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Gornell University Library
Ithaca, New York

COMSTOCK MEMORIAL LIBRARY
ENTOMOLOGY

BOUGHT WITH THE INCOME OF A FUND
GIVEN BY THE STUDENTS OF

JOHN HENRY COMSTOCK
PROFESSOR OF ENTOMOLOGY

1915

ornell University Libra’

olin,anx

Cornell University

Library

The original of this book is in
the Cornell University Library.

There are no known copyright restrictions in
the United States on the use of the text.

http://www.archive.org/details/cu3 1924031715752

A MANUAL OF ZOOLOGY

MANUAL OF ZOOLOGY

BY

T. JEFFREY PARKER, D.Sc., F.R.S.

PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF OTAGO,
DUNEDIN, N.Z.

AND

WILLIAM A. HASWELL, M.A., D.Sc., F.R.S.

PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF SYDNEY, N.S.W.

REVISED AND ADAPTED FOR THE USE OF AMERICAN
SCHOOLS AND COLLEGES

New Work
THE MACMILLAN COMPANY
LONDON: MACMILLAN & CO,, Lp.
1900

All rights reserved

CopyRIGHT, 1900,

By THE MACMILLAN COMPANY.

Norbsood Press
J. S. Cushing & Co. — Berwick & Smith
Norwood Mass. U.S.A.

PREPACE

In planning the present work the aim of the authors has
been to provide a manual embodying a course of study
adapted to the requirements of the student chiefly in higher
classes of schools, and to some extent in junior classes of
universities. To make this, within the necessarily narrow
limits of space imposed, anything more than a bare synopsis,
it has been necessary to restrict the extent of the ground
covered. This has been done (1) by leaving out altogether
certain classes of existing animals; (2) by omitting all de-
scriptions of extinct groups ; (3) by dealing only very briefly
with embryology. Opinions must differ as to the best selec-
tion of groups for an elementary manual of this kind. But
broadly, there can, it has appeared to us, be little doubt that
what should be omitted, or only briefly dealt with, are the
groups of rare occurrence and uncertain relationships, the
greater part of the space being devoted to the more familiar
representatives of the large phyla.

A course of laboratory and museum instruction, supple-
mented by work in the field and on the seashore, is abso-
lutely necessary in order that any sound knowledge of

Vv

vi PREFACE

zoology may be attained. The present manual does not
provide such instruction, but is intended to be used in
association with it, and the examples selected for de-
scription are such as may under most circumstances be
readily obtained.

The general plan is similar to that followed in the Zext
Book of Zoology by the same authors, but the restricted
space has necessitated considerable modifications. We
have not adopted the method, followed in various recent
manuals, of beginning with one of the larger Invertebrata
or with a vertebrate, and working from that upwards and
downwards. The reasons given for such a mode of treat-
ment we understand to be that if we begin with the simplest
animals, the Protozoa, we discourage and embarrass the
beginner by introducing him at once into a world entirely
new to him, requiring him at the same time to learn the use
of an entirely unfamiliar instrument the microscope. But in
our opinion, the difficulty is much less than is alleged by the
advocates of the alternative method, and the advantage of
presenting the facts at the outset in a natural and logical
order by far outweigh any such disadvantages. We are con-
vinced that any general acquaintance which the student may
possess beforehand with a rabbit or a crayfish will be of little
real value to him when he begins to take up seriously the
study of its structure. Moreover an elementary knowledge
of the use of the microscope is absolutely essential to any
adequate study of Zoology as an intellectual discipline, and

this difficulty, such as it is, may as well be met first as last.

PREFACE vii

Owing to the lamented death of Professor T. Jeffrey
Parker, at a time when but little progress had been made
with this work, his actual share in it has been but slight :
but as it was planned between us, and the earlier parts had
the advantage of his revision, and more especially as it owes
a great deal to his work in the Zext-Book it has been
thought right to let it appear under our joint names as origi-
nally intended.

I have to express very great indebtedness to Professor W.
Newton Parker for the pains he has taken in revising the
proof-sheets and for many valuable suggestions which he has
made during the progress of the work.

Wiitiiam A. HASWELL.

PREFACE TO THE AMERICAN EDITION

Tuts American edition of Parker and Haswell’s useful
and concise “ Manual of Zoology” has been adapted for the
use of American schools. Common American forms closely
similar to the European or Australasian ones described in
the English edition, have been mentioned, so that the
student can use the book in examining the allied typical
forms from his own country. In the majority of cases the
European species differ only in trivial characteristics, so
that one general description will answer for both.

In a very few cases the American editor has revised and
corrected views or statements not believed to be correct.
For example, few, if any, American zoologists would regard
Limulus as an undoubted Arachnidan.

A few additional American animals have been referred to
and figured, while a few cuts not reproduced in the English
edition have been copied from Parker and Haswell’s
“ Text-book of Zoology,” and also from Sedgwick’s “'Text-

book of Zoology.”

CONTENTS

PREFACE TO THE ENGLISH EDITION .
PREFACE TO THE AMERICAN EDITION
List oF ILLUSTRATIONS

INTRODUCTION -
Definition of zoology
Binomial nomenclature
Individual variations
Hybrids
Definition of mixploleey
Definition of histology .
Definition of eee
Classification
Phyla
Organic evolution
Genealogical tree
Paleontology
Fossils .
Succession of life in time
Phylogeny 5 A - :
Distribution of animals, in space a in time
The plankton
The necton .
The benthos
Definition of a fauna
Zoo-geographical regions
Definition of physiology :
Definition of ethology or binomics

xi

xvil

xii CONTENTS

SECTION I

PAGE

PHYLUM PROTOZOA. ; ‘ , ‘ : ip . <4
Class 1. The Rhizopoda : é ‘ : 3 A - 14
Example of the Class— Amba proteus . 5 a . 4

Class 2. The Mastigophora ; 5 e w 34
Example of the Class — Luglena vir les £ zi : 3 34

Class 3. TheInfusoria . : ? : » 45
Example of the Class Parana clum 5 asain j » 45

Class 4. The Sporozoa. : : ; 3 : he G55
Example of the Class — Afonocystis agilis . ; ‘ » 55

SECTION II

THE METAZOA . : : . F . ‘ : - 59
Oosperm or egg. ‘ . ; 3 ‘ x é » $59
Male cell or sperm . : ; . ‘ . : 2 60
Fertilisation ; : : % : ; A - 60
Segmentation of the oosperm ‘ , 5 : é - 60
Germinal layers. : é F ‘ : . é ~ 162
Tissues, epithelium : : : : ; é : “ 63
Glands, ducts . 4 ‘ ‘ ‘ : ‘ j x 63
Connective tissues ‘ : 5 P : ‘ ‘ ~ “65
Fibrous tissue : ; f % 5 2 ; = i605

Fat x: : : - , 5 , ; : : - 65
Cartilage. : ‘ : , : : . ‘ - 66

Bone. , i a ‘ ‘ z F ‘ f s “66
Muscular tissue. ‘ : P F z re ‘5 : 6
Nerve tissue, ganglia, nerves : é 7 , ‘ . 66
Organs : : ‘ a é ‘ A - 66
Exoskeleton , 5 ‘ “ : 3 ‘ 2 OF
Endoskeleton ; ‘ : ‘ é 5 ‘ é a 167
Organs of digestion —. fi : : : : ‘ « 68
Organs of respiration . ‘ : ‘ ‘ : j - 40
The blood . - , 7 3 % ‘ Fa . 2 70
Blood vascular system . P e 5 é . s FO
Heart . ; é ‘ ‘ 4 . ‘é i ‘ 71

Organs of excretion ‘i ‘ 4 ‘ ‘ é : . #1

CONTENTS

The brain

Reproduction

The phyla of the gael iloeiiowe
Tabular view of the phyla

SECTION III

PHYLUM PORIFERA . °
Example of the Phiylim anil creat Sees Rhesus

SECTION IV

PHYLUM CC@LENTERATA
Class 1. The Hydrozoa
Example of the Class — Odelia .
Class 2. The Scyphozoa
Example of the Class— Aurelia aurita
Class 3. The Actinozoa ‘
Example of the Class — Zeadlia crassicornis
Class 4. The Ctenophora . :
Example of the Class — Hormzphora oe .

SECTION V

PHYLUM PLATYHELMINTHES : ‘ : : :
Class 1. The Trematoda : :
Example of the Class — Distomum tepaticun :
Class 2. The Turbellaria .
Example of the Class — Planarta torva
Class 3. The Cestoda
Example of the Class — Tenia siibicm
Class 4. The Nemertinea .
Example of the Class — 7e¢rastemma

SECTION VI

PuHyLuM NEMATHELMINTHES
Class. The Nematoda
Example of the Class — Ascaris uk eee

xili

129
129
137
138

138
145
145

149
149
149

xiv CONTENTS

SECTION VII

PHYLUM ECHINODERMATA .
Class 1. The Asteroidea
Example of the Class — Asterias gules as
Class 2. The Ophiuroidea

Example of the Class — Ophioglypha een tosa

Class 3. The Echinoidea

Example of the Class — S¢r a ene otus
Class 4. The Holothuroidea

Example of the Class — Holothuria diilis:
Class 5. The Crinoidea

Example of the Class — Antedon

SECTION VIII

ROTIFERA, POLYZOA, AND BRACHIOPODA
Class 1. Rotifera ;
Example of the Class — Br eas pines
Class 2. Polyzoa 3
Example of the Class — Buse questions 1a
Class 3. Brachiopoda

Example of the Gis — Ironia neces :

SECTION IX

PHYLUM ANNULATA
Class 1. The Chetopoda ‘
Example of the Class — Werezs Liniek wit.
Class 2. The Hirudinea 7
Example of the Class — A7rudo alm

SECTION X

PHYLUM ARTHROPODA
Class 1. The Crustacea :
Example of the Class — pe me
Class 2. The Onychophora
Example of the Class — Peripatus

PAGE
157
157
157
169
169
170
170
173
173
174
174

178
178
178
181
181
184
184

188
188
189
203
203

212
213
213
236
236

CONTENTS

Class 3. The Myriapoda

Example of the Class — Siolapendea morsitans .

Class 4. The Insecta :
Example of the Class — Per eee americana
Class 5. The Arachnida
Example of the Class — Scorpio

SECTION XI

PHYLUM MOLLuscA : ;
Class 1. The Pelecypoda . :
Example of the Class — Anodonta cygnea
Class 2, The Amphineura
Byaraple of the Class — Chiton ner
Class 3. The Gastropoda :
Example of the Class — Helix nemor ne ;
Class 4. The Cephalopoda
Example of the Class — Maudzlus Yonditte us

SECTION XII

PHYLUM CHORDATA .
Subphylum 1. The Adetochorda
Example of the Sulphylent—— Belenz nes
Subphylum 2. The Urochorda . .
Example of the Subphylum — Asezdia
Subphylum 3. The Vertebrata .

Examples of the Subphylum — Amphioxus, pe omyzon,

Pisces, etc. : 5
Division A. The Acrania .

Example of the Division — Appiee us eee

Division B. The Craniata

Examples of the Division, the dsatei, fiesea: i rabbit :

Class 1. Cyclostomi .

Example of the Class — Petromyzon marinus .

Class 2. Pisces .

Examples of the Class — shares; perc: ai ine fishes

XV

PAGE
239
239
241
241
254
254

xvi

CONTENTS

Subclass 1. Elasmobranchii
Example of the Subclass — Scy///um and ae Jus
Subclass 2. Holocephali (omitted)
Subclass 3. Teleostomi
Example of the Subclass — Sabovofex 70
Subclass 4. Dipnoi
Example of the Subclass — ee Z
Class 3. Amphibia : :
Example of the Class— Rana temporaria
Class 4. Reptilia 3
Examples of the Class — Leads, ‘tes, eeendile
Class 5. Aves
Example of the Class — Cited in
Class 6. Mammalia : : :
Example of the Class — Lepus cuniculus .

PAGE
366
366
394
394
395
405
405
407
408
433
434
456
457
491
491

=
e

ain en |
© ONAN PW NH HOW ON AUN PW DN

wRHRKNKANBKDN
SevyvankdsP 8&8

LIST OF ILLUSTRATIONS

. Amceba proteus

. Amceba polypodia

. Quadrula, Hyalosphenia, toneella. Didiugin

. Forms of Foraminifera . ‘

. Shells of Foraminifera .

. Actinophrys sol

. Actinosphzerium eichhornii

. Forms of Heliozoa

. Liteocircus annularis

. Actinomma asteracanthion

. Collozoum inerme .

. Euglena viridis

. Forms of Mastigophora

. Forms of Choanoflagellata

. Forms of Dinoflagellata

. Noctiluca miliaris .

. Volvox globator

. Paramcecium caudatum

. Forms of Ciliata

. Forms of Tentaculifera .

. Forms of Ciliata

. Vorticella

. Monocystis agilis .

. Gregarina

. Ovum of a sea- ecebie <
. Diagram of maturation and fertilization ist ovum
. Segmentation of the oosperm

. Forms of epithelium F
. Diagram illustrating the structure f sands ;

xvii

PAGE

xvill LIST OF ILLUSTRATIONS

Wo Os WwW
Ona Am SW N

5W WW WW W

bs
Ke)

o 5

Bones of arm with biceps muscle

. Viscera of male frog

. Hydra

. Sycon ciliatum

. Sycon gelatinosum :

. Sycon gelatinosum, magnilied

. Sycon gelatinosum, transverse section

. Ascetta primordialis

. Section of Spongilla

. Skeleton of sponges

. Sponge spicules

. Obelia colony

2. Nematocysts of Iydr

. Dissection of ene :
. Development of Laomedea and iediendvilen
. Structure of Hydra

. Petasus and Glossocodon

. Bougainvillea ramosa

. Physalia

. Physalia arethusa

. Halistemma tergestinum

. Aurelia aurita, partly dissected

. Aurelia aurita, development

. Tessera princeps

. Tealia crassicornis

. Sea-anemone, in sections

. Common sea-anemone

. Corallium rubrum .

. Aleyonium palmatum

. Tubipora musica

. Pennatula sulcata .

. Flabellum curvatum

. Astreea pallida :
. Dendrophyliia nigrescens and } Ncdrersaxe: aspera
. Cancrisocia on back of a crab ; S

. Hormiphora plumosa F ;

6. Hormiphora plumosa, section of a tentacle

. Idyia roseola .

LIST OF ILLUSTRATIONS

. Distomum hepaticum, natural size

. Distomum hepaticum, anatomy

. Distomum hepaticum, development :

. Trematodes: Amphistomum and Homalogaster .

. Structure of a triclad turbellarian

. Planaria polychroa

. Tzenia solium : :

. Teenia solium, head magniued

. Tenia solium, proglottis

. Development of tape-worm : : :
. Cyst of Tzenia echinococcus with dueiee: -cyst sa scolices
. Diagram of organs of a Nemertine. .

. Tetrastemma, structure

. Ascaris lumbricoides :

. Ascaris lumbricoides, dissection of papal

. Diagram of nervous system of Nematoda :

. Ascaris lumbricoides, posterior end of male dissected .

. Trichina spiralis . é

. Starfish, showing tube feet

. Starfish, vertical section through an arm

. Starfish, diagrammatic sections

. Asterias rubens, digestive system .

. Ambulacral systems of a starfish .

. Anthenea, dorsal surface

. Anthenea, ventral surface

. Ophioglypha lacertosa .

. Strongylocentrotus

. Corona of sea-urchin :

. Apical systems of plates of sea- sitchin a

. Cucumaria planci

. Antedon :

. Metacrinus interruptus

. Brachionus rubens

IOI.
102.
103.
104.
105.

Bugula avicularia

Plumatella

Pedicellina . :

Magellania flavescens . : A
Magellania lenticularis, sagittal section

xIK

PAGE
130
131
135
136
137
138
139
140
141
142
144
146
147
150
ISI
152
153
155
158
161
164
165
166
167
168
169
171
172
172
174
175
177
179
182
183
184
185
186

XX

LIST OF ILLUSTRATIONS

5. Nereis dumerilii, natural size

. Nereis dumerilii, parapodium

8. Nereis dumerilii, set .

. Nereis dumerilii, anatomy

. Nereis dumerilii, transverse section

. Section through the eye of Nereis

. Brain and connecting nerves of Nereis

3. Serpulz in their tubes .

Trochosphere of Eupomatus

. Lumbricus agricola

. Lumbricus, sete .

. Hirudo medicinalis i

. Head of Hirudo medicinalis, showing the aie e jaws
. Head of Hirudo quinquestriata

20. Nephridium of the medicinal leech

Transverse section of Hirudo

2. Diagram of blood-channels of leech

23. Astacus fluviatilis

. Appendages of Astacus :
. Astacus fluviatilis, dissection fan sia side
. Respiratory organs of Astacus fluviatilis

. Thorax of crayfish, transverse section

. Diagram of the circulation in the crayfish

. Nervous system of Astacus fluviatilis

. Reproductive organs of Astacus fluviatilis

. Cancer pagurus

. Pagurus bernhardus

. Apus glacialis

. Development of Apus .

5. Cyclops and Calocalanus

. Lepas anatifera

. Peripatus capensis :

8. Peripatus capensis, head, cte.

. Internal organs of Peripatus

. Scolopendra

. Periplaneta americana .

2. Mouth-parts of the cockroach

3. Pieris rape, larva, and pupa

FIG.

144.
145.
146.
147.
148.
149.
150.
51.
152.
153.
154.
155.
156.
157.
158.
159.
160.
161.
162.
163.
164.
165.
166.
167.
168.
169.
170.
171.
172.
173.
174.
175.
176.
177.
178.
179.
180.
181.

LIST OF ILLUSTRATIONS

Carpet beetle, larva, and pupa

Culex and larva

Internal organs of ecloueh

Periplaneta, its tracheal system

Periplaneta, nervous system

Honey bee, queen, worker, and drone

Red ant, male, worker, and female
Euscorpio ,

Scorpion, ventral side .

Scorpion, internal organs

Epeira diadema

Cattle tick

Itch mite :

Limulus, ventral view .
Anodonta cygnea, entire animal .
Anodonta cygnea, right valve, and animal
Anodonta, section of shell and mantle
Anodonta cygnea, animal ;
Anodonta cygnea, dissection from left side :
Anodonta cygnea, sections of gills
Anodonta, diagram of circulatory system
Anodonta, embryo and glochidium

Mytilus edulis

Teredo navalis

Chiton spinosus

Chiton, ventral view

Chiton, nephridial and eehital systems
Helix nemoralis

Triton nodiferus, shell x
Triton nodiferus, median section of shell
Solarium perspectivum, under side

Terebra oculata, shell .

Cypreea moneta, animal eepanded in its shell
Doris tuberculata

Shell-bearing Pteropoda

Patella vulgata, animal, ventral view

Limax, lung-cavity, etc.

Triton nodiferus . : - . . .

xxi

xxii

TiG.

182.
183. }
184.
185.
186.
187.
188.
189.
190.
gl.
192.
193.
194.
195.
196.
197.
198.
199.
200.
201.
202.
203.
204.
205.
200.
207.
208,
209.
210.
211,
212.

213

214.
215.
216.
217.
218.
219.

LIST OF ILLUSTRATIONS

Sepia cultrata

Nautilus pompilius

Nautilus pompilius, section of ell
Spirula peronii

Sepia cultrata, shell

Loligo vulgaris

Argonauta argo

Chromatophore of Sepia

Sepia cultrata, dissected

Nautilus pompilius, anatomy

Sepia officinalis, jaws

Sepia officinalis, enteric canal
Nautilus pompilius, oral surface of male aad fanate

Balanoglossus

Balanoglossus, diagrammatic Sanaa section of anterior end .

Ascidia

Ascidia : ‘

Ascidia, diagram of ieee section

Ascidia mammillata, larva :
Diagram of metamorphosis of larva into iced Aasidign
Botryllus violaceus 7 P
Amphioxus lanceolatus, venti and site view
Amphioxus, diagram of anatomy .

Amphioxus lanceolatus, sections .

Dogfish, fins, etc.

Lacerta viridis

Lepus cuniculus, lateral view ahcbelien with mane at boay a

Scyllium, vertebrae
Lizard, vertebriv of
Lepus cuniculus
Scyllium canicula

. Lacerta agilis, three views of eealt

Fore and hind limbs of vertebrate, diagram
Tooth, longitudinal section, semi-diagrammatic
Scyllium canicula, dissection :
Lacerta agilis, viscera in their natural selaend
Circulation of a fish, diagram

Scyllium canicula, brain, dorsal view

LIST OF ILLUSTRATIONS

. Eye of man, diagrammatic horizontal section
. Petromyzon marinus

. Myxine glutinosa, head

. Petromyzon marinus

. Scyllium canicula, side view of skull

. Scyllium, pectoral arch

. Scyllium canicula, dissection

. Diagram of the vascular system of a fish

. Scyllium catulus .

. Dogfish, egg-case

. Scyllium, embryo, with silts: etc.

. Lamna cornubica

. European sting-ray (imloghas setae

. Skeleton of Urolophus testaceus .

. Heptanchus, side view of skull

. Salmo fario, fins, etc. ‘
. Salmo fario, caudal end of vertebral alia

. Pleuronectes cynoglossus

. Ctenoid and ganoid scales

. Polypterus birchir

. Skull of sturgeon

. Salmo fario, entire skull, left sae)

2. Premaxille of Sargus .

. Hippocampus (sea-horse)

. Ceratodus fosteri

. Ceratodus fosteri, anterior nortan of sikcicton
. Rana temporaria

. Rana temporaria, skeleton

. Rana temporaria, skull, different views

. Rana esculenta, shoulder girdle

. Rana esculenta, pelvic girdle from right re
. Rana temporaria, dissection from left side

2. Rana temporaria, heart with cavities laid open
. Rana temporaria, arterial system, etc. .

. Rana temporaria, venous system, etc.

. Rana esculenta, brain from above and below
. Rana esculenta, urinogenital organs of male .
. Rana esculenta, urinogenital organs of female

xxiii

PAGE
357
361
362
363
371
373
376
378
382
385
386
387
388
399
391
395
397
398
399
399
400
4ol
402
404
495
406
409
412
413
415
416
417
420
421
424
426
428
429

XXIV

LIST OF ILLUSTRATIONS

. Rana temporaria, stages in life-history

. Salamandra maculosa .

. Siren lacertina

. Pygopus lepidopus

. Hatteria punctata

. Grecian tortoise, Testudo graeca

. Skeleton of crocodile

. Cistudo lutaria

. Chelone midas

. Skull of rattlesnake

. Pectoral arch and sternum of eens ails

. Heart of monitor, Varanus .

. Brain of alligator, from above ‘

. Pineal eye of Hatteria punctata, section

. Poison apparatus of rattlesnake :
. Columba livia, diagram with most of feathers dese cuad
. Columba livia, feather .

. Pterylosis of Columba livia

. Columba livia, bones of the trunk

. Columba livia, cervical vertebra

. Columba livia, sacrum of nestling

. Columba livia, skull of young

. Columba livia, hyoid apparatus

. Columba livia, bones of left wing a

. Columba livia, bones of left manus of nestling
. Columba livia, left innominate of nestling

. Columba livia, bones of left hind-limb

. Columba livia, part of left foot of embryo

. Columba livia, muscles of left wing

. Columba livia, dissection from right side

288. Heart of pigeon, dorsal aspect

. Columba livia, brain, different views

. Eye of pigeon

. Columba livia, right Tienbianens iseyenth e ear

> Columba livia, male urinogenital organs

. Columba livia, female urinogenital organs

. Feather of cassowary

. Wing of nestling of Opithecuwms sna of adit Antiers

469

471
472
473
475
478
479
480
481
482
482
484
486

LIST OF ILLUSTRATIONS

. Gallus bankiva, domestic fowl, egg at time of hatching

. Lepus cuniculus, side view of skeleton with outline of body
. Lepus cuniculus, atlas and axis

. Lepus cuniculus, skull, side, and ventral view

. Lepus cuniculus, shoulder girdle ‘

. Lepus cuniculus, distal end of fore-leg wade carpus

. Lepus cuniculus, innominate bones and sacrum .

. Lepus cuniculus, bones of hind foot

. Lepus cuniculus, lateral dissection of head, neck, and ee
. Lepus cuniculus, stomach, intestine, and liver, etc.

. Lepus cuniculus, heart, from right side

. Lepus cuniculus, the vascular system :

. Lepus cuniculus, larynx, ventral and dorsal views

. Lepus cuniculus, brain, dorsal and ventral view

. Lepus cuniculus, two dissections of brain

. Lepus cuniculus, longitudinal vertical section of ee

. Lepus cuniculus, urogenital organs : é :
. Lepus cuniculus, anterior end of vagina, with right uterus, etc.
. Duck-bill, Ornithorhynchus anatinus

. Spiny ant-eater, Echidna aculeata

. Virginian Opossum, Didelphys virginiana

. Dasyure, Dasyurus viverrinus

. Rock wallaby, Petrogale xanthopus

. Koala, Phascolarctos cinereus

. Unau, or two-toed sloth

. Tatu armadillo, Dasypus sexcinctus

. Scaly ant-eater, Manis pentadactyla

. Aard-vark, Orycteropus capensis .

. Killer, Orca gladiator .

. Section of upper jaw, with tele lites, of ‘Balenapen

. Harbor seal, Phoca vitulina .

. Bat, Synotus barbastellus

XXV

MANUAL OF ZOOLOGY

INTRODUCTION

Zoology, the branch of Natural History which deals with
animals, is one of the two subdivisions of the great science of
Biology, which takes cognizance of all organisms, or things
having-life, as distinguished from such lifeless natural objects
as rocks and minerals. The second of the two subdivisions
of Biology is Botany, which deals with plants.

The subject-matter of Zoology, then, is furnished by the
animals which inhabit the land-surface, the air, and the
salt and fresh waters of the globe; the aim of the science
is to find out all that can be known of these animals,
their structure, their habits, their mutual relationships, their
origin.

The first step in the study of Zoology is the recognition
of the obvious fact that the innumerable individual animals
known to us may be grouped into what are called species,
the members of which resemble one another so closely that
to know one is to know all. The following example may
serve to give the reader a fairly accurate notion of what
zoologists understand by species, and of the method of
naming species which has been in use since the time of the
great Swedish naturalist Linnzeus.

B I

2 MANUAL OF ZOOLOGY

The domestic cat, the European wild cat, the ocelot, the
leopard, the tiger, and the lion are animals which agree with
one another in the general features of their organisation —
in the number and form of their bones and teeth, in the
possession of retractile claws, and in the position and
characters of their internal organs. No one can fail to
see that these animals, in spite of differences of size, colour,
markings, etc., are all, in the broad sense of the word,
“cats.” This is expressed in the language of systematic
Zoology by saying that they are so many species of a single
genus.

According to the system of dnomial nomenclature intro-
duced by Linneus, each kind of animal receives two names
—one the generic name, common to all species of the
genus; the other the specific name, peculiar to the species
in question. Both generic and specific names are Latin in
form, and are commonly Latin or Greek in origin, although
frequently modern names of persons or places, with Latinised
terminations, are employed. In giving the name of an ani-
mal, the generic name is always placed first, and is written
with a capital letter, the specific name following it, and
being written, as a rule, with a small letter. For instance,
to take the examples already referred to, the domestic cat is
called Fehs domestica, the European wild cat / cazus, the
leopard F. pardus, the tiger /. “gris, the lion & “o. Thus
the systematic name of an animal is something more than a
mere appellation, since it indicates the affinity of the species
with other members of the same genus: to name an animal
is, in fact, to classify it.

It is a matter of common observation that no two indi-
viduals of a species are ever exactly alike: two tabby cats,
for instance, however they may resemble one another in the
general characters of their colour and markings, invariably

INTRODUCTION 3

present differences in detail by which they can be readily
distinguished. Jndividual variations of this kind are of
universal occurrence. Moreover, it often happens that
the members of a species are divisible into groups distin-
guishable by fairly constant characters: among domestic
cats, for instance, we find white, black, tabby, gray, and tor-
toiseshell cats, besides the large long-haired Persian breed,
and the tailless Manx cat. All these are distinguished as
varieties of the single species, Fes domestica.

It is often difficult to decide whether two kinds of ani-
mals should be considered as distinct species or as varieties
of a single species, and no universal rule can be given for
determining this point. Among the higher animals mutual
fertility is a fair practical test, the varieties of a species
usually breeding freely with one another and producing fer-
tile offspring, while distinct species either do not breed
together or produce infertile Ayd77ds or mules. Compare,
for instance, the fertile mongrels produced by the union of
the various breeds of domestic dog with the infertile mule
produced by the union of the horse and ass. But this rule
is not without exception, and in the case of wild animals is,
more often than not, impossible of application: failing it,
the only criterion of a “good species” is usually the pres-
ence of constant differences from allied species. Suppose,
for instance, that a naturalist receives for description a
number of skins of wild cats, and finds, after an accurate
examination, that in some specimens the tail is two-thirds
the length of the body and the skin of a uniform reddish
tint with a few markings on the head, while in the rest the
tail is nearly half as long as the body and the skin tawny
with black stripes. If there are no intermediate grada-
tions between these two sets of individuals, they will be
placed without hesitation in distinct species: if, on the

4 MANUAL OF ZOOLOGY

other hand, there is a complete series of gradations between
them, they will be considered to form a single variable
species.

As, therefore, animals have to be distinguished from one
another largely by structural characters, it is evident that
the foundations of a scientific Zoology must be laid in
Morphology, the branch of science which deals with form
and structure. Morphology may be said to begin with an
accurate examination of the external characters ; the divi-
sions of the body, the number and position of the limbs,
the characters of the skin, the positions and relations of the
mouth, eyes, ears, and other important structures. Next the
internal structure has to be studied, the precise form, posi-
tion, etc., of the various organs, such as brain, heart, and
stomach being made out: this branch of morphology is
distinguished as Anatomy. And, lastly, the various parts
must be examined by the aid of the microscope, and their
minute structure, or Histology, accurately determined. It
is only when we have a fairly comprehensive knowledge of
these three aspects of a given animal — its external charac-
ters, its rough anatomy, and its histology — that we can with
some degree of safety assign it to its proper position among
its fellows.

An accurate knowledge of the structure of an animal in
its adult condition is not, however, all-sufficient. Nothing
has been made more abundantly clear by the researches of
the last half-century than that the results of anatomy and
histology must be checked, and if necessary corrected, by
Embryology — ¢.c. by the study of the changes undergone
by animals in their development from the egg to the adult
condition. A striking instance is afforded by the common
barnacles which grow in great numbers on ships’ bottoms,
piers, etc. The older zoologists, such as Linnzus, grouped

INTRODUCTION 5

these creatures, along with snails, mussels, and the like, in
the group Mollusca, and even the great anatomical skill of
Cuvier failed to show their true position, which was made out
only when Vaughan Thompson, about fifty years ago, proved,
from a study of the newly hatched young, that their proper
place is among the Crustacea, in company with crabs,
shrimps, and water-fleas.

Given a sound knowledge of the anatomy, histology, and
embryology of animals, their Classification may be attempted
— that is, we may proceed to arrange them in groups and
sub-groups, each capable of accurate definition.

The general method of classification employed by zoolo-
gists is that introduced by Linnzeus, and may be illustrated
by reference to the group of cats which we have already
used in the explanation of the terms genus, species, and
variety.

We have seen that the various kinds of true cat — domes-
tic cat, lion, tiger, etc. — together constitute the genus
felis. Now there is one member of the cat-tribe, the
cheetah, or hunting leopard, which differs from all its allies
in having imperfectly retractile claws and certain peculiari-
ties in its teeth. It is therefore placed in a distinct genus,
Cynelurus, to mark the fact that the differences separating
it from any species of Felis are of a more fundamental char-
acter than those separating the species of Felis from one
another.

The nearest allies of the cats are the hyenas, but the
presence of additional teeth and non-retractile claws — to
mention only two points— makes the interval between
hyenas and the two genera of cats far greater than that
between Felis and Cynzlurus. The varying degree of differ-
ence is expressed in classification by placing the hyenas in
a separate family, the yenide, while Felis and Cynzelurus

6 MANUAL OF ZOOLOGY

are placed together in the family Ae@de. Similarly the
civets and mongooses form the family Vverrid@ , the dogs,
wolves, jackals, foxes, etc., the family Camde,; bears, the
family Ursid¢@,; and so on.

All the foregoing animals have sharp teeth adapted to a
flesh diet, and their toes are armed with claws. They there-
fore differ fundamentally from such animals as sheep, deer,
pigs, and horses, which have flat teeth adapted for grinding
vegetable food, and hoofed feet. The differences here are
obviously far greater than those between any two of the
families mentioned above, and are emphasised by placing
the flesh-eater in the order Carnivora, the hoofed animals
in the order Ungulata. In the same way gnawing animals,
such as rats, mice, and beavers, form the order Rodentia ;
pouched animals, such as kangaroos and opossums, the
order Marsupiaha,; and so on.

Carnivora, Ungulata, Rodentia, Marsupialia, etc., although
differing from one another in many important respects, agree
in the possession of a hairy skin and in the fact that they all
suckle their young. They thus differ from birds, which have
a covering of feathers, and hatch their young from eggs.
The differences here are considerably more important than
those between the orders of quadrupeds referred to, and are
expressed by placing the latter in the class A/ammadia, while
birds constitute the class Aves. In the same way the scaly,
cold-blooded lizards, snakes, tortoises, etc., form the class
keptia,; the slimy-skinned, scaleless frogs, toads, and sala-
manders the class Amphiéia ; and the finned, water-breathing
fishes the class Pisces.

Mammals, birds, reptiles, amphibians, and fishes all agree
with one another in the possession of red blood and an inter-
nal skeleton — an important part of which is the backbone
or vertebral column —and in never having more than two

INTRODUCTION 7

pairs of limbs. They thus differ in some of the most funda-
mental features of their organisation from such animals as
crabs, insects, scorpions, and centipedes, which have colour-
less blood, a jointed external skeleton, and numerous limbs.
These differences—far greater than those between classes
—are expressed by placing the backboned animals in
the phylum or sub-kingdom Chordaza, the many-legged
armoured forms in the phylum Arthropoda. Similarly, soft-
bodied animals with shells, such as oysters and snails, form
the phylum JAZo/usca, polypes and jellyfishes the phylum
Celenterata. And, finally, the various phyla recognised by
zoologists together constitute the kingdom Animalia.

Thus the animal kingdom is divided into phyla, the phyla
into classes, the classes into orders, the orders into families,
the families into genera, and the genera into species, while
the species themselves are assemblages of individual animals
agreeing with one another in certain constant characters. It
will be seen that the zz@zzdva/ is the only term in the series
which has a real existence: all the others are mere groups
formed, more or less arbitrarily, by man.

To return to the animal originally selected as an example,
it will be seen that the zoological position of the domestic
cat is expressed as follows : —

Kingdom — ANIMALIA.
Phylum — Cuorparta.
Class — Mamata.
Order — CarRNIvoRA.
Family — Fehide.
Genus — Felis.
Species —F. domestica.

The object of systematic zoologists has always been to

8 MANUAL OF ZOOLOGY

find a natural as opposed to an artificial classification of
animals. Good instances of artificial classification are the
grouping of bats with birds on the ground that both possess
wings, and of whales with fishes on the ground that they both
possess fins and live in the water. An equally good example
of a natural classification is the grouping of both bats and
whales under the head of Mammalia because of their agree-
ment, in all essential points of anatomy, histology, and
embryology, with the hairy quadrupeds which form the bulk
of that class.

With the older zoologists the difficulty was to find some
general principle to guide them in their arrangement of
animals — some true criterion of classification. It was
believed by all but a few advanced thinkers that the in-
dividuals of each species of animal were descended from
a common ancestor, but that the original progenitor of each
species was totally unconnected with that of every other,
having, as Buffon puts it, “participated in the grace of a dis-
tinct act of creation.” ‘To take an instance: all wolves were
allowed to be descended from a pair of ancestral wolves, and
all jackals from a pair of ancestral jackals, but the original
pair in each case was supposed to have come into being by
a supernatural process of which no explanation could or
ought to be offered. Nevertheless it was obvious that a
jackal was far more like a wolf than either of them was like
a tiger, and that in a natural system of classification this fact
should be expressed by placing the wolf and jackal in one
family, the tiger in another.

All through the animal kingdom the same thing occurs:
no matter what group we take, we find the species com-
posing it resemble one another in varying degrees, or, as it
is sometimes expressed, have varying degrees of relationship
to one another. On the view that each species was sepa-

INTRODUCTION 9

rately created, the word relationship was used in a purely
metaphorical sense, as there could, of course, be no real
relationship between two groups of animals having a totally
independent origin. But it was assumed that creation had
taken place according to a certain scheme in the Divine
Mind, and that the various species had their place in this
scheme like the bits of glass in a mosaic. The problem of
classification was thus to discover the place of each species
in the pattern of the unknown design.

The point of view underwent a complete change when,
after the publication of Darwin’s Ovigin of Species in 1859
the Doctrine of Descent or of Organic Evolution came to
be generally accepted by biologists. A species is now
looked upon, not as an independent creation, but as having
been derived by anatural process of descent from some pre-
existing species, just as the various breeds of Domestic Fowl
are descended from the little jungle-fowl of India. On this
view the resemblances between species referred to above are
actually matters of relationship, and species are truly allied
to one another in varying degrees, since they are descended
from a common ancestor. Thus a natural classification
becomes a genealogical tree, and the problem of classifica-
tion is the tracing of its branches.

This, however, is a matter of extreme difficulty. Repre-
senting by a tree the whole of the animals which have ever
lived on the earth, those existing at the present day would
be figured by the topmost twigs, the trunk and main
branches representing extinct forms. Thus the task of
arranging animals according to their relationships would be
an almost hopeless one but from two circumstances: one,
that remains of many extinct forms have been preserved :
the other, that the series of changes undergone by an ani-
mal in its development from the egg often forms an epitome

Io MANUAL OF ZOOLOGY

of the changes by which, in the course of ages, it has been
evolved from an ancestral type. Evidence furnished by the
last-named circumstance is, of course, furnished by embry-
ology: the study of extinct animals constitutes a special
branch of morphology to which the name Paleontology is
applied.

The solid crust of the earth is composed of various kinds
of rocks divisible into two groups: (1) /gneous rocks, such
as granite and basalt, the structure of which is due to the
action of the internal heat of the globe, and which originate
below the surface and are not arranged in layers or strata ;
(2) Agueous or sedimentary rocks, which arise by the disin-
tegration, at the surface of the earth, of pre-existing rocks,
the fragments or débris being carried off by streams and
rivers and deposited at the bottom of lakes or seas. Being
formed in this way by the deposition of successive layers or
strata, the sedimentary rocks have a s¢ratified structure, the
lowest being in every case older than the more superficial
layers. The researches of geologists have shown that there
is a general order of succession of stratified rocks ; that they
may be divided into three great groups, each representing
an era of time of immense but unknown duration, and that
each group may be subdivided into more or fewer syséems
of rocks, each representing a lesser feviod of time.

Imbedded in these rocks are found the remains of various
extinct animals in the form of what are called fosse/s. In
the more recent rocks the resemblance of these to the hard
parts of existing animals is perfectly clear; we find shells
hardly differing from those we pick up on the beach, bones
easily recognisable as those of mammals, birds, or fishes,
and so on. But in the older rocks the fossils are in many
cases so different in character from the animals existing at
the present day as to be referable to no existing order. We

INTRODUCTION II

find birds with teeth, great aquatic reptiles as large as whales,
fishes, molluscs, Crustacea, etc., all of an entirely different
type from any now existing. We thus find that the former
were in many cases utterly unlike the present animal inhabi-
tants of the globe, and we arrive at the notion of a succession
of life in time, and are even able, in exceptionally favourable
circumstances, to trace back existing forms to their extinct
ancestors.

By combining the results of comparative morphology,
embryology, and palzontology we get a department of
Zoology called Phylogeny, the object of which is to trace
the pedigrees of the various groups. There are, however,
very few cases in which this can be done with any approach
to exactness ; most “ phylogenies ”’ are purely hypothetical,
and merely represent the views at which a particular zoolo-
gist has arrived after a more or less exhaustive study of the
group under discussion.

Animals may also be studied from the point of view of
Distribution. One aspect of this study is inseparable from
Paleontology, since it is obviously necessary to mention in
connection with a fossil the particular system or systems of
rocks in which it occurs: thus we distinguish geological
distribution or distribution in time.

The distribution of recent forms may be studied under
two aspects, their horizontal or geographical distribution,
and their vertical or bathymetrical distribution. To men-
tion the latter first, we find that some species exist only on
plains, others —hence called a/fine forms — on the higher
mountains ; that some marine shells, fishes, etc., always keep
near the shore (“/ora/ species), others live at great depths
(abyssal species), while others ( pe/agic species) swim on the
surface of the ocean. Among aquatic animals, moreover,
whether marine or fresh-water, three principal modes of life

12 MANUAL OF ZOOLOGY

are to be distinguished. There are animals such as jelly-
fishes, which float on or near the surface of the water, and
are carried about passively by currents; such forms are
included under the term Plankfon. Most fishes, whales, and
cuttle-fishes, on the other hand, are strong swimmers, and
are able to traverse the water at will in any direction ; they
together constitute the Meson. Finally, such animals as
crabs, oysters, sponges, zoophytes, etc., remain permanently
fixed to or creep over the surface of the bottom, and are
grouped together as the Bezthos.

Under the head of geographical distribution we have such
facts as the absence of all land-mammals, except bats in
New Zealand and the Polynesian Islands, the presence of
pouched Mammals, such as kangaroos and opossums, only
in some parts of America and in Australia and the adjacent
islands, the entire absence of finches in Australasia, and so
on. We find, in fact, that the fawna — 7c. the total animal
inhabitants — of a country is to a large extent independent
of climate, and that the faunze of adjacent countries often
differ widely. In fact, it is convenient in studying the geo-
graphical distribution of animals largely to ignore the ordi-
nary division into continents, and to divide the land-surface
of the globe into what are called z00-geographical regions.

There are still two departments of zoological science to
be mentioned. As it is impossible to have a right under-
standing of a machine without knowing something of the
purpose it is intended to serve, so the morphological study
of an animal is imperfect without some knowledge of its
Physiology, 7.e. of the functions performed by its various
parts, and the way in which they work together for the
welfare of the whole.

Not only may we study the action of a given animal’s
organs, but also the actions of the animal as a whole, its

INTRODUCTION 13

habits, its relations to other animals, whether as friends, as
enemies, or as prey, to the vegetable kingdom, and to its
physical surroundings, such as temperature, humidity, etc.
In a word, the whole question of the relation of the organism
to its exvronment gives us a final and most important
branch of Natural History which has been called Ethology
or Bionomics.

SECTION I.—PHYLUM PROTOZOA

1. THE RHIZOPODA

THE simplest members of the animal kingdom are for the
most part, too small to be visible without the aid of a micro-
scope, or at least so small as to appear to the unassisted eye
as extremely minute specks, not distinguishable, unless in
unusually active movement, from small particles of non-living
matter. Representatives of this class of simple minute ani-
mals are to be found living under a variety of different con-
ditions; they are abundant in fresh water, running or
stagnant, and they are equally numerous in the sea, while
they are also to be found living in the fluids of cavities in
the bodies of higher animals. An example which will serve
to illustrate some of the main features of the class is the
Proteus animalcule or Amoeba. Amceba (Fig. 1) is some-
times to be found by searching with the aid of the micro-
scope in water from stagnant pools. To the unpractised
beginner it is a difficult task to discriminate between the
microscopic particles of non-living matter which form the
main part of the sediment at the bottom of such a pool —
débris of animals, vegetable or mineral nature —and the
object of which he is in search. Numerous minute bodies
will doubtless be seen which their active movements among
the motionless particles show to be endowed with life. But

14

SECT. I PHYLUM PROTOZOA 5

Ameeba is not one of these. It is to be recognised as a
glassy-looking, irregularly shaped particle with a definite out-
line. From a particle of some crystalline mineral substance,
to which such a description would equally well apply,
Amceba would soon be distinguishable owing to the cir-
cumstance that it is constantly changing its shape.

This change is effected by the pushing out of projections
or processes, called pseudopods or pseudopodia ( psd), which

Fic. 1.—Ameba proteus, a living specimen. c. vac, contractile vacuole,
nu, nucleus; psd, pseudopods. (From Parker's Bzodogy, after Gruber.)
undergo various alterations of size and shape, and may be-
come withdrawn, other similar processes being developed
in their place. At the same time careful watching shows
that the Ameeba is also, with extreme slowness, changing its
position. ‘This it effects by a kind of streaming motion. A
‘projection forms itself on one side, and the entire substance
of the Amceba gradually streams into it; a fresh projec-
tion appears towards the same side, the streaming move-
ment is repeated, and, by a constant succession of such
movements, an extremely gradual locomotion, which it often
takes very close watching to detect, is brought about. In
these movements, it is to be noticed, the Amceba is influenced

16 MANUAL OF ZOOLOGY SECT.

to some extent by contact with other minute objects ; when
the processes come in contact with small grains of sand or
other similar particles, their movements are modified in such
a way that the Amceba, in its slow progress onwards, passes
on one side of them, so that it might be said to feel its way
among the solid particles in a drop of sediment.

Judging from the nature of the movements, we are obliged
to infer that the substance of which this remarkable object is
composed must be soft and semi-fluid, yet not miscible with
the water, and, therefore, preserving a sharp contour. These
and other characteristics to be mentioned subsequently
enable us to conclude that we have to do with the substance
of complex chemical composition termed protoplasm, which
constitutes the vital material of all living organisms whether
animals or plants. In Amceba the protoplasm is clearly dis-
tinguishable into two parts, an outer homogeneous, glassy-
looking layer completely enclosing a more granular internal
mass.

Examination of the Amceba with a fairly high power of the
microscope reveals the presence in its interior of two objects
which with a low power we should be likely to overlook. One
of these is a small rounded body of a homogeneous appear-
ance, which preserves its form during all the changes which
the Amceba as a whole undergoes. This is termed the
nucleus (Fig. 1, 2) ; it is enclosed in an extremely delicate
membrane, and consists of a protoplasmic material differing
from that which forms the main bulk of the Amceba in con-
taining a substance which refracts the light more strongly
and which has a stronger affinity for certain colouring
matters. The other minute object to be distinguished in the
interior appears as a clear rounded space (c¢. vac) in the
protoplasm. When this is watched it will be observed to
increase gradually in size till it reaches a maximum of, let us

I PHYLUM PROTOZOA 1]

say, a fifth of the total diameter of the Amceba, when by a
sudden contraction of its walls, it suddenly disappears, to
reappear presently and gradually grow again to its maxi-
mum size. This pulsating clear space is the contractile
vacuole.

By watching the Amceba carefully for some time we may
be enabled to observe that the movements of the proto-
plasm of the body not only effect locomotion, but are con-
nected also with the reception of certain foreign particles
of organic nature —z.e., either entire minute animals or
plants, or minute fragments of larger forms — which form the
Jood of the Amoeba, —into the interior of the protoplasm.
A process of the protoplasm is pressed against such a par-
ticle of food, which becomes sunk in the soft substance,
and passes gradually into the interior. Here it becomes
surrounded by a little globule of watery fluid, and by
degrees partially or wholly disappears; the part, if any,
which remains, subsequently passes outwards from the pro-
toplasm into the surrounding water. The matter which dis-
appears evidently mixes with the protoplasm and adds to its
bulk.

When food is abundant the Amceba increases in bulk —
more food being ingested than is required for simply main-
taining the size unaltered —and soon a remarkable change
takes place. The processes become withdrawn, and a fissure
appears dividing the Amceba into two parts (Fig. 2). This
fissure grows inwards, and the two parts become more and
more completely separated from one another, till eventually
the separation becomes complete, and we have two dis-
tinct Amcebe resulting from the division of the one. While
the protoplasm has been undergoing this division into two
halves the nucleus also divides, and each of the two new
Amcebee possesses a nucleus similar to the original one,

Cc

18 MANUAL OF ZOOLOGY SECT.

and developed from it by division. It is mainly by this
simple process of division into two, or dinary fission, as it is
called, that reproduction or multiplication takes place in the
Amceba.

Fic. 2.—Ameeba polypodia in successive phases of division. ‘The light spot is the
contractile vacuole; the dark the nucleus. (From Lang’s 7ext-Book, after
F. E. Schulze.)

Amceba thus consists of an undivided particle of proto-
plasm containing a nucleus. To such a particle the term
cell is applied. In higher groups the animal when fully
developed, consists of a number of such cells, usually differ-
ing in character in different parts ; and simple animals, such

i PHYLUM PROTOZOA 19

as Ameeba, in which the entire animal consists throughout
life of a single cell, are distinguished as wce//u/ar from the
multicellular form in which a number of cells are combined.
The whole of the great group or phylum of animals — the
Protozoa — to which Amceba belongs, are distinguished from
all the remaining groups of the animal kingdom — the
Metazoa —by their unicellular character.

Among the Protozoa a large number resemble Amceba in
the possession of pseudopodia or processes of the protoplasm.
The pseudopodia-bearing Protozoa constitute one of the great
divisions or c/asses into which the Protozoa are divided by
zoologists — the class known as the Rhizopoda. In only a
comparatively small proportion of the members of this class
have the pseudopodia the comparatively short and blunt
shape which they have in Amceba. All the Rhizopoda with
comparatively short and thick pseudopodia are grouped
together to form one of the leading divisions or orders of
Rhizopoda—the order Lobosa. Amceba is one of the
simplest of these. The largest among the near relatives of
Ameeba is Pe/omyxa, which may be as much as 8 mm. in
diameter, so that it is readily visible to the naked eye; its
pseudopodia are very short and broad, and, instead of a
single nucleus, it contains a large number as well as many
contractile vacuoles. Other Lobosa differ from Ameeba in
the presence of a shell or ¢es/ enclosing the protoplasm.
One of these is Diffugra (Fig. 3, D), which is very common
in fresh water. Difflugia has a flask-shaped test formed of
agglutinated sand-grains and other foreign particles. The
main bulk of the protoplasm is contained in the interior of
the shell, but comparatively long pseudopodia are capable of
being pushed out through the mouth of the flask. It pierces
the wall of the cells of Spirogyra, inserts its pseudopods, lift-
ing the entire cell-contents out and passing them into its

20 MANUAL OF ZOOLOGY SECT,

body within the shell (Stokes). An even commoner member
of the group is Arcela (Fig. 3, C). Arcella has a shell
much wider than that of Difflugia, convex on one side, flat on
the other. In the middle of the flat surface is a rounded
opening. The shell of Arcella is of a transparent, tough

eh
rE

&

Fic. _3.—A, Quadrula symmetrica; B, Hyalosphenia lata; C, Arcella vulgaris;
D, Difflugia pyriformis. (From Lang’s Comparative Anatomy, after Schulze
and Wallich.)

material, which is said to be chztno¢d from the fact that it

appears to resemble a substance termed chitin, of a horny

consistency, very general in its occurrence in the integument
of animals. ‘This chitinoid test exhibits a minute pattern
when examined under a high power of the microscope.

I PHYLUM PROTOZOA 21

The bulk of the protoplasm is, as in Difflugia, enclosed
within the test, but a considerable portion of it may be
pushed out in the form of pseudopods. Several nuclei and
a contractile vacuole are contained in the protoplasm. The
body of the animal is colourless, and is attached to its test,
says Stokes, “ by fine threads of its own substance.” There
are several species in our fresh-water pools, among them
Arcella vulgaris (Fig. 3, C).

All the rest of the Rhizopoda differ from the Lobosa in
having the pseudopodia in the shape of slender threads.
Of these a remarkable and interesting group is the order
Foraminifera. A Foraminifer has a shell which is nearly
always composed of carbonate of lime. This we can readily
demonstrate by placing a drop of hydrochloric or nitric acid
on a mass of the shells, when they dissolve with efferves-
cence. In some Foraminifera the shell has a wide opening
on the exterior as in Difflugia and Arcella; in others there
is no large opening, but the wall of the shell is perforated
by a number of minute pores scattered over its surface.
The greater part of the protoplasm is enclosed within the
shell, but part of it (Fig. 4) streams out from the single
large opening, or from the pores, in the form of slender
thread-like radiating pseudopodia, which, when they come
in contact with one another, may coalesce, and may in this
way give rise to a network. The protoplasm in the interior
contains a nucleus, but no contractile vacuole. The shape
of the shell is sometimes spherical, sometimes flask-shaped,
sometimes oval or elliptical. Only in a comparatively small
number of Foraminifera does it remain simple (z, 2) ; in the
great majority, though the shell when first formed is simple,
a little process or bud of protoplasm soon projects through
the wide opening or through the pores; this increases in
size, and becomes enclosed in a shell like the original one,

22 MANUAL OF ZOOLOGY SECT.

NG :
3.Squammulina 4Miliola
Fic. 4.— Various forms of Foraminifera. In y, Miliola, a, shows theliving animal;

4, the same killed and stained; a@, aperture of shell; /, food particles; 2x,
nucleus; s#, shell. (From Biitschli’s Protozoa and Claus’s Zoology.)

I PHYLUM PROTOZOA 23

but usually a size larger, remaining in firm connection with
it, the cavities of the two remaining in communication with
one another through the original opening or openings at
which the bud first appeared. From this second shell in
turn a bud is given off in the same manner, and the process
is repeated again and again, until, instead of a single particle
of protoplasm enclosed in a single shell, there is formed a
composite structure, made up of a number of particles of
protoplasm, each with its nucleus, and each enclosed in a
shell, the whole of the shells being firmly united together,
and the whole of the particles of protoplasm being in con-
tinuity through the apertures of communication. The
several parts of such a compound shell, which are known as
the chambers, are variously arranged in different Forami-
nifera (Fig. 5), according to the way in which the succes-
sive buds have been given off. In some the buds succeed
one another in a straight line, and the compound shell
which results (7) has consequently its chambers arranged
in a straight row. Or the chambers may be developed
alternately on opposite sides of the original cell (5), or
with the new chambers entirely overlapping their prede-
cessors (¢). In other cases the development of the buds
takes a winding course, the resulting shell having its cham-
bers arranged in some form of spiral, like the spiral of a
watch-spring or of acorkscrew. Such a spiral shell (6—zz)
assumes a great variety of forms in different Foraminifera,
owing to differences, not only in the shape of the chambers
themselves, but also in the nature of the spiral in which they
are arranged.

In many cases the shell is further complicated by the
development of what is termed the swpplemental shell (Fig.
5,86), a deposit of carbonate of lime outside the original
shell, traversed by a complex system of fine canals contain-

24 MANUAL OF ZOOLOGY SECT.

ing protoplasm, and sometimes produced into a number of
relatively large spines.

Though the great majority of Foraminifera have dense
shells composed of carbonate of lime, there are many in
which the shell resembles that of Difflugia in being com-
posed of foreign particles, such as sand-grains, cemented
together ; these are termed the avenaceous Foraminifera ;
some of these have one large opening, some a number of
pores. In certain fresh-water forms, such as Gromia, the
shell is chitinoid. In Gromia (Fig. 4, 7) the chitinoid shell
has a wide mouth through which the protoplasm protrudes
to form a layer enclosing the shell and giving off the
pseudopodia.

Little is known of the reproduction of the Foraminifera.
But in some a remarkable mode of reproduction has been
observed. The protoplasm in the interior of the shell divides
up into a number of particles. Each of the bodies thus
formed possesses, instead of pseudopodia, a single delicate
whip-like appendage — the /?age//um — which lashes to and
fro and propels the embryo Foraminifer through the water.
Such a flagellum-bearing embryo is termed a flage//u/a.

All the Foraminifera, with the exception of Gromia and
one or two allied forms, are marine, and the greater number
are pelagic —7.c., live in the surface waters of the open sea —
though they occur also inshore, and at almost all depths.
The pelagic Foraminifera are most abundant in warm lati-
tudes, where they occur in enormous numbers. The ocean
floor at depths of five hundred to twenty-eight hundred
fathoms is covered in many places with a mud-like deposit
which effervesces and dissolves when acid is added, and
which, when examined under the microscope, is found to
consist mainly of the shells of Foraminifera, which must
have fallen down from above on the death of the animals.

I PHYLUM PROTOZOA 25

3.

odosaria

1.Nummulites

9.Planorbulina

Fic. 5.—Shells of Foraminifera. In 3, 4, and 5, a shows the surface view, and a
section; Sa isa diagram of a coiled cell without supplemental skeleton; 84 of
a similar form with supplemental skeleton (s. s#); and so of a form with over-
lapping whorls; in sza@ half the shell is shown in horizontal section; 4 is a ver-
tical section; «, aperture of shell; 1—15, successive chambers, 1 being always
the oldest or initial chamber, (After Carpenter, Brady, and Bitschli.)

26 MANUAL OF ZOOLOGY SECT.

From the name of the genus— Glodigerina (Fig. 5, 6) —
which occurs in the greatest abundance in this deposit, it is
known as the Glodigerina ooze. In the deepest parts of the
ocean the Globigerina ooze is entirely absent, the calcareous
shells of the Foraminifera apparently becoming entirely dis-
solved before they can reach such great depths. It is inter-
esting to note that similar deposits were formed in previous
geological periods —the beds of cha/k of the Cretaceous
period consisting, like the Globigerina ooze, in great rheasure
of the shells of Foraminifera, though apparently not formed
under the same conditions of depth. Another case of
massive deposition of Foraminifera in a former geological
period is the Mummuhtic Limestone, a bed of limestone
made up, for the most part, of the shells of comparatively
gigantic Foraminifera, the Nummulites (Fig. 5, zz).

A Rhizopod by no means uncommon in fresh water is
the so-called sun-animalcule, Actinophrys sol. The body

Fic. 6.—Actinophrys sol. a, axial filaments of pseudopods; 7, nucleus;

Pp, pseudopod. (From Lang’s Comparative Anatomy, after Greenacher.)
of Actinophrys (Fig. 6) is nearly spherical, and contains a
large nucleus and numerous vacuoles, some of which, situ-
ated near the surface, are contractile. The most charac-
teristic feature is formed by the pseudopodia, which, instead

I PHYLUM PROTOZOA 27

of being comparatively short and thick, as in Amceba and in
the other Lobosa, or extremely delicate, flexible, and thread-

ighly magnified;
(From

» nuclei.

; med, medulla; 22

A, the entire organism; B, a small portion, hi

c. vac, contractile vacuole

oa, after Hertwig and Lesser.)

cort, cortex;

chr, chromatophore;

Fic. 7. — Actinosphzrium eichhornii.
Biitschli’s Proto.

like, as in the Foraminifera, are slender, but comparatively
stiff, and stand out straight from the surface of the sphere
in a radiating manner: they are capable of only very slow

28 MANUAL OF ZOOLOGY SECT.

movements. The pseudopodia owe their stiffness to the
presence of a rod of chitinoid material which lies in the axis
of each, and extends inward toward the middle of the pro-
toplasm. A large nucleus lies in the centre of the body. A
good many other genera are known which have pseudopodia
of the same general character as those of Actinophrys, and
these are accordingly grouped together as an order of
Rhizopoda — the order Heliozoa. Of these other genera of
Heliozoa, Actnospherium (Fig. 7) is somewhat more com-
plex in structure than Actinophrys, the protoplasm being
divided into a central mass — the ezdosare — in which the
vacuoles are small, and an outer layer — the ecéosarc — in
which they are very large. Numerous nuclei are present,
and bodies containing chlorophyll — the characteristic green
colouring matter of plants. It frequently occurs in com-
pany with Actinophrys, among the leaves of Lemna and
other plants, and feeds on microscopic forms, also Rotifers
(Stokes). Some of the Heliozoa, instead of being composed
like Actinophrys entirely of soft protoplasm, have support-
ing and protecting hard parts. Such hard, or compara-
tively hard, parts in any animal, whatever form they may
assume, whether that of an enclosing shell or crust, or a
system of internal bones or other firm structures, are known
under the general term of skelefon. In those Heliozoa in
which a skeleton occurs it is sometimes a shell of aggluti-
nated sand-grains, like the shell of Difflugia, or of the arena-
ceous Foraminifera; or it may consist of loosely matted
needle-like bodies composed of silica (Fig. 8, 7); or there
may, as in C/a¢hrulina, be a sphere of silica, perforated by
numerous openings, enclosing the protoplasm. C/lathrulina
elegans (Fig. 8, 7) 1s common in many ponds, attached to
the rootlets of Lemna, or duck-weed (Stokes).
Reproduction takes place, as in Amceba, by binary fission.

I PHYLUM PROTOZOA 29

2.Nuclearia
3.Clathrusina

Fic. 8.— Various forms of Heliozoa. 3a, the entire animal; 34, the flagellula;
c. vac, contractile vacuole; g, gelatinous investment; 27, nucleus; fsd@, pseudo-
pods; sf, siliceous skeleton; sf, spicules, (From Biitschli’s Protozoa, after
Schulze and Greeff.)

30 MANUAL OF ZOOLOGY SECT.

But in some genera the process of fission under some circum-
stances remains incomplete, the two protoplasmic bodies
to which the fission gives rise remaining connected together
by a bridge or isthmus of protoplasm, instead of becoming
separated off in the shape of two independent animals, as in
Ameeba. Further, these two bodies may each in turn divide
in the same incomplete way, so that four Heliozoans are
developed, all remaining connected together; and by further
repetitions of the same process a structure may be formed
consisting of a large number of units all connected together
by living substance. A structure of this kind, formed as a
result of repeated incomplete division (or, in other cases,
budding) from an original simple animal, is termed a colony,
and the elements or units of which it is composed are termed
zootds. How such a colony of unicellular Protozoa is to
be distinguished from a multicellular animal or Metazoan
(p. 19) will be explained ata later stage. It will at once be
apparent that the compound Foraminifera are of the nature
of colonies of unicellular zooids, each occupying one of the
chambers of the shell, formed as the result of a process
of repeated budding.

In addition to the process of multiplication by fission
multiplication also takes place in some Heliozoa by a pro-
cess known as the formation of sfoves. In spore-formation
(a form of which has already been referred to as occurring in
the Foraminifera) the protoplasm breaks up into numerous
small parts, each of which eventually develops into the form
of the parent. Usually the Protozoan passes into a qui-
escent condition before this takes place; the pseudopodia
become withdrawn, and the whole becomes enclosed in a
firm envelope or sforocyst,; this process is known as encys¢a-
tion. The spores in some of the Heliozoa, when set free,
are provided each with two flagella (Fig. 8, 3, 4) which

1 PHYLUM PROTOZOA 31

subsequently become lost, pseudopodia appearing in their
place.

The Radiolaria are marine Rhizopoda which have exceed-
ingly delicate, thread-lke pseudopodia (Fig. 9, fsa) and a
skeleton usually composed of silica. This skeleton may be
composed of loosely woven needle-like bodies or spicules ;
more usually it is in the form of a globular, conical, star-
shaped, or disc-shaped shell, perforated by numerous open-
ings, and often supported by spines which radiate out from

Fic. 9. — Liteocircus annularis. cent. caps, central capsule; ert. caps. pr, extra-
capsular protoplasm; zw. caps. fr, intra-capsular protoplasm; 7, nucleus;
psd, pseudopods; ske/, skeleton; z, cells of Zooxanthella. (After Biitschhiy,
from Parker’s Bzology.)

the centre; sometimes (Fig. 10) there are several such

shells one within the other. In some Radiolaria the skele-

ton is composed not of silica, but of a chitinoid substance
called acanthin. Embedded in the protoplasm is a perfor-

ated membranous sac, the central capsule (Figs. 9 and 10,

cent. caps), in the protoplasm within which is a single

nucleus or a number of nuclei, and a number of oil-drops.

There is no contractile vacuole, but in many Radiolaria the

protoplasm outside the central capsule contains numerous

non-contractile vacuoles, the presence of which gives it a

frothy appearance.

32 MANUAL OF ZOOLOGY SECT.

Radiolaria which give rise to colonies are exceptional, but
a few cases occur. In these (Fig. 11) the central capsule
divides again and again giving rise to a number of central
capsules which remain embedded in a firm gelatinous sub-

pheres broken
s, central capsule;

. 2, middle, sé. 3, inner

1; ww, nucleus; sk. 7, outer, sé
oa, after Haeckel and Hertwi

(From Biitschli’s Proto

Bi
£.)

f the skeleton to the animal; cemz?. caf.

g the relations o

away; B, section showin

a
o
2)
o
s
iA
o
re
x,
<
s
8
Ny

sphere of skeleton.

Fic. to. — Actinomma asteracanthion. A, the shell with portions of the two outer s

stance — the vacuolated protoplasm outside the central cap-
sules. Such a mass, which may attain considerable size,
floats about freely in the sea.

I PHYLUM PROTOZOA 33

In addition to reproduction by simple binary fission,
spore-formation also occurs in some of the Radiolaria. The
protoplasm contained in the central capsule breaks up into
small masses, each of which becomes a flagellula provided
with a flagellu'n (Fig. 44, 2, F).

In most of the Radiolaria there occur in the extra-capsular
protoplasm minute yellow cells (Fig. 9, z), which multiply

Fic. 11.— Collozoum inerme. A—C, three forms of the entire colony, nat. size;
D, a small colony showing the numerous capsules (c. cafs) and extra-capsular
protoplasm with vacuoles (vac); E, spores containing crystals (c); mega- and
microspore, (From Biitschli’s Protozoa, after Hertwig and Brandt.)

independently by binary fission. It has been proved that
these are microscopic unicellular plants (Zooxanthella) of
the class Algze, which live in the substance of the protoplasm
of the living Radiolarian. Such an intimate association
between two living organisms is known as symédzosis. There
can be no doubt that this association is beneficial both to the
Radiolarian and to the Alga. It is characteristic of the
plant cell that under the action of light and in the presence
D

34 MANUAL OF ZOOLOGY SECT.

of the specially vegetable green colouring matter, chlorophyll,
it is able to utilise for its nutrition the carbon dioxide
or “carbonic acid gas” present in the air. ‘The carbon is
seized and made use of by the plant cell for the building up
of such compounds as starch and sugar, while the oxygen is
set free. The animal cell, on the other hand, is continually
using up oxygen and giving off carbon dioxide in the process
of respiration, while it is unable, in the absence of chloro-
phyll, to manufacture such substances as starch and sugar.
Thus in this close association or symbiosis between the Zoox-
anthella and the Radiolarian, the latter benefits the former
by supplying it with carbonic acid and other substances by
which it is nourished, while the Alga contributes to the
respiration of the Radiolarian by the oxygen which it gives
off, and to its nutrition by the sugar and other substances
which it forms.

2. THE MASTIGOPHORA

We have seen that the spores by which multiplication is
effected in some of the Rhizopoda (Heliozoa, Radiolaria)
are characterised by the presence of slender whip-like
appendages — the flagella. Ina great number of Protozoa
such a flagellate condition of the cell is not merely a tempo-
rary larval one, as in the cases already dealt with, but is the
ordinary and permanent condition of the adult animal.
These permanently flagellate Protozoa constitute the class
Mastigophora — a very numerous group, mostly of very
small size. A good example of this class, very abundant in
fresh-water pools, in which it may be present in such
enormous numbers as to impart to the water a distinct
green colour, is Euglena viridis (Fig. 12). Another species
or variety of Auvglena viridis, is so abundant at times as to
colour the water blood-red (Stokes).

I PHYLUM PROTOZOA 35

The body of Euglena (£, 4) is spindle-shaped, and has
at the blunt anterior end a depression, the gullet (Ff. es),
from the inner surface of which springs a single long flagellum
(7). The organism is propelled through the water by the

nterior end further enlarge

3. 12. — Euglena viridis.

} ™
ved

Fu

lashing movements of the flagellum, which is always directed
forwards ; it can also perform slow, worm-like movements of
contraction and expansion (4—JD), but anything like the

36 MANUAL OF ZOOLOGY SECT. I

free pseudopodial movements which characterise the Rhizo-
poda, is precluded by the presence of a very thin skin or
cuticle which invests the body. There is a nucleus (zz)
near the centre of the body, and at the anterior end a con-
tractile vacuole (4, ¢c. vac), leading into a large non-con-
tractile space or reservotr (7) which discharges into the
gullet.

The greater part of the body is coloured green by the
characteristic vegetable pigment, chlorophyll, and contains
grains of paramylum (H, p), a carbohydrate allied to
starch. In contact with the reservoir is a bright red speck,
the stigma (pg), formed of a pigment allied to chlorophyll
and called hematochrome. It seems probable that the
stigma is a light-perceiving organ or rudimentary eye.

Euglena is nourished like a typical green plant; it de-
composes the carbon dioxide of the air dissolved in the
water, assimilating the carbon and setting free the oxygen.
Nitrogen and other elements it absorbs in the form of min-
eral salts in solution in the water. But it has also been
shown that the movements of the flagellum create a whirl-
pool by which minute fragments are propelled down the
gullet and into the soft internal protoplasm. There seems
to be no doubt that in this way minute organisms are taken
in as food. Euglena thus combines the characteristically
animal (Ao/ozorc) with the characteristically vegetable (ho/o-
phytic) mode of nutrition.

Sometimes the active movements cease; the animal comes
to rest and surrounds itself with a cyst or cell-wall of cellulose
(the characteristic material of the cell-wall of plants), from
which, after a quiescent period, it emerges to resume active
life. It is during the resting condition that reproduction
takes place by the division of the body in a median plane
parallel to the long axis (G@). Under certain circumstances

1.Trachelomonas

C.t0e
3.Astasiopis —
2. Oikomonas (?)

Tu

7 Tetramita

ae” 9.Cryptomonas
B.0ikomonas

6.Dallingeria 10. Diplomita

1. Dinobryon 12.Syncrypta 13.Anthophysa 14.Rhipidodendron

Fic. 13. — Various forms of Mastigophora. In 2, flagellate (a) and ameeboid (4)
phases are shown; in 5, flagellate (2) and heliozoan (4) phases; in & are shown
two stages in the ingestion of a food particle (/); cr, chromatophores;
c. vac, contractile vacuole; f, food particle; g, gullet; 2, nucleus; /, lorica;
p, protoplasm; fer, peristome; 7. 7, vacuole of ingestion. (Mostly from Biit-
schli’s Protozoa, after various authors.)

37

38 MANUAL OF ZOOLOGY SECT.

multiple fission takes place, and flage//lula, t.c., young pro-
vided with flagella, are produced, which, sometimes after
passing through an ameeboid stage, develop into the adult
form.

In the other Mastigophora the body may have a shape
similar to that of Euglena, or may be longer and narrower,
or, on the other hand, may be short and thick, ovoid or
globular. Anterior and posterior ends are nearly always
distinguishable, the former being that which is directed
forwards in progression. Usually there are distinct dorsal
and ventral surfaces, the former being that which is habitually
directed upwards. In most cases the body is equal-sided
or bilaterally symmetrical, 7.¢., is capable of being divided
into two equal lateral portions along the median vertical
plane ; but sometimes it is unsymmetrical, one side differ-
ing more or less from the other. In most the body is, as
in Euglena, naked ; but some have a chitinoid shell or Zovzca,
while others have a firm cell-wall of cellulose which may
present an elaborate pattern of strips, dots, etc., and may be
produced into long processes. Most of the Mastigophora
are, like Euglena, free-swimming, but some are permanently
attached by means of a slender stalk (Fig. 13, 70, 73, 74;
Fig. 14; 2,3):

The number and arrangement of the flagella vary greatly.
The number may be one, as in Euglena, or two, three, or four.
In forms with two flagella these are both attached at or near
the anterior end, and often take on different functions, one
of them, directed forwards, being alone used in locomotion,
while the other is trailed behind when the animal is swim-
ming freely, or is used to anchor it to various solid bodies.
In one large group of Mastigophora, the Choanoflagellata
(Fig. 14), there is, surrounding the base of the flagellum, a
remarkable vase-like prolongation of the protoplasm, ex-

1 PHYLUM PROTOZOA 39

ceedingly delicate and transparent, called the co/ar. This
is contractile, and, though its precise functions are not yet

ion of flagell-

(After Saville Kent.)

c, the produ

: 2,

4.Proterospongia.

3.Polyoeca.

2.Salpingoeca.
of Choanoflagellata.
contractile vacuole; /7, fla)

14. — Various forms
c, collar; ¢. vac,

1.Monosiga.
ula;

Vic.

certainly known, there is evidence to show that its move-
ments cause a flow of water, with minute particles in sus-
pension, up the outside of the collar and down the inside,

40 MANUAL OF ZOOLOGY SECT.

the solid particles being then ingested in the soft protoplasm
between the base of the flagellum and that of the collar.
Both-collar and flagellum may be withdrawn, and the animal

ged, andéa
; fi. 2, transverse
; mu’, micronucleus;

4.Polykrikos

ga is an undischar;

fi. 1, longitudinal flagellum;

u“, Meganucleus
li’s Protozoa.)

3.Prorocentrum

2 shows the shell only;
ntc, nematocys
(From Bii

chr, chromatophores;

2.Ceratium

ansverse groove,

oO
>
°
9°
a
bn

te gi

2. gr, longi

discharged stinging-capsule;
pg) pigment spot;

flagellum;

1.Glenodinium
Fic. 15.— Various forms of Dinoflagellata.

pass into an Amceba-like or amwdoid form. In another
group —the Dinoflagellata (Fig. 15)— there are two fla-
gella, one springing from a longitudinal groove extending
along the anterior half of the body, and the other lying in a

I PHYLUM PROTOZOA 41

transverse groove which completely encircles the body ; the
former alone acts as an organ of locomotion, the latter lies
habitually in the groove and performs undulating move-
ments. Noctiluca (Cystoflagellata) (Fig. 16), which is the
largest member of the class, being about half a millimetre
in diameter, has two flagella, one of which is modified in
a remarkable manner. The body of Noctiluca is globular,
with a cleft along one side so that it resembles a miniature
peach. From this springs a very large and stout flagellum

Fic. 16.— Noctiluca miliaris. «a, the adult animal; 4, c, flagellule; dg, tentacle;
J, flagellum; 7z, mouth; ~, nucleus. (From Lang, after Biitschli.)

or ¢entacle, which is marked with a number of transverse

lines or striations ; and a second flagellum, of comparatively

small size, lies in the gullet.

Though all the Mastigophora are characterised by the
possession of flagella, there are a few, such as Mastgameba
(Fig. 13, ¢), which also possess pseudopodia, and may be
capable of amceboid movements.

.Nutrition is effected in a variety of different ways. Some
forms live in decaying organic infusions, not taking in solid
food-particles, but absorbing nourishing matter in a dis-

42 MANUAL OF ZOOLOGY SECT.

solved form from the substances in the infusion. Others,
living in internal cavities of the bodies of higher animals,
receive, in a similar way, nourishment from the juices of the
animal they infest. Organisms, whether plants or animals,
which receive their nourishment in the former of these two
ways, are said to be saprophytic as regards their nutrition,
while such as obtain it from other living organisms are said
to be parasitic. But a large proportion of the Mastigophora
are neither saprophytes nor parasites, and are nourished in
one of two other ways, or in both of them. Many take in
minute solid particles of organic matter, usually in the form
of minute living organisms. In many such cases, there is,
as in Euglena, an aperture, the mouth, opening into a short
passage, the gullet, by which the food is received into the
protoplasm in the interior of the body; but this is not
always present, and in such cases (Fig. 13, 8) the food-parti-
cles are taken in by a process not unlike that which we have
seen to occur in Amceba. But, on the other hand, many of
the Mastigophora are not distinguishable from plants by their
mode of nutrition ; and on that ground, taken in connection
with their structure, which is in nearly all respects that of
a typical unicellular plant, have almost equal claims to be
ranked in either the vegetable or the animal kingdom.
They have a cell-wall of cellulose like a plant cell, they
contain chlorophyll or a red colouring matter, Aematochrome,
of similar composition, and they have no mouth. They
must, therefore, be nourished precisely after the manner
of a green plant, and, if they are assigned to the animal
kingdom instead of to the vegetable, it can only be because
the possession of flagella seems to ally them with forms that
are of undoubted animal character.

Colonies are of frequent occurrence among the Mastigo-
phora. Sometimes there is a branching slender stalk

I PHYLUM PROTOZOA 43

bearing a single zooid or a group of zooids at the end of
each of the branches (Fig. 14, 3), the whole colony being
fixed by the base of the main stalk, and the flagellum serving
for the capture of food-particles and not for locomotion.

Tic. 17. — Volvox globator. A, entire colonys enclosing several daughter- colonies:
B, the same during sexual maturity; C, four zooids in optical section; Dt—
asexual formation of daughter-colony; E, zooid which has become conweed
into a mass of microgametes; F, microgamete; G, megagamete surrounded by
microgametes; H, zygote; a, early stages in the formation of daughter-colonies;
Al, flagellum; ov, ovy, megagametes; fg, pigment spot; sy, zooids containing
microgametes. (From Parker's Biology, after Cohn and Kirchner.)

Sometimes (Fig. 17) the colony is of a more massive char-
acter, the zooids being embedded in a clump of gelatinous
material, with the end bearing the flagellum projecting on
the exterior: usually such colonies are free-swimming.

44 MANUAL OF ZOOLOGY SECT.

Multiplication is effected most commonly by the simple
process of binary fission (Fig. 11, 20), which may take place
either in the active or in an encysted condition. In some
cases the fission is mu/f#ple, the protoplasm dividing not
merely into two, but into a greater number of parts, each
destined to develop into the adult form.

We also meet in the Mastigophora with what may be
regarded as the simplest mode of sexwa/ reproduction. In
some forms two individuals come together and become
completely fused, the process being known as conjugation,’
and the body formed by the union of the cells being known
as a zygote. The protoplasm of the latter divides by mul-
tiple fission into very minute spores. These, when first
liberated by the rupture of the zogote, are mere granules,
but soon the flagella are developed. In some cases the con-
jugating cells or game/es are of two sizes, union always taking
place bétween a large cell or megagame¢e and a small cell or
microgamete. In Volvox, which is a free-swimming spheri-
cal colony (Fig. 17, 2, #, G) this difference between the
two sets of conjugating cells reaches its extreme, pro-
ducing a condition of things closely resembling what we
find in the sexual reproduction of higher forms. Certain
of the zooids enlarge and form megagametes, others divide
repeatedly and give rise to groups of microgametes, each
of the latter having the form of a rod-like body with two
flagella. ‘The microgametes escaping, swim about freely and
conjugate with the motionless megagametes to form a zygote,
which, after a time divides to give rise to a new colony.

Mastigophora occur under the most various conditions,
to some of which reference has been already made. Many
kinds live in fresh water ; others are abundant in the sea.
Noctiluca and others among the marine forms are phos-

1 Conjugation has also been observed to occur in many Rhizopods.

I PHYLUM PROTOZOA 45

phorescent, and are usually the agents by means of which
the diffuse phosphorescence of the sea is produced. Others,
again, are saprophytes, while others are parasites of higher
animals.

3. THE INFUSORIA

Often to be found in great numbers, in stagnant pools,
organic infusions, etc., is Paramecium, the “ slipper-shaped
animalcule,” a Protozoan of comparatively large size, about
4 mm. in length, which moves about very actively like
Euglena, but with a more regular and more rapid move-
ment, and by means of organs of locomotion differing in
character from the flagellum of the latter. The body of
Parameecium (Fig. 18, 4, B) is covered with what appear
under the microscope like small delicate hairs arranged in
longitudinal rows. These are the c/a; they are in inces-
sant to-and-fro vibration, and it is by their means that the
Paramcecium moves about and obtains its food. In shape
the body is somewhat cylindrical, rounded at the anterior
and bluntly pointed at the posterior end. On one side,
the ventral, is a large oblique depression, the duccal groove
(duc. gr), leading into a short gullet (gw/), which, as in
Euglena, ends in the soft internal protoplasm. The prcto-
plasm is differentiated into a firmer superficial layer, the
cortex (cort), and a semi-fluid central mass, the medulla
(med), and is covered superficially by a thin cuticle. The
cilia are prolongations of the cortex, and perforate the
cuticle.

In the cortex are found two nuclei. One of these, the
meganucleus (nu), is a comparatively large ovid body; the
other, the micronucleus (pa. nw), is a small rounded body
closely applied to the meganucleus. Two contractile

46 MANUAL OF ZOOLOGY SECT. 1

vacuoles (c. vac) are present. Each is connected with a
series of radiating spindle-shaped cavities in the protoplasm
which serve as feeders to it; after the contraction of the
vacuole these cavities are seen gradually to fill, apparently
receiving water from the surrounding protoplasm ; they then
contract, discharging the water into the vacuole, the latter
rapidly enlarging while they disappear from view ; finally
the vacuole contracts and discharges its contents externally.

The cortex contains minute radially-arranged sacs called
trichocysts (trch). When the animal is irritated, more or
fewer of these suddenly discharge a long delicate thread
(C), which, in the condition of rest, is very probably coiled
up within the sac.

Food, in the form of small living organisms, is taken in
by means of the current caused by the cilia of the buccal
groove. The food-particles, enclosed in a globule of water,
or “food-vacuole”” (/. vac), circulate through the proto-
plasm, where the soluble parts are gradually digested and
assimilated. Effete matters are egested at a definite ana/
Spot posterior to the mouth, where the cortex and cuticle
are less resistant than elsewhere. The whole feeding pro-
cess can readily be observed in this and other Infusoria by
placing in the water some insoluble colouring matter, such
as carmine or indigo, in a fine state of division, the minute
particles of the colouring matter, which are taken into the
mouth in the way described, being readily observed as they
become received into food-vacuoles and circulate in the
central protoplasm.

Multiplication takes place by transverse fission (D), the
division of the body being preceded by that of both nuclei.
It has been proved, however, that multiplication by binary
fission cannot go on indefinitely, but that after it has been
repeated a certain number of times, it is interrupted by

|!
~S x i}

SS

cC.vace

Fic. 18.— Paramecium caudatum. A, the living animal from the ventral aspect;

B, the same in optical section: the arrow shows the course taken by food-particles;

, a specimen which has discharged its trichocysts; D, diagram of binary fission;

buc. gr, buccal groove; cort, cortex; cuz, cuticle; c. vac, contractile vacuole; /,

vac food vacuole; gu/, gullet; med, medulla; 22, meganucleus; fa. 27%, micro-
nucleus; ¢ych, trichocysts. (From Parker's Bzology.)

47

48 MANUAL OF ZOOLOGY SECT. I

conjugation. In this very remarkable and characteristic
process two Paramcecia become applied by their ventral
faces, but do not fuse ; their meganuclei break up and dis-
appear, and an interchange of the substance of the micro-
nuclei of the two conjugating individuals takes place, with
the result that each develops a new meganucleus, and a
new micronucleus, partly formed of the substance of its own
micronucleus, partly that of the other Paramcecium.

The possession of cilia is the distinctive feature of the class
Infusoria among the Protozoa. But in one section of the
class —the order Tentaculifera —cilia are only present in
the young, their place in the adult being taken by append-
ages known as éenéacles. The form of the body in the
Infusoria (Fig. 19) is very varied ;+ it may be globular,
ovoid (z), kidney-shaped (2), trumpet-shaped (3), vase-
shaped (9), produced into a long, flexible, neck-like pro-
cess (5), or into large paired lappets (6), flattened from
above downwards, or elongated and divided into a series
of segments. Most are free-swimming, but many are fixed,
usually by means of a slender stalk (9).

The arrangement of the cilia also varies greatly. Some,
like Paramcecium, have small cilia of uniform character
distributed over the entire surface. Others have different
kinds of cilia on different parts of the surface, while in
others the cilia are entirely confined to certain regions.
An instance of the latter arrangement is the common
stalked form Vorticedia, with its allies such as Zpzstylis (9),
in which the cilia are confined to the free extremity. These
cilia produce rapid currents, and the pistylis, says Stokes,
select from them anything they may want, and let the rest
sweep by. In another group, again, the body, which is of
flattened shape, bears on its dorsal surface a small number
of very fine motionless cilia, while on its ventral the cilia are

1.Prorodon 2.Nycrotherus

8.Anoplophyra ce 2
9.Epistrylis

ZDiophrys

Sgn | | |

Law 12..Multicilia 13,Lophomonas

4 Fac “ 18.Trachelius 19.0phryoglena
: 16.Condylostoma y
15 Didinium "17 0pdlinopsis

Various forms of Ciliata. ga shows part of a colony, 4 a single zooid, and
¢acouple of nematocysts; @, anus; ¢. vac, contractile vacuole; /. vac, food
vacuole; g, gullet; mg. v7, meganucleus; #2. 27, micronucleus; ti, mouth;
nu, nucleus; xtc, nematocyst; 7, tentacle; 7. sé, undulating membrane; vac,
non-contractile vacuole; vs¢, vestibule. (From Biitschli’s #votozea, after vari-
ous authors. )

E 49

Fic. 19. —

50 MANUAL OF ZOOLOGY SECT

very strong, and are modified into the shape of hooks, bris-
tles, or plates with fringed ends. The hooks and plates do
not vibrate rhythmically like ordinary cilia, but are moved
asa whole at the will of the animal, such Infusoria being
able, in addition to swimming freely through the water,
to clamber by the aid of these specially modified cilia over
the surface of weeds, etc. Tentacles may be present in
addition to cilia (14), and a number of other exceptional
modifications (zo-z3) occur which cannot be specially re-
ferred to here.

In addition to cilia, many genera possess delicate sheets
of protoplasm, or wadulating membranes (uw. mb) in connec-
tion with the peristome. These contract so as to pro-
duce a wave-like movement which aids in the ingestion
of food.

The sentacles, which, in the Tentaculifera (Fig. 20), take
the place of cilia in the adult, are elongated cylindrical
structures, capable of protrusion and retraction, and having
the distal end expanded into a sucker. The tentacle is
practically tubular, the core consisting of a semi-fluid proto-
plasm, while the outer part is tolerably firm. Infusoria and
other organisms are caught by the tentacles, the cuticle of
the prey is pierced or dissolved where the sucker touches
it, and the semi-fluid protoplasm can then be seen flowing
down the tentacle into the body of the captor. A single
tentacle alone may be present (3), or the tentacle may be
branched (4), the extremity of each of the branches being
suctorial. In some forms (5) the tentacles are devoid of
sucker-like extremities, and can be moved about actively to
catch the prey.

The meganucleus is often ovoid, as in Paramcecium. In
other cases it may be long and band-like (Fig. 19, 3,
mg. nu), horseshoe-shaped (9), very long and constricted

1 PHYLUM PROTOZOA

6. Sphaerophrya

4.Dendrocometes
3.Rhyncheta 5. Bphetate

TT

9.Dendrosoma

Fic. 20.— Various forms of Tentaculifera. za and 2, two species of Podophrya ;
¢,a tentacle much enlarged; 2a, Acrneta jolyt ; 26, 4. tuberosa; in 6 the ani-
mal has captured several small Ciliata; Sa, a specimen multiplying by budding;
86, a free ciliated bud; ga, the entire colony; 94, a portion of the stem; gc, a
liberated bud; a@. organism captured as food; 4. c, brood cavity: 4d, bud;
¢. vac, contractile vacuole; mg. uw, meganucleus; sz. 2, micronucleus;
¢, tentacle. (After Biitschli and Saville Kent.)

52 MANUAL OF ZOOLOGY SECT,

at intervals so as to look like a string of beads, or branched.
In nearly all cases one or more micronuclei are present.
In Vorticella and others there is a single contractile vacuole
which opens, as in Euglena, through the intermediation of
a reservoir into the gullet. In other Infusoria there may
be one, two, or many contractile vacuoles. In some instances
the protoplasm is hollowed out by numerous non-contractile
vacuoles. Trichocysts mainly occur in the forms with a uni-
form coating of cilia: more complicated bodies of similar
character termed nemavocysts (9, ¢) occur in some cases.

A mouth is absent in many parasitic forms, and nourish-
ment is obtained by the absorption of the digested food of the
animal in which the infusorian is parasitic. In the Tentacu-
lifera, in which a mouth is also absent, nourishment is drawn
in by means of the tentacles in the manner already described.
In the rest there is a mouth and gullet, usually situated, as in
Parameecium, at the end of a buccal groove, or peristome.

In Vorticella and its allies (Fig. 19, 9, and Fig. 22) the
body is in the shape of a wine-glass, the stem of which is
represented by a slender stalk (s¢), while the rim is the
equivalent of the peristome (fev) ; in the area which the
peristome encloses is an elevated disc of protoplasm, be-
tween which and the peristome on one side is the opening
of the mouth (wdzh): the only cilia present run in a spiral
band round the peristome, round the edge of the disc, and
dowr iato the gullet (gw//7). An anal spot is present in
Vorticella and many other forms ; in a few there is, instead,
a distinct anal aperture (Fig. 19, 2 a).

A chitinoid skeleton (Fig. 21) occurs in a few forms;
usually it is bell-shaped, sometimes it is perforated by a
number of apertures (7) so that it resembles in appearance
the skeleton of some of the Radiolaria. A chitinoid lid or
operculum (2,3, 0p) may be fixed to the edge of the peri-

de

I PHYLUM PROTOZOA 53

stome, and when the animal is retracted into its case, accu-
rately closes the mouth of the latter.
Colonies occur in many of the Infusoria. Some allies of

ae:
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Fic. 21.— Various forms of Ciliata.

LDictyoeysta

Vorticella (Fig. 19, 9) develop highly complex colonies, the
slender stalk branching again and again, and each terminal
branch ending in a zooid. A remarkable colonial form is

54 MANUAL OF ZOOLOGY. SECT.

Dendrosoma (Fig. 20,9), one of the Tentaculifera: it has
a creeping stem from which branches spring upwards,
each terminating in a zooid with suctorial tentacles ; and

Fic. 22.—-Vorticella. A, B, living specimens in different positions; C, optical

section; D!, D2, diagrams illustrating coiling of stalk; E!, E*, two stages in
binary fission; E*, free zooid; F1, F?, division into mega- and microzooids;
G), Ce, conjugation; H!', multiple fission of encysted form; H?, H®, develop-
ment of spores; ax. /, axial fibre; cort, cortex; cw, cuticle; ¢. vac, contractile
vacuole; d, disc; gw//, gullet; 7, microzooid; mth, mouth; 2, meganucleus;
per, peristome, (From Parker’s Bzology, partly after Saville Kent.)

I PHYLUM PROTOZOA 55

the single nucleus extends as a narrow branching cord
throughout the axis of the entire colony.

Transverse fission is the universal method of reproduc-
tion ; and budding also occurs. Spore-formation has been
observed in a few forms.

Conjugation, in the form of a temporary union of two
individuals, with interchange of the substance of the micro-
nuclei, occurs in many of the ciliate Infusoria. In some
forms the conjugating individuals become completely fused.
The effect of the process of cohingation seems to be in-
creased activity in multiplication by fission.

In mode of life the Infusoria are as varied as the Mastigo-
phora. Some are holozoic, some saprophytic, some parasitic.
Of the parasitic forms some give rise to definite diseases
in the bodies of their hosts. The skin affection known as
eczema, for example, seems to be caused by the presence
of parasitic Vorticelle.

4. THE SPOROZOA

In the interior of certain organs, termed the seminal
vesicles, of the earthworm will often be found a parasitic
Protozoan — Monocystis agilis (Fig. 23) — which exempli-
fies another of the classes of the phylum, the class Sporozoa.
It is flattened, elongated, pointed at both ends, and performs
slow movements of expansion and contraction (4, &),
reminding us of those of Euglena. There are neither
pseudopodia, nor flagella, nor cilia. There is a firm
cuticle, and the protoplasm is divided into a denser
superficial portion, the cov¢ex, and a central semi-fluid mass,
the medulla. There is a large clear nucleus, but no trace of
contractile vacuole, or of mouth or gullet. Reproduction
takes place by a peculiar and characteristic process of spore-
formation. Either a single individual, or two individuals,

56 MANUAL OF ZOOLOGY SECT.

closely applied together, but not actually fused, become
encysted. Multiple fission then takes place, the proto-
plasm becoming divided (C) into an immense number of
spindled-shaped spores, each surrounded by a_ strong

C, cyst

ng (M) in a group of sperm-cells of the earthworm;
(After Biitschli and Huxley.)

sperms of the earthworm; J/, young Monocystis;

A, B, two individuals in different stages of contraction;
worm.

ystis surrounded by
sperm-cells of earth

D—F, development of your

23. — Monocystis agilis.

S, newly liberated Monoc
nu, nucleus; sf, sperms 0

containing spores;

Fic.

chitinoid coat, and thus differing markedly from the naked
spores of Rhizopoda and, Mastigophora. The protoplasm
of each spore then undergoes fission, becoming divided

r _ PHYLUM PROTOZOA 57

into a number of somewhat sickle-shaped bodies, which are
arranged within the spore-coat somewhat like a bundle of
sausages. By rupture of the spore-coat these fakiform
young, as they are termed, are liberated, and at once begin

pseudopod;
s Protozoa.)

? the epimerite (ef) is cast
pores have been discharged; D, four

cyst; dex, deutomerite; ef, epimerite; ¢,

pr, protomerite; psd. 7, short
(From Biitschli’

y embedded in enteric epithelial

2

a
7
hen 4
qs ra]
z g
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Rs
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sto
Pses -8.
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S

A, twos
ges in the development of G. gigantea s

gelatinous investment of c

off; C, cyst of G. blattarum
psd. 2, long pseudopod

cells of cockroach; B1, B

Fic. 24.— Gregarina.
sta:

active movements, the thin end of the body moving to and
fro like aclumsy flagellum. ‘They enter the clumps of devel-
oping sperms of the earthworm, and afterwards escape into
the cavity of the seminal vesicle and grow into the adult form.

58 MANUAL OF ZOOLOGY SECT. I

All the Sporozoa are parasitic, and all are characterised
by the absence of pseudopodia, flagella, and cilia; and of
mouth and gullet, and by the formation of spores enclosed
in chitinoid coats. Gregarina (Fig. 24) differ from Mono-
cystis in having the medullary part of the protoplasm divided
into two sections, known as the profomerite (pr), and
deutomerite (dew), by a sort of partition, with, in the young
condition, a third division, the ef:merife (ef) in front; and
in the more complex form of the cysts, which have delicate
canals or sporoducts (spd) through which the spores escape.
Some of the Sporozoa ( Cocctdium and others) are parasites,
not like Monocystis and Gregarina, in the cavities of organs,
but in the interior of cells, such as the cells lining the intes-
tine of higher animals. The various forms of the disease
known as malaria in Man have been proved to be due to the
presence of a Sporozoan (Hemamaba laverani ) which in-
vades and destroys, at a certain stage in its life-history, the
red corpuscles of the blood. Another form (Afiosoma
bigeminum) causes the Texas fever in cattle, the infection
being carried by ticks. These parasites cause high fever,
anzemia, bloody urine, and the number of red-blood corpus-
cles is diminished in one week to one-sixth of the normal
amount. Sadesia ovis in the blood of the ox causes the dis-
ease known as hzemoglobinurea, and another form produces
asimilar disease insheep. A parasite of the tzetse fly, which’
is a flagellate heematozoan, is the cause of the tzetse disease
in southern Africa. These organisms live in the marrow and
lymphatics, and flush at intervals into the general blood
stream. ‘The disease is communicated by the tzetse fly from
the wild game, the herds of which are the fester spots which
maintain the disease. The silkworm disease called pedbrine
is due to one of the Myxosporidia, Glugea bombycis, which
inhabits all the tissues of the caterpillar of Bombyx mort.

SECTION II.—THE METAZOA

WHILE the Protozoa are predominantly unicellular, and of
extremely simple structure, the rest of the animal kingdom,
grouped together under the comprehensive title of Metazoa,
are all multicellular in the adult condition, and have, except
in some of the lowest groups, a more or less elaborate struc-
ture owing to the presence of complicated systems of organs
for carrying on the various functions of animal life. Such
an animal as a lobster or a frog, for example, may readily
be ascertained to be made up of a complicated system of
parts, —skeleton, muscles, digestive organs, blood vessels,
and so on, — and it requires only the most superficial micro-
scopic examination of the substance of these various parts
to render it evident that each is built up of an immense
multitude of cells. A lobster or a frog, however, or any
other Metazoan, consists, in the earliest stage of its exist-
ence, of a single cell, the oosperm, formed by the union
of a male cell or sfevm with a female cell or ovum. The
ovum (Fig. 25) is usually spherical in shape, with one or
more enclosing membranes, with cell-protoplasm enclosing
a large nucleus (germinal vesicle, as it is often termed in
this case), in which are contained one or more small,
rounded bodies (germinal spot or spots). The ovum may
contain, in addition to the protoplasm, a quantity of non-
protoplasmic material or yolk.

59

60 MANUAL OF ZOOLOGY SECT.

Before the changes begin which lead to the formation
of the multicellular Metazoan, another cell, the made cell or
sperm, has to unite with the ovum or female cell. Before
this takes place, the ovum throws off portions of its substance
(Fig. 26, foZ) in the form of two little rounded bodies —
the polar bodies. This preliminary process is known as the
maturation of the ovum. The male cell or sperm is a
relatively small cell, usually motile, which penetrates into

Fic. 25. — Ovum of a Sea-Urchin, showing the radially striated cell-membrane, the
protoplasm, containing yolk- granules, the large nucleus (germinal vescicle) , with
its network of chromatin and a large nucleolus (germinal spot). (From) Bal-
four’s Embryology, after Hertwig.)

the ovum, and coalesces with it—the coalescence being
what is termed fertilisation or impregnation — and the
immediate result being that, instead of separate ovum and
sperm, we have a compound body, the oosperm, formed by
their union, but not differing at first in any marked degree
from the simple ovum, and containing a single nucleus
representing both the nucleus of the sperm and that of the
ovum.

On impregnation follows the process of segmentation of
the oosperm. The nucleus first divides into two; then the

Ba THE METAZOA 61

oe

Fic. 26, — Diagram illustrating the maturation and fertilisation of the ovum. A, formation of
first polar globule; B, beginning of fertilisation, sperms approaching the micropyle or
aperture in the enclosing membrane of the ovum through which the sperm enters; C, forma-
tion of the male pronucleus; D, approximation of the male and female pronuclei; E, forma-
tion of segmentation-nucleus; Q cent, female centrosome; ¢ cent, male centrosome (the
centrosomes are cell-structures not further referred to in this work); ze, egg-membrane;
microp, micropyle; fol, polar bodies; Q prox, female pronucleus; 3 x07, male pronu-
cleus; seg. zuc?, segmentation nucleus.

62 MANUAL OF ZOOLOGY SECT.

substance of the protoplasm becomes cleft into two parts
(Fig. 27), each half containing one of the nuclei, so that
two complete cells result. This process, it will be observed,
is essentially the same as the dcnary fission of Amoeba and
other Protozoa: in the Metazoan, however, the two cells
do not become separated from one another as the two
parts of the divided Amceba do, but remain in contact and
undergo further changes. Each of them divides (Fig. 27)

Fic. 27. — Various stages in the segmentation of the oosperm. (From Gegenbaur’s
Comparative Anatony.)

in the same manner into two— four cells being thus formed ;
the four divide to form eight, the eight to form sixteen,
and so on; until, by this process of division and sub-
division, the oosperm becomes segmented into a large
number of comparatively small cells. In this mass of cells
an arrangement into layers, the germinad layers, becomes by
and by discernible; and from these layers of cells are
developed eventually all the parts of the body of the
Metazoan.

II THE METAZOA 63

This mode of development is, however, not entirely with-
out parallel among the Protozoa. In the colonial Volvox
(p. 43, Fig. 17) it will be remembered that male cells or
microgametes (sperms) and female cells or megagametes
(ova) are developed, and that by the coalescence of a
microgamete with a megagamete a compound cell, the
zygote (oosperm), is formed, which undergoes division to
give rise to an adult Volvox.

As the various parts become gradually moulded from the
cells of the germinal layers, the form and arrangement of
the cells of the different parts become modified in different
ways, so that the cellular structure comes to differ widely;
and, as a result, we find in the fully formed animal a
variety of different kinds of material, — tissues, as they are
termed,— such as muscle, bone, gristle, nerve, all derived
from the cells of the germinal layers. Of such tissues the
following are the most important. An ef7chefium is a thin
stratum of cells covering some surface, external or internal ;
it may be one cell thick, or several cells thick. The cells of
which an epithelium is composed vary greatly in form in
different cases (Fig. 28): they may be beset at their free
surfaces with cilia (a), like the cilia of the Infusoria, or with
flagella, like those of the Mastigophora (/), or may be
amoeboid (4), sending out pseudopodia like a Rhizopod.
The epithelium which covers the outer surface is known
as the efedermis or deric epithelium; that which lines the
interior of the digestive organs is the evéric epithelium.

Glands (Fig. 29) are formed by modification of epithe-
lial cells. In many cases a single cell of the epithelium
forms a gland, which is then termed a wnicellular gland
(A, B). The secretion (or substance which it is the func-
tion of the gland to form or collect) gathers in such a case
in the interior of the cell, and reaches the surface of the

64 MANUAL OF ZOOLOGY SECT.

Fic. 28. — Various forms of epithelium. a, ciliated epithelium; 4, columnar; d, sur-
face view of the same; c, tessellated; e¢, the same from the surface; /, flagellate
epithelium with collars; g, flagellate epithelium without collars; 4, epithelium
of intestine with pseudopodia; 7, stratified epithelium; %, deric epithelium of a
marine planarian with pigment cells, rod cells, and sub-epithelial glands. (From
Lang’s Comparative Anatomy.)

II THE METAZOA 65

epithelium through a narrow prolongation of the cell, which
serves as the duct of the gland. In other cases the gland is
multicellular (D, G), formed of a number of cells of the
epithelium, lining a depression or infolding, simple or com-
plex in form, of the latter. In the central cavity of such a

Fic. 29. — Diagram to illustrate the structure of glands. 4, unicellular glands in an
epithelium; 2, unicellular glands lying below epithelium and communicating
with the surface by narrow processes (ducts); C, group of gland cells; D, group
of gland cells lining a depression; £ and /, simple multicellular gland; G,
branched multicellular gland. (From Lang.)

gland the secretion collects to reach the surface through

a passage, the duc?.

The general name of connective “issues is applied to a
number of tissues which play a passive part in the economy
of the animal, connecting and supporting or protecting the
various organs. Sometimes connective tissue is gelatinous
in character, sometimes fidrous. Fat or adipose tissue is

F

66 MANUAL OF ZOOLOGY SECT.

usually developed by modification of fibrous connective
tissue, the cells becoming distended with oily matter.
Cartilage is a firm but elastic material, readily cut with a
knife, which forms an important constituent of the skeleton
in higher animals. Bove differs from cartilage in being
much denser and harder, owing to its being strongly
impregnated with limey matter (carbonate and phosphate
of lime).

Muscular tissue is the material by means of which nearly
all the movements of the Metazoa are effected. It consists
of bundles of microscopic fibres, which in the living condi-
tion have the special property of contractility, contracting,
z.e. becoming shorter and thicker, when stimulated. Bundles
or bands of these form the organs known as muscles. Verve
“issue, which is the sensitive, conducting, and stimulating
tissue of the body, consists of nerve-cells and nerve-fibres ;
groups of the former constitute zerve-gangha, bundles of
the latter form nerves.

Associated with the multicellular character of the Metazoa
is the possession of a variety of different parts or organs
adapted to carrying out different functions in the life of
the animal. Such a formation of organs is faintly fore-
shadowed in the unicellular body of the Protozoa; the
contractile vacuoles, the nucleus, the pseudopodia, flagella,
and cilia, the gullet, etc., are all to be looked upon as organs
subserving certain functions. But in the Metazoa, with the
exception of some of the lower groups, the development
of organs for the carrying on of the functions of animal life
— organs of locomotion, organs for protection and support,
organs of digestion, respiration, and reproduction — is
carried much further.

Some of the chief functions which are carried on in the
body of an animal have already been briefly referred to in

II THE METAZOA 67

the account of the Protozoa. The special study of these
constitutes, as already pointed out in the Introduction, the
science of Physiology, which forms accordingly an important
part of the study of Zoology, and a part to which frequent
reference will be made in dealing with the structure of the
various groups of animals.

The various internal parts of an animal are supported
and protected by the sé7z and the skeleton. The skin or in-
tegument consists of a layer of cells — the epfzdermis — with,

Fic. 30. — Bones of the human arm and fore-arm with the biceps muscle, showing
the shortening and thickening of the muscle during contraction and the conse-
quent change in the relative position of the bones — viz., flexion of the fore-arm
on the upper arm. (From Huxley's Physzology.)

superficial to it, in many animals, a non-cellular layer known

as the cuf#cle, and below it usually a fibrous layer, the

dermis. The skeleton is, as already explained in the
section on the Protozoa, a system of hard parts, external or
internal, serving for the protection and support of the softer
substance of the body. When these hard parts are external
they form an exoskeleton, when internal an endoskeleton.

An exoskeleton is formed by the thickening and hardening

of portions of one or other of the layers of the integument,

— cuticle, epidermis, or dermis. An endoskeleton usually

68 MANUAL OF ZOOLOGY SECT.

consists either of cartilage, or of bone, or of both. The
parts of the skeleton in the higher animals, whether external
or internal, usually consist of a number of distinct pieces
which are movably articulated together, and these have the
additional important function of serving for the attachment
of muscles, constituting a jointed framework on which the
muscles act in bringing about the various movements of the
body and its appendages (Fig. 30).

The nutrition of the Metazoa is in some cases, as in some
of the Protozoa, effected by food being absorbed in a
dissolved form through the general surface. In the great
majority, however, the food, liquid or solid, is received
through an opening —the mouth—into a cavity in the
interior of the body—the digestive or enteric cavity. In
most cases this has the form of a longer or shorter tube or
canal, beginning at the mouth and ending at a second exter-
nal opening —the azws. This digestive or enteric canal
consists usually of a number of different parts, through which
the food passes in succession, each part having its special
function to perform in connection with nutrition. In most
cases there are organs in the neighbourhood of the mouth
serving for the seizure of food ; these may be simply ¢ezdacles,
or soft, finger-like appendages, or they may have the form of
jaws, by means of which the food is not only seized but torn
to pieces, or ground into small fragments, in the process
of mastication. In general we can distinguish in the enteric
canal a buccal cavity, a pharynx, an esophagus or gullet, a
stomach, and an intestine. It is in the stomach and anterior
part of the intestine that the food becomes acted upon by
certain digestive secretions, the effect of which is to render
the various ingredients soluble, and thus fitted to be absorbed
through the wall of the enteric canal, so as to reach the
various parts of the body and supply them with nourish-

II THE METAZOA 69

ment. These digestive secretions are partly produced by
the cells of the epithelium of the canal, which are modified
to form unicellular or multicellular glands (p. 65), partly by
certain large special digestive glands, salivary glands, liver,
and pancreas. The nutrient parts of the food are by this
means so acted upon that they are ready to be absorbed,
and in most animals pass into the blood, to be distributed

Fic. 31.— General view of the viscera of a male frog, from the right side. a,
stomach; 4, urinary bladder; c, small intestine; c/, cloacal aperture; d, large
intestine; ¢, liver; f, bile duct; g, gall bladder; %, spleen; 7, lung; 4, larynx;
2, fat body; mz, testis; , ureter; 0, kidney; #, pancreas; s, cerebral hemi-
sphere; sf, spinal cord; 7, tongue: x, auricle; 27, urostyle; 7, ventricle;
v.s, vesicula seminalis; w, optic lobe; -r, cerebellum; y, Eustachian recess;
z, nasal sac. (From Marshall.)

throughout the body. The insoluble and indigestible ingre-
dients of the food pass on through the posterior part of the
intestine, and reach the exterior cee the anal aperture
as the feces.

A supply of oxygen is necessary for the carrying on of the
chemical changes in the tissues on which vital activity is
dependent. At the same time, as a result of these changes,

70 MANUAL OF ZOOLOGY SECT.

carbonic anhydride (carbonic acid gas) is constantly being
produced. The taking in of oxygen and giving off of car-
bonic anhydride is the process of respiration. The task of
facilitating the entry of oxygen and the passage outwards of
carbonic anhydride is in most of the Metazoa performed
by a set of organs known as organs of respiration; but in
many respiration takes place through the general surface,
and special organs for carrying on this function are absent.
When organs of respiration are present, they are either
processes or g@l/s (dranchiw) adapted for the respiration of
air dissolved in water; or Zumgs or other cavities which are
adapted for the direct respiration of air. Through the thin
membrane lining the gill, or lungs, the oxygen passes and
enters the blood in vessels immediately underneath the
membrane, to be conveyed, like the food, throughout the
system and supplied to the several parts. At the same
time the carbonic anhydride, brought to the gill or lung by
the same means, passes outwards into the surrounding water
or air, and is thus got rid of.

The blood consists of a fluid A/asma, in which float
numerous cells — the dlood corpuscles. Sometimes the blood
is colourless ; usually it is bright red, owing to the presence
of a red colouring matter, termed Aemoglobin, which is
sometimes confined to certain of the corpuscles, sometimes
diffused throughout the plasma. Hemoglobin has a strong
affinity for oxygen, and is thus of importance in connection
with respiration.

In order to carry on its functions as a conveyer of
nutriment and of oxygen throughout the body, the blood
flows in a systemy of vessels —the blood vascular system —
which ramify throughout all the organs. Through this
system of vessels it is driven in a more or less regular
course, either by pulsating contractions of the muscular

IL THE METAZOA 71

walls of the blood-vessels themselves, or by the agency of a
special organ, the Aeart. ‘The heart is essentially a sac with
muscular walls. Its cavity is in communication with the
main blood-vessels, and its walls contract regularly and
drive the blood through the system of vessels, the direction
of flow being regulated by a system of valves.

The nitrogenous waste-matters which are produced as a
result of the chemical changes that accompany vital action
in the various organs, are separated out and got rid of bya
system of organs known as the organs of excretion, or renal
organs —this process of elimination being known as the
process of renal excretion.

It is by means of the nervous system that the animal
receives impressions from the exterior and from the internal
organs, and that the various internal parts are brought into
vital communication with one another. The nervous system
extends as a complicated system of nerves or bundles of
nerve-fibres throughout all parts of the body. Large
aggregations of nerve-cells and nerve-fibres forming the
centres of the system are known as nerve-ganglia. When
one of these, or a group of them, situated towards the
anterior end, preponderates in size over the others, it
is termed the dvazz. Forming an important part of the
nervous system are the organs of the special senses, —
sight, hearing, smell, and taste, each of which is an organ
adapted for the reception of impressions of a special kind
from the exterior, — the impressions of light, of sound waves,
of the particles and substances that produce the sensations
of smell and taste. The less specialised sense of touch and of
heat and cold is diffused generally over the integument, in
which there are frequently special cells, or groups of cells,
with nerve-fibres terminating in them, that are concerned
with such sensations.

72 MANUAL OF ZOOLOGY SECT.

The organs of sexual reproduction are the gonads, in
which male and female cells or sperms and ova are
produced, with the gonoducts or canals by which these
cells reach the exterior. The gonads in which male cells
or sperms are produced are called #szes, and their ducts
are the sperm-ducts. The gonads in which female cells
or ova are formed are called ovaries, and their ducts
oviducts. Sometimes testes and ovaries occur in distinct
male and female individuals, when the animal is said to be
unisexual, or to have the sexes distinct. In other cases
both ovaries and testes occur in the same individual, when
the animal is said to be hermaphrodite, or to have the sexes
united. In some instances the same gonad produces both
sperms and ova—assuming the character of a hermaphrodite
gonad or ovo-testis.

In many animals the ova are fertilised by the sperms
after they have passed out from the body, and the develop-
ment takes place externally —a condition which is known
as oviparity. But in others the ova are fertilised while still
in the ovary or oviduct of the parent, and the development
may take place in the oviduct, usually in a special dilated
part of the latter —the w¢erws—so that the young only
escape to the exterior after they have attained a compara-
tively advanced stage of their development — when the
animal is said to be wuiparous.

Besides the sexual process of reproduction by means
of ova and sperms, there are in many classes of animals
various asexval modes of multiplication. One of these —
the process of s¢mple fission — has been already noticed in
connection with the reproduction of Protozoa. The forma-
tion of spores is an asexual mode of multiplication which
occurs only in the Protozoa, and has been described in the
account of that group. Multiplication by dudding takes

II THE METAZOA 73

place in a number of different classes of animals. In this
form of reproduction a process or dud (Fig. 32, 6@) is given
off from some part of the parent animal; this bud sooner
or later assumes the form of the complete animal, and may
become detached from the parent either before or after its

Fic. 32. —Fresh-water polype (hydra), two specimens, the one expanded the other
contracted, showing multiplication by budding. 6d! dd? dd%, buds in various
stages of growth, (From Parker's Szology.)

development has been completed, or may remain in perma-
nent vital connection with it.

When the buds, after becoming fully developed, remain
in vital continuity with the parent, a sort of compound
animal, consisting of a greater or smaller number of con-
nected units, is the result. Such a compound organism is

74 MANUAL OF ZOOLOGY SECT.

termed a co/ony, and the component units are termed zoozds.
In some cases such a colony is produced by a process which
is more correctly termed incomplete fission than budding.
The various systems of organs, — digestive, circulatory,
nervous, excretory, etc., — present under one form or an-
other in all the higher groups of animals, are variously
arranged and occupy various relative positions in different
cases, producing a number of widely different plans of
animal structure. According as their structure conforms
to one or another of these great plans, animals are referred
to one or another of the corresponding great divisions or
phyla of the animal kingdom. That animals do present
widely differing plans of structure is a matter of common
knowledge. We have only to compare the true fish, such
as cod, haddock, etc., in a fishdealer’s shop with the
lobsters and the oysters, to recognise the general nature
of such a distinction. The first named are characterised by
the possession of a backbone and skull, with a brain and
spinal cord, and of two pairs of limbs (the paired fins) :
they belong to the great vertebrate or backboned group —
the division Vertebrata of the phylum Chordata. The
lobsters, on the other hand, in which these special verte-
brate structures are absent, possess a jointed body enclosed
in a hard jointed case, and a number of pairs of limbs also
enclosed in hard jointed cases, and adapted to different
purposes in different parts of the body — some being feelers,
others jaws, others legs: their general type of structure is
that which characterises the phylum Arthropoda. The
oysters, again, with their hard calcareous shell secreted by a
pair of special folds of the skin constituting what is termed
the mane, and with a special arrangement of the nervous
system and other organs which need not be described here,
are referable to the phylum JoUusca. Other familiar

1 THE METAZOA 75

animals are readily to be recognised as belonging to one or
other of these great phyla. A prawn, a crab, a bluebottle
fly, a spider, are all on the same general plan as the
lobster: they are jointed animals with jointed limbs, and
they have the internal organs occupying similar positions
with relation to one another. They are all members of the
phylum Arthropoda. Again, a mussel, a snail, a squid, are
all to be set side by side with the oyster as conforming
to the same general type of structure ; they are all members
of the phylum AfoZusca. Finally a dog, a lizard, a fowl, are
obviously nearer the fish: they all have skull and backbone,
brain and spinal cord, and two pairs of limbs; they are all
members of the great group Chordata.
Altogether twelve phyla are to be recognised, viz. : —

I. Protozoa VII. Molluscoida
II. Porifera VIII. Echinodermata
Ill. Calenterata IX. Annulata
IV. Platyhelminthes X. Arthropoda
V. Nemathelninthes XI. Mollusca

VI. Zrochelminthes XII. Chordata

SECTION III.—PHYLUM PORIFERA

Tue Porifera, or sponges, belong to the lowest group of
the Metazoa. They live fixed to the surface of rocks, or to
submerged timber or seaweeds, so as to be incapable of
locomotion ; and have, in most cases, a general form which
suggests the vegetable rather than the animal kingdom.
But, in essentials, as will presently become
evident, the sponges are distinctly animal in
character, and the resemblances to plants
are entirely superficial.

The majority of sponges are compli-
cated and difficult to understand, owing to
their elaborate mode of branching and the
fusion of the branches, and to the exceed-
ingly intricate character of the skeletal
parts, aside from their cellular structure.
. Some, however, are free from these com-
Fic. 33-7 Syconcili- plications ; and it is in one of these that
pintey Hyatt), the main characteristics of sponges are

best studied. Such a simple form is Sycon,
a small sponge living attached to rocks on the seashore
towards or below low-water mark. Sycon gelatinosum’ has
the form of a tuft, one to three inches long, of branching

1 This is an Australasian species, but the following account will apply in
all essential respects to Sycon ciliatum (Fig. 33) and S. clarkii of the coast
of New England.

76

SECT, II PHYLUM PORIFERA 17

cylinders (Fig. 34), all connected together at the base,
where it is attached to the surface of seaweeds, rocks, or
other solid bodies submerged in the sea. It is flexible,
though of tolerably firm consistency. On the outer surface
are to be detected, under the microscope, groups of minute
pores — the zzhalant pores. At the free end of each of the
cylindrical branches is a small but distinct opening, sur-
rounded by what appears like a delicate fringe. When the
branches are bisected longitudinally (Fig. 35), it is found
that the terminal openings (0) lead into narrow passages,

Fic. 34.—Sycon gelatinosum. Entire sponge, consisting of a group
of branching cylinders (natural size).

wide enough to admit a stout pin, running through the axis
of the cylinders; and the passages in the interior of the
various branches join where the branches join—the pas-
sages thus forming a communicating system. On the wall of
the passages are numerous fine’ apertures which require a
strong lens for their detection. The larger apertures at the
ends of the branches are the oscw/a of the sponge, the pas-
sages the paragastric cavities. If the living Sycon is placed
in sea-water with which has been mixed some carmine pow-
der, it will be noticed that the minute particles of the
carmine seem to be attracted towards the surface of the

78 MANUAL OF ZOOLOGY SECT.

sponge, and will often be seen to pass into its substance
through the minute pores already mentioned as occurring in
groups between the elevations on the outer surface. This
would appear to be due to the passage of a current of water

Fic. 35.—Sycon gelatinosum. A portion slightly magnified; one cylinder (that
to the right) bisected longitudinally to show the central paragastric cavity
opening on the exterior by the osculum, and the position of the incurrent and
radial canals; the former indicated by the black bands, the latter dotted. 7
marks the position of three of the groups of inhalant pores at the outer ends of
the incurrent canals; 0, osculum.

into the interior of the sponge through these minute open-
ings dotted over the surface; and the movement of the

floating particles shows that a current is at the same time
flowing out of each of the oscula. A constant circulation of

HI PHYLUM PORIFERA 79

water would thus appear to be carried on — currents moved
by some invisible agency flowing through the walls of the
sponge to the central paragastric cavities, and passing out
again by the oscula.

If a portion of the Sycon is firmly squeezed, there will
be pressed out from it first sea-water, then, when greater
pressure is exerted, a quantity of gelatinous-looking matter,
which, on being examined microscopically, proves to be
partly composed of a protoplasmic material consisting of
innumerable, usually more or less broken, cells with their
nuclei, and partly of a non-protoplasmic, jelly-like substance.
When this is all removed there remains behind a toughish,
felt-like material, which maintains more or less completely
the original shape of the sponge. This is the ske/eton or
supporting framework. A drop of acid causes it to dissolve
with effervescence, showing that it consists of carbonate of
lime. When some of it is teased out and examined under
the microscope, it proves to consist of innumerable, slender,
mostly three-rayed microscopic bodies (Fig. 36, sf) of a
clear, glassy appearance. These are the calcareous spicules
which form the skeleton of the Sycon.

Covering the outer surface of the sponge is a single layer
of flattened, scale-like cells —the ectoderm (Fig. 36, ec) —
through which project regularly arranged groups of needle-
like and spear-like spicules (sf'). The paragastric cavities
are lined by a layer of cells (¢7), which are like those of the
ectoderm in general shape; this is the evdoderm of the
paragastric cavity. Running radially through the thick
wall of the cylinders are a large number of regularly
arranged straight passages. Of these there are two sets,
those of the one set—the zncurrent canals (£C) — nar-
rower, and lined by ectoderm similar to the ectoderm of
the surface; those of the other set—the radial or

"

i

Mh

Me

Fic. 36. —Sycon gelatinosum. Transverse section through the wall of a cylinder
(parallel with the course of the canals), showing one incurrent canal (/C), and
one radial (#) throughout their length; sf, triradiate spicules; sp’, oxeote
spicules of dermal cortex (dc); sf'', tetraradiate spicules of gastral cortex (gc);
ec, ectoderm; ez, endoderm; #7, pore membrane; //, prosopyles; @f, apopyle ;
dz, diaphragm; exc, excurrent passage; PG, paragastric cavity; em, early
embryo; ez’, late embryo. The arrows indicate the course of the water through

the sponge.
80

SECT, Ti PHYLUM PORIFERA 8

flagellate canals (&) —rather wider, octagonal in cross-
section, and lined by endoderm continuous with the lining
of the paragastric cavity. The incurrent canals end blindly
at their inner extremities, not reaching the paragastric
cavity; externally each becomes somewhat dilated, and the
dilations of neighbouring canals often communicate. These
dilated parts are closed externally by a thin membrane —
the ore membrane, perforated by three or four openings —
the inhalant pores already referred to. The flagellate canals
are blind at their ow¢er ends, which lie at a little distance
below the surface ; internally, each communicates with the
paragastric cavity by a short, wide passage, the excurrent
canal (exc). Incurrent and flagellate canals run side by
side, separated by a thin layer of sponge substance, except
at certain points, where there exist small apertures of com-
munication — the frosopyles (pp) — uniting the cavities
of adjacent incurrent flagellate canals.

The ectoderm lining of the incurrent canals is of the
same character as the ectoderm of the outer surface. The
endoderm (2) of the flagellate canals, on the other hand, is
totally different from that which lines the paragastric cavity.
It consists of cells of columnar shape, ranged closely together
so as to form a continuous layer. Each of these flagellate
endoderm cells, or collared cells, as they are termed, is not
unlike one of the choanoflagellate Protozoa (p. 38) ; it has
its nucleus, one or more vacuoles, and, at the inner end, a
single, long, whip-like flagellum, surrounded at its base by a
delicate, transparent, collar-like upgrowth, similar to that
which has already been described as occurring in the
Choanoflagellata. If a portion of a living specimen of the
sponge is teased out in sea-water, and the broken fragments
examined under a tolerably high power of the microscope,
groups of these collared cells will be detected here and

G

82 MANUAL OF ZOOLOGY SECT.

there, and in many places the movements of the flagella

will be readily observed. It is to these movements that the ©
formation of the currents of water passing along the canals

is due.

The short passage or excurrent canal, which leads inwards
from the flagellate canal to the paragastric cavity, differs
from the former in being lined by flattened cells similar to
those of the paragastric cavity; it is partly separated from
the flagellate canal by a thin diaphragm (Fig. 36, a),
perforated by a large circular central aperture — the apopyle
(ap) — which is capable of being contracted or dilated ; its
Opposite aperture of communication with the paragastric
cavity, which is very wide, is termed the gastric ostium of
the excurrent canal.

The effect of the movement of the flagella of the cells in
the flagellate canals is to produce currents of water running
from without inwards along the canals to the paragastric
cavity. This causes water to be drawn inwards through the
prosopyles from the incurrent canals, and, indirectly, from
the exterior through the perforated membranes at the outer
ends of the latter.

Between the ectoderm of the outer surface and of the
incurrent canals, and the endoderm of the inner surface and
of the flagellate canals, are a number of spaces filled by an
intermediate layer — the mesoderm or mesogl@a — in which
the spicules of the skeleton are embedded. The
spicules (Fig. 36, sf.), each of which is developed in a
single cell of the middle layer, are regularly arranged, and
connected together in such a way as to protect and support
the soft parts of the sponge. Most are, as already noticed,
of triradiate form. Large numbers, however, are of simple
spear-like or club-like shape (sf'). The sexual reproductive
cells —the ova (Fig. 36, ov) and sperms —are developed

II PHYLUM PORIFERA 83

immediately below the flagellate endoderm cells of the
flagellate canals, and in the same situation are to be found
developing embryos (em, em').

The simplest sponges are vase-shaped or cylindrical in
form, either branched or unbranched, and, if branched,
with or without anastomosis or coalescence between neigh-
bouring branches. But the general form of the less sim-
ple sponges differs widely from that of such a branching
cylinder as is presented by Sycon (Fig. 34).

From the point to which the embryonic sponge becomes
attached, it may spread out horizontally, following the ir-
regularities of the surface on which it grows, and forming
a more or less closely adherent encrustation like that of an
encrusting lichen. In other cases the sponge grows at first
more actively in the vertical than in the horizontal direction,
and the result may be a long, narrow structure, cylindrical
or compressed, and more or less branched. Sometimes
vertical and horizontal growth is almost equal, so that event-
ually there is formed a thick, solid mass of a rounded or
polyhedral shape, with an even, or lobed, or ridged surface.
Very often, after active vertical growth has resulted in the
formation of a comparatively narrow basal part or stalk,
the sponge expands distally, growing out into lobes or
branches of varying forms, and frequently anastomosing.
Sometimes after the formation of the stalk with root-like
processes for attachment, the sponge grows upwards in such
a way as to form a cup or tube with a terminal opening.
Sometimes the sponge grows from a narrow base of attach-
ment into a thin flat plate or lamella; this may become
divided up into a number of parts or lobes, which may
exhibit a divergent arrangement like the ribs of an open
fan.

84 MANUAL OF ZOOLOGY SECT.

Sycon belongs to a type of sponges intermediate between
the very simplest forms on the one hand, and the more
complex on the other. The
simplest and most primitive
of known sponges is one
named Ascetta primordialis
(Fig. 37). It is vase-shaped,
contracted at the base to
form a sort of stalk, by the
expanded extremity of which
it is attached; at the oppo-
site or free end is the circular
osculum. So far there is a
considerable resemblance to
Sycon gelatinosum ; but the
structure of the wall in Ascetta
is extremely simple. Regu-
larly arranged over the sur-
face are a number of small
rounded apertures, the in-
halant or incurrent pores ;
but, since the wall of the
sponge is very thin, these
apertures lead directly into
the central or paragastric
cavity, the long passages or
canals through which the

es communication is effected in

Me onde vot mevacike Sycon being absent. “The
Se Lae ean wall consists of the same
three layers as in Sycon; but

the middle one, though it contains a small number of
spicules, is very thin ; the endoderm, which lines the

Ill PHYLUM PORIFERA 85

paragastric cavity, consists throughout of flagellate collared
cells similar to those of the flagellate canals of Sycon.

The majority of sponges, however, are more complicated
in structure than Sycon. One of the causes of their
complexity being that the canals, instead of being simple
and straight, become branched, forming a system, often
highly complicated, of ramifying channels. In these more
complex sponges the flagellate. collared cells are confined to

Ne

i aii
a

Fic. 38. — Vertical section of a fresh-water sponge (Spongilla), showing the arrange-
ment of the canal-system. CC, ciliated chambers; D/, dermal pores; Ex,
excurrent canals; GO, openings of the excurrent canals; PG, paragastric
cavity; SD, subdermal cavities; O, osculum. (Modified from Leuckart and
Nitsche’s diagrams.)

certain rounded dilatations of the canals—the flagellate
chambers.

Moreover, in the more complex forms the development
of branches from the originally simple sponge, and the
coalescence of neighbouring branches with one another,
greatly obscure the essential nature of the sponge as a
colony of zooids similar to the branches of Sycon; and
this effect is increased by the development of a variety of
infoldings of the ectoderm which appear in the higher
forms.

86 MANUAL OF ZOOLOGY SECT.

The elements of the ske/e/on differ in character in the
two sub-classes into which the sponges are divided. In
the Calcarea, of which Sycon is an example, they consist
of calcareous spicules, usually triradiate in form. In the
Non-Calcarea the skeleton either consists of spongin fibres
alone (Fig. 39, A), or of siliceous spicules alone, or of a
combination of spongin fibres with siliceous spicules (2) :
in some (Myxospongie) skeletal parts are altogether
absent. Spongin is a substance allied to silk in compo-
sition; the fibres are exceedingly fine threads, which branch
and anastomose, or are woven and felted together in such a
way as to form a firm, elastic supporting structure. The
siliceous spicules (Fig. 40) are much more varied in shape
than the spicules of the Calcarea, and in a single kind of
sponge there may be a number of widely differing forms of
spicules, each form having its special place in the skeleton
of the various parts of the sponge-body. In most Non-
Calcarea siliceous spicules and spongin fibres combine to
form the supporting framework, the relative development of
these two elements varying greatly in different cases. But in
certain groups of the Non-Calcarea, including the common
washing sponges, spicules are completely absent, and the
entire skeleton consists of spongin. In some Non-Calcarea
which are devoid of spicules, the place of these is taken
by foreign bodies — shells of Radiolaria, grains of sand, or
spicules from other sponges (Fig. 39, C). In others, again,
such as the Venus’s flower-basket (Zuplectel/a), the glass-
rope sponge (Ayalonema), and others, the skeleton consists
throughout of siliceous spicules bound together by a siliceous
cement. ;

Reproduction in the Sponges is effected either sexually or
asexually. The process by which, in all but the simplest
forms of sponges, a colony of zooids is formed from the

Ill PHYLUM PORIFERA 87

originally simple cylinder or vase, may be looked upon as
an asexual mode of reproduction by budding. Asexual

B.Pachychalina

Fic. 39. — Microscopic structure of the skeleton in various sponges. A, Euspongia,
network of spongin fibres; B, Pachychalina, spongin strengthened by siliceous
spicules; C, Spongelia, spongin strengthened by various foreign siliceous
bodies, fragments of spicules of other sponges, etc. (After Vosmaer.)

88 MANUAL OF ZOOLOGY SECT.

multiplication also assumes the form in some cases of a
process of production of internal buds in the shape of
groups of cells called gemmudles, which eventually become
detached and develop into new individuals. In the fresh-
water sponges (Sfongilide) multiplication takes place very
actively by means of such gemmules, each of which is a
spherical group of cells enclosed in an envelope composed
of peculiarly shaped siliceous spicules, termed amphidises
(Fig. 40, right side). All sponges multiply by a sexual
process — by means of male cells, or sperms, and female

Fic. 40. — Various forms of sponge spicules. (From Lang’s Text-Book.)

cells, or ova. Ova and sperms are developed in the same
sponge, but rarely at the same time. The cell destined to
form sperms divides into a number of small cells, giving
rise to a rounded mass of sperms. The latter, when
mature, have oval or pear-shaped heads and a long taper-
ing appendage or tail. Each cell destined to form an ovum
enlarges, and eventually assumes a spherical form. After a
sperm has penetrated into its interior and effected impreg-
nation, it usually becomes enclosed in a brood-capsule
formed for it by certain neighbouring cells, and in this
situation, still enclosed in the parent sponge, it undergoes

Ill PHYLUM PORIFERA 89

the earlier stages of its development. Eventually it becomes
free as a ciliated larva, which pursues a free existence for a
time, swimming about by the agency of the cilia, till after
a time it becomes fixed and develops into the adult form.

Fresh-water sponges (Sfongil/lide) live in rivers, lakes, etc.
Marine sponges occur in all seas, and at all depths, from the
shore between tide marks to the deepest abysses of the ocean.

Sponges do not appear to be edible by fishes, or even
the higher crustaceans or molluscs. Countless lower animal
forms, however, burrow in their substance, if not for food,
at least for shelter, and the interior of a sponge is frequently
found to be teeming with small crustaceans, annelids, mol-
luscs, and other invertebrates. None of the sponges are
true parasites. The little boring sponge, CZona, burrows
in the shells of oysters and other bivalves, and even into
solid limestone, but for protection and not for food. But
the sponge frequently lives in that close association with
another animal or plant to which the term messmateism, or
commensalism is applied — associations which benefit one or
both. Thus some species of sponge are never found grow-
ing except on the backs or legs of certain crabs. In these
cases the sponge protects the crab and conceals it from its
enemies, while the sponge benefits by being carried from
place to place, and thus obtaining freer oxygenation. Cer-
tain cirripede crustaceans (members of the order to which
the barnacles and acorn-shells belong) are invariably found
embedded in certain species of sponge. Frequently a
sponge and a zoophyte grow in intimate association, so
that they seem almost to form one structure. Thus the
glass-rope sponge (A/valonema) is always found associated
with a zoophyte (fadythoa), and there are many other in-
stances. Sponges often also grow in very close association
with certain low forms of plants (4/@).

SECTION IV.—PHYLUM CC@ELENTERATA

In the previous section we saw that the simplest type
of sponge has the general character of a cylinder, closed
at one end and open at the other, and having the walls
perforated by minute pores, and composed of three layers,
—ectoderm, mesoglcea, and endoderm, the last consisting
of collared flagellate cells.

In such an organism as this, imagine the pores to disap-
pear, the internal cavity thus coming to communicate with
the exterior by a single terminal aperture; the mesoglcea
to be replaced by a very thin, structureless layer containing
no cells; the endoderm cells to lose their collars; and a
circlet of arm-like processes, or tentacles, formed of the
same layers as the body-wall, to be developed round the
terminal aperture. The result would be a folype, and
would serve as a type of the general structure of the group
of animals with which we are now concerned.

The most familiar examples of Ccelenterata are the horny,
seaweed-like hydroids, or, as they are sometimes called,
“zoophytes,” to be picked up on every sea-beach, jelly-
fishes, sea anemones, and corals. The phylum is divided
into four classes as follows : —

Class 1. — Hydrozoa, including the fresh-water polypes,
zoophytes, many jellyfishes,—mostly of small size,—and a
few stony corals.

go

SECT. IV PHYLUM CCELENTERATA gI

Class 2.— Seyphozoa, including most of the large jelly-
fishes.

Class 3.— Actinozoa, including the sea-anemones, 2nd
the vast majority of stony corals.

Class ¢.—Ctenophora, including certain peculiar jelly-
fishes known as “‘comb-jellies.”’

1. THE HYDROZOA

Obelia, which is a good example of the class, is a common
zoophyte occurring in the form of a delicate, whitish, or light
brown, almost fur-like growth on the wooden piles of piers
and wharfs. Odela commissurals occurs on the coast of
New England almost at low-water mark, being exposed only
at the lowest tides. With it, north of Cape Cod, may be
found Odela gelatinosa, a rather stouter species, but similar
in general appearance. Odea geniculata is abundant on
Laminaria or the “devil’s apron,” giving the fronds when
submerged a downy appearance. The following account
refers to a common European species: It consists of
branched filaments about the thickness of fine sewing
cotton; of these, some are closely adherent to the timber,
and serve for attachment, while others are given off at right
angles, and present at intervals short lateral branches, each
terminating in a bud-like enlargement. The structure is best
seen under a low power of the microscope. The organism
(Fig. 41) is a colony, consisting of a common stem or axis,
on which are borne numerous zooids.

The large majority of the zooids have the form of little
conical structures (P, z—P, 4), each enclosed in a glassy,
cup-like investment or Aydrotheca (hth), and produced dis-
tally into about two dozen arms or “néacles (¢): these
zooids are the polipes or hydranths. Less numerous, and

92 MANUAL OF ZOOLOGY SECT. IV

found chiefly towards the proximal region of the colony, are
long cylindrical bodies or dlaséostyles (dls), each enclosed
in a transparent case, the gonangium or gonotheca (gth),
and bearing numerous small lateral offshoots, varying greatly
in form according to their stage of development, and known
as medusa-buds (m.bd¢). By studying the development of
these structures, and by a comparison with other forms, it
is known that both blastostyles and medusa-buds are zooids,
so that the colony is “morphic, having zooids of three
kinds.

To make out the structure in greater detail, living speci-
mens should be observed under a high power. A polype
is then seen to consist of a somewhat cylindrical, hollow
body, of a yellowish colour, joined to the common stem by
its proximal end and produced at its distal end into a
conical elevation, the manubrium or hypostome (mnb),
around the base of which are arranged the twenty-four
tentacles in a circle. Both body and manubrium are hol-
low, containing a spacious cavity, the ezteron (ent), which
communicates with the outer world by a mouth (mth), an
aperture placed at the summit of the manubrium. The
mouth is capable of great dilatation and contraction, and
accordingly the manubrium appears now conical, now
trumpet-shaped. Under favourable circumstances small
organisms may be seen to be caught by the tentacles and
carried towards the mouth to be swallowed. The hydro-
theca (A/h) has the form of a vase or wine-glass, and is
perfectly transparent and colourless. When irritated — by
a touch, or by the addition of alcohol or other poison — the
polype undergoes a very marked contraction: it suddenly
withdraws itself more or less completely into the theca, and
the tentacles become greatly shortened and curved over the
manubrium (P. 2).

Fic. 41.—Obelia sp. A, portion of a colony, with certain parts shown in longi-

tudinal section; B, medusa; C, the same, with reversed umbrella; D, the same,
oral aspect; Bd. 7, 2, buds ; bls, blastostyle ; c@, coenosarc; ect, "ectoderm:
end, endoderm ; e7t, enteric cavity; eth, gonotheca ( (gonangium) : ‘nth, hydro-
theca; 2, lithocyst ; m.b6d, medusa-bud; 7226, manubrium; msgi, mesogloza ;
mth, mouth; 2, perisarc: Pe F2p dy polypes ; vad.c, radial canal; ¢,
tentacle; 7/, velum.

& 93

94 MANUAL OF ZOOLOGY SECT.

The various branches of the common stem show a very
obvious distinction into two layers: a transparent, tough,
outer membrane, of a yellowish colour and horny con-
sistency, the perisarc (pf), and an inner, delicate, granular
layer, the cwnosare (cv), continuous by a sort of neck or
constriction with the body of each hydranth. The ccenosarc
is hollow, its tubular cavity being continuous with the
cavities of the polypes, and containing a fluid in which a
flickering movement may be observed, due to the presence
of vibrating cilia. In the blastostyle both mouth and tenta-
cles are absent, the zooid ending distally in a flattened disc ;
the hydrotheca of the polype is represented by the gono-
theca (gh), which is a cylindrical capsule enclosing the
whole structure, but ultimately becoming ruptured at its
distal end to allow of the escape of the medusa-buds.
These latter are, in the young condition, mere hollow off-
shoots of the blastostyle: when fully developed they have
the appearance of saucers attached by the middle of the
convex surface to the blastostyle, produced at the edge into
sixteen very short tentacles, and having a blunt process, the
manubrium, projecting from the centre of the concave sur-
face. They are ultimately set free through the aperture in
the gonotheca as little medusze or jellyfish (B-D), which
will be described hereafter.

The microscopical structure of Obelia reminds us, in its
general features, of that of such a simple sponge as Ascetta,
but with many characteristic differences. The body is
composed of two layers of cells, the ectoderm and the
endoderm, the latter ciliated; between them is a very
delicate transparent membrane, the mesoglea or supporting
Jamella, which, unlike the intermediate layer of sponges,
contains no cells and is practically structureless.

The perisarc or transparent outer layer of the stem shows

Iv PHYLUM CCELENTERATA 95

no cell-structure, but only a delicate lamination. It is, in
fact, not a cellular membrane or epithelium, like the ecto-
derm and endoderm, but a cwéicle, formed, layer by layer,
as a secretion from the ectoderm cells (see p. 67). It is
of chitinoid or horn-like consistency, and, like the lorica
of many Protozoa, serves as a protective external skeleton.

Embedded in the ectoderm are numerous clear, ovoid
bodies, the s#nging-capsules or nematocysts (Fig. 42), serving
as weapons of offence. Each consists (A) of a tough, ovoid
capsule, full of a gelatinous material, and invaginated at one
end in the form of a hollow process continued into a long,
coiled, hollow thread. The whole apparatus is developed in
an interstitial cell called a cnidoblast (end), which, as it ap-
proaches maturity, migrates towards the surface, and becomes
embedded in one of the large ectoderm cells. At one point
of its surface the cnidoblast is produced into a delicate pro-
toplasmic process, the cnzdocil or trigger-hatr (cnc) : when this
is touched — for instance by some small organism brought
into contact with the waving tentacles— the cnidoblast un-
dergoes a sudden contraction, and the pressure upon the
stinging-capsule causes an instantaneous eversion of the
thread (B), at the base of which are minute barbs. The
threads or the gelatinous substance are poisonous and
exert a numbing effect on the animals upon which the
Obelia preys.

The structure of the Medusz — formed as we have seen
by the development of medusa-buds liberated from a
ruptured gonangium— yet remains to be considered. The
convex surface of the bell or umbrella (Fig. 41, B-D) by
which the zooid was originally attached to the blastostyle, is
distinguished as the ex-wmébrella, the concave inner surface
as the swb-umbrella. From the centre of the sub-umbrella
proceeds the manubrium (md), at the free end of which is

96 MANUAL OF ZOOLOGY SECT.

the four-sided mouth (sth). Very commonly as the medusa
swims the umbrella becomes turned inside out, the sub-

mele

Fic. 42.— Nematocysts of hydra. A, undischarged; B, discharged; C, nerve-
supply; cd, cnidoblast; czc, cnidocil; 2, nucleus; #fc, nematocyst; xv.c,
nerve-cell. (From Parker’s Bzology, after Schneider.)

umbrella then forming the convex surface, and the manu-

brium springing from its apex (Fig. 41, C).

Iv PHYLUM CCELENTERATA 97

The mouth (Figs. 41, C, D, and 43, mth) leads into an
enteric cavity which occupies the whole interior of the
manubrium, and from its dilated base sends off four delicate
tubes, the radial canals (rad. c), which pass at equal
distances from each other through the substance of the
umbrella to its margin, where they all open into a c7rcular
canal (cir. c), running parallel with and close to the
margin. By means of this system of canals the food, taken

end lam

7
3

AGED

Fic. 43. — Dissection of a medusa with rather more than one-quarter of the umbrella
and manubrium cut away (diagrammatic). The ectoderm is dotted, the endo-
derm striated, and the mesogloea black. c/r. c, circular canal; exd. lam,
endoderm lamella; gow, gonad; 7, lithocyst; 26, manubrium; sth, mouth;
rad. ¢c, radial canal; v/, velum.

in at the mouth and digested in the manubrium, is dis-

tributed to the entire medusa.

The edge of the umbrella is produced into a very narrow
fold or shelf, the vewm (Fig. 43, v/), and gives off the
tentacles (7), which are sixteen in number in the newly-born
medusa (Fig. 41, 2), but which are very numerous in the
adult. At the bases of eight of the tentacles — two in each
quadrant — are minute globular sacs (7), each containing a

H

98 MANUAL OF ZOOLOGY SECT.

calcareous particle or “thite. These are the marginal sense-
organs or lithocysts: they were formerly considered to be
organs of hearing, and are hence frequently called otocysés -
in all probability their function is to guide the medusa by
enabling it to judge of the direction in which it is swim-
ming. The marginal organs, in this case, may therefore be
looked upon as organs of the sense of direction.

In the description of the fixed Obelia-colony no mention
was made of cells set apart for reproduction, like the ova and
sperms of a sponge. As a matter of fact, such sexual cells
are only found, in their fully developed condition at least, in
the meduse. Hanging at equal distances from the sub-
umbrella, in immediate relation with the radial canal, are
four ovoid bodies (Fig. 43, gow), each containing a mass of
cells which are developed either into ova or into sperms. As
each medusa bears organs of one sex only (testes or ovaries
as the case may be), the individual medusze are @ecious.

When the gonads are ripe, the sperms of the male
medusz are shed into the water and carried by currents to
the females, impregnating the ova, which thus become
oosperms or unicellular embryos. The oosperm undergoes
complete segmentation (Fig. 44, 4-7), and is converted
into an ovoidal ciliated body called a planula (G, 7). The
planula swims freely for a time (/7), and then settles down
on a piece of timber, seaweed, etc., fixes itself by one end
(#), and becomes converted into a Aydrua or simple polype
(Z, MZ), having a disc of attachment at its proximal end,
and at its distal end a manubrium and circlet of tentacles.
Soon the hydrula sends out lateral buds, and, by a frequent
repetition of this process, becomes converted into the com-
plex Obelia-colony with which we started.

This remarkable life-history furnishes the first example we
have yet met with of a/ternation of generations, or metagenesis.

Iv PHYLUM CCSLENTERATA 99

The Obelia-colony is sexless, having no gonads, and develop-
ing only by the asexual process of budding ; but certain of
its buds—the medusze — develop gonads, and from their
impregnated eggs new Obelia-colonies arise. We thus have
an alternation of an asexual generation — the Obelia-colony
—with a sexual generation, the medusa.

Fic. 44.—Stages in the development of two zoophytes (A-H, Laomedea, I-M,
Eudendrium) allied to Obelia; A-F, stages in segmentation; G, the planula
enclosed in the maternal tissues; H, the free-swimming planula; I-M, fixation
of the planula and development of the hydrula. (From Parker’s Biology, after
Allman.)

The majority of the Hydrozoa resemble Obelia in form-
ing fixed colonies ; but there are a few exceptional cases in
which the animal remains simple. One of these is Hydra,
the Fresh-water Polype. In Hydra the entire organism (Fig.

45) consists of a simple cylindrical body with a conical hypos-

SCALE FOR A

Fic. 45.— Hydra. A vertical section of entire animal; B, portion of transverse
section, highly magnified; C, two large ectoderm cells; D, endoderm cell of
H. viridis ; E, large nematocyst; F, small nematocyst; G, sperm; a, ingested
diatom; éd.1, dd.2, buds; chs, chromatophores; cv6/, cnidoblast; czc, cnidocil;
ect, ectoderm; end, endoderm; ext. cav, enteric cavity; evt. cav', its prolonga-
tion into the tentacles; /7, flagellum; Ay, hypostome or manubrium; zw¢. c, in-
terstitial cells; 7. #7, muscle processes; sth, mouth; asg?, mesoglea; xct,
large, and z¢c!, small nematocysts; 7%, nucleus; ov, ovum; ovy, ovary; psd,
pseudopods; sfy, spermary; vac, vacuole.

100

SECT. IV PHYLUM CCELENTERATA IOI

tome and a circlet of from six to eight tentacles surrounding
the mouth. It is ordinarily attached, by virtue of a sticky
secretion from the proximal end, to weeds, etc., but is capable
of detaching itself and moving from place to place after the
manner of a looping caterpillar. The tentacles are hollow,
and communicate freely with the enteron. There is no
perisarc. Buds are produced which develop into Hydre ;
but these are always detached sooner or later, so that a
permanent colony is never formed. There are no special
reproductive zooids, but simple ovaries (ovy) and testes
(spy) are developed, the former nearer the proximal, the
latter nearer the distal end of the body.

In nearly all the remaining Hydrozoa that do not form
colonies the form assumed is not that of the Aodyse, but that
of the medusa (Fig. 46), a polype stage never being
developed, and the animal resembling in all essential
respects the medusze of Obelia; the chief difference of
importance being the presence of sense-organs in the form
of hollow, club-shaped appendages, the ¢estaculocysts, con-
taining calcareous bodies of “¢hites. These simple free-
swimming medusiform Hydrozoa (Zrachyline) develop ova
and sperms which give rise to free-swimming ciliated larvee ;
but the latter, instead of becoming fixed and developing into
plant-like colonies, remain free, and develop directly into
medusze like those from which they originated. The fixed
zoophyte stage is thus absent in the life-history, and an
alternation of generations is not recognisable.

In the colonial Hydrozoa, which constitute the great
majority of the class, the colony in most instances resem-
bles that of Obelia in being a fixed structure consisting of a
slender branching stem, covered over by perisarc, and bear-
ing zooids and blastostyles. In many the perisarc is
produced to form hydrothecz and gonothece for the

102 MANUAL OF ZOOLOGY SECT,

protection of the polypes and blastostyles respectively ;
but in others (Fig. 47) these protecting structures are
absent. The polypes resemble those of Obelia in all es-

rs
°
me)
°
°
°
0
@
°
o)
N

, gonad; 7224, manubrium; 7th, mouth;
, tentaculocyst; ¢g, tongue; v7, velum

ctr. c, circular canal; gon
, recurrent canal; /, tentacle; ¢c

vad. c, radial canal; rc. ¢

(After Haeckel.)

Fie. 46. — Two Trachyline.

sential respects, but differ in the number and arrangement
of the tentacles and other minor points. In many medusz
are developed from blastostyles as in Obelia, and when
fully formed become free. The shape of the medusa

Iv PHYLUM CCELENTERATA 103

differs in different forms, more particularly as regards the
umbrella. There is always a manubrium, with gastric

Fic. 47. — Bougainvillearamosa. A, entire colony, natural size; B, portion of the
same magnified ; C, immature medusa ; cz. c, circular canal ; cz, cuticle or
perisarc ; et. cav, enteric cavity ; /d, polype or hydranth ; 4yf, hypostome or
manubrium ; sed, medusa; 726, manubrium ; vad. c, radial canal ; ¢, tentacle ;
v, velum, (From Parker’s Bzo/ogy, after Allman.) This is closely allied to the

New England B. supercilians.

104 MANUAL OF ZOOLOGY SECT.

cavity, and a marginal and four radial canals, and a velum
is universally present. But lithocysts are not present in all,
their place being taken by specks of red or black pigment
—the ocedi or rudimentary eyes —at the bases of the ten-
tacles. The number and arrangement of the tentacles is
subject to considerable variation. The gonads are some-
times, as in Obelia, developed in the radial canals, some-
times in the manubrium. In size the medusze range from
about 1 up to 400 millimetres (16 inches) in diameter.

In many of the zoophytes, however, the medusze never
become detached from the colony, developing the ova and
sperms witheut becoming free. In such cases the charac-
teristic medusa structure is more or less imperfectly de-
veloped, and in many forms is not at all recognisable, the
buds corresponding to those which in Obelia give rise to
medusz merely developing into rounded outgrowths termed
sporosacs, in the interior of which the ova and sperms are
formed.

The reproductive buds are not in all cases formed, as in
Obelia, on distinct, peculiarly modified, mouthless zooids.
In many instances, whether they are destined to give rise
to medusze or sporosacs, the buds spring directly from the
ccenosarc, or from the ordinary zooids.

A small group of Hydrozoa—the Hydrocorallina — in-
cluding the Millepores (A@d/epora) and S#ylaster, form
colonies, the supporting material of which, instead of being
chitinoid, is of calcareous and stony character, like the
substance of a coral.

The colonies of Hydrozoa are not in all instances at-
tached, like those of Obelia and the other hydroid zoo-
phytes. In one large order, the Siphonophora, the colonies
of zooids float or swim freely in the sea. In some Siphono-
phora there are no organs for active locomotion, and the

IV PHYLUM CCELENTERATA 105,

colony drifts about, completely at the mercy of wind and
tide, buoyed up by a bladder-like float or pnewmatophore
containing air. Such a passively floating form is the
Portuguese Man-of-war (Physalia) (Figs. 48, 49) which has
an elongated float, pointed at the ends, and produced above,
along its upper edge, into a crest or sail (c7.). At one end
is a minute aperture communicating with the exterior.
From the under side of the float hang polypes (/), feelers,
groups of medusa-buds looking like bunches of grapes of
a deep blue colour, and long retractile tentacles, sometimes
several feet in length, and containing batteries of stinging-
capsules powerful enough to sting the hand as severely as a
nettle. The male reproductive buds remain attached and
take the form of sporosacs, while the female buds apparently
become detached as free meduse. Physalia arethusa is
common in the West Indies, and, borne northward by the
Gulf Stream, is occasionally met with on the coast of
southern New England, and off Nova Scotia.

In such a Siphonophoran as Halistemma (Fig. 50), on
the other hand, there is a long, slender, flexible stem or
ccenosarc, at the upper end of which is a comparatively
small float. Next to this come a number of closely set,
transparent structures (vc), having the general characters
of unsymmetrical medusze without manubria, each being a
deep, bell-like body, with a velum and radiating canals.
During life these szzmming-bells or nectocalyces contract
rhythmically, —7z.e., at regular intervals,—thus serving to
propel the entire organism through the water. Below the
last nectocalyx the character of the structures borne by the
stem changes completely: they are of several kinds, and
are arranged in groups which follow one another at regular
intervals.

Some of these are unmistakable polypes (f) differing,

MANUAL OF ZOOLOGY SECT.

106

= yea =

ate 8h

atau

.
G

SAT WEEE cy,

he taseren a6
dopa ete en eae ee =

*yeee on

The living animal

Fic. 49.—Physalia arethusa, natural

Fic. 48. — Physalia.

(After Agassiz.)

s1ze.

cr
crest ; A, polype ; pz, pneumatophore,
r (After Huxley.)

floating on the surface of the sea.

float, or air-sac.

PHYLUM CQAELENTERATA 107

8

LSS,
2

Ee

XK

S
DEL

f{
p
sf |
@
§
Q
A
J "4 ;
4
( Wile
f
Fic. 50.—Halistemma tergestinum. A, the entire colony; B, a single group of
i c@, coenosarc; @z, dactylozooid; “ph, hydrophyllium or bract; xet,

zooids ;
nectocalyx or swimming-bell; zéc.

pneumatophore or float, s, s', sporocysts;

battery of nematocysts; p..polype; pr,
#, tentacle. (After Claus.)

108 MANUAL OF ZOOLOGY SECT.

however, from those we have hitherto met with, in having
no circlet of tentacles round the mouth, but a single, long,
branched tentacle (¢) arising from its proximal end, and
bearing numerous groups or “ batteries’ of stinging-capsules
(ntc). Others are dactylozovids or feelers (dz) —mouth-
less polypes, each with an unbranched tentacle springing
from its base. Near the bases of the polypes and dactylo-
zooids spring groups of sporosacs (B, s, s'), some male,
others female; and finally delicate, leaf-like transparent
bodies — the dracés or hydrophyllia (hph) — partly cover the
sporosacs. Halistemma occurs in the Atlantic and Mediter-
ranean. A closely related form (Agalmopsis cara) occurs
off the coast of New England.

2. THE SCYPHOZOA

Aurelia, which may be taken as an example of the
Scyphozoa, is the most common of our larger jellyfishes,
and is often found cast up on the sea-shore, where it is
readily recognisable by its gelatinous saucer-shaped umbrella,
from eight to twelve, and sometimes fifteen inches in diam-
eter, having near the centre four red or purple horseshoe-
shaped bodies — the. gonads — lying embedded in the
jelly.

The general arrangement of the parts of the body (Fig.
51) is very similar to what we are already familiar with in
the hydrozoan jellyfishes (Figs. 41 and 43). Most con-
spicuous is the concavo-convex wmbrella, the convex sur-
face of which, or ex-wmbrella, is uppermost in the ordinary
swimming position. The outline is approximately circular,
but is broken by eight notches, in each of which lies a pair
of delicate processes, the marginal lappets (mg. /p) with a
peculiar sense-organ, between the pairs of lappets the edge

Iv PHYLUM CC&ELENTERATA 109

of the umbrella is fringed by numerous close-set marginal
tentacles (ft).

In the centre of the lower or sub-umbrella surface is a
four-sided aperture, the mouzh (m¢h), borne at the end of

Vi | 1

A we ul

fa, uy)
i Vi 4

|

a

A

Fic. 51.—Aurelia aurita. Ventral view—two of the oral arms are removed; a.7.c,
radial canal; gow, gonads; ¢.7.c, radial canal; mg. /f, marginal lappet; mth,
mouth; ov. a, oral arm; /.7.c, radial canal; s.g.f, sub-genital pit; 7,
tentacles.

an extremely short and inconspicuous manudbrium.: sur-
rounding it are four long delicate processes, the ora/ arms

1IO MANUAL OF ZOOLOGY SECT.

(or. a), situated one at each angle of the mouth and uniting
round it.

At a short distance from each of the straight sides of the
mouth is a nearly circular aperture leading into a shallow
pouch, the swd-genital pit (s. g. p), which lies immediately
beneath one of the conspicuously coloured gonads (gov).

The mouth leads by a short tube or gw/e/, contained
in the manubrium, into a spacious s/omach, which is
produced into four wide inter-radial gastric pouches, which
extend about halfway from the centre to the circumference.
In the outer or peripheral wall of each gastric pouch are
three small apertures, leading into as many radial canals
(a.r.c, t.r.c, prc), which pass to the edge of the umbrella
and then unite in a very narrow circular canal.

Each gonad (gov.) is a horseshoe-shaped frill-like structure
situated on the floor of the gastric pouch. When mature, its
products — ova or sperms — are discharged into the stomach,
and pass out by the mouth. The sexes are lodged in distinct
individuals.

Lying parallel with the inner or concave border of each
gonad is a row of delicate filaments supplied with stinging-
capsules. These are the gastric filaments: their function
is to kill or paralyse the prey taken alive into the stomach
(compare Fig. 53, g./).

The development and life-history of Aurelia present
several striking and characteristic features. The impreg-
nated egg-cell or oosperm becomes converted into a closed
two-layered sac or planiula (Fig. 52, A), similar to that of
a Hydrozoon. The planula swims about by means of the
cilia with which its ectodermal cells are provided, and, after
a brief free existence, settles down, loses its cilia, and be-
comes attached by one pole. At the opposite pole a mouth
is formed. On two opposite sides of the mouth hollow

Iv PHYLUM CCZLENTERATA III

Fic. 52. — Aurelia aurita, development. A, planula; B, C, formation of the gullet
or stomodzum; D, transverse section of young scyphula; E, scyphula; F,
longitudinal section of same; G, division of scyphula into ephyrulae; H, ephy-
rula from the side; I, the same from beneath. In A-D and F the ectoderm
is unshaded, the endoderm striated, and the mesoglcea dotted. a, lobes of
umbrella; #274, manubrium; 277, mouth; sf, septal funnel; st, stomodeum;
z, tentacle; #7, tanioles, or gastric ridges. (From Korschelt and Heider’s
Embryology.)

112 MANUAL OF ZOOLOGY SECT.

processes grow out, forming the first two tentacles; soon
two others appear at right angles to these. Subsequently
other tentacles appear. At the same time the attached or
proximal end is narrowed into a stalk-like organ of attach-
ment (E).

The outcome of all these changes is the metamorphosis
of the planula into a polype (F), not unlike a Hydra. The
Scyphozoon-polype is called a Scyphula. The Scyphula some-
times multiplies by budding. After a time it undergoes a
process of transverse fission (G), becoming divided by a series
of constrictions which deepen until the polype assumes the
appearance of a pile of saucers, each with its edge produced
into eight bifid lobes. Soon the process of constriction is
completed, the saucer-like bodies separate from one another,
and each, — except the first topmost one, which falls off and
dies, — turning upside down, begins to swim about as a small
jellyfish called an Zfhyruda (H, 1), which grows rapidly
and eventually develops into the adult Aurelia.

The rest of the Scyphozoa resemble Aurelia in the gen-
eral features of their structure, but there is a good deal
of variation in certain points (Fig. 52). Thus the umbrella,
instead of being a saucer-shaped disc, as in Aurelia, is often
conical or cup-shaped or cubical. In some, tentaculocysts
are not developed, and in others the oral arms are absent.
Lucernaria differs somewhat widely from the rest in being
attached by means of a short stalk developed from the centre
of the ex-umbrella. In the Rfzzostomee the mouth is
obliterated by the union of the bases of the oral arms, the
food being taken in through a large number of minute orifices
scattered over the surface of the arms, and leading into a
system of fine canals, which join together to form larger
canals, eventually opening into the gastric cavity. Many of
the Scyphozoa pass through an alternation of generations

Iv PHYLUM CCELENTERATA 113

similar to that which has been described in the case of
Aurelia, with a fixed scyphistoma stage; but in others the
ciliated larvee developed from the ova give rise directly to

Fic. 53.—-Tessera princeps. A, external view; B, vertical section; g. /, gastric
filament; gov, gonad; 7.7.2, tentacle; #24, manubrium; th, mouth; £.r.t,
tentacle: st, stomach; ¢, taniole or gastric ridge. Antarctic Ocean. (After
Haeckel.)

jellyfishes like the parent, without the intercalation of any

fixed stage.
The Scyphozoa are all marine, and the majority are
pelagic, t.e., swim freely in the surface waters of the ocean.

I

114 MANUAL OF ZOOLOGY SECT.

A few inhabit the deep sea, and have been dredged from
as great a depth as 2000 fathoms. Nearly all are free-
swimming in the adult state; some, however, live on coral-
reefs or mud-banks, and are found resting, in an inverted
position, on the ex-umbrella; and a few, such as Lucernaria,
are able to attach themselves at will by a peduncle. Many
are semi-transparent and glassy, but often with brilliantly
coloured gonads, tentacles, or radial canals. In many cases
the umbrella, oral arms, etc., are highly coloured, and some
species are phosphorescent. They are all carnivorous, and,
although mostly living on smaller organisms, are able, in the
case of the larger species, to capture and digest crustaceans
and fishes of considerable size.

3. THE ACTINOZOA

The simplest and most familiar of the Actinozoa are the
Sea-anemones, which are to be found attached to rocks,
seaweeds, shells, etc., on the sea-shore. When expanded a
sea-anemone has the form of a cylindrical column attached
to a rock or other support by a broad dase. The distal or
free surface of the column, termed the asec or peristome,
bears in the middle an elongated, slit-like aperture—the
mouth, Springing from the disc and encircling the mouth
are numerous cylindrical zezézcles, disposed in circlets, their
total number being some multiple of five.

Obviously the sea-anemone is a polype, formed on the
same general lines as a polype of the Hydrozoa. But
certain important differences from the Hydrozoan polype
become manifest when we examine the internal structure
(Fig. 54). The mouth does not lead at once into a spacious
undivided enteric cavity, but into a short tube (gw/), having
the form of a flattened cylinder, which hangs downward

IV PHYLUM CCELENTERATA 115

into the interior of the body, and terminates in a free edge.
This tube is called the gu//e¢ or stomodeum. Its inner
surface is marked with two longitudinal grooves (sgph),
known as the gullet-grooves or s¢phonoglyphes. The gullet
does not simply hang freely in the interior cavity, but is
connected with the body-wall by a number of radiating

ey
pe ost.7

Hee J ie a Hoe HA soph
mes. 4 a ed aH THA &. 270

mes.3 g Ly;

™mes:2

N
§

Fic. 54.—Tealia crassicornis. Dissected specimen; gon, gonads; gz/, gullet;
Z. m, longitudinal muscle; /, lappet; es. 4, primary, mes. 2, secondary,
mes. 3, tertiary mesenteries; es. /, mesenteric filaments; 2th, mouth;
ost. I, ost. 2, ostia or aperture in mesenteries; %. , parietal muscle; sgfh,
siphonoglyphe; s. #, sphincter muscle; ¢. #, transverse muscle.

partitions, the complete or primary mesenteries (mes. I) ;
between these are incomplete secondary mesenteries (mes. 2),
which extend only part of the way from the body-wall to

the gullet, and “rtiary mesenteries (mes. 3), which are
hardly more than ridges on the inner surface of the body-

116 MANUAL OF ZOOLOGY SECT.

wall. Thus the entire enteric cavity of a sea-anemone is
divisible into three regions: (1) the gwdet or stomodeum,
communicating with the exterior by the mouth, and opening

The ectoderm

cn, cinclis or aperture in

c chamber; mes, mesentery; 7zes./, mesenteric

ac, acontium;

and transverse (B) sections of a sea-anemone.
-wall; gzé, gullet: zzz. mes. c, intermesenteri

the mesoglcea black.

h, mouth; ost, ostium; Z, pore; 7, tentacle.

filament; zz

Fic. 55. — Diagrammatic vertical (A)
is dotted, the endoderm striated,
body

below into (2) a single main digestive cavity, the stomach,
which gives off (3) a number of radially arranged cavities,
the inter-mesenteric chambers. The free edges of the
mesenteries below the gullet are produced into curious

Iv PHYLUM CCELENTERATA 117

twisted cords, the mesenteric filaments (mes. F), answering
to the gastric filaments of Scyphozoa. Stinging-capsules
occur in the ectoderm, and are also very abundant in the
mesenteric filaments. They resemble in general character
the nematocysts of Hydrozoa, but are of a more elongated
form, and the thread is usually provided at the base with
very numerous slender barbs.

In virtue of possessing both stinging-capsules and gland-
cells, the mesenteric filaments perform a double function.
The animal is very voracious, and is able to capture and
swallow small fishes, molluscs, sea-urchins, etc. The prey
is partly paralysed before ingestion by the nematocysts of
the tentacles, but the process is completed, after swallowing,
by those of the mesenteric filaments. Then, as the captured
animal lies in the stomach, the edges of the filaments come
into close contact with one another and practically surround
it, pouring out at the same time a digestive juice secreted
by their gland-cells. Gees nwtia Tay/ Let DA 18%

Sea-anemones are dicecious, the sexes being lodged in
distinct individuals. The gonads—ovaries or testes—are
developed in the substance of the mesenteries (Fig. 54,
gon), a short distance from the edge, and, when mature,
often form very noticeable structures. The development
of sea-anemones resembles, in its main features, that of
Scyphozoa, but there is no alternation of generations.

Our common sea-anemone, Metridium marginatum (Fig.
56), lives under stones near low-water mark,

Two main divisions or sub-classes of the Actinozoa are
recognised,—the Zoantharia and the Alcyonaria, the
former including the sea-anemones, the Madrepores, and
other stony corals, and the horny black corals; the latter
the “dead men’s fingers,’ red coral, organ-pipe coral,
“sea-fans,” and “sea-pens.’’ The principal distinguishing

118 MANUAL OF ZOOLOGY SECT.

features of the two sub-classes are, that in the Zoantharia
the tentacles and mesenteries are usually very numerous,
and are arranged, as a rule, in multiples of five or six, and

Fic. 56. — The common Sea-anemone. ‘Fic. 57. —Corallium rubrum, portion of
(After Emerton.) colony. Enlarged twice. (After Lacaze-
Duthiers.)

that the tentacles are simple in form; while in the Alcyo-
naria (Fig. 58) the tentacles and mesenteries are always
eight in number, and the tentacles are pinnate, 7e., each
of them consists of a main stem with two rows of lateral
branchlets.

Only the sea-anemones (with a few exceptions) and a
few Madrepore corals remain simple, the rest all giving
rise to more or less extensive colonies, of a variety of differ-
ent forms, by continuous budding. The structure of the
zooids is similar to that of the sea-anemone in all essential
respects. In many of the Alcyonaria two forms of zooids
are to be distinguished in each colony (amorphism of the
zooids), ordinary zooids, and s¢phonozootds, which are smaller,
and are devoid of tentacles and of gonads.

Iv PHYLUM CCZLENTERATA * 119

None of the sea-anemones have a true skeleton ; in some,
however, there is a thick cuticle, and several kinds enclose
themselves in a more or less complete tube, which may be
largely formed of discharged nematocysts. In some Alcyo-

Fic. 58. —Alcyonium palmatum. A, entire colony natural size; B, spicules.
Mediterranean Sea. (After Cuvier.)

naria, such as the “ dead men’s fingers ” ( A4/cyonium, Fig. 58),

the skeleton consists of minute, scattered, irregular deposits

of carbonate of lime called spicules. Alcyonium carneum

occurs below tide-mark off the New England coast. In

Tubipora (the “ organ-pipe coral’”’) (Fig. 59) there is a con-

120 MANUAL OF ZOOLOGY SECT.

tinuous calcareous tube for each polype. In the red coral
of commerce (Fig. 57), which inhabits the Mediterranean
Sea, there is an extremely hard calcareous branched rod
which extends as an axis through the ccenosarc. In the
black corals (Antipathes and allies) there is a horn-like
axis ; and in Gorgonia there
is a similar skeleton, some-
times partly calcareous, with the
addition of numerous spicules.
In the sea-pens (Fig. 60) the
colony is supported by an un-
branched horny axis. Pennatula
aculeata lives in deep water in
the North Atlantic.

In the Madrepore corals we
have a skeleton of an entirely
different type, consisting, in fact,
of a more or less cup-like calca-
reous structure secreted from the
ectoderm of the base and column
of the polype. When formed by
a solitary polype such a “cup-
Fic. 59. — Tubipora musica. Skel- coral” is known as a corallite ;

eton of entire colony. Natural | Lacie 4

Ecos IndianOcean. in the majority of species a large

number — sometimes many thou-
sands — of corallites combine to form a coral/um, the skele-
ton of an entire coral-colony.

The structure of a corallite is conveniently illustrated by
that of the solitary genus Flabellum (Fig. 61, A, B). It
has the form of a short conical cup, much compressed,
so as to be oval in section. Its wall or ¢keca is formed
of dense stony calcium carbonate, the proximal end pro-
duced into a short stalk or peduncle. From the inner

Iv PHYLUM CCELENTERATA 121

surface of the theca a number of radiating partitions, the
septa, proceed inwards or towards the axis of the cup,
some of them meeting in the middle to form an irregular
central mass or columella, which in some kinds of corals
forms an independent, pillar-like
structure arising from the middle
of the base.

In the living condition the
polype fills the whole interior of
the corallite, and projects beyond
its edge to a greater or less degree
according to its state of expan-
sion. The septa alternate with
the mesenteries, each being in-
vested by an in-turned portion of
the body-wall; so that, though
having at first sight the appear-
ance of being internal structures,
they are really external, lying alto-
gether outside the enteric cavity,
and are in contact throughout
with the ectoderm.

The almost infinite variety in

form of the compound corals is Fic._60.—Pennatula sulcata.
i : Entire colony. Natural size.
due, in the main, to the various wes branch. (After
methods of budding. According
to the mode of budding, massive corals are produced in
which the corallites are in close contact with one another,
as in Astrea (Fig. 62); or tree-like forms, such as Den-
drophyliia (Fig. 63, A), in which a common calcareous
stem, the cenenchyma, is formed by calcification of the
ccenosarc,! and gives origin to the individual corallites.

1See p. 94.

122 MANUAL OF ZOOLOGY SECT.

Sep. sep.7

Fic, 61.— A, B, two views of Flabellum curvatum. Natural size. C, semi-dia-
grammatic view of a simple coral; D, portion of a corallite; E, F, diagram ofa
simple coral in longitudinal and transverse section; ectoderm dotted, endoderm
striated, skeleton black. 4.//, basal plate; co/, columella; e. t#, epitheca; gud,
gullet; ses., mes. I, mes. 2, mesenteries; mes, 7, mesenteric filaments; sep,
septa; #, tentacle; #2, theca. (A and B after Moseley; C and D after Gilbert
Bourne.)

Iv PHYLUM CCELENTERATA 123

It is by this last-named method, the ccenosarc attaining
great dimensions, and the individual corallites being small
and very numerous, that the most complex of all corals,
the Madrepores (Fig. 63, B), are produced.

The Actinozoa are remarkable for the variety and _brill-
iancy of their colour during life. Every one must have
noticed the vivid and varied tints of sea-anemones ; but in

Fic. 62. — Astrea pallida, the living sees Natural size. Fiji Islands. (After
ana.

life the corals also exhibit a marvellously varied and _ gor-

geous colouring ; and the same holds good of many of the

Alcyonaria.

Many Actinozoa, like many sponges (p. 89), furnish
examples of commensalism, a term used for a mutually
beneficial association of two organisms of a less intimate
nature than occurs in symbiosis. An interesting example
is furnished by the sea-anemone Adamsia palhata. This
species is always found on a univalve shell—such as that of
a whelk —inhabited by a hermit-crab. The sea-anemone
is carried from place to place by the hermit-crab, and in

124 MANUAL OF ZOOLOGY SECT.

this way secures a more varied and abundant food-supply
than would fall to its lot if it remained in one place. On
the other hand, the hermit-crab is protected from the attack
of predaceous fishes by retreating into its shell and leaving
exposed the sea-anemone, which, owing to its toughness,

Fic. 63.— A, Dendrophyllia nigrescens; B, Madrepora aspera. Natural size.
co, corallites; cs, coenosarc; #, polypes. Pacific Ocean. (After Dana.)

and to the pain caused by its poisonous stinging-capsules,
is usually avoided as an article of food.

A similar case is that of Cancrisocia, of the China seas,
which lives on the back of a crab (Dorippe facchino,
Fig. 64). The crab carries, for its protection when young,
a small shell over its back, which it holds in this position by

IV PHYLUM CCSLENTERATA 125

means of its two reversed pairs of hind legs. The sea-
anemone appears to have fixed itself when young to the

Fic. 64. — Cancrisocia living as a commensal on the back of a crab, (After Verrill.)

shell, and afterwards, by its growth, spread over the back of
the crab, taking the place of the shell.

4. THE CTENOPHORA

The Ctenophora or comb-jellies are a group of free-
swimming, gelatinous, transparent animals which occur, some-
times in enormous numbers, in the surface waters of the sea.
The animal (Fig. 65) has the appearance of a mass of clear
jelly, usually of a globular shape; and no pulsating move-
ments, such as those by means of which a Medusa propels
itself, are to be observed. Running over the surface, nearly
from pole to pole of the globular body, there will be observed
a series of eight bands of flashing points of light. These are
found, when examined more closely, to consist of rows of
long cilia, which run at right angles to the long axis of the

126 MANUAL OF ZOOLOGY SECT.

band. The cilia of each row are cemented together at
their bases, free from one another distally, so that each row
is comb-shaped, the basal cemented parts of the cilia
forming the back of the comb, the free portions the teeth.
It is by the paddling action of the numerous swimming

Fic. 65.—Hormiphora (Cydzfpe) plumosa. A, from the side; B, from the aboral
pole. mth, mouth; s. 4/7, swimming plates; ¢ and 4, tentacles. Natural size.
Mediterranean Sea. (After Chun.)

combs of these eight bands that the ctenophore is propelled
through the water.

Laterally there is situated a pair of long slender tentacles,
each provided with numerous little tag-like processes, and
having its base lodged in a sheath into the interior of which
the whole tentacle can be retracted. At one pole, the orad,
is an opening, the mouth: and at the opposite pole is
a pair of minute pores, the excretory pores, which are the

IV PHYLUM CCELENTERATA 127

openings of a pair of canals given off from the enteric cavity.
Between the two excretory pores is a remarkable structure,
which is the nerve-centre as well as an organ of special
sense. The mouth leads into a flattened tube, the gullet,
and this again leads into a cavity, the znfundibulum, which

Fic. 66.—Hormiphora plumosa. A, transverse section of one of the branches of
a tentacle; B, two adhesive cells (ad.c,) and a sensory cell (s.c) highly magni-
fied. cv, cuticle; 2, nucleus. (After Hertwig and Chun.)

probably corresponds to the stomach of the sea-anemone.

From this cavity certain canals are given off.
Stinging-capsules are not developed, their place being

taken by a number of peculiar cells called adhesive cells, with

which the branches of the tentacles are covered. An
adhesive cell (Fig. 66, B) has a convex surface, produced into
small papillae, which readily adheres to any surface with
which it comes in contact, and is with difficulty separated.

In the interior of the cell is a spirally coiled filament, the

delicate inner end of which can be traced to the muscular

axis of the tentacular branch. ‘These spiral threads act as
springs, and tend to prevent the adhesive cells from being

128 MANUAL OF ZOOLOGY SECT. IV

torn away by the struggles of the captured prey. An allied
form is Pleuwrobrachia, very abundant off our shores.

In some of the Ctenophora the body is produced into a
pair of lateral lobes. In Bevroé, instead of being globular, it
is more nearly cylindrical, with an extremely wide mouth
and gullet, and without tentacles. In
the “Venus’s girdle” (Cestws), it is
compressed and almost ribbon-like.
All are free-swimming ; colonies are
never formed ; and there is never any
kind of skeleton.

The Ctenophora are usually per-
fectly transparent, and quite colour-
less, save for delicate tints of red,
brown, or yellow on the tentacles or
Fic. 67.—Idyia roseola. On ridges on the inner surface of the

Ree nncmral sine ad Site; gullet. Cestus has, however, a deli-

See a ae z cate violet hue, and, when irritated,
wows 0h) Paddles. (Afr shows a beautiful blue or bluish-green
fluorescence ; while Beroé is coloured
rose-pink, and Idyia is of a brilliant pink. The most
primitive form to be found on our coast is /dya (Fig. 67),
which is a simple oval sphere, the interior of which forms an
immense digestive cavity, in which entire large animals may
be engulfed.

SECTION V.—PHYLUM PLATYHEL-
MINTHES

Tue Platyhelminthes or Flat-worms are a group of animals
which, though of a low type of organisation, yet show in
many cases a great advance on the Ccelenterata, in the
possession of systems of organs of a more or less elaborate
character for the carrying on of the various functions.
Many are internal parasites of higher animals; others are
parasites on the outer surface (external parasites) ; others
again are non-parasitic.

1. THE TREMATODA

A good and easily procurable example of the flat-worms
is the Liver-fluke of the sheep (Distomum hepaticum),
which lives as a parasite in the liver, in the interior of the
larger bile-ducts of the infested animal. It is a soft-bodied
worm, of flattened, leaf-like shape (Fig. 68), with a trian-
gular process, the head ode, projecting from the broader
end. When the liver-fluke is compared with a zooid of Ode/a,
or with a Medusa or a sea-anemone, a striking difference in
the general disposition or symmesry of the parts is at once
recognisable. In the latter, as in the Ccelenterata in general,
the prevailing arrangement is a radia/ one, the parts being
disposed in a radial manner round the azn axis of the body,
which is an imaginary line running through the middle of

K 129

130 MANUAL OF ZOOLOGY SECT.

the mouth and enteric cavity. In the fluke, on the other
hand, the parts are disposed to the right and left of an
imaginary median vertical plane,
along which the entire animal
is capable of being divided into
two completely symmetrical,
right and left, halves. The type
of symmetry here exemplified is
termed Jdc/ateral; it has already
been met with in some of the
Protozoa, and is characteristic

need ; of nearly all animals higher than
Fic. 68.—Distomum hepaticum.

Natural size. excr,excretory the Coelenterata.

Picts oases ee The broader end of the body

SOR is determined as anterior, ow-
ing to the mouth and the central part of the nervous
system being situated at that extremity. One of the broad
flat surfaces is the dorsal, the other the ventral. The
mouth (mo), situated at the anterior extremity of the head-
lobe, is surrounded by a muscular oral sucker, and some
distance back, on the ventral surface, just behind the head-
lobe, is a second much larger posterior sucker (sckr).
Between the two suckers is a median aperture, the gen7¢al
opening (repr), through which a curved muscular process,
the c’vrus or penis, may be protruded. In the middle of
the posterior end of the body is a minute opening, the
excretory pore (excr).

The surface is covered with innumerable minute spinules,
but vibratile cilia are absent.

The mouth (Fig. 68, mo) leads to a small, bulb-like body,
the pharynx (Fig. 69, 2), with thick muscular walls and a
small cavity. From this a short passage, the esophagus,
leads to the zvéestine. The latter (2?) is frequently a very

v PHYLUM PLATYHELMINTHES 131

conspicuous structure, owing to its being filled with the
dark biliary matter on which the fluke feeds. It divides
almost immediately into two main limbs, right and left, and
from each of these are given off, both internally and ex-

Fic. 69. —Distomum hepaticum. Internal organisation. General view of the
anterior portion of the body, showing the various systems of organs as seen from
the ventral aspect. 7, ejaculatory duct; “, female reproductive aperture; zyt,
anterior portion of the intestine (the rest is not shown); oa, commencement of
oviduct; ov, ovary; f, penis; fp, pharynx; sh, shell-gland; ¢e, testes; zt,
uterus; vdj, left vas deferens; wd, right vas deferens; wz¢, lobes of vitelline
glands; vs, vesicula seminalis. (After Sommer.)

ternally, a number of blind branches or caca, those on the
inner side being short and simple, while those on the outer

side are longer and branched. ‘The two limbs of the intes-
tine, with their branches, thus form a complicated branching

132 MANUAL OF ZOOLOGY SECT.

system, the ramifications of which extend throughout the
whole of the body. There is no anus, or aperture of com-
munication between the intestine and the exterior, the only
external opening of the alimentary system being through the
mouth.

A branching system of vessels —the wader-vessels or
vessels of the excretory system — ramify throughout the body.
A longitudinal maznz crunk opens outwards by means of the
excretory pore. In front it gives off four large trunks, each
of which branches repeatedly, the branches giving off smaller
vessels, and these again still smaller twigs, until we reach a
system of extremely fine microscopic vessels, or capillaries.
Each of these ends internally in a slight enlargement
situated in the interior of a large cell, a fame-cell, with a
bunch of vibratile cilia, or a single thick cilium, in the
interior.

The, fluke has a nervous system, the arrangement of
which partakes of the bilateral symmetry of the body. The
central part of this system consists of a ring of nerve matter,
which surrounds the cesophagus, and presents two lateral
thickenings or ganglia containing nerve-cells, and a single
ganglion situated in the middle line below. . From this are
given off a number of nerves, of which the chief are a pair
of lateral cords running back to the posterior end and
giving off numerous branches. There are no organs of
special sense.

The reproductive organs are constructed on the hermaph-
rodite plan, z.e., both male and female organs occur in the
same individual. The male part of the apparatus consists of
testes, sperm-ducts or vasa deferentia, and cirrus. The és/es
(ze) are two greatly ramified tubes which occupy the middle
part of the body, one situated behind the other. From each
testis there runs forward a duct, the vas deferens, the two

v PHYLUM PLATYHELMINTHES 133

vasa deferentia (v. @) opening anteriorly into an elongated
sac, the vesicula seminalis (v. s), from which a narrow tube —
the eyaculatory duct (e7)— leads to the male aperture at the
extremity of the cirrus. The female part of the apparatus
consists of a single ovary, an oviduct, a uterus, vitelline or
yolk-glands, vitelline ducts and shell-glands. The ovary (ov)
is a branched tube situated on the right side in front of the
testes: the branches open into a common duct, the owduct
(od). The witelline glands (vit) consist of very numerous
minute rounded follicles, which occupy a considerable zone
in the lateral regions of the body. The two main zztel/ine
ducts, right and left, run transversely inwards to open into a
small sac—the yolk reservoir. From this a single median
duct passes to join the oviduct. Around the junction is a
mass of unicellular shed/-glands (sh. gl). The wéerus (ut) is
a wide convoluted tube formed by the union of the median
vitelline duct and the oviduct. In front it opens close to
the base of the penis. A canal termed the canal of Laurer
leads from the junction of the oviduct and median vitel-
line duct to open externally on the dorsal surface of the
body.

Each ovum on impregnation becomes surrounded by a
mass of vitelline matter or yolk, derived from the yolk-
glands. It then becomes enclosed in a chitinous shell,
the substance of which is derived from the secretion of the
shell-glands. The completed egg remains for a time in the
uterus; afterwards it is discharged, and, passing down
the bile-ducts of the sheep into the intestine, reaches the
exterior with the feeces. When it escapes from the egg, the
ciliated embryo, as it is termed (Fig. 70, 4), has the form of
a somewhat conical body, covered all over with vibratile
cilia, and with two spots of pigment, the eye-spozs, near the
broader or anterior end, which is provided with a triangular

134 MANUAL OF ZOOLOGY SECT,

head-lobe ( pap). There is no vestige of internal organs, with
the exception ofa pair of flame-cells. The ciliated larva swims
about in water, or moves over damp herbage for a time, and
perishes unless it happens to reach a pond-snail (Zzmnea),
as a parasite of which it is alone able to enter into the next
phase of its life-history. When it meets with the snail,
destined to form the second or intermediate host of the
parasite, the embryo bores into it by means of the head-
lobe. Established in the interior, it grows rapidly into the
form of an elongated sac, the sforocyst (Fig. 70, B), with an
internal cavity. Eventually cells are budded off from the
interior of the sporocyst, each of which gives rise to a body
called a vedia (C). When fully formed the redia is a
cylindrical body, having a mouth leading to a pharynx, fol-
lowed by a simple sac-like intestine, and a system of excre-
tory vessels. The rediz, after escaping from the interior of
the sporocyst, bud off internally cells which either give rise
to a fresh generation of rediz or to bodies termed cercaria.
The latter (DY) are provided with long tails, with anterior
and posterior suckers, a mouth and pharynx, and a bifid
intestine. These escape through an aperture in the wall of
the redia, and, moving actively by means of their tails, force
their way out from the body of the snail. They then, losing
the tail, become encysted, attached to blades of grass or
herbage. The transference of the larval fluke to its final
host, the sheep, is effected if the latter swallow the grass on
which the cercaria has become encysted. The young fluke
then escapes from the cyst, and forces its way up the bile-
ducts to the liver, in which it rapidly grows, and, developing
reproductive organs, attains the adult condition.

The liver-fluke is an example of the class of flat-worms
known as Trematoda. These are all parasitic. Some are
internal parasites, and in the adult condition inhabit, for the

v PHYLUM PLATYHELMINTHES 135

most part, the enteric canal, the liver, or the lungs of some
animal of the Vertebrate or back-boned class (fishes, amphib-
ians, reptiles, birds, or mammals), swallowing the digested

Fic. 70.— A-D, development of Distomum hepaticum.
A, ciliated larva; 8, sporocyst, containing rediz in
various stages of development; C, redia, containing a
daughter redia, and cercarie; 1, fully developed cer-
caria. 6.0f, birth opening; em, enteron of redia; cye,
eye-spots; gast, gastrula stage of redia; germ, early
stages in the formation of cercaria; wf, intestine of
cercaria; 707, morula stage in the development of
cercarie; @s, cesophagus; o7.sz, oral sucker; pap,
head-lobe of ciliated embryo; #4, pharynx; pyoc, pro-
cesses of redia; vent.sw, ventral (posterior) sucker.
(After Thomas.)

food or various secretions of their host. Others are external
parasites, living on some part of the outer surface of their
host, and feeding on mucus or other secretions of the in-

136 MANUAL OF ZOOLOGY SECT,

tegument. The leaf-like form exemplified in the liver-fluke
prevails in most (Fig. 71), but a more elongated form some-
times occurs. The anterior end is distinguished from the
posterior by its shape, by the arrangement of the suckers,
and, in many of those Trematodes that are external para-
sites, by the presence of eyes. Suckers are universal in
their occurrence. They are always ventrally placed, their
chief function being to fix the parasite to the surface of its

Fic. 71.— Trematodes. A, Amphistomum, B, Homalogaster. gh, genital
aperture; 7, mouth; s, posterior sucker; Ze, testes; w/t, vitelline glands.
(After M. Braun.)

host in such a way as to facilitate the taking in by the

mouth of animal juices and epithelial @r’s. Their number

and arrangement vary considerably. There are nearly
always present an anterior set (or, as in the liver-fluke,

a single anterior sucker surrounding the mouth), and

a posterior set or a single large posterior sucker. There

v PHYLUM PLATYHELMINTHES

137

are no cilia on the surface, and a well-developed enteric

canal is always present.
A remarkable series of
metamorphoses, such as
that which has been de-
scribed in the liver-fluke,
is characteristic of the
internally parasitic forms ;
in the ectoparasitic or
externally parasitic Tre-
matodes development is
direct, the young animal
when it escapes from the
egg differing little from
the adult except in size.

2. THE TURBELLARIA

The Turbellaria are a
class of flat-worms which,
though for the most part
non-parasitic,resemble the
Trematodes very closely,
the chief difference being
the presence of a coating
of vibrating cilia, and the
absence, in the majority,
of suckers. The leaf form
is the prevailing one (Fig.
72), but in many the body
is elongated and ribbon-
like, or subcylindrical. In

ze

rad

Fic. 72. —General plan of the structure of a
Triclad Turbellarian. cz, brain; e, eye;
g, ovary; 7, median limb of the intestine;
2», left limb; 7, right limb; 7x, longitudinal
nerve-cord; 7, mouth; od, oviduct; ph,
pharynx; #, testes; fe, tentacles; vd, vas
deferens; 7, uterus; @, ejaculatory duct;
€, vagina; ¢ &, common genital aperture.
(After Von Graff.)

some the anterior end is retractile, and may be everted as

138 MANUAL OF ZOOLOGY SECT.

a proboscis. The mouth is never at the extreme anterior
end, but is always ventrally placed, sometimes behind the
middle. A few multiply by budding, and these may give
rise to chains of individuals, which subsequently become
separated. In the lowest Tur-
bellaria the intestine is repre-
sented merely by a nucleated
mass of protoplasm ; in others it
is a simple sac; in the major-
ity it is branched. The general
structure of the other internal
organs very closely resembles
that of the corresponding parts
} in the Trematodes.
Fic. 73.— Planaria polychroa(a), ‘Turbellaria occur in the sea,
lugubris (6), torva’ (c), about . :
thrice the natural size.’ (After in fresh water, and also in damp
Schmidt, from Claus.) ais 1
localities on land. The great
majority are non-parasitic, their food consisting of minute
aquatic animals and plants of various kinds. An example
is Flanaria torva of our fresh-water pools and streams

(Big. 73.2)

3. THE CESTODA

The class Cestoda or tape-worms are all internal parasites,
and in the adult condition live in the enteric canal of verte-
brates. The tape-worms are much more completely adapted
to a life of parasitism than the Trematodes: they have no
digestive system, and are nourished by the imbibition,
through the general surface, of liquid nutriment derived
from the digested food of the vertebrate host. The shape
of a typical tape-worm is widely different from that of a
trematode. A tape-worm (Fig. 74) is flattened like a
trematode, but is extremely elongated, the length being

139

PHYLUM PLATYHELMINTHES

ed.

reduc

Fic. 74. — Tenia solium.
specimen

140 MANUAL OF ZOOLOGY SECT.

many times, often hundreds of times, the greatest breadth,
so that the animal assumes the form of a long, narrow ribbon
or tape. This ribbon is not continuous, but is made up of
a string of segments or proglottides. ‘Towards one end the
body becomes narrower, terminating in a rounded knob —
the head or sco/ex. On the head (Fig. 75) is a circlet
of hooks borne on a rounded prominence, the vostel/um,
which is capable of being protruded and retracted to a
certain extent; at the sides are four suckers. By means of
these hooks and suckers the head is
attached to the wall of the intestine
of the host, the elongated body lying
free in its interior. The part of the
body just behind the head (weck) is
not divided into segments. The most
anterior segments are much shorter than
those further back, and not so distinctly
separated off from one another. The
surface is devoid of cilia, as in the
Trematodes. A digestive cavity is, as
already stated, absent; but there is a
= ms distinct zervous system, and a system
Fic. 75.—Head of Tenia of zwater-vesse/s with flame-cells. In the
solium, magnified. ; :

(After Leuckart.) | posterior region of the body each pro-
glottis (Fig. 76) is found to contain a

complete set of hermaphrodite reproductive organs similar
in general plan to those of the liver-fluke. The ova, when
fertilised, are enclosed in a chitinoid shell, and received
into a uterus. In the most posterior segments the wérus
is a large branched tube distended with enormous quantities
of these eggs, and the other parts of the reproductive appa-
ratus have become absorbed. These “ripe” proglottides,
as they are termed, drop off, one by one, from the pos-

v PHYLUM PLATYHELMINTHES 141

terior end, and reach the exterior with the feces of the
host. At the same time new proglottides are constantly
being formed by the appearance of new ring-like grooves
behind the neck region. This dropping off of ripe proglot-
tides from the posterior end, and the formation of new ones
behind the neck, results in a gradual shifting backwards of
the proglottides. As each proglottis passes backwards from
its point of origin, it gradually develops the various parts
of the reproductive apparatus in its interior, until, when

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Fic. 76.—A proglottis of Tania solium with mature reproductive apparatus.
can. excret, longitudinal excretory canals with transverse connecting vessels;
gi. vit, vitelline glands; »erv. 7, longitudinal nerves; ov, ov, ovaries; for. gen,
genital pore; schéd, shell-glands; fer, uterus; vag, vagina; vas. def, vas
deferens. The numerous small round bodies are the lobes of the testes. (After
Leuckart.)

it has reached the posterior region, it possesses a com-
plete set of reproductive organs, and, as it reaches the
extreme posterior end, it has become ripe, z.e., has its uterus
distended with eggs.

In the interior of each of the eggs in the ripe proglottides
is an embryo consisting of a rounded mass of cells bearing
six chitinoid hooks — the six-hooked or hexacanth embryo
(Fig. 77, A). After the egg has been discharged from the
free proglottis, it has to reach the enteric canal of a second

142 MANUAL OF ZOOLOGY SECT.

kind of animal —a second or intermediate host — in order
that the embryo may be enabled to enter the next phase of
its life-history. In the case of some tape-worms, this second
or intermediate host is, like the first or permanent host, a
vertebrate animal: in the case of others it is some inver-

D

Fic. 77. — Development of Tape-worm. A, hexacanth embryo; B, Proscolex of
Tenta sagruata; C-E, stages in the formation of the scolex of the same; C,
the invagination before the hooks and suckers have become developed; D, after
the appearance of the hooks and suckers; E, partly evaginated; F, fully
evaginated scolex of 7. solzu7 with caudal vesicle; G, scolex of 7. serrata
with the remains of the vesicle; H, young tape-worm of 7. serrata. (After
Leuckart.)

tebrate animal such as an earth-worm, a centipede, or an
insect. This transference of the hexacanth embryo to the
second host is a passive migration, not an active one, as in

v PHYLUM PLATYHELMINTHES 143

the case of the ciliated embryo of the Trematodes, the egg
being received into the enteric canal of the second host with
the water or food. The digestive fluids of this second host
dissolve the egg-shell and set free the contained embryo,
which bores its way by means of its hooks to some part of
the body in which it is destined to pass through the next
phase of its life-history, and there becomes encysted (B).
The phase which follows presents two main varieties. In
cases in which the second host is an invertebrate animal, the
hooked embryo develops into a form to which the name of
Cysticercoid is given; when, on the other hand, the inter-
mediate host is a vertebrate, the form assumed is nearly
always that termed Cysdéicercus or bladder-worm. In both
cases a tape-worm head is developed, with the rostellum,
hooks, and suckers of the adult. In the Cysticercus (C-H)
this is formed from the wall of a relatively large cyst or
bladder into which the hooked embryo develops.

In a very small number both of Cysticercoids and of
Cysticerci more than one tape-worm head is formed. Thus
Tenia cenurus of the dog has a bladder-worm stage
occurring in the sheep and rabbit, which gives rise to several
tape-worm heads. But the most striking instance of mul-
tiple production of tape-worm heads in a bladder-worm is
Tenia echinococcus, well known as the cause of the disease
termed hydatids, common in man and in various domestic
animals. In this case the hooked embryo develops into a
large mother-cyst, from the interior of which daughter-cysts
are budded off. Eventually from the walls of these daughter-
cysts (Fig. 78) are formed numerous tape-worm heads.

The transference to the first or final host is effected by the
second or intermediate host, or the part of it containing the
Cyticercus or Cysticercoid, being taken into the enteric canal
of the final host. Sometimes, if the intermediate host is

144 MANUAL OF ZOOLOGY SECT.

a small animal, such as a water-flea, this may take place
“accidentally”; in other cases the intermediate host
actually forms the food of the final host. Thus, to give two
instances, a Cysticercoid having as an intermediate host an
earth-worm is taken with the latter into the enteric canal of
a sea-gull — its final host ; a Cysticercus which occurs in the
liver of rats and mice is received into the enteric canal of
the cat. In this way the Cysticercus or Cysticercoid is set
free in the enteric canal of the final host; the tape-worm
head becomes attached by means of its hooks and suckers
to the wall of the intestine, and the long segmented body
of the tape-worm is developed behind.

Fic. 78.—Cyst of Tania echinococcus with the developing daughter-cyst and
scolices. (After Leuckart. )

The commonest human Cestode parasites in the United
States and Canada are Tenia sohum and T. saginata (T.
medtocaneliata), the latter being the more common pest.
The Cysticercus stage of the former occurs chiefly in the
flesh of the pig; that of the latter in the flesh of the ox;
and the relative prevalence of these two tape-worms in
different countries varies with the habits of the people with
regard to flesh-eating: where more swine’s flesh is eaten
in an imperfectly cooked state Zenza solium is the more
prevalent, where more beef, Z. saginaza.

v PHYLUM PLATYHELMINTHES 145

Bothriocephalus latus, a very large tape-worm without
hooks, is a common human parasite in eastern countries.
Its Cysticercus occurs in the pike and certain other fresh-
water fishes. It has not become endemic, or naturalized,
in the United States.

4. THE NEMERTINEA

The Nemerteans are non-parasitic, unsegmented worms,
most of which are marine, only a few forms living on land
or in fresh water. They are commonly looked upon as
nearly related to the Turbellaria, and were formerly in-
cluded in that class; but they are in some respects higher
in organisation than the Turbellaria, and they exhibit cer-
tain special features distinguishing them from the rest of the
lower worms.

The body (Figs. 79 and 80) is narrow and elongated,
cylindrical or depressed, unsegmented, and devoid of ap-
pendages. In length it varies, in different species, from a
few millimetres to as much as ten metres. The entire sur-
face is covered with vibratile cilia.

The mouth (m) is at or near the anterior extremity on
the ventral aspect. Close to it above there is an opening
through which can be protruded a very long muscular organ,
the proboscis (pr), the possession of which is one of the
most characteristic features of this class of worms. The
proboscis is hollow: when it is extended to its utmost, a
part still remains which is not capable of being everted, and
at the junction between the eversible and non-eversible
parts, z.¢., at the extremity of the organ when it is fully
protruded, there is in many of the Nemerteans a pointed or
serrated stylet (Fig. 80, s¢), which probably permits of the
proboscis being used as a weapon: when a stylet is absent,

L

146 MANUAL OF ZOOLOGY SECT.

the surface of the extremity is sometimes abundantly
provided with sénging-capsules ; sometimes it is beset with
glandular adhesive papille. The proboscis is capable of

Fic. 79. — Diagram of the organs of a Nemertine, from below. a, anus; dr, brain;
div, coeca; long. nc, longitudinal nerve-cords; m, mouth; , nephridia; ov,
ovaries; £7, probosis. (After Hubrecht.)

being retracted within the interior of an investing sheath,
the proboscis sheath.

v PHYLUM PLATYHELMINTHES 147

brob!_4

MMU MET TT

Fic. 80.—Tetrastemma. General view of the internal organs. av, anus; ac. st,
accessory stylet ; cer. g, brain: cz. gr, ciliated groove; dors. ves, dorsal vessel ;
tat, ne, lateral nerve; Jat. ves, lateral vessel: efA, nephridium; of. neph,
nephridial aperture ; #7041, eversible part of proboscis : #7067, non-eversible part
of proboscis; 470d. af, aperture for the protrusion of the proboscis; retv. mus,
retractor muscle of the proboscis; s¢, stylet. (From Hatschek’s Lehrduch.)

148 MANUAL OF ZOOLOGY SECT. V

The alimentary canal (Fig. 79) is a simple tube distin-
guishable into wsophagus with longitudinally folded walls,
and zéestine with lateral cwca (div). It ends in an anal
opening (a) situated near the posterior extremity of the
body.

The Nemerteans possess a system of d/o0d-vessels with
well-defined walls formed of an epithelium and a layer of
muscle. There are three principal longitudinal trunks —a
median dorsal and two lateral. The blood follows no
regular course through the vessels, but is moved about by
the muscular contractions of the body.

The excretory vessels of the Platyhelminthes are repre-
sented in the Nemertine worms by a pair of greatly coiled
and branched tubes (Fig. 80, zef/), opening on the exterior ;
the fine terminal branches of the system are provided with
ciliary flames, and cilia occur also in the course of the
vessels themselves.

The ervous system is in some respects more highly
developed than in the Zurbellaria. The drain (Fig. 80,
cer. g) is composed of two large ganglia with lobed surfaces,
connected together by two comméssures, dorsal and ventral,
between which pass the proboscis and its sheath. From the
brain pass backwards a pair of thick nerves which run
throughout the length of the body.

yes are present in the majority of Neimerteans, and in
the most highly organised species occur in considerable
numbers.

Most species are @ecious. The ovaries (Fig. 79, ov) and
vestes are situated in the intervals between the intestinal
ceeca. The ovary or testis is a sac, the cells lining which
give rise to ova or spermatozoa ; when these are mature each
sac opens by means of a narrow duct leading to the dorsal
surface, where it opens by a pore.

SECTION VI.—PHYLUM NEMATHEL-
MINTHES

Tue Nemathelminthes or round-worms are so named
because the body instead of being compressed from above
downwards, as in the flat-worms, is rounded, z.¢., cylindrical.
The majority of the members of the phylum belong to the
class of the Nematoda or round-worms in a more restricted
sense. A good example of these is the common round-
worm of man (Ascaris lumbricoides), which is a common
parasite in the human intestine ; or the nearly allied Ascaris
suilla of the pig. When fresh the animal is of a light
yellowish-brown colour ; it is marked with four longitudinal
streaks, two of which, very narrow and pure white in the
living worm, are respectively dorsal and ventral in position,
and are called the dorsal (Fig. 81, d. 7) and ventral (v. 2)
Zines: the other two are lateral in position, thicker than the
former and brown in colour, and are distinguished as the
lateral lines. The mouth is anterior and terminal in position,
and is bounded by three lobes, or Zs, one median dorsal
(d. dp), the other two ventro-lateral (v. 4). A very minute
aperture on the ventral side, about two millimetres from
the anterior end, is the excretory pore (ex. p). At about the
same distance from the pointed and down-turned posterior
end is a transverse aperture with thickened lips, the anus
(an), which in the male serves also as a reproductive
aperture, and gives exit to a pair of needle-like chitinoid

149

150 MANUAL OF ZOOLOGY SECT.

bodies, the penial sete (pn. s). In the female the repro-
ductive aperture or govopore is separated from the anus, and

(After

C, posterior
ex, p, ex-
p.

an, anus; d. /f, dorsal lip; d.2, dorsal line;
uv. dp, ventral li

B, the same from below;
v. 2, ventral line;

A, anterior end from above;

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3)

z
g
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uv
ie)
a
ie
oO
&
es
fo}
Q
2
is
fom
ie
ps
=,
ee
Zea
oon

is situated on the ventral surface about one-third of the

length of the body from the anterior end (Fig. 82, gp).
The outer surface of the body is furnished by a delicate,

transparent, elastic membrane, of a chitinoid nature, the

VI PHYLUM NEMATHELMINTHES

cuticle. It is wrinkled trans-
versely so as to give the animal
a segmented appearance. Be-
neath the cuticle is a proto-
plasmic layer containing scat-
tered nuclei and longitudinal
fibres, and representing a syz-
cytial ectoderm, t.e., an ecto-
derm in which the cell-bodies
are not differentiated, and its
cellular nature is recognisable
only by the nuclei.

Beneath the ectoderm is a
single layer of muscular fibres
of peculiar structure, arranged
longitudinally, and bounding
the body-cavity.

The muscular layer is not
continuous, but is divided into
four longitudinal bands or
quadrants, two dorso-lateral
and two ventro-lateral, owing
to the fact that at the dorsal,
ventral, and lateral lines the
ectoderm undergoes a great
thickening and projects in-
wards, between the muscles,
in the form of four longitudi-
nal ridges. It is this arrange-
ment that gives rise to the
lines seen externally.

The mouth leads into the
anterior division of the enteric

der epltm

§#

der. epthm, deric epithelium;

icle;

, that of the right side i

3; gp,

Semi-diagrammatic dissectic
ex. v, excretory vessel
Nv. Yr, Nerve-ring; ovy, ovary

mth, mouth;

wf, uterus.

ex, p, excretory pore;

Fic. 82. — Ascaris lumbricoides.
layer;

152

MANUAL OF ZOOLOGY

SECT.

canal, the pharynx or stomodeum (Fig. 82, A), with very

on
ag
—un
D
un
Po)
<_<
dn
<I

| hon

Fic. 83. — Diagram of nervous
system of Nematoda. c, com-
missures; d@/x, dorsal nerve;
Asn, posterior lateral nerve;
on, upper and wz, under
portion of nerve-ring; sg,
lateral swellings; v2, ventral
nerve. (From Lang, after
Biitschli.)

muscular walls. Posteriorly the
pharynx opens into the ¢ntestine
(in¢), a thin walled tube, flattened
from above downwards. Posteriorly
the intestine narrows considerably
to form the short rectum, which
opens externally by the anus (a7).
The food, consisting of the semi-
fluid contents of the intestine of the
host, is sucked in by movements of
the pharynx, and is then absorbed
into the system through the walls
of the intestine. The food being
already digested by the host, there
is no need of digestive gland-cells
such as occur in animals which pre-
pare their own food for absorption.

Between the enteric canal and
the body-wall is a distinct space, the
ceelome or dJedy-cavity, containing a
clear fluid.

The excretory system presents a
certain resemblance to that of Pla-
todes. It consists of two longitu-
dinal canals (ex. v), one in each
lateral line. Anteriorly they pass
to the ventral surface, unite with
one another, and open by the
minute excretory pore (ex. p) al-
ready noticed.

The nervous system consists of a
ring (zz. 7) surrounding the pharynx

VI PHYLUM NEMATHELMINTHES

153

and giving off six nerves forwards and six backwards (Fig.

83). Of the latter, two are
of a considerable size and
run in the dorsal and ven-
tral lines respectively (d/n,
vin).

The reproductive organs
are formed on a peculiar
and very characteristic pat-
tern. The sts (Fig. 84,
ts) is a long coiled thread,
occupying a considerable
portion of the body-cavity.
At its posterior end it is
continuous with the zas
deferens. The vas deferens,
in its turn, becomes con-
tinuous with a wide canal,
the vesicula seminalis (vs.
sem), which opens by a
short, narrow, muscular
tube, the ductus cjaculato-
vius, into the rectum. Be-
hind the rectum, and open-
ing into its dorsal wall, are
paired muscular sacs (s)
containing the fenial sete
(p. ns) already noticed.
The anterior end of the
testis consists of a solid
mass of sexual cells ; pass-
ing backwards there is

U

der. epthm, epidermis;

testis; vs. sem, vesicula seminalis.

ie

cu, cuticle;

an, anus;

3 5, Sacs containing penial seta; ¢s,

i posterior extremity of male, dissected.

. S, penial seta

Fic. 84. — Ascaris lumbricoides
m, muscular layer; px. 5

found a cord or rachis occupying the axis of the tube and

154 MANUAL OF ZOOLOGY SECT. VI

having the sperm-cells attached to it; still further back the
sperms become gradually differentiated, and are finally set
free in the vas deferens.

The organs of the female (Fig. 82) resemble those of
the male, but are double instead of single. There are two
coiled, thread-like ovaries (ovy), each passing insensibly
into a uterus (w/). In the ovary, as in the testis, the eggs
are developed in connection with an axial cord or rachis.
The two uteri unite in a short muscular vagéna (vag) which
opens, as already seen, on the ventral surface of the body
(gzp) at about one-third of the entire length from the head.

The Nematodes in general vary greatly in size, from about .
I mm. or less to two metres (six feet) in the case of the
Guinea-worm, the length always being great in proportion to
the diameter, and the body being always bluntly pointed at
the anterior end, and either pointed or forked posteriorly.

The mouth is frequently armed with spines by means of
which the worms draw blood from the intestinal blood-
vessels of their host. Many free-living forms have a sharp
stylet for piercing the tissues of the plants on which they
feed, and a suctorial apparatus for absorbing their juices.

The nervous system has in most the same general struc-
ture as in Ascaris, and the same holds good of the repro-
ductive apparatus. A few are hermaphrodite, but, instead
of a double set of reproductive organs as in Platyhelminthes,
they have organs similar to those of the female Ascaris, the
gonads producing first sperms and afterwards ova.

One of the most terrible parasites of man is a nematode
called Zrichina spirals (Fig. 85), a minute worm, the male
(C) a little over r mm. (;); inch) in length, the female (B)
about 3 mm. (4 inch). In the adult or sexual condition it
lives in the intestine of man, the pig, and other mammals.
Internal impregnation takes place, the eggs develop in the

=

:
E

fa;

LEFF TTY
<r

Fic. 85. — Trichina spiralis. A, encysted form in muscle of host; B, female; C,
male. 6A, connective tissue envelope; cy, cyst; de, ejaculatory duct; e, em-
bryos; f fat globules; 4, testis; #z. /, muscle fibre; oe, pharynx; ov, ovary;
wo, gonopore; 2H, cell masses in intestine. (From Lang’s Comparative

Anatomy, after Claus.)
155

156 MANUAL OF ZOOLOGY SECT. VI

uterus of the female, and the minute young (B, ¢), to the
number of at least about a thousand, are born alive. Soon
after birth the young worms migrate through the walls of
the intestine and reach the voluntary muscles of the host,
such as those of the limbs, back, tongue, etc. Each worm
enters a muscle-fibre and coils itself up in the muscle-
substances (A); a spindle-shaped cyst (cy) is formed round
it, and the muscle undergoes more or less degeneration.
This process gives rise to various morbid symptoms in the
host, but, after some months the cysts become calcified and
the danger to the infected individual is over. In order that
further development of the encysted and sexless Trichine
should take place, it is necessary for the infected flesh of
the host to be eaten by another animal in which the worm
is capable of living, ¢.g., that of man by pig or rat, or that
of a pig by man. When this is done the cysts are dissolved
by the digestive juices, the worms escape, develop repro-
ductive organs, and copulate, the young migrating into the
muscles and producing the disease as before.

It will be noticed that in this case the parasite is able to
exist in various hosts, and that both sexual and asexual stages
are passed through in the same host, dispersal of the species
taking place by the flesh of an infected animal being eaten
by another, either of the same or of a different species.

The female Guinea-worm (Dracunculus medinensis) attains
a length of 30-200 cm. (1-6 feet), and lives in the sub-
cutaneous connective tissue of man. The eggs develop in
the uterus, and the newborn young pass out of the body of
the host through abscesses caused by the presence of the
parasite. If, as must often be the case, they escape into
water, they make their way into the body of a water-flea
(Cyclops), and in this condition probably reach their human
host once more in his unfiltered drinking water.

SECTION VII.— PHYLUM ECHINODER-
MATA

THE starfishes, brittle-stars, sea-urchins, feather-stars, and
their allies, many of which are familiar objects on the sea-
shore, are grouped together as the phylum Echinodermata.
Even a superficial comparison of a starfish, a brittle-star, and
a sea-urchin will reveal unmistakable points of agreement.
All have a hard surface more or less abundantly provided
with pointed spines: in all the symmetry is distinctly
radial; and, if the animals are examined in the living
condition while immersed in sea-water, it will be found that
all are provided with rows of soft retractile tubular append-
ages acting in the starfish and sea-urchin as the organs of
locomotion by means of which the animal creeps slowly
along. Examination of the external structure shows, as will
presently become evident, that the resemblance is not a
merely superficial one, but extends to all the systems of
internal organs.

1. THE ASTEROIDEA

The body of a starfish, such as the common English red
starfish, Asterias rubens, or 4. vz/earis, of our American
coast, is enclosed in a tough, hard integument, containing
numerous plates or ossicles, as they are termed, of calcareous
material. This exoskeleton is not completely rigid in the

157

158 MANUAL OF ZOOLOGY SECT.

fresh condition, but presents a certain limited degree of
flexibility. The body (Fig. 86) is star-shaped, consisting of
a central part, the cenéral disc, and five symmetrically
arranged processes, the avms or rays, which, broad at the
base, taper slightly towards their outer extremities. There
are two surfaces, one the dorsal or abactinal, directed up-

Fic. 86. — Starfish. General view of the ventral surface, showing the tube-feet.
(From Leuckart and Nitsche’s Diagrams.)

wards in the natural position of the living animal ; the other,
the ventral or actinal, directed downwards. The dorsal sur-
face is convex, the ventral flat; the colour of the former is
much darker than that of the latter.

In the centre of the ventral surface (see Fig. 92) is a five-
rayed aperture, the acé/nostome, and running out from this in
a radiating manner are five narrow grooves, each running
along the middle of the ventral surface of one of the arms

VII PHYLUM ECHINODERMATA 159

to its extremity. Bordering each of the ambulacral grooves
there are either two or three rows of movable calcareous
spines, the ambulacral spines. External to the ambulacral
spines are additional rows of stout spines, which are not
movable.

On the convex dorsal surface there are a number of short,
stout spines arranged in irregular rows parallel with the long
axes of the rays. These are supported on irregularly shaped

* ossicles buried in the integument. In the soft interspaces
between the ossicles are a number of minute pores, the
dermal pores, scarcely visible without the aid of a lens.
Through each of these pores projects a very soft filiform
process, one of the dermal branchie or papule (Fig. 88,
Resp. c@), which is capable of being entirely retracted.

Very nearly, though not quite, in the centre of the dorsal
surface is an aperture, the anus (an), wide enough to admit
of the passage of a moderately stout pin. On the same sur-
face, midway between the bases of the two rays, is a flat,
nearly circular plate, the surface of which is marked by
a number of radiating, narrow, straight, or slightly wavy
grooves: this is the madreportte.

Attached to the spines of the ventral surface, in the inter-
vals between them, and in the intervals between the spines
on the dorsal surface, are a number of very small, almost
microscopic, bodies, which are termed the pedicellaria@ (Fig.
88, Fed). Each of these is supported on a longer or shorter
flexible stalk, and consists of three calcareous pieces, a
basilar piece at the extremity of the stalk, and two jaws,
which are movably articulated with the basilar piece, and
are capable of being moved by a certain set of muscular
fibres, so as to open and close on one another like the jaws
of a bird.

In a well-preserved specimen there will be seen in each

160 MANUAL OF ZOOLOGY SECT.

of the ambulacral grooves two double rows of soft tubular
bodies ending in sucker-like extremities ; these are the ¢de-
feet (Figs. 86, 88, Z. #), of which, in Asterias, there are
four rows in each arm. In a living specimen they will
be seen to act as the locomotive organs of the animal. They
are capable of being greatly extended, and when the star-
fish is moving along, it will be observed to do so by the
tube-feet being extended outwards and forwards (7.¢., in the
direction in which the animal is moving), their extremities °
becoming fixed by the suckers, and then the whole tube-
foot contracting so as to draw the body forward ; the hold
of the sucker then becomes relaxed, the tube-foot is stretched
forwards again, and so on. The action of all the tube-feet,
extending and contracting in this way, results in the steady
progress of the starfish over the surface. With the aid of
the tube-feet the starfish is also able to right itself if it is
turned over on its back.

At the extremity of each of the ambulacral grooves is to
be distinguished a small bright red spot, the eye (Fig. 88, A,
oc), and over it a median process, the /enéacle (7), similar
to the tube-feet but smaller and without the terminal sucker.
The tentacles have been ascertained by experiment to be
olfactory organs, the starfish being guided to its food much
more by this means than by the sense of sight. If one of
the arms be cut across transversely (Fig. 87 and Fig. 88, B)
and the cut surface examined, the dorsal part of the thick,
hard wall of the arm will present the appearance of an arch
(with its convexity upwards), and the ventral part the form
of an inverted V, the ends of the limbs of which are con-
nected with the ventral ends of the dorsal arch by a very
short, flat, horizontal portion. Enclosed by these parts is a
space, a part of the ccelome or Jody-cavity, and below, be-
tween the two arms of the V, is the ambulacral groove,

VII PHYLUM ECHINODERMATA 161

The dorsal arch is supported by a number of irregular
ossicles. The V-shaped ventral part of the body-wall—
z.e., the walls of the ambulacral groove —is supported
by two rows of elongated ossicles, the amdulacral ossicles
(Fig. 88, Amd. os), which meet together at the apex or
summit of the groove like the rafters supporting the roof
of a house, but with a movable articulation allowing of

Fic. 87. — Starfish. Vertical section through an arm. asp, ampulle ; ef, epider-
mis; rad. amb, radial vessel of the ambulacral system; s points to the septum
dividing the blood-vessel into two parts; xad. me, radial nerve of the epidermal
system; sf, spaces in mesoderm of body-wall; z./, tube-feet. (From Leuckart,
after Hamann.)

separation or approximation of the two rows so as to open
or close the groove. Between the ambulacral ossicles of
each row are a series of oval openings, the amdbulacral pores,
one between each contiguous pair of ossicles. In the ventral
groove lie the tube-feet (47). Each tube-foot is found to
correspond to one of the ambulacral pores. When the tube-
foot is drawn upon, it is seen to be continuous with one of
M

162 MANUAL OF ZOOLOGY SECT.

a series of little bladder-like bodies, the ampu//e, which lie
on the other side of the ambulacral ossicles, z.¢., in the
cavity of the arms. When one of them is squeezed the cor-
responding tube-foot is distended and protruded, the cavities
of the tube-foot and the ampulla being in communication
by means of 2 narrow canal running through the ambulacral
pore ; and it is in this way that the foot is protruded in the
living animal. The corresponding ampulla being contracted
by the contraction of the muscular fibres in its walls, the
contained fluid is injected into the tube-foot and causes its
protrusion.

Running along the ambulacral groove, immediately below
where the ambulacral ossicles of opposite sides articulate, is
a fine tube, the radial ambulacral vessel (Fig. 87, rad. amb,
Fig. 88, B, Rad. Amb. V; Fig. 90, 7), which appears in
the transverse section as a small rounded aperture. From
this short side branches (Fig. 90 7’) pass out on either side
to open into the bases of the tube-feet. Below the radial
ambulacral vessel is a median thickening of the integument
covering the ambulacral groove ; this marks the position of
the radial nerve (Figs. 87 and 88, Rad. ne) of the epidermal
nervous system, and is traceable as a narrow thickened band
running throughout the length of the groove, and terminat-
ing in the eye at its extremity, while internally it becomes
continuous with one of the angles of a pentagonal thickening
of a similar character, the merve-pentagon, which surrounds
the mouth.

The two radial nerve-bands of the deep nervous systems
are thickenings of the lining membrane of a space overlying
the radial nerve and underlying the radial ambulacral system.
A channel throughout the length of the arm above the
radial nerve forms part of a system of channels which are
usually regarded as constituting a dlood-vascular system.

vu PHYLUM ECHINODERMATA 163

This radial blood-vessel, as it is termed, is divided lon-
gitudinally by a vertical septum into two lateral halves.
Internally it communicates with an ora ring-vessel surround-
ing the mouth and likewise divided into two by a septum.
When the dorsal wall of the central disc is dissected away,
the remainder of the organs come into view. The rows of
ambulacral ossicles appear on this view as ridges, the
ambulacral ridges, one running along the middle of the
ventral surface of each arm to its extremity, and extending
inwards to the corresponding angle of the mouth. At the
sides of each of these ridges appear the rows of ampulle.
Within the pentagonal actinostome is a space, the peristome,
covered with a soft integument, and in the centre of this is a
circular opening, the true mowzh, the size of which is capable
of being greatly increased or diminished.

The mouth is found to open through a short passage, the
esophagus, into awide sac, the cardiac division of the stomach
(Fig. 88, s¢; Fig. 89, card. st). This is a five-lobed sac,
each of the lobes of which is opposite one of the five arms.
The walls of the sac are greatly folded, and the whole is
capable of being everted through the opening of the mouth,
folded over some object desired as food, and then retracted
into the interior, the retraction being effected by means of
special retractor muscles which arise from the sides of the
ambulacral ridges. This cardiac division of the stomach
communicates dorsally with a much smaller chamber, the
pyloric division of the stomach, and this in turn opens into a
very short conical zz/estine, which leads directly upwards to
open at the small anal aperture. The pyloric division of
the stomach is pentagonal, each angle being drawn out to
form a pair of large, tree-like appendages, the pyloric caca
(Figs. 88 and 89, fy/. ce@c), which extend to near the
extremity of the arm. The walls of the pyloric czeca are

164 MANUAL OF ZOOLOGY SECT.

glandular : they secrete a digestive fluid, and are therefore to
be looked upon as digestive glands. It is found by experi-
menting with this digestive fluid that it has an action on

Fic. 88.— Diagrammatic sections of a starfish. A vertical section passing on the
right through a radius, on the left through an inter-radius. The off-side of the
ambulacral groove with the tube-feet (7. #) and ampullz (Azz) are shown in
perspective. B, transverse section through anarm. The ectoderm is coarsely
dotted, the nervous system finely dotted, the endoderm radially striated, the
mosoderm evenly shaded, the ossicles of the skeleton black, and the ccelomic
epithelium represented by a beaded line. asd. 0s, ambulacral ossicles; amp,
ampulle; az, anus; C. Amd, IV’, circular ambulacral vessel; C. B. 1’, septum
of ring blood-vessel; Cd. c@, cardiac ceca; Ca/, ceelome; Cai. Epithm,
coelomic epithelium; Der. Epithm, deric epithelium: Derm, mesoderm; Ext.
Lpthm, enteric epithelium; /wt. ce, intestinal ceca; Mdpr, madreporite; Mes,
mesentery; A7th, mouth; Vv. R, nerve ring; oc, eye; os, ossicles of body-wall;
ova, oviduct; Ped, pedicellarize ; th, perihzemal spaces; pyt. c@c, pyloric ceca;
Rad. amb. v, radial ambulacral vessel; Rad. B. V, points to septum in the
radial blood-vessel; Rad. Nw, radial nerve; Resp. c@, dermal branchie; St,
stomach; Sz. c, stone-canal; /¢, tentacle; 7. F, tube-feet. (From Parker’s
Biology.)

food-matters similar to that exerted by the secretion of the

pancreas in the Vertebrata, converting starch into sugar,
proteids into peptones, and bringing about the emulsification

VIL PHYLUM ECHINODERMATA 165

of fats. From the short intestine are given off inter-radially
two hollow appendages, the znéestinal ceca (Fig. 89, iné.
c@c), each with several short branches of irregular shape.
Running downwards from the madreporite to near the
border of the mouth, is an S-shaped cylinder, the madreporic
or stone-canal (Fig. 88, St. c). The walls of this canal are
supported bya series of calcareous ossicles. The interior of

pyt-coee
Fic. 89,—Asterias rubens. Digestive system. an, anus; card. st, cardiac

division of the stomach; zt. cec, intestinal casca; »adr, madreporite; ply.
c@c, pyloric ceca; pyl. st, pyloric division of the stomach. (From Leuckart.)

the madreporic canal communicates above with the exterior
through the grooves of the madreporite. Below, the canal
opens into a wide, five-sided, ring-like canal, the rimg-vessel
of the ambulacral system. From this are given off the five
radial ambulacral vessels, passing to the extremities of the
arms. From the pentagonal canal are given off also a series
of five pairs of appendages, the Polan vesicles (Fig. 90, ap),

166 MANUAL OF ZOOLOGY SECT.

— pear-shaped, thin-walled bladders with long narrow necks,
— which are placed inter-radially. On the sides of the neck
of each Polian vesicle (except in the inter-radius containing
the madreporic canal, where there is one on one side only)
project inwards a pair of little rounded glandular bodies, the
racemose vesicles, or Tiedemann’s vesicles, the interior of
each of which is divided into a number of chambers.

Fic. 90.—Ambulacral system of a starfish. a, ampulle; af, Polian vesicles; c,
circular canal; 7z, madreporite; 7’, madreporic canal; , tube-feet; 7, radial
vessels; »’, branches to ampulle. (After Gegenbaur.)

Accompanying the madreporic canal there is an organ, —
the ovoid gland, — the relationships and function of which
have given rise to a considerable amount of difference of
opinion. It is a fusiform body, the interior of which is
divided up into a number of freely communicating spaces.

VIL PHYLUM ECHINODERMATA 167

The starfish is wsdsexual, each individual possessing
either ovaries (Fig. 88, ov) or ¢estes, which appear very
similar until they are examined microscopically. They
consist of masses of rounded follicles, like bunches of
minute grapes, a pair in each inter-radial interval. The
ducts, by means of which the ova, or sperms, reach the

Fic. 91.—Anthenea. View of dorsal surface. (After Sladen.)

exterior, open on the dorsal surface (Fig. 88, A, Oza)
through a number of perforations on a pair of sieve-like
plates, situated inter-radially close to the bases of the arms.

Other starfishes, while resembling Asterias in most re-
spects, differ from it in a number of less important points.
Thus though the number of arms is usually five, in some
species it is eight, in others more, and in some of those with

168 MANUAL OF ZOOLOGY SECT.

more than five arms the number is inconstant. The pro-
portions borne by the arms to the central disc also vary
greatly in different kinds, the arms being in many instances
relatively longer, in many relatively shorter than Asterias, and
in the latter case (Figs. 91 and 92) the central disc is cor-
respondingly increased in extent. In some extreme instances
of this modification the starfish assumes the form of a five-

Fic. 92. — Anthenea. View of ventral surface. From New Zealand. (After Sladen.)

angled disc, in which the arms are represented merely by the
angles. In all cases the arms are hollow, each containing
a prolongation of the body-cavity containing the ceca; and
in all the mouth is in the centre of the ventral surface, and
narrow ambulacral grooves run out from it in a radiating
manner to the extremities of the arms. In some starfishes
there are but two rows of tube-feet in each arm. An anus

VII PHYLUM ECHINODERMATA 169

is sometimes absent; in Aséerias vulgaris it is minute,
almost closed. The spines and pedicellariz differ in their
form and arrangement in different kinds of starfish, as also,
though in a less degree, the tube-feet. The starfishes con-
stitute one of the five classes of living Echinodermata, the
class Asteroidea.

2. THE OPHIUROIDEA

The Brittle-stars bear many resemblances to the true star-
fishes, but have a number of special features of sufficient

Fic. 93.— Ophioglypha lacertosa. A, outline, of the natural size; B, central disc,
dorsal view; C, the disc, ventral view showing the mouth and genital fissures.
(From Nicholson and Lydekker’s Pal@ontology.)

importance to justify their being regarded as constituting a

separate class, which is termed the Ophiuroidea. Like

170 MANUAL OF ZOOLOGY SECT.

Asterias, the brittle-star (Fig. 93) has a star-shaped body
with a central disc and five radiating arms. But the arms,
instead of appearing merely as radiating prolongations of the
central disc, are sharply marked off from it, and have rather
the appearance of appendages. They are solid, long, slender,
and tapering, clothed with plate-like ossicles and_ beset
laterally with spines. They are highly flexible, and instead
of creeping along slowly like a starfish the brittle-star moves
with comparative activity by means of lateral movements
of the arms. As in the starfish there are distinct dorsal
and ventral surfaces, the former having the mouth in its
centre. An anus is absent, and the madreporite is on the
ventral surface instead of the dorsal. ‘There are no ambula-
cral grooves, and the tube-feet project at the side of the
arm. ‘The internal structure is similar in most respects to
that of the starfish, but the radial prolongations of the
body-cavity into the arms are absent, and there are no
pyloric czeca. In certain of the Ophiuroidea the arms are
branched.

3. THE ECHINOIDEA

The Sea-urchins (Class Echinoidea) differ much more
widely from the starfishes than the brittle-stars. The body
(Fig. 94) is not star-shaped, but globular. At one pole is
the mouth, at the other the anus. The body is enclosed in
a shell or corona (Fig.95), formed of firmly united plate-
like ossicles arranged in rows which run from oral to aboral
poles. Supported on these are numbers of long, slender,
sharp-pointed, freely movable spines (Fig. 94). Running
over the surface from near the oral to near the aboral poles
are five bands of tube-feet which are capable of being
extended into long slender tubes (Fig. 94). These have

VIL PHYLUM ECHINODERMATA 17I

sucker-like extremities and, like the tube-feet of the starfish,
are the organs of locomotion. A remarkable and charac-

, \y

PQA’
SSN \Y i ‘

WW x F
Y)' Sui
ain

\ N\

Fic. 94. — Strongylocentrotus. Entire animal, with the tube-feet extended beyond
the ends of the spines. (From Brehm’s 7hzerleben.)

teristic feature of the internal structure is the presence of a
complicated apparatus for mastication known as A7is/otle’s
lantern, consisting of five jaw-like parts, each bearing a

172

Amb

Fic. 95. — Corona of sea-urchin with the spines removed to show the arrangement

of the plates, lateral view.
Ap, apical (aboral) pole;
Thierreich.)

MANUAL OF ZOOLOGY

SECT.

L[nt.amb

Amé, ambulacral zone with its perforated plates;
Int. amb, inter-ambulacral zones.

(From Bronn’s

sharp tooth. The points of these five teeth can be seen
through the opening of the mouth. The enteric canal has

Peas

ae
Le

Fic. 96.— Apical system of plates and
saboral extremities of zones of the shell
of a sea-urchin. amb, ambulacral
zones; gen, genital plates; zu¢. amb,
inter-ambulacral zones; adr, madre-
porite; oc, ocular plates; ferzpr, peri-
proct. (After Leuckart.)

no radiating coeca. The five
ducts of the reproductive or-
gans open on five ossicles, the
genital plates (Fig. 96, gen),
which with five smaller ocw-
lar plates (oc) each bearing
a rudimentary eye, form a
complete ring round the
space ( perifr) at the anal
pole, in the middle of which
is the anus; a madreporite
is amalgamated with one of
the genital plates.

vil PHYLUM ECHINODERMATA 173

In the Heart-urchins (Spatangus) the body is heart-shaped
instead of globular, and in the Cake-urchins (represented by
our Echinarachnius parma) it is flattened and disc-like. In
most respects, however, these ¢7vegu/ar sea-urchins are very
closely allied to the ordinary or regular forms, and with the
latter they constitute the third class of Echinodermata, the
Echinoidea.

4. THE HOLOTHUROIDEA

Also widely different from the starfishes in the general
form of the body are the Holothurians (class Holothuroidea).
Some of these are known as sea-slugs from their slug-like
appearance, others as sea-cucumbers. One is termed the
“cotton-spinner”’ from the cottony filaments which it dis-
charges when irritated or removed from the water. Certain
large tropical forms which abound on coral reefs in the Pacific,
are used as food and form the object of a fishing industry in
connection with which they are known as Béche-de-mer
or trepang (folothuria eduhs). Our Floridan trepang is
Hf, floridana ; a more northern form is Pentacta frondosa.
A Holothurian (Fig. 97) is roughly comparable to a sea-
urchin the body of which has been drawn out in the direc-
tion of the line joining mouth and anus, so that it has
assumed a long and slender form. But there is only
exceptionally a rigid shell of plates, the body-wall being
nearly always flexible and sometimes quite soft and sup-
ported by calcareous spicules, and usually one side, habitu-
ally directed downwards, is often modified as a ventral
surface. A circlet of ¢enéacées surrounds the mouth. Five
regular zones of ¢ude-fee¢ sometimes run from mouth to
anus: sometimes those on the dorsal surface may be modi-
fied ; sometimes the tube-feet are scattered over the entire

174 MANUAL OF ZOOLOGY SECT.

surface, in some forms (such as the worm-like Syrapéa and
its allies) tube-feet are entirely absent.

Fic. 97. —Cucumaria planci. Entire animal seen from the ventral surface, with the
tentacles expanded, and the tube-feet projected outwards. (From Hertwig’s
Lehrbuch, after Ludwig.)

5. THE CRINOIDEA

The Feather-stars and their allies constituting the class
Crinoidea, bear some superficial resemblances to the star-
fishes and brittle-stars, but with some important points of
difference. The body of a feather-star (Fig. 98) is star-
shaped, with a cenéral disc and five arms which are bifurcate

vil PHYLUM ECHINODERMATA 175

at their bases. On that surface of the central disc which is
directed upwards in the natural position of the animal, is in
the centre the mouth and on one side the anus. On the

(From Leuckart and

pean coasts.

Nitsche’s Diagrams.)

Fic. 98.—Antedon. Side view of entire animal. Euro

opposite surface are attached whorls of slender curved cy-
lindrical appendages, the cr, by means of which the
animal is able to anchor itself temporarily to a rock or a
seaweed. ‘The arms are long, flexible and tapering, shaped

176 MANUAL OF ZOOLOGY SECT.

somewhat like a feather, with a main axis and a pair of
lateral rows of short slender branches, the pevnules. The
arms act as the locomotive organs of the animal, their wav-
ing movements propelling it slowly through the water. Tube-
feet are not developed as such; but are represented by a
great number of very minute simple processes, the ¢endacles,
which border grooves running along the upper surfaces of
the arms and of the pinnules.

Some of the Crinoidea, the stalked Crinoids (Fig. 99),
chiefly occurring at great depths in the sea are supported on
a long slender s/a/k by which they are permanently fixed.
In the ordinary feather-stars the larva passes through a
stage in which it is attached by means of a stalk like the
stalked Crinoids: after a time the stalk becomes absorbed
and the young feather-star becomes free.

Our two species of Antedon live in deep water off the
New England coast.

A remarkable feature of the Echinodermata is the prevail-
ing radial arrangement of their parts, a feature in which they
resemble the very much more simply organised Ccelenterata.
But underlying this there is to be detected a more obscure
arrangement of the body in right and left halves, just as in
the dclateral animals we have been more recently dealing
with. This deeper bilateral symmetry is almost completely
disguised by the radial arrangement of most of the parts.
In the larva the symmetry is strongly bilateral and it is only
by passing through a remarkable metamorphosis in which
parts of the larva are sometimes altogether discarded that
the radially constructed adult form is developed.

177

PHYLUM ECHINODERMATA

VII

(After P. H. Carpenter.)

Fic. 99. — Metacrinus interruptus.

SECTION VIII.—ROTIFERA, POLYZOA
AND BRACHIOPODA

1. THE ROTIFERA

A group of Metazoa of microscopic size, the Rotifera or Wheel
Animalcules, which are of exceedingly common occurrence in fresh
water, and are also found, though much less abundantly, in the sea, are
readily mistaken on a superficial examination for Infusoria on account
not only of their minuteness and the general resemblance in shape of
many of them to certain members of that class, but of the presence of
cilia as organs of locomotion. A more careful examination, however,
shows that these minute creatures are relatively highly organised multi-
cellular animals, and reveals certain general features of resemblance
between them and the Trochosphere, which is the characteristic larval
form in a phylum to be subsequently dealt with, the Annulata (Section
IX.).

The majority of the Rotifera are free-swimming. The cilia, by means
of which the swimming movements are effected, are confined to one
extremity of the body, the anterior or oral, and are borne on a very
characteristic organ termed the ¢rochal disc (Fig. 100, ¢v.d@). This is in
its simplest form a disc with a prominent rim, fringed with strong cilia,
and surrounds the oral end. The mode of movement of the cilia is
such as to cause the trochal disc to assume the appearance of a rapidly
rotating wheel, and it is to this circumstance that the name Rotifera or
Wheel-bearer is applied to the group. Sometimes, however, the form
of the trochal disc is less simple, the disc with its circlet of cilia hecom-
ing divided into lobes, or drawn out into long processes. In some
forms ciliated prominences are present within the circlet of cilia, and
in others there is a second circlet internal to the first.

The body is usually distinguishable into the ¢z& and the ¢az? (2).
The latter, which is situated at the extremity of the body most remote

178

SECT. vat ROTIFERA, POLYZOA, AND BRACHIOPODA_ 179

from the trochal disc, is frequently divided by a series of freely-movable
joints into a number of tubular segments like the parts of a telescope.
It is provided at its extremity in many forms with a pair of processes
which act like the blades of a pair of forceps in enabling the animal to

Fic. roo. —Brachionus rubens. A, from the dorsal aspect ; B, from the right side.
a, anus ; 4”, brain; d. f, dorsal feeler; c. g/, cement gland; c/, cloaca; ec. 2,
ciliary lobes ; c. v, contractile vesicle; ¢, eye-spot ; z¢, intestine ; 77, lorica ;
7. f, lateral feeler ; #z, muscular bands ; xf, nephridial tubes ; ov, ovary ; ph,
pharynx ; st, stomach; ¢, tail; ¢. d, trochal disc; v#, vitellarium. (After
Hudson and Gosse.)

temporarily attach itself. In many forms in which the tail is well-
developed locomotion may be effected not only by swimming by the
movements of the cilia of the trochal disc, but by creeping or looping

180 MANUAL OF ZOOLOGY SECT.

movements like those of a leech, the oral end and the extremity of the
tail being alternately attached. In Rotifers, which are permanently
fixed, attachment is effected through the intermediation of the tail,
which is drawn out to form a long narrow stalk. In others the tail is
absent, or represented only by a pair of ciliated processes.

The trunk is in some Rotifers enclosed in a glassy cuirass or /orica
formed of a thickening of the cuticle. One remarkable form — Pedalion
— has six hollow appendages terminated by feathered setze: and a few
other forms are provided with simple or fringed setz.

The stalked forms inhabit tubes into which the animal can completely
retract itself, the substance of the tube being either a delicate gelatinous
material, or composed of pellets of mud, or of the animal’s feces.

The structure of the internal organs is simple. The alimentary
canal usually terminates in an anal aperture (a). There is a large
pharynx (f/) containing a masticatory apparatus, the mastax, usually
consisting of three chitinous pieces, or jaws, of complicated form. The
nervous system consists of a single ganglion (47), situated towards the
oral end; and thereare usually one or several very simple eyes (¢). In
close relation to the brain are one or several processes, the ¢actzle rods
(d@. f), tipped with non-motile cilia, connected with the ganglion by
means of nerves. A pair of longitudinal excretory vessels (7p), pro-
vided at intervals with short branches terminating in flame-cells, usually
open into a contractile vesicle which discharges into the terminal part
of the intestine.

The males differ greatly from the females, being nearly always much
smaller and degenerate in structure. Three kinds of eggs are produced:
large and small swmmer eggs which always develop without fertilisation
(parthenogenesis) and thick-shelled wizer eggs, which probably require
to be fertilised.

A few Rotifers live in the sea, but the majority are fresh-water forms,
occuring in lakes, streams, ponds, and even in puddles the water of
which is rendered foul and opaque by mud and sewage. Frequently
the water in which they live is dried up, and the thick-shelled winter
eggs may then be widely dispersed by wind. It is even stated that the
adult animals may survive prolonged desiccation and resume active life
when again placed in water. Many forms cling to the bodies of higher
animals in order to obtain a share of their food, thus leading a sort
of commensal existence. Others go a step further and become true
external or internal parasites.

VIII ROTIFERA, POLYZOA, AND BRACHIOPODA 181

2. THE POLYZOA

The Polyzoa are an extensive class of animals for the most part
marine, which, from the general form that they assume, are readily
mistaken for hydroid zoophytes (Hydrozoa, p. 91). They occur as
fixed colonies, the form of which varies greatly, supported by an exo-
skeleton which is sometimes gelatinous, sometimes chitinoid, sometimes
calcareous. They either encrust rocks, forming little patches, or they
grow up with a plant-like habit. Most usually the colony is a branch-
ing, plant-like structure, though it may assume other forms. The
whole consists essentially of a number of minute chambers, or zowcza,
as they are termed, each formed by the exoskeleton of one of the
zooids. Each zocecium (Figs. 101 and 102) has an aperture, sometimes
capable of being closed by a lid or operceedum, through which the oral
extremity of the zooid is capable of being protruded. At this pro-
trusible oral end of the zooid is a circular or horseshoe-shaped ridge or
lophophore bearing a number of simple, slender, ciliated tentacles
(cent). In many Polyzoa the colony bears a series of remarkable
appendages, the avicz/aria, of the nature of modified zooids. A typical
avicularium (Fig. 101, avic) has very much the appearance of a bird’s
head supported on a very short stalk, with a movable part representing
the lower jaw, which becomes separated from or approximated to the
part representing the upper jaw by movements which closely resemble
the movements of opening and closing of the bird’s mouth. These are
probably defensive organs. The mouth (vo) is a large aperture in the
middle of the oral extremity within the lophophore : the anus is situated
near it, but outside the lophophore. The digestive canal is a U-shaped
tube, divided into pharynx ( f/), stomach (s¢ow), and intestine (77),
suspended within a wide body-cavity. There is no vascular system, and
the central part of the nervous system consists of a single ganglion
(Fig. 102, gang), placed between mouth and anus. The sexes are
united, and there is a free-swimming cilia larva.

Probably allied to the ordinary Polyzoa thus briefly characterised,
and usually assigned to that class, are three genera, Pedicellina (Fig.
103), Loxosoma and Urnatella, the first two colonial, the third solitary,
which, among other special features, have the anus situated within the
circlet of the tentacles. These are known as the Endoprocta, as

Fic. ror. —Bugula avicularia. Two zooids, magnified. az, anus; avic, avicularia;
emb, embryo enclosed in the occium; /rz2¢, funiculus; gas¢, muscular bands

passing from the stomach to the body-wall; zvZ, intestine; 70, mouth, o@c,
ocecium ; @s, cesophagus ; ov, ovary ; ph, pharynx ; ret, parieto-vaginal muscles ;
sp, spermatidia : s¢o, stomach.

182

ROTIFERA, POLYZOA, AND BRACHIOPODA 183

SECT. VIII

“Syse[qoreys ‘ozvzs : yOeUIO}s “Zs ! a]OSNUI 1OJDeIOI 64734
1q # uM 1

‘

Cueay sayy)

: pur]s aanonpordar eda $ sndeydosa ‘a

SyINour ‘owe | auNsayut 7v7 : uOIsues “svvF ‘payluseu Auojoo v jo uon10g *eT[I}eUINTG — ‘Zor “OTT

distinguished from the Ectoprocta or ordinary Polyzoa, in which

the anus, as we have seen, is external to the lophophore and tenta-

cles.

184 MANUAL OF ZOOLOGY SECT.

Fic. 103. — Pedicellina. Showing successive stages (numbered 7 to 6) in the
development of zooids by budding. az, anus; gang, ganglion; #0, mouth;
tent, tentacles (retracted). (After Hatschek.)

3. THE BRACHIOPODA

The Brachiopoda, or Lamp-shells, are a group of marine animals
which present certain important features of resemblance to the Polyzoa,
and on that account are placed with them in a special phylum to which
the name Molluscoida is applied. The Brachiopoda are solitary,
never giving rise to colonies like those of the Polyzoa, and one of their
most striking characteristics is the possession of a calcareous shell which
bears a remarkable resemblance to that of the members of a widely
different group, the Pelecypoda of the phylum Mollusca, the group to
which the mussels, oysters, and clams belong. The shell (Fig. 104)
consists of two pieces or valves, one dorsal (d@. v), the other ventral
(v. v), and the animal is attached by a horny stalk or peduncle (Fig.
105, #@) which passes through an aperture (Fig. 104 7) in a process,
the deak (6), of the ventral valve. In the natural state the peduncle is
attached to a rock or other support, and the animal lies with the ventral
valve uppermost and the two valves gaping slightly. The end of the
valve at which the peduncle is situated is regarded as posterior, the

VIL ROTIFERA, POLYZOA, AND BRACHIOPODA 185

opposite end as anterior. The two valves articulate together by a more
or less distinct hinge situated at the posterior end, and the movements
of both opening and closing of the shell about this hinge are effected
by means of muscles passing internally between the valves.

Fic, 104. —Magellania flavescens. A, the entire shell from the dorsal aspect; B,
from the left side ; C, interior of ventral valve ; D, of dorsal valve ; ad. 1, adduc-
tor impressions ; 4, beak; c.f, cardinal process; @, deltidium : d. 7, divaricator
impressions; d@.v, dorsal valve; /, foramen; /. 7, protractor impressions ;
s, tooth-socket ; s. 2, shelly loop; sf, septum; ¢, tooth; v. v, ventral valve.
Australian seas. (After Davidson.)

The body of the animal occupies a relatively small part of the space
contained in the interior of the shell and lies toward the posterior end.

186 MANUAL OF ZOOLOGY SECT.

The rest of the space is lined by a pair of folds of the body-wall, the
mantle-folds (Fig. 105), @. , v.m), the edges of which are beset with
minute sete (s). In the space (mandle-cavity) lined by these mantle-

pl. st,

New Zealand

heart ; zz, intestine; 7A, 7/1,
, peduncle:

d. gl, digestive gland ; d. »,
; nph, nephridium ; Ad,

} v. v, ventral valve of shell.

d.v, dorsal valve of shell; gov1, gon®, gonads; ht,
1, its coiled process ; #¢, mouth
» ventral lobe of mantle ;

(ph, lophophore ; ph
pallial sinuses; s, sete; v. 22

dorsal mantle-lobe ;
coast.

Fic. 105. — Magellania lenticularis. Sagittal section of the entire animal.
lip;

folds lies a /ophophore (ép/), usually of complicated form, fringed with
long ciliated tentacles, and supported in many cases by a delicate,
sometimes simple, sometimes complicated, shelly process of the dorsal
valve, the shelly loop (Fig. 104, s. 7). The mouth (Fig. 105, mth),

VIII ROTIFERA, POLYZOA, AND BRACHIOPODA 187

situated in the middle of the anterior body-wall within the lophophore,
leads into a V-shaped digestive canal (s¢. 27¢), which may or may not
terminate in an anal aperture. A heart is present in the form of a con-
tractile sac, and there is a feebly developed vascular system. The
central part of the nervous system is in the form of a nerve ring,
with ganglia, which surrounds the cesophagus. There is a pair of large
funnel-shaped nephridia (7) which act also as reproductive ducts,
leading from the ccelome to the mantle-cavity. The sexes are some-
times separate, sometimes united.

The Brachiopoda are all marine. They are widely distributed geo-
graphically, and live at various depths, from between tide-marks to
twenty-nine hundred fathoms. At the present day the class includes
only about twenty genera and a hundred species, but in former geo-
logical periods the Brachiopoda were much more numerous, 106 genera
being known from the palaeozoic rocks, there being nearly two thou-
sand fossil species.

Lingula pyramidata occurs in sand at or near low water from Chesa-
peake Bay to Florida. Our common northern species, Terebratulina
seplentrionalts, lives north of Cape Cod, attached to rocks in from ten
to fifty fathoms.

SECTION IX.—PHYLUM ANNULATA

AN earthworm, a lobworm, and a leech, when compared
with one another, will at once be seen to possess certain
features in common. Each is bilaterally symmetrical, long
and relatively narrow in shape, is transversely ringed or
jointed, and has a soft integument ; each has a mouth open-
ing towards the anterior end and a smaller anal aperture
towards the posterior end. The earthworm and the lob-
worm, moreover, resemble one another in possessing a
number of bristles, extremely short in the former, disposed
regularly in groups along the rings of the body. The ringed
or annulate appearance is found, on a closer inspection, to
be due to the elongated body being made up of a row of
similar parts, the segments or mefameres, which are remark-
ably uniform throughout the length of the body, not only in
external appearance, but in internal structure. A general
correspondence is found to exist in the disposition of the
internal organs of all the three, and the conclusion is arrived
at that they are all members of one phylum. The phylum
in question, the Annulata, comprises the earthworms, the
class of the marine segmented worms or Annelids to which
the lobworm belongs, the leeches and certain other groups.

1. THE CHATOPODA

The rows of bristles above referred to as disposed along
the segments of the body in the earthworm and the lobworm
188

SECT. IX PHYLUM ANNULATA 189

constitute one of the distinguishing features of the class
Chetopoda or “bristle-footed” worms of the phylum
Annulata. Of these a good and common example is Néreis
—a marine Annelid of common occurrence under stones
and among shells and seaweed on the
sea-shore in all parts of the world. The
following account of the European WVerezs
dumerilit will apply, with slight differences,
to our common JVereis virens.

In shape (Figs. 106-109) the body,
which may be about 7 or 8 centimetres
in length, is long and narrow, approxi-
mately cylindrical, somewhat narrower
towards the posterior end. A very distinct
head, bearing eyes and tentacles, is recog-
nisable at the anterior end; the rest is
divided by a series of ring-like narrow
grooves into a corresponding series of seg-
ments or metameres, which are about eighty
in number altogether ; and each of these
bears laterally a pair of movable muscular
processes called the favapodia, provided
with bundles of bristles or se¢e. The head
(Fig. 109) consists of two parts, the fro-
stomium (prest) and the fperistomium
(perist). The former bears on its dorsal
surface four large rounded eyes, in front Fic. 106.—Nereis du-
a pair of short cylindrical senzacles (tent), eee ieee hee
and further back a pair of somewhat “**?
longer stout appendages or palpi (falp). The feristo-
mium, which presents some resemblance to the segments of
the body, though wanting the parapodia, bears laterally four
pairs of long slender cylindrical tentacles (ferist, sent):

190 MANUAL OF ZOOLOGY SECT,

on its ventral aspect is a transversely elongated aperture,
the aperture of the mouth. The segments of the body
differ little in external characters from one another through-
out the length of the worm. Each bears laterally a pair of
parapodia which in the living animal are usually in active
movement, aiding in creeping, or acting as a series of oars
for propelling it through the water. When one of the para-
podia (Fig. 107) is examined more attentively it is found
to be biramous, or to consist of two distinct divisions —a
dorsal, which is termed the zotopodium (noto), and a ventral,

dors.ctrr

vent.cirr

Fic. 107.—Nereis dumerilii. A single parapodium magnified. ac, aciculum;
dors. ctrr, dorsal cirrus; xeuro, neuropodium; zoto, notopodium; vent. cirr,
ventral cirrus. (After Claparéde.)

which is termed the ewropodium (neuro). Each of these
is further subdivided into several lobes, and each bears a
bundle of setae. Each of the bundles of sete is lodged in
a sac formed by invagination of the epidermis, the seé#gerous
sac, and is capable of being protruded or retracted and
turned in various directions by bundles of muscular fibres
in the interior of the parapodium. In each bundle there
is, in addition to the ordinary sete, a stouter, straight, dark-
coloured seta (ac), the pointed apex of which projects only
a short distance on the surface ; this is termed the aciculum.
The ordinary sete (Fig. 108) are exceedingly fine, but

1X PHYLUM ANNULATA IgI

stiffsh, chitinous rods, of which two principal kinds are
recognisable ; both have a terminal d/ade articulating with
the main shaft of the seta by a distinct joint. On the
dorsal side of the parapodium is a short cylindrical, tentacle-
like appendage, the dorsal cirrus
(Fig. 107, dors. cirr), and a similar,
somewhat shorter, appendage, the
ventral cirrus (vent. cirr), is situated
on its ventral side. The last segment
of the body, the anal segment, bears
posteriorly a small rounded aperture,
the anus, this segment is devoid of
parapodia, but bears a pair of appen-
dages, the ana/ cirri, similar in char-
acter to the cirri of the ordinary
segments, but considerably longer.
On the ventral surface, near the
bases of the parapodia, there is in
each segment a pair of very fine aper-
tures, the openings of the nephridia.
The enteric cana/ is a straight tube
running throughout the length of the
body from the mouth to the anus.
Between the outer surface of this
tube and the inner surface of the wall
of the body is a considerable space ,.. 55 _ Nereis aumerilii.

— ) aery 7 Seta highly magnified.
the calom, body cavity, or pert jhe Goa ea

visceral cavity — filled with a fluid, the

celomic fluid. The space is divided by a series of transverse
partitions or sepa passing inwards from the body-wall to the
walls of the alimentary canal opposite the grooves between
the segments, and thus dividing the ccelom into a series of
chambers, each of which corresponds to one of the seg-

vert. vtss

70, COE

Fic. 109.— Nereis dumerilii. Semi-diagrammatic view of the anterior portion of
the body, with the dorsal body-wall removed, so as to show the alimentary canal,
the septa, the blood-vessels and the nephridia; a portion of the intestine removed
so as to show the ventral blood-vessel and nerve-cord which lie below. dors. vess,
dorsal vessel; ¢7, cesophageal glands; zzz, beginning of intestine; we. co, nerve
cord; xefh, nephridia; ws, esophagus; pals, palp; parva, parapodia; ferzst,
peristome; erzst. tent, peristomial tentacles; 44, pharynx with its jaws; prest,
prostomium; vez. vess, ventral vessel.

192

SECT. IX PHYLUM ANNULATA 193

ments. These partitions are not complete, spaces being
left around the alimentary canal and elsewhere, through
which neighbouring chambers communicate.

The mouth leads into a wide cavity, the buccal cavity
continued back into a pharynx (Fig. 109, ph). In the
pharynx are a number of very small dark brown chitinous
denticles, which are very regularly arranged. The posterior
part of the pharynx has very thick walls composed of
bundles of muscular fibres, which are concerned in the
movement of a pair of laterally placed chitinous 7aws.

Behind the pharynx the alimentary canal narrows con-
siderably to form a tube, the wsophagus (es), which runs
through about five segments to open into the intestine.

The anterior part of the alimentary canal is capable of
being everted as a prodvoscis until the jaws are thrust forth
and thus rendered capable of being bronght to bear on some
small living animal, or fragment of animal matter, to be
seized and swallowed as food.

Into the cesophagus open a pair of large unbranched
glandular pouches, or ceca (g/), which probably are of the
nature of digestive glands. The cz/estine (int) is a straight
tube of nearly uniform character throughout, regularly con-
stricted between the segments.

Nereis has a well-developed system of vesseds filled with
blood of a bright red colour. A main dorsal vessel (Figs.
10g and 110, dors. vess) runs from one end of the body to the
other above the alimentary canal, and is visible in places
through the body-wall in the living animal. It, as well as
the majority of the vessels, undergoes contractions which are
of a peristaltic character— waves of contraction passing
along the wall of the vessel so as to cause the movement of
the contained blood. These peristaltic contractions are
more powerful in the case of the dorsal vessel than in that

oO

SECT.

MANUAL OF ZOOLOGY

194

of any of the others, and run with great regularity from

behind forwards, so as to drive a current of blood in that

direction.

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Along the middle of the ventral surface below the alimen-
tary canal runs another large longitudinal vessel, the ventral
vessel (vent. vess), in which the current of blood takes a

IX PHYLUM ANNULATA 195

direction from before backwards. Connecting the dorsal
and ventral vessels, there are in each segment two pairs of
loop-like transverse vessels which give off branches to the
parapodia, the alimentary canal, and neighbouring parts.

There is a well-developed zervous system (Fig. 112) which
is bilateral and metameric in its arrangement, like the other
systems of organs. Situated in the prostomium is a large
bilobed mass of nerve-matter containing numerous nerve-
cells, the cerebral ganglion or brain (c). This gives off
tentacular nerves to the tentacles and palpi, and two pairs
of short thick of#c nerves to the eyes. Behind, two thick
nerve strands, the esophageal connectives (a), curve round
the mouth in the peristomium to meet on the ventral aspect
behind the mouth and below the pharynx. The cesophageal
connectives, with the cerebral ganglion, thus form a ring
around the anterior part of the enteric canal. Running
backwards from the point of union of the cesophageal con-
nectives, along the entire length of the body of the worm,
on the ventral aspect, is a thick cord of nerve-matter, the
ventral nerve-cord (h). In each segment this cord presents
a little dilatation from which nerves are given off to the
various parts of the segment: and each of these enlarge-
ments is really double, consisting of a pair of closely-united
ganglia. The intermediate parts of the cord, between suc-
cessive pairs of ganglia, are also double, consisting of a pair
of longitudinal connectives enclosed in a common sheath.
Given off behind from the cerebral ganglion is a system of
fine nerves with occasional small ganglia, the séomatogastric
or visceral system, distributed to the anterior part of the
alimentary canal.

The tentacles and palpi, as well as the cirri, are probably
organs of the sense of touch. The only other sense-organs
are the four eyes, situated on the prostomium. The eye

196 MANUAL OF ZOOLOGY SECT.

(Fig. 111) consists of a darkly pigmented cup, the vena
(ve), with a small rounded aperture, the pupi/, and enclosing
a mass of gelatinous matter, the Zens (/).

Pe ies ¥

\ AS REHISS\ ;
ali ~ th te MD
Ww en yh

Fic. 111. —Section through an eye of Nereis. co, cornea; cz, cuticle; 7, lens; 7,
layer of rods; xe, retina. (After Andrews.)

The organs which are supposed to perform the function
of excretion are a series of metamerically arranged pairs of
internally ciliated tubes, the segmental organs or nephridia
(Figs. 109 and 110, zeph) occurring in all the segments of
the body. Each of these has an external opening or nephri-
diopore, a fine circular pore capable of being widened or
contracted, situated on the ventral surface not far from the
base of the ventral cirrus, and opening internally into the
ceelom through a ciliated bell or funnel, the xephrostome,
projecting through the mesentery into the cavity of the seg-
ment next in front of that in which the body of the organ
lies.

IX PHYLUM ANNULATA 197

Nereis is unisexual. The sexual elements, ova or sperms,
are formed from temporary masses of cells (ovaries or “estes),
which are developed towards the breeding season by a pro-

Fic. r12.—Nereis. Anterior portion of nervous system, comprising the brain, the
cesophageal connectives, and the anterior part of the ventral nerve-cord. (After
Quatrefages. )

liferation of the cells of the membrane ( fevitoneum) lining

the ccelom and the structures it contains.

Ova and sperms, when fully ripe, are discharged, reaching

198 MANUAL OF ZOOLOGY SECT.

the exterior, in the case of the sperms probably through the
nephridia ; in the case of the ova, which are much too large
to pass out in this way, probably through apertures tempo-
rarily formed by rupture of the body-wall ; and impregnation
takes place by contact between the two sets of elements
while floating freely in the sea-water.

yes

oy)

ney

vat

z

<
SX

Fic. 113. —Serpule with their tubes. (After Quatrefages.)

Other annelides which may be collected along with Nereis
on the sea-shore will be found to resemble it in the seg-
mented character of the body, and the presence of para-
podia with sete, but to differ from it in the general shape,
the number of the segments, the form of the parapodia, and
the arrangement and shape of the sete, the form of the
head with its eyes and tentacles, and other points. Many

IX PHYLUM ANNULATA 199

possess 6vanchie, organs which are absent as such in Nereis,
in the form of simple or branched vascular processes ar-
ranged in pairs on the dorsal side of the parapodia, through-
out the whole or a part of the length of the body, or (Fig.
113) confined to the head-end. All such marine worms
belong to the sub-class Polycheta of the Chetopoda.
Though many of them move about freely like Nereis, others
live permanently in tubes of a membranous or shelly mate-

Fic. 114.—A, B, C, three stages in the development of the Trochosphere of
Eupomatus, from the side. am, anus; /%, blastoceele; 7, polar cells of the
mesoderm; wd, mid-gut; 2, larval head-nephridium; of, otolith; sf, neural
plate; st, stomodeum; w#, preoral ciliated ring; w,, post-oral ciliated ring.
(From Lang’s Comparative Anatomy.)

rial. The tube-inhabiting Polycheta (Fig. 113) usually
present marked modifications of form in accordance with
their mode of life. The branchiz when present are usually
confined to the head-end, so that they can easily be thrust
out through the opening of the tube, and the body is fre-

200 MANUAL OF ZOOLOGY SECT.

quently divisible into regions owing to more or less marked
differences in the development of the parapodia and other
points, between the anterior part which may be thrust out

Fic. 115.—Lumbricus agricola. A, entire specimen, lateral view ; B, ventral view
of anterior portion of the body, magnified. 7, 75, 33, first, fifteenth, and thirty-
third segments. The black dots represent the sete. (After Vogt and Jung.)

of the tube and the posterior parts which habitually remain
enclosed in it. All the Polychzta, with one or two ex-
ceptions, have the sexes separate, and have a free-swimming

IX PHYLUM ANNULATA 201

pelagic larva, the Zrochosphere (Fig. 114), provided with one
or several circlets of cilia.

When a common earthworm is compared with Nereis,
certain resemblances are at once discernible. The earth-
worm (Fig.115) has the same elongated cylindrical body,
divided by ring-like grooves into a large number of seg-
ments or metameres. But the well-developed head-region
is absent, as are the eyes, palpi, and tentacles, and the
parapoda are not present, nor the dorsal and ventral cirri.
Setz, however, are present (Fig. 116), though so short as to
be distinguishable with difficulty; two
double rows run along each side of the
ventral surface, so that there are alto-
gether eight of these short setze on each
segment. A thickened zone—the saddle
or cliteHlum—is to be observed extend-
ing over five segments, in front of the
middle of the body. In internal struc-
ture there is a considerable resemblance ;
but the reproductive organs are her-
maphroditic in arrangement and more
complex in structure than in Nereis.
There are two special male ducts or vasa Fic. 116, — Lumbricus,

: : seta, highly magnified.
deferentia, opening on the ventral sur-
face of the fifteenth segment, and female ducts or oviducts
opening on the fourteenth.

The fertilised ova of the earthworm are enclosed, together
with a quantity of an albuminous fluid in a cocoon, the wall
of which is formed of a viscid secretion from the glands of
the clitellum, hardened and toughened by exposure to the
air. The cocoon is deposited in the earth, and the embryos
develop into complete, though minute, worms before they
make their escape. At a certain stage the embryos are

202 MANUAL OF ZOOLOGY SECT.

nourished by swallowing the albuminous fluid contained in
the cocoon.

The earthworms, together with a number of allied fresh-
water forms, constitute the sub-class Oligocheta of the
Cheetopoda. As a group they are distinguished from the
Polycheeta by the sexes being united in the same individual,
with the ovaries and testes compact and few in number, by
the absence of parapodia and cirri, the non-development of
a distinct head-region, and the absence of a free larval stage.

Very few Cheetopoda are true parasites, but a considerable
number are to be set down as commensals, habitually associ-
ating with another animal for the sake of food and shelter.
The earthworms burrow in soil containing decaying vegetable
matter, passing the mould through their intestine and subse-
quently throwing it off in the shape of “castings” on the
surface. They also feed on decaying leaves, and sometimes
on animal substances. Some of the fresh-water Oligocheta
manufacture tubes of mud held together by a tenacious
secretion from glands in the integument. Some of the
Polycheta move about freely or burrow in sand, or even in
rock or in the shells of molluscs; some occupy temporary
tubes ; others inhabit permanent tubes sometimes of parch-
ment-like consistency, sometimes hardened by deposition of
grains of sand, small fragments of shell or other foreign
bodies, sometimes of dense, shelly, calcareous material.
These tubes: are usually firmly fixed to a rock or a seaweed
or other foreign body. While the free-living Polycheta are
carnivorous in their diet, those that inhabit permanent tubes
are vegetable feeders.

A few Polycheta are pelagic. The majority live among
sand, mud, rock, or seaweed in shallow water, or actually
between high- and low-water limits; but they also occur at
all depths in the ocean.

IX PHYLUM ANNULATA 203

2. THE HIRUDINEA

A good example of the Hirudinea is the medicinal leech
(Hirudo), various species of which are to be found in ponds,
swamps, and slowly flowing streams in various parts of the
world.

It is a vermiform animal, some 6-10 cm. (2-3 inches) in
length, but is capable of contracting and elongating itself
so as to produce great alterations in form and proportion.
It moves by “looping” movements, and is also a good
swimmer. The body (Fig. 117) is depressed or flattened
dorso-ventrally, the dorsal surface convex, the ventral flat-
tened. The anterior end presents a ventrally directed, cup-
like hollow, the an/erior sucker (a.s),in the middle of which
is a small aperture, the mouth (mth). The hinder end bears
a disc-like posterior sucker (p.s), also directed downwards,
and at its junction with the trunk, on the dorsal surface, is
the very small median azzs (a).

The whole body is encircled by close-set transverse grooves,
dividing it into annui. These, like the annuli of some
earthworms, are more numerous than the true segments or
metameres, the study of the internal organs showing that,
except at the two extremities, each segment contains five
annuli. On the ventral surface of the fifth annulus of each
segment is a pair of minute apertures, the xephridiopores
or excretory apertures (7. p. 7-77); of these there are
altogether seventeen pairs, marking the fifth rings of the
sixth to the twenty-second segments.

The anterior sucker bears on its dorsal surface five pairs
of small black spots, the eyes (e. 7, ¢. 5).

The perfectly definite and comparatively small number of
metameres in the leech offers a striking point of contrast

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Fic. 117. —Hirudo medicinalis. A, dorsal; B, ventral aspect. a@, anus; @. Ss,
anterior sucker; ¢. 7, first pair of eyes; ¢. 5, fifth pair; gf. %, male gonopore;
gp. %, female gonopore; mth, mouth; 7. 7, first pair of nephridiopores;
np. 17, seventeenth pair; .s, posterior sucker; s.#, sensory papilla; I-XXVI,
segments. (Partly after Whitman.)

204

SECT. IX PHYLUM ANNULATA 205

with what we have met with in the Chetopoda, and is to be
looked upon as a mark of higher differentiation.

The alimentary organs are greatly modified in accordance
with the blood-sucking habits of the animal. Surrounding
the mouth are three jaws,
one median and dorsal, the
other two ventro - lateral.
Each has the form of a com-
pressed muscular cushion,
with a sharp, evenly curved,
free edge covered with chi-
tin, which is produced into
numerous serrations or ceecth
(Fig. 118). By means of its
muscles each jaw can be

Fic. 118.— a, Head of Hirudo medici-

moved backwards or for- nalis, showing the three jaws(&); 4,
: one of the jaws isolated, with the finely
wards through a certain arc, toothed free edge. (After Sedgwick.)

and the three, acting to-
gether, produce the characteristic triradiate bite in the skin
of the animal upon which the leech preys.

The mouth leads into a muscular pharynx (Fig. 119, ph),
situated in the fourth to seventh segments. Radiating
muscles pass from its walls to the integument, and by their
contraction dilate its cavity and suck in blood made by the
jaws. Around the pharynx are numerous unicellular sa/-
vary glands, which open close to the mouth ; their se-
cretion has the effect of preventing the coagulation of the
blood taken as food.

The pharynx communicates by a very small aperture with
the second and largest division of the enteric canal, the
huge crop (cr), a thin-walled tube extending from the eighth
to the eighteenth segment, and produced into eleven pairs of
lateral pouches (¢7, cv. z, zz). The crop is capable of great

crt. |

gnei

Fic. 119.—Hirudo quinquestriata. Dissection from the dorsal aspect, a@, anus;
br, brain; cv. 7, first diverticulum of crop, contracted; cv. r', the same expanded;
cr. rr, the last diverticulum of the crop, contracted; cv. r', the same expanded;
d. ef, ductus ejaculatorius; gv. 7-23, ganglia of ventral nerve-cord ; zw#f. in-
testine ; 7. 7, lateral vessel ; $4. 1-17, nephridia ; ov. s, ovarian sac; f, penis;
ph, pharynx ; f. s, posterior sucker ; cf, rectum; st, stomach ; fs. r—gQ, testes;
va, vagina; v. d, vas deferens ; v. seve, vesicula seminalis.

206

SECT. IX PHYLUM ANNULATA 207

dilation, and its form varies greatly according to whether it
is empty or gorged with blood. Posteriorly the crop com-
municates by a minute aperture with the stomach (sf), a
tubular chamber which is the digestive portion of the canal ;
the blood is passed into it from the crop with extreme
slowness, and undergoes an immediate change, its colour
turning from red to green. The digestion of a whole
cropful of blood takes many months. The stomach is
continued into a narrow zntestine (int) ; this passes into a
somewhat dilated rectum (7c), which turns slightly upwards
and opens by the anus (az) in the last annulus.

The excretory system consists of seventeen pairs of
nephridia (nph. r-r7), situated in segments 6-22. A
typical nephridium (Fig. 120) has the general form of a loop
passing upwards from the ventral body-wall, produced into an
offshoot which extends inwards (mesially) to the correspond-
ing testis, and connected posteriorly with a small bladder or
vesicle (Fig. 120, vs). The free end is swollen into a lobed
mass which lies in a blood sinus (Fig. 114, 7s?) ; comparison
with other Hirudinea shows that this dilated end of the
nephridium represents a nephrostome which has lost its open
funnel-like end in correlation with the absence of a distinct
ccelom.

There is a complex vascular system, containing, like that of
the earthworm, red blood, the plasma coloured with hzmo-
goblin and containing sparsely distributed colourless corpus-
cles. But a striking difference from the preceding anneli-
dan types is found in the fact that the blood-containing spaces
are of two kinds,— d/ood-vessels proper, having muscular walls,
and blood-sinuses, the walls of which are devoid of muscle.

The two principal blood-vessels are lateral in position
(Figs. 119 and 122, 2. v), running fore and aft at the level of
the middle of the nephridia and uniting with one another at

208 MANUAL OF ZOOLOGY SECT.

the anterior and posterior ends of the body. They send off
branches both dorsally and ventrally, some of which anasto-
mose with one another. The ultimate branches break up
into capillaries in the integument, nephridia, etc.

The two principal sinuses are respectively dorsal (@. 5) and
ventral (v. s), the former lying just above the enteric canal
in the middle dorsal line, the latter occupying a similar

Fic. 120. — Nephridium of the medicinal leech. a. 2, apical lobe; 7. 7, middle lobe;
n. pf, nephridiopores; st, nephrostome; ». 2, recurrent lobe; 7. 2, testis lobe;
vs, vesicle ; vs. a, vesicle duct. (After Bourne.)

position on the ventral side, and enclosing the ventral
nerve-cord.

The nervous system is of the usual annulate type. There
is a small vain (Fig. 119, 67) situated above the anterior
end of the pharynx immediately behind the median dorsal

IX PHYLUM ANNULATA 209

jaw. It is connected by a very short pair of cesophageal
connectives with the ventral nerve-cord, which consists of
twenty-three well-marked rounded ganglia (gz. z-27) united
by delicate double connectives. The first, or sub-cesopha-
geal ganglion is larger than the others, and is shown by
development to be made up of five united embryonic
ganglia: the last ganglion is also of unusual size, and results
from the fusion of six distinct ganglia in the embryo. The
ventral nerve-cord is contained in the ventral sinus.

3 1
“Sus no ow

Fic. 121.— Transverse section of Hzrudo.: diagrammatic; cv, crop; d@. s, dorsal
sinus which encloses the dorsal vessel ; 7. v, lateral vessel ; 2. c, nerve cord;
nph., nephridium; zst¢., nephrostome ; ov, ovary; fs, testis ; v. s, ventral sinus.
(After Bourne. )

The principal sense organs are the eyes, of which there are
five pairs situated round the margin of the anterior sucker
on the dorsal side, one pair in each of the five segments.
They occupy positions taken in the succeeding segments by
a series of papille, the /atera/ sense-organs, with which they
are obviously homologous. The margin of the anterior
sucker also bears a large number of godlet-shaped organs,
which are very probably organs of taste. The minute
structure both of these and of the lateral sense organs is

P

210 MANUAL OF ZOOLOGY SECT.
very similar to that of the eyes. The function of the lateral
sense organs is unknown.

The leech is moncecious.

There are nine pairs of éestes

(Fig. 119, és), in the form of small spherical sacs situated in
segments 12-20.

Each gives off from its outer surface a
narrow éfferent duct, which opens into a common vas deferens

(v.@). In the tenth segment the vas deferens increases in
width and forms a complex coil, the vestcula seminalis

as

wae ee + ee - - - 0 ef - ge N--- e+ ee ee ee
vo SS Pier
’

SN Gare = =

GUD

PEL)

ReneS TS TE TES EL

pt ie Eee cath lays aaa oe aaa alge

Fic. 122.— Diagram of principal blood channels of leech ; d. s, dorsal sinus; 2.
lateral vessel ; v.s, ventral sinus containing nerve-cord.

(v. sem), from which is continued anteriorly a somewhat
dilated muscular tube, the ductus cjaculatorius (da. 6).
From each ejaculatory duct a narrow tube passes to the base
of the penzs (f), a curved eversible muscular organ which
opens on the ventral surface of the second annulus of the
tenth segment, in the middle line.

The ovaries are coiled filamentous bodies, each enclosed

1X PHYLUM ANNULATA 211

in a small globular ovarian sac (ov. s), situated in the
eleventh segment. From each ovarian sac a short oviduct
passes inwards and backwards, and unites with its fellow in
a median duct which opens into a curved muscular tube, the
vagina (va), which opens in the middle line on the ventral
surface of the second annulus of the eleventh segment, z.e.,
one segment behind the male aperture.

The leeches are a comparatively uniform group; but
some of the class differ from the medicinal leech in more
or less important points. Thus in one section there are no
jaws, and the anterior end of the body is capable of being
retracted within the part immediately behind it or thrust
forward as a proboscis or introvert. In the great majority
respiration takes place through the skin, as in the medicinal
leech ; but in one genus, Branchellion, which is an external
parasite on certain fishes, gills are present in the form of
delicate lateral outgrowths of the segments.

The majority of the Hirudinea are inhabitants of fresh
water, and live, like the medicinal leech, by sucking the
blood of higher animals. Others are permanent external
parasites; others again are carnivorous, feeding on snails
and other Mollusca.

SECTION X.—PHYLUM ARTHROPODA

IF we examine and compare, even quite superficially, a
crayfish, a scorpion, a centipede, and a blue-bottle fly, we
see at once that, while they manifestly do not belong to any
of the groups of animals studied hitherto, they are all con-
nected together by certain broad common features. They
all have a hard, or at least tough, integument; they all have
the body more or less clearly divided into segments, and
they all have a system of appendages, feelers, jaws, legs, etc.,
adapted to different uses in the different animals mentioned,
and in different parts of the body of the same animal, but
agreeing in being covered with a hard or tough integument
like that of the body itself, and in being divided into seg-
ments by a number of joints. These features, together with
certain points in the arrangement and structure of the
internal parts, are characteristic of the members of the phy-
lum Arthropoda, a group of very great extent, comprising,
among others, four large classes, each exemplified by one of
the four familiar animals above referred to.

Of these the crayfish differs from the rest in being an
aquatic animal and in having organs of respiration, gills, or
branchiz adapted -to this mode of life. The remaining
three are, with a few exceptions, air-breathers. The cray-
fish is a representative of the class Crustacea of the phylum
Arthropoda ; the scorpion of the class Arachnida, the cen-

212

SECT. X PHYLUM ARTHROPODA 213

tipede of the class Myriapoda, and the blue-bottle fly of the
class Insecta.

1. THE CRUSTACEA

The class Crustacea comprises a very large number of
Arthropods, the great majority of which are inhabitants
either of fresh water or of salt. Familiar examples of Crus-
tacea are the crayfishes, lobsters, shrimps, and prawns, the
crabs and hermit-crabs, the sand-hoppers, and woodlice,
the barnacles, and acorn-shells. As an example of the
Crustacea the Fresh-water Crayfish should be studied.
The following description applies more especially to the
common European crayfish (Potamobia pallipes),’ but the
American species of Astacus will be found to correspond in
all essential respects, while the lobster also presents but slight
differences.

It is to be noticed, in the first place, that the crayfish,
like Nereis, is a bilaterally symmetrical animal, and that the
bilateral symmetry is complete, the right and left halves of
the body being exactly alike. The crayfish, it is to be
noticed, also resembles Nereis and the leech in being
metamerically segmented, the segmentation being most
clearly distinguishable in the posterior region of the body.
Here, however, the external resemblance ceases. Instead
of the soft integument of Nereis and the leech, the crayfish
has a hard enclosing crust or exoskeleton formed of the
thickened and calcified cuticle, and, in place of the un-
jointed, short parapodia of Nereis, there are a series of
variously modified appendages, feelers, jaws, legs, etc.,
which, like the body itself, are enclosed in a hard exo-
skeleton, having a jointed character, the appendages thus

1 More commonly named Astacus fluviatilis,

214 MANUAL OF ZOOLOGY SECT.

being divided into series of movable segments which are
termed the podomeres.

The body of the crayfish (Fig. 123) is divided into two
regions — an anterior, the cephalothorax (cth), which is
covered by a broad shield or carapace; and a posterior,
the addomen (ab), which is divided into distinct segments,
movable upon one another in a vertical plane. The cepha-

Fic. 123. Astacus fluviatilis, side view of male. a,, antennule; a2, antenna;
ab, abdomen; cth, cephalothorax; #d, gill-cover; 7, rostrum; 8, third maxilli-
pede; 9, first leg; zo-73, remaining legs; zg, uropod; XIV, first abdominal
segment; XIX, sixth abdominal segment. (From Lang’s Comparative
Anatomy.)

lothorax is again divided into two regions —an anterior, the
head, and a posterior, the horax — by a transverse depres-
sion, the cervical groove. The carapace is developed from
the dorsal regions of both head and thorax, and is free only
at the sides of the thorax,' where it forms a flap or g7d/-cover

1 This was the view of Huxley, but it is the opinion of American authors
that the carapace is the enlargement of the fused tergites or dorsal region of
two head-segments, z.e., the second antennal and mandibular; those of

the succeeding cephalothoracic segments being atrophied. — AMERICAN
EDITOR,

x PHYLUM ARTHROPODA 215

(Ad) on each side, separated from the actual body-wall by
a narrow space in which the gills are contained. The cara-
pace is made of chitin, strongly impregnated with carbonate
of lime so as to be hard and but slightly elastic.

The abdomen is made up of seven segments: the first six
(XIV-XIX) of these are metameres in the strict sense of
the word, and have a ring-like form, presenting a broad
dorsal region or ¢ergum,; a narrow ventral region or sternum ;
and downwardly directed lateral processes, the plewra. The
seventh division of the abdomen is the ¢edson; it is reduced
in size, flattened horizontally, and divided by a transverse
groove into anterior and posterior portions. All seven seg-
ments are calcified, and are united to one another by chiti-
nous articular membranes; the first segment is similarly
joined to the thorax.

It has been stated that the abdominal segments are
movable upon one another in a vertical plane, 7.¢., the
whole abdomen can be extended or straightened, and fleved
or bent under the cephalothorax ; the segments are incapa-
ble of movement from side to side. This is due to the fact
that, while adjacent segments are connected dorsally and
ventrally by flexible articular membranes, they present at
each side a Ainge, placed at the junction of the tergum and
pleuron, and formed by a little peg-like process of one seg-
ment fitting into a depression or socket in the other. A line
drawn between the right and left hinges constitutes the avs
of articulation, and the only possible movement is in a plane
at right angles to this axis.

The ventral and lateral regions of the thoracic exoskeleton
are produced into the interior of the body in the form of a
segmental series of calcified plates, so arranged as to form a
row of lateral chambers in which the muscles of the limbs
lie, and a median tunnel-like passage or sternal canal, con-

216 MANUAL OF ZOOLOGY SECT.

taining the thoracic portion of the nervous system. The
entire endophragmal system, as it is called, constitutes a kind
of internal skeleton.

The head exhibits no segmentation ; its sternal region is
formed largely by a shield-shaped plate, the efzstoma, nearly
vertical in position. The ventral surface of the head is, in
fact, bent so as to face forwards instead of downwards. The
cephalic region of the carapace is produced in front into a
large median spine, the vostrum (Fig. 123, 7): immediately
below it is a plate from which spring two movably articu-
lated cylindrical bodies, the eye-s¢a/ks, bearing the eyes at
their ends.

Among the appendages one’s attention is attracted by the
long feelers (Fig. 123, a, @)) attached to the head, the
five pairs of legs (9-73) springing from the thorax, and
the little fin-like bodies arising from the sterna of the abdo-
men. It will be convenient to begin with the last-named
region.

The third, fourth, and fifth segments of the abdomen bear
each a pair of small appendages, the abdominal feet or p/o-
pods (Fig. 124,70). Each consists of an axis or protopodite,
consisting of a very short proximal (7. z) and a long distal
(pr. 2) podomere, and bearing at its free end two jointed
plates, fringed with sete, the endopodite (en) and exopodite
(ex). These appendages act as fins, moving backwards and
forwards with a regular swing, and probably aiding in the
animal’s forward movements.

In the female a similar appendage is borne on the second
segment, while that of the first is more or less rudimen-
tary. In the male the first and second pleopods (9g) are
modified into incomplete tubes which act as copulatory
organs (gonofoda). ‘The sixth pair of abdominal limbs (zz)
are alike in the two sexes; they are very large, both endo-

x PHYLUM ARTHROPODA 217

and exopodite having the form of broad flat plates; in the
natural position of the parts they lie one on each side of the
telson, forming with it a large five-lobed tail-fin; they are

3.Mandible

Law

a ir)
LAntennule 7 oiAahenna

&. 2"! Maxilla 6.1*Maxilliped 8.34Leg

7, 3.4 Maxilliped

en

bse prt Z prt

.Copulatory Organs 10. Swimming Foot P

1l.Uropod

Fic. 124. — Typical appendages of Astacus. en. 7-5, podomeres of endopodite;
ep, epipodite; ex, exopodite; 77, flagella; g, gill; px. 7, fx. 2, podomeres of
protopodite; 7-3, podomeres of axis of antennule. (After Huxley.)

therefore conveniently called w7opods or tail-feet. The telson
itself bears no appendages.

218 MANUAL OF ZOOLOGY SECT.

The thoracic appendages are very different. The four
posterior segments bear long, slender jointed gs (8), upon
which the animal walks ; in front of these is a pair of very
large legs terminating in huge claws or che/e, and hence
called chelipeds (Fig. 123,9). The three anterior segments?
bear much smaller appendages, more or less leg-like in
form, but having their bases toothed to serve as jaws; they
are distinguishable as maxidiipeds or foot-jaws (Fig. 124, 6, 7).

The structure of these appendages is best understood by
a consideration of the “Aird maxilliped (7). The main por-
tion of the limb is formed of seven podomeres arranged in
a single series, strongly calcified, and, with the exception of
the second and third, which are fused, movably articulated
with one another. The second podomere, counting from the
proximal end, bears a many-jointed, feeler-like organ (ex),
and from the first springs a thin folded plate (cf), having a
plume-like gill (g) attached to it. Obviously such an ap-
pendage is biramous, but with one of its branches greatly in
excess of the other ; the first two segments of the axis ( pv. 7,
pr. 2) form the protopodite, its remaining five segments
(en. z-5) the endopodite, and the feeler, which is directed
outwards, or away from the median plane, the exopodite
(ex). The folded plate (¢f) is called the epipodite ; in the
natural position of the parts it is directed upwards, and lies
in the gill-cavity between the proper wall of the thorax and
the gill-cover.

The five /egs (8) differ from the third maxilliped in their
greater size, and in having no exopodite ; in the fifth or last
the epipodite also is absent. The first three of them have
undergone a curious modification, by which their ends are

1 By most authors the maxillipedes are regarded as belonging to the
head, the number of pairs of thoracic appendages being considered as
five. — AMERICAN EDITOR.

x PHYLUM ARTHROPODA 219

converted into pincers or che/z ; the fourth segment (en. ¢)
of the endopodite (sixth of the entire limb) is produced
distally so as to form a claw-like projection (ez. ¢'), against
which the terminal segment (ev. 5) bites. The first leg is
much shorter than any of the others and its chela is of im-
mense size, and forms an important weapon of offence and
defence. The second maxiliped resembles the third, but is
considerably smaller ; the fs¢ (6) has its endopodite greatly
reduced, the two segments of its protopodite large and leaf-
like, and no gill is connected with the epipodite.

The head bears a pair of mandibles and two pairs of
maxillz in relation with the mouth, and in front of that aper-
ture a pair of antennules and one of antenne. The hindmost
appendage of the head is the second maxilla (5), a markedly
foliaceous appendage ; its protopodite (f7. z, pr. 2) is cut
up into lobes; the exopodite (ev) is modified into a
boomerang-shaped plate, which, we shall see, is an impor-
tant accessory organ of respiration. The fivs¢ maxilla (4) is
a very small organ, having neither exo- or epipodite. The
mandible (3) is a large, strongly calcified body, toothed along
its inner edge, and bearing on its anterior border a little
three-jointed, feeler-like body, the pa/p.

The anéenna (2) is of great size, being nearly as long as
the whole body. It consists of an axis of five podomeres,
the fifth or last of which bears a long, flexible, many-jointed
structure, or flagellum (1), while from the second segment
springs a scale-like body or sguame (ex).

The antennule (z) has an axis of three podomeres (z-?),
ending in two many-jointed flagella (7. z and 2).

The eye-stalks, already noticed, arise just above the an-
tennules, and are formed each of a small proximal and a
large distal segment. They are sometimes counted as
appendages serially homologous with the antenne, legs, etc.

220 MANUAL OF ZOOLOGY SECT. X

If, as seems probable, the eye-stalks and antennules are to
be looked upon as belonging to a preoral region corre-
sponding to the prostomium, of Nereis, then it will be seen
that the body of the crayfish consists of a prostomium,
eighteen metameres, and a telson. The prostomium bears
eye-stalks and antennules ; the first four metameres are fused
with the prostomium to form the head, and bear the an-
tennz, mandibles, first maxille, and second maxille; the
next eight metameres (5th—12th), constitute the thorax,
and bear the three pairs of maxillipeds and the five pairs of
legs; the remaining six metameres (13th-18th), together
with the telson, constitute the abdomen, and bear five pairs
of pleopods and one of uropods.

The digestive organs (Fig. 125) are somewhat complicated.
The mou¢h lies in the middle ventral line of the head, and is
bounded in front by the labrum, at the sides by the mandi-
bles, and behind by a pair of delicate lobes, the paragnatha.
It leads by a short wide gw//e¢ (a) into a capacious stomach,
which occupies a great part of the interior of the head, and
is divided into a large anterior or cardiac division (¢.s), and
a small posterior or pyloric division ( ps) ; the latter passes
into a narrow and very short small intestine (md), from
which a somewhat wider /arge intestine (hd) extends to the
anus (an), situated on the ventral surface of the telson.

In the cardiac division of the stomach the chitinous lining
is thickened and calcified in certain parts, so as to form a
complex articulated framework, the gaséric mill, on which
are borne a median and two lateral ¢ee¢h, strongly calcified
and projecting into the cavity of the stomach. Two pairs
of. strong muscles arise from the carapace, and are inserted
into the stomach ; when they contract they move the mill in
such a way that the three teeth meet in the middle and com-
plete the comminution of the food begun by the jaws. The

Fic. 125.—Astacus fluviatilis, dissection from the right side. aa, antennary
artery; a4, abdomen; ax, anus; 4. d, bile duct; 4f g, cheliped; 4%, ventral
nerve-cord; cs, cardiac division of stomach; cth, cephalo-thorax: em, dorsal
muscles; fz, ventral mucles; g, brain; 4, heart; Ad, large intestine; /7, liver;
md, small intestine; 0, ostium; oa, ophthalmic artery; oaa, superior abdominal
artery; @, gullet; A/. 1-5, pleopods; f/. 6, uropod; fs, pyloric division of
stomach; sa, sternal artery; ¢, testis and telson; aa, inferior abdominal artery;
vd, vas deferens; vdo, male genital aperture. (From Lang after Huxley.)

221

222 MANUAL OF ZOOLOGY SECT.

separation of the teeth is effected partly by the elasticity of
the mill, partly by delicate muscles in the walls of the
stomach. The pyloric division of the stomach forms a
strainer; its walls are thickened and produced into nu-
merous sete, which extend quite across the narrow lumen
and prevent the passage of any but finely divided particles
into the intestine. ‘Thus the stomach has no digestive func-
tion, but is merely a masticating and straining apparatus.
On each side of the cardiac division is found at certain
seasons of the year a plano-convex mass of calcareous
matter, the gastrolith.

The digestion of the food and to some extent the absorp-
tion of the digested products are performed by a pair of
large glands (/7), lying one on each side of the stomach
and anterior end of the intestine. They are formed of
finger-like sacs or ceca, which discharge into wide ducts
opening into the small intestine, and are lined with glandu-
lar epithelium derived from the endoderm of the embryo.
The glands are often called livers, but as the yellow fluid
they secrete digests proteids as well as fat, the name hepato-
pancreas is often applied to them, or they may be called
simply digestive glands, The crayfish is carnivorous, its food
consisting largely of decaying animal matter.

The digestive organs and other viscera are surrounded by
a body-cavity, which is in free communication with the blood-
vessels and itself contains blood.

There are well-developed respiratory organs, in the form
of gi//s, contained in a narrow branchial chamber, bounded
internally by the proper wall of the thorax (Fig. 127, ep),
externally by the gill-cover or pleural region of the carapace
(kd). Each gill consists of a stem giving off numerous
branchial filaments, so that the whole organ is plume-like.
The filaments are hollow, and communicate with two paral-

x PHYLUM ARTHROPODA 223

pb;

Fic. 126. — Respiratory organs of Astacus fluviatilis. In A the gill-cover is removed
and the gills undisturbed; in B the podobranchia are removed and the outer
arthrobranchiz turned down. ay, antennule; as, antenna; adj, first; abo,
second abdominal segment; avd. 7-72, inner arthrobranchiaw; avé,. 7-12, outer
arthrobranchiz: ef. 5, scaphognathite; 4/6. z7-13, pleurobranchiz; Add. 7-73,
podobranchs; A?. s, first pleopod; 6-73, thoracic appendages. (From Lang’s
Comparative Anatomy, after Huxley.)

lel canals in the stem —an external, the afferent branchial
vein, and an internal, the efferent branchial vein.
According to their point of origin, the gills (Fig. 126) are

224 MANUAL OF ZOOLOGY SECT.

divisible into three sets, — first, podobranchie or foot-gills,
springing from the epipodites of the thoracic appendages,
from which they are only partially separable; secondly,
arthrobranchi@ or joint-gills, springing from the articular
membranes connecting the thoracic appendages with the
trunk; and thirdly, plewrobranchia or wall-gills, springing
from the lateral walls of the thorax, above the attachment of
the appendages.

At the base of each antenna is an organ of a greenish
colour, the anéennary or green gland, by which the function
of renal excretion is performed. The gland is cushion-
shaped; it discharges into a thin-walled sac or urinary
bladder which opens by a duct on the proximal segment of
the antenna. The glands already referred to as occurring in
the gills are also supposed to have an excretory function.

The circulatory organs are ina high state of development.
The heart (Figs. 125, 127, 2) is situated in the dorsal region
of the thorax, and is a roughly polygonal muscular organ
pierced by three pairs of apertures or ost#a (0) guarded by
valves which open inwards. It is enclosed in a spacious
pericardial sinus (Fig. 127, pc), which contains blood.
From the heart spring a number of narrow tubes, called
arteries, which serve to convey the blood to various parts of
the body. At the origin of each artery from the heart are
valves which allow of the flow of the blood in one direction
only, viz., from the heart to the artery. From the anterior
end of the heart arise five vessels, and from the posterior
end two, which are practically united at their origin.

All these arteries branch extensively in the various organs
they supply, becoming divided into smaller and smaller
offshoots, which finally end in microscopic vessels called
capillaries. These latter end by open mouths which com-
municate with the dlood-sinuses (Fig. 128, s), spacious

x PHYLUM ARTHROPODA 225

cavities lying among the muscles and viscera, and all com-
municating, mediately or immediately, with the sternal sinus
(s4.5),a great median canal running longitudinally along the
thorax and abdomen, and containing the ventral nerve-cord
and the sternal and ventral abdominal arteries. In the

Fic. 127. — Transverse section of thorax of crayfish, diagrammatic. adm, ventral
abdominal muscles; 6/, leg; 4, ventral nerve-cord; d, intestine; dm, dorsal
muscles of abdomen; ef. wall of thorax; %, heart; &, gills; Ad, gill-cover;
2, liver; ov, ovary; fc, pericardial sinus; sa. sw, sternal artery; vs, ventral
sinus. The arrow shows the direction of the blood-current. (From Lang’s
Comparative Anatomy.)

thorax the sternal sinus sends an offshoot to each gill in the

form of a well-defined vessel, which passes up the outer

side of the gill and is called the afferent branchial vein

(af. br. v; see also Fig. 127). Spaces in the gill-flaments
Q

226 MANUAL OF ZOOLOGY SECT.

place the afferent in communication with the efferent
branchial vein (ef. br. v), which occupies the inner side of
the gill-stem. The efferent branchial veins open into six
branchio-cardiac veins (br. ¢.v), which pass dorsally in close
contact with the lateral wall of the thorax and open into the
pericardial sinus (fed. s).

The whole of this system of cavities is full of blood, and
the heart is rhythmically contractile. When it contracts,
the blood contained in it is prevented from entering the

‘weg sts

Fic. 128. — Diagram of the circulation in the crayfish; heart and arteries, scarlet;
veins and sinuses containing non-aérated blood, blue; those containing aérated
blood, pink. a, artery; af dr. v, afferent branchial vein; 47. ¢. v, branchio-
cardiac vein; of. br. v, efferent branchial vein; Az, heart; ped s, ‘pericardial
sinus; s, sinus; st. s, sternal sinus; v1, ostium with valves; v?, arterial valves.
The arrows show the direction of the current.

pericardial sinus by the closure of the valves of the ostia,
and therefore takes the only other course open to it, viz.,
into the arteries. When the heart relaxes, the blood in the
‘arteries is prevented from regurgitating by the valves at their
origins, and the pressure of blood in the pericardial sinus
forces open the valves of the ostia and so fills the heart.
Thus in virtue of the successive contractions of the heart,
and of the disposition of the valves, the blood is kept con-

x PHYLUM ARTHROPODA

stantly moving in one direction, viz.,
from the heart by the arteries to the
various organs of the body, where it
receives carbonic acid and other waste
matters; thence by sinuses into the
great sternal sinus; from the sternal
sinus by afferent branchial veins to the
gills, where it exchanges carbonic acid
for oxygen ; from the gills by efferent
branchial veins to the branchiocardiac
veins, thence into the pericardial sinus,
and so to the heart once more.

The nervous system (Fig. 129) con-
sists of a brain (g) and a ventral nerve-
cord, united by cesophageal connectives
(sc). The ventral cord is double, but the
right and left halves have undergone
partial fusion, so that the ganglia, and
in the abdomen the connectives also,
appear single instead of double. The
ventral cord contains twelve of these
ganglia, the first is infra-cesophageal,
being larger than the others and formed
by the union of the ganglia belonging
to the last three cephalic and first three
thoracic segments. All the remaining
segments have their own ganglia, with
the exception of the telson, which is sup-
plied from the ganglion of the preced-
ingsegment. There isa visceral system
of nerves (s) supplying the stomach,
originating in part from the brain and in
part from the cesophageal connectives.

224

Fic. 129. — Nervous system
of Astacus fluviatilis.
ég, sub-cesophageal gang-
lion; cs, commissural
ganglion; g, brain; s,
visceral nerve; sc, ce-
sophageal connective; y,
post-cesophageal commis-
sure; IV-VIII, thoracic
ganglia; 7-6, abdominal
ganglia. (From Lang's
Comparative Anatomy,
after Vogt and Yung.)

228 MANUAL OF ZOOLOGY SECT.

Sensory organs. — The eyes differ entirely in structure
from those of any animal that has been described hitherto.
Each is a compound structure, being made up of a large
number of distinct elements termed the ommatidea. The
chitinous cuticle covering the distal end of the eye-stalk is
transparent, divided by delicate lines into square areas or
facets, and constitutes the cornea. Each facet of the
cornea marks the position of the outer end of an omma-
tideum, optically separated from its neighbours by black
pigment.

The antennules contain two sensory organs, to which are
assigned the functions of smell and hearing respectively.
The offactory organ is constituted by a number of extremely
delicate o/factory sete, borne on the external flagellum. The
auditory organ is a sac formed by invagination of the dorsal
surface of the proximal segment, and is in free communica-
tion with the surrounding water by a small aperture.

Reproduction. — The crayfish is dicecious, and presents a
very obvious sexual dimorphism. The abdomen of the
female is much broader than that of the male; the first
and second pleopods of the male are modified into tubular
or rather spout-like copulatory organs (Fig. 124,9); and the
reproductive aperture is situated in the male on the proximal
podomere of the fifth leg, in the female on that of the third.

The “sts (Fig. 130, B, 4 ~) lies in the thorax, just
beneath the floor of the pericardial sinus, and consists of
paired anterior lobes (4) and an unpaired posterior lobe (7).
From each side goes off a convoluted vas deferens (vd),
which opens on the proximal segment of the last leg. The
sperms are curious non-motile bodies produced into a num-
ber of stiff processes ; they are aggregated into vermicelli-
like spermatophores by a secretion of the vas deferens.

The ovary (A, ov, z) is also a three-lobed body, and is

x PHYLUM ARTHROPODA 229

similarly situated to the testis; from each side proceeds a
thin-walled oviduct (od), which passes downwards, without
convolutions, to open on the proximal segment of the third
or antepenultimate leg. The eggs are of considerable size.

The ova, when laid, are fastened to the sete on the
pleopods of the female by the sticky secretion of glands
occurring both on those appendages and on the segments

=

eb Fis

i
¢

Fic. 130. — Reproductive organs of Astacus fluviatilis. A, female; B, male; od,
oviduct; oe, external opening of the same; ov, ovary; #, testis; «, unpaired
posterior portion of gonad; vd, vas deferens, (From Lang’s Comparative
Anatomy, after Huxley.)

themselves ; they are fertilised immediately after laying, the
male: depositing spermatophores on the ventral surface of
the female’s body just before oviposition.

The lobsters, shrimps, prawns, crabs, and hermit-crabs
all resemble the crayfish in the number and disposition of
the segments, the presence of a carapace covering both
head and thorax, the general structure and arrangement of

230 MANUAL OF ZOOLOGY SECT.

Fic. 131.— Cancer pagurus. A, dorsal; B, ventral aspect. amt. 7, antennule;
ant. 2, antenna; add. 1, abd. 3, abd. 7, abdominal segments; £, eye-stalk;
2.1, 2.5, legs; mex. 3, third maxillipedes. A, after Bell.)

x PHYLUM ARTHROPODA 231

the appendages, and the essential features of the internal
anatomy. The crabs and the hermit-crabs differ from the
other forms mentioned, mainly in the abdomen being re-
duced. In the crabs (Fig. 131) this region is extremely
small, its appendages are only feebly developed, and it is

Fic. 132. Pagurus bernhardus. ch, chela of first right leg; 7.4, 7.5, fourth and
fifth legs; ¢, abdominal terga; ~f, uropods. (After Bell.)
permanently flexed on the sternal surface of the cephalo-
thorax, so that it is completely concealed from view when
the animal is looked at from above.! In the hermit-crabs

1The European Cancer is represented by our common Cancer irro-
ratus, and the explanation of Fig. 131 will equally well apply to our species.

232 MANUAL OF ZOOLOGY SECT.

(Fig. 132) the abdomen with its appendages is imperfectly
developed, and not enclosed completely in a hard exoskele-
ton, this region being sheltered in the shell of a whelk
or other univalve mollusc
which the hermit-crab drags
about with it."

The crustaceans enumer-
ated above, together with
the sand-hoppers, woodlice
and their allies, and a large
number of others, form one
or two sub-classes into which
the class Crustacea is di-
vided—the sub-class Mala-
costraca. The Malacostraca
are highly organised Crus-
tacea, usually of consider-
able size, and nearly all
have a thorax of eight and
an abdomen of seven seg-
ments. The appendages
are highly differentiated.
There is a gastric mill, and
the renal organs are in the

133. — Apus glacialis, ventral aspect.
abd. f, abdominal feet; art. 7, antes form of antennary glands.

nule; azz. 2, antenna; /ér, labrum; wed, ‘
mandible; #zx, first maxilla; ov, aper- The other sub-class is

ture of oviduct; s./ f/, sub-frontal
plate; s#. 2, shell-gland; £2. /, thoracic the Entomostraca. The

feet; th. f.7, fi acic foot. ,
arta rst thoracic foot. (After E-ntomostraca, which are

even more numerous than
the Malacostraca, are of comparatively simple organisation,
and usually of small, often almost microscopic, size. The

1 Our common American hermit-crab is Eupagurus fpollicaris; the
right chela is still larger than in Pagurus bernhardus of the European coast,

x PHYLUM ARTHROPODA 233

number of segments is variable, and the appendages are not
so highly differentiated as in the Malacostraca. A carapace
developed from the head is often present. There is no gas-
tric mill, and the renal organs are not antennary glands, but

Fic. 134. — Three stages in the development of Apus. /s, frontal sensory organ;
L, digestive gland; s, carapace; 4-4, cephalic appendages; I-XIII, body seg-
ments and appendages. (From Lang’s Comparative Anatomy.)

shell-glands opening at the bases of the second maxille. The
larva nearly always leaves the egg as a characteristic form
called the Wauplius (Fig. 134, A), which occurs also, though

234 MANUAL OF ZOOLOGY SECT.

L.Cyclops

2.Calacalanus

Fic. 135. —1@, female Cyclops, from the right side; 4, dorsal view; C, antenna of
male; D, swimming-foot. aéd. 7, first abdominal segment; avt. z, antennule;
ant. 2, antenna; c. th, cephalo-thorax; e, median eye; ev, endopodite; ¢. s, egg-
sac; ex, expodite; ov, ovary; pr. 1, pr.2, protopodite; 7, rostrum; s./, swim-
ming-feet; #4. 2, 22.6, thoracic segments. (After Huxley, Gerstaecker, Hartog,
and Giesbrecht. )

x PHYLUM ARTHROPODA 235

exceptionally, as a free-swimming stage in the Malacostraca,
the Nauplius stage in that sub-class being usually passed
through in the egg. The Nauplius is an oval unsegmented
body with a median eye, and three pairs of short appen-
dages provided terminally with long hairs.

Fic. 136.— Lepas anatifera. A, the entire animal; B,its anatomy. a’, antennule;
c, carina; cd, cement gland; 7, digestive gland; »z, adductor muscle; od, ovi-
duct; ov, ovary; #, (in B) penis and (in A) peduncle; s, scutum; 7, tergum and
testis; vd, vas deferens. (From Lang’s Comparative Anatomy, after Darwin
and Claus.)

Most of the Entomostraca are free-swimming, and the
majority of them, such as the water-fleas (Fig. 135) and-
their allies, are of almost microscopic minuteness, though a
few, such as Afus and the brine-shrimp, are of compara-
tively large size. Many Entomostraca, however, become

236 MANUAL OF ZOOLOGY SECT.

fixed in the adult condition as external parasites, mainly
of fishes. Many of those parasitic Entomostraca undergo
a degradation of structure, a retrograde metamorphosis, as it
is termed. Comparatively highly organised in their free-
swimming larval stages, these lose when they attain the adult
parasitic condition some, if not all, of their characteristic
crustacean features, and may lose all trace of segmentation
and of jointed appendages. Also characterised by degrada-
tion of structure, though in a less degree than some of the
parasitic forms, are the barnacles (Fig. 136) and acorn-
shells ( C?rripedes), which are not parasitic, but are perma-
nently fixed in the adult condition to a rock or a beam of
timber or other submerged object. In the larval condition
these are free-swimming, distinctly segmented, and provided
with a number of jointed appendages ; in the adult state they
become fixed, lose their segmentation, though retaining some
of their jointed appendages, and become enclosed in a fold
of the integument in which are developed a series of cal-
careous plates. The attachment of the cirripede is by the
head; while the posterior portion of the body is free, and is
capable of being thrust out with a series of six pairs of many-
jointed appendages or ¢/vri, borne on the thorax through a
slit in the enclosing shell. In the barnacles the head-region
is drawn out into a stalk (A, #) ; in the acorn-shells the stalk
is absent.

2. ONYCHOPHORA

The class Onychophora comprises only the aberrant genus Peripatus,
which is interesting owing to certain primitive features which it presents
— features which afford some reason for regarding it as intermediate
between such forms as the Annulata on the one hand, and the higher
Arthropoda on the other.

Peripatus (Fig. 137) is a caterpillar-like animal of approximately
cylindrical form, and not divided into segments; it has a fairly well-

x PHYLUM ARTHROPODA 237

marked head and a series (14-42) of short stumpy appendages. The
integument is thrown into a number of fine transverse wrinkles and is

Eee
ay
Par, ae

zi
“a

Oy Ao cumin

2 OA nines i

pth
y 3 5 2 3

re
B * =

Fic. 137. — Peripatus capensis, lateral view. (From Balfour.)

beset with numerous conical papillz, each capped with a little chitinous
spine. The head (Fig. 138) bears a pair of antenne, a pair of eyes, a

fs aw

Fic. 138. Ventral view of head of Peripatus capensis, with antennz, jaws, oral
papillz, and first pair of legs. (After Balfour.)

pair of jaws, and a pair of short processes — the ora/ fapille. On the
surface of the oral papille are situated a pair of glands, the s/me glands.

iS}

38 MANUAL OF ZOOLOGY SECT.

pana faiduadtnretaiindteneetan sete ee

cox. gld

oh

r aannnmrntniih

an.

Fic. 139. — Dorsal view of the internal organs of Peripatus. az, anus; azt, an-
tenne ; drx, brain; cox. gld, coxal gland of the seventeenth leg; ¢ ge, male
genital aperture ; ze. co, nerve-cord; wefh, nephridia; phar, pharynx; sal. gld,
salivary gland; s/. g/d, slime gland ; s¢om, stomach. (Combined from Balfour.)

x PHYLUM ARTHROPODA 239

Each jaw is composed of two curved, falciform, chitinous plates; they
lie at the sides of the mouth enclosed by a circular lip. The jaws, as
well as the oral papilla, are developed as modified limbs. The Zegs are
not jointed; each consists of a proximal part and a small distal part or
foot, terminating in a pair of horny claws.

In the internal anatomy (Fig. 139) the most important features are the
presence of organs of respiration in the form of trachez, unbranched or
little branched tubes, groups of which open on little depressions of the
integument, the external openings or s¢¢gmaza of which are in some
species distributed irregularly over the surface, in others arranged in
longitudinal rows; the presence of a series of pairs of nephridia (sef/)
similar to those of the Annulata, and of a nervous system consisting
of a brain (477), situated in the head, and two widely separate nerve
cords (ze. co) which run parallel with one another throughout the
length of the body, and are not dilated into distinct ganglia. The
sexes are distinct.

The various species of Peripatus are all terrestrial, and are found in
damp localities under bark, or dead timber, or stones. Four species
occur in South Africa, one in South America, and one in the West
Indies, one in New Zealand, and two in Australia.

3. THE MYRIAPODA

The class Myriapoda, including the centipedes and the
millipedes, consists of tracheate Arthropoda, which bear
many features of resemblance to the insects. There is a
distinct head, bearing a single pair of many-jointed antenne,
a pair of eyes, and from two to four pairs of jaws; and a
trunk, not distinguishable into regions, but consisting of
a number of similar segments, each bearing either one pair
of legs or two. A system of air-tubes or trachez similar to
those of Peripatus or the insects open by a series of stigmata
(in centipedes on alternate segments) on the sides or lower
surfaces of the segments.

The head in the Myriapoda (Fig. 140) is as well marked
off as in an insect ; it appears to be composed of about four

240 MANUAL OF ZOOLOGY SECT.

fused segments. The avéenne consist sometimes of many,

(Paly th
Cotas

Fic. 140. — Scolopendra, or cen-
tipede. (From Cuvier’s A x-
ztmal Kingdom.)

sometimes of comparatively few seg-
ments. A pair of eyes, situated on
the dorsal surface of the head, con-
sist of aggregations of ocelli except
in Scutigera, in which there are com-
pound eyes, differing, however, in
their structure from those of insects.
There are in millipedes a movable
labrum, a pair of mandibles, and: a
pair of fused maxilie. In the cen-
tipede there are three pairs of jaws
in front of the poison-fangs. The
mandibles have no palps; one-or
both pairs of maxillz usually possess
palps.

The number of segments in the
body varies from 12 to 173. In the
millipedes (Dzplopoda) the dorsal
walls of the segments are very
strongly arched; in the centipedes
(Chilopoda) the segments are all
dorso-ventrally compressed, with dis-
tinct tergal and_ sternal shields
(sewta) separated laterally by inter-
vals of comparatively soft skin on
which the stigmata open. In the
centipede each segment bears a pair
of jointed legs; of these the most
anterior pair is extended forwards
to form a pair of poison-fangs, at
the extremity of the pointed ter-
minal joint of which opens the duct

x PHYLUM ARTHROPODA 241

of a poison gland. In the millipedes each segment behind
the fourth or fifth bears two pairs of legs, the four or five
most anterior having only one pair each, except one segment
which is footless. In most of the millipedes and their allies
the appendages of the seventh segment are modified in the
male to form copulatory organs.

The enteric canal is straight and is much simpler in
character than that of the Insecta. The heart is in the form
of a long tube, consisting of as many chambers as there are
segments in the body. The breathing organs are air-tubes
or tracheze, resembling those of larval insects, such as cater-
pillars.

4. THE INSECTA

The class Insecta, comprising the cockroaches, grass-
hoppers, dragon-flies, beetles, butterflies, house-flies, and
bees, with their many allies, though it is a very extensive one,
including as it does a larger number of species than any
of the other classes of the Arthropoda, is yet characterised
by a remarkable degree of uniformity, no such extremes of
modification occurring as are observable among the Crustacea.
The body of an insect, like that of a crustacean, is segmented,
and bears a series of pairs of jointed appendages. The
surface is covered with a chitinous cuticle, forming an exo-
skeleton, which is sometimes comparatively thin, sometimes
thick and hard. Like the body of the crustacean, that of
the insect is divisible into certain vegions. In the Insecta
these regions are quite constant in their disposition, and are
always three in number, — ead in front, shorax in the middle,
and abdomen behind. The head is found, when its develop-
ment is traced, to be formed by the union with the head-lobe
of the embryo of some five segments, but in the adult no

trace of segmentation is distinguishable. The thorax always
R

242 MANUAL OF ZOOLOGY SECT.

consists of three segments, which are usually firmly united
together. The abdomen contains from ten to eleven seg-
ments.

The appendages are also very constant in their arrange-
ment throughout the Insecta, though variously modified in
form in the different orders,
in accordance with differ-
ences in mode of life. The
head (Fig. 141) bears a
pair of antennz, a pair of
mandibles, and two pairs
of maxille. The antennz
vary a good deal in size
and shape in different
insects. The mandibles
(Fig. 142, md) lie at the

Fic. 141. — Periplaneta americana. Lateral «j .
view of the head and its appendages. sides of the mouth, aly

Kees pong tape ach Sees &% front of which is a mova-
ae eS ae max?, second pair ble labrum or upper lip
(4%r). Each mandible is

a single solid piece, and is devoid of palp. The second pair
of maxillee (#x. 2) are united in their basal portions to form
a lower lip (¢adzum). Jointed palpi (fw) are borne both
by the first pair of maxille (maxillary palpi) and by the
second (abial palfi). All the jaws become differently
modified in the different orders in accordance with differ-
ences in the nature of the food. Insects, which like cock-
roaches and beetles, masticate hard substances, have the
mandibles strong and sharp and the maxillze well developed,
and adapted to act as masticatory organs. Insects which,
like cicadas, bugs, lice, and plant-lice, live on the juices of
plants or animals, have the jaws in the form of sharp stylets,
enclosed in a sheath or proboscis, for piercing the integu-

x PHYLUM ARTHROPODA 243

ment. Intermediate conditions also occur. In the Hyme-
noptera (bees, wasps, etc.), for example, the mouth-parts are
adapted both for biting and for licking and sucking; the
mandibles and maxillz are sharp and lancet-like, the middle
part of the labium is produced into a long median tongue,
at the sides of which are a pair of accessory tongues ( para-

lor

Fic. 142. — Mouth-parts of the Cockroach. 47, labrum; sd, mandible; 1x ,, an-
terior pair of maxilla; #z, mentum; ve and a7, outer and inner divisions of the
second pair of maxille; £7, labial palp; 7, maxillary palp; st, stipes; s7,
submentum. (From Lang’s Comparative Anatomy.)

glosse). In the Hemiptera (bugs, lice, etc.) the labium is

modified to form a sucking proboscis enclosing the stylet-

like mandibles and maxillee.

In the Diptera (house-flies, gnats, etc.) the mandibles,

244 MANUAL OF ZOOLOGY SECT.

usually not developed in the males, are biting or piercing
organs, while the basal parts of the labium form a proboscis
enclosing a sharp spine developed from a process on the
roof of the mouth (Avpopharynx).

In the Lepidoptera, or butterflies and moths, the mandi-
bles are aborted in the adult and the maxille are developed
into elongated half-tubes, which are united and form a com-
plete tube capable of being coiled up in a spiral manner
under the head, the extremity in some cases being provided
with hooks or spines for rupturing the nectaries of flowers.

Fic. 143. — Butterfly (Pieris rap@), with caterpillar and chrysalis stages.
(After Riley.)

Each of the three segments of the thorax always bears
a pair of jointed legs which do not present such marked
modifications as the appendages of the head. The terminal
part (¢avsus) is made up of a number (not more than five)
of short segments, and ends in a pair of claws, often with
an adhesive pad or sucking disc between them.

In addition to the legs, the second and third segments of
the thorax usually bear each a pair of wings. The wings
are thin transparent expansions of the integument sup-
ported by a system of branching ribs, called vecns, or ner-

x PHYLUM ARTHROPODA 245

vures. In most of the butterflies and moths (Fig. 143) the
wings are opaque, owing to their being covered with numer-
ous overlapping microscopic scales to which the various
colours of the wing are due. In the beetles (Fig. 144),
locusts, and others, on the other hand, the posterior wings
alone are membranous, the anterior pair being converted
into hard and tough cases—the e/ytra—which, when
folded up, cover over and protect the delicate posterior
wings. In the bugs and their allies, the anterior wings are

Fic. 144. d, Carpet beetle (Anthrenus scrophulari@) with larva a, 4, and pupa, c.
(After Riley, from Bulletin of Division of Entomology, United States Depart-
ment of Agriculture.)

thick and opaque at the bases only. In the house-flies,
gnats (Fig. 145), and their allies (order Dipéera), the ante-
rior wings alone are developed, the posterior being rep-
resented by vestiges, the /alteres or balancers. In the
bee-parasites the fos/erior pair of wings are alone devel-
oped, the anterior pair being vestigial. In some insects
(springtails, lice, fleas) wings are entirely absent in all
stages. In others again, as certain moths, they are present
in one sex — usually the male — and absent in the other.

246 MANUAL OF ZOOLOGY SECT.

The abdomen is devoid in the adult, except at the
posterior extremity, of any paired limbs. At the posterior
end there are frequently appendages forming the sting,
ovipositor and genital processes, which may be of the
nature of modified limbs.

Fic. 145. — Culex, mosquito, and larva. (After Guérin and Percheron.)

The digestive canal (Fig. 146) consists of a number of
parts. It is nearly always considerably longer than the
body, and is longer in vegetable-feeding than in carnivorous
forms. The mouth leads into a buccal cavity into which
the ducts of a pair of large salivary glands open.

Following upon this is a narrow esophagus (@s), which
dilates behind into a crop (cr) for the storage of food.
The place of the crop in sucking insects is taken by a
stalked sac, usually termed the sucking stomach, but which
is more properly a food reservoir. The essential processes

247

PHYLUM ARTHROPODA

x

of digestion are carried on in an elongated chamber with
glandular walls, the chyle stomach, which may be divided

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Sometimes there is intercalated between

the crop and chyle stomach a muscular chamber frequently

into several parts.

containing chitinous teeth, the gvzzard (giz), or proventricu-

248 MANUAL OF ZOOLOGY SECT.

dus. Appended to the chyle stomach at its anterior end are
in many insects a number of tubular pouches, the hepatic
caca (ce@c). At the junction of the chyle stomach with the
small intestine, or further back, there open a number (from
2 to over 100) of narrow tubular appendages, the Mal-
pighian tubes (sa/p), which are the organs of renal ex-
cretion. The intestine is usually
elongated, its posterior portion is
dilated to form a wide rectum,
which opens in the anal aperture
on the last segment. Anal glands
A: producing an odoriferous secretion
Prem t often open into the rectum.
=>: The organs of respiration are a sys-
tem of fine branching tubes, the zra-
chee (Fig. 147), which communicate
with the exterior through valvular
Hy” { apertures known as s#gmaza situated
5 ; at the sides of the segments. These
| trachezee form a completely ramify-
ing system which conveys the air to
all the parts of the body. The wall
of the tubes is strengthened by a
series of spirally wound chitinous
fibres, each fibre or thread making
principal truneeor the tpchea! from one to four or five turns around
SM the trachez. In some insects, mainly
those adapted for active flight, the tracheal system is dilated
in certain parts of the body to form large av sacs. In the
aquatic larvee of some insects there is a series of soft external
simple or divided processes —the ¢racheal gills — attached
to the abdominal segments, and richly supplied with trachez
which have no communication with the exterior.

Lm
pile DU

Fic. 147.— Periplaneta. View
of the arrangement of the

x PHYLUM ARTHROPODA 249

The blood-vascular system is, in comparison with the
other systems of organs, not very highly developed, the need
of an elaborate system of vessels being greatly diminished
by the thorough way in which all the organs are supplied

with oxygen by means of the
trachez. The blood is colour-
less, or faintly yellowish or green-
ish. A contractile tubular heart
divided internally into a row of
eight chambers by a system of
valves extends through the abdo-
men on the dorsal aspect.

The nervous system (Fig. 148)
is on the same general plan as in
the Crustacea. There is a double
supra - cesophageal ganglion or
brain (47), a sub-cesophageal
ganglion (7zf), also double, and
a series of thoracic and abdomi-
nal pairs of ganglia, which are
closely united together in the
middle line. The brain is rela-
tively large in the higher insects,
and is divided into several lobes.
It gives off nerves to the antennze
and ocelli and the labrum, and
on each side it gives off a large
lobe, the optic ganghon, on which
the compound eye rests. A pair
of esophageal connectives (conn)

Ne
a thor. 3
SS
I sscaes
Ir, a
ee IN
ey) H arereer,
A
1h
__flll\
pases || ere
JN aba G~
Mi
4 \ >
4 | RY
Al \\N
Fic. 148. — Periplaneta. General

view of the nervous system.
aéd. 6, sixth abdominal ganglion ;
ant, antennary nerve ; 47, brain ;
conn, cesophageal connective ;
zuf, sub-cesophageal ganglion ;
opt, optic nerve ; thor. 1, thor. 2,
thor. 3, first, second, and third
thoracic ganglia. (After Miall
and Denny.)

pass backwards on either side of the mouth from the brain

to the sub-cesophageal ganglia.

These connectives are very

short, and, as a consequence, the brain and sub-cesophageal

250 MANUAL OF ZOOLOGY SECT.

ganglia are closely approximated. There are sometimes
three pairs of thoracic and as many as eight of abdominal
ganglia in the adult insect, but in many there is a greater or
less degree of concentration of the ventral ganglionic chain.

The most highly developed organs of special sense are the
large compound eyes which are situated on the sides of the
head. The surface of the compound eye is marked out, as
in the case of the crayfish, into a great number of minute
hexagonal facets, each of which corresponds to one of the
elements (ommatdia) of which the eye is made up. In
addition to the large compound eyes most insects have
simple unfaceted eyes or oce/i. In a few insects eyes are
entirely wanting.

The antennez and palpi are the organs of touch, and these
appendages seem also to be the seat of the olfactory sense.
The sense of taste is probably also developed in some
insects in minute papillz on the ef7pharynx which forms
the roof of the mouth and also at the base of the maxille.
Special nerve-endings supposed to be auditory occur in
various parts of the body in some cases.

The sexes are always separate, and the males and females
are very commonly distinguishable from one another by
various modifications of form and of coloration. Some
insects, such as the Aphides and bees and wasps, present us
with the unusual phenomenon of parthenogenesis, 7.e., ova
are formed, as in ordinary female insects, in organs corre-
sponding to the ovary of the latter, and these are developed
without fertilisation. In the case of the Aphides, an autumn
generation of completely developed males and females is
followed by a spring generation consisting entirely of
females; these are both parthenogenetic and viviparous.
In the bees the workers (imperfectly developed females)
occasionally produce ova which, without fertilisation, de-

x PHYLUM ARTHROPODA 251

velop into males (drones). In one or two groups, includ-
ing the scale insects (Coccide), and gall insects ( Cynipide),
males are never developed, so that reproduction is exclu-
sively parthenogenetic. Pedogenesis accompanies parthe-
nogenesis in certain of the Diptera or two-winged insects,
z.¢., the larva produces ova and embryo without impregna-
tion.

The eggs when laid are protected from injury by a num-
ber of methods: they may be buried in the earth, or laid in
the interior of certain plants or even animals. The deposi-
tion of eggs by means of an ovipositor in the leaves or other
parts of plants gives rise to swellings — ga//s —iti the inte-
rior of which the young insects are protected and nourished.
In the case of many insects the eggs are enclosed in a
cocoon ; in others they are enclosed in gelatinous or waxy
material.

In some instances the young insect, when it escapes from
the egg, has exactly the form of the parent, except that per-
haps the wings have not yet grown. But in most instances
there is a metamorphosis. In some this is comparatively
slight and gradual, the adult insect differing from the larva
only in comparatively unimportant points, and the segments
and appendages of the latter becoming directly converted
into those of the former. Such a metamorphosis is said to
be cnxcomplete. The term complete is applied to the meta-
morphosis of the majority of insects, in which the larva
differs so completely from the zmago, or perfect insect, in
external form, the nature of the appendages and the internal
organisation, that there is need of a quiescent or pupa stage
during which the whole animal, or a considerable part of it,
undergoes an entire transformation. The butterflies and
moths (Lepidoprera) (Fig. 143) may be taken as a good
example of such a complete metamorphosis. ‘The larve, or

252 MANUAL OF ZOOLOGY SECT.

caterpillars, are worm-like, but with well-developed jaws,
three pairs of jointed thoracic legs, and a number of un-
jointed stumpy abdominal legs. Eventually the caterpillar
spins a cocoon of a silky substance, enclosed within which,
and covered with a tough skin, it passes through a quiescent
or pupa condition — the condition of the chrysais. From
the interior of this the imago subsequently emerges with all
the parts of the adult insect fully formed.

In mode of life there is a very considerable difference
between different orders and families of insects. Some
are parasites in the strict sense throughout life. This is the
case, for instance, in the Strepsiptera (bee-parasites),
the females of which live permanently ensconced between the
joints of the abdomen of their hosts. The lice and bird-
lice are external parasites throughout life; bugs and fleas,
though not adhering to their hosts, are parasites as regards
their diet. Many insects are parasites in the larval condi-
tion, though free in the adult state. This holds good, for
example, of the larvae of the ichneumons, which develop in
the interior of the bodies of other insect-larve, also of
the larve of the bot-flies, which inhabit the alimentary canal
of mammalian hosts (horses, oxen, sheep, rhinoceroses,
tapirs).

In accordance with the high grade of the structure of
their various systems of organs, insects exhibit a correspond-
ingly high degree of functional activity. The quantity of
food consumed and assimilated is great in comparison with
the bulk of the body, and the energy expended in muscular
contractions is of very considerable amount. It is estimated
that while the muscular force exerted by a horse bears a ratio
of about 0.7 to its own weight (reckoned as 1), the muscu-
lar force of an insect bears a ratio to its weight of from
about 14 to about 23. Insects are also distinguished among

x PHYLUM ARTHROPODA 253

the Invertebrata by the keenness of their senses. The
sense of sight is, as we should expect from the elaborate
character of the optic organs, the most highly developed,
many insects having been shown by experiment to have a
keen sense of colour ; but a sense of smell, the seat of which is
in the antennz, can be shown to exist in a high degree, and

Fic. 149. — Honey bee (Apis mellifica). @, queen (perfect female) ; 6, worker (im-
perfect female); and c, drone (male). (After Brehm.)

the parts about the mouth bear nerve-endings concerned in a
well-developed sense of taste. A sense of hearing does not
appear to be universally present, but is well marked in such
forms as produce sounds. At the same time insects are
remarkable for the instincts, often leading to results of an
elaborate character, which guide them in the pursuit of food

Fic. 150. — Red ant (Formica rufa). Male, worker, and female.

and the protection and rearing of their young. Among
the insects which are the most highly endowed in this respect
are some — the ants, bees, wasps, and termites — which live
together in organised associations or communities, the various
individuals composing which are distinguishable into sexwa/
_ individuals, neuter workers, and soldiers (Figs. 149 and 150),

254 MANUAL OF ZOOLOGY SECT.

each specially organised for the part which it has to play in
the economy of the community.

5. THE ARACHNIDA

The Arachnida, comprising the scorpions and spiders,
the mites and ticks, the king-crabs, and a number of other
families, is a much less homogeneous group than the Insecta,
approaching the Crustacea in the variety which it presents
in the arrangement of the segments and their appendages.
In most members of the class, however, there is an
anterior region of the body—the cephalothorax — repre-
senting both head and thorax, and a posterior part or
abdomen, which is typically composed of a number of dis-
tinct segments ; in some cases cephalothorax and abdomen
are united.

Scorpions are inhabitants of warm countries, the largest
kinds being found in tropical Africa and America. They
are nocturnal animals, remaining under stones or in holes
and crevices during the day, and issuing forth at night to
hunt for their prey, which consists of spiders and insects.
These they seize with their pincer-claws and sting to death
with their caudal spine, afterwards sucking their juices.

There are a number of different species of scorpions,
divided into several genera, which differ from one another
in comparatively unimportant points, so that the following
general description will apply almost equally well to any of
them.

A scorpion (Fig. 151) has a long narrow body, in super-
ficial appearance not unlike that of a crayfish. There is a
small cephalothoracic shield or carapace, covering over dor-
sally a short anterior region or cephalothorax. This is followed
by a long posterior region or abdomen, the terminal part

x PHYLUM ARTHROPODA 255

of which in the living animal is habitually carried over the
back (Fig.151), constituting the “ tail,” at the end of which
the sting is placed. The cara-
pace bears a pair of large eyes
about its middle, and several
pairs of smaller eyes on the
antero-lateral margin. ‘The an-
terior, broader part of the ab-
domen, which is termed the
pra-abdomen, consists of seven
segments, each of which is pro-
tected by firm, chitinous, dorsal,
and ventral plates, or vga and
sterna. The tergum and sternum
of each segment are separated
from one another laterally by
intervals of soft skin, except in
the seventh, where they are
united laterally for a longer or
shorter distance. The posterior,
narrower part of the abdomen,
known as the fost+abdomen, con-
sists of five segments, each en- Fic. 151— Euscorpio. ce
closed in a complete investing
ring of hard chitinous matter. Articulating with the last
segment of the post-abdomen is a terminal appendage, the
caudal spine or s/g, swollen at the base and acutely pointed
at the apex, where open the ducts of two fozson glands.
The anal opening is situated on the ventral surface of the
last segment of the post-abdomen, immediately in front of
the sting.

The aperture of the mouth, which is very small, is at the
anterior end of the cephalothorax on its ventral aspect ; a

7

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re «

256 MANUAL OF ZOOLOGY SECT.

lobe which overhangs it in front is the Zadrum. On each
side of the mouth is a three-jointed appendage — the chehicera
(Fig. 152, che?) —which is terminated by a chela. Behind
these are the very large pincer-claws, or pedipalpi (ped),
each composed of six podomeres and terminating in power-
ful chele. The basal joint of each pedipalp has a process

Fic. 152.—Scorpion. Ventral surface of the cephalothorax and pra-abdomen.
chel, chelicerze; of, operculum; fect, pectines; fed, pedipalpi; s¢zg, stigmata.

which bites against the corresponding process of the other
pedipalp, these processes thus performing the functions of
jaws. Following upon the pedipalpi are four pairs of walk-
ing legs, each composed of seven podomeres, the last of
which is provided with a pair of small curved and pointed

x PHYLUM ARTHROPODA 257

horny claws. The basal segments of the first two pairs of
walking legs are modified so as to perform to some extent
the function of jaws.

All the six pairs of appendages hitherto described — the
chelicerze, the pedipalpi, and the four pairs of walking legs
— belong to the cephalothorax. The first segment of the
pre-abdomen (Fig. 152) has a narrow sternum, on which
there is placed a soft rounded median lobe divided by a
cleft ; this is termed the genital operculum (op.) ; at its base
is the opening of the genital duct. To the sternum of the
second segment of the pree-abdomen are attached a pair of
remarkable appendages of a comb-like shape, — the pectines
(pect), — each consisting of a stem, along the posterior mar-
gin of which is a row of narrow processes, somewhat like the
teeth of a comb; the function of these appendages is doubt-
ful, but is probably sensory. The remainder of the segments
of the pree-abdomen, and all those of the post-abdomen, are
devoid of appendages. The sterna of the third, fourth, fifth,
and sixth segments of the pra-abdomen, which are very
broad, bear each a pair of oblique slits—the s#gmata
(st#g) — leading into the pulmonary sacs.

All the appendages of the scorpion are post-oral in posi-
tion, and the most anterior — the cheliceree —are probably
best regarded as corresponding to the antenne of the cray-
fish, the equivalent of the crayfish’s antennules and of the
antenne of the cockroach not being present. The pedi-
palpi would then be the homologues of the mandibles of
the insect and the crustacean.

The organs of respiration in the scorpions are in the form
of pulmonary sacs or book-lungs (Fig. 153, pu/), the stig-
mata or external openings of which have already been
referred to. Each pulmonary sac is a compressed chamber
lined with a thin cuticle. The lining membrane is raised

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SECT.

MANUAL OF ZOOLOGY

258

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x PHYLUM ARTHROPODA 259

up into numerous delicate laminz lying parallel with one
another, like the leaves of a book. Into the numerous nar-
row spaces between the lamine the air penetrates, and oxy-
genates the blood which enters the interior of the laminz
from the ventral blood-sinus. In the United States the
common scorpion from Florida to North Carolina is Buthus
carolinianus; other species occur in Utah, New Mexico,
etc., and in Southern California.

The Spiders (Fig. 154) differ from the scorpions in hav-
ing the abdomen short, rounded, and unsegmented, in having
the chelicerze subchelate and
provided with poison glands,
the ducts of which open at
their extremities, and the pedi-
palpi simple, the terminal joint SNE dT We
in the male being expanded, ea)
and the whole appendage be- d 5
ing used as an intromittent : nS
organ for the transference of
the sperm to the genital open-
ing of the female. At the
extremity of the abdomen is
a peculiar apparatus, the avachnidium or spinning organ.
This consists of four or six appendages, the sp:nnerezs, on
the surfaces of which open the numerous ducts of the spin-
ning glands secreting the material of which the web is com-
posed. The fine threads of viscid secretion issuing from
the ducts harden on exposure to the air, and are worked up
into the web by means of the posterior legs. ‘There are six
or eight eyes on the carapace. The organs of respiration
are either four pulmonary sacs similar to those of the scor-
pion, or two pulmonary sacs, and a system of tracheze
resembling those of insects.

B
Fic. 154. —Spider (Epeira diadema).

260 MANUAL OF ZOOLOGY SECT.

In the Mites and Ticks (Fig. 155) no distinction into
regions is recognisable, but there are the same series of
paired appendages as in the scorpions and spiders. The
cheliceree and pedipalpi, and also the legs, differ somewhat
in form in different groups, in accordance with differences
in mode of life. Organs of respiration, when present, take
the form of trachez. The cattle tick, Zxodes bovis, is the
medium of conveyance of the Texas cattle disease.

Fic. 155. — Cattle Tick. Above, nat. size, Fic. 156. — Itch mite (Sarcoptes scabi-
side view; below, dorsal view, en- wi). (After Leuckart.)
larged. (From Packard.)

The Xiphosura or King-crabs, an order comprising the
single genus Limulus, differ widely from the scorpions and
spiders.' Limulus (Fig. 157) is a marine arthropod breath-

1 The Xiphosura, with their fossil allies, the Eurypterida, are by some
authors regarded as forming a distinct class, by others they are included
among the crustacea. It seems better to refer them to a distinct class, the
Merostomata.— AMERICAN EDITOR,

x PHYLUM ARTHROPODA 261

ing by gills, in which the body consists of two regions, — the
cephalothorax and the abdomen. ‘The former is covered

Fic. 157.— Ventral view of Limulus. 7-0, appendages of cephalothorax; add,
abdomen; cefh, cephalothorax; oferc, operculum, behind which are seen the
series of abdominal appendages; ¢e/s, caudal spine or telson. (From Packard,
after Kingsley.)

over by a broad shield or carapace, bearing two large com-
pound and two smaller, simple eyes. The segments of the

262 MANUAL OF ZOOLOGY SECT.

abdomen (nine in number) are united together, being cov-
ered dorsally by a continuous abdominal carapace. At the
posterior end is attached a very long, narrow, caudal spine
which is a modification of the ninth abdominal segment of
the larva. The anterior appendages (Fig. 157) somewhat
resemble those of the scorpion. In front of the mouth is
a pair of short, three-jointed, chelate appendages, the ched-
cer@, at the sides of a labrum or upper lip. Behind these
follow a series of five pairs of legs, the bases of all of which,
with the exception of the last, are covered with spines, and
have the action of jaws, while the extremities are for the
most part chelate. ‘The first pair of appendages of the
abdomen are flat plates, which are united together in
the middle line and together form the broad operculum
(oferc), overlapping all the posterior appendages ; on its
posterior face are the two genital apertures. The posterior
appendages, of which there are five pairs, are thin, flat
plates to which the gills are attached; each of them is
divided by sutures into a small inner ramus or endopodite,
and a larger external ramus or exopodite. A labrum (7os-
trum) lies in front of the mouth, and between the sixth pair
of appendages is a pair of processes, the chilaria.

In their mode of life the Arachnida present almost as great
a diversity as the Insecta. Some Acarida are parasites
throughout life. Most of the other groups of Arachnida
are predaceous, preying for the most part on insects or
other arachnids. To capture the insects which constitute
their food, the majority of spiders construct a web formed
of the threads secreted by the arachnidium. The primary
function of the threads formed from the secretion of the
spinning organ is to constitute the material for the manufac-
ture of a cocoon for enclosing the eggs, and in some arach-
nids this is the sole purpose to which they are devoted. In

x PHYLUM ARTHROPODA 263

others there is added a nest for the protection of the eggs
and of the parent itself; this in many cases becomes a per-
manent lurking place which the spider inhabits at all sea-
sons, and from which it darts out to capture its prey; in the
trap-door spider the nest has a closely fitting hinged lid.
In very many spiders the secretion is used mainly to form
the web by means of which the prey is snared, with the
addition frequently of a nest in which the spider lies in
wait. A subsidiary function of the threads is to aid in loco-
motion, the spider being enabled by means of them to let
itself down safely from considerable heights, and even to
float in the air.

Some of the mites, as already mentioned, are parasitic ;
others feed on various kinds of fresh or decaying animal or
vegetable substances. Most free Acarida are terrestrial,
some are aquatic.

The Xiphosura are marine, living from low-water mark to
the depth of a few fathoms in warm seas, burrowing in sand ;
their food consists of various kinds of marine annelids.
Limulus polyphemus inhabits our coast from Florida to, and
just east of the mouth of, the Kennebec River, Maine.

SECTION XI.—PHYLUM MOLLUSCA

Groupep together in the Phylum Mollusca are a large as-
semblage of animals exhibiting as great a diversity in their
structure as is observable among the Arthropoda. ‘The ani-
mals popularly known as “ shell-fish,” such as the mussels,
oysters, and scallops, the whelks, limpets, and snails, to-
gether with the cuttle-fishes and many others, are compre-
hended within this extensive phylum. If we compare a
mussel, a whelk, and a cuttle-fish, we may experience a
difficulty in finding a sufficient number of features common
to all three to justify us placing them together in one phylum.
They are all unsegmented, and are devoid of the continuous
enclosing crust and the jointed appendages of the Arthro-
poda; and they all possess, in different forms, a calca-
reous shell, with, in relation to it, a specially modified area
of the skin, the mane; but it is only on a careful analysis
and comparison of the various parts that we are enabled
to arrive definitely at the conclusion that they all present
us with modifications of the same general plan of structure.

Five classes are comprised in the phylum; (1) the Pele-
cypoda, or bivalved shell-fish, such as mussels, cockles,
oysters, scallops, etc. ; (2) the Amphineura ; (3) the Gastro-
poda, including the univalved shell-fish, such as periwinkles,
whelks, snails, slugs, etc. ; (4) the Scaphopoda or elephant’s
tusk shells ;’ and (5) the Cephalopoda, including the cuttle-
fishes, squids, octopi, and nautili.

1 Not further referred to in this work.

264

SECT. XI PHYLUM MOLLUSCA 265

1. THE PELECYPODA

A Fresh-water Mussel will serve as a convenient example
of the Pelecypoda.' Fresh-water mussels are found in rivers
and lakes in most parts of the world. Anodonta cygnea, the
swan-mussel, is the commonest species in England; but
the pearl-mussel, Unio margaritifer, is found in mountain
streams, and other species of the same genus are universally
distributed. Unio complanatus is the common fresh-water
pearl-mussel in the Eastern United States, and Anodonta
fluviatilis represents the European A. cygnea.

Fic. 158. — Anodonta cygnea. The entire animal. A, from the left side; B, from
the posterior end. d@. f. a, dorsal pallial aperture; ex. sph, exhalant siphon;
Jt, foot; 7. sph, inhalant siphon; 27g, ligament; 22, mantle; 222, umbo. (After
Howes.)

The mussel (Fig. 158) is enclosed in a brown shell formed
of two separate halves or va/ves hinged together along one
edge. It lies on the bottom, partly buried in the mud or sand,
with the valves slightly gaping, and in the narrow cleft thus
formed a delicate, semi-transparent substance (#7) is seen,

1 The earlier and quite as appropriate name of this class is Lamel/ibran-
chiata, — AMERICAN EDITOR,

266 MANUAL OF ZOOLOGY SECT,

the edge of the mantle or pallium, The mantle really con-
sists of separate halves or Joes corresponding with the
valves of the shell, but in the position of rest the two lobes
are so closely approximated as to appear simply like a mem-
brane uniting the valves. At one end, however, the mantle
projects between the valves in the form of two short tubes,
one (ex. sph) smooth-walled, the other (77. sh) beset with
delicate processes or fimbrie. By diffusing particles of
carmine or indigo in the water it can be seen that a current
is always passing in at the fimbriated tube, hence called the
inhalant siphon, and out at the smooth or exhalant siphon.
Frequently a semi-transparent, tongue-like body (/%) is
protruded between the valves at the opposite side from the
hinge, and at the end furthest from the siphons; this is the
foot; by its means the animal is able slowly to plough its
way through sand or mud. When the mussel is irritated,
the foot and siphons are withdrawn and the valves tightly
closed. In a dead animal, on the other hand, the shell
always gapes, and it can then be seen that each valve is
lined by the corresponding lobe of the mantle, that the
exhalant siphon is formed by the union of the lobes above
and below it, and is thus an actual tube; but that the boun-
dary of the inhalant siphon facing the gape of the shell is
simply formed by the approximation of the mantle lobes, so
that this tube is a temporary one.

The hinge of the shell is dorsal, the gape ventral, the end
bearing siphons posterior, the end from which the foot is
protruded anterior; hence the valves and mantle-lobes are
respectively right and left.

In a dead and gaping mussel the general disposition of
the parts of the animal is readily seen. The main part of the
body lies between the dorsal ends of the valves; it is pro-
duced in the middle ventral line into the keel-like foot, and

XI PHYLUM MOLLUSCA 267

on each side, between the foot and the corresponding mantle-
lobe, are two delicate striated plates, the g///s. Thus the
whole animal has been compared to a book, the back being
represented by the hinge, the covers by the valves, the fly-
leaves by the mantle-lobes, the two first and the two last
pages by the gills, and the remainder of the leaves by the
foot.

When the body of the mussel is removed from the shell
the two valves are seen to be united along a straight Ainge-
fine (Fig. 159, A, A”. 2), by a tough, elastic substance, the
hinge-ligament (Fig. 158, @v) passing transversely from valve
to valve. It is by the elasticity of this ligament that the
shell is opened ; it is closed, as we shall see, by muscular
action ; hence the mere relaxation of the muscles opens the
shell. In Anodonta the only junction between the two valves
is afforded by the ligament, but in Unio each is produced
into strong projections and ridges, the A/nge-teeth, separated
by grooves or sockets, and so arranged that the teeth of one
valve fit into the sockets of the other.

The valves are marked externally by a series of concentric
lines (Fig. 158) parallel with the free edge or gape, and
starting from a swollen knob or elevation, the wméo (um),
situated towards the anterior cdge of the hinge-line. These
lines are “nes of growth. The shell is thickest at the umbo,
which represents the part first formed in the young animal,
and new layers are deposited under this original portion, as
secretions from the mantle.

The inner surface of the shell also presents characteristic
markings (Fig. 159,A). . Parallel with the gape and at a
short distance from it is a delicate streak (f/. 7) caused by
the insertion into the shell of muscular fibres from the edge
of the mantle; the streak is hence called the palial Line.
Beneath the anterior end of the hinge the pallial line ends

268

MANUAL OF ZOOLOGY SECT.

in an oval mark, the anterior adductor impression (a. ad),
into which is inserted one of the muscles which close the

Fic. 159. — Anodonta cygnea. A, interior of right valve; B, the animal removed

from the shell. a@. ad, anterior adductor or its impression; @. 7, anterior retrac-
tor or its impression; d. g, digestive gland, seen through mantle; ex. sph, exhal-
ant siphon; /#, foot; g?, gills, seen through mantle; %. 7, hinge-line; zx. sph,
inhalant siphon; hd, kidney, seen through mantle; %. 0, Keber’s organ, seen.
through mantle; 7, mantle ; p. ad, posterior adductor or its impression; Zc,
pericardium, seen through mantle; pl. l, pallial line ; 2. a, pallial muscles;
p. 7, posterior retractor or its impression 3 pre, protractor or its impression,

shell. A similar but larger posterior adductor impression
(p. ad) lies beneath the posterior end of the hinge.

The shell consists of three layers. Outside is a brown

horn-like layer, the periostracum (Fig. 160, prs), composed

xl PHYLUM MOLLUSCA 269

of conchiolin, a substance allied in composition to chitin.
Beneath this is a prismatic layer (prc), formed of minute
prisms of calcium carbonate separated by thin layers of
conchiolin ; and lastly, forming the internal part of the
shell, is the acre (7) or ‘“ mother-of-pearl,” formed of
alternate layers of carbonate of lime and conchiolin arranged
parallel to the surface. ‘The periostracum and the prismatic
layer are secreted from the edge of the mantle only, the
pearly layer from the whole of its outer surface. The hinge

Fic. 160. —Vertical section of shell and mantle of Anodonta; c?, connective-tissue
layer of mantle; e/.7, its outer epithelium; e/.2, its inner epithelium; 2, nacreous
layer of shell; Arc, prismatic layer; xs, periostracum. (After Claus.)

ligament is continuous with the periostracum, and is to be

looked upon simply as a median uncalcified portion of the
shell, which is therefore, in strictness, a single continuous
structure.

By the removal of the shell the Jody of the animal (Fig.
159, B) is seen to be elongated from before backwards,
narrow from side to side, produced on each side into a
mantle-lobe (), and continued ventrally into a keel-like

MANUAL OF ZOOLOGY SECT.

270

wsceral mass (Fig. 161, v. m), which passes below and in

front into the foot (/7).

A

Thus each valve of the shell is in

contact with the dorso-lateral region of the body of its own

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side together with the corresponding mantle-lobe, and it is

from the epithelium (Fig. 160, ¢f.z) covering these parts

The whole

that the shell is formed as a cuticular secretion.

XI PHYLUM MOLLUSCA 271

space between the two mantle-lobes, containing the gills,
visceral mass, and foot, is called the mantle-cavity.

Of the muscles the largest and most important are the
anterior and posterior adductors (Figs. 159 and 161, a, ad,
p. ad ), great cylindrical muscles, passing transversely across
the body, and inserted at either end into the valves of the
shell, which are approximated by their contraction.

The ca/om is reduced to a single ovoidal chamber, the
pericardium (Fig. 161, gc) lying in the dorsal region of the
body, and containing the heart and part of the intestine. In
the remainder of the body the space between the ectoderm
and the viscera is filled by the muscles and connective
tissue.

The mouth (Fig. 161, mth) lies in the middle line just
below the anterior adductor. On each side of it are two
triangular flaps, the ¢ternad (2. int. plp) and external (2. ext.
PD) labial palps, both are ciliated externally. The mouth
leads by a short gw//e¢ (Fig. 162, gu/) into a large stomach
(st), which receives the ducts of a pair of irregular, dark-
brown, digestive glands (d. gl). The tnéestine (int) is given
off from the posterior end of the stomach, descends into the
visceral mass where it is coiled upon itself, then ascends
parallel to its first portion, turns sharply backwards, and
proceeds, as the rectum (rct), through the pericardium,
where it traverses the ventricle of the heart, and above the
posterior adductor, finally discharging by the anws (a) into
the exhalant siphon or cloaca. The stomach contains, at
certain seasons of the year, a gelatinous rod, the crystalline
style.

The gills consist, as we have seen, of two plate-like
bodies on each side between the visceral mass and the
mantle ; we have thus a z7ghtand a /eft outer (Fig. 161, 2. ext.
gf) anda vightand a leftinner gill (2. int. gl). Seen from the

272 MANUAL OF ZOOLOGY SECT.

surface each gill presents a delicate double striation, being
marked by faint lines running parallel with, and by more
pronounced lines running at right angles to, the long axis of
the organ. Moreover, each gill is double, being formed of
two similar plates, the zzmer and outer lamella, uniting with
one another along the interior, ventral, and posterior edges
of the gill, but free dorsally. The gill has thus the form of
a long and extremely narrow bag open above (Figs. 162 and
163) ; its cavity is subdivided by vertical bars of tissue, the
inter-lamellar junctions (¢. 2.7.), which extend between the
two lamelle, and divide the intervening space into distinct
compartments or wader tubes (w.?) closed ventrally, but
freely open along the dorsal edge of the gill. The vertical
striation of the gill is due to the fact that each lamella is
made up of a number of close-set gil/-filaments (f) ; the
longitudinal striation to the circumstance that these fila-
ments are connected by horizontal bars, the zz¢er-filamental
junctions (i. f.7). At the thin, free, or ventral edge of
the gill the filaments of the two lamelle are continuous with
one another, so that each gill has actually a single set of
V-shaped filaments, the outer limbs of which go to form
the outer lamella, their inner limbs the inner lamella.
Between the filaments, and bounded above and below by
the inter-filamental junctions, are minute apertures, or ostia
(os), which lead from the mantle-cavity through a more or
less irregular series of cavities into the interior of the water
tubes. The filaments themselves are supported by chitinous
rods (7), and are covered with ciliated epithelium, the large
cilia of which produce a current running from the exterior
through the ostia into the water tubes, and finally escaping
by the wide dorsal apertures of the latter. The whole organ
is traversed by blood-vessels.

Owing to this arrangement it will be seen that the water

273

PHYLUM MOLLUSCA

XI

tubes all open dorsally into a suprabranchial chamber,
continuous posteriorly with the cloaca and thus opening on

the exterior by the exhalant siphon.

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The physiological importance of the gills will now be

By the action of their cilia a current is produced

which sets in through the inhalant siphon into the pallial

obvious.

274 MANUAL OF ZOOLOGY SECT.

cavity, and out at the exhalant siphon. The ingoing cur-
rent carries with it not only oxygen for the aération of the

aNDue Wee

LEPTEPR GIT)

Fic. 163.— Anodonta cygnea. A, transverse section of outer; B, of inner gill;
C, diagram of gill-structure; D, transverse section of gill-filament. 4. c, blood-
corpuscle; 4. v, blood-vessels; cf, chitin; /, branchial filaments; ¢f, epithelium;
z. f. 7, inter-filamental junction; z. 2, inner lamella; 2. Z. 7, inter-lamellar junction;
o. 2, outer lamella; os, external ostium; os’, internal ostium; 7, chitinous rods;
w.?, water tubes. (A, B, and D, after Peck.)

blood, but also diatoms, Infusoria, and other microscopic
organisms, which are swept into the mouth by the cilia cov-

XI PHYLUM MOLLUSCA 275

ering the labial palps. The outgoing current carries with
it the various products of excretion and the feces passed
into the cloaca. The action of the gills in producing the
food current is of more importance than their respiratory
function, which they share with the mantle.

The excretory organs are a single pair of curiously
modified zephriaia, situated one on each side of the body
just below the pericardium. Each nephridium consists of
two parts, a brown spongy glandular portion or kidney (Fig.
162, 4d), and a thin-walled non-glandular part or Jladder
(42) communicating with one another posteriorly, while in
front the kidney opens into the pericardium (7. p. ap), and ©
the bladder on to the exterior by a minute aperture (7. af),
situated between the inner gill and the visceral mass. Thus
the whole organ, often called after its discoverer, the organ
of Bojanus, is simply a tube bent upon itself, opening at one
end into the ccelom, and at the .other on the external
surface of the body.

The circulatory system is well developed. The ear? lies
in the pericardium and consists of a single ventricle (Figs.
162 and 164, v) and of right and left auricles (au). The
ventricle is a muscular chamber which has the peculiarity
of surrounding the rectum (Fig. 162); the auricles are
thin-walled chambers communicating with the ventricle by
valvular apertures opening towards the latter. From each
end of the ventricle an artery is given off, the anéerior
aorta (Fig. 162, a. ao) passing above, the posterior aorta
(p. av) below the rectum. From the aortze the blood passes
into arteries (Fig. 164, art. z,ar¢. 2) which, ramifying all over
the body, finally form an extensive network of vessels, many
of which are devoid of proper walls and have therefore the
nature of sinuses.

The nervous system is formed on a type quite different

276 MANUAL OF ZOOLOGY SECT.

from anything we have yet met with. On each side of the
gullet is a small cerebro-pleural ganglion (Fig. 162, ¢. pl.
gn) united with its fellow of the opposite side by a nerve-
cord —the cerebral commissure passing about the gullet.
Each cerebro-pleural ganglion also gives off a cord, the cere-
bro-pedal connective, which passes downwards and backwards
to a pedal ganglion ( pd. gn) situated at the junction of the

Dy

=e
af. ore

Q

Fic. 164.— Diagram of the circulatory systems of Anodonta. Vessels containing
aérated blood red, non-aérated blue. af. dr.v, afferent branchial veins: ao,
aorta; art.s, artery to mantle; art 2, artery to body generally; az, auricle;
of. br.v, efferent branchial veins; nuph.v, nephridial veins; fc, pericardium; v,
ventricle; v.c, vena cava. The arrows show the direction of the current.

visceral mass with the foot; the two pedal ganglia are so

closely united as to form a single bilobed mass. From each
cerebro-pleural ganglion there further proceeds a long ceve-
bro-visceral connective which passes directly backwards

through the kidney, and ends in a wsceral ganglion (v. gn)

xI PHYLUM MOLLUSCA 277

placed on the ventral side of the posterior adductor muscle.
The visceral, like the pedal ganglia, are fused together.

Sensory organs are poorly developed, as might be expected
in an animal of such sedentary habits. In connection with
each visceral ganglion is a patch of sensory epithelium form-
ing the so-called olfactory organ or, better, osphradium,
the function of which is apparently to test the purity of
the water entering by the respiratory current. Close to the
pedal ganglion a minute otocyst is sometimes found. Sen-
sory cells — probably tactile — also occur round the edge of
the mantle, and especially on the fimbriz of the inhalant
siphon.

The sexes are separate. The gonads (Fig. 162, gon) are
large, paired, racemose glands, occupying a considerable
portion of the visceral mass amongst the coils of the intes-
tine ; the testis is white, the ovary reddish. The gonad of
each side has a short duct which opens (g. af) on the sur-
face of the visceral mass just in front of the renal aperture.

In the breeding season the eggs, extruded from the gen-
ital aperture, pass into the suprabranchial chamber and so to
the cloaca. There, in all probability, they are impregnated
by sperms introduced with the respiratory current. The
oosperms are then passed into the cavities of the outer gills,
which they distend enormously. Thus the outer gills act as
brood-pouches, and in them the embryo develops into a
peculiar larval form known as Glochidium.

The Glochidium (Fig. 165) has a bivalved shell produced
ventrally into incurved hooks beset with spines. After a
time it is ejected from the mantle-cavity and falls to the
bottom of the water, where it lies until it has the oppor-
tunity of becoming attached to the gills or skin of a fish.
Fixed firmly by means of the hooked valves the larva remains
as an external parasite for about ten weeks, becoming en-

278 MANUAL OF ZOOLOGY SECT.

cysted by an overgrowth of the skin or mucous membrane
of their host. In the meantime a metamorphosis is taking
place, and when the young mussel becomes free it has begun
to assume the form and structure of the adult.

The majority of the members of the class Pelecypoda
resemble the fresh-water mussel in the main features above
described. They are bilaterally symmetrical, laterally com-
pressed, with a mantle consisting of paired right and left
lobes, secreting a bivalved calcareous shell. A distinct head
is never present. There is on the ventral surface a muscu-

D.--~
Fic. 165.— A, advanced embryo of Anodonta; B, free glochidium. _/, provisional

byssus; s, shell; si, hooks ; sz, adductor muscle; so, sense organs; w, cilia.
(From Korschelt and Heider’s E£7bryology.)

lar foot ; there are two abductor muscles, and there are two
pairs of gills. But, on looking over a collection of shells of
various bivalves, it will be found that certain of them differ
from that of the fresh-water mussel in not having the two
valves of the shell alike. This inequality between the
two valves of the shell is strongly marked in the scallops,
and even more so in the oysters. The oysters are also
examples of Pelecypods, which have only one adductor
muscle instead of two; and the oyster, which is unable to

XI PHYLUM MOLLUSCA 279

move from place to place, and in the case of some species is
permanently fixed to some rock or other solid body by the
substance of the larger valve, has no foot. The inhalant
and exhalant siphons are sometimes absent, sometimes
much longer than in the fresh-water mussel, as in the clam
(MGa arenaria). Posterior to the foot there is in many
Pelecypods a gland termed the dyssus gland, secreting silky
threads which serve to attach the animal temporarily or
permanently, as, for example, in the sea mussel (AZpélus)
(Fig. 166). In most Pelecypoda the gills (cfenidia, p. 271)

Fic. 166.— Mytilus edulis, attached by byssus (By) toa piece of wood. F, foot;
S, exhalant siphon. (From the Cambridge Natural History.)

are simpler in character than in the fresh-water mussels.

In one group, Protobranchia (Nucula, etc.), they take the

form of a pair of plume-like organs, and are primitive in

shape and structure.

A remarkably modified member of this class of molluscs
is the ship-worm, Zeredo, which is very destructive to ships’
timbers, piles of jetties, etc. The valves of the shell are
extremely small, and the general surface of the mantle
secretes a continuous shelly tube lining the burrow in which
the elongated worm-like body of the mollusc lies. Highly

280 MANUAL OF ZOOLOGY SECT.

= =
5 f

ss

Fic. 167.—Teredo navalis, in
a piece of timber. P, pallets;
SS, siphons; T, tube; V, valve;
ofshell. (From the Cambridge
Natural History.)

a few others.

Although none of the Pelecy-
poda are microscopic, they present
a considerable range in size, from
the little fresh-water Cyc/as, about
1 cm. long, to the giant clam (Z77-
dacna gigas) of the Indian and
Pacific Islands, which is sometimes
60 cm. (two feet) in length and
500 pounds in weight. ‘The nacre-
ous inner layer of the shell of the
pearl oyster (AZeleagrina marga-
ritifera), which is of unusual thick-
ness, constitutes the ‘‘ mother-of-
pearl” of commerce, employed
for many ornamental purposes.
Pearls are deposits of nacre formed
around sand grains or other foreign
bodies, either between the mantle
and shell, or in the soft parts in
the pearl oyster and the pearl mus-
sel (Unio complanatus), etc.

Most Pelecypoda are sluggish
in habit, progressing only by slow
movements of the foot, and some
are permanently fixed during adult
life by the byssus. The scallops,
however, swim freely by clapping
the valves together. The cockles
(Cardium), Trigonia, etc., jump
by sudden movements of the foot,

XI PHYLUM MOLLUSCA 281

and the razor-fish (.So/ev) jerks itself forward by suddenly
withdrawing its very large foot, and thus ejecting water
through the siphons. The only parasitic genus is Enzo-
valva, found in the gullet of a Holothurian.

Pelecypoda are abundant both in fresh water and the sea ;
the marine forms are mainly littoral. None are pelagic or
terrestrial.

2. THE AMPHINEURA

A class of molluscs which comprises only a small number of repre-
sentatives, most of them of rare occurrence and of simple organisation,
is the Amphineura. With the exception of the Chitons these have no
shell and are devoid of a foot, so that though probably related to the
more typical molluscs, and to be referred to the same phylum, they are
wanted in some of the most characteristic features exhibited by the
members of the other classes. All the
Amphineura are bilaterally symmetri-
cal, more or less elongated molluscs,
with the mouth at the anterior and the
anus at the posterior end.

The commonest, as well as the most
highly organised, of the Amphineura
are the Chitons, marine molluscs which
are to be found adhering firmly, like
limpets, to rocks and stones on the
seashore, or in deep water. The body
is dorso-ventrally compressed, convex
above, and presents below a broad flat
foot (narrow in Chitonel/us), which acts
not only as an organ for effecting creep-
ing movements, but also as a sucker for
enabling the animal when at rest to Fic. 168.—Chiton spinosus, dorsal

: A view. (From the Cambridge
adhere firmly, like a limpet, to the sur- Natural History.)
face of arock. The most remarkable

external feature of the Chiton is the presence on the dorsal surface of
a calcareous shell (Fig. 168), made up of no fewer than eight trans-
versely elongated pieces or valves, arranged in a longitudinal row, artic-

282 MANUAL OF ZOOLOGY SECT.

ulating together and partly overlapping one another. They are some-
times partly, sometimes completely, covered over by the mantle. Each
valve consists of two very distinct layers, a more superficial and a deeper,
the latter formed of a compact calcareous substance, the former perfo-
rated by numerous vertical canals for the lodgment of the sense organs,
to be presently referred to. External to the valves the dorsal integu-
ment (mantle) of Chiton and its allies is usually beset with a number
of horny or calcified tubercles and spicules. The mantle develops only
very slight lateral flaps, and under cover of these are a series of small
gills or ctenidia (Fig. 169, ct), to the
number of fourteen to eighty. The
mouth and anus are both median, situ-
ated at the anterior and_ posterior
extremities respectively.

The buccal cavity always contains a
well-developed odontophore. The in-
testine is elongated and coiled. There
are salivary glands and a large paired
liver. There is a well-developed heart,
consisting of a median ventricle and
two lateral auricles. The pericardial
cavity in which it lies is a space of con-
siderable extent in the posterior region
of the body, below the two last valves
of the shell.

cai The central part of the nervous sys-

Fic. 169.—Chiton, ventral view.
an, anus; cten, ctenidia; ft, foot; ae :
mant, mantle edge; #o, mouth. ring, consisting of a thicker dorsal
(After Pelseneer. )

tem comprises an cesophageal nerve-

cerebral portion not differentiated into
ganglia, and a thinner ventral daccal commissure. Two pairs of longi-
tudinal nerve-cords, pedal and pallial, are given off from this poste-
riorly. The former, which give off nerves to the foot, are joined by
numerous commissures passing beneath the enteric canal. The large
cords contain nerve-cells throughout their length.

The conspicuous organs of special sense present on the head of Gas-
tropods (see p. 289) are absent in the Chitons. A pair of processes
situated in front at the sides of the mouth have the character of labial
palps. Remarkable sensory organs, the micresthetes and the megales-
thetes, lie in the canals already mentioned as occurring in the super-

xI PHYLUM MOLLUSCA 283

ficial layer of the shell valves. The megaleesthetes may take the form
of eyes, with cornea, lens, pigment layer with iris, and retina.

There are two symmetrical nephridia (lig. 170) opening internally
into the pericardium by a ciliated funnel-like opening (1. peri. ap), and

Fic. 170. —Chiton, nephridial and genital systems. am, anus; cten, ctenidia; gen.
apf, genital aperture; gov, gonad; gonod, gonoduct; mo, mouth; meph. af,
nephridial aperture; 2. fe77. af, aperture from nephridia to pericardium. (From
Simroth, after Haller and Lang.)

opening on the exterior (seph. ap), between two of the posterior
ctenidia. Each consists of a looped main tube, into which open
numerous minute tubules which ramify among the viscera. The sexes
are distinct. The testis and ovary (gov) are similar in appearance,

284 MANUAL OF ZOOLOGY SECT.

differing only in colour when the products are mature. Each is an un-
paired sac marked by a series of slight lateral constrictions. The larva
is a Trochosphere.

All the Amphineura are marine. The Placophora (Chitons) occur
at all depths, thougn most abundant on the shores between tidal limits.
‘The shell-less forms (Aplacophora), on the other hand, are rare in very
shallow water, and absent altogether from the littoral zone; some have
been found at considerable depths (down to 1250 fathoms). The Placo-
phora are all vegetable feeders, their food consisting of minute algze
and diatoms. The Aplacophora subsist on small animals. The Placo-
phora, when at rest, adhere firmly to the surface of a rock or a block
of coral by means of the sucker-like foot. When forcibly detached the
animal curls itself up into a ball, and will only after a considerable time
slowly extend itself again. All their movements are extremely slug-
gish. The Aplacophora are unable to fix themselves in this way; many
of them occur twined round the stems of zoophytes, sometimes attached
by a thread of viscid mucus.

38. THE GASTROPODA

The class Gastropoda comprises the snails and slugs,
limpets, whelks, periwinkles, sea-hares, and the like.
They are distinguished by the possession of a shell of a
univalve character, consisting of a single piece, and by the
mantle not being developed into two lateral folds, as in the
Pelecypoda. There is a distinct head, bearing eyes and
tentacles. The body is inequilateral, and the foot is ven-
trally situated, forming a large creeping disc.

If we look at a living Gastropod, such as a snail (Fig.
171) when fully extended, the want of symmetry appears
at first sight to be limited to the spiral shell, which is in
itself unsymmetrical, and is held obliquely, the head part
and the “tail”? part appearing when superficially examined,
quite bilaterally symmetrical. But a closer examination,
especially after removal of the shell, shows that the depar-

XI PHYLUM MOLLUSCA 285

ture from symmetry is very marked. The left side of the
body has become very much more strongly developed than
the right, and this side of the body is drawn out into a
spirally twisted prominence — the wisceral spiral — enclos-
ing the liver and other organs. ‘The anal aperture, instead
of being median and posterior, is situated on the right side,
and in front of it on the same side is the reproductive
aperture.

SCR.A
asm P
pulm
Fic. 171.— Helix nemoralis. an, anus; ge. af, genital aperture ; oc. tent. pos-
terior eye-bearing tentacles ; p/m, opening of pulmonary sac ; ¢en¢, anterior
tentacles. (After Pelseneer.)

The shell is of simple conical form in the limpets. In
most of the Gastropoda it is in the shape of a spiral (Figs.
172, 173) with the turns usually in close contact with one
another, the inner walls of the turns coalescing to form an
axial, hollow, or solid column — the co/umel/la._ By far the
greater number of such spiral shells are dextra/, 7.¢., if we
begin at the apex of the spiral to reach the opening of the
shell we have to pass from left to right with the columella
always on our right-hand side; ina few cases, however, the
spiral is s¢n7stra/, taking the opposite direction from that
of the ordinary dextral shell. The form of the shell varies
with the degree of obliquity with which the whorls are set

286 MANUAL OF ZOOLOGY SECT.

on the axis. When the obliquity is very slight (Fig. 174),
the spiral is nearly flat; when the obliquity is great, an
elongated tapering shell, such as that represented in Fig.
175, is the result. Sometimes the later whorls completely

Fic. 172. — Shell of Triton nodiferus. Natural size. New Zealand.

cover over the earlier ones, so that the spiral form of the shell
is concealed. Sometimes only the apical portion of the shell
is spiral, the remainder being a straight or sinuous cylinder.
The mouth of the shell has usually a prominent margin or

XI PHYLUM MOLLUSCA 287

peristome, which is sometimes entire and continuous, some-
times is broken by a deep notch or a spout-like prolonga-
tion or cana/, formed in connection with the development

Fic. 173. — Longitudinal median section of the shell of Triton nodiferus.

of a spout-like prolongation of the mantle, the siphon,
which lies in it. The mouth of the shell in many Gastro-
poda is capable of being closed by means of an operculum

288 MANUAL OF ZOOLOGY SECT.

borne on the foot. In some terrestrial forms in which an
operculum is absent, the opening may be closed up during
winter by a layer of hardened mucous matter to which the
name of efiphragm is applied. Lateral folds of the mantle
are in some of the Gastropoda (Fig. 176) reflected over
the shell, and may completely cover it. In some cases
these folds unite by their edge, so that the shell comes to
be enclosed in a complete sac of the mantle; such enclosed
shells are always imperfectly developed and incapable of
covering the body. Thus in Afpdysza (the “Sea-hare”’) and

ey,
ria.
Pax

Ley
4

es
a

ik

Fic. 174. — Shell of Solarium perspectivum from the under side.
(From the Cambridge Natural History.)

other allied forms the shell is greatly reduced, thin and
horny, and concealed within the mantle, while in the
nudibranch (Fig. 177), members of the same sub-order, it
is entirely absent. The shell is also completely absent in
some of the pelagic forms (Heteropoda and Preropoda); in
others, though present and external, it is too small to
enclose the animal. In the slugs the shell is vestigial and
concealed by the mantle.

The Gastropoda have a well-marked head, separated
from the body by a constriction or weck, The mouth,

XI PHYLUM MOLLUSCA 289

situated at the anterior end of the head on its ventral
aspect, is in many instances provided with a protrusible
probosis or iz¢rovert, sometimes of considerable length.
On the dorsal surface of the head are a
pair of tentacles which vary a good deal in
shape, but are usually cylindrical or club-
shaped. In most cases the eyes are situ-
ated on tubercules at the bases of the ten-
tacles, or elevated towards the middle;
but in the snails and slugs (Pudmonata)
(Fig. 171) the eyes are elevated on the
extremities of a second, longer pair of
tentacles (oc. zent) placed behind the first.

The mantle is usually developed into a
fold, the mande-flap, originally posterior,
but subsequently becoming shifted round
to the right-hand side. This covers over
a cavity, the manitle-cavity, situated ante-
riorly, in which are situated the anal and
nephridial apertures and the ctenidia. The
edges of the mantle-Alap may become united
together in such a way as to form a cham-
ber opening on the exterior by a compara-
tively narrow opening. In many the edges
of this aperture are drawn out into a spout-
like prolongation open ventrally, the
siphon, which lies in the corresponding
prolongation of the peristome of the shell,
and serves as a channel for the ingress fic. 175.—Shell of
and egress of water. In some Gastro- 7°7?r cculata.
pods, however, there is no definite mantle-cavity, the anus,
nephridial apertures, and ctenidia merely lying under cover

of a comparatively slightly developed lateral mantle-flap.
U

290 MANUAL OF ZOOLOGY SECT.

The foot varies in the extent of its development in the
different families of the class. It usually presents an
elongated, flat, ventral surface on which the animal creeps

Fic. 176. — Cypreea moneta (Cowrie). Showing the mantle, provided with marginal ‘
tentacles, partly enveloping the shell. Sr, branchia; M, M, mantle; F, foot;
T, tentacles at the edge of the mantle. (From Cooke, after Quoy and Gaimard.)

by wave-like contractions of the muscular tissue. In the
typical Gastropods the foot is usually distinguishable into
three parts, a middle part or mesopodium which is the most

°

oo
pce

2 ac

Fic. 177.—Doris (Archidoris) tuberculata. a, anus; 47, branchie; », penis;
rh, rh, tentacles. (From the Cambridge Natural History.)

important, with a smaller anterior propodium and posterior
metapodium. The whole foot becomes reduced in a few
Gastropods that remain fixed. The metapodium very fre-

XI PHYLUM MOLLUSCA 291

quently bears a disc or stopper, the operculum, usually
horny, or partly calcified, by means of which the aperture
of the shell is closed when the animal is retracted.

In some forms, such as the sea-hares (Apdsza), the foot
develops a pair of lateral lobes, the ef:fodia, which act as
fins; and in the Pteropods (Fig. 178), which are specially
modified for a pelagic existence, these constitute the largest
part of the foot.

The organs of respiration in the majority of the aquatic
Gastropoda are in the form of gills or c/enzdia, usually plume-
shaped appendages consisting of a central stem bearing two

Fic. 178. — Shell-bearing Pteropoda. 7,/, fins; 2, liver; 0, ovary; sh, shell.
(From Cooke, after Souleyet.)

rows of compressed filaments or lamelle, or a single row.
Two ctenidia may be present or only one may be developed;
they are enclosed in the mantle-cavity.

In the Nudibranchs two ctenidia are absent, but their
place as breathing organs is taken by a number of secondary
branchi@, sometimes simple, sometimes branched or pin-
nate processes, which are distributed over the dorsal surface,
as in Zofs, or as in Doris (Fig. 177), forming a circlet
surrounding the anus, or, as in Pleurophyliidia, a row on
each side beneath the mantle-flap.

292 MANUAL OF ZOOLOGY SECT.

In the limpets (/a/e//a and its allies?) (Fig. 179) the
true ctenidia are represented only by a pair of vestiges,
and respiration is carried on by a number of secondary
branchiz (g. 7) in the form of lamellee situated between the
short lateral fold of the mantle and the foot. In the Pul-
monata, and in some members of other groups, ctenidia are
absent, and the mantle-cavity, completely enclosed except

]
i

Fic. 179. — Patella vulgata, seen from the ventral side. /, foot; g./, circlet of
gill lamella; +. ¢, edge of the mantle; 2, attachment muscle; s/, slits in the
attachment muscle; s/, shell; 7, efferent branchial vessel; v', aorta; ve, smaller
vessels. (From the Caméridge Natural History.)

for a small rounded opening, has the function of a pud-

monary sac or lung (Fig. 180), its roof being richly sup-

plied with blood-vessels; in the aquatic forms its function
is apparently as much hydrostatic as respiratory. In some
of the Pulmonata there is a return to a completely aquatic

mode of respiration accompanied by the development of

1 Our common eastern American limpet is Acmea testudinalis,

XI PHYLUM MOLLUSCA 293

secondary gills —vascular processes of the wall of the
mantle-cavity.

Puly

Fic. 180.— Pulmonary cavity and related parts in a slug (Limax). aort, aorta;
aur, auricle; neph, ReBhedinn: peric, pericardium, laid open; px/. ap, pul-
monary aperture; fz/. 7, pulmonary vein with its ramifications; recf, rectum;
ur, ureter; vent, ventricle. (After Pelseneer.)

Digestive Organs. — In many Gastropods there is a long
proboscis capable of being everted and retracted, at the
extremity of which the mouth is placed. A single curved
horny jaw lies on the roof of the buccal cavity in the Pul-
monata; in most marine Gastropoda the place of this is
taken by two lateral pieces.

A characteristic feature of the alimentary canal of the
Gastropoda, which, however, they share with some Amphi-
neura and with the Cephalopoda, is the possession of an
odontophore and radula, situated ina thick-walled chamber,
the duccal cavity, into which the mouth opens. From the
floor of the cavity rises an elevation, the odontophore, which
is somewhat elongated in the direction of the long axis of
the body and compressed laterally. Over the summit of
the odontophore runs longitudinally a narrow strap-like
body, the vadula or lingual ribbon (Fig. 181, rad), beset

294 MANUAL OF ZOOLOGY SECT.

with numerous minute horny or siliceous teeth arranged in
transverse rows. Posteriorly this toothed ribbon extends
into a narrow curved pouch, the vadwlar sac (Fig. 181, rad.
sac), extending backwards from the posterior and lower
aspect of the buccal cavity. Anteriorly it does not extend
beyond the odontophore prominence. The latter contains
cartilages (cart), serving for the support of the whole appa-
ratus, and is capable of being extruded, with the radula
which it bears, through the opening of the mouth by the
contraction of sets of protractor muscular fibres. Inserted

OAT bod.cav

cart rad.sac

Fic. 181. — Triton nodiferus. Diagrammatic longitudinal vertical section of buccal
cavity. dod. cav, body cavity; cart, cartilage of odontophore; zaw, right jaw;
@s, esophagus; rad, radula; vad. sac, radula sac.

into the radula itself are sets of bands of muscular fibres by
which it can be drawn backwards and forwards over the
odontophore as over a pulley, the effect being a rasping of
any hard substance against which it is pressed. The entire
buccal cavity is capable of being drawn forwards towards
the mouth opening, or backwards into the introvert, by thé
contraction of strands of muscular fibres passing from its
wall to the wall of the body.

The heart is enclosed, as in the fresh-water mussel, in a

XI PHYLUM MOLLUSCA 295

cavity, the pericardium. It consists, in nearly all cases, of
only two chambers, an auricle and a ventricle.

The nervous system and organs of special sense are in
most Gastropoda more highly developed than they are in
the fresh-water mussel. There are distinct cerebral and
pleural, as well as pedal and visceral, ganglia. Well-
developed eyes are present in the majority, and there are
otocysts, osphradia or water-testing organs, and usually
olfactory organs in the shape of special groups of cells on
the tentacles.

The nephridia are granular tubes or chambers communi-
cating, as in the fresh-water mussel, with the pericardial
cavity on the one hand, and with the exterior on the other.
Two nephridia right and left may be present, or only one.

The sexes are separate in some Gastropoda; in others,
such as the snails and slugs, they are united; and in the
latter case their structure is highly complex. The larva is
a Trochosphere, which subsequently develops into a form
known as-the Veliger. In the Veliger the prototroch, or
ciliated pree-oral ridge of the Trophosphere, becomes drawn
out into a bilobed flap bordered with strong cilia. There
is a shell, a distinct foot bearing an operculum, and ten-
tacles and eyes are present on the head-region. The shell
is at first of simple conical form and the anus is placed in
the middle line posteriorly. It is only as development
advances that one side of the body becomes more rapidly
developed than the other, and the anus becomes shifted
forwards, the shell at the same time in the great majority
taking on a spiral form, and the visceral prominence
enclosed within it acquiring a corresponding shape.

Two main divisions or sub-classes of the Gastropoda are
recognised — the Streptoneura and the Euthyneura. The
former comprises the majority of the marine univalves,

296 MANUAL OF ZOOLOGY SECT.

such as the limpets, ear-shells, cowries, tritons, whelks, and
cones. The latter includes the water-breathing sea-hares
and nudibranchs and the air-breathing snails and slugs.
The chief general points of distinction between the two
groups are that in the Streptoneura the visceral nerve-cords
are twisted into a figure 8, and the sexes are separate,
while in the Euthyneura the twisting of the nerve-cords is
absent and the sexes are united in the same individual.

Only a few aberrant families of Gastropoda are parasites.
Most are aquatic, all the most primitive forms being in-
habitants of the sea. Of the marine families the majority
move by creeping over the sea-bottom, some burrowing in
mud or sand, some in solid rock; some are able to float in
a reversed position, adhering to frothy mucus secreted by
the glands of the foot; certain exceptional forms such as
Vermetus are fixed in the adult condition by the substance
of the shell. A few families—the Heteropoda and the
Pteropoda— are specially modified for a pelagic mode of
existence, and swim through the water by flapping move-
ments of the lobes of the foot, which act as fins. Gastro-
pods are found at considerable depths — up to nearly three
thousand fathoms— in the ocean. Many forms, however,
are inhabitants of fresh water, while many Pulmonata are
terrestrial, and occur even towards the summits of the
highest mountains.

4. THE CEPHALOPODA

The class Cephalopoda, including the cuttle-fishes, squids,
Octopi, argonauts, and Nautili, is the highest of the Mollusca,
its members being very much more active and powerful
in their movements than the rest of the Mollusca, and much
more highly endowed as regard their higher senses. The

XI PHYLUM MOLLUSCA 297

body (Figs. 182, 183, 185, 187) is bilaterally symmetrical.
The foot, instead of extending along the ventral surface

Fic. 182. —Sepia cultrata.: Entire animal viewed from the dorsal aspect. New
Zealand.

of the body in the region behind the mouth, as it does in
Pelecypoda and Gastropoda, occupies a more anterior posi-

298 MANUAL OF ZOOLOGY SECT.

tion, and surrounds the mouth. A distinct head is pres-
ent, and the foot assumes the appearance of a system of
appendages of the head. In the cuttle-fishes (Fig. 182),

Jas inf

Fic. 183.— Nautilus pompilius, diagrammatic lateral view of a female specimen
enclosed in its shell. cart, cartilage; ctex, ctenidia; a, hood; zz/, funnel;
Jaws, jaws; mant, mantle: want’, dorsal mantle-fold overlapping the coil of the
shell; zs, position of lateral mass of muscle; zzd, nidamental glands; seft,
first septum; szf/, siphuncle. (After Keferstein.)

squids (Fig. 187), Octopi, and Argonauts (constituting the
sub-class Dibranchiata) the main part of the foot is composed

XI PHYLUM MOLLUSCA 299

of either eight or ten long, highly extensible and contractile
appendages, the arms, the inner surfaces of which are beset
with numerous suckers, rendering them powerful grasping
organs. These are arranged in a circlet surrounding the
mouth. The posterior part of the foot appears to be repre-
sented by the fumne/, a wide tube through which water is

sn

Fic. 184. — Section of the shell of Nautilus pompilius, showing the septa (s, s), the
septal necks (s. 2., s. 2.), the siphuncle (sz, represented by dotted lines), and the
large body-chamber (ch). (From the Caméridge Natural History.)

driven out from the mantle-cavity. In the Nautili (Fig. 183),
(sub-class Tetrabranchiata), the place of the arms with their
suckers is taken by a number of lobes bearing sheathed
tentacles surrounding the mouth, and a funnel is also pres-
ent, though it does not form a complete tube.

300 MANUAL OF ZOOLOGY SECT.

To compare such a cephalopod as a cuttle-fish or squid
with a fresh-water mussel or a snail, it is advisable to place
it in a position which it quite naturally assumes when not
swimming, with the head and its arms downwards and
the body sloping away from this upwards and backwards.
In this position we distinguish antero-dorsal and postero-
ventral surfaces, oral and aboral extremities, and right and
left borders. A shell is present in nearly all Cephalopods,
but is only external in the female argonaut and in Nautilus.
In the latter (Fig. 184) it is in the form of a flat spiral, the
interior of which is divided by a series of transverse partitions
or septa into a corresponding series of chambers. The last
chamber opens widely on the exterior, and this alone lodges
the body of the animal, the remaining chambers being filled
with gas.

Perforating the middle of all the septa in succession is a
spiral tube — the szphwncle— continuous with the centro-
dorsal region of the visceral prominence. In the course
of its growth the body of the Nautilus shifts forwards at
intervals into a newly formed chamber, and a new sep-
tum is formed closing the latter off from the cavity last
occupied.

The Nautilus inhabits the coral reefs of the Pacific, at a
depth of a few fathoms. Of existing Dibranchiata, Sprrula
(Fig. 185) alone has a shell comparable to that of Nautilus.
The shell of Spirula is of spiral form, the turns of the spiral,
however, not being in close contact. Internally it is divided
into chambers by a series of septa, and these are perforated
by a siphuncle. Again, as will be seen by comparing Figs.
183 and 18s, the relation of the soft parts to the shell is the
reverse of what obtains in Nautilus, the shell of Spirula curv-
ing backwards, that of Nautilus forwards. Moreover the
shell of Spirula is an internal structure, being almost com-

XI PHYLUM MOLLUSCA 301

pletely covered by the mantle. Its shell has been found
cast ashore on Nantucket.

In the other Dibranchiata the shell
may consist of three parts, — a horny
pen or pro-ostracum, a calcareous
guard, and a part termed the phrag-
mocone. ‘The last, which alone repre-
sents the shell of Spirwla, has the
form of a cone divided internally by
a series of septa perforated by a si-
phuncle. These parts are most com-
pletely developed in the extinct genus
Lelemnites, in which the shell con-
sists of a straight, conical, chambered
phragmocone, with a siphuncle, en-
closed in a calcareous
sheath, the guard, pro- b =
duced into a horny or eee as

sucker; f, funnel; 5, so,

calcareous plate, the projecting portions of the

shell, the internal part of
pro-ostracum. In the — whichis indicated by dotted

cuttle-fish of the Medi- ines (From Cooke.)
terranean Sea (Sefza) the shell is a leaf-like
body, with a rounded and comparatively
broad oral end, and a narrower aboral pro-
vided with a sharp projecting spine. The
main mass of the shell consists of numerous,
closely arranged, thin laminz of calcareous
composition, between which are interspaces
containing gas. The spine-like projecting
point represents the guard, and the main

Fic. 186.—Shell of

Sepia cultrata, substance of the shell is to be looked upon

posterior view,

reduced. as the pro-ostracum and phragmocone, the
septa of the latter being represented by the calcareous

302 MANUAL OF ZOOLOGY SECT.

lamellez. In Zoégo’ (the squids) the shell (Fig. 187, B) is
long, narrow, and completely horny; it corresponds to the
pro-ostracum, the phragmocone being entirely absent.

Fic. 187. —Loligo vulgaris. A, entire animal, dorsal view; B, horny internal shell
or pen. (From Keferstein.)

In Octopus the shell is represented only by a pair of
rudiments with which muscles are connected. In Avgonauta
there is no shell in the male, but the female has an external
shell (Fig. 188) of a remarkable character. This is a deli-

1 Our common American species is Loligo pealit.

XI PHYLUM MOLLUSCA 303

cate spiral structure, the internal cavity of which is not
divided into chambers. It is not secreted by the mantle
like the shells of other Mollusca, but by the surfaces of a
pair of the arms ending in expanded disc-like extremities,
which become applied to its outer surface; its chief func-
tion is to carry the eggs. The argonaut inhabits deep water,
70 to 100 miles off the coast of New England, its shells
being in very rare cases found cast ashore on our coast
south of Cape Cod.

Fic. 188. — Shell of Argonauto argo.

In addition to the shell there is in all the Cephalopoda an
internal skeleton of cartilage supporting and protecting the
nerve-centres and other parts.

The cuttle-fishes and other Dibranchiata when alive will
be observed to undergo frequent changes of colour, and
blushes of different hues are to be noticed passing over the
surface. These are due to the presence of numerous con-
tractile, pigment-containing cells or chromatophores, situated
in the deeper layers of the integument over the entire

304 MANUAL OF ZOOLOGY SECT.

surface, which contract and expand under nervous influence
(Fig. 189).

On the postero-ventral aspect of the body the mantle
encloses a wide cavity, the manéle-cavity (Figs. 190, 191),
in which the ctenidia are lodged, and on the wall of which
are situated the anal, excretory, and reproductive apertures.
The mantle-cavity communicates at its oral end by a wide
slit with the exterior; but this is capable of being closed,

Fic. 189. —Chromatophore 71 Sepia, magnified. wc, nuclei in wall of sac; pzgmz,
pigment; vad. mus, sadiating strands of muscle. (After Vogt and Jung.)

so that, when the walls of the cavity contract, a stream of
water is ejected through the funnel, and the animal is
propelled in the aboral direction. Swimming is also effected
in the Dibranchiata by means of a pair of fins in the shape
of muscular, lateral flaps. The ctenidia (cm) are plume-
like, and are either two (Didranchiata) or four (TZetra-
branchiata) in number.

The mouth is provided with a pair of horny or calcified
jaws (Fig. 192, B) similar in shape to the jaws of a parrot.
The buccal cavity contains an odontophore. Opening into

XI PHYLUM MOLLUSCA 395

infeart
mantl.cart A ie
Ls ha
liv Ak L.sb.g
i : TRULS
ee pee] recé
inkd. E ee lneple
: Ee ovid
acnid i ster
L.ridk

Fic. 190. — Sepia cultrata, female seen from the posterior aspect, the wall of the
mantle-cavity divided along the middle line and the two flaps thus formed spread
out so as to expose the contents. ac. xza, accessory nidamental glands; az,
anal aperture with its lateral appendages; /, membranous fold attaching the
ctenidium to the wall of the mantle-cavity ; 7/, external opening of funnel: zf.
cart, infundibular cartilage; zz. s, ink-sac; zvk. a, ink-duct; Zzg, ligamentous
band which extends from the anterior wall of the mantle-cavity to the ovary, cut
across; /7v, liver; 2. cten, left ctenidium: 7. wep, left nephridial aperture : /.27d,
left nidamental gland; 2. s¢. g, left stellate ganglion: ant. cart, mantle cartilage 5
mo, mouth; wes, neck muscles; ov, ovary ; ov7d, oviduct; vec, rectum.

x

306 MANUAL OF ZOOLOGY SECT.

the terminal part of the intestine close to the anal aperture
is the duct of a peculiar gland — the zvk gland (Fig. 193, 7).
This secretes a black substance, the 77%, which is discharged
when the animal is irritated or alarmed, and mingling with
the water in the mantle-cavity is discharged as a dark cloud,
under cover of which the animal may elude the pursuit of
an enemy.

The heart and vascular system reaches a high stage of
development. ‘The heart consists of a median ventricle and

Fic. 191. — Nautilus pompilius, interior of mantle-cavity of a male specimen with
the postero-ventral wall reflected. a. /. neph.af, oral left nephridial aperture ;
an, anus; cten, ctenidia ; 2. 3 ap, left reproductive aperture ; 2. azz. os, left oral
osphradium ; 2 visc. ap, left viscero-pericardial aperture ; sat, flaps of mantle;
pen, penis; p. 2. neph. ap, aboral left nephridial aperture; p. 7. neph. ap, aboral
right nephridial aperture ; fost. os, aboral osphradia; 7. vzsc. ap, right viscero-
pericardial aperture.

two or four elongated lateral auricles or branchio-cardiac
vessels conveying the blood from the ctenidia to the ventricle.

The nervous system is highly developed, and its principal
central parts, representing the cerebral, pedal, and visceral
ganglia of other molluscs, with their commissures and con-

XI PHYLUM MOLLUSCA 307

nectives, form a ring round the gullet. There are a pair of
large eyes situated on the head. In the cuttle-fishes and
other Dibranchiata these have a highly complicated structure,

Fic. 193. — Sepia officinalis, enteric
canal. a, anus; 8. d, one of the
bile ducts; 4 #2, buccal mass; c,
caecum; 7, ink-sac; 7. d, ink-duct;
J, jaws; @, 2, liver lobes; @, cesoph-
agus; #, pancreatic appendages!;

Fic. 192. —Sepia officinalis, jaws. A, zz yr, rectum; s. g, salivary glands;
stfu; B, removed and slightly enlarged. st,stomach. (From the Camébridge
(From the Cambridge Natural History.) Natural History.)

and contain representatives of all the principal parts of the
eye of a fish or other vertebrate. In Nautilus the eye is of

1 This organ is by Sedgwick regarded as renal in its nature, being the
unpaired portion of the kidneys. (See Sedgwick's Zext-book of Zoology,

i, PP. 433, 437-)

308 MANUAL OF ZOOLOGY SECT.

much simpler structure. ‘There is a pair of otocysts, and
sensory processes or depressions supposed to be olfactory
are also present. Osphradia occur only in Nautilus.

There are either two (Dibranchiata) or four (TZefra-
branchiata) nephridia, which are in the form of sacs opening
into the mantle-cavity, and in the Dibranchiata communi-
cating with the pericardium. ‘Through each of these runs
one of the principal veins, round which the secreting tissue
of the nephridium is aggregated.

The sexes are distinct. The ova are always large, con-
taining a large quantity of yolk. No metamorphosis, such
as is general in other groups of Mollusca, is known to occur
in any Cephalopod.

The Cephalopoda are all marine, and range from tidal
limits to a considerable depth. Squids swim like fishes in
schools, rising to the surface and darting out of the water,
and sometimes leaping so vigorously as to fall on the decks
of large vessels. A large number are pelagic. ‘They are,
nearly without exception, carnivorous. In length they range
from an inch or two to as much as fifty feet—the gigantic
members of the group, such as Architeuthis, being by a long
way the largest of invertebrate animals, and like the other
classes of Mollusca they are most abundant in tropical and
warm temperate seas.

As already stated, the class is divided into two sub-classes,
the Dibranchiata and the Tetrabranchiata — the latter com-
prising only the Nautili (in addition to many fossil forms),
the former including all the rest of the living members of
the class. In the former the forefoot assumes the character
of acirclet of either eight or ten arms bearing suckers sur-
rounding the mouth. The funnel forms a complete tube.
The shell is usually internal ; when external its cavity is not
divided by septa. There are two ctenidia, two nephridia,

XI

PHYLUM MOLLUSCA 309

and two auricles. An ink gland is present. In the latter,
on the other hand, the forefoot has the character of lobes
bearing tentacles; the funnel does not form a complete

Fic. 194. — Oral surface of a male (A) and female (B) Nautilus pompilius in an

expanded state, 4 natural size, linear. a, shell; 4, external annular lobe carry-
ing 1g tentacles on each side, and anteriorly enlarged to form the hood; c, right
and left inner lobes, each carrying 12 tentacles in the female, and divided in the
male into two parts; a, posterior inner lobe; e, oral cone; /, tentacles of the
outer annular lobe projecting from their sheaths; g, two anterior tentacles of this
lobe belonging to the hood; 7, superior, &, inferior, ophthalmic tentacle; 7, eye;
2, lamellated organ on the posterior inner lobe of the female; 2, paired lami-
nated organ on each side of the posterior inner lobe of the female; 0, funnel;
p, spadix; g, antispadix. (After Bourne, from Sedgwick.)

tube. There is an external, chambered, spiral shell. There
are four ctenidia, four nephridia, and four auricles. The
ink gland is absent.

SECTION XII.— PHYLUM CHORDATA

THE Phylum Chordata comprises all the vertebrate ani-
mals (fishes, amphibians, reptiles, birds, and mammals),
together with the Urochorda or Ascidians, and the Adelo-
chorda or Balanoglossus and its allies. The name Chordata
is derived from one of the most important of the few but
striking common features by which the members of this
extensive phylum are united together—the possession,
either in the young condition, or throughout life, of a
structure termed the chorda dorsalis or notochord. This is
a cord only of cells, typically developed from the endoderm,
extending along the middle line on the dorsal side of the
enteric cavity, and on the ventral side of the central part
of the nervous system. It becomes enclosed in a firm
sheath and forms an elastic supporting structure. In the
Vertebrata (with the exception of Amphioxus and the lam-
preys and hag fishes) it becomes in the adult replaced more
or less completely by a segmented bony or cartilaginous
axis — the spinal or vertebral column. Another nearly uni-
versal common feature of the Chordata is the perforation
of the wall of the pharynx, either in the embryonic or larval
condition only, or throughout life, by a system of clefts —
the branchial clefts; and a third is the almost universal
presence at all stages, or only in the larva, of a cavity or
system of cavities, the zew7oce@/e, in the interior of the body,

lying above the central nervous system.
310

SECT. XII PHYLUM CHORDATA

1. THE ADELOCHORDA

Of somewhat doubtful relationships both to
one another and to the other Chordata are cer-
tain remarkable marine animals which have
been grouped together under the name of
Hemichorda or Adelochorda. These are
Balanoglossus and its allies, which occur in
shallow water on the coasts of most of the
warmer parts of the world, and two are deep-
sea animals, Rhabdopleura and Cephalodiscus.

Balanoglossus (Fig. 195) is a soft-bodied,
cylindrical, worm-like animal, the surface of
which is uniformly ciliated. It is divisible into
three regions: in front there is a large, club-
shaped, hollow organ—the prodoscis ; imme-
diately behind the proboscis and encircling its
base is a prominent fold—the co//ar,; the
third region or ¢vwzh is long and nearly cylin-
drical, but somewhat depressed.

Balanoglossus lives in the sea, burrowing
in sand or mud by means of its proboscis. It
occurs as far north as Salem, Mass., between
tide-marks. Numerous glands in the integu-
ment secrete a viscid matter to which grains
of sand adhere in such a way as to form a
fragile temporary tube. The proboscis (Fig.
195, pr, Fig. 196, prob) has muscular walls;
its cavity opens on the exterior usually by a
single minute aperture—the froboscis pore
(Fig. 196, prod. po) —rarely by two. The
collar (Fig. 195, co) is also muscular, and
contains one cavity or two (right and left)
separated from one another by dorsal and
ventral mesenteries, and completely cut off
from the proboscis. The collar cavity com-
municates with the exterior by a pair of collar
pores —ciliated tubes leading into the first
gill-slit or first gill-pouch.

\)

|

2
2
<
=
=
=
>=
~
4

>

311

ges; ef, prominences formed by

, collar; gen, genital rid

_6r, branchial region; co
hepatic coeca; f7, proboscis. (After Spengel.)

Entire animal.

Fic. 195. — Balanoglossus.

312 MANUAL OF ZOOLOGY SECT.

On the dorsal surface of the anterior part of the trunk is a double
row of small slits —the gid/-sti¢s (Fig. 195, 6r,) —each row situated in
a longitudinal furrow; these slits increase in number throughout. The

vent wn

veU.v

Fic. 196. —Balanoglossus. Diagrammatic sagittal section of anterior end. card.
s, cardiac sac; a@zv, diverticulum (supposed notochord); dors. 2, dorsal nerve
strand; dors. sin, dorsal sinus; dors. v, dorsal vessel; 720, mouth; prob, pro-
boscis; #706. fo, proboscis pore; 70d. skel, proboscis skeleton; vent. 2, ven-
tral nerve strand; vet. v, ventral vessel. (After Spengel.)

ccelom of the trunk is divided into two lateral closed cavities by a verti-
cal partition (dorsal and ventral mesenteries).

The mouth (Fig. 196, 7o,) is situated ventrally at the base of the
proboscis, within the collar. Into the dorsal half of the anterior portion

XII PHYLUM CHORDATA 313

of the alimentary canal open the internal gill-openings. The gill-
pouches are supported by a chitinoid skeleton consisting of a number
of separate parts.

The posterior part of the alimentary canal is a nearly straight tube
with, in its middle part, paired hepatic caca (Fig. 195, hep), which
bulge outwards in a series of external prominences. Posteriorly it
terminates in an anal aperture situated at the posterior extremity of the
body. Throughout its length it lies between the dorsal and ventral
divisions of the vertical partition, which act as mesenteries.

In front the dorsal wall of this anterior portion of the alimentary
canal gives off a diverticulum (Fig. 196, div), the lumen of which
extends nearly to the anterior end. This diverticulum consists of
epithelium with gland cells and of a sort of retiform connective tissue;
it is supposed to be homologous with the sotochord of the typical
Chordata.

There is a blood-vascular system with dorsal (dors. v) and ventral
(vend. v) longitudinal trunks. The nervous system consists of dorsal
(dors. x) and ventral strands (ven. 2), which extend throughout the
length of the body. The part of the dorsal cord which lies in the collar
lies deeper than the rest, and contains a canal or a number of spaces.
Between the collar and the trunk the dorsal and ventral strands are
connected by a ring-like thickening. There are no organs of special
sense,

The sexes are separate; the ovaries and testes are saccular organs
arranged in a double row along the branchial region of the trunk and
further back; they open on the exterior by a series of pores.

The course of the development differs in different species. In some
it is comparatively direct; in others there is a metamorphosis. In the
latter case the embryo assumes a larval form termed Zornarda, which
is somewhat like an Echinoderm larva, with a pair of ciliated bands,
one of which is considered prz-oral, and the other post-oral, and an
independent circlet of strong cilia at the posterior end.

Usually associated with Balanoglossus are two aberrant animals —
Cephalodiscus and Rhabdopleura — formerly regarded as Polyozoa.
These both resemble Balanoglossus in having the body divided into
three parts or regions —a proboscis, with a proboscis cavity, a collar
with a collar-cavity communicating with the exterior by a pair of collar-
pores, and a ¢rank with two distinct lateral cavities; and in the presence
of a structure resembling a notochord with the same relations to the

314 MANUAL OF ZOOLOGY SECT.

nervous system as in Balanoglossus. They both differ from Balano-
glossus in having the alimentary canal bent on itself, so that the anal
opening is situated not far from the mouth, in the presence of tentacles
arising from the collar; and in the comparatively small size of the
proboscis.

2. THE UROCHORDA

Still more unlike a vertebrate in general appearance than Balano-
glossus, and yet, as the earlier stages show, indubitably to be assigned
to the Chordate phylum, are the Ascidians or Sea-squirts and their
allies.

Sea-squirts are familiar objects on rocky sea-
shores, where they occur often in large associa-
tions, adhering firmly to the surface of the rock.
They also live free in sand and in mud, at differ-
ent depths, some being deep-sea forms. When
touched the Ascidian ejects with considerable
force two fine jets of sea-water, which are found
to proceed from two apertures on its upper end.
The shape of the Ascidian, however, can only
be profitably studied in the case of specimens
that are completely immersed in the sea-water,
specimens not so immersed always undergoing
contraction. In an uncontracted specimen!
(Fig. 197) the general shape is that of a short
cylinder with a broad base by which it is fixed
to the rock. The free end presents a large

2 rounded aperture, and some little distance from
iis aie it on one side is a second of similar character.
Fic. 197.--Ascidia, en- || Y
tire animal seen from The former aperture is termed the orad, the
tvnodnay latter the @éria/. A strong current of water
will be noticed, by watching the movements of
floating particles, to be flowing steadily in at the former and out of the
latter. When the animal is removed from the water both apertures

become narrowed, so as to be almost completely closed, by the contrac-

1 The European species, whose anatomy is here described, is approxi-
mately represented by our common large Ascidia callosa, which lives in
deep water off the Maine coast.

X11 PHYLUM CHORDATA 315

tion of sphincters of muscular fibres which surround them. At the same
time the walls of the body contract, streams of water are forced out
through the apertures, and the bulk becomes considerably reduced.

Fic. 198. — Dissection of Ascidia from the right-hand side. The greater part of the
test and mantle has been removed from that side so as to bring into view the
relations of these layers and of the internal cavities and the course of the alimen-
tary canal, etc. av, anus; aty. af, atrial aperture; exd, endostyle; gox, gonad;

gonod, gonoduct; Avf, hypophysis; Ay. d, duct of hypophysis; #a7t, mantle;

ne. gn, nerve-ganglion; ws. af, aperture of cesophagus; ov. af, oral aperture;
(After Herdman.)

ph, pharynx; stom, stomach; fezt, tentacles; zest, test.

The outer layer of the body-wall is composed of a tough translucent
substance forming a thick ¢ées¢ or tunte (Fig. 198, ¢est). This proves,

316 MANUAL OF ZOOLOGY SECT.

when analysed, to consist largely of the substance ce//ulose, which has
already been referred to (p. 36) as a characteristic component of the
tissues of plants, and which is rare in its occurrence in the animal
kingdom.

When the test is divided (Fig. 198), the soft wall of the body or
mantle (mant), as it is termed, comes into view, and the body is
found to be freely suspended within the test, attached firmly to the lat-
ter only round the oral and atrial apertures. The mantle follows the
general shape of the test, and at the two apertures is produced into short
and wide tubular prolongations, which are known respectively as the ova/
and atrial siphons (Fig. 199, atr. siph). These are continuous at their
margins with the margins of the apertures of the test, and round the
openings are the strong sphincter muscles by which closure is effected.
Within the body-wall is a cavity, the atrzal or peribranchial cavity
(a¢r. cav) communicating with the exterior through the atrial aperture.

The oral aperture leads by a short and wide oral passage into a
chamber of large dimensions, the pharynx or branchial chamber (ph).
This is a highly characteristic organ of the Urochorda. Its walls are
pierced by a number of slit-like apertures, the stigmata (Fig. 199, stig)
arranged in transverse rows. Through these the cavity of the pharynx
communicates with the atrial or peribranchial cavity, which completely
surrounds it except along one side. The edges of the stigmata are
beset with numerous strong cilia, the action of which is to drive currents
of water from the pharynx into the atrial cavity. It is to the move-
ments of these cilia lining the stigmata that are due the currents of
water already mentioned as flowing into the oral and out of the atrial
apertures, the ciliary action drawing a current in through the oral
aperture, driving it through the stigmata into the atrial cavity, whence
it reaches the exterior through the atrial aperture. The stigmata are
all vertical in position; those of the same row are placed close together,
separated only by narrow vertical bars; neighbouring rows are sepa-
rated by somewhat thicker horizontal bars ; in all of these bars run
blood-vessels.

It has been already mentioned that the atrial cavity does not com-
pletely surround the pharynx on one side. This is owing to the fact
that on the side in question, which is ventral in position, the wall of the
pharynx is united with the mantle along the middle line. Along the
line of adhesion the inner surface of the pharynx presents a thickening
in the form of a pair of longitudinal folds separated by a groove. To

XII

PHYLUM CHORDATA 317

this structure, consisting of the two ventral longitudinal folds with the
groove between them, the term ezdostyle is applied. The cells covering

Fic.

the

onsiph fx
Zent ri | ; neg
e YP tigm
test fig eae
y li) ul i Lh i i ‘\ alr. siph
cre Fe EU OOOO Gf
OD in GUE IN eee
mant a Cia HOO f) Weta iut fi i E GaSe
is Li ih a He Lut iy f Boece
ye tt i Gin Guu vy IL Beck
ventv & i | ee elt y
iz ‘
Wa Ue @ a
7 dl + visce.br
oncar \ TA z
| aE: 4—o0e9
stom
ht

ees

cardvise

199. — AScidia, diagram of longitudinal section from the left-hand side, the test
and mantle removed. adv. cav, atrial cavity; atv. szph, atrial siphon; ‘br. car,
branchio-cardiac vessel; card. visc, cardio-visceral vessel; gonod, gonoduct;
ht, heart; Ayp, hypophysis; mant, mantle; 2. g7, nerve-ganglion; @s, cesopha-
gus ; ov, ovary; vect, rectum; sitzg, stigmata; stom, stomach; Zext, tentacles;
test, testis; ty. v, transverse vessel ; vent. U, ventral vessel; wzsc. br, viscero-
branchial vessel. (After Herdman. )

endostyle are large cells of two kinds — ct/tated cells and gland cells,

—the former beset at their free ends with cilia, the action of which is

318 MANUAL OF ZOOLOGY SECT.

to drive floating particles that come within their influence outwards
towards the oral aperture, the latter secreting and discharging a viscid
mucous matter. Anteriorly the endostyle is continuous with a ciliated
ridge which runs circularly round the anterior end of the pharynx. In
front of this circular ridge, and running parallel with it, separated from
it only by a narrow groove, is another ridge of similar character; these
are termed the per?-pharyngeal ridges, the groove between them is the
peri-pharyngeal groove. Dorsally, 7.c., opposite the endostyle, the
posterior peri-pharyngeal ridge passes into a median, much more
prominent, longitudinal ridge, the dorsal /amina, which runs along the
middle of the dorsal surface of the pharynx to the opening of the
cesophagus. The mucus secreted by the gland cells of the endostyle
forms viscid threads which entangle food-particles (microscopic organ-
isms of various kinds); the cilia of its ciliated cells drive these forwards
to the peri-branchial groove, around which they pass to the dorsal
lamina, and the cilia of the cells of the latter drive them backwards to
the opening of the cesophagus.

Some little distance in front of the anterior peri-pharyngeal ridge, at
the inner or posterior end of the oral siphon, is a circlet of delicate
tentacles (Fig. 198, zen).

The cesophagus leads from the pharynx (near the posterior end of
the dorsal lamina) to the stomach, which, together with the intestine,
lies embedded in the mantle on the left-hand side. The stomach is a
large fusiform sac. The intestine is bent round into a double loop, and
runs forwards to terminate in an ava/ aperture, situated in the atrial
cavity. There is no liver; but the walls of the stomach are glandular,
and a system of delicate tubercles which ramify over the wall of the
intestine is supposed to be of the nature of a digestive gland.

The Ascidian has a well-developed blood system. The heart is a
simple muscular sac, situated near the stomach in a pericardium forming
part of the primitive ccelom. Its mode of pulsation is very remarkable.
The contractions are of a peristaltic character, and follow one another
from one end of the heart to the other for a certain time; then follows
a short pause, and, when the contractions begin again, they have the
opposite direction. Thus the direction of the current of blood through
the heart is reversed at regular intervals.

The nervous system is of an extremely simple character. There is a
single nerve-ganglion, which lies between the oral and atrial apertures,
embedded in the mantle. This is elongated in the dorso-ventral direc-

XII PHYLUM CHORDATA 319

tion, and gives off at each end nerves which pass to the various parts
of the body.

Lying on the ventral side of the nerve-ganglion is a gland — the sz-
neural gland, A duct runs forward from it and opens into the cavity
of the pharynx; the termination of the duct is dilated, and this terminal
dilatation is folded on itself in a complicated way to form a tubercle,
the dorsal tubercle, which projects into the cavity of the pharynx.

The excretory system is represented by a single nephridium, which
consists of a mass of clear vesicles, without a duct, lying in the second
loop of the intestine.

The sexes are united. The ovary and the testis are closely united
together, and lie on the left-hand side of the body in the intestinal
loop. Continuous with the cavity of each is a duct — oviduct or spermi-
duct, as the case may be — which opens into the atrial cavity close to
the anus.

So far we have met with no feature that could with certainty be looked
upon as indicating alliances with the Chordata. But, though the adult
Ascidian is devoid of any such features, there is in the course of its life-
history a larval stage in which Chordate affinities are unmistakably
indicated. In this stage the young Ascidian is free-swimming, and in
general shape bears some resemblance to a minute tadpole, consisting
of an oval trunk and a long, laterally compressed tail. The tail is fringed
with a caudal fin, which is merely a delicate outgrowth of the thin test
covering the whole of the surface; running through the delicate fringe
are a series of strive presenting somewhat the appearance of the fin-rays
of afish’s fin. At the anterior end are three processes, the adhesive
papille. In the axis of the tail is the notochord (z0/0), which at this
stage consists of a cylindrical cord of gelatinous substance enclosed in a
layer of cells. Parallel with this runs, on the dorsal side, the narrow cau-
dal portion of the nerve-cord, and at the sides are bands, or muscular
fibres. Inthe trunk the nerve-cord is dilated, and, further forwards,
expands into a vesicle, the sevse vesicle (sens. ves) with an otocyst (0/0)
and a well-developed eye (eve). The enteric canal is distinguishable
into pharynx, cesophagus, stomach, and intestine. The pharynx opens
on the exterior by the mouth: in its ventral floor the endostyle (ezd)
has become developed; its walls are pierced by stigmata, the number
of which varies; a ciliated sac opens into it below the trunk part of
the nerve-cord. The atrial cavity has become formed round the phar-
ynx, and opens on the exterior by asingle aperture (a¢). The heart

320 MANUAL OF ZOOLOGY SECT.

and pericardial cavity have become developed. In this tailed, free-
swimming stage the larva remains only a few hours; it soon becomes
fixed by the adhesive papilla, and begins to undergo the retrogressive
metamorphosis by which it attains the adult condition.

The chief changes involved in the retrogressive metamorphosis (Figs.
200 and 201) are increase in the number of pharyngeal stigmata, the
diminution, and eventually the complete disappearance, of the tail with
the contained notochord and caudal part of the nerve-cord, the dis-
appearance of the eye and the otocyst, the dwindling of the trunk part
of the nervous system to a single ganglion and the formation of the
reproductive organs. Thus, from an active, free-swimming larva, with
well-developed organs of special sense, and provided with a notochord
and well-developed nervous system, there is a retrogression to the fixed

med alr sens.ves eil.gr

Fic. 200 — Free-swimming larva of Ascidia mammillata, lateral view. adh, adhe-
sive papillz; a/7, alimentary canal; a¢,, atrial aperture; c7/. gr, ciliated groove;
end, endostyle; eye, eye; med, nerve-cord; xoto, notochord; ofo, otocyst; sens.
ves, sense vesicle; s¢zg, earliest stigmata. (From Korschelt and Heider, after
Kowalewsky.)

inert adult, in which all the parts indicative of affinities with the Ver-
tebrata have become aborted.

A remarkable feature of the Ascidians is that, though many remain
simple, others give rise to colonies by a process of budding. In some
of these compound forms, distinguished as the Composite Ascidians, the
tests of the zooids are united together to form a mass of gelatinous
consistency in which the zooids of the colony lie embedded (Fig. 202).
These compound forms, such as Amaroucium, are common on the New
England coast in shallow water.

A minute animal which swims about in the surface waters of the sea
has in most respects an extremely close resemblance to the tailed larva

XII PHYLUM CHORDATA 321

Fic. 201.— Diagram of the metamorphosis of the free, tailed larva into the fixed
Ascidian. A, stage of free-swimming larva; B, larva recently fixed; C, older
fixed stage. adh, adhesive papilla; atr, atrial cavity; cz. gr, ciliated groove;
end, endostyle; At, heart; med, ganglion of trunk; 2. gz, nerve-ganglion; zofo0,
notochord: ov, oral aperture; rect, rectum; sews. ves, sense vesicle; st7g, stig-
mata; sto/, stolon; ¢, tail. (From Korschelt and Heider, after Seeliger.)

Y

322 MANUAL OF ZOOLOGY SECT.

of an Ascidian, being of similar shape, with a rounded body and a long
tail-like appendage attached to the ventral side, and with a distinct
notochord. This, however, is an adult animal, known as Appendicula-
ria. It never becomes fixed and retains permanently its chordate
characteristics.

Fic. 202. — Botryllus violaceus. 7, oral apertures; c/, opening of common cloacal
chamber. (After Milne-Edwards.)

A number of other Urochorda are permanently free-swimming, but
these are all almost, if not quite, as thoroughly metamorphosed as the
Ascidians, so that their true affinities only become clear when their
life-histories are followed.

3. THE VERTEBRATA

The Sub-phylum Vertebrata comprises the lancelets, the
lampreys and their allies, the fishes, the amphibians, the
reptiles, the birds, and the mammals. The lancelets occupy
an extremely isolated position with regard to the other mem-

XII PHYLUM CHORDATA 323

bers of the sub-phylum, and are best regarded as consti-
tuting by themselves a division, which, for reasons which
will be manifest shortly, is designated Acrania, the rest of
the sub-phylum being known as Cvaniata.

A. THE ACRANIA

This isolated group, the Acrania, comprises only a single family, the
two genera (Branchiostoma and Asymmetron) of which are distin-
guished from one another by comparatively slight differences.

Branchiostoma (more widely known under the name of Amphioxus),
the lancelet, is a small transparent animal, occurring in the sea near
the shore and burrowing in sand; its length does not exceed 5.8 cm.

6 mip

B myom dorsfr. dorsf”

ic. 203. — Amphioxus lanceolatus. A, ventral; B, side view of the entire animal.
an, anus; aff, atriopore; cad. f, caudal fin; ctr, cirri; dors. f, dorsal fin;
dors. f. r, dorsal fin-rays; gov, gonads; #¢//, metapleure; 7zyom, myomeres,
uch, notochord; ov. Ad, oral hood; vent. f, ventral fin; vent. / v, ventral fin-
rays. (After Kirkaldy.)

or less than two inches. Its form will be obvious from Fig. 203. The
body is elongated, pointed at either end, and compressed. The anterior
two-thirds is roughly triangular in transverse section, presenting right
and left sides, inclined towards one another, above, and a convex ven-
tral surface. The posterior third is nearly oval in section, the right
and left sides meeting above and below in a somewhat sharp edge.

Extending along the whole of the dorsal border is a median longi-
tudinal fold, the dorsal fin (dors. f); this is continued round the

324 MANUAL OF ZOOLOGY SECT.

posterior end of the body and extends forwards, as the ventral fin
(vent. f), as far as the spot where the oval gives place to the trian-
gular transverse section. The portion of the continuous median fold
which extends round the pointed posterior extremity of the body is
somewhat wider than the rest, and may be distinguished as the caudal
jin (cd. f). In the anterior two-thirds of the body there is no median
ventral fin, but at the junction of each lateral with the ventral surface
is a paired longitudinal fold, the metapleure (mtpl), which extends
forward to the oral hood mentioned in the next paragraph.

Below the pointed anterior extremity is a large median aperture
surrounded by a frill-like membrane, the oval hood ( or. hd), the edge
of which is beset with numerous tentacles or cirvrz7. The oral hood
encloses a cup-shaped cavity or vestibule, al the bottom of which is the
mouth (Fig. 204, mth). Immediately in front of the anterior termina-
tion of the ventral fin and partly enclosed by the metapleures is a
rounded aperture of considerable size, the a/rzpore (atrp), and a short
distance from the posterior extremity of the body is the azus (an),
placed unsymmetrically on the left side of the ventral fin. The post-
anal portion of the body is distinguished as the ¢az/.

Amphioxus ordinarily lives with the greater part of the body buried
in sand, only the anterior end with the expanded oral hood protruding.
It also swims in the vertical position, and frequently lies on one side
on the sand; it burrows, head foremost, with great rapidity. It occurs
on the American coast as far north as Cape Hatteras. A current of
water is constantly passing in at the mouth and out at the atriopore.

The muscular layer (my) is remarkable for exhibiting metameric
segmentation. It consists of a large number — about sixty — of muscle
segments or myomeres, separated from one another by partitions of
connective tissue, the myocommas, and having the appearance, in a
surface view, of a series of very open V’s with their apices directed
forwards (Figs. 203 and 204).

The chief of the skeletal or supporting structures of the lancelet is
the xotochord (Figs. 203 and 204, ch), a cylindrical rod, pointed at
both ends, and extending from the anterior to the posterior end of the
body in the median plane. It lies immediately above the enteric tract
and between the right and left myomeres. It is composed of a peculiar
form of cellular tissue, known as notochordal tissue, formed of large
vacuolated cells extending from side to side of the notochord, and
having the nuclei confined to its dorsal and ventral regions, Around

XII PHYLUM CHORDATA

these cells is a xotochordal
sheath of connective tissue
which is produced dorsally
into a canal for the ner-
vous system.

The oral hood is sup-
ported by a ring (Fig. 204,
sk) of cartilaginous con-
sistency, made up of sepa-
rate rod-like pieces ar-
ranged end to end, and
corresponding in number
with the cirri.

The pharynx is sup-
ported by delicate oblique
rods of a chitinoid mate-
rial, the gidl-rods (br. r).
The dorsal fin is supported
by a single series, and the
ventral fin by a double
series, of fiz rays (dors.
f- rv), short rods of con-
nective tissue.

The mouth (mh), as
already mentioned, lies at
the bottom of the vestibule

or cavity of the oral hood
(or.hd@). It isa small cir-
cular aperture surrounded
by a membrane, the velum 2
(wv?) acting as a sphincter, §
the free edge of which is F
produced into a number
of velar tentacles (vl. t). §&
The mouth leads into
the largest section of the
enteric canal, the pharynx
(ph), a high compressed
chamber extending through
the anterior half of the

dorsfr coel

HINT

WwW
tN
wm

br, brain;

atrp, atriopore;

; br. sep. 2, secondary branchial lamella; 47. 7. 1, primary; 47. ~. 2,

cent. c, central canal;

cel, celom; dors. f, dorsal fin; dors. fr, dorsal fin-
mith, mouth; »#zyom, myomeres; ch, notochord;

c7r, cirri;

mut, intestine; 27, liver; my
or. f. hd, oral hood; pf, pharynx; s#, skeleton of oral hood and cirri (dotted); sf. cd, spinal

an, anus; afr, atrium; azz’, its posterior prolongation:
; vent. f, ventral fin; vent. fr, ventral fin-ray; vel, velum; v/. ¢, velar tentacles.

br. sep. 1, primary
gon, gonad;

e. Sp, eye-spot;

br. f, brown tunnel;

olf. p, olfactory pit;

: en. ce, encephalocele;

secondary branchial rod; cazd./, caudal fin;
, nephridia;

Fic. 204. — Diagram of the anatomy of Amphioxus.
br. cl, branchial clefts;

326 MANUAL OF ZOOLOGY SECT.

body. Its walls are perforated by more than a hundred pairs of narrow
oblique clefts, the gid/-slzts or branchial apertures (br. c), which place
the cavity of the pharynx in communication with the atrium (see
below). From the posterior end of the pharynx goes off the tubular
intestine (int) which extends backwards, almost in a straight line to
the anus.

On the ventral wall of the pharynx is a longitudinal groove, the
endostyle, lined by ciliated epithelium containing groups of gland-cells.
Like the homologous organ in Ascidia (p. 317), the glands secrete a
cord of mucus in which food particles are entangled and carried by the
action of the cilia to the intestine. A somewhat similar structure, the
chipharyngeal groove, extends along the dorsal aspect of the pharynx;
its sides are formed by ciliated cells, which, at the anterior end of the
groove, curve downwards, as the peri-pharyngeal bands, and join the
anterior end of the endostyle.

From the ventral region of the anterior end of the intestine is given
off a blind pouch, the Aver (27) or hepatic cecum, which extends for-
wards to the right of the pharynx; it is lined with glandular epithelium
and secretes a digestive fluid.

The gid/-slits (6r. cl) are long narrow clefts, nearly vertical in the
expanded condition, but very oblique in preserved and contracted
specimens — hence the fact that a large number of clefts always appear
in a single transverse section (Fig. 205).

The branchial septa or lamelle (Fig. 204, br. sep), or portions of the
pharyngeal wall separating the clefts from one another, are covered
by an epithelium composed, except on the outer face, of greatly elon-
gated and ciliated cells. Each septum is supported towards its outer
edge by one of the chitinoid branchial rods (br. r) already referred
to.

The gill-clefts lead into a wide chamber occupying most of the space
between the body-wall and the pharynx and called the aérium (Fig.
204, atr). It is crescentic in section, surrounding the ventral and
lateral regions of the pharynx, but not its dorsal portion. It ends
blindly in front; opens externally, behind the level of the pharynx, by
the atriopore (@/7p); and is continued backwards by a blind, pouch-
hke extension (a?) lying to the right of the intestine. As in Ascidia
the cilia lining the gill-clefts produce a current setting in at the mouth,
entering the pharynx, passing thence by the gill-slits into the atrium
and out at the atriopore. The current, as in Tunicata and Balano-

XII PHYLUM CHORDATA 327

glossus, is both a respiratory and a food current, the animal feeding
passively on the minute organisms in the surrounding water.

There is a system of blood-vessels, but no heart. A contractile
median ventral vessel, the veztra/ aorta, runs forward in the ventral
wall of the pharynx, and gives off lateral branches, the afferent bran-
chial vessels, which pass upwards in the branchial lamellae. Efferent
branchial vessels receive the blood from the wall of the pharynx and
open dorsally into a pair of longitudinal vessels, the dorsa/ aorte. The

Fic. 205. — Amphioxus lanceolatus. A, transverse section of the pharyngeal re-
gion. a, dorsal aorta; 8, atrium: c, notochord; co, coelom; e, endostyle; g,
gonad; £6, branchial lamelle2; 4d, pharynx; Z, liver; my, myomere; 7, neph-
ridium; 7, neuron or dorsal nerve tube; sv, spinal nerves; sf, gill-slits. B,
transverse section of the intestinal region; @¢7, atrium; coe/, ccelom; d. ao,
dorsal aorta: zw#, intestine; 7zyom, myomere: xc, notochord: zex, neuron;
s. int. v, subintestinal vein. (A, from Hertwig, after Lankester and Boveri; B,
partly after Rolph.)

latter join to form a median dorsal aorta, which runs backwards imme-
diately below the notochord and above the intestine.

The principal organs of excretion are about ninety pairs of peculiarly
modified zephridia (Fig. 204, np/) situated above the pharynx and in
relation with the main ccelomic cavities.

An excretory function has also been assigned to a single pair of
organs called the drown funnels (Fig. 204, Or. f); also situated on the
dorsal aspect of the pharynx at its posterior end.

328 MANUAL OF ZOOLOGY SECT.

The central nervous system is a rod-like organ, the ewron or dorsal
nerve-cord (Fig. 204), contained within and completely filling a median
longitudinal sezral canal which lies immediately above the notochord.
It is traversed by an axial canal, which becomes dilated at the anterior
extremity. From this nerve-cord regularly arranged nerves are given
off.

At the level of the anterior end of the nerve-cord is a narrow ciliated
depression, the olfactory pit (Fig. 204, off p) opening externally on
the left side of the snout and connected at its lower end with a median
hollow process of the nerve-cord. This structure is supposed to be an
organ of smell.

The organ of sight is an unpaired pigment spot (e) in the front wall
of the brain; it is therefore a median eye. A peculiar structure, the
groove of Hatschek, on the roof of the oral hood, is supposed to have a
sensory fanction, and may be an organ of taste. Lastly, the sensory
cells on the buccal cirri give those organs an important tactile function.

The sexes are separate, but there is no distinction, apart from the
organs of reproduction, between male and female. The gowads (Fig.
204, gon) are about twenty-six pairs of pouches arranged metamerically
along the body-wall and projecting into the atrium so as largely to fill
up its cavity.

When ripe the inner walls of the gonadic pouches burst, and the ova
or sperms make their way into the atrium and thence by the atriopore
to the external water, where impregnation takes place.

B. THE CRANIATA

The fishes, amphibians, reptiles, birds, and mammals are
grouped together under the general designation Cranzaza,
derived from one of the features which these animals have
in common, viz., the presence of a skull or cranium. In
order to understand the general characteristics of the Craniata,
it will be advisable to examine and compare representatives
of some of the principal classes. For this purpose a dogfish,
a lizard,’ and a rabbit will be a good and convenient selection.

1 The anatomy of the Avmo/is or ‘' American chameleon” of the Southern
States is essentially like that of the European lizard.

XII PHYLUM

Not only must entire and,
if convenient, living speci-
mens be examined, but
prepared skeletons of all
three must be availa-
ble for examination, and
preparations showing the
various systems of inter-
nal organs, notably the di-
gestive system, the heart,
and the brain.

An external comparison
appears at first sight to
reveal few points of agree-
ment between the three
selected examples. The
skin, the general shape,
the movements, are all
widely different. A few
features common to all
three are, however, to be
recognised. It will be~
observed that in all three
are distinguishable a head
region, in front, a ¢runk
region (by far the largest),
in the middle, and a /az/
region, differing greatly in
its development, behind.
The head region bears
anteriorly the opening
of the mouth, bounded
above and below by jaws

Muth i Ait
mH ann
th i

echt
i)

na

CHORDATA

AM,
HN ea
Mt a

oe

a

ly removed to show the

gfish (Mustelus antarcticus), with a strip of skin in the middle of the bod

Fic. 206. — Side view of Do

etl;

pu. S, pelvic

external branchial apertures;

ext. br. ap,
pet. J, pectoral fin;

mymt, Myomeres; 2. a, nasal aperture;

d.f.1,d f.2, dorsal fins; e, eye;

c. d. f, caudal fin;

mth, mouth;

329

myc, myocommas;
(From Parker’s Biology.)

v. /, ventral fin.

muscles. am, anus;
lateral line;
sf, spiracle;

fin;

330 MANUAL OF ZOOLOGY SECT.

bearing teeth ; near the mouth are a pair of smaller aper-
tures— the nostrils or nasal apertures, and at the sides
of the head region are the pair of conspicuous eyes ;
while further back the pair of prominent auricles or pin-
ne, with the wide apertures at their bases, mark very
conspicuously the position of the auditory organs in the

Fic. 207. — Lacerta viridis. (After Brehm.)

rabbit, less clearly indicated in the lizard, and still less
in the dogfish. On the lower (ventral) surface, towards
the posterior end of the trunk, will be observed in all three
apertures which serve as the orifices through which the
intestine and the ducts of the urinary and genital organs
communicate with the exterior. A further resemblance

XI PHYLUM CHORDATA 331

between the lizard and the rabbit consists in the presence
of two pairs of jointed limbs, anterior and posterior, the
principal divisions of which correspond in their general
arrangement. In the dogfish these are found to be rep-
resented by very different-looking structures, the pavred fins.
At this point all external resemblance ceases, and we see
nothing but differences.

The skin of the dogfish, though almost smooth, is harsh to
the touch, and, when we examine it with a lens, this is found
to be due to the presence of innumerable minute hard gran-

Fic. 208. — Lepus cuniculus. Lateral view of skeleton with outline of body.

ules, set closely together so as to give the surface the charac-
ter of a fine file. The general shape of the body is adapted
to cleaving the water rapidly,—long and narrow, nearly
fusiform, pointed at the ends, —and the fins are obviously
swimming organs. The fins are all of the same general
character, so far as their superficial appearance is con-
cerned ; they are all of the nature of flap-like outgrowths,
thick at the base, where they are obviously supported by
hard parts, thinner towards the margins, where their sole

332 MANUAL OF ZOOLOGY SECT.

support is a series of slender fibres of horny character.
Besides the two pairs of fins which have already been re-
ferred to as taking the places of the anterior and posterior
pairs of limbs in the lizard and rabbit, certain others are to
be recognised which are of a totally different character,
being median or unpaired; these, which are not in any
way represented in either the lizard or the rabbit, are the
two dorsal, the single ventral, and the single caudal, the
last fringing the tail.

Behind the eye in the dogfish will be noticed a small
aperture which seems to occupy very nearly the position
occupied by the opening of the ear in the rabbit. This
opening, however, the sfrac/e, does not lead into the ear,
but into the cavity of the pharynx. Further back there
are, on each side, five slit-like apertures in a row: these
are the branchial or gill-clefts, and are not present in the
lizard or the rabbit. In the living fish it will be observed
that there are regular movements of the mouth, spiracles,
and branchial clefts, indicating that water is being rhythmi-
cally taken in through the mouth and expelled by the
spiracles and branchial clefts. Those are the movements
of respiration.

The mouth is situated some little distance behind the
anterior extremity of the head, on the ventral side. In
front of it are the nasal openings (nostrils), which are also
ventrally situated.

In the lizard the surface is covered with a system of
overlapping horny scales. The head is separated from the
trunk by a distinct constricted region, the eck. The tail
is extremely long and narrow. The two pairs of limbs,
anterior and posterior, or Zectoral and pelvic, are adapted to
running on the surface of the ground. Each consists of
three divisions, — arm, fore-arm, and hand, —the anterior

XI PHYLUM CHORDATA 333

limb, thigh, leg, and foot in the posterior; and each hand
and each foot contains five slender digits, each provided
at its extremity with a curved and pointed horny claw.
Slight rhythmical movements of dilatation and contraction
of the anterior portion of the trunk are the movements of
respiration, by means of which air is alternately drawn into
and expelled from the lungs through the nostrils.

In the rabbit the place of the scales of the lizard is taken
by the coating of hairs constituting the fur. The limbs
present the same main divisions as in the lizard, though the
proportions of the parts are very different, and the hind foot
has only four toes. Between the head and trunk the neck
region is more sharply marked off than in the lizard. Aris-
ing from the posterior part of the head, behind the eyes,
are a pair of very prominent auditory pinne or auricles, at
the base of each of which is the corresponding ear-opening.
Movements of respiration resembling those of the lizard,
but much more marked, are to be detected in the living
animal.

When the skeletons of these three animals are examined
and compared, it will be found that they are constructed on
the same general plan with differences in details. In the
dogfish it is mainly composed of cartilage; in the others,
mainly of bone. In all there is a rod-like axis, the sp:nad
or vertebral column supporting the trunk and tail, but not
continued into the head, where its place is taken by the
skull, The spinal column consists of a row of similar
segments, the vertebre, which articulate with one another.
Each vertebra consists of a neutral solid portion, the cez-
trum or body; an arch of bone or cartilage, the mewral
arch, situated on the dorsal side of the centrum, and cer-
tain processes. The series of centra form together a strong
axial support for the entire body and tail; the series of

334 MANUAL OF ZOOLOGY SECT,

neural arches enclose a canal, the ewra/l canal, on the
dorsal side of the centra. By the interlocking of certain
processes— the articulating processes — of the neural arches
the vertebre in the lizard and rabbit are yet more firmly
united together.

In the dogfish the centra have deeply concave anterior
and posterior faces, so that when the vertebra are in posi-

Fic. 209. — A, three trunk vertebre of Scyllium from the side; B, a single trunk
vertebra viewed from one end; C, three caudal vertebra from the side; D, a
single caudal vertebra from one end. c,centrum; /. a, hemal arch; z. a, neural
arch; ¢7. gr, transverse process. (After Hasse.)

tion there are hollows of considerable extent between the

centra formed by the apposition of these concave faces.

This form of centrum is termed amphicelous. ‘The entire

spinal column is distinguishable into two regions,— the

region of the ¢wzk in front and the region of the ¢az/

XII PHYLUM CHORDATA 335

behind. In the region of the trunk the vertebree bear very
small ribs in the form of short rods of cartilage; in the
caudal region ribs are absent; but each vertebra bears, in
addition to the neural arch, a ventrally situated arch of
similar shape — the hema/ arch.

In both the lizard and the rabbit the vertebrae are com-
posed entirely of bone. In the former the centra have
concave anterior and convex posterior surfaces— and the
vertebre are accordingly said to be procelous. In the lat-
ter the surfaces are flat, and the discs of fibro-cartilage, the
inter-vertebral discs, are intercalated between the vertebre.

rb=

Fic. 210. — Vertebre of Lizard. A, anterior, B, posterior, view of a thoracic ver-
tebra; C, lateral, D, anterior, view of atlas vertebra; E, lateral view of axis.
cent, centrum; yf, hypapophysis of axis; Zaft, lateral piece of atlas; Zzg, liga-
mentous band dividing the ring of the atlas into two; 2ez, neural arch of atlas;
od, odontoid process; fr. zy, pre-zygapophysis; f¢. zy, post-zygapophysis; 7d,
rib; sf, spine; vent, ventral piece of atlas.

In both the spinal column is divisible into five regions, — the
cervical, the thoracic, the dumbar, the sacra/, and the caudal.
The cervical region is the most anterior. In the rabbit the
vertebrae of the cervical region are devoid of ribs; in the
lizard they have short ribs with the exception of the first
three. The first and second vertebree in both the rabbit
and the lizard are specially modified in connection with the
movements of the head on the trunk. The vertebrze of the

336 MANUAL OF ZOOLOGY SECT.

thoractc region are characterised by the possession of 7ids,
which, in the case of the most anterior, are connected with
the breast-bone or sternum by slender cartilaginous sternal
vis. In the Zembar region there are no ribs. The sacral
region is distinguished by its relations with the hind limb.
The caudal region, short in the rabbit, very long in the
lizard, lies behind the sacral. The ribs connected with the
thoracic vertebre are slender curved rods, which lie in
the side walls of the anterior part of the trunk; the most
anterior of them with their continuations, the sternal ribs,
form half-loops extending from the spinal column dorsally

cent
Fic. 211. — Lepus cuniculus. A, atlas and axis, ventral aspect; od, odontoid pro-
cess of axis. B, lateral view of axis; art, articular facet for occipital condyle;
od, odontoid process; ft. sy, post-zygapophysis; sf, neural spine. C, thoracic
vertebra, lateral view. cent, centrum; fac, facet for rib; met, metapophysis;
pr. sy, pre-zygapophysis; fz. sy, post-zygapophysis; 7d, rib; sf, spinous process.
to the sternum ventrally. The szernwm or breast-bone,
absent in the dogfish, lies in the middle of the wall of the
ventral region of the trunk. In the lizard it is a rhomboidal
plate of cartilage ; in the rabbit it is bony, and divided up
into a number of segments known as the stevnedbre.

In the embryo of each of the three forms used as illus-
trations, the spinal column passes through a stage in which
it consists merely of a continuous cylindrical rod of cells —
the zotochord, corresponding to the notochord of Amphi-

oxus—which becomes enclosed in a sheath. In some

XII PHYLUM CHORDATA 337

Craniates it never passes beyond this stage, but remains of
the nature of a persistent notochord, as it is termed. But in
the great majority the notochord becomes enclosed in a
sheath of cartilage, and thus becomes divided up into a
number of segments. Eventually ossification sets in, and
the series of completely formed bony vertebree becomes
developed.

As already mentioned, the spinal column does not extend
into the head region. The skeleton of this region is the
complex cartilaginous or bony structure known as the skudZ.
The chief part of this is a case, the cranium, in the interior
of which the brain is lodged, and the walls of which afford
support to three pairs of organs of special sense, — the zasal
or olfactory organs in front, the eyes in the middle, and the
ears or auditory organs behind. The cavity of the cranium
opens behind by a rounded foramen, the foramen magnum,
into the anterior end of the neural canal enclosed by the
neural arches of the vertebree ; and the posterior region of
the cranium articulates movably with the first vertebree of
the spinal column. In addition to the cranium the skull
or skeleton of the head comprises certain elements known
as the wisceral arches. The foremost of these forms the
jaws, the second is the Ayozd, and mainly supports the
tongue, the remainder are the dranchial arches.

In the dogfish the cranium remains in the primitive
condition of a cartilaginous case, with complete walls and
floor, but with the roof partly formed of fibrous membrane.
In the lizard and rabbit the substance of the cartilage is
replaced by a number of cartilage bones, i.e, bones which
take the place of pre-existing cartilage, to which are super-
added a number of membrane bones, t.e., bones, the site of
which was not preoccupied by cartilage ; the whole united
together so as to form a structure of considerable com-

zZ

MANUAL OF ZOOLOGY SECT,

338

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gre pou, uohy

XII PHYLUM CHORDATA 339

plexity. The visceral arches in the dogfish are composed
of a system of rods of cartilage. The first visceral arch
forms the upper and lower jaws, between which the open-
ing of the mouth is situated. The jaws are connected on
each side with the skull behind by means of a cartilage
known as the hyomandibular, which is a part of the second
or hyoid arch ; the rest of the hyoid arch and the branchial
arches, which are five in number, lie in the lateral and ven-
tral walls of the pharynx and support the gills.

In both the lizard and the rabbit the branchial arches
are not present as such, the only well-developed visceral
arches being the first and second. The upper jaw is
formed of certain membrane bones, and in the lower jaw
also the cartilage completely disappears, its place being
taken by bones which are early completely united together,
so as to form the bony lower jaw or mandible. In the
lizard the mandible articulates on each side with the pos-
terior region of the skull through the intermediation of a
bone known as the guwadraze, which is an element of the
first visceral arch. In the rabbit the articulation between
the mandible and the skull is direct, no quadrate inter-
vening.

The skeleton of the limbs in the dogfish differs widely
from that of the lizard and rabbit. In all three we dis-
tinguish the limb-arch from the skeleton of the free part
of the limb itself. The limb-arch (pectoral or pelvic) is a
cartilage or a system of bones with which the base of the
free part of the limb articulates, and has the function of
connecting the limb with the trunk and serving for the
origin of many of the muscles moving the limb. In the
dogfish the entire skeleton of the limbs is composed of
cartilages which are so arranged as to support the thin
broad expanse of the fin. In both the lizard and the

A

extnar gf

Fic. 213. —Skull of Lacerta agilis. A, from above; B, from below; C, from the
side. ang, angular: a~é, articular; das. oc, basi-occipital ; bas. Atg, basi-pterygoid
processes; Jas. sph, basi-sphenoid; co/, epi-pterygoid; cor, coronary; dent,
dentary; et, ethmoid; ex oc, ex-occipital; ert. var, external nares; for. mag,
foramen magnum: /, frontal; z#¢. var, internal nares; 7x, jugal; dcr, lacyr-
mal; max, maxilla; was, nasal; oc. cond, occipital condyle; olf, olfactory
capsule; of. ot, opisthotic; oft 7, optic nerve; fad, palatine; far, parietal;
par, parasphenoid; far./, parietal foramen; £. w+, pre-maxilla; p7./7, pre
frontal; pzg, pterygoid, At. 07d, post orbital; gw, quadrate; s. ang, supra-
angular; s. 07d, supra-orbitals; sg, squamosal; szfra. ¢.1, supra-temporal 1;
supra. t.2, supra-temporal 2; trans, transverse; supra. oc, supra-occipital; vow,
vomer. (After W. K. Parker.)

340

SECT. XII PHYLUM CHORDATA 341

rabbit the skeleton of the limbs is constructed on a general
plan, common to the limbs of all Craniata but the fishes,
and known as the fentadacty/e, in allusion to the five digits
in which the limb typically terminates. In the pectoral
limb the upper arm has a single long bone known as the
humerus; at its proximal end this is movably articulated
with the pectoral arch. The forearm contains two long

IL
A B
act6
FE
PU
cor

OE BOR wx UL
JU oman

ra
cn. OGG 35 — on. 2
dst. 55; De ast.s ane xen fy ‘ast. 5
ea iw 8 mtts. ie 5

Fic. 214. — Diagrams of the fore (A) and hind (B) limbs with the ett act,
acetabulum; g/, glenoid cavity; #. cor, procoracoid; /-V, digits. Cartilage
bones — cn.1, cn.2, centralia; COR, coracoid; dst. 5-1, distalia; FE, femur;
FI, fibula; fi, fibulare:; HU, humerus: IL, ilium; int, intermedium ; IS,
ischium; mtcp. 1-5, metacarpals; mt. ts. 1- 5, metatarsals; ph phalanges:
PU, pubis: RA, radius; ra, radiale; TI, tibia; ti, tibiale; UL, ulna; ul,
ulnare, membrane bone; CL, ‘clavicle.

bones — radius and wna — articulating proximally with the
distal end of the humerus. The skeleton of the hand con-
sists of three principal parts, — the carpus, the metacarpus,

342 MANUAL OF ZOOLOGY SECT.

and the phalanges. The carpus or wrist consists of a num-
ber of small irregularly shaped bones arranged in two trans-
verse rows, proximal and distal, with a central bone between
the rows. The meéacarpus consists of five narrow bones
forming the support of the basal parts of the five digits,
and articulating proximally with the distal row of carpals.
The rest of the skeleton of the digit is formed of a row
of small bones, the phalanges, the last of which — wngual
phalanx — is modified in shape to support the horny claw.

The skeleton of the hind-limb corresponds closely with
that of the fore-limb. The pelvic arch consists on each side
of three bones which become firmly united together, one
of these, the 2/wm, is dorsal in position, the other two, pudzs
and ¢schium, are ventral, the pubis being anterior to the
ischium. The ilia articulate firmly with the sacral region
of the spinal column ; the pubes unite ventrally in an articu-
lation known as the fwdzc symphysis, and in the lizard the
ischia are similarly connected. Laterally where the three
bones unite is a cup-like cavity — the acetabulum — which
forms the socket for the head of the thigh-bone.

The thigh has a single long bone, the femur. The leg
has two bones, the “za and fibula, the former, which is
internal, being the larger of the two, and the latter in the
rabbit not being distinct from the former towards the distal
end. In the foot are a number of ¢arsa/ bones correspond-
ing to the carpals of the hand, a series of metatarsals corre-
sponding to the metacarpals and a series of phalanges.

When the skin of the trunk of the dogfish is removed
there will be found immediately beneath it a thick layer
of muscle. This is distinctly divided into segments or
myomeres similar to those of Amphioxus, and this, with the
division of the vertebral column into segments or vertebree
(which, however, do not exactly correspond in arrangement

XII PHYLUM CHORDATA 343

with the myomeres), indicates that the body, like that of
Nereis or an Arthropod, is metamerically segmented. In
the lizard and rabbit the metamerism of the muscular sys-
tem, though distinguishable at an early stage, becomes lost
in the adult, and the muscles take on a much more compli-
cated arrangement.

On the jaws are a series of teeth, the function of which
is to seize the food, and in the rabbit cut it into fragments,
and crush it into yet smaller particles, in order to prepare it
for the process of digestion. In the dogfish the teeth are
numerous and of uniform character throughout, small with
sharp points directed backwards. At
their bases they are fixed to the surface
of the cartilage of the jaw by means of
dense fibrous tissue. In the lizard the
teeth are also of uniform character
(homodont dentition). They are of a
simple conical shape, and fixed to the
bone of the jaws. In the rabbit the
teeth are distinctly visible into sets, dif-
fering from one another in shape and
function (heterodont dentition). Their
bases are lodged in sockets or a/veo/ in
the substance of the jaws.

The structure of the tooth is the same
in all three cases. The main mass of
the tooth consists of dentine, a densely Fic. 215.— Longitudinal

‘: , . section of a tooth, semi-

calcified material permeated by delicate diagrammatic. ’ PH,

= : pulpcavity; PH’',open-

parallel tubules. The free surface is ingofsame; 22, den-

covered with a layer of still harder mate- ea ewes
rial, the exame/, and the basal portion is | “P'™S /*7#?r4/2)

covered with a layer of cemenz, which is similar in micro-

scopic structure to bone.

344 MANUAL OF ZOOLOGY SECT. XII

The anterior part of the cavity into which the mouth
leads is the 4ucca/ cavity, the posterior part is the pharynx.
On the floor of the buccal cavity is, in the lizard and in the
rabbit, a mobile muscular prominence, the /ongue, repre-
sented in the dogfish by a much less prominent and little
mobile process.

From this a wide tube leads backwards to open into a
spacious chamber, the stomach. From the stomach the
intestine, a more or less coiled tube, leads eventually to the
anal aperture. In the dogfish and in the lizard the anus
opens into a chamber, the c/oaca, which also receives the
ducts of the urinary and reproductive organs. In the rabbit
a cloaca is absent, and the anus is separate from the urino-
genital opening. The mucous membrane of the enteric
canal contains numerous glands, the secretions of which play
an important part in digestion ; the most important of these
secretions is the gastric juice secreted by the glands of the
stomach. In addition, special large digestive glands are
present producing secretions, also having the function of
acting on the various components of the food in such a way
as to facilitate the passage of the useful ingredients from the
cavity of the alimentary canal to the blood-vessels. In the
rabbit these special large digestive glands are the sadvary
glands, the “ver, and the pancreas; in the dogfish and
lizard the salivary glands are absent, though in the latter
there are numerous small glands, the ducca/ glands, in the
wall of the buccal cavity. The secretion of the salivary
glands, the sa#va, enters the cavity of the mouth through
the ducts of the glands. It contains a ferment, psfyaln,
which has the property of converting starch into sugar.
The liver is in all three a relatively large organ, fixed by
folds of peritoneum to the dorsal wall of the abdominal
cavity and divided by fissures into a number of lobes, Its

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345

346 MANUAL OF ZOOLOGY SECT.

duct, the dz/e ducé, conveys its secretion, the Jd7/e, into
the most anterior part of the intestine known as the dvo-
denum. The duct gives off a diverticulum which expands
into a rounded sac, the gad/-bladder; this acts as a recep-
tacle for the bile when it is not required. The bile has an
important action on the fatty matters of the food, converting
them into an emuz/sion and decomposing a small proportion
into glycerine and fatty acid. In addition to secreting the
bile the liver has another function to perform: it acts as
a storehouse for surplus carbohydrates absorbed from the
food. The carbohydrates —compounds of the nature of
starch and sugar — are converted in the liver into a sub-
stance known as g/ycogen or animal starch, which becomes
stored up in the cells to be given out again to the blood as
it is required for nutrition during the intervals of fasting ;
this function of the liver is known as the glycogenic function.

The pancreas, which is a much smaller gland than the
liver, produces a secretion, the pancreatic juice, which has
the effect of converting starch into sugar, proteids into
soluble modifications known as fef/ones, and of assisting in
the emulsification of fats. The duct of the pancreas also
opens into the duodenum. The nutrient matters of the
food, rendered soluble by the action of the various digestive
fluids, pass into the blood contained in the blood-vessels in
the wall of the enteric canal, and are thus conveyed through-
out the body to be distributed. The fatty matters, however,
pass into a system of minute vessels — the /actea/s — which
ramify in the wall of the intestine. The lacteals are not
blood-vessels, but belong to the Awnphatc vascular system to
be referred to presently. The lacteals combine together
and in the rabbit open into a large trunk — the horacic duct
— by means of which the absorbed emulsion, or chyée as it is
termed, is conveyed to one of the great veins.

XII PHYLUM CHORDATA 347

The body-cavity in which the enteric canal and other
organs are contained is lined with a membrane, the Zev7-
toneum. ‘This is reflected over the surface of the contained
structures, and folds of it serve to suspend the various organs
and connect them together. The best developed of these
folds is the mesenéery (defective in the dogfish), by means
of which the intestine is attached to the dorsal wall of the
body-cavity.

The organs of respiration of the dogfish are gz//s adapted
for receiving oxygen from the air dissolved in sea-water ;
those of the lizard and the rabbit are lungs adapted for
breathing air directly. The movements of respiration have
been already referred to. In the dogfish these movements
have the effect of causing water to be taken in by the mouth,
and to pass out from the pharynx to the exterior through
the gill-slits. In passing out, the water flows over the gills,
which are sets of vascular elevations on the walls of a series
of five pairs of chambers—the éranchial sacs opening
internally into the pharynx, and externally communicating
with the surrounding water through the branchial slits. In
this way the needed oxygen is constantly being taken up,
and the carbon dioxide given off. The walls of the branchial
sacs are supported by the hyoid and branchial arches.

Inspiration and expiration of air in the lizard and rabbit
take place through the nostrils. The nasal chambers into
which the nostrils lead communicate internally with the
mouth-cavity or the pharynx through a pair of apertures
known as the zvéernal or posterior nares. On the floor of
the pharynx behind the root of the tongue is a slit-like
aperture, the g/o/f#is, opening behind into a chamber known
as the /arymx, the wall of which is supported by cartilages.
From the larynx the air passes backwards along a tube, the
trachea, the wall of which is supported by numerous rings

348 MANUAL OF ZOOLOGY SECT.

of cartilage. The trachea bifurcates when it enters the
body-cavity, each of the two branches, or d7vnchi as they
are termed, passing to the
corresponding lung. In the
lizard the lung is in essence
a thin-walled sac with elas-
tic walls. In the wall of
the sac immediately out-
side, the delicate internal
epithelium is a rich net-
work of blood-vessels, into
the blood contained in
which oxygen from the air
in the cavity of the lung
readily passes, while the
carbonic acid is at the
same time given off. In
the rabbit the lung is of
much more complicated
structure, but the essential
relations are the same.
In the lizard the lungs
lie in the anterior part of
the general body-cavity.
In the rabbit the anterior
part of the body-cavity,
containing the lungs and
the heart, is separated off
from the posterior part,
containing the greater por-
ED. rectum: GB, gallbladder; 77, tion of the enteric canal and
heart; Lg. Lg’. the lungs; 47, stomach: other organs, by a muscular

AID, small intestine; Oe, oesophagus;

Pn, pancreas; Tyr, trachea. (After wo a
Wisdersheim:) partition concave poster

E
Fic. 217. — Lacerta agilis. General view
of the viscera in their natural relations.
Bi, urinary bladder; Cz, post-caval vein;

XII PHYLUM CHORDATA 349

orly,—the daphragm,—the anterior portion of the cavity
being known as the cavity of the ¢torax, and the posterior
as that of the abdomen.

The air in the lungs, as it is constantly losing oxygen and
gaining carbon dioxide, requires to be frequently renewed ;
and the respiratory movements which have already been
referred to are the movements indicative of this renewal ; in
the movement of vesfiraton air is drawn into the lungs,
which become fully distended; in that of experaton, the
greater part of the air is driven out again, and the lung
collapses. In the rabbit inspiration and expiration are
effected by the movements of the ribs and of the diaphragm,
by which the dimensions of the cavity of the thorax are
increased or diminished.

The blood-vascular system is highly developed in all the
three examples. The blood is of a red colour, owing to
the presence of red corpuscles containing a red colouring
matter termed hemoglobin.

The blood-vessels are of three kinds, — ar¢eries, veins, and
capillaries. The arteries have firm and elastic walls, which
do not collapse when the vessel is empty; they contain
arterial blood, 7.e., blood which contains abundance of
oxygen. The veins have thin, non-elastic walls which col-
lapse when the vessel is empty and contain valves ; the con-
tained venous blood is darker in colour than the arterial, and
has been deprived of oxygen in the tissues. Both arteries
and veins ramify extensively, the ultimate branches being of
very small size. Connecting together the ultimate branches
of the arteries and the ultimate branches of the veins is a
system of microscopic vessels — the capillaries.

The feart is ventral and anterior in position. In the dog-
fish it will be found to lie in a space, the pericardial cavity,
between the two rows of gills, and separated behind from the

350 MANUAL OF ZOOLOGY SECT.

general body-cavity (abdomen) in which the majority of the
internal organs are contained, by a transverse fibrous parti-
tion. It consists of four chambers, — the sinus venosus, aurt-
cle, ventricle,and conus arteriosus. The venous blood enters
the sinus venosus from the great veins and passes through
the other three chambers in succession in the order given.
All the chambers contract rhythmically, and by their con-
tractions the blood is propelled from chamber to chamber,
and finally driven out from the heart, its passage in the
opposite direction being prevented by the presence of
valves. These are placed in the openings leading from
chamber to chamber, and are so arranged that while they
permit the ready passage of the blood in the direction above
given, they close up the opening when pressure is exerted in
the opposite direction ; thus, for example, when the auricle
contracts, the valve guarding the opening leading back into
the sinus venosus closes that opening, while the valve in the
opening leading into the ventricle opens freely, and the
blood passes readily in that direction. The ventricle is by
far the most muscular of the four chambers, since it is
mainly by its contractions that the blood is forced through
the system of vessels. The blood which is forced out from
the heart by the contractions of the ventricle passes into a
series of vessels which carry it all to the gills. Here it
enters a system of capillaries in the gills, and these being
separated from the surrounding water only by a thin mem-
brane, oxygen readily enters the blood, and the carbon
dioxide collected in the various tissues and organs of the
body is given off. The blood then enters a set of larger
vessels, which combine to form a large trunk, the dorsal
aorta. Branches from this distribute blood to all parts of
the body, where it enters the systems of capillaries, and
whence it is carried back again to the heart by the ve7ns.

XII PHYLUM CHORDATA 351

In the lizard the heart and the circulation are somewhat
more complicated than in the dogfish. There is a sinus
venosus as before. The auricle is completely divided into
two chambers, right and left, by a partition. Into the right
auricle the sinus venosus drives the venous blood from the
great veins; into the left open the pulmonary veins, bring-
ing the oxygenated blood from the lungs. Both the auricles
open into the ventricle, the cavity of which is partly divided
by a septum. From the ventricle are given off the main
arteries (systemic arteries) which branch throughout all parts

Fic. 218. — Diagram illustrating the course of the circulation in a fish. Vessels
containing aérated blood, red; those containing non-aérated blood, blue; lym-
phatics, black. B, capillaries of the body generally; E, of the enteric canal;
G, of the gills; K, of the kidneys; L. of the liver; T, of the tail. @. dx. a,
afferent branchial arteries; aw, auricle; ¢c. a, conus arteriosus; @. ao, dorsal
aorta; e. dr. a, afferent branchial arteries; /. ’ v, hepatic portal vein; 4. v,
hepatic vein; ke, lacteals; ¢y, lymphatics; pr. cv. v, pre-caval veins; 7». p. v,
renal portal veins; s. v, sinus venosus; v, ventricle; v. ao, ventral aorta. The
arrows show the direction of the current.

of the body, and the pu/monary arteries, which pass direct
to the lungs. By various arrangements of the parts which
need not be described at present, the venous blood from
the right auricle is mainly guided into the pulmonary arte-
ries, and passes to the lungs to obtain oxygen and part with
its carbon dioxide ; while the arterial blood is mainly guided

352 MANUAL OF ZOOLOGY SECT,

to the systemic arteries. A certain degree of mixing, how-
ever, of the venous and arterial currents takes place as they
pass through the ventricle.

In the rabbit this mixing of the arterial and venous cur-
rents is entirely prevented, owing to the ventricle being
completely divided into two chambers — right and left.
The right auricle opens into the right ventricle, and fills it
with venous blood from the great veins. From the right
auricle the blood is driven through a pulmonary artery to the
lungs. From the lungs the oxygenated blood is returned
by means of the pulmonary veins to the left auricle; from
the left auricle it enters the left ventricle, and from the
latter is driven out through the system of systemic arteries
to all parts of the body. ‘There are thus two distinct cur-
rents of blood constantly passing simultaneously through the
heart, but entirely cut off from one another, viz., a venous
current on the right side and an ar¢erzaZ on the left. The
blood of the rabbit has a much higher temperature than
that of the dogfish or lizard.

In all the three examples the veins which carry the
venous blood towards the heart from the stomach, intestine,
and pancreas unite together to form a large vein, the hepatic
portal, which ramifies in the substance of the liver, and
forms the main source of the blood supply of that organ.
In the dogfish and lizard, but not in the rabbit, veins con-
vey blood from the posterior region to the kidneys, forming
what is termed a vena/ portal system.

The nervous system is highly developed. The central
nervous system consists of the brain and spinal cord. The
brain is, as already stated, contained in the cavity of the
cranium ; the spinal cord, continuous with the posterior end
of the brain, extends through the neural canal roofed over
by the series of neural arches of the vertebra.

xu PHYLUM CHORDATA 353

The spinal cord is similar in essential respects in all three
examples. It is a cylindrical cord of nerve matter, having
running along the middle of its dorsal surface a fissure, the

Lot

Fic. 219. — Dorsal view of the brain of Scyllium canicula. The posterior division
of the brain is the medulla oblongata (V//), on the dorsal surface of which is
stown one of the central ventricles (F. rho). The large cerebellum (HH)
nearly covers the optic lobes (MA). The diencephalon (ZA) shows in the
middle one of the central ventricles, and the place of attachment of the pineal
body (Gf). The prosencephalon (/’#/ ) gives off the olfactory lobes (Tro, L. of).
The following nerves are shown: optic (//), trochlear (//’), trigeminal (V’),
facial (V//), auditory (VZ//), glossopharyngeal (/X°), and vagus (XX).
(From Wiedersheim.)

dorsal longitudinal fissure, and along the middle of its ven-
tral surface, a second fissure, the ventral longitudinal fissure.

2A

354 MANUAL OF ZOOLOGY SECT.

Through its substance from end to end runs a narrow canal,
the central canal.

In the brain of the dogfish the most anterior portion is
a thick mass of nerve matter indistinctly divided into two
lateral portions by a shallow depression. This is the fvo-
sencephalon of the fore-brain. A pair of lobes given off
from this in front are the olfactory lobes. The prosencepha-
lon with a narrow region, @encephalon or thalamencephalon,
behind it, constitute the fore-dvain. Behind the fore-brain
a pair of oval lobes, the ofc lobes, constitute the dorsal
portion of the md-drain, which comprises, in addition, a
thick mass of longitudinal nerve-fibres, lying below, and
connecting the hind-brain with the fore-brain. An elon-
gated median mass, indistinctly divided into lobes, is the
cerebellum, the anterior portion of the hind-brain. The
posterior division of the hind-brain, — medulla oblongata, —
broad in front, tapers posteriorly where it passes into the
spinal cord.

The central canal of the spinal cord expands in the me-
dulla oblongata into a wide shallow cavity, roofed over only
by a thin membrane ; this is known as the fourth ventricle.
From this runs forwards a narrow passage, the 7/er or ague-
duct of Sy/vius, expanding in front in the thalamencephalon
into a laterally compressed cavity, the “hird ventricle. From
this are given off a pair of lateral ventricles, passing into
the prosencephalon, each giving off a prolongation into the
corresponding olfactory tube.

The roof of the third ventricle is very thin; it is pro-
duced into a slender process — the epiphysis or pineal body.
Its side walls are formed of two masses, the optic thalami;
its floor is produced into a hollow prolongation, the zzfun-
aibulum, to the end of which a vascular body, the Aypophyses
or pituitary body is applied.

XII PHYLUM CHORDATA 355
s

In the brain of the lizard the same parts are recognisa-
ble as in the dogfish, the chief differences being that the
prosencephalon is deeply-divided by a median longitudinal
fissure into two lobes, the cerebral hemispheres, and that
the cerebellum is very small. In the rabbit also we rec-
ognise the same parts. But the whole brain is larger in pro-
portion to the bulk of the body; the cerebral hemispheres
are much more highly developed, and the cerebellum is not
only of large relative size, but is of complicated structure.

The peripheral nervous system consists of the spinal and
cerebral nerves given off from the spinal cord and the brain
respectively, with their ramifications through all parts of the
body. A pair of spinal nerves emerge from the neural
canal between each adjoining pair of vertebre. Each
spinal nerve arises from the spinal cord by two roots—a
dorsal and a ventral; the former is dilated into a ganglion.
Experiments prove that the dorsal root contains the sensory
fibres of the nerves, 7.¢., those fibres which are concerned
in carrying impulses from the various parts to the nerve
centres to be translated in consciousness into sensations.
When, for example, the skin of some part of the body is
touched, the impulse by means of which we become con-
scious of the contact passes from the surface through
branches of the spinal nerves, and enters the spinal cord
through the dorsal root, in order to be transmitted to the
brain. The ventral root, on the other hand, contains the
motor fibres; the fibres through which impulses which lead
to the contraction of muscles pass outwards from the central
nervous system.

More or less extensive intercommunications take place
between the spinal nerves that are situated opposite the
origin of the limbs ; these spzza/l nerve plexuses give off the
nerves to the limbs.

356 MANUAL OF ZOOLOGY SECT.

The cerebral or cranial nerves correspond pretty closely
in their general arrangement in the three examples. The
offactory nerve-fibres, which originate from the olfactory
lobes, the epic nerves, which are derived from the thalamen-
cephalon, and the auditory nerves which originate from the
medulla oblongata, are the nerves of the special senses of
smell, sight, and hearing respectively, the first ending in the
epithelium of the nasal cavities, the second in the retina of
the eye, and the third in the epithelium of the interior of
the inner ear. Other cranial nerves supply the muscles
that move the eyeball, the skin of the head, the muscles of
the jaws, the tongue, pharynx, heart, stomach, etc.

The structure of the eye is in all essential respects the
same in all the three examples ; such differences as there
are will be referred to later. The eye of a bullock or a
sheep, being larger, may with advantage be substituted.
The eyeball is globular, and is encased in a rough opaque
capsule, the sc/ero#c. It lies in the cavity of the orbit, and
is capable of being turned about in various directions by a
number of muscles inserted into it. On the side of the
eyeball directed towards the light, the opaque sclerotic is
replaced by a transparent membrane, the cornea, which
forms a window through which the rays of light enter the
eye. Within the sclerotic is a more delicate pigmented
layer, the choroid. ‘Towards the cornea the choroid passes
into a circular pigmented diaphram, the 277s, the opening
of which is known as the puzpz/. Through the pupil, the
size of which is capable of being increased or diminished,
the light is admitted into the interior of the eye. The sen-
sitive part of the eye, the part on which the image produced
by the rays of light proceeding from an object must fall in
order to produce the sensation of sight, is a soft gray layer
lining that part of the cavity of the eye which lies within the

XII PHYLUM CHORDATA 357

iris. The rays of light are brought to a focus on the retina
mainly by means of the crystaline lens, a firm, glassy body
situated within the iris. The cornea also assists in this, as
does a gelatinous substance, the vitreous humour, which fills
the part of the cavity of the eyeball internal to the lens.

The ear in the dogfish is imbedded in the cartilage of
the posterior part of the skull (auditory region). It con-
sists of a somewhat complicated structure termed the

Fic. 220. — Diagrammatic horizontal section of the eye of man. c, cornea; ch.
choroid (dotted); C. P, ciliary processes; e. c, epithelium of cornea; e. c/,
conjunctiva; fc, yellow spot; /, iris; Z, lens; ON, optic nerve; OS, ora
serrata; o-x, optic axis; fg. c. R, anterior non-visual portion of retina; P. £,
pigmented epithelium (black); A, retina; sf. 7, suspensory ligament; Sc/,
sclerotic; V. H, vitreous body. (From Foster and Shore’s Phystology.)

membranous labyrinth, with soft walls and an_ internal
epithelium in which the fibres of the auditory nerve termi-
nate. Contained in the interior of the labyrinth is a fluid,
the endolymph, in which there are suspended particles of

358 MANUAL OF ZOOLOGY SECT.

carbonate of lime, the o“#/ths. In the lizard and rabbit
there are superadded to this, the essential part of the ear,
certain accessory parts. The most important of these is
the Ampanum or drum of the ear. This is a cavity to the
outside of the auditory region of the skull (the region in
which the membranous labyrinth is enclosed). The tym-
panum communicates with the pharynx through a passage
known as the Lustachian passage. Externally the cavity of
the tympanum is closed by a tense, drum-like membrane,
the Ampanic membrane. The tympanic membrane is set
in vibration by the waves of sound, and the vibrations are
transmitted across the tympanic cavity by a slender rod of
bone (in the lizard) or a chain of minute bones (in the
rabbit). The inner end of the rod or chain of bones is
inserted into a membrane covering over a small aperture in
the outer wall of the auditory region of the skull, which
forms the inner wall of the tympanic cavity, and by this
means the vibrations are communicated to the endolymph
of the membranous labyrinth and affect the terminations
of the auditory nerve-fibres. In the lizard the tympanic
membrane is nearly on a level with the skin of the head,
and its position is conspicuously indicated by a brown
patch situated behind the eye. In the rabbit the tympanic
membrane is more deeply sunk, and a wide passage, the
passage of the outer ear, leads to it from the exterior. The
ear of the rabbit also differs from that of the lizard in the
presence of the prominent auricle or pinna of the ear to
which reference has been already made.

The &zdneys, or organs of renal excretion, though they
differ in form in the three examples are not widely different
in essential structure. Their function is the secretion of
urine, which consists of water containing various nitrogenous
waste matters in solution. Essentially the kidney is a mass

XII PHYLUM CHORDATA 359

of tubules by whose agency the process of secretion is car-
ried on, the whole being richly supplied with blood-vessels.
Eventually the tubules open into a duct, the veer. In the
lizard and the rabbit there is present a median thin-walled
sac, the wrinary bladder, in which the urine is stored, to be
discharged at intervals. In the rabbit the ureters open into
the bladder, and the latter opens on the exterior by a median
canal, the wre¢hra. In the lizard the ureters and the bladder
have independent openings into the cloaca, and the bladder
is filled only by regurgitation from the latter chamber.

The sexes are distinct in all three. There are two ¢sées,
each with its duct or vas deferens. In the female there are
two ovaries, which are solid bodies in which the ova lie im-
bedded. In the dogfish, when mature, the ova are of large
size, containing a great quantity of food-yolk. The ova of
the rabbit are extremely small, while those of the lizard are
of a size intermediate between those of the other two.
Each ovum is enclosed in a follicle—the Graafian follicle —
with a wall composed of small cells. When the ovum
approaches maturity the follicle projects on the surface of
the ovary, and eventually the wall becomes ruptured and
the ovum escapes into the body-cavity.

The oviducts, of which there are two, are not connected
with the ovaries, each opening anteriorly into the body-
cavity by a wide opening. In the dogfish and the lizard
the oviducts remain practically distinct from one another
throughout; in the rabbit the posterior parts are united to
form a median chamber, the body of the wserus, and a
median passage, the vagina, leading to the exterior. The
ova in all three, when discharged from the ovaries, enter the
wide openings of the oviducts and are impregnated during
their passage backwards. In both the dogfish and the lizard
each fertilised ovum becomes enclosed while in the oviduct

360 MANUAL OF ZOOLOGY SECT.

in a tough shed/, and is discharged when development has
only begun. In the rabbit the fertilised ovum is received
into the uterus and there undergoes its development, the
young rabbit when born differing little, save in size, from the
adult. The nourishment of the fe¢us or uterine young of
the rabbit is effected by means of a special vascular structure
known as the J/acen‘a, by means of which nutrient material
passes from the blood of the mother to that of the foetus ;
and after birth the young rabbit receives its nourishment
for a time exclusively from the secretion of a set of glands
of the mother—the mammary or milk glands.

CLASS I. CYCLOSTOMI

The iowest of existing Craniate Vertebrates are certain
fishlike animals known as “lampreys” and “hag-fishes,”
or “slime-fishes,” which are looked upon as constituting the
class of Craniata, to which the name of Cyclostomi is ap-
plied. Of them it is here possible only to make the briefest
mention. The lampreys (/e¢romyzon and other genera)
and the hag-fishes or slime-fishes (AZvxine and Bdellostoma)
are somewhat eel-like in general shape, that is to say, they
have a long and narrow body without marked external dis-
tinction into regions, and with a soft and slimy integument.
Of the fins of such a fish as the dogfish the median or un-
paired series alone are represented, paired fins corresponding
to the limbs of the higher Craniata being entirely absent.
There is a dorsal fin divided into two in the lampreys, undi-
vided in the hag-fishes, which is continued as a tail fin round
the posterior or caudal extremity of the body. On the
lower or ventral surface of the anterior or head-end is a deep
hollow — the buccal funnel, much more conspicuous in the
lampreys than in the hags, at the bottom of which the small

XII PHYLUM CHORDATA 361

opening of the mouth is situated. There are no jaws, but
on the inner surface of the buccal funnel and on the tongue
—a fleshy (?) process below the opening of the mouth. In
Myxine the funnel is edged with slender, flexible processes
or tentacles. At the sides of the head are the eyes, well
developed and conspicuous in the lamprey, imperfect and
buried beneath the skin in Myxine, and on the upper surface
is a single median aperture, the nostril. Further back at

Fic. 221. — Petromyzon marinus. Ventral (A), lateral (B), and dorsal (C) views
of the head. yr. cl. s, first gill-cleft; duc. /, buccal funnel; eye, eye; th, mouth;
na. ap, nasal aperture; /, papilla: fv, pineal area; ¢. s, ¢. 2, ¢. 3, teeth of buccal
funnel; ¢. 4, teeth of tongue. (After W. K. Parker.)

the sides of the head are, in the lamprey, a series of seven
pairs of slits, the gill-slits, leading to the gill-pouches ; in
Bdellostoma there are six pairs of small gill-slits, in Myxine
only a single aperture on each side.

The skeleton is very unlike that of the true fishes, and

362 MANUAL OF ZOOLOGY SECT. XII

is in some respects-extremely primitive. The spinal col-
umn is represented merely by a thick persistent notochord,
enclosed in a sheath, with, in the lampreys, small carti-

N2.AD na.ap

@

2 @ 6 6-8-0

oes.cl.d

Fic. 222. — Head of Myxine glutinosa (A) and of Bdellostoma forsteri (B), from
beneath. 47. af, branchial aperture; 4”. cd. z, first branchial cleft; 722, mouth;
na. ap, nasal aperture; oes. ct. d, cesophageo-cutaneous duct. The smaller open-

ings in A are those of the mucous glands. (After W. K. Parker.)

laginous processes representing neural and heemal arches.
The skull is cartilaginous, and is peculiarly modified. Be-
hind it in the lamprey is a remarkable basket-like apparatus,

364 MANUAL OF ZOOLOGY SECT.

composed of cartilaginous processes. This branchial basket,
as it is termed, supports the gill-sacs.

The gill-sacs, of which there are either six or seven pairs,
are the organs of respiration, representing the gills of the
true fishes. In the lamprey each of these communicates
‘with the exterior by the corresponding gill-slit, and inter-
nally opens into a common passage, the respiratory tube
which leads in front into the buccal cavity. In Bdellostoma
each gill-pouch has its own internal opening through a
narrow tube into the pharynx, as well as its external open-
ing through a small gill-slit. In Myxine, on the other
hand, though each pouch has a separate internal commu-
nication with the pharynx, the tubes leading outwards from
the gill-pouches of each side all join to form a common
tube, which opens on the exterior by the single gill-slit.

The other systems of organs are not so remarkable. The
alimentary canal, the heart, and the brain are not widely
different from those of the true fishes. A peculiar feature
is that there is only a single nasal sac (opening by the single
nasal aperture already referred to) instead of the pair
developed in all other Craniates ; in Myxine its cavity com-
municates by a passage with the cavity of the mouth. In
the lamprey, in addition to paired eyes having the typical
vertebrate structure, there is connected with a lobe in the
roof of the fore-brain a median or pineal eye of simpler
structure and imperfectly understood function.

Lampreys live mainly in rivers and estuaries. Their food
consists chiefly of small aquatic animals, such as worms,
small crustaceans, etc.; but they also sometimes attach
themselves to the bodies of fishes, by means of the sucker-
like buccal funnel, and rasp off portions of the flesh with the
horny teeth of the tongue. Myxine actually makes its way
into the interior of the bodies of large fishes, such as the

xl PHYLUM CHORDATA 365

cod, consuming the flesh in its passage, and thus becomes
for a time an internal parasite —the only example among
the Vertebrata of sucha condition. In the free state Myxine
usually lies buried in the sand, with only the anterior end,
with the nasal aperture, projecting on the surface. By
means of the passage leading from the nasal sac to the
mouth, water passes in and out through the nasal aperture,
and the process of respiration is carried on while the ani-
mal remains almost completely hidden.

The geographical distribution of the Cyclostomi is some-
what remarkable. /e¢romyzon is found on the coasts and
in the rivers of Europe, North America, Japan, and West
Africa. Of the allied genera one, /chthyomyzon, occurs on
the western coast of North America ; another, Afordacia, in
Tasmania and Chili; a third, Geo¢ria, in the rivers of Chili,
Australia, and New Zealand. Myxine occurs in the North
Atlantic and on the Pacific Coast of South America, includ-
ing the Straits of Magellan; Bdellostoma on the coasts of
South Africa, New Zealand, and Chili.

CLASS II. PISCES

The class Pisces or Fishes includes the Elasmobranchii or
cartilaginous fishes (sharks, dogfishes, and rays), the Teleo-
stomi or bony fishes (such as perch, pike, mackerel, cod,
sole, salmon, sturgeon, and bony pike), and the Dipnoi or
lung-fishes. In these the organs both of respiration and
of locomotion are adapted for an aquatic mode of life. The
chief and, in the majority, the only organs of respiration
are the gills, which are in the form of series of vascular
processes attached to the branchial arches and persisting
throughout life. The organs of locomotion are the paired
pectoral and the pelvic fins, and the unpaired dorsal,

366 MANUAL OF ZOOLOGY SECT.

ventral, and caudal; these are all supported by fin-rays of
dermal (p. 372) origin. A hard external covering of scales
developed in the dermis is usually present. In the en-
doskeleton the notochord is usually replaced more or less
completely by cartilaginous or bony vertebre; there is a
well-developed skull and a system of well-formed visceral
arches, of which the first forms the upper and lower jaws, the
latter movably articulating with the skull, and both nearly
always bearing teeth. An air-bladder is frequently present,
and in certain exceptional cases acquires the function of a
lung or chamber for breathing air.

Sub-class I. Elasmobranchii

A dogfish may be selected as a convenient example of
the sub-class and of the class Pisces. Dogfishes occur at
slight depths off the coasts in all quarters of the globe. The
commonest European forms are the rough hound (Scydlium
canicula), the lesser spotted dogfish (.S. catulus), the
piked dogfish (Acandhias vulgaris), and the smooth hound
(Mustelus vulgaris). Allied species of the southern hemi-
sphere are Scy/um, Acanthias, and Mustelus anarcticus.
On the coast of Northeastern America the common dogfish
is Afustelus canis, For the description which follows, any
of these species wil be found to serve very well.

A slight general account of the dogfish has already been
given in the introduction to the Craniata; this has now to be
extended and supplemented. The general shape (Fig. 206)
may be described as fusiform ; at the anterior or head-end it
is broad and depressed ; posteriorly it tapers gradually and
is compressed from side to side. The head terminates
anteriorly in a short blunt snout. The tail is narrow and
bent upwards towards the extremity. The entire surface is

XII PHYLUM CHORDATA 367

covered closely with very minute hard flacoid scales or
dermal teeth somewhat larger on the upper surface than
on the lower. These are pointed, with the points directed
somewhat backwards, so that the surface appears rougher
when the hand is passed over it forwards than when it is
passed in the opposite direction. When examined closely,
each scale is found to be a minute spine situated on a
broader base. The spine consists of dentine covered with a
layer of enamel; the base is composed of bone, and the
whole scale has thus the same essential structure as a tooth.
Along each side of the head and body runs a faint depressed
longitudinal line or slight narrow groove, — the dazeral “ine.

As in fishes in general, two sets of fins are to be
recognised, — the wzpaired or median fins, and the pazred or
lateral. These are all flap-like outgrowths, running vertically
and longitudinally in the case of the median fins, nearly
horizontally in the case of the lateral; they are flexible,
but stiffish, particularly towards the base, owing to the
presence of a supporting framework of cartilage. Of the
median fins, two — the dorsa/— are situated, as the name
indicates, on the dorsal surface: they are of triangular
shape ; the anterior, which is the larger, is situated at about
the middle of the length of the body, the other a little
further back. The cawda/ fringes the tail; it consists of a
narrower dorsal portion and a broader ventral, continuous
with one another round the extremity of the tail, the latter
divided by a notch into a larger, anterior, and a smaller,
posterior lobe. ‘The tail is heterocercadl, t.e., the posterior
extremity of the spinal column is bent upwards and lies in
the dorsal portion of the caudal fin. The ven/ra/ or
so-called ama/ fin is situated on the ventral surface, opposite
the interval between the anterior and posterior dorsals ; it
resembles the latter in size and shape.

368 MANUAL OF ZOOLOGY SECT.

Of the /atera/ fins there are two pairs, the pectoral and the
pelvic. The fectora/ are situated at the sides of the body,
just behind the head. The e/vic, which are the smaller, are
placed on the ventral surface, close together, in front of the
middle of the body. In the males the bases of the pelvic fins
are united together in the middle line, and each has connected
with it a clasper or copulatory organ. ‘The latter is a stiff rod,
on the inner and dorsal aspect of which is a groove leading
forwards into a pouch-like depression in the base of the fin.

The mouth —a transverse, somewhat crescentic opening
—is situated on the ventral surface of the head, near its
anterior end. In front and behind it is bounded by the
upper and lower jaws, each bearing several rows of teeth
with sharp points directed backwards. The nostrils are sit-
uated one in front of each angle of the mouth, with which
each is connected by a wide groove, the nasobuccal groove.
A small rounded aperture, the sfzvacle, — placed just behind
the eye, —leads into the large mouth-cavity or pharynx.
Five pairs of slits running vertically on each side of the neck,
the branchial shits, also lead internally into the mouth-
cavity. A large median opening on the ventral surface at
the root of the tail, between the pelvic fins, is the opening
leading into the cloaca, or chamber forming the common
outlet for the intestine and the renal and reproductive organs.
A pair of small depressions, the aédominal pores, situated
behind the cloacal opening, lead into narrow passages open-
ing into the abdominal cavity.

The skeleton is composed entirely of cartilage, with, in
certain places, depositions of calcareous salts. As in Verte-
brates in general, we distinguish two sets of elements in the
skeleton, — the axial set and the appendicular, the former
comprising the skull and spinal column, the latter the limbs
and their arches.

XII PHYLUM CHORDATA 369

The spinal column is distinguishable into two regions, —
the region of the trunk and the region of the tail. In the
trunk region each vertebra (Fig. 209, 4) consists of a centrum
(¢), neural arch (wa), and transverse processes (/. pr).
In the caudal region there are no transverse processes, but
infertor or hemal arches (D,h. a) take their place. The
centra of all the vertebree are deeply biconcave or amphi-
celous, having deep conical concavities on their anterior
and posterior surfaces. Through the series of centra runs
the notochord, greatly constricted in the centrum itself,
dilated in the large spaces formed by the apposition of the
amphiccelous centra of adjoining vertebre. The concave
anterior and posterior surfaces of the centra are covered
by a dense calcified layer, and eight radiating lamelle of
calcified material run longitudinally through the substance
of the centrum itself. Each neural arch consists of a pair
of rod-like neural processes, which form the sides, and two
pairs of compressed neural plates (one placed opposite the
centrum, the other or 7ufrcalary cartilage, opposite the
interval between adjoining centra), which form the roof of
the arch, together with usually two nodules — the repre-
sentatives of meural spines — which form the keystones.
The transverse processes are very short: connected with
each of them is a cartilaginous rudimentary 774 about half
an inch in length.

The cranium (Fig. 224) is a cartilaginous case, the wall
of which is continuous throughout, and not composed, like
the skulls of higher vertebrates, of a number of distinct ele-
ments (bones) fitting in together. At the anterior end is a
rostrum, consisting of three cartilaginous rods converging as
they extend forwards and meeting at their anterior ends.
At the sides of the base of this are the olfactory capsules

(olf. cp),—thin rounded cartilaginous sacs opening widely
2B

370 MANUAL OF ZOOLOGY SECT.

below, —the cavities of the two capsules being separated
from one another bya thin septum. The part of the roof of
the cranial cavity behind and between the olfactory capsules
is formed, not of cartilage, but of a tough fibrous membrane,
and the space thus filled in is termed the anéerior fontanelle ;
in contact with the lower surface of the membrane is the
pineal body, to be afterwards mentioned in the account of
the brain. Each side wall of this part of the skull presents
a deep concavity, the o7éz¢ over which is a ridge-like
prominence, the swpra-orbital crest, terminating anteriorly
and posteriorly in obscure processes termed respectively the
pre-orbital and post-orbital processes. Below the orbit is a
longitudinal 7¢2/ra-orbital ridge.

Behind the orbit is the audfory region of the skull (aud.
cp), a mass of cartilage in which the parts of the mem-
branous labyrinth of the internal ear are embedded. On
the upper surface of this posterior portion of the skull are
two small apertures situated in a mesial depression. These
are the openings of the agueductus vestibuli (endolymphatic
ducts), leading into the vestibule of the membranous laby-
rinth. Behind this again is the occipital region, forming the
posterior boundary of the cranial cavity, and having in the
middle a large rounded aperture, the foramen magnum,
through which the spinal cord contained in the neural canal
and protected by the neural arches of the vertebree becomes
continuous with the brain, lodged in the cranial cavity. On
either side of this is an articular surface, the occipital
condyle, for articulation with the spinal column.

A number of smaller apertures or foramina, chiefly for
the passage of nerves, perforate the wall of the skull.

In close connection with the cranium are a number of
cartilages composing the wsceral arches (Fig. 224). These
are incomplete hoops of cartilage, mostly segmented, which

37!

PHYLUM CHORDATA

XII

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372 MANUAL OF ZOOLOGY SECT.

lie in the sides and floor of the mouth-cavity or pharynx.
The first of these forms the upper and lower jaws. The
upper jaw, or palato-quadrate (up.7), consists of two stout
rods of cartilage firmly bound together in the middle line
and bearing the upper (or anterior) series of teeth. The
lower jaw, or AZeckel’s cartilage (2. 7), likewise consists of
two stout cartilaginous rods firmly united together in the
middle line, the union being termed the symfhysis. At their
outer ends the upper and lower jaws articulate with one
another by a movable joint. In front the upper jaw is
connected by a ligament with the base of the skull.

Immediately behind the lower jaw is the hyord arch. This
consists of two cartilages on each side, and a mesial one in
the middle below. The uppermost cartilage is the hyo-man-
dibular (hy. m) ; this articulates by its proximal end with a
distinct articular facet on the auditory region of the skull;
distally it is connected by ligamentous fibres with the outer
ends of the palato-quadrate and Meckel’s cartilage. The
lower lateral cartilage is the ceravo-hyal (hy. cn). Both the
hyo-mandibular and cerato-hyal bear a number of slender
cartilaginous rods —the branchial rays of the hyoid arch
(4r.r). The mesial element, or dasz-Aya/, lies in the floor
of the pharynx. Behind the hyoid arch follow the dranchial
arches, which are five in number. Each branchial arch con-
sists of several cartilages and bears branchial rays.

The skeleton of all the fins — paired and unpaired — pre-
sents a considerable degree of uniformity. The main part
of the expanse of the fin is supported by a series of flattened
segmented rods, the preryerophores or cartilaginous fin-rays,
which lie in close apposition ; in the case of the dorsal fins
these are calcified along their axes. At the outer ends of
these are one or more rows of polygonal plates of cartilage.
On each side of the rays and polygonal cartilages are a

XII PHYLUM CHORDATA 373

number of slender horny fibres of dermal origin. In the
smaller median fins there may be an elongated rod of carti-
lage constituting the skeleton, or cartilage may be entirely
absent. In the pectoral fin (Fig. 225) the fin-rays are
supported on three dasa? cartilages articulating with the
pectoral arch. The latter is a strong hoop of cartilage in-
complete dorsally, situated immediately behind the last of

Fic. 225. — Ventral view of pectoral arch of Seyllium with right pectoral fin. The
pectoral arch is divisible into dorsal (Act. g) and ventral (ct. g') portions,
separated by the articular facets (avt._f) for the fin. The pectoral fin is formed
of three basal cartilages (4s. 7-3?) and numerous radials (rad); its free edge is
supported by dermal rays (@. f. 7). (Modified from Marshall and Hurst.)

the branchial arches. It consists of a dorsal, or scapular,
(per. g) and a ventral, or coracoid, portion (fect. g'), the
coracoid portions of opposite sides being completely con-
tinuous across the middle line, while the scapular are sepa-
rated by a wide gap in which the spinal column lies.
Between the two portions are the three articular surfaces
for the three basal cartilages. The three basal cartilages of

374 MANUAL OF ZOOLOGY SECT.

the fin are named, respectively, the anterior, pro-preryeium
(4s. 7), the middle, meso-pterygium (bs. 2), and the pos-
terior, meta-pterygium (bs. 3). Of these the first is the
smallest, and the last the largest. The fe/wic fin has only a
single basal cartilage, articulating with the pelvic arch, with
which also one or two of the fin-rays articulate directly. The
pelvic arch is a nearly straight bar of cartilage which runs
transversely across the ventral surface of the body, just in
front of the cloacal opening.

The mouth leads into a very wide cavity, the pharynx
(Fig. 216, fh), into which opens at the sides the internal
apertures of the branchial clefts and of the spiracle. From
this runs backwards a short wide tube, the wsophagus (gu),
which passes behind into the stomach. The stomach is
a U-shaped organ, with a long left limb (cd. s/) continuous
with the cesophagus, and a short right (py? s¢) passing
into the intestine. At the py/orws—the point where the
stomach passes into the intestine —is a slight constriction
followed by a thickening. The czéstine consists of two
parts, —small intestine or duodenum, and large intestine.
The former is very short, only an inch or two in length.
The iatter (2) is longer and very wide ; it is divisible into
two portions, — the co/on in front and the recéwm behind.
The former is very wide and is characterised by the pres-
ence in its interior of a sfira/ valve, a fold of the mucous
membrane which runs spirally round its interior and both
retards the too rapid passage of the food, and affords a
more extensive surface for absorption. The rectum differs
from the colon in being narrower and in the absence of the
spiral valve ; it opens behind into the cloaca.

There is a large diver (2. /r, r. 7) consisting of two elon-
gated lobes. A rounded sac, the gal/-dladder, lies em-
bedded in the left lobe at its anterior end. The duct of

XII PHYLUM CHORDATA 375

the liver, the dz duct, runs from the liver to the intes-
tine. Proximally it is connected with the gall-bladder and
by branch ducts with the right and left lobes of the liver.
It opens into the commencement of the colon.

The pancreas (pan) is a light-coloured compressed gland
consisting of two main lobes with a broad connecting isthmus
lying in the angle between the right-hand limb of the stomach
and the small intestine. Its duct enters the wall of the small
intestine and runs in it for about half an inch, opening event-
ually at the point where the small intestine passes into the
colon.

Connected with the rectum on its dorsal aspect is an oval
gland, the rectal gland (rc¢. g/), about three-quarters of an
inch in length.

The spleen (spl) is a dark-red or purple body attached to
the convexity of the U-shaped stomach, and sending a narrow
lobe along the right-hand limb.

The organs of respiration in the dogfish are the gids,
situated in the five gid/-pouches. Each gill-pouch is an
antero-posteriorly compressed cavity opening internally into
the pharynx and externally by the gill-slit. The walls of the
pouches are supported by the branchial and hyoid arches with
their rays, the first pouch being situated between the hyoid
and first branchial arches, the last between the fourth and
fifth branchial arches. On the anterior and posterior walls
of the pouches are the gis, each hemibranch consisting of a
series of close-set parallel folds or plaits of highly vascular
mucous membrane. Separating adjoining gill-pouches and
supporting the gills are a series of broad ¢vterbranchial septa,
each containing the corresponding branchial arch with its
connected branchial rays. The most anterior hemibranch is
borne on the posterior surface of the hyoid arch. The last
gill-pouch differs from the rest in having gill-plaits on its

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376

SECT. XII PHYLUM CHORDATA 377

anterior wall only. On the anterior wall of the spiracle is a
rudimentary gill, the pseudo-branch or spiracular gill, in
the form of a few slight ridges.

The Aeartis situated in the pericardial cavity, on the ventral
aspect of the body, in front of the pectoral arch and between
the two series of branchial pouches. The heart consists of
four chambers, — sinus venosus (s.v), auricle (au), ventri-
cle (v), and conus arteriosus (c. art), through which the
blood passes in the order given. The szus venosus is a thin-
walled, transverse, tubular chamber, into the ends of which
the great veins open. It opens into the auricle by an aper-
ture, the sénu-auricudar aperture. The auricle is a large,
triangular, thin-walled chamber, situated in front of the sinus
venosus and dorsal to the ventricle. Its apex is directed
forwards, and its lateral angles project at the sides of the
ventricle ; it communicates with the ventricle by a slit-like
aperture guarded by a two-lipped valve. The ventricle is a
thick-walled, globular chamber, forming the most conspicu-
ous part of the heart when looked at from the ventral sur-
face. From it the conus arteriosus runs forwards as a
medium stout tube to the anterior end of the pericardial
cavity, where it gives off the ventral aorta. It contains two
transverse rows of valves, anterior and posterior, the former
consisting of three, the latter of three or four. The ventral
aorta (Fig. 227, v.a@o) gives origin to a series of paired affer-
ent branchial arteries (a. br.a), one for each branchial
pouch.

From the gills the blood passes by means of the efferent
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series of loops, one running around the margin of each of
the first four internal branchial clefts: a single vessel runs
along the interior border of the fifth branchial cleft and
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SECT. XII PHYLUM CHORDATA 379

chial vessels run inwards and backwards from the loops
under cover of the mucous membrane of the roof of the
mouth to unite in a large median trunk — the dorsal aorta
(d.a0). From the first efferent vessel, that from the first
or hyoidean gill, arises the carotid artery, which runs for-
wards and bifurcates to form the zaéernal and external
caroud arteries (c.a), supplying the head with arterial
blood.

The dorsal aorta runs backwards throughout the length
of the body-cavity, giving off numerous branches, and is
continued as the caudal artery (cd.a), which runs in the
canal enclosed by the inferior arches of the caudal vertebre.

The veins are very thin-walled, and the larger trunks are
remarkable for their dilated character, from which they
have obtained the name of szzuses, though they are true
vessels and not sinuses in the sense in which the word is
used in dealing with the Invertebrates.

The venous blood is brought back from the head by a
pair of jugular or anterior cardinal sinuses (7. v), and from
the trunk by a pair of posterior cardinal sinuses (crd.v). At
the level of the sinus venosus the anterior and posterior car-
dinals of each side unite to form a short, nearly transverse
sinus, the precaval sinus or ductus Cuviert ( pr.cv.v) which
is continued into the lateral extremity of the sinus venosus.

There are two portal systems of veins, the renal portal
and the hepatic portal (h.p.v), by which the kidneys and
liver, respectively, are supplied with venous blood. The cau-
dal vein (cd.v), which brings back the blood from the tail,
running, along with the caudal artery, through the inferior
arches of the vertebree, divides on entering the abdominal
cavity into right and left rexa/ portal veins (7.p.v), which
end in a number of afferent renal veins supplying the kidneys.

The hepanc portal vein (h. p.v) is formed by the conflu-

380 MANUAL OF ZOOLOGY SECT,

ence of veins derived from the intestine, stomach, pancreas,
and spleen, and runs forwards to enter the liver a little to
the right of the middle line. The blood from the liver
enters the sinus venosus by two hepatic sinuses (h.v) placed
close together.

The fore-brain consists of a rounded, smooth prosen-
cephalon (Fig. 219, V. H), divided into two lateral parts by
a very shallow median longitudinal groove. From its antero-
lateral region each half gives off a thick cord, which dilates
into a large mass of nerve matter, the olfactory lobe (L. of),
closely applied to the posterior surface of the correspond-
ing olfactory capsule. The diencephalon (Z//) is com-
paratively small; its roof is very thin, while the floor is
composed of two thickish masses, the optic thalamt. At-
tached to the roof is a slender tube, the epiphysis cerebri or
pineal body (Gp), which runs forwards and terminates in a
slightly dilated extremity fixed to the membranous part of
the roof of the skull. Projecting downwards from its floor
are two rounded bodies, the Zod7 tnfertores, which are dilated
portions of the ¢zfundibulum ; and attached to this, behind,
is a thin-walled sac ,— the pituitary body or hypophysis cerebri
having a pair of thin-walled vascular lateral diverticula, — the
sacci vasculost, and having on its ventral surface a median
tubular body attached at its posterior end to the floor of the
skull. In front of the infundibulum, and also on the lower
surface of the diencephalon, is the opie chiasma, formed by
the decussation of the fibres of the two optic nerves. The
mid-brain (JZH’) consists of a pair of oval optic lobes
dorsally, and ventrally of a band of longitudinal nerve-fibres
corresponding to the crura cerebri of the higher vertebrate
brain. The cerebellum (/7//) is elongated in the antero-
posterior direction, its anterior portion overlapping the
optic lobes, and its posterior the medulla oblongata. Its

XII PHYLUM CHORDATA 381

surface is marked with a few fine grooves. The medulla
oblongata (/V/ ), broad in front, narrows posteriorly to pass
into the spinal cord. The fourth ventricle (F. rho) is a
shallow space on the dorsal aspect of the medulla oblongata
covered only by a thin vascular membrane, the choroid
plexus ; it is wide in front and gradually narrows posteriorly.
At the sides of the anterior part of the fourth ventricle are a
pair of folded ear-shaped lobes, the corpora restiformia.

The fourth ventricle is continuous behind with the cen-
tral canal of the spinal cord. In front it is continuous with
a narrow passage, the z/er (z¢e7), which opens anteriorly into
a wider space, the dacale or third ventricle (dia) occupying
the interior of the diencephalon. From this opens in front
a median prosocele, which gives off a pair of paraceles
(fara) extending into two lateral portions of the prosen-
cephalon.

A series of nerves arise in pairs from the brain and spinal
cord. From the spinal cord the nerves arise segmentally,
one pair corresponding to each myomere, and pass through
apertures in the neural arches of the vertebree. Each arises
by two roots, a dorsal and a ventral. The dorsal root is
dilated into a ganglion, and contains only sensory fibres ;
the ventral root is non-ganglionated, and is motor. A
longitudinal ganglionated sympathetic nerve, extending along
the dorsal region of the ccelome, is connected with the
spinal nerves, and sends branches to the viscera, blood-
vessels, etc.

From the brain arise ten pairs of nerves, some of which
are sensory, others motor, others mixed. Three are the
nerves of the principal sense organs: the first, or o/factory,
supplying the organ of smell (Fig. 228, o/f. s) ; the second,
or optic, the retina of the eye, and the eighth, or auditory,
the organ of hearing. ‘The third, or oculomotor, the fourth,

382 MANUAL OF ZOOLOGY SECT.

or ¢rochlear (path), and the sixth, or adducent, go to the
muscles of the eye; the fifth, or ¢7geminal (oph. V, mx. V,
mnad. V), to the snout and jaws; the seventh, or factal (ofh.

erect | }

eacl.rect poe

SPp.CO lalvag

Fic. 228.—Scyllium catulus. Dissection of the brain and spinal nerves from the
dorsal surface. The right eye has been removed. The cut surfaces of the
cartilaginous skull and spinal column are dotted. The ophthalmicus profundus
and the buccal branch of the facial are not represented. c/. r-c/. 5, branchial
clefts; ef, epiphysis; ev¢. rect, external rectus muscle of the eye-ball; g7. ph,
glossopharyngeal; Aor. can, horizontal semicircular canal; Ay. mud. VII, hyo-
mandibular portion of the facial; zz/ 0/, inferior oblique muscle; zut. rect,
internal rectus muscle; Za¢. vag, lateral branch of vagus; ax. V’, maxillary
division of the trigeminal; o// cfs, olfactory capsule; olf s, olfactory sac;
oph. I. VI, superficial ophthalmic branches of trigeminal and facial; path,
fourth nerve; //. I’//, palatine branch of facial; sf. co, spinal cord; | sfzr,
spiracle; s. rect, superior rectus muscle; s. 04/, superior oblique; vag, vagus;
vest, vestibule. (From Marshall and Hurst.)

VII, pl. VIL, hy. mnd. VIT), to the palate, lower jaw, and
hyoid arch; the ninth, or glossopharyngeal (g/. ph), to the

XII PHYLUM CHORDATA 383

hyoid and first branchial arches; and the tenth, or zagus
(vag), to the remaining branchial arches, as well as to the
heart, stomach, and lateral line.

Besides the lateral line, which is probably the seat of a
delicate tactile sense, and the tongue, which is presumably
an organ of taste, there are the three pairs of characteristic
sensory organs, the structure and position of which are very
characteristic of vertebrates. These are the olfactory organs,
the eyes, and the auditory organs. The olfactory organs are
a pair of cup-like sacs on the under side of the snout, en-
closed in the olfactory capsules and opening externally by
the nostrils. They are lined with mucous membrane, which
is raised up into ridges so as to increase the surface. The
general structure of the eyes has already been described
(p. 356). The ear consists of the membranous labyrinth
(p. 357), which is enclosed in the cartilage of the auditory
region of the skull. It consists of a sac called the vestibule
(Fig. 228, vest), with which are connected three tubes,
called from their form the semicircular canals. Two of these,
the anterior and posterior canals, are vertical in position,
and are united with one another at their adjacent ends; at
the other end each is dilated to form a bulb-like swelling,
the ampulla. The third, or horizontal canal (hor. can),
opens at each end into the vestibule, and has an ampulla
at its anterior end. The vestibule gives off a tube, the
endolymphatic duct, which opens at the auditory aperture
already referred to on the top of the head. Endolymph
containing otoliths (p. 358) fills the interior of the labyrinth,
and it is immediately surrounded externally by a space con-
taining a similar watery fluid, the Aeri/vmph. The fibres of
the auditory nerve are distributed to various parts of the
internal epithelium of the vestibule and semicircular canals.
There seems little doubt that the membranous labyrinth

384 MANUAL OF ZOOLOGY SECT,

has not only an auditory, but also an equilibrating function,
z.e., that the fish is enabled by its means to maintain its
equilibrium in the water.

The kidneys (Fig. 227, &) are long flat lobulated
bodies lying one on each side of the backbone in the
posterior part of the abdominal cavity. From the ventral
surface of each spring numerous delicate ducts which unite
into a single tube, the wre/er, opening directly into the
cloaca in the female, in the male into a small paired cham-
ber, the wrogenital sinus (ug. s), which opens into the
cloaca (¢?).

In the male dogfish the testes are a pair of large soft
organs situated in the body-cavity, and united with one
another posteriorly. From the anterior end of each arise
numerous delicate efferent ducts, which enter a long convo-
luted spermiduct or vas deferens (v. def) leading posteriorly
to the urogenital sinus. In the female there is a single
ovary suspended to the dorsal body-wall by a fold of peri-
toneum. In the adult it is studded all over with rounded
projections, the ova. There are two oviducts, a right and a
left, which extend along the whole length of the dorsal wall
of the ccelom below the kidneys. Anteriorly they unite
with one another below the gullet, and just in front of the
line and at the point of junction is a single aperture of con-
siderable size, by which both tubes communicate with the
ceelom ; posteriorly they open into the cloaca. About the,
anterior third of each oviduct is narrow ; its posterior two-
thirds is wide and distensible, and at the junction of the
parts is a yellowish glandular mass, the she/-gland.

Internal impregnation takes place, the spermatic fluid of
the male being passed, by means of the claspers, into the ovi-
ducts of the female. The ova, when ripe, break loose from
the surface of the ovary into the ccelom, and thence pass,

XII PHYLUM CHORDATA 385

through the common aperture, into one or other of the ovi-
ducts, where fertilisation (p. 393) occurs. As it passes into
the dilated portion of the oviduct, the oosperm (p. 60) of
Scyllium becomes surrounded by a horn-like egg-shell (Fig.
229), secreted by the shell-gland, and having the form of a
pillow-case produced at each of its
four corners into a long tendril-like
process. The eggs are laid among
seaweed, to which they become
attached by their tendrils. In some
other dogfishes (Acanthias, Mus-
telus) a mere vestige of the egg-shell
is formed, and the eggs undergo the
whole of their development in the
oviducts, the young being eventu-
ally born alive with the form and
proportions of the adult.

The great size of the egg is due
to the immense quantity of yolk
which it contains; its protoplasm
is almost entirely aggregated at one
pole in the form of a small disc.
When segmentation of the oosperm
takes place, it affects the protoplasm
alone, the inactive yolk taking no
part in the process. The disc of
protoplasm divides to form a little Fic. 229. — Dogfish, egg-case.
heap of cells, the d/astoderm, situ- alse
ated at one pole of the undivided sphere of yolk. The
blastoderm subsequently spreads out as a sheet of cells
over the yolk which it ultimately completely encloses.
While this extension of the blastoderm is taking place, its
middle part becomes raised up into a ridge-like thick-

2c

386 MANUAL OF ZOOLOGY SECT.

ening, which is moulded, step by step, into the form of
the embryo fish. The head, trunk, and tail acquire dis-
tinctness, and become more and more clearly separated off
from the bulk of the egg, the latter taking the form of a
yolk-sac attached by a narrow stalk to the ventral surface of
the embryo (Fig. 230).

In this condition the various parts of the adult fish can
be recognised, but the proportions are different, and the

Fic. 230.— A, embryo of Scyllium with yolk-sac (x 14); B, under-side of head
enlarged. 67. f, branchial filaments protruding through gill-clefts; b7. _/',
branchial filaments projecting through spiracle; cd./, caudal fin; a. 7, dorsal
fins; e,eye; ex. dr. ap, external branchial apertures; #¢4, mouth; za, nostrils;
pet. f, pectoral fin: pv. f, pelvic fin; st, yolk-stalk; v. f, ventral fin; ys. s,
yolk-sac. (After Balfour, slightly altered.)

head presents several peculiarities. The gill-filaments (47. /)
are so long as to project through the external branchial
apertures and the spiracle (47. /) in the form of long threads
abundantly supplied with blood-vessels, and apparently
serving for the absorption of nutriment — the albumen in
the egg-shell in the case of Scyllium, secretions of the ovi-
duct in the viviparous forms. Besides this mode of nutrition
the yolk-sac communicates with the intestine by a narrow
duct, through which absorption of its contents is constantly

XI PHYLUM CHORDATA 387

going on. By the time the young fish is ready to be born
or hatched, the greater part of the yolk-sac has been drawn
into the ccelom, a mere vestige of it still dangling from the
ventral surface of the body.

In all the most important features of their organisation
there is a considerable degree of uniformity among the
Elasmobranchii.

In general shape the sharks (Fig. 231), for the most part,
are somewhat fusiform and slightly compressed laterally. In
the rays (Fig. 232), on the other hand, there is great dorso-

Fic. 231. — Shark (Lamna cornubica). (From Dean’s Fishes.)

ventral compression. The head is in many cases produced
forwards into a long rostrum, which is of immense length
and bordered with triangular teeth in the saw-fish shark
(Pristophorus) and saw-fish ray (Prists). In the hammer-
head shark the anterior part of the head is elongated trans-
versely.

There are well-developed median and paired fins. The
caudal fin is well developed, and, as a rule, strongly hetero-
cercal in the sharks and shark-like rays, feebly developed
in most of the latter group. The dorsal and ventral fins
are large in the sharks, the former completely divided into
two ; in the rays the dorsal fin is usually small, and the ven-

388 MANUAL OF ZOOLOGY SECT.

tral absent. The paired fins are very differently developed
in the two groups. In the sharks both pairs are well devel-
oped, the pectoral being the larger. In the rays or skates
the pectoral fins are extremely large, very much larger than
the pelvic, fringing the greater part of the length of the
flattened body, and becoming prolonged forwards on either

Fic. 232. — European sting-ray (Urolophus cruciatus). (After Giinther.)

side and even in front of the head, so that the animal presents
the appearance of a broad fleshy leaf.

In all recent Elasmobranchs the male has, connected with
the pelvic fins, a pair of grooved appendages, the claspers
or plerygodia, which subserve copulation.

The mouth is situated on the ventral surface of the head,
usually a considerable distance from the anterior extremity.

XII PHYLUM CHORDATA 389

In front of each angle of the mouth on the ventral surface
is the opening of one of the olfactory sacs, each of which
is connected by a groove, the naso-buccal groove, with the
mouth-cavity. Behind the mouth, on the dorsal surface
in the rays, and at the side in the sharks, is the spiracle.
Along the sides of the neck in the sharks, and on the ven-
tral surface in the rays, is on either side a row of slit-like
apertures, the branchial slits or branchial clefts. These
are usually five in number on each side; but in Hexanchus
and Chlamydoselachus there are six, and in Heptanchus
seven. A large cloacal opening is situated just in front of
the root of the tail, and a pair of small openings placed in
front of it, the abdominal pores, lead into the abdominal
cavity.

When the integument develops any hard parts, as is the
case in the majority of the Elasmobranchs, they take the
form, not of regular scales, as in most other fishes, but of
numerous hard bodies, which vary greatly in shape, are
usually extremely minute, but are in some cases developed,
in certain parts of the surface, into prominent tubercles or
spines. When these hard bodies are, as is commonly the
case, small and set closely together in the skin, they give
the surface very much the character of a fine file; and the
skin so beset, known as “shagreen,” is used for various
polishing purposes in the arts. This is the J/acozd form of
exoskeleton, to which reference has been already made.
Each of the hard bodies has the same structure as a tooth,
being composed of dentine, capped with enamel, and sup-
ported on a bony base, representing the cement or crusta
petrosa of the tooth, The dermal fin-rays are horny. The
skeleton is composed of cartilage, with, in many cases,
deposition of bony matter in special places, notably in the
jaws and the vertebral column. The entire spinal column

390 MANUAL OF ZOOLOGY SECT.

may be nearly completely cartilaginous (Hexanchus and
Hebtanchus), but usually the centra are strengthened by

ill
NV

ONTO
May UY
iA

SEPSererrerre ss

EPEPpeees:

Fic. 233. —Skeleton of sting-ray (Urolophus testaceus), ventral view. a. v. fp,
anterior vertebral plate; das. dr, basi-branchial plate; 47. 7-d7.5, branchial
arches. ‘The branchial rays are represented as having been removed, the round
dots indicate their articulations with the arches. c/, skeleton of clasper; 4. m,
hyomandibular; “y, hyoid arch; Zaé, labial cartilage; 27g, ligament connecting
the hyomandibular with the palato-quadrate and Meckel’s cartilage; mck,
Meckel’s cartilage; 7s. pt, mesopterygium; 7¢. At, metapterygium of pectoral
fin: md. pt', metapterygium of pelvic fin; as, nasal cartilage; pal, palato-
quadrate; fect, pectoral arch; A/, pelvic arch; fro. pt, propterygium; sf, spiracu-
lar cartilage.

xl PHYLUM CHORDATA 391

radiating or concentric lamelle of calcified cartilage or
bone, or they may be completely calcified. They are
deeply amphiccelous, the remains of the notochord _per-
sisting in the large spaces between the concave surfaces
of contiguous centra. In the rays the anterior part of the
spinal column becomes converted into a continuous solid
cartilaginous and bony mass—the anéerior vertebral plate
(Fig. 233, @. v. @). Two main regions only are distinguish-

pe. orb

Fic. 234.— Lateral view of the skull of Heptanchus. mck, Meckel’s cartilage;
pal. qu, palato-quadrate; pt. orb, post-orbital process of the cranium, with
Shick the palato-quadrate articulates. (After Gegenbaur.)

able in the spinal column —the pre-caudal region and the

caudal, the latter being distinguished by the presence of in-

ferior or hemal arches. In the pre-caudal region short ribs
may be developed, but these are sometimes rudimentary or
entirely absent.

The skull is an undivided mass of cartilage, hardened, in
many cases, by deposition of osseous matter, but not con-
taining any separate bony elements. In all, the jaws are

392 MANUAL OF ZOOLOGY SECT.

connected with the skull through the intermediation of a
hyomandibular cartilage, or proximal element of the hyoid
arch; in the great majority this is the sole articulation of
the jaws with the skull posteriorly, and the skull is on that
account said to be Ayostyfic ; but in Hexanchus and Hep-
tanchus (Fig. 234) the upper jaw has a direct articulation
with the skull behind the orbit, and the arrangement is
termed amphistyic. There are always five pairs of bran-
chial arches, except in Hexanchus and Chlamydoselachus,
which have six, and Heptanchus, in which there are seven.

The basal cartilages of the pectoral fin are typically three,
as in the dogfish, but there are sometimes four, and the
number may be reduced to two. There are usually two
such cartilages in the pelvic fin, and one alone may be
present.

Electric organs — organs in which electricity is formed
and stored up, to be discharged at the will of the fish —
occur in several Elasmobranchs. They are best developed
in the electric rays (Zorpedo and Aypnos) in which they
form a pair of large masses running through the entire thick-
ness of the body between the head and the margin of the
pectoral fin. By means of the electric shocks which they
are able to administer at will to animals in their immediate
neighbourhood, these torpedo rays are able to ward off the
attacks of enemies and to kill or paralyse their prey.!

Teeth are developed in all on the palato-quadrate or
upper jaw and Meckel’s cartilage or the lower jaw. They
are arranged in several parallel rows, and are developed
from a groove at the back of the jaw, successive rows
coming to the front, and, as they become worn out, falling
off and becoming replaced by others. In the sharks the
teeth are usually large and may be long, narrow, and pointed,

1 Torpedo occidentalis occurs on the southern coast of New England.

XII PHYLUM CHORDATA 393

or triangular with serrated edges, or made up of several
sharp cusps; in the rays, however, the teeth are more or
less obtuse, sometimes, as in the eagle rays, forming a con-
tinucus pavement of smooth plates covered with enamel,
adapted to crushing food consisting of such objects as
shell-fish and the like.

The various divisions of the en¢ertc canal are similar in
all members of the class to what has already been described
in the case of the dogfish. A spiral valve is always present
in the large intestine, though its arrangement varies con-
siderably in the different families. The rectum always ter-
minates in a ¢c/oaca into which the urinary and genital ducts
also lead.

The respiratory organs have in all the same general
arrangement as in the dogfish. The inter-branchial septa
are of considerable breadth and the gill-filaments are
attached to them along their entire length.

The heart also has in all essential respects the same
structure throughout the group, the most characteristic
feature being the presence of a conus arteriosus which is
rhythmically contractile and contains several rows of valves.

Impregnation is internal in all the Elasmobranchii with
the exception of the Greenland shark (Lemargus), the
claspers acting as intromittent organs by whose agency the
semen is transmitted into the interior of the oviducts. In
all Elasmobranchs the ova are very large, consisting of a
large mass of yolk with, on one side, a disc of protoplasm,
the germinal disc. The ripe ovum ruptures the delicate
wall of the follicle in which it is enclosed and escapes into
the abdominal cavity to enter one of the oviducts, as already
stated in the case of the dogfish. Impregnation takes place
in the oviduct, and in the oviparous forms the impregnated
ovum becomes enclosed in a chitinous shell secreted by the

394 MANUAL OF ZOOLOGY SECT.

shell-gland. Enclosed in the shell, the form of which varies
in different groups, the egg passes to the exterior and under-
goes development until the young fish is fully formed, when
it escapes by rupturing the egg-shell. In the viviparous
forms, on the other hand, the ovum undergoes its develop-
ment in the uterus; and the young fish, when it escapes to
the exterior, has assumed all the features of the adult.

The habits of the active, fierce, and voracious sharks,
which live in the surface waters of the sea waging war on
all and sundry, are in strong contrast with those of the more
sluggish rays, which live habitually on the bottom, usually in
shallow water, and feed chiefly on crustaceans and molluscs,
with the addition of such small fishes as they can capture.

As a group, the Elasmobranchs, more particularly the
sharks, are distinguished by their muscular strength, the
activity of their movements, and also by the acuteness of
their senses of sight and smell. The only deep-water
Elasmobranch known is a species of ray, which extends to
a depth of over 600 fathoms.

Sub-class III. Teleostomi ?

The great majority of existing fishes belong to the sub-
class Teleostomi. As a matter of convenience we may look
upon the Teleostomi as consisting of two main divisions, —
the Teleostei, in which are included all the commonest and
most familiar fishes, such as the perch, pike, mackerel, cod,
sole, herring, eel, salmon, etc., and the Ganoidei or Ganoids,
such as the sturgeon, body pike (Lefidosteus), and bow-fin
(Amia) of North America, and the Folypterus of the Nile.
They are distinguished from Elasmobranchs by the posses-

1 Sub-class II, the small group Holocephali, or Chimzeras and their
allies, is one of the groups omitted from this work, See Preface.

XII PHYLUM CHORDATA 395

sion of an operculum or gill-cover, by the absence of a
cloaca, by having the primary skull and shoulder-girdle
complicated by the addition of membrane-bones, and by
possessing bony instead of horn-like fin-rays.

A typical Teleostomian, such as a trout (Fig. 235)! ora
herring, has a long compressed body nearly half of which
is formed by the tail, pointed anterior and posterior ends, a
large vertical tail-fin, a head of moderate size, and a terminal
mouth. Such a form is eminently fitted for progression
through the water. But from this characteristic fish form

pets

Fic. 235.—Salmo fario. a. 7, adipose lobe of pelvic fin; am, anus; c. /, caudal
fin; @. f 17, first dorsal; @ f. 2, second dorsal or adipose fin; @. /, lateral line;
7 operculum; pct. f, pectoral fin; pu. /, pelvic fin; v. f, ventral fin. (After
ardine. )

there are many striking deviations. The body may be
greatly elongated and almost cylindrical, as in the eels; or
of great length and strongly flattened from side to side, as
in the ribbon-fishes ; or the head may be of immense pro-
portional size and strongly depressed, as in certain shore-
fishes, such as the fishing-frog ; or, as in the beautiful reef-
fishes, the whole body may be as high as it is long. The
mouth sometimes has a ventral position, as in the Elasmo-
branchs, with the snout prolonged over it; this is the case,

1 Our common brook trout in the northeastern states is Sa/mo fontinalis.

396 MANUAL OF ZOOLOGY SECT.

for example, in the sturgeons (Fig. 240). On the other
hand, in the ground-feeding “‘ star-gazers ” and some others,
the lower jaw is underhung like that of a bull-dog, and the
mouth becomes dorsal in position. A dcak may be pro-
duced by the elongation of the upper jaw, as in the sword-
fish, or of the lower jaw, as in the half-beak or czar-fish, or
of both jaws as in the bony pike.

An operculum or gill-cover (of), a flap which covers the
gills of each side and bounds in front the single, usually
crescentic gill-opening, is always present, and is supported
by four membrane bones. Ventrally the operculum is pro-
duced into a thin membranous extension, the dranchio-
stegal membrane, which is in nearly all cases supported by a
series of bony rays. Spiracles are absent except in certain
of the Ganoids.

There are dorsal, ventral, and caudal median fins. The
dorsal is usually divided into two; in a few it is partly or
wholly supported by a series of finlets. The caudal is in
the majority of a type to which the term homocercal is
applied. The homocercal caudal fin is divided into two
equal or sub-equal lobes, upper and lower, so that it appears
symmetrical externally, though the posterior portion of the
spinal column which supports it is strongly bent upwards
and terminates in the upper lobe. In some of the Ganoids,
however, this upward curvation of the caudal part of the
spinal column does not occur, and the tail is symmetrical
internally as well as externally ; in these the tail is said to
be adiphycercal. In many Ganoids the tail is heterocercad, as
in nearly all the Elasmobranchs (p. 367). In some Teleos-
tomi dorsal, caudal, and ventral fins are united into a con-
tinuous fold. The dermal fin-rays of the caudal fin and a
portion or all of those of the rest of the fins are slender
flexible rods divided into a series of short segments and

XII PHYLUM CHORDATA 397

usually branching at the free ends. In many, however, the
anterior portions of the dorsal, ventral, and pelvic fins are
supported not by flexible jointed rays, but by stiff unjointed
sharp spines.

The paired fins, pectoral and pelvic, are usually thin and
flexible, supported mainly, or exclusively, by jointed rays.
The pectorals always retain their normal position, just
behind the gill-cleft, but the pelvics always become more or
less shifted forwards from their typical position beside the
vent; when they are not placed as far forwards as the

UST

Fic. 236. —Salmo fario. Caudalend of vetebral column. CN,centrum; D.F.R,
dermal fin-rays; H. SP, hemal spine; H. ZYG, hamal zygapophysis; N. SP,
neural spine; N. ZYG, neural zygapophysis; UST, urostyle.

middle of the abdomen, they are said to be abdominal in
position ; when further forwards, nearly beneath the pectorals,
they are said to be thoracic ; when still further, actually in
front of the pectorals and beneath the throat, they are said
to be jugular in position.

A very remarkable deviation from the typical form occurs
inthe flat-fishes (Pleuronectde, including the soles, plaice, .
flounders, turbots, etc.). The body (Fig. 237) is very
deep and strongly compressed ; the fish habitually rests on
the bottom, in some species on the right, in others on the

398 MANUAL OF ZOOLOGY SECT.

left side. The under side is usually pure white, the upper
dark. The eyes are both on the upper side, and the skull
is distorted so as to adapt the orbits to this change of
position.”

Fic. 237. — Pleuronectes cynoglossus (craig-fluke), from the right side. da. f,
dorsal fin; 7 e, left eye; Act. f, pectoral fin; pv. /, pelvic fin; ~. e, right eye;
v.f, ventral fin. (After Cuvier.)

In many Teleostei, such as the eels, the skin is devoid
of hard parts; but in most cases there is an exoskeleton
developed in the derm. In the majority this takes the form
of scales, rounded plates of bone embedded in pouches of
the derm, and overlapping one another from behind for-
wards. When the free border of the scales presents an
even curve, they are called cycloid scales; when the free
edge is produced into small spines, they are distinguished
as cfenoid scales (Fig. 238). In exceptional cases the scales
may be so large and strong as to form a rigid armour.

1 Our common flounders are Paradlichthys dentatus from the southern

coast of New England, and Pseudopleuronectes americanus from the coast
north of Cape Cod.

XII PHYLUM CHORDATA 399

Sometimes there is an armour formed of stout bony plates,
or scutes, while in other cases, as in the “ file-fishes,” the
exoskeleton takes the form of minute spines like the

Fic. 238. — A, ctenoid scale; B, ganoid scale. (After Giinther.)

shagreen of sharks, or as in many globe-fishes of long bony
spines ; lastly, in Polypterus (Fig. 239) and Lepidosteus are
found rhomboid or ganoid scales in the form of rhomboidal
plates of bone covered externally by a layer of enamel or
ganoin and joined together by pegs and sockets.

SS ee

PYS

Fic. 239. — Polypterus birchir. A, entire animal; B, ventral
view of throat. az, anus; dr. #2, branchiostegal membrane;
c.f, caudal fin; d. /, dorsal finlets; jug. £7, jugular plates;
na, nostril: pct. f, pectoral fin; pv. /, pelvic fin; v._/, ven-
tral fin. (After Cuvier.)

In the sturgeon the spinal column consists of a persistent
notochord with cartilaginous arches ; in the rest bony verte-
bree are present, the centres of which are nearly always
bi-concave.

400 MANUAL OF ZOOLOGY SECT.

In the sturgeons (Fig. 240) and their allies the cranium
is an undivided mass of cartilage with a few isolated carti-
lage bones, and covered over dorsally by membrane bones.
In most of the other members of the group it is mainly or
entirely composed of numerous cartilage and membrane
bones (Fig. 240). Both upper and lower jaws are bounded
by membrane bones (/. mx, mx, dent). The jaws are con-
nected with the skull by the intermediation of a hyomandib-

Fic. 240. — Skull of sturgeon, with the membrane bones removed. a, pharyngo-
branchial; 4, antorbital process; AR, articular; 4, epibranchial; c, cerato-
branchial; C, notochord; Co, basi-branchials; d@, hypobranchial; De, dentary;
GK, auditory capsule; H//, hyomandibular; /y, hyoid cornu; //, inter-hyal;
Md, mandible; Na, nasal capsule; Gé, neural arches; P/, post-orbital pro-
cess; PQ, palato-quadrate; Ps. Ps'. Ps'', parasphenoid; Psf, neural spines;
Qu, quadrate; R, rostrum; Rz, ribs; Sf. NV, foramina for spinal nerves; Sy,
symplectic; }/7S, vertebral column; 2, vagus foramen; /-/’, branchial arches.
(From Wiedersheim’s Comparative Anatomy.)

ular (Avom) which, however, probably does not correspond
with the cartilage so named in the dogfish and other Elas-
mobranchs. The pectoral arch is complicated by the addi-
tion of membrane bones, of which the most constant are a
pair of large clavicles. The pelvic arch is vestigial or absent.

Two genera of Teleostomi possess electric organs, — the
electric catfish (AZalapterurus) and the electric eel (Gym-
notus) ; the former occurs in fresh waters of tropical Africa,

401

PHYLUM CHORDATA

XII

and the latter in Brazil and the Guyanas. Some Teleostomi

are toothless,

but in most instances teeth are present, and

may be developed, not only on the pre-maxilla and maxilla

of the upper jaw, and the dentary of the lower, but on a

2D

402 MANUAL OF ZOOLOGY SECT,

number of other bones in the wall of the mouth. In most
of the Teleostei the maxilla is devoid of teeth, and does not
enter into the upper boundary of the mouth opening. In
the great majority the teeth are small and very numerous,
adapted for preventing the struggling prey from slipping out
of the mouth, but quite unfitted for either tearing or crush-
ing ; but in many instances teeth are comparatively large and
few in number, and in some (Fig. 242) there is a marked
differentiation of the teeth, those in front of the jaws being

Fic. 242. — Premaxille of Sargus, showing teeth. (After Owen.)

pointed or chisel-shaped, and adapted for seizing or cutting,
while the back teeth have rounded surfaces adapted for
crushing. The teeth may be either simply embedded in the
mucous membrane so as to be detached when the bones
are macerated or boiled, or they may be implanted in the
sockets of the bone or ankylosed to it. Their succession
is perpetual, 7.e., injured or worn-out teeth are replaced at
all ages. The Ganoids have a spiral valve in the intestine ;
this is absent in the Teleostei. Cceca (the pyloric ceca)
are commonly developed at the junction of the stomach and
small intestine. ‘The anus is always distinct from, and in
front of, the urogenital apparatus, there being no cloaca
such as occurs in Elasmobranchs. The gills are usually

XII PHYLUM CHORDATA 403

comb-like, consisting of rows of slender branchial filaments.
The inter-branchial septa are reduced as compared with
those of the Elasmobranchs, the branchial filaments project-
ing freely beyond them. Asa rule, the gills are developed
in the first four branchial arches.

A characteristic structure of the Teleostomi is the az7-
bladder or swimming bladder, which, however, is not present
in all. It is an elongated sac with elastic walls situated in
the body-cavity immediately below the spinal column. In
some cases (Ganoids and some Teleostei) it communicates
with the gullet by a duct, the puewmatc duct, in the rest it
is a closed sac. It is sometimes divided into compartments,
or produced into lateral offshoots. In some of the Ganoids
its wall is sacculated, assuming an appearance not unlike
that of the lung of one of the higher air-breathing verte-
brates. The air-bladder seems able to act as a sort of
accessory organ of respiration. Its normal function, how-
ever, appears to be hydrostatic, z.e., it serves to keep the fish
of the same specific gravity as the water ; variations in press-
ure, as the fish ascends or descends, are regulated by ab-
sorption or secretion of gas.

In the Ganoids the heart has a structure very similar to
that of the dogfish, consisting of a sinus venosus, auricle,
ventricle, and conus arteriosus — the last being rhythmically
contractile like the other chambers, and containing rows of
valves. In Teleostei there is no such conus arteriosus; but
there is always a large bulb-like dilation of the base of the
ventral aorta, the du/bus aorte. The optic nerves of the
Ganoids agree with those of Elasmobranchs and of Verte-
brates in general in forming a chiasma, whereas in the
Teleostei they simply cross one another or decussate.

Most Teleostomi are oviparous, the eggs being impreg-
nated after they are laid. Many instances of parental care

404 MANUAL OF ZOOLOGY SECT.

of the young are known, the most familiar being that of the
male stickleback, which constructs a nest of weeds fastened
together by a glutinous secretion of the kidneys, and
jealously guards the developing young. In the sea-horse
(Hippocampus, Fig. 243) and the pipe fish (Sygnathus)
the young are developed in a pouch in the abdomen of the
male. In Aspfredo, one of the cat-fish tribe, the eggs are

Fic. 243. — Hippocampus (sea-horse). In B, the operculum is removed to show the
gills. 47. af, branchial aperture; 4rd. J, brood-pouch; ad. /, dorsal fin; g. gills;
pet. f, pectoral fin. (From Claus and Giinther. )

pressed into the soft spongy skin of the belly, and thus
carried about by the parent. The ova, although containing
a large proportional amount of yolk, are always small as
compared with those of Elasmobranchs, never exceeding
5 to 10 mm. in diameter, and being usually much smaller.

XII PHYLUM CHORDATA

They are rarely protected by
an egg-shell. They are pro-
duced in immense numbers,
a single female sometimes lay-
ing several millions. In such
cases the mortality among
the unprotected embryos and
young is immense. The eggs
may be felagic, 1.e., so light
as to float when laid, as in the
cod, haddock, turbot, sole,
etc., or demersal, t.e., 30 heavy
as to sink to the bottom, as in
the herring, salmon, trout, etc.

Sub-class IV. Dipnoi

The Dipnoi or lung-fishes,
comprising as their living rep-
resentatives only the Queens-
land Ceratodus (Fig. 244),
or Burnet salmon, and the
mud-fishes, Profopterus and
Lepidosiren, of certain South
African and South American
rivers respectively, are fishes
of such well-marked and spe-
cial features that by some
zoologists they are separated
from the true fishes and re-
garded as constituting a sepa-
rate class of Vertebrates. One
of their peculiar features is

405

(From Dean, after Giinther.)

Fic. 244. — Ceratodus Forsteri. Reduced.

406 MANUAL OF ZOOLOGY SECT.

indicated by their name Dipnoi; not only do these animals
breathe by means of gills like ordinary fishes, but they have
a highly developed apparatus for the respiration of air —
a single lung in the case of Ceratodus, a pair of lungs
(united in front) in the other two genera. ‘They have bony
scales and dermal fin-rays; but the paired fins are con-
structed on a totally different type from those of any other
living fish. The fin, pectoral or pelvic as the case may be,
is leaf-like, or very long and narrow, and the skeleton (Fig.
245) consists of a central axis in the form of a slender, taper-

Fic. 245. — Ceratodus Forsteri. Lateral view of the anterior portion of the skeleton.
A, anterior median membrane bone of the roof of the skull; B, posterior median
membrane bone. éas, basal cartilage of the pectoral fin; 47, branchial arches;
7nt, inter-operculum; aw, plate overhanging branchial region; sch, Meckel’s
cartilage; occ. rd, occipital rib; of, operculum; Aa/, palato-quadrate; pct, pec-
toral arch; xs, ribs; sub. orb, sub-orbital bones; sg, squamosal; supra. sc,
supra-scapula.

ing, jointed rod of cartilage, with a row of smaller jointed
rods of cartilage on either side of it. This form of fin-skele-
ton, which occurs in certain groups of fossil fishes, as well as
in Dipnoi, has been termed the archipterygium. The noto-
chord is persistent, and the cranium (Fig. 245) consists of a
mass of cartilage with little ossification, but with the addition

xII PHYLUM CHORDATA 407

of a number of membrane bones ; the skull is awéostylic, the
lower jaw articulating with a palato-quadrate process (pa/),
corresponding to the palato-quadrate of the dogfish, but im-
movably fixed to the side of the skull. There are four or
five cartilaginous branchial arches (47). The gills are cov-
ered over by an operculum. A cloaca is present, and the
intestine contains a spiral valve. The structure of the heart
is more complicated than in ordinary fishes, owing to the
sinus venosus and the auricle being both imperfectly divided
into two parts. There is a contractile conus arteriosus, which
has a spirally twisted form, and is partly or completely divided
internally by a longitudinal septum. A pulmonary artery,
carrying blood to the lung or lungs, is given off from the
afferent branchial system. The blood is returned from
the lung or lungs by means of a pulmonary vein, which
opens into the left division of the sinus venosus, and
through it reaches the left division of the auricle.

CLASS III. AMPHIBIA

The larve of the newts or efts, and those of the frogs
(familiar to every one under the name of tadpoles), bear a
close resemblance in form and movements to the fishes.
But, as they approach maturity, these fish-like larvee undergo
a metamorphosis, fitting them for the amphibious mode of
life which gives its name to the class: pentadactyle limbs are
developed, and lungs for breathing air take the place of gills
as the organs of respiration, while a corresponding advance to
a higher type of structure occurs in the other parts. The
Amphibia thus occupy an intermediate position between the
fishes on the one hand and the higher air-breathing Verte-
brates (reptiles, birds, and mammals) on the other. In
addition to the possession of limbs constructed on the pen-

‘408 MANUAL OF ZOOLOGY SECT.

tadactyle type, or type of the chetropterygium, the Amphibia
differ from the fishes in the entire absence of fin-rays, and
from all fishes but the Dipnoi, in the presence of lungs for
breathing air in the adult: the larval gills become absorbed
in the majority of Amphibia before maturity is reached, but
in some are retained throughout life, the animal breathing,
like the Dipnoi, by means of both lungs and of gills.

The most convenient example of the Amphibia for special
study is a frog. The following description and figures have
reference more specially to the European species of the
genus Rana,— R. temporaria and R. esculenta, — but they
will be found to apply to any American frog or toad, except
in a few features which are chiefly quite superficial, some of
which will be referred to subsequently.

The “wnk is short and stout, and is continued, without
the intermediation of a neck, into the broad depressed “ead.
There is no trace of a tail, the anus being terminal. The
mouth also is terminal, and is characterised by its ex-
traordinary width, the gape extending considerably behind
the eye. On the dorsal surface of the snout are the small
nostrils ; the eyes are large and prominent, and each is pro-
vided with an upper eyefid in the form of a thick fold of skin
and a nictitating membrane —a much thinner fold which
arises from the lower margin of the eye and can be drawn
up over it. Close behind the eye is a circular area of
tensely stretched skin, the Ampanic membrane, a structure
not met with in any fish; as we shall see, it is an accessory
part of the auditory organ. There is no trace of branchial
apertures.

The back has a peculiar bend or hump, in the sitting
posture, marking the position of the sacral vertebra (see
p- 410). The limbs are of very unequal size. The /ore-
Zimbs are short, and each consists of an upper arm, which,

XII PHYLUM CHORDATA 409

in the ordinary position, is directed backwards and down-
wards from the shoulder joint ; a fove-arm, directed down-
wards and forwards from the elbow; and a hand, ending in
four short tapering dgits, directed forwards. The Aind-limb
is of great size ; in the usual squatting posture the shigh is
directed downwards, outwards, and forwards from the thigh-
joint, the shank inwards, backwards, and upwards from the

Fic. 246. — Rana temporaria. (From Mivart.)

knee. The /vos consists of two parts,—a tarsal region directed
downwards from the heel-joint, and five long, slender digits
united by thin folds of skin or weds. Thus the limbs are
placed in such a way that the elbow and knee face one
another, and the first digit —that of the hand probably rep-
resenting the second or index-jinger, that of the foot, the

410 MANUAL OF ZOOLOGY SECT,

hallux or great toe—is turned inwards or towards the
median plane of the body.

The skin is soft and slimy, owing to the secretion of
mucous glands ; there is no trace of an exoskeleton.

The vertebral column (Fig. 247) is remarkable for its
extreme shortness ; it consists of only nine vertebree (V. 1-
V. 9), the last followed by a slender, bony rod, the wrostyle
(UST). The second to the seventh vertebra are similar
in character. The centrum (B, cv) is somewhat depressed,
and has a concave anterior and a convex posterior face —a
form known as procelous. Each half of the neural arch
consists of two parts, —a pillar-like pedicle (pd) springing
from the centrum and extending vertically upwards, and a
flat, nearly horizontal damina (4m), forming, with its fellow,
the roof of the neural canal. ,

The zygapophyses (a. zg) or yoking processes are far
_ better developed than in any fish. Laterally the neural
arch gives off on each side a large outstanding ¢ransverse
process (tr. pr) ; its crown is produced into a very small and
inconspicuous wewral spine. The first or cervical vertebra
(V. 1) has a very small centrum and no transverse processes.
There are no anterior zygapophyses, but at the junction of
centrum and arch there occurs on each side a large oval
concave facet for articulation with one of the condyles of the
skull (see p. 411). The eighth vertebra has a biconcave
centrum ; that of the ninth or sacral vertebra (V.9) is con-
vex in front and presents posteriorly a double convexity
articulating with a double concavity on the anterior end of
the urostyle.

The sku (Figs. 247, 248) consists of a narrow drain-case,
produced behind into great outstanding auditory capsules,
and in front into large o/factory capsules. The whole of the
bones of the ufper aw are immovably fixed to the cranium

XII PHYLUM CHORDATA 411

so that the only free parts are the Jower jaw and a
small plate, the Ayotd apparatus, partly bony and _ partly
cartilaginous, which supports the tongue, and is the sole
representative of the entire visceral or gill-bearing skeleton
of the fishes.

A cartilaginous cranium comparable with that of the dog-
fish, but very thin and delicate, forms the foundation of the
skull of the frog; but superadded to this are a number of
cartilage bones—or bones which replace portions of the
cartilage, and membrane bones — or bones which are formed
in membrane, independently of the cartilage. There are
five cartilage bones, the paired exoccipitals and pro-ofics, and
the median sphenethmoid. The exoccipitals (EX. OC) lie
in the posterior or occipital region of the skull and bound the
large opening or foramen magnum (for. mag) at the posterior
end of the skull through which the spinal cord, contained in
the neural canal enclosed by the neural arches of the vertebre,
becomes continuous with the brain, contained in the cavity
of the cranium. Below the foramen magnum are a pair of
oval projections, the occipital condyles (oc. cn), for articu-
lation with the first vertebra of the spinal column. The
second pair of cartilage bones, the pro-otcs (PR. OT), are
ossifications in the roof of the auditory capsule, situated
just in front of the exoccipitals, with which they become
firmly united. The sphenethmoid (SP. ETH) is a peculiar
ossification of somewhat complex form, which lies partly in
the wall of the anterior portion of the cranial cavity, partly in
the wall of the posterior portions of the nasal cavities or
olfactory sacs.

To this cartilaginous cranium with its cartilage bones
certain membrane bones are added. Covering the roof
of the brain-case are two long narrow bones called the
Jronto-parietals (FR. PA), because they are formed by the

Fic. 247. — Rana temporaria. A, the skeleton from the dorsal aspect; the left half of the shoulder
girdle and the left fore and hind limbs are removed, as also are the membrane bones on the
left side of the skull. Cartilaginous parts dotted. Names of cartilage bones in thick, those

of membrane bones in italic capitals. @.c. Ay, anterior cornu of hyoid; actd, acetabulum;
AST, astragalus; 4. Ay, basi-hyal; C, calcar; CAL, calcaneum; EX. OC, ex-occipital; FE,
femur; fox. fon', fontanelles; FR. PA, fronto-parietal; HU, humerus; IL, ilium; AX,
maxilla; ol. cf, olfactory capsule; c#. pr, otic process; f. c. Ay, posterior cornu of hyoid;
PMX, premaxilla; PR. OT, pro-otic; RA: UL, radio-ulna; SP. ETH, sphenethmoid; SQ,
squamosal; S. SCP, supra-scapula; ss, suspensorium; TI. FI, tibio-fibula; ¢7. A7, transverse
process; UST, urostyle; V. 1, cervical vertebra; V. 9, sacral vertebra; 1’O, vomer; /-V
digits. B, the fourth vertebra, anterior face. a. svg, anterior zygapophysis; cz. centrum,
dm, lamina; x. sf, neural spine; fd, pedicle; 77. fr, transverse process. (After Howes,
slightly altered. )

413

PHYLUM CHORDATA

SECT. XII

union of a pair of /ronéads in front with a pair of parietals

Over the olfactory capsules are a pair of triangular

nasals (VA), and applied to their ventral surfaces small

behind.

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On the ventral surface of the skull

is a large T-shaped parasphenoid (PA. SPH), its stem
underlying the base of the cranium, while its two arms ex-

tend outwards beneath the auditory capsules.

paired vomers (VO).

414 MANUAL OF ZOOLOGY SECT.

The palato-quadrate cartilage is unossified ; but in relation
to its anterior portion is a palatine (PAL) membrane bone
and to its posterior portion a pfrerygoid (PTG). The former
is a slender rod-like bone directed transversely on the lower
surface of the skull. The latter is a larger three-rayed bone,
having an anterior, an inner, and a posterior arm. The
posterior portion of the palato-quadrate cartilage, the guad-
rate or suspensorium (sus), connects the lower jaw with the
posterior region of the skull. Internally it is covered over
by the inner and posterior arm of the pterygoid ; externally
a hammer-shaped membrane bone, the sgvamosal (SQ)
is applied to it. The upper jaw is formed by three mem-
brane bones, the small premaxilla (PACX ) in front, then
the long narrow maxilla (7X ), and finally the short guad-
ratojugal (QU. JU) which is connected posteriorly with
the quadrate. The mandible contains on each side a per-
sistent Meckel’s cartilage as a sort of core, ossified at its
anterior end, outside which are two membrane bones. The
hyoid is a squarish plate of cartilage (4. Ay) with two pairs of
processes (a@.¢. hy, p. c. hy), the posterior of which is ossified.

The scapula is ossified and is connected by its dorsal
edge with a swpra-scapula (Fig. 247, S. SCP) formed partly
of bone, partly of calcified cartilage, and developed from
the dorsal region of the embryonic shoulder-girdle. The
coracoid (Fig. 249, Co) is also ossified, while the procora-
coid is represented by a bar of cartilage, having a membrane
bone, the clavicle (C7), closely applied to it. The supra-
scapula overlaps the anterior vertebre ; the coracoid and
procoracoid are connected ventrally by a cartilage, the efz-
coracoid (Co'), which is in close contact with its fellow of
the opposite side in the middle ventral line, so that the
entire shoulder-girdle, like that of the dogfish, forms a
single inverted arch.

XII PHYLUM CHORDATA 415

Passing forwards from the anterior ends of the united
epicoracoids is a rod of bone, the episternum (Lp), tipped
by a rounded plate of cartilage, the omos/ernum , and passing
backwards from their posterior ends is a similar but larger
bony rod, the sternum (Sz), also tipped by a cartilaginous
plate, to which the name xiphisternum (Kn) is applied.

Fic. 249.— Rana esculenta. The shoulder girdle from the ventral aspect. Co,
coracoid; Co’, epicoracoid; C/, clavicle; G, glenoid cavity; £/, episternum;
Fe, fenestra between procoracoid and coracoid; A‘C, cartilage separating scapula
and clavicle; A, xiphisternum; 7, junction of epicoracoids; S, scapula;
St, sternum. (From Wiedersheim’s Comparative Anatomy.)

The four limbs deviate from the typical structure (p. 341)
chiefly in the fusion of the radius and ulna into a single
radio-ulna (Fig. 247, RA. UL) and in the presence of only
four complete digits with a vestigial one on the radial side.
In all probability the latter represents the pollex, and the

416 MANUAL OF ZOOLOGY SECT.

complete digits are the second to the fifth of the typical
hand. Six carpals only are present.

The pelvic arch (Figs. 247 and 250)
is very peculiarly modified; it re-
sembles in form a bird’s “ merry-
thought,” consisting of two long
curved bars articulating in front with
the transverse processes of the sacral
vertebra and uniting posteriorly in
an irregular vertical disc of mingled
bone and cartilage which bears on
each side a deep, hemispherical
acetabulum (Fig. 250, G) for the ar-
ticulation of the thigh-bone. The

curved rods are the za (ZZ, P) ;

UG a dia ton ie ast they expand posteriorly and unite
side Caecum; i642 with one another in the median plane
ae Poi De Dior to form the dorsal portion of the disc
and about one-half of the acetabulum.

The posterior portions of the disc and the acetabulum are
furnished by the zschéa (/s), fused with one another in the
sagittal plane, and their ventral portions by the similarly
united pubes (Kn). The ilium and ischium are formed of
true bone, the pubis of calcified cartilage ; the union of the
elements in the median plane is called the symphysis. In
the Avnad-Zimd the tibia and fibula are fused to form a single
tihio-fibula (Fig. 247, TI. FI), and the two bones in the
proximal row of the tarsus, namely, the tibiale or astraga-
dus (AST) and the fibulare or ca/caneum (CAL), are greatly
elongated and provide the leg with an additional segment.
There are three tarsals in the distal row, one of which ap-
pears to represent a central, another the first distal carpal,
and the third the fused second and third. There are five

XII PHYLUM CHORDATA 417

well-developed digits, and on the tibial side of the first is a
spur-like structure or cadar (C), formed of three bones, a
metatarsal and two phalanges: such a rudimentary digit is
called a pre-hallux.

The mouth leads into a wide ducca/ cavity having in its
roof the posterior nares (Fig. 251, p. na), a pair of projec-
tions due to the downward bulging of the large eyes, and the

20

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= - = a S

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Fic. 251. Rana temporaria. Dissection from the tefi side; the viscera somewhat
displaced. am, anus; 4.d, bile duct; 4. hy, body of hyoid; 62, urinary bladder;
é/', its opening into cloaca: c.art, conus arteriosus; cdl, cerebellum; c/,
cloaca: cn. 3, centrum of third vertebra: cp. ad, corpus adiposum; c76. /, cere-
bral hemisphere: d. 7y. s, dorsal lymph sinus; du, duodenum: ef. cov, epicora-
coid; exs. ¢, Eustachian tube: FR. PA, fronto-parietal; ¢/, glottis; gw/, gullet;

IL, ilium; 1s, ischium; da, kidney; edie left auricle; 7 “Ing, left lung
liver; mM. MCK, mento-meckelian; #. a. 7, neural arch of first vertebra
olfactory lobe; oft. 7, optic lobe; 0. sT, omo- and epi-sternum; fed, peri-
cardium; PILX, premaxilla; fx, pancreas; # wa, posterior naris; fx, pubis;
ret, rectum; 7. dng, right lung; s.zvt, small intestine; sf. cd, spinal cord;
SPH. ETH, sphenethmoid; sf/, s spleen; st, stomach; s.zv, sinus venosus; fg,
tongue; ¢s, testis; 7, ureter; «7’, its aperture into the Cloaca: UST, urostyle;
v, ventricle; v.dy.s, ventral lymph sinus; vo. ¢, vomerine teeth; ws. sem,
vesicula seminalis.

Eustachian tubes (eus. t, vide infra). On its floor is the
large tongue (¢ng), attached in front and free behind, where

it ends in a double point ; by means of its muscles it can be
2E

418 MANUAL OF ZOOLOGY SECT.

suddenly projected, point foremost, from the mouth, and is
used in the capture of insects. Immediately behind the
tongue is the glofWs (g/). Teeth are arranged in a single
series round the edge of the upper jaw, attached to the pre-
maxilla and maxille ; there is also a small patch of teeth
(vo. 2) on each vomer just internal to the posterior nostril.
The teeth are small conical bodies, their bases ankylosed to
the bones ; their only use is to prevent the polished or slimy
bodies of the prey— insects and worms — from slipping out
of the mouth.

The buccal cavity narrows towards the Aharynx, which
leads by a short guwdet (guZ) into a stomach (st) consisting of
a wide cardiac and a short, narrow pyloric division. The
duodenum (du), or first portion of the swal/ intestine, passes
forwards parallel with the stomach; the rest of the small
intestine is twisted into acoil. The large intestine or rectum
(vet) is very wide and short, and passes without change of
diameter into the cloaca (¢/).

The Zver (Zr) is two-lobed ; between the right and left
lobes lies a large gal/-bladder. The pancreas (pn) is an
irregular gland surrounding the bile duct, into which it
pours its secretion ; the sf/een (sf/) is a small, red globular
body attached near the anterior end of the rectum.

The /ungs (2. lng, r. mg) are elastic sacs lying in the
anterior part of the ccelom above the heart and liver ; their
size and appearance vary greatly according to their state of
distention. Each contains a spacious cavity, and has its
walls raised into a complete network of ridges abundantly
supplied with blood-vessels. The two lungs open anteriorly
into a small /aryngo-tracheal chamber which communicates
with the mouth by the narrow slit-like g/o/Hs. The walls of
the laryngo-tracheal chamber are supported by a cartilagi-
nous framework, and its mucous membrane is raised into a

XII PHYLUM CHORDATA 419

pair of horizontal folds, the vocal chords, by the vibration of
which the croak of the frog is produced.

In breathing, the frog keeps its mouth closed, and, by
depressing the floor of the mouth draws air into the buccal
cavity through the nostrils. The floor of the mouth is then
raised, the nostrils are closed, and the air is forced through
the glottis into the lungs. The skin is also an important
respiratory organ.

The pericardium (Fig. 251, ped) is not a separate cham-
ber, as in fishes, but the heart, enclosed in a pericardial
membrane, lies in the general ccelomic cavity between the
gullet above and the epicoracoids below. The heart con-
sists of a sinus venosus (Figs. 251 and 252, s.v), right
and left auricles (7. au,/. au), a ventricle (v, vt), and a
conus arteriosus (¢. @7f). As in Dipnoi, the sinus venosus
opens into the right auricle, the pulmonary veins into the
left ; a striking advance is seen in the greatly increased size
of the left auricle and its separation by a complete partition,
the septum auricularum (Fig. 252, spt. aur), from the right.
The two auricles open by a common auriculo-ventricular
aperture, guarded by a pair of valves (av. v. v), into the sin-
gle ventricle. The conus springs from the right side of the
base of the ventricle ; it is separated from the latter by three
small semilunar valves, and is traversed obliquely along its
whole length by a large flap-like longitudinal valve (4)
which springs from its dorsal wall and is free ventrally. The
conus passes without change of diameter into a éuus aorte,
the two being separated by a semilunar valve and by the
free end of the longitudinal valve. The bulbus gives off two
branches, right and left, each of them divided by two longi-
tudinal partitions into three vessels, — an inner or anterior,
the carotid trunk (car. tr), a middle, the systemic trunk or
aortic arch, and an outer or posterior, the pulmo-cutaneous

420 MANUAL OF ZOOLOGY SECT.

trunk (pul. cu. tr). The carotid and systemic trunks com-
municate separately with the bulbus, the two pulmo-cuta-
neous trunks communicate with the anterior end of the
conus by a single aperture placed just below the free end of
the longitudinal valve.

cangl lg.@

cara—q
syst.er
pul.cu.tr

Fic. 252.— Rana temporaria. The heart from the ventral aspect with the cavities
laid open. a, a’, bristle in left carotid trunk; au. v. v, auriculo-ventricular
valves; 6, 4’, bristle i in left systemic trunk; c,c’, bristle in left pulmo-cutaneous
trunk; cay. a, carotid artery; car. g/, carotid plexus; c. art, conus arteriosus;
car. tr, carotid trunk: 2. au, left auricle; Ze. a, lingual artery; 2. v, longitudinal
valve; pul. cu. tr, pulmo-cutaneous trunk; “pul v, aperture of pulmonary veins;
vy. an, right auricle: S. au, ap, sinu-auricular aperture; sft. avr, septum auricu-
larum; v.v', valves; vz, ventricle.

After being bound together in the way described for a
short distance, the carotid, systemic, and pulmo-cutaneous
trunks separate from one another. The carotid trunk divides

XII

PHYLUM CHORDATA 421

Fic. 253. Rana temporaria. The arterial system, with the heart, lungs, kidneys,

and left testis, from the ventral aspect. car, carotid artery; car. g/, carotid
gland; c. art, conus arteriosus; car. ty, carotid trunk; c@/. mes, coeliaco-
mesenteric artery; cu, cutaneous artery; @. ao, dorsal aorta; du, duodenal
artery; gs, gastric artery; Af, hepatic artery; 2/, iliac artery; zt, intestinal
arteries; 4d, kidney; 7. au, left auricle; 2g, lingual artery; fx/, pulmonary
artery; fxd. cu. tr, pulmo-cutaneous trunk; 7. az, right auricle; 7, renal
arteries; sf/, splenic artery; sys. tr, systemic trunk; spm, spermatic artery;
ts, testis; v, ventricle.

422 MANUAL OF ZOOLOGY SECT.

into carotid (Figs. 252, car. a and 253, car) and Aingual (lz)
arteries for the supply of the head, the former having at its
base a small swelling, the carotid gland (car. gl), consisting
of a plexus of blood-vessels. The systemic trunks curve
round the gullet and unite with one another above it to form
the dorsal aorta (d. ao), from which, or from one of the
systemic trunks themselves, the arteries to all parts of the
body, except the head, the lungs, and the skin, are given off.
The pulmo-cutaneous trunk divides into two, a pulmonary
artery (pul) to the lung, and a cu¢aneous artery (cu) to the
skin.

The blood from the head and fore-limbs is returned by
veins which unite to form a pair of large trunks, the pre-
cavals, which open separately into the sinus venosus.

One portion of the blood from the hind-limb is carried
forward by a vein which unites with its fellow of the oppo-
site side to form the abdominal vein (Fig. 254, abd), which
passes forwards, in the ventral body-wall, to the level of
the sternum, where it turns inwards and divides into two
branches, both breaking up into capillaries in the liver.
Just as it enters the liver it is joined by the hepatic portal
vein (hp. pt), bringing the blood from the stomach, intes-
tine, spleen, and pancreas. The rest of the blood from
the hind-limb is carried by the venxa/ portal vein to the
corresponding kidney.

The blood is collected from the kidneys by the rena/
veins (rn), which unite to form the large unpaired pos¢-caval
vein (pt. cv). This passes forward through a notch in the
liver, receives the hepatic veins (hp) from that organ, and
finally opens into the sinus venosus. Thus the blood from
the hind-limbs has to pass through one of the two portal
systems on its way back to the heart ; part of it goes by the
renal portal veins to the kidneys, and thence by the renal

XII PHYLUM CHORDATA 423

veins to the post-caval, part by the abdominal vein to the
liver, and thence by the hepatic veins to the post-caval.
Lastly, the blood which has been purified in the lungs is
returned by the pulmonary veins (pul) directly to the left
auricle.

It will be perceived that the blood poured into the right
auricle is mostly impure or venous, that poured into the
left fully aérated or arterial. When the auricles contract,
which they do simultaneously, each passes its blood into the
corresponding part of the ventricle, which then instantly
contracts, before the venous and arterial bloods have time
to mix. Since the conus arteriosus springs from the right
side of the ventricle, it will at first receive only venous
blood, which, on the contraction of the conus, might pass
either into the bulbus aorte or into the aperture of the
pulmo-cutaneous trunks. But the carotid and systemic
trunks are connected with a much more extensive capillary
system than the pulmo-cutaneous, and the pressure in them
is proportionally great, so that it is easier for the blood to
enter the pulmo-cutaneous trunks than to force aside the
valves between the conus and the bulbus. A fraction of a
second is, however, enough to get up the pressure in the
pulmonary and cutaneous arteries, and in the meantime the
pressure in the arteries of the head, trunk, etc., is constantly
diminishing, owing to the continual flow of blood towards
the capillaries. Very soon, therefore, the blood forces the
valves aside and makes its way into the bulbus aorte. Here
again the course taken is that of least resistance ; owing to
the presence of the carotid gland the passage of blood into
the carotid trunks is less free than into the wide, elastic,
systemic trunks. These will, therefore, receive the next
portion of blood, which, the venous blood having been
mostly driven to the lungs, will be a mixture of venous and

424 MANUAL OF ZOOLOGY SECT.

gm se Pv

Fic. 254. Rana temporaria. The venous system with the heart, lungs, liver,
kidneys, and right testis, from the dorsal aspect. add, abdominal vein; br,
brachial vein; cd, cardiac vein; ds. Zmb, dorso-lumbar vein; az, duodenal vein;
ext. Ji, external jugular vein; fm, femoral vein; gs, gastric vein; Ap, hepatic
vein; Ap. pt, hepatic portal vein; zv?, intestinal veins; z7d¢. 72, internal jugular
vein; kd, kidney; 7. az, left auricle; 2zg, lung; dvr, liver; ms. cu, musculo-
cutaneous vein; pr. cv, pre-caval vein; pt. cv, post-caval vein; px, pulmonary
vein; pv, pelvic vein; 7. ax, right auricle; 1, renal veins; rn. pt, renal portal
vein; sc, sciatic vein: sf/, splenic vein; sz, spermatic vein; s. v, sinus venosus;
ts, testis; ves, vesical veins.

XII PHYLUM CHORDATA 425

arterial. Finally, as the pressure rises in the systemic trunks,
the last portion of blood from the ventricle, which, coming
from the left side, is arterial, will pass into the carotids and
so supply the head.

The lymphatic system is very well developed, and is
remarkable for the dilatation of many of its vessels into
immense 4mph sinuses. The lymph is pumped into the
veins by two pairs of lymph-hearts, one situated beneath
the supra-scapule, the other beside the posterior end of the
urostyle.

The Jrain (Fig. 255) has a very small cerebellum (WH 7),
large optic lobes (47/7), a well-developed diencephalon,
and large hemispheres and olfactory lobes, the latter fused
in the median plane.

The first spinal nerve performs the function of the
hypoglossal, one of the cranial nerves of higher Vertebrates
supplying the muscles of the tongue: it passes out between
the first and second vertebree. The spinal cord is short,
and ends in a delicate filament, the f/um ferminale. In
correspondence with the number of vertebre there are only
ten pairs of spinal nerves, of which the second and third
unite to form a drachial plexus giving off the nerves to the
fore-limb, while the seventh to the tenth join to form a
lumbo-sacral plexus giving off the nerves to the hind-limb.

The o/factory sacs have each two openings: the azérior
narts or external nostril and the fosterior naris (Fig. 251,
p. na), or internal nostril, which opens into the mouth
immediately external to the vomer.

The eye and the auditory organ have the usual structure,
but in connection with the latter there is an important
accessory organ of hearing not hitherto met with. Bounded
externally by the tympanic membrane, and internally by the
outer wall of the auditory capsule, is a considerable space,

426 MANUAL OF ZOOLOGY SECT.

the ¢vympanic cavity (cav), which communicates with the
mouth by the short Eustachian tube already noticed (Fig.
251, ews. ¢), so that a probe thrust through the tympanic
membrane from outside passes directly into the mouth. In

Fic. 255.— Rana esculenta. The brain. A, from above; B, from below. ch. oft,
optic chiasma; HH, cerebellum; Ayf, pituitary body: /n/, infundibulum;
L. ol, olfactory lobe; AZed, spinal cord; 47H, mid-brain; WH, medulla ob-
longata; 7h. oft, optic thalamus; Tr. oft, optic tract; ”H, cerebral hemi-
sphere; ZH, diencephalon; /—_X, cerebral nerves; Y//. (1), hypoglossal (first
spinal) nerve. (From Wiedersheim’s Comparative Anatomy.)

the roof of the tympanic cavity lies a slender rod of bone
and cartilage, the codumella, its head, or extra-columella,
attached to the inner surface of the tympanic membrane, its

XII PHYLUM CHORDATA 427

handle united to the sages, a nodule of cartilage which is
fixed in the membrane of the fenestra ovals (p. 358).
Sonorous vibrations striking the tympanic membrane are
communicated by the columella and stapes to the fenestra
ovalis, thence to the perilymph, and thence to the mem-
branous labyrinth. The connection of the Eustachian tube
with the mouth obviates undue compression of the air in
the tympanic cavity.

The &cdneys (Figs. 251 and 253, Ad, and Figs. 256
and 257, JV) are flat, somewhat oval bodies of a dark
red colour, lying in the posterior region of the ccelom.
On the ventral face of each is an elongated, yellow adrena/,
and irregularly scattered nephrostomes occur on the same
surface. They do not, however, communicate with the
urinary tubules, but with the renal veins, and serve to propel
the lymph from the ccelom to the venous system. The
ureters (Ur) pass backwards from the outer borders of the
kidney, and open into the dorsal wall of the cloaca (C7).

Opening into the cloaca on its ventral side is a bilobed,
thin-walled, and very delicate sac, the urinary bladder (Fig.
251, 42), into which the urine passes by gravitation from
the cloaca when the anus is closed.

The ¢estes (Fig. 256, Ho) are white ovoid bodies lying
immediately ventral to the anterior ends of the kidneys, to
which they are attached by folds of peritoneum. From the
inner edge of each pass a number of delicate vasa efferenta,
which enter the kidney and become connected with the
urinary tubules. The spermatic fluid is thus passed into
the urinary tubules and carried off by the ureter, which is
therefore a urinogenital duct in the male frog. A vesicula
seminalis opens by numerous small ducts into the outer side
of the ureter. Attached to the testis are lobed bodies of a
bright yellow colour, the fat-dodies (RK).

428 MANUAL OF ZOOLOGY SECT.

The ovaries (Fig. 257, Ov) are large folded sacs, on the
surface of which the black and white ova project. A fat-
body is attached to each. ‘The oztducts (Od) are greatly
convoluted tubes, the narrow anterior ends of which open
into the ccelom by small
apertures ( O7) placed close
to the bases of the lungs.
Their posterior ends are
wide and thin-walled (U7),
and open into the cloaca
(?). The ova break loose
from the surface of the
ovary and enter the cce-
lomic apertures of the ovi-
ducts, the walls of which
are glandular, and secrete
an albuminous fluid having
the property of swelling up
in water. The eggs receive
a coating of this substance
as they pass down the ovi-
ducts, and are finally stored
up in the thin-walled pos-
Fic. 256. —Rana esculenta. Urinogenital tone pernions Oe ners

organs of the male. Ao, dorsal aorta; tubes, which in the breed-

Cl, cloaca; Cv, post caval vein; FA, fat , :

bodies; HO, testes; V, kidneys: S, Ing season become im-

apertures of ureters into cloaca; U+r, 3

ureters. (From Wiedersheim’s Com- mensely dilated and serve

parative Anatomy.) ‘ 2 :

as uteri. The eggs are laid
in water in large masses ; each has one black and one white
hemisphere, the former always directed upwards, and is sur-
rounded by a sphere of jelly. During oviposition the male
sheds his spermatic fluid over the eggs, and the sperms
making their way through the jelly impregnate them.

xII PHYLUM CHORDATA 429

When the embryo escapes from the egg by the rupture of
the egg-membrane it swims about as a little fish-like creature
or fadpole, with two pairs of branched external gills and a

Fic. 257.—Rana esculenta. Urinogenital organs of the female. JV, kidneys;
Od, oviduct; Of, its ccelomic aperture; Ov, left ovary (the right is removed) ;
P, cloacal aperture of oviduct; S. S', cloacal apertures of ureters; Ut, uterine
dilatation of oviduct. (From Wiedersheim’s Comparative Anatonty.)

long tail. There is no mouth, and eyes have not yet become
developed. On the lower surface of the head is a pair of

430 MANUAL OF ZOOLOGY SECT.

suckers by which the tadpole is able to attach itself to
water-weeds. Soon a pair of external gills appears, the
mouth and gill-slits are formed, and the eyes appear. The
mouth is small, bounded by lips beset with horny papille,

Fic. 258.— Rana temporaria. Stages in the life-history, from the newly-hatched
Tadpoles (1) to the young Frog (8). 2a is a magnified view of 2. (From

Mivart.)
and provided with a pair of horny jaws. The enteric canal
grows to a great length and is coiled like a watch-spring, and
the tadpole browses upon the water-weeds which form its

XII PHYLUM CHORDATA 431

staple food, though it also eats decaying leaves and the flesh
of dead animals.

Soon the external gills show signs of shrivelling, and at
the same time zvéernal gills, like those of fishes, are devel-
oped on the branchial arches. A fold of skin, the operculum,
appears on each side, in front of the gills, growing from the
region of the hyoid arch, and extends backwards until the
gill-slits and external gills are covered and there is only a
single small external branchial aperture on each side. On
the right side the operculum soon unites with the body-wall
so as to close the branchial aperture, but on the left side
the opening remains for a considerable time as the sole exit
of the water. At this time the tadpole is to all intents
and purposes a fish.

The lungs now appear, and the larva is for a time truly
amphibious, rising periodically to the surface to breathe air ;
the single branchial aperture, however, soon closes, and
henceforth respiration is purely aerial.

In the meantime the limbs are developed. The hind-
limbs appear as little rounded buds, one on each side of the
root of the tail. The fore-limbs arise beneath the operculum,
and are therefore hidden at first; soon, however, they
emerge by forcing their way through the operculum. As
the limbs increase in size, the tail undergoes a progressive
shrinking. The mouth widens, the intestine undergoes a
relative diminution in length, and vegetable is exchanged
for animal diet. The little tailed frog can now leave the
water and hop about upon land ; its tail is soon completely
absorbed, and the metamorphosis is complete.

The frogs and toads are all closely allied as regards all
the main features of their structure —the chief differences
between the many genera and species being in such super-
ficial characteristics as coloration and proportions. In

432 MANUAL OF ZOOLOGY SECT.

some teeth are altogether absent; in others the webs
between the toes are not developed; in some tree-frogs
(/f/a and allied genera) the toes terminate in sucking
discs. A less superficial point of divergence from the
structure of the common American frogs is to be observed in
some members of the group, such as the tree-frogs and toads
(Ala, Bufo, and others), in which the two halves of the
shoulder-girdle, instead of being firmly united in the mid-

Fic. 259. Salamandra maculosa. (After Cuvier.)

dle line, overlap one another. In one small group the
tongue is absent. In some, again, there is no fish-like, gill-
bearing larva or tadpole — the young animal emerging from
the egg with the limbs formed, with no gills and no tail.
All the frogs and toads are grouped together to form an
order of Amphibia — the Anura or tailless Amphibia.

The newts and salamanders (Fig. 259), with a number of
other less widely known forms, differ from the frogs and
toads in the possession in the adult of a well-developed tail.
These constitute the order Urodela or tailed Amphibians.
Of these tailed Amphibians, some, such as the newts and

XII PHYLUM CHORDATA 433

salamanders, lose both gills and gill-
slits completely in the adult: while in
others (such as Proteus, Mecturus, and
Stren), either gills are retained through-
out life, or, as in the American AZeno-
poma, or hell-bender, gill-slits remain
as a permanent record of their pres-
ence in the larva. In some of the
tailed Amphibians the limbs are well-
developed; in others they are very
small.

Widely different. in many respects
from both the Anura and Urodela are
a group of Amphibia—the Gymno-
phiona—which are quite snake-like
in appearance, owing to the elongated
and narrow form of the body and the
entire absence of limbs. The group is
represented by the blind snake (Ce-
cia) of Central and South America.

CLASS IV. REPTILIA

The class Reptilia comprises the
lizards and snakes, the tuataras, the
turtles and tortoises, and the alligators
and crocodiles. On a superficial com-
parison of these with the Amphibia, it
might be inferred that there is a close
alliance between the two groups; but
this impression becomes weakened
when a closer examination is made of

:, Fic. 260. — Siren lacer-
the structure and development, and it ‘tina. (From Mivart.)

2F

434 MANUAL OF ZOOLOGY SECT.

at length becomes evident that in the Reptilia we have
to do with a class of Vertebrates which stand on a dis-
tinctly higher plane than the Amphibia. One significant
feature of the Reptilia which marks them off sharply
from the Amphibia is that the lungs are the sole organs
of respiration, gills never being developed at any stage.
Another is the development in the embryo of two struc-
tures known as the amnion and the aHantzois, not devel-
oped in lower groups of Vertebrates, but present in the
embryos of all the higher. The amnion is a thin membrane
which covers over the body of the embryo, the space between
it and the latter being tensely filled with a watery fluid. The
amnion thus forms a sort of water-cushion, protecting the
delicate and fragile embryo from the effects of any shocks
which may be sustained by the eggs. The allantois, repre-
sented in the frog by the urinary bladder, is a membranous
structure developed as a hollow outgrowth of the enteric
canal at its posterior end. It becomes highly vascular, and
acts as an embryonic respiratory organ.

There are four well-marked orders of living reptiles : —

1. The Squamata, comprising the Lacertilia or lizards
(including the iguanas, monitors, skinks, geckos, chameleons,
and others), and the Ophidia or snakes (including the vipers
and rattlesnakes, pythons, boas, sea-snakes, etc.).

2. The Rhynchocephalia, including only the New Zealand
Tuatara (Hatteria).

3. The Chelonia, including the land tortoises, soft tor-
toises, river and marsh tortoises, and the turtles.

4. The Crocodilia, including the crocodiles, gavials, the
alligators and caimans.

The most striking external difference between a typical
lizard (Fig. 207) and the frog are in the covering of scales
in the case of the former, the comparative smallness of its

XII PHYLUM CHORDATA 435

head, and the presence of a distinct neck, the great length
of the caudal region, the shortness of the limbs, and the
approximate equality in length of the anterior and posterior
pairs. The anterior limbs are situated just behind the
neck, springing from the trunk towards the ventral surface.
The fore-limb, like that of the frog, is divided into three
parts, the upper-arm or d7vachium, the fore-arm or ani-
brachium, and the hand or manus, there are five digits
provided with horny claws, the first digit or pollex being
the smallest. The hind-limbs arise from the posterior end
of the trunk towards the ventral aspect; each, like that of
the frog, consists of three divisions — thigh or femur, shank
or crus, and foot or pes. The pes, like the manus, termi-
nates in five clawed digits, of which the first or hallux is the
smallest. The head is somewhat pyramidal, slightly de-
pressed ; the openings of the external nares are situated
above the anterior extremity. The mouth is a wide slit-
like aperture running round the anterior border of the head.
At the sides are the eyes, each provided with upper and
lower opaque movable eyelids, and with a transparent third
eyelid or nictitating membrane, which, when withdrawn, lies
in the anterior angle of the orbit. Behind the eye is a
circular brown patch of skin, — the Aympanic membrane, —
corresponding closely to that of the frog, but somewhat
sunk below the general level of the skin. The trunk is
elongated, strongly convex dorsally, flatter at the sides and
ventrally. At the root of the tail on the ventral surface is
a slit-like transverse aperture — the anus or cloacal aperture.
The tail is cylindrical, thick in front, gradually tapering to
a narrow posterior extremity ; it is nearly twice as long as
the head and trunk together.

There is an exoskeleton of horny epidermal sca/es covering
all parts, differing in size in different positions.

436 MANUAL OF ZOOLOGY SECT.

In some groups of lizards the tail is comparatively short
and thick; and in others it is depressed and expanded into
a leaf-like form. In the chamzleons the long and tapering
tail is used as a prehensile organ, the coiling of which
round branches of the trees in which the animal lives, aids
in maintaining the balance of the body in climbing from
branch to branch.

In the limbs there is likewise a considerable amount of
variation in the different groups of the Lacertilia. Moder-
ately long pentadactyle limbs, like those of Lacerta, are the
rule. In the chameleons both fore- and hind-limbs become
prehensile by a special modification in the arrangement and
mode of articulation of the digits. In these remarkable
arboreal reptiles the three innermost digits of the manus are
joined together throughout their length by a web of skin,
and the two outer digits are similarly united ; the two sets
of digits are so articulated that they can be brought against
one another with a grasping movement much analogous to
the grasping movements of a parrot’s foot or the hand of
man. A similar arrangement prevails in the pes, the only
difference being that the two innermost and three outermost
digits are united. In some groups of Lacertilia, on the
other hand, such as the blind-worms (Angus), limbs are
entirely absent, or are represented only by mere vestiges ;
and numerous intermediate gradations exist between these
and forms, such as Lacerta, with well-developed limbs. The
limbless lizards, such as the glass-snake, and Pygopus (Fig.
261), bear a very close resemblance to the snakes, not only
in the absence of the limbs, but also in the general form of
the body and the mode of locomotion.

The body of a snake is elongated, narrow, and cylindrical,
usually tapering towards the posterior end, sometimes with,
more usually without, a constriction behind the head. In

XII PHYLUM CHORDATA

437

the absence of limbs, the beginning of the short caudal
ing. The fore-limbs are never represented even by vestiges ;

region is only indicated by the position of the cloacal open-

in some’ pythons there are inconspicuous vestiges of hind-
limbs, in the form of small claw-like processes. The mouth
of the snake is capable of being very widely opened by the

free articulation of the lower jaw, and it is this mainly which
distinguishes it from the snake-like lizards.

But other, less

i

Ss

Se
Se

AO
Ie
scica

Fic. 261.— Pygopus lepidopus.

(After Brehm.)

conspicuous, points of distinction are the absence of movable
eyelids in the snake, and also the absence of a tympanum.
Hatteria, the New Zealand Tuatara (Fig. 262), the only
living representative of the Rhynchocephalia, is a lizard-like

reptile with a well-developed laterally-compressed tail, and

pentadactyle extremities, very similar to those of a typical

the middle of the dorsal surface.

lizard. The upper surface is covered with small granular
scales, and a crest of compressed spine-like scales runs along

covered with transverse rows of large squarish plates.

The lower surface is

438 MANUAL OF ZOOLOGY SECT.

In the Chelonia (Fig. 263) the body is short and broad,
enclosed in a hard “shell,” consisting of a dorsal part or
carapace and a ventral part or plastron. ‘These are firmly
united, apertures being left between them for the head and
neck, the tail and the limbs. The neck is long and mobile ;
the tail short. The limbs are fully developed, though short.
In some (land and fresh-water tortoises) they are provided
each with five free digits terminating in curved horny claws ;
in the turtles the digits are closely united together, and the

Fic. 262.—Hatteria punctata. (After Brehm.)

limb assumes the character of a “ flipper” or swimming
paddle. The cloacal aperture is longitudinal.

The Crocodilia, the largest of living reptiles, have the
trunk elongated and somewhat depressed, so that its breadth
is much greater than its height. The snout is prolonged,
the neck short, the tail longer than the body and compressed
laterally. The limbs are relatively short and powerful, with
five digits in the manus and four in the pes, those of the
latter being partly or completely united by webs of skin.

XII PHYLUM CHORDATA 439

x

The eyes are very small; the nostrils placed close to the
end of the snout and capable of being closed by a sphincter
muscle. The cloacal aperture is a longitudinal slit.
Characteristic of the Squamata is the development in the
epidermis of horny plates, the sca/es, which cover the entire
surface, overlapping one another in an imbricating manner.
Sometimes they are similar in character over all parts of the
surface ; usually there are specially developed scales — the

head shields — covering the upper surface of the head. In
the majority of snakes the ventral surface is covered with a

row of large transversely elongated scales, the ventra/ shields.
In some lizards (chameleons and geckos) the scales are
reduced and modified into the form of minute tubercles or
granules. In some lizards special developments of the
scales occur in the form of large tubercles or spines.

In the snake-like Amphisbzenians there are no true scales,

440 MANUAL OF ZOOLOGY SECT.

with the exception of the head shields, but the surface is
marked out into annular bands of squarish areas.

In addition to the modification of the scales, the integu-
ment of the chameleons is remarkable for the changes of
colour which it undergoes, these changes being due to the
presence in the dermis of pigment cells which contract
or expand under the influence of the nervous system,
in a way that reminds one of the integument of the
Cephalopoda.

In the Chelonia, scales, when developed, are confined to
the head and neck, the limbs and the tail, but in all of them,
with the exception of the soft tortoises, both dorsal and ven-
tral surfaces are covered by a system of large horny plates.
A series of horny head-shields usually cover the dorsal sur-
face of the head. Beneath the horny plates of the dorsal
and ventral surfaces are the bony carapace and plastron,
partly composed of dermal bones, but so intimately united
with elements derived from the endoskeleton that the entire
structure is best described in connection with the latter
(p- 443)-

In the Crocodilia, the dorsal surface is covered with longi-
tudinal rows of sculptured horny plates, beneath which are
bony dermal scutes of corresponding form. The ventral
surface of the body is covered with scales like those of a
lizard. The horny plates of the dorsal surface of the tail are
elevated into a longitudinal crest.

A periodical ecds’s or casting and renewal of the outer
layers of the horny epidermis takes place in all the Reptilia.
Sometimes this occurs in a fragmentary manner; but in
snakes and many lizards the whole comes away as a con-
tinuous slough.

The verfebr@ are always fully ossified. Only in the
geckos and Hatteria are the centra amphiccelous, with

XII PHYLUM CHORDATA

remnants of the notochord in
the inter-central spaces. In
most of the others the centra
are proccelous, a ball-like con-
vexity on the posterior surface
of each centrum projecting
into a cup-like concavity on
the anterior face of the next.
The various regions of the
spinal column are well marked
in most of the lizards, in the
Chelonia, and in the Croco-
dilia (Fig. 264). In the snakes
and many of the snake-like
lizards only two regions are
distinguishable — pre - caudal
and caudal. In the others
there is a sacral region com-
prising two vertebre, which
have strong transverse pro-
cesses for articulation with
the ilia. The first and sec-
ond vertebrz are always modi-
fied to form an atlas and
axis. Ribs are developed in
connection with all the ver-
tebrz of the pre-sacral or pre-
caudal region; in the caudal
region they are usually replaced
by inferior arches. In the fly-
ing lizards (Draco) a num-
ber of the ribs are greatly
produced, and support a pair

L

Ss
is Nps .
Fe

HY, humerus;
(From
£

U, ulna.

Fe, femur;
T, tibia;

F, fibula;

Sta, abdominal ribs;

c, scapula;

D, thoracic region of spinal column;

: C, caudal region:
J, ischium; JZ, lumbar region; A, radius; #7, ribs; S, sacrum;

Fic. 264. — Skeleton of crocodile.
Zittel.)

442 MANUAL OF ZOOLOGY SECT.

of wide flaps of skin at the sides of the body, acting as
wings or rather as parachutes. In Hatteria and Crocodilia
(Fig. 264) each rib has connected with it posteriorly a flat-

tened curved cartilage, the wcrnate.

Fic. 265.—Cistudo lutaria. Skeleton seen from below; the plastron has been
removed and is represented on one side. C, costal plate; Co, coracoid; e, ento-
lastron; Zf, epiplastron; #, fibula; “e, femur; A’, humerus; //, ilium; /s,
ischium; J/, marginal plates; Mz, nuchal plate; 4, pubis; Pro, pro-cora-
coid; Py, pygal plates; A, radius; Sc, scapula; 7, tibia; U, ulna. (From

Zittel.)

In the Chelonia (Fig. 265) the total number of vertebrz
is always smaller than in the members of the other orders.
The cervical and the caudal are the only regions in which
the vertebree are movable upon one another. The vertebree

XII PHYLUM CHORDATA 443

of the trunk, usually ten in number, are immovably united
together. Each of the neural spines, from the second to
the ninth inclusively, is expanded into a flat plate, and the
row of neural plates (Fig. 266, V), thus formed constitutes
the median portion of the carapace. The ribs are likewise
immovable; a short distance from its origin each passes
into a large bony costal plate (C), and the series of costal
plates uniting by their edges form a large part of the cara-
pace on either side of the row of neural plates. The cara-
pace is made up of the neural and costal plates supplemented
by a row of margina/ plates (Figs. 265 and 266, 47) running
along the edge, and nuchal (Mu) and pygal (Py) plates

Fic. 266. — Chelone midas. Transverse section of skeleton. C, costal plate; C’,
centrum; 1, marginal plate; P, lateral element of plastron; FR, rib; ’, expanded
neural plate. (After Huxley.)

situated respectively in front of and behind the row of
neural plates.

The bony elements of the plastron of the Chelonia are an
anterior and median plate and six pairs of plates —the six
pairs probably being of similar nature to the abdominal
ribs of the Crocodilia.

The s#ernum in the Lacertilia is a plate of cartilage with a
bifid posterior continuation. In the Ophidia and Chelonia
it is absent. In the Crocodilia it is a broad plate with a
posterior continuation or Ayposfernum, extending backwards
as far as the pelvis.

444 MANUAL OF ZOOLOGY SECT.

A series of ossifications — the abdominal ribs, with a mesial
abdominal sternum —-\ie in the wall of the abdomen in the
Crocodilia (Fig. 264, S¢z), and similar ossifications occur
also in the monitors and in Hatteria. The elements of
the plastron of the Chelonia are probably of a similar
character.

In the skw@ ossification is much more complete than in
the Amphibia, the primary chondrocranium persisting to a
considerable extent only in some lizards and in Hatteria,
and the number of bones is much greater.

The parasphenoid is reduced, and its place is taken by
large basi-occipital, basi-sphenoid, and pre-sphenoid bones.
The lower jaw articulates with the skull through the interme-
diation of a quadrate bone, which is movable in the lizards
and snakes, fixed in Hatteria, the Chelonia, and Crocodilia.

A remarkable feature of the skull of the snakes (Fig. 267),
is the free articulations of the bones of the jaws, permitting
of the mouth being opened very wide so as to allow the
passage of the relatively large animals which the snake
swallows whole ; this wide opening of the mouth is further
aided by the two halves of the mandible not being firmly
fixed together anteriorly, but merely connected together by
means of elastic tissue, so that they are capable of being
widely separated from one another.

In accordance with their purely aérial mode of respira-
tion, the wsceral arches are much more reduced in the
Reptilia than in the Amphibia in general. The only well-
developed post mandibular arch is the hyoid, and even
this may undergo considerable reduction (Ophidia). The
branchial arches, except in so far as they may contribute to
the formation of the tracheal rings, are not represented in
the adult, with the exception of most Chelonia, in which the
first branchial arch persists.

XII PHYLUM CHORDATA 445

In the lizard (Fig. 268) and crocodiles there is a cross-
shaped membrane-bone, the ¢a/erclavicle or episternum (epist),
in relation to the pectoral arch and sternum. In the limb-
less lizards the pectoral arch may be absent or may be well
developed ; it is completely wanting in all snakes. In the
pelvic arch the ischium is separated from the pubis by a wide
space not developed in the Amphibia. Slight vestiges of hind-
limbs occur in some pythons alone among the Ophidia.

Fic. 267. — A, lateral view of skull of rattlesnake (Crotalus). &. O, basi-occipital;
B.S, basi-sphenoid; £. O, exoccipital; /. O, fossa ovalis; Za, conjoined lac-
rymal and pre-frontal; Z. /, articulation between-lacrymal and frontal; 1/7,
mandible; Mx, maxilla; Ma, nasal; P/, palatine; Px, pre-maxilla; P. Sph,
pre-sphenoid; P#, pterygoid; Ox, quadrate; Sg, squamosal; //. l’, foramina
of exit of the second and fifth cranial nerves. B, transverse section at point
lettered Bin Fig. A; 7, trabeculae. (After Huxley.)

In the lizards teeth are present in the pre-maxille, the
maxilla, the mandible, and usually the palatines. These
are in most lizards small and simple, and uniform in shape
and arrangement. A Mexican Lizard, Heloderma, which
also occurs in Utah and Arizona, differs from all the rest in

446 MANUAL OF ZOOLOGY SECT.

having teeth which are perforated for the ducts of poison-
glands. In the snakes (Fig. 267) teeth are rarely devel-
oped on the pre-maxille, but are present on the maxille,
palatines, pterygoids, and sometimes the transverse bones,
as well as the dentary of the mandible. They may be of
the same nature throughout, solid, elongated, sharp-pointed
teeth, which are usually strongly recurved, so that they have
the character of sharp hooks, their function being rather to

Fic. 268. — Pectoral arch and sternum of a lizard (Lacerta agilis). c/, clavicle;
cor, coracoid; ep. cor, epicoracoid; efzst, episternum; g/e7, glenoid cavity for
head of humerus; fp». cor, pro-coracoid; 7.7 — 7. 4, first to fourth sternal ribs;
sc, scapula; s¢, sternum; szfra. sc, supra-scapula. (After Hoffman.)

hold the prey and prevent it slipping from the mouth while

being swallowed than to masticate it. Non-venomous snakes

possess teeth only of this character. In the venomous snakes,
more or fewer of the maxillary teeth assume the character
of poison-fangs. These are usually much larger than the
ordinary teeth, and either grooved or perforated by a canal

XII PHYLUM CHORDATA 447

for the passage of the duct of the poison-gland. In the
vipers there is a single large curved poison-fang with small
reserve-fangs at its base, these being the only teeth borne
by the maxilla, which is very short ; in the venomous colu-
brine snakes the poison-fangs are either the most anterior or
the most posterior of a considerable range of maxillary teeth.
In the vipers the large poison-fang is capable, owing to the
maxilla in which it is fixed being movable on a hinge-joint,
of being rotated through a considerable angle, and moved
from a nearly horizontal position, in which it lies along the
roof of the mouth, embedded in folds of the mucous mem-
brane, to a nearly vertical one when the snake opens his
mouth to strike its prey.

In Hatteria there are pointed, triangular, laterally-
compressed teeth, arranged in two parallel rows, one along
the maxilla, the other along the palatine. The teeth of the
lower jaw, which are of similar character, bite in between
these two upper rows, all the rows becoming worn down
in the adult in such a way as to form continuous ridges.
Each pre-maxilla bears a prominent, chisel-shaped incisor,
represented in the young animal by two pointed teeth. In
the young Hatteriaa tooth has been found on each vomer —
a condition exceptional among reptiles.

In the Chelonia, teeth are entirely absent, the jaws being
invested in a horny layer in such a way as to form a structure
like a bird’s beak.

The Crocodilia have numerous teeth which are confined
to the pre-maxillz, the maxille, and the dentary. They are
large, conical, hollow teeth, devoid of roots, each lodged in
its socket or alveolus, and each becoming replaced, when
worn out, by a successor developed on its inner side.

In the enéeric canal of the Reptiles the principal special
features to be noticed are the muscular, gizzard-like stomach

MANUAL OF ZOOLOGY SECT.

448

of the Crocodilia, the presence of a rudimentary czecum at
the junction of small and large intestines in most Lacertilia
and in the Ophidia, and the presence of numerous large
cornified papille in the cesophagus of the Turtles.

The Reptiles have all an
elongated ¢rachea, the wall
of which is _ supported
by numerous cartilaginous
rings. The anterior part
of this is dilated to form the
larynx, the wall of which
is supported by certain spe-
cial cartilages —the cricoid
and the arytenoids. The
trachea bifurcates posteri-
orly to form two bronchi,
right and left, one passing
to each lung.

The Zungs of the Lacer-
tilia and Ophidia are sim-
ple and sac-like, like those
of the frog. In the Croco-
dilia and Chelonia they are
of a more complex char-
acter, being divided inter-

Fic. 269. — Heart of monitor (Varanus)

guarded by valves.

dissected to show the cavity of the
ventricle and the vessels leading out
from it. A. A’, auricles; Ao, dorsal
aorta; Ap. AP’, pulmonary arteries;
(sc, subclavian artery; Ca. Ca', caro-
tids; RA. RA, roots of dorsal aorta;
Trea, innominate trunk; V, ventricle;
tS right aortic arch; *, left aortic arch,
(From Wiedersheim.)

nally by septa into a number
of chambers.

In the heart (Fig. 269)
the sinus venosus is always
distinct, and is divided into
two parts by a septum;

its aperture of communication with the right auricle is
There are always two quite distinct

XII PHYLUM CHORDATA 449

auricles, as in the Amphibia, the right oat 3 the venous

blood from the body, the
left the oxygenated blood
brought from the lungs by
the pulmonary veins. But
a vital point of difference
between the heart of the
reptile and that of the am-
phibian is that in the
former the ventricle is al-
ways more or less com-
pletely divided into right
and left portions. Inallthe
Lacertilia, Ophidia, and
Chelonia the ventricle is
incompletely divided by
a septum which does
not entirely cut off the
two portions of the
cavity from one another.
But in the Crocodilia
the cavity is completely
divided, so that we may
speak of distinct right
and left ventricles.

The drain of Reptiles
is somewhat more highly
organised than that of the
Amphibia. The cerebral
hemispheres are well de-
veloped in all. The mid-
brain consists usually of

two closely approximated oval optic lobes.

2G

Fic. 270.— Brain of alligator, from above.

B. ol., olfactory bulb; G. /, epiphysis ;
HH, cerebellum ; Med, spinal cord ; A/7,
optic lobes ; NH, medulla oblongata ;

VH, cerebral hemispheres ; I—XJ, cra-
bs nerves ; 1, 2, first and second spinal
nerves. (After Wiedersheim. )

The cerebellum

450 MANUAL OF ZOOLOGY SECT.

is always of small size, except in the Crocodilia (Fig. 270),
in which it is comparatively highly developed, and consists
of a median and two lateral lobes.

The eyes are relatively large, with a cartilaginous sclerotic
in which a ring of bony plates is developed in some cases.
Most reptiles have both upper and lower eyelids and nicti-
tating membrane. The greater number of the geckos and
all the snakes constitute exceptions, movable eyelids being
absent in both these groups. In the chameleons there is
a single circular eyelid with a central aperture.

The middle ear is absent in the snakes, though a colu-
mella auris is present, embedded in muscular and fibrous
tissue.

Developed in close relation to the epiphysis there is in
many lizards (Lacerta, Varanus, Anguis, Grammatophora,
and others) and in Hatteria, a remarkably eye-like organ —
the pineal eve (Fig. 271), which is situated in a foramen of
the cranial roof immediately under the integument, and
covered over by a specially modified, transparent scale.
Like the epiphysis itself, the pineal eye is developed as a
hollow outgrowth of the roof of the diencephalon; the
distal end of this becomes constricted off as a hollow sphere,
while the remainder becomes converted into a nerve. The
nerve degenerates before the animal reaches maturity, so
that the organ would appear—though evidently, from its
structure, an organ of sight — to have now entirely or nearly
lost its function.

Though fertilisation is always internal, most Reptilia are
oviparous, laying eggs clothed in a tough, parchment-like or
calcified shell. These are usually deposited in holes and
left to hatch by the heat of the sun. In the crocodiles they
are deposited in a rough nest and guarded by the mother.
In all cases development has only progressed to a very early

XII PHYLUM CHORDATA 451

stage when the deposition of the eggs takes place, and it is
only after a more or less prolonged period of incubation that
the young, fully formed in almost every respect, emerge
from the shell and shift for themselves. Many lizards,

Fic. 271. — Section of the pineal eye of Hatteria punctata. , blood-vessels; %,
cavity of the eye filled with fluid; 4, capsule of connective tissue; 7, lens; 7,
molecular layer of the retina; 7, retina; s¢, stalk of the pineal eye; -r, cells in
the stalk. (From Wiedersheim, after Baldwin Spencer.)

however, and a few snakes are viviparous, the ova being
developed in the interior of the oviduct, and the young
reaching the exterior in the completely formed condition.

452 MANUAL OF ZOOLOGY SECT.

The lizards are for the most part terrestrial animals,
usually extremely active in their movements and endowed
with keen senses. The majority readily ascend trees, and
many kinds are habitually arboreal ; but the chameleons
are the only members of the group which have special modi-
fications of their structure in adaptation with an arboreal
mode of life. The skinks and the amphisbzenians are
swift and skilful burrowers. The geckos are enabled by the
aid of the sucker-like discs on the ends of their toes to run
readily over vertical or overhanging smooth surfaces. A
few lizards, on the other hand, live habitually in fresh water.
The flying lizards (Draco) are arboreal, and make use of
their wings — or, to speak more accurately, aéroplane or para-
chute (thin folds of skin supported by the greatly produced
ribs) — to enable them to take short flights from branch to
branch. Chalmydosaurus and certain other genera are
exceptional in frequently running on the hind-feet, with the
fore-feet entirely elevated from the ground. A tolerably
high temperature is essential for the maintenance of the
vital activities of lizards, low temperatures bringing on an
inert condition, which usually passes, during the coldest
part of the year, into a state of suspended animation or
hibernation. The food of lizards is entirely of an animal
nature. The smaller kinds prey on insects of all kinds, and
on worms. Chameleons, also, feed on insects, which they
capture by darting out the extensile tongue covered with a
viscid secretion. Other lizards supplement their insect diet,
when opportunity offers, with small reptiles of various kinds,
frogs and newts, small birds and their eggs, and small mam-
mals, such as mice and the like. The larger kinds, such as
the monitors and iguanas prey exclusively on other ver-
tebrates ; some, on occasion, are carrion-feeders. Most
lizards lay eggs enclosed in a tough calcified shell. These

XII PHYLUM CHORDATA 453

they simply bury in the earth, leaving them to be hatched
by the heat of the sun. Some, however, are viviparous ; in
all cases the young are left to shift for themselves as soon as
they are born.

Snakes are also usually extremely active and alert in their
movements ; and most are very intolerant of cold, under-
going a hibernation of greater or less duration during the
winter season. Many live habitually on the surface of the
ground—some kinds by preference in sandy places or
among rocks, others among long herbage. Some (tree-
snakes) live habitually among the branches of trees.
Others (fresh-water snakes) inhabit fresh water; others
(sea-snakes) live in the sea. The mode of locomotion of
snakes on the ground is extremely characteristic, the
reptile moving along by a series of horizontal undulations
brought about by contractions of the muscles inserted into
the ribs, any inequalities on the surface of the ground
serving as fulcra against which the free posterior edges
of the ventral shields (which are firmly connected with the
ends of the ribs) are enabled to act. The burrowing blind-
snakes and other families of small snakes feed on insects
and worms. All the rest prey on vertebrates of various
kinds — fishes, frogs, lizards, snakes, birds and their eggs,
and mammals. The pythons and boas kill their prey by
constriction, winding their body closely round it and draw-
ing the coils tight till the victim is crushed or asphyxiated.
Some other non-venomous snakes kill with bites of their
numerous sharp teeth. The venomous snakes sometimes,
when the prey is a small and weak animal such as a frog,
swallow it alive: usually they first kill it with the venom of
their poison-fangs.

When a venomous snake strikes, the poison is pressed out
from the poison-gland by the contraction of the masseter

454 MANUAL OF ZOOLOGY SECT.

(Fig. 272, J/c), one of the muscles which raise the lower
jaw: it is thus forced along the duct (Gc) to the aperture
(za), and injected into the wound made by the fang. The
effect is to produce acute pain with increasing lethargy and
weakness, and in the case of the venom of some kinds of
snakes, paralysis. According to the relative amount of the
poison injected and the degree of its virulence (which differs
not only in different kinds of snakes, but in the same snake
under different conditions) the symptoms may result in
death, or the bitten animal may recover. The poison is a

Fic. 272.— Poison apparatus of rattlesnake. A, eye; Gc, poison-duct entering
the poison-fang at t ; Aw, muscles of mastication partly cut through at * ; A/c,
masseter or constrictor muscle; A/c’, continuation of the constrictor muscle to the
lower jaw ; 4, nasal opening ; S, fibrous poison-sac ; 3, tongue ; za, opening of
the poison-duct ;_ zf/, pouch of mucous membrane enclosing the poison-fangs.
(From Wiedersheim.)

clear, slightly straw-coloured or greenish liquid ; it preserves
its venomous properties for an indefinite period, even if -
completely desiccated. The poisonous principles are cer-
tain proteids not to be distinguished chemically from other
proteids which have no such poisonous properties. Immu-
nity against the effects of the poison, and relief of the symp-
toms after a bite has been inflicted, have been found to be
conferred by injections of the serum of animals which have

XII PHYLUM CHORDATA 455

been treated with injections of increasing doses of the
poison.

The majority of snakes are viviparous. Some, however,
lay eggs, which, nearly always, like those of the oviparous
lizards, are left to be hatched by the heat of the sun, some
of the Pythons being exceptional in incubating them among
the folds of the body.

Hatteria lives in burrows in company with mutton-birds
(Puffinus), and feeds on insects and small birds. It lays
eggs enclosed in a tough parchment-like shell. The eggs
are laid in November, and the embryos pass the winter in
a state of hibernation unknown to any other vertebrate
embryo, not emerging from the egg until nearly thirteen
months have elapsed (Dendy).

Of the Chelonia some (land-tortoises) are terrestrial ;
others (fresh-water tortoises) inhabit streams and ponds,
while the sea-turtles and luths, or leather-backed turtles,
inhabit the sea. Even among reptiles they are remarkable
for their tenacity of life, and will live for a long time after
severe mutilations, even after the removal of the brain; but
they readily succumb to the effects of cold. Like most
other reptiles, the land and fresh-water tortoises living in
colder regions hibernate in the winter ; in warmer latitudes
they sometimes pass through a similar period of quiescence
in the dry season. ‘The food of the green turtles is exclusively
vegetable ; some of the land tortoises are also exclusively
vegetable feeders ; other Chelonia either live on plant food,
together with worms, insects, and the like, or are com-
pletely carnivorous. All are oviparous, the number of eggs
laid being usually very great (as many as 240 in the sea-
turtles) ; these they lay in a burrow carefully prepared in
the earth, or, in the case of the sea-turtles, in the sand of
the sea-shore, in a round hole about fifteen or twenty inches

456 MANUAL OF ZOOLOGY SECT.

deep and ten inches in diameter, and having covered them
over, leave them to hatch.

The crocodiles and alligators, the largest of living reptiles,
are in the main aquatic in their habits, inhabiting rivers,
and, in the case of some species, estuaries. Endowed with
great muscular power, these reptiles are able, by the move-
ments of the powerful tail and the webbed hind-feet, to
dart through the water with lightning-like rapidity. By
lying in wait motionless, sometimes completely submerged
with the exception of the extremity of the snout bearing
the nostrils, they are often able by the suddenness and
swiftness of their onset to seize the most watchful and timid
animals. In the majority of cases the greater part, and in
some the whole, of their food consists of fishes; but all the
larger and more powerful kinds prey also on birds and
mammals of all kinds, which they seize unawares when they
come down to drink or attempt to cross the stream.
On land their movements are comparatively slow and
awkward, and they are correspondingly more timid and
helpless.

The Crocodilia are all oviparous, and the eggs, as large in
some species as those of a goose, are brought forth in great
numbers (sometimes roo or more), and either buried in the
sand or deposited in rough nests.

CLASS V. AVES

In many respects birds are the most highly specialised of
Craniata. As a class they are adapted for aerial life, and
almost every part of their organisation is modified in ac-
cordance with the unusual environment. The non-conduct-
ing covering of feathers; the modification of the fore-limbs
as wings, of the sternum and shoulder-girdle to serve as

xa PHYLUM CHORDATA 457

origins of the wing-muscles, and of the pelvic girdle and
hind-limbs to enable them to support the entire weight of
the body on land; the perfection of the respiratory system,
producing a higher temperature than in any other animals, —
all these peculiarities are of the nature of adaptations to
flight.

The common or domestic pigeon is known under many
varieties which differ from one another in size, proportions,
coloration, details in the arrangements of the feathers, and
in many points of internal anatomy.

The following description refers especially to the common
dovecot pigeon.

In the entire bird (Fig. 273) the plump trunk appears to
be continued insensibly into the small, mobile head, with its
rounded brain-case and prominent deak formed of the upper
and lower jaws covered by horny sheaths. The head, neck,
and trunk are invested in a close covering of feathers, all
directed backwards and overlapping one another. Posteriorly
the trunk gives origin to a number of outstanding feathers
which constitute what is ordinarily called the tail. From
the anterior region of the trunk spring the wngs, also
covered with feathers, and, in the position of rest, folded
against the sides of the body. The legs spring from the
hinder end of the trunk, but, owing to the thick covering
of feathers, only the feet are to be seen in the living bird,
each covered with sca/es and terminating in four digits
(dg z'— dg 4'), three directed forwards and one backwards.

In order to make a fair comparison of the outer form
with that of other craniate types, it is necessary to remove the
feathers. When this is done the bird is seen to have a
long, cylindrical, and very mobile neck, sharply separated
both from head and trunk. The true tail is a short, conical
projection of the trunk, known as the wropygiwm, and giving

458 MANUAL OF ZOOLOGY SECT,

origin to the group of large feathers (7c?) to which the word
“tail”? is usually applied. On the dorsal surface of the
uropygium is a papilla bearing on its summit the opening of

Fic. 273. — Columba livia. The entire animal from the left side with most of the
feathers removed. ad. dg. rx, ad-digital remex; a/. sf, ala spuria; az, anus;
au. ap, auditory aperture; cb. rmg, cubital remiges; cv, cere; dg. 1,2, 3, digits
of manus; dg. 7', 2', 3’, 4’, digits of pes; Av. pt, humeral pteryla; dg, ligament
of remiges; ma. dg. rmg, mid-digital remiges; a, nostril; wed. mz, nictitating
membrane; ov. x7, “oil gland; pr. dg. rmg, pre- -digital remiges; pr. ‘pig, pre-
patagium; fz. pte, post-patagium; 7cf, mesial rectrix of right side; xed’, sacs
of left rectrices; sf. Az, spinal pteryla; ts, mitts, tarso-metatarsus; 7. aft,
ventral apterium, or featherless space.

XII PHYLUM CHORDATA 459 .

a large gland, the oz/-gland (o.g/), used for lubricating or
“preening ’’ the feathers.

The wings show the three typical divisions of the fore-
limb, upper arm, fore-arm, and hand, but the parts of the
hand are closely bound together by skin, and only three
imperfectly marked digits, the second (dg 2) much larger
than the first (dg z) and third (dg 3), can be distinguished.
In the position of rest the three divisions of the wing are
bent upon one another in the form of a Z: during flight the
entire wing is straightened out at right angles to the trunk.
In the hind-limb the short thigh is closely bound to the
trunk: the foot is clearly divisible into a proximal portion,
the farso-metatarsus (ts. méts) and four digits, of which one,
the hallux (dg z'), is directed backwards, the others, the
second, third, and fourth of the typical foot, forwards.

The mouth is terminal and is guarded by the elongated
upper and lower beaks; it has, therefore, a very wide gap.
On each side of the base of the upper beak is a swollen
area of soft skin, the cere (cr) surrounding the vostril (na),
which has thus a remarkably backward position. The eves
are very large, and each is guarded by an upper and a lower
eyelid and a transparent nictitating membrane (ct. m). A
short distance behind the eye is the auditory aperture
(au. ap), concealed by feathers in the entire bird, and lead-
ing into a short external auditory meatus, closed below
by the tympanic membrane. The ans or cloacal aper-
ture (a7), is a large, transversely elongated aperture placed
on the ventral surface at the junction of the uropygium with
the trunk.

The exoskeleton is purely epidermal, like that of the
lizard, which it also resembles in consisting partly of horny
scales. These cover the tarso-metatarsus and che digits of
the foot, and are quite reptilian in appearance and structure.

460 MANUAL OF ZOOLOGY SECT.

Each digit of the foot is terminated by a claw which is also
a horny product of the epidermis, and the beaks are of the
same nature. The rest of the body, however, is covered by
feathers, a unique type of epidermal product found nowhere
outside the present class.

Fic. 274.—Columba livia. A, proximal portion of a remex. ca/, calamus; znf.
numb, inferior umbilicus; ~ch, rachis; sp. «226, superior umbilicus. B, filo-
plume. C, nestling-down. (C, from Bronn’s Thzerretch.)

A feather (Fig. 274) is an elongated structure consisting
of a hollow stalk, the ca/amus or quill (ca/), and an ex-
panded distal portion, the vexi//um or vane. At the
proximal end of the quill is a small aperture, the ¢nferior
umbilicus (inf. umb), into which fits, in the entire bird, a

XII PHYLUM CHORDATA 461

small conical prolongation of the skin, the feather papilla.
A second extremely minute aperture, the superior umbilicus
(sup. umb), occurs at the junction of the quill with the vane
on the inner or ventral face of the feather, 7.c., the face
adjacent to the body.

The vane has a longitudinal axis or rachis (rch) contin-
uous proximally with the quill, but differing from the latter
in being solid. To each side of the rachis is attached a kind
of membrane forming the expanded part of the feather and
composed of dards, delicate thread-like structures which
extend obliquely outwards from the rachis. In an uninjured
feather the barbs are closely connected so as to form a con-
tinuous sheet, but a moderate amount of force separates
them from one another, and it can readily be made out with
the aid of a magnifying glass that they are bound together
by extremely delicate oblique filaments, the dardudes, having
the same general relation to the barbs as the barbs themselves
to the rachis.

Adjacent barbules interlock by means of a system of min-
ute hooklets and flanges, and in this way the parts of the
feather are so bound together that the entire structure offers
great resistance to the air.

Among the contour feathers which form the main cover-
ing of the bird and have the structure just described, are
found jiloplumes (Fig. 274, B), delicate hair-like feathers
having a long axis and a few barbs, devoid of locking
apparatus, at the distal end. Nestling pigeons are covered
with a temporary investment of down feathers (C), in which
also there is no interlocking of the barbs: when these first
appear each is covered by a horny sheath like a glove finger.

Feathers, like scales, arise in the embryo from papille of
the skin formed of derm with an epidermal covering. The
papilla becomes sunk in a sac, the feather-follicle, from

462 MANUAL OF ZOOLOGY SECT.

which it subsequently protrudes as an elongated feather-germ,
its vascular dermal interior being the /eather-pu/p. ‘The
horny substance of the feather is formed from the epidermis
of the feather-germ.

The feathers do not spring uniformly from the whole sur-
face of the body, but from certain defined areas (Fig. 275),

Fic. 275.— Pterylosis of Columba livia. A, ventral; B, dorsal. ad. f#, alar
pteryla or wing-tract; c. fz, cephalic pteryla or head-tract; cd. At, caudal
pteryla or tail-tract; cv. pf, crural pteryla; cx. aft, cervical apterium or neck-
space; fm. ft, femoral pteryla; Az. ft, humeral pteryla; Jat. aft, lateral
apterium; sf. ft, spinal pteryla; v. af, ventral apterium; wv. Az, ventral pteryla.
(After Nitsch.)

the feather tracts or pteryle (sp. pt, hu. pt, etc.), separated
from one another by featherless spaces or apferia (v. apt,
etc.), from which only a few filoplumes grow.

In the wings and tail certain special arrangements of the
feathers are to be distinguished. When the wing is stretched

XII PHYLUM CHORDATA 463

out at right angles to the trunk, twenty-three large feathers
(Fig. 273) are seen to spring from its hinder or post-axial
border: these are the remiges or wing-quills. Twelve of
them are connected with the ulna and are called cuditals
or secondaries (cb. rmg). The rest are known as primaries.
In the tail there are twelve long rectrices ( ret) or tail-quills
springing in a semicircle from the uropygium. The whole
feather-arrangement is known as the peerylosis.

car

Fic. 276. —Columba livia. The bones of the trunk. acy. cor, acrocoracoid;
a. tr, anti-trochanter; actd, acetabulum; car, carina sterni; cd. v, caudal verte-
bre; cor, coracoid; cv. 7, cervical ribs; £ ¢7s, probe passed into foramen
triosseum; fur, furcula; gl. cv, glenoid cavity; 2/, illum; zs, ischium; 7s. for,
ischiatic foramen; oéf. 2, obturator notch; pz, pubis; pyg. st, pygostyle; scp.
scapula; s. scr, syn-sacrum; sf, sternum; st. x, sternal ribs; th. v. s, first, and
th. v. 5, last thoracic vertebra; x#c, uncinates; v7. 7, vertebral ribs.

.

The vertebral column is distinguished from that of most
other Craniata by the great Jength and extreme mobility of
the neck, the rigidity of the trunk region, and the shortness
of the tail. There are fourteen cervical vertebrz, the last
two of which have double-headed ribs (Fig. 276, cv. 7) each

464 MANUAL OF ZOOLOGY SECT.

having its proximal end divisible into the Aead proper articu-
lating with the centrum of the vertebra, and a ¢wdercle with
the transverse process: their distal ends are free, not uniting
with the sternum. In the third to the twelfth there are
vestigial ribs (Fig. 277, 7?), each having its head fused with
the centrum, and its tubercle with the transverse process.
The whole rib thus has the appearance of a short, backwardly
directed transverse process perforated at its base.

The centra of the cervical vertebra differ from those of
all other Vertebrata in having saddle-shaped surfaces, the
anterior face (Fig. 277, A) being
concave from side to side and
convex from above downwards.
This peculiar form of vertebra is
distinguished as heterocelous.

The first two vertebre, the
atlas and axis, are specially
modified. The atlas is a ring-
like bone with an articulation on
its anterior surface for the single
occipital condyle of the skull.
notase leatnaiiA eee eee The ants has projecting forwards

vical vertebra; A, anterior; from its centrum, a peg-like pro-

B, posterior face. a@. syg, an-

terior zygapophysis; cz, cen- cess, the odontoid process, which
trum; 2, a,neuralarch; £. zyg,

posterior zygapophysis: 7, rib; lies in the lower part of the ring
vr. f, vertebrarterial foramen.
of the atlas.

Between the last cervical vertebra and the pelvic region
come four thoracic vertebrae (Fig. 276), the first three
united into a single mass, the fourth free. They all bear
ribs, each consisting of a vertebral (vr. 7) and a sternal
(sé. 7) portion, and articulating with the vertebra by a double
head. Springing from the posterior edge of the vertebral
rib is an waernade (Fig. 276, wc), resembling that of Hatteria

xu1 PHYLUM CHORDATA 465

and the crocodile, but formed of bone and ankylosed with
the nib.

Following upon the fourth thoracic are about twelve
vertebrz all fused into a single mass (Fig. 276, s. ser), and
giving attachment laterally to the
immense pelvic girdle. The
whole of this group of vertebra
has, therefore, the function of a
sacrum, differing from that of a
reptile in the large number of
vertebree composing it. The

tp u

first of them bears a pair of free
ribs, and is, therefore, the fifth
or last thoracic (#2. v. 5). The
next five or six have no free
ribs, and may be looked upon
as lumbar (Fig. 278, /1—s*).

Fic. 278.—Columba livia. Sac-

Next come two sacral vertebrae rum of a nestling about
. ; fourteen days old), ventral
(c') homologous with those of aspect. cl, centrum of first
eae 2 mee sacral vertebra; c!, centrum of
the lizard. The remaining five fifth caudal: ¢. 7, first sacral
5 : nb; 21, centrum of first lumbar;

vertebre of the pelvic region are 2, of third lumbar; s!. of fourth
lumbar; s*, of sixth lumbar;

caudal. Thus the mass of ver- tr. ~, transverse process of
c , : first lumbar; fr. f', of fifth

tebrze supporting the pelvic girdle lumbar: ¢r. '', of first sacral.

z A z (From Parker’s Zootomy.)
in the pigeon is a compound

sacrum, or syz-sacrum, formed by the fusion of the posterior
thoracic, all the lumbar and sacral, and the anterior caudal
vertebre.

The syn-sacrum i: followed by six free caudals and the
vertebral column ends posteriorly in an upturned, compressed
bone, the prgostle or ploughshare-bone (Fig. 276, pyg. sf),
formed by the fusion of four or more of the hindermost
caudal vertebre.

The sternum (Fig. 276, st) is one of the most character-

2H

466 MANUAL OF ZOOLOGY SECT,

istic parts of the bird’s skeleton. It is a broad plate of bone
produced ventrally, in the sagittal plane, into a deep keel or
carina sterni (car), formed, in the young bird, from a separate
centre of ossification. ‘The posterior border of the sternum
presents two pairs of notches, covered, in the recent state,

Fic. 279. —Columba livia. Skull of young specimen. A, dorsal; B, ventral; C,
left side. a@/. s, alisphenoid; av, angular; a”, articular; 4 0, basi-occipital;
d, dentary; ¢. 0, ex-occipital; ex, aperture of Eustachian tube; 4. m, foramen
magnum; /7-, frontal; 7.0. s, inter-orbital septum; 7, jugal; Zc, lachrymal; J. s,
lambdoidal suture; mz. et, mesethmoid; wx, maxilla; vex. £, maxillo-palatine
process; a, va’, na'', nasal; 0. c, occipital condyle; ov. /, orbital plate of
frontal; fa, parietal; fa. s, parasphenoid (rostrum); //, palatine; f. wx, pre-
maxilla, fz, pterygoid; gz, quadrate; s. av, supra-angular; s. 0, supra-occipital:

sg, squamosal, ¢y, tympanic cavity; I1.—XII, foramina for cerebral nerves.
(From Parker's Zootomy.)

XU PHYLUM CHORDATA 467

by ligament ; its anterior edge bears a pair of deep grooves
for the articulation of the coracoids.

The sku (Fig. 279) is distinguished at once by its
rounded brain-case, immense orbits, and long pointed beak.
The foramen magnum (f/m) looks downwards as well as
backwards, so as to be visible in a ventral view, and on its
anterior margin is a single, small, rounded, occipital condyle
(o.c). Most of the bones, both of the cranial and facial
regions, are firmly ankylosed in the adult, and can be made
out only in the young bird.

The premaxille (Fig. 279, p. mx) are united into a large
triradiate bone which forms
practically the whole of the
upper beak. The maxille
(Fig. 279, mx), on the other
hand, are small, and have
their anterior ends produced
inwards into spongy maxi//o-
palatine processes (Fig. 279,
mx.p). The slender poste-
rior end of the maxilla is
continued backwards by an
equally slender jugal (jz)
and quadrato - jugal to the
quadrate. The latter (Fig.
279, gi) is a stout three-

rayed bone articulating by Fi. 280.— Columbia livia. Hyoid ap-
. c paratus. The cart:laginous parts are

two facets with the roof dotted. 3 7.1, basi-branchials: 4 hy,
- : basi-hyal: c. 67, cerato - branchial;

of the tympanic cavity, and <. Ay, Kyoid commu; ef. 87, epi-

: a branchial.

presenting below a condyle

for articulation with the mandible: the mandible of the

young bird consists of a cartilage bone, the articular (Fig.

279, ar), and four membrane bones, which all coalesce in the

408 MANUAL OF ZOOLOGY SECT.

adult. The hyvoid apparatis (Fig. 280), is of characteristic
form, having an arrow-shaped body (4. #y) with a short pair
of anterior cornua (c. 4y) derived from the hyoid arch, and
a long pair of posterior cornua (c¢. 47, ef. dv) from the first

Fic. 28: —Columba livia. Skeleton of the left
wing. cf. mtcp, carpo-metacarpus; Aw, hu-
merus; fA/.7, phalanx of first digit; 4.2’,
ph.2'', phalanges of second digit; /A4.3,
phalanx of third digit: f7. for, pneumatic
foramen; 7a, radius; ra’, radiale; #2, ulna;
#é', ulnare.

branchial. The co/u-
mela is a rod-shaped
bone ankylosed to the
stapes, and bearing at
its outer end a three-
rayed cartilage or ex-
tra-columella fixed to
the tympanic mem-
brane.

The shoulder-girdle
(Fig. 276) is quite un-
like that of other Cra-
niates. There is a pair
of stout, pillar - like
coracoids (cor) articu-
lating with deep facets
on the anterior border
of the sternum and
directed upwards, for-
wards, and outwards.
The dorsal end of each
is produced into an
acrocoracoid process
(acr. cor), and below
this, to the posterior
aspect of the bone, is
attached by ligament a
sabre-shaped scapula
(scp) which extends

xi PHYLUM CHORDATA 469

backwards over the ribs, and includes, with the coracoid, an
acute angle, the coraco-scapular angle. The glenoid cavity
(g/. cv) is formed in equal proportion by the two bones ; in-
ternal to it the scapula is produced into an acromuion process.
In front of the coracoids is a slender V-shaped bone, the
Jurcula (fur) or “ merrythought,” the apex of which nearly
reaches the sternum, while each of its extremities is attached
by ligament to the acromion and acro-coracoid processes
of the corresponding side in
such a way that a large aper-
ture, the foramen triosseum
(f. ¢rs) is left between the
three bones of the shoulder-
girdle. The furcula is a mem-
brane bone and _ represents
fused clavicles and __inter-
clavicle.

Equally characteristic is the
skeleton of the fore-limb. The
humerus (Fig. 281, Aw) is a
large, strong bone, with a
greatly expanded head and
a prominent ridge for the in- gy, 282. —Columba livia. Left manus
sertion of the pectoral muscle. 1,2 nestling. |, The cartilaginous

parts are dotted. cf. 1, radiale;

: - cp. 2, ulnare; mcp. 1, 2, 37, meta-
The radius (7a) is slender carpals; fA. 7, phalanx of first digit;

and nearly straight, the wma 4.2, 24-2» phalanges of second
stouter' and ‘pently ‘curved. Feo) | Ue
There are two large free car-

pals, a radiale (ra') and an wlnare (w/'), and articulating
with these is a bone called the carpo-metacarpus (cp. mtcp),
consisting of two rods, that on the preaxial side strong and
nearly straight, that on the postaxial side slender and curved,

fused with one another at both their proximal and distal

470 MANUAL OF ZOOLOGY SECT.

ends; the proximal end is produced pre-axially, into an
outstanding step-like process.

The study of its development shows that this bone is
formed by the union of the distal carpals with three meta-
carpals (Fig. 282), the second and third of which are the
two rod-like portions of the bone, the first, the step-like
projection. Articulating with the first metacarpal is a single
pointed phalanx (fA. 7); the second metacarpal bears two
phalanges, the proximal one ( f/. 2') produced postaxially
into a flange, the distal one (fA. 2") pointed; the third
metacarpal bears a single pointed phalanx (fA. 3).

|e =e
obf pu

Fic. 283. — Columba livia. Left innominate of a nestling. The cartilage is dotted.
ac, acetabulum; a. ¢r, anti-trochanter; 72, pre-acetabular; and 27’, post-acetab-
ular portion of ilium; zs, ischium; 2 s._f, ischiatic foramen; 0d. /, obturator
notch; pz, pubis. (From Parker's Zootomy.)

The pelvic girdle (Fig. 283). The eum (i7) is an
immense bone, attached by fibrous union with the whole
of the syn-sacrum and becoming ankylosed with it in the
adult. As usual it furnishes the dorsal portion of the acetab-
ulum. The ventral portion of the acetabulum is furnished
in about equal proportions by the pubis and ischium
(Fig. 283): it is not completely closed by bone, but is
perforated by an aperture covered by membrane in the
recent state. Both pubis and ischium are directed sharply

XII PHYLUM CHORDATA

471

backwards from their dorsal or acetabular ends, and lie

nearly parallel. Neither is-
chiurm nor pubis unites ven-
trally with its fellow to form
a symphysis.

In the hind-limb the femur
(Fig. 284, fe) is a compara-
tively short bone. Its proxi-
mal extremity bears a promi-
nent ¢rochanter (tr) and a
rounded head (hd). Its dis-
tant end is produced into
pulley-like condyles. Articu-
lating with the femur is a
very long bone, the “dz0-
tarsus (tt. ts) ; its distal end
is pulley-like, not concave
like the corresponding ex-
tremity of the tibia of other
Amniota. The study of its
development shows that the
pulley-like distal end of the
bone (Fig. 285, #/') con-
sists of the proximal tarsals,
—astragalus and calcaneum,
—which at an early period
unite with the tibia and give
rise to the compound shank-
bone of the adult. The fdu/a
(Fig. 284, 7%) is very small,
much shorter than the tibia,
and tapers to a point at its
distal end.

s; ts. mitts,

7, head; wetts. 1,

3
nm
>
5
is
a
a
5
=
°
1S)
+,
oO
a

Fic.

472 MANUAL OF ZOOLOGY SECT.

Following the tibio-tarsus is an elongated bone, the sarso-
metatarsus (ts. mtts), presenting at its proximal end a con-
cave surface for: the tibio-tarsus, and at its distal end three
distinct pulleys for the articulation of the three forwardly
directed toes. In the young bird the proximal end of
this bone is a separate cartilage (Fig. 285, #/*), repre-
senting the distal tarsals, and followed by three distinct
metatarsals, belonging respectively
to the second, third, and fourth
digits. To the inner or preaxial
side of the tarso-metatarsus, near its
distal end, is attached by fibrous
tissue a small irregular bone, the
first metatarsal (m/¢s.z). The back-
wardly directed hallux has two pha-
langes, the second or inner toe
three, the third or middle toe four,
and the fourth or outer toe five. In
all four digits the distal or ungual

Fic. 285.— Columba livia, phalanx is pointed and curved, and

Part of left foot of an un-
hatched embryo (magni. Serves for the support of the horny

fied). he cartilage is 1
dotted. wztl. 2, second; claw.

inuth’ metatarsals eeavie;, A further peculiarity is the fact
Clee oh e dicate; that the larger proportion of the
Sony) oom Parkers bones contain no matrow, but are
filled during life with air, and are
therefore said to be pneumatic. The cavities of the various
bones open externally in the dried skeleton by apertures
called preumatic foramina (Fig. 281, pn. for), by which, in
the entire bird, they communicate with the air-sacs (vide
infra).
As might naturally be expected, the muscles of the fore-
limb are greatly modified. The powerful downstroke of the

XI PHYLUM CHORDATA 473

wing, by which the bird rises into and propels itself through
the air, is performed by the fectoralis (Fig. 286, pct), an
immense muscle having about one-fifth the total weight of
the body; it arises from the whole of the keel of the
sternum (car. sz), from the posterior part of the body of

hu ‘ie prpigm prnb Bret.
corbrbr gle tnsly\tnebr tnsacc|extcp.rd Pp
gb.clU_ is -

See! cor DONE

Fic. 286.— Columba livia. The principal muscles of the left wing; the greater
part of the pectoralis (fect) is removed. car. st, carina sterni; c/, furcula; cor,
coracoid; cor. br. br, coraco-brachialis brevis; cor. br. lg, coraco-brach’alis
longus; cp. st, corpus sterni; e¢x¢. cp. rd, extensor carpi radialis: ext. cp. ul,
extensor carpi ulnaris; 7. cp, w/. flexor carpi ulnaris; g/. c, glenoid cavity: fn,
head of humerus: Az’, its distal end; fct, pectoralis; pct’, its cutedge: pct'’, its
insertion; fxn. 7, pronator brevis: prv. dg, pronator longus; px. pig, pre-
patagium; ft. ptgm, post-patagium; sé. cli, sub-clavius; sé. edz, its tendon of
Insertion passing through the foramen triosseum, and dotted as it goes to the
humerus; ¢vs. acc, tensor accessorius; tvs. dy, tensor brevis; tus. lg, tensor
longus; tvs. mm. f, tensor membranz posterioris ale.

that bone (cf. s#), and from the clavicle (c/), filling nearly
the whole of the wedge-shaped space between the body
and the keel of the sternum, and forming what is commonly
called the “breast” of the bird. Its fibres converge to
their insertion (gc/"') into the ventral aspect of the humerus

474 MANUAL OF ZOOLOGY SECT. XII

(Au, hu'), which it depresses. ‘The elevation of the wing is
performed, not, as might be expected, by a dorsally placed
muscle, but by the swd-clavius (sb. clv), arising from the
anterior part of the body of the sternum, dorsal to the
pectoralis, and sending its tendon (sé. cv) through the
foramen triosseum to be inserted into the dorsal aspect of
the humerus. In virtue of this arrangement, the end of the
foramen acting like a pulley, the direction of action of the
muscle is changed, the backward pull of the tendon raising
the humerus.

Digestive Organs.— The mouth (Fig. 287) is bounded
above and below by the horny beaks, and there is no trace
of teeth. The songue (tng) is large and pointed at the tip.
The pharynx leads into a wide and distensible gud/et (gu),
which soon dilates into an immense reservoir or crop (¢7f)
situated at the base of the neck, between the skin and the
muscles and immediately in front of the sternum. In this
cavity the food, consisting of grain, undergoes a process of
maceration before being passed into the stomach. From
the crop the gullet is continued backwards into the s/omach,
which consists of two parts, the proventriculus (prun) and
the gizzard (giz). The proventriculus appears externally
like a slight dilatation of the gullet, but its mucous mem-
brane is very thick and contains numerous gastric glands
so large as to be visible to the naked eye. The gizzard has
the shape of a biconvex lens; its walls are very thick and
its lumen small. The thickening is due mainly to the im-
mense development of the muscles which radiate from two
tendons, one on each of the convex surfaces. The epi-
thelial lining of the gizzard is very thick and horny, and
of a yellow or green colour: its cavity always contains small
stones, which are swallowed by the bird to aid the gizzard
in grinding up the food.

Fic. 287. Columba livia. Dissection from the right side. The body-wall, with
the vertebral column, sternum, brain, etc., are in sagittal section: portions of the
gullet and crop are cut away and the cloaca is opened; nearly the whole of the
ilium is removed, and the duodenum is displaced outwards. @. ao, aortic arch;
bd. 1, bd. 2, bile-ducts; 6. faér, bursa Fabricii; cé/, cerebellum; c@, right
ceecum; cfdiz2, coprodeum; cr, cere; crb. h, left cerebral hemisphere: cxf,
crop; cr. v. 7, first cervical vertebre; dz. caw, diacaele: dnt, dentary; duo,
duodenum; exs. af, aperture of Eustachian tubes; g7z, gizzard (dotted behind
the liver); g/, glottis; gz/, gullet; 722, ilium; 7. 07d. sf, inter-orbital septum;
kd, right kidney; dvg, right lung; Zr, liver (right lobe); 2a, bristle passed from
nostril into mouth; 042. sef, oblique septum; o. g7, oil gland; fcd, pericardium;
pmx, pre-maxilla; 2, pancreas; fx. 6, pineal body; pyd. 7-3, pancreatic
ducts; fr. cv, right pre-caval; prdm, proctodeum; frzv2, proventriculus
(dotted behind liver); At. cz, post-caval; pty. 4, pituitary body: fyg. st, pygo-
style; ». az, right auricle; ». 67, right bronchus; xct, rectum; 7. wut, right
ventricle; sf. cd, spinal cord; sf/, spleen (dotted behind liver); s. 744, sinus
rhomboidalis; s. scx, syn-sacrum; sf, carina sterni; syv, syrinx; ¢/. v. 7, first,
and ¢h. v. 5, fifth thoracic vertebra: ¢zg, tongue; ¢v, trachea; ¢s, right testis;
ur, aperture of left ureter; #xd, urodaum; v. df, aperture of left vas deferens.

475

476 MANUAL OF ZOOLOGY SECT.

The duodenum (duo) leaves the gizzard quite close to the
entrance of the proventriculus and forms a distinct loop
enclosing the pancreas. The rest of the small intestine is
called the zim (77m) : it passes without change of diameter
into the rectum or large intestine (7c7¢), the junction between
the two being marked only by a pair of small blind pouches
or caca (cw). The cloaca is a large chamber divided into
three compartments.

There are small duccal glands opening into the mouth, but
none that can be called salivary. The “ver (/r) is large, and
is divisible into right and left lobes, each opening by its own
duct (4. d. 7, 6. d@. 2), into the duodenum: there is no gall
bladder. The pancreas (pn) is a compact reddish gland
lying in the loop of the duodenum, into which it discharges
its secretion by three ducts (fz. @. 7-3). A thick-walled
glandular pouch, the dursa Fabrici (6. fabr), lies against
the dorsal wall of the cloaca in young birds, and opens into
the cloaca: it atrophies in the adult.

The spleen (sf/) is an ovoid red body, of unusually small
proportional size, attached by peritoneum to the right side
of the proventriculus. ‘There are paired ¢hyvords at the base
of the neck; and, in young pigeons, there is an elongated
thymus on each side of the neck. The adrena/s (Fig. 292,
adr) are irregular yellow bodies placed at the anterior ends
of the kidneys.

The glottis (Fig. 287, g/7) is situated just behind the root
of the tongue and leads into the Zaryx, which is supported
by cartilages, but does not, as in other vertebrates, function
as the organ of voice. From the larynx an elongated tube,
the frachea or windpipe, the wall of which is supported by
numerous bony rings, runs back along the ventral aspect of
the neck to enter the body-cavity, where it divides into the
right (7. dr) and left d7onchz, one passing to each of the lungs.

XII PHYLUM CHORDATA 477

At the junction of the trachea with the bronchi is found
the characteristic vocal organ, the sy77wx (sy), occurring in
no other class.

The /ungs (Fig. 287, wg) are very small in comparison
with the size of the bird, and are but slightly distensible,
being solid, spongy organs, not mere bags with sacculated
walls, as in Amphibia and many reptiles. Their dorsal sur-
faces fit closely into the spaces between the ribs and have
no peritoneal covering ; their ventral faces are covered by a
strong sheet of fibrous tissue, the pulmonary aponeurosis or
pleura, a special development of the peritoneum. Into this
membrane are inserted small, fan-like costo-pulmonary mus-
cles, which arise from the junction of the vertebral and sternal
ribs.
Each main bronchus gives off secondary bronchi, and
these branch again, sending off tubes which end blindly near
the surface of the lung and give off blind dilations commonly
known as alveo#i. In addition to these, each main bronchus
also gives off branches which end in a series of thin-walled
air-sacs, which lie in the body-cavity, and are in communi-
cation with the pneumatic cavities of the bones.

The heart (Fig. 288) is of great proportional size, and like
that of the crocodile consists of four chambers, ¢.e., the right
and left auricles, and right and left ventricles. There is no
sinus venosus, that chamber being, as it were, absorbed into
the right auricle (Fig. 288, A, x. aw). The right ventricle
(Fig. 288, B) partly encircles the left, the former having a
crescentic, the latter a circular cavity in transverse sections.
The left auriculo-ventricular valve has the usual membranous
structure consisting of two flaps connected with the wall of
the ventricle by tendons, but the corresponding valve of the
right side (R. V) is a large muscular fold, very characteristic
of the class.

478 MANUAL OF ZOOLOGY SECT.

The right auricle receives the right and left pre-cavals
(7. pre, 4. pre) and the post-caval (fc), the left, four large
pulmonary veins (J. 7). The left ventricle (Fig. 288, Zvi),
as in the crocodile, gives origin to the right aortic arch
(a. ao), but the right ventricle (7. 77) gives off only one
trunk, the pulmonary artery, which soon divides into two

Fic. 288.— A, heart of the pigeon, dorsal aspect. a. ao, arch of aorta; dr. a,
brachial artery: br. v, brachial vein; ¢c.c, common carotid: 7#, jugular; 7. av,
left auricle; 7. f. a, left pulmonary artery; 2 77, left ventricle; pe. v, left pre-

caval; pic, post- caval; p.v, pulmonary veins; ~. az. 7. az", right auricle; ~ ~. a,
right pulmonary artery; 7. prc, right pre-caval; ». v7, right ventricle. B, heart
of a bird with the right ventric ‘opened L. V, septum ventriculorum; R. V,
right ventricle; V, right auriculo-ventricular valve. (A, from Parker’s Zootomy;
B, from Headley’s Brae)

(7. p.a., 2 p.a). The left aortic arch is absent in the adult,
and it is the right alone which is continued into the dorsal
aorta. The result of this is that the systemic arteries re-
ceive pure arterial blood from the left side of the heart, and
the only mingling of aérated and non-aérated blood is in the

XII PHYLUM CHORDATA 479

capillaries. This is perhaps the most important physiologi-
cal advance made by birds over reptiles.

The aortic arch curves over the right bronchus to reach
the dorsal body-wall, and then passes directly backwards as
the dorsal aorta.

Fic. 289.— Columba livia. The brain; A, from above; B, from below; C, from
the left side. cé, cerebellum; c. 4, cerebral hemispheres; /, flocculus; 7/, in-
fundibulum; 22. 0, medulla oblongata; o. 2, optic lobes; 0. 7, optic tracts; fz,
pineal body; II-XIII, cerebral nerves; sf. 7, first spinal nerve. (From Parker’s
Zootomy.)

The drain completely fills the cranial cavity, and is re-
markable for its short, broad, rounded form. The cercbelum

480 MANUAL OF ZOOLOGY SECT.

(Fig. 289, c. 2) is of great size, and has a large median portion
and two small lateral lobes or floccul (/) ; the surface of
the middle lobe is marked by grooves passing inwards in a
radiating manner and carrying with them the grey matter,
the extent of which is thus greatly increased. The hemz-
Spheres (¢. h) extend backwards to meet the cerebellum,
and the eptic lobes (0. 7) are thereby pressed outwards so
as to take up a lateral instead of the usual dorsal position.

Fic. 290. —The eye. A, in sagittal section; B, the entire organ, external aspect;
en, cornea; ch, choroid; cl. pr, ciliary processes; 77, iris; 7, lens; opt. nv,
optic nerve; fct, pecten; rt, retina; sc/, sclerotic; sc/. A/, sclerotic plates.
(After Vogt and Yung.)

The eye (Fig. 290) is not even approximately globular,
but has the form of a biconvex lens. Sclerotic plates
are present, and there is a large fecten in the form of a
plaited and strongly pigmented membrane projecting into

xu PHYLUM CHORDATA 481

the cavity of the eye from the entrance of the optic
nerve.

The auditory organ (Fig. 291) is chiefly distinguished
from that of reptiles by the great development of the cochlea.
The tympanic cavity and columella have the same arrange-
ment as in the frog; the narrow Eustachian tubes open by
a common aperture (Fig. 287,
eus. ap) in the roof of the
pharynx.

The &edneys (Fig. 287, Ad, Figs.
292 and 293, &) have a very
characteristic form. Each is a
flattened organ divided into three
main lobes and fitted closely into
the hollows of the pelvis. The
ureters (ur) are narrow tubes
passing directly backwards to
open into the middle compart-
ment, or the cloaca.

The estes (Figs. 287 and 292, Fic. 291.—Columba livia. The

right membranous labyrinth,

zs) are ovoid bodies, varying outer aspect; #4, ampulla of
‘ posterior canal; FB, posterior
greatly in size according to the canal; HA, ampulla of hori-
5 zontal canal; A&A, horizontal
season, attached by the perito- canal; Zag, cochlea or lagena:
mr, membrane of Reissner;
neum to the ventral surfaces of ph, basilar part of cochlea; S,
5 : sacculus; SA, ampulla of
the anterior ends of the kidneys. anterior canal; SZ, anterior
: (canal. From Wiedersheim, af-

From the inner border of each ter Hasse.)

goes off a convoluted was def-

evens (vd), which passes backwards, parallel with the
ureter, to open into the cloaca on the extremity of a
small papilla. The posterior end of the spermiduct is
slightly enlarged to form a vestcula seminalis (v.s). The
female organs (Fig. 293) are remarkable for the more or
less complete atrophy of the right ovary and oviduct.

21

482 MANUAL OF ZOOLOGY SECT.

The ff ovary (ov) is a large organ in the adult bird, its
surface studded with follicles or ovisacs, varying in size
from about 15 mm. in diameter downwards, and each
containing a single ovum. The “ff oviduct (2 of) 1s
long and convoluted ; its anterior end is enlarged to form
a wide, membranous ccelomic funnel (/. ed") into which the

Fic. 292. Columba livia Ma'e [ic. 293. —Columba livia. Female urino-

urino-genital organs. adr, ad- genital organs. c/.2, urodaum; c/. 3,
renal; cé. 2, urodeum; c/. 3, proctodaum; 4%, kidney; 2. od, left ovi-
proctodzum; 4%, kidney; és, duct; 2. od’, its cloacal aperture; 2. od'',
testis, that of the right side dis- its coelomic funnel; 7 od'"', its coelomic
placed; 7, ureter; #7’, aper- aperture; ov, ovary; 7. ed, right oviduct;
ture of ureter; vd, vas deferens; rv. od', its cloacal aperture: a», urete

va’, its cloacal aperture; v7. s, ur’, its cloacal aperture. (From Parker’s
vesicula seminalis. (From Par- Zootomy.)
ker’s Zootomy.)

ripe ova pass on their liberation from the ovisacs; the rest
of the tube has thick, muscular walls, lined with glandular
epithelium, and opens into the urodzum.

Internal impregnation takes place. As the ova or

XII PHYLUM CHORDATA 483

“yolks”? pass down the oviduct, they are invested with the
secretions of its various glands ; first with layers of albumen
or “ white,’’ next with a parchment-like shell-membrane, and
lastly with a white calcareous she//. They are laid, two at a
time, in a rough nest, and are zzcubated or sat upon by the
parents for fourteen days, the temperature being in this way
kept at about 40° C. (104° F.). At the end of incubation
the young bird is sufficiently developed to break the shell
and begin free life. It is covered with fine down, and is fed
by the parents with a secretion from the crop, the so-called
“‘ pigeon’s milk.”

Of recent birds two main divisions are recognised —
the Ratite and the Carinate — the former comprising only
the emus (Dromaus), cassowaries (Caswarius), and kiwis
( Apeeryx), the South American ostriches (AAea), and the true
ostriches (S¢rw¢hio) ; and the latter including all the rest.

One of the most characteristic features of birds in
general is the covering of feathers — peculiar epidermal
structures which differ widely in shape and arrangement
from their equivalents, the horny scales of reptiles and the
hairs of mammals. The arrangement of the feathers
follows closely that briefly described as observable in the
pigeon, with great diversity in detail. The distribution of
the contour feathers in feather tracts or pteryle separated
from one another by featherless tracts or apfferza is almost
universal in the Carinatz, but is not distinguishable in the
Ratitee except in the young condition. In many birds
each feather has a secondary vein or after-shaft, as it is
termed, springing from the main shaft near the umbilicus,
and sometimes (Fig. 294) this may be as large as the main
shaft itself. A shedding or “moulting” of the feathers
takes place at regular intervals, usually annually —a new set
of feathers growing from the pulps of the old ones.

484

oss
eee
Po
S eee
boSscg

so

N
Sy
Ss

MANUAL OF ZOOLOGY SECT.

(From Headley.)

Feather, showing after-shaft and disconnected barbs.

Fic. 294. — Casuarius (Cassowary).

The colours of feathers present great
variety. Black, brown, red, orange,
and yellow colours are due to the pres-
ence of definite pigments, 7.¢. are
absorption colours. White, and in some
cases yellow, is produced by the total
reflection of light from the spongy, air-
containing substance of the feather,
there being, as in nearly all other natu-
ral objects, no such thing as a white
pigment. Blue, violet, and in some
cases green, are produced by the light
from a brown pigment becoming bro-
ken up as it passes through the super-
ficial layer of the feathers in its passage
to the eye; no blue or violet pigments
occur in feathers, and green pigments
are very rare. The beautiful metallic
tints of many birds are entirely the
result of structure, owing their existence
to a thin, transparent, superficial layer,
which acts as a prism: in such feathers
the colour changes according to the
relative position of the bird and of the
eye of the observer with regard to
the source of light.

There is also infinite variety in the
general coloration of birds. In many
the colouring is distinctly protective,
harmonising with the environment, and
even changing with the latter, as in the
ptarmigan, which is greyish brown in
summer, white in winter, the former

XII PHYLUM CHORDATA 485

hue helping to conceal the bird among herbage, the latter on
snow. Frequently, as in pheasants and birds of paradise, the
female alone is protectively coloured, while the male presents
the most varied and brilliant tints enhanced by crests, plumes
or tufts of feathers on the wings, elongated tail, etc. etc.
These have been variously explained as “ courtship colours”’
for attracting the female; as due simply to the exuberant
vitality of the male bird, or as helping to keep the number of
males within proper limits by rendering them conspicuous to
their enemies. Such ornaments as the bars and spots on
the wings and tail of many gregarious birds, such as plovers,
fully exposed only during flight, and often widely different
in closely allied species, have been explained as “ recog-
nition marks,’”’ serving to enable stragglers to distinguish
between a flock of their own and of some other species.
The toothless jaws with the horny sheaths forming the
bill are universal in the class. But the dimensions and
form of the bill vary very widely in different groups of birds.
It may be extremely short and wide for catching moths and
other flying insects, as in swifts and goatsuckers ; short and
conical for eating fruit, as in finches; strongly hooked for
tearing the bodies of animals, as in birds of prey, or for
rending fruits of various kinds, as in parrots ; long, conical,
and of great strength, as in storks; slender and elongated,
as in swifts, ibises, and curlews; broad and flattened for
feeding in mud, as in ducks and geese; expanded at the
end, as in spoonbills; immensely enlarged, as in hornbills
and toucans. It is most commonly bent downwards at the
tip, but may be straight or curved upwards, as in the avocet,
or bent to one side, as in the New Zealand crook-billed
plover. It is sometimes, as in the toucans, brilliantly
coloured, and there may also be bright coloration of the
cere, as in the macaws, and of naked spaces on the head,

486 MANUAL OF ZOOLOGY SECT.

as in the cassowaries. In the latter the head is produced
into a great horny prominence or “ casque,” supported by
an elevation of the roof of the skull. The cere is frequently
absent. The nostrils are placed at the base of the beak,
except in Apteryx, in which they are at the tip.

The essential structure of the wing — apart from its feathers
—is very uniform. Asa rule all three digits are devoid of
claws, as in the pigeon, but the ostrich has claws on all

at , onplgm

SS ee
“sg >

\ J
Bats
‘a
ao

Fic. 295. —A, wing of nestling of Op7sthocomus ; B, wing of adult Apteryx ; both
from the inner (ventral) aspect; cd. z, first cubital remex; dg. 7, dg. 2, dg. 3,

digits; pr. pgm, pre-patagium; Pz. fem, post-patagium. (A, after Pycraft;
B, after T. J. Parker.) : 3 ,

three digits; rhea on the first, and sometimes the second
and third; the cassowary, emu, and kiwi (Fig. 295, B)
on the second; and the crested screamer (Chauna) and
‘two other species, and, as a rare abnormality, the common
fowl and the goose, on the first. With these exceptions, the

Xu PHYLUM CHORDATA 487

hand of the adult bird has lost all the characters of a fore-
foot ; but in the young of the hoatzin ( Opisthocomus) claws
are present on the first two digits (Fig. 295, A), which are
sufficiently mobile to be used in climbing. Besides the
true claws, horny spurs are sometimes present on the carpus
and metacarpus.

There is almost every gradation in the proportional
length of the hind-limb, from birds in which nothing but
the foot projects beyond the contour feathers, and even the
toes may be feathered, to the long-legged storks and cranes,
in which the distal part of the tibio-tarsus is covered with
scales as well as the foot. In aquatic forms a fold of skin
or web is stretched between the toes, sometimes including
all four digits, as in the cormorants ; sometimes leaving the
hallux free, sometimes forming a separate fringe to each
digit, as in the coots and grebes. As to the toes them-
selves, the commonest arrangement is for the hallux to be
directed backwards, and Nos. 2, 3, and 4 forwards, but in
the owls No. 4 is reversible, 7.e. can be turned in either
direction, and in the parrots, woodpeckers, etc., it, as well
as the hallux, is permanently turned backwards. In the
swifts, on the other hand, all four toes turn forwards. The
hallux is frequently vestigial or absent, and in the ostrich
No. 4 has also atrophied, producing the characteristic two-
toed foot of that bird.

The following are the most essential general features of the
skeleton of birds. More or fewer vertebrz from the regions
in front of and behind the sacral fuse with the true sacral
vertebrz to form the composite syn-sacrum. The posterior
caudal vertebrze are fused together to form a fpygostle.
The bones of the skull early unite, the sutures becoming
entirely obliterated. There is a single rounded occipital
condyle. The premaxille are very large and form the

488 MANUAL OF ZOOLOGY SECT.

greater part of the upper jaw. The sternum is broad, and
is usually provided with a prominent keel or carina as in
the pigeon, but the carina is absent in the Ratite, and
is rudimentary or absent in some flightless Carinate. The
clavicles and interclavicle unite to form a furcula. The
distal carpals and metacarpals unite to form a carpo-
metacarpus. The pubes and ischia run downwards and
backwards parallel with one another; and neither the pubes
nor the ischia unite in a symphysis, but remain widely
separated at their distal ends, except in the ostrich, in
which the pubes unite distally, and the South American
ostriches in which the ischia unite while the pubes remain
free. Universally characteristic of the skeleton of the hind-
limb is the union of the tibia with the proximal element of
the tarsus to form a tibio-tarsus, and of the distal element of
the tarsus with the second, third, and fourth metatarsals to
form a tarso-metatarsus, the ankle-joint being situated
between these bones. The skeleton always contains air-
cavities to a greater or less extent.

The presence of crop, proventriculus, and gizzard, as in
the pigeon, is universal among birds. The gizzard is most
powerful in grain-eating birds, thinner-walled in flesh-eaters.
There is a pair of cceca in most birds at the junction of the
large and small intestines. The voice of birds is always
produced not in the larynx, as in other higher vertebrates,
but in a syrinx situated either, as in the pigeon, at the
junction of the trachea and bronchi, or at the anterior ends
of the bronchi, or the posterior end of the trachea. The
system of air-sacs connected with the bronchi described in
the account of the pigeon is of universal occurrence.

The temperature of the blood is always high. The heart
in all has the same main features as in the pigeon: it has
four distinct chambers, two auricles and two ventricles, and

XU PHYLUM CHORDATA 489

there is a single aortic arch, situated on the right side. In the
brain the most characteristic points are che short rounded
hemispheres, the large folded cerebellum produced forwards
to meet the hemispheres, and the laterally placed optic
lobes. The internal ear has a large curved cochlea, and
the eye has a pecten. The right ovary and oviduct are
more or less completely aborted.

Fic. 296. —Gallus bankiva (domestic fowl). Semi-diagrammatic view of the egg
at the time of hatching. a, air-space; a/6, dense layer of albumen; a/4', more
fluid albumen; 4/, blastoderm; ch, chalaza; sh, shell; sk. mz, shell-membrane;
sh. 1, sh. 2, its two layers separated to enclose air-cavity. (From Marshall’s
Embryology, slightly altered.)

The ovum is always large, owing to the great quantity of
food-yolk ; the protoplasm forms a small germna/ disc at one
pole. Impregnation is internal, and as the incipient egg or
oosperm passes down the oviduct, it is coated by successive
secretions from the oviducal glands. It first receives a coat
of thick, viscid a/dumen (Fig. 296, a), which, as the egg

490 MANUAL OF ZOOLOGY SECT.

rotates during its passage, becomes coiled at either end into
a twisted cord, the cha/asa (ch). Next, more fluid albumen
(alb') is deposited layer by layer, then a tough, parchment-
like shel-membrane (sh. m) and finally a calcareous shed/
(sh). The shell-membrane is double, and at the broad end
of the egg the two layers are separate and enclose an air-
cavity (2). The shell may be white or variously coloured
by special pigments: it consists of three layers, and is
traversed by vertical pore-canals, which are unbranched in
the Carinate and in Apteryx, branched in the other Ratite.
The eggs may be laid on the bare ground or on the rocks
by the seashore, as in penguins and auks, or on the ledges
on inaccessible cliffs as in the sooty albatross (Diomedea
Juliginosa) ; but as a rule a nes¢ is constructed for their
reception by the parent birds. This may be simply a hole
in the sand, as in the ostrich ; a mere clearing on the hill-
side surrounded by a low wall of earth, as in the wandering
albatross (Diomedea exulans) ; or a cylinder with excavated
top, built of grass, earth, and manure, as in the mollymawks
(Diomedea melanophrys, etc.). It may take the form of a
burrow, as in many petrels, kingfishers, and sand-martins, or
it may be more or less elaborately built or woven of sticks,
moss, leaves, hair, or feathers, showing every stage of con-
structive skill from the rude contrivance of sticks of the
pigeon and eagle, to the accurately constructed cup- or
dome-shaped nests of many familiar Passeres. In the tailor-
bird (Orthotomus) it is formed of leaves sewn together, the
beak acting as needle: in a Malayan swift (Codlocalia) it is
largely built of the secretion of the bird’s buccal glands.
After the egg is laid, the process of development is ar-
rested unless the temperature is kept up to about 40° C.
(104° F.) : this is usually done by the heat of the body
of the parent birds, one or both of which sit upon, or ¢xcu-

XII PHYLUM CHORDATA 401

bate, the eggs until the young are hatched, but in the Aus-
tralian mound-makers (J/egapodius) the eggs are buried in
heaps of decaying vegetable matter, the decomposition of
which generates the necessary heat.

ore CLASS VI. MAMMALIA

The class Mammalia, the highest of the Vertebrata, com-
prises the Monotremes and Marsupials, the hoofed and
clawed quadrupeds, the whales and porpoises and sea-cows,
the rodents, bats, and insectivores, the lemurs and apes, and
the human species. All mammals, though many are aquatic,
are air-breathers throughout life, lungs being, as in reptiles
and birds, the sole organs of respiration. The blood of
mammals has a high temperature, resembling in that re-
spect the blood of birds, and differing from that of reptiles
and amphibia. The scales of reptiles and the feathers of
birds are replaced in mammals by peculiar epidermal struc-
tures, the hairs, usually developed in such quantities as to
form a thick soft covering or fur.

The rabbit (Zepus cuniculus) will serve as a convenient
example of the class.!

The rabbit (Fig. 297) is a four-footed or quadrupedal ani-
mal, having the whole surface of its body covered with soft
fur. The head bears below its anterior extremity the mouth
in the form of a transverse slit bounded by soft lips. The
upper lip is divided by a longitudinal cleft, running back-
wards to the nostrils and exposing the chisel-shaped zxc7sor
teeth. Behind the incisor teeth the hairy integument pro-
jects on each side into the cavity of the mouth. At the end
of the snout, above the mouth, are the nostrils in the shape

1 The following account will apply in all but very slight details to our
cotton-tail rabbit or to our American hare.

492 MANUAL OF ZOOLOGY SECT.

of two oblique slits. The large eyes, situated at the sides
of the head, have each three eyelids, an upper and a lower
hairy lid, and an anterior hairless third eyelid or nictttatng
membrane, supported by a plate of cartilage. Vibrisse —
very long stiff hairs—are scattered above and below the eyes
and on the snout. Behind the eyes and a little nearer the
summit of the head, are a pair of very long flexible and
movable external ears or pinn@. These are somewhat
spout-shaped, expanding distally and are usually placed
vertically with the concavity directed laterally and some-

Fic. 297. —Lepus cuniculus. Lateral view of skeleton with outline of body.

what forwards, leading to the external auditory opening.
The weck is a distinct constriction, but relatively short as
compared with the neck of the pigeon. The wn is distin-
guishable into zhorax in front and aédomen behind. On
the ventral surface of the abdomen in the female are four or
five pairs of little papillae —the as.

At its posterior end, below the root of the tail, is the aza/
opening, and in front of this in the male is the penzs, with a
small terminal wrinogenital aperture and with the ¢eszes, each
in a prominent s¢vota/ sac, at the sides : and in the female

XII PHYLUM CHORDATA 493

the opening of the vw/va. The tail is very short and covered
with a tuft of fluffy hair.

The fore- and hind-imbs, both of which take part in loco-
motion and in supporting the weight of the animal, differ
considerably in size —the fore-limbs being much shorter
than the hind-limbs. Both have the same general divisions
as in the lizard. The upper arm is almost completely
hidden by the skin, being applied closely against the side of
the body. The manus is provided with five digits, each
terminating ina horny claw. ‘The thigh is also almost hidden
by the skin; the ses has four digits only, all provided with
claws.

The spinal column of the rabbit is divisible, like that of
the pigeon, into five regions — the cervical, the thoracic, the
‘lumbar, the sacral, and the caudal. In the cervica/ region
there are seven vertebree ; in the “horacic twelve or some-
times thirteen, in the /zmdar seven, or sometimes six, in the
sacral four, and in the cazda/ about fifteen.

The centra of the vertebree in a young rabbit consists of
three parts —a middle part, which is the thickest, and two
thin discs of bone — the efzphyses — anterior and posterior,
applied respectively to the anterior and posterior faces of
the middle part or centrum proper. Between successive
centra in an unmacerated skeleton and thin disc-like plates
of fibro-cartilage — are the ¢nter-vertebral discs.

The first vertebra or a//as (Fig. 298, B) resembles the cor-
responding vertebra of the pigeon in being of the shape of
a ring without any solid centrum like that of the rest. On
the anterior face of its lateral portions are two concave arti-
cular surfaces (a7v/) for the two condyles of the skull. The
second vertebra or ax7s (Band C) bears on the anterior face
of its centrum a peg-like process — the odontoid process (od)
—which fits into the ventral part of the ring of the atlas.

404 MANUAL OF ZOOLOGY SECT.

The thoracic vertebre all have elongated spines. The
transverse processes are short and stout; each bears near
its extremity a small, smooth articular surface or évbercular
Jacet for the tubercle of arib. On the anterior and posterior
borders of each vertebra is a little semi-lunar facet, the
capitular face?, situated at the junction of the centrum and
the neural arch. The two contiguous semi-lunar facets of
successive vertebra form between them a cup-like concavity

into which the head or capitu/um of a rib is received.

Fic. 298. — Lepus cuniculus. A, atlas and axis, ventral aspect. od, odontoid pro-
cess of axis. B, lateral view of axis. av, articular facet for occipital condyle:
od, odontoid process; 7. 51, post-zygapophysis; sf, neural spine. C, thoracic
vertebra, lateral vi cent, centrum; fac, facet for rib; ct, metapophysis;
pr. 2y, prezygapophysis; ft. zy, post-zygapophysis; 74, rib; sf, spinous process.

In the lumbar region the spines are comparatively short,
and both transverse processes and bodies ‘are devoid of
facets.

The sacral vertebrae are firmly ankylosed together to
form a single composite bone, the sacrwm. The first and
second bear great expanded Jateral plates — sacral ribs —
with roughened external surfaces for articulation with the
ilia.

Of the caudal vertebrae the more anterior resemble those
of the sacral region and have similar processes ; but as we
pass backwards in the caudal region all the processes gradu-

XII PHYLUM CHORDATA 495

ally diminish in size, the most posterior vertebra being
represented merely by nearly cylindrical centra.

There are twelve pairs of 770s, of which the first seven are
true ribs, z.e. are connected by their cartilaginous sternal
ribs with the sternum; while the remaining five, the so-
called false or floating ribs, are not directly connected with
the sternum. All, except the last four, bear two articular
facets, one on the vertebral extremity or capzulum, and the
other on a little elevation or /wdercée situated at a little dis-
tance from this, the former for the bodies, the latter for the
transverse processes of the vertebre.

The sternum (Fig. 300) consists of six segments or s/erne-
bre. The first or manubrium sterni or presternum is larger
than the rest, and has a ventral keel. With the last is con-
nected a rounded cartilaginous plate, the xiphisternum.

The skudl (Fig. 299), if we leave the jaws out of account,
is not at all unlike that of the pigeon in general shape.
The length is great as compared with either the breadth or
the depth; the maxillary region, or region of the snout
(corresponding to the beak of the pigeon), is long in pro-
portion to the rest, the orbits closely approximated, being
separated only bya thin inter-orbital partition, and the optic
foramina united into one. But certain important differences
are to be recognised at once. One of these is in the mode
of union of the constituent bones. In the pigeon, as we
have seen, long before maturity is attained, the bony ele-
ments of the skull, originally distinct, become completely
fused together so that their limits are no longer distinguish-
able. In the rabbit, on the other hand, such fusion between
elements only takes place in one or two instances, the great
majority of the bones remaining distinct throughout life.
The lines along which the edges of contiguous bones are
united— the swéwres as they are termed —are sometimes

496 MANUAL OF ZOOLOGY SECT, XIT

straight, sometimes wavy, sometimes zig-zagged, serrations
of the edges of the two bones interlocking ; in some cases
the edges of the bones are bevelled off, and the bevelled
edges overlap, forming what is termed a sgvamous suture.

Another conspicuous difference between the skull of the
rabbit and that of the pigeon is in the mode of connection
of the lower jaw, which in the former articulates directly with
the skull, the quadrate, through which the union is effected
in the pigeon, being apparently absent. Certain large
apertures which are distinguishable are readily identified with
the large openings in the skull of the pigeon. In the pos-
terior wall of the skull is a large rounded opening, the
foramen magnum, flanked with a pair of smooth rounded
elevations or condyles for articulation with the first vertebra,
these obviously corresponding to the single condyle situated
in the middle below the foramen in the pigeon. A large
opening situated at the end of the snout and looking forwards
obviously takes the place of the evterna/nares of the pigeon ;
and a large opening in the roof of the mouth leading forward
to the external nasal opening, plainly represents, though
much wider and situated further back, the /zéernadl or poste-
rior nares of the pigeon ; while the rounded tubular opening
situated at the side of the posterior part of the skull, some
distance behind the orbit, is evidently the same as the
auditory aperture of the pigeon.

Surrounding the large opening of the foramen magnum
are the bones of the occ/pifa/ region of the skull, the swpra-ex-
and dasi-occipitals. The first of these (s. 0¢ ) is a large plate
of bone above the foramen magnum. The ex-occipitals lie
at the sides of the opening and each bears the greater part
of the somewhat oval prominence or condyle with which the
corresponding surface of the atlas or first vertebra articulates.
The dast-occipifalis a median plate of bone, almost horizontal

B, ventral view. ang. proc, angular
; 6. oc, basi-occipital ;
ler,

0. sph, orbito-sphenoid; fa,

I.0C

Fic. 299. — Lepus cuniculus. Skull: A, lateral view:
as, ali- sphenoid (external pterygoid process)
zut. pa, inter-parietal; 7, jugal;

process of mandible;
cond, condyle; /, frontal;
opt. fo, optic foramen;

6. sph, basi-sphenoid ;
lacrymal; max, maxilla; xas, nasal;
parietal; fad, palatine: pal. max, palatine plate of Seale far. oc, par-occipital pro-
cess; pal. ~p. max, palatine process of pre-maxilla; f. wax, pre- maxilla: per, periotic;
pt, pterygoid; . ¢. sg, post-tympanic process of squz amosal: s. oc, supra-occipital; sg,
ty. ud, tympanic bulla; vo, vomer; zyg. max, zygomatic process of maxilla.

squamosal ;
2K 497

498 MANUAL OF ZOOLOGY sect.

in position, which forms the floor of the most posterior part
of the cranial cavity ; it bears the lower third of the occipital
condyles. Articulating in front with the basi-occipital is a
plate of bone, also horizontal in position, which forms the
middle part of the floor of the cranial cavity. This is the
basi-sphenoid; on its upper surface is a depression, the se//a
turcica or pituitary fossa, in which the pituitary body rests.
In front of it is another median bone of laterally compressed
form, the pre-sphenotd. Connected laterally with the basi-
sphenoid and pre-sphenoid are two pairs of thin irregular
plates, the a/-sphenotd (as) behind and the ordrto-sphenoid
(0. sph) in front. The ali-sphenoids are broad wing-like
bones, each produced below into a bilaminate process, the
plerygoid process.

The boundary of the anterior part of the brain case is
completed by a narrow plate of bone, the criériform plate
of the e/amord, perforated by numerous small foramina for
the passage of the olfactory nerves. This cribriform plate
forms a part of a median vertical bone, the mesethmozd, the
remainder of which, or /amina perpendicularts, forms the bony
part of the partition (completed by cartilage in the unma-
cerated skull) between the nasal cavities. Fused with the
mesethmoid are two lateral, thin-twisted bones, the e/imo-
turbinads, and with its inferior edge articulates a long median
bone with a pair of delicate lateral wings, the vomer. Roof-
ing over the part of the cranial cavity, the walls and floors of
which are formed by the sphenoid elements, is a pair of
membrane bones, the farzefals (pa), and further forward
another pair, the frontals (fr). Between the supra-occipital
and the parietals is a median ossification, the zv/er-parietal
(int. pa). Below the parietal and frontal is a broad bone (sg),
the superior margin of which is bevelled off. This is the
squamosal. It gives off in front a strong zygomatic process,

xII PHYLUM CHORDATA 499

which curves outwards, then downwards, and finally forwards,
to unite with the jvga/ in the formation of the svgomatic arch.
Below the root of the process is a hollow, the g/enoid fossa.

Between the occipital and parietal bones, below and
behind the squamosal, are the Zympanic and periofic bones.
The tympanic forms the bony part of the wall of the
external auditory meatus; below it is dilated to form a
process (zy. du/) projecting on the under surface of the
skull, the dua tympani. The periotic (f. of) is a bone
of irregular shape enclosing the parts of the membranous
labyrinth of the internal ear; externally it presents two
small openings, the fenestra ovalis and fenestra rotunda,
visible only when the tympanic is removed. The periotic
and tympanic are ankylosed together, but are loosely con-
nected with the surrounding bones.

Roofing over the olfactory cavities are two flat bones,
the zasals (nas). In front of the nasals are the pre-maxille
—large bones which form the anterior part of the snout,
bear the upper incisor teeth, and give off three processes.
The maxille (max), which form the greater part of the
upper jaw and bear the premolar and molar teeth, are
large, irregularly shaped bones, the upper surfaces of which
are spongy. They give off internally horizontal processes,
the palatine processes, which unite to form the anterior part
of the bony palate. A strong process which is given off
from the outer face of each maxilla and turns outwards and
then backwards to unite with the zygomatic process of the
squamosal and thus complete the zygomatic arch, is a
separate bone in the young, the malar or jugal (ju).

The rest of the narrow bony palate, forming the roof of
the mouth and the floor of the nasal cavities, is formed by
the palatine plates of the palatine bones. The ptervgords
are small irregular bones, each of which articulates with

500 MANUAL OF ZOOLOGY SECT.

the palatine in front and the ali-Sphenoid behind. The
lachrymals are small bones, one situated in the anterior
wall of each orbit, perforated by a small aperture — the
lachrymal foramen.

The mandible, or lower jaw, consists of two lateral halves
or rami, which articulate with one another in front by a
rough articular surface or symphysis, while behind they
diverge like the limbs of a letter V. In each ramus is a
horizontal portion (anterior), which bears the teeth, and a
vertical or ascending portion, which bears the articular
surface or condyle for articulation with the glenoid cavity
of the squamosal ; in front of the condyle is the compressed
coronoid process. The angle where the horizontal and as-
cending processes meet gives off an inward projection or
angular process.

The Ayord, which, as in the pigeon, is the only other
post-oral visceral arch represented in the adult, consists of
a stout thick body or éasz-hya/, a pair of small anterior
cornua or cerato-hyals, and a pair of long backwardly directed
cornua or “hyvo-hyals.

The auditory ossicles, contained in the cavity of the middle
ear, and cut off from the exterior, in the unmacerated skull,
by the tympanic membrane, are extremely small bones,
which form a chain extending, like the columella auris of
the pigeon, from the tympanic membrane externally to the
fenestra ovalis internally.

The elements of the fecforal arch (Fig. 300) are fewer
than in the pigeon. ‘There is a broad thin triangular scapu-
lar, the base or vertebral edge of which has a thin strip of
cartilage (the supra-scapular cartilage) continuous with it.
Along the outer surface runs a ridge, the sf7ne, the spine
ends below in a long process, the acremion process (a),
from which a branch process or mefacromion (ma) is given

XII PHYLUM CHORDATA 501

off behind. At the narrow lower end of the scapula is a
concave surface, the glenoid cavity, into which the head
of the humerus fits, and immediately in front of this is a
small inwardly curved process, the coracoid process (c),
which is represented by two separate ossifications in the
young rabbit. A slender rod, the clavicle (cl), is con-
nected with the acromion process externally and with the
sternum internally by means of fibrous tissue.

At the proximal end
of the humerus are to
be recognised: (1) A
rounded head for ar-
ticulation with the
glenoid cavity of the
scapula ; (2) externally
a greater; and (3) in-
ternally a lesser tuber-
osity for the insertion
of muscles. At the
distal end are two ar-

Fic. 300.— Lepus cuniculus. Shoulder-girdle

ticular surfaces, one with anterior end of sternum of young speci-
Z men. a, acromion; af, pre-scapular fossa;

large and pulley-like, c, coracoid; c/, ossified clavicle; a, meta-
cromion; mss, meso-scapular segment; ost,

trochlea, for the ulna; pre-sternum; fc, pre-coracoid; f/f, post-scapu-

lar fossa; sx, sternal ribs. (After Flower.)

the other smaller, cafv-
tellum, for the radius: laterally are two prominences or
condyles, an internal and an external.

The radius and ulna are firmly fixed together so as to be
incapable of movement, but not actually ankylosed. The
radius articulates proximally with the humerus, distally with
the scaphoid and lunar bones of the carpus. The ulna pre-
sents on the anterior aspect of its proximal end a deep fossa,
the greater sigmoid cavity, for the trochlea of the humerus ;
the prominent process on the proximal side of this is the

502 MANUAL OF ZOOLOGY SECT.

olecranon process. Distally it articulates with the cunei-
form.

The carpal bones (Fig. 301), nine in number, are all
small bones of irregular shape. Eight of these are arranged
in two rows, a proximal and a distal; the ninth, cez¢rale
(cent), lies between the two rows. ‘The bones of the proxi-
mal row are —taken in
order from the inner to the
outer side — scaphoid (sc),
lunar (orsemi-lunar) (lun),
cuneiform (cun), and pisi-
form. Those of the dis-
tal row are reckoned in
the same order, ¢rapeztum
(47pm), trapezoid (trp),
magnum (mag), and wnei-
form (unc).

Fic. 301.—Lepus cuniculus. Distal end ‘The five metacarpals ale
of fore-arm and carpus, dorsal view, the a]] small but relatively nar-

bones bent towards the dorsal side so as

to be partly separated: cew?, centrale; row and elongated bones
cun, cuneiform; Zu, lunar; mag, mag- aes A
num; vad, radius; sc, scaphoid; ¢-/z, the first being smaller than
trapezoid; Zp, trapezium; w/z, ulna;

unc, unciform; /-I’, bases of metacar- the rest. Each of the five
pals. (After Krause.)

digits has three phalanges,
except the first which has only two. The distal (ungual)
phalanges are grooved dorsally for the attachment of the
horny claw.

The pelvic arch (Fig. 302) contains the same elements
as in the pigeon, but the union of the ilium with the sacrum
is less intimate, the acetabulum is not perforated, and the
pubes of opposite sides unite ventrally in a symphysis (sv).
The ilium and ischium meet in the acetabulum or articular
cavity, which they contribute to form for the head of the
femur, but the remainder of the cavity is bounded, not by

XII PHYLUM CHORDATA 503

the pubis, but by a small intercalated ossification, the
cotloid bone. The tum (i/) has a rough surface for
articulation with the sacrum. Between the pwdis (pub) in
front and the ¢schzwm (isch) behind is a large aperture, the
obturator foramen (obt). The femur has at its proximal
end a prominent ead for articulation with the acetabulum,
external to this a prominent process, the great trochanter,
and internally a much smaller, the lesser trochanter, while
a small process or “hird
trochanter is situated on
the outer border a little
below the great trochan-
ter. At its distal end
are two prominences or
condyles, with a depres-
sion between them. Op-
posite the knee-joint, or
articulation between the
femur and the tibia, is a
small bone or knee-cap,
the patella. The tibia
has at its proximal end
two articular surfaces for
the condyles of the fe-
mur ; distally it has also

Fic. 302.—Lepus cuniculus. Innominate

two articular surfaces, bones and sacrum, ventral aspect. acet,
% acetabulum; 2/, ilium; zsch, ischium ; obt,
one, internal, for the obturator foramen; fxd, pubis; sacr,

sacrum; sy, symphysis.

astragalus, the other for
the calcaneum. The fibula is a slender bone which becomes
completely fused distally with the tibia.

The tarsus consists of six bones of irregular shape
arranged in two rows, one of the bones, the wazeular
(Fig. 303, zazv), being intercalated between the two rows.

504 MANUAL OF ZOOLOGY SECT.

In the proximal row are two bones, the as¢ragalus (asf) and
the calaneum (cal), both articulating with the tibia; the
calcaneum presents behind a long calcaneal process. The
distal row contains three bones, the mesocuneiform, ectocunet-
form, and cuboid (cub) ; the enzo-
cunetform, which commonly forms
the most internal member of this
row in other mammals, is not pres-
ent as a separate bone.

There are four metatarsals, the
hallux or first digit being absent.
Each of the digits has three pha-
langes, which are similar in character
to those of the manus.

The ccelom of the rabbit differs
from that of the pigeon in being
divided into two parts by a trans-
verse muscular partition, the da-
phragm. The anterior part, or
thorax, contains the heart and the
roots of the great vessels, the lungs
and bronchi, and the posterior part
of the cesophagus. ‘The posterior
part or addomen contains the stom-

eee ach and intestine, the liver and
ie epee ey the spleen, the kidneys,

Skeleton of pes; asé,astrag- ureters and urinary bladder, and the

alus; cad, calcaneum; cvé :

cuboid; cw, cuneiforms; Organs of reproduction.

ne eae The teeth (Fig. 299) are lodged
in sockets or a/veoi in the pre-maxille, the maxille,
and the mandible. In the pre-maxille are situated four
teeth, the four upper incisors. Of these the two anterior
are very long, curved, chisel-shaped teeth, which are

xu PHYLUM CHORDATA 595

devoid of roots, growing throughout life from persistent
pulps. Enamel is present as a thick layer on the ante-
rior convex surface only, which accounts for the bevelled-
off character of the distal end, the layer of enamel being
much harder than the rest, which therefore wears more
quickly away at the cutting extremity of the tooth. The
second pair of incisors of the upper jaw are small teeth which
are lodged just behind the larger pair. In the lower jaw are
two incisors, which correspond in shape with the anterior
pair of the upper jaw. The remaining teeth of the upper
jaw are lodged in the maxilla. Canines, present in most
mammals as a single tooth on each side, are here entirely
absent, and there is a considerable space, or dastema, as it
is termed, between the incisors and the teeth next in order,
the pre-molars. Of these there are three in the upper jaw
and two in the lower. They are long, curved teeth devoid
of fangs, the first smaller than the others. Behind the pre-
molars are the mo/ars, three on each side both in the upper
and lower jaws.

Opening into the cavity of the mouth are the ducts of
four pairs of salivary glands. On the floor of the mouth is
the muscular tongue, covered with a mucous membrane
which is beset with many papilla. The roof of the mouth
is formed by the padaze. The anterior part, or hard palate,
is crossed by a series of transverse ridges of its mucous
membrane. The posterior part, or soft palate, ends behind
in a free pendulous flap (the w/z) in front of the opening
of the posterior nares. Behind the mouth or buccal cavity
proper is the pharynx. The pharynx is divided into two
parts, an upper or wasa/ division, and a lower or buccal
division, by the soft palate. Into the nasal division open in
front the two posterior nares and at the sides the openings
of the Eustachian tubes. The nasal division is continuous

malrby, ff

mes.ell

506

MANUAL OF ZOOLOGY SECT.

with the buccal division round the posterior free edge of

the
the

soft palate. From the buccal division leads ventrally
slit-like opening of the glottis into the larynx and

trachea; overhanging the glottis is a leaf-like movable
flap (Fig. 304, ef) formed of a plate of yellow elastic

car

tilage covered with mucous membrane: this is the

epiglottis. Behind, the pharynx becomes continuous with

mes.ellh

érb

Fic.

ee cbt

stoi,
cer EF at

or AG

304. — Lepus cuniculus. Lateral dissection of the head, neck, andthorax. The

head and spinal column are represented in mesial vertical section: the left lung
is removed; the greater part of the nasal septum is removed so as to show the
right nasal cavity with its turbinals. a@ovt, dorsal aorta; 4. hy, basi-hyal; cd,
cerebellum; cev, cerebral hemispheres; cor. v, coronary vein; da, diaphragm;
ep, epiglottis; ez, opening of Eustachian tube into pharynx; Za, larynx; 7.7.7,
left jugular vein; 2 sd. a, left subclavian artery; /. sé. v, left subclavian vein;
med, medulla; mes. eth, mesethmoid; a2. ¢74, maxilla-turbinal; @s, esophagus;
olf, olfactory lobe; /. a, pulmonary artery; /. max, pre-maxilla; pr. st, pre-
sternum; At. c, post-caval vein; 72. zg, root of left lung with bronchus and pul-
monary veins and artery cut across; s. g7, sub-lingual salivary gland; s. 1x. gid,
sub-maxillary salivary gland; st, sternebre; ¢zg, tongue; ¢7, trachea; ¢rd,
ethmo-turbinals; ved. #7, soft palate.

the wsophagus or gullet (@s). The latter is a narrow but
dilatable muscular tube, which runs backwards from the
pharynx through the neck and thorax to enter the cavity of
the abdomen through an aperture in the diaphragm, and
opens into the stomach,

XII PHYLUM CHORDATA 507

The stomach (Fig. 305) is a wide sac, much wider at the
end (cardiac), at which the cesophagus enters, than at the
opposite or pyloric end, where it passes into the small
intestine. The small intestine is an elongated, narrow,
greatly coiled tube, the first part of which or duodenum
(du and dv) forms a U-shaped loop. The large intestine is
a wide tube, the first and greater part of which, termed the
colon, has its walls sacculated, a structure which is absent in
the short, straight posterior part or rectum (rect). At the
junction of the small with the large intestine is a very wide
blind tube, the cecum, which is of considerable length and is
marked by a spiral constriction, indicating the presence in
its interior of a narrow spiral valve. At its extremity is a
small, fleshy, finger-like vermiform appendix.

The intestine, like that of the pigeon, is attached through-
out its length to the dorsal wall of the abdominal cavity by
a mesentery or fold of the lining membrane or peritoneum.

The “ver is attached to the diaphragm by a fold of the
peritoneum. Its substance is partly divided by a series of
fissures into five lobes. A thin-walled gall-bladder lies in a
depression on its posterior surface. The common dzle duct,
(¢. 6. @) formed by the union of the cystic duct from the
gall-bladder and hepatic ducts from the various parts of the
liver, runs to open into the duodenum near the pylorus.

The pancreas (pn) is a diffused gland in the fold of
mesentery passing across the loop of the duodenum. Its
single duct, the pancreatic duct (pn. @), opens into the
distal limb of the loop.

The heart (Fig. 306) is situated in the cavity of the
thorax, a little to the left of the middle line, and lies
between the two pleural sacs enclosing the lungs. The peri-
cardial membrane enclosing the heart consists of two layers,
a parietal, forming the wall of the pericardial cavity, and a

Fic. 305. —Lepus cuniculus. The stomach, duodenum, posterior portion of rectum

and liver (in outline) with their arteries veins, and ducts. A. the coeliac artery of
another specimen (both x 2). The gullet is cut through and the stomach some-
what displaced backwards to show the ramifications of the coeliac artery (ca. a);
the duodenum is spread out to the right of the subject to show the pancreas
(fu); the branches of the bile duct (c. 4. 2), portal vein (f. v) and hepatic
artery (4. a), are supposed to be traced some distance into the various lobes of
the liver. @. 7. a, anterior mesenteric artery; caz, caudate lobe of liver, with
its artery, vein, and bile duct; c. 6. d, common bile duct; cd. st, cardiac portion
of stomach; c. 27. a, common iliac artery; ca. a, coeliac artery; cy. a, cystic
artery; cy. d@, cystic duct; d. ao, dorsal aorta; dz, proximal, and az’, distal
limbs of duodenum; dz. a, duodenal artery; dz. ha, in (A), duodeno-hepatic
arter a, gastric artery and vein; g. é, gall-bladder; 4. a, hepatic artery;
&. d, left bile duct; 2. c, left central lobe of liver, with its artery, vein, and bile
duct; 2. g. 7, lieno-gastric vein; 2. 2, left lateral lobe of liver, with its artery,
vein, and bile duct; zs, branch of mesenteric artery and vein to duodenum;
mis. ry, mesorectum; mm. v, chief mesenteric vein; @s, cesophagus; /. m7. a,
posterior mesenteric artery; /. #. v, posterior mesenteric vein; fz, pancreas;
pu. d, pancreatic duct; #. v, portal vein; Ay. st, pyloric portion of stomach;
ret, rectum; 7». c, right central lobe of liver, with artery, vein, and bile duct;
spg, Spigelian lobe of liver, with its artery, vein, and bile duct; sf/, spleen; sf. a,
splenic artery. (From Parker’s Zootomy.)

508

SECT. XII PHYLUM CHORDATA 509

visceral, immediately investing the heart. Between the two
is a narrow Cavity containing a little fluid, the pericardial
fiuid. In general shape the heart resembles that of the
pigeon, with the apex directed backwards and slightly to
the left, and the base forwards. Like that of the pigeon, it
contains right and left auricles and right and left ventricles,
the right and left sides of the heart having their cavities
completely separated off from one another by inter-auricular
and inter-ventricular partitions.

TPES ao

Fic. 306.— Lepus cuniculus. Heart, seen from the right side, the walls of the
right auricle and right ventricle partly removed so as to expose the cavities.
ao, aorta; f. ov, fossa ovalis; 7. fr. c, opening of pre-caval; mz. fap, musculi
papillares; Az. c, post-caval; f/. c', opening of post-caval; 7. prc, right pre-
hee y. pul, right pulmonary artery; sem. v, semi-lunar valves; ¢7z, tricuspid
valve.

Into the right auricle open three large veins, the ght
and “ft pre-caval veins and the single post-cava/, the first
into the anterior part, the second into the left-hand side of
the posterior portion, and the third into the dorsal surface.

Projecting forwards from it is an ear-like aurtcular appendix.
On the septum is an oval area where the partition is thinner

510 MANUAL OF ZOOLOGY SECT. XII

than elsewhere; this is the /ossa ova/is, it marks the
position of an aperture, the foramen ovale, in the fecetus.
The cavity of the right auricle communicates with that of
the right ventricle by the wide right auriculo-ventricular
opening. This is guarded by a valve, the ¢rzcuspid, com-
posed of three membranous lobes or cusps, so arranged and
attached that while they flap back against the walls of
the ventricle to allow the passage of blood from the
auricle to the ventricle, they meet together across the
aperture so as to close the passage when the ventricle
contracts. The lobes of the valve are attached to muscular
processes of the wall of the ventricle, the mscudi papillares,
by means of tendinous threads called the chorde tendinee.
The right ventricle, much thicker than the auricle, forms
the right side of the conical apical portion, but does not
extend quite to the apex. Its walls are raised up into
muscular ridges called co/umne carneea. It gives off in
front, at its left anterior angle, the pulmonary artery, the
entrance to which is guarded by three pouch-like sem-lanar
valves.

The left auricle, like the right, is provided with an
auricular appendix. Into this cavity on its dorsal aspect
open together the right and left pulmonary veins. A large
left auriculo-ventricular opening leads from the cavity of the
left auricle into that of the left ventricle; this is guarded by
a valve, the mz¢raZ, consisting of two membranous lobes or
cusps with chord tendineze and musculi papillares. In
the walls of the ventricle are column carnee rather more
strongly developed than in the right. At the basal
(anterior) end of the left ventricle is the opening of the
aorta, guarded by three semi-lunar valves similar to those
at the entrance of the pulmonary artery. The coronary
arteries, which supply the muscular substance of the heart,

Fic. 307.—Lepus cuniculus. The vascular system. The heart is somewhat dis-
placed towards the left of the subjec the arteries of the right and the veins
of the left side are in great measure removed. a, arch of the aorta; a. efg,
internal mammary artery; @._/, anterior facial vein; a. 7, anterior mesenteric
artery; a. fh, anterior phrenic vein; az. 7, azygos vein; 4, branchial artery;
c. 72. a, common iliac artery; ca, coeliac ieee d. ao, dorsal aorta; e.c, external

carotid artery; ¢. 7/. a, external iliac artery; 72. v, external iliac Poe Jibs
external jugular vein; Sm. a, femoral artery; Fae Vv, femoral vein; A. vu, heoaue
veins; 7. Cy are carotid artery; 72. cs, intercostal vessels; 7. 7x, internal
jugular vein; 7 J, ilio-lumbar artery and vein; zz, innominate artery; /. az,

left auricle; 7c. c, left common carotid artery; 2. prc, left pre-caval vein;
2. v, left ventricle; 7. sc, median sacral artery; #. @, pulmonary artery; /. efg,
epigastric artery and vein; /. /, posterior facial vein; #. #, posterior mesenteric
artery; #. #4, posterior phrenic veins; Pfc, post-caval veins; f. 7, pulmonary
vein; 7, renal artery and vein; ». az, ight auricle; +. c. c, right common
carotid artery; 7». Arc, right pre-caval vein; vy. v, right ventricle; scZ. a, right
sub-clavian artery; scl. v7, sub- clavian vei spm, spermatic artery and vein;
vs. $, Superior vesical artery and vein; #/, uterine artery and vein; 77, vertebral
artery. (From Parker’s Zootomy.)
511

512 MANUAL OF ZOOLOGY SECT.

are given off from the aorta just beyond the semi-lunar
valves. The corresponding vein opens into the terminal
part of the left pre-caval. The pulmonary artery divides
into two, a right and a left, each going to the corresponding
lung.

The aorta gives origin to a system of arterial trunks by
which the arterial blood is conveyed throughout the body.
It first runs forwards from the base of the left ventricle,
then bends round the left bronchus, forming the a7ch of the
aorta (Fig. 307, a), to run backwards through the thorax
and abdomen, in close contact with the spinal column, as
the dorsal aorta (ad. ao).

The system of cava/ veins which open into the right
auricle consists of the vight and left pre-cavals and of the
single pos¢-caval. From the liver the blood is carried to the
post-caval by the Aepatic veins.

The hepatic portal system consists, as in other vertebrates,
of a series of veins conveying blood from the various parts
of the alimentary canal to the liver, the trunks of the system
uniting to form the single large portal vein (Fig. 307, p. 2).
There is no renal portal system.

Respiratory Organs. — The /aryx (Fig. 308) is a cham-
ber with walls supported by cartilage, lying below and
somewhat behind the pharynx, with which it communicates
through a slit-like aperture. It contains the vocal cords.
Leading backwards from the larynx is the ¢rachea or wind-
pipe (Fig. 308, 7), a long tube, the wall of which is sup-
ported by cartilaginous rings which are incomplete dorsally.
The trachea enters the cavity of the thorax and there divides
into the two éronchi, one passing to the root of each lung.

The /vngs (Fig. 304) are enclosed in the lateral parts of
the cavity of the thorax. Each lung lies in a cavity lined
by a membrane — the cavity of the pleural sac or pleural

x PHYLUM CHORDATA 513

membrane. The right and left pleural sacs are separated
by a considerable interval owing to the development in the
partition between them of a space, the mediastinum, in
which lie the heart and other organs. The lung is attached
only at its root where the pleural membrane is reflected
over it. In this respect it differs widely from the lung of
the bird. It differs also in its minute structure. The
bronchus entering at the root divides and subdivides to
form a ramifying system of tubes, each of the ultimate
branches of which, or “minal bronchioles, opens into a

Fic. 308. —Lepus cuniculus. Larynx: A, ventral view; B, dorsal view; ary,
arytenoid: cv, cricoid; ef, epigiottis; sat, cartilage of Santorini; ¢/, thyroid,
ty, trachea. (From Krause, after Schneider.)

minute chamber or 7afundibulum, consisting of a central
passage and a number of thin-walled az7-vesicles or alveoli
given off from it.

The sféeen is an elongated, compressed, dark red body
situated in the abdominal cavity in close contact with the
stomach, to which it is bound by a fold of the peritoneum.
The ¢kymus, much larger in the young rabbit than in the
adult, is a soft mass, resembling fat in appearance, situated
in the ventral division of the mediastinal space below the
base of the heart. The ¢2vrord is a small brownish, bilobed
glandular body situated in close contact with the ventral
surface of the larynx.

2L

514 MANUAL OF ZOOLOGY skCT,

The neural cavity, as in the pigeon, contains the central
organs of the cerebro-spinal nervous system, the drain and
spinal cord. The brain (Fig. 309) of the rabbit contains

(After

=
aa
a ¢ 4 ‘op
: in
a gQ set |
2

cé', median

ep, epiphysis;
m. 6, mid-brain

Ss
~

4. 0, olfactory lobe;
cr, cauro-cerebri;

Ap, hypophysis;

B, ventral.
7, medulla oblongata; #. v, pons Varolii; i-xii, cranial nerves.

. 6, hind-brain;

A, dorsal view;
cé'', lateral lobe of cerebellum;
h

Brain.

(vermis) ; |
longitudinal fissure;

Sips

Lepus cuniculus.

(corpora quadrigemina) ; 7a

lobe of cerebellum
Wiedersheim.)

. 6, parencephala;

Fic. 309. —

the same principal parts as that of the pigeon, with certain
differences, of which the following are the most important.
The surface of the cerebral hemispheres (Fig. 309, f 4,

xl PHYLUM CHORDATA 515

Fig. 310, c. 4), which are relatively long and narrow, presents
certain depressions or sulci, which, though few and indis-
tinctly marked, yet divide the surface into lobes or con-
volutions not distinguishable in the case of the pigeon or
the lizard. A slight depression, the Sylvan fissure, at
the side of the hemisphere separates off a lateral portion or
temporal lobe (Fig. 311, ch”) from the rest. There are
very large club-shaped olfactory lobes at the anterior ex-
tremities of the cerebral hemispheres. Connecting together
the two hemispheres is a commissural structure, the corpus
callosum (Fig. 310, cp. cZ), not present in the pigeon ; this
runs transversely above the level of the lateral ventricles.
Below the corpus callosum is another characteristic structure
of a commissural nature, the fornix (4. fo), a narrow median
strand of longitudinal fibres which bifurcates both anteriorly
and posteriorly. Below the corpus callosum, between it and
the fornix, the thin inner walls of the hemispheres (septum
lucidum) (sp. lu.) enclose a small, laterally compressed cav-
ity, the so-called fi/th ventricle or pseudocele; this is not
a true ventricle, but merely a space between the closely
apposed hemispheres.

The lateral ventricles of the cerebral hemispheres are
much more extensively developed than in the brain of the
pigeon, and of somewhat complex shape.

The floor of the anterior portion of the lateral ventricle
is formed of an eminence of gray matter, the corpus
striatum (cp. s). The right and left corpora striata are
connected together by a narrow transverse band of white
fibres, the anterior commissure (a. Co).

The diaccele (zv*) is a laterally compressed cavity. From
the posterior part of the roof of the diaccele arises the
peduncles of the pineal body, and just beyond their point of
origin is the posterior commissure (p. co), a delicate trans-

516 MANUAL OF ZOOLOGY SECT.

verse band of fibres connecting together the posterior
parts of the optic thalami. The latter (o. #2) are large

Fic. 310.— Lepus cuniculus. Two dissections of the brain from above (nat. size).
In A, the left parencephalon is dissected down to the level of the corpus callo-
sum; on the right the lateral ventricle is exposed. In B, the cerebral hemi-

spheres are dissected to a little below the level of the anterior genu of the corpus
callosum; only the frontal lobe of the left hemisphere is retained; of the right, a
portion of the temporal lobe also is left; the velum interpositum and pineal body
are removed, as well as the greater part of the body of the fornix, and the whole
of the left posterior pillar; the cerebellum is removed with the exception of a part
of its right lateral lobe; @, co, anterior commissure; a. /o, anterior pillar of for-
nix; a@. fx, anterior peduncles of cerebellum: 3, Jo, body of fornix; cé1, superior
vermis of cerebellum; cé?, its lateral lobe; c. gz, corpus geniculatum; c. #4, cere-
bral hemisphere; ch. f/, choroid plexus; cf. c/, corpus ‘callosum: cp. s, corpus
striatum; c. ~s, corpus restiforme; d@.f, dorsal pyramid; /, flocculus; Af. 1,
hippocampus major; 7. co, middle commissure: o. 71, anterior; 0. 22, posterior
lobes of corpora quadrigemina; o. ¢#, optic thalamus; of7, optic tract; p. co, pos-
terior commissure; # /o, posterior peduncles of cerebellum; /. va, fibres of pons
Varolii forming middle peduncles of cerebellum; sf. 2, septum lucidum; sé. Z,
stria longitudinalis; ¢. s, tania semicircularis; vw. vz, valve of Vieussens; v*,
third ventricle; v*, fourth ventricle, (From Parker’s Zootomy.)

masses of mixed gray and white matter forming the lateral
portions of the diencephalon ; they are connected together

XII PHYLUM CHORDATA 517

by a thick mass of gray matter,-the middle or soft commis-
sure (m. co) passing across the diaccele. The floor of the
diencephalon is produced downwards into a mesial rounded
process, the “ber cinereum or infundibulum (inf) to which
the pituitary body is attached. In front of this, on the
ventral aspect of the brain, is a thick curved transverse
band of nerve fibres, the united optic tracts, from the ante-
rior border of which the optic nerves are given off. Behind
the tuber cinereum is a rounded elevation, the corpus
mammillare (¢c. ma).

In the mid-brain the dorsal part is remarkable for the
fact that each optic lobe is divided into two by a transverse
furrow, so that two pairs of lobes, the corpora guadrigemina,
are produced. On the ventral region of the mid-brain the
crura cerebvt are far more prominent than in the lower
groups. In the hind-brain the cerebellum (Fig. 310, cb', cb")
is very large ; it consists of a centra/ lobe or vermis and two
lateral lobes divided by very numerous fissures or sulci into
a large number of small convolutions. Each lateral lobe
bears an irregularly shaped prominence, the flocculus. On
section (Fig. 311, cd) the cerebellum exhibits a tree-like
pattern (arbor vite), brought about by the arrangement of
the white and gray matter. On the ventral aspect of the
hind-brain a flat band of transverse fibres, the pons Varolit,
connects together the lateral parts of the cerebellum.

The cranial nerves are similar to those of the pigeon in
most respects, differing in some of the particulars of their
arrangement and distribution.

The rabbit, like most other vertebrates, possesses a
sympathetic nervous system, consisting of a series of ganglia
united together by commissural nerves and giving off
branches to the various internal organs.

In the organs of special sense the following special

518 MANUAL OF ZOOLOGY SECT.

features are to be seen when a comparison is made with the
pigeon. In the eye, the sclerotic is composed entirely of
dense fibrous tissue; the pecten is absent. In the ear the
principal point of difference is in the special development
of the cochlea. This part of the membranous labyrinth,
instead of retaining the simple curved form which it pre-
sents in the bird, is coiled on itself in a close spiral of two
and a half turns.

Fic. 311. —Lepus cuniculus, Longitudinal vertical section of the brain (nat. size).
Letters as in the preceding figure; in addition, cd, cerebellum, showing arbor
vite; c.c, crus cerebri; ch, parencephalon;: ch, temporal lobe; c. wa, corpus
mammillare; f. 7, foramen of Monro; zuf, infundibulum; dy, lyra; we. o, me-
dulla oblongata; 0. ch, optic chiasma; o/f, olfactory lobe; pty, pituitary body;
vd. 2p, velum interpositum; v. vz, valve of Vieussens; //, opticnerve. (From
Parker’s Zootomty.)

The special features of the middle ear with its auditory
ossicles have been already referred to.

The kidneys are of somewhat compressed oval shape,
with a notch or Az/vs on the inner side. They are in
close contact with the dorsal wall of the abdominal cavity,
the right being somewhat in advance of the left. Towards
the hilus the tubules of the kidney converge to open into
a wide chamber, the fe/’s, which forms the dilated
commencement of the ureter. When the kidney is cut

XII PHYLUM CHORDATA 519

across, its substance is seen to be divided into a central
mass or medulla and a peripheral portion or corvfex. An
adrenal (suprarenal) body lies in contact with the anterior
end of each kidney. The wretr (Fig. 312, wr) runs back-

A

Fic. 312.—Lepus cuniculus. The urogenital organs. A, of male; B, of female,
from the left side (half nat. size). The kidneys and proximal ends of the ureters,
and in B, the ovaries, Fallopian tubes and uteri are not shown. am, anus; bl,
urinary bladder: ¢.c, corpus cavernosum; c. s, corpus spongiosum ; es gl,
Cowper's gland; g. cl, glans clitoridis; g. 4, glans penis; /. g?, perinea al gland;
p. gf’, aperture of its duct on the perineal space; #7, anterior, #7’, posterior, and
pr", lateral lobes of prostate; ct, rectum; 7. g/, rectal gland; w. g. a, urino-
genital aperture; 7. #z, uterus masculinus; #7, ureter; va, vagina; vb, vesti-
bule; wv. d, vas deferens. (From Parker's Zootomzy.)

wards to open not into a cloaca but directly into the wrnary
bladder (67). The latter is a pyriform sac with elastic
walls which vary in thickness according as the organ is

520 MANUAL OF ZOOLOGY SECT.

dilated or contracted. In the male the openings of the
ureters are situated much nearer the posterior narrower
end or neck than in the female.

In the male rabbit the ¢szes are oval bodies, which,
though in the young animal they occupy a similar position
to that which they retain throughout life in the pigeon,
pass backwards and downwards as the animal approaches
maturity until they come to lie each in a scro/ad sac situated
at the side of the urogenital opening. The cavity of each
scrotal sac is in free communication with the cavity of the
abdomen by an opening, the zzguinal canal. A convo-
luted efrdidymis, closely adherent to the testis, forms the
proximal part of the vas deferens. The vasa deferentia
(vd) terminate by opening into a urogenital canal, or
urethra, into which the neck of the urinary bladder is con-
tinued. A prostate gland (fr) surrounds the commence-
ment of the urethra, the neck of the bladder, and the
terminal parts of the vasa deferentia. A diverticulum of the
urethra, the wterus mascudinus (um), lies embedded in
the prostate gland close to the neck of the bladder. A
small pair of ovoid glands, Cowper's glands (c. gl), lie just
behind the prostate close to the side of the urethra.

The terminal part of the urethra traverses a cord of
vascular tissue, the corpus spongiosum (c.s), which forms the
dorsal portion of the penis. A loose fold of skin, the
prepuce, encloses the penis.

In the female the ovaries are small ovoid bodies attached
to the dorsal wall of the abdomen behind the kidneys. The
Graafian follicles enclosing the ova form only very small
rounded projections on their outer surface.

The oviducts in the anterior part of their extent (Fal/opian
tubes) are very narrow and slightly convoluted. They open
into the abdominal cavity by wide funnel-shaped openings,

x PHYLUM CHORDATA 521

with fimbriated or fringed margins. Posteriorly each passes
into a thick-walled w/erus. The two uteri open sepa-
rately into a median tube, the vagina (va). The vestibule
(Fig. 312, vd), or urogenital canal, is a wide median
passage, into which the vagina and the bladder open. On
its ventral wall is a small, hard, rod-like body, the c/z77s,
corresponding to the penis of the male, and composed of
two very short corpora cavernosa attached anteriorly to the

Lut

Fic. 313. —Lepus cuniculus. The anterior end of the vagina, with the right uterus,
Fallopian tube, and ovary (nat. size). Part of the ventral wall of the vagina is
removed, and the proximal end of the left uterus is shown in longitudinal section

fl. t, Fallopian tube; 77. ¢’, its peritoneal aperture; /. w#, left uterus; 2. 2’, left
os uteri; 7. «¢, right uterus; 7. #¢', right os uteri; s, vaginal septum; va,
vagina. (From Parker's Zootomy.)

ischia, with a terminal soft conical glans chitoridis (g. cl).
The vulva, or external opening of the vestibule, is bounded
laterally by two prominent folds, the /adia mayora.

The rabbit is viviparous. The ovum, which is of rel-
atively small size, after it has escaped from its Graafian
follicle, passes into the oviduct, where it becomes fertilised,
and reaches the uterus, in which it develops into the fetus,

522 MANUAL OF ZOOLOGY SECT.

as the intra-uterine embryo is termed. The young animal
escapes from the uterus in a condition in which all the parts
have become fully formed, except that the eyelids are still
closed, and the hairy covering is not yet completed. As
many as eight or ten young are produced at a birth, and
the period of gestation, z.e., the time elapsing between the
fertilisation of the ovum and the birth of the young animals
is thirty days. Fresh broods may be born once a month
throughout a considerable part of the year, and, as the
young rabbit may begin breeding at the age of three
months, the rate of increase is very rapid.

During intra-uterine life the young rabbit is nourished by
an organ called the placenta, formed by an intimate union
between certain structures, the fcetal membranes, derived
from the embryo, and a specially modified part of the wall
of the uterus. By means of the placenta a close connection
is established between the blood-system of the foetus and
that of the parent, and nourishment is thus received by the
former from the latter.

After birth the young rabbits are nourished for a time
wholly by the milk or secretion of the mammary glands of
the mother.

The following are the principal general features which
characterise the Mammalia as a class : —

The Mammalia are air-breathing vertebrates, with warm
blood, and with an epidermal covering in the form of hairs.
The bodies of the vertebree are in nearly all mammals
ossified each from three independent centres, one of which
develops into the centrum proper, while the others give
rise to thin discs of bone, the epiphyses. Also charac-
teristic of the spinal column of mammals are the discs of
fibro-cartilage termed inter-vertebral discs, which intervene
between successive centra.

XII PHYLUM CHORDATA 523

The skull has two condyles in connection with the atlas,
instead of the single condyle of the reptiles and birds ; and
the lower jaw articulates with the skull in the squamosal
region without the intermediation of the separate quadrate
element always present in that position in birds and reptiles.
Each of the long bones of the limbs is composed in the
young condition of a central part or shaft and terminal
epiphyses, the latter only becoming completély united with
the shaft at an advanced stage. In the pectoral arch the
coracoid of the birds and reptiles is usually represented
only by vestiges, which unite with the scapula in the adult.

Mammals are typically aphyodont, 7.e., have two sets of
teeth — a milk or deciduous set, and a permanent set ; some
are monophyodont, t.e., have only one set. The teeth are
thecotont, t.e., the base of each tooth is embedded in a
distinct socket or alveolus in the substance of the bone of
the jaw; and nearly always the teeth in different parts of
the jaw are clearly distinguishable by differences of shape
into incisors, canines, and grinding teeth, z.c., are heterodont,
in some instances the teeth are all alike (homodont). A
cloaca is absent except in the Prototheria.

A movable plate of cartilage, the epiglottis, overhangs the
glottis or passage leading from the pharynx into the cavity
of the larynx. -

A partition of muscular fibres, usually with a tendinous
centre, the diaphragm, divides the cavity of the body into
two parts, — an anterior, the thorax, containing the heart and
lungs, and a posterior, the abdomen, containing the greater
part of the alimentary canal with its associated glands, the
liver and pancreas, and the renal and reproductive organs.

The lungs are freely suspended within the cavity of the
thorax. The heart is completely divided into two halves,
a right and a left, between which there is no aperture of

524 MANUAL OF ZOOLOGY SECT.

communication. Each half consists of an auricle and a
ventricle, opening into one another by a wide opening,
guarded by a valve composed of three membranous cusps
on the right side, two on the left. The right ventricle gives
off the pulmonary artery ; the left gives off the single aortic
arch, which passes over to the left side, turning round the
left bronchus in order to run backwards as the dorsal aorta.
The blood is warm. ‘The red blood-corpuscles are non-
nucleated and usually circular.

‘The two cerebral hemispheres, in all but the monotremes
and marsupials, are connected together by a band of trans-
verse fibres, the corpus callosum, not represented in the
lower vertebrates. The dorsal part of the mid-brain is
divided into four optic lobes, the corpora quadrigemina.
On the ventral side of the hind-brain is a transverse band of
fibres, the pons Varolii, by which the lateral portions of the
cerebellum are connected together.

The ureters, except in the Prototheria, open into the
bladder.

Mammals are all, with the exception of the monotremes,
viviparous. The foetus is nourished before birth from the
blood-system of the parent through a special development
of the foetal membranes and the lining membrane of the
uterus, termed the placenta. After birth the young mam-
mal is nourished for a longer or shorter time by the milk or
secretion of the mammary glands of the parent.

The class Mammalia is divisible into two main divisions
or sub-classes, the Prototheria and the Theria.

The Prototheria are mammals in which the mammary
glands are devoid of teats ; the oviducts are distinct through-
out, and there is a cloaca into which the ureters and the
urinary bladder open separately. In the centra of the
vertebrae the epiphyses are absent or more imperfectly de-

xII PHYLUM CHORDATA 525

veloped ; the bones of the skull early coalesce by the oblit-
eration of the sutures ; there is a large coracoid articulating
with the sternum, and a T-shaped episternum, and there is a
pair of epipubic (marsupial) bones. In the brain a corpus
callosum is absent. The ova are discharged in an early stage
of their development, enclosed in a tough shell.

This sub-class comprises a single living order, the Mono-
tremata, including the duck-bill or Platypus ( Ornithorhyn-
chus) and spiny ant-eater (Echidna).

The Theria are mammals in which the mammary glands
are provided with teats ; the oviducts are united in a longer
or shorter part of their extent, and there is no cloaca, the
ureters opening into the base of the bladder. The centra of
the vertebrze possess distinct epiphyses ; the bones of the
skull in most instances do not completely coalesce, most of
the sutures remaining distinguishable throughout life; the
coracord is represented by vestiges, and an episternum is
absent as a distinct bone. The early development of the
young takes place in the uterus.

Of the Theria again there are two sections, the Metatheria
or Marsupialia and the Eutheria.

The section Metatheria comprises all the pouch-bearing
mammals or marsupials, such as the opossums, the dasyures,
the bandicoots, the wombats, the phalangers, and the kan-
garoo, nearly all, with the exception of the opossums, con-
fined to the Australian region. They are characterised by
the possession of a pouch or marsupium, within which the
young, born in rudimentary and helpless condition, are
sheltered. They also possess a pair of peculiar bones, the
epipubic or marsupial bones (present also in the Prototheria),
attached to the pubes.

In the Eutheria marsupium and marsupial bones are
absent. This section comprises the great majority of

526 MANUAL OF ZOOLOGY SECT.

mammals, which, when the fossil forms are left out of
account, are capable of being arranged in nine orders : —

1. Ldenfata, comprising the sloths, ant-eaters, and arma-
dillos.

2. Cetacea, including the whales, porpoises, and dolphins.

3. Sirenia, or dugongs and manatees.

4. Ungulata, avery large order, comprising among others,
the horses, tapirs, and rhinoceroses, the ruminants (camels,
oxen, sheep, goats, antelopes, giraffes, and deer), the pigs
and hippopotami, the hyraxes, and the elephants.

Fic. 314. — Duck-bill (Oraithoriynchus anatinus). (After Vogt and Specht.)

5. Carnivora, or the cats, dogs, bears, weasels, and otters,
and the seals and walruses.

6. Rodentia, a large order, including, among many others,
the rats and mice, hares and rabbits, squirrels, beavers, and
porcupines.

7. Insectivora, including the moles, shrews, and hedge-
hogs.

8. Chiroptera, or bats, and fruit-eating bats (flying foxes).

XII PHYLUM CHORDATA 527

9. Primates, comprising the lemurs, apes, and monkeys,
and the human species.

The two genera of the Prototheria, Ornithorhynchus and
Echidna, differ somewhat widely from one another in gen-
eral appearance. The former (Fig. 314) has the surface
covered with a close soft fur, and has the upper jaw pro-
duced into a depressed muzzle, not unlike the beak of a
duck, covered with a smooth, hairless integument. The eyes
are very small, and there is no auditory pinna. The legs are

Fic. 315.—Spiny Ant-eater (Echidna aculeata). (After Vogt and Specht.)

short, and the five digits end in strong claws, and are con-
nected together by a web, so that the limbs are equally
adapted for burrowing and for swimming. The tail is elon-
gated and depressed, covered with fur. The male has a
sharp-pointed, curved spur on the inner side of the foot,
having the duct of a poison-gland opening at its apex.
Echidna (Fig. 315) has the body covered above with
strong-pointed spines, between which are coarse hairs; the

528 MANUAL OF ZOOLOGY SECT.

lower surface is covered with hair only. The jaws are pro-
duced into a rostrum which is much narrower than that of
Ornithorhynchus. ‘The eyes are small, and there is no audi-
tory pinna. ‘The tail is vestigial.

‘The opossums (Didephyide) (Fig. 316) are arboreal
rat-like marsupials, with elongated naked muzzle, with well-
developed, though nailless, opposable hallux, and elongated
prehensile tail. The Dasyuride (Australian native cats,
tasmanian devil, thylacine, etc.) have the pollex often rudi-

Fic. 316. — Virginian Opossum (Didelphys virginiana). (After Vogt and Specht.)

mentary, the foot four-toed, the hallux, when present, small
and clawless, and the tail not prehensile.

The bandicoots (Peramelid@) are burrowing marsupials,
the size of which varies from that of a large rat to that of
a rabbit. They have an elongated pointed muzzle, and, in
some cases, large auditory pinne. The first and fifth digits
of the fore-foot are vestigial or absent, the remaining three

xu PHYLUM CHORDATA 529

nearly equally developed. In the hind-foot the fourth toe
is much longer and stouter than the others, while the second
and third are small and slender, and united together by a
web of skin, and the first is vestigial or absent. The marsu-
pium has its opening directly backwards.

The wombats (Phascolomyide) are large, heavy, thick-
bodied, burrowing animals, with short flattened heads, short
thick limbs, provided with strong claws on all the digits
except the hallux, and with the second, third, and fourth of

Fic. 317.—Dasyure (Dasyurus viverrinus). (After Vogt and Specht.)

the hind-foot partly connected together by skin. The tail
isvery short. The kangaroos and their allies (A/acropodide)
(Fig. 318) are adapted, as regards their limbs, for swift
terrestrial locomotion. They have a relatively small head
and neck, the fore-limbs small, and each provided with five
digits ; the hind-legs long and powerful; rapid progression
is effected by great springing leaps, with the body inclined
forwards and the fore-limbs clear of the ground. The
foot is narrow and provided with four toes, the hallux
being absent ; the two inner (second and third) small and
2M

530 MANUAL OF ZOOLOGY SECT.

united together by integument, while the middle one is
very long and powerful. The tail is very long, and usually
thick. There is a large marsupium.

Fic. 318. — Rock wallaby (Petrogale xanthopus). (After Vogt and Specht.)

The Phalangers (Phalangeride) are climbing Marsupials
which have both fore- and hind-feet prehensile ; the second
and third toes of the hind-foot slender and united by a
web, as in the kangaroo, but the hallux, which is nailless,

XII PHYLUM CHORDATA 531

opposable to them; the fourth and fifth nearly equal; the
tail is well developed and prehensile. The koalas (Fig. 319)
differ from the phalangers mainly in the relatively thicker
body and the vestigial tail.

The sloths (Bradipodide) (Fig. 320) are more completely
adapted, in the structure of their limbs, to an arboreal life

Fic. 319. — Koala (Phascolarctos cinereus). (After Vogt and Specht.)

than any other group of the Mammalia. They have a
short, rounded head, with small pinnz and long slender
limbs, the anterior much longer than the posterior, with
the digits, which are never more than three in number, long,
curved, and hook-like, adapted for enabling the animal to
hang and climb, body downwards, among the branches of
trees. The tail is rudimentary. The body is covered with
coarse hairs.

The ordinary ant-eaters (AZjrmecophaga) have a greatly

532 MANUAL OF ZOOLOGY SECT.

elongated snout, with the mouth as a small aperture at its
extremity, small eyes, and the auditory pinna sometimes
small, sometimes well developed. There are five digits in
the fore-foot, of which the third has always a very large,

Fic. 320. — Unau, or two-toed sloth (Cholepus didactylus).
(After Vogt and Specht.)

curved, and pointed claw, rendering the manus an efficient
burrowing organ. The toes of the hind-foot, four or five in
number, are sub-equal and provided with moderate-sized

XII PHYLUM CHORDATA 533

claws. The tail is always very long, and is sometimes pre-
hensile. The body is covered with long hair.

In the armadillos (Dasyfodide) (Fig. 321) the head is
comparatively short, broad, and depressed. The number of
complete digits of the fore-foot varies from three to five ;
these are provided with powerful claws, so as to form a very
efficient burrowing organ. The hind-foot always has five
digits with smaller claws. The tail is usually well developed.

Fic. 321. —Tatu armadillo (Dasypus sexciuctus). (After Vogt and Specht.)

The most striking external feature of the armadillos is the
presence of an armour of bony dermal plates. This usually
consists of a scapular shield of closely united plates covering
the anterior part of the body, followed by a series of trans-
verse bands separated from one another by hairy skin, and a
posterior pelvic shield. The tail is also usually enclosed in
rings of bony plates, and a number protect the upper surface
of the head. Dasypus occurs in southwestern Texas.

In the scaly ant-eaters (AZanrs) (Fig. 322) the head is
produced into a short pointed muzzle. The limbs are short

534 MANUAL OF ZOOLOGY SECT.

Fic. 322 —Scaly ant-eater (Manis pentadactyla), (After Vogt and Specht.)

Fic. 323. — Aard-vark (Orycteropus capensis). (After Vogt and Specht.)

XII PHYLUM CHORDATA 535

and strong, with five digits in each foot. The upper surface
of the head and body, the sides of the latter, and the entire
surface of the tail are covered with an investment of rounded
horny epidermal scales. The lower surface is covered with
hair, and there are a few coarse hairs between the scales.
There are five digits in both manus and pes.

The aard-varks (Fig. 323) have a thick-set body, the head
produced into a long muzzle with a small tubular mouth, the
pinne of great length, the tail long and thick. The fore-
limbs are short and stout, with four toes. The hind-limb

Fic. 324. — Killer (Orca gladiator). (After True.)

is five-toed. The surface is covered with thick skin with
sparse hairs.

The Cetacea (Fig. 324), among which are the Jargest of
existing mammals, are characterised by the possession of a
fusiform fish-like body, tapering backwards to the tail, which
is provided with a horizontally expanded caudal fin divided
into two lobes or “ flukes,” and a relatively large head, not
separated from the body by any distinct neck. A dorsal

536 MANUAL OF ZOOLOGY SECT.

median fin is usually present. The fore-limbs take the form
of flippers, with the digits covered over by a common integu-
ment and devoid of claws ; the hind-limbs are absent. The
mouth is very wide ; the nostrils are situated on the summit

we of the head, and the auditory
y=. _;., pinna is absent. Hairs are
oe a 4 completely absent, or are rep-
resented only by a few bristles
about the mouth. In the
whale-bone whales (Fig. 325)
the nostrils have two exter-
nal slit-like apertures ; in the
toothed whales, porpoises, and
dolphins, on the other hand,
the two nostrils unite to open
by a single crescentic valvular
aperture.

In the Sirenia also the body
is fish-like, with a horizontal
caudal fin, the fore-limbs flip-
per-like, the hind-limbs absent,
and the integument almost
hairless. But the body is dis-
tinctly depressed, and the
head is by no means so large
Meta aan aebse Ja" with in proportion as in the Ceta-

Owen.) cea, and has a tumid truncated
muzzle, not far back from the extremity of which the nostrils
are situated. There is no dorsal fin.

In the Ungulata vera the claws or nails of other mammals
are replaced by thick solid masses, the Aoofs, investing the
ungual phalanges and bearing the weight of the body. The
number of digits is more or less reduced, and the limbs as a

Vhs

XII PHYLUM CHORDATA 537

whole are usually specially modified to act as organs of
swift locomotion over the surface of the ground, their move-
ments being restricted by the nature of the articulations to
antero-posterior movements of flexion and extension. The
metacarpal and metatarsal regions are relatively very long.
In the sub-order Artiodactyla (or cattle, sheep, antelopes,
giraffes, deer, camels, pigs, and hippopotami) the third
and fourth digits of each foot form a symmetrical pair, and
in the majority are the only digits that are completely devel-
oped. Characteristic of the ruminants are the cephalic
appendages known as horns and anders. The horns of the
oxen, sheep, goats, and antelopes, sometimes developed in
both sexes, sometimes only in the males, are horny sheaths
supported on bony cores, which are outgrowths of the frontal
bones. In the giraffes the horns, which are short and occur
in both sexes, are bony structures covered with soft skin, and
not at first attached by bony union to the skull, though sub-
sequently becoming firmly fixed. The antlers of the deer,
which, except in the case of the reindeer, are restricted to
the male sex, are bony growths enclosed only while immature
in a layer of skin, the “ velvet,” covered with very soft short
fur. Antlers are shed annually, and renewed by the growth
of fresh vascular bony tissue from the summit of a pair of
short processes of the frontal bones, the pedicles.

In the pigs the legs are relatively short, and the two lat-
eral toes of both manus and pes are fully developed, though
scarcely reaching the ground. The surface is covered with
a scanty coat of coarse bristles. There is a truncate mobile
snout, the anterior end of which is disc-shaped and free from
hairs. A remarkable feature of the males is the development
of the canine teeth of both jaws into large, upwardly curved
tusks.

In the hippopotami the body is of great bulk, the limbs

538 MANUAL OF ZOOLOGY SECT.

very short and thick, the head enormous, with a transversely
expanded snout, prominent eyes, and small pinne. The
tail is short and laterally compressed. The toes are four in
each manus and pes, all reaching the ground. The surface
is naked, with only a few hairs in certain positions ; the skin
is of great thickness.

In the sub-order Perissodactyla (horses, tapirs, rhinoce-
roses) the third digit is either the only complete one in both
fore- and hind-foot (horses) or there are only three digits,
second, third, and fourth in each (rhinoceroses), or there
are four in the fore-foot and three in the hind (tapirs). The
horses (Zgwid@) have the distal divisions of the limbs slen-
der, the metacarpals and metatarsals nearly vertical to the
surface of the ground, the single hoof massive and with a
broad lower surface. Though the head is elongated, the
nasal region is not produced into a proboscis. ‘The tail is
short or moderately long, and is either beset throughout with
a large number of very long coarse hairs, or with a tuft of
such specially developed hairs at the extremity. A mane of
similar large hairs usually runs along the dorsal surface of the
neck. ‘There is a wart-like callosity above the wrist, and in
the true horses a second a little below the heel or “ hock.”

The tapirs have the body more massive than the horses,
and the limbs, especially the distal segments, shorter and
stouter. The nasal region is produced into a short proboscis.
The surface is beset with a scanty covering of hairs. The
tail is vestigial.

In the rhinoceroses the body is extremely massive, the
limbs short and stout, each digit provided with a hoof-like
nail. There is a short soft muzzle. Either one or two
remarkable median horns are borne on the nasal region, not
attached directly to the skull ; these are epidermal structures
which are formed of a dense aggregation of slender fibre-

XII PHYLUM CHORDATA 539

like elements. The eyes are small, the auditory pinna well
developed. The surface is devoid, or nearly devoid, of hairs,
and the skin is enormously thick, and in some species
thrown into deep folds. The tail is narrow and of moderate
length.

The hyraxes are small, somewhat rabbit-like animals,
with slender limbs and vestigial tail. There are four func-
tional digits in the manus and three in the pes, all provided
with short flat nails, except the innermost of the pes, which
has a curved claw. The body is covered with soft fur.

The elephants, the largest of existing terrestrial mammals,
have the limbs much more typically developed than in the
true Ungulates, there being five comparatively short digits,
enclosed in a common integument, in each foot, all of them
in the fore-, and three or four in the hind-foot terminating in
a broad flat nail. The limbs are very stout and pillar-like,
and the thigh and leg when at rest are in a straight line
instead of being, as in the Ungulata vera, placed nearly at
right angles to one another —a circumstance which gives a
characteristic appearance to the hind-quarters. The nasal
region is produced into a proboscis or “ trunk,” a mobile
cylindrical appendage, longer than the rest of the head, at
the extremity of which the nostrils are situated. There is
in the male a pair of enormous tusks, the incisors of the
upper jaw. The eyes are small, the pinna of the ear enor-
mous. The tail is small. The skin is very thick and pro-
vided with only a scanty hairy covering.

In the Carnivora the typical number of digits is sometimes
present, or, more usually, there are five in the fore- and four
in the hind-foot, or four in both. The extremities of the
digits are provided with compressed curved claws, which
may be very long and sharp, when they are capable, when
not in use, of being retracted into a sheath of skin situated

540 MANUAL OF ZOOLOGY SECT.

at their bases ; or relatively short and blunt, when they are
incompletely or not at all retractile. The otters (Lutra)
differ from the rest in having short limbs with the toes
connected by webs of skin.

The Pinnipedia, or seals and walruses (Fig. 326), have
the proximal segments of the limbs short, so that the arm
and thigh and nearly all the fore-arm and leg are enclosed
in the common integument of the trunk, and the manus and
pes elongated. The earless seals (Phocide@) are much more
completely adapted to an aquatic life than the eared seals

Fic. 326.— Harbor Seal (Phoca vitulina).

(Otariide) and walruses (Zrichechide), being unable to flex
the thigh forwards under the body, so that the hind-limbs
may aid in supporting the weight, and thus being only able
to drag themselves along very awkwardly when on dry land.
The pinna of the ear is absent in the earless seals and
walruses, well developed in the eared seals. The surface in
all is covered with a thick soft fur. In the fur seals there
are two kinds of hairs, those of the one kind being longer
and coarser and scattered through the more numerous shorter
and finer hairs composing the fur proper. A remarkable

XII PHYLUM CHORDATA 541

feature of the walruses is the presence of a pair of large tusks,
the enlarged canine teeth, projecting downwards from the
upper jaw.

Though some of the rodents (beavers, water voles) are
aquatic, some (squirrels and tree-porcupines) are arboreal,
while others (the majority of the order) lead a terrestrial
life and are active burrowers ; they are on the whole a very
uniform group, and exhibit few such remarkable modifica-
tions as are to be observed in some of the other orders of
mammals. They are nearly all furry animals with five-toed,
plantigrade, or semi-plantigrade limbs. The tail is usually
elongated, and may be naked or covered with fur; but
sometimes, as in the rabbits and hares, it is very short. A
few special modifications, however, have to be noted in cer-
tain families of rodents. The flying squirrels have on each
side a fold of skin, the patagium, which serves as a parachute.
The African flying squirrels (Anomalurus) are remarkable
also on account of the presence of a series of overlapping
horny scales on the lower surface of the basal part of the tail.
The Jerboas (Yzpus) and their allies are characterised by
the great relative length of the hind-limbs— the mode of
locomotion of these remarkable rodents being by a series of
leaps not unlike the mode of progression of the kangaroo —
and by the reduction of the number of the toes to three in
some of them. The porcupines (Ay sé7cid@) have numerous
elongated spines or “ quills” among the hairs of the dorsal
surface, and some of them have prehensile tails.

The Insectivora are, in general, small, furry, burrowing
mammals with plantigrade limbs and an elongated muzzle.
But there is a considerable range of modification within the
order in adaptation to different modes of life. The cobegos
( Galeopithecus) have a fold of skin extending along each side
of the neck and body and continued between the hind-legs,

542 MANUAL OF ZOOLOGY SECT.

enclosing the tail; the fore- and hind-feet are both webbed,
and the tail is prehensile. The hedgehog (2rinaceus) has
the surface beset with pointed spines. The moles (Za/a)
and their allies, which are active burrowers, have the limbs
very short and stout and provided with extremely strong
claws. ‘The jumping shrews (JZacrosceledida) have slender
limbs adapted to progressing by leaps on the surface of the
ground.

The Chiroptera (Fig. 327) are the only mammals which
are capable of active flight. The fore-limbs have the seg-

Fic. 327. — Bat (Syvotus barbastelius). (After Vogt and Specht.)

ments greatly elongated, especially the fore-arm and the
four ulnar digits, and these support a thin fold of the integu-
ment which stretches to the hind-limbs and constitutes the
wing. A fold also extends between the hind-limbs and may
or may not involve the tail. The pollex is much shorter
than the other digits, directed forwards, and terminates in a
well-developed curved claw ; in the Megachiroptera, but not
in the Microchiroptera, the second digit also has a claw; the
other digits are always clawless. The position of the hind-
limbs is peculiar, and the knee is directed backwards instead

XII PHYLUM CHORDATA 543

of forwards as in other mammals ; the five digits of the foot
are all provided with claws. So complete is the adaptation
of the limbs to the purpose of flight that bats are only able
to shuffle along with great difficulty on the ground, though
with the aid of their claws they are able to climb and to
suspend themselves from branches of trees by the hind-feet.

In the lemurs and their allies (Prosimi?) the body is
slender, and the limbs adapted for an arboreal existence.
The hallux is divergent from the other digits of the foot
and opposable to them, and the same holds good, in some
cases, of the pollex. In some, all the digits are provided
with claws, or all but the hallux. More commonly all the
digits are provided with flat nails, except the second of the
pes, which always has a claw. The eyes are very large.
The muzzle is sometimes elongated, sometimes short ; the
nostrils are slit-like. The tail is sometimes absent or short ;
more usually it is greatly elongated, but it is never prehen-
sile. The surface is always covered with soft fur.

Of the remaining groups of Primates the Hapilide or
marmosets are small squirrel-like animals with all the digits
except the hallux provided with pointed claws, with the
pollex incapable of opposition, the tail non-prehensile, and
without cheek-pouches or callous patches over the ischia.
The Cebide, or American monkeys, resemble the Hapalidz
in the negative characters of the absence of ischial callosities
and of cheek-pouches, and of the power of opposition in the
hallux. But the limbs are much longer, the digits are all
provided with flat nails, and the tail is frequently prehensile.
The Cercopithecide, or baboons and macaques, all have
brightly coloured bare callous patches of skin (callosities)
over the ischia, and most of them have cheek-pouches for the
storage of food. All the digits are provided with flat nails.
The tail may be long or short or absent; when present it is

544 MANUAL OF ZOOLOGY SECT. XII.

never prehensile. The pollex when developed is always
opposable to the other digits. In the Simiidee or man-like
apes, a tail is never developed, and there are no cheek-
pouches ; ischial callosities are only present in the gibbons.
The gibbons can walk in an upright position without the
assistance of the fore-limbs; in the others, though in pro-
gression on the surface of the ground, the body may be held
in a semi-erect position with the weight resting on the hind-
limbs, yet the assistance of the long fore-limbs acting as
crutches is necessary to enable the animal to swing itself
along.

INDEX

Aard-vark, 535.

Abactinal end, of starfish, 158.

Acanthias vulgaris, 366.

Acanthin, 31.

Acetabulum, 342; of frog, 416.

Aciculum of Annelids, 1go.

Acineta, 51.

Acmeea testudinalis, 292.

Acrania, 323.

Acromion process, 500.

Actinobolus, 49.

Actinomma asteracanthion, 32.

Actinophrys sol, 26, 28.

Actinospherium, 27, 28.

Actinostome, 158.

Actinozoa, 9I, 114.

Adamsia palliata, 123.

Adelochorda, 311.

Adrenals, of birds, 476; of frog, 427.

Agalmopsis cara, 108.

Air-bladder, 403.

Air-sacs, of birds, 472, 477; of in-
sects, 248.

Air-vesicles, 513.

Albatross, 490.

Alcyonaria, 118, 119.

Alcyonium carneum,119; palmatum,
II9.

Alisphenoid, 498.

Allantois, 434.

Alligator, 434, 438, 456; brain, 449.

Alveolus, 504.

Amaroucium, 320.

Ambulacral groove, 160, 161.

Ambulacral pores, 161.

Ambulacrum, 160.

Amnion, 434.

2N

|
|
|

Ameeba, 14, 19; polypodia, 18; pro-
teus, 14.

Amphiccelous vertebra, 334.

Amphineura, 281.

Amphibia, 407.

Amphidiscs, 88.

Amphioxus lanceolatus, 323.

Amphistomum, 136.

Ampulla, 162.

Anemone, sea, II5, 117.

Anguis, 436.

Animalcules, wheel, 178.

Annelida, 188, 191.

Annulata, 188.

Annuli of leeches, 203.

Anodonta cygnea, 265, 270, 273, 274;
fluviatilis, 265; circulatory system,
of, 276.

Anolis, 328.

Anomalurus, 541.

Anoplophyra, 49.

Ant-eater, 526, 531; scaly, 533; spiny,
525) 527-

Antedon, 175.

Antelope, 526, 537

Antenna, 219.

Antennule, 219.

Antlers, 537.

Anthenea, 167.

Anthophysa, 37.

Anthrenus scrophularize, 245.

Antipathes, 120.

Ant, red, 253; neuter, 253; soldier,
253; worker, 253.

Anura, 432.

| Anus, 46; of Antedon, 175; of star-

fish, 159; absent in starfish, 170; of

545

546

INDEX

round worms, 149; of birds, 459; | Aspredo, 404.

of reptiles, 435; of scorpion, 255.

Aorta, of mammals, 512; of molluscs,
275; of vertebrates, 350.

Ape, 544.

Aphides, 250.

Apiosoma bigeminum, 58.

Apis mellifica, 253; parthenogenesis
in, 250.

Aplacophora, 284.

Aplysia, 288, 291.

Apopyle, 82.

Appendicularia, 322.

Appendix vermiformis, 507.

Apteria, 462, 483.

Apteryx, 483.

Apus glacialis, 232, 275.

Arachnida, 254; lungs or pulmonary
sacs, 257.

Arachnidium, 259.

Arbor vitze of cerebellum, 517.

Arcella vulgaris, 20.

Arch, hemal, 335, 369; hyoid, 337,
372; pectoral, 339, 373, 406, 445;
446, 500; neural, 410; pelvic, 339,
416, 445, 470, 502.

Arches, branchial, 337, 372, 407; vis-
ceral, 337, 370, 444.

Archidoris tuberculata, 290.

Archipterygium, 406.

Architeuthis, 308.

Argonauta argo, 302, 303.

Arteries, of vertebrates, 349, 379, 419,
422; coronary, 510; pulmonary,
352, 407; systemic, 351.

Arthropoda, 212.

Armadillo, 526, 533.

Artiodactyla, 537.

Aristotle’s lantern, 171.

Ascaris lumbricoides, 149,151; suilla,
149.

Ascetta primordialis, 84.

Ascidia callosa, 314;
320.

mammillata,

Ascidians, 314; blood system, 318;
heart, 318; larva of, 319; nervous |
system, 318.

Astacus fluviatilis, 213, 221.
Asterias rubens, 157; vulgaris, 157.

| Asteroidea, 157.

Astraea, 121; pallida, 123.

Astragalus, 504.

Asymmetron, 323.

Atlas, 493; of birds, 464.

Atriopore, 326.

Atrium, 326.

Auditory capsules, 410.

Aurelia aurita, 108, 111.

Auricles, of birds, 477; of mammals,
510; of rabbit, 333; of sharks, 377;
of vertebrates, 350, 407.

Aves, 456.

Avicularium, 181.

Axis, 493; of birds, 464.

Babesia bovis, 58.

Baboon, 543.

Balanoglossus, 311, 313.

Bandicoot, 525, 528.

Barbs, of feathers, 461.

Barbules, 461.

Basi-sphenoid, 498.

Bat, 526, 542.

Bdellostoma, 360, 361, 364.

Beak, of birds, 457; of bivalve shells,
267; of Brachiopod shells, 184; of
czar fish, 396; of sword fish, 396.

Bear, 526.

Beaver, 526, 541.

Bee, 250; honey, 253; parasites, 252.

Beetle, carpet, 245.

Belemnites, 301.

Bells, swimming, Ios.

Beroé, 128.

Bile, 346.

Bill, of birds, 485; modifications of,
485.

Binomial nomenclature, 2.

Biology, definition of, 1.

Bionomics, 13.

Birds, 456; colors of, 484; egg, 483,
489, 490; limbs of, 459; mouth of,
459; voice of, 488; wings of, 459.

INDEX

Bladder, air, 403; gall, 346, 374;
of molluscs, 275; swimming, 403;
urinary, 519; of crustacea, 224;
frog, 427; vertebrates, 359.

Blastoderm, of sharks, 385.

Blastostyle, 92.

Blood, 70; corpuscles, 70; of insects, |
249; vascular system of insects, |

249; of birds, 488; of starfish, 162;
of vertebrates, 349, 422, 423.

Blood-vessels, 70; of annelid worms,
193, 207, 260; of crustacea, 224,
226; nemertean worms, 148.

Body-cavity of starfish, 160.

Body, pituitary, 354.

Bojanus, organ of, 275.

Bombyx mori, 58.

Bone, 66.

Bone quadrate, 339.

Bones, of birds, 472; cartilage, 337,
411; epipubic, 525; marsupial,
525; membrane, 337, 4II.

Bothriocephalus latus, 145.

Botryllus violaceus, 322.

Bougainvillea ramosa, 103;
cilians, 103.

Brachionus rubens, 179.

Brachiopoda, 184.

Bract, 108.

Bradypodide, 531.

Brain, 71; of annelid worms, 195,
197, 208 ; of birds, 479; of crustacea,
227; of insects, 249; of Peripatus,
239; of mammals, 514; of reptiles,
449; of shark, 353, 380; fore, 354.

Branchellion, 211.

Branchial basket of lamprey, 364.

Branchiz, of annelid worms, I99;
secondary in Gastropod molluscs,
291.

Branchiostoma, 323.

Breast-bone, 336.

Brittle-stars, 169.

Bronchi, of birds, 476; of lizard, 348;
of mammals, 512.

Bronchioles, 513.

Bud, 73.

super-

547

| Budding, 72.

Buds, medusa, 92.
| Bufo, 432.
| Bugula avicularia, 182.
Bulbus aortze, 403, 419.
Bulla tympani, 499.
Bursa Fabricii, 476.
Buthus carolinianus, 259.
Byssus, 279.

Calamus, 460.
Calcaneum, 416, 504.
Calcarea, 86.

Calcar, of frog, 417.
Camel, 526, 537.

Canal, of gastropod shell, 287; ingui-
nal, 520; neural, 334; radial, 97.
Cancer irroratus, 231; pagurus, 230.

Cancrisocia, 124.
Capillaries of vertebrates, 349.
Capitulum, 495.
| Capsule, central, 31.
| Carapace, 214; of crustacea, 233.
| Cardium, 280,
| Carina sterni, 466.
Carinatz, 483.
| Carnivora, 6, 526, 539.
| Carpal bones, 502.
| Carpo-metacarpus, 469.
| Carpus, 341.
Cartilage, 66; cerato-hyal, 372; hyo-
mandibular, 339, 372; intercalary,
| 369; Meckel’s, 372.
| Casque, 486.
| Cassowary, 483.
Cat, 2, 5, 7, 526.
| Caudal vertebrae, 335.
Cavity, atrial, 315; pericardial, 315,
| 349.
| Cavity, buccal, 293, 294; of verte-
brates, 344, 459, 505. ‘
Cebidz, 543.
| Cell, 18; flame, 132, I40.
| Cells, adhesive, 127; pigment, 303.
| Cellulose, in ascidian test, 315.
| Cement, of tooth, 343.
| Centrale, 502.

548

Centra, of birds, 464; of mammals,
493; of vertebrae, 333.

Cephalodiscus, 311, 313.

Cephalopoda, 296.

Cephalothorax of arachnida, 254.

Ceratium, 4o.

Ceratodus fosteri, 4o5.

Cercaria, 134; of fluke-worm, 134.

Cercopithecidz, 543.

Cere, 459, 486; absence of, 486.

Cerebellum, 354; of birds, 479, 489;
of mammals, 517.

Cerebral hemispheres, 355, 480, 514,
524.

Cervical vertebrae, 335.

Cestoda, 138.

Cestus, 128.

Cetacea, 526, 535.

Cheetopoda, 188.

Chalaza, 490.

Chalk, how formed, 26.

Chameleon, American, 328.

Chauna, 486.

Chela, of arachnida, 256; of crusta-
cea, 218, 219.

Cheliceres, 257, 262.

Cheliped, 218.

Chelonia, 434, 438, 455.

Chiasma, optic, 380.

Chilaria of Limulus, 262.

Chilopoda, 240.

Chiroptera, 526, 542.

Chitin, 20.

Chitonellus, 281.

Chiton spinosus, 281.

Chlamydosaurus, 452.

Chlamydoselachus, 389.

Chlorophyll, 28.

Choanoflagellata, 38.

Chorda dorsalis, 310.

Chordata, 310.

Chromatophores, 303, 304.

Chrysalis, 252.

Chyle, 346.

Ciliata, 49.

Circulation of frog, 423.

Cirri of amphioxus, 323.

INDEX

Cirrus, of annelid worms, I91; of cri-
noids, 175; of fluke-worms, 130.

Cistudo lutaria, 442.

Clam, 279; giant, 280.

Claspers, of sharks, 368.

Classification, 5, 8.

Clathrulina elegans, 28, 29.

Clavicle, 414, 501.

Clavicles, of sturgeon, 400.

Claws, 486; of birds, 460, 486,

Cliona, 89.

Clitellum, 201.

Clitoris, 521.

Cloaca, 344, 407, 476; of Prototheria,
523; of sharks, 393.

Cnidoblast, 95.

Cnidocil, 95.

Cobego, 541.

Coccidium, 58.

Cochlea, of birds, 489; of mammals,
518.

Cockle shell, 280.

Cockroach, 242, 243, 247.

Cocoon, of earthworms, 201.

Codonella, 49.

Coeca, of fluke-worms, 131; hepatic,
of Amphioxus, 326; hepatic, of
Balanoglossus, 313; hepatic, of in-
sects, 248; intestinal, of starfish,
165; pyloric, of starfish, 163; rec-
tal, of birds, 476; worms, 193.

Ceecilia, 433.

Ceelenterata, go.

Ccelom, of mammals, 504; of mol-
lusecs, 271; of starfish, 160; of
worms, IgI.

Ccenenchyma, 121.

Coenosare, 94.

Collar, 39.

Collozoum inerme, 33.

Colocalanus, 234.

Colonies, 42.

Colony, 30.

Colors of birds, 484.

Columba livia, 457.

Columella, 285; of birds, 468; of
corals, 121.

INDEX

Column, spinal, 333, 369; spinous,
335; vertebral, 335; of frog, 410.

Comb-jellies, 125.

Commissures of brain, 515.

Conchiolin, 269.

Condyle of skull of birds, 467.

Condyles, of bird's leg, 471; occipi-
tal, of frog, 411.

Condylostoma, 49.

Conjugation, 44, 48, 55.

Conus arteriosus, 350, 419; of Dipnoi,
407 ; of sharks, 377; of Teleostomi,
403.

Coracoid bone of birds, 468.

Corallite, 120.

Corallum, 120,

Corallium rubrum, 118.

Coral, red, 120.

Cord, spinal, 353.

Cords, vocal, of frog, 419; of mam-
mals, 512.

Cornea of eye of Crustacea, 228.

Corona of Echinoidea, 170, 172.

Corpora, cavernosa, 521; quadri-
gemina, 517; restiformia, 38r1.

Corpus, callosum, 515; mammillare,
517; spongiosum, 520; striatum,
O25:

Cortex, 45,55; of kidneys, 519.

Cowrie, 290.

Crab, 124, 230; hermit, 231; king, 260.

Craniata, 323, 328.

Cranium, 328, 337; of sharks, 369.

Crayfish, 213.

Crinoidea, 174; stalked, 176.

Crocodilia, 434, 438, 456.

Crop, of birds, 474, 488; of insects,
246; of leeches, 205.

Crura cerebri, 380, 517.

Crustacea, 213.

Cryptomonas, 37.

Ctenidia, 271, 279, 282, 291, 304.

Ctenophora, 91, 125.

Cubitals, 463.

Cuboid, 504.

Cucumaria planci, 174.

Cucumber, sea, 173.

549

Cuneiform, 502, 504.

Cuticle, 95; of nematoid worms, 151,

Cuttlefish, 296, 300.

Cyclas, 280.

Cyclidium, 49.

Cyclops, 156, 234.

Cyclostomi, 360.

Cydippe, 126.

Cypraea moneta, 290.

Cyst, daughter of tape worms, 143;
mother of tape worms, 143.

Cysticercoid embryo, 143.

Cysticercus,, 143.

Cystoflagellata, 41.

Dactylozooids, 108.

Dallingeria, 37.

Dasypus sexcinctus, 533.

Dasyurus, 525, 528, 529.

Deer, 526, 537.

Dendrocometes, 51.

Dendrophyllia, 121, 124.

Dendrosoma, 51, 54.

Dentine, 343.

Dentition, heterodont, 343;
dont, 343.

Deutomerite, 58.

Devil, tasmanian, 528.

Diaccele, 515.

Diaphragm, 349, 504, 523.

Dibranchiata, 298, 300, 301, 308.

Dictyocysta, 53.

Didinium, 49.

Difflugia, 19, 21, 24; pyriformis, 20.

Digestion, 69; in vertebrates, 344,
346.

Digestive glands of starfish, 164.

Digit, 341; of birds, 459; of frog,
409; of mammals, 502.

Dimorpha, 37.

Dimorphism, 118.

Dinobryon, 37.

Dinoflagellata, 40.

Dicecious worms, 148.

Diophrys, 49.

Diphyodont dentition, 523.

Diplomita, 37.

homo-

55°

Diplopoda, 240.

Dipnoi, 365, 405.

Diptera, 243, 245.

Dipus, 541.

Disc, trochal, 178.

Discorbina, 25.

Disease, cattle, 58; silkworm, 58.

Distomum hepaticum, 129, 135.

Distribution, bathymetrical, 11; geo-
graphical, 11; geological, 11; z0o-
geographical, 11.

Division, self, 18, 44.

Dog, 526.

Dogfish, 366.

Dolphin, 526, 536.

Dorippe facchino, 124.

Doris tuberculata, 290, 291.

Down feathers, 461.

Draco, 441, 452.

Dracunculus medinensis, 156.

Dromeus, 483.

Duck-bill, 525.

Duct, 65; ejaculatory, of leech, 210;
pneumatic, 403.

Dugong, 526.

Duodenum, 346; of birds, 476; of
mammals, 507.

Ear, of bird, 459; of crustacea, 228;
of frog, 426; of mammals, 518; of
vertebrates, 383.

Earthworm, 201, 202.

Ecdysis, 440.

Echidna, 525, 527.

FEchinarachnius parma, 173.

Echinodermata, 157.

Echinoidea, 170.

Ectoderm, 79.

Ectoprocta, 183.

Ectosarc, 28.

Eczema, caused by a parasitic vorti-
cella, 55.

Edentata, 526.

Egg, 59, 60; segmentation of, 60.

Egg-shell, 360; of bird, 483; of mol-
luses, 265; of sharks, 384.

Eggs, of crocodiles, 456; demersal,

INDEX

405; of frog, 428; pelagic, 405; of
reptiles, 451; of sharks, 385; of
turtles, 455; summer and winter,
180; of reptiles, 452.

Elasmobranchii, 365.

Electric catfish, 400.

Electric eel, 400.

Elephant, 526.

Elytra, 245.

Embryo, ciliated, of flat-worms, 133;
cysticercoid, 143; hexacanth, 141.

Embryology, 4.

Embryo of shark, 386.

Emu, 403.

Enamel, 343.

Encystation, 30.

Endoderm, 79.

Endolymph, 357.

Endopodite, 216.

Endoprocta, 181.

Endosarc, 28.

Endoskeleton, 67.

Endostyle, 317, 319.

Enteron, 92.

Entomostraca, 232.

Entovalva, 281.

Eolis, 291.

Epeira diadema, 259.

Ephelota, 51.

Ephyrula, rr2.

Epicoracoid bone, 414.

Epidermis, 63.

Epiglottis, 506.

Epimerite, 58.

Epipharynx of insects, 250.

Epiphragm, 288.

Epiphysis cerebri, 354, 380.

Epipodia, 291.

Epipodite, 218.

Episternum, of frog, 415; of reptiles,
445-

Epistoma of crustacea, 216.

Epistylis, 48, 49.

Epithelium, 63, 64; deric, 63.

Equidee, 538.

Ethmoid, 498.

Ethmo-turbinals, 498.

INDEX

Ethology, 13.

Euglena viridis, 34, 36.

Euplectella, 86.

Eupomatus, trochosphere of, 199.

Eurypterida, 260.

Euspongia, 87.

Eustachian tube, 358, 417, 505.

Eutheria, 525.

Euthyneura, 295.

Evolution, 9.

Excretion, 71.

Excretory pore of nematoda, 152.

Excretory system of nematoda, 152.

Excretory vessels of flat-worms, 132;
of nemertean worms, 148.

Exoccipital bones of frog, 411;
mammals, 496.

Exopodite, 216.

Exoskeleton, 67; of sea urchin, 157,
of starfish, 157.

Eye, of birds, 459, 480, 489 ; choroid of,
356; compound, of crustacea, 228 ;
iris of, 356; of frog, 408; of insects,
250; of mammals, 518; median, of
amphioxus, 328; of molluscs, 280,
283, 289, 307; of nemertean worms,
148; of nereis, 196; pineal, 364,

of

450; pupil of, 356; of starfish, 160; |

of vertebrates, 356, 425, 450.
Eyeball, 356.
Eyelid, of frog, 408.
Eye-spot, of fluke-worm, 133.
Eye-stalk, 216, 219.

Facets of eye, 228.

Facial nerve, 382.

Fallopian tubes, 520.

Fat bodies of frog, 427.

Fauna, 12.

Feather, follicle of, 461; germ of, 462;
papilla of, 461; pulp of, 462; tracts,

462.

Feathers, 460, 483; colors of, 484;
contour of, 461; cubital, 463;
primaries, 463; rectrices, 463;

secondaries, 463.
Feather-stars, 174.

55!

Felis, 2, 5, 7.

Femur, 342; of birds, 471.

Fibula, 342, 416; of birds, 471.

Fibulare, 416.

Filoplumes, 461.

Fimbrize of mussel, 266.

Finger, index, 409.

Fins, 332, 365, 372; lateral, 368;
median, 367; paired, 367; rays of,
365; of shark, 406; unpaired, 367.

Fin-skeleton, of ceratodus, 406.

Fish, circulation in, 351.

Fishes, 365; bony, 394; cartilaginous,
365; teeth of, 402.

Fission, binary, 18, 28, 44.

Flabellum, 120; curvatum, 122.

Flagellula, 24, 33, 38.

Flagellum, 24, 33, 36,38; of crustacea,
219.

Flat-fish, 397.

Flat-worms, 137.

Flight, muscles of, in birds, 474.

Flocculi, of bird's brain, 480.

Flounder, 397.

Fluid, coelomic, 191.

Fluke-worm, 129, 135.

Feeces, 69.

Foetus, 360, 521.

Folliculina, 49.

Fontenelle, 570.

Foot, of frog, 409; of molluscs, 266,
280, 281, 290. ‘i

Foramen magnum, 337.

Foramina, 370; pneumatic, 472.

Foraminifera, 21, 25, 26.

Formica rufa, 253.

Fornix, 515.

Fossils, ro.

Fox, flying, 526.

Frog, brain, 425; eyes, 408; limbs,
408; metamorphosis of, 429;
mouth, 408; nervous system, 425;
nostrils, 408.

Frondicularia, 25.

Frontal bones of frog, 411; of lizard,
349.

Fronto-parietal bones, 411.

552

Funnel of Cephalopoda, 299, 304.
Furcula, 488.

Galeopithecus, 541.

Gametes, 44.

Ganglion, optic, 249; of mussel, cere-
bro-pleural, 276; pedal, 276; vis-
ceral, 276.

Ganodei, 394.

Gastrolith, 222.

Gastropoda, 284.

Generations, alternation of, 98.

Genital opening of flat-worms, 130.

Genital plates of Echinoidea, 172.

Geotria, 365.

Germinal spot, 59.

Germinal vesicle, 59.

Gestation, 522.

Gibbon, 544.

Gill-cover, 214.

Gill-slits of Balanoglossus, 312.

Gill, spiracular, 377.

Gills, 70; of annelid worms, 199;
of crustacea, 222; of frog, 431; of
molluscs, 267, 271, 279, 282, 291,
304 ; secondary, 293; tracheal, 248 ;
of vertebrates, 347, 375.

Giraffe, 526, 537.

Girdle, pelvic, of birds, 470.

Gizzard, of birds, 474, 488; of insects,
247.

Gland, 63; byssus, 279; Cowper's,
520; digestive, 27; digestive of
starfish, 164; green, 224; mam-
mary, 360; milk, 360; of fluke-
worm, 133; ovoid, 166; prostate,
520; rectal, 375; salivary, 69; sali-
vary of vertebrates, 344; shell, 133,
233, 384; subneural, 319.

Glands, buccal, 476; clitoridis, 521;
thyroid, 476.

Glenodinium, 4o.

Globigerina, 25, 26; 00ze, 26,

Glochidium, 277.

Glossocodon, Io2.

Glottis, 347, 418; of birds, 476.

Glugea bombycis, 58.

INDEX

Glycogen, 346.

Goat, 526.

Gonads, 72; of mussel, 277. |
Gonangium, 92, 95.

Gonopoda, 216.

Gonopore of nematoid worms, 150.
Gonotheca, 92.

Graafian follicle, 359, 520.
Gregarina, 57, 58.

Gromia, 22, 24.

Groove, buccal, 45.

Growth, lines of, in bivalve shells, 267.
Guinea worm, 156.

Gymnophiona, 433.

Gymnotus, 400.

Heemameeba laverani, 58.

Heemal arch, 335.

Hzematochrome, 36.

Hag-fish, 360.

Hair, trigger, 95.

Halistemma, 105, 107.

Hallux, of birds, 459; of frog, 410.

Hand of frog, 409.

Hapilidee, 543.

Hare, 526; American, 491.

Hatschek, groove of, 328.

Hatteria, 437, 455.

Heart, 71; of birds, 477, 488; of crus-
tacea, 224; of Dipnoi, 407; of frog,
419; of mammals, 507; of mol-
luscs, 275, 294, 306; of reptiles, 448;
of sharks, 377; of vertebrates, 349.

Hedgehog, 526, 542.

Heliozoa, 28, 29.

Hell-bender, 433.

Heloderma, 445.

Hemichorda, 311.

Hemiptera, 243.

Hemispheres, cerebral, 355.

Hen’s egg, 489.

Hepato-pancreas, 222.

Heptanchus, 389, 390, 392.

Hermaphroditism, in flat-worms, 132,

Heteropoda, 288, 296.

Hexanchus, 389, 392.

Hilus of kidney, 518.

INDEX

Hingeof bivalve shells, 267 ; teeth, 267.
Hippocampus, 404.

Hippopotamus, 526, 537.

Hirudinea, 203.

Hirudo, eyes of, 209; lateral sense-

organs, 209; medicinalis, 204;
quinquestriata, 206,

Histology, 4.

Hoatzin, 487.

Hock, 538.

Holothuria edulis, 173; floridana,
173.

Holothuroidea, 173.

Homalogaster, 136.

Hoof, 536.

Hormiphora plumosa, 126.

Horns, 537.

Horse, 526, 538; sea, 404.

Host, of guinea worm, 156; of para-
sitic worms, 134, 142, 144.

Hound fish, rough, 366.

Humerus, 341; of birds, 469.

Hyalonema, 89.

Hyalosphenia lata, 20.

Hybrids, 3.

Hydatids, 143.

Hydra, 73, 96, 99, 100.

Hydranths, 91.

Hydrocorallina, 104.

Hydropbyllia, 108.

Hydrotheca, 91.

Hydrozoa, go, 91.

Hydrula, 98.

Hyla, 432.

Hyoid apparatus of birds, 468; of
frog, 411; of mammals, 500.

Hypopharynx, 244.

Hypophysis cerebri, 354, 380.

Hyposternum, 443.

Hypostome, 92.

Hyrax, 526, 539.

Hystricidze, 541.

Ichthyomyzon, 365.

Idyia roseola, 128.

Ilium, 342; of birds, 470, 476; of frog,
416; of mammals, 503.

553
Imago, 251.
Incisor teeth of rabbit, 491.
Incubation, 483, 490.
Infundibulum, 127, 354, 380; of

brain, 513, 517.

Infusoria, 45.

Ink gland of Cephalopoda, 306.

Ink sac of Cephalopoda, 306.

Insecta, 241; abdomen, 242; head,
242: thorax, 242; appendages of
head, 242; of thorax, 242; muscu-
lar force of, 252.

Insectivora, 526, 541.

Interclavicle, 445.

Intestine of vertebrates, 374, 418, 447.

Introvert, 289.

Ischium, 342; of bird, 470; of frog,
416.

Itch mite, 260.

Jaws, of Cephalopoda, 304; of leech,
205; of Peripatus, 239; of starfish,
159; upper, of frog, 410; of verte-
brates, 343.

Jellyfish, go.

Jerboa, 541.

Kangaroo, 525, 529.

Kidneys, of birds, 481; of frogs, 427;
of mammals, 518; of molluscs, 275,
283, 295; of vertebrates, 358, 384.

King crab, 260, 263.

Kiwi, 483.

Koala, 531.

Labia majora, 521,

Labrum, of Arachnida, 256; of in-
sects, 242; of Limulus, 262; of
Myriapoda, 240.

Lacerta viridis, 330.

Lachrymal bones, 500.

Lachrymal foramen, 500.

Lacrymaria, 49.

Laemargus, 393.

Lagena, 25.

Lamellze of molluscan gills, 272, 274.

Lamellibranchiata, 265.

554

Lampreys, 360, 364.

Lamp-shells, 184.

Larva, of anaelid worms, 199; of in-
sects, 251.

Larynx, 347; of birds, 476; of mam-
mals, 506, 512.

Laurer, canal of, 133.

Layers, germinal, 62.

Leech, eyes of, 209; sense-organ of,
209; medicinal, 203.

Legs, of crustacea, 218; of insects,
244; of mammals, 493: of reptiles,
435:

Lemur, 543.

Lens, crystalline, 357.

Lepas anatifera, 235.

Lepidoptera, 251.

Lepidosiren, 405.

Lepus cuniculus, 491.

Limb of vertebrates, 332, 459, 493.

Limpet, 285, 292.

Limulus, 260, 263.

Line, lateral, 367, 383; pallial, 267.

Lingula pyramidata, 187.

Liteocircus annularis, 31.

Lithite, 98.

Lithocysts, 98.

Liver, 69;
418; of vertebrates, 374.

Liver-fluke, 129, 135; of vertebrates,

344, 507.
Lizards, 436; flying, 441; habits,
452.

Lobe, temporal, of mammals, 515.

Lobes, olfactory, 354, 380; optic, 480.

Lobosa, 19.

Loligo pealii, 302; vulgaris, 302.

Lophomonas, 49.

Lophophore, of Brachiopods, 186; of
Polyzoa, 181.

Lorica, 38; of Rotifers, 180.

Loxosoma, 181.

Lucernaria, 112.

Lumbar vertebrae, 335.

Lumbricus agricola, 200.

Lunar bones, 502.

Lungs, 70; book, of Arachnida, 257 ; |

of birds, 476; of frog, |

INDEX

of birds, 477; of fishes, 365, 405;
of frog, 418, 431; of lizards, 348,
448; of mammals, 512; of molluscs,
292.

Lutra, 540.

Lymphatic vessels, 425.

Macaque, 543.

Macropodide, 529.

Macrosceledidee, 542.

Madrepora aspera, 124

Madrepore, 120.

Madreporic canal, 165.

Madreporite, 159.

Magellania flavescens, 185; lenticu-
laris, 186.

Magnum, 502.

Malacostraca, 232.

Malapterurus, 400.

Malar bone, 499.

Malaria caused by Protozoa, 58.

Malphigian tubes, 248,

| Mammalia, 491.
Mammary glands, 360.

| Manatee, 526.

| Mandible, of vertebrates, 339, 500.

| Mandibles, of crustacea, 217, 219; of
insects, 242; of Myriapoda, 240.

Manis, 533.

Mantle, of ascidians, 315 ; of molluscs,
266, 289; cavity, 271, 289, 304.

Manubrium, 92, 94, 95, 109.

Marmoset, 543.

Marsupium, 525.

| Mastigamceba, 37, 41.
Mastigophora, 34.

Maxilla, of crustacea, 218, 219; of
insects, 242.

Maxillary palpus of insects, 242.

Maxilliped, 218.

Medulla, 45, 55; of kidney, 519; ob-
longata, 354.

Medusa-buds, g2.

Megagamete, 44.

Megaleesthetes, 282.

Meganucleus, 45, 50.

Megapodius, 491.

INDEX

Meleagrina margaritifera, 280.

Membrane, branchiostegal, 396; nic- |
titating, 435; tympanic, 408, 435;
undulating, 50.

Menopoma, 433.

Merostomata, 260,

Mesentery, 115, 347, 507.

Mesoglzea, 94.

Mesopodium, 290.

Metacarpus, 342.

Metacrinus interruptus, 177.

Metagenesis, 98.

Metameres, 189.

Metamorphosis, of crustacea, 235; of
frog, 429; of insects, 251; retro-
grade, of ascidians, 320.

Metapleure, 323.

Metapodium, 290.

Metatarsal bones, 504.

Metatarsus, 342.

Metatheria, 525.

Metazoa, Ig, 59.

Metridium marginatum, 117.

Mice, 526.

Micreesthetes, 282.

Microgamete, 44.

Micronucleus, 45.

Miliola, 22.

Milk, pigeon’s, 483.

Mill, gastric, of crawfish, 220.

Millepora, 104.

Mite, 260; itch, 260.

Mole, 526, 542.

Molar teeth, 505.

Mollusca, 264; characters of, 364;
naked, 291, 296.

Molluscoidea, 184.

Monkey, 543.

Monocystis agilis, 55, 56.

Monotremata, 525.

Monosiga, 39.

Mordacia, 365.

Morphology, 4.

Mound-maker bird, 491.

Mouth, 92; of fishes, 368, 374; of
fluke-worms, 130; of frog, 408, 417.

Mud-fish, 405.

555

| Multicilia, 49.

Muscle, adductor, of bivalve shells,
208, 271.

Muscle, of birds, 472; of vertebrates,
342.

Mussel, fresh water, 265, 270, 273,
274; brain of, 276; nervous system
of, 276; Sea, 270.

Mustelus anarcticus, 366; canis, 366;
vulgaris, 366.

Mya arenaria, 279.

Myomeres, 342.

Myriapoda, 239.

Myrmecophaga, 531.

Mytilus edulis, 279.

Myxine, 360; glutinosa, 362, 364.

Myxospongiz, 86.

Nacre of shell, 269.

Naked molluscs, 291, 296.

Name, generic, 2; specific, 2.

Nares, 347, 417, 425, 505; of mam-
mals, 496.

Nauplius, 233.

Nautilus pompilius, 298, 300, 306, 309.

Nectocalyces, 105.

Necturus, 433.

Nematelminthes, 149.

Nematocysts, 52, 95, 96.

Nematoda, 149.

Nematodes, 154.

Nemertean worms, 145.

Nemertinea, 145.

Nephridia, of Amphioxus, 327; of
annelids, 196; of leech, 207, 208;
of molluscs, 275, 283, 295, 308.

Nephridiopores, 203.

Nephrostomes of frog, 427.

Nereis dumerilii, 189, 192,
virens, 189.

Nerve cord of Amphioxus, 328.

Nerve-pentagon, 162.

Nerves, 71; auditory, 356; cranial,
356; cerebral, 356; hypoglossal,
425; olfactory, 356, 381; optic, 356,
381, 517; peripheral, 355.

Nervous system, of annelids, 195; of

194;

556

crustacea, 227; of insects, 249; of
molluscs, 275, 282, 295, 296, 306;
of Nematoda, 152; of nemertean
worms, 148; of fluke-worm, 132; of

starfish, 162; of tape-worm, 149; of

vertebrates, 355, 380, 381.

Nest, birds’, 490.

Neuroccele, 310.

Neuropodium of annelid worms, 1go.

Newt, 432.

Nictitating membrane, 408, 435, 492.

Noctiluca miliaris, 41.

Nodosaria, 25.

Nomenclature, binomial, 2.

Nostrils, in Apteryx, 486; of birds,
459; of frog, 408.

Notochord, 310, 313, 324, 336, 337,
366, 406.

Notochordal sheath, 325.

Notopodium of annelid worms, 190.

Nuclearia, 29.

Nucleus, 16, 45.

Nucula, 279.

Nudibranch molluscs, 291, 296.

Nummulites, 25.

Nyctotherus, 49.

Obelia, 99; commissuralis, 91; gela-
tinosa, 91; geniculata, 91.

Ocelli, 104.

Ocellus of insects, 250.

Octopus, 302.

Ocular plates of Echinoidea, 172.

Odontoid process, 493.

Odontophore, 293, 304.

(Esophagus of starfish, 163; of in-
sects, 246,

Oikomonas, 37.

Oil glands of birds, 459.

Olfactory capsules, 410.

Olfactory pit of Amphioxus, 328.

Olfactory sacs of frogs, 425.

Oligocheeta, 202.

Ommatidia, of crustacea, 228;
insects, 250.

Omosternum, 415.

Onychophora, 236.

of

INDEX

| Oosperm, 59, 60, 62.

| Opalinopsis, 49.

| Operculum, 52; of bony fish, 396; of

Dipnoi, 407 ; of gastropod molluscs,
291, 295; genital, of scorpion, 257;
of Limulus, 262; of Polyzoa, 181.
Ophioglypha lacertosa, 169.
Ophiuroidea, 169.
Ophrydium, 53.
Ophryodendron, 51.
Ophryoglena, 49.

| Opisthocomus, 487.

| Opossum, 525, 528.

| Optic chiasma, 380.

| Optic lobes, 380, 480.

| Opie thalami, 354, 516; of sharks,

| 380.

| Orbito-sphenoid, 498.

| Organs, 66.

Ornithorhynchus, 525, 527.

Osculum, 77.

Osphradium, 277, 295; in Nautilus,
308.

Ossicles, ambulacral, 161; auditory,
500; of starfish, 157.

| Ostium, 82.

Ostrich, 483.

Otaridze, 540.

Otocysts, 98; of mussels, 277; of
Cephalopods, 308.

Otoliths of vertebrates, 358.

Otter, 526, 540.

Ovaries, of birds, 482 ; offrog, 427, 428;
of mammals, 520; of shark, 384; of
starfish, 107; of vertebrates, 359.

Ovary, 101, 133; of crustacea, 228.

Oviducts, of birds, 482; of crustacea,
229; of mammals, 520; of verte-
brates, 359, 428.

Ovum, 59, 60; fertilization of, 61;
maturation of, 61; of mammals,
521; of vertebrates, 359, 384.

Oxen, 526, 537.

Oyster, pearl, 280.

Pachychalina, 87.
Peedogenesis in insects, 251.

INDEX

Pagurus bernhardus, 231.

Palzeontology, Io,

Palate, 505.

Palatine bone, 414, 499.

Pallial line, 267.

Pallium, 266.

Palpi, of annelid worms, 189; of mol-
luscs, 271, 282.

Palpus of insects, 242.

Palythoa, 89.

Pancreas, 69, 344, 346, 375, 418, 507;
of birds, 476.

Pancreatic appendages of molluscs,

307.

Papilla, adhesive, of nemertean
worms, 146,

Papulze of starfish, 159.

Paraglossze of insects, 243.

Paralichthys dentatus, 398.

Paramcecium caudatum, 45, 47.

Paramylum, 36.

Parapodia of annelids, 189.

Parasitic worms, 156.

Parasphenoid bone of frogs, 413.

Parietal bones of frogs, 413.

Parthenogenesis, in insects, 250; in
Rotifers, 180.

Patagium, 541.

Patella, 292; of mammalian leg, 503.

Pearl, mother of, 269; mussel, 265,
280; oyster, 280.

Pebrine, 58.
Pecten, 280; of eye of bird, 480,
489.

Pectines of scorpion, 257.
Pedalion, 180.

Pedicellina, 181, 184.
Pedicellarize, 159.

Pedicles, 537.

Pedipalpi, 256; of spider, 259.
Peduncle, 120.

Pelagic animals, 291, 308.
Pelecypoda, 265, 278, 280.
Pelomyxa, I9.

Pelvic arch, 445.

Pelvic fin, 374, 406.

Pelvis of mammalian kidney, 518.

557

Penis, of fluke-worms, 130; of mam-
mals, 520; nematoid worms, setz
of, 149.

Pennatula aculeata, 120; sulcata, 121.

Pen of cuttle-fish, 3or.

Pentacta frondosa, 173.

Peptones, 346.

Peramelidz, 528.

Pericardium, 295; of frog, 419; of
molluscs, 271.

Perilymph, 383.

Periostracum, 268,

Periotic bones, 499,

Peripatus, 236.

Periplaneta americana, 242.

Perisare, 94.

Perissodactyla, 538.

Peristome, 52, 163, 287.

Peristomium, 189.

Peritoneum, 347; of annelid worms,
197.

Pinna, auditory, 333.

Pinnipedia, 540.

Pinnules of crinoids, 176.

Pipe fish, 404.

Pisces, 365, 394; teeth of, 4o2.

Placenta, 360.

Placophora, 284.

Plaice, 397.

Planaria, lugubris, 138; polychroa,
138; torva, 138.

Plankton, 12.

Planorbulina, 25.

Planula, 98, IIo.

Plates, in reptiles, 443.

Platyhelminthes, 129.

Platypus, 525.

Pleopoda, 216.

Pleural membrane, 513.

Pleura sac, 513.

Pleurobrachia, 128.

Pleuronectes cynoglossus, 398.

Pleuronectidze, 397.

Petasus, 102.

Petromyzon, 360; marinus, 361, 363.

Phalanges, 342, 502, 530; ungual, 342.

Pharynx, of Amphioxus, 325; of an-

558

nelid worms, 193; of leech, 205;
ascidian, 365; of mammals, 505;
of vertebrates, 344.

Phascolomyidz, 529.

Phocidze, 540.

Phragmocone, 301.

Phylogenes, 11.

Phylum, 7, 74, 75.

Physalia arethusa, Ios.

Physiology, 12.

Pieris rapze, 244.

Pig, 526, 537.

Pigeon, domestic, structure of, 457.

Pigeon’s milk, 483.

Pigment cells of molluscs, 303.

Pineal body, 354, 380; eye, 364, 450.

Pleurophyllidia, 29r.

Ploughshare, 465.

Pneumatic duct, 403.

Pneumatophore, Ios.

Podobranchiee, 224.

Podomeres, 214.

Podophrya, 51.

Poison apparatus of reptiles, 454.

Poison fang of reptiles, 447, 453, 454.

Poison glands, of scorpion, 255;
of spider, 259; of reptiles, 453.

Poison, of reptiles, 454; immunity
against, 454.

Polar bodies, 60.

Polian vesicles, 165.

Polycheeta, 199.

Polykrikos, 40.

Polyoeca, 39.

Polype, go.

Polypterus birchir, 399.

Polyzoa, 181.

Pons Varolii, 517.

Porcupine, 526, 541.

Pore, excretory, of fluke-worms, 130;
of round-worms, 149.

Porifera, 76.

Porpoise, 526, 536.

Portuguese man-of-war, 105.

Post-abdomen, 255.

Potamobia pallipes, 213, 221.

Pree-abdomen, of scorpions, 255.

INDEX

Pre-maxillze, 499.

Pre-hallux, 417.

Premaxilla of frog, 414.

Prepuce of mammals, 520.

Pre-sphenoid, 498.

Presternum, 495.

Primates, 527, 543.

Pristiphorus, 387.

Pristis, 387.

Proboscis, of annelid worms, 193; of
Balanoglossus, 311; of gastropod
molluscs, 289, 293; of leech, 211;
of nemertean worms, 145; sheath
of, 146.

Process, articulating, 334; odontoid,
464.

Procoracoid bone of frog, 414.

Proglottis, 140.

Pro-ostracum, 301.

Pro-otic bones of frog, 411.

Propodium, 290.

Prorocentrum, 40.

Prorodon, 49.

Prosencephalon, 380.

Prosimii, 543.

Prosopyle, 81.

Prostomium of annelids, 189.

Proterospongia, 39.

Proteus, 433.

Protobranchia, 279.

Protomerite, 58.

Protoplasm, 16.

Protopodite, 216.

Protopterus, 405.

Prototheria, 524.

Prototroch, 295.

Protozoa, I4.

Proventriculus of birds, 474, 488.

Pseudocecele, 515.

Pseudopleuronectes americanus, 398.

Pseudopodia, 15.

Pteropoda, 288, 291, 296.

Pterygiophores, 372.

Pterygodia, 388.

Pterygoid, bones, 414, 499.

Pterygoid process, 498.

Pterylee, 462.

INDEX

Pterylosis, 462, 463.

Ptyalin, 344.

Pubis, 342; of birds, 470; of frog,
416: of mammals, 503.

Pulmonary sacs of Arachnida, 257.

Pupa, 251.

Pygopus, 436, 437.

Pygostyle, 465, 487.

Pyxicola, 53.

Quadrate bone, 414.
Quadrato-jugal, 414.
Quadrula symmetrica, 20.
Quill, 460.

Rabbit, 331, 491, 526.

Rachis, 461.

Radiale, 469.

Radiolaria, 31.

Radio-ulna of frog, 415.

Radius, 341, 501; of bird, 469.

Radula, 293.

Radula sac, 293.

Rana esculenta, 408, 415, 429; tem-
poraria, 408, 412, 413, 417, 420, 421;
metamorphosis of, 430.

Rat, 526.

Ratitae, 483.

Rattlesnake, skull of, 445.

Ray, 388, 394; electric, 392; sting, 388.

Razor fish, 281.

Rectrices, 463.

Rectum, of molluscs, 271; of mam-
mals, 507.

Remiges, 463.

Reproduction, 18, 24, 72.

Reptilia, 433.

Respiration, 70; of vertebrates, 332,
349.

Rhabdopleura, 311.

Rhinoceros, 526, 538.

Rhipidodendron, 37.

Rhizopoda, 14, I9.

Rhizostomee, 112.

Rhyncheta, 51.

Rhynchocephalia, 434.

Ribbon, lingual, 293.

559

Rib, 336.

Ribs, of birds, 463, 494; false, 495;
floating, 495.

Rodentia, 526, 541.

Rostellum, 140.

Rostrum, 216.

Rotalia, 22.

Rotifera, 178.

Ruminants, 526.

Sac, scrotal, 520.

Saccammina, 25.

Sacral vertebrze, 335.

Sacrum, 494.

Salamander, 432.

Salamandra maculosa, 432.

Salmo, fario, 395, 401; fontinalis, 395.

Salmon, Burnet, 4os.

Salpingoeca, 39.

Saprophytes, 45.

Saprophytic, 42.

Saw-fish, 387.

Scales, ctenoid, 398; cycloid, 398;
ganoid, 399; of legs of birds, 459;
placoid, 367; of reptiles, 435, 439.

Scallop shell, 280.

Scaphoid, so2.

Scapula, 414; of birds, 468.

Sclerotic, 356; plates of bird's eye,
480.

Scolex, 140.

Scolopendra, 240.

Scorpion, 255, 259; anatomy of, 258;
carapace of, 255.

Scuta, 240.

Scutes of bony fishes, 399.

Scutigera, 240.

Scyllium, canicula, 338, 345, 366, 371,
376; catulus, 366.

Scyphozoa, 91, 108.

Scyphula, 112.

Sea-hare, 288, 291, 296.

Sea-horse, 404.

Sea-squirts, 314.

Sea-urchins, 170.

Seal, 526, 540; earless, 540.

Segmental organs of annelids, 196.

560

Segmentation of egg, 60.

Segments of worms, 189.

Sella turcica, 498.

Sense organ, 108.

Sense organs of leech, 209; of mol-
luses, 282.

Sepia cultrata, 297, 301, 305.

Septa, 121; of annelid worms, IgI.

Serpula, 198.

Setze, of annelids, 190, 201; olfactory,
of crustacea, 228; penial, 149, 150,
153.

Setigenous sac of annelids, 190.

Shark, Greenland, 393.

Sheath, proboscis, of nemertean
worms, 146.

Sheep, 526, 537.

Shell, Cephalopod, 300.

Shell-fish, 266.

Shell-gland of fluke-worm, 133.

Shell-glands, 133; of crustacea, 233.

Shell membrane, 490; nacre of, 269;
periostracum, 269; prismatic layer
of, 269; supplemental, 23; vesti-
gial, 288.

Shells, dextral, 285; sinistral, 285.

Shields of reptiles, 439.

Ship-worm, 279.

Shoulder-girdle, of birds, 468; of
frog, 414.

Shrew, 526; jumping, 542.

Simiidze, 544.

Sinistral shells, 285.

Sinus venosus, 350, 407, 419.

Siphon, of molluscs, 266; of gastro-
pod mollusc, 289.

Siphonoglyphes, 115.

Siphons of ascidians, 315.

Siphonozooids, 118.

Siphophora, 104.

Siphuncle, 300.

Siren, 433.

Sirenia, 526, 536.

Skeleton, 28, 67; of birds, 487; of
fish, 368; of sponges, 79.

Skull, autostylic, 407; of birds, 467 ;
of frog, 410; of mammals, 495;

INDEX

of reptiles, 444; of vertebrates, 328,
333, 337, 339.

Slits, branchial, of sharks, 368 ; gill, of
Amphioxus, 326; of Balanoglos-
sus, 312.

Sloth, 526, 531, 532.

Slug, 288, 293.

Snail, 284.

Snake, 436, 446, 453; glass, 436; ovi-
parous, 455; viviparous, 455.

Soldier ant, 253.

Sole, 297.

Solen, 281.

Species, 3; abyssal, 11; alpine, 11;
littoral, 11; pelagic, 11, 24.

Sperm, 59.

Spermiduct of shark, 384.

Sphaerophrya, 51.

Sphenethmoid bone of frog, 411.

Spicule, 31, 119.

Spicule of sponge, 79, 88.

Spider, 259.

Spine, caudal, of Limulus, 262.

Spines, ambulacral, 159; neural, 369.

Spinnerets, 259.

Spiracle of shark, 332, 368, 386.

Spiroloculina, 25.

Spirula peronii, 300, 301.

Spleen, 375, 418; of birds, 476; of
mammals, 513.

Sponges, 76.

Spongelia, 87.

Spongilla, 85, 89.

Spores, 30.

Sporocyst, 30, 134; of fluke-worm,134.

Sporoduct, 58.

Sporozoa, 55.

Spot, anal, 46.

Spur of birds, 487.

Squamata, 434.

Squamosal bone, 414, 498.

Squammulina, 22.

Squid, 296, 300.

Squirrel, 526, 541; flying, 541.

Starfish, 157.

Stentor, 49.

Sternebrze, 336, 495.

INDEX

Sternum, 255, 336; of birds, 465, 488;
of frog, 415; of reptiles, 443.

Stichotricha, 53.

Stickleback, 406.

Stigma, 36.

Stigmata, of ascidians, 315; of in-
sects, 248; of scorpion, 257.
Stinging capsules, 52, 95, 108;

nemertean worms, 146.
Stomach, chyle, 247.
Stomach, of mammals, 506; of star-
fish, 163; of vertebrates, 374, 418.
Stomach, sucking, of insects, 246.
Stomodzeum of Nematoda, 152.
Stomogastric nerves, 195.
Stone-canal of Echinoderms, 165.
Strepsiptera, 252.
Streptoneura, 295.
Strongylocentrotus, 171.
Struthio, 483.
Sturgeon, 399, 400.
Stylaster, 104.
Stylet of nemertean worms, 145.
Sucker of distoma, 130, 136.
Suprascapular bone of frog, 414.
Suspensorium, 414.
Sutures of skull, 496.
Swan mussel, 265.

of

Swift, 4go.

Swimming, act of in squid, 304,
308.

Sycon ciliatum, 76; gelatinosum,
76.

Sylvian fissure, 515.

Symbiosis, 33.

Symmetry, bilateral, of worms, 130;
radial, 176.

Sympathetic nerves of vertebrates,
381, 517.

Symphysis, of jaw, 500; pubic, 352,
502; of frog, 416.

Synapta, 174.

Syncrypta, 37.

Syncytial ectoderm, 151.

Syngnathus, 404.

Syn-sacrum, 465, 487.

Syrinx, 488.

20.

561

Tadpole, 429.

Teenia ccenurus, 143; echinococcus,
143, 144; Saginata, 142, 144; ser-
rata, 142; solium, 139, 141, 144.

Tail, diphycercal, 396; heterocercal,
367, 396; homocercal, 367, 396.

Tailor bird, 490.

Talpa, 542.

Tape-worms, 138, 144; human, 138,
141.

Tapir, 526, 538.

Tarso-metatarsus, 472.

Tarsus, 342, 411, 503; of insects, 244.

Tealia crassicornis, 115.

Teeth, dermal, 467; heterodont, 523;
homodont, 523; thecodont, 523; of
leech, 205 ; of sharks, 392; of shells,
267; stomach, of crawfish, 220; of
vertebrates, 343, 418, 446, 504; ca-

nine, 505; incisor, 504; molar,
505; premolar, 505.

Teleostei, 394.

Teleostomi, 394.

Telson, 217.

Tentacles, 48, 50, 91; of annelid

worms, 189; of crinoids, 176; of
molluscs, 289; of starfish, 160.

Tentaculifera, 48, 50, 51.

Tentaculocysts, ror.

Terebra oculata, 289.

Terebratulina septentrionalis, 187.

Teredo navalis, 279, 280.

Tergum, 255.

Tessera princeps, 113.

Test, 19; of ascidians, 315.

Testes, Io1, 132; of birds, 481; of
crustacea, 228 ; of fluke-worm, 132;
of frog, 427; of mammals, 520; of
Nematoda, 153; of starfish, 167;
of vertebrates, 359.

Tetrabranchiata, 299, 308.

Tetramita, 37.

Tetrastemma, 147.

Texas cattle disease, 260.

Texas cattle fever, 58.

Theca, 92, 120.

Thecodont teeth, 523.

562

Theria, 524, 525.

Thoracic vertebrze, 335.

Thorax, of insects, 241; of mammals,
504.

Thuricola, 53.

Thylacine, 528.

Thymus, 513; of birds, 476.

Thyroid, 513.

Thyroid glands, 476.

Tibia, 342, 416.

Tibio-fibula of frog, 416.

Tibio-tarsus of birds, 471.

Tick, 260; cattle, 260.

Tintinnidium, 49.

Tissues, 63.

Toad, 432.

Toe, great, of frog, 410.

Toes, of birds, 487.

Tongue, of birds, 474; of frog, 417;
of vertebrates, 344.

Torpedo occidentalis, 392.

Trachea, of birds, 476; of mammals,
512; of reptiles, 347, 448.

Tracheze of insects, 248.

Trachelomonas, 37.

Trachelius, 49.

Trachosphere of molluscs, 295.

Trachylinz, 102.

Trapezium, 502.

Trapezoid, 502.

Tree, genealogical, 9.

Trematoda, 134; ectoparasitic, 137.

Trichechidz, 540.

Trichina spiralis, 154.

Trichocysts, 46.

Triclad Turbellaria, 137.

Tridacna gigas, 280.

Trigeminal nerves, 382.

Trigger-hair, 95.

Trigonia, 280.

Triton nodiferus, 286, 294.

Trochanter, 471, 503.

Trochosphere of annel:d worms, 201.

Trout, 395.

Tuatara, 437, 438.

Tube-feet,of Echinoidea,170; of Holo-
thuroidea, 173; of starfish,160, 161.

INDEX

Tubipora musica, I19.

Tunic of ascidians, 315.
Turbellaria, 137.

Turbot, 397.

Turtles, 434, 438, 455.
Tympanic bones, 499.
Tympanum, 358; of frog, 408.
Tzetse fly, 58.

Ulna, 341, 501; of birds, 469.

Ulnare, 469.

Umbilicus of feather, 460.

Umbo of shells, 267.

Umbrella, 95.

Unau, 532.

Unciform, 502.

Ungulata, 526, 536.

Unio complanatus, 265, 280; mar-
garitifer, 265.

Urchin, sea, egg of, 60.

Urchins, cake, 173; heart, 173.

Ureter, 359; of frog, 427; of mam-
mals, 519; of shark, 384.

Urethra, 359, 520.

Urinary tubes, 248.

Urine, 358.

Urnatella, 181.

Urochorda, 314; larva, 319.

Urodela, 432.

Urolophus testaceus, 390.

Uropoda, 217.

Uropygium, 457, 463.

Uterus, masculinus, 520; of Nema-
toda, 154; of tape-worm, 140; of
vertebrates, 359; of worms, 133.

Vacuole, contractile, 17, 36, 45; food,
46.

Vagina, of leech, 211; of vertebrates,
359, 521.

Vagus nerve, 383.

Valve, spiral, 374; of shark, 393, 402.

Valves, mitral, 510; semi-lunar, 510;
of shells, 265.

Vane of feather, 460.

Variation, 3.

Vascular system of a fish, 378.

INDEX

Vas deferens, of fluke-worm, 132; of
mammals, 520; of vertebrates, 359;
of worms, 132.

Vein, pulmonary, 407, 423; renal
portal, 422.

Veins, hepatic, 352; pulmonary, 351;
of vertebrates, 349, 350, 379.

Veliger, 295.

Velum, 97.

Velvet, of deer horns, 537.

Ventricle, of brain, fourth, 354, 380;
lateral, 354; third, 354; fifth, 514.

Ventricles of heart of vertebrates,

0.

Venus’s flower-basket, 86 ; girdle, 128.

Vermetus, 296.

Vermiform appendix, 507.

Vermis, 517.

Vertebra, 333, 440, 463 ; amphiccelous,
334, 440; heteroccelous, 464; pro-
coelous, 335, 410, 441.

Vertebrata, 322; brain of, 354; cir-
culation of, 349; nervous system of,
350; respiration of, 349.

Vertebral column, 333, 369; of birds,
463; of frog, 410; of mammals, 493.

Vesicles, Polian, 165; racemose, 166;
Tiedemann'’s, 166.

Vesicula seminalis of worms, 133.

Vessels, water, of flat worms, 132; of
Platyhelminths, 132.

Vexillum, 460.

Vibrissze of rabbit, 492.

Visceral arches, 337, 444.

Visceral mass of molluscs, 270.

563

Visceral nerves, of crustacea, 227; of
worms, 195.

Viviparity, 72.

Voice of birds, 488.

Vole, 541.

Volvox globator, 43, 44.

Vomer bone, of frog, 413.

Vorticella, 48, 52,54; parasitic, 55.

Vulva, 521.

Wallaby, 530.

Walrus, 526, 540.

Wasp, 250.

Weasel, 526.

Whale, 526, 536.

Wheel animalcules, 178,

Whelk, 296.

Wings, of birds, 459; muscles of,
474; of insects, 244; veins of, 244.

Wombat, 529.

Worker ant, 253.

Worm, blind, 436.

Xiphosura, 260, 263.
Xiphisternum, 415.

Yolk-sac, of shark, 386.

Zocecium, 181.

Zooid, 30, 91.

Zoology, definition of, 1.
Zoophytes, go.
Zooxanthella, 33.
Zygomatic arch, 499.
Zygomatic process, 498.
Zygapophysis of frog, 410.

A TEXT-BOOK OF ZOOLOGY

BY

T. JEFFERY PARKER, D.Sc., F.R.S.
Professor of Biology in University of Otago, Dunedin, N.Z.

AND

WILLIAM A. HASWELL, M.A., D.Sc., F.R.S.
Professor of Biology tn the Untuersity of Sydney, N.S.W.

In two volumes, containing many illustrations

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