoprocta, 568.
Entovalva, 327, 341,345,

349.

Eolis = Aeolis.
Eosphora, 309.
Eozoon, 15.
Epallax, 97.
Epenthesis, 134.
Ephelota. 52, 53.
Ephesia, 476.
Ephipodonta, 347.
Ephydatia, 96.
Ephyra, 157, 161, 167.
Ephyroninae, 158, 166.
Epibdella, 234.
Epibulia, 149, 156.
Epiclintes, 49.
Epimerite, 57.
Epipodia, 318.
Epipodium, 357.
Epistome, 551 ; of Pho-

ronis, 543.
Epistome, 551.
Epistreptophyllum, 196.
Epistylis, 39, 41, 51.
Epitheca, 194.
Epithelio-muscle, 100.
Epithetosoma, 533.
Epizoanthus, 189.
Erato, 400.
Eretmia, 310.

602

INDEX.

Ereutho, 486.

Euplotes, 49.

Eriographidae, 490.

Eupolia, 272.

Eriographis, 491.

Eupolynoe, 478.

Erpocotyle, 236.

Eupoinatus, 473, 491.

Errina, 129.

Eupompe, 478.

Ersaea, 149.

Eupsammia, 196.

Ersaeid, 148.

Eur. = Europe.

Erviliina, 46.

Eurato, 491.

Erycinidae, 347.

Eurete, 93.

Erylus, 94.

Eurhamphaea, 207.

Erythropodium, 178.

Eurylepta, 223.

Eschara. 566. ' ; Euryleptidae, 210.

Escharina, 565.

Eurypltgma, 92.

Escharoides, 566.

Eurypylous, 77.

Esperella, 96.

Eurythoe, 480.

Esperiopsis, 96.

Eusamytha, 486.

Eteone, 479.

Eusmilia, 195.

Euaster, 85.

Euspongia, 98.

Euborlasia, 272.

Euspora, 59.

Eucarphus, 491.

Eustrongylus, 284.

Eucecryphalus, 23.

Eusyllis, 476.

Eucharis, 207.

Euthclepus, 485.

Eucliilota, 134.

Euthyneura, 402.

Euchlanis, 310.

Eutima, 134.

Euchlora, 207.

Eutimalphes, 134.

Euchone, 491.

Eutimeta, 134.

Eucope, 134.

Eutirniuni, 134.

Eucopium, 134.
Eucrambessa, 168.

Eutreptia, 31.
Evactis, 187.

Eucratea, 564.

Exconjugate, 43.

Eucyrtidium, 23.

Excretion in polyps, 102.

Eudendrium, 130.

Excretion pores of me-

Eudictyum, 92.

dusae, 113.

Eudorina, 32.

Exocoele, 184.

Eudoxella, 149.

Exogastric,424; coil,384.

Eudoxia, 146.

Exogeny, 55.

Eudoxid, 148.

Exogone, 467, 476.

Eudriloides. 502, 511. j Exoplasiii, 3.

Eudrilus, 506, 511.

Exosporeae, 16, 17.

Eugamy, 43.

Exumbrella, 108.

Euglena, 31.

Exuviaella, 34.

Euglenina, 28.

Eyes of Gastropoda, 367.

Euglypha, 13.

Eugorgia, 183.

Fabricia, 463, 464, 491.

Euichthydina, 311.

Fabularia, 13.

Eulalia, 479.

Falciform body, 58.

Eulamellibranchiata,

Farciminaria, 565.

347.

Farrea, 93.

Eulima, 402.

Farrella, 556, 567.

Eumenia, 489.

Fascicled, 125

Eunemertes, 271.

Fasciculipora, 566.

Eunephthya, 179. Fasciolaria, 397.

Eunice, 481. Favia, 196.

Eunicea, 183.

Favositidae, 178.

Euphrosyne, 462, 480.
Euphyllia, 195.

Fecampia, 220.
Female, 70.

Euphysa, 131.

Fenja, 188.

Eupilcma, 168.

Ferussacia, 416.

Euplectella, 92.

Fieldingia, 93.

Euplocamus, 412.

Fig-shell, 400.

Euplokamis, 207.

Filaria, 275,278,280,288.

Filibranchiata, 345.
Filigrana, 468.
Filograna, 491.
Fiona, 410, 413.
Firoloida, 402
Fission of embryonic

polyzoa, 563 ; zone of

507.
Fissurella, 360, 361, 367,

376, 380, 385, 394.
Flabelligera, 489.
Flabellina, 14.
Flabelluin, 194.
Flagellata, 27.
Flame-cell, 209.
Fletcherodrilus, 510.
Floresca, 167.
Floscula, 167.
Floscularia, 301, 307.
Floscnlaridae, 300.
Fluke, 238.
Flustra, 554, 565.
Flustramorpha, 566.
Flustrella, 559, 567.
Flustrina, 565.
Folliculina, 48.
Foot of Lamellibranch,

330; ofMolhisca, 318;.

of Nautilus, 42-2.
Foraminifera, 11.
Forcepia, 96.
Forcipate, 307.
Forskalia, 153.
Forskalioj)sis, 153.
Fossarus, 398.
Foveolaria, 565.
Frcdericella, 568.
Freshwater Gastropoda,.

386 ; Medusa, 134 ;

Streptoneura, 385.
Fridericia, 509
Fringing reef, 171.
Frondicularia, 14.
Frondipora, 566.
Frontal area, 40 ; cirri,.

49 ; organ, 218.
Frontonia, 47.
Fulcrum, 307.
Fulgur, 397.
Fuligo, 17.
Fulla, 179.
Fungia, 196.
Fungiacyathus, 194.
Fimiculina, 181.
Funiculus, 551.
Funnel of Cephalopoda,

422 ; of Ctenophore, 197.
Furcularia, 309.
Fusulina, 15.
Fusus, 397.
f.w.= fresh-water.

INDEX.

603

Gadinia, 362, 375, 414,

415.

Galatea, 347.
Galaxea, 196.
Galeolaria, 149.
Galeomina, 347.
Galeommidae, 327.
Gamete, 27.
Gamooystis, 58, 59.
Ganglion cells, 100.
Gapes, 285.
Garveia, 130.
Gasterostomum, 240.
Gastral ostia, 112.
Gastralia, 92.
Gastrana, 347.
Gastrobasal, 142.
Gastrochaena, 348.
Gastrocotyle, 236.
Gastrodiscus, 238.
Gastroparietal, 578.
Gastrophanella, 95.
Gastropoda, 356.
Gastropteron, 362, 406.
Gastrostyla, 49.
Gastrotricha, 310.
Gastrotrocha, 475.
Gastrothylax, 238.
Gastro vascular space, 99.
Gastrozooid, 128.
Gelliodes, 96.
Gellius, 96.

Gemellaria,109,131,564.
Gemellipora, 566.
Gemmaria, 130, 131, 189.
Gemmulatrochus, 194.
Gemmule, 87.
Gen. = genital.
Gena, 395.
Genethyllis, 479.
Genital setae, 506.
Geobdella, 516, 527.
Geodesmus, 222.
Geodia, 94.

Geonemertes, 270, 271.
Geoplana, 222.
Georissa, 395.
Geoscolex, 503, 511.
Gephyra, 187.
Gephyrea armata, 527,

534.

Gephyrophora, 566.
Gerard ia, 190.
Grrda, 51.
Gersemia, 179.
Gersemiopsis, 179.
Geryones, 136.
Geryonia, 136.
Giant fibres, 463, 497.
Gigantorhynchus, 297.
Gland-shields, 484.

Glandina, 416.
Glass-snail, 416.
Glaucoma, 47.
Glancus, 412.
Gleba, 371, 406.
Glenodinium, 34.
Globiceps, 131.
Globigerina, 11, 14.
Glochidium, 344.
Gloidium, 11.
Glossatella, 51.
Glossiphonia, 526.
Glossocodon, 136.
Glossoconus, 136.
Glottidia, 584, 585.
Glngea, 64, 68.
Glycera, 482.
Glyphidrilus, 511.
Gnathobdellidae, 526.
Gnathostoma, 275.
Godefroyia, 181.
Golfingia, 539.
Gonactinia, 189.
Gonad = generative

gland.

Gonadial coelom, 314.
Gonads medusae, 117.
Gonangium, 126.
Gonatus, 445.
Goniada, 482.
Goniatites, 444.
Goniastraea, 196.
Gonidial groove, 104

Alcyonaria, 177.
Goniodoma, 34.
Goniodoris, 412.
Gonium, 32.
Gono-palpon, 155.
Gonospora, 59.
Gonophore, 119, 126.
Gonosome, 126.
Gonostomum, 49.
Gonostyles, 139.
Gonotheca, 126.
Gonynema, 134.
Gonyostomum, 31.
Gordiodrilus, 510.
Gordius, 293.
Gorgonacea, 181.
Gorgonia, 183.
Gorgonellidae, 183.
Gossea, 135, 311.
Graffilla, 220.
Grammaria, 133.
Grantessa, 90.
Grantia, 90.
Grassia, 51.
Greefia, 479.
Green oyster, 346.
Gregarina, 59.
Gregarinida, 56.

Gromia, 13.
Grubea, 476.
Grubianella, 486.
Gt. Brit. = Great Britain.
Guard polyp, 126.

,, of shell, 425.,/
Guinea-worm, 289.
Guivillea, 397.
Gumminidae, 95.
Guynia, 194.
Gymnoblastea, 129.
Gymnoblastic, 126.
Gymnocoryne, 130.
Gymnodininm, 34.
Gymnoglossa, 402.
Gymnolaemata, 564.
Gymnomyxa, 3.
Gymnophrys, 11.
Gymnosarca, 178.
Gymnostomata, 45.
Gypsina, 14.
Gyrator, 214, 220.
Gyrocoryna, 48.
Gyrocorys, 48.
Gyrocotyle, 256.
Gyrodactylus, 227, 236.

Haastia, 98.

Habrodictyum, 92.

Haeckelia, 207.

Haemadipsa, 527.

Haemamoeba, 63.

Haematococcus, 32.

Haementaria, 526.

Haemerythrin of Poly-
chaeta, 465.

Haemocoele is a perivis-
ceral cavity containing
blood.

Haemocoele of Gastro-
poda, 375.

Haemocoelic body-
cavity, 317.

Haemocyanin in Gastro-
poda, 373 ; Mollusca,
321, 336.

Haemoglobin in Chaeto-
derma, 355 ; in Gastro-
poda, 373 ; Hirudinea,
518 ; Mollusca, 321,
336 ; Nemertea, 268 ;
Neomenia, 354 ; Oligo-
chaetcs, 497 ; Poly-
chaeta, 465.

Haemoglobinurea, 63.

Haemopis, 527.

Haemosporidia, 61.

Haimea, 178.

Halatractus, 130.

Halcampa, 188.

Halcampella, 188.

604

INDEX.

Halcyonellea, 567.
Halecimn, 132.
Halia, 396.
Halichondria, 96.
Halichondrina, 95.
Halicornaria, 133,
Haliclystus, 117, 164.
Halicryptus, 541.
Halicyathus, 164.
Haliomma, 23.
Haliotis, 360, 361, 362,

367, 376, 386, 394.
Haliphysema, 13.
Halipteris, 181.
Halisarca, 93
Halisceptrum, 181.
Halisiphonia, 132.
Halistemma, 153.
Halla, 480.
Halme, 98.
Halocordyle, 130.
Halodora, 479.
Halomitra, 196.
Halopsis, 134.
Halopsyclie, 408.
Halopyrajnis, 149.
Haloseris, 196.
Halosydna, 478.
Halteria, 49.
Halteridium, 63.
Hamacantha, 96.
Hamingia, 531, 533.
Hapalia, 207.
Haplobranchus, 491.
Haplodiscus, 219.
Haplophyllia, 194.
Haploj)hysae, 141.
Haplorhiza, 168.
Harniothoe, 478.
Harpa, 397.
Harp-shell, 397.
Hartea, 178.
Hastigerina, 14.
Haswellia, 566.
Haueriua, 13.
Head of Annelida, 447.
Hebella, 132.
Hectocotylised arm, 440.
Hectocotylus, 421.
Hedge-snail, 416.
Hedrioblast, 120, 126.
Hedruris, 289.
Hekaterobranclms, 485.
Helcion, 394.
Heliastraea, 196.
Helicina, 372, 395.
Heliodrilus, 511.
Heliolites, 177.
Heliopora, 179.
Heliosphaera, 23.
Heliozoa, 18.

Helix, 380, 416.
Helmet-shell, 400.
Hemicardium, 348.
Hemidasys, 311.
Hemifusus, 397.
Hemipodus, 482.
Hemistomum, 238.
Hemitubifex, 508.
Hemphillia, 416.
Henlea, 509.
Henneguya, 68.
Hernuulion, 478.
Hernfcea, 413.
Hermaphrodite, 70 ;

duct, 378.
Hermella, 492.
Hermelliformia, 491.
Hemiione, 459, 478.
Hermodice, 480.
Hero, 412.
Herophila, 182.
Herpetomonas, 30.
Herpobdella, 526.
Herpolitha, 196.
Hertwigia, 92.
Hesione, 477.
Hesperodrilus,495, 508.
Heteractis, 188.
Heterakis, 284.
Heterochaeta, 508.
Heterocheilus, 284.
Heterocoela, 90.
Heterocordyle, 130.
Heterocotylea, 233.
Heterodactyla, 187.
Heterodera Schaclitii,

290.

Heterodoris, 374, 412.
Heterogamy Trematoda, !

232.

Heteromastigoda, 31.
Heteromeyenia, 96.
Heteromita, 31.
Heteromonadina, 30.
Heteronema, 31, 98.
Heteronemertini, 272.
Heteronereis, 467.
Heteropegma, 90.
Heterophenacia, 485.
Heterophrys, 19.
Heterophymia, 94.
Heteropia, 90.
Heteroplon, 133.
Heteropoda, 397, 400.
Heteropsammia, 196.
Heterorraphidae, 96.
Heterostegina, 15.
Heterostephanns, 130.
Heterosyllid, 468.
Heteroterebella, 485.
Heteroxenia, 178.

Hexabraiichus, 412.
Hexaceratina, 93.
Hexacotyle, 236.
Hexact, 91.
Hexactinella, 93.
Hexactinellida, 90.
Hexactinia, 183.
Hexactiniae, 186.
Hexalaspis, 23.
Hexamitus, 31.
Hexarthra, 310.
Hexaster, 92.
Hexasterophora, 92.
Hexastylus, 23.
Hibernacula, 556.
Himantostonia, 168.
Hinge, 324.
Hinnites, 347.
Hippocrene, 131.
Hipponoa, 480.
Hipponyx, 398.
Hippopodius, 150.
Hippopus, 348.
Hippospongia, 98.
Hippothoa, 566.
Hijijmraria, 567.
Hircinia, 98.
Hirmidium, 33.
Hirudinea, 512.
Hirudo. 513, 516, 518,

519, 526.
Histiopsis, 445.
Histioteuthis, 420, 426,

445.

Histriobdella, 455.
Histriodrilus, 455, 457.
Holascus, 92.
Holaxonia, 182.
Holocladina, 15.
Holophrya, 45.
Holorhynchocoelomia,

271.

Holosticha, 49.
Holostomatous, 361.
Holostomidae, 232.
Holostomum, 238 ; ser-

pens, 226.
Holozoic, 2.
Homalogaster, 238.
Homalogyra, 356, 398.
Homocoela, 89.
Homorraphidae, 95.
Hood of Nautilus, 421.
Hoplitophrya, 47.
Hoplochalina, 96.
Ho})lonemertini, 266.
Hoplophora, 94.
Hormathia, 187.
Hormiphora, 207.
Hormogaster, 506, 511.
Hornera, 566.

INDEX.

605

Horseleech, 527; sponge,

Hypsiconms, 490. Isops, 94.

87, 98.

Hystrichis, 289. Isotricha, 47.

Hubrechtia, 270.

Hystrix marina, 478.

Huxleya, 564.

Janita, 491.

Hyalea, 406.

lanthella, 93. Janthina, 357, 367, 368,

Hyalinoecia, 481.

Ichthyaria, 565. 380, 393, 396. -'

Hyalocylix, 406.

Ichthydium, 311. Janua, 491.

Hyalodiscus, 11.

Ichthyobdella, 513, 526. Janus, 385, 410, 411r

Hyalonema, 92.

Ichthyonema, 289. 413.

Hyalonemertes, 271.
Hyalopomatopsis, 491.

Iciligorgia, 182. Jasmineira, 491.
Icterus-haematuria, 63. Jeffreysia, 398.

Hyalosphenia, 12.

Idalia, 412. Jelly, 99.

Hyalospora, 59.

Idia, 133. Jensenia, 220.

Hyalostylus, 92.

Idiosepius, 440,441, 445.

Jouaunetia, 348.

Hyattella, 97.

Idmonea, 566.

Hybocodon, 130, 131.

Idol-shell, 399.

Kaliapsis, 94.

Hvdatid cyst. 253.

Ilioparietal, 578.

Karyolysus, 62.

Hydatina, 305, 306, 309.

Illoricata, 308.

Karyophagus, 63.

Hydra, 127; tuba, 159.

Ilyactis, 188.

Kefersteinia, 477.

Hydractinia, 130.

Ilyanthus, 188.

Kellya, 347.

Hydrallmania, 133.

Ilyodrilus, 508.

Keroeides, 182.

Hydranth, 125.

Ilyogenia, 511.

Kerona, 49.

Hydranthea, 130.

Immediate eggs, 305.

Kerria, 511.

Hydnophora, 195.

Imogine, 222.

Key-hole limpet, 394.

Hydrida, 127.

Imperforate shell, 361.

Kinetoskias, 553, 565.

Hydrobia, 398.

Inarticulata, 566, 585.

Klossia, 61.

Hydrocaulus, 125.

Incl. = including.

Koellikeria, 240.

Hydrocena, 395.

Incudate, 307.

Kophobelemnon, 181.

Hydrocephalis, 125.

Incus, 307.

Kraussina, 585.

Hydrocladium, 126.

Inermia, 93.

Kropnia, 591.

Hydrocorallinae, 127.

Infundibulum of Cteno-

Kynotus, 511.

Hydrocyst, 138, 139.

phore, 197.

Hydroecium, 145.

Infus. = infusion.

Labial commissure, 366.

Hydroides, 491.

Infusoria, 24.

Labial palps, 335 ; of

Hydrolaridae, 130.

Inioteuthis, 445.

gastropoda, 356, 366.

Hydrophanes, 479.

Ink sac, 417, 424.

Labidurus, 284.

Hydrophore,132.

I nter canal, 76.

Labiopora, 129.

Hydrophyllium, 139.

Intermesenterial, 184.

Labium of shell, 361.

Hydrophyton, 125.

Internal budding, 7.

Labrorostratus, 471.

Hydrorhiza, 121, 125.

Internemal, 136.

Labrum of shell, 361.

Hydrosorna, 125.

Internode, 549.

Labyrinthula, 17.

Hydrotheca, 125.

Interradial, 118.

Laceration, 169.

Hydrozoa, 123.

Interseptal loculi, 194.

Lachnobolus, 17.

Hymedesmia, 97.

Intertentacular organ,

Lacinularia, 308.

Hymeniacidon, 96.

552.

Lacrymaria, 45.

Hymenolepis, 251, 261.

Intracapsular sarcode,

Lacuna, 398.

Hymenomonas, 32.

20.

Lacydonia, 479.

Hymeraphia, 96.

Intramesenterial, 184.

Laeocochlis, 399.

Hypanthea, 132.

lophon, 96.

Laetmonice, 478.

Hyperiodrilus, 511.

Iphione, 478.

Lafoea, 133.

Hypnogorgia, 182.

Irene, 134.

Lagena, 14, 397.

Hypobianchial gland,

Irenium, 134.

Lagenipora, 566.

345; of gastropoda, 358.

Iridogorgia, 182.

Lagenophrys, 51.

Hypocoma, 52, 53.

Isakis, 284.

Lagisca, 478.

Hypodermis, 275.

Isaurus, 189.

Lagoon island, 173.

Hypophare, 77.

Isidella, 182.

Lamellaria, 362, 398.

Hypophorella, 556.

Isis, 182.

Lamellibranchiata, 324.

Hypopyxis, 133.

Ismenia, 355.

Lampetia, 207.

Hyporhynchus, 220.

Isocardia, 325, 347.

Lamprodeima, 17.

Hypostome, 100.

Isomastigoda, 31.

Lanassa, 485.

Hypotricha, 49.

Isopleura, 387.

Land-leech, 527.

606

INDEX.

Land - planarians, 221,
222.

Land-snails, 416.

Land-sole, 416.

Langia, 272.

Lanistes, 361.

Lanuginella, 92.

Laodice, 133, 134.

Laoraedia, 131.

Laononie, 491.

Lar, 130.

Laranda, 481.

Larcoidea, 23.

Larval kidneys of gastro-
poda, 382.

Lasaea, 345, 347.

Lateral organs of nemer-
tea, 267.

Laterals of radula, 370.

Latirus, 397.

Latrnncalia, 97.

Lanrer's canal, 226.

Leachia, 445.

Leaena, 485.

Leanira, 478.

Lecanocephahis, 276.

Leda, 328, 337, 345.

Leeches, 512, 526.

Lefroyella, 93.

Leiblein, gland of, 371.

Leimacopsis, 222.

Leiocephalus, 488.

Leioclione, 488.

Leioderniatium, 95.

Leiopathes, 190.

Leioptihnn, 181.

Leiosella, 98.

Leiotealia, 187.

Leiotropic shell, 360.

Lelapia, 90.

Lembadion 39, 47.

Leinbus, 47.

Lemnisci, 294.

Leocarpus, 17.

Leodora, 491.

Leonnra. 168.

Lepeta, 394.

Lepidametria, 478.

Lepidasthenia, 478.

Lepidoderma, 17. 311.

Lepidomenia, 355.

Lepidonotus, 478.

Lepidopleuvus, 478.

Lepocinclis, 31.

Lepralia, 566.

Leptastraea, 196.

Leptobrachia, 168.

Leptochiton, 392.

Leptoconclms, 396.

Leptodera, 281, 290.

Leptodiscus, 36, 37.

Leptogorgia, 183.
Leptomedusae, 133.
Lepton, 347.
Leptopenns, 196.
Leptoplana, 222.
Leptopoma, 398.
Leptopsamraia, 197.
Leptoptilnm, 181.
Leptoria, 195.
Leptoscyphus, 131, 132.
Leptoseris, 196.
Leptostoma, 516, 527.
Leptotheca, 67.
Lessepsia, 96.
Lesueuria, 207.
Leucandra, 90.
Leucariste, 486.
Leucascus, 90.
Leucia, 478
Leucilla, 90.
Leucochloridium, 231.
Leucodore, 483.
Lencoella, 182.
Leucon, 77.
Leucophrys, 42, 47.
Leucosolenia, 75, 89.
Leucyssa, 90.
Levant sponge, 98.
Libyodrilus, 498, 511.
Licea, 17.
Lichenopora, 566.
Lichnophora. 50.
Lictorella, 133.
Lieberkulmia, 13, 49.
Ligula, 247, 255.
Lilaea, 149.

Lima, 338,341,347, 344.
Limacina, 360, 361, 362,

372, 406.

Limapontia, 385, 414.
Limax, 357, 361, 362,

416

Limestone, 10.
Limicolae, 508.
Limnaea, 380, 414, 415.
Limnaeidae, l)reathingof,

375.

Limnatis, 527.
Limnias, 299, 308.
Limnocnida, 122, 137.
Limnocodiuin, 122, 134.
Limnodrilus, 508.
Limnorea, 131.
Limopsis, 345.
Limpet, 394.
Linantha, 167.
Lindbladia, 17.
Linerges, 167.
Lineus, 272.
Lingula, 258, 575, 577,

578, 584, 585.

Lingulina, 14.
Lingulinopsis, 14.
Liniscus, 167.
Linophysa. 155.
Linuche, 167.
Lionotus, 46.
Liostomum, 526.
Liotia, 395.
Lipobranchius, 489.
Lipocephala, 324.
Liponema, 188.
Liriantha, 136.
Liriope, 136.
Lithactinia, 196.
Lithistida, 94.
Lithocircus, 23.
Lithodonms, 331, 344,

346.

Lithoglyphus, 398.
Litholophus, 23.
Lithophyllia, 195.
Litiopa, 357. 398.
Littorina, 374, 380, 386,

398.

Lituaria, 181.
Lituola, 13.
Livcr-iluke, 238.
Lizusa, 131.
Lizzella, 131.
Lizzia, 131.
Lob-worm, 488.
Lobatae, 207.
Lobiger, 404, 406.
Lobophytum, 179.
Lobopsammia, 197.
Lobnlaria, 179.
Loimiii, 485.
Loligo, 441, 445.
Loligopsi.s, 445.
Loliolus, 441, 445.
Lomanotus, 412.
Looping snail, 398.
Lopadorhynchus, 474,

Lophocercus, 406.
Lophochaeta, 508.
Lophogorgia, 183.
Lophobelia, 195.
Lophophore, 551.
Lophopus, 556, 568.
Lophoseris, 196.
Lophosmilia, 195.
Loricata, 309.
Lottia, 376.
Love-dart, 379.
Lovenella, 132.
Loven's larva, 451, 453.
Loxocephalus, 47.
Loxodes, 46.
Loxophylluni, 46.
Loxosoina, 549, 572.

INDEX,

607

Lubomirskia, 96.
Lucemaria, 111, 164.
Lucina, 340, 347.
Lucinidae, 328, 342.
Lucinopsis, 348.
Luffaria, 98.
Lug-worm, 488.
Lumbriconereis, 47 1,481.
Lunibriculus, 508.
Lumbricus, 494, 497, 502,

504, 505, 512.
Lunula, 325.
Lunularia. 566.
Lutraria, 328, 348.
Lycastis, 479.
Lyclmagalnia, 153.
Lyclmorhiza, 168.
Lycogala, 17.
Lycoridae, 479.
Lygomorpha, 181.
Lyidium, 94
Lymphatic gland of Mol-

lusca, 321.

Lyonsia, 328. 331, 349.
Lyonsiella, 349.
Lysarete, 480.
Lysidice, 481.
Lysippe, 486.
Lyssacina, 92.
Lytocarpus, 133.

m. = marine.
Ma.n. = Macronucleus.
Macandrewia, 94.
Maoduffia, 481. *
Macho-polyp, 126.
Maclurea, 395.
Macraspis, 237.
Macrobdella, 526.
Macromesentery, 189.
Macronucleus, 40.
Macrorhynchus, 220.
Macrostomum, 219.
Mactra, 347.
Madoniactis. 188.
Madraeis, 195.
Madrepora, 197.
Madreporaria, 191.
Maeandrina, 195.
Maeandrospongidae, 93.
Magalia, 477.
Magelona, 465, 484.
Magilus, 357, 386, 396.
Magog, 97.
Magosphaera 51.
Malacobdella, 270, 272.
M alacodermata, 183.
Malacosaccus, 92.
Malacotylea, 232, 237.
Malaria, 63.
Maldane, 488.

Male, 70.
Mallcate, 307.
Malleus, 307, 346.
Malmgrenia, 478.
Manayunkia, 471, 491.
Manicina, 195.
Mantle, 319, 358.
Mantle-cavity, 319 ; of

gastropoda, 374.
Manubrium, 108.
Mar. = marine.
Margarita, 17, 395.
Margaritana, 327, 347.
Margaritella, 93.
Margelis, 131.
Margelliuni, 131.
Marginal cirri, 49.
Marginal anchors, 117 ;

bodies, 115.

. Marginals of radula, 370.
Marginella, 397.
Marginulina, 14.
Marionia, 411, 509.
Marmanema, 135
Marphysa, 467, 481.
Marsenina, 362, 377, 398.
Marsupialida, 166.
Mastax, 303.
Mastiganioeba, 27, 30.
Mastigias, 168.
Mastigocerca, 309.
Mastigophora, 26, 27,

566.

Mastigopod, 4.
Mastobranchus, 486.
Mathilda, 399.
Meandroseris, 196.
Mecynostomum, 219.
Medora, 167.
Medusa, 108.
Medusites, 162.
Medusoid, 120, 126.
Medusome, 139.
Megagamete, 42.
Megachacta, 511.
Megalactis, 188.
Megalomastoma, 398.
Megalospheric, 7.
Megalotrocha, 301, 308.
Meganephric nephridia,

498.

Mcgapora, 565.
Megascleres, 81, 82.
Megasclerophora, 94.
Megascolex, 510.
Megascolides, 494. 498,

501, 502, 506, 510.
Megastoma, 31.
Megcrlia, 585.
Melaenis, 478.
Mclampus, .415.

Melania, 380. 386, 399.

Melanopsis, 399.

Meleagrina, 327, 341,
346.

Melibe, 412.

Melicerita, 565. ;

Melicerta, 303, 307.

Melicertaria, 132.

Melicertella, 134.

Melicertidium, 134.

Melicertissa, 134.

Melicertum, 133, 134.

Meliiderma, 96.

Melinna, 486.

Melirmopsis, 486.

Melitodes, 182.

Melittionidae, 93.

Melophysa, 153.

Melusina, 167.

Membranella, 39.

Membranipora, 556, 565.

Membraniporella, 565.

Menella, 183.

Menipea, 565.

Menoidium, 31.

Mera, 491.

Mermis, 275, 282, 289.

Mermithidae, 289.

Meromyaria, 276.

Merona, 129.

Mertensia, 207.

Mertensid larva, 201.

Merulina, 196.

Mesacmaea, 188.

Mesenchytraeus, 503,
509.

Mesenterial filament. 103.

Mesenteries (Anthozoa),
103.

Mesenteron of mollusca,
320.

Mesocena, 35.

Mesodinium, 46.

Mesoglaea, 99.

Mesogonion, 135.

Mesonema, 134.

Mesonemertini, 270.

Mesostomum, 215, 219.

Mesotrocha, 475.

Mesozoa, 243.

Metacineta, 53.

Metadrilus, 511.

Metagenesis, 122.

Metameric segmentation,
315.

Metamorphosis of Gas-
tropod larva, 383.

Metanemertini, 271.

Metapodium, 357.

Metastatic, 228, 238.

Metastatica, 237.

608

INDEX.

Metazoa, 70.
Metonanchora, 96.
Metopidia, 310.
Metopus, 48.
Microcalthrop, 85.
Microcliaeta, 494, 511.
Microciona, 96.
Microcodon, 300, 309.
Microcotyle, 236.
Microcyst, 16.
Microdrilus, 510.
Microgamete, 29, 43.
Microglena. 31.
Microgonidinm, 29.
Microhydra, 127.
Micromesentery, 189.
Micronucleus, 40.
Microplana, 222.
Micropora, 565.
Mieroporella, 566.
Microptilum, 181.
Microrhabd, 8.5.
Microsclere, 81, 83.
Mioroscolex, 510.
Microspheric, 7.
Microstoma, 211.
Microstomidae, 218.
Microstomum, 214, 219.
Microtaeniinae, 254,261.
Microthorax, 47.
Miorotriod, 85.
Micriira, 272.
Mikrogromia, 13.
Mildewed wheat, 290.
Miliolina, 13.
Millepora, 129.
Millsonia, 510.
Mimosella, 567.
Mi.n . = Micronucleus.
Minchinia. 61.
Mineralogists, 398.
Minyas, 100, 187.
Miracidium, 229.
Mischer's tubes, 68.
Mitactis, 187.
Mitra, 397.
Mitraria, 475.
Mitre-shell, 397.
Mitrocoma, 134.
Mitrocomella, 134.
Mitroconiium, 134.
Mitrophyes, 149.
Mnernia, 207.
Mnemiopsis, 208.
Mnestra, 123 ; parasitica,

109.

Modeeria, 131.
Modiola, 346.
Modiolaria. 344, 346.
Modulus, 399.
Molleria, 395.

Mollusca, 316.

Monact, 91.

Monactine, 84.

Monad ina, 30.

Monas, 30.

Monaulic, 378.

Monaxon, 82.

Monaxonida, 95.

Mouera, 4.

Monhystera, 291.

Monie'zia, 246, 262.

Moniligaster, 506, 510.

MonoWa, 19.

Monocaulus, 130.

Monocerconionas, 31.

Monocotyle, 234.

Monocystidea, 59.

Monocystis, 59.

Monodonta, 395.

Monogastric, 146.

Monogenea, 233.

Monogenetic, 228.

Mononiyaria, 326, 330.

Monopectinate, 396 ;
ctenidium, 374.

Monophyes, 149.

Monopvlaria, 21, 23.

Monosiga, 33.

Monosporea, 60.

Monoporus, 219.

Monostomnni, 225, 240;
faba,226; flavum,229,
231 ; mutabile, 229,
231.

Monostyla, 310.

Monothalamia, 11.

Monotocardia, 395.

Monotus, 220.

Monoxenia, 178.

Monozoic, 21, 60, 244.

Montacuta, 345, 347.

Montipora, 197.

Monura, 310

Mopsea, 182.

Mopsella, 182.

Moseleya, 196.

Mother-of-pearl, 326.

Mouth-vacuole, 28.

Mucronella, 566.

Muggiaea, 149.

Miiller's larva, 218.

Multicilia, 51.

Murex, 361, 378, 380,
386, 396.

Muriceides, 182.

Mussa, 195.

Mussels, 346 ; fresh-
water, 347.

Mutela, 347.

Mya, 348.

Myacea, 348.

Mycedium, 196.
Mycetophyllia, 195.
Mycetopus, 347.
Mycetozoa, 15.
Myliusia, 93.
Myochama, 349.
Myocyte, 57.
Myophane, 38.
Myopsida, 445.
Myrianida, 471, 476,
Myriastra, 94.
Myriothela, 130.
Myriozoum, 566.
Mystides, 479.
Mytilacea, 346.
Mytilia, 310.
Mytilidae, 328, 341.
Mytilus, 330, 331, 342,

346.

Myxastrum, 19.
Myxicola, 463, 464, 491.
Myxidium, 67.
Myxilla, 96.
Myxobolus, 66, 68.
Myxodictyum, 11.
Myxoniycetes, 15.
Myxopod, 5.
Myxosoma, 67.
Myxospongida, 95.
Myxosporidia, 64.
Myzobdella, 509.
Myzostoniida, 492.

N.Am. = North America.
N.Z.=New Zealand.
Nacreous, 326.
Nadina, 219.
Nais, 448, 494, 507, 509.
Nannodendron, 179.
Napopora, 197.
Narica, 398.
Narcomedusae, 136.
Nassa, 396.
Nassela, 23.
Nassoidea, 23.
Nassula, 46.
Natica, 361, 369, 386,

397, 509, 510.
Nauphanta, 167, 479.
Nausicaa, 167.
Nausithoe, 167.
Nautilus, 417, 420, 421,

424,433-441,443,444.
Navicella, 361.
Nectalia, 153.
Nectocalyx, 139.
Nectonema, 293.
Nectonemertes, 271.
Nectophysa, 155.
Nectosome, 139.
Neda, 409.

INDEX.

609

Needham's sac, 439.

Nellia, 565.

Nemathelminthes, 273.

Nematobotkrium, 240.

Nematocvat, 39, 101,211;
in Mollusca, 412.

Nematoda, 274.

Nematogen, 242.

Nematomorpha, 292.

Nematonereis, 481.

Nematophore. 126.

Nematoxys, 284.

Nemertca, 263.

Nemertodrilus, 511.

Nemertopsis. 271.

Nemopsis, 131.

Neohelia, 195.

Neomenia, 355.

Neopelta, 94.

Neorhynchus, 296, 297.

Neosiphonia, 94.

Neottis. 485.

Nephelis, 518, 519, 523,
524 526.

Nephridia, 450 ; megane-
phric, 498 ; plectone-
phric, 500; rectal, 502;
pepto-. 450.

Nephridial coelorn, 314.

Nephridiopore, 3 1 4.

Nephridium of Gastro-
poda, 376 ; Polyzoa,
553.

Nephroselmis, 32.

Nephthya, 179

Nephthys, 459, 475,
480.

Nereidiformia, 475.

Nereilepas. 479.

Nereis, 465, 468, 471,
473, 479.

Nerilla, 476.

Nerinaea, 399.

Nerine, 475, 483.

Nerita. 361, 380, 395.

Neritina, 395.

Neritopsis, 395.

Nerve cells, 100.

Nerves in Medusae, 114.

Nethea, 94.

Neuropodium, 460.

Nicidion, 481.

Nicolea, 485

Nicomache 488.

Nidalia, 179.

Nidamental glands, 440.

Nitzsohia, 234

Noctiluca. 35, 37.

Nodosaria, 14.

Nonionina, 15.

Notamia, 565.

Notarchus, 357, 362,

407.

Notaulax, 491.
Noteus, 310.
Notholca, 310.
Notobranchaea, 374,408.
Notocirrus, 481.
Notocotyle, 240.
Notomastus, 486.
Notomrnata, 300, 309.
Notophyllum, 479.
Notopodium, 460.
Notops, 309.
Notopygos, 462. 480.
Nototrochus, 194.
Notykus, 511
Nubecnlaria, 13.
Nuchal cirrus, 481.
Nuclearia, 19.
Nucleus of operculum,

361.
Nucula, 328, 331, 336,

337, 345.
Nuculidae, 341.
Nudibranchiata, 409.
Nullipore, 171.
Nummulites, 10, 15.
Nutrition of Sponge, 80.
Nychia, 478.
Nyctotherus, 38, 48.

Obelaria, 134.
Obelia, 132. 134.
Oceanapia, 96.
Ocelli medusae, 116.
Ocnerodrilus, 510.
Octobothrium, 226, 235.
Octocanna, 134.
Octochaetus, 501, 502,

505, 511.
Octomeralia, 166.
Octonenia, 134.
Octophellia, 188.
Octopoda, 321, 445.
Octopus, 433, 440, 446.
Octorchandra, 134.
Octorchidium, 134.
Octorchis, 134.
Oculina, 195.
Ocyroe, 208.
Odontobius. 291.
Odontocyathus. 194.
Odontophora, 291, 320.
Odontophore, 320, 369.
OdontosylHs, 476.
Odostornia, 377.
Oecistes, 308.
Oegopsida, 420, 438, 445.
Oerstedia, 271 ; pallida,

268.
Ogmogaster, 240.

2 R

Oikomonas, 30.

Oligocelis, 221.

Oligoceras, 98.

Oligochaeta, 493.

Oligocladus, 223.

Oligognathus, 471.

Oligonema, 17.

Oligosilicina, 95.

Oligosporea, 61.

Oligotricha, 49.

Olindias, 135.

Oliva, 386, 397.

Olivancillaria, 397.

Olivella, 356, 361, 397.

Olullanus, 235.

Olynthus, 75, 89.

Omalostomum, 219.

Ommatostrephes, 444.

Omphaloponia, 491.

Omphalopomopsis, 491.

Onchidiopsis, 377, 398.

Onchidium, 368, 378,
385, 414, 416.

Onchnesoma, 537, 539.

Onchobothrium, 259.

Onchocotyle, 236.

Oncholaimus, 291.

Onchopora, 565.

Oiichoporella, 565.

Onchosphere, 251.

Onchotrochus, 194.

Onuphis, 481.

Onychochaeta, 511.

Onychodactylus, 46.

Onychodromus, 49.

Onychoteuthis, 421,445.

Oocorys, 400.

Ooecium, 550.

Ootype, 226.

Opalina, 40, 41, 48.

Opalinopsis, 47.

Opercularia, 51.

Operculina, 15.

Operculum of Gastro-
poda, 357, 361; of
Polyzoa, 550.

Ophelia, 467, 487.

Ophioides, 132.

Ophiodiscus, 187.

Ophiodromus, 477.

Ophrydium, 51.

Ophryocystis, 69.

Ophryodendron, 54.

Ophryoglena, 47.

Oj)hryoscolex, 49.

Ophryotrocha, 481.

Opisthobranchiata, 403

Opisthobranchiate, 374.

Opisthodon, 46.

Opisthotrema, 240.

Opistonnmi, 220.

610

INDEX.

Oractis, 189.
Oral vacuole, 33.
Orbiculina, 13.
Orbitoides, 15.
Orbitolites, 13.
Orbulina, 11, 14.
Orbuliuella, 19.
Orcadella, 17.
Orchistoma, 134.
Organ pipe coral, 178.
Organidus, 178.
Oria, 491.
Orifice, 550.
Ormer, 394.
Orpiella, 416.
Orthoceras, 444.
Orthoconcha, 326.
Orthodon, 46.
Orthonectidae. 240.
Orthospora, 60.
Oscarella, 95.
Osculum, 72.
Osphradium, 320 ; of

Gastropoda, 366;

Laniellibranch, 333.
Os sepiae, 417.
Ostrea, 330, 346.
Ostreidae, 328, 338, 341.

342, 344.
Othonia, 491.
Otina, 415.
Otoconia, 367.
Otocyst, 214.
Otocysts of Medusae,

115; of Polychaeta,

463.

Otolith, 367.
Otomesostomum, 219.
Otoplana, 221.
Otoporpa, 113.
Ototyphlonernertes, 271.
Ovicell, 550.

Oviposition of Gastro-
poda, 380: of Oligo-

cliaeta, 506.
Ovula, 400.
Ovum, 70.
Owenia, 207, 484.
Oxea, 82.
Oxydromus, 477.
Oxyhexact, 92.
Oxyrrhis, 31.
Oxysoma, 284.
Oxytricha, 49.
Oxyuris, 275, 279, 284.
Oyster, 346.
Ozobrancbus, 526

Pachastrella, 94.
Pacbychalina, 96.
Pachydrilus, 509.

Pacbymatisma, 94.
Pacbypsaniniia, 196.
Hachyseris, 196.
Paedophykx, 476.
Paleae, 460.
Palepbyra, 167.
Pali, 193.
Pallial bay, 326 ; cavity,

319.

Pallium, 319.
Palmicellaria, 566.
Palmyra, 478.
PaloLa, 481.
Palpacles, 139, 151.
Pal}» of Polychaeta, 459.
Palpon, 138, 139.
Paludicella, 556, 567.
Paludina, 363, 376, 380,

381, 383, 395, 399.
Paludomus, 399.
Palytboa, 189.
Panartus, 23.
Pandaea, 131.
Pandora, 349.
Pandorina, 32.
Panthalis, 478.
Paper-nautilus, 446.
Papyrula, 94
Paractidae, 188.
Paractiuia, 187.
Paractis. 187.
Paractius, 480.
Paradrilus, 511.
Paragastric canal, 201.
Paragorgia. 182.
Paralcyoniuin. 179.
Paramenia, 355.
Paramaecium, 40, 47.
Paramoeba, 29.
Paramuricea, 182.
Paramylum, 28.
Paranepbtbya, 179.
Parantipatbes, 190.
Paranthus, 187.
Parapedal commissure,

409.

Paraphellia, 187.
Parapodium, 357, 458.
Paraseison, 310.
Parasmilia, 195.
Parasitic Gastropoda,

386,402; Lamellibran-

cbiata, 345 : Mollusca,

323.

Parazoantlms, 189.
Parenchyma, 209, 211.
Parenchymalia, 92.
Parenchytraeus, 509.
Parendrilus, 511.
Parieto- vaginal muscles,

550.

Parisis, 182.
Parmacella, 416.
Parmopborus, 361, 395.
Parmula, 96.
Paroral cilia, 49.
Partbenogenesis, 70.
Partbenogonidium, 32.
Pasythea, 564.
Patella, 360, 362, 367,

369,371.372,374,376,

380, 385, 394.
Patellina, 14.
Patera, 167.
Pavonaria, 181.
Pavoniiia, 13.
Peacbia, 188.
Pearl oyster, 327, 346.
Pearly-nautilus =

Nautilus.

Pebrin-disease, 64, 68.
Pectantbis, 135.
Pectantbus asteroides,

109.
Pecten, 331, 332, 333,

334, 341, 342, 347.
Pectinaria, 462, 486.
Pectinatella, 568.
Pectinia, 195.
Pectinibranchiata, 395.
Pectinidae, 328.
Pectis, 135.
Pectunculus, 333, 345.
Pectyllis, 135.
Pedal ganglion, 31 P ;

gland, 357.
Pedalion, 302, 310.
Pedetes, 309.
Pedicellina, 572.
Pedipes, 415.
Prduin, 347.
Pegantha, 136.
Pegasia, 136.
Pelagia, 167.
Pelagobia, 479.
Pelagonemertes, 266,270,

271.

Pelecypoda, 324.
Peiodera, 290.
Pelodrilus, 504, 508.
Pelodytes, 277, 280.
Pelogenia, 478.
Pelomyxa, 11.
Peloscolex, 508.
Pelosina, 13.
Pelta, 404, 405, 406.
Pemmatodiscus, 208.
Pen, 425.

Penis, 215 ; of Gastro-
poda, 378.
Pennaria 130.
IVinmtula, 181.

INDEX.

611

Peimatulacea, 179.

Pentact, 91.

Peptonephridia, 450.

Peraclis, 406.

Peranemiiia, 31.

Perforated shell, 361.

Pericardia! gland, 322,
436 ; glands of Lam-
ellibrauchs, 341.

Pericardium of Gastro-
poda, 375, 377.

Perichaena, 17.

Perichaeta, 501, 506, 510.

Pericolpa, 111, 165.

Pericrypta, 165.

Perieystio, 139.

Peridiriium, 34.

Perigonimus, 130.

Perionyx, 510.

Periostracum, 326.

Peripalma, 165.

Periphragella, 93.

Periphylla, 111, 165.

Peripylaria, 21, 22.

Perisark, 124.

Perisiphonia, 133.

Peristome, 40: of shell,
361.

Peristomium, 447.

Peritrachelius, 284.

Peritrieha, 50.

Peritromus, 49.

IVrivisceral cavity of
Gastropoda, 375.

Periwinkle, 398.

Perna, 336, 346.

Pernemal, 136.

Peromednsae, 165.

Peronia, 414, 416.

Peronium, 113.

Perradial, 118.

IVi-sa, 135.

Petachnum, 135.

Petalonionadina, 31.

Petaloproctus, 488.

Petal ostoma, 539.

Petasata. 135.

Petasus, 135.

Petricolidae, 348.

Petrosia, 96.

Petta, 486.

Pliacellae, 111.

Phacollophora, 167.

Phacotliscns, 23.

Phaeotus, 32.

Phacus, 31.

Phaeoconchia, 24.

Phaeocystina, 24.

Phaeodaria, 23.

Phaeodinia, 24.

Phaeodium, 24.

Phaeogromia, 24.

Phaeosphaeria, 24.

Phagocata, 210, 221.

Phakellia, 96.

Phalacroma, 35.

Phalansterium, 33.

Phanerocarpae, 159.

Phanerocephala, 475.

Phanerocodonic, 126.

Phaneta, 395.

Phascolion, 539.

Phascolodon, 46.

Phascolosoma, 536, 539.

Phasianella, 395.

Pheasant-shell, 395.

Phellia, 188.

Phelloderma. 96.

Phenacia, 485.

Pheronema 92.

Pherusa, 489.

Phialidium, 134.

Phialis, 134.

Phialiuni, 134.

Philine, 362, 405, 406.

Philodina, 299, 300, 304,
308.

Philomedusa, 188.

Philomycus, 416.

Philonexis.421,441,446.

Phloeodictyinae, 96.

Pholadacea, 348.

Pholadidea, 348.

Pholadomya, 349.

Pholas, 327, 331, 344,
348.

Pholoe, 478.

Phoriospongia, 98.

Phoronidea, 542.

Phoronis, 451, 547.

Phosphorescence of Ce-
phalopoda, 426 ; of
earthworm, 508 ; of
Polyzoa, 556.

Phractaspis, 23.

Phractopelta, 23.

Phragmocone, 425.

Phreatothrix, 508.

Phreodrilus, 509.

Phreoryctes, 504, 505, !
508.

Phylactella, 566

Phylactocarps, 126.

Phylactolaemata, 567.

Phyllactis. 187.

Phyllaplysia, 407.

Phyllastraea, 196.

Phyllidia, 371, 412.

Phyllirhoe, 374, 412.

Phyllobothrium, 259.

Phyllobranclms, 413.

Phyllochaetopterus, 484.

Phyllocomus, 486.
Phyllocotyle, 236.
Phyllocyst, 145.
Phyllodoce, 467, 479
Phyllominyas, 187.
Phyllomitus, 31. *
Phyllonella, 234.
Phyllophysa, 153.
Phyllorhiza, 168
Phyllospongia, 98.
Phymactis, 187.
Phymanthus, 187.
Phymastraea, 196.
Phymosoma, 536, 539.
Physa, 416.
Physalia, 156.
Physalidae, 154.
Physaloptera, 235.
Physarella, 17.
Physarum, 17.
Physcosoma, 536, 539.
Physematium, 21, 23.
Physogyra, 195.
Physonectae, 150.
Physophora, 150, 153.
Phytomastigoda. 32.
Pilema, 168.
Pileocephalus, £9.
Pileolaria, 491.
Pileopsis, 398.
Pilidium, 269.
Pilochrota, 94.
Pilulina, 13.
Pinaciophora, 19.
Pinacocystis, 19.
Pinna, 327, 336, 338, 341,

346.

Pinnoctopus, 446.
Pinulus, 92
Pionosyllis, 476.
Pirula, 400.
Piscicola. 513, 526
Pisidium, 341, 347.
Pista, 485.
Pistillum, 154
Placinastrella, 94.
Placocyathus, 194.
Placophora, 387.
Placortis, 95.
Placospongia, 94.
Placostegus, 491.
Placotrochus, 194.
Placuna, 345.
Placunella, 234.
Plagiochaeta, 511.
Plagiopogon, 46.
Plagiostomum, 214, 220.
Plagiotoma, 48.
Plagoniscus, 23.
Plagonium, 23.
Plakina, 95.

612

INDEX.

Plakopus, 11.

Planaria, 210, 215. 218,

221.

Planaxis, 399.
Planocera, 222.
Planorbis, 321, 373, 414,

416.

Planorbulina, 14.
Planula, 124, 159.
Plasmodium, 15.
Platyaspis, 237.
Platycaulos, 183.
Platycotyle, 236.
Platydrilus, 511.
Platygorgia, 183.
Platyhelminthes, 209.
Platypoda, 397.
Platytheca, 30.
Platytrochus, 194.
Plaxipliora, 392.
Plectanium, 23.
Pleotanocotyle, 236.
Plectoidea, 23.
Plectonephric nephridia,

498, 500.
Pleione, 480.
Pleionogaster, 510.
Pleistophora, 68.
Plerogyra, 195.
Pleroma, 94.
Plesiastraea, 196.
Plesioseris, 196.
Pleural ganglion, 319,

331, 362.

Pleurobrachia, 207.
Pleurobranchaea, 362,

403, 409.

Pleurobranchioidea, 408.
Pleurobranchus, 362,385,

409.

Pleuroceridae, 399.
Pleuroconcha, 326.
Pleurocorallium, 182.
Pleurocotyle, 235.
Pleuronema, 47.
Pleurophyllidia, 412.
Pleurostomella, 13.
Pleurotomaria, 361, 394.
Pleurotricha, 49.
Pleurotrocha, 309.
Plexaura, 183.
Pliobothrus, 129.
Pliodon, 347.
Plocamia, 96.
Ploeophysa, 153.
Ploima, 302, 308.
Pluinarella, 182.
Plumatella, 561, 568.
Plumolialichondria, 96.
Plumnlaria, 133.
Pneumadenia, 154.

Pneumatocyst, 139.
Pneumatophore, 139.
Pneumatosac, 139.
Pneumoderma, 407, 408.
Pneumophysa, 155.
Pneumothyrae, 143.
Pocillopora, 195.
Podocoryne, 130, 131.
Podocyathus, 53.
Podolampas, 34.
Podophrya, 52, 53.
Podospfhgia, 97.
Podostoma, 11.
Poecillastra. 94
Polar-capsule, 66.
Policella, 181.
Poliopogon. 92.
Pollicita, 476.
Polyaraea, 196.
Polyarthra, 302, 309.
Polybostrichus, 471,

476.

Polycanna, 134.
Polycera, 412.
Polycelis, 210, 221.
Polychaeta, 458.
Polychoerus, 219.
Polycirrus, 465, 486.
Polyclada, 222.
Polycladus, 222.
Polyclonia, 167.
Polycolpa, 136.
Polycotyle, 238.
Polycyathus, 194.
Polycystidea, 59.
Polycystina, 22.
Polycyttaria, 22.
Polydinida, 35.
Polydiscus, 23.
Polydora, 472, 483.
Polyeunoa, 478.
Polygastric, 146.
Polygordius, 451, 452.
Polykrikos, 33, 35.
Polylophus, 92.
Polyrnastia, 97.
Polymastigina, 31.
Polymitus, 62.
Polymorphina, 14.
Polymorphism, 9, 121 ;

of Polychaeta, 467.
Polymyaria, 276.
Polynoe, 467, 474, 478.
Polyodontes. 478.
Polyoeca, 33.
Polyophthalmus, 458,

463, 472, 487.
Polyopis, 188 272.
Polyorchis, 134.
Polyp, 100 ; and Medusa,

119 ; Anthozoan, 102.

Polyp-head, 125.
Polyphragma, 491.
Polyphyes, 150.
Polyphyllia, 196.
Polyptde, 550.
Polypi mnaria, 133.
Poly podium, 123.
Polyrhabdus, 92.
Polyrlma, 167.
Polysiphonia, 188.
Polysiphonic, 125.
Polyspondylium, 18.
Polysporea. 61.
Polystomella, 15.
Polystomidium, 188.
Polystomum, 226, 236

integeri'iinum, 227,

228. 233.
Polythalamia, 11.
Polytoma, 29, 32.
Polytoreutus, 511.
Polytrema, 14.
Polytremacis, 177.
Polytrocha, 475.
Polyxenia, 136.
Polyzoa, 549.
Polyzoic, 60.
Pomatias, 398.
Pomatiopsis, 398.
Pomatoceros, 473, 491.
Pomatostegus, 491.
Pompholyx, 310.
Pompholyxophiys, 19.
Pond-snail, 415.
Pontobdella, 513, 518

519, 521, 526
Pontodrilus, 510.
Pontogenia, 478.
Pontoscolex, 503, 506,

511.

Porella, 566.
Porifera, 72.
Porina, 566.
Poritella, 95.
Porites, 197.
Porodiscus, 23.
Poromya, 341, 342, 349.
Porosa, 193.
Porospora, 58, 59.
Porpalia, 144.
Porpema, 144.
Porpita, 144.
Porpitella, 144.
Porpitidae, 143.
Portellia, 480.
Portuguese man of war,

154.

Posteriodendron, 30
Potamides, 399.
Potamilla, 490.
Potamis, 490.

INDEX.

613

Potamolepis, 96.
Poterion, 97.
Poulpe, 446.
Pourtalosmilia, 195.
Praxilla, 488.
Pray a, 149.
Prestomiurn, 447.
Preussia, 511.
Pri&puloidea. 540.
Priapulus, 541.
Primary mesentery, 184.

,, zooecium, 560.
Primite, 57.
Primnoa, 182.
Primnoella, 182.
Primnoisis, 182.
Prionastraea, 196.
Prionognathus. 480.
Prionospio, 483.
Prismatic layer, 326, 327.
Pristina, 509.
Proales, 309.
Proboscidae, 214.
Proceraea, 476.
Procerodes, 221.
Procharagma, 166.
Procharybdis, 166.
Procotyla, 221.
Proctodaeum of mollusca,

320.

Proctonotus, 413.
Procyanea, 167.
Productidae, 585.
Proglottis. 244.
Prohelia, 195.
Promesostomum, 219.
Proneomenia, 355.
Pronepbridia of Oligo-

chaeta, 502.
Pronucleus, 45.
Propilidium, 395.
Propodium, 357.
Proporus, 219.
Prorhynchocoelomia.

271.

Prorhynchus, 219.
Prorocentrimi, 34.
Prorodori, 45.
Prorotrichina, 46.
Prosadenoporus, 271.
Prosbosoidactyla, 134.
Proserpina, 395.
Prosobranchiate, 374.
Prosodus, 78.
Prosopyle, 75.
Prosorochmus, 269, 271.
Prostalia, 91.
Prostate of Oligochaeta,

504.

Prostlieceraeus, 223.
Prosthiostomum, 223.

Prostomum, 214.
Protactiniae, 189.
Protamoeba, 11.
Protanthea, 189.
Protantheae, 189.
Proteleia, 94.
Proteosoma, 63.
Proterospongia, 33.
Protiara, 131.
Protis, 491.
Protoalcyonaria, 178.
Protobranchiata, 345.
Protocaulon, 181.
Protodrilus, 451, 452,

453, 457.
Protogene, 11.
Protohydra, 127.
Protomerite, 56.
Protomonas, 29.
Protomyxa, 11.
Protonemertini, 270.
Protoplasm, 1.
Protoptilnm, 181.
Prototrichia, 17.
Protozoa, 1.
Protula, 466, 491.
Protulides, 491.
Provortex, 220.
Proxenetes, 220.
Prunoidea, 23.
Pmno})hracta, 23.
Psamathe, 477.
Psammastra, 94.
Psamminidae, 98.
Psammobia, 348.
Psammocora, 196.
Psammogorgia, 183.
Psammolyce, 478.
Psammopemma, 98.
Psammoplysilla, 98.
Psammoryctes, 508.
Psarnmoseris, 196.
Psarnmosphaera, 13.
Pseudalius, 235.
Pseudaxine, 236.
Pseudaxonia, 182.
Pseudoceridae, 210.
Pseudoceros, 217, 223.
Pseudocotyle, 234.
Pseudogorgia, 178.
Pseudolamell ibranchiata ,

346.

Pseudomelaniidae, 399.
Pseudonavicella, 58.
Pseudopallium, 356.
Pseudopodium, 1 ; in

Rotifera, 299.
Pseudorbabdite, 211.
Pseudorhynchus, 220.
Psilacabaria, 182.
Psilotricha, 49.

Psorosperms, 64.
Psygmobranchus, 473,

491.

Ptenoglossa, 396.
Pteroceras, 361, 399.
Pterocyclus, 398. ^
Pterodina, 310.
Pteroeides, 181.
Pteroessa, 309.
Pteronella, 234.
Pteronema, 131.
Pteropathes, 190.
Pteropoda Gymnoso-

niata, 407 ; Theooso-

mata, 406.
Pterosyllis, 476.
Pterotrachea, 356, 362,

385, 401, 402.
Ptilosarcus, 181.
Ptychobothrmm, 256.
Ptychogena, 134.
Ptychostomum, 47.
Puberty, 43.
Pullenia, 14.
Pulmonary cavity, 374.
Pulmonata, 414.
Pulsellum, 352.
Pulvinulina, 14.
Puncturella, 394.
Pupa, 380, 416.
Pupilla, 362, 394.
Pupina, 398.
Purpura, 396.
Pustularia, 362, 400.
Pustulopora, 566.
Pycnanthus, 187.
Pyrenoid, 28.
Pvrophacus, 34.
Pyrula, 400.
Pytheas, 96.
Pyxidicula, 12.

Q.J.M,S. = Quarterly
Journal of Micro-
scopical Science.

Quadriloncbe, 23.

Quadrula, 12.

Quasillina, 97.

Quinqueloculine, 9.

Rachidean tooth, 370.
Rachiglossa, 396.
Racodiscula 94
Radiolaria, 20.
Radula, 320, 369.
Ragactis, 188.
Rainey's corpuscles, 68.
Ramate, 307.
Ramulus, 126.
Ranms, 307.
Ranella, 400.

614

INDEX.

Raphidiophrys, 19.

Rhizoxenia, 178.

Raspailia, 96.

Rhodactis, 186.

Rataria, 144.

Rhodaraea, 197.

Rathkea,'131.

Rhodope, 414.

Rattulus, 309.

Rhodophysa, 153.

Razor shell, 348.

Rhodopidae, 414.

Receptaculura seminis,

Rhodopsammia, 197.

215.

Rhorabogen, 242.

Recluzia, 396.

Rhopalia, 115, 116, 154.

Red coral, 182.

Rhopalonema, 135.

Redia, 229.

Rhopalophorus, 240.

Regadrella, 92.

Rhopilajna, 168.

Reithrodrilus, 511.

Rhopolactis, 188.

Reniera, 96.

Rhynchelmis, 502, 504,

Renilla, 181.

508.

Reptadeonella, 566.

Rhyncheta, 53.

Retepora, 565.

Rhynchobdellidae, 526.

Reteporella, 565.

Rhynchobothrium, 259.

Reticularia, 17.

Rhynchocoelom, 265.

Retinacula, 294.

Rhynchodemus, 222.

Rhabdammina, 13.
Rhabdite, 211.

Rhynchoflagellata, 35.
Rhynchonella, 574, 577,

Rhabditis, 275, 290.

580, 585.

Rhabditis-form, 280.

Rhynchoneerella. 479.

Rhabdocalyptus, 92.

Rhynchozoon, 566.

Rhabdocoela, 219.

Ridleia, 97.

Rhabdodictyum, 92.

Rimella, 94.

Rhabdogaster, 292.

Rimula, 395.

Rhabdogonium, 14.

Rimulina, 14.

Rhabdome, 83.

Ringicula, 406.

Rhabdomonas, 31.

Ripistes, 509.

Rhabdonema, 277, 280,

Rissoa, 398.

281, 290.
Rhabdopectella, 92.

River-limpet, 416.
River-snail, 399.

Rhabdospheres, 11.

Rod-apparatus, 38.

Rhabdostyla, 51.

Roman snail, 416.

Rhabdus, 82.

Rosette plates, 554.

Rhacella, 95.

Rossella, 92.

Rhagon, 77.

Rossia, 441, 445.

Rhaphidophlus, 96.

Rostellaria, 399.

Rhapide, 86.

Rostellum, 245.

Rhegraatodes, 134.

Rostrum of shell, 425.

Rhinodrilus, 501, 506,

Rotalia, 14.

511.

Rotaliform, 14.

Rhinophores, 366.

Rotifer, 304, 308.

Rhinops, 309.

Rotifera, 299.

Rhipidiglossa, 357, 394.

Round-worm, 284.

Rhipidodendron, 31.

Rugosa, 175.

Rhizammina, 13.

Runcina, 362, 403, 406.

Rhizochalina, 96.

Rhizocline, 131.

S. Am. = South America.

Rhizogeton, 129.

Sabella, 465, 472, 490.

Rhizomastigina, 30.

Sabellaria, 492.

Rhizophysa, 155.

Sabellastarte, 491.

Rhizopoda, 6.

Sabellides, 486.

Rhizopsammia, 197.

Sabelliformia, 490.

Rhizostoma, 108, 109,

Sabinotrochus, 194.

111.

Saccammina, 13.

Rhizostomae, 167.

Saccobdella, 310.

Rhizota, 300, 307.

Saccocirrus, 453, 457.

Rhizotroclms, 194.

Saccoglossa, 413.

Sacconereis, 471, 476.
Saccosoma, 533.
Sacculus, 309.
Sagartia, 187.
Sagartidae, 188.
Sagenella, 13.
Sagitella, 482.
Sagitta, 83, 591.
Sagittated calamary,444.
Sagittocyst, 211.
Salacia, 155.
Salicornaria, 565.
Salinella, 243.
Salmaciua, 466, 468,

491.

Salpina, 309.
Salpingoeca, 33.
Salvatoria, 477.
Sam us, 94.
Samythopsis, 486.
Sandalolitha, 196.
Sanguinolaria, 348.
Saphenella, 134.
Saphenia, 134.
Sapropliytic, 2.
Sarakka, 179.
Sarcenchyme, 79.
Sarcoeystis, 69.
Sarcode, 1.
Sarcodictyon, 178.
Sarcodictyum, 21.
Sarcodina, 3.
Sarcomatrix, 21.
Sarcophiarithus, 188.
Sarcophyllum, 181.
Sarcophyton, 179.
Sarcoplegma, 21.
Sarcosporidia, 68, 69.
Sarcostyle, 126.
Sarcotheca, 126.
Sarsia. 131.
Satellite, 57.
Savaglia, 190.
Saxicava, 331, 348.
Scaeurgus, 440, 446.
Scalaria, 361, 396.
Scalibregma, 489
Scaphander, 405, 406.
Scaphidiodon, 46.
Scaphopoda, 349.
Scapophyllia, 195.
Scandium, 309.
Schistocepbalus, 258.
Scliizocyathus, 194.
Schizogamy, 469.
Schizopathes, 191.
Schizoporella, 566.
Schizotricha, 133.
Schultzia, 220.
Schwagerina, 15.
Scioberetia, 347.

INDEX.

615

Scirtopoda, 310.
Scissurella, 361, 394.
Sciurella, 133.
Scleranthelia, 178.
Scleraxonia, 182.
Sclerisis, 182.
Scleritoderma, 94.
Sclerobelemnon, 181.
Scleroblast, 81.
Sclerocheilus, 489.
Sclerogorgidae, 182.
Sclerohelia, 195.
Scleronephthya, 179.
Scleroplegma, 93.
Scleroptilum, 181.
Sclerostornuni, 235, 280.
Sclerothamnus, 93.
Sclerotiura, 15.
Scoleciformia, 487.
Scolecolepis, 483.
Scolex, 251, 253.
Scollops, 347.
Scolopes, 97.
Scoloplos, 482.
Scopula, 92.
Scorpion-shell, 399.
Scrobicularia, 347.
Scruparia, 564.
Scrupocellaria, 565.
Scurria, 394.
Scutibranchia, 393.
Scutum, 395.
Scutus, 395.
Scyllaea, 412.
Scyphidia, 51.
Scyphistoma, 107.
Scyphomedusae,157, 162.
Scypho-j)olyp, 107.
Scytalium, 181.
Scytophorus, 189.
Sea-anemone, 183.
Sea- hare, 407.
Sea-mouse, 478.
Secondary mesentery,

184 ; symmetry in

Gastropods, 385.
Seison, 304, 310.
Seisonacea, 310.
Selcnaria, 566.
Semantis, 23.
Semele, 347.
Semostomae, 167.
Semperella, 92.
Semperina, 182.
Senescence, 43.
Sense cells, 100.
Sense-organs Medusae,

115.
Sepia, 417, 439, 440, 441,

445.
Sepiadariidae, 445.

Sepiola, 445.
Sepiostaire, 425.
Sepioteuthis, 445.
Septa, 112 ; of corals,

192.

Septaria, 395.
Septata, 59.
Septibranchiata, 344.
Serialaria, 552.
Seriatopora, 195.
Serpula, 491.
Serosporidia, 69.
Sertularia, 133.
Setae, 447.
Setidiura, 95.
Setosella, 565.
Sexual reproduction, 71.
Shell of Cephalopoda,

424 ; Gastropoda, 358.
Shell-gland of Gastro-
poda, 381.
Shepherdella, 13.
Shipworm, 349.
Sicyonis, 188.
Sideractis, 188
Siderastraea, 196.
Sideroderma, 96.
Sigalion, 478.
Sigaretus, 361, 397.
Sigma, 84.
Sigmatella, 98.
Sigmatophora, 93.
Silenia, 349.
Silicoflagellata, 35.
Siliquaria, 399.
Silkworm disease, 64, 68.
Sinistral shell, 360.
Sinupalliatae, 326.
Sinuses of Hirudinea,

517.
Siphon, 138, 139; of

of Echiuroidea, 530 ;

of Gastropoda, 358 ;

Lamellibranch, 328 ;

of Nautilus, 424.
Siphonactinia, 188.
Siphonanthae, 144.
Siphonaria, 362, 375,

379, 414, 415.
Siphonicytara, 565.
Siphonidium, 94.
Siphonochalina, 96.
Siphonodentalium, 352.
Siphonogaster, 511.
Siphonoglyphe, 104;

Alcyonaria, 177.
Siphonogorgia, 179.
Siphonophora, 137.
Siphonostoma, 462, 489.
Siphonostomata, 360.
Siphonostomatous, 361.

Siphonozooid, 177.

Siphonula; 144, 148.

Siphoptychium, 17.

Siphosome, 139.

Sipunculoidea, 534.

Sipunculus, 536, 5S9.

Six-hooked embryo, 251.

Skeleton of sponge, 80.

Skenea, 398.

Slavina, 509.

Sleeping sickness, 289.

Slit, 361.

Slug, 416.

Smaragdia, 395.

Smaragdinella, 406.

Smilotrochus, 194.

Smittia, 566.

Solarium, 361, 396.

Solen, 328, 331, 333,
336, 348.

Solenastraea, 196.

Solenocaulon, 182.

Solenoconchae, 349.

Solenocurtus, 348.

Solenogastres, 352.

Solenomya, 331, 337,
341, 345.

Solenopharynx, 220.

Solenophorus, 256.

Solenophrya, 53.

Solenosmilia, 195.

Sollasella, 97.

Solmaris, 137.

Solmissus, 137.

Solmoneta, 137.

Solmundella, 137.

Solmundus, 137.

Somatocyst, 145.

Somite, 453.

Sorocelis, 221.

Sorophora, 17.

Sorosphaera, 13.

Sosane, 486.

Spadella, 591.

Spadix of Nautilus, 421.

Sparganophilus, 511 .

Spathidium, 45.

Sperm injection, 217,227,
249 ; sacof Oligochaeta,
503 ; reservoir of Oli-
gochaeta, 503.

Spermatheca of Oligo-
chaeta, 505.

Spermatophore of Cepha-
lopoda, 440.

Spermatophores of Hiru-
dinea, 523; of Nautilus,
421 ; of Oligochaeta,
505, 507.

Spermatozoon, 70.

Spermiducal gland, 504.

616

INDEX.

Sphaerastrum, 19.
Sphaerocapsa, 23.
Sphaerodorum, 476.
Sphaeroidea, 23.
Sphaeroidina, 14.
Sphaeromyxa, 67.
Sphaeronectes, 149.
Sphaerophracta, 23.
Sphaerophrya, 52, 53.
Sphaerospora, 67.
Sphaerosyllis, 476.
Sphaerozoum, 23.
Sphaerularia, 282, 291.
Sphenoides, 149.
Sphenumonas, 31.
Sphenophyllia, 195.
Sphenopus, 189.
Sphenotrochus, 149.
Sphinctrella, 94.
Sphyranura, 236.
Sphyrocephalus, 222.
Sphyrophysa, 153.
Spicata, 181.
Spicula nematoda, 278.
Spicules of sponges, 81-

84.

Spiculum amoris, 379.
Spilophora, 291.
Spindle muscle, 319.
Spinipora, 129.
Spintharophora, 97.
Spinther, 480.
Spio, 475, 483.
Spiochaetopterus, 484.
Spionifonnia, 483.
Spiral metamerism, 494 ;

zooid, 126.
Spirastrella, 97.
Spire, 84.
Spirialis, 360.
Spirillina, 14.
Spirobranchns, 491.
Spirochona, 50.
Spirograplus, 490.
Spiroloculina, 13.
Spiroptera, 279, 289.
Spirorbis, 466, 467, 491.
Spirosperma, 508.
Spirostonmm, 48.
Spirotricha, 48.
Spiroxys, 289.
Spirula, 425, 440, 445.
Spirulirostra, 425.
Spondylomorum, 32.
Spondylus. 333, 334,

344, 347.

Sponge spicules, 81-84.
Spongelia, 98.
Spongelidae, 98.
Spongidae, 97.
Spongilla, 96.

Spongillidae, 72.
Spongin, 73.
Spongiobranchaea, 408.
Spongioderma, 182.
Spongodes, 179.
Spongodiscus, 23.
Spongomonas, 31.
Spongophare, 77.
Spongurus, 23.
Sporadopora, 129.
Sporangia, 16.
Spores, 5.
Sporoblast, 66.
Sporocyst, 229.
Sporogony, 120.
Sporophore, 16.
Sporosac, 120.
Sporozoa, 54.
Sporozoite, 60.
Spyroidea, 23.
Squamulina, 13.
Squid, 425.
Stachyodes, 182.
Stachyptilum, 181.
Staircase shell, 396.
Stannomidae, 98.
Statoblast, 555.
Stauractis, 188.
Stauraglaura, 135.
Stauridae, 175.
Stauridium, 130, 131.
Staurobrachinm, 134.
Staurocephalus, 480.
Staurodiscus, 134.
Stauromedusae, 163.
Staurophora, 134.
Staurospbaera, 23.
Staurostoma, 134.
Staurotheca, 133.
Steenstrupia, 109, 131.
Steganophthalmata, 117.
Steganoporella, 565.
Stelospongia, 98.
Stelletta, 94.
Stemonitis, 17.
Stenella, 182.
Stenogorgia, 183.
Stenohelia, 129.
Stenoptycha, 167.
Stentor, 38, 40, 48.
Stenostomum, 214, 219.
Stephalia, 154
Stephanactis, 187.
Stephanaria, 196.
Stephania, 477.
Stephanium, 23.
Stephanoceros, 300, 301,

307.

Stephanomia, 153.
Stephanophyes, 149.
Stephanophyllia, 196.

Stephauopogon, 46.

Steplianops, 309.

Stephauoseris, 196.

Stephanosphaera, 32.

Stephanospira, 153.

Stepliauotrochus, 194.

Stephoidea, 23.

Stephonalia, 154.

Stenocephalus, 59.

Stercutus, 509.

Stereosoma, 177, 178.

Sternaspis, 450, 462, 465,
489.

Sthenelais, 478.

Sthenonia, 167.

Stichodactylinae, 186.

Stichopathes, 190.

Stichotricha, 49.

Stigmata in Protozoa, 28.

Stigmosphaera, 23.

Stilifer, 361, 386, 402.

Stiliger, 413.

Sting-winkle, 396.

Stoeba, 94.

Stolonifera, 178, 567.

Stoloteuthis, 445.

Stomach of Ctenophore,
197.

Stomatella, 362, 395.

Stomatia, 395.

Stomatogastric commis-
sure, 319, 362.

Stomatopora, 566.

Stomidia, 186.

Stomobrachium, 134.

Stomodaeum of Mol-
lusca, 320.

Stomolophus, 168.

Stomotoca, 131.

Stomphia, 187.

Streptaster. 85.

Streptocaulus, 133.

Streptoneura, 364, 392.

Strobalia, 153.

Strobila, 157, 243.

Stabilisation, 160.

Strombidium, 49.

Strombus, 378, 386, 399.

Strongyle, 83.

Strongylidae, 278.

Strongylidium, 49.

Strongylus, 284.

Strophogorgia, 182.

Structureless lamella, 99.

Struthiolaria, 400.

Stryphnus, 94.

Stuhlmannia, 511.

Stylactis, 130.

Stylaria, 509.

Stylarioides, 489.

Stylaster, 129.

INDEX.

617

Stylatula, 181.
Stylifer, 357, 402.
Styliola, 406.
Stylobelemnon, 181.
Stylochoplana, 211, 222.
Stylochrysalis, 32.
Styloclms, 222.
Stylocometes, 54.
Stylocordyla, 97.
Stylocyathus, 194.
Stylodrilus, 508.
Stylommatophora, 416.
Stylonycliia, 43, 49.
Stylophora, 195.
Stylorhynchus, 59.
Stylosphaera, 23.
Stylorhiza, 168.
Stylostichon, 96.
Stylostonram, 223.
Stylus, 84.
Subcerebral commissure,

409.

Suberia, 182.
Suberites, 97.
Suberitidae, 97.
Suberogorgia, 182.
Subgenital pits, 118.
Subintestinal ganglion,

364.

Submytilacea, 347.
Subradular organ, 371,

389.

Subsagittal, 199.
Substomachal, 199.
Subtentacular. 199.
Subtransversal, 199.
Subumbrella, 108.
Sub ventral, 199.
Succinea, 416.
Suckers of Cephalopod,

421.

Sulcastrella, 94.
Sulculus, 184.
Sulcus, 184.
Summer egg, 217, 304.
Sun animalcule, 19.
Supercytis, 566.
Supporting lamella, 99.
Supraintestinal ganglion ,

364.

Sutroa, 508,
Suture, 361.
Swiftia, 183.
Sycantha, 90.
Sycetta, 90.
Sycon, 75, 90.
Syculmis, 90.
Sycyssa, 90.
Syli'ides, 476.
Syllis, 467, 471, 476.
Symbiosis, 20, 211, 218. !

Sympagella, 92.
Symphyllia, 195.
Symplocostorna, 291 .
Sym podium, 178.
Sympyla, 95.
Synapticula, 92, 193.
Synaptychus, 444.
Synaraea, 197.
Synchaeta, 309.
Syncoryne, 130.
Syncrypta, 32.
Syndictyon, 131.
Syngamus, 235.
Synops, 94.
Synthecium, 133.
Synura, 32.
Syringammina, 13.
Syringopora, 178.
Syzygium, 57.

Tabulae, 193.

Tabulata, 191.

Taegeria, 92.

Taenia, 260 ; cucume-
rina, 247 ; saginata,
244; solium, 244.

Taenioglossa. 397.

Taenioles, 108.

Tamoya, 166.

Taonius, 445.

Tapes, 348.

Tapeworm, 243.

Taphrocampa, 309.

Taster, 139.

Taxipathes, 191.

Tealia, 187.

Tealidium, 187.

Tectibranchiata, 403.

Tedania, 96

Teeth of radula, 370.

Telamone, 477.

Telepsavus, 484.

Telesto, 178.

Telethusidae, 488.

Teleudrilus, 511.

Tellina, 333, 340, 345,
347.

Tellinacea, 347.

Telmatodrilus, 508.

Telotrocha, 475.

Temnocephala, 234.

Temp. = temperate.

Tentacle sheath, 550.

Tentacular cirri, 459.

Tentaculata, 207.

Tentaculocyst, 116.

Tentilla, 140.

Tentorium, 97.

Terebella, 462, 463, 485.

Terebellides, 486.

Terebelliformia, 484.

Terebellum, 399.
Terebra, 371, 397.
Terebratella, 585.
Terebratula, 577, 584,

585.

Terebratulina, 585C
Terebripora, 556.
Teredo, 327, 329, 330,

331, 336, 342, 343.

349.

Tessaradoma, 566.
Tessera, 111, 164.
Tesserantha, 164.
Tesseronae, 162.
Testacca, 11.
Testacella, 385, 416.
Testamoebiformia, 15.
Testicardines, 585
Tethya, 97.
Tethyopsilla, 94.
Tethyopsis, 94.
Tethys, 412.
Tethyspira, 97.
Tetilla, 94.
Tetrabranchiata, 443.
Tetracladidae, 94.
Tetracoralla, 175.
Tetract, 91.
Tetractinellida, 93
Tetraglena, 470.
Tetragonus, 512.
Tetrameralia, 162.
Tetrameres, 289.
Tetramita, 28. 29.
Te train itus, 31.
Tetranema, 134.
Tetraonchus, 236.
Tetrarhynchus,245, 259.
Tetrastemma, 269, 270,

271.

Tetrodictyidae, 93.
Texas fever, 63.
Textularia, 13.
Thala, 397.
Thalamopora, 14.
Thalassema, 530, 533.
Thalassianthus, 188.
Thalassicolla, 20, 23.
Thalassolampe, 22.
Thalassophysa, 23.
Thalassopila, 22.
Thalassoplancta, 23.
Thalassosphaera, 23.
Thalenessa, 478.
Thamnitis, 131.
Thamnostoma, 131.
Thamnostylus, 131.
Thaumactis, 187.
Thaumantaria, 133.
Thaumantias, 132, 134.
Theca, 193,

618

INDEX.

Thecidium, 578, 581,

585.

Thecocladium, 133.
Thecopsamraia, 196.
Thecosphaera, 23.
thelactis, 187.
Thelepus, 485.
Thelohania, 68.
Thenea, 94.
Theodisca, 482.
Theodoxia, 395.
Theonella, 94.
Thesea, 183.
Third vas deferens, 226.
Thoosa, 97.
Thoreota, 98.
Thorectandra, 98.
Thouarella. 182.
Thracia, 349.
Thread-cell. 101.
Thread-worms, 274.
Thrinacophora. 96.
Tlirombus, 95.
Tlmiaria, 133.
Tlmrainmina, 13.
Thyca, 357, 371, 398.
Thyroscyphus, 132.
Thysanostonia, 168.
Thysanozoon, 217, 223.
Thysanus, 194.
Tiara, 131.
Tiarina, 46.
Ti'.ropsis, 109, 134.
Ticlioseris, 196.
Tiotlmainiia, 406.
Tima, 134.
Tinoporus, 14.
Tintinnidiuni, 49.
Tintinnopsis, 49.
Tiiitiinius. 49.
Titanideum, 182.
Titiscania, 395.
Tokophrya, 52, 53.
Tornopteris, 465, 472,

479.

Top shell, 395.
Toreimia, 167.
Tornatiua, 406.
Tomote, 82.
Toxa, 84.
Toxochalina, 96.
Toxoclytus, 168.
Toxoglossa, 397.
Toxorchis, 134.
Trachelius, 46.
Trachelomonas, 31.
Tracheophysae, 141.
Trachomedusae, 135.
Trachycaulus, 92.
Trachynenia, 135.
Trachyphyllia, 195.

Trachypora, 196.
Trachytedania, 96.
Travisia, 487.
Travisiopsis, 482.
Trematoda. 223.
Trematotrochus, 194.
Tremaulidiuni, 95.
Tremoctopus, 420, 421,

441, 446.

Trepomonas, 28, 31.
Tretolophus, 95.
Triact, 91.
Triage, 83.
Triaenophorus, 258.
Triarthra. 302, 309.
Triaulic, 379.
Triaxon, 84.
Triaxonia, 90.
Tribrachiuin, 94.
Trichamphora, 17.
Trichia, 17.
Trichina. 236, 278.
Trichinosis, 288.
Trichobranchidae, 486.
Trichoeephalus, 235, 279.
Trichochaeta, 511.
Ti-K-hocyst, 39.
Trichodal, 86.
Trichoderma, 292.
Trichodina, 50.
Trichodinopsis, 50.
Trichodrilus, 508.
Trichogaster, 49.
Trichomastix, 31.
Trichomonas, 31.
Trichoplirya, 54.
Trichoplax, 243.
Trichoptilum, 181.
Trichosomum, 236.
Trichostenmia, 97.
Tridiostonmta, 46.
Trichotropis. 398.
Triclada, 221.
Tri.lacna. 331, 348.
Tridacophyllia, 195.
Triforis, 399.
Trigaster, 511.
Trigger, 101.
Trigonia, 345.
Trigoniidae, 328, 341.
Trigonoporus, 222.
Trilobus, 30, 291.
Triniorpliism, 9.
Trinema, 13.
Trinephrus, 500, 510.
Triod, 84.
Triopa, 412.
Triptolemus, 94.
Tripylaria, 21, 23.
Tristomuni, 234.
Tritaxia, 13.

Triticella, 567.

Triton, 400.

Tritonia, 411.

Tritonioidea, 411.

Trochal disc, 299.

Trochammina, 13.

Trochetia, 516, 519, 526.

Trochilia, 46.

Trochocyathus, 194.

Trochopus, 234.

Trochoseris, 196.

Trochosphaera, 308.

Trochosphere of Gastro-
poda, 381 ; of Rotifera,
307.

Trochotoma, 394.

Troclms, 367, 376, 395.

Trophi, 303.

Trophon, 396.

Trophonia, 489.

Trophosome, 126.

Tropidocera, 289.

Truncatella, 398.

Truncatulina, 14.

Trymohelia, 195.

Trvpaiiosonia, 30.

Trypanosyllis, 476.

Tube Rotifera, 303.

Tubclla, 96.

Tubercula pulicrtatis,
506.

Tubiclava, 129.

Tubicolaria, 301.

Tubitex, 505. 508.

Tubipora, 178.

Tubucellaria, 565.

Tubularia, 130.
I Tubulina, 17.

Tvibulipora. 566.

Tun, 400.

Turbanella, 311.

Turbdliiria, 210.

Turbhmria, 197.

Turbin el lidae, 397.

Turbinolia, 194.

Turbo, 376, 395.

Turkey sponge, 87, 98.

Turricula, 397.

Tunis, 131.

Turritella, 399.

Turritigera, 565.

Turrito})sis. 131.

Tykonus, 511.
! Tylenchus, 282, 290.
I Tylodina, 409.

Tylopatlies, 190.

Tylosoma, 537, 539.

Tylote, 83.

Tympanidiuni. 23.

Typhacus, 502, 506, 510.

Typhloscolex, 472, 482.

INDEX.

619

Typhlosole, 497.
Tyrrhena, 477.

Udonella, 234.
Ulangia, 195.
Ulmaris, 167.
Ulophyllia, 195.
Ultradextral shell, 361.
Umbellnla, 181.
Unibilicated shell, 361.
Umbones, 325.
Umbonula, 566.
Umbrella, 409.
Umbrosa, 167.
Uncinais, 509.
Uucinate, 92, 307.
Uncinatedcalamaiy, 445.
Uncinataria, 93.
Uncini, 460 ; of radula,

370.

Uncus, 307.
Undosa, 167.
Undulating membrane,

39.
Unguiculate operculum,

361.

Ungulina, 347.
Unio, 327, 332, 342, 347.
Unionidae, 328.
Unyoria, 511.
Urceolarina, 50.
Urceolus, 303.
Urnatella, 572.
Urobenus, 511.
Urocentrimi, 47.
Urocyclus, 416.
Uroglena, 30.
Urolabes, 291.
Uroleptus, 49.
Uronema, 47.
Uronychia, 49.
Urosalpinx, 396.
Urosoma, 49.
Urospora, 59.
Urostyla, 49.
Urotricha, 45.
Urozona, 47.
Uruguaya, 96.
Ute, 90.
Utclla, 90.
Uteriporus, 221.
Uvigerina, 14.

Vacuole contractile, 1.
Vaginicola, 51.
Vagi n ul ina, 14.
Vagirmlus, 378, 385, 414,

416.

Valencinia, 272.
Valkeria, 567.
Vallisia, 235.

Valvata, 361, 377, 378,

380, 395, 399.
Valves of shell, 324.
Valvulina, 13.
Vampyrella, 19.
Vanadis, 479.
Varices, 361 ; of shell,

361.

Vascular lamella, 112.
Vas deferens, 217.
Vela of Argonaut, 420.
Velarium, 157.
Velella, 144.
Veliger larva, 323 ; of

Gastropoda, 382.
Velum, 109, 299, 342.
Velutina, 398.
Veneracea, 348.
Venerupis, 348.
Ventral in Actinaria

Alcyonaria, 177, 184 ;

in Cestoda, 247 ; cirri,

49 ; Nematoda, 276 ;

Pennatulacea, 180.
Venus, 333, 348.
Venus' girdle (Cestus),

208.

Verania, 445.
Veretillum, 181.
Vermetus, 357, 361, 362,

380, 367, 386, 399.
Vermiculus, 509.
Vermilia, 491.
Verneuilina, 13.
Versura, 168.
Vertebralina, 13.
Vertigo, 416.
Vesicula seminalis, 217.
Vesicularia, 567.
Vetrovermis, 509.
Vetulina, 95.
Vexillum, 208.
Vibrac. = vibracula.
Vibracula, 553.
Victorella, 556, 567.
Villogorgia, 182.
Vincularia, 565.
Virgularia, 181.
Virgulina, 13.
Visceral commissure,

319, 362 ; sac, 319.
Vitellarium, 209.
Vitello-intestinal, 226.
Vitrina, 380, 416.
Voeringia, 179.
Vogtia, 150.
Voluta, 397.
Volvox, 29, 32.
Volvula, 406.
Vomerula, 96.
Vortex, 211, 220.

Vorticella, 38, 40, 41,51.
Vorticeros, 220.
Vorticlava, 130.
Vosmaeropsis, 90.
Vulsella, 345, 346.

>

Wageneria, 256.
Waldheimia, 576. 577,

585.

Wall, coral, 192.
Walteria, 92.
Webbina, 13.
Weberella, 97.
Wentle-trap, 398.
Wheel animalcule, 299.
Whelk, 396.
Willetta, 134.
Willia, 134.
Wing shell, 399.
Winter egg, 217, 304.
Worm shell, 399.
Wrightella, 182.
Wrightia, 130.

Xenia, 178.
Xenophora, 398.
Xenospongia, 97.
Xiphosphaera, 23.

Yoesia, 96.
Yoldia, 328, 345.
Yungia, 213, 223.

Z. /. w. ^.=Zeitschrift
fiir wissenschaftliche
Zoologie.

Zanclea, 131.

Zoantharia, 183.

Zoantheae, 189.

Zoanthus, 189.

Zoariiim, 556.

Zonites, 386, 416.

Zonephyra, 167.

Zoobotryon, 552, 567.

Zooecium, 549 ; primary,
560.

Zoopilus, 196.

Zoospore, 7.

Zoothamnium, 43, 51.

Zooxanthella, 21.

Zospeum, 416.

Zygartus, 23.

Zygobranchiate, 394.

Zygocanna, 134.

Zygocannota. 134.

Zygocannula, 134.

Zygocircus, 23.

Zygodactyla, 134.

Zygoneury, 365, W*.

Zygote, 27.

Zygote-nucleus, 4 4 .

PLYMOUTH :

WILLIAM BRENDON AND SOX,
PRINTERS.

KBTUR* T0 ,£2ff JS, BORROWED

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re subject to immediate recall.

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